In situ fabrication of conducting polymer composite film as a chemical resistive CO2 gas sensor

In this study, an easy to fabricate and low-cost, resistive-type CO2 gas sensor made of poly(3,4-ethylenedioxythiophene) (PEDOT) and branched polyethylenimine (BPEI) layers was fabricated on an interdigitated electrode. The PEDOT film was made by in situ polymerization and the BPEI layer was subsequently drop-coated on top of the PEDOT film. Upon exposure to 1000 ppm CO2 at 95% relatively humidity (RH) of the BPEI-PEDOT composite sensor, the synergistic effect of BPEI on CO2 sensing was subsequently investigated. The sensors showed no response (i.e. % of conductivity increase) if the sensor film was only made of a PEDOT layer without any BPEI. However, the response increased significantly to a value of 3.25% upon the addition of a layer of BPEI. The sensors also showed no obvious decay in the sensing response during repeated usages, providing the reusability of the technique for CO2 detection. As for sensor's selectivity, the sensors showed higher response for CO2 than for O2. Originally, the sensor showed a long recovery time of nearly 1 h. However, the long recovery time can be significantly shortened to approximately 10 min by heating the sensors at higher temperature for CO2 desorption. Thus, this easy and inexpensive fabrication process demonstrated that the sensor might have characteristics sufficient for real-world CO2 detection.