Electrocatalytic water splitting to hydrogen (H2) is an ideal approach to generate renewable energy. One of the major drawbacks is the tightly coupled kinetically sluggish and energy inefficient anodic oxygen evolution reaction (OER) with hydrogen forming a cathodic half-cell reaction which leads to a significant reduction in overall cell efficiency. In this context, before reviewing the literature, we have first briefly analyzed the energetics of overall water splitting, problems, and challenges under different pH conditions which can be useful for the further understanding of the process. Replacement of the anodic OER by a thermodynamically favorable substrate oxidation offers flexibility, value addition, and energy efficiency in the case of hybrid or assisted water electrolysis to afford hydrogen. Recent progress in terms of sacrificial oxidants in hybrid water electrolysis are discussed in this context, where the sacrificial oxidants are so chosen that the oxidation often leads to its value addition. Also here, we have offered insights into interface designing in heterostructures by modulating chemical and electronic environments for the enhancement of the intrinsic catalytic activity and stability. The effect of incorporation of such materials into the overall water splitting reaction, their catalytic active sites, and interactions with intermediates are thoroughly explored. This review can be a good complement for better understanding of the elucidation of the interface role in hybrid water electrolysis for future commercial applications.

Electrocatalytic hydrogen (H2) generation became a prime research topic in the last decade since H2 is a clean source of energy and combustion as it does not produce CO2. Conventional electrolysis is associated with the formation of oxygen via the oxygen evolution reaction (OER) at the anode. This kinetically sluggish multistep four-electron transfer OER process needs additional energy to split water. Substitution of the OER process by the easily oxidizable substrate oxidation reaction could be a lucrative way to get H2 at a much lower potential budget than the conventional one. Biomass-derived chemicals like bioalcohols (methanol, ethanol, glycerol (GlyOH), butanol, 5-hydroxymethylfurfural (HMF) obtained from hydrolysis or fermentation of biomass) could be easily oxidized to value-added commodity chemicals like formic acid, acetic acid, propionic acid, acetone, and 2,5-furandicarboxylic acid (FDCA) at the anode part of the electrolyzer. Thermodynamically, the bond dissociation energy of “C–H” and “O–H” bonds of these organic substrates is much lower than the “O–H” bond dissociation energy of water. So, to make the overall substrate oxidation reaction kinetically more feasible, an efficient electrocatalyst needs to be developed. Herein, we present a noble metal-free Ni1–x Co x Se electrocatalyst for efficient and selective conversion of alcohol molecules to value-added commodity chemicals. Particularly, Ni0.9Co0.1Se composition showed the best substrate oxidation activity compared to pristine NiSe, CoSe, and other state-of-the-art catalysts. The substrate scope is verified with methanol, ethanol, isopropanol, ethylene glycol (EGOH), GlyOH, and malic acid. Both experimental and theoretical understanding (DFT) established the fact that Co doping manipulates the NiII → NiIII OOH redox chemistry and accelerates the formation of active hypervalent Ni(Co)OOH species at a lower potential budget than NiOOH. For all catalyses, Ni0.9Co0.1Se shows superior activity with 80–100% product conversion along with a Faradaic yield of 80–95%.

No abstract