Electrochemical CO2 Capture, Release, and Reduction by a Benzothiadiazole Molecule with Multiple Redox States.

Using small organic molecular redox carriers to reversibly capture CO2 and convert it to carbon-based chemicals is a promising approach to mitigate the ongoing climate crisis. 2,1,3-benzothiadiazole (BT) is an interesting unit due to its proven interaction with CO2 upon reduction and the ease of tuning its structure. In this work, by introducing two CN in BT, the molecule 2,1,3-benzothiadiazole-4,7-dicarbonitrile (BTDN) has multiple reduced states as compared to BT and is found to interact with CO2 at multiple reduced states. The work is carried out with a combination of (spectro-)electrochemical and computational studies. Cyclic voltammetry experiments in the presence of CO2 show a clear interaction between BTDN and CO2 upon the second reduction of BTDN and a large current increase at the third reduction. Density functional theory calculations prove a large variety of possible CO2-bound species that can match the experimental data. The binding of CO2 on BTDN is found to be reversible upon the oxidation of the species, especially with low concentrations of CO2. From NMR and IR experiments, certain amount of reduced product - oxalate is detected after bulk electrolysis at the third reduction potential in the presence of CO2, showing the potential toward electrocatalysis after structural tuning and systematical optimization.