Two-dimensional ReSe2 has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), but its catalytic activity needs to be further improved. Herein, we synthesized Re1–x Mo x Se2 alloy nanosheets with the whole range of x (0–100%) using a hydrothermal reaction. The phase evolved in the order of 1T″ (triclinic) → 1T′ (monoclinic) → 2H (hexagonal) upon increasing x. In the nanosheets with x = 10%, the substitutional Mo atoms tended to aggregate in the 1T″ ReSe2 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 H2SO4), with a current of 10 mA cm–2 at an overpotential of 77 mV (vs RHE) and a Tafel slope of 42 mV dec–1. First-principles calculations of the three phases (1T″, 2H, and 1T′) predicted a phase transition of 1T″-2H at x ≈ 65% as well as the production of a 1T′ phase along the composition tuning, which are consistent with the experiments. At x = 12.5%, two Mo atoms prefer to form a pair along the Re4 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.

Two-dimensional GeP nanosheets were synthesized to probe the thickness-dependent band gap and electrical properties, which were supported by first-principles calculations that predicted the band gap of monolayers to be 2.3 eV.

2D MoS2 nanostructures have recently attracted considerable attention because of their outstanding electrocatalytic properties. The synthesis of unique Co–Ru–MoS2 hybrid nanosheets with excellent catalytic activity toward overall water splitting in alkaline solution is reported. 1T′ phase MoS2 nanosheets are doped homogeneously with Co atoms and decorated with Ru nanoparticles. The catalytic performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is characterized by low overpotentials of 52 and 308 mV at 10 mA cm−2 and Tafel slopes of 55 and 50 mV decade−1 in 1.0 m KOH, respectively. Analysis of X‐ray photoelectron and absorption spectra of the catalysts show that the MoS2 well retained its metallic 1T′ phase, which guarantees good electrical conductivity during the reaction. The Gibbs free energy calculation for the reaction pathway in alkaline electrolyte confirms that the Ru nanoparticles on the Co‐doped MoS2 greatly enhance the HER activity. Water adsorption and dissociation take place favorably on the Ru, and the doped Co further catalyzes HER by making the reaction intermediates more favorable. The high OER performance is attributed to the catalytically active RuO2 nanoparticles that are produced via oxidation of Ru nanoparticles.