Iron‐Locked Hydr(oxy)oxide Catalysts via Ion‐Compensatory Reconstruction Boost Large‐Current‐Density Water Oxidation

Nickel-iron based hydr(oxy)oxides have been well recognized as one of the best oxygen-evolving catalysts in alkaline water electrolysis. A crucial problem, however, is that iron leakage during prolonged operation would lead to the oxygen evolution reaction (OER) deactivation over time, especially under large current densities. Here, the NiFe-based Prussian blue analogue (PBA) is designed as a structure-flexible precursor for navigating an electrochemical self-reconstruction (ECSR) with Fe cation compensation to fabricate a highly active hydr(oxy)oxide (NiFeO_x H_y ) catalyst stabilized with NiFe synergic active sites. The generated NiFeO_x H_y catalyst exhibits the low overpotentials of 302 and 313 mV required to afford large current densities of 500 and 1000 mA cm^-2 , respectively. Moreover, its robust stability over 500 h at 500 mA cm^-2 stands out among the NiFe-based OER catalysts reported previously. Various in/ex situ studies indicate that the Fe fixation by dynamic reconstruction process can reinforce the Fe-activated effect on the OER amenable to the industrial-level large current conditions against the Fe leakage. This work opens up a feasible strategy to design highly active and durable catalysts via thermodynamically self-adaptive reconstruction engineering.