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 (ZnCo 2 S 4 ) was derived by hydrothermal treatment of metal salt precursors and thioacetamide, followed by calcination at 700 °C for ZnCr 2 O4 to create a ZnCo 2 S 4 /ZnCr 2 O 4 composite nanostructure enriched with Zn 0.76 Co 0.24 S. The electrochemical performance of the composition-dependent ZnCo 2 S 4 /ZnCr 2 O 4 nanostructure enriched with Zn 0.76 Co 0.24 S 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.