Multiple Effects Induced by Mo6+ Doping in BiVO4 Photoanodes

Mo6+ doping increases the photoelectrochemical performance of BiVO4 photoanodes in water oxidation. Herein, the underlying mechanisms is elucidated through a systematic structural, morphological, and photoelectrochemical investigation on photoelectrodes of pure and Mo6+ doped BiVO4 prepared by a novel multistep spin-coating deposition approach, leading to multilayer flat films with high optical transparency. Transient absorption spectroscopy in the nano- to microsecond time scale reveals a longer lifetime of photogenerated holes in the doped films. Besides confirming that Mo6+ ions improve the electron transport in the material bulk, impedance spectroscopy also reveals the crucial role of the dopant on the surface properties of BiVO4 photoanodes. The presence of intrabandgap states, acting as traps of photogenerated charge carriers in pure BiVO4, is detected through the build-up of the interfacial surface state capacitance. The limited activity of pure BiVO4 in water oxidation is largely improved upon 3 at% Mo6+ incorporation, ensuring a more efficient charge carrier transport with respect to pure BiVO4, together with the beneficial passivation of its trap surface states.