Novel aqueous flow battery using CO2 redox with a bifunctional homogeneous Ir catalyst

To suppress CO2 emissions, technologies that incorporate CO2 capture, utilization, and storage are being actively developed. Particularly, batteries using CO2 redox reactions are one of the most promising systems that combine energy conversion and storage. However, the stoichiometric reactions of CO2 and metal restrict the CO2 storage capacity of previously proposed systems. Applying catalyst-mediated CO2 redox is expected to provide flexible control of the CO2 storage capacity without dependence on the metal content. Herein, we report novel aqueous flow battery using CO2–formate redox with a bifunctional homogeneous Ir catalyst. Using of an Ir catalyst bearing a 4-hydroxy-N-methylpicolinamidate ligand was demonstrated for 50 cycles, with a maximum discharge capacity of 1.5 Ah L-1, capacity decay of 0.20% cycle-1, and total turnover number of 3,500. Furthermore, as the design concept, the CO2 storage capacity of the catalyst-based flow battery was improved more than 1000 times compared to the previously proposed system.