Experimental and Computational Investigation of Lanthanide Ion Doping on BiVO 4 Photoanodes for Solar Water Splitting

N-type bismuth vanadate (BiVO4) has emerged as one of the most promising photoanodes for use in water-splitting photoelectrochemical cells in recent years. However, its photoelectrochemical properties may be further enhanced by optimizing its band gap and its charge-transport properties. Doping at the V5+ and O2- sites of BiVO4 has proven to be an effective strategy to alter the oxide electronic band structure and/or charge-transport properties, but the effect of doping at the Bi3+ site is not nearly as well understood. In this study, we performed a combined experimental and theoretical study of BiVO4 doped with lanthanide (Ln) elements (La, Ce, Sm, and Yb) at the Bi3+ site, and we elucidated the effect of doping on the electronic band structure and charge-transport properties of BiVO4. Furthermore, we performed density functional theory calculations to investigate the combined effect of the Ln doping and oxygen vacancies, which are intrinsic defects in BiVO4. Our results showed that for some cases, the simultaneous consideration of Ln doping and O vacancy leads to changes that cannot be obtained by the sum of the changes caused by Ln doping alone and O vacancy alone, which was critical for understanding the experimental results. The various ways that the Ln dopants modified the electronic band structure and charge-transport properties of BiVO4 demonstrated in this study can provide useful guidelines for the tuning of the composition of oxide-based photoelectrodes.