Figure 7: The performance of the cathodes after operation, after the immersion treatment 1, and after the immersion treatment 2 (a: cathode 1 treated in citrate buffer (pH 3.0)→citrate buffer (pH 3.0)→MES buffer (pH 5.5), b: cathode 2 treated in acetate buffer (pH 4.0)→ acetate buffer (pH 4.0)→ MES buffer (pH 5.5), c: cathode 3 treated in MES buffer (pH 5.5)→ MES buffer (pH 5.5), d: cathode 4 not treated→ citrate buffer (pH 3.0), e: cathode 5 not treated→ MES buffer (pH 5.5), f: cathode 6 not treated→Milli-Q water (pH 7.0)→ CHES buffer (pH 9.2)).