In it, C. Randall looked at thin-film Nafion on carbon substrates to better understand Nafion structure in PEM fuel cell and hydrolyzed catalyst layers. We find structure can vary with substrate hydrophobicity & roughness, but the non-interfacial region is consistent across substrates.In it, C. Randall looked at thin-film Nafion on carbon substrates to better understand Nafion structure in PEM fuel cell and hydrolyzed catalyst layers. We find structure can vary with substrate hydrophobicity & roughness, but the non-interfacial region is consistent across substrates.