Electrochemical cell for composition-dependent electronic conductivity and chemical diffusion coefficient measurements applied to mixed-conductivity intercalation compounds

Abstract

An electrochemical cell is described which allows composition-dependent measurements of the electronic conductivity and the chemical diffusion coefficient of mixed ionic–electronic conducting compounds. The composition of the compounds can be varied in situ by performing coulometric titrations according to Faraday's law. The electronic conductivity is obtained by means of dc four-point measurements with ionically blocking electrodes employing the van der Pauw method. The chemical diffusion coefficient is obtained from a combination of an electrochemical long-time polarization and short-time depolarization technique applied to the asymmetric cell proposed. The galvanic cell has been applied to investigate the transport properties of the intercalate Ag_xNbS₂(0.60 < × < 0.77) at 100 °C. The chemical diffusion coefficient increases considerably with increasing silver content of the intercalate with values in the range of 10^–5 cm² s^–1. The electronic conductivity decreases with increasing silver concentration with typical values around 1000 S cm^–1. Additionally, the temperature dependence of the electronic conductivity of Ag_0.6NbS₂ indicates metallic behaviour of the silver intercalate. The variation of the conductivity with composition can roughly be interpreted in terms of a single-carrier (hole) rigid-band model.