Phase-Transition Mo<sub>1–<i>x</i></sub>V<sub><i>x</i></sub>Se<sub>2</sub> Alloy Nanosheets with Rich V–Se Vacancies and Their Enhanced Catalytic Performance of Hydrogen Evolution Reaction
Ik Seon Kwon, In Hye Kwak, Tekalign Terfa Debela, Ju Yeon Kim, Seung Jo Yoo, Jin-Gyu Kim, Jeunghee Park, Hong Seok Kang
Abstract
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.