Conducting polymer gas sensors

Abstract

Recent results with solid-state semiconductor gas sensors based on organic sensor elements are reviewed. Devices based on metal phthalocyanines show useful responses to NO₂. Lead phthalocyanine combines the highest conductivity with the maximum sensitivity to NO₂. A thin-film lead phthalocyanine sensor has successfully been used to monitor NO_x produced by shot-firing in coal mines. To obtain reasonable conductance and speed of response and recovery, phthalocyanine sensors have been operated at 170°C. Conducting polymer materials, and particularly chemically doped polypyrrole, show responses to toxic gases at ambient temperature. Initial work, using polypyrrole black impregnated filter paper, showed a response to ammonia. More recently, using polypyrrole films electrochemically deposited over electrode arrays, responses to nitrogen dioxide and hydrogen sulphide have also been obtained. Organic-semiconductor gas sensors may have advantages compared to metal-oxide devices in their sensitivity to toxic gases and in their ability to operate at or near room temperature. However, the mechanisms of device function are not yet well understood.