Electrochemical reduction of oxygen on gold nanoparticle-electrodeposited glassy carbon electrodes

The electrochemical reduction of oxygen (O2) on Au nanoparticle-electrodeposited glassy carbon electrodes (GCEs) has been performed in 0.1 M phosphate buffer solution (pH 7.2). Two well-separated electrochemical reduction peaks for O2 on GCE were observed at about -750 and -2000 mV vs. Ag/AgCl/KCl (sat.) i.e., a peak separation of ca. 1250 mV. Those two peaks were attributed to the two-step four-electron reduction of O2 to H2O through H2O2. A remarkable decrease of the separation of the two peaks (down to 550 mV) along with a significant positive shift of the two reduction peaks of O2 to -350 and -9880 mV, respectively, were observed upon loading of a very minute amount of Au nanoparticles onto the GCE (typically 2.78 × 10-7 g cm-2). Further positive potential shift of the two peaks along with a concurrent decrease of the peaks separation could be achieved by controlling the extent of Au loading on the GCE. Au-electrodeposited GCE with an equivalent Au film thickness of 10 nm showed almost the same behavior toward the O2 reduction as the bulk Au electrode. These observations were interpreted in view of the increase of the effective (real) surface area of the Au film by the increase of its thickness, as indicated by scanning electron micrographs in addition to the characteristic cyclic voltammogram for Au nanoparticle-electrodeposited GCEs in N2-saturated 0.05 M H2SO4.