Guideline for synthesis and surface chemistry characterization of 2D Mo/Ti solid solutions based MXene. Application to hydrogen evolution reaction in alkaline media

2D MXenes have gained an ever-increasing attention in various application fields owing to the combination of their layered structure with their excellent physico-chemical properties. MXene properties can be strongly tuned by modifying the M element in the Mn+1XnTx structure. Among them, Mo-based MXenes are beginning to be successfully explored in many areas. However, few studies dealt with the synthesis and characterization of the (Mo,Ti)n+1CnTx solid solutions. The aim is to understand their complex chemistry in terms of structure, microstructure and surface chemical composition and to compare them with those of mono-metallic Mo2CTx and Ti3C2Tx MXenes as well as parent MAX phases. Then, the potential of these materials as HER (hydrogen evolution reaction) catalysts is determined in alkaline medium, never done so far, and their activity is correlated with their surface chemistry. It is particularly shown that Mo2Ti2C3Tx MXenes are a credible alternative to Mo2CTx MXenes since the surface properties of both MXenes are similar while their composition is quite different. Indeed, the (Mo,Ti)n+1CnTx MXenes require lower temperatures and shorter time for the synthesis than for Mo2CTx MXenes, a great advantage from an industrial point of view. Finally, this study aims at providing a roadmap to carry out the synthesis and characterization of (Mo,Ti)n+1CnTx MXenes.