An Environmental Monitoring CO2 Sensor Based on LLZO Solid Electrolyte Film and WC – Li2CO3 Auxiliary Phase

As the requirements for information accuracy in various application fields continue to increase, the grid-based deployment of CO2 sensors is playing an increasingly crucial role in air quality monitoring, agricultural intelligent regulation, and climate change research. For large-scale applications, the sensors are required to have low cost, small size, long lifespan, and low power consumption. In this study, by comparing different doping elements, a high-quality Ga-doped LLZO solid electrolyte film was selected, providing an ion transmission channel for the device to operate at lower temperatures. Doping WC in the auxiliary phase Li2CO3 increased the electronic conductivity, and its high hardness formed a pinning effect, achieving the key goals of promoting electrochemical reactions and improving the structural stability of the auxiliary phase. The 10 wt % WC-Li2CO3 auxiliary phase possesses excellent ionic and electronic conductivity as well as structural stability. The sensitivity of the fabricated CO2 sensor can reach -18.87 mV/decade, and the optimal working temperature is reduced to 265°C. The adsorption response speed and desorption response speed are 3 s and 20 s, respectively. Compared with similar CO2 sensors, it has obvious advantages. Moreover, the sensor exhibits good stability in repetitive tests, humidity tests, temperature tests in different environments, and long-term operation tests. Additionally, a one-week real-time monitoring of CO2 concentration in the office was conducted, and the output results were stable and reliable, showing good regularity.