Extended Data Fig. 4: DHAQ concentration tracking.
a, Cycling of battery composed of 5 mL 100 mM DHAQ2− in the negolyte and 20 mL of a mixture of 100 mM K4[Fe(CN)6] and 50 mM K3[Fe(CN)6] in the posolyte. Galvanostatic cycling at ±50 mA/cm2 with potential holds at 1.0 V and 1.5 V and current cutoff of ±1 mA/cm2 during normal cycles. Three electrochemical oxidation treatments before an aliquot was removed from negolyte reservoir on day 10 for concentration measurement. b, Cyclic voltammograms of 20 mM DHAQ2− in 1 M KOH on glassy carbon working electrode. Pristine DHAQ2− electrolyte measured before and after dilution by 10% to verify resolution of measurement. Cycled DHAQ2− data refers to an aliquot removed from negolyte in part a, after ~25% capacity had been lost. No change in peak current suggests DHAQ2− concentration has not changed during cycling after regeneration treatment. c & d, Comparison of DHAQ2− NMR peak integral with respect to DMSO internal standard. Similarity of the peak integral of cycled electrolyte which had lost ~25% of capacity to that of pristine DHAQ2− does not indicate overall decrease in DHAQ2− concentration. An aliquot of the cycled DHAQ2− was taken for 1H NMR measurement when ~25% capacity was lost on day 10.5. e, LC−MS result of the cycled DHAQ2−. The peak at 10.8–11.1 min is from DHAQ2−, which is the sole compound detected. Other peaks are from background, which can be ignored.
