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Radiotracer techniques are developed to measure the proton and bisulfate‐ion diffusion coefficients in Nafion‐117 membranes containing aqueous sulfuric acid. Sulfur‐35 is used to mimic the more‐abundant, naturally occurring sulfur‐32 in obtaining the bisulfate‐ion diffusion coefficient. In a novel development of this work, the proton diffusion coefficient is obtained by also utilizing sulfur‐35 transport rates. When the transport model developed in Part I of this study is used to simulate the experiments, a single, concentration‐independent diffusion coefficient is found to represent accurately bisulfate‐ion transport over concentrations ranging from 0.003 to 1.0 M sulfuric acid: this lends substantial support to our understanding of the phenomena occurring within these membranes. A Bruggeman‐type relationship (which incorporates structural information of a porous medium so as to relate the diffusion coefficients within the porous phase to those of a free solution) is shown to represent surprisingly well the bisulfate‐ion diffusion coefficient, which casts doubt on previously proposed structure theories for this class of materials. Our results indicate that the membrane pores are of approximately uniform cross‐sectional area and 60Å in breadth.
Verbrugge et al. (1990) studied this question.