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.