Fabrication of SnO2 Particle-Layers using the Electrospray Method and Gas Sensing Properties for H2

The particle layers of SnO₂ were prepared using the electrospray pyrolysis method from SnCl₂ ethanol solution on the glass substrates heated at 773 K. Pyrex and quartz glass were used for the substrates. The effects of the concentration and the conductivity of the precursor solutions on the morphology and gas sensitivity of the SnO₂ layers were investigated. The sensitivity measurements were carried out for 0.5% H₂ in synthetic air at the operating temperature of 573 K and that was defined by the resistance ratio of the specimen under synthesized dry-air (R_air) and 0.5% H₂ (R_gas), R_air/R_gas. Among the examined concentrations of 1× 10^–4, 1× 10^–3 and 1× 10^–2 mol dm^–3, the layer prepared at 1× 10^–3 mol dm^–3 exhibited the maximum sensitivity of 20. The particle sizes were 110(30), 160(40), and 150(35) nm in diameter at 1× 10^–4, 1× 10^–3, and 1× 10^–2 mol dm^–3, respectively. The values in the parentheses indicate the standard deviation of the measured data. On the other hand, the conductivity of the solution exerted no significant influence on the sensitivity, which was adjusted by the addition of dilute hydrochloric acid. The particle size decreased with the conductivity and became 134(30), 105(20) and 87(20) nm in diameter at 7.8, 27.0 and 86.6 S cm^–1, respectively. Under all the conditions the layers had the dendrite-like structure, indicating the in-flight particle formation. The crystallite size was evaluated to be 6 nm from XRD using the Scherrers equation. These particles of 87–160 nm was thought to consist of smaller primary particles (crystallites). The Pd doping by 1 wt% to SnO₂ enhanced the gas sensitivity by a factor of 4.