Comparative study on oxygen reduction velocity and it's reaction activity was performed on various pure metals and structural alloys mainly in buffered and non-buffered neutral aqueous solutions containing air, using the rotating disk electrode. The used metallic electrodes were Pt, Au, Ni, Cu, Brass, Inconel 600, Ti, Mo, SUS 304 and SUS 316. On the cathodic polarization curves, Tafel region in which oxygen reduction reaction at the electrode surface being rate determining, oxygen diffusion region in which constant current being independent of potential increase, and hydrogen evolution one generally appear in turn with the cathodic increase in the potential. However, distinctive diffusion current was not observed on some electrodes except for Pt, Au, Ni, Cu and Mo. This could be considered to result from oxide/oxyhydroxide film on those electrodes.
It is most reasonable that oxygen reduction velocity could be determined and/or compared by the exchange current density so far as the polarization curve has only a Tafel slope. In the cases of Pt, Au, Ni, Cu and Mo, the exchange current was obtained from extrapolation of Tafel line to zero in overvoltage. Those values are given in the text.
On the other hand, the order in the overvoltage at a constant current in Tafel region is taken in order to compare the reaction activity in all. In this study, 1.0*10^<-4> A/cm^2 was taken as a constant current. The order in the reactivity for oxygen reduction reaction obtained from such a procedure was as follows ; Pt Ni*Au Cu Brass> SUS 304> SUS 316> Inconel 600> Ti