Effects of Pt loading onto SnO2 electrodes on CO-sensing properties and mechanism of potentiometric gas sensors utilizing an anion-conducting polymer electrolyte

Abstract

Gas-sensing properties of electrochemical CO sensors utilizing Pt-loaded SnO2 electrodes and an anion-conducting polymer electrolyte have been investigated mainly at 30 °C in wet synthetic air (57%RH), and the effects of the Pt loading onto SnO2 on the CO-sensing properties and their CO-sensing mechanism have been discussed in this paper. The amount of Pt loaded onto SnO2 (0.5–5.0 wt%) and the subsequent heat-treatment at 500 °C in air were effective in enhancing the CO responses and the CO selectivity against H2. The sensing-electrode potential was governed by mixed potential resulting from electrochemical CO (or H2) oxidation and O2 reduction, and all the results obtained indicated that the oxidation rate of CO molecules was electrochemically quite faster than that of H2 molecules on the mono-dispersive and oxidized Pt species as an active site, which were doped at the surface SnO2 lattice. On the other hand, the heat treatment at 250 °C in H2 after the Pt loading reduced the surface of Pt-loaded SnO2 and drastically enhanced both CO and H2 responses and thus decreased the CO selectivity against H2. This effect arose probably from the reduced Pt species with metallic surface, which were quite active against both CO and H2 anodic reactions.