Electrochemical Oxygen Evolution Catalyzed by Zn_0.76Co_0.24S‑Enriched ZnCo₂S₄/ZnCr₂O₄ Nanostructures

Finding a suitable replacement for expensive and scarce precious metal electrocatalysts for the oxygen evolution reaction (OER) remains a challenging task. There is a need to research highly efficient and long-lasting catalysts based on transition metals that are readily available on Earth for electrochemical oxygen evolution. In this study, zinc cobalt sulfide (ZnCo₂S₄) was derived by hydrothermal treatment of metal salt precursors and thioacetamide, followed by calcination at 700 °C for ZnCr₂O4 to create a ZnCo₂S₄/ZnCr₂O₄ composite nanostructure enriched with Zn_0.76Co_0.24S. The electrochemical performance of the composition-dependent ZnCo₂S₄/ZnCr₂O₄ nanostructure enriched with Zn_0.76Co_0.24S was then tested along with its constituents, and it was found that the OER activity is not linearly proportional to the composition. We also evaluated the OER activity at pH 7.0 in a neutral medium and the OER electrochemical performance in an alkaline medium. Zn–Co–S is preferable to Zn- and Cr-based thio-spinel as it increases electronic conductivity and decreases charge transfer resistance. Both of these properties are necessary for generating the high oxidative valency of Co species during the OER process. The material’s unique composition and remarkable stability make it highly desirable for future research in this field.