the ex-situ three-electrode set-up were carried out. The potential was swept between 0.3 V and 0.85 V versus Ag|AgCl (3 M KCl). Voltammograms with 5 different voltage sweeping rates were recorded: 0.01 V s -1 , 0.025 V s -1 , 0.05 V s -1 , 0.075V s -1 and 0.1 V s -1 . The order of voltage sweeping rates was randomized to minimize any unexpected time effect from the system.