Anisotropic alloying of Re1-xMoxS2 nanosheets to boost the electrochemical hydrogen evolution reaction

Two-dimensional transition metal dichalcogenides have recently attracted much attention as excellent electrocatalysts for the hydrogen evolution reaction (HER). Herein, Re1-xMoxS2 alloy nanosheets in the entire composition range were synthesized using a hydrothermal reaction. High-resolution scanning transmission electron microscopy revealed anisotropic atomic distribution of the alloy phase, in which the Re and Mo atoms tend to segregate along a crystallographic axis. The phase transition occurs from the triclinic phase (1T '') ReS2 to the monoclinic phase (1T ') MoS2 at 50% Mo. Re0.5Mo0.5S2 exhibited the highest electrocatalytic HER activity, which was characterized by a current density of 10 mA cm(-2) at an overpotential of 98 mV (vs. RHE) and a Tafel slope of 54 mV dec(-1) in 0.5 M H2SO4. Extensive calculations using spin-polarized density functional theory showed that the most energetically stable configuration consists of separated MoS2 and ReS2 domains along the b axis, and the 1T '' -> 1T ' phase transition at 50% Mo, which agrees with the experimental results. The Gibbs free energy along the HER pathway indicates that the best performance at Mo 50% is due to the formation of S-H or Mo-H (at S vacancies) on the MoS2 domain.