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

Abstract 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 μm) and thin films (1–2 μm) of the material using a Kelvin probe with gold grid as reference electrode. The effect was found to be independent of preparation. Between 23°C and 100°C, maximum sensitivity is reached at about 50°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.