Molecular simulation of gas adsorption, diffusion, and permeation in hydrated Nafion membranes

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\u2019s adsorption property is examined in terms of the solubility and adsorption isotherms for gases, includingH2, O2, andN2. The adsorption capacity of hydrated Nafion is shown to be strong forO2 andN2 but not forH2. 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 ofH2 and O2 are represented by self-diffusion coefficients, with the results showing thatH2 diffusion in Nafionmembranes 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.Peer reviewed: YesNRC publication: Ye