Genuine Active Species Generated from Fe₃N Nanotube by Synergistic CoNi Doping for Boosted Oxygen Evolution Catalysis

The surface reconstruction of oxygen evolution reaction (OER) catalysts has been proven favorable for enhancing its catalytic activity. However, what is the active site and how to promote the active species generation remain unclear and are still under debate. Here, the in situ synthesis of CoNi incorporated Fe₃N nanotubes (CoNi–Fe₃N) on the iron foil through the anodization/electrodeposition/nitridation process for use of boosted OER catalysis is reported. The synergistic CoNi doping induces the lattice expansion and up shifts the d-band center of Fe₃N, which enhances the adsorption of hydroxyl groups from electrolyte during the OER catalysis, facilitating the generation of active CoNi–FeOOH on the Fe₃N nanotube surface. As a result of this OER-conditioned surface reconstruction, the optimized catalyst requires an overpotential of only 285 mV at a current density of 10 mA cm⁻² with a Tafel slope of 34 mV dec⁻¹, outperforming commercial RuO₂ catalysts. Density functional theory (DFT) calculations further reveal that the Ni site in CoNi–FeOOH modulates the adsorption of OER intermediates and delivers a lower overpotential than those from Fe and Co sites, serving as the optimal active site for excellent OER performance.