Tailoring the oxygen vacancies and electronic structures of the hex-WO3 (1 0 0) crystal plane with heteroatoms for enhanced hydrogen evolution performance

Abstract

Due to the difficulty of developing noble materials for large-scale applications, transition metal oxide materials have become popular alternatives for the hydrogen evolution reaction. However, compared to commercial Pt/C, poor conductivity and hydrogen evolution activity are common for transition metal oxides, including WO3-x-based semiconductors, so it is therefore necessary to ameliorate the electrode self-properties to be suitable for H2 production. Here, different ratios of S2- and Ni2+ salts are introduced into hexagonal WO3 and Ni0.4WO3-xSx is prepared successfully after oxygen vacancies and WOS and Ni–W-O bonds are formed on the surface of the Ni0.4WO3-xSx nanorods. The X-ray photoelectron, Raman and electrochemical impedance spectroscopy results show that the incorporation of Ni and S atoms can increase the number of oxygen vacancies and the conductivity for hydrogen evolution, simultaneously demonstrating that the WOS and NiWO bonds are the main active sites of the Ni0.4WO3-xSx nanorods. Density functional theory calculations further indicate that the ΔGH* of NiWO3-xSx is closer to 20 % commercial Pt/C. The Tafel slope reduces to 87.3 mV/dec when approaching the Volmer–Heyrovsky kinetic mechanism reaction. Finally, the onset potential is 53 mV. The overpotential is 173 mV at 10 mA/cm2, which is 68 % lower compared to hexagonal WO3.