Enhanced Charge Injection and Collection of Niobium-Doped TiO₂/Gradient Tungsten-Doped BiVO₄ Nanowires for Efficient Solar Water Splitting

Extensively investigated BiVO4 photoanode for solar water splitting suffers from low product of light absorption and charge separation efficiency (ηabs × ηsep) due to the lack of high surface area supporting materials as a charge collector. Such a host|guest heterostructure is not only effective but also attractive, but it is too complicated to understand the original process of ηsep. Here, a host–guest heterostructure of Nb-doped TiO2 nanowires supporting BiVO4 nanoparticles is fabricated to investigate its visible-light charge injection efficiency (ηinj) and charge collection efficiency (ηcol). With the aid of gradient W doping in BiVO4 guest, the Nb-doped TiO2|gradient W-doped BiVO4 (N:T|g-W:B) produces ηinj = 82% and ηcol = 95% to yield a very high value for ηabs × ηsep of 55.3% at 0.6 VRHE, which is one of the highest values among these nanostructure-host|BiVO4-geust photoanodes. By being further coated with Co–Pi, the photoanode simultaneously achieves a high value of ηtrans for efficient solar water splitting.