Growing concerns about environmental hazards of current fossil fuel-dependent society have led to development of technologies for sustainable energy cycle. Water electrolyzer plays key role in converting renewable electricity to chemical energy by fabricating fuel in this cycle. The bottleneck in efficient electrolyzer is oxygen evolution reaction(OER), which requires significant amount of overpotential. As conventional precious metal based OER catalysts have shown limitations such low stability and high cost, earth-abundant 3d transition metal oxides have been explored as alternative OER catalyst with high activity and cost-effectiveness. A variety of materials have been reported, including (oxy)hydroxides, spinels, perovskites and organometallics. Among them, Ni-Fe (oxy)hydroxide particularly shows promising activity in alkaline electrolysis. Although the origin of high activity and reaction mechanism of Ni-Fe (oxy)hydroxide is still on debate, recent progress reveals that active sites of Ni-Fe (oxy)hydroxide are located at the edge or defect sites of (oxy)hydroxide sheet. This show the limitation of (oxy)hydroxide material fabricated by conventional electrodeposition or hydrothermal method, because only limited number of active sites are exposed and most of the metal sites remain inactive.
In this study, we adopted a novel approach to electrochemically activate Ni-Fe alloy substrate to generate highly active OER catalyst. In contrast to conventional electrodeposition or hydrothermal method in which precursor ions in solution are deposited as catalyst, our method turns the elements in substrate to active sites with optimal structure and composition. The specific OER activity of activated Ni-Fe is significantly higher than previously reported (oxy)hydroxide catalyst. Voltammetric analysis of Ni redox behavior reveals that activated Ni-Fe shows distinct feature from conventional (oxy)hydroxide sheet and has certainly higher density of active sites. Moreover, easy tuneability of substrate composition and microstructure makes it possible to add other elements and change structure, suggesting strategies to enhance activity and stability of the catalyst. This study provides a novel platform for designing electrocatalysts not only for water oxidation but also for other electrochemical applications.