ZIF-67-derived Co–N–C supported nickel cobalt sulfide as a bifunctional electrocatalyst for sustainable hydrogen production via alkaline electrolysis

Abstract

As non-renewable resources are finite and cannot be utilized indefinitely, hydrogen (H₂) has emerged as a promising alternative for clean and sustainable energy. The cost-effective hydrogen production to meet large-scale commercial demand poses a significant challenge. Water electrolysis, powered by electricity derived from renewable resources, stands out as a viable route towards sustainable hydrogen production, with electrocatalysis playing a pivotal role in this process. Notably, materials derived from metal–organic frameworks (MOFs) exhibit excellent physicochemical properties, making them promising candidates for electrocatalysis. In this study, we synthesized zeolitic imidazolate framework-67 (ZIF-67) and its derived Co–N-doped carbon (Co–N–C) supported NiCo₂S₄ on nickel foam (NF), namely NF@ZIF-67@NiCo₂S₄ and NF@Co–N–C@NiCo₂S₄, using a hydrothermal method. The electrocatalytic activity of these synthesized materials for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was systematically evaluated using various electrochemical techniques. The NF@ZIF-67@NiCo₂S₄ material demonstrates overpotentials of 248 and 359 mV for OER and HER at the current density of 50 mA cm⁻², whereas, NF@Co–N–C@NiCo₂S₄ exhibits overpotentials of 239 and 351 mV, respectively. Furthermore, the catalysts exhibit excellent stability in both OER and HER even under high applied potentials. Moreover, to assess their catalytic performance in a full-cell configuration, two alkaline electrolyzer cells were assembled: NF@ZIF-67@NiCo₂S₄(+)∥NF@ZIF-67@NiCo₂S₄(−) and NF@Co–N–C@NiCo₂S₄(+)∥NF@Co–N–C@NiCo₂S₄(−). These two electrolyzers demonstrated cell potentials of 1.62 V and 1.59 V at 10 mA cm⁻², respectively, showcasing their efficacy in overall water-splitting.