The electrochemically active surface area (ECSA) of the disk was determined by calculating the charge from the reduction peak in the characterization CV between 0.05 and 1.75 V (0.1 M H2SO4, 50 mV s -1 as shown in Fig. ) and dividing it by the specific charge of one monolayer of Au (390 μC cm -2 ) 20,21 .