CO-sensing properties of doped SnO2 sensors in H2-rich gases

Differently doped thick film SnO2 sensors were investigated in reducing atmospheres with high H-2 content. Such atmospheres appear in reforming processes frequently used for the production of hydrogen for the operation of fuel cells. The thermodynamic stability of SnO2 against reduction to the metal limits the operation temperature to temperatures below 320degreesC. Pt-, Pd-, and Au-doped SnO2-sensors showed sensitivity to CO. A maximum sensitivity was found for SnO2 sensors doped with 2 wt.% Pt at around 220 degreesC. The cross-sensitivities to hydrogen, carbon dioxide, and water are much lower. Typical response time (tau(63)) to changes in the CO content of about 2-3 s were found. diffuse reflectance infrared Fourier transform (DRIFT)-spectroscopy indicates that the surface of SnO2 is covered mainly with formate, OH, and methoxy (OCH3) groups. A simple model describing the resistance changes upon changes in CO concentration is proposed. (C) 2004 Published by Elsevier B.V.