Phase-Transition Mo1-xVxSe2 Alloy Nanosheets with Rich V-Se Vacancies and Their Enhanced Catalytic Performance of Hydrogen Evolution Reaction

Alloys of transition-metal dichalcogenide can display distinctive phase evolution because of their two-dimensional structures. Herein, we report the colloidal synthesis of Mo1-xVxSe2 alloy nanosheets with full composition tuning. Alloying led to a phase transition at x = 0.7 from the semiconducting 2H phase MoSe2 to the metallic 1T phase VSe2. It also produced significant V and Se vacancies, which became the richest in the 2H phase at x = 0.3-0.5. Extensive spin-polarized density functional theory calculations consistently predicted the 2H-1T phase transition at x = 0.7, in agreement with the experimental results. The vacancy formation energy also supports the formation of V and Se vacancies. Alloying in the 2H phase enhanced the electrocatalytic performance toward hydrogen evolution reaction (HER) at x = 0.3 (in 0.5 M H2SO4) or 0.4 (in 1 M KOH). The Gibbs free energy along the HER pathway indicates that this maximum performance is due to the highest concentration of active V and Se vacancy sites.

Automated summary

In this study, Mo1-xVxSe2 alloy nanosheets were synthesized using a colloidal method to tune composition and induce phase transitions. The phase transition from the semiconducting MoSe2 to metallic VSe2 was observed at x = 0.7, along with the formation of significant V and Se vacancies. Density functional theory calculations confirmed the experimental results and showed enhanced electrocatalytic performance for hydrogen evolution reaction at specific compositions due to the presence of active vacancy sites.