Single-Phase High-Entropy Oxide Nanoparticles for Wide Dynamic Range Detection of CO₂

Monitoring wide-range carbon dioxide (CO2) levels with superior sensing performance is extremely important for environmental, human health, safety, and space applications. The reported chemiresistive sensors in the literature have critical drawbacks such as high-temperature operation and long response and recovery times (∼25 min), which remains a challenge for developing CO2 sensors. Against these drawbacks, we report Gd0.2La0.2Y0.2Hf0.2Zr0.2O2 (Y-HEC)-based sensors obtained by depositing Y-HEC on a glass substrate with different electrodes such as gold (Au), indium tin oxide (ITO), and silver (Ag) for CO2 gas detection. The as-fabricated Y-HEC sensor with an ITO electrode displayed a maximum sensing response (46.7%) to 10000 ppm CO2 gas at room temperature over other electrodes, which is attributed to the optimized Schottky barrier height between the ITO and Y-HEC. Furthermore, the experimental findings of the sensor with an ITO electrode revealed superior sensing characteristics such as wide-range CO2 gas detection (250–10000 ppm), faster response and recovery times (49–200 s), high repeatability, strong selectivity to CO2 over other gases, good long-term stability, and room temperature operation. Improvements in the CO2-sensing performance are attributed to nonagglomerated nanoparticles leading to the porous structure and high surface area, and intrinsic oxygen vacancies. We present an easy strategy to synthesize sensing materials and improve the desirable sensing performance for the development of practical applications of CO2 sensors.