Printed flexible sensors functionalized with TiO2 nanowires for room temperature CO2 gas sensing

The monitoring of CO₂ concentration is important for the environment and health. The present work reports a printed silver electrodes CO₂ sensor with TiO₂ nanowires coated on the surface. The silver electrode sensor was printed with a Voltera PCB printer. TiO₂ nanowires were attached to the electrodes by an electro-deposition method. Variations in resistance of the sensing element by the exposure of CO₂ gas were successfully observed at room temperature without additional heat. The printed CO₂ sensor shows responses from 78 ppm to more than 1055 ppm with a response time of 92 seconds and a recovery time of 25 seconds. The selectivity experiment displays that the printed sensor does not respond to methane, CO, NH₃, H₂, or H₂S at 1000 ppm or higher concentration but it is slightly sensitive to humidity. The response is 2% for 1000 ppm CO2 while the response is 0.7% when the relative humidity changes from 48% to 99%. The present results display a facile method to develop highly sensitive and selective CO₂ sensors operating at room temperature.