The impact of crossover on electrolyte degradation was investigated in the 2,6-DHAQ/ferrocyanide redox flow battery using the same on-line 1 H NMR crossover detection method we developed previously (Figure , Methods S1 and S2). Both the anolyte (0.1 M 2,6-DHAQ) and catholyte (0.25 M ferrocyanide with 0.04 M ferricyanide) were prepared in 1 M KOH in D2O, and the redox flow cell was equipped with a Nafion 211 membrane. The 1 H NMR apparatus was connected to the catholyte side (Figure ) so that 2,6-DHAQ crossover and any subsequent side reactions could be observed. In our previous work, 2,6-DHAQ crossover rates were found to decrease over time when at high state of charge. One possible explanation for this was that some of the 2,6-DHAQ material was undergoing side reactions following its crossover into the catholyte. To further investigate this observation here, we applied a 1.5 V cell voltage hold to keep the battery at a high state-of-charge whilst looking for further evidence of side reactions (Methods S2).