The effect of initial conductivity and doping anions on gas sensitivity of conducting polypyrrole films to NH3

The action of ammonia on free-standing polypyrrole films doped with ClO4- and TsO(-) having a high conductivity in the range 10-65 S cm(-1) has been investigated. The gas sensitivity of conducting polypyrrole films to NH3, at room temperature, is dependent on the initial conductivity of the polypyrrole films and doping anions. A low conductivity causes an increase in sensitivity of polypyrrole films to NH3. The films containing ClO4- counterions display a high sensitivity, in the range 88 to 155% at 10 ppm NH3, whereas those including TsO(-) have a low sensitivity of around 20%. It is found that the sensitivity values of ClO4- - and TsO(-)-doped polypyrrole films remain constant for a period of 60 days in an ambient environment. The polypyrrole films formed by electrochemical oxidative polymerization are found to possess detectable sensitivity in the form of an increase in resistivity for NH3 gas.