Nafion membrane channel structure studied by small-angle X-ray scattering and Monte Carlo simulations

Abstract

The structure of Nafion 117 membranes was studied through SAXS experiments and 2D pattern simulations. Measurements were taken for different moisture conditions by synchrotron radiation, and for different temperatures through X-ray tube irradiation. The experimental profiles were fitted through simulations based on a new structural model including: the amorphous polymer matrix, polymer crystallites, and inverse core-shell type channels conformed by water cylinders and sulfonic chains. The geometrical parameters intervening in the simulation of the SAXS patterns were optimized for each experimental condition. This approach allowed the proper description of the experimental SAXS profiles for the various moisture conditions studied. In addition, a recent lamelar model was also included in the assessments, and the corresponding performances were discussed.

Ionic Mobility in Ion-Exchange Membranes

“…According to the small-angle X-ray scattering data, the membrane pores in the swollen state have sizes of 4–5 nm, and the sizes of channels connecting them are 1–2 nm [ 87 , 88 ]. The proton-acceptor ability of –SO 3 − groups is significantly lower than that of water molecules, due to which SO 3 H groups dissociate, forming hydrated proton (H + (H 2 O) n ).…”

Systematic Characterization of Degraded Anion Exchange Membranes Retrieved from Vanadium Redox Flow Battery Field Tests

“…Small-angle x-ray scattering (SAXS) was applied to correlate the materials’ parameters with structural changes in the membrane due to degradation phenomena. According to Bordin et al [ 15 ], who apply the Schmidt-Rohr model, the crystallites are responsible for the main part of low-q scattering, often also called matrix knee. They estimated approximately 3/4 of the intensity resulting from the crystals.…”

“…Many models can give satisfactory descriptions of the scattering pattern. In the Schmidt–Rohr model, also used by Bordin et al [ 15 ] a convincing explanation for the high ion transport capabilities has been given, suggesting oriented cylindrical ionomer channels with quite big diameters (2–4 nm) penetrating the whole membrane. Another important feature of this model is the presence of polymer crystallites in the amorphous phase, not being responsible for the ion transport, but stabilizing the membrane and also the ionomer channels.…”

Composite Nafion-CaTiO3-δ Membranes as Electrolyte Component for PEM Fuel Cells

“…The first peak, also called the matrix knee, corresponds to the fluorocarbon polymer crystallites randomly distributed in the amorphous polymer matrix. Here, it is observed at q values close to 0.06 Å −1 and its intensity depends on the polymer’s degree of crystallinity [ 27 ].…”