Phosphomolybdic Acid-Bipolar Membrane: An Efficient and Reversible Coupling for Alkaline Water Electrolysis

Alkaline water electrolysis can be a feasible choice for large-scale hydrogen production using noble-metal-free electrocatalysts. A bipolar membrane-based decoupled electrolysis system is constructed for alkaline water with phosphomolybdic acid as an electron-coupled proton buffer. The decoupled electrolysis system exhibits high efficiency and good stability for multiple oxygen and hydrogen evolution cycles, and the O2 and H2 evolution proceeds in the near-stoichiometric ratio (1:2) at separate times. IR, 31P NMR, and MS results further reveal that phosphomolybdic acid has excellent reversibility for alkaline water electrolysis. Moreover, phosphomolybdic acid can display a notable 6e-redox activity, which helps improve the energy and capacity density of the present system. Noble-metal-free materials (such as NiFe-layered double hydroxide and Ni3S2 nanosheet on Ni foams) can be used as active oxygen- and hydrogen-evolving reaction electrocatalysts in this electrolysis system.