A finite element model for mixed potential sensors

Many studies are dealing with the behavior of mixed potential sensors. However, a quantitative description of the processes leading to the sensor signals has not yet been carried out. This paper describes a first approach to address the question to what extent a mixed potential sensor can be modelled in a finite element model. In 1D geometry, the electrochemical reactions that lead to signal formation, but also the gas phase reactions at the electrodes, were taken into account. Polarization curves, taken by a novel and for such research optimized setup, are used to determine the electrochemical parameters. Those are necessary to quantify the kinetics and electrical properties of the sensor system. It will be shown how to deduce other analyte concentrations and sensor temperatures from a single data set. In addition, the geometry of the electrode can be modified. In the model, the sensor signal is calculated for the analytes propene, hydrogen and carbon monoxide and compared with measured values. In particular, it shows the limitations of the conventionally used simplified mixed potential theory, since a complete Butler-Volmer equation has to be used for each analyte, especially for small analyte concentrations. This model serves as a basis for even more detailed studies that further elucidate the mechanisms behind mixed potential formation in mixtures or by varying the electrode configuration.