Use of impedance spectrometry for self-monitoring of amperometric gas sensors

The sensitivity of an amperometric gas sensor is proportional to its electrochemically active surface. This area reduces due to deposits and dust layers and therefore should be monitored automatically during operation. The double-layer capacitance and the charge-transfer conductivity are also proportional to the active area of the electrodes. For self-monitoring, both values can be obtained with high accuracy by impedance-spectroscopy measurements, independently of the gas concentration. The double-layer capacitance is determined by model-based evaluation of the impedance spectra of the total sensing system, characterized by nine parameters. The analysis shows that only two out of these nine parameters are sample specific and have to be determined during operation, whereas the remaining ones are irrelevant or type specific only.