Flexible Carbon Dioxide Sensors Based on Polyethyleneimine – A Study on Their Aging and Potential Solutions

CO₂ sensors, being widely utilized in indoor air quality monitoring, ventilation systems, automotive emission control, and healthcare, can be constructed using various materials and technologies. In recent years, polymers have been considered a popular sensing candidate due to their low cost, outstanding processability, and excellent compatibility with other materials. Polyethyleneimine (PEI) is a polymer that can interact with CO₂ molecules and generate measurable responses; thus, it’s been extensively explored in the development of CO₂ sensors. Even though many researchers have studied the stability of pure PEI, there are few studies for their real applications (i.e., CO₂ sensors) since it determines the sensor lifetime. Therefore, in this work, a systematic analysis of the screen-printed, PEI-based chemiresistive CO₂ sensors was conducted with emphasis on the sensors’ aging behavior along with the mechanism. More importantly, we have demonstrated solutions to address the sensor aging by selecting the proper molecular weight PEI and doing the chemical modification on PEI. The produced sensors exhibit much better cycling stability compared to the control sample.