Exceptional performance of hierarchical Ni-Fe oxyhydroxide@NiFe alloy nanowire array electrocatalysts for large current density water splitting

Water electrolysis represents a promising sustainable hydrogen production technology. However, in practical application which requires extremely large current densities (>500 mA cm^-2), the oxygen evolution reaction (OER) becomes unstable and kinetically sluggish, which is a major hurdle to large-scale hydrogen production. Herein, we report an exceptionally active and binder-free NiFe nanowire array based OER electrode that allows durable water splitting at current densities up to 1000 mA cm^-2 up to 120 hours. Specifically, NiFe oxyhydroxide (shell)-anchored NiFe alloy nanowire (core) arrays are prepared via a magnetic-field-assisted chemical deposition method. The ultrathin (1-5 nm) and amorphous NiFe oxyhydroxide is in situ formed on the NiFe alloy nanowire surface, which is identified as an intrinsically highly active phase for the OER. Additionally, the fine geometry of the hierarchical electrode can substantially improve charge and mass (reactants and oxygen bubbles) transfer. In an alkaline electrolyte, this OER electrode can yield current densities of 500 and 1000 mA cm^-2 stably over 120 hours at overpotentials of only 248 mV and 258 mV respectively, which are dramatically lower than any recently reported overpotentials. Notably, the integrated alkaline electrolyzer (with pure Ni nanowires as HER electrode) is demonstrated to reach the current density of 1000 mA cm^-2 with super low voltage of 1.76 V, outperforming the state-of-the-art industrial catalysts. Our result may represent a critical step towards an industrial electrolyzer for large-scale hydrogen production by water splitting.