Facile synthesis of stable 1T′-WSe2 for HER application

Researchers are increasingly drawn to WSe2 due to its wide-ranging applications in electronic, optoelectronic, and catalytic materials. Like other transition metal dichalcogenides, it has different polymorphs, viz., 1T, 1T′, and 2H phases. A hexagonal close-packed layer-type structure of 2H-WSe2 is well studied and possesses a semiconducting behavior. However, the literature lacks a detailed study of crystallographic structure, facile synthesis, and different physical properties of 1T′-WSe2 (or 1T-phase). In this article, we synthesized a stable flower-like 1T′-WSe2 nanosheet in a facile solvothermal process. We also tried to explore the structural details using the Rietveld refinement of the powder x-ray diffraction data. The different Raman vibrational modes and phonon calculation based on the density functional theory (DFT) were performed to understand the stability of the 1T′-WSe2 phase. The flower-like 1T′-WSe2 nanosheet shows better catalytic activity for the hydrogen evolution reaction (HER) with an onset potential of −0.21 mV and overpotential 0.47 mV in comparison with the 2H-phase of WSe2 nanosheet. The DFT calculations also support the experimental data on the HER of 1T′-WSe2, establishing the suitability of the 1T′-phase for HER activity with the lowest value of the change in Gibbs free energy of hydrogen adsorption, ΔGH = 0.43 eV, for the monolayer.