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

采用旋转圆盘电极，主要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和反应活性进行了对比研究。使用的金属电极有Pt、Au、Ni、Cu、黄铜、Inconel 600、Ti、Mo、sus304和sus316。在阴极极化曲线上，电极表面氧还原反应速率决定的Tafel区、恒流与电位升高无关的氧扩散区和析氢区一般随阴极电位升高依次出现。然而，除了Pt、Au、Ni、Cu和Mo外，在其他电极上没有观察到明显的扩散电流，这可能是由于这些电极上的氧化/氢氧化物膜造成的。在极化曲线只有塔菲尔斜率的情况下，用交换电流密度来确定氧还原速度是最合理的。在Pt， Au, Ni， Cu和Mo的情况下，交换电流由过电压的塔菲尔线外推到零得到。这些值在文本中给出。另一方面，取恒流时过电压在Tafel区的阶数，以便比较两者的反应活性。本研究取1.0*10^<-4> A/cm^2为恒流。在此过程中得到的氧还原反应的反应活性顺序如下：Pt Ni*Au Cu Brass> SUS 304> SUS 316> Inconel 600> Ti

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