Adsorbed water as key to room temperature gas-sensitive reactions in work function type sensors:: the carbonate-carbon dioxide system

In this work, it was found that exposure of barium carbonate to carbon dioxide (0.003%-5%) as active gas in wet synthetic air as carrier gas leads to an increase in work function between 50 and 150 meV at room temperature. Other carbonates show a similar behaviour and lower sensitivities. Without humidity in the carrier gas, the sensitivity of barium carbonate disappears. Measurements were performed on pressed pellets, thick films (10-100 mu m) and thin films (1-2 mu m) of the material using a Kelvin probe with gold grid as reference electrode. The effect was found to be independent of preparation. Between 23 degrees C and 100 degrees C, maximum sensitivity is reached at about 50 degrees C. The work function change is attributed to the formation of dimeric HCO3- species which have been identified using diffuse reflectance infrared fourier transform (DRIFT) spectroscopy. (C) 1999 Elsevier Science S.A. All rights reserved.