Bilayer Au/Cr nanocoatings on AAO nanoporous membrane for ultrafast, selective CO₂ detection at room temperature

The development of efficient carbon dioxide gas sensors that operate at room temperature remains a significant challenge due to limitations in sensitivity, selectivity, and energy efficiency. In this study, we present a novel multilayered sensor platform based on porous aluminum oxide membranes, which are sequentially coated with thin layers of chromium and gold. Three distinct configurations—single-layer (Au/Cr/AAO), double-layer (Au(2)/Cr(2)/AAO), and triple-layer (Au(3)/Cr(3)/AAO) coatings—were fabricated using controlled physical deposition techniques and thoroughly characterized using electron microscopy, elemental analysis, optical spectroscopy, and electrical response measurements under carbon dioxide exposure. Among these, the double-layer structure exhibited enhanced surface roughness and uniform nanoparticle distribution, leading to improved gas adsorption capabilities. When exposed to carbon dioxide concentrations up to 4440 parts per million, this configuration demonstrated the highest sensitivity, rapid response times ranging from 1.38 to 3.45 min, and quick recovery between 1.0 and 1.9 min under ambient conditions. The sensing mechanism is attributed to surface interactions with reactive oxygen species and efficient electron transfer across the metal interfaces. Compared to previously reported sensors, this design offers a unique combination of low energy consumption, room-temperature operation, and high performance, making it a promising candidate for real-time environmental monitoring of carbon dioxide. • Optimized Au/Cr layering enhances CO₂ adsorption for superior gas sensing at RT. • Surface roughness improves nanoparticle distribution, boosting sensor response. • Rapid CO₂ detection with resistance changes ensures high sensitivity & reliability. • Achieves fast response (1.38–3.45 min) and recovery (1.0–1.9 min) for CO₂ sensing. • Low-power multilayered Au/Cr/AAO sensor offers stability for environmental use.