A novel approach for improving photoelectrochemical water splitting performance of ZnO-CdS photoanodes: Unveiling the effect of surface roughness of ZnO nanorods on distribution of CdS nanoparticles

Abstract

Zinc oxide (ZnO) nanostructure has attracted great attention as an outstanding material for photoelectrochemical (PEC) water splitting devices. The surface area of ZnO plays a vital role in the distribution of narrow band gap semiconductors to maximize light absorption capability. Herein, ZnO nanorods with smooth surface (ZnO-P) were fabricated on the surface of fluorine doped tin oxide (FTO) by a hydrothermal process. Optimum deposition of cadmium sulfide (CdS) nanoparticles was obtained on the surface of ZnO-P to obtain the best PEC water splitting performance in ZnO-P/CdSx heterojunction. Employing sulfidation treatment, calcination, and hydrothermal process on ZnO-P resulted in the synthesis of branched ZnO nanorods (ZnO-B) with higher crystallinity, larger surface roughness, and lower concentration of oxygen vacancy sites compared to ZnO-P nanorods. Higher surface area of ZnO-B nanorods provided larger nucleation sites for loading of CdS nanoparticles, leading to a unique distribution of CdS nanoparticles with a uniform size. Optimum deposition of CdS on the ZnO-B sample provided a novel photoanode (ZnO-B/CdS30) with larger light absorption than the ZnO-P/CdS30 sample. Furthermore, the ZnO-B/CdS30 photoanode benefited from extensive semiconductor/solution interfaces for efficient transfer of collected photogenerated holes from the surface of CdS nanoparticles to the solution.