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CP: Chemische Physik
CP 28: Poster: Neue Methoden
CP 28.6: Poster
Monday, March 22, 1999, 18:00–20:00, R52/R72
Electrochemical impedance of inhomogeneous porous electrodes and membranes — •P.H. Nguyen1 and G. Paasch2 — 1Experimentalphysik II, Universit"at Bayreuth, D-95440 Bayreuth — 2Institut f"ur Festk"orper- und Werkstofforschung Dresden, Postfach 270016, D-01171 Dresden
A transfer matrix method is presented for the calculation of the electrochemical impedance of porous systems. It is based on the two-phase model and applies to systems with parameters which are not constant across the layer. The layer is divided into a number of slabs and in each slab all parameters are replaced by their mean values. The potentials and the currents of two adjacent slabs are connected by a matrix, in the general case a 4× 4-matrix. The potential propagation in the whole layer is determined by the product matrix. The impedance for both a layer coating a metallic current collector and a porous membrane embedded in the electrolyte (or the porous layer with electrolyte-filled pores in between two metallic current collectors) can be expressed by the elements of the product matrix. It is demonstrated that e.g. gradients of the resistivities can result in significant qualitative modifications of the impedance. This concerns especially the low frequency pseudo-capacitive behaviour which is transformed into a dependence resembling the well known empirical description by constant phase elements often used to interpolate experimental data.