Zeolite-based Impedimetric Gas Sensor Device in Low-cost Technology for Hydrocarbon Gas Detection

Abstract

Due to increasing environmental concerns the need for inexpensive selective gas sensors is increasing. This work deals with transferring a novel zeolite-based impedimetric hydrocarbon gas sensor principle, which has been originally manufactured in a costly combination of photolithography, thin-film processes, and thick-film processes to a low-cost technology comprising only thick-film processes and one electroplating step. The sensing effect is based on a thin chromium oxide layer between the interdigital electrodes and a Pt-loaded ZSM-5 zeolite film. When hydrocarbons are present in the sensor ambient, the electrical sensor impedance increases strongly and selectively. In the present work, the chromium oxide film is electroplated on Au screen-printed interdigital electrodes and then oxidized to Cr2O3. The electrode area is covered with the screen-printed zeolite. The sensor device is self-heated utilizing a planar platinum heater on the backside. The best sensor performance is obtained at a frequency of 3 Hz at around 350 °C. The good selectivity of the original sensor setup could be confirmed, but a strong cross-sensitivity to ammonia occurs, which might prohibit its original intention for use in automotive exhausts.

Selective mixed potential ammonia exhaust gas sensor

“…Besides that, impedimetric sensors based on zeolites [14][15][16][17] or on strong acids like tungstated zirconia [18,19], or resistive molybdenum oxide based sensors [20] are suggested and investigated.…”

Integrated impedance based hydrocarbon gas sensors with Na‐zeolite/Cr2O3 thin film interfaces: Electrochemical mechanism of the impedance changes

“…A careful control of the purity, microstructure and thickness of the chromia films is essential for the fabrication of reliable sensors. This is best achieved with established thin film deposition techniques by physical or chemical vapour deposition, while fabrication concepts entirely based on thick film printing techniques are questionable 44.…”

Kompostite auf Basis von Zeolithen oder geordnet mesoporösen Oxiden für Anwendungen in der Photonik und Sensorik

“…So wirken ZSM-5-Filme, die in einfacher Dickschichttechnik und mit Galvanikprozessen mit einer Chromoxid-Grenzfläche kombiniert werden, als hoch selektive Kohlenwasserstoffsensoren [66]. Ein deutlicher Anstieg der Impedanz bei niedrigen Frequenzen tritt nur auf, wenn zwischen dem Zeolithen und dem p-leitenden Cr 2 O 3 ein deutlicher Grenzflächenkon-takt vorliegt und die unterschiedlichen Leitfä-higkeiten für Sauerstoffionen in den beiden Materialien zum Tragen kommen [67]. Interessant ist auch der Ansatz, Zeolithschichten auf nur halbwegs selektive konduktometrische Gassensoren (vor allem p-leitende Halbleitergassensoren) aufbringen und damit deren Selektivität zu erhöhen und somit hochwirksame Sensoren für Kohlenwasserstoffe zu entwickeln [68].…”