Through-plane Structural Analysis of Engineered Nafion Surfaces

The thin-film structures of Nafion, a model perfluorinated ionomer, impact advances in proton-exchange membrane fuel cells (PEMFC). Engineered Nafion surfaces were developed by Dowd et al. to alter the surface composition and wettability of Nafion^[a]. Using neutron reflectometry (NR), we probe the through-plane structure of Nafion thin-films. Buried layers of phase-separated lamellae were observed in Nafion thin-films at Au, Pt, and SiO₂ interfaces by Dura et al.^[b] and DeCaluwe et al^[c]. We developed and applied titanium nitride (TiN) substrates to minimize the neutron scattering contrast to interface structures thus optimizing the sensitivity of NR to the presence and structure of the engineered Nafion surface. Unprocessed Nafion thin-films were studied via NR in dry (0% RH) and humidified (92% RH) conditions with H₂O and D₂O vapor. Future research will measure the engineered Nafion thin-films to independently determine water uptake differences and possible surface layers after modification. We intend to expand the work to other substrates that may be sensitive to a modified Nafion surface, such as titanium dioxide (TiO₂) and sputtered carbon (C).

^[a]10.1149/2.1081702jes ^[b]10.1021/ma802823j ^[c]10.1039/C4SM00850B