Efficient Solar Energy Storage Using A TiO2/WO3 Tandem Photoelectrode in An All-vanadium Photoelectrochemical Cell

Abstract

Using a photoelectrochemical (PEC) cell to convert solar energy to either electricity or chemical fuels has attracted much attention in the last four decades. However, two major obstacles that hinder wide-spread application of this approach lie in the relatively wide bandgap of chemically stable semiconducotrs, e.g., TiO2, and the rapid recombination of photogenerated charge carriers once they are generated within the semiconductors. We reported herein a method that utilized vanadium redox pairs, which are commonly used in vanadium redox-flow batteries (VRB), to mitigate charge carrier recombination and thus to improve photoresponse in regenerative solar energy storage for the first time. The results showed significant improvement in photocurrent during photo-charging of the all-vanadium PEC storage cell with the addition of a very low morlarity of vanadium redox species (0.01M) to the acid electrolytes. Additonally, the photocurrent was almost doubled even with a TiO2 electrode when two vanadium redox species were used in a full-cell configuration instead of a half-cell setup. To further enhance the light absorption, a TiO2/WO3 tandem electrode was studied and compared to the TiO2 electrode in various vanadium redox electrolytes. The tandem electrode showed higher photoresponse in all electrolytes investigated. Furthermore, the important role of vanadium redox species and WO3 have been discussed.