A study of water influence on CO response on gold-doped iron oxide sensors

A temperature programmed desorption (TPD) study of the water- and CO-interaction with the surface of gold-doped iron oxide sensors is presented. TPD data has shown that CO does not adsorb in the absence of water. The adsorption of CO occurs when water is present as coadsorbate, through the formation of a surface formate intermediate. TPReaction of CO with oxygen in both dry and wet air has shown that water also promotes CO oxidation, likely via the same formate intermediate. The effect of water on the CO sensing of Au/Fe2O3 sensors was also investigated. Current response data at different temperatures and relative humidity were fitted by the equation S = ICO/Iair = k[CO]β, with the sensitivity (k) and exponential (β) factors dependent on the temperature and relative humidity (RH). Moreover, in wet air, the maximum of response, TM, shifts to higher temperature with respect to dry air. To explain the results of electrical tests two different sensing mechanisms which operate in dry and wet air, respectively, have been suggested.