Enhanced performance of novel calcium/aluminum co-doped zinc oxide for CO2 sensors

Calcium/aluminum co-doped zinc oxide (ZnO:(Ca,Al)) nanoparticles (NPs), with 1 at% of Al and different Ca (1-5 at%) content, have been successfully synthesized by a simple sol-gel method. Synthesized nanoparticle samples were used to fabricate thick film resistive semiconductor gas sensors for CO2 detection in air. The screen-printed sensing layer on the ceramic substrate has been characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analysis to assess the morphological, microstructural properties and reveal defect features, respectively. Sensing tests demonstrated the strong influence of the Ca and Al on the sensing performance towards CO2. Light excitation by means of an UV source (400 nm) has been used to enhance the sensor performance. The positive influence of humidity on the sensor performance was also established. The optimized sensor, based on ZnO doped with 3 at% Ca and 1 at% Al showed promising performances towards CO2, ensuring high response and fast dynamics at operating temperature as low as 200 °C.