Electrocatalysts for the hydrogen evolution reaction in alkaline and neutral media. A comparative review

With interest in renewable energy sources and in the decarbonisation of industry rapidly accelerating, alkaline water electrolysis can now be regarded as a key technology enabling efficient energy conversion and storage. Since an alkaline environment is suitable for a vast range of materials with satisfactory chemical stability under operating conditions, the topic of catalysts for the alkaline route could give rise to confusion in the community. Hence, the focus of this review is on analysing the current situation in the electrocatalysis of the hydrogen evolution reaction in an alkaline and a neutral environment, presenting the main group of materials studied, and discussing their potential to achieve industrial relevance. It addresses the main limitations of common parameters used for evaluating and comparing the catalytic activity and stability of selected catalysts. Furthermore, the review provides a comprehensive comparison of catalyst activities with respect to the individual groups depending on their composition as well as to the most used cations and cation-based materials. For the sake of clarity, the comparison is also presented in graphical form. Finally, based on the literature data, fundamental material characteristics to be evaluated in the development of new catalysts for electrochemical water splitting are proposed.