Figure 6. EIS profiles for [Fe(CN)6]^4-/3- redox couple in 1 M KCl for PGEs without pretreatment (black) and after treatment with sulfuric acid (red) or PBS (green). Frequency range – 50,000-0.1 Hz; AC amplitude – 10 mV; 9.7 frequencies per decade; DC potential = E_1/2.