Solar Redox Flow Batteries with Organic Redox Couples in Aqueous Electrolytes: A Minireview

In recent years, research in solar energy storage with photoelectrochemical cells (i.e., solar redox flow batteries: SRFBs) has resurged. This development is emerging in parallel with the growing field of research into organic redox couples intended for aqueous redox flow batteries (RFBs) in a range of different pH environments. In a solar flow battery, the dissolved electroactive molecules are charged directly from solar radiation by semiconductor photoelectrodes. The charged solution can then at a later stage be converted into electricity, and solar flow batteries are as such an approach to build integrated solar energy generation and storage devices. Research in RFBs and SRFBs has from their beginning been mutually linked by use of the same organic redox molecules in the electrolyte, such as quinones. Despite the long research history (since 1976), metallic-based, acidic SRFBs have shown only incremental development, while research in the use of organic redox pairs appears more promising. This review focuses on the historical development of the use of organic redox pairs in both RFBs and SRFBs and in particular on the mutual exchange of methods and materials between the two fields.