We now explore how varying the electron density of quinones impacts electrochemical CO 2 capture through a F-substituted AQ series. F is a good candidate to be used for fine-tuning because (i) F substituents tend to show a strong negative inductive effect of an EWG that predomi-nates the positive resonance effect of an EDG, (ii) there are various ways to fluorinate AQ selectively and (iii) the small size of F minimises steric effects, whereas larger substituents can decrease the CO 2 capturing ability, as previously observed in Cl-substituted quinones. The thermodynamics governing the electron transfer and chemical steps for AQ derivatives with increasing number of F-substituents were quantified from DFT calculations. Figure shows that the computed E • EE increases from -1.54 V to -1.17 V against Fc + /Fc upon substitution of one to eight F atoms, and is generally directly proportional to the number of F substitutions made. As more electron density is withdrawn from the oxygens in the Q 2-anion, the reduced form is more delocalised and stabilised against re-oxidation. The increase in reduction potential varies slightly for different positions of substitutions for F, as seen previously in the case of other substituents. When EDGs are substituted instead, the opposite effect is seen (Figure ). Overall, increasing the number of F substitutions leads to an approximately linear increase in the reduction potentials of AQ. In the context of electrochemical CO 2 capture, the EE step ( ) is more thermodynamically favourable as electron density of quinones are tuned with increasing number of EWGs, which should impart improved stability in oxygen.