Co-P covalent interaction strengthens electron relocation in Ce-O-Co for enhanced water oxidation via lattice oxygen mechanism

Abstract

Due to restrictive linear relationship between intermediates in adsorption evolution mechanism (AEM) of oxygen evolution reaction (OER), a higher overpotential must be overcome for conversion of *O to *OOH. Activating lattice oxygen mechanism (LOM) can address the AEM’s challenges by facilitating O-O coupling. However, via LOM pathway, extracting electrons from metal-oxygen (M−O) bonds usually results in structural instability. Herein, we propose an effective method to stabilize LOM-catalysts by combining cerium dioxide with cobalt phosphide (CeO₂/CoP heterostructure). CeO₂ acts as an electron buffer to retain/provide electrons at different stages, while CoP with strong Co-P covalency enhances structural/catalytic stability in strongly-alkaline conditions. CeO₂/CoP exhibits an OER overpotential of only 225 mV at 10 mA cm⁻². Initially, CeO₂ acquires electrons from CoP to accelerate surface reconstruction and form high-valence Co^δ+ (CoOOH). Then, CoOOH acquires electrons from the 4f-orbital of Ce through the Ce-O-Co interface, rather than from the M−O bond, thus ensuring OER stability. For water splitting, bifunctional CeO₂/CoP-assembled electrolyzer requires a cell-voltage of only 1.54 V to achieve 10 mA cm⁻² and retains 89.5 % of its activity after 72 h of cycling. It highlights that leveraging electron-buffering metal species can enhance the LOM stability, thereby enabling its application in bifunctional electrocatalysis.