Very low Pt-Pd based electrocatalysts for oxygen reduction reaction

Abstract

In the present manuscript very low-platinum electrocatalysts, Pd97Pt3/C, Pd98Pt2/C, Pd99Pt1/C and pure Pd/C are prepared and examined for oxygen reduction reactions (ORR) with the rotating electrode technique. From the analysis of the results the addition of Pt to the pure Pd enhances significantly the ORR activity. More specifically, the Pd98Pt2/C electrocatalyst exhibits the highest intrinsic activity, with ca. 0.75mAcm-2 exchange current density. However, further increment of the Pt loading against Pd loading, (Pd97Pt3/C) reduces dramatically the intrinsic catalytic activity from 0.75mAcm-2 to 0.2mAcm-2. The Tafel slopes at low potential values are calculated 127, 128, 156 and 94 mV per decade for the Pd97Pt3/C, Pd98Pt2/C, Pd99Pt1/C and Pd/C, respectively, indicating one electron transfer at the rate determining step. While the calculated Tafel slope at high potential values indicates two electrons transfer at the rate determining step. The lower Tafel slope of the Pd/C shows that some OHads intermediates were involved.