A metastable hexagonal-IrSe2 with activated basal-plane selenium atoms for efficient hydrogen electrocatalysis

Developing novel layered transition metal dichalcogenides (TMDs) has gained tremendous interest due to their attractive physicochemical properties and promising applications. Herein, for the first, quasi-monolayered hexagonal -IrSe 2 ( h -IrSe 2 ) nanosheets with metastable two-dimensional structure to the thermodynamically stable orthorhombic counterpart ( o -IrSe 2 ) have been prepared via the colloidal synthesis. Atomic-resolution transmission electron microscopy and spectroscopic characterizations confirm the 1 T configuration of the as-synthesized h -IrSe 2 , constructed from Ir-Se octahedra units. The metastable h -IrSe 2 exhibits significantly enhanced performance for hydrogen evolution/oxidation reactions in alkaline media compared to o -IrSe 2 , even surpassing the metallic Ir nanoparticles. In situ Raman spectra and theoretical calculations reveal that the Se sites on the basal-plane of h -IrSe 2 are the actual active sites. The obtained quasi-monolayered lamellar morphology of h -IrSe 2 provides abundant basal-planes, thereby leading to increased effective electrochemical active area and enhanced mass activity. The activation of the basal-plane Se atoms could be attributed to the reduced local interband energy separation between the lowest empty d -band on Ir and the occupied p -band on Se, which is responsible for the optimized binding strength of the key intermediates during hydrogen electrocatalysis. • Successful synthesis of quasi-monolayered hexagonal -IrSe 2 nanosheets. • Enhanced hydrogen electrocatalytic activity of metastable hexagonal -IrSe 2 . • Se atoms on the basal plane are the active sites.