CO gas sensing properties of Cd(OH)₂/CdO thin films synthesized by SILAR method

Cd(OH)₂/CdO thin films were synthesized on glass substrates by the SILAR method at 30, 40, and 50 SILAR cycles. The effects of the SILAR cycle and sensor operating temperature on the structural, morphological, and CO gas-sensing properties of the films were investigated. XRD studies revealed that synthesized films had a polycrystalline hexagonal phase of Cd(OH)₂, and after static gas sensing measurements, the hexagonal phase was transformed to cubic phase of CdO with the effect of operating temperature. SEM analyses confirmed the phase conversion and showed that the morphological properties of films improved with operating temperature. Cd(OH)₂/CdO thin film-based sensors were fabricated and static-dynamic gas sensing measurements were made towards CO gas. The detection limit and operating temperature values of sensors were determined. The optimal operating temperature was found to be 157 °C for all sensors. The CO sensing results demonstrated that the sensor with 40 SILAR cycles has the highest sensitivity for 50–500 ppm CO gas concentration values at 157 °C compared to the others. The sensing responses of sensors increased from 24% to 40% for 50 ppm CO gas and from 44% to 69% for 500 ppm CO gas at 157 °C, depending on SILAR cycle. The activation energy (E_a) values of sensors were found to change between 0.396–0.684 eV in the Cd(OH)₂ phase regions and 0.495–0.912 eV in the CdO phase regions, with the SILAR cycle. The response and recovery times of sensor with 40 SILAR cycles were found to be 84.2 s and 40.8 s for 50 ppm CO gas at 157 °C, respectively. Furthermore, the sensor demonstrated excellent selectivity to CO gas compared to CO₂, CH₄, and NH₃ gases. Finally, our findings highlight the potential of Cd(OH)₂/CdO nanomaterials synthesized using a simple process and in different SILAR cycles as a promising material to enhance the sensing properties of CO gas sensors.