Elucidation of Activity Enhancement Factors for the Oxygen Reduction Reaction on Platinum and Palladium Single Crystal Electrodes

This headline article focuses on the oxygen reduction reaction (ORR), cathodic reaction of fuel cells, on well-defined high index planes of Pt and Pd for the elucidation of factors enhancing the activity for the ORR. The surfaces with (111) terrace edge have high activity for the ORR on Pt electrodes. Pt(331) = 3(111)-(111) gives the highest activity for the ORR in the stepped surfaces of Pt. Incorporation of one kink atom among eleven step atoms further enhances the activity of Pt(331). On single crystal electrodes of Pd, however, terrace edge deactivates the ORR and wide (100) terrace enhances the activity. Effects of Pt oxides (PtOH and PtO) on the ORR have been examined using vibrational spectroscopy. Infrared reflection absorption spectroscopy (IRAS) shows that PtOH prevents the ORR on Pt electrodes. Nanoparticle surface enhanced Raman spectroscopy (NPSERS) indicates that PtO also blocks the ORR on Pt(100) of which ORR activity is the lowest. The ORR activity of Pt is also enhanced by the modification of the surfaces by amines with long alkyl chains such as octylamine (OA) and amine with pyrene ring (PA). Modification by OA/PA increases the ORR activity on n(111)-(111) surfaces of Pt with terrace atomic rows more than 7. The activity of flat Pt(111) is enhanced most remarkably by OA/PA. However, the ORR of Pt(100), of which surface is also composed of flat terrace, is deactivated significantly. (c) The Electrochemical Society of Japan, All rights reserved.