Controlling electron spin could lead to an efficient way to split water to generate hydrogen to power fuel cells, according to research at the Weizmann Institute of Science in Rehovot, Israel and Eindhoven University of Technology in The Netherlands. The approach precludes formation of hydrogen peroxide as a byproduct, an issue that has made hydrolysis problematic. The team has demonstrated that when electron spins are aligned hydrogen peroxide is not formed because the ground state of hydrogen peroxide needs two electrons with opposite spins. Oxygen, by contrast, is generated when the electrons have parallel spins. The key was to coat the electrodes with titanium dioxide and to use a chiral, supramolecular structure, aggregates of zinc porphyrins to take control of the electron spin.