Integrated impedance based hydrocarbon gas sensors with Na-zeolite/Cr_2O_3 thin film interfaces: Electrochemical mechanism of the impedance changes

摘要

This study aims to clarify the mechanism of a hydrocarbon gas sensor effect, which involves impedance changes of a Na+ ion conducting Pt-doped zeolite layer in contact with chrornia (O_2O_3) films as electrodes. Based on our previous studies on sensing characteristics and model experiments with asymmetrical cells, a coherent picture of the sensing mechanism is derived: The impedance change is attributed to the process of Na~+ ion insertion from the zeolite into the chromia film. The impedance of this interface process is a function of the electrical potential at the interface. Combined with the observation that gas sorption in the zeolite micropores causes changes of the electrochemical potential at the zeolite surface, these two effects explain the observed sensor effect. The sensor response as predicted from this theory agrees well with the experimental data of the original sensor. Implications for the development of integrated devices are discussed.