THE ROLE OF ADDITIVES IN TIN DIOXIDE-BASED GAS SENSORS

The role of additives (PdCl2, Al2O3 and Nb2O5) in SnO2 gas sensors has been examined by X-ray photoelectron spectroscopy (XPS) and analyses of the gas-sensing behavior. Al2O3-doped SnO2 shows a slight increase in sensitivity to CO and CH3CN as compared with pure SnO2. On the contrary, Nb2O5-doped SnO2 shows the opposite trend. The sensitivity of PdCl2-doped SnO2 to both CO and CH3CN in the low-temperature region below 300-degrees-C is greatly increased. The major oxidation states of Pd in 0.5 wt.% PdCl2-doped SnO2 sintered at 800-degrees-C and 650-degrees-C are 4+ and 2+, respectively. The binding energies (BEs) of Sn 3d5/2 and O 1s1/2 remain almost constant up to 1.0 wt.% PdCl2 loading. When exposed to H-2 at foom temperature, the major oxidation state of Pd in 0.5 wt.% PdCl2-doped SnO2 sintered at 800-degrees-C changes from 4+ to 2+. This change in the oxidation state of Pd, along with the enhanced sensitivity to CO below 200-degrees-C, my suggest the electronic interaction of Pd with SnO2 at low temperature. The combustion products of CH3CN with 1.0 wt.% PdCl2-doped SnO2 powder are confirmed to be CO2, H2O and CO by gas chromatography (GC).