Journal of Power Sources (v.216, #)
Improving the chemical compatibility of sealing glass for solid oxide fuel cells: Blocking the reactive species by controlled crystallization
by Teng Zhang; Qi Zou; Fanrong Zeng; Shaorong Wang; Dian Tang; Hiswen Yang (pp. 1-4).
The chemical compatibility of sealing glass is of great importance for Solid oxide fuel cell (SOFC). In this work, the interfacial reaction between sealing glass and Cr-containing interconnect alloy is characterized by reacting Cr2O3 powders with a representative SrO-containing glass crystallized by different heat-treatment schedules. The crystalline structure and crystalline content of sealing glass are determined by X-ray diffraction. The results show that the fraction of Cr6+ decreases from 39.8 ± 1.9% for quenched glass to 8.2 ± 0.4% for glass crystallized at 900 °C for 2 h. In addition, the interfacial reaction can be further reduced with increasing crystallization temperature and time as well as the addition of nucleation agent (TiO2). The formation of some Sr-containing crystalline phases, Sr2SiO4 and Sr(TiO3), contributes to the improvement of chemical compatibility of sealing glass, in agreement with the results of thermodynamic calculations.► Interfacial reaction can be reduced by controlled crystallization of sealing glass. ► Sr-containing crystalline is critical for the chemical stability of sealing glass. ► The improved chemical stability can be explained by thermodynamic models.
Keywords: Solid oxide fuel cell; Interfacial reaction; Controlled crystallization; Chemical compatibility; Thermodynamic calculation
Study of a graphene-like anode material in N-methyl- N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid for Li-ion batteries
by Maciej Galinski; Ilona Acznik (pp. 5-10).
Graphene nanosheets or reduced graphite oxide materials recently have attracted great attention because of their excellent electrochemical properties such as excellent electrical conductivity and high specific capacity originating from their structure, i.e., two-dimensional layers with one-atomic thickness. This work is focused on reduced graphite oxide (RGO) applied as negative electrode in Li-ion cell with ionic liquid ( N-methyl- N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, Py13TFSI) as electrolyte. Three different electrochemical techniques, e.g., galvanostatic charging/discharging, cyclic voltammetry and electrochemical impedance spectroscopy were applied for full electrochemical characterisation of these materials. The results proved that RGO gives good reversible capacity of ca. 550 mAh g−1 (at current density of 50 mA g−1) working together with the ionic liquid. This value is comparable to that characteristic for cells operating with conventional electrolyte (cyclic carbonates).► Presented work concerns graphene-like material as an anode in lithium-ion cell. ► Conventional electrolyte was replaced by ionic liquid. ► Satisfactory capacity of the material working with ionic liquid was obtained. ► Mechanism of Li storage in these materials is determined to be quite complex. ► No well-defined charging/discharging plateau was recorded.
Keywords: Graphite oxide; Graphene sheets; Ionic liquids; Lithium-ion batteries
Reversible aging behavior of La0.8Sr0.2MnO3 electrodes at open circuit
by Harry Abernathy; Harry O. Finklea; David S. Mebane; Xiaoke Chen; Kirk Gerdes; Maria D. Salazar-Villalpando (pp. 11-14).
La0.8Sr0.2MnO3 (LSM) electrodes on yttria-stabilized zirconia (YSZ) electrolytes were characterized at open circuit by impedance spectroscopy. An initial irreversible change in the polarization resistance is observed for cells aged with no prior current activation. After the initial break-in, the polarization resistance rises with time at 700 °C and decays at 800 °C, reversibly, over repeated temperature cycles. The initial irreversible break-in and subsequent reversible cycling behavior suggests multiple processes happening within the time and temperatures measured. The authors propose that these processes are (1) changes in the wetting behavior of the LSM on the YSZ and (2) the reversible segregation/desegregation of cations within LSM. Between 700 °C and 800 °C, there is a transition temperature at which the segregation behavior of cations to the cathode surface changes. These measurable changes in the impedance behavior of LSM indicate that cation segregation, while considered by some to be part of the cathode activation process, may be dictated by thermodynamic factors, and thus not strictly dependent on the passage of current through the cathode.► Aging behavior of LSM changes between 700 °C and 800 °C. ► Aging behavior is a mixture of reversible and irreversible changes in impedance. ► Reversible changes explained by reverse in cathode cation segregation behavior. ► Irreversible changes explained by microstructural changes of porous cathode.
Keywords: SOFC; Cathode; LSM; Cation segregation; Impedance; Polarization resistance
Proton exchange membrane micro fuel cells on 3D porous silicon gas diffusion layers
by S. Kouassi; G. Gautier; J. Thery; S. Desplobain; M. Borella; L. Ventura; J.-Y. Laurent (pp. 15-21).
Since the 90's, porous silicon has been studied and implemented in many devices, especially in MEMS technology. In this article, we present a new approach to build miniaturized proton exchange membrane micro-fuel cells using porous silicon as a hydrogen diffusion layer. In particular, we propose an innovative process to build micro fuel cells from a “corrugated iron like” 3D structured porous silicon substrates. This structure is able to increase up to 40% the cell area keeping a constant footprint on the silicon wafer. We propose here a process route to perform electrochemically 3D porous gas diffusion layers and to deposit fuel cell active layers on such substrates. The prototype peak power performance was measured to be 90 mW cm−2 in a “breathing configuration” at room temperature. These performances are less than expected if we compare with a reference 2D micro fuel cell. Actually, the active layer deposition processes are not fully optimized but this prototype demonstrates the feasibility of these 3D devices.► We present a new approach to build miniaturized proton exchange membrane micro-fuel. ► We built fuel cells using 3D structured porous silicon substrates to increase the cell active surface. ► We performed fully porous “corrugated iron” like substrates by silicon electrochemistry. ► The prototype peak power performance was measured to be 90 mW cm2 in a “breathing configuration” at room temperature.
Keywords: 3D; Porous silicon; PEMFC; Micro fuel cell
Microwave hydrothermal synthesis of high performance tin–graphene nanocomposites for lithium ion batteries
by Shuangqiang Chen; Yong Wang; Hyojun Ahn; Guoxiu Wang (pp. 22-27).
Tin–graphene nanocomposites are prepared by a combination of microwave hydrothermal synthesis and a one-step hydrogen gas reduction. Altering the weight ratio between tin and graphene nanosheets has critical influences on their morphologies and electrochemical performances. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) analysis confirm the homogeneous distribution of tin nanoparticles on the surface of graphene nanosheets. When applied as an anode material in lithium ion batteries, tin–graphene nanocomposite exhibits a high lithium storage capacity of 1407 mAh g−1. The as-prepared tin–graphene nanocomposite also demonstrates an excellent high rate capacity and a stable cycle performance. The superior electrochemical performance could be attributed to the synergistic effect of the three-dimensional nanoarchitecture, in which tin nanoparticles are sandwiched between highly conductive and flexible graphene nanosheets.► Sn–GNS were prepared by a microwave hydrothermal synthesis and a one-step H2 reduction. ► Sn nanoparticles are homogenously sandwiched between highly conductive and flexible GNS. ► Altering the ratio between tin and graphene had critical influences on their morphologies. ► Sn–GNS exhibited a high lithium storage capacity of 1407 mAh g−1.
Keywords: Graphene nanosheets; Tin nanoparticles; Microwave hydrothermal synthesis; Hydrogen reduction; Lithium ion batteries
Enhanced electrocatalytic performance of Pt monolayer on nanoporous PdCu alloy for oxygen reduction
by Linxi Hou; Huajun Qiu (pp. 28-32).
By selectively dealloying Al from Pd xCu20− xAl80 ternary alloys in 1.0 M NaOH solution, nanoporous PdCu (np-PdCu) alloys with different Pd:Cu ratios are obtained. By a mild electrochemical dealloying treatment, the np-PdCu alloys are facilely converted into np-PdCu near-surface alloys with a nearly pure-Pd surface and PdCu alloy core. The np-PdCu near-surface alloys are then used as substrates to fabricate core–shell catalysts with a Pt monolayer as shell and np-PdCu as core by a Cu-underpotential deposition–Pt displacement strategy. Electrochemical measurements demonstrate that the Pt monolayer on np-Pd1Cu1 (Pt/np-Pd1Cu1) exhibits the highest Pt surface-specific activity towards oxygen reduction, which is ∼5.8-fold that of state-of-the-art Pt/C catalyst. The Pt/np-Pd1Cu1 also shows much enhanced stability with ∼78% active surface retained after 10,000 cycles (0.6–1.2 V vs. RHE). Under the same condition, the active surface of Pt/C drops to ∼28%.► Pt monolayer-covered nanoporous PdCu catalysts are prepared by a Cu-underpotential deposition–Pt displacement strategy. ► Compared with Pt/C catalyst, the Pt monolayer-modified nanoporous PdCu show much enhanced activity and stability for oxygen reduction reaction (ORR). ► Pt monolayer on PdCu alloy core with a Pd:Cu ratio of 1 shows the highest activity for ORR.
Keywords: Dealloying; Electrocatalyst; Fuel cell
Two-step carbon coating of lithium vanadium phosphate as high-rate cathode for lithium-ion batteries
by Quan Kuang; Yanming Zhao (pp. 33-35).
Carbon-coated Li3V2(PO4)3 was firstly prepared at 850 °C via two-step reaction method combined sol–gel and conventional solid-state synthesis by using VPO4/carbon as an intermediate. Two different carbon sources, citric acid and glucose as carbon additives in sequence, ultimately deduced double carbon-coated Li3V2(PO4)3 as a high-rate cathode material. The Li3V2(PO4)3/carbon with 4.39% residual carbon has a splendid electronic conductivity of 4.76×10−2 S cm−1. Even in the voltage window of 2.5–4.8 V, the Li3V2(PO4)3/carbon cathode can retain outstanding rate ability (170.4 mAh g−1 at 1.2 C, 101.9 mAh g−1 at 17 C), and no degradation is found after 120 C current rate. These phenomena show that the two-step carbon-coated Li3V2(PO4)3 can act as a fast charge-discharge cathode material for high-power Li-ion batteries. Furthermore, it's believed that this synthesize method can be easily transplanted to prepare other lithiated vanadium-based phosphates.► A novel carbon-coating method for Li3V2(PO4)3 via two-step reaction is presented. ► The sol–gel and solid-state reaction are combined by using VPO4 as an intermediate. ► The end product has a high conductivity of ∼10−2 S cm-1 with 4.39% residual carbon. ► Even in 2.5–4.8 V, the Li3V2(PO4)3/C cathode can retain outstanding rate ability. ► No degradation is found after Li3V2(PO4)3/C testing at extreme high rate (120 C).
Keywords: Lithium-ion batteries; Cathode material; Carbon coating; Lithium vanadium phosphate; Rate ability
Organic and inorganic surface passivations of TiO2 nanotube arrays for dye-sensitized photoelectrodes
by Hun Park; Changduk Yang; Won-Youl Choi (pp. 36-41).
Surface passivation of photoelectrodes is widely used to improve the performance of dye-sensitized solar cells (DSCs). We use the organic and inorganic materials as a surface-passivating layer of photoelectrodes and introduce the effect of surface passivation on the power conversion efficiency of DSCs. TiO2 nanotube arrays are fabricated by anodic oxidation of Ti foil for photoelectrodes of DSCs. Surface passivating layers are conducted by immersing photoelectrode in various precursor solutions. MgO and WO3 are selected for inorganic passivation. PC61BM is used for organic passivation. In case of inorganic passivation, a basic material (MgO) which has a high isoelectric point (pI >7) shows higher power conversion efficiency of 2.63% by increasing of open circuit voltage ( Voc) to 0.74 V than bare sample of 2.55%. But, an acidic material (WO3) shifts Voc to low potential resulting in a worse efficiency of DSCs. In case of organic passivation, PC61BM enhances photocurrents and decreases Voc value compared to bare sample. The power conversion efficiency of PC61BM-coated DSCs is overall improved due to enhanced photocurrents despite of Voc offset to low potential. Back-transfer electron blocking, dye adsorption, TiO2 conduction band shifting, and additional charge generation by surface passivation are discussed.► TiO2 nanotube arrays as photoelectrode in DSCs. ► Organic passivation layer for TiO2 nanotube arrays. ► Inorganic passivation layer for TiO2 nanotube arrays. ► Power conversion efficiency is improved by passivation layer.
Keywords: Dye-sensitized solar cells; Titanium dioxide; Nanotube; Surface passivation
Evaporation-induced self-assembled silica colloidal particle-assisted nanoporous structural evolution of poly(ethylene terephthalate) nonwoven composite separators for high-safety/high-rate lithium-ion batteries
by Jung-Ran Lee; Ji-Hye Won; Jong Hun Kim; Ki Jae Kim; Sang-Young Lee (pp. 42-47).
A facile approach to the fabrication of nanoporous structure-tuned nonwoven composite separators is demonstrated for application in high-safety/high-rate lithium-ion batteries. This strategy is based on the construction of silica (SiO2) colloidal particle-assisted nanoporous structure in a poly(ethylene terephthalate) (PET) nonwoven substrate. The nanoparticle arrangement arising from evaporation-induced self-assembly of SiO2 colloidal particles allows the evolution of the unusual nanoporous structure, i.e. well-connected interstitial voids formed between close-packed SiO2 particles adhered by styrene-butadiene rubber (SBR) binders. Meanwhile, the PET nonwoven serves as a mechanical support that contributes to suppressing thermal shrinkage of the nonwoven composite separator. The aforementioned structural novelty of the nonwoven composite separator plays a key role in providing the separator with advantageous characteristics (specifically, good electrolyte wettability, high ionic conductivity, and benign compatibility with electrodes), which leads to the better cell performance than a commercialized polyethylene (PE) separator.Display Omitted► New nonwoven composite separators for use in high-safety/high-rate lithium batteries. ► Provision of a facile route to fine-tune porous structure of the nonwoven separators. ► Silica colloidal particle-assisted nanoporous structural evolution in PET nonwovens. ► Interstitial voids formed from evaporation-induced self-assembly of SiO2 colloidal particles. ► The structural novelty allows lower thermal shrinkage and superior cell performance.
Keywords: Lithium-ion batteries; High-safety/high-rate; Nonwoven composite separators; Colloidal silica particles; Evaporation-induced self-assembly; Nanoporous structure
Where do poly(vinyl alcohol) based membranes stand in relation to Nafion® for direct methanol fuel cell applications?
by Jatindranath Maiti; Nitul Kakati; Seok Hee Lee; Seung Hyun Jee; Balasubramanian Viswanathan; Young Soo Yoon (pp. 48-66).
Though fuel cells have been considered as a viable energy conversion device, their adaptation for practical applications has been facing certain challenging issues regarding the availability of appropriate materials and components. For low temperature fuel cells, membranes that are cost effective and also competitive to Nafion® are the major requirements especially for Direct Methanol Fuel Cells (DMFC). Proton conductivity and methanol crossover are the two main characteristics that are of great concern for the development of suitable, alternate, and viable membranes for DMFC applications, though other factors including environmental acceptability are also important. In this regard, in recent time's poly (vinyl alcohol) based membranes have been developed as a viable alternative. This presentation therefore assesses the technological advances that have been made and the impediments that are faced in this development. This critical assessment exercise, it is presumed, may contribute toward a speedy development of this critical component for a viable fuel cell based energy economy.► Development of PVA based membrane for DMFC application. ► Alternate membranes in the near future. ► Examined the data of PVA membranes in the past one decade for DMFC application. ► Commercial feasibility being examined. ► Prescribed appropriate directions for the development of PVA based membranes.
Keywords: Poly (vinyl alcohol); Stability; Durability; Polymer electrolyte membrane; Direct methanol fuel cell
Molecular catalysis of the oxygen reduction reaction by iron porphyrin catalysts tethered into Nafion layers: An electrochemical study in solution and a membrane-electrode-assembly study in fuel cells
by Qinggang He; Tawanda Mugadza; Xiongwu Kang; Xiaobing Zhu; Shaowei Chen; John Kerr; Tebello Nyokong (pp. 67-75).
This study was motivated by the need for improved understanding of the kinetics and transport phenomena in a homogeneous catalyst system for the oxygen reduction reaction (ORR). Direct interaction between the sulfonic groups of Nafion and an Fe(III) meso-tetra( N-methyl-4-pyridyl) porphine chloride (Fe(III)TMPyP) compound was observed using FTIR and in situ UV–Vis spectroelectrochemical characterizations. A positive shift of the half wave potential value ( E1/2) for ORR on the iron porphyrin catalyst (Fe(III)TMPyP) was observed upon addition of a specific quantity of Nafion ionomer on a glassy carbon working electrode, indicating not only a faster charge transfer rate but also the role of protonation in the oxygen reduction reaction (ORR) process. A membrane electrode assembly (MEA) was made as a sandwich of a Pt-coated anode, a Nafion® 212 membrane, and a Fe(III)TMPyP + Nafion ionomer-coated cathode. This three-dimensional catalysis system has been demonstrated to be working in a H2/O2 proton exchange membrane (PEM) fuel cell test.► There exists ionic interaction between sulfonic groups of Nafion and FeTMPyP. ► The half wave potential value ( E1/2) for FeTMPyP was positively shifted by modifying the electrode with Nafion. ► Fuel cell molecular catalysis system has been demonstrated to be working based on a FeTMPyP + Nafion ionomer-coated cathode.
Keywords: Non-noble metal; Iron porphyrin; Oxygen reduction reaction; Nafion; Three-dimensional catalysis
High-capacity cathodes for lithium-ion batteries from nanostructured LiFePO4 synthesized by highly-flexible and scalable flame spray pyrolysis
by N.A. Hamid; S. Wennig; S. Hardt; A. Heinzel; C. Schulz; H. Wiggers (pp. 76-83).
Olivine, LiFePO4 is a promising cathode material for lithium-ion batteries due to its low cost, environmental acceptability and high stability. Its low electric conductivity prevented it for a long time from being used in large-scale applications. Decreasing its particle size along with carbon coating significantly improves electronic conductivity and lithium diffusion. With respect to the controlled formation of very small particles with large specific surface, gas-phase synthesis opens an economic and flexible route towards high-quality battery materials. Amorphous FePO4 was synthesized as precursor material for LiFePO4 by flame spray pyrolysis of a solution of iron acetylacetonate and tributyl phosphate in toluene. The pristine FePO4 with a specific surface from 126–218 m2 g−1 was post-processed to LiFePO4/C composite material via a solid-state reaction using Li2CO3 and glucose. The final olivine LiFePO4/C particles still showed a large specific surface of 24 m2 g−1 and were characterized using X-ray diffraction (XRD), electron microscopy, X-ray photoelectron spectrocopy (XPS) and elemental analysis. Electrochemical investigations of the final LiFePO4/C composites show reversible capacities of more than 145 mAh g−1 (about 115 mAh g−1 with respect to the total coating mass). The material supports high drain rates at 16 C while delivering 40 mAh g−1 and causes excellent cycle stability.► Nanosized FePO4⋅ xH2O was synthesized using highly scalable flame spray pyrolysis. ► High purity Nano-LiFePO4/C composite was produced by a subsequent solid-state reaction. ► Material consists of LiFePO4 NPs homogeneously distributed in a carbon matrix. ► Material has a good discharge capacity of more than 140 mAh g−1. ► Very high drain rates of 16 C while delivering 40 mAh g−1 are shown without degradation.
Keywords: Flame spray pyrolysis; Nanoscale FePO; 4; Specific surface area; LiFePO; 4; /C composite; Electrochemical properties
A combined photovoltaic and Li ion battery device for continuous energy harvesting and storage
by Vidhya Chakrapani; Florencia Rusli; Michael A. Filler; Paul A. Kohl (pp. 84-88).
The design, fabrication, and initial analysis of a continuous energy harvesting and storage device for wireless sensor applications were undertaken. A Si nanowire-based photovoltaic (PV) device and Li ion battery were integrated onto a single Si substrate. The three terminal device consisted of separate positive terminals for each component and a shared negative electrode. The effect of Li+ incorporation into the planar PV electrode was evaluated. The current–voltage behavior of the PV device was tolerant to high Li+ concentrations. A titanium nitride layer between the battery and PV portions of the shared electrode was shown to be an effective diffusion barrier to Li+ incorporation.► Integrated photovoltaic and Li ion battery device for continuous energy harvesting and storage. ► Material and processing challenges involved in building the proposed integrated device. ► Identification of TiN as a diffusion barrier layer for Li ions.
Keywords: Photovoltaic cell; Li ion battery; Integrated device; Silicon nanowires
Chromium poisoning and degradation at Gd0.2Ce0.8O2-impregnated LaNi0.6Fe0.4O3−δ cathode for solid oxide fuel cell
by Bo Huang; Xin-jian Zhu; Rui-xuan Ren; Yi-xing Hu; Xiao-yi Ding; Ye-bin Liu; Zong-yao Liu (pp. 89-98).
The degradation of cathode performances by chromium poisoning is studied at two cathodes LaNi0.6Fe0.4O3− δ (LNF) and 21.3 wt.% Gd0.2Ce0.8O2 (GDC)-impregnated LaNi0.6Fe0.4O3− δ on the scandia stabilized zirconia (ScSZ) electrolyte. Specific polarization resistance ( Rp) increases with time to the power of 1/3 and 1/5 in LNF and 21.3 wt.% GDC-impregnated LNF cathode after operating under a cathodic current density of 50 mA cm−2 under exposure of Cr vapors at 750 °C for 370 h and 1042 h, respectively. electrochemical impedance spectroscopy (EIS) illustrate that LNF exhibits far greater Rp than that of 21.3 wt.%GDC-impregnated LNF under exposure of Cr vapors due to strong Cr deposition at LNF/ScSZ interface. No significant degradation in performance has been observed after 1042 h of operating under a cathodic current density of 50 mA cm−2 under exposure of Cr vapors at 750 °C due to very little Cr deposition at 21.3 wt.%GDC-impregnated LNF/ScSZ interface, suggesting little poisoning effect for O2 reduction on 21.3 wt.%GDC-impregnated LNF cathode. The results demonstrate that 21.3 wt.%GDC-impregnated LNF cathode has a high resistance toward Cr deposition and high tolerance toward Cr poisoning.► Rp increases with time to the power of 1/3 and 1/5 in LNF and 21.3 wt.%GDC-impregnated LNF under Cr exposure. ► LNF exhibits far greater Rp than that of 21.3 wt.%GDC-impregnated LNF under Cr exposure. ► No significant degradation in performance is observed under Cr exposure in 21.3 wt.%GDC-impregnated LNF.
Keywords: Chromia-forming alloy; Chromium poisoning; Electrochemical properties; Impedance spectroscopy; Oxygen reduction; Solid oxide fuel cell
A new hybrid redox flow battery with multiple redox couples
by Wei Wang; Liyu Li; Zimin Nie; Baowei Chen; Qingtao Luo; Yuyan Shao; Xiaoliang Wei; Feng Chen; Guan-Guang Xia; Zhenguo Yang (pp. 99-103).
A redox flow battery using V4+/V5+ vs. V2+/V3+ and Fe2+/Fe3+ vs. V2+/V3+ redox couples in chloric/sulfuric mixed acid supporting electrolyte was investigated for potential stationary energy storage applications. The Fe/V hybrid redox flow cell using mixed reactant solutions and operated within a voltage window of 0.5–1.7 V demonstrated stable cycling over 100 cycles with energy efficiency ∼80% and negligible capacity fading at room temperature. A 66% improvement in the energy density of the Fe/V hybrid cell was achieved compared with the previously reported Fe/V cell using only Fe2+/Fe3+ vs. V2+/V3+ redox couples.► Two redox couples were employed in an aqueous redox flow battery system. ► Stable cycling of over 100 cycles was demonstrated with negligible capacity fading. ► Fe/V hybrid redox flow battery represents the most efficient use of the expensive vanadium source.
Keywords: Redox flow battery; Hydrochloric acid; Sulfuric acid; Fe; V; Energy storage
Simulation of demand management and grid balancing with electric vehicles
by James Druitt; Wolf-Gerrit Früh (pp. 104-116).
This study investigates the potential role of electric vehicles in an electricity network with a high contribution from variable generation such as wind power. Electric vehicles are modelled to provide demand management through flexible charging requirements and energy balancing for the network. Balancing applications include both demand balancing and vehicle-to-grid discharging.This study is configured to represent the UK grid with balancing requirements derived from wind generation calculated from weather station wind speeds on the supply side and National Grid data from on the demand side. The simulation models 1000 individual vehicle entities to represent the behaviour of larger numbers of vehicles. A stochastic trip generation profile is used to generate realistic journey characteristics, whilst a market pricing model allows charging and balancing decisions to be based on realistic market price conditions.The simulation has been tested with wind generation capacities representing up to 30% of UK consumption. Results show significant improvements to load following conditions with the introduction of electric vehicles, suggesting that they could substantially facilitate the uptake of intermittent renewable generation. Electric vehicle owners would benefit from flexible charging and selling tariffs, with the majority of revenue derived from vehicle-to-grid participation in balancing markets.► We model integration of electric vehicles and wind power into an electricity grid. ► The electric vehicle behaviour is driven by driver needs and electricity prices. ► The model calculates benefits for electricity supplier and individual drivers. ► Real-time market pricing information is important for drivers.
Keywords: Electric grid balancing; Demand management; Wind generation; Electric vehicles; Vehicle-to-grid
Nanocomposite SnO2–Se thin film as anode material for lithium-ion batteries
by Xing-Le Ding; Qian Sun; Fang Lu; Zheng-Wen Fu (pp. 117-123).
The electrochemical properties of nanocomposite SnO2–Se thin film prepared by pulsed laser deposition method have been investigated by cyclic voltammetry and charge/discharge measurements. A large reversible specific capacity of 958.8 mAh g−1 in SnO2–Se/Li cell cycled between 0.01 and 3.0 V is achieved. Our results have demonstrated that nanocomposite SnO2–Se exhibits larger capacity and better cycle performance than pure SnO2 and SnSe. The electrochemical reaction mechanisms of SnO2–Se with lithium are examined by X-ray diffraction, high resolution transmission electron microscopy, selected-area electron diffraction and spectroelectrochemical measurements. The reversible oxidation/reduction reaction of SnO2 and selenidation/reduction reaction of SnSe are revealed.► In this paper, nanocomposite SnO2–Se thin film electrode was fabricated by pulsed laser deposition. ► We examined the electrochemical properties of nanocomposite SnO2–Se electrode. ► SnO2–Se/Li cells exhibited a large reversible specific capacity of about 958.8 mAh g−1. ► The reversible oxidation/reduction reaction mechanism of SnO2–Se with lithium was revealed.
Keywords: Tin oxide–selenide; Pulsed laser deposition; Nanocomposite; Lithium ion batteries
Highly durable anode supported solid oxide fuel cell with an infiltrated cathode
by Alfred Junio Samson; Per Hjalmarsson; Martin Søgaard; Johan Hjelm; Nikolaos Bonanos (pp. 124-130).
An anode supported solid oxide fuel cell with an La0.6Sr0.4Co1.05O3− δ (LSC) infiltrated-Ce0.9Gd0.1O1.95 (CGO) cathode that shows a stable performance has been developed. The cathode was prepared by screen printing a porous CGO backbone on top of a laminated and co-fired anode supported half cell, consisting of a Ni–yttria stabilized zirconia (YSZ) anode support, a Ni–scandia-doped yttria-stabilized zirconia (ScYSZ) anode, a ScYSZ electrolyte, and a CGO barrier layer. LSC was introduced into the CGO backbone by multiple infiltrations of an aqueous nitrate solution followed by firing. The cell was tested at 700 °C under a current density of 0.5 A cm−2 for 1500 h using air as oxidant and humidified hydrogen as fuel. The electrochemical performance of the cell was analyzed by impedance spectroscopy and current–voltage relationships. No measurable degradation in the cell voltage or increase in the resistance from the recorded impedance was observed during long term testing. The power density reached 0.79 W cm−2 at a cell voltage of 0.6 V at 750 °C. Post test analysis of the LSC infiltrated-CGO cathode by scanning electron microscopy revealed no significant micro-structural difference to that of a nominally identical untested counterpart.► Electrochemically stable anode supported cell (ASC) with an LSC infiltrated-CGO cathode. ► No measurable degradation during 1500 h long operation at 700 °C and 0.5 A cm−2. ► No change in impedance spectra recorded in situ. ► Post test characterization revealed no change in microstructure of the LSC infiltrate. ► ASC power density reached 0.79 W cm−2 at 750 °C at a cell voltage of 0.6 V.
Keywords: Cathode; Infiltration; Solid oxide fuel cells; Mixed ionic and electronic conductor; Electrochemical impedance spectroscopy; Scanning electron microscopy
Shape evolution of patterned amorphous and polycrystalline silicon microarray thin film electrodes caused by lithium insertion and extraction
by Yu He; Xiqian Yu; Geng Li; Rui Wang; Hong Li; Yeliang Wang; Hongjun Gao; Xuejie Huang (pp. 131-138).
Silicon is the most promising high capacity anode material to replace graphite for developing next generation high energy density Li-ion batteries. In this approach, patterned amorphous and microcrystalline Si thin film electrodes (a-Si and μc-Si) have been prepared by rf-sputtering and etched further by a reactive ion etching (RIE) system to form square-shape microcolumn electrodes with controllable size (5 × 5 μm width, 500 nm height, aspect ratio of width/height is 10:1) and array distance (5 μm). It has been found that the volume expansion and contraction of a-Si and μc-Si are anisotropic, about 180% along vertical direction and 40% along lateral direction. The total volume variation changes linearly with the increase of lithium insertion content up to ∼310% for a-Si and ∼300% for μc-Si. It occurs nearly reversibly. In addition, it is observed that the original square-shape Si column transforms into the dome-like appearance after lithium insertion and changes into bowl shape after lithium extraction gradually. Radial-like curved cracks are formed after 5−10 cycles and the neighboring Si columns tend to merge together when the distance of the columns is less than 1 μm.Shape evolution and quantitative volume variation of patterned amorphous and microcrystalline Si microcolumn electrodes after lithium insertion and extraction are investigated using ex-situ AFM and SEM.Display Omitted► Shape evolution of Si columns upon lithium insertion and extraction. ► Anisotropic, linear and reversible volume changes. ► ∼300% volume change after fully lithium insertion and extraction. ► Cracking and irreversible electrochemical agglomeration.
Keywords: Silicon; Pattern; Thin film electrode; Lithium ion batteries; Atomic force microscopy; Shape
A comparison of sputtered and mechanically milled Cu6Sn5 + C materials for Li-ion battery negative electrodes
by J.S. Thorne; J.R. Dahn; M.N. Obrovac; R.A. Dunlap (pp. 139-144).
Sn27Cu33C40 produced by mechanical milling is compared with Sn27Cu31C42 and Sn26Cu31C43 produced by magnetron sputtering for use as anode materials in Li-ion batteries. The sputtered samples were found to be amorphous/nanostructured and had a greater degree of atomic intermixing in comparison to the milled sample, which was more crystalline. Samples were incorporated as electrodes in Li-half cells and had a capacity of about 400 mAh g−1. Significant capacity loss was observed beginning near the 50th cycle for the mechanically milled sample, while little capacity loss was observed for the sputtered samples after 100 cycles. Despite its good cycling performance, amorphous Cu6Sn5 + C was found to crystallize as Li is cycled, resulting in the aggregation of Cu6Sn5 grains. Structural changes during lithiation and delithiation as well as the evolution of the electrochemistry are compared and contrasted for the two materials.► Electrochemical cycling characteristics of nanostructured Sn–Cu–C are reported. ► The study provides a systematic comparison of sputtered and milled samples. ► Microstructural changes during cycling are investigated. ► Results help to understand cycling behavior of commercial Sn-based anodes. ► Provides insight into reactions in commercially viable CuSn-based materials.
Keywords: Cu; 6; Sn; 5; Sn–Cu–C; Li-ion batteries; Mechanical milling; Nanostructured materials
A3V2(PO4)3 (A = Na or Li) probed by in situ X-ray absorption spectroscopy
by Maja Pivko; Iztok Arcon; Marjan Bele; Robert Dominko; Miran Gaberscek (pp. 145-151).
Two stable modifications of A3V2(PO4)3 (A = Na or Li) were synthesized by citric acid assisted modified sol–gel synthesis. The obtained samples were phase pure Li3V2(PO4)3 and Na3V2(PO4)3 materials embedded in a carbon matrix. The samples were tested as half cells against lithium or sodium metal. Both samples delivered about 90 mAh g−1 at a C/10 cycling rate. The change of vanadium oxidation state and changes in the local environment of redox center for both materials were probed by in-situ X-ray absorption spectroscopy. Oxidation state of vanadium was determined by energy shift of the absorption edge. The reversible change of valence from trivalent to tetravalent oxidation state was determined in the potential window used in our experiments. Small reversible changes in the interatomic distances due to the relaxation of the structure in the process of alkali metal extraction and insertion were observed. Local environment (vanadium–oxygen bond distances) after 1st cycle were found to be the same as in the starting material. Both structures have been found very rigid without significant changes during alkali metal extraction.► In situ V XANES study in Li3V2(PO4)3 and Na3V2(PO4)3. ► In situ V EXAFS study in Li3V2(PO4)3 and Na3V2(PO4)3. ► Local environment of V atoms in NASICON structure during alkali metal deinsertion/insertion.
Keywords: Li; 3; V; 2; (PO; 4; ); 3; Na; 3; V; 2; (PO; 4; ); 3; XAS; Li-ion batteries; Sodium batteries; NASICON
A quasi-three-dimensional non-isothermal dynamic model of a high-temperature proton exchange membrane fuel cell
by Jaeman Park; Kyoungdoug Min (pp. 152-161).
A quasi-three-dimensional non-isothermal dynamic model of a high-temperature proton exchange membrane fuel cell, operating with a polybenzimidazole membrane, has been developed. In the model, dynamic equations of energy conservation, species conservation and electrochemical reaction are solved within a simplified quasi-three-dimensional geometry. With this simplified geometry, the model can predict the distribution of fuel cell characteristics and physical phenomena in a high-temperature proton exchange membrane fuel cell during the steady and the transient states within minutes, without using a computational fluid dynamics program. The simulation results of the current–voltage polarization curve are validated with the experimental data reported in the literature. The simulation results show a good agreement with the experimental data and show that the variation of temperature strongly affects the fuel cell’s performance. In particular, the simulation results show that the transient response of the cell voltage is dependent upon that of the cell temperature.►The model can predict dynamic characteristics of High-Temperature PEM Fuel Cell. ►Increased cell temperature results in enhanced fuel cell performance. ►In transient state, the second time delay is related to the MEA temperature. ►The transient response of the voltage is strongly dependent on the cell temperature.
Keywords: High temperature; Polybenzimidazole; Proton exchange membrane fuel cell; Modeling
Carbon-coated nanoclustered LiMn0.71Fe0.29PO4 cathode for lithium-ion batteries
by Minki Jo; HoChun Yoo; Yoon Seok Jung; Jaephil Cho (pp. 162-168).
Carbon-coated clustered LiMn0.71Fe0.29PO4 ( c-LMFP) nanoparticles are prepared from ball-milling with a mixture of ∼40 nm thick LMFP nanoplates obtained by polyol method and carbon black. The clustered nanocomposite structure of c-LMFP turns out to have advantages of improved volumetric energy density and electrochemical performance. The c-LMFP exhibits increased tap density of 0.9 g cm−3, compared with the as-prepared LMFP nanoplates (0.6 g cm−3), providing with high volumetric discharge capacity of 243 mA h cm−3 at 0.1C and 128 mA h cm−3 even at 7C at 21 °C. At elevated temperature (60 °C), the capacity retention of c-LMFP remains excellent (100% of its initial capacity (165 mA h g−1) at the same cycling condition as 21 °C). In sharp contrast, capacity of carbon-coated LiMnPO4 ( c-LMP) exhibits volumetric discharge capacity of 72 mA h cm−3 at 5C and decays rapidly at 60 °C after 40 cycles (capacity retention of 58%). The better cycling stability of c-LMFP than that of c-LMP is believed to be associated with mitigated Mn2+ dissolution by Fe2+ substitution.► Carbon-coated nanoclustered LiMn0.71Fe0.29PO4 were prepared. ► The clustered morphology resulted in improved tap density and volumetric capacity. ► The carbon-coated LiMn0.71Fe0.29PO4 exhibited much better performance than the carbon-coated LiMnPO4. ► The ex-situ surface analyses were carried out using Raman spectroscopy, TOF-SIMS, and ICP-OES.
Keywords: Lithium-ion battery; Cathode; Nanoparticle; Polyol method; Olivine; Carbon-coating
Enhanced nanoscale conduction capability of a MoO2/Graphene composite for high performance anodes in lithium ion batteries
by Akkisetty Bhaskar; Melepurath Deepa; T.N. Rao; U.V. Varadaraju (pp. 169-178).
A MoO2/Graphene composite as a high performance anode for Li ion batteries is synthesized by a one pot in-situ low temperature solution phase reduction method. Electron microscopy and Raman spectroscopy results confirm that 2D graphene layers entrap MoO2 nanoparticles homogeneously in the composite. X-ray photoelectron spectroscopy shows the presence of oxygen functionalities on graphene, which allows intimate contact between MoO2 nanoparticles and the graphene. Conductive atomic force microscopy reveals an extraordinarily high nanoscale electronic conductivity for MoO2/Graphene, greater by 8 orders of magnitude in comparison to bulk MoO2. The layered nanostructure and the conductive matrix provide uninhibited conducting pathways for fast charge transfer and transport between the oxide nanoparticles and graphene which are responsible for the high rate capability, a large lithium ion capacity of 770 mAh g−1, and an excellent cycling stability (550 mAh g−1 reversible capacity retained even after 1000 cycles!) at a current density of 540 mA g−1, thereby rendering it to be superior to previously reported values for neat MoO2 or MoO2/Graphene composite. Impedance analyses demonstrate a lowered interfacial resistance for the composite in comparison to neat MoO2. Our results demonstrate the enormous promise that MoO2/Graphene holds for practical Li-ion batteries.Display Omitted► MoO2/Graphene composite by a one pot low temperature in-situ solution reduction method. ► Uniform entrapment of MoO2 nanoparticles in 2D graphene scaffolds. ► An eight order increase in nanoscale conductivity of MoO2/Graphene relative to MoO2. ► Unparalleled reversible capacity of 770 mAh g−1 at 540 mA g−1 for MoO2/Graphene. ► A coulombic efficiency of almost 100% retained even after 1000 cycles.
Keywords: Molybdenum dioxide; Graphene; Lithium ion batteries; Conducting atomic force microscopy; Anode
Surface studies of high voltage lithium rich composition: Li1.2Mn0.525Ni0.175Co0.1O2
by Surendra K. Martha; Jagjit Nanda; Gabriel M. Veith; Nancy J. Dudney (pp. 179-186).
This article reports the evidence of surface film formation due to the oxidation of electrolyte upon high voltage cycling (4.9 V) of the lithium rich cathode, Li1.2Mn0.525Ni0.175Co0.1O2. We have studied the chemical composition of this surface film using electrochemical impedance, X-ray Photoelectron and micro-Raman spectroscopies and the results are compared against the pristine electrode. In order to distinguish the changes in the surface film composition induced by prolonged electrochemical cycling versus chemical passivation effect, we studied the surface composition of cathode powders aged with electrolytes at 60 °C. Our results show that after 150 cycles, the electrodes showed a rapid drop in capacity due to increase in the surface film resistance resulting in limited capacity utilization.► High voltage cycling (4.9 V) of lithium rich Li1.2Mn0.525Ni0.175Co0.1O2 cathode. ► Surface film formation because of the oxidation of electrolyte. ► Studies of surface film using EIS, XPS and micro-Raman spectroscopy. ► Increase in cell impedance due to formation of polycarbonates, LiF, Li xPF y etc. ► Formation of thick surface film is the dominant reason for decrease in capacity.
Keywords: Lithium battery; Li-rich MNC; Impedance; Surface chemistry; XPS; Micro-Raman spectroscopy
MnO2–graphene hybrid as an alternative cathodic catalyst to platinum in microbial fuel cells
by Qing Wen; Shaoyun Wang; Jun Yan; Lijie Cong; Zhongcheng Pan; Yueming Ren; Zhuangjun Fan (pp. 187-191).
Manganese dioxide–graphene nanosheet (MnO2/GNS) hybrid is used as an alternative cathode catalyst for oxygen reduction reaction in air-cathode microbial fuel cell (MFC). The results show that the nanostructured MnO2/GNS composite exhibit an excellent catalytic activity for oxygen reduction reaction due to MnO2 nanoparticles closely anchored on the excellent conductive graphene nanosheets. As a result, MFC with MnO2/GNS as air cathode catalyst generates a maximum power density of 2083 mW m−2, which is higher than that of MFC with pure manganese dioxide catalyst (1470 mW m−2). Therefore, MnO2/GNS nanocomposite is an efficient and cost-effective cathode catalyst for practical MFC applications.► MnO2–graphene nanosheet (MnO2/GNS) hybrid is prepared under microwave irradiation. ► The electrode modified by MnO2/GNS exhibits high catalytic activity for ORR. ► Microbial fuel cells with MnO2/GNS generates a maximum power density of 2083 mW m−2.
Keywords: Microbial fuel cell; Graphene; Manganese dioxide–graphene hybrid; Oxygen reduction reaction
An improved high-power battery with increased thermal operating range: C–LiFePO4//C–Li4Ti5O12
by K. Zaghib; M. Dontigny; A. Guerfi; J. Trottier; J. Hamel-Paquet; V. Gariepy; K. Galoutov; P. Hovington; A. Mauger; H. Groult; C.M. Julien (pp. 192-200).
The carbon-coated LiFePO4 and C–Li4Ti5O12 particles of 90 nm in diameter have been tested as active elements of electrodes of Li-ion batteries. The 18650-size cell using the usual electrolyte 1 mol L−1 LiPF6 in ethylene carbonate (EC) and diethylene carbonate (DEC) displays a charge capacity of 650 mAh at low C-rate and retains more than 80% of rated capacity at 60C charge rate (1 min). 2032-size coin cells have been tested with different electrolytes: 1.5 mol L−1 lithium tetrafluoroborate LiBF4 in EC+ γ-butyrolactone (GBL), and 0.5 mol L−1 lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2, LiTFSI) + 1 mol L−1 LiBF4 in EC + GBL, aiming to replace the less stable LiPF6 salt. The LiTFSI-based electrolyte can be used owing to the low operating voltage that avoids the corrosion of the aluminum of the collector. This electrolyte shows the best results as the performance is even higher at 60 °C. The infrared images show that the temperature of the cell never reaches this temperature during cycling, making this battery a high-power battery with remarkable thermal stability. The maximum temperature reached by the cell is 34 °C at 40C-rate and 40 °C at 60C. The free EC-based electrolytes even operate at 80 °C by using 1 mol L−1 lithium bis(fluorosulfonyl)imide (LiFSI) in GBL or 1 mol L−1 LiFSI in PC + GBL, thus increasing importantly the operating temperature range for the battery. The carbon coated on LTO depresses the evolution of gases during charge discharge.► The 18650 cell was charged at 60C (1 min) with 80% of rated capability. ► Li4Ti5O12 allows the replacement of LiPF6 salt by LiTFSI and LiFSI in free EC for lower temperature. ► C–LTO depress the gas during charge discharge cycling and make technology very safe.
Keywords: Li-ion battery; Electrode performance; Thermal behavior; Electrolyte stability
MnO/reduced graphene oxide sheet hybrid as an anode for Li-ion batteries with enhanced lithium storage performance
by Y.J. Mai; D. Zhang; Y.Q. Qiao; C.D. Gu; X.L. Wang; J.P. Tu (pp. 201-207).
Relatively small hysteresis in voltage, appropriate electromotive force and low average delithiation voltage make MnO, among many transition metal oxides. MnO/reduced graphene oxide sheet (MnO/RGOS) hybrid is synthesized by a two-step electrode design consisting of liquid phase deposition of MnCO3 nanoparticles on the surface of graphene oxide sheets followed by heat treatment in flowing nitrogen. As an anode for Li-ion batteries, the MnO/RGOS hybrid electrode shows a reversible capacity of 665.5 mA h g−1 after 50 cycles at a current density of 100 mA g−1 and delivers 454.2 mA h g−1 at a rate of 400 mA g−1, which is obviously better than that of bare MnO electrode. Those reasons for such enhanced electrochemical properties are investigated by galvanostatic intermittent titration technique (GITT) as well as electrochemical impedance spectroscopy (EIS). The probable origins, in the term of thermodynamic and kinetic factors, for the marked hysteresis in voltage observed between charge and discharge are also discussed.► MnO/RGOS hybrid is synthesized by a two-step electrode design. ► As an anode material, it displays superior lithium storage performance. ► Reasons for such enhanced performance are investigated by TEM, GITT and EIS. ► The probable origins of hysteresis in voltage are discussed.
Keywords: Manganese monoxide; Graphene; Hybrid; Lithium ion battery
Sm0.5Sr0.5CoO3−δ-infiltrated cathodes for solid oxide fuel cells with improved oxygen reduction activity and stability
by Fucun Wang; Dengjie Chen; Zongping Shao (pp. 208-215).
Sm0.5Sr0.5CoO3−δ (SSC)-impregnated cathodes are fabricated by the solution infiltration of metal nitrates. The effects of complexing agents on the phase structure and the effects of pore formers on the porosity of the scaffold are examined and optimized. The thermal expansion behavior, electrical conductivities and electrochemical performance of the cathodes are characterized and optimized. A pure perovskite phase is formed after heating at 800 °C by adding a relatively small quantity of glycine as the complexing agent. Polyvinyl butyral is selected as the pore former for the preparation of porous Sm0.2Ce0.8O1.9 (SDC) scaffolds. The thermal expansion coefficient increases slightly from 12.74 × 10−6 K−1 to 13.28 × 10−6 K−1 after infiltrating 20 wt% SSC into the SDC scaffold. The infiltrated cathode with 20 wt% SSC + 80 wt% SDC shows the electrical conductivity of 15 S cm−1 at 700 °C. A well-connected SSC network is formed in the cathode after infiltrating 20 wt% SSC into the SDC scaffold. Cathode polarization resistance values as low as 0.05 Ω cm2, peak power density values as high as 936 mW cm−2 and stable performance throughout 325 h of operation at 700 °C suggest that the cathodes with the 20 wt% SSC-infiltrated SDC are suitable for practical application. However, for the SSC infiltrated into the 8 mol% yttria-stabilized zirconia scaffold, the interfacial reaction continues to occur during the stability test at 700 °C. SDC is preferred as a scaffold for the infiltration of SSC to ensure long-term operational stability.► Sm0.2Ce0.8O1.9 (SDC) was preferred as a porous scaffold for the infiltration. ► A pure Sm0.5Sr0.5CoO3−δ (SSC) phase was formed with glycine as a complexing agent. ► Electrical conductivities of ∼15 S cm−1 were achieved with 20 wt% SSC + 80 wt% SDC. ► A stable performance was obtained with a 20 wt% SSC + 80 wt% SDC electrode. ► A 20 wt% SSC + 80 wt% SDC electrode showed a resistance of 0.05 Ω cm2 at 700 °C.
Keywords: Solid oxide fuel cells; Cathodes; Infiltration; Long-term stability
A lithium-ion battery separator prepared using a phase inversion process
by Xiaosong Huang (pp. 216-221).
A battery separator is a porous membrane that separates the positive and negative electrodes while maintaining a good ionic flow. A method of making separators made of polyetherimide through a phase-inversion process is described. The membranes prepared by this process showed uniform porous structures as indicated by the scanning electron microscope (SEM) images. The membranes also exhibited satisfactory tensile properties and enabled high ionic conductance when saturated with a liquid electrolyte for lithium-ion batteries. Coin cells with this type of separators were prepared. Stable cycling performance and improved rate capabilities were observed when tested at room temperature.► Phase inversion is used to make a membrane with a uniform porous structure. ► The membrane shows satisfactory tensile strength at break. ► The membrane saturated with a liquid electrolyte enables good ionic conductance. ► Cells with this separator show excellent rate capability.
Keywords: Phase inversion; Battery separator; Porous; Rate capability; Lithium ion battery
Rechargeable hybrid aqueous batteries
by Jing Yan; Jing Wang; Hao Liu; Zhumabay Bakenov; Denise Gosselink; P. Chen (pp. 222-226).
A new aqueous rechargeable battery combining an intercalation cathode with a metal (first order electrode) anode has been developed. The concept is demonstrated using LiMn2O4 and zinc metal electrodes in an aqueous electrolyte containing two electrochemically active ions (Li+ and Zn2+). The battery operates at about 2 V and preliminarily tests show excellent cycling performance, with about 90% initial capacity retention over 1000 charge–discharge cycles. Use of cation-doped LiMn2O4 cathode further improves the cyclability of the system, which reaches 95% capacity retention after 4000 cycles. The energy density for a prototype battery, estimated at 50–80 Wh kg−1, is comparable or superior to commercial 2 V rechargeable batteries. The combined performance attributes of this new rechargeable aqueous battery indicate that it constitutes a viable alternative to commercial lead-acid system and for large scale energy storage application.► New concept in rechargeable aqueous batteries. ► Deposition/dissolution anode and intercalation cathode in aqueous electrolyte. ► Energy storage system with large capacity retention and long cycle life. ► Alternative to commercial lead-acid batteries and for load leveling applications.
Keywords: Aqueous electrolyte; Electrochemistry; Intercalation; Metal electrode; Rechargeable battery
Development and characterization of glass-ceramic sealants in the (CaO–Al2O3–SiO2–B2O3) system for Solid Oxide Electrolyzer Cells
by Hichem Khedim; Hélène Nonnet; François O. Méar (pp. 227-236).
The efficiency of glass-ceramic sealants plays a crucial role in Solid Oxide Electrolyzer Cell performance and durability. In order to develop suitable sealants, operating around 800 °C, two parent glass compositions, CAS1B and CAS2B, from the CaO–Al2O3–SiO2–B2O3 system were prepared and explored. The thermal and physicochemical properties of the glass ceramics and their crystallization behavior were investigated by HSM, DTA and XRD analyses. The microstructure and chemical compositions of the crystalline phases were investigated by microprobe analysis. Bonding characteristic as well as chemical interactions of the parent glass with yttria-stabilized zirconia (YSZ) electrolyte and ferritic steel-based interconnect (Crofer®) were also investigated. The preliminary results revealed the superiority of CAS2B glass for sealing application in SOECs. The effect of minor additions of V2O5, K2O and TiO2 on the thermal properties was also studied and again demonstrated the advantages of the CAS2B glass composition. Examining the influence of heat treatment on the seal behavior showed that the choice of the heating rate is a compromise between delaying the crystallization process and delaying the viscosity drop. The thermal Expansion Coefficients (TEC) obtained for the selected glass ceramic are within the desired range after the heat treatment of crystallization. The crystallization kinetic parameters of the selected glass composition were also determined under non-isothermal conditions by means of differential thermal analysis (DTA) and using the formal theory of transformations for heterogeneous nucleation.► New glass-ceramic formulation for sealing applications. ► Influence of heat treatment on the seal behavior and crystallization process. ► Glass-ceramic/Metal and glass-ceramic/ceramic interfaces and interactions. ► Effect of V2O5, K2O and TiO2 on thermal properties. ► Determination of crystallization kinetic parameters of the selected composition.
Keywords: Solid Oxide Electrolyzer Cell (SOEC); Sealing materials; Glass-ceramic; Metal–glass interface
Integrated thermal and energy management of plug-in hybrid electric vehicles
by Mojtaba Shams-Zahraei; Abbas Z. Kouzani; Steffen Kutter; Bernard Bäker (pp. 237-248).
In plug-in hybrid electric vehicles (PHEVs), the engine temperature declines due to reduced engine load and extended engine off period. It is proven that the engine efficiency and emissions depend on the engine temperature. Also, temperature influences the vehicle air-conditioner and the cabin heater loads. Particularly, while the engine is cold, the power demand of the cabin heater needs to be provided by the batteries instead of the waste heat of engine coolant. The existing energy management strategies (EMS) of PHEVs focus on the improvement of fuel efficiency based on hot engine characteristics neglecting the effect of temperature on the engine performance and the vehicle power demand. This paper presents a new EMS incorporating an engine thermal management method which derives the global optimal battery charge depletion trajectories. A dynamic programming-based algorithm is developed to enforce the charge depletion boundaries, while optimizing a fuel consumption cost function by controlling the engine power. The optimal control problem formulates the cost function based on two state variables: battery charge and engine internal temperature. Simulation results demonstrate that temperature and the cabin heater/air-conditioner power demand can significantly influence the optimal solution for the EMS, and accordingly fuel efficiency and emissions of PHEVs.► PHEVs' optimal energy management strategy (EMS) is highly influenced by temperature. ► DP algorithm considers both battery charge and engine temperature state variables. ► Optimal charge depletion trajectory represents an optimal engine temperature trajectory. ► Real-time sub-optimal EMS can be realised by following the optimal charge trajectory.
Keywords: Energy management strategy; Temperature; Thermal management; Plug-in hybrid electric vehicle; Optimal control; Dynamic programing
Direct synthesis of oxygen-deficient Li2MnO3− x for high capacity lithium battery electrodes
by Kei Kubota; Takayuki Kaneko; Masaaki Hirayama; Masao Yonemura; Yuichiro Imanari; Kenji Nakane; Ryoji Kanno (pp. 249-255).
Oxygen-deficient Li2MnO3− x (0 < x < 0.19) have been directly synthesized from lithium-rich manganese oxide, Li2MnO3, using metal hydrides (CaH2 and LiH) as reducing agents at reaction temperatures of 255–265 °C. The structure of the reduced phase determined by X-ray diffraction experiments has oxygen vacancies in the layered structure, causing slightly larger lattice parameters than the stoichiometric Li2MnO3. Reversible oxygen insertion and extraction from the deficient structure observed by the TG measurements suggests fast oxygen diffusion in the layered rock-salt structure. The oxygen-deficient phase shows extremely large 1st charge and discharge capacities of 388 and 305 mAh g−1, respectively.► The new oxygen deficient phase was directly synthesized by reduction treatment. ► The phase showed reversible oxygen insertion and extraction. ► A 1st discharge capacity of 305 mAh g−1 without a 1st charge plateau above 4.4 V.
Keywords: Lithium batteries; Layered cathode material; Lithium manganese oxide; Metal hydride; Anomalous capacity; Li; 2; MnO; 3
A core-shell structured, metal–ceramic composite-supported Ru catalyst for methane steam reforming
by Hyun Chul Lee; Yulia Potapova; Doohwan Lee (pp. 256-260).
Methane steam reforming on a metal–ceramic composite-supported ruthenium catalyst is studied at high temperatures. The core-shell structured Al2O3@Al composite consisting primarily of an Al metal core with a high surface area γ-Al2O3 overlayer is obtained by hydrothermal oxidation. Under the synthesis condition, primary Al2O3@Al particles aggregate to form a hierarchal secondary structure with macrosize inter-pores. This core-shell composite support enhances the heat conductivity and provides a high surface area for fine dispersion of a catalytic Ru component on the γ-Al2O3 overlayer. The Ru/Al2O3@Al catalyst exhibits significantly higher CH4 conversion than the conventional Ru/Al2O3 catalyst, indicating its superior properties for methane steam reforming at high temperatures contributed due to the fine Ru dispersion and facilitated heat and mass transfer via the unique catalyst structure. This metal–ceramic composite catalyst is stable in the reforming reaction for an extended time, suggesting reasonable stability in its physicochemical properties.► Hydrothermal oxidation of Al metal particles was carried out at elevated temperatures. ► It formed a core-shell structured Al2O3@Al metal–ceramic composite. ► The structure offered superior heat conductivity, surface area, and hierarchal pores. ► We used it as a support of ruthenium catalyst for methane steam reforming. ► The catalyst resulted in significantly enhanced hydrogen production yields.
Keywords: Core-shell catalyst; Metal–ceramic composite; Fuel processing; Fuel cell
Preparation and properties of novel sulfonated poly( p-phenylene- co-aryl ether ketone)s for polymer electrolyte fuel cell applications
by Xuan Zhang; Zhaoxia Hu; Yanli Pu; Shanshan Chen; Jiani Ling; Huiping Bi; Shouwen Chen; Lianjun Wang; Ken-ichi Okamoto (pp. 261-268).
A series of sulfonated poly( p-phenylene- co-aryl ether ketone) (SPP- co-PAEK) membranes are successfully prepared from 2,5-dichloro-3′-sulfobenzophenone and 2,2′-bis[4-(4-chlorobenzoyl)] phenoxyl perfluoropropane through Ni(0)-catalyzed copolymerization for polymer electrolyte membrane fuel cell (PEFC) applications. The obtained SPP- co-PAEKs have fairly high reduced viscosities and give ductile and transparent membranes with good mechanical strength. All the membranes exhibit comparable or even better proton conductivities than that of Nafion 112 in the full hydrate state. In addition, the membranes showed almost isotropic proton conductive behavior with σ⊥/ σ|| values in the range of 0.85–0.92. Fuel cell operation using SPP- co-PAEK(3/1) (IEC = 2.0 meq g−1, thickness of 38 μm, feed gases: H2/air) exhibited rather good performances: open circuit voltage of 0.94 V, cell voltage at 1.0 A cm−2 of 0.61 V, and output at 1.7 A cm−2 of 0.85 W cm−2 under 90 °C and 82/68% relative humidity condition. The results suggested that these SPP- co-PAEK membranes are promising candidates for PEFC applications.A series of sulfonated poly( p-phenylene- co-aryl ether ketone) (SPP- co-PAEK) membranes were successfully prepared through Ni(0)-catalyzed copolymerization and had fairly high viscosity to give tough, flexible and transparent membranes. The membrane of SPP- co-PAEK(3/1) (IEC = 2.0 meq g−1) showed high polymer electrolyte fuel cell (PEFC) performance with open circuit voltage (OCV) of 0.94 V, cell voltage at 1.0 A cm−2 ( V1.0) of 0.61 V, and output at 1.7 A cm−2 of 0.85 W cm−2 under 90 °C and 82/68% relative humidity condition (82% RH and 68% RH for anode and cathode, respectively).Display Omitted► Sulfonated poly( p-phenylene-co-aryl ether ketone) were prepared by Ni(0)-catalyzed copolymerization. ► The anisotropic proton conductivity ratio for the membranes was about 0.85–0.92. ► SPP-co-PAEK(3/1) showed OCV of 0.94 V and output of 0.85 W/cm2 (90 °C, 82/68 %RH). ► They exhibited good fuel cell performance on a 300 h durability test.
Keywords: Sulfonated poly(; p; -phenylene-; co; -aryl ether ketone) membranes; Ni(0)-catalyzed copolymerization; Polymer electrolyte membrane fuel cell; Proton conductivity
Magnetic-field effect on dye-sensitized ZnO nanorods-based solar cells
by Fengshi Cai; Jing Wang; Zhihao Yuan; Yueqin Duan (pp. 269-272).
We reported on the effect of an external magnetic field on the photovoltaic performance of Ru-bipyridyl dye N719 or CdS-sensitized ZnO nanorods-based solar cells (DSCs). At the short circuit, increases in photocurrent of ∼25% and ∼34% can be obtained at an external magnetic fields of less than 10 mT for N719 and CdS-DSCs, respectively, which in turn increase the energy conversion efficiency of ∼31% and ∼46%. This increase in photocurrent is attributed to an increase in the efficient separation of electron–hole pairs and a decrease in electron transport resistance in ZnO nanorods film under applied magnetic field. These interesting magnetic-field effects can lead to new potential applications in enhanced DSCs efficiency.► The effect of a magnetic field on the photovoltaic performance was investigated. ► Photocurrent was enhanced at magnetic fields of less than 10 mT. ► Applied magnetic field increased the efficient separation of electron–hole pairs.
Keywords: Dye-sensitized solar cells; Magnetic-field; Zinc oxide nanorods; Photovoltaic performance
Safe positive temperature coefficient composite cathode for lithium ion battery
by Hai Zhong; Chan Kong; Hui Zhan; Caimao Zhan; Yunhong Zhou (pp. 273-280).
Ethylene vinyl acetate (EVA) based positive temperature coefficient (PTC) material with a transition temperature ( T c) of 90 °C is proposed and successfully fabricated in this study. It is further introduced into LiFePO4 cathode by directly mixing it with LiFePO4 powder, binder and conductive carbon or sandwiching it between the current collector and LiFePO4 electrode membrane. Thus obtained LiFePO4/PTC composite electrodes both show a self-current-limiting effect at 90 °C. The electrochemical properties of the LiFePO4/PTC composite electrodes are determined in terms of galvanostatic charging/discharging, cyclic voltammograms and electrochemical impedance spectroscopy measurements. Comparing with bare LiFePO4 electrode, both LiFePO4/PTC composite electrodes show no degradation in cycling stability, rate capability and electrochemical kinetic property at room temperature. The results indicate that the proposed LiFePO4/PTC composite electrode with the suitable T c of 90 °C can effectively prevent thermal runaway before the occurrence of side reactions and better protect lithium ion battery during the abnormal temperature increasing.► The Tc of PTC material is about 90 °C, much lower than the previously reported. ► They can endow the electrode with a current limiting effect at around 90 °C. ► It will not impose any negative effect on its electrochemical property. ► PTC composite also can be used with LiCoO2 or LiCo1/3Mn1/3Ni1/3O2, etc.
Keywords: Positive temperature coefficient; Ethylene vinyl acetate; Self-current-limiting effect; Safety; Lithium ion battery
Preparation, structural characterization and catalytic properties of Co/CeO2 catalysts for the steam reforming of ethanol and hydrogen production
by Adriana S.P. Lovón; Juan J. Lovón-Quintana; Gizelle I. Almerindo; Gustavo P. Valença; Maria I.B. Bernardi; Vinícius D. Araújo; Thenner S. Rodrigues; Patrícia A. Robles-Dutenhefner; Humberto V. Fajardo (pp. 281-289).
In this paper, Co/CeO2 catalysts, with different cobalt contents were prepared by the polymeric precursor method and were evaluated for the steam reforming of ethanol. The catalysts were characterized by N2 physisorption (BET method), X-ray diffraction (XRD), UV–visible diffuse reflectance, temperature programmed reduction analysis (TPR) and field emission scanning electron microscopy (FEG-SEM). It was observed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. Physical–chemical characterizations revealed that the cobalt content of the catalyst influences the metal-support interaction which results in distinct catalyst performances. The catalyst with the highest cobalt content showed the best performance among the catalysts tested, exhibiting complete ethanol conversion, hydrogen selectivity close to 66% and good stability at a reaction temperature of 600 °C.► Ceria-supported cobalt catalysts, with different cobalt contents, were prepared by the polymeric precursor method. ► The catalysts were evaluated for the steam reforming of ethanol for hydrogen production. ► The cobalt content of the catalyst influences the metal-support interaction which results in distinct catalyst performances. ► The catalyst with the highest cobalt content showed the best performance among the catalysts tested.
Keywords: Cobalt; Cerium; Ethanol steam reforming; Hydrogen; Pechini method
Effect of aqueous electrolytes on the electrochemical behaviors of supercapacitors based on hierarchically porous carbons
by Xiaoyan Zhang; Xianyou Wang; Lanlan Jiang; Hao Wu; Chun Wu; Jingcang Su (pp. 290-296).
Hierarchically porous carbons (HPCs) have been prepared by sol–gel self-assembly technology with nickel oxide and surfactant as the dual template. The porous carbons are further activated by nitric acid. The electrochemical behaviors of supercapacitors using HPCs as electrode material in different aqueous electrolytes, e.g., (NH4)2SO4, Na2SO4, H2SO4 and KOH are studied by cyclic voltametry, galvanostatic charge/discharge, cyclic life, leakage current, self-discharge and electrochemical impedance spectroscopy. The results demonstrate that the supercapacitors in various electrolytes perform definitely capacitive behaviors; especially in 6 M KOH electrolyte the supercapacitor represents the best electrochemical performance, the shortest relaxation time, and nearly ideal polarisability. The energy density of 8.42 Wh kg−1 and power density of 17.22 kW kg−1 are obtained at the operated voltage window of 1.0 V. Especially, the energy density of 11.54 Wh kg−1 and power density of 10.58 kW kg−1 can be achieved when the voltage is up to 1.2 V.► Comparable electrochemical performances in various aqueous electrolytes. ► In 6.0 M KOH the supercapacitor performs the best electrochemical behaviors. ► The highest energy density of the supercapacitor in 6.0 M KOH is 11.54 Wh kg−1. ► In 6.0 M KOH the supercapacitor has the shortest relaxation time of 0.62 s.
Keywords: Hierarchically porous carbon; Supercapacitor; Aqueous electrolyte; Electrochemical behaviors
Glucose microfluidic fuel cell based on silver bimetallic selective catalysts for on-chip applications
by F.M. Cuevas-Muñiz; M. Guerra-Balcázar; J.P. Esquivel; N. Sabaté; L.G. Arriaga; J. Ledesma-García (pp. 297-303).
A glucose microfluidic fuel cell with outstanding performance at zero flow condition is presented. Polarization tests showed that bimetallic materials based in silver (AuAg/C as anode, PtAg/C as cathode) exhibit tolerance to byproducts and crossover effect. This allowed achieving one of the highest power densities reported for glucose fuel cells, up to a value of 630 μW cm−2 using two separated laminar flows of reactants. Furthermore, the tolerance to crossover effect caused by the selectivity of PtAg/C to oxygen reduction reaction in presence of glucose permitted using a single flow containing a mixture of glucose/oxygen, yielding a performance as high as 270 μW cm−2. Microfluidic fuel cell was further evaluated with a simulated body fluid solution that contained salts commonly present in the human blood plasma, reaching a power of 240 μW cm−2 at zero flow. These results envisage the incorporation of this fuel cell as a portable power source in Lab-on-a-Chip devices without the need of external pumps.► Glucose microfuel cell with outstanding performance at zero flow condition is showed. ► Bimetallic materials based on Ag exhibit tolerance to byproducts and crossover effect. ► Microfluidic fuel cell was evaluated with a simulated body fluid solution at zero flow. ► This fuel cell can be used as a portable power source in Lab-on-a-Chip applications.
Keywords: PtAg nanoparticles; AuAg nanoparticles; Simulated body fluid
Ac impedance analysis of lithium ion battery under temperature control
by Toshiyuki Momma; Mariko Matsunaga; Daikichi Mukoyama; Tetsuya Osaka (pp. 304-307).
Ac impedance spectra of electrochemical systems are analyzed by considering adequate equivalent circuits, while the differentiation of responses for each elemental step is sometimes difficult. In this study, enlarged impedances were measured by lowering the temperature of a lithium ion battery (LIB) to make the separation of confusing responses easier. The impedance spectra obtained at the temperatures between −20 °C and 20 °C showed drastic change in sizes with shifting of the characteristic frequency. The analysis of impedance spectra using an equivalent circuit revealed changes in resistance of each component and shifting of the time constant for each elemental step. The frequency domain of impedance response of solid electrolyte interphase (SEI) was found to overlap with that of the inductive component of the outer electric lead at 20 °C in our study. The impedance measurement at the low temperatures is considered to be useful for the detection of the SEI and the accurate evaluation of LIB.Display Omitted► Ac impedance of LIB was measured at low temperature to enlarge the impedance. ► At the temperature below 0 °C another arc of semicircle appeared. ► At 20 °C the hidden arc was found to be small. ► The hidden arc was also overlapping with kinetic impedance and inductive locus. ► The hidden impedance response was attributed to the SEI impedance.
Keywords: Electrochemical impedance spectroscopy; Lithium ion battery; Low temperature; Enlarged impedance; Time constant; SEI
Efficient ceramic anodes infiltrated with binary and ternary electrocatalysts for SOFCs operating at low temperatures
by A. Mohammed Hussain; Jens V.T. Høgh; Wei Zhang; Nikolaos Bonanos (pp. 308-313).
Electrocatalyst precursor of various combinations: Pt, Ru, Pd, Ni and Gd-doped CeO2 (CGO) were infiltrated into a porous Sr0.94Ti0.9Nb0.1O3 (STN) backbone, to study the electrode performance of infiltrated ceramic anodes at low temperature ranges of 400–600 °C. The performance of the binary electrocatalyst infiltrated ceramic backbones are Pt–CGO>Ru–CGO>Pd–CGO>Ni–CGO. Ternary electrocatalyst of Ni–Pd–CGO and Ni–Pt–CGO showed the lowest polarization resistance of 0.31 and 0.11 Ωcm2, respectively at 600 °C in H2/3% H2O. The average particle size of the ternary electrocatalyst was larger than the binary Pd–CGO and Pt–CGO due to the particle coarsening of Ni nanoparticles. High resolution transmission electron microscopic analysis on the best performing Ni–Pt–CGO electrocatalyst infiltrated anode reveals the formation of Ni–Pt nanocrystalline alloy and a homogenous distribution of nanoparticles on STN backbone.► Infiltration of Ni, Pt, Pd, Ru and CGO electrocatalysts precursors. ► Strontium titanate based ceramic anodes with an addition of Ni in noble metals containing electrocatalysts. ► Binary and ternary electrocatalyst for hydrogen oxidation. ► Low temperature solid oxide fuel cells.
Keywords: Low temperature solid oxide fuel cell anodes; Porous Sr; 0.94; Ti; 0.9; Nb; 0.1; O; 3; Infiltration; Noble metals; Ni and CGO electrocatalyst
Performance evaluation of an integrated small-scale SOFC-biomass gasification power generation system
by Suranat Wongchanapai; Hiroshi Iwai; Motohiro Saito; Hideo Yoshida (pp. 314-322).
The combination of biomass gasification and high-temperature solid oxide fuel cells (SOFCs) offers great potential as a future sustainable power generation system. In order to provide insights into an integrated small-scale SOFC-biomass gasification power generation system, system simulation was performed under diverse operating conditions. A detailed anode-supported planar SOFC model under co-flow operation and a thermodynamic equilibrium for biomass gasification model were developed and verified by reliable experimental and simulation data. The other peripheral components include three gas-to-gas heat exchangers (HXs), heat recovery steam generator (HRSG), burner, fuel and air compressors. To determine safe operating conditions with high system efficiency, energy and exergy analysis was performed to investigate the influence through detailed sensitivity analysis of four key parameters, e.g. steam-to-biomass ratio (STBR), SOFC inlet stream temperatures, fuel utilization factor ( Uf) and anode off-gas recycle ratio (AGR) on system performance. Due to the fact that SOFC stack is accounted for the most expensive part of the initial investment cost, the number of cells required for SOFC stack is economically optimized as well. Through the detailed sensitivity analysis, it shows that the increase of STBR positively affects SOFC while gasifier performance drops. The most preferable operating STBR is 1.5 when the highest system efficiencies and the smallest number of cells. The increase in SOFC inlet temperature shows negative impact on system and gasifier performances while SOFC efficiencies are slightly increased. The number of cells required for SOFC is reduced with the increase of SOFC inlet temperature. The system performance is optimized for Uf of 0.75 while SOFC and system efficiencies are the highest with the smallest number of cells. The result also shows the optimal anode off-gas recycle ratio of 0.6. Regarding with the increase of anode off-gas recycle ratio, there is a trade-off between overall efficiencies and the number of SOFC cells.► We evaluate an integrated small-scale SOFC-biomass gasification power generation system through energy and exergy. ► We examine the effects of steam-to-biomass ratio, SOFC inlet stream temperatures, fuel utilization factor and anode off-gas recycle ration on system performance. ► The results show the optimal operating parameters and their effects on SOFC stack, gasifier and system performance.
Keywords: Solid oxide fuel cell; Biomass gasification; System analysis; Power generation system; Exergy analysis
Low-viscosity ether-functionalized pyrazolium ionic liquids as new electrolytes for lithium battery
by Ming Chai; Yide Jin; Shaohua Fang; Li Yang; Shin-ichi Hirano; Kazuhiro Tachibana (pp. 323-329).
Four new functionalized ILs based on pyrazolium cations and bis(trifluoromethylsulfonyl)imide anions (TFSI−) are synthesized and characterized. These ILs show low-melting point and low-viscosity characteristics, and the viscosity of OEPZ–TFSI is 41.2 mPa s at 25 °C. These IL electrolytes with 0.4 mol kg−1 LiTFSI have good chemical stability against lithium metal. Li/LiFeO4 cells using these IL electrolytes without additives own good electrochemical performance, and the cells using OMPZ–TFSI and OEPZ–TFSI electrolytes own better rate property.► New ether-functionalized pyrazolium ILs are reported. ► They have low-viscosity and low-melting point characteristics. ► Li/LiFePO4 cells using these IL electrolytes have good electrochemical performance.
Keywords: Ionic liquid; Lithium battery; Functionalized cation; Electrolyte
Ionic liquid diffusion properties in tetrapod-like ZnO photoanode for dye-sensitized solar cells
by Kun-Mu Lee; Wei-Hao Chiu; Chih-Yu Hsu; Hsin-Ming Cheng; Chia-Hua Lee; Chun-Guey Wu (pp. 330-336).
Dye-sensitized solar cells (DSCs) are a promising PV device to solve global energy-related problems because it is clean, inexhaustible and readily available. In order to improve the stability and reliability of the DSCs, ionic liquid (IL) electrolyte is a good choice for replacement of volatile solvent electrolyte systems (e.g. acetonitrile). However, the high viscosity of ionic liquids leads to mass-transport limitations on the photocurrents in the DSCs. In this report, a new porous photoanode made by tetrapod-like ZnO (T-ZnO) nanopowders provides not only a fast electron transport path in ZnO but also an efficient ionic diffusion pathway in the photoanode pore, comparing to the spherical commercial ZnO (C-ZnO) nanopowders. In addition, the ionic diffusion dynamics of T-ZnO and C-ZnO devices are characterized by electrochemical impedance analysis (EIS), photocurrent transient dynamics. We observed the presence of a tetrapod-like framework, which allowed the photoanode to provide a more efficient ionic diffusion pathway than conventional one made of commercial spherical nanopowders provided.Display Omitted► The tetrapod-like ZnO nanopowder provides fast electron transport in ZnO and efficient ionic diffusion pathway in the photoanode pore. ► The recombination rate of T-ZnO-based DSC is lower than that of C-ZnO one. ► The ion diffusion ability in tetrapod-like ZnO is about two times improvement, which enables the regeneration ability of dye molecular by redox couples.
Keywords: Dye-sensitized solar cells; Electrochemical analysis; Ionic diffusion; Tetrapod-like ZnO
The influence of channel wettability and geometry on water plug formation and drop location in a proton exchange membrane fuel cell flow field
by Alexandru Herescu; Jeffrey S. Allen (pp. 337-344).
The critical volume of liquid water required to form a plug in a channel having mixed wettability similar to that found in the flow field of a proton exchange membrane (PEM) fuel cell is computed for a range of gas diffusion layer (GDL) and bipolar plate wettabilities and channel bend dihedral angles. Three gas diffusion layers (GDL) with 80, 110 and 150° contact angles are considered while the bipolar plate wettabilities are varied with static contact angles ranging from 50 to 130°. The critical volume is an intrinsic property of the channel-GDL configuration and has direct implications for the liquid holdup, the water distribution in the flow fields of PEM fuel cells as well as on the pumping parasitic power loss. The plug volume correlations may be used as an optimization tool for water management in channels of mixed wettability. The effect of cross-section geometry on the critical volume is also investigated through a comparison between a square and a trapezoidal channel. Mixed wettability drop simulations reveal that water can be passively removed from the GDL surface to the bipolar plate if the latter has a lower contact angle, potentially avoiding the flooding of the porous electrodes.► We have successfully modeled the minimum volume required to plug a fuel cell channel. ► The effect of degradation of fuel cell components on channel flooding is assessed. ► The utility of Surface Evolver for fuel cell designed has been shown. ► Combinations of bipolar plate and GDL wettabilities can passively move water.
Keywords: PEM fuel cell; Channel flooding; Surface evolver
Experimental study of an air-cooled thermal management system for high capacity lithium–titanate batteries
by Michael R. Giuliano; Ajay K. Prasad; Suresh G. Advani (pp. 345-352).
Lithium–titanate batteries have become an attractive option for battery electric vehicles and hybrid electric vehicles. In order to maintain safe operating temperatures, these batteries must be actively cooled during operation. Liquid-cooled systems typically employed for this purpose are inefficient due to the parasitic power consumed by the on-board chiller unit and the coolant pump. A more efficient option would be to circulate ambient air through the battery bank and directly reject the heat to the ambient. We designed and fabricated such an air-cooled thermal management system employing metal-foam based heat exchanger plates for sufficient heat removal capacity. Experiments were conducted with Altairnano's 50 Ah cells over a range of charge-discharge cycle currents at two air flow rates. It was found that an airflow of 1100 mls−1 per cell restricts the temperature rise of the coolant air to less than 10 °C over ambient even for 200 A charge-discharge cycles. Furthermore, it was shown that the power required to drive the air through the heat exchanger was less than a conventional liquid-cooled thermal management system. The results indicate that air-cooled systems can be an effective and efficient method for the thermal management of automotive battery packs.► An air-cooled system to maintain safe Li-ion battery operating temperatures was designed. ► The role of state-of-charge on battery thermal behavior was identified. ► Li-ion battery cooling with ambient air is a viable solution. ► This design is more energy efficient than traditional liquid-cooled designs.
Keywords: Battery electric vehicle; Hybrid electric vehicle; Lithium–titanate battery; Metal foam heat exchanger; Thermal analysis; Battery cooling
Influence of Mn content on the morphology and improved electrochemical properties of Mn3O4|MnO@carbon nanofiber as anode material for lithium batteries
by Gang Yang; Yuhong Li; Hongmei Ji; Haiying Wang; Po Gao; Lu Wang; Haidong Liu; João Pinto; Xuefan Jiang (pp. 353-362).
A series of composites manganese oxide/carbon with one-dimensional structure are synthesized using electrospinning. The phase composition, morphology and electrochemical performance of MnO x/carbon are studied, which affected by the manganese concentration in precursor and subsequent carbonization conditions. The manufacture of MnO x/carbon is composed of two steps including thermal stabilization (at 250 °C in air) and carbonization (at 700 °C in nitrogen). The main functional groups of samples are well identified by FT-IR spectra. The sample Mn33_3h with the lowest manganese content presents the construction structure which amorphous and/or nanosized MnO x with smaller crystal size are grown and enwrapped in carbon fiber during carbonization. Mn33_3h presents the initial charge and discharge capacities of 1054.1 and 665.6 mAh g−1, and the discharge capacity at the 50th cycle remains 99.7% of that at the 2nd cycle. Beside the well rate capability at the range of current densities from 20 to 1000 mA g−1, Mn33_3h presents very good recovery ability after high rate cycling at 1000 mA g−1. The advantages of this composite structure as well as its high capacity make manganese oxide a very attractive candidate as an anode material for the next generation of rechargeable lithium ion batteries.► Composites MnO x/carbon synthesized through thermal stabilization and carbonization. ► Phase composition, morphology and capacity affected by Mn concentration in precursor. ► Mn33_3h with the lowest manganese content presents the best electrochemical properties. ► Discharge capacity of Mn33_3h at the 50th cycle remains 99.7% of that at the 2nd cycle. ► Composite structure of MnO x/carbon is efficient to improve capacity and cycleability.
Keywords: Manganese oxides; Carbon fiber; Composite structure; Anode materials; Lithium batteries
Effect ofl-arginine on the catalytic activity and stability of nickel nanoparticles for hydrolytic dehydrogenation of ammonia borane
by Tetsuo Umegaki; Qiang Xu; Yoshiyuki Kojima (pp. 363-367).
Amorphous nickel catalysts were synthesized by reducing the nickel(II) species in an aqueous NaBH4/NH3BH3 solution with and withoutl-arginine. The nickel catalyst withl-arginine maintains relatively high activity for hydrolysis of NH3BH3 to generate a stoichiometric amount of hydrogen with the cycle number up to 11 (827 mL s−1 (mol-Ni)−1 at the 11th cycle withl-arginine = 35 mg), while the reaction rate in the presence of the bare nickel catalyst was relatively low through the cycle number up to 11 (232 mL s−1 (mol-Ni)−1 at the 11th cycle). After catalytic reaction, the nickel catalyst withl-arginine possesses the high dispersion (diameters of nickel nanoparticles <5 nm), while the agglomerate of nickel in the bare nickel catalyst is observed. The results indicate thatl-arginine maintains the dispersion of nickel nanoparticles (diameters of nickel nanoparticles <10 nm), leading to higher activity against cycle tests than the bare nickel catalyst.► Amorphous Ni catalysts were synthesized in an aqueous NaBH4/NH3BH3 solution. ► We study the effect of addition ofl-arginine in the synthesis process. ► Ni species aggregate after cycle tests for NH3BH3 hydrolysis withoutl-arginine. ► Ni particles withl-arginine show high dispersion and activity for the cycle tests.
Keywords: Nickel nanoparticles; l; -Arginine; Ammonia borane; Hydrolytic dehydrogenation
Structural, electrochemical and thermal stability investigations on LiNi0.5− xAl2 xMn1.5− xO4 (0 ≤ 2 x ≤ 1.0) as 5 V cathode materials
by G.B. Zhong; Y.Y. Wang; X.J. Zhao; Q.S. Wang; Y. Yu; C.H. Chen (pp. 368-375).
A series of Al-substituted spinel powders LiNi0.5− xAl2 xMn1.5− xO4 (0 ≤ 2 x ≤ 1.0) have been prepared and the effects of Al concentration on the structural, electrochemical and thermal properties are investigated. The XRD patterns show that impurity arises when 2 x ≥ 0.6. The FTIR and Raman spectra indicate that the introduction of Al in the LiNi0.5Mn1.5O4 increases the disordering degree of Ni/Mn ions, changing the spinel structure from P4332 toFd3¯m. Cyclic voltammetry tests show that the voltage step between Ni2+/Ni3+ and Ni3+/Ni4+ have a sudden leap at 2 x = 0.075, responding to the structural difference of the spinels. The Al concentration is optimized in the range of 0.05 ≤ 2 x ≤ 0.1, in which the cyclic stability and rate capability of the LiNi0.5− xAl2 xMn1.5− xO4 spinels are significantly improved. At room temperature the LiNi0.45Al0.10Mn1.45O4 presents the best cycle performance with the capacity retention of 95.4% after 500 cycles at 1C rate, and the best rate capability with the discharge capacity of 119 mAh g−1 at 10C rate, which is about 93.7% of its capacity at 0.5C. The thermal properties of the spinels have been tested by C80 calorimeter and the results show that introduction of Al in LiNi0.5Mn1.5O4 can effectively suppress the exothermic reaction below 225 °C, thus improve the safety of the high voltage cathode material.► Al-doped compounds LiNi0.5− xAl2 xMn1.5− xO4 (0 ≤ 2 x ≤ 1.0) with a wide doping range are prepared and characterized. ► The optimal Al concentration in the LiNi0.5− xAl2 xMn1.5− xO4 is 0.05 ≤ 2 x ≤ 0.10. ► The thermal stability of LiNi0.5− xAl2 xMn1.5− xO4 electrodes before 225 °C is effectively improved by Al-doping.
Keywords: Lithium-ion batteries; Spinel; Aluminum doping; Lithium nickel manganese oxide; Thermal stability
Selection of battery technology to support grid-integrated renewable electricity
by Jason Leadbetter; Lukas G. Swan (pp. 376-386).
Operation of the electricity grid has traditionally been done using slow responding base and intermediate load generators with fast responding peak load generators to capture the chaotic behavior of end-use demands. Many modern electricity grids are implementing intermittent non-dispatchable renewable energy resources. As a result, the existing support services are becoming inadequate and technological innovation in grid support services are necessary. Support services fall into short (seconds to minutes), medium (minutes to hours), and long duration (several hours) categories. Energy storage offers a method of providing these services and can enable increased penetration rates of renewable energy generators. Many energy storage technologies exist. Of these, batteries span a significant range of required storage capacity and power output. By assessing the energy to power ratio of electricity grid services, suitable battery technologies were selected. These include lead-acid, lithium-ion, sodium-sulfur, and vanadium-redox. Findings show the variety of grid services require different battery technologies and batteries are capable of meeting the short, medium, and long duration categories. A brief review of each battery technology and its present state of development, commercial implementation, and research frontiers is presented to support these classifications.► Renewable electricity places additional strain on the electricity grid. ► Grid support services to provide flexibility are becoming more important. ► Battery energy storage systems offer a broad range of storage abilities. ► Lithium-ion and lead–acid batteries are suitable for short duration services. ► Sodium–sulfur and vanadium redox batteries are suitable for long duration services.
Keywords: Battery energy storage; Renewable energy storage; Battery technologies; Renewable energy integration
Sulfonated block-graft copolyimide for high proton conductive and low gas permeable polymer electrolyte membrane
by Kota Yamazaki; Gang Wang; Manabu Tanaka; Hiroyoshi Kawakami (pp. 387-394).
This paper addresses issues surrounding the design of the proton exchange membrane for fuel cells, and more specifically, the role of the polymer architecture on the proton conductivity and gas permeability. In this study, we describe the syntheses and characterizations of sulfonated block, graft, random-graft, and block-graft copolymers. The proton conductivity and oxygen permeability of the novel sulfonated block-graft copolyimide, S- bg-PI, showed 0.44 S cm−1 at 80 °C and 98%RH and 3.2 × 10−12 cm3(STP) cm/(cm2 sec cmHg) at 35 °C and 76 cmHg, respectively, while those of Nafion indicated 0.15 S cm−1 and 1.1 × 10−10 cm3(STP) cm/(cm2 sec cmHg) under the same conditions, respectively. The apparent selectivity ratio calculated from the proton and oxygen transports of S- bg-PI was 103 times larger than that determined in Nafion, indicating that the novel sulfonated block-graft copolyimide membrane has excellent properties for fuel cell applications.Display Omitted► A series of sulfonated block and/or graft polyimides were synthesized. ► The S- bg-PI membrane showed higher proton conductivity than Nafion and other SPI membranes. ► Oxygen permeability of the S- bg-PI membrane was much lower than those of other membranes. ► The novel S- bg-PI membrane with excellent properties is expected for fuel cell applications.
Keywords: Fuel cell; Polymer electrolyte; Proton conductivity; Gas permeability
Hydrothermal-synthesized Co(OH)2 nanocone arrays for supercapacitor application
by F. Cao; G.X. Pan; P.S. Tang; H.F. Chen (pp. 395-399).
Co(OH)2 nanocone arrays are prepared by a facile hydrothermal synthesis method. The Co(OH)2 nanocones are single crystalline in nature and have an average diameter of about 200 nm. The pseudocapacitive behavior of the Co(OH)2 nanocone arrays is investigated by cyclic voltammograms (CV) and galvanostatic charge–discharge tests in 2 M KOH. As cathode for supercapacitor, the Co(OH)2 nanocone arrays exhibit a capacitance of 562 F g−1 at 2 A g−1 as well as rather good cycling stability. The enhanced supercapacitor performances are due to the porous array architecture providing fast ion and electron transfer, large reaction surface area and good strain accommodation.► β-Co(OH)2 nanocone arrays are prepared by a hydrothermal synthesis method. ► β-Co(OH)2 nanocone arrays with high capacitance for supercapacitors application. ► 1D nanocone arrays structure keeps structure stable with good strain accommodation.
Keywords: Cobalt hydroxide; Nanowire arrays; Supercapacitor; Porous film
Combinatorial search for oxygen reduction reaction electrocatalysts: A review
by Min Ku Jeon; Chang Hwa Lee; Geun Il Park; Kweon Ho Kang (pp. 400-408).
Oxygen reduction reaction (ORR) is one of the most interesting research issues in the academia and industries due to its importance in polymer electrolyte membrane fuel cells. Development of new ORR catalysts with low cost and high activity is under intensive research, but it is a time-consuming process because of wide range of alloys to be explored. Combinatorial synthesis and high-throughput screening techniques were suggested as new experimental approaches to accelerate the ORR electrocatalyst research. The combinatorial method is focused on the synthesis of concentrated arrays and quick evaluation of the arrays via various screening techniques. In this report, the combinatorial approaches for the ORR catalyst research were reviewed based on the screening methods. Four screening techniques of optical screening, scanning electrochemical microscopy, multielectrode half cell, and multielectrode full cell were introduced as the representative ones. Other approaches were also briefly introduced. Merits and limitations of each method were discussed and representative research results of each method were shown in detail.► High-throughput screening techniques for ORR electrocatalysts were reviewed. ► Four major screening techniques were introduced. ► Merits and limitations of each technique were discussed along with recent results.
Keywords: Oxygen reduction reaction; Electrocatalyst; Polymer electrolyte membrane fuel cell; Combinatorial synthesis; High-throughput screening
Stability of solid oxide fuel cell anodes based on YST–SDC composite with Ni catalyst
by Pramote Puengjinda; Hiroki Muroyama; Toshiaki Matsui; Koichi Eguchi (pp. 409-416).
Ceramic material based on composite of yttria-doped SrTiO3 (YST) and samaria-doped ceria (SDC) incorporated with Ni catalyst has been evaluated as an anode of solid oxide fuel cell to substitute the use of conventional Ni-based cermets. The results indicated the advantages of suitable Ni addition which could remarkably enhance the electrochemical performance of anode due to the superior in catalytic activity of SDC and Ni towards fuel oxidation. Temperature-programmed reduction (TPR) profiles indicated the existence of bulk-free and interacted NiO in the composites. The cells with Ni/YST–SDC (20 wt% NiO) anodes exhibited stable performance in the prolong operation with tremendously severe conditions in methane fuel with low steam to carbon ratio (S/C = 0.1) and highly humidified hydrogen fuel (40% H2O–H2) compared with the conventional Ni-based cermets. Small amount of deposited carbon was observed and played insignificant effects on the electrochemical performance after the operation for 100 h. The stable performance was ascribable to the excellence in YST–SDC ceramic framework that effectively suppressed the carbon formation. Furthermore, the Ni/YST–SDC anode showed high tolerance in encountering with the redox cycles. From these results, Ni/YST–SDC composite is considered to be a promising candidate for SOFC anode material operating in severe conditions.► The use of Ni/YST–SDC ceramic anode was proposed to replace Ni-based cermet. ► Addition of nickel enhances the electrochemical performance without drawback effects. ► The excellence of YST–SDC ceramic framework could maintain the stable performance. ► Ni/YST–SDC offers certain advantages and highly stable performance in severe conditions.
Keywords: Ceramic anodes; Solid oxide fuel cells; Stable performance; Severe conditions; Redox tolerance
Performance and short-term stability of single-chamber solid oxide fuel cells based on La0.9Sr0.1Ga0.8Mg0.2O3−δ electrolyte
by M. Morales; J.J. Roa; J. Tartaj; M. Segarra (pp. 417-424).
In the present work, the performance of La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte-supported SOFCs was evaluated under single-chamber conditions. For this purpose, two single cells, one with and the other without Sm0.2Ce0.8O3− δ (SDC) buffer layer between anode and electrolyte, were studied in order to determine and compare the performance and short-term stability of cells under single-chamber conditions. The reactivity of the Ni-SDC anode with SDC (for the cell with buffer layer) and the LSGM electrolyte (for the cell without buffer layer) were studied by X-ray diffraction. The reaction between Ni and LSGM during anode sintering and cell operation leads to a substantial loss in the cell performance when no buffer layer is present. As a result, maximum power densities of 246 and 132 mW cm−2 were obtained for the buffered and non-buffered cells respectively, at 800 °C, under optimized gas composition (CH4/O2 = 1.2) and a total flow rate of 400 ml min−1. After 55 h operating at 750 °C and 6 thermal cycles, the performances of both cells were decreased around 25–30 mW cm−2.► Electrical properties of cells with LSGM electrolyte operated in methane–air mixtures. ► Cell performance was not significantly affected operating under optimal SC-SOFC conditions. ► Operating conditions to minimize the degradation of electrodes at short-term were well established. ► Performance stability of buffered cell at short-time was similar to that for non-buffered one.
Keywords: Solid oxide fuel cells; Lanthanum gallate; Single-chamber fuel cell; Methane; Buffer layer
Microstructure and supercapacitive properties of buserite-type manganese oxide with a large basal spacing
by Zhenjie Sun; Dong Shu; Hongyu Chen; Chun He; Shaoqing Tang; Jie Zhang (pp. 425-433).
A hydration-layered structure of buserite-type manganese oxide (Mg–buserite) was successfully synthesized by an ion exchange method. The as-prepared Mg–buserite possesses a large basal spacing of 10 Å, and contains Mg2+ ions and two sheets of water molecules in the interlayer region. The supercapacitive behaviors of Mg–buserite were systematically investigated by cyclic voltammetry (CV), galvanostatic charge–discharge (CD) experiments and electrochemical impedance spectroscopy (EIS). The results showed that the specific capacitance of the Mg–buserite electrode sharply increased during the initial 500 cycles and reached a maximum of 164 F g−1 at approximately the 500th cycle at a scan rate of 1 mV s−1, and then it remained an almost constant value and decreased slightly upon prolonged cycling. After 22,000 cycles, the specific capacitance decreased by approximately 6% of the maximum specific capacitance. The superior capacitive behavior and excellent cycling stability of the as-prepared Mg–buserite are attributed to the large basal spacing, which can accommodate a larger amount of electrolyte cations and provide more favorable pathways for electrolyte cations intercalation and deintercalation. The experimental results demonstrate that Mg–buserite is a promising candidate as an electrode material for supercapacitors.► Mg–buserite with a large basal spacing of 10 Å was successfully synthesized. ► Mg2+ and two sheets of H2O molecules occupy the interlayer region of Mg–buserite. ► The maximum specific capacitance of Mg–buserite is 164 F g−1 at 1 mV s−1. ► The specific capacitance of Mg–buserite decreased only 6% after 22,000 cycles. ► The superior capacitive behaviors are attributed to the large basal spacing.
Keywords: Manganese oxide; Buserite; Large basal spacing; Supercapacitor; Cycle stability
Progressive activation of degradation processes in solid oxide fuel cell stacks: Part II: Spatial distribution of the degradation
by Arata Nakajo; Fabian Mueller; Jacob Brouwer; Jan Van herle; Daniel Favrat (pp. 434-448).
Solid oxide fuel cell (SOFC) stack design must yield the highest performance, reliability and durability to achieve the lowest cost of electricity delivered to end-users. Existing modelling tools can cope with the first aim, but cannot yet provide sufficient quantitative guidance in the two others.Repeating unit models, with as degradation processes the decrease in ionic conductivity of the electrolyte, metallic interconnect corrosion, anode nickel particles coarsening and cathode chromium contamination are used to investigate their distribution, evolution and interactions in a stack. The spatial distribution of the degradation is studied for the operating conditions optimised in Part I for the highest system electrical efficiency during long-term operation under constant system power output.Current-voltage characterisations performed at different times underestimate the degradation. In the present conditions, the degradation of the cathode dominates. The lower and more uniform cathode overpotential in counter-flow configuration, combined with the beneficial effect of internal reforming on reducing the air-fuel ratio yields the highest lifetime, because it alleviates chromium contamination and interactions between the degradation processes. Increasing the operating temperature alleviates cathode chromium contamination. The beneficial decreases of the cathode overpotential exceed the detrimental higher release rate of chromium species from the metallic interconnect.► Analysis of the combined effect of multiple degradation processes in SOFC stacks. ► Distribution and interactions between degradation phenomena in SOFC stacks. ► Simulation of the effects of stack design and operation on lifetime. ► Counter-flow lowers cathode Cr contamination, compared with co-flow. ► Components stacking practically affects the choice of optimal operating conditions.
Keywords: Solid oxide fuel cell; Degradation; Chromium contamination; Creep
Progressive activation of degradation processes in solid oxide fuel cells stacks: Part I: Lifetime extension by optimisation of the operating conditions
by Arata Nakajo; Fabian Mueller; Jacob Brouwer; Jan Van herle; Daniel Favrat (pp. 449-463).
The degradation of solid oxide fuel cells (SOFC) depends on stack and system design and operation. A methodology to evaluate synergistically these aspects to achieve the lowest production cost of electricity has not yet been developed.A repeating unit model, with as degradation processes the decrease in ionic conductivity of the electrolyte, metallic interconnect corrosion, anode nickel particles coarsening and cathode chromium contamination, is used to investigate the impact of the operating conditions on the lifetime of an SOFC system. It predicts acceleration of the degradation due to the sequential activation of multiple processes. The requirements for the highest system efficiency at start and at long-term differ. Among the selected degradation processes, those on the cathode side here dominate. Simulations suggest that operation at lower system specific power and higher stack temperature can extend the lifetime by a factor up to 10, because the beneficial decrease in cathode overpotential prevails over the higher release of volatile chromium species, faster metallic interconnect corrosion and higher thermodynamic risks of zirconate formation, for maximum SRU temperature below 1150 K. The counter-flow configuration, combined with the beneficial effect of internal reforming on lowering the parasitic air blower consumption, similarly yields longer lifetime than co-flow.► Analysis of the combined effect of multiple degradation processes in SOFC stacks. ► Acceleration of the degradation and sequential activation of processes is predicted. ► Optimisation of the operating conditions can extend lifetime by a factor up to 10. ► Operating conditions for the highest performance and the best durability differ. ► Overpotential rather than current density influences the degradation behaviour.
Keywords: Solid oxide fuel cell; Degradation; Repeating unit model; Chromium contamination; Optimisation
Effect of the Pt/Ru intermetallic boundary on the carbon monoxide electrooxidation: Excess electrocatalytic activity
by María S. Rau; María R. Gennero de Chialvo; Abel C. Chialvo (pp. 464-470).
The carbon monoxide oxidation reaction was studied on smooth Pt, Ru and Pt/Ru (Ru partially covered by Pt islands) rotating disc electrodes on acid solution saturated with CO gas ( PCO = 1 atm) through steady state measurements. The current density vs. overpotential plot of the Pt/Ru electrode shows a profile qualitatively similar to the sum of both curves corresponding to pure Pt and Ru. On this basis, the excess electrocatalytic activity was defined as the difference between the current densities of the bimetallic electrode and those corresponding to the pure metals, which allowed evaluating the contribution of the intermetallic region to the reaction. It was verified that this property depends on overpotential, defining two ranges of positive excess values, 0.6 ≤ η/V < 0.82 and 0.88 < η/V ≤ 1.0, separated by the range 0.82 ≤ η/V ≤ 0.88, where the contribution of the boundary region is negligible. A simple model was developed, which explains the experimental results on the basis of the spillover of the adsorbed reaction intermediates, while the reaction between adsorbed species on both sides of the intermetallic edge is not feasible.Display Omitted► Study of the carbon monoxide oxidation reaction on Pt, Ru and Pt/Ru electrodes. ► Evaluation of the contribution to the reaction of the intermetallic region on Pt/Ru. ► Quantification of such contribution through the excess electrocatalytic activity.
Keywords: Carbon monoxide electrooxidation; Pt/Ru electrode; Synergistic effect; Spillover
Performance of vapor-fed direct dimethyl ether fuel cell utilizing high temperature polybenzimidazole polymer electrolyte membrane
by Jay Neutzler; Guoqing Qian; Kevin Huang; Brian Benicewicz (pp. 471-474).
There is increasing interest in dimethyl ether (DME) as a synthetic fuel. It has present-day relevance and introduces an effective path forward as an energy-dense, low-pressure hydrogen carrier/storage fuel for fuel cells with applications in transportation, stationary, and portable power. Direct reaction DME fuel cells have particular relevance to portable power. This study presents the performance of the vapor-fed direct reaction of DME using high temperature Polybenzimidazole (PBI) Polymer Electrolyte Membrane (PEM). Catalyzed PBI membrane utilized a Pt/Ru black anode and a Pt/C supported cathode. Performance was evaluated from temperatures of 180 °C–210 °C and at pressures from 100 kPa to 300 kPa. A strong performance correlation was observed in this study for these temperatures and pressures. A peak power density of 50 mW cm−2 was achieved at 180 °C without back pressure, whereas, an increase to 129 mW cm−2 was achieved at 210 °C at 300 kPa pressure.The performance of high temperature PBI PEMFCs with direct vapor-fed DME are investigated with emphasis on the critical variables of cell operation; temperature, back pressure, and humidity.► Direct reaction DME produced notable power utilizing PBI membrane. ► Performance increases with increasing temperatures of 180 °C–210 °C. ► Performance increases more notably more from 100 to 200 kPa, than 200–300 kPa. ► Humidification effects were less critical and may provide additional benefits. ► A peak power density of 129 mW cm−2 was achieved at 210 °C and 300 kPa.
Keywords: Dimethyl ether; Polybenzimidazole; PEM; Fuel cell; Synthetic fuel; Performance
New easy way preparation of core/shell structured SnO2@carbon spheres and application for lithium-ion batteries
by Xuecheng Chen; Krzysztof Kierzek; Karolina Wilgosz; Jacek Machnikowski; Jiang Gong; Jingdong Feng; Tao Tang; Ryszard J. Kalenczuk; Hongmin Chen; Paul K. Chu; Ewa Mijowska (pp. 475-481).
A novel way for the synthesis of core/shell structures composed of tin oxide nanoparticles confined in mesoporous hollow carbon spheres (SnO2@MHCS) is newly reported. The materials which have a uniform size distribution, good structural stability and large surface area show superior cycling performance and are suitable for high-power anodes. Core/shell structured SnO2@MHCS takes advantage of the virtues of SnO2 and porous carbon in lithium-ion battery. This structure provides a rapid lithium transport pathway and boasts a highly reversible capacity. When the SnO2/C ratio is 78.6/21.4 (w/w), the surface area of SnO2@MHCS is 183 m2 g−1 and specific capacity value is 450 mAh g−1 at 1/5 C after 50 cycles. The SnO2@MHCS materials have large potential in next-generation lithium-ion batteries.► Core/shell structures composed of tin oxide nanoparticles confined in mesoporous hollow carbon spheres are reported. ► The materials have a uniform size distribution, good structural stability, and large surface area. ► Core/shell structure exhibits superior cycling performance comparing with hollow carbon spheres. ► When the SnO2/C ratio is 78.6/21.4 (w/w), the surface area of SnO2@MHCS is 183 m2 g−1. ► The specific capacity value is 450 mAh g−1 at 1/5 C after 50 cycles.
Keywords: Core/shell; Hollow carbon spheres; Tin oxide; Lithium-ion battery
Effect of doping LiMn2O4 spinel with a tetravalent species such as Si(IV) versus with a trivalent species such as Ga(III). Electrochemical, magnetic and ESR study
by A. Iturrondobeitia; A. Goñi; V. Palomares; I. Gil de Muro; L. Lezama; T. Rojo (pp. 482-488).
Three cathode compounds for lithium ion batteries, LiMn2O4, LiMn1.95Si0.05O4 and LiMn1.9Ga0.1O4 have been synthesized by the freeze-drying method. All samples present partially sintered particles of 80 nm average size, corresponding to single crystalline phases with cubic spinel structure. The substitution of a little portion of Mn(IV) by Si(IV) in the crystal framework leads to more expanded and regular MnO6 octahedra, whereas the replacement of some Mn(III) by Ga(III) induces the opposing effect. The ESR measurements support the effectiveness of doping as an evolution of the width of the resonance signal with the composition is observed. A complete magnetic study has been carried out, including ac and dc magnetic susceptibility measurements at different fields, FC and ZFC, and magnetization versus field. Due to the in-built magnetic frustration in spinel structure and the competition between different exchange pathways, the insertion of small quantities of dopants causes significant differences in the magnetic behaviour. The electrochemical study has revealed very good values of specific capacity for LiMn1.95Si0.05O4 reaching 146 mA h g−1 and 139 mA h g−1 at C/10 and 1C rates, respectively. A capacity retention up to 75% has been observed for the three samples after 300th cycles.► We synthesize three spinel compounds for lithium ion batteries. ► Si insertion leads to more expanded and regular MnO6 octahedra. ► Magnetic measurements corroborate the insertion of the dopants. ► LiMn1.95Si0.05O4 gives the best electrochemical performance.
Keywords: Doped spinel; Cathode; Structural stability; Lithium-ion batteries; Magnetic disorder; Improved specific capacity
Thermal modelling of battery configuration and self-discharge reactions in vanadium redox flow battery
by Ao Tang; Jie Bao; Maria Skyllas-Kazacos (pp. 489-501).
During the operation of vanadium redox flow battery, the vanadium ions diffuse across the membrane as a result of concentration gradients between the two half-cells in the stack, leading to self-discharge reactions in both half-cells that will release heat to the electrolyte and subsequently increase the electrolyte temperature. In order to avoid possible thermal precipitation in the electrolyte solution and prevent possible overheating of the cell components, the electrolyte temperature needs to be known. In this study, the effect of the self-discharge reactions was incorporated into a thermal model based on energy and mass balances, developed for the purpose of electrolyte temperature control. Simulations results have shown that the proposed model can be used to investigate the thermal effect of the self-discharge reactions on both continuous charge–discharge cycling and during standby periods, and can help optimize battery designs and fabrication for different applications.► Precipitation of vanadium ions occurs at low or high electrolyte temperature. ► Vanadium ion diffusion leads to self-discharge and capacity loss. ► Self-discharge reactions release heat into the supporting electrolyte. ► Mathematical modelling can help with predicting the variation in electrolyte temperature and the loss of capacity. ► Temperature and rebalancing control systems can be developed based on the model to optimize the battery operation.
Keywords: Vanadium redox flow battery; Thermal modelling; Self-discharge reactions; Electrolyte temperature
Electrocatalysis of oxygen reduction at poly (4-amino-3-hydroxynaphthalene sulfonic acid) and platinum loaded polymer modified glassy carbon electrodes
by Berhanu W. Zewde; Shimelis Admassie (pp. 502-507).
The electrochemical polymerization of p-(4-amino-3-hydroxynaphtalene sulfonic acid) is investigated by using cyclic voltammetry. Low amount of platinum is loaded (17–303 μg) on the polymer modified glassy carbon electrode. The electrocatalytic activity of the modified electrodes towards oxygen reduction reaction is investigated. The polymer modified glassy carbon electrode shows a two electron reduction of oxygen to hydrogen peroxide and the platinum loaded polymer modified glassy carbon electrode shows a direct four electron reduction of oxygen to water. The chronocoulometric study of the oxygen reduction reaction shows similar results to those obtained with other techniques. Koutecky–Levich plot analysis is used to predict the mechanism and evaluate the kinetic parameters. Temkin adsorption isotherm is observed for lower platinum loading and Langmuirian for high platinum loading.► p-(AHNSA) is a new for electrocatalysis of oxygen reduction reaction. ► Electrochemical deposition of platinum metal on p-(AHNSA) is possible. ► It will contribute the research for reducing the amount of platinum. ► It will contribute for attaining the 1 g of platinum/kWh aim.
Keywords: 4-Amino-3-hydroxynaphtalene sulfonic acid; Platinum; Oxygen reduction reaction; Glassy carbon electrode
In-situ synthetize multi-walled carbon nanotubes@MnO2 nanoflake core–shell structured materials for supercapacitors
by Huajun Zheng; Jiaoxia Wang; Yi Jia; Chun'an Ma (pp. 508-514).
A new type of core–shell structured material consisting of multi-walled carbon nanotubes (MWCNTs) and manganese dioxide (MnO2) nanoflake is synthesized using an in-situ co-precipitation method. By scanning electron microscopy and transition electron microscope, it is confirmed that the core–shell nanostructure is formed by the uniform incorporation of birnessite-type MnO2 nanoflake growth round the surface of the activated-MWCNTs. That core–shell structured material electrode presents excellent electrochemical capacitance properties with the specific capacitance reaching 380 F g−1 at the current density of 5 A g−1 in 0.5 M Na2SO4 electrolyte. In addition, the electrode also exhibits good performance (the power density: 11.28 kW kg−1 at 5 A g−1) and long-term cycling stability (retaining 82.7% of its initial capacitance after 3500 cycles at 5 A g−1). It mainly attributes to MWCNTs not only providing considerable specific surface area for high mass loading of MnO2 nanoflakes to ensure effective utilization of MnO2 nanoflake, but also offering an electron pathway to improve electrical conductivity of the electrode materials. It is clearly indicated that such core–shell structured materials including MWCNTs and MnO2 nanoflake may find important applications for supercapacitors.Display Omitted► A facile in-situ co-precipitation method is developed to synthesize the MWCNTs@MnO2 core–shell structured material. ► Birnessite-type MnO2 nanoflakes chemically grew around the surface of the MWCNTs. ► The material had the high specific capacitance (380 F g−1) and power density (11.28 kW kg−1). ► The material showed excellent capacitance retention (82.7%) after 3500 cycles.
Keywords: Supercapacitor; Manganese dioxide nanoflake; Carbon nanotube; Core–shell structure
Effect of glycol-based coolants on the suppression and recovery of platinum fuel cell electrocatalysts
by Yannick Garsany; Sreya Dutta; Karen E. Swider-Lyons (pp. 515-525).
We use cyclic and rotating disk electrode voltammetry to study glycol-based coolant formulations to show that individual constituents have either negligible or significant poisoning effects on the nanoscale Pt/carbon catalysts used in proton exchange membrane fuel cells. The base fluid in all these coolants is glycol (1, 3 propanediol), commercially available in a BioGlycol coolant formulation with an ethoxylated nonylphenol surfactant, and azole- and polyol-based non-ionic corrosion inhibitors. Exposure of a Pt/Vulcan carbon electrode to glycol-water or glycol-water-surfactant mixtures causes the loss of Pt electrochemical surface area (ECSA), but the Pt ECSA is fully recovered in clean electrolyte. Only mixtures with the azole corrosion inhibitor cause irreversible losses to the Pt ECSA and oxygen reduction reaction (ORR) activity. The Pt ECSA and ORR activity can only be recovered to within 70% of its initial values after aggressive voltammetric cycling to 1.50 V after azole poisoning. When poisoned with a glycol mixture containing the polyol corrosion inhibitor instead, the Pt ECSA and ORR activity is completely recovered by exposure to a clean electrolyte. The results suggest that prior to incorporation in a fuel cell, voltammetric evaluation of the constituents of coolant formulations is worthwhile.► Suppression and recovery of Pt/VC in glycol-based coolant formulations was studied. ► Glycol/water mixture causes loss of Pt ECSA and lowers ORR activity. ► Full recovery is achieved by transfer of poisoned electrode to clean electrolyte. ► Addition of surfactant to the coolant formulation does not affect the Pt/VC electrocatalysts. ► Azole corrosion inhibitors cause irreversible losses to the available Pt ECSA.
Keywords: Pt/VC electrocatalysts; Fuel cells; PEMFCs; ORR; RDE
Modification of Nafion membrane by Pd-impregnation via electric field
by Xuelin Zhang; Yufeng Zhang; Li Nie; Xiaowei Liu; Limin Chang (pp. 526-529).
This paper presents an improved impregnation–reduction (I–R) method for modifying a Nafion membrane that achieves a lower methanol crossover. During impregnation of the Nafion membrane in Pd(NH3)4Cl2 solution, an electric field was conducted across the membrane to enhance the migration of Pd ions. After impregnation, Pd ions were reduced to form Pd nanoparticles by soaking the membrane in NaBH4 solution. The test results show that the Pd–Nafion membrane prepared by the improved I–R method has higher proton conductivity and lower methanol permeability than that prepared by usual I–R method.► Pd–Nafion membrane was prepared by an improved imprenation–reduction method. ► Electric field was used to enhance the movement of Pd ion toward Nafion membrane. ► Methanol crossover of Nafion membrane was lowered by the improved modification method.
Keywords: Nafion; Methanol crossover; Direct methanol fuel cell; Nanocomposite membrane
A new stochastic algorithm for proton exchange membrane fuel cell stack design optimization
by Uttara Chakraborty (pp. 530-541).
This paper develops a new stochastic heuristic for proton exchange membrane fuel cell stack design optimization. The problem involves finding the optimal size and configuration of stand-alone, fuel-cell-based power supply systems: the stack is to be configured so that it delivers the maximum power output at the load's operating voltage. The problem apparently looks straightforward but is analytically intractable and computationally hard. No exact solution can be found, nor is it easy to find the exact number of local optima; we, therefore, are forced to settle with approximate or near-optimal solutions. This real-world problem, first reported in Journal of Power Sources 131, poses both engineering challenges and computational challenges and is representative of many of today's open problems in fuel cell design involving a mix of discrete and continuous parameters. The new algorithm is compared against genetic algorithm, simulated annealing, and (1+1)-EA. Statistical tests of significance show that the results produced by our method are better than the best-known solutions for this problem published in the literature. A finite Markov chain analysis of the new algorithm establishes an upper bound on the expected time to find the optimum solution.► Develops a new, original algorithm for PEM fuel cell stack design optimization. ► Solves a PEMFC problem that is analytically intractable and computationally hard. ► Outperforms three state-of-the-art methods on three performance metrics. ► Claims of improved results are statistically validated. ► A Markov chain analysis of the algorithm is provided.
Keywords: Proton exchange membrane fuel cell; PEMFC stack; Optimization; Heuristic; Simulation; Markov chain