Hexagonal RuSe 2 Nanosheets for Highly Efficient Hydrogen Evolution Electrocatalysis

Layered transition metal dichalcogenide (TMD) nanomaterials are 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 layered TMDs based on metals from other groups still remains a challenge. Herein, we demonstrate by atomic-resolution transmission electron microscopy that hexagonal RuSe2 (h-RuSe2 ) nanosheets with a mixture of 2H and 1T phases can be obtained by a facile bottom-up colloidal synthetic approach. The obtained h-RuSe2 , which can be transformed into the thermodynamically favorable phase of cubic RuSe2 (c-RuSe2 ) only after annealing at 600 °C, exhibits Pt-like HER performance, with a fivefold turnover frequency enhancement compared to the c-RuSe2 in alkaline media. Experimental results and density functional theory (DFT) calculations reveal that the enhanced adsorption free energies of H2 O (ΔG H 2 O * ), optimized adsorption free energies of H (ΔGH* ), and increased conductivity of h-RuSe2 contribute to its superior HER activity.