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 s and a recovery time of 25 s. 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.