Unveiling the Geometric Site Dependence of Co‐Based Spinel Oxides in the Halogen Evolution Reaction

Abstract

AbstractCobalt‐based spinel oxides, such as Co3O4, have emerged as promising electrocatalysts for chlorine and bromine evolution reactions (CER and BrER) in recent years. However, the role of Co valence in determining the exceptional performance of Co3O4 for both CER and BrER remains ambiguous due to the coexistence of both octahedrally coordinated Co3+ (Co3+Oh) and tetrahedrally coordinated Co2+ (Co2+Td) sites, despite their high catalytic activity and stability. Herein, combining experiment results and electrochemical data analysis, the Co3+Oh site functions as the primary active site for CER is demonstrated. In contrast, for BrER, both Co3+Oh and Co2+Td sites exhibit good catalytic activity, with Co3+Oh sites displaying better BrER catalytic performance than Co2+Td sites. To further enhance the CER catalytic activity of the Co3+Oh site, inert Co2+Td is replaced with Cu2+ cations. As expected, CuCo2O4 featuring an optimized Co3+Oh site demonstrates an overpotential of 24 mV at a current density of 10 mA cm−2 while exhibiting exceptional stability for ≈60 h, surpassing the performance of the majority of non‐noble and even noble metal‐based electrocatalysts reported to date. Therefore, the study elucidates the significance of geometric configuration‐dependent activity in electrocatalytic halogen evolution reactions.