Recent advances in Mo-based electrocatalysts toward the hydrogen evolution reaction and the hydrogen oxidation reaction

As one of the clean and renewable energy sources, hydrogen has been widely regarded as the solution to the fossil crisis in the future. The highly efficient hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) via electrocatalysts in alkaline/acid medium are crucial for efficient hydrogen generation and energy conversion with green H-2 as the medium. Thus, the development of highly active, environmentally friendly, low cost and stable electrocatalysts is very important for the safe and efficient application of H-2. Compared with noble-metal materials, Mo-based electrocatalysts have attracted a lot of attention due to their high HER/HOR activities and cost-effectiveness. However, the development of Mo-based electrocatalysts is still in the early stage. In this review, the mechanisms of the HER/HOR in alkaline/acid media are firstly summarized in detail. Subsequently, the recent development and superiorities of Mo-based electrocatalysts in the field are documented with a particular focus. Finally, the challenges and future directions in the emerging field of Mo-based electrocatalysts for the HER/HOR are also presented.