Limiting currents and sodium transport numbers in nafion membranes

Kontturi, Kyösti; Mafé, Salvador; Manzanares, José A.; Murtomäki, Lasse; Viinikka, P.

doi:10.1016/0013-4686(94)85102-6

Cited by 12 publications

(12 citation statements)

References 23 publications

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“…6 and references therein), with transport numbers significantly lower than those predicted by the homogeneous membrane model. 6,48,49 These findings are in qualitative agreement with the predictions of the model in Fig. 5.…”

Section: Resultssupporting

confidence: 89%

“…Since ionic diffusion in fixed charge membranes constitutes a complex phenomenon where many effects are simultaneously present, 1,30 it is unlikely that we could obtain accurate values for E a,s and D s using a simple model incorporating only the Coulombic term of eqn. (6). However, the calculated activation energies for surface diffusion provide interesting clues to microscopic parameters, as it was argued in previous experimental studies.…”

Section: Resultsmentioning

confidence: 54%

“…4 and t +,b ¼ 0.5. The dashed curve corresponds to the transport number given by the Donnan model 1,6 with D +,m ¼ D À,m ¼ 2 Â 10 À5 cm 2 s À1 . The curves are parametric in the fixed charge concentration X.…”

Section: Resultsmentioning

confidence: 99%

“…The interpretation of ionic equilibrium and transport in polymer fixed charge membranes (ion exchange membranes) has usually invoked the existence of two kinds of counterions: [1][2][3][4][5][6][7][8] those located close to the membrane fixed charges and those forming (together with their corresponding coions) the electroneutral salt taken by the membrane upon swelling. The latter ions distribute over regions where the influence of the membrane fixed charges is very small, and are thus supposed to exhibit properties similar to those of the external solution.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, when modeling the electrical properties of these membranes, theories have usually considered the membrane as composed of two or more conducting regions. [4][5][6]9,10 We study here a model membrane composed by pores having two conducting regions. In the surface region the electric current is carried exclusively by the mobile positive ions (counterions) around the negative fixed charges attached to the pore boundaries.…”

Section: Introductionmentioning

confidence: 99%

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Modeling of surface vs. bulk ionic conductivity in fixed charge membranes

Mafé

Manzanares

Ramı́rez

2003

Phys. Chem. Chem. Phys.

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A two-region model for describing the conductivity of porous fixed charge membranes is proposed. In the surface region, the conductivity is due to the mobile positive ions (counterions) around the negative fixed charges. In the pore center region, the conductive properties resemble those of the external electrolyte solution because the fixed charges are assumed to be effectively neutralized by the counterions in the surface region. Activation energies and surface diffusion coefficients are estimated by assuming that the counterion jump from a fixed charge group is the rate limiting process for surface transport. The barrier energy for this jump is calculated using a simple electrostatic model with two microscopic parameters, the sum of the counterion and fixed charge hydration radii and the local dielectric constant. The bulk conductivity is obtained from experimental data. The total membrane conductivity and the counterion transport number are then calculated as functions of the external solution concentration for several pore radii and membrane fixed charge concentrations. The results are compared with those given by the Donnan model for homogeneous membranes and by the numerical solution of a continuous model based on the Poisson-Boltzmann equation extended to finite size ions. The study of the membrane conductivity for a series of electrolytes allows to distinguish clearly between the mechanism characteristic of the bulk ionic conductivity and that of surface conductivity. The surface conductivity is found to be significant for narrow pores at low external solution concentrations.

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Section: Resultssupporting

confidence: 89%

Section: Resultsmentioning

confidence: 54%

Section: Resultsmentioning

confidence: 99%