To assess the impact of oxygen, the CV of unsubstituted AQ under O 2 in DMSO was measured, with the changes in the data supporting some reactivity of AQ with O 2 (Figure ). To avoid the possibility of parasitic reactions after cathodic activation, intuitively one would select a quinone with EWGs and a more positive reduction potential, assuming that the reduction potential is both a measure of how likely reduced quinone get re-oxidised by oxygen or chemically react with an electrochemically reduced oxygen species. However, as we have shown through DFT, the reactivity of the quinone to CO 2 is weaker (main implication of the trade-off) and through CV experiments, the form of the CV is changed with a smaller positive shift of the second reduction peak. Therefore, just naively adding EWGs not only reduces CO 2 capture ability but also does not necessarily solve the O 2 reactivity problem. To this end, we provide some rough guidelines for fine-tuning to optimise the efficiency of quinone-mediated electrochemical CO 2 capture in DMSO: