Charge transport mechanism in pressed pellets of polymer proton conductors

The charge transport inside some polymer proton conductors, prepared by chemical doping of poly(propargyl alcohol) and poly(p-diethynylbenzene) with acids, or by electrochemical polymerisation of thionaphtheneindole, has been investigated. All the systems, studied as powder pressed pellets between two gold electrodes, show very low electrical conductivity due to electrons motion. In presence of environmental humidity the conductivity increases dramatically as a consequence of proton migration through the material. A mechanism for the charge transport through the materials, based on the proton conductivity of a thin layer of acid aqueous solution adherent to the polymer grains, has been hypothesised. Since the investigated doped polymers show a reversible conductivity Variation as a function of water content, they are proposed as materials for humidity sensor construction.