Increasing energy demand to find everlasting and eco-friendly resources is now mainly dependent on green hydrogen production technology. Water electrolysis has been regarded as a clean route for green H 2 production with zero carbon emission, but different bottlenecks in the development of electrodes impeded its realization. Recently, transition metal oxides (TMO) have gained tremendous attention as suitable cathodes and anodes due to their sustainability under harsh conditions, high redox features, maximum supportive capability, easy modulation in valence states, and enhanced electrical conductivity. In this review, we have highlighted the role of transition metal oxides as active and supported sites for electrochemical water splitting. We have proposed different perspectives for the rational design of TMO-based electrode materials, i.e., electronic state modulation, modification of the surface structure to control the aerophobicity and hydrophilicity, acceleration of the charge and mass transport, and stability of the electrocatalyst in harsh environments. We have systemically discussed the insights into the relationship among catalytic activity, certain specified challenges, research directions, and perspectives of electrocatalysis of the OER and HER.

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His current research interests include development of electrode materials for solid oxide fuel cells (SOFCs) and thermoelectric devices, and porous electrocatalysts for chemical-assisted hydrogen evolution reaction (CAHER).

Nickel-based chalcogenides have recently gained considerable interest due to their potential as efficient electrocatalysts for overall water splitting. For example, nickel sulfide (NiS x ) with suitable chemisorption energy for both oxygen- and hydrogen-containing intermediates can catalyze both half-cell reactions. Here, we report the synthesis of Ni3S2 nanostructures of ∼8 nm mean size, anchored over electrospun N-doped carbon nanofibers using microwave synthesis. Careful optimization of the process parameters enabled the structural synthesis of three different types of Ni3S2 (mostly amorphous, partially crystalline, and mostly crystalline) over carbon nanofibers. Scanning and high-resolution transmission electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the catalysts and electrochemical performance evaluated in an alkaline medium. The partially crystalline phase of Ni3S2 supported over carbon nanofibers was the best-performing catalyst for the oxygen evolution reaction (OER) due to its high electrochemically active surface area, N-doping of carbon, presence of a crystalline and amorphous mixed phase, and high conductivity of the carbon support which resulted in a low overpotential of 270 mV for the OER with a Tafel slope of only 51 mV/dec and a low charge transfer resistance of 1.08 Ω. Moreover, the catalyst was stable and yielded more than 95% Faradaic efficiency in both the oxygen evolution and hydrogen evolution reactions.