Multiple Effects Induced by Mo ⁶⁺ Doping in BiVO ₄ Photoanodes

Mo 6+ doping increases the photoelectrochemical performance of BiVO 4 photoanodes in water oxidation. Herein, the underlying mechanisms is elucidated through a systematic structural, morphological, and photoelectrochemical investigation on photoelectrodes of pure and Mo 6+ doped BiVO 4 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 Mo 6+ ions improve the electron transport in the material bulk, impedance spectroscopy also reveals the crucial role of the dopant on the surface properties of BiVO 4 photoanodes. The presence of intra‐bandgap states, acting as traps of photogenerated charge carriers in pure BiVO 4 , is detected through the build‐up of the interfacial surface state capacitance. The limited activity of pure BiVO 4 in water oxidation is largely improved upon 3 at% Mo 6+ incorporation, ensuring a more efficient charge carrier transport with respect to pure BiVO 4 , together with the beneficial passivation of its trap surface states.