The cathodic peak was shifted to more negative potentials with the decrease in size of nanoparticles from 0.80 V (Au) to 0.70 V (GC/AuNP/E) and 0.68 V GC/AuNPs/C corresponded to the reduction of the formed gold oxides [39–42].
On the other hand, the oxygen evolution starts at less positive potentials to the electrodes containing AuNPs than gold electrode and the residual current was higher in the electrodes with nanoparticles, these changes may be due to the amount of exposedcarbon and gold as well as aggregation on the electrode surface