Strategically improving the oxygen evolution reaction performance of ZnCo2S4 nanoflakes: role-specific redox-additive electrolytes

Abstract

Energy harvesting through the oxygen evolution reaction (OER) is one of the most successful and economical methods. Consequently, designing new strategies is necessary to enhance the electrocatalytic performances of sustainable OER catalysts in the current scenario. Herein, a two-fold strategy comprising synthesis and operation vis-à-vis electrodeposition and the mild addition of a redox-additive electrolyte was employed for this purpose in a ternary sulfide catalyst, ZnCo₂S₄. Highly porous nanoflakes of ZnCo₂S₄ were obtained on nickel foam via a simple electrodeposition method. Moreover, the synergy between KOH and the adopted redox-additive electrolytes (K₃[Fe(CN)₆] or KFCN and hydroiodic acid or HI) remarkably improved the performance of the ZnCo₂S₄ catalyst in the OER. It was observed that KFCN delivered a very low onset potential of ∼1.45 V and an overpotential of 364 mV at 100 mA cm⁻², whereas an onset potential of 1.527 V and an overpotential of 477 mV at 100 mA cm⁻² were observed for the KOH electrolyte. The catalyst further showed an impressive double-layer capacitance of 10.76 mF cm⁻² and a stability of 95% even after 12 hours, which was only 74% in the case of the KOH electrolyte. In contrast, HI showed an enhanced diffusion coefficient value of 5.8 × 10⁻¹² cm² s⁻¹ with a low Tafel slope of 142 mV dec⁻¹. In the device configuration, the catalyst demonstrated low charge transfer and solution resistance, with an excellent current stability of 80% after 12 hours of continuous oxygen evolution in the mixed electrolyte solution of KOH and KFCN. Thus, the proposed strategy gives new insights into boosting the electrocatalytic performance of similar ternary sulfides in the OER.