A CO2 sensor with polymer composites operating at ordinary temperature

Many CO2 sensors proposed to date require high operation temperature (e.g., 400 degreesC for solid electrolytes) to detect CO2 with a high sensitivity , which restricts the wide application of CO2 sensors. We have found that c omposites consisting of the emeraldine base-polyaniline (EB-PAn) and poly(v inyl alcohol) (PVA) serve as a promising CO2 sensor operating at room tempe rature with a high sensitivity. The logarithm of electrical conductivity of the EB-PAn/PVA composite is proportional to the log of CO2 concentration. For the composite with 13 wt % EB-PAn and 87 wt % PVA, the Linear relations hip holds in the concentration range from 50 ppm to 5% at 30% relative humi dity. This composite is insulating in a moist atmosphere without CO2. With the addition of CO2, however, carbonate ions are formed by the hydrolysis o f CO2, and these ions equilibrate with the atmospheric CO2. The carbonic ac id is reversibly incorporated to and ejected from the EB-PAn depending on t he concentration of atmospheric CO2, and the conductivity varies between co nducting and insulating levels. (C) 2000 The Electrochemical Society. S0013 -4651(00)03-054-8. All rights reserved.