A self-protection phenomenon in the Nafion membrane when it breathes in methanol-saturated air

Abstract

Ex situ characterizations based on TGA and XRD techniques revealed that MeOH vapor had little influence on the Nafion microstructures. To reveal the underlying mechanism, in this study, we designed new FTIR-based equipment to track in situ the microstructural changes of a bulk Nafion membrane in MeOH-saturated air. First, an interesting MeOH-breathing phenomenon was found in the ionic domains of Nafion. It demonstrated that there existed a dynamic equilibrium between the sorption and desorption processes of MeOH vapor in Nafion. Second, the FTIR results also detected the high stability of the hydrophobic regions of Nafion in MeOH vapor. The super-acid -CF2-SO3H always retained a small quantity of bonded H2O (H(+)(H2O)n) inside the Nafion membrane. MeOH vapor was absorbed first into the hydrophilic regions, however, the interactions between -CF2-SO3H and MeOH vapor were much weaker than those between -CF2-SO3H and H(+)(H2O)n. Therefore, a protective layer composed of residual water formed in the lumen of the hydrophilic ionic domains of Nafion, which protected its hydrophobic regions from the MeOH attack. Hereby, the self-protection ability of Nafion in MeOH vapor was detected for the first time. This work gave a new insight into the complex interplay between Nafion and MeOH vapor.

Impacts of Organic Sorbates on the Ionic Conductivity and Nanostructure of Perfluorinated Sulfonic-Acid Ionomers

“…This reveals a clear need to understand structure–property relationships of ion-conducting membranes in the presence of organic chemical species. Previous studies, primarily driven by the need to improve and tune performance in DMFCs, investigated the effects of ethanol and methanol on diffusion and conductivity in Nafion. − A number of studies have probed the ionomer structure using NMR, permeability, FTIR, and X-ray and neutron scattering. − Some studies also investigated and modeled how the interactions between the ion form and alcohol solution influence membrane properties. ,− However, as most of the studies focused on one alcohol or a specific transport property, the understanding of structure–swelling–conductivity relationships with a wider range of sorbates of varying polarities is limited. With the emergence of new technologies employing ionomers in chemically rich environments, it is even more pertinent to elucidate their impact on ionomers’ local environment and transport functionality.…”