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 catalyze its conversion 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 cur-rent increase at the third reduction. DFT calculations show a large variety of possible CO2-bound spe-cies that can potentially match the experimental data. The binding of CO2 on BTDN is shown to be re-versible upon the oxidation of the species, especially with low concentrations of CO2. From gas chro-matography, NMR and IR experiments, certain amount of oxalate was detected after bulk electrolysis.