The same crossover rate analysis was also carried out for the periods of cell rest and constantcurrent discharge. Interestingly, the crossover rates during the rest periods at higher state-of-charge were slightly elevated at lower state-of-charge (see Figure ). As Nafion is a negatively charged cation-exchange membrane, it was expected that there would be more charge-repulsion (i.e. Donnan exclusion) and hence lower crossover for 2,6-DHAQ 4-compared to 2,6-DHAQ 2-. Our results do not support this assumption, possibly indicating that the effective size and/or charge of 2,6-DHAQ 4-is smaller than that of 2,6-DHAQ 2-. Interestingly, however, this trend is lost toward the end of the cycle in Cell 2. We believe that this may be the result of quinone-ferricyanide interactions, which leads to 2,6-DHAQ precipitation from the catholyte at high state-of-charge.