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 WOx nanowhisker stems, which offer a large surface area and efficient charge transport path. The assembly of CdSe/CdS narrow bandgap cosensitizers on hierarchical ZnO/WOx nanostructures is shown to enhance light harvesting in the visible light region. The cosensitized ZnO/WOx 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/WOx 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/cm2 at −0.5 V (vs SCE) under 1.5 AM irradiation for hydrogen generation.