Preparation of total VOC sensor with sensor-response stability for humidity by noble metal addition to SnO2

Noble metals addition to SnO2 was examined in order to develop high sensitive total volatile organic compounds (T-VOC) sensors with high stability for humidity. The noble metals loaded SnO2 thick films were prepared, and their sensor responses were measured for various kinds of VOC gases and a T-VOC test gas. The results of the measurements for various kinds of VOC gases showed that simultaneous addition of Pt, Pd and Au or simultaneous addition of Pt and Au were useful for sensitization for VOC gases giving a small response for the unloaded SnO2 thick films. These sensors could detect 0.056 ppm of the T-VOC test gas, and the sensor responses increased with increasing the concentration of the T-VOC test gas. The series of additives with Pd was effective to improve the stability for humidity. The sensor loaded with Pt, Pd and Au simultaneously satisfied both high sensitivity to the T-VOC test gas and sensor-response stability for humidity. The results of X-ray photoelectron spectroscopy of the sensor showed that most of loaded palladium exists as PdO. In addition, it was suggested by the shift of binding energy of a Sn3d orbit and an O1s orbit that the electronic sensitization was dominant in the sensor. It was supposed that the electronic sensitization was effective for the sensor response stability for humidity. From these results, the combination of the chemical sensitization by Pt-Au addition and the electronic sensitization by Pd addition gives high sensitivity to the T-VOC test gas and stability for humidity to the Pt-Pd-Au loaded SnO2 thick films, and it is expected that the SnO2 thick film with Pt, Pd and Au will be applicable to T-VOC gas sensor.