When we tested Cu/C in 0.1 M H2SO4 + 0.4 M K2SO4 and 0.1 M H2SO4 + 0.4 M Cs2SO4, half of the electrode was covered by Kapton tape and the effective area of the electrode was 0.5 cm 2 . The effective area of electrode in all the other cases was 1 cm 2 .