Estimation of the Diffusion Coefficient and Solubility for a Gas Diffusing Through a Membrane

Abstract

Analysis of the data obtained by the electrochemical monitoring technique for diffusion of a gas through a membrane is considered. It is shown that combining a numerical method with a nonlinear parameter estimation technique provides a means to determine values for the diffusion coefficient and the solubility of the diffusing gas. It is shown that better accuracy can be obtained for the diffusion coefficient and solubility of this gas by using the method presented and all experimental data rather than only part of the data, as has often been done in the past.

Study of Ionic Conductivity Profiles of the Air Cathode of a PEMFC by AC Impedance Spectroscopy

“…10. To determine the accuracy of values obtained for this parameter, a 95% confidence interval 10,[13][14][15][16] for (l/ 0 ) was found by using…”

Oxygen Diffusion Coefficient and Solubility in a New Proton Exchange Membrane

“…The steady-state limiting and reaction currents are described by Eq. 5 and 6, respectively [5] [ 6] where n e is the number of electrons in the electrochemical reaction of interest, s O2 is the stoichiometric coefficient of oxygen and is taken to be one-half, A is the cross-sectional area of the working electrode, and F is Faraday's constant. Fan 4 solved the above system of equations using the LaPlace transform techniques resulting in Eq.…”

A Bipartite Expression for the Transient Amperometric Current at a Membrane Covered Planar Electrode to Characterize Solute Diffusion Through the Membrane

“…Electrochemical methods, particularly amperometry, have been especially used to characterize electroactive solute transport at membrane barriers [4 -11]. McBreen et al [5] proposed a planar electrode for the amperometric detection of hydrogen through a metal membrane forty years ago, and more recently, Kimble et al [7] estimated the diffusion coefficient of hydrogen through a propriety ion exchange membrane. Tarnowski et al [8] were similarly able to characterize oxygen transport at a refunctionalized fluoropolymeric membrane; Compañ et al [9,11] characterized oxygen diffusion through silicone and hydrogel membranes; Kim et al [10] determined oxygen transport through a fluorinated ethylene propylene membrane.…”

“…Under a zero order approximation, i.e., the terms with m > 0 are neglected, Equation 7 simplifies to [5,7]:…”

“…This is an embryonic version of the bipartite expression for the membrane covered planar electrode proposed here. Recently, Kimble et al [7] determined diffusion coefficients by fitting Equations 4, 8 and 9, and their numerical solutions to observed currents by means of a least square fit; the numerical solution was calculated in finite difference form [7]. These researchers concluded that a numerical method provided the only accurate solution to Equation 1.…”