Large-current polarization-engineered FeOOH@NiOOH electrocatalyst with stable Fe sites for large-current oxygen evolution reaction

NiFe-based (oxy)hydroxides are among the most efficient electrocatalysts for the oxygen evolution reaction (OER). However, significant Fe leakage during the OER results in unsatisfactory stability. Herein, a large-current (1.5 A cm^–2) galvanostatic reconstruction was used to fabricate FeOOH@NiOOH (eFNO_L) with both fixed Fe sites and exposed high-index crystal facets (HIFs). Compared to FeNiOOH with low-index crystal facets, the phase-separated FeOOH@NiOOH showed a higher binding energy towards Fe, and the HIFs significantly improved the catalytic activity of FeOOH. The optimized eFNO_L catalyst exhibits ultralow overpotentials of 234 and 272 mV, yielding substantial current densities of 100 and 500 mA cm^–2, respectively, with a small Tafel slope of 35.2 mV dec^–1. Moreover, due to the stabilized Fe sites, its striking stability over 100 h at 500 mA cm^–2 with 1.5% decay outperforms most NiFe-based OER catalysts reported recently. This study provides an effective strategy for developing highly active and stable catalysts via large-current electrochemical reconstruction.