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Novel catalytic materials are under investigation to find convincing energy alternatives. In this context, transition metal selenides (TMSes) are found to be feasible, ecofriendly, and effective electrocatalysts with futuristic characteristics. A deep and comprehensive investigation on metal selenides for energy conversion and storage application is summarized in this review article. Different methods such as hydrothermal, solvothermal, coprecipitation, hot injection, successive ionic layer adsorption reaction, polyol, and others can be used for the synthesis of metal selenides based electrocatalysts, with different morphologies and compositions. The morphology of metal selenides is strongly controlled by factors such as reaction time, temperature, pH of the reaction medium, and surfactant. The electrochemical applications of metal selenides are governed by morphology, active spots for reaction, surface engineering, and confinement. It is concluded that TMSes deliver high performance with large surface area, which is possible due to their porous or 3D morphology. The TMSes with multimetal or with doping metal/nonmetals perform better compared to single atoms. It is concluded that the reaction mechanism of hydrogen evolution reaction and oxygen evolution reaction is a primary tool to better understand the system to develop more efficient catalysts for practical application.

The advancement of spotless hydrogen energy generation is being accelerated by the advancement in nonprecious electrocatalysts for effective hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. In this review, the main focus is given to the most significant innovations in the surface topography, morphological shape, size distribution, and electrocatalytic functionality of highly engineered molybdenum nitride catalysts, equal to or even better than state-of-the-art electrocatalyst for HER and OER. Different morphological or interfacial engineering techniques, such as in situ electrospinning, topochemical methods, and classic chemical methods for synthesizing nonprecious molybdenum nitride electrocatalysts, are extensively covered. Molybdenum nitrides are discovered the excellent electrocatalyst, and the factors that can improve its electrocatalytic properties, such as morphological tuning, controlled geometrical composition, pH effect, hybrid and electronic structures, the effect of temperature, and effects of active sites, are comprehensively discussed.

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