Interfacial Engineering of Iron–Cobalt Hydroxide Nanosheet on Nickel Oxide Heterostructure for Efficient Overall Water Splitting by Reducing the Energy Barrier

Designing cost-effective and durable bifunctional electrocatalysts is critical for efficient water electrolysis and sustainable hydrogen production. Herein, we report an interfacial engineering approach to construct layered iron-cobalt hydroxides (Fe_1-<i>x</i>Co_<i>x</i>(OH)₂@<b>S1</b>, where "<b>S1</b>" represents the molar ratio of Fe:Co (3:1) and <i>x</i> = 0.25) with optimized Fe-O-Co active centers. The engineered heterointerface promotes charge redistribution and accelerates reaction kinetics, thereby reducing adsorption energy barriers for the key intermediates. The Fe_1-<i>x</i>Co_<i>x</i>(OH)₂@<b>S1</b> electrode achieves low overpotentials of ∼0.270 V for oxygen evolution and ∼0.192 V for hydrogen evolution at 10 mA cm^-2, alongside a turnover frequency of 0.165 s^-1 and high mass activity (∼11.2 A g^-1). When used as both an anode and cathode, the symmetric electrolyzer operates at only 1.61 V to deliver 10 mA cm^-2, rivaling the RuO₂∥Pt/C benchmarks. These results highlight the crucial role of Fe-Co-Ni interfacial coupling in modulating electronic structures and catalytic energetics. This work offers a generalizable strategy for developing advanced multimetal hydroxide catalysts toward highly efficient alkaline water electrolysis.