Metal hydride mediated water splitting: Electrical energy saving and decoupled H2/O2 generation

Abstract Reversible hydrogen absorption/desorption, the very fundamental property of metal hydrides (MHs), can be utilized to innovate the water splitting process. Spontaneous hydrogen absorption by a MH electrode shifts the water reduction potential to 0.3 V above the reversible hydrogen electrode. Then, the absorbed hydrogen can be released to give H2 by thermal dehydrogenation at mild temperature below 70 °C by utilizing low grade heat. The MH mediated water splitting combines the electrochemical hydrogen absorption in Ni-MH batteries and the thermal dehydrogenation in gas phase hydrogen storage, which significantly reduces the electrical energy consumption for water splitting up to 25 kJ (mol H2)−1 compared to an ideal hydrogen evolution catalyst and also automatically leads to decoupled H2/O2 generation. The advantages and mechanisms of the MH mediated water splitting are demonstrated by MH electrodes with surface Pd coating.