Si/ZnO core–shell nanowire arrays for photoelectrochemical water splitting

n-Type Si nanowire (NW) arrays coated with a thin layer of ZnO were fabricated via a two-step route combined with metal-assisted chemical etching and sol-gel processes. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction were utilized to characterize the core/shell structure. The obtained Si/ZnO core/shell NW arrays exhibit about 8% optical reflectance in visible region, implying good optical absorption. Water splitting performance of Si/ZnO NW arrays was studied. The photoconversion efficiency for Si/ZnO NW arrays reaches 0.38% upon exposure to the illumination with a light intensity of 10 mW/cm2, which is higher than those of the planar bilayer structure of Si/ZnO (0.19%) and the pure planar ZnO (0.09%). The relationship between the illumination intensity and the photoconversion efficiency of Si/ZnO NW arrays was also discussed.