Coupling adsorbate evolution and lattice oxygen mechanisms via FeOCo/V interfacial bonds in δ-FeOOH/CoVP-B for...

Transition metal phosphides (TMPs) hold considerable promise as electrocatalysts for alkaline oxygen evolution reaction (OER). However, inadequate activity and stability continue to limit their practical application. To address this challenge, we designed a nanoarray consisting of cobalt‑vanadium phosphide (CoVP) rich in phosphorus vacancies and coated with δ-FeOOH (denoted as δ-FeOOH/CoVP-B). It delivers an overpotential of 241 mV at 10 mA cm^-2, a Tafel slope of 34.3 mV dec^-1 and outstanding durability with a degradation rate of only 0.30 mV h^-1 over 168 h at 500 mA cm^-2. Multiple characterizations confirm that δ-FeOOH and phosphorus vacancies synergistically form FeOCo/V interfacial bonds. This interfacial bond causes a redistribution of charges and increases the framework's structural rigidity, thereby effectively suppressing uncontrolled structural dissociation at high potentials. Electrochemical analysis, in situ characterization and theoretical calculations further reveal that, via the substrate following the adsorbate evolution mechanism (AEM) pathway, δ-FeOOH triggers the lattice oxygen mechanism (LOM) at the interface by enhancing the covalency of interfacial CoO bonds, while simultaneously altering the active sites' d-band centers in a bidirectional manner, thereby endowing the reaction intermediates with moderate adsorption strength. This dual mechanism circumvents the scaling limitations of the conventional AEM and avoids the structural collapse typical of pure LOM, enabling both high efficiency and robust stability. This work elucidates the dual role of the FeOCo/V interface in directional electronic modulation and structural stabilization and provides valuable insights for developing high-performance, long-lifetime TMP-based OER electrocatalysts.