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.