Electrochemical reduction of oxygen on thin-film Pt electrodes in acid solutions

The electrochemical reduction of oxygen on thin-film platinum electrodes in 0.1 M HClO4 and 0.05 M H2SO4 solutions has been investigated using the rotating disk electrode (RDE) method. Thin films of Pt (0.25–20 nm thick) were prepared by vacuum evaporation onto glassy carbon substrate. The surface morphology of Pt films was examined by transmission electron microscopy (TEM). The specific activity of O2 reduction was higher in HClO4 and decreased with decreasing film thickness. In H2SO4, the specific activity was lower and appeared to be independent of the Pt loading. The values of Tafel slopes close to −120 mV dec−1 in high current density range and −60 mV dec−1 in low current density range were obtained for all electrodes in both solutions, indicating that the mechanism of O2 reduction is the same for thin-film electrodes as for bulk Pt. The number of electrons transferred per O2 molecule was close to four for all thin Pt films studied.