Effect of electrodes and zeolite cover layer on hydrocarbon sensing with p-type perovskite SrTi0.8Fe0.2O3-δ thick and thin films

Screen-printed thick film as well as pulsed laser deposited thin film sensors of the perovskite SrTi0.8Fe0.2O3-delta (STF20) with gold electrodes present poor hydrocarbon selectivity when exposed to different gases (hydrocarbons, hydrogen, NO, and CO). By employing Pt-electrodes, response to H-2 and CO is eliminated. In the case of thick film devices, only NO cross interference persists. The selectivity of the thick films is further increased by applying a Pt doped zeolite (ZSM-5) as a cover layer. By adjusting the thickness of the ZSM-5 cover layer, the film selectively senses mainly saturated hydrocarbons such as propane, suppressing the response towards all the other gases. This effect is attributed to the catalytic effect of the high Pt-content of the ZSM-5 zeolite. Application of a ZSM-5 cover layer to thin films enhances the sensor output response to propane, thus reducing selectivity for unsaturated hydrocarbons. A sensor configuration having Pt electrodes on top of an STF20 thick film with an additional 50 mu m cover layer of ZSM-5 was found to be the most suitable to selectively sense saturated hydrocarbons. Thin film STF20 sensors equipped with Pt-IDC electrodes and without the zeolite cover layer, were found to perform best for unsaturated hydrocarbons at 400 degrees C.