Oxygen reduction on carbon supported Pt and PtRu catalysts in alkaline solutions

In this paper, carbon supported Pt and PtRu were employed as oxygen reduction catalysts in 0.1 M NaOH solutions. Onset potentials for oxygen reduction reactions (ORRs) for both catalysts are similar (around 0.05 V vs. Hg/HgO/OH(-)). At an ORR overpotential of 0.29 V, the values of kinetic ORR current (I(k)) on the PtRu/C catalyst, normalized to geometric area and active surface area, are 3 and 14 times lower, respectively, than those measured on the Pt/C catalyst. Rotating ring-disk electrode (RRDE) measurements show that the H(2)O(2) yields on both catalysts are negligible at potentials higher than -0.3 V, and the yields are less than 4% even at higher overpotentials, indicating that the ORR mechanism on the PtRu/C is the same as that on the Pt/C, i.e., the 4e(-) transfer is the predominant pathway. The values of activation energy of the ORR on the Pt/C and PtRu/C are similar at low current densities - about 40 and 35 kJ mol(-1), respectively. The simultaneous electro-oxidation of ethanol (EOR) and electro-reduction of 02 was studied in O(2)-saturated 0.1 M NaOH solutions. For the Pt/C, the ORR is suppressed by ethanol adsorbates at potentials lower than -0.05 V vs. Hg/HgO/OH(-) when both ethanol and oxygen exist in the solution. At potentials higher than -0.05 V, the FOR is suppressed by the ORR. The high FOR oxidation current on the Pt/C cathode would produce mixed potentials and degrade fuel cell. performance. For the PtRu/C, the FOR has little influence on the ORR. The stability tests show that PtRu/C is stable under fuel cell cathode working conditions. (c) 2009 Elsevier B.V. All rights reserved.