Hierarchical sheet-on-sheet heterojunction array of a β-Ni(OH)/Fe(OH) self-supporting anode for effective overall alkaline water splitting.

Rationally designing high-performance non-noble metal electrocatalysts is of essence to improve energy conversion efficiency in water splitting. Herein, a unique 3D hierarchical sheet-on-sheet heterojunction between Fe(OH) and β-Ni(OH) on pretreated Ni foam (NiFe-HD/pre-NF) was fabricated by a two-step strategy involving the interfacial hydrolysis-deposition of Fe and electrodeposition of Ni. The presence of the Ni-O-Fe bridge at the Fe(OH)/β-Ni(OH) heterointerface can induce interfacial electronic redistribution to form Ni in NiFe-HD/pre-NF, and further strengthen the adsorption of OH and weaken the O-H bond to change the rate-determining step (RDS) for accelerating OER kinetics. Benefiting from the sheet-on-sheet architecture and dual-phase synergism on NiFe-HD/pre-NF, the optimal NiFe-HD/pre-NF exhibits excellent OER performance with a lower overpotential of 256 mV at 100 mA cm, a small Tafel slope of 81 mV dec, high intrinsic activity and robust stability. Alkaline water-splitting using NiFe-HD/pre-NF as the anode requires ultralow cell voltages of 1.62 V and 1.83 V at current densities of 100 mA cm and 400 mA cm, respectively, which are comparable with commercial alkaline water electrolysis, and operates steadily at a current density of 100 mA cm for 85 h without decay. This work proposes a facile strategy for constructing heterojunctions and modulating electronic interaction to develop electrocatalysts with new architectures.