Percolation conductivity in Nafion membranes

Abstract

synopsisThis article deals with the method of determination of a threshold volume fraction of the conductive phase within perfluorosulfonic acid ionomer Nafion. Experiments have been performed with the commercial Nafion-120 and Nafion-427 membranes equilibrated with concentrated sodium chloride and sodium hydroxide solutions at 353 K. It has been stated that the insulator-to-conductor transition in membranes occurs at the critical volume fraction of the conductive phase (VJ equal to 0.1. The same V, has been estimated for a geometrical cluster-network model. Lower than the theoretical V, for a classical dense-packed-hard-sphere model (V, = 0.15), the volume fraction for the membranes is caused mainly by channels connecting the ionic clusters. The critical exponent t has been calculated for both membranes and found to be equal to 1.6 for Nafion-120 and 1.5 for Nafion-427. Both these constants correspond to those theoretically predicted for 3D systems. The ratios of sodium ion mobility in the internal membrane solution to its mobility in the equilibrating NaCl or NaOH solutions (U + / u +) are below unity, and they are dependent on the nature and concentration of the electrolyte.

Theoretical analyses on water cluster structures in polymer electrolyte membrane by using dissipative particle dynamics simulations with fragment molecular orbital based effective parameters

“…The crucial interaction parameters among DPD particles were evaluated through our new protocol with FMO. 76,77 Furthermore, the network connectivity of water clusters was evaluated through the percolation analysis of formed water clusters in PEM, 15,58,[85][86][87][88] since such an effective index should relate with the conductivity. Naon and SPEEK were compared.…”

Separation of the Intramembrane Diffusion Potential and the Donnan Potential on the Basis of the Potential Transient Measurement: Application to the Analysis of Reverse Ion Permeation Driven by pH Difference

“…Thus, the parameter defined (19) as the ratio of the molar volume of hydrophilic region in the membrane at a pH to that of Na form in which the ion exchange sites are perfectly occupied by Na ϩ ions was assumed to be constant. For the ion transports across the membranes with heterogeneous structure, three or four types of theories have been applied, i.e., the percolation theory (23,24), the theory on the basis of the nonequilibrium thermodynamics (25), and the theory starting with the Nernst-Planck equation (26,27). For the present membrane systems, the Nernst-Planck equation has been applied to the reverse permeation across the membrane to obtain the apparent diffusion coefficient of the ion in the membrane.…”

Estimation of Diffusion Coefficients in Biomembranes

“…Different theories have been proposed to understand ion transport across membranes with heterogeneous structures: the percolation theory (12,13), theory based on nonequilibrium thermodynamics (14), and theory beginning with the Nernst-Planck equation (15,16) in which the transport properties are generally interpreted by means of an asymmetric potential (17)(18)(19)(20)(21). The theory for asymmetric membranes, which assumes only electrical double layers and exclusion of ions in the membrane, seems to be applicable to bilipid layer membranes.…”