For the EECC scheme, the shift in ∆G • CC is plotted against the shift in E • EE for the F-substituted AQ series (Figure (c)) and a range of mono-substituted AQ derivatives 4(d)). A similar trade-off between the thermodynamics of cathodic activation and nucleophilic addition of CO 2 is seen for the EECC scheme with a larger gradient that that of the EEC scheme. It would therefore still be very difficult to fine-tune the electron density of AQ using these functional groups to favour both the electron transfer and chemical steps.