Another interesting observation was the appearance of a new singlet peak in the 1 H NMR spectrum of the ferricyanide catholyte after the addition of 2,6-DHAQ (Figure , asterisk), which we assign as formamide. This assignment was based on the chemical shift difference of this peak relative to water and control experiments in samples where a formamide standard was intentionally added (Methods S6, Figure ). Notably, formamide was also observed in the 1 H NMR spectra of freshly prepared 2,6-DHAQ anolyte and ferrocyanide catholytes (Figure ), and in aged samples of ferricyanide catholytes (Figure ). The key new observation from the on-line simulated-crossover experiment is that the addition of 2,6-DHAQ appeared to initiate the formation of formamide in the catholyte (Figure ). It is important to note that, although 2,6-DHAQ anolytes contain some formamide impurities (Figure ), the rate at which it appeared in the system was significantly slower than that of 2,6-DHAQ mixing (Figure ). This shows that formamide is being formed by a chemical reaction within the system, indicating a possible relationship between the formation of formamide and the loss of ferricyanide. As cyanide is the only nitrogen-containing component in the catholyte and anolyte, it is most likely being formed as an intermediate product of cyanide decomposition. To gain further insight into the mechanism of these crossover-driven side reactions, the same on-line 1 H NMR simulated-crossover experiment was carried out with another common AORFB anolyte, anthraquinone-2,7-disulfonic acid (2,7-AQDS) in 1 M KOH. Excitingly, though an initial drop in ferricyanide was observed, the addition of 2,7-AQDS did not result in a significant increase in ferricyanide loss rate (Figure ). Similarly, 2,7-AQDS appeared to be much more stable in ferricyanide and was lost at a rate of (8.8 ± 0.6) x 10 -6 mol dm -3 h -1 , which is nearly four times slower than 2,6-DHAQ (Figure ). This important result shows that the crossover-driven side reactions reported herein can be mitigated by changing the anolyte structure.