Enhanced bifunctional electrocatalytic activities of hybrid Co(OH)2/MOF-derived materials for green hydrogen production by electrochemical water splitting

Abstract

Hybrid materials are emerging as promising because of their unique synergetic properties, resulting from the individual components and structures. Especially, for electrochemical water splitting, a couple of catalytically active, affordable, and stable materials are Co₃O₄ and its corresponding sulphide (Co₃S₄) as reported by researchers. Nevertheless, the resultant catalytic activities are not satisfactory for commercial use. In this work, to boost their catalytic activities, we have successfully synthesized a hybrid Co(OH)₂/ZIF-67-derived Co₃O₄ on Ni foam (NF) and converted it into Co₃S₄ by a simple hydrothermal method. Co₃O₄@NF needs only 318 mV overpotential for the OER to reach 20 mA cm⁻² current density. Interestingly, this overpotential is decreased to 260 mV after sulphurization. However, Co₃O₄@NF and Co₃S₄@NF need only 178 and 180 mV overpotentials for the HER to reach 20 mA cm⁻², respectively. Thus, both materials show excellent bifunctional catalytic activities and stability at relatively high applied potential. Mainly, when Co₃O₄@NF(+)‖Co₃O₄@NF(−), Co₃S₄@NF(+)‖Co₃S₄@NF(−), and Co₃S₄@NF(+)‖Co₃O₄@NF(−) electrolyzers were fabricated and tested for overall water splitting, they showed a cell potential of only 1.61, 1.63 and 1.63 V to drive 10 mA cm⁻², respectively. Thus, these materials can be an alternative to precious materials to develop alkaline electrolyzers.