Buffer for Immersion 0 (before MFC operation) Buffer for Immersion 1 (after MFC operation) Buffer for Immersion 2 (after Immersion 1) Cathode 1 Citrate buffer (pH 3.0) Citrate buffer (pH 3.0) MES buffer (pH 5.5) Cathode 2 Acetate buffer (pH 4.5) Acetate buffer (pH 4.5) MES buffer (pH 5.5) Cathode 3 MES buffer (pH 5.5) MES buffer (pH 5.5) - Cathode 4 - Citrate buffer (pH 3.0) - Cathode 5 - MES buffer (pH 5.5) - Cathode 6 - Milli-Q water (pH 7.0) CHES buffer (pH 9.2)

Table 1: Summary of the immersion treatments performed for the cathodes.