Core-shell photoanode developed by atomic layer deposition of Bi2O3 on Si nanowires for enhanced photoelectrochemical water splitting

Core-shell nanowire (NW) arrays, which feature a vertically aligned n-type Si NW core and a p-type alpha-Bi2O3 shell, are developed as a highly efficient photoanode that is suitable for water splitting. The morphology and structure of the heterostructure were characterized by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and x-ray diffraction (XRD). The deposition of Bi2O3 nanolayers on the surface of the smooth Si NWs causes the surface of the NWs to become rough. The as-prepared core-shell NW photoelectrode has a relatively low reflectance in the visible light region, suggesting good light absorption. The core-shell NW arrays show greatly improved photoelectrochemical water-splitting performance. Photoelectrochemical stability for over 16 h under constant light illumination and fixed bias potential was achieved, illustrating the good stability of this core-shell NW photoanode. These Si/Bi2O3 core-shell NW arrays effectively combine the light absorption ability of the Si NWs and the wide energy gap and chemical stability of Bi2O3 for water splitting. This study furthers the attempts to design photoanodes from low-cost, abundant materials for applications in water splitting and photovoltaics.