A Comparative Study for Oxygen Reduction Velocity on Many Kinds of Metal Electrodes

采用转盘电极，在含空气的缓冲和非缓冲中性水溶液中，对各种纯金属和结构合金的氧还原速度及其反应活性进行了比较研究。所用的金属电极是铂、金、镍、铜、黄铜、Inconel600、钛、钼、SUS 304和SUS 316。在阴极极化曲线上，随着阴极电位的升高，电极表面氧还原反应的Tafel区、恒电流与电位无关的氧扩散区和析氢区一般依次出现。但除铂、金、镍、铜和钼外，其余电极均未观察到明显的扩散电流。这可以认为是由于电极上的氧化物/氢氧化膜所致。当极化曲线只有Tafel斜率时，氧还原速度可以通过交换电流密度来确定和/或比较是最合理的。在铂、金、镍、铜和钼的情况下，交换电流是从塔菲尔线外推到过电压为零得到的。另一方面，塔菲尔区恒流过电压的顺序是为了比较所有的反应活性。在本研究中，将1.0×10^~(-4)A/cm^2作为恒定电流。由该过程得到的氧还原反应的反应性顺序为：铂镍*金铜黄铜；SUS 304；

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