Characterization and enhanced carbon dioxide sensing performance of spin-coated Na- and Li-doped and Co-doped cobalt oxide thin films.

Recognizing the substantial effects of carbon dioxide on human health and the environment, monitoring CO levels has become increasingly vital. Owing to energy constraints and the widespread application of CO gas sensors, it is important to design cost-effective, more efficient, and faster response CO gas sensors that operate at room temperature and involve a low-cost technique. This study aims to develop a cost-effective and efficient CO gas detector that functions at room temperature and uses less power than traditional high-temperature CO sensors. In this study, we achieved this by employing innovative CoO thin films with optimized spinel-structured p-type semiconductors through spin-coating, facilitated by Li and Na doping as well as Li/Na codoping. Doping with 3% Li/Na reduced the crystallite size from 92.4 to 8.03 nm and increased the band gap from 3.31 to 3.69 eV. At room temperature (30 °C), the sensor response improved significantly, increasing from 50% to 345.01% for 3% Li-CoO upon the addition of 3% Na at a concentration of 9990 ppm. This performance surpasses that of most metal-oxide-based CO sensors reported in the literature. Additionally, this optimized sensor demonstrated a very short response time of 18.8 s and a recovery time of 16.4 s at a CO concentration of 9990 ppm diluted with air. It outperformed other films in terms of sensitivity, stability, response and recovery times, and performance across a wide range of relative humidity levels (43-90%). The sensor exhibited superior selectivity for CO than for N, H, and NH. Overall, the 3% Li, Na-CoO sensor is well-suited for climate change mitigation and industrial applications.