Electrochemical measurements on cells, I: Simulation of potential distribution with an embedded probe

Measurements of electric potential in electrochemical devices such as solid oxide fuel cells (SOFC) or solid oxide electrolyzer cells (SOEC) are often made by placing a reference electrode on the surface. Measurement of electric potential with embedded electrodes (probes) has also been reported [1]. In a typical SOFC, it is assumed that the electronic conductivity is negligible compared to the ionic conductivity. The establishment of local thermodynamic equilibrium, an assumption made in virtually all transport theory, requires that the electronic conductivity cannot be set to zero mathematically [2,3]. Thus, to elucidate the role of electronic conduction in a predominantly ionic conductor, it is necessary to incorporate the electronic conductivity. Also, local equilibrium demands that transport of both ions and electrons (holes) be taken into account to describe the local chemical potential of electrically neutral species, such as oxygen. The local chemical potentials of electrically neutral species determine the thermodynamic stability and thus also the device stability.