For higher voltage, pairing Fe(Bhmbpy)3 at pH 3 with Cr chelate 1,3-propylenediaminetertaacetic acid (CrPDTA) at pH 9 can reach an OCV about 2.2 V, with net acid-base crossover flux lower than 0.2 nmol s -1 cm -2 . Suitable redox candidates are listed in Table , from which we can find redox pairs allowing operating our pH-decoupling-recovery design with various values of OCV and crossover flux. With the pH recovery system we demonstrated, long-term practicability can be maintained.