Gas Diffusion in the Dried and Hydrated Nations

Gas diffusivity and solubility in Nation have been investigated in dried and hydrated states. In the dried state the K+-form membrane had a higher solubility and a smaller diffusivity han the acid-form one, because the former con-tained 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 Nation. The diffusivity of hydrogen in the Nafion-Pd composite, in which palla-dium 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 Nation 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. Solid polymer electrolyte (SPE) water electrolysis tech-nology is a promising method for large-scale and high efficiency hydrogen generation (1). Basic and applied studies for developing a highly efficient SPE wate