High performance of TiO₂/Cu_xO photoelectrodes for regenerative solar energy storage in a vanadium photoelectrochemical cell

Photocatalysts for harvesting solar energy to either electricity or chemical fuels have attracted much attention recently, but they have big obstacles such as wide bandgaps and rapid charge recombinations to overcome for final applications. In this study, we investigates a useful method to utilize vanadium redox pairs, which are commonly applied for vanadium redox flow batteries, to diminish charge recombinations and thus to enhance photocurrent response in regenerative solar energy storage. The results reveal significant improvements in photocurrent density by forming cuprous and cupric oxides in TiO₂/Cu_xO electrodes under solar AM 1.5 illuminations using the vanadium photoelectrochemical storage cell at 0.025 mol L^-1 of vanadium redox species in the acid electrolytes. In addition, the stabilized photocurrent density of the copper content optimized TiO₂/Cu_xO electrodes is almost tripled from the TiO₂ only electrode because the charge recombinations can be mitigated with the content optimized TiO₂/Cu_xO electrodes. Therefore, the optimized TiO₂/Cu_xO electrode results in the highest charge storing performance in the catholyte chamber, and the roles of vanadium redox species are also clearly demonstrated.