Phase Evolution of Re<sub>1-<i>x</i></sub>Mo<i><sub>x</sub></i>Se<sub>2</sub> Alloy Nanosheets and Their Enhanced Catalytic Activity toward Hydrogen Evolution Reaction.
basic_science · Level V
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- Record sourced from PubMed, PMID 32813497.
- Also identified by DOI 10.1021/acsnano.0c05159.
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Abstract
Two-dimensional ReSe<sub>2</sub> has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), but its catalytic activity needs to be further improved. Herein, we synthesized Re<sub>1-<i>x</i></sub>Mo<i><sub>x</sub></i>Se<sub>2</sub> alloy nanosheets with the whole range of <i>x</i> (0-100%) using a hydrothermal reaction. The phase evolved in the order of 1T″ (triclinic) → 1T' (monoclinic) → 2H (hexagonal) upon increasing <i>x</i>. In the nanosheets with <i>x</i> = 10%, the substitutional Mo atoms tended to aggregate in the 1T″ ReSe<sub>2</sub> phase with Se vacancies. The incorporation of the 1T' phase makes the alloy nanosheets more metallic than the end compositions. The 10% Mo substitution significantly enhanced the electrocatalytic performance toward HER (in 0.5 M H<sub>2</sub>SO<sub>4</sub>), with a current of 10 mA cm<sup>-2</sup> at an overpotential of 77 mV (<i>vs</i> RHE) and a Tafel slope of 42 mV dec<sup>-1</sup>. First-principles calculations of the three phases (1T″, 2H, and 1T') predicted a phase transition of 1T″-2H at <i>x</i> ≈ 65% as well as the production of a 1T' phase along the composition tuning, which are consistent with the experiments. At <i>x</i> = 12.5%, two Mo atoms prefer to form a pair along the Re<sub>4</sub> chains. Gibbs free energy along the reaction path indicates that the best HER performance of nanosheets with 10% Mo originates from the Mo atoms that form Mo-H when there are adjacent Se vacancies.