title: Generalized equivalent circuits for mixed conductors: silver sulfide as a model system.
abstract: The generalized equivalent circuit for Hebb-Wagner polarization in the frequency domain proposed by Jamnik and Maier (J Electrochem Soc 146:4183, 1999) includes the space-charge polarization that was previously neglected. In the present work, using a self-coded Fortran program, the completely generalized equivalent circuit is successfully applied to a mixed conducting silver sulfide with an AgI electrode that suppresses the electronic flow. A whole set of fit parameters, such as geometric capacitance, partial conductivities, chemical capacitance or diffusivity, and the blocking and shunting characteristics of electrodes are independently but self-consistently obtained over a range of silver activities, as controlled by a galvanic cell. The interfacial capacitance was found to be much larger than the diffuse space-charge double-layer capacitance and was thus ascribed to the adsorption capacitance at the core of the interface, which should be connected in parallel with the space-charge double-layer polarization. Two simplified equivalent circuits were shown to be good approximations for the spectra at the extreme low and high silver activity, respectively.
authors.affiliation: School of Materials Science and Engineering, Chonnam National University, Gwangju, 500-757 Korea.
authors.forename: Jong-Sook
authors.initials: JS
authors.lastname: Lee
authors.affiliation: National Institute of Chemistry, 1000 Ljubljana, Slovenia.
authors.forename: Janez
authors.initials: J
authors.lastname: Jamnik
authors.affiliation: Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Maier
keywords: Adsorption capacitance; Chemical diffusion; Hebb–Wagner polarization; Impedance spectroscopy; Mixed conductor; Space-charge polarization