We then evaluated the thermodynamics of the chemical CO 2 capture step for our F-substituted AQ series (Figure ). For the EEC scheme, the computed Gibbs free energy change ∆G • C increases by 20 kJ mol -1 upon substitution of one to eight F atoms. Again, the effect is approximately linear (solid line in Figure ), and there is no consistent trend in position of substitution. This effect can be explained by considering the electron density available in Q 2-for bonding with CO 2 to form Q(CO 2 ) 2-. AQ-F 8 has a lower charge density on the oxygen than unsubstituted AQ in its Q 2-form and therefore has a lower affinity for binding to CO 2 . The O CO 2 bond length calculated by DFT of the Q(CO 2 ) 2-form is 1.529 Å in AQ-F 8 compared to 1.495 Å in AQ, indicating a weaker bond being formed due to more electron density being delocalised away from the oxygens in Q 2-. Similarly for the EECC scheme, increasing the number of F substitutions also leads to an approximately linear increase in the Gibbs free energy change in capturing two CO 2 ∆G • C (dashed line in Figure ). The trend line for the EECC scheme has gradient slightly larger than twice that of the EECC scheme, consistent with the second CO 2 being less thermodynamically favourable than the first (Figure ). Overall, in the context of electrochemical CO 2 capture, the chemical steps are less thermodynamically favourable as more EWGs are added, supporting a trade-off between redox potential and CO 2 affinity, as suggested by previous experimental work on functionalised benzoquinones. To explore this result experimentally, we measured the CVs of unsubstituted AQ, 1,4-F-AQ and AQ-F 8 under N 2 and under CO 2 (Figure ). For all cases, the re-duction wave positions of the first electron transfer (6) remain unchanged in the presence and absence of CO 2 . This behaviour is in line with the quinone in all cases needing to be first activated by reduction to Q -or Q 2- before capturing CO 2 , as observed in previous studies. For both AQ and 1,4-F-AQ, the second reduction wave (7) appears to shift underneath the first reduction wave, in agreement with previous work. In contrast, for AQ-F 8 a smaller shift of the second reduction wave is observed, and two redox processes can be clearly observed under CO 2 . The smaller positive shift of the second reduction peak for AQ-F 8 indicates less stabilisation of the reduced species by CO 2 than for AQ and 1,4-F-AQ, and suggests a smaller binding constant to CO 2 , as predicted by our DFT calculations. The reduction in height of the second reduction wave for AQ-F 8 is an indication of some reactivity with CO 2 , to form either Q(CO 2 ) 2- or Q(CO 2 ) 2- 2 species. Overall, these experimental results are qualitatively consistent with the predictions of our DFT calculations, providing support for the calculated trade-off between redox potential and CO 2 capture strength. A more detailed study of the detailed capture mechanisms of these molecules is beyond the scope of this work, and is under investigation in our laboratory.