pH-Tuning a Solar Redox Flow Battery for Integrated Energy Conversion and Storage

The intermittent nature of renewable energy sources such as solar and wind requires an energy storage method for future viability. Integrated solar energy conversion and storage devices such as solar redox flow batteries offer an innovative approach to this problem. Herein, we demonstrate electrolyte pH to be a valuable and tunable parameter for optimization of aqueous solar redox flow batteries. This can be accomplished by utilizing a pH-dependent redox anolyte and pH-independent catholyte to effectively tune the cell voltage by varying the operating pH, which allows direct integration of a dye-sensitized photoelectrode. A quinone–iodine redox flow battery can achieve high columbic efficiency over ∼90% for 50 cycles under mild pH conditions (pH ∼ 2–8). Furthermore, a pH-tunable solar redox flow battery can be charged using only solar illumination, thus allowing for integrated energy conversion and storage within a single device