Gas Diffusion in the Dried and Hydrated Nafions

Gas diffusivity and solubility in Nafion have been investigated in dried and hydrated states. In the dried state the K+‐form membrane had a higher solubility and a smaller diffusivity than the acid‐form one, because the former contained not as much tightly bound water. These values of the dried membranes were near those reported in the PTFE membrane as a backbone material of Nafion. The diffusivity of hydrogen in the Nafion‐Pd composite, in which palladium particles were deposited in the vicinity of the ion‐exchange sites, was examined, in order to clarify a gas diffusing path in the dried state. The value of the diffusion coefficient was close to that reported for the Pd membrane, showing that gas had diffused through a portion of the polymeric ions. When the Nafion was hydrated, the solubility decreased a little and the diffusivity increased remarkably, approaching the values in water. Since the water was contained mainly in the ion clusters formed by the polymeric ions, it appears that gas diffuses through a portion of the polymeric ions (e.g., clusters and channels) in the hydrated state.