Estimation of the electrodes’ three phase boundary sites in electrochemical exhaust gas sensors before and after electric polarization

A theoretical model for quantifying the number of three phase boundary sites using the impedance spectrum of porous electrodes is presented and validated in exhaust gas sensors. The sensing responses and impedance spectra are registered before and after polarizing the sensors at high temperatures under different atmospheres and elapsed times. After polarizing under an oxidant atmosphere, the sensors do not modify their output response neither their impedance spectra. When polarizing for 3 min at 680 °C and under a reducing atmosphere, the sensing parameters improve (higher sensitivity and lower response times) and the impedance spectrum of the sensors changes. In this case, fitting with the proposed impedance model suggests that the number of three phase boundary sites in the electrode increases after polarizing.