BiVO4 Photoanodes in Combination with Heterogeneous Oxygen Evolution Catalysts for Solar Water-Splitting
- Nate Lewis, George L. Argyros Professor of Chemistry, California Institute of Technology
- Bruce Brunschwig, Director of the Molecular Materials Research Center, California Institute of Technology
- Josh Spurgeon, Staff Scientist at the Joint Center for Artificial Photosynthesis, California Institute of Technology
There is an increasing effort in the semiconductor photocatalysis field to store solar energy by efficiently splitting water into oxygen and hydrogen fuel using sunlight. However, no semiconductor material that clearly meets all the criteria for an effective photoanode has yet been discovered. BiVO4 is a promising candidate for the photoanode because it is an n-type semiconductor that has a good valence band edge alignment for water oxidation and a relatively low band gap of 2.4 eV. It is oxidatively stable, and is composed of earth-abundant elements. Due to the poor catalytic ability of BiVO4, a sacrificial reagent or a catalyst is required to oxidize water. Thin films of BiVO4 were prepared by electrodeposition on conductive FTO-covered glass substrates. We sought to improve the current-voltage performance and faradaic efficiency of oxygen production of BiVO4 by using various methods to incorporate oxygen evolution catalysts. Increased stability of BiVO4 under basic condition, in which most earth abundant catalysts behave more actively, was also sought by decorating the BiVO4 film with oxygen evolution catalysts, including IrO2, RuO2, Co3O4, and NiFeOx. BiVO4 is known to give much higher photocurrent under back-side illumination than front-side illumination. We investigated an optimal thickness of the material that maximizes the photoelectrochemical properties under front-side illumination for application as the top cell in a tandem configuration.