Figure 9: The performance of the cathode 1, 2, and 3 after the immersion treatment 0 and 1. (C1: treated in citrate buffer (pH 3.0)→citrate buffer (pH 3.0), C2: treated in acetate buffer (pH 4.0) →acetate buffer (pH 4.0), C3: treated in MES buffer (pH 5.5)→MES buffer (pH 5.5)).