Highly sensitive ammonia sensing at room temperature with Ce/Pr mixed oxide/oxidized MWCNT composite

Ammonia is a hazardous atmospheric pollutant of major industrial relevance, yet reliable room-temperature (RT) detection in real conditions remains challenging for conventional metal-oxide sensors due to high operating temperatures, poor sensitivity and selectivity, humidity effects and limited real air validation. Herein, we report a chemiresistive NH₃ gas sensor based on a Ce/Pr mixed oxide nanocomposite with oxidized multi-walled carbon nanotubes. The sensing layer, deposited by a simple and cost-effective airbrush spray-coating technique and thoroughly structurally and morphologically characterized, exhibits superior detection performance at RT. In real air at 40% relative humidity and RT, the sensor exhibits an exceptionally strong and low-noise response of 7.1% to just 200 ppb NH₃, whereas the mixed oxide alone showed no detectable signal below 10 ppm. Furthermore, the device achieves an ultra-low detection limit of ∼60 ppb and an unusually broad linear range of more than three orders of magnitude (0.2-500 ppm), supported by 32 concentration points. Notably, the sensor response remains stable across a wide relative humidity range (35% to 70%) and displays excellent operational stability by retaining a reproducible signal over 240 consecutive measurements in real air. Selectivity tests demonstrated negligible cross-sensitivity to common gases (CH₄, CO, CO₂, H₂) and representative volatile organic compounds. Importantly, equivalent response amplitudes were obtained when alternating between real and synthetic air, which underscores the sensor's reliability in real environments. Overall, these results establish this hybrid material as a robust and highly sensitive platform for sub-ppm ammonia detection in challenging samples such as air and breath.