BiVO4 Photoelectrodes for Use in Solar Water Splitting

Many recent efforts have focused on the development of n-type semiconductors that can serve as efficient photoanodes for solar water oxidation.  Desirable photoanodes should have a small bandgap to utilize a significant portion of visible light, and a valence band (VB) edge that is positive enough to provide sufficient overpotential for the water oxidation reaction.  The position of the conduction band (CB) edge or the flatband potential of the photoanode is also important because it determines the potential of the photoexcited electrons that will be used for the cathode reaction (i.e., water reduction).  If these electrons do not have sufficient overpotential to reduce water, an external bias needs to be provided, effectively reducing the cell efficiency.  Bismuth vanadate (BiVO₄) has recently emerged as a promising material for use as a photoanode in water splitting photoelectrochemical cells.  It is because it absorbs a substantial portion of the visible spectrum (bandgap energy, ca. 2.4 eV) and has a favorable conduction band (CB) edge position very near the thermodynamic H₂ evolution potential.  Significant advancement in the understanding and construction of efficient BiVO₄-based photoanode systems has been made within a short period of time owing to various newly developed ideas and approaches.  In this presentation, we will discuss our recent efforts in improving the photoelectrochemical properties of BiVO₄ photoanodes, which include an enhancement in photon absorption and charge transport properties.  These efforts resulted in an applied bias photon-to-current efficiency (ABPE) for water splitting higher than 2% using all oxide-based electrodes.