Electrocatalysts for hydrogen evolution reaction

In addition to the historical importance of water electrolysis, hydrogen evolution reaction (HER) is the heart of various energy storage and conversation systems in the future of renewable energy. The HER electrocatalysis can be well conducted by Pt with a low overpotential close to zero and a Tafel slope around 30 mV dec^?1; however, the practical developments to satisfy the growing demands require cheaper electrocatalysts. Noble metals are still the promising candidates, though further improvement is needed to enhance the HER efficiency in performance. Three categories of non-noble metal electrocatalysts are under heavy investigations: (i) alloys, (ii) transition metal compounds, and (iii) carbonaceous nanomaterials. The most practical option, based on the electrocatalytic activity and electrochemical stability, seems to be the transition metal compounds MX (where M is Mo, W, Ni, Co, etc. and X is S, Se, P, C, N, etc.). Among these compounds, some like MoS₂ and WC can display metallic properties and a Pt-like electrocatalytic activity, but they still need serious modifications for the practical performance. In general, similar strategies have been employed to improve the HER performance of all of these materials such as doping (both cation and anion), controlling the crystallinity and amorphism, and increasing the active sites by changing the morphology. Another important issue is the chemical and physical structure of the carbon-based catalyst support, as carbon is normally a vital component even for the Pt electrocatalysts.