Hexagonal RuSe2 Nanosheets for Highly Efficient Hydrogen Evolution Electrocatalysis.

Layered transition metal dichalcogenide (TMD) nanomaterials have emerged as promising alternatives to platinum (Pt) for the hydrogen evolution reaction (HER). However, the family of layered TMDs is mainly limited to Group IV-VII transition metals, while the synthesis of other group metals based layered TMDs still remains a challenge. Herein, for the first time, we demonstrate by atomic-resolution transmission electron microscopy that hexagonal RuSe2 (h-RuSe2) nanosheets with the mixture of 2H and 1T phases, a new member of layered TMDs family, can be obtained by a facile bottom-up colloidal synthetic approach. The obtained h-RuSe2, which can be transferred into the thermodynamically favorable phase of cubic RuSe2 (c-RuSe2) only after annealing at 600 °C, exhibits Pt-like HER performance, with a 5-fold turnover frequency enhancement compared to the c-RuSe2 under alkaline media. Experimental results and density functional theory (DFT) calculations reveal that the enhanced adsorption free energies of H2O (ΔGH2O*), optimized adsorption free energies of H (ΔGH*) and increased conductivity of h-RuSe2 contribute to its superior HER activity.