Effect and siting of Nafion® in a Pt/C proton exchange membrane fuel cell catalyst

► 30 wt% Nafion® appears to be primarily on the external surface of the C support. ► Nafion® blocks micropores and only partially blocks the meso-macropore openings. ► No evidence of Nafion® affecting H2 or CO adsorption or H2 activation on Pt. ► Partial blocking of the C support pore openings cause diffusion problems for molecules larger than H2.