Unveiling the superior oxygen evolution reaction performance of β-CoMoO ₄ nanorods: Insights into catalytic mechanisms and active site dynamics

Cobalt-based oxides are renowned for their excellent activity in the oxygen evolution reaction (OER), making them promising alternatives to precious metal catalysts. Among these, β-CoMoO₄, with its wolframite structure, exhibits superior OER performance compared to widely studied cobalt-based perovskite oxides. However, its underlying catalytic mechanism remains largely unexplored. In this study, we synthesized β-CoMoO₄ using a hydrothermal method and achieved remarkable OER catalytic performance in an alkaline environment, with an overpotential of 366 mV at a current density of 10 mA/cm² and an intrinsic activity of 180 μA/cm_ox² at 1.55 V (vs. reversible hydrogen electrode (RHE)). Following OER activation, the micron-sized rod-like structure of β-CoMoO₄ dissociates as a whole and reconstructs into amorphous CoOOH, forming a hexagonal flake structure on the scale of hundreds of nanometers. This transformation provides abundant surface active sites with a low-coordination structure. By combining <i>in situ</i> X-ray absorption fine structure (XAFS) with cyclic voltammetry (CV) scanning, we investigated the kinetic behavior of the active sites of β-CoMoO₄ as a function of potential. The results indicate that the Co ions in this low-coordination structure can be pre-oxidized at relatively low voltages. Therefore, the excellent OER performance of β-CoMoO₄ is attributed to its unique bulk-phase reconstruction behavior and the strong deprotonation ability of the <i>in situ</i> generated amorphous low-coordination active structure. Our research provides valuable insights for the development of new and efficient cobalt-based oxide electrocatalysts for water-splitting applications.