Role of Pt aggregates in Pt/SnO2 thin films used as gas sensors -: Investigations of the catalytic effect

Fine dispersions of metal aggregates such as Pt, Pd, or Cu in metal oxides are well known to improve the electrical sensitivity and selectivity of solid-state gas sensors put in contact with reducing gases (CO and H2S, for instance) of solid-state gas sensors. The improvement originates in the catalytic role played by the aggregates in regard to gas oxidation/reduction. The details of the solid-gas interactions are nevertheless not fully understood. To further investigate the role of Pr aggregates in the sensing mechanisms results of in situ X-ray absorption and Anger electron spectroscopy from Pt/SnO2 films have been combined. Films with a Pt concentration in the range 0.6-6 atom % have been prepared using a modified chemical vapor codeposition method. Results show that the sensing mechanism in mainly driven by the CO oxidation catalyzed by the aggregates: first a spillover effect occurs between CO, chemisorbsd oxygen, and PtOy aggregates, and in a second step, after a period of time depending on temperature, the aggregates are reduced/oxidized provided that they are small enough. The correlations between Pt particle behavior and film electric properties are discussed. (C) 2000 The Electrochemical Society. S0013-4651(00)01-035-1. All rights reserved.