Journal of Power Sources (v.196, #8)
Computational design and optimization of fuel cells and fuel cell systems: A review
by M. Secanell; J. Wishart; P. Dobson (pp. 3690-3704).
▶ We highlight the importance of developing numerical optimization formulations for the design of fuel cell and fuel cell systems. ▶ We review numerical optimization formulations presented in the literature for fuel cell and fuel cell system design during the past 15 years. ▶ We present an overview of numerical optimization and multi-objective optimization algorithms used in fuel cell design. ▶ We highlight the key findings in fuel cell design and optimization during the last 15 years. ▶ We provide a discussion on the state-of-the-art in fuel cell optimization and suggest future research topics in the area of fuel cell and fuel cell systems design.The design of fuel cells is a challenging endeavour due to the multitude of physical phenomena that need to be simultaneously optimized in order to achieve proper fuel cell operation. Fuel cell design is a multi-objective, multi-variable problem. In order to design fuel cells by computational design, a mathematical formulation of the design problem needs to be developed. The problem can then be solved using numerical optimization algorithms and a computational fuel cell model. In the past decade, the fuel cell community has gained momentum in the area of numerical design. In this article, research aimed at using numerical optimization to design fuel cells and fuel cell systems is reviewed. The review discusses the strengths, limitations, advantages, and disadvantages of optimization formulations and numerical optimization algorithms, and insight obtained from previous studies.
Keywords: Fuel cell design; Polymer electrolyte fuel cell design; Solid oxide fuel cell design; Numerical optimization; Sensitivity analysis
Thermal stability, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of PrNi0.4Fe0.6O3− δ, a potential cathode material for IT-SOFCs
by Jeanette Rebello; Vladimir Vashook; Dimitro Trots; Ulrich Guth (pp. 3705-3712).
A typical exponential decay curve of the relative conductivity with time during stepwise change in temperature at constant oxygen concentration in gas phase (experimental curve and a perfect model fit).The potential use of a double B mixed-perovskite as a promising cathode material in intermediate temperature solid oxide fuel cells (IT-SOFCs) has been anticipated as a result of this work. A thorough investigation of some important parameters like thermal stability, thermal expansion, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of the PrNi0.6Fe0.4O3− δ ceramic sample have been investigated as functions of temperature (20–1000°C) and oxygen partial pressure (0.6–21,000Pa). According to the measurements, the composition was phase stable at pO2>1Pa up to 1000°C and shows p-type semiconductivity with a low conductivity versus pO2 dependence.The perovskite has been found to have comparable thermal expansion coefficients with those of commonly used solid electrolytes like CeO2 and ZrO2 based oxides. In case of the chemical diffusion experiments higher oxygen diffusion mobility observed during reduction processes in comparison with those during oxidation have been explained by the already known formation of neutral defect clusters.
Keywords: IT-SOFC; Cathode material; Double-B-site mixed perovskite; Electrical conductivity; Oxygen non-stoichiometry; Chemical diffusion; Oxygen exchange
Catalytic activity of Ni-YSZ anodes in a single-chamber solid oxide fuel cell reactor
by Sylvio Savoie; Teko W. Napporn; Bertrand Morel; Michel Meunier; Réal Roberge (pp. 3713-3721).
▶ Methane conversion always results in both the partial and complete oxidation products. ▶ Low temperature operation may give rise to significant dilution of the syngas species. ▶ Use of gas distribution plates noticeably enhance the conversion rates. ▶ The presence of hot spots may induce the cracking of thin film electrolytes. ▶ Small anode thicknesses lower the H2/CO ratio well below 2.0 at high temperature.The importance of heterogeneous catalysis in single-chamber solid oxide fuel cells (SC-SOFC) is universally recognized, but little studied. This work presents a thorough investigation of the catalytic activity of three Ni-YSZ half-cells in a well-described single-chamber reactor. One in-house electrolyte-supported and two commercially available anode-supported half-cells composed of anodes with thicknesses ranging from 50μm to 1.52mm are investigated. They are exposed to methane and oxygen gas mixtures within CH4:O2 flow rate ratios ( Rin) of 0.8–2.0 and furnace temperatures of 600–800°C. The conversion of methane always results in the formation of syngas species (H2 and CO). However, their yields vary considerably based on the individual anode, the operating temperature, and Rin. The SC-reactor design and the presence of hot-spots at the reactor entrance bring the methane and oxygen conversion rates well above the limit expected from experiments carried out with anode half-cells only. Major variations in the H2/CO ratio are observed. In lowering the temperature from 800°C to 600°C, it spreads from well below to well above the stoichiometric value of 2.0 expected for the partial oxidation reaction. To optimize the SC-SOFC any further, the findings stress the need to undertake even more catalytic studies of its electrode materials under actual structure and morphology as well as final reactor configuration.
Keywords: Single-chamber SOFC; Ni-YSZ anode; Catalytic activity; Methane conversion; Selectivity
Impact of SO2 poisoning of platinum nanoparticles modified glassy carbon electrode on oxygen reduction
by M.I. Awad; M.M. Saleh; T. Ohsaka (pp. 3722-3728).
▶ SO2 poisoning of platinum nanoparticles modified glassy carbon (nano-Pt/GC) and polycrystalline platinum (poly-Pt) electrodes changes the adsorption mode of molecular oxygen. ▶ SO2 poisoning changes the oxygen reduction mechanism from the one-step four-electron reduction to water to the stepwise reduction involving the formation of H2O2 as an intermediate. ▶ Nano-Pt/GC electrode shows an improved resistance to SO2 poisoning compared with the poly-Pt electrode. ▶ The poisoned nano-Pt/GC electrode could be recovered by cycling the potential in the potential range of oxygen reduction reaction. ▶ Platinum oxide has a crucial role in SO2 poisoning and recovery of the Pt electrode.An extraordinary recovery characteristic of Pt-nanoparticles from SO2 poisoning is introduced in this study. Platinum nanoparticles (nano-Pt) modified glassy carbon electrode (nano-Pt/GC) has been compared with polycrystalline platinum (poly-Pt) electrode towards SO2 poisoning. Two procedures of recovery of the poisoned electrodes were achieved by cycling the potential in the narrow potential range (NPR, 0–0.8V vs. Ag/AgCl/KCl (sat.)) and wide potential range (WPR, −0.2 to 1.3V). The extent of recovery was marked using oxygen reduction reaction (ORR) as a probing reaction. SO2 poisoning of the electrodes changed the mechanism of the oxygen reduction from the direct reduction to water to the stepwise reduction involving the formation of H2O2 as an intermediate, as indicated by the rotating ring-disk voltammetry. Using the WPR recovery procedure, it was found that two potential cycles were enough to recover 100% of the activity of the ORR on the nano-Pt/GC electrode. At the poly-Pt electrode, however, four potential cycles of the WPR caused only 79% in the current recovery, while the peak potential of the ORR was 130mV negatively shifted as compared with the fresh poly-Pt electrode. Interestingly, the NPR procedure at the nano-Pt/GC electrode was even more efficient in the recovery than the WPR procedure at the poly-Pt electrode.
Keywords: SO; 2; Platinum nanoparticles; Oxygen reduction; Glassy carbon
Double-perovskites YBaCo2− xFe xO5+ δ cathodes for intermediate-temperature solid oxide fuel cells
by Jingfeng Xue; Yu Shen; Tianmin He (pp. 3729-3735).
▶ YBaCo2− xFe xO5+ δ double-perovskites were developed as cathode materials for IT-SOFCs. ▶ The cathodes were chemical compatibility with LaGaO3-based electrolyte. ▶ The area specific resistances of these cathodes were lower than 0.15Ωcm2 at 700°C. ▶ The single cells with these cathodes exhibited higher power densities.Double-perovskites YBaCo2− xFe xO5+ δ (YBCF, x=0.0, 0.2, 0.4 and 0.6) are synthesized with a solid-state reaction and are assessed as potential cathode materials for utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs) on the La0.9Sr0.1Ga0.8Mg0.115Co0.085O2.85 (LSGMC) electrolyte. The YBCF materials exhibit chemical compatibility with the LSGMC electrolyte up to a temperature of 950°C. The conductivity of the YBCF samples decreases with increasing Fe content, and the maximum conductivity of YBCF is 315Scm−1 at 325°C for the x=0.0 sample. A semiconductor–metal transition is observed at about 300–400°C. The thermal expansion coefficient of the YBCF samples increases from 16.3 to 18.0×10−6K−1 in air at temperatures between 30 and 900°C with increase in Fe content. The area-specific resistances of YBCF cathodes at x=0.0, 0.2 and 0.4 on the LSGMC electrolyte are 0.11, 0.13 and 0.15Ωcm2 at a temperature of 700°C, respectively. The maximum power densities of the single cells fabricated with the LSGMC electrolyte, Ce0.8Sm0.2O1.9 (SDC) interlayer, NiO/SDC anode and YBCF cathodes at x=0.0, 0.2 and 0.4 reach 873, 768 and 706mWcm−2, respectively. This study suggests that the double-perovskites YBCF (0≤ x≤0.4) can be potential candidates for utilization as IT-SOFC cathodes.
Keywords: Solid oxide fuel cell; Double perovskite; Cathode; Electrical conductivity; Thermal expansion; Electrochemical performance
Application of complementary analytical tools to support interpretation of polymer-electrolyte-membrane fuel cell impedance data
by Sunil K. Roy; Helena Hagelin-Weaver; Mark E. Orazem (pp. 3736-3742).
▶ The interpretation of low-frequency inductive impedance spectroscopy loops in terms of platinum oxidation was confirmed. ▶ The amount of oxidized Pt in the near surface region of the catalyst was similar to the amount of oxidized Pt in a 3 ML PtO x film on a single crystal Pt surface. ▶ Reduction of electrochemically active area was inferred from the evaluation of interfacial capacitance. ▶ ICP-MS data showed trace amounts of Pt in the fuel cell effluent. ▶ Results support the premise that the low-frequency inductive features in the impedance response provide information useful for understanding the reduction of fuel cell performance.A series of ex situ techniques, including scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and inductively coupled plasma-mass spectroscopy were used to study morphological and chemical changes associated with the aging of a membrane electrode assembly in a polymer-electrolyte-membrane fuel cell. These results were correlated with the results of in situ electrochemical measurements, including measurement of steady-state polarization curves and electrochemical impedance spectroscopy. The results support the premise that the low-frequency inductive features seen in the impedance response provide information useful for understanding phenomena, such as platinum oxidation, that lead to reduction of fuel cell performance. The reduction in electrochemically active surface area, obtained from the high-frequency part of the impedance response, was consistent with the observed agglomeration of platinum particles and platinum oxidation.
Keywords: X-ray diffraction; X-ray photoelectron spectroscopy; Transmission electron microscopy; Scanning electron microscopy; Capacitance; Impedance spectroscopy
Effects of operating conditions on durability of polymer electrolyte membrane fuel cell Pt cathode catalyst layer
by Shinsuke Ohyagi; Toshihiko Matsuda; Yohei Iseki; Tatsuyoshi Sasaki; Chihiro Kaito (pp. 3743-3749).
In this study, we investigated the effects of humidity and oxygen reduction on the degradation of the catalyst of a polymer electrolyte membrane fuel cell (PEMFC) in a voltage cycling test. To elucidate the effect of humidity on the voltage cycling corrosion of a carbon-supported Pt catalyst with 3nm Pt particles, voltage cycling tests based on 10,000 cycles were conducted using 100% relative humidity (RH) hydrogen as anode gas and nitrogen of varying humidities as cathode gas. The degradation rate of an electrochemical surface area (ECSA) was almost 50% under 189% RH nitrogen atmosphere and the Pt average particle diameter after 10,000 cycles under these conditions was about 2.3 times that of a particle of fresh catalyst because of the agglomeration of Pt particles.The oxygen reduction reaction (ORR) that facilitated Pt catalyst agglomeration when oxygen was employed as the cathode gas also demonstrated that Pt agglomeration was prominent in higher concentrations of oxygen. The ECSA degradation figure in 100% RH oxygen was similar to that in 189% RH nitrogen. It was concluded that liquid water, which was dropped under a supersaturated condition or generated by ORR, accelerated Pt agglomeration. In this paper, we suggest that the Pt agglomeration degradation occurs in a flooding area in a cell plane.
Keywords: Polymer electrolyte fuel cells; Cathode catalyst layer; Pt agglomeration; Voltage cycling; Electrochemical surface area
Prediction and analysis of the cathode catalyst layer performance of proton exchange membrane fuel cells using artificial neural network and statistical methods
by N. Khajeh-Hosseini-Dalasm; S. Ahadian; K. Fushinobu; K. Okazaki; Y. Kawazoe (pp. 3750-3756).
▶ For the first time, artificial neural network approach together with statistical methods (ANOM and ANOVA methods) are employed for modeling, prediction, and analysis of an agglomerate cathode catalyst layer (CL) performance. ▶ ANOM and ANOVA methods allow us extract physical explanations regarding the underlying system modeled using the ANN approach. ▶ Cathode CL thickness and the membrane volume content in CL were found to be the most significant structural parameters affecting the CL performance.A mathematical model was developed to investigate the cathode catalyst layer (CL) performance of a proton exchange membrane fuel cell (PEMFC). A numerous parameters influencing the cathode CL performance are implemented into the CL agglomerate model, namely, saturation and eight structural parameters, i.e., ionomer film thickness covering the agglomerate, agglomerate radius, platinum and carbon loading, membrane content, gas diffusion layer penetration content and CL thickness. For the first time, an artificial neural network (ANN) approach along with statistical methods were employed for modeling, prediction, and analysis of the CL performance, which is denoted by activation overpotential. The ANN was constructed to build the relationship between the named parameters and activation overpotential. Statistical analysis, namely, analysis of means (ANOM) and analysis of variance (ANOVA) were done on the data obtained by the trained neural network and resulted in the sensitivity factors of structural parameters and their mutual combinations as well as the best performance.
Keywords: Artificial neural network; Proton exchange membrane fuel cell; Catalyst layer; Agglomerate model; Analysis of means; Analysis of variance
A thermophilic microbial fuel cell design
by Sarah M. Carver; Pertti Vuoriranta; Olli H. Tuovinen (pp. 3757-3760).
▶ A microbial fuel cell (MFC) was designed for operation at thermophilic temperatures. ▶ The MFC assembly was successfully operated with glucose at 57°C. ▶ The design effectively eliminated anolyte and catholyte evaporation. ▶ Polarization curve showed minimal activation losses. ▶ Overshoot phenomenon was apparent in the mass transfer region of polarization curve.Microbial fuel cells (MFCs) are reactors able to generate electricity by capturing electrons from the anaerobic respiratory processes of microorganisms. While the majority of MFCs have been tested at ambient or mesophilic temperatures, thermophilic systems warrant evaluation because of the potential for increased microbial activity rates on the anode. MFC studies at elevated temperatures have been scattered, using designs that are already established, specifically air-cathode single chambers and two-chamber designs. This study was prompted by our previous attempts that showed an increased amount of evaporation in thermophilic MFCs, adding unnecessary technical difficulties and causing excessive maintenance. In this paper, we describe a thermophilic MFC design that prevents evaporation. The design was tested at 57°C with an anaerobic, thermophilic consortium that respired with glucose to generate a power density of 375mWm−2 after 590h. Polarization and voltage data showed that the design works in the batch mode but the design allows for adoption to continuous operation.
Keywords: Air cathode; Cathode chamber; Cellulose; Microbial fuel cell; Thermophilic microorganisms
Solid oxide fuel cell with compositionally graded cathode functional layer deposited by pressure assisted dual-suspension spraying
by Jared McCoppin; Daniel Young; Thomas Reitz; Adam Maleszewski; Sharmila Mukhopadhyay (pp. 3761-3765).
► Compositionally graded CFL fabricated by pressurized duel suspension spraying system. ► Addition of the compositionally graded CFL increased the area-specific ohmic resistance. ► Compositionally graded CFL overall effective at reducing the charge transfer resistance. ► Supports previously reported evidence that grading the CFL can improve SOFC performance. ► Inexpensive deposition system that can produce a viable compositionally graded CFL.In this work, the benefit of compositionally grading a cathode functional layer (CFL) for solid oxide fuel cells (SOFCs) is explored. Cells are prepared wherein either a standard cathode functional layer (SCFL) or a linearly compositionally graded cathode functional layer (CGCFL) is placed between the cell electrolyte and cathode current collecting regions. The electrochemical performance of these cells is compared with a SOFC cell containing no CFL. All cells are fabricated using a pressurized dual-suspension spraying system. Electrolytes, cathode functional layer, and cathode current collecting materials are deposited on a powder compacted anode support. SEM and EDAX area maps are taken to study the resulting micro-structures and to verify that the desired CFL profiles are produced. The EDAX area map verifies that a compositionally graded CFL and a SCFL are obtained. The cells are analyzed using impedance spectroscopy to evaluate the electrochemical performances of each cell. The open circuit voltage (OCV) and peak power densities of all three cells are 1.04V with 80mWcm−2, 1.12V with 108mWcm−2, and 1.08V with 193mWcm−2 at 850°C for the SCFL cell, the cell without a CFL, and the compositionally graded CFL cell respectively. The results show that this approach is a viable means for producing SOFC functional layers with unique composition and interfacial properties.
Keywords: Functional layer; Compositionally graded cathode; Solid oxide fuel cells (SOFC); Anode supported; Spray processing
Development of a novel pseudo bipolar piezoelectric proton exchange membrane fuel cell with nozzle and diffuser
by Hsiao-Kang Ma; Jyun-Sheng Wang; Ya-Ting Chang (pp. 3766-3772).
▶ In this study, an innovative design for a PZT-PEMFC-ND bi-cell with pseudo bipolar electrodes is developed to achieve a higher power in the stack design to solve water-flooding problems and improve cell performance. This innovative design, with a reaction area of 8cm2, contains two cells with two outside anodes and two inside cathodes that share a common PZT vibrating device for pumping air flow. ▶ The PZT vibration frequency and cell temperature are the important operating parameters for increasing the performance of the PZT-PEMFC-ND module. The optimal PZT vibration frequency is f=180Hz at a temperature of 40°C. And, the optimal geometry parameters are AR at 11.25 under θ=5°. ▶ The PZT-PEMFC-ND bi-cell generates 1W at T=40°C, f=180Hz, AR=11.25, and θ=5°. When compared with the single cell, the performance of the PZT-PEMFC-ND bi-cell was 1.6 times greater. The net power output of the bi-cell is about 0.8W, due to the power consumption of 0.2W for the PZT device at 180Hz.Previous studies of a piezoelectric proton exchange membrane fuel cell with nozzle and diffuser (PZT-PEMFC-ND) have shown that a PZT device could solve the cathode flooding problems and improve cell performance. In this study, an innovative design for a PZT-PEMFC-ND bi-cell with pseudo bipolar electrodes is developed to achieve a higher power in the stack design to solve water-flooding problems and improve cell performance. This new design, with a reaction area of 8cm2, contains two cells with two outside anodes and two inside cathodes that share a common PZT vibrating device for pumping air flow. The influence of the varying aspect ratio (AR) of the diffuser elements on the unit cell-flow rate is investigated using a three-dimensional transitional model. The simulation results show that a proper AR value of 11.25 for the diffuser, with a smaller diffuser angle of 5°, could ensure a smoother intake of the air and, thus, better cell performance. The experimental results show that the performance of the PZT-PEMFC-ND bi-cell can be 1.6 times greater than that of the single cell.
Keywords: Piezoelectric; Fuel cell; Nozzle; Diffuser; Air-breathing; Pseudo bipolar design
Optimization of polytetrafluoroethylene content in cathode gas diffusion layer by the evaluation of compression effect on the performance of a proton exchange membrane fuel cell
by Hao-Ming Chang; Chien-Wei Lin; Min-Hsing Chang; Huan-Ruei Shiu; Wen-Chen Chang; Fang-Hei Tsau (pp. 3773-3780).
▶ A special test fixture to measure the effect of compression on fuel cell performance. ▶ Determine the optimal PTFE contents in gas diffusion layer and micro porous layer. ▶ The optimal PTFE content in GDL is found to be 5% at compression ratio 30%. ▶ The optimal PTFE content in MPL is found to be 30% at compression ratio 30%.This research investigates the optimal polytetrafluoroethylene (PTFE) content in the cathode gas diffusion layer (GDL) by evaluating the effect of compression on the performance of a proton exchange membrane (PEM) fuel cell. A special test fixture is designed to control the compression ratio, and thus the effect of compression on cell performance can be measured in situ. GDLs with and without a microporous layer (MPL) coating are considered. Electrochemical impedance spectroscopy (EIS) is used to diagnose the variations in ohmic resistance, charge transfer resistance and mass transport resistance with compression ratio. The results show that the optimal PTFE content, at which the maximum peak power density occurs, is about 5wt% with a compression ratio of 30% for a GDL without an MPL coating. For a GDL with an MPL coating, the optimal PTFE content in the MPL is found to be 30% at a compression ratio of 30%.
Keywords: Proton exchanger membrane fuel cell; Gas diffusion layer; Microporous layer; Polytetrafluoroethylene; Compression ratio
Transient behavior analysis of a new designed passive direct methanol fuel cell fed with highly concentrated methanol
by Weiwei Cai; Songtao Li; Ligang Feng; Jing Zhang; Datong Song; Wei Xing; Changpeng Liu (pp. 3781-3789).
▶ A passive DMFC is manufactured for high concentration or neat methanol feeding. ▶ This design wouldn’t increase the CO2 releasing resistance. ▶ The new DMFC can continuously operate about 4.5 times longer than a conventional DMFC.A new structure of passive direct methanol fuel cell (DMFC) with two methanol reservoirs separated by a porous medium layer is designed and a corresponding mathematical model is presented. The new designed passive DMFC can be directly fed with highly concentrated methanol solution or neat methanol. The porosity ( ɛpr) of the porous medium layer is optimized using the proposed model. Some operation parameters are also optimized by both the numerical calculation and experimental measurement. The new designed DMFC can be continuously operated for about 4.5 times longer than a conventional passive DMFC with the optimum parameters. The methanol crossover during the same discharging is only about 50% higher.
Keywords: Passive direct methanol fuel cell; Highly concentrated methanol; Mathematical model
High-fidelity stack and system modeling for tubular solid oxide fuel cell system design and thermal management
by K.J. Kattke; R.J. Braun; A.M. Colclasure; G. Goldin (pp. 3790-3802).
▶ A thermally coupled tubular SOFC system model is presented. ▶ High-fidelity stack model captures thermofluidic interactions in/around the stack. ▶ Radiation dominates heat transfer from small scale (<1kW) stacks. ▶ Strong relationship between cell performance and radiation view factors develops. ▶ Cell power disparities revealed ranging from 7.6 to 10.8W.Effective thermal integration of system components is critical to the performance of small-scale (<10kW) solid oxide fuel cell systems. This paper presents a steady-state design and simulation tool for a highly-integrated tubular SOFC system. The SOFC is modeled using a high fidelity, one-dimensional tube model coupled to a three-dimensional computational fluid dynamics (CFD) model. Recuperative heat exchange between SOFC tail-gas and inlet cathode air and reformer air/fuel preheat processes are captured within the CFD model. Quasi one-dimensional thermal resistance models of the tail-gas combustor (TGC) and catalytic partial oxidation (CPOx) complete the balance of plant (BoP) and SOFC coupling. The simulation tool is demonstrated on a prototype 66-tube SOFC system with 650W of nominal gross power. Stack cooling predominately occurs at the external surface of the tubes where radiation accounts for 66–92% of heat transfer. A strong relationship develops between the power output of a tube and its view factor to the relatively cold cylinder wall surrounding the bundle. The bundle geometry yields seven view factor groupings which correspond to seven power groupings with tube powers ranging from 7.6–10.8W. Furthermore, the low effectiveness of the co-flow recuperator contributes to lower tube powers at the bundle outer periphery.
Keywords: SOFC; System analysis; Modeling; Thermal management; Stack design; CFD
Effect of cation contamination and hydrated pressure loading on the mechanical properties of proton exchange membranes
by Ruiliang Jia; Binghong Han; Kemal Levi; Takuya Hasegawa; Jiping Ye; Reinhold H. Dauskardt (pp. 3803-3809).
▶ Bulge test is used to simulate hydrated pressurized loading on PEMs in fuel cells. ▶ Water absorption reduces elastic moduli and fracture resistance of PEMs. ▶ Elastic moduli of PEMs increase with the increasing radius of cation exchanged. ▶ Cation contamination makes PEMs more brittle and reduces fracture resistance of PEMs.Perfluorosulfonic acid (PFSA) polymer membranes are widely used as electrolyte thin films to transport protons in proton exchange membrane (PEM) fuel cells. The mechanical degradation of the membrane represents a common failure mode that limits the operational life of the fuel cells. In the present work, effect of contamination related to cation exchange on the mechanical reliability of PEMs was investigated. We applied the bulge test technique to assess the mechanical properties of Nafion® PFSA membranes simulating pressure loading on hydrated PEMs in fuel cells. The corresponding elastic moduli of Nafion® before and after cation exchange were analyzed and compared with the results measured by uniaxial tension experiments at selected humidity conditions, showing increasing stiffness with the increase of cation radius. We also used the out-of-plane tearing test method to characterize the fracture behaviors of PEMs. The effects of cation exchange and water absorption on mechanical and fracture properties of PEMs at different temperatures are discussed in terms of cation and water interactions with the molecular structure of PFSA polymers.
Keywords: Abbreviations; PFSA; perfluorosulfonic acid; PEM; proton exchange membrane; DIW; distilled waterPerfluorosulfonic acid polymer; Proton exchange membrane; Nafion; ®; Bulge test; Tearing; Cation exchange
Modeling of the Ballard-Mark-V proton exchange membrane fuel cell with power converters for applications in autonomous underwater vehicles
by Chien-Hsing Lee; Jian-Ting Yang (pp. 3810-3823).
This paper studies the transient response of the output voltages of a Ballard-Mark-V 35-cell 5kW proton exchange membrane fuel cell (PEMFC) stack with power conversion for applications in autonomous underwater vehicles (AUVs) under load changes. Four types of pulse-width modulated (PWM) dc–dc power converters are employed to connect to the studied fuel cell in series for converting the unregulated fuel cell stack voltage into the desired voltage levels. The fuel cell model in this paper consists of the double-layer charging effect, gases diffusion in the electrodes, and the thermodynamic characteristic; PWM dc–dc converters are assumed to operate in continuous-conduction mode with a voltage-mode control compensator. The models of the study's fuel cell and PWM dc–dc converters have been implemented in a Matlab/SIMULINKTM environment. The results show that the output voltages of the studied PEMFC connected with PWM dc–dc converters during a load change are stable. Moreover, the model can predict the transient response of hydrogen/oxygen out flow rates and cathode and anode channel temperatures/pressures under sudden change in load current.
Keywords: Fuel cells; Autonomous underwater vehicles; Voltage-model control; dc–dc converters
Performance study of a solid oxide fuel cell and gas turbine hybrid system designed for methane operating with non-designed fuels
by Yang Li; Yiwu Weng (pp. 3824-3835).
▶ Mathematical models of all the components in the hybrid system are defined. Detailed thermal dynamic model of the SOFC developed in this paper includes convectional heat transfer between gas and solids as well as radiation and conduction between solid materials. Thus the SOFC model can be used to calculate the radial temperature gradients, which is the main source of stress. ▶ New design points are defined for the hybrid system operating with non-designed fuels. ▶ The performance of a methane-based hybrid system operating with non-designed fuels is discussed both at its design point and part-load conditions. ▶ Three possible measures are introduced and investigated to increase the power output of the hybrid system operating with non-designed fuel.This paper presents an analysis of the fuel flexibility of a methane-based solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system. The simulation models of the system are mathematically defined. Special attention is paid to the development of an SOFC thermodynamic model that allows for the calculation of radial temperature gradients. Based on the simulation model, the new design point of system for new fuels is defined first; the steady-state performance of the system fed by different fuels is then discussed. When the hybrid system operates with hydrogen, the net power output at the new design point will decrease to 70% of the methane, while the design net efficiency will decrease to 55%. Similar to hydrogen, the net output power of the ethanol-fueled system will decrease to 88% of the methane value due to the lower cooling effect of steam reforming. However, the net efficiency can remain at 61% at high level due to increased heat recuperation from exhaust gas. To increase the power output of the hybrid system operating with non-design fuels without changing the system configuration, three different measures are introduced and investigated in this paper. The introduced measures can increase the system net power output operating with hydrogen to 94% of the original value at the cost of a lower efficiency of 45%.
Keywords: Solid oxide fuel cell; Gas turbine; Hybrid system; Ethanol; Hydrogen; Methane
Optical humidity sensing, proton-conducting sol–gel glass monolith
by Haibin Li; Dongliang Jin; Qingchun Yu; Hengyong Tu (pp. 3836-3840).
Display Omitted▶ Optical humidity sensing, proton-conducting sol-gel glass monolith is prepared. ▶ The glass monolith exhibits proton conductivities of of ca. 10−1Scm−1. ▶ The transmittance of the glass monolith changes with humidity. ▶ This glass monolith is utilized for optical humidity measurements.An integrated, crack-free glass monolith is prepared via a modified sol–gel approach. It has an accessible network of channels consisting of anisotropic pores of widths ca. 20–50nm and lengths ca. 100–250nm. The glass monolith exhibits a transparency change based on humidity, which is utilized as a basis for optical humidity measurements. On the other hand, the glass monolith shows high proton conduction in humid atmosphere, and its proton conductivity reaches a value of 0.12Scm−1 at 30°C and 80% relative humidity.
Keywords: Glass monolith; Sol–gel; Proton conduction; Humidity sensor; Fuel cell
Performance of a novel La(Sr)MnO3-Pd composite current collector for solid oxide fuel cell cathode
by Chuan Wang; Xianshuang Xin; Yanjie Xu; Xiaofeng Ye; Lijun Yu; Shaorong Wang; Tinglian Wen (pp. 3841-3845).
▶ Pd connects LSM particles well. ▶ Pd–LSM composite has a good electrical conductivity. ▶ Current collection layer reduces the contact resistance.The electrochemical performance of LSM–Pd composite material as current collector of SOFC cathode is studied on (La0.8Sr0.2)0.9MnO3 (LSM90) cathode. The influence of Pd content on contact resistance is investigated. The investigation shows that the contact resistance of LSM–Pd is about 20mΩcm2 at 750°C when the composite contains 8wt% Pd, and it could be comparable to pure Pt. The ohmic resistance of a single cell using LSM–Pd composite is about 255mΩcm2 that contains 4wt% Pd as current collector, this value is close to that of a cell using expensive Pt paste as current collector.
Keywords: Solid state oxide fuel cell; Current collector; Cathode; Contact resistance
Prediction of the effective coefficient of thermal expansion of heterogeneous media using two-point correlation functions
by J. Milhans; D.S. Li; M. Khaleel; X. Sun; H. Garmestani (pp. 3846-3850).
▶ In this study, a statistical continuum mechanics model is developed to predict overall coefficient of thermal expansion for glass-ceramic SOFC seals. ▶ The model developed uses two-point correlation functions to represent microstructure. ▶ The model we developed is sensitive to anisotropy in the microstructure. ▶ We find that the results fall within upper and lower bounds and are accurate to measured coefficient of thermal expansion.Statistical continuum mechanics is used to predict the coefficient of thermal expansion (CTE) for solid oxide fuel cell glass-ceramic seal materials with different morphology and crystallinity. Two-point correlation functions are utilized to represent the heterogeneous microstructure morphology and phase distribution. The model uses two-point correlation functions in conjunction with local properties to predict the effective CTE. Prediction results are comparable to experimental CTE results. The advantage of using the statistical continuum mechanics model in predicting the effective properties of anisotropic media is shown, using the ability to take the microstructure into consideration.
Keywords: Solid oxide fuel cell; Coefficient of thermal expansion; Statistical continuum mechanics; Correlation function
Use of mechanical tests to predict durability of polymer fuel cell membranes under humidity cycling
by T.T. Aindow; J. O’Neill (pp. 3851-3854).
▶ Mechanical fatigue testing mimics membrane stresses during humidity cycling. ▶ Cycles to failure in fatigue can be used to predict new membrane life. ▶ Fatigue testing of degraded membranes gives predictions of remaining life.A mechanical fatigue life analysis of the type used for lifetime predictions in structural materials has been adapted to characterize PEM fuel cell membranes. It is shown that a stress vs. cycles-to-failure ( S– N) curve analysis is capable of: (1) predicting the mechanical durability of PEM membranes under humidity cycling, and (2) assessing the fraction of membrane life remaining in degraded MEAs. Mechanical fatigue testing was performed in a dynamic mechanical analyzer (DMA) at 60°C and 90% relative humidity (RH) under different values of stress amplitude, and the results were used to plot the S– N curve. The stress amplitude for the S– N curve was then mapped to the equivalent change in RH as a methodology for characterizing membrane mechanical resistance to humidity cycling.
Keywords: PEMFC; Membrane durability; Relative humidity cycling; Mechanical fatigue; Membrane life prediction; S; –; N; curve
A new Gd-promoted nickel catalyst for methane conversion to syngas and as an anode functional layer in a solid oxide fuel cell
by Wei Wang; Chao Su; Ran Ran; Zongping Shao (pp. 3855-3862).
▶ Gd-promoted Ni–Al2O3 catalyst presents good coking resistance toward methane. ▶ This catalyst also shows good catalytic activity for methane conversion. ▶ The GdNi–Al2O3 catalyst yields high-quality syngas for chemical synthesis. ▶ The fuel cell with the GdNi–Al2O3 catalyst layer delivers high power output.The effect of lanthanide promoters on a Ni–Al2O3 catalyst for methane partial oxidation, steam reforming and CO2 reforming at 600–850°C is systematically investigated. The promoters include La2O3, CeO2, Pr2O3, Sm2O3 and Gd2O3. GdNi–Al2O3 shows comparable catalytic activity to LaNi–Al2O3 and PrNi–Al2O3 but higher activity than CeNi–Al2O3 and SmNi–Al2O3 for all three reactions. The O2-TPO results show that GdNi–Al2O3 possesses the best coke resistance among those tested. It also displays good stability at 850°C for 300h. Raman spectroscopy indicates that the addition of lanthanide promoters can reduce the degree of graphitization of the carbon deposited on Ni–Al2O3. The GdNi–Al2O3 is further applied as an anode functional layer in solid-oxide fuel cells operating on methane. The cell yields peak power densities of 1068, 996 and 986mWcm−2 at 850°C, respectively, for operating on methane–O2, methane–H2O and methane–CO2 gas mixtures, which is comparable to operating on hydrogen fuel. GdNi–Al2O3 is promising as a highly coking-resistant catalyst layer for solid-oxide fuel cells.
Keywords: Solid-oxide fuel cells; Nickel–alumina; Anode catalyst layer; Methane; Carbon deposition; Lanthanide promotion
A composite of borohydride and super absorbent polymer for hydrogen generation
by Z.P. Li; B.H. Liu; F.F. Liu; D. Xu (pp. 3863-3867).
▶ A new composite material composed of sodium borohydride, sodium hydroxide and sodium polyacrylate for the borohydride hydrolysis to generate hydrogen is prepared by ball milling. ▶ Water content and NiCl2 content in the catalyst precursor solution significantly affect the hydrogen generation kinetics of the composite. ▶ A hydrogen evolution mechanism of the composite is suggested.To develop a hydrogen source for underwater applications, a composite of sodium borohydride and super absorbent polymer (SAP) is prepared by ball milling sodium borohydride powder with SAP powder, and by dehydrating an alkaline borohydride gel. When sodium polyacrylate (NaPAA) is used as the SAP, the resulting composite exhibits a high rate of borohydride hydrolysis for hydrogen generation. A mechanism of hydrogen evolution from the NaBH4–NaPAA composite is suggested based on structure analysis by X-ray diffraction and scanning electron microscopy. The effects of water and NiCl2 content in the precursor solution on the hydrogen evolution behavior are investigated and discussed.
Keywords: Underwater vehicle; Sodium borohydride; Hydrogen evolution; Composite material; Gel; Borohydride hydrolysis
Electrodeposited porous-microspheres Li–Si films as negative electrodes in lithium-ion batteries
by Rongguan Lv; Jun Yang; Jiulin Wang; Yanna NuLi (pp. 3868-3873).
The porous-microspheres Li–Si film (PMLSF) was first electrodeposited via multi-step constant current technique on Cu foil. This film was mainly composed of irregular and inter-connected porous-microspheres with different sizes ranging from several micrometers to several tens of micrometers. As negative electrodes for lithium-ion battery, the PMLSF electrode exhibited high initial coulombic efficiency and good cycling stability.Display Omitted▶ Li and Si are co-deposited from a non-aqueous electrolyte solution. ▶ The porous-microspheres Li–Si film is first prepared via electrodeposition. ▶ Co-deposition of Li and Si leads to a high initial coulombic efficiency (>90%). ▶ The particular film morphology favors a superior cycling stability.A porous-microspheres Li–Si film (PMLSF) is prepared by multi-step constant current (MSCC) electrodeposition on Cu foil. Its structure and morphology are characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). As negative electrodes of lithium-ion batteries, the PMLSF electrode delivers the first gravimetric and geometric charge capacities of 2805.7mAhg−1 and 621.9μAhcm−2 at the current density of 25.5μAcm−2, and its initial coulombic efficiency is as high as 98.2%. When the PMLSF electrode is cycled in VC-containing electrolyte, the superior cycling performance can be obtained. After 50 cycles, 96.0% of its initial capacity is retained at the current density of 50.0μAcm−2. Electrochemical impedance spectra (EIS) research confirms the positive effect of VC additive on the behavior of the PMLSF electrode.
Keywords: Porous Li–Si film; Electrodeposition; Negative electrode; Lithium-ion battery
Favorable combination of positive and negative electrode materials with glyme–Li salt complex electrolytes in lithium ion batteries
by A. Orita; K. Kamijima; M. Yoshida; K. Dokko; M. Watanabe (pp. 3874-3880).
Rate capabalities of the LiFePO4/Li4Ti5O12 cells using the conventional organic electrolyte and Li salt–glyme complex electrolyte.Tetraglyme (G4)–lithium bis(trifluoromethanesulfonyl)amide (TFSA) complexes with different G4 ratio were investigated. An increase in the amount of G4 led to the decrease in the viscosity, and increase in the ionic conductivity of the complex, and G4–LiTFSA showed higher thermal stabilities than the conventional organic electrolyte, when the molar ratio of G4 was more than 40mol%. The increase in the G4 amount improved the rate capabilities of Li/LiCoO2 cells in the range where the molar ratio of G4 was between 40mol% and 60mol%. The stable Li ion intercalation–deintercalation was not observed in the Li/graphite cell of [Li(G4)][TFSA] (G4: 50mol%) without additives. However, the additives for forming solid electrolyte interface (SEI) film, such as vinylene carbonate, vinylethylene carbonate, and 1,3-propane sultone, led to the charge–discharge performance comparable to that of the conventional organic electrolyte. The adoption of Li4Ti5O12 and LiFePO4 led to excellent reversibilities of the Li half cells using [Li(G4)][TFSA], probably because of the favorable operation voltage. In the case of the LiFePO4/Li4Ti5O12 cell, the cell with [Li(G4)][TFSA] showed the better rate capability than that with the conventional organic electrolyte, when the rate was less than 1 CmA, and it is concluded that [Li(G4)][TFSA] can be the candidate as the alternative of organic electrolytes when the most appropriate electrode-active materials are used.
Keywords: Ionic liquid; Lithium batteries; Glyme; Ether; Electrolyte
Overcharge protection effect and reaction mechanism of cyclohexylbenzene for lithium ion batteries
by Norio Iwayasu; Hidetoshi Honbou; Tatsuo Horiba (pp. 3881-3886).
▶ Three aromatic compounds were used as overcharge protection agents. ▶ Cyclohexylbenzene proved to be the most effective overcharge protection agent. ▶ The overcharge protection effect is enhanced by high concentration and temperatures.We studied the relationship between the structure of aromatic compounds and the overcharge protection effect, using cyclohexylbenzene, isopropylbenzene, and toluene as the overcharge protection agents. Cyclohexylbenzene proved to be the most effective overcharge protection agent among these aromatic compounds. The effect is enhanced using a higher concentration of cyclohexylbenzene and elevated temperatures. The reaction product of cyclohexylbenzene was analyzed using field desorption mass spectrometry to elucidate its reaction mechanism. The results suggested that some of the overcharge reaction products of CHB were more reactive than that of IPB, which is consistent with the better suppressing effect on overcharging of the active material in the positive electrode.
Keywords: Lithium ion batteries; Aromatic compounds; Cyclohexylbenzene; Overcharge protection agent; Field desorption mass spectrometry
Facile synthesis of hierarchically structured Fe3O4/carbon micro-flowers and their application to lithium-ion battery anodes
by Shuangling Jin; Honggui Deng; Donghui Long; Xiaojun Liu; Liang Zhan; Xiaoyi Liang; Wenming Qiao; Licheng Ling (pp. 3887-3893).
▶ Fe3O4/carbon micro-flowers are prepared from the iron alkoxide precursor. ▶ Carbon is in situ generated from the organic components of alkoxide precursor. ▶ The composite combines the advantages of hierarchical structure and carbon coating. ▶ Anode material for lithium-ion battery with excellent electrochemical performance.A flower-like Fe3O4/carbon nanocomposite with nano/micro hierarchical structure is prepared by controlled thermal decomposition of the iron alkoxide precursor, which is obtained via an ethylene glycol-mediated solvothermal reaction of FeCl3 and hexamethylenetetramine (HMT) in the absence of any surfactant. The nanocomposite is characterized by the assembly of porous nanoflakes consisting of Fe3O4 nanoparticles and amorphous carbon that is in situ generated from the organic components of alkoxide precursor. When used as the anode materials for the lithium-ion batteries, the resultant nanocomposite shows high capacity and good cycle stability (1030mAhg−1 at a current density of 0.2C up to 150 cycles), as well as enhanced rate capability. The excellent electrochemical performance can be attributed to the high structural stability and high rate of ionic/electronic conduction arising from the synergetic effect of the unique nano/micro hierarchical structure and conductive carbon coating.
Keywords: Lithium-ion battery; Anode; Nanocomposite; Magnetite; Carbon
Investigation on the charging process of Li2O2-based air electrodes in Li–O2 batteries with organic carbonate electrolytes
by Wu Xu; Vilayanur V. Viswanathan; Deyu Wang; Silas A. Towne; Jie Xiao; Zimin Nie; Dehong Hu; Ji-Guang Zhang (pp. 3894-3899).
▶ Use in situ GC/MS to investigate gas evolution during charging process. ▶ Li2O2 is chargeable to release O2 in high conversion. ▶ Li2O2 reacts with NMP and PVDF, but seems not to react with carbonate solvents. ▶ Carbonate species are formed during discharge in carbonate electrolytes. ▶ Nearly no Li2O2 is formed during discharge in carbonate electrolytes.The charging process of Li2O2-based air electrodes in Li–O2 batteries with organic carbonate electrolytes was investigated using in situ gas chromatography/mass spectroscopy (GC/MS) to analyze gas evolution. A mixture of Li2O2/Fe3O4/Super P carbon/polyvinylidene fluoride (PVDF) was used as the starting air electrode material, and 1-M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in carbonate-based solvents was used as the electrolyte. We found that Li2O2 was actively reactive to 1-methyl-2-pyrrolidinone and PVDF that were used to prepare the electrode. During the first charging (up to 4.6V), O2 was the main component in the gases released. The amount of O2 measured by GC/MS was consistent with the amount of Li2O2 that decomposed during the electrochemical process as measured by the charge capacity, which is indicative of the good chargeability of Li2O2. However, after the cell was discharged to 2.0V in an O2 atmosphere and then recharged to ∼4.6V, CO2 was dominant in the released gases. Further analysis of the discharged air electrodes by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy indicated that lithium-containing carbonate species (lithium alkyl carbonates and/or Li2CO3) were the main discharge products. Therefore, compatible electrolytes and electrodes, as well as the electrode-preparation procedures, need to be developed for rechargeable Li-air batteries for long term operation.
Keywords: Li–O; 2; battery; Li; 2; O; 2; electrode; Gas chromatography/mass spectroscopy technique; Charging process; Gas evolution; Carbonate electrolyte
Influence of the binder types on the electrochemical characteristics of natural graphite electrode in room-temperature ionic liquid
by Koichi Ui; Jun Towada; Sho Agatsuma; Naoaki Kumagai; Keigo Yamamoto; Hiroshi Haruyama; Ken Takeuchi; Nobuyuki Koura (pp. 3900-3905).
Display Omitted▶ The cycling curves of the NG-3 electrode using the PVdF binder are shown in Fig. (a). ▶ The cycling curves of the NG-3 electrode using the PAA binder are shown in Fig. (b). ▶ The use of the PAA binder improved the initial cycling efficiency of it. ▶ The use of the PAA binder repressed the reduction reaction of SOCl2.To improve the electrochemical characteristics of the natural graphite (NG-3) negative electrode in the LiCl saturated AlCl3-1-ethyl-3-methylimizadolium chloride+thionyl chloride (SOCl2) melt as the electrolyte for non-flammable lithium-ion batteries, we examined the influence of the binder types on its electrochemical characteristics. The cyclic voltammograms showed that the reduction current at 1.2–3.2V vs. Li/Li(I) was repressed using polyacrylic acid (PAA) as the binder. The charge–discharge tests showed that the discharge capacity and the charge–discharge efficiency of the NG-3 electrode coated with the PAA binder at the 1st cycle were 322.8mAhg−1 and 65.6%, respectively. Compared with the NG-3 electrode using the conventional poly(vinylidene fluoride) binder, it showed considerably a better cyclability with the discharge capacity of 302.1mAhg−1 at the 50th cycle. Li(I) ion intercalation into the graphite layers could be improved because the NG-3 electrode coated with the PAA binder changed to a golden-yellow color after the 1st charging, and the formation of first stage LiC6 was demonstrated by X-ray diffraction (XRD) measurement. In addition, the XRD and X-ray photoelectron spectroscopy indicated that one of the side reactions during charging was the formation of LiCl on the graphite surface regardless of the binder types.
Keywords: Graphite; Negative electrode; Lithium-ion battery; Ionic liquid; Polyacrylic acid; Binder
A non-aqueous electrolyte for the operation of Li/air battery in ambient environment
by Sheng S. Zhang; Kang Xu; Jeffrey Read (pp. 3906-3910).
▶ Partially fluorinated solvents increase dissolution kinetics and solubility of oxygen in non-aqueous electrolytes. ▶ Use of fluorinated solvent increases specific capacity and power capability of Li/air battery. ▶ Tris(2,2,2-trifluoroethyl) phosphate (TFP) significantly outperforms other partially fluorinated solvents. ▶ Dissolution kinetics and solubility of oxygen play more important role than the ionic conductivity and viscosity of electrolyte in determining discharge performance of Li/air battery. ▶ The TFP-based electrolytes with low volatility can support long-term operation of Li/air cells in dry ambient environments, and be suitable for rechargeable Li/air battery.In this work we report a non-aqueous electrolyte that supports long-term operation of the Li/air battery in dry ambient environments based on a non-hydrolytic LiSO3CF3 salt and a low volatility propylene carbonate (PC)/tris(2,2,2-trifluoroethyl) phosphate (TFP) solvent blend. By measuring and analyzing the viscosity of PC/TFP solvent blends, the ionic conductivity of electrolytes, and the discharge performance of Li/air cells as a function of the PC/TFP weight ratio, we determined the best composition of the electrolyte is 0.2m (molality) LiSO3CF3 7:3wt. PC/TFP for Li/O2 cells and 0.2m LiSO3CF3 3:2wt. PC/TFP for Li/air cells. Discharge results indicate that Li/air cells with the optimized electrolyte are significantly superior in specific capacity and rate capability to those with baseline electrolytes. More interestingly, the improvement in discharge performance becomes more significant as the discharge current increases or the oxygen partial pressure decreases. These results agree neither with the viscosity of the solvent blends nor the ionic conductivity of the electrolytes. We consider that the most likely reason for the performance improvement is due to the increased dissolution kinetics and solubility of oxygen in TFP-containing electrolytes. In addition, the electrolyte has a 5.15V electrochemical window, which is suitable for use in rechargeable Li/air batteries.
Keywords: Tris(2,2,2-trifluoroethyl) phosphite; Tris(2,2,2-trifluoroethyl) phosphate; Non-aqueous electrolyte; Ionic conductivity; Viscosity; Li/air battery
Application of electrolyte using novel ionic liquid to Si thick film anode of Li-ion battery
by Hiroyuki Usui; Yoshihisa Yamamoto; Kazuhide Yoshiyama; Toshiyuki Itoh; Hiroki Sakaguchi (pp. 3911-3915).
▶ An applicability of a novel ionic liquid was investigated as an electrolyte of Li-ion battery. ▶ We studied anode property of Si thick-film electrodes prepared by a gas-deposition method. ▶ The novel ionic liquid achieved large initial capacity and excellent cycling performance. ▶ Influence of cation structure on charge-transfer in electrode reaction was discussed.An applicability of a novel ionic liquid, consisting of 1-methoxyethoxymethyl(tri- n-butyl)phosphonium cation and bis(trifluoromethanesulfonyl)amide anion, was investigated as an electrolyte of Li-ion battery using a thick film electrode of Si prepared by a gas-deposition method. The electrochemical properties in the novel ionic liquid were compared to those in a commercial ionic liquid and a typical organic solvent of propylene carbonate. The initial discharge capacity of 3450mAhg−1 and excellent cycling performance were achieved in the novel ionic liquid. The novel ionic liquid was confirmed to effectively suppress a collapse and an electrical isolation of the Si thick film induced by pulverization during charge–discharge cycling. The excellent performance is possibly attributed to more effective desolvation of Li ions from the anions due to its lower dielectric constant compared with the propylene carbonate solvent.
Keywords: Gas deposition; Anode; Li-ion battery; Ionic liquid; Thick film; Si
Preparation of Co–Sn alloy film as negative electrode for lithium secondary batteries by pulse electrodeposition method
by Koichi Ui; Shinei Kikuchi; Yasuhiro Jimba; Naoaki Kumagai (pp. 3916-3920).
Display Omitted▶ The cycle performance of the Sn film electrode is shown Fig. (a). ▶ The cycle performance of the Co–Sn alloy film electrode is shown Fig. (b). ▶ The Sn film electrode showed a gradual capacity fade during 10–20 cyclings. ▶ The cyclability of the Co–Sn alloy film electrode is better than that of the Sn film electrode. ▶ Alloying Sn with Co dramatically improved the cyclabilty of the Sn based electrode.In order to easily and simply improve the cyclability of the Sn film negative electrode, we selected Co as a matrix metal and tried to prepare the Co–Sn alloy film negative electrode by a pulse electrodeposition method. The surface morphology of the deposit was almost the same as that of the Sn film, although aggregation partially occurred. The content rate of Co and Sn in the deposit was almost the same as the composition percentage in the electrodeposition bath. X-ray diffraction measurement showed that the deposited film could be assigned to a metastable Co–Sn alloy, while the co-deposition of crystalline Sn was not observed. The galvanostatic charge–discharge tests indicated that the discharge capacity and the charge–discharge efficiency of the Co30.5Sn69.5 alloy film electrode at the 1st cycle were 529.2mAhg−1 and 87.9%, respectively. Furthermore, the film electrode showed a good cyclability and discharge capacity of 470.5–617.5mAhg−1 during 50 cyclings. Alloying Sn with inactive Co could effectively improve the cyclability of the Sn film electrode prepared by the pulse electrodeposition method.
Keywords: Lithium secondary battery; Negative electrode; Tin–cobalt alloy; Pulse electrodeposition
Online estimation of internal resistance and open-circuit voltage of lithium-ion batteries in electric vehicles
by Yi-Hsien Chiang; Wu-Yang Sean; Jia-Cheng Ke (pp. 3921-3932).
▶ This study is motivated to develop a unified method for estimating open-circuit voltage (OCV) and internal resistance of a lithium-ion battery via online voltage and current measurements. These two parameters can be used to determine battery state-of-charge (SoC) as well as state-of-health (SoH) via the built-in lookup tables that define the relationships between SoC/SoH and OCV/internal resistance. However, the lookup tables that shall take into account the thermal effect are not defined in this study. ▶ An adaptive control approach is employed to develop an estimated algorithm such that the developed method with the following merits: (1) online estimation; (2) simple mathematical operation; (3) specific load pattern or system excitation input, typically for an estimation system, is unnecessary; (4) no need prior time-intensive training; (5) easy implementation in comparison with existing methods. ▶ The proposed method has been verified through simulations and experiments.State-of-charge (SoC) and state-of-health (SoH) define the amount of charge and rated capacity loss of a battery, respectively. In order to determine these two measures, open-circuit voltage (OCV) and internal resistance of the battery are indispensable parameters that are obtained with difficulty through direct measurement. The motivation of this study is to develop an online, simple, training-free, and easily implementable scheme that is capable of estimating such parameters, particularly for the lithium-ion battery in battery-powered vehicles. Based on an equivalent circuit model (ECM), the electrical performance of a battery can be formulated into state-space representation. Also, underdetermined model parameters can be arranged to appear linearly so that an adaptive control approach can be applied. An adaptation algorithm is developed by exploiting the Lyapunov-stability criteria. The OCV and internal resistance can be extracted exactly without limitations of a system input signal, such as persistent excitation (PE), enhancing the method applicability for vehicular power systems. In this study, both simulations and experiments are established to verify the capability and effectiveness of the proposed estimation scheme.
Keywords: Internal resistance; Open-circuit voltage; State-of-charge; State-of-health; Adaptive control; Equivalent circuit model
A nonlinear viscoelastic–viscoplastic constitutive model for ionomer membranes in polymer electrolyte membrane fuel cells
by Wonseok Yoon; Xinyu Huang (pp. 3933-3941).
▶ We have developed a nonlinear viscoelastic-viscoplasticconstitutive model for describing the finite deformation of the ionomer membrane for PEMFCs. ▶ The stress in the constitutive relationship is obtained from summation of two molecular networks acting in parallel; the model isstrain-rate, temperature, and hydration dependent. ▶ The model can accurately describe the stress-strain behavior of both vapor and liquid water equilibratedionomer membranes after choosing appropriate material parameters.This paper describes a phenomenological constitutive model for ionomer membranes in polymer electrolyte membrane fuel cells (PEMFCs). Unlike the existing approaches of elasto-plastic, viscoelastic, and viscoplastic model, the proposed model was inspired by micromechanisms of polymer deformation. The constitutive model is a combination of the nonlinear visco-elastic Bergström–Boyce model and hydration–temperature-dependent empirical equations for elastic modulus of ionomer membranes. Experiment results obtained from an uniaxial tension test for Nafion NR-111 membrane under well controlled environments were compared with simulated results by the finite element method (FEM) and the proposed model showed fairly good predictive capabilities for the large deformation behavior of the Nafion membrane subjected to the uniaxial loading condition in a wide range of relative humidity and temperature levels including liquid water.
Keywords: PEMFC; Nafion; Ionomer membrane; Viscoelastic; Viscoplastic; Constitutive model
Cycle-life model for graphite-LiFePO4 cells
by John Wang; Ping Liu; Jocelyn Hicks-Garner; Elena Sherman; Souren Soukiazian; Mark Verbrugge; Harshad Tataria; James Musser; Peter Finamore (pp. 3942-3948).
▶ Cycling induced capacity fade of a LiFePO4 battery was investigated and cycle-life models were established based on the cycling results from a large cycle-test matrix which included three important parameters, temperature (−30 to 60°C), depth of discharge, DOD (90–10%), and discharge rate (C-rate, ranging from C/2 to 10C). ▶ The effects of test parameters (time, temperature, DOD, rate) were investigated and discussed. The results show that the capacity loss is strongly affected by time and temperature, while the effect of DOD is less important at a slow discharge rate, e.g., C/2. ▶ We demonstrated that capacity fade followed a power law relationship with charge throughput between 15 and 60°C. We established a simple battery life model that accounts for Ah throughput (time), C-rates, and temperature and achieves qualitative agreement with experimental data. ▶ The model equations indicated that power law factors were valued very close to 0.5. This square-root of time dependence provides detailed insights of the capacity fading behaviors and further confirms the aging mechanisms that involve diffusion and parasitic reactions leading to loss of active lithium.In this report, cycling induced capacity fade of a LiFePO4 battery was studied and cycle-life models were established. Cell life data for establishing the model were collected using a large cycle-test matrix. The test matrix included three parameters, temperature (−30 to 60°C), depth of discharge (DOD) (90–10%), and discharge rate (C-rate, ranging from C/2 to 10C, with the 1C rate corresponding to 2A). At the low C-rates, experimental results indicated that the capacity loss was strongly affected by time and temperature, while the DOD effect was less important. At the high C-rates, the charge/discharge rate effects became significant. To establish a life model, we adopt a power law equation in which the capacity loss followed a power law relation with time or charge throughput while an Arrhenius correlation accounted for the temperature effect. This model, when parameters were allowed to change with C-rates, was found to represent a large array of life cycle data. Finally, we discuss our attempts in establishing a generalized battery life model that accounts for Ah throughput (time), C-rate, and temperature.
Keywords: LiFePO; 4; battery; Life model; Cell aging; Cycle life
Safe and fast-charging Li-ion battery with long shelf life for power applications
by K. Zaghib; M. Dontigny; A. Guerfi; P. Charest; I. Rodrigues; A. Mauger; C.M. Julien (pp. 3949-3954).
We report a Li-ion battery that can be charged within few minutes, passes the safety tests, and has a very long shelf life. The active materials are nanoparticles of LiFePO4 (LFP) and Li4Ti5O12 (LTO) for the positive and negative electrodes, respectively. The LiFePO4 particles are covered with 2wt.% carbon to optimize the electrical conductivity, but not the Li4Ti5O12 particles. The electrolyte is the usual carbonate solvent. The binder is a water-soluble elastomer. The “18650” battery prepared under such conditions delivers a capacity of 800mAh. It retains full capacity after 20,000 cycles performed at charge rate 10C (6min), discharge rate 5C (12min), and retains 95% capacity after 30,000 cycles at charge rate 15C (4mn) and discharge rate 5C both at 100% DOD and 100% SOC.
Keywords: Li-ion batteries; Olivines; Titanates
First-principles modelling of lithium iron oxides as battery cathode materials
by Michele Catti; Merced Montero-Campillo (pp. 3955-3961).
Display Omitted▶ Electrochemical reaction energies are computed quantum-mechanically. ▶ ‘Corrugated layer’ LiFeO2 cathode deintercalates Li to Li1− xFeO2 in the first charge. ▶ Li1− xFeO2 transforms to ferrimagnetic spinel-like LiFe5O8 in the first discharge. ▶ LiFe5O8↔rocksalt-type Li3Fe5O8 in subsequent discharge/charge cycles. ▶ Magnetic ordering stabilizes the compounds involved to different extent.Starting from published charge/discharge curves and X-ray data on Pmmn-LiFeO2 and LiFe5O8 as cathode materials vs. Li anode, a scheme of electrochemical reactions is proposed to explain the unclear electrode functionality of the ‘corrugated layer’ LiFeO2 phase. The scheme was validated by quantum-mechanical calculations (CRYSTAL09 code, hybrid B3LYP Hamiltonian) on a number of structural models for Li1− xFeO2, LiFe5O8, and Li3Fe5O8. Magnetic interactions were taken into account, finding antiferromagnetic (Li1− xFeO2) and ferrimagnetic (LiFe5O8 and Li3Fe5O8) orderings as stable states. At variance with spinel-like LiFe5O8, Li3Fe5O8 displays a rocksalt-type superstructure. The computed energies for reactions (I) 4LiFeO2→4Li0.75FeO2+Li, (II) 4Li0.75FeO2+Li→4/5LiFe5O8+8/5Li2O, and (III) 1/2LiFe5O8+Li↔1/2Li3Fe5O8 are 4.44, −3.62, and −2.10eV, respectively. Such values compare satisfactorily with the average charge/discharge voltages observed for positive electrodes made up of Pmmn-LiFeO2 and of LiFe5O8.
Keywords: First-principles calculations; Lithium iron oxides; Theoretical charge/discharge energy
Development and performance characterization of an electric ground vehicle with independently actuated in-wheel motors
by Rongrong Wang; Yan Chen; Daiwei Feng; Xiaoyu Huang; Junmin Wang (pp. 3962-3971).
This paper presents the development and experimental characterizations of a prototyping pure electric ground vehicle, which is equipped with four independently actuated in-wheel motors (FIAIWM) and is powered by a 72V 200Ah LiFeYPO4 battery pack. Such an electric ground vehicle (EGV) employs four in-wheel (or hub) motors to independently drive/brake the four wheels and is one of the promising vehicle architectures primarily due to its actuation flexibility, energy efficiency, and performance potentials. Experimental data obtained from the EGV chassis dynamometer tests were employed to generate the in-wheel motor torque response and power efficiency maps in both driving and regenerative braking modes. A torque distribution method is proposed to show the potentials of optimizing the FIAIWM EGV operational energy efficiency by utilizing the actuation flexibility and the characterized in-wheel motor efficiency and torque response.
Keywords: Electric vehicles; In-wheel motors; Four-wheel independently actuated; Efficiency
Using vehicle-to-grid technology for frequency regulation and peak-load reduction
by Corey D. White; K. Max Zhang (pp. 3972-3980).
This paper explores the potential financial return for using plug-in hybrid electric vehicles as a grid resource. While there is little financial incentive for individuals when the vehicle-to-grid (V2G) service is used exclusively for peak reduction, there is a significant potential for financial return when the V2G service is used for frequency regulation. We propose that these two uses for V2G technology are not mutually exclusive, and that there could exist a “dual-use” program that utilizes V2G for multiple uses simultaneously. In our proposition, V2G could be used for regulation on a daily basis to ensure profits, and be used for peak reduction on days with high electricity demand and poor ambient air quality in order to reap the greatest environmental benefits. The profits for the individual in this type of dual-use program are close to or even higher than the profits experienced in either of the single-use programs. More importantly, we argue that the external benefits of this type of program are much greater as well. At higher V2G participation rates, our analysis shows that the market for regulation capacity could become saturated by V2G-based regulation providers. At the same time, there is plenty of potential for widespread use of V2G technology, especially if the demand for regulation, reserves, and storage grows as more intermittent renewable resources are being incorporated into the power systems.
Keywords: Batteries; Electric transportation; Emissions; Air quality; Power systems
New accelerated charge methods using early destratification applied on flooded lead acid batteries
by K. Mamadou; T.M.P. Nguyen; E. Lemaire-Potteau; C. Glaize; J. Alzieu (pp. 3981-3987).
▶ A new charge method is proposed for fast charges and accelerated charges of flooded lead acid batteries using early destratification with charge acceptance measurements. The modification of a “12h” charger with an algorithm of the early destratification enables the battery to be available for a discharge in duration of the order of 4–6h. This division of the charge duration of a factor two is obtained without increasing the charger power.A traditional charge process for flooded lead acid batteries (FLABs) lasts generally from 8 to 14h. Nowadays, many applications of FLABs require reduction of the charge duration, for instance, a 4h-charge for FLABs in grid energy storage or 1h-charge for FLABs in electric buses. These are called accelerated charge and fast charge. Such reductions of charge time imply the use of a new charge process. One way to reduce the charge duration is to perform an early destratification step without waiting for the end of charge. The new charge method proposed in this paper (early destratification method – ED) focuses on the reduction of the charge time for FLABs using early destratification, which is performed and controlled using charge acceptance measurement during the charge. Laboratory experiments presented here aim first to develop charge acceptance measurements followed by an ED charge method compared to an IUi traditional charge process.
Keywords: Lead acid batteries; Charge acceptance; Stratification; Overcharge; Fast charge
Study of the influence of carbon on the negative lead-acid battery electrodes
by Petr Bača; Karel Micka; Petr Křivík; Karel Tonar; Pavel Tošer (pp. 3988-3992).
▶ Graphite concentrations ≥2% are detrimental for cycle life of lead electrodes. ▶ Mechanical pressure positively influences the cycle life. ▶ The rate of formation decreases with rising graphite concentration.Experiments were made with negative lead-acid battery electrodes doped with different concentrations of powdered carbon. It turned out that the rate of formation decreased with the rising concentration of carbon added into the active material. During accelerated cycling in the PSoC regime, the cycle life showed a maximum at a concentration of carbon near 1%, whereas at lower or higher concentrations the cycle life was profoundly lower. A marked increase of the active mass resistance with the cycle number was recorded at carbon concentrations above 2%. Orientation experiments showed that compression of the lead-acid laboratory cells caused an increase of the cycle life of the negative electrode in the studied regime.
Keywords: Lead battery electrodes; Doping with carbon; Accelerated testing
Lead-acid batteries in micro-hybrid vehicles
by Joern Albers; Eberhard Meissner; Sepehr Shirazi (pp. 3993-4002).
▶ Overview of functions of micro-hybrid vehicles and battery duty. ▶ Vehicle investigation of micro-hybrid vehicles available in Europe from 2006 to 2010: different functionality streams observed. ▶ Laboratory test “dynamic pulse cycling” (DPC) for simulation of micro-hybrid battery duty: test description and results. ▶ Influence of acid stratification on flooded batteries. ▶ Effects of rest phases on stratified flooded batteries: description of processes and results of laboratory and real-life tests.More and more vehicles hit the European automotive market, which comprise some type of micro-hybrid functionality to improve fuel efficiency and reduce emissions. Most carmakers already offer at least one of their vehicles with an optional engine start/stop system, while some other models are sold with micro-hybrid functions implemented by default.But these car concepts show a wide variety in detail—the term “micro-hybrid” may mean a completely different functionality in one vehicle model compared to another. Accordingly, also the battery technologies are not the same. There is a wide variety of batteries from standard flooded and enhanced flooded to AGM which all are claimed to be “best choice” for micro-hybrid applications.A technical comparison of micro-hybrid cars available on the European market has been performed. Different classes of cars with different characteristics have been identified. Depending on the scope and characteristics of micro-hybrid functions, as well as on operational strategies implemented by the vehicle makers, the battery operating duties differ significantly between these classes of vehicles.Additional laboratory investigations have been carried out to develop an understanding of effects observed in batteries operated in micro-hybrid vehicles pursuing different strategies, to identify limitations for applications of different battery technologies.
Keywords: Lead-acid battery; AGM; VRLA; Enhanced flooded battery; Micro-hybrid vehicles; Acid stratification
Vanadium solid-salt battery: Solid state with two redox couples
by Tomoo Yamamura; Xiongwei Wu; Suguru Ohta; Kenji Shirasaki; Hiroki Sakuraba; Isamu Satoh; Tatsuo Shikama (pp. 4003-4011).
Display Omitted▶ New vanadium solid salt battery for potential use in hybrid vehicles and Smart-Grids. ▶ Two kinds of vanadium solid salts are supported on carbon felts. ▶ A cell performance of 1.34V and 77Whkg−1 was achieved. ▶ The energy density was enhanced by 250–350% versus vanadium redox-flow batteries.We present the “vanadium solid-salt battery” (VSSB), which has high energy density, is low cost, is easily recycled, operates at ambient temperature, and has no requirement for special solvents. The VSSB contains two types of vanadium solid salts that are supported on carbon felts with a minimal amount of hydrosulfuric acid added to moisten the ion-exchange membrane. The optimized VSSB shows a cell potential of 1.34V, excellent reproducibility for charging and discharging for nearly 100cycles, a high energy efficiency (87%) and a high energy density (77Whkg−1 at 5mAcm−2 using the carbon felt XF208). The energy density is enhanced by 250–350% compared with conventional vanadium redox-flow batteries.
Keywords: Solid salt battery; High energy density; Hybrid vehicles; Smart grid; Vanadium
New molten salt systems for high temperature molten salt batteries: Ternary and quaternary molten salt systems based on LiF–LiCl, LiF–LiBr, and LiCl–LiBr
by Syozo Fujiwara; Minoru Inaba; Akimasa Tasaka (pp. 4012-4018).
Display Omitted▶ New ternary or quaternary molten salt electrolyte systems have been developed. ▶ These electrolyte systems have no instable anions nor expensive cations. ▶ Some of electrolyte systems have no environmentally unfavorable F- anion. ▶ LiCl-LiBr-NaCl-KCl system improves the high rate discharge capability more than 20%.Using a new simulative technique developed by us, we systematically investigated new ternary or quaternary molten salt systems, which are based on LiF–LiCl, LiF–LiBr, and LiCl–LiBr binary systems, for use as electrolytes in thermal batteries, and evaluated their ionic conductivities and melting points experimentally. It was confirmed experimentally that LiF–LiBr–KF (melting point: 425°C, ionic conductivity at 500°C: 2.52Scm−1), LiCl–LiBr–KF (405°C, 2.56Scm−1), LiCl–LiBr–NaF–KF (425°C, 3.11Scm−1), LiCl–LiBr–NaCl–KCl (420°C, 2.73Scm−1), and LiCl–LiBr–NaBr–KBr (420°C, 2.76Scm−1) meet our targets for both melting point (350–430°C) and ionic conductivity (2.0Scm−1 and higher at 500°C). A single cell using the newly developed LiCl–LiBr–NaCl–KCl molten salt as an electrolyte was prepared, and the DC-IR of the cell decreased by 20% than that of a single cell using the conventional LiCl–KCl molten salt. It was therefore concluded that the use of new quaternary molten salt systems can improve the discharge rate-capability in practical battery applications because of their high ionic conductivities.
Keywords: Molten salt; Thermal battery; Electrolyte; Simulation; Ionic conductivity; Melting point
Preparation of silver-modified La0.6Ca0.4CoO3 binary electrocatalyst for bi-functional air electrodes in alkaline medium
by Shuxin Zhuang; Kelong Huang; Chenghuan Huang; Hongxia Huang; Suqin Liu; Min Fan (pp. 4019-4025).
▶ Silver-modified La0.6Ca0.4CoO3 binary catalysts were prepared by the chemical reduction method using N2H2 as the reducing agent, which were used as catalysts for bi-functional air electrodes in alkaline medium. ▶ Based on EIS analysis, the introduction of silver on the LCCO surface decreases intrinsic and kinetic impedance for the oxygen reduction reaction. ▶ Results from cycles test indicated silver-modified La0.6Ca0.4CoO3 binary catalysts were stable and sustainable.Silver-modified La0.6Ca0.4CoO3 composites for molecular oxygen reduction and evolution reaction are prepared by a chemical reduction process using N2H4 as the reducing agent at room temperature. The La0.6Ca0.4CoO3 catalysts are modified with silver content that vary from 0.3 to 30wt.% without damaging their microstructure. The electrochemical behavior of La0.6Ca0.4CoO3 catalysts with different silver loadings is studied on classical bilayer gas diffusion electrodes. The electrocatalytic properties of these composites are evaluated by polarization curves and electrochemical impedance spectroscopy in alkaline electrolyte. The silver loading is found to have a significant impact on the electrode performances, which facilitate or block the electrochemical processes of the gas diffusion electrodes. The binary catalyst electrodes exhibit higher electrocatalytic activities than that of the electrodes with only La0.6Ca0.4CoO3 as the catalyst. In this paper, the best performance was achieved when the silver loading was 3.0wt.%.
Keywords: Perovskite; Oxygen reduction; Oxygen evolution; Bi-functional electrode
Numerical study of thermoelectric power generation for an helicopter conical nozzle
by Tarik Kousksou; Jean-Pierre Bédécarrats; Daniel Champier; Pascal Pignolet; Christophe Brillet (pp. 4026-4032).
This paper investigates the electric power extractable from an helicopter conical nozzle equipped with thermoelectrical modules. The thermoelectric nozzle is heated by the final exhaust gas from helicopter turbine and cooled by oil. A computer model has been developed to simulate the performance of the thermoelectric system. Results were obtained for various operating conditions showing that the electrical power produced in real operating conditions is significant but currently insufficient if we consider the weight-to-power ratio. The numerical model is also used to optimize the electric power showing a good potential for the future.
Keywords: Thermoelectric generator; Power generation; Numerical simulation; Low Mach number; Helipcopter conical nozzle; Waste heat recovery
A new method for dynamic performance improvement of a hybrid power system by coordination of converter's controller
by Majid Nayeripour; Mohammad Hoseintabar; Taher Niknam (pp. 4033-4043).
In this paper, a new strategy for modeling and controlling a hybrid power generation system that contains a fuel cell (FC) and super capacitor (SC) system is proposed. The main drawback of FC systems is its slow dynamic because the FC current slope must be limited in order to prevent fuel starvation problems and to improve its efficiency and lifetime. To overcome this slow dynamic and to improve dynamic performance, a new control strategy is proposed to combine FC system with SC system. The proposed control strategy can be also used for cold starting and different types of FC systems with different dynamics. The control strategy is capable of determining the desired FC power to prolong FC system lifetime and keeps the AC and DC voltages around its nominal value in transient event by supplying propulsion power and recuperating FC energy. The minimum SC system is computed in new method and used to meet the load demand to constraint the DC bus voltage and enhances power regulation under various active and reactive load conditions. Two different case studies are used to obtain the simulation results using MATLAB/SIMULINK to verify the validity of the proposed control strategy.
Keywords: Solid oxide fuel cell; Cold start; Dynamic model; Bi-directional converter; Unidirectional converter
Tailoring of RuO2 nanoparticles by microwave assisted “Instant method” for energy storage applications
by Abirami Devadas; Stève Baranton; Teko W. Napporn; Christophe Coutanceau (pp. 4044-4053).
▶ RuO2 synthesized via microwave assisted instant method structural and morphological characterisation. ▶ RuO2 as an electrocatalyst for oxygen evolution reaction. ▶ RuO2 as a supercapacitor electrode material.RuO2 nanoparticles are synthesized by Instant method using Li2CO3 as stabilizing agent, under microwave irradiation at 60°C and investigated for the anodic oxygen evolution reaction (OER) and for their supercapacitance properties in 0.5M H2SO4 medium. Structural and morphological characterizations of RuO2 are investigated by in situ X-ray diffraction (XRD), thermogravimetric analysis (TG-DTA), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDS) and Raman spectroscopy. The TEM images of as prepared material show the uniform distribution of RuO2 nanoparticles with mean diameter of ca. 1.5nm. Analysis on as prepared material indicates the structural formula as [RuO2·2.6H2O] 0.7H2O with low crystallinity. The influence of annealing temperature on RuO2 is studied in light of electrocatalytic activity for oxygen evolution reaction (OER) and capacitance. Electrochemical performances of RuO2 electrodes are followed by current–potential curves, galvanostatic charge–discharge cycles and evolved oxygen measurements. The amount of oxygen gas evolved during the OER by the crystalline RuO2 is found to be consistent with the electrical energy supplied to the catalyst. The cyclic voltammogram of RuO2 exhibits the typical capacitance behavior with highly reversible nature. The specific capacitance of hydrous RuO2 is found to be 737Fg−1 at the scan rate of 2mVs−1, by the balanced transport of proton through the structural water and electron transport along dioxo bridges, which makes a suitable material for energy storage. The specific capacitance decreases with increase in the crystallinity of RuO2. The present study shows the potential method to synthesize rapid and uniform nano particles of RuO2 for water electrolysis and supercapacitors.
Keywords: RuO; 2; Instant method; Microwave; In situ; XRD; OER; Supercapacitor
Seasonal energy storage system based on hydrogen for self sufficient living
by M. Bielmann; U.F.Vogt; M. Zimmermann; A. Züttel (pp. 4054-4060).
.Display Omitted▶ Comparison of battery only off-grid energy system to H2 hybrid system. ▶ Onsite generated H2 is used as a fuel for cooking and fuel cell for electricity. ▶ Battery provides short term storage, hydrogen provides seasonal storage. ▶ H2 hybrid system requires 25% battery capacity of battery only system. ▶ H2 hybrid system is 40% smaller and lighter with same usability.SELF is a resource independent living and working environment. By on-board renewable electricity generation and storage, it accounts for all aspects of living, such as space heating and cooking as well as providing a purified rainwater supply and wastewater treatment, excluding food supply. Uninterrupted, on-demand energy and water supply are the key challenges. Off-grid renewable power supply fluctuations on daily and seasonal time scales impose production gaps that have to be served by local storage, a function normally fulfilled by the grid. While daily variations only obligate a small storage capacity, requirements for seasonal storage are substantial.The energy supply for SELF is reviewed based on real meteorological data and demand patterns for Zurich, Switzerland. A battery system with propane for cooking serves as a reference for battery-only and hybrid battery/hydrogen systems. In the latter, hydrogen is used for cooking and electricity generation. The analysis shows that hydrogen is ideal for long term bulk energy storage on a seasonal timescale, while batteries are best suited for short term energy storage. Although the efficiency penalty from hydrogen generation is substantial, in off-grid systems, this parameter is tolerable since the harvesting ratio of photovoltaic energy is limited by storage capacity.
Keywords: Off-grid; Photovoltaic; Lithium battery; Electrolysis; Metal hydride; Fuel cell
State-of-charge prediction of batteries and battery–supercapacitor hybrids using artificial neural networks
by T. Weigert; Q. Tian; K. Lian (pp. 4061-4066).
▶ State-of-charge of batteries and battery–supercapacitor hybrids is predicted. ▶ Good correspondence between prediction and observed results was demonstrated. ▶ Prediction is performed by ANN based on short initial segment of discharge curve. ▶ Prediction is resilient to changes in operating conditions and physical structure.The state-of-charge (SOC) of batteries and battery–supercapacitor hybrid systems is predicted using artificial neural networks (ANNs). Our technique is able to predict the SOC of energy storage devices based on a short initial segment (less than 4% of the average lifetime) of the discharge curve. The prediction shows good performance with a correlation coefficient above 0.95. We are able to improve the prediction further by considering readily available measurements of the device and usage. The prediction is further shown to be resilient to changes in operating conditions or physical structure of the devices.
Keywords: State-of-charge prediction; Battery lifetime prediction; Battery–supercapacitor hybrid; Pulse discharge; Artificial neural networks
Inner pressure characterization of a sealed nickel-metal hydride cell
by D.J. Cuscueta; H.R. Salva; A.A. Ghilarducci (pp. 4067-4071).
▶ We study the inner pressure of gases inside a sealed Ni-MH cell. ▶ The inner cell at continuous use does not increase for Ic up to 0.5C. ▶ Overcharges at high rates significantly increase the inner cell pressure. ▶ Efficient fast charge by charging the cell up to 90% of nominal capacity. ▶ The cut-off discharge criterion at high rates for the complete discharge of battery.This paper studies the electrochemical behaviour of the pressure inside a sealed Ni-MH cell due to gases evolved under different charge/discharge currents and states of charge (SOC). The work is focused to determine the best procedure to get fast charge and long cycle life without detrimental effects on the battery and possible hazards affecting the safety of the user. The device was studied under a wide range of charge current (0.1–5C), establishing that optimum conditions to minimize the inner pressure during uninterrupted use are obtained if either charge rates up to 0.5C or higher rates not surpassing 90% of the nominal capacity are employed. Charge times corresponding to the range between 80% and 130% of the nominal capacity were also tested, analyzing the effect of overcharges on inner pressure, discharge capacity, efficiency and integrity of the cell. It was verified that charging the cell up to 130% at 2C rate reaches an inner pressure 5 times higher than that obtained at 0.5C. High rate discharge was also characterized at uninterrupted use of the cell, demonstrating the importance of the cut-off discharge criterion at high rates, to avoid the inner gases accumulation due to incomplete discharge of electrodes and overcharge in a following electrochemical cycle.
Keywords: Ni-MH battery; Inner pressure; Electrochemical characterization; Fast charge
Electrical double layer capacitors with sucrose derived carbon electrodes in ionic liquid electrolytes
by Lu Wei; G. Yushin (pp. 4072-4079).
▶ A low-cost renewable carbon material with uniform pore size and high surface area was prepared using sucrose as precursor. ▶ A systematic study on processing-structure–property relationships has been performed. ▶ Sucrose-derived carbon demonstrated excellent electrochemical performance in supercapacitors based on ionic liquids. ▶ The proposed technology suggests a great promise for the new generation of high-energy non-flammable supercapacitors.Activated carbons were prepared via a pyrolysis of sucrose followed by activation in the stream of CO2 gas for 2–6h at 900°C to tune the pore size distribution (PSD) and increase the specific surface area (SSA). The porosity of the activated sucrose derived carbons (ASCs) has been characterized using N2 sorption measurements. Increasing activation time led to the significant increase in SSA and pore volume of ASCs, among which sucrose derived carbon with 6h activation time (ASC-6h) exhibited the highest SSA of 1941m2g−1 and the highest micropore volume of 0.87cm3g−1. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge cycle tests have been applied to investigate the capacitive performance of the ASC electrodes in ionic liquids (ILs) at room and elevated temperatures. The ASC-6h electrodes in ethyl-dimethyl-propyl-ammonium bis (trifluoromethylsulfonyl) imide (EdMPNTf2N) showed specific capacitance in excess of 170Fg−1 at 60°C, whereas the same electrodes in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) showed slightly lower capacitance but significantly better rate performance.
Keywords: Electrochemical double layer capacitor; Activated carbon; Sucrose; Ionic liquid
Concentrated NaClO4 aqueous solutions as promising electrolytes for electric double-layer capacitors
by Jiao Yin; Cheng Zheng; Li Qi; Hongyu Wang (pp. 4080-4087).
▪.▶ Concentrated NaClO4 aqueous solutions as electrolytes for electric double-layer capacitors (EDLCs). ▶ High ionic conductivity leads to the elevation of rate capability. ▶ Low hydration numbers cause the increase in specific capacitance. ▶ Low freezing points guarantee EDLCs work well in cold environments.Concentrated NaClO4 aqueous solutions have been proposed as the electrolytes in electric double-layer capacitors. The advantages of this kind of electrolytes have been addressed in the terms of enlarged specific capacitance, enhanced rate capability and elevated low-temperature performance of porous carbon electrodes. Thermal analysis, ionic conductivity measurement and Raman spectroscopic investigations have been performed on the NaClO4 aqueous solutions in conjunction with the electrochemical study of porous carbon electrodes in this kind of electrolytes. The correlation between the hydration number of ions in the solutions and capacitive behavior of porous carbon has been clarified. The rate performance improvement in porous carbon electrode has also been connected to the increase in ionic conductivity of the electrolytes. The enhanced capacitance retention of porous carbon electrode at low temperatures in concentrated solutions has been ascribed to a fall of freezing point.
Keywords: Porous carbon electrodes; Electric double-layer capacitors; NaClO; 4; aqueous solutions; Electrolytes; Raman spectra
Synthesis of mesoporous polythiophene/MnO2 nanocomposite and its enhanced pseudocapacitive properties
by Qing Lu; Yikai Zhou (pp. 4088-4094).
Mesoporous nanocomposite of polythiophene and MnO2 has been synthesized by a modified interfacial method, aiming to develop electrode materials for supercapactitors with an enhanced cycle performance and high-rate capability. The N2 adsorption/desorption isotherm test of the prepared hybrid indicates a high surface area and a typical mesoporous feature. A uniform hierarchical microstructure with submicron-spheres assembled from ultrathin nanosheet with diameters less than 10nm has been confirmed by field-emission scanning electron microscopy and transmission electron microscopy. The employed interfacial synthesis is found to be advantageous to retard the overgrowth of nuclei. The retention of 97.3% of its initial capacitance after 1000 cycles at a charge/discharge rate of 2Ag−1 indicates excellent cycle performance of the nanocomposite electrode. At a high-rate charge/discharge process of 10Ag−1, the nanocomposite electrode retained 76.6% of its capacitance at 1Ag−1, suggesting good high-power capability. The important roles of polythiophene in the as-prepared nanocomposite are highlighted in terms of their functions on enhancing the electrical conductivity and constraining the dissolution of manganese oxides during charge–discharge cycles.
Keywords: Manganese oxide; Polythiophene; Mesoporous nanocomposite; Supercapacitor
Dual functions of activated carbon in a positive electrode for MnO2-based hybrid supercapacitor
by Peng-Cheng Gao; An-Hui Lu; Wen-Cui Li (pp. 4095-4101).
▶ In this study we model a hybrid supercapacitor with a MnO2&Carbon composite-based positive electrode. ▶ The supercapacitor integrated approximate symmetric and asymmetric behaviors in the range of 0–1.1V and 1.1–2.0V. ▶ The AC introduced in positive electrode increases capacitance and decreases internal resistance. ▶ The dual functions of AC as the conductive and capacitive substance of positive electrode were indicated. ▶ The maximum capacitance was calculated, and thus an optimal mass proportion can be achieved through a mathematic process.Utilizing the dual functions of activated carbon (AC) both as a conductive agent and an active substance of a positive electrode, a hybrid supercapacitor (AC-MnO2&AC) with a composite of manganese dioxide (MnO2) and activated carbon as the positive electrode (MnO2&AC) and AC as the negative electrode is fabricated, which integrates approximate symmetric and asymmetric behaviors in the distinct parts of 2V operating windows. MnO2 in the positive electrode and AC in the negative electrode together form a pure asymmetric structure, which extends the operating voltage to 2V due to the compensatory effect of opposite over-potentials. In the range of 0–1.1V, both AC in the positive and negative electrode assemble as a symmetric structure via a parallel connection which offers more capacitance and less internal resistance. The optimal mass proportions of electrodes are calculated though a mathematical process. In a stable operating window of 2V, the capacitance of AC-MnO2&AC can reach 33.2Fg−1. After 2500 cycles, maximum energy density is 18.2Whkg−1 with a 4% loss compared to the initial cycle. The power density is 10.1kWkg−1 with an 8% loss.
Keywords: Hybrid supercapacitor; Aqueous electrolyte; Positive electrode; Activated carbon; Manganese dioxide
Graphene-conducting polymer nanocomposite as novel electrode for supercapacitors
by Humberto Gómez; Manoj K. Ram; Farah. Alvi; P. Villalba; Elias (Lee) Stefanakos; Ashok Kumar (pp. 4102-4108).
▶ The novel graphene (G)–polyaniline (PANI) composite material have been synthesized using oxidative polymerization technique and a specific capacitance of 300–500Fg−1 at a current density of 0.1Ag−1 was observed. ▶ G–PANI nanocomposite material displays an interesting structure where graphene flakes could be seen embedded in the polyaniline suggesting a graphene interconnection with the polymer network. ▶ The cyclic voltammetry (CV) behavior of G–PANI film obtained on graphite substrate at different binders (N-methyl-2-pyrrolidone (NMP) and nafion) differ in 2M H2SO4 and 2M HCl electrolytic systems. It is also remarkable to note that the G–PANI composite retains the characteristic features of CV for around 100 cycles.A novel graphene–polyaniline nanocomposite material synthesized using chemical precipitation technique is reported as an electrode for supercapacitors. The graphene (G)–polyaniline (PANI) nanocomposite film was dissolved in N-Methyl-2-pyrrolidone (NMP) and characterized using Raman, FTIR, Scanning Electron Microscopy, Transmission Electron Microscopy, and cyclic voltammetry (CV) techniques. The interesting composite structure could be observed using different ratios of graphene and aniline monomer. The supercapacitor is fabricated using G–PANI in N-Methyl-2-pyrrolidone (NMP) and G–PANI-Nafion films on graphite electrodes. A specific capacitance of 300–500Fg−1 at a current density of 0.1Ag−1 is observed over graphene–PANI nanocomposite materials. The aim of this study is to tailor the properties of the capacitors through the optimization of their components, and packaging towards a qualification for portable systems applications. Based on experimental data shown in this work, conducting polymer nanocomposite capacitor technology could be viable, and could also surpass existing technologies when such a novel approach is used.
Keywords: Conducting polymers; Batteries; Polyaniline; Graphene; Supercapacitors
Physical and electrochemical characteristics of supercapacitors based on carbide derived carbon electrodes in aqueous electrolytes
by Jaanus Eskusson; Alar Jänes; Arvo Kikas; Leonard Matisen; Enn Lust (pp. 4109-4116).
FIB-SEM, XPS and gas adsorption methods have been used for the characterisation of physical properties of microporous carbide derived carbon electrodes prepared from Mo2C at 600°C (noted as CDC-Mo2C). Cyclic voltammetry, constant current charge/discharge, and electrochemical impedance spectroscopy have been applied to establish the electrochemical characteristics for supercapacitors consisting of the 1M Na2SO4, KOH, tetraethyl ammonium iodide or 6M KOH aqueous electrolyte and CDC-Mo2C electrodes. The N2 sorption values obtained have been correlated with electrochemical characteristics for supercapacitors in various aqueous electrolytes. The maximum gravimetric energy, Emax, and gravimetric power, Pmax, for supercapacitors (taking into consideration the active material weight) have been obtained at cell voltage 0.9V for 6M KOH aqueous supercapacitor ( Emax=5.7Whkg−1 and Pmax=43kWkg−1). For 1M TEAI based SC somewhat higher Emax (6.2Whkg−1) and comparatively low Pmax (7.0kWkg−1) have been calculated.
Keywords: Carbide derived carbon; Aqueous electrolyte; Molybdenum carbide; Supercapacitor; Tetraethyl ammonium iodide; Energy and power performance
Performance and stability of electrochemical capacitor based on anthraquinone modified activated carbon
by Grégory Pognon; Thierry Brousse; Laurent Demarconnay; Daniel Bélanger (pp. 4117-4122).
A series of high surface area activated carbon powders modified with various loadings of electroactive anthraquinone groups was obtained by the spontaneous reduction of the corresponding in situ generated diazonium derivative on activated carbon. The diazotation and grafting reactions are fast and efficient and by varying the stoichiometry of these reactions the grafting amount can be controlled. With appropriate reaction conditions, the attachment of anthraquinone groups allows to double the capacitance of the modified carbonaceous material (195Fg−1) compared to the unmodified carbon (100Fg−1) due to the contribution of the redox reaction of grafted anthraquinone molecules. Long time galvanostatic charge–discharge cycling experiments were performed for composite electrodes prepared using modified carbons having two different AQ loadings (e.g. 6.7 and 11.1wt.%). Following 10000 charge/discharge cycles, only a 17% loss of the faradaic capacitance was observed for these two carbons. Thus, this hybrid bifunctional material appears to be an excellent candidate for application as active electrode in electrochemical capacitors.
Keywords: Hybrid multifunctional material; Electrochemical capacitor; Carbon; Organic derivatization; Anthraquinone; Diazonium
Exaggerated capacitance using electrochemically active nickel foam as current collector in electrochemical measurement
by Wei Xing; Shizhang Qiao; Xiaozhong Wu; Xiuli Gao; Jin Zhou; Shuping Zhuo; Sandy Budi Hartono; Denisa Hulicova-Jurcakova (pp. 4123-4127).
▶ Most works reporting high capacitance applied nickel foam as current collector. ▶ Surface chemistry and electrochemical properties of nickel foam are investigated. ▶ Nickel foam can bring about substantial errors to the capacitance value. ▶ An electrochemically inert current collector should be used for capacitive testing.In the past decades, nickel and cobalt oxide/hydroxide materials have been investigated intensively for supercapacitor applications. Some works report very high specific capacitance values, up to 3152Fg−1, for these materials. By contrast, some other works report quite modest capacitance values, up to 380Fg−1 for the same materials prepared using same strategy. It is found that most works reporting very high capacitance value applied nickel foam as current collector. In this paper, surface chemistry and electrochemical properties of nickel foam are investigated by XPS analysis, cyclic voltammetry and galvanostatic charge–discharge measurement. The results show that using nickel foam as current collector can bring about substantial errors to the specific capacitance values of electrode materials, especially when small amount of electrode active material is used in the measurement. It is suggested that an electrochemically inert current collector such as Ti or Pt film should be used for testing electrochemical properties of nickel and cobalt oxide/hydroxide positive electrode materials.
Keywords: Supercapacitor; Pseudocapacitance; Nickel foam; Redox reaction; Cyclic voltammetry
Modeling and characterization of supercapacitors for wireless sensor network applications
by Ying Zhang; Hengzhao Yang (pp. 4128-4135).
▶ An equivalent circuit is developed to model supercapacitors. ▶ The charging, redistribution and self-discharge are characterized. ▶ The model predicts self-discharge better than two- and three-branch models. ▶ The model provides a better tool for supporting self-powered WSN research.A simple circuit model is developed to describe supercapacitor behavior, which uses two resistor–capacitor branches with different time constants to characterize the charging and redistribution processes, and a variable leakage resistance to characterize the self-discharge process. The parameter values of a supercapacitor can be determined by a charging-redistribution experiment and a self-discharge experiment. The modeling and characterization procedures are illustrated using a 22F supercapacitor. The accuracy of the model is compared with that of other models often used in power electronics applications. The results show that the proposed model has better accuracy in characterizing the self-discharge process while maintaining similar performance as other models during charging and redistribution processes. Additionally, the proposed model is evaluated in a simplified energy storage system for self-powered wireless sensors. The model performance is compared with that of a commonly used energy recursive equation (ERE) model. The results demonstrate that the proposed model can predict the evolution profile of voltage across the supercapacitor more accurately than the ERE model, and therefore provides a better alternative for supporting research on storage system design and power management for wireless sensor networks.
Keywords: Supercapacitor modeling; Charging; Redistribution; Self-discharge; Wireless sensor networks
Composite LiFePO4/AC high rate performance electrodes for Li-ion capacitors
by N. Böckenfeld; R.-S. Kühnel; S. Passerini; M. Winter; A. Balducci (pp. 4136-4142).
▶ LiFePO4 and activated carbon as active materials for Li-ion capacitor cathode. ▶ Composite electrodes based on aqueous processing containing CMC as binder.▶ Increased electronic conductivity compared to carbon-black containing electrodes. ▶ About 70mAhg−1 in charge-discharge tests at 50C/1D.This manuscript reports the performance of composite electrodes based on the mixture of two, electrochemically active, materials: lithium iron phosphate (LiFePO4) and activated carbon (AC). The sodium salt of carboxymethylcellulose (CMC) was used as binder to cast the composite electrodes out of aqueous slurries. The investigated electrodes display high specific capacity and high cycling stability. Upon constant current tests with a charge rate of 50C and a discharge rate of 1D, the electrodes display a capacity of ca. 70mAhg−1 while 60mAhg−1 are delivered during pulse sequence tests at 100C. These results indicate such electrodes as promising candidates for the realization of lithium-ion capacitors.
Keywords: Lithium-ion capacitors; LiFePO; 4; AC; CMC; Aqueous processing
Cubic titanium dioxide photoanode for dye-sensitized solar cells
by Jinho Chae; Misook Kang (pp. 4143-4151).
Display Omitted▶ Cubic titanium dioxide photoanode for dye-sensitized solar cells. ▶ Photoelectronic efficiency enhanced compared to that achieved using a commercial spherical TiO2. ▶ Cubic TiO2 with a special morphology to overcome the aforementioned electron loss. ▶ An energy conversion efficiency of approximately 9.77% was achieved in the cubic TiO2-DSSC.Following from the recently evolved concept of significantly improving the photovoltaic efficiency in dye-sensitized solar cells (DSSCs) by reducing the loss of electrons on the spherical surface of titanium dioxide, this study examines the synthesis of cubic TiO2 with a special morphology to overcome this electron loss and investigates its application to DSSCs. Cubic TiO2 is synthesized by an advanced rapid hydrothermal method, with the addition of an amine species additive. Transmission electron microscopy (TEM) images confirm the cubic shape of the TiO2 particles with a diameter less than 5–10nm. Using N719 dye under illumination with 100mWcm−2 simulated sunlight, the application of cubic TiO2 to DSSCs affords an energy conversion efficiency of approximately 9.77% (4.0-μm thick TiO2 film), which is considerably enhanced compared with that achieved using a commercial, spherical TiO2. Electrostatic force microscopy (EFM) and impedance analyses reveal that the electrons are transferred more rapidly to the surface of a cubic TiO2 film than on a spherical TiO2 film.
Keywords: Cubic titanium; Amine species additives; Dye-sensitized solar cell; Photovoltaic efficiency; Electrostatic force microscopy; Impedance
Low band gap dyes based on 2-styryl-5-phenylazo-pyrrole: Synthesis and application for efficient dye-sensitized solar cells
by J.A. Mikroyannidis; D.V. Tsagkournos; P. Balraju; G.D. Sharma (pp. 4152-4161).
A new series of low band gap dyes,C1,C2 andS, was synthesized. The quasi solid state DSSCs with dyeS showed an overall power conversion efficiency (PCE) of 4.17% which is higher than the other dyes (3.26% forC2 and 2.59% forC1). By increasing the molecular weight of poly(ethylene oxide) in electrolyte, the PCE of the DSSC based onS increased up to 4.8%.Display Omitted▶ A new series of low band gap photosensitizers for dye-sensitized solar cells (DSSCs). ▶ New dyes based on 2-styryl-5-phenylazo-pyrrole. ▶ Power conversion efficiency of 4.17% for dyeS which contains sulfonic acid anchoring group. ▶ Power conversion efficiency of 4.8% for dyeS by increasing the molecular weight of PEO in electrolyte.A new series of low band gap dyes,C1,C2 andS, based on 2-styryl-5-phenylazo-pyrrole was synthesized. These dyes contain one carboxy, two carboxy and one sulfonic acid anchoring groups, respectively. They were soluble in common organic solvents, showed long-wavelength absorption maximum at ∼620nm and optical band gap of 1.66–1.68eV. The photophysical and electrochemical properties of these dyes were investigated and found to be suitable as photosensitizers for dye sensitized solar cells (DSSCs). The quasi solid state DSSCs with dyeS showed a maximum monochromatic incident photon to current efficiency (IPCE) of 78% and an overall power conversion efficiency (PCE) of 4.17% under illumination intensity of 100mWcm−2 (1.5AM), which is higher than the other dyes (3.26% forC2 and 2.59% forC1). Even though dyeS contains one sulfonic acid anchoring group, the higher PCE for the DSSCs based on this dye has been attributed to the higher dye loading at the TiO2 surface and enhanced electron lifetime in the device, as indicated by absorption spectra and electrochemical impedance spectra measurements. Finally, by increasing the molecular weight of poly(ethylene oxide) (PEO) in electrolyte, the PCE also increases up to 4.8% for the electrolyte with PEO molecular weight of 2.0×106. This improvement has been attributed to the enhancement in iodide ions diffusion due to the increase in free volume of polymer gel electrolyte.
Keywords: Pyrrole; Azo dyes; Low band gap; Dye-sensitized solar cells; Electron lifetime
Elucidation of electrochemical properties of electrolyte-impregnated micro-porous ceramic films as framework supports in dye-sensitized solar cells
by Hseng Shao Chen; Shingjiang Jessie Lue; Yung Liang Tung; Kong Wei Cheng; Fu Yuan Huang; Kuo Chuan Ho (pp. 4162-4172).
.Display Omitted▶ Micro-porous ceramic framework supports are used in dye-sensitized solar cells. ▶ Electrochemical properties in symmetric cells and solar cells are measured. ▶ Porous supports slow down electrolyte evaporation rate. ▶ Framework porosity correlates with charge transfer resistance and diffusivity of tri-iodide ions. ▶ Solar cells with ceramic supports render higher efficiency after aging.This study investigates the electrochemical properties of electrolyte-impregnated micro-porous ceramic (Al2O3) films as framework supports in dye-sensitized solar cells (DSSCs). A field-emission scanning electron microscope (FE-SEM) is used to characterize the morphology on both surfaces of the ceramic membranes, which exhibit high porosity (41–66%) and an open cylindrical pore structure. Electrochemical impedance analysis reveals that the conductivity of the electrolyte-impregnated ceramic membrane is lower (6.24–9.39mScm−1) than the conductivity of the liquid electrolyte (25mScm−1), with an Archie's relationship by a power of 1.81 to the porosity value. The diffusivity of tri-iodide ions(I3−) is slowed from 1.95×10−5 to 0.68×10−5cm2s−1 in the ceramic-containing cells. The exchange current density at the Pt-electrolyte interface decreases slightly (less than 5%) when the Al2O3 membranes were used in the symmetric cells, implies that the contact of the denser ceramic top structure on the Pt electrode does not interfere with theI3− charge transfer. The ceramic films can prevent solvent evaporation and maintain conductivity. The long-term cell efficiencies are evaluated up to 1248h under alternating light soaking and darkness (3 days/4 days) cycles. The cells containing the ceramic films outperform the control cells.
Keywords: Limiting current density; Tri-iodide diffusion coefficient; Porosity; Electrolyte-filled micro-porous framework; Cell performance