Figure 1 shows the cyclic voltammograms and ORR Tafel plots in 0.1 M HClO4 for Pt (111) surfaces bare and coated with Nafion® film, which was confirmed to be uniform by scanning electron microscopy. The results indicate that ORR activity is suppressed significantly (by over 80%) by the ionomer, while the coverage of the sulfonate moieties adsorbed on the Pt surface is estimated to be small (0.08 ML) from the adsorption peak in the CV by assuming that the adsorption is a one-electron-transfer process (-SO3– + Pt → -SO3 – Pt + e-).
To further investigate the effect of ionomers, low-molecular-weight sulfonic acids were employed as model compounds for the side-chains of ionomers, and the interface was analyzed by in-situ surface enhanced infrared absorption spectroscopy (SEIRAS). Figure 2a shows the SEIRA spectrum of perfluoro-(2-ethoxyethane) sulfonic acid (PESA, C2F5OC2F4SO3H) adsorbed on polycrystalline Pt film. The spectrum reveals the presence of strong bands due to the asymmetric stretching modes of SO3-and the absence of them due to the asymmetric stretching mode of COC. These observations and the surface selection rule in SEIRAS suggest that the perfluoroalkyl chain is almost parallel to the surface as depicted in Fig. 2b. The orientation of the molecule is presumably determined by the interaction between the ether group and surface and can elucidate the significant ORR suppression by the small coverage with the sulfonate; not only the sulfonate moiety but also the perfluoroalkyl chain blocks Pt sites for ORR. In the meeting, further analytical results as well as promising strategies for suppressing the catalyst poisoning with ionomers will be discussed.
 K. Shinozaki, J.W. Zack, S. Pylypenko, B.S. Pivovar, S.S. Kocha, J. Electrochem. Soc., 162F1384-F1396 (2015).
 R. Subbaraman, D. Strmcnik, V. Stamenkovic, N.M. Markovic, Journal of Physical Chemistry C, 114 8414-8422 (2010).