Molecular Simulation of Gas Adsorption, Diffusion, and Permeation in Hydrated Nafion Membranes

Abstract

Molecular simulations were performed to characterize hydrated Nafion membranes in terms of gas adsorption, diffusion, and permeation. The experimental results validate the molecular model of Nafion with respect to material density, morphology, free volume, and water diffusivity. Nafion’s adsorption property is examined in terms of the solubility and adsorption isotherms for gases, including H2, O2, and N2. The adsorption capacity of hydrated Nafion is shown to be strong for O2 and N2 but not for H2. Due to the dilution effect, N2 is able to suppress the loading of O2 and protect the fuel cell from fuel crossover. The dynamic behaviors of H2 and O2 are represented by self-diffusion coefficients, with the results showing that H2 diffusion in Nafion membranes is nearly 1 order of magnitude faster than O2 diffusion. The effects of water content and the concentration of adsorbed gases were verified, and a close correlation of Nafion free volume to gas transport properties was revealed. On the basis of the solution-diffusion mechanism, the permeabilities of H2 and O2 in hydrated Nafion membranes are calculated and compared with corresponding experiments, and the permeability of H2 is found to be approximately twice that of O2.

Molecular Analysis of Structural Effect of Ionomer on Oxygen Permeation Properties in PEFC

“…This trend is consistent with the results of previous research. 23,29,64 In this study, the structural factors on the oxygen diffusivity in bulk Nafion membrane have not been clarified. It is difficult to analyze the oxygen pathway in a bulk Nafion membrane with a sufficiently high reliability because of a very small number of oxygen molecules.…”

Nafion Ionomer Dispersion in Mixtures of 1‐Propanol and Water Based on the Martini Coarse‐Grained Model

“…Theoretically, many molecular dynamics (MD) simulations of PFSA membranes have been performed to study proton and oxygen transport within the morphology of PFSA membranes and ionomer thin films . Most atomistic simulation studies have primarily focused on the solid state of ionomers in PEMs and CLs with a water volume fraction significantly below 50%.…”

Numerical simulation of gas permeation and internal current through hydrated Nafion membranes

“…Modeling approaches for describing gas permeation and internal current through the hydrated Nafion membranes have not been well developed and validated in comparison with experimental results, especially when considering complex microstructures of polymers systems [13].…”