Ion and water transport characteristics of perfluorosulfonated ionomer membranes are investigated in the mixed cation form of H/Fe, H/Ni, and H/Cu systems. Nafion membranes, which were equilibrated with HCl/FeCl3, HCl/NiCl2, or HCl/CuCl2 mixed aqueous solutions of various mixing ratios, were prepared as test samples, and equilibrium and transport properties were measured systematically. Membrane cationic composition showed that trivalent cations had more affinity than divalent cations. Also larger valence cations caused less water content in the membrane. The membrane ionic conductivity was markedly influenced by counterions, and H+ mobility u H + was altered according to the nature of coexisting cations. In the presence of Cu2+, u H + increased from its inherent value, while in the presence of Fe3+, u H + decreased to a large extent, Ni2+ bringing about nearly no change in u H + . The ionic transference number of H+ was also influenced by coexisting cations in several ways. Despite the unique influence of impurity cations on the mobility of H+, the mobility of impurity cations was not affected by the presence of H+. The interaction between adjacent cationic species in the membrane ion exchange sites, although plausible in general for multivalence cations, appeared to be not specific due probably to the shielding of the cationic charge by water molecules or by sulfonic acid groups. The water transference coefficient t H 2 O as measured by streaming potential measurements showed unique changes with membrane ionic composition, and t H 2 O increased from 2.5 to over 13 by the presence of impurity ions. These impurity ions were found to result in more water molecules dragged than in the case of individual ions, when coexisting with the H+ ion. Overall, it was noted that the water molecules within the influence of impurity cations appeared to play a large role in the H+ movement in the membrane.

The effect of contamination by Ca2 ions in proton conductive membranes f or polymer electrolyte fuel cells was investigated systematically. Ion and water transport characteristics of Nafion membranes, which were equilibrated with 0.02 to 0.03 kmol m3 of HC1/CaCl2 mixed solutions of various mixing ratios, were studied by electromotive force analysis. Membrane composition analysis, showed that Ca2 has much higher affinity than H to the ion exchange sites in Naf ion membranes. The water content in the membrane, as expressed by the amount of water per cationic site }120/SO;, decreased about 19% from 21 for H-form membrane to 17 for Ca-form membrane. The water transference coefficient was obtained from streaming potential measurements of Nafion 115 membranes of various H/Ca2 cationic compositions. The water transference coefficient increased from 2.5 toward 11 as the Ca2 content in the membrane increased, especially when the equivalent fraction of H in the cationic exchange sites x became less than 0.5. Ionic transference numbers for H in the membrane, determined by a new electromotive force method, showed rapid decrease when the cationic site occupancy by H became less than 0.5. Membrane conductivity changed linearly with H composition in the membrane. In strong contrast to the interaction mode between H and Ca cations during ionic conduction, which appeared almost independent, a certain extent of interference was observed among water molecules as they were carried along by cations in the membrane. It was predicted that if Ca2 ions enter the fuel-cell membrane, they cause serious effects to membrane drying and result in deterioration of fuel-cell performance. The advantage of this methodology in the study of transport characteristics of fuel-cell membranes is stressed due to ease and accuracy of measurements.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-02-07 to IP

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The mechanism of how impurity cations suppress the kinetics of oxygen reduction reaction on platinum surface covered with perfluoro-sulfonated ionomer film was studied in 0.1 N H2SO4 in the presence of various kinds of impurity ions of several concentrations. Impurity cations tested were Li+, Na+, K+, Ca2+, Fe3+, Ni2+, and Cu2+ with the amount of 0.1%, 1%, and 10% as compared with H+ in the solution. Platinum disk of a rotating disk electrode was spin-coated with Nafion solution, and after drying the Nafion film-covered platinum was obtained. The electrochemical measurements were performed to evaluate both charge transfer and diffusion kinetics of oxygen reduction at the Nafion film-covered electrode. It was discovered that the impurity ions hindered enormously the rate of charge-transfer step at platinum covered with perfluoro-sulfonated ionomer. The suppression started already at 0.1% level of impurity concentration, but did not increase much at over 1% level. No suppression effect for oxygen reduction was observed for a bare platinum in the solution containing impurity ions, indicating that the effect is specific to the metal electrode−ionomer membrane interface. Also both the diffusion coefficient of oxygen and oxygen concentration in the membrane decreased by the presence of impurity cations. It was implied that all the process is related to the reorientation of polymer networks in the membrane, which might bring about the modification of electric double layer at the platinum−ionomer interface.