Controlled engineering of WS2 nanosheets–CdS nanoparticle heterojunction with enhanced photoelectrochemical activity

Abstract

We report the well-controlled preparation of WS2 nanosheets–CdS nanoparticle heterojunction for photoelectrochemical (PEC) water splitting application. The WS2 nanosheets with an average thickness of ~5nm and lateral dimensions of ~200nm were synthesized via liquid phase exfoliation of bulk WS2 in water/ethanol solution, followed by deposition onto ITO substrate via electrophoretic method. CdS nanoparticles were grown via facile successive ion layer absorption and reaction (SILAR) method. Using these two well-controlled methods, CdS/WS2/ITO and WS2/CdS/ITO systems were fabricated. The loading of WS2 nanosheets was controlled by the deposition condition and the heterojunction was optimized for enhanced photoelectrochemical response under simulated sunlight irradiation. The fabricated electrodes were characterized by various analytical techniques as well as PEC response and electrochemical impedance spectroscopy (EIS). Our results showed that the CdS/WS2/ITO heterojunction exhibits a stable photo-current density which is 3 times higher than the CdS/ITO electrode. In contrast, photo-current density of the WS2/CdS/ITO electrode was lower than that of the bare CdS/ITO, indicating that an appropriate energy level cascade is essential for achieving enhanced PEC response. A charge transfer mechanism was proposed to explain the observed PEC enhancement. This work indicates that the exfoliated WS2 nanosheet is a promising material for stable photoelectrochemical applications.