CO sensing properties and mechanism of Pd doped SnO2 thick-films

Pd doped SnO2 nano-particles were synthesized using co-precipitation method. The resistances of the samples first decrease and then increase, which maybe influenced by the Pd doping and temperature effect. The CO response of SnO2 was improved by doping with Pd. At low temperature range, the response decreases with increasing of operating temperature, which was caused by the physical adsorption. At higher operating temperature (160-400 °C), the response of Pd doped SnO2 for CO increases at first, undergoes a maximum at 260 °C, and finally drops. The 1.5 wt.% PdO doping SnO2 was verified to be significantly sensitive. The largest gas sensitive response of 6.59 was found at 260 °C in 400 ppm CO atmosphere. For 200 ppm CO, the response and recovery time were about 43 s and 10 s, respectively. The possible CO sensing mechanisms for Pd doped SnO2 sensors were investigated with first principles calculations. The calculation results showed that CO molecule can grab O from the pre-adsorbed oxygen on Pd4 cluster or the PdO cluster on the SnO2 (110) surface forming CO2. These processes may play important role in CO sensing for Pd doped SnO2. The calculated result is a good explanation of the experimental observation.