Comparing the black and the green curves (before and after holding the potential at 1.0 V RHE for 15 min) in Figs. and, a larger reduction current is apparent in the green curve in the first negative going scan at around 0.8 V RHE . This feature is related to the degree of electrode oxidation at high potentials. In general, the size of the reduction peak depends on the upper potential limit of the CV as well as on the time and potential at which the electrode is kept (see also Fig. ). Hence, the larger reduction peak in the green curve is caused by holding the potential at 1.05 V for 15 min.