Highly Efficient Photoelectrochemical Hydrogen Generation Using Hierarchical ZnO/WOx Nanowires Cosensitized with CdSe/CdS

A photoelectrochemical device with a novel hierarchical heterostructure coupled with narrow bandgap semiconductors is demonstrated for efficient hydrogen generation via water splitting. The heterostructures consist of ZnO nanowire branches grown on WO x nanowhisker stems, which offer a large surface area and efficient charge transport path. The assembly of CdSe/CdS narrow bandgap cosensitizers on hierarchical ZnO/WO x nanostructures is shown to enhance light harvesting in the visible light region. The cosensitized ZnO/WO x heterostructures demonstrate efficient light absorption up to a wavelength of 800 nm as well as enhanced photoelectrochemical properties when used as photoanodes. Furthermore, CdSe/CdS cosensitized ZnO/WO x has a type II cascade band structure, resulting in efficient charge transport, which was confirmed by open circuit voltage decay measurements. Our photoelectrochemical system produced a high photocurrent density of 11 mA/cm 2 at −0.5 V (vs SCE) under 1.5 AM irradiation for hydrogen generation.