Modulating Coordination-Driven Metal-Oxygen Interaction Triggers Oxygen Evolution in Polymorphic and High-Entropy Phosphate Electrocatalyst

Abstract

Engineering metal-oxygen (M‒O) interactions for catalyzing oxygen evolution reaction (OER) by tuning the coordination geometry of metal sites is crucial for improving catalytic performance, which remains unexplored, especially in structurally diverse phosphate-based catalysts. Herein, two NaCoPO₄ (NCP) polymorphs with distinct metal coordinations: orthorhombic-Pnma (CoO₆) and hexagonal-P6₅ (CoO₄) denoted as O-NCP and H-NCP, respectively are synthesized through unique quenching-based synthesis, to investigate the impact of coordination geometry on M‒O covalency and OER performance. The CoO₄ (H-NCP) polymorph delivered superior OER activity with low overpotential at 10 mA cm⁻² (η₁₀ = 303 mV) and long-term stability than CoO₆-based O-NCP. Spectroscopic and computational studies linked the superior activity of CoO₄ to higher Co‒O covalency, enhanced metal electronic states near the Fermi level, and improved electrochemical reconstruction. Further, M‒O covalency regulated OER mechanism, where high-covalent CoO₄ follows conventional concerted proton-electron transfer pathway, while CoO₆ entails a non-concerted pathway, where the lattice oxygen participation remains unfavorable due to downshifted O 2p band center. Further, OER-active tetrahedral metal is demonstrated in a high-entropy catalyst requiring lower η₁₀ of ≈284 mV. This study unlocks a unique strategy for designing next-generation OER catalysts with superior activity and durability, harnessing the interplay between metal coordination and metal-oxygen covalency.