Ex-situ UV-VIS spectra of the electrodes in different states of charge submerged in 3 M ZnSO4 were used to study the dissolution behavior of OTQC (Figure ). The results showed the following trend of solubility (1.6 V >>> 0.9 V > 0.25 V), indicating that the dissolution of the oxidized species into the electrolyte could present a cause for the capacity fading. To test the hypothesis, OTQC was galvanostatically cycled in a Zn battery using a narrower voltage window between 0.9 V and 0.25 V (Figure ). The use of a narrower window decreased specific capacity, but on the other hand, greatly improved the cycling stability, which is consistent with the ex-situ UV-VIS solubility tests.