MXene and Their Composites for Hydrogen Evolution Reactions

As emerging two-dimensional (2D) materials, MXenes have shown promises as catalysts for hydrogen evolution reactions (HERs). MXenes benefit from the large electron density on their surfaces that can facilitate water and/or proton reduction in addition to their large active surface area with optimum hydrogen adsorption energy. Moreover, HER activity of MXenes strongly depends on their compositions, morphologies, defect density, and surface chemistries, offering an opportunity to tune their catalytic performance. Recently, several MXene compositions such as Ti2CTx, Ti3C2Tx, Mo2CTx, Mo2TiC2Tx, V2CTx, and Mo1.33CTx as well as their composites have been shown, experimentally, to be efficient HER catalysts. In addition to experimental works, computation studies have provided insights into reaction mechanisms, thermodynamic stability, proton adsorption free energy, and the resulting HER performances. This chapter summarizes and critically analyzes recent developments in MXenes as HER catalysts from both experimental and theoretical standpoints. The chapter begins with introducing criteria and material requirements for HER catalysts, followed by an introduction to MXenes structures and properties related to HERs. Then theoretical calculation methodologies focusing on HER activities of various MXenes are introduced. Finally, experimental results of MXenes and their composites as HER electro- and photocatalysts are presented together with the related computational calculations. Throughout the chapter, we highlight the advantages of MXenes being two-dimensional platforms with the opportunities to tune their properties and HER performances by manipulating their chemical compositions, including transition metals, surface terminations, and composite formation.