Electrochemical CO2 Fixation and Release Cycle Featuring a Trinuclear Zinc Complex for Direct Air Capture.

CO2 capture technology can mitigate greenhouse gas emissions and global warming. CO2 capture driven by electrochemical reactions is attractive because the operation is carried out at normal temperature and pressure and involves a simple input system using electrical energy. Although promising metal complexes with high CO2 fixation performance have been reported, there are few studies on systems that combine electrochemical reactions and metal complexes. Here, we demonstrated stable CO2 fixation-release cycles using an electrochemical system with trinuclear Zn(II) complex (Zn3L) as the CO2 fixative and an ionic liquid as a supporting electrolyte for the stable operation. This system showed a faster CO2 fixation rate than that of an aqueous alkaline solution at the same concentration. Continuous release and refixation of CO2 were achieved by decomposition and reconstruction of the complex structure induced by H+ and OH- supplied from a bipolar membrane equipped in the electrolytic cell. The CO2 fixation-release cycle was demonstrated even for dilute CO2 (450 ppm) in air, where the CO2 capture rate reached approximately 46 % of CO2 contained in the air under an air flow condition of 200 mL ⋅ min-1. This case, combining electrochemical drive and metal complexes, will provide a new option for CO2 capture technology.