Towards a ‘proton flow battery’: Investigation of a reversible PEM fuel cell with integrated metal-hydride hydrogen storage

An innovative concept for integrating a metal hydride storage electrode into a reversible proton exchange membrane (PEM) fuel cell is described and investigated experimentally. This new concept has the potential to increase roundtrip efficiency compared to the conventional hydrogen-based electrical energy storage system by eliminating the intermediate steps of hydrogen gas production, storage, and recovery. As only an inflow of water is needed in the charge mode, and air in discharge mode, the system is called a ‘proton flow battery’. A hydrogen storage electrode was fabricated from a novel composite metal hydride–nafion material, and found to have acceptably high proton and electron conductivities. Its hydrogen storage capacity was measured to be 0.6 wt% of hydrogen, although the amount of hydrogen recovered to run the device in fuel cell mode was much lower. These results provide initial confirmatory evidence that the proton flow battery concept is technically feasible, though additional research is still required to enhance both storage capacity and reversibility.