Galvanic Cells with Solid Electrolytes for Kinetic Investigations

Abstract

Besides their use for thermodynamic measurements, galvanic cells with solid electrolytes have become increasingly important for kinetic studies in solids and at surfaces and phase boundaries of solids. As has been discussed in Chap. 8, thermodynamic measurements using such cells allow to determine Gibbs reaction energies ΔG or to obtain activities or chemical potentials in mixtures and chemical compounds. With the aid of polarization measurements on suitable galvanic cells, it is possible (see Sect. 6.3) to obtain information about partial conductivities in solids; this already represents an application of galvanic cells in kinetic studies. Other kinetic measurements with solid-state galvanic cells involve diffusion processes or diffusion-controlled reactions, reactions taking place at the phase boundary solid/gas, or solid/solid respectively. Kinetic investigations of this type are made possible because galvanic cells containing solid auxiliary electrolytes, which exhibit virtually pure ionic conductivity, not only provide thermodynamic information via the emf but also allow direct determination of reaction rates via measurements of the current flow within a suitably constructed cell. The combination of rate measurements (via electric currents) with measurements of thermodynamic quantities (via emf’s) often permits the analysis of kinetic processes. This will be discussed in the following for six typical examples:

• 1. Diffusion of oxygen in metals,

• 2. formation of nickel sulfide on nickel,

• 3. transfer of silver across the phase boundary silver/silver sulfide,

• 4. electrochemical studies of evaporation and condensation,

• 5. the electrochemical Knudsen cell,

• 6. chemical diffusion in metal oxides and sulfides.