High-Temperature CO₂ Sensor with Second-Level Response for Diesel Engine Exhaust Gas Detection Applications

Diesel engines in the field of transportation are one of the important sources of carbon dioxide (CO₂) emissions, and incomplete combustion and complex working conditions make it difficult to accurately calculate their CO₂ emissions by using the intake volume. In addition, the high temperature and harsh environment of exhaust gas also put higher requirements on the response speed, stability, and high-temperature resistance of the sensor. In this study, Co₃O₄ was doped into the auxiliary phase Na₂CO₃ as a catalyst and stabilizer to improve the sensor sensitivity, and solid electrolyte NASICON was doped to improve the sensor response speed. The results show that when the doping ratio of Na₂CO₃ and NASICON is the same as 10 wt %, the response to CO₂ of 5000 ppm can reach -67 mV, and the full-range second-level response to CO₂ is realized. The detection range is up to 0-180,000 ppm, the sensitivity is -64 mV/decade, the sensor has good selectivity to CO₂, the response change in the range of 20-98% RH is negligible, and the response change in 60 days is only -8.66%. This sensor had good reproducibility. In addition, the in situ on-board CO₂ sensing probe and test system were developed. The sensor response was calibrated against the measurement values of standard instruments on the entire vehicle. Based on the calibration results, a regression curve was established and the vehicle was tested; the test results and the standard instrument test value deviation are basically less than 10% to verify the practicality of the component in the exhaust gas detection.