Ionic‐Bonding Engineering of Metastable CoMoO ₄ for Durable Oxygen Evolution Electrocatalysis

ABSTRACT

Thermodynamically metastable materials with high‐energy crystal structures have emerged as promising electrocatalyst candidates owing to their structural and electronic flexibility, offering viable route to reduce dependence on noble‐metal‐based catalysts. Among them, CoMoO ₄ , which exhibits phase‐dependent Mo‐O polyhedral frameworks in α‐ and β‐polymorphs, has attracted considerable attention as an oxygen evolution reaction (OER) catalyst. However, its practical application is limited by structural instability arising from labile metal‐oxygen framework during repetitive electrochemical operation. Herein, we report pnictogen‐doping strategy using Sb and Bi to stabilize metastable CoMoO ₄ by modulating the local metal‐oxygen bonding environment while preserving high OER activity. The doped CoMoO ₄ catalysts delivered a high current density of approximately 230 mA cm ⁻² at 2.0 V in 1 M KOH. In particular, Sb‐doped β‐CoMoO ₄ exhibited enhanced electrochemical durability, retaining 93% of its initial current density after 1000 cycles, whereas pristine β‐CoMoO ₄ retained only 64%. Sb‐doped β‐CoMoO ₄ also showed lower operating potential at 10 mA cm ⁻² than pristine β‐CoMoO ₄ , decreasing from 1.34 to 1.29 V. In addition, the quasi‐redox peak associated with the Co ²⁺ /Co ³⁺ transition near 1.1 V, which is related to CoOOH formation and concurrent Co/Mo cation dissolution during the OER process, was effectively suppressed by doping with Sb or Bi. These results indicate that pnictogen doping enhances the structural robustness of metastable CoMoO ₄ by strengthening the metal‐oxygen bonding framework and mitigating cation leaching during electrochemical cycling. Overall, this work demonstrates that ionic‐bonding engineering is effective strategy for stabilizing metastable oxide electrocatalysts while maintaining or slightly enhancing OER performance. These findings provide useful guidance for designing fatigue‐tolerant, noble‐metal‐free electrocatalysts for practical water‐splitting applications.