Vanadium Dissolution Eliminate the Lattice Distortion of Co-O Octahedron during Oxygen Evolution for Water Splitting

Abstract

The electrocatalysts for high-energy consumed anodic oxygen evolution reaction (OER) especially in water splitting are generally prone to reconfiguration, so the dynamic structural evolution mechanisms should be deeply investigated. Herein, coral-like nanoarray assembled by nanosheets were synthesized via the layered effect of cobalt (Co) and the one-dimensional guiding effect of vanadium (V). The unique structure facilitates the full contact between active sites and electrolyte to enhance the electrocatalytic activity. The hydrogen evolution reaction (HER) and OER activity can be respectively promoted through modulating the electronic structure with nitrogen and phosphate anions. Thus, the assembled anion exchange membrane electrolyzer exhibits a direct current energy consumption of 4.31 kWh Nm^–3@250 mA cm^–2 at 70°C. It only required 1.88 V voltage to achieve a current density of 500 mA cm^–2 with excellent stability over 200 h. Operando synchrotron radiation and Bode phase angle analyses reveal that the dissolution of vanadium species makes the distorted Co-O octahedral to regular octahedral structure during OER, accompanying by a decrease of band gap and a shortening of the Co-Co bond length. Such a structural evolution plays as the key active site for the formation of oxygen-containing intermediates, thereby accelerating the reaction kinetics.