Ni-MOF-based electrodes: A promising strategy for efficient overall water splitting

Abstract

Hydrogen is a promising energy source to replace fossil fuels. Among the methods of generating hydrogen, electrochemical water splitting is distinguished by its ecologically friendly, high efficiency, sustainability, and ability to produce this element without the limitation of geological conditions and scaling devices. However, electrochemical water splitting is thermodynamically unfavorable, especially because its oxidation half-reaction (OER) and commercially available catalysts are expensive and not abundant in natural resources. The efficacy of commonly employed HER catalysts, such as Pt/C, is well-established. However, their high cost and limited natural resources present significant impediments. Given the slow kinetics of OER and the requisite catalyst demand for both HER and OER, it is paramount to pursue alternative solutions that are cost-effective, facile, and more widely accessible. Various new technologies and active materials have recently been developed in electrochemical water splitting for hydrogen production. There are still many knowledge gaps, including how preparation methods, chemical composition, and morphology of electrocatalysts affect both half-reactions of water splitting. Therefore, this work presents a smart approach to selectively activate NiMOF-based active materials in HER and OER. We demonstrate high-performance electrocatalysts based on Nickel/metal-organic frameworks (NiMOF) fabricated via two routes: A - drop cast on pristine Nickel foam with improved activity in OER (flower-like structure), B - Ni foam in situ impregnated by NiMOF during synthesis with improved activity in HER (rectangular-like structure). It allows the demonstration of highly efficient and robust electrocatalysts. Furthermore, in-situ studies on structural changes in the active materials have been conducted to reveal water-splitting half-reaction mechanisms.