A novel carbon-based ionic conductor for humidity sensors

Carbon films modified by means of Na2CO3 were tested as a novel material for the construction of humidity sensors. On the contrary, to "virgin" carbon films and carbon films modified by some alkali metal compounds like hydroxides, acetates or chlorides, the Na2CO3-modified materials exhibit a mixed conduction mechanism. Beside hole/electron conduction the novel carbon, films behave as ionic conductor provided relative humidity is high enough. During carbonisation, the applied modifier forms nano-crystals of Na2CO3 on the surface and in the bulk of semiconductor carbon matrix. The inorganic nano-crystals dissolve and dissociate in the layer of adsorbed water. Ions produced in this way increase electric conductivity of the system contributing significantly to total electric current passing through the carbonate-modified carbon films. The novel carbon material is highly sensitive to water vapour. Water adsorption induced resistance changes of the film are reversible and therefore the material may be applied to the construction of humidity sensors. Carbon films obtained by means other alkali metal carbonates as modifiers behave in a similar way. (c) 2005 Elsevier B.V. All rights reserved.