Multilayer (Cr/Au)n/PAA nanoporous membrane for ultrafast, selective CO2 detection at room temperature

Abstract

Achieving high-performance CO₂ sensing at room temperature remains a significant challenge due to persistent trade-offs between sensitivity, selectivity, and energy efficiency. In this study, we present a robust and scalable gas sensing platform based on nanoporous anodic aluminum oxide (PAA) membranes functionalized with sequentially deposited nanolayers of Cr and Au. Three distinct multilayer sensor structures, (Cr/Au)ⁿ/PAA with n = 1, 2, and 3, were developed using a modified fabrication process that combined two-step anodization, pore widening, and RF sputtering. These configurations were thoroughly characterized through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), UV–vis spectroscopy, and electrical response analysis under CO₂ exposure. Among them, the (Cr/Au)³/PAA sensor exhibited the most pronounced performance, achieving a high relative response of 160.69% at 4440 ppm CO₂, with rapid response and recovery times ranging from 60.4–95.95 s and 24.42–99.04 s, respectively. These enhancements are attributed to the optimized multilayer architecture, which increases surface roughness, active site density, and charge transfer efficiency. The sensing mechanism is governed by reversible interactions between CO₂ molecules and pre-adsorbed oxygen species, modulating the carrier concentration within the metallic layers. Long-term stability tests over 30 days confirmed excellent repeatability, while selectivity measurements revealed a strong preference for CO₂ over interfering gases such as C₂H₂ and H₂. This work demonstrates a promising route toward low-power, high-fidelity gas sensors and establishes a versatile framework for tailoring gas selectivity and sensitivity through nanoscale interface engineering.