Abstract
Hydrogen has been considered as the cleanest renewable energy and an ideal alternative to fossil fuels. Electrocatalytic Hydrogen Evolution Reaction (HER) via water splitting also plays an indispensable role in high-efficiency energy con- version. Compared with the well-investigated acidic HER, the relatively slow kinetics and unclear mechanism of HER in alkaline environ- ments largely make the design of electrocatalysts a trial-and-error process, retarding the scalable development of efficient, sustainable hydrogen production. Furthermore, two-dimensional transition metal dichalcogenides (2D TMDs) have been demonstrated to be promising acidic/ alkaline HER catalysts in water electrolysis due to their outstanding atom-level thickness and surface-based properties. To minimise the gap between fundamentals and practical applications of alkali-active electrocatalysts, a class of 2D ultrathin nanomaterials show an infusive
potential in identifying related key descriptors and principles. In this article, a general overview based on the principles of HER is presented, especially key parameters for evaluating the activity. Next, according to the basics of HER, the controversial mechanism of the alkaline HER process is comprehensively discussed, especially the detailed comparison with the acidic HER in three aspects: proton donors, energy barriers and roles of active sites. Then, modulation strategies of 2D TMDs for HER in electrocatalysis are analysed together with the theoretical calculations, electrochemical experiments and surface modification. Finally, an overall perspective of the rational design of highly efficient electrocatalysts under alkaline solutions in water splitting system is proposed.
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