Fe(DIPSO) electrolyte was prepared by dissolving FeCl3 and DIPSO with a ratio of 1:1.5, with NaCl and NaOH adjusting the whole ion concentration (total anion equaling 1.3 M) and initial pH to 13. The electrolyte was filtered before usage. DBEAQ electrolyte was prepared by dissolving 0.1 M DBEAQ in 1 M KCl, with KOH adjusting the pH to 12. When using DBEAQ, 1.3 M KCl was used instead of NaCl in the center chamber when running the three-chamber cell.