Photo-Ionic Cells: Two Solutions to Store Solar Energy and Generate Electricity on Demand

A solar energy conversion concept based on the photoinduced separation of a pair of redox species in a biphasic liquid cell is presented. The redox pair is subsequently discharged in an electrochemical flow cell to generate electricity. To illustrate this generic concept, we have revisited the thionine/cobalt EDTA system where, upon light excitation, the excited thionine dye is quenched in the aqueous solution by the [Co­(II)­EDTA]^2– complex to form both [Co­(III)­EDTA]⁻ and reduced thionine, namely leucothionine, that partitions to the organic phase. As a result, solar energy is converted to a redox pair, leucothionine/[Co­(III)­EDTA]⁻. The two immiscible liquid phases are separated, and the redox energy is stored in the respective electrolyte solutions. These two solutions can then be electrochemically discharged in a flow cell to generate electricity on demand. The electrode reactions involved are the reoxidation of leucothionine to thionine in the organic solvent and the reduction of the Co­(III) complex in water.