Adsorption-induced conductance changes of thin Pt films and PtPd/TiO2 gas sensors

Abstract

Chemisorption of H2 and O2 and resulting changes in electrical conductance of a typical gas sensing material, PtPd/TiO2, and thin Pt films on glass are studied and compared. The activation energy of conduction increases as Pt film thickness decreases. Chemisorption of H2 on thin Pt films causes an increase in conductance and activation energy of conduction. O2 chemisorption results in a decrease in conductance and increase in activation energy of conduction. Alteration in the number of charge carriers and reduction in charge carrier mobility are the mechanisms proposed for the observed changes. Compared to thin Pt films, relatively large changes in electrical conductance are observed upon chemisorption of gases on TiO2 supported PtPd. The role of the oxide substrate in the observed chemical interaction and electronic response is discussed. The electronic changes upon adsorption/desorption of gases are reversible for thin Pt films but only partially reversible for TiO2 supported PtPd.