Oxygen-Bridged Fe-Ni Heterointerfaces Confined in Hierarchical MoxC/N-Doped Carbon Enable Bifunctional Pathway for Efficient Oxygen Evolution

Abstract

The oxygen evolution reaction (OER) suffers from slow multistep kinetics, requiring catalysts capable of providing efficient charge transfer and robust active sites. Here, we report a highly efficient O-bridged Fe-Ni heterointerface confined within hollow hierarchical molybdenum carbide/nitrogen-doped carbon (MoxC/NC) microspheres. The hierarchical MoxC/NC scaffold, derived from a metal-polydopamine complex, prevents metal sintering during high-temperature conversion and stabilizes ultrasmall NiO domains. Subsequent Fe treatment anchors FeOOH species onto surface-exposed NiO, generating abundant O-bridged Fe-Ni heterointerfaces. X-ray photoelectron and absorption spectroscopy reveal the formation of strongly coupled Ni-O-Fe linkages, while operando Raman spectroscopy confirms their transformation into FeOOH-NiOOH active species under OER conditions. These O-bridged interfaces promote a bifunctional pathway in which Fe acts as the primary oxygen-evolving center and Ni serves as the proton-accepting center, thereby accelerating OER kinetics. As a result, FeOOH-NiO@MoxC/NC achieves an overpotential of 374 mV at 100 mA cm -2 , a Tafel slope of 77.8 mV dec -1 , and a turnover frequency of 2.69 s -1 at 350 mV, outperforming RuO2. Furthermore, the catalyst maintains over 300 hours of stable operation at 500 mA cm -2 in anion-exchange membrane electrolyzers. This work highlights a rational interfacial-engineering strategy that leverages O-bridged Fe-Ni heterointerfaces to achieve highly active and durable OER electrocatalysts.