A critical review on transition metal phosphide based catalyst for electrochemical hydrogen evolution reaction: Gibbs free energy, composition, stability, and true identity of active site

The current state of global green H2 demand from water required an efficient and robust catalyst to mitigate greenhouse-gas emissions to the atmosphere. The transition metal phosphides (TMPs) based catalysts are found to be stand out an alternative to the state-of-art Pt/C catalysts for hydrogen evolution reaction (HER). However, systematic desertion is required to assess the recent development and progress towards TMPs based catalyst for HER for thoughtful knowledge to encourage the develop an efficient, robust, and durable catalyst. The current progress made to improve the efficiency, and durability of as-synthesized TMPs based catalyst for HER, include nanostructure synthesis, integration with supports materials, and hybrid structure synthesis. The realization of the individual role of each constituting element of the TMPs-based catalyst is the fundamental pillar to develop an efficient electrocatalyst. Herein, an overview is presented of recent research progress on TMPs for electrochemical HER. The review elaborated on the fundamental aspect of HER kinetics at the TMPs-based catalyst surface, the effect of composition, and pH for 3d (Fe, Co, Ni, and Cu) to higher transition metal (Mo, W, Rh, Ru, Pd, Ir, and Pt) phosphide. The current review also systematically compiled an experimental and theoretical study on HER. Furthermore, we also highlight the urgent need for pre and post-analysis to evaluate the true identity active site and the durability of the TMPs. Finally, the conclusions are drawn with future opportunities and challenges for the development of transition TMPs based.