| Abstract
| - The paper is concerned with the small signal ac impedance of porous film electrodes in contact with solution.An overview is presented of the standard transmission line model with two transport channels and a crosswiseelement. The simplest configurations are discussed: a single resistance in one of the channels, and either aninterfacial capacitor or a RC transfer circuit at the pore's wall. The resulting relaxation functions are classifiedin terms of two characteristic frequencies: one for coupled transport and interfacial polarization and anotherone for the interfacial reaction. Subsequently, these models are extended in order to describe porous electrodeswhere the interfacial polarization displays complex properties, i.e., frequency dispersion. The capacitive elementis described by a constant-phase element (CPE), and it is shown that the fractionary exponent provides anadditional and measurable degree of freedom in the parameter space of the relaxation function, whosedetermination can be exploited as a supplementary tool for analysis. The analysis of impedance measurementsof TiO2 nanoporous photoelectrodes in negative bias voltage shows that the suggested approach is capable ofidentifying two characteristic relaxation frequencies in a frequency-resolved measurement on this system.
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