Mechanisms of Ion and Water Transport in Perfluorosulfonated Ionomer Membranes for Fuel Cells

Abstract

To clarify transport mechanisms of ions and water molecules in perfluorosulfonated ionomer membranes, various membranes, such as one Nafion, two Aciplex, and four Flemion types, having different equivalent weight values (EW) were examined. H-, Li-, and Na-form samples were prepared for each membrane by immersion in 0.03 M HCl, LiCl, and NaCl aqueous solutions, and their properties in the fully hydrated state were investigated systematically. The water content of the membranes showed the tendency that the size and/or the number of ionic cluster region increases with decreasing EW value and the Li-form membranes have the most largely expanded ionic cluster regions. The ionic conductivity of the H-form membranes was considerably higher than that of the Li-and Na-form membranes. It was suggested that the proton in the membranes transports by the hopping mechanism and the Li + and Na + ions by the vehicle mechanism. In addition, the ionic conductivity of all membranes increased with increasing water content within the same kinds of membranes. Although the cation concentration in the membranes is insensitive to the EW value, the cation mobility increased with decreasing EW value. This means that the increased mobility of the carrier cations is the major factor to enhance the ionic conductivities due to the expansion of the ionic cluster regions. The water transference coefficients for the Li-and Na-form membranes showed higher values than those of the H-form membranes, while the water permeabilities gave the inverse tendency. This means that the water molecules in the Li-and Na-form membranes interact with the Li + and Na + cations more strongly than the proton when the cations move in the membranes, and as a result the diffusion of the water molecules is reduced. All of the above results were in good agreement with the results of the self-diffusion coefficients of the water molecules and the Li + cation in the membranes measured by pulsed field gradient NMR.

Thinning of Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells Due to Foreign Cation Contamination

“…Once the cations enter the ionomer, they displace protons resulting in reduced ionic conductivity and water content, as well as lower gas permeability of the ionomer. 5,6,[13][14][15][16][17][18] Other researchers confirmed the findings of Okada group as well. 9,20,25,31,33 23 Pozio et al 19 investigated the degradation in PEFC that was caused by iron contamination from SS316L end plates and reported that contamination of the membrane electrode assemblies with iron led to degradation of the ionomer, revealed by a massive fluoride losses.…”

Functional macromolecules and smart polymer networks for ion separation, reduction and delivery

“…Figure 6.18a shows the FTIR spectra of S (25) As shown in Table 6 The mobile cations move through the water-swollen polymer and water facilitates cation transport from sulfonate group to sulfonate group. 65,148 Therefore, the mobility of the ions depends on the swelling degree of the matrix. 65 The water swelling of S(25)PAEK and S (25) …”

“…65,148 Therefore, the mobility of the ions depends on the swelling degree of the matrix. 65 The water swelling of S(25)PAEK and S (25) …”

“…For the S(25)PAEK membranes, where only sulfonate groups are present and which does not contain crown ether moieties, potassium ion transport is facilitated by a vehicle mechanism from sulfonate group to sulfonate group. 65 The mobility of the ions depends on the exchange kinetics between H + and K + ions at the sulfonate group, the swelling state of the polymer matrix and the diffusional jump distance between the carrier (sulfonate) groups. 66 In addition to sulfonate-cation interactions, crown ether-cation complexation also influences the overall potassium ion transport in the S(25)C(75)PAEK membrane.…”

Relação morfologia-propriedades elétricas de eletrólitos compósitos de Nafion para célula a combustível de alta temperatura

“…As diferentes membranas diferem basicamente quanto à composição, densidade e comprimento dos grupos laterais de forma que ambos alteram o estado de agregação dos íons na matriz que influenciam nas propriedades elétricas do ionômero. Estudos sobre a morfologia e as propriedades de transporte de água e íons destes materiais apontaram as membranas Nafion e Dow como os eletrólitos mais apropriados para aplicações em células a combustível de baixa temperatura [21,22,23].…”