Carbon nanotube ammonia gas sensor: a comparative analysis between impedance spectroscopy and resistive measurements

Ammonia (NH3) is potentially a hazardous gas that can be a threat to both human health and the environment. This is why, sensitive, fast, low-cost, and accurate sensing techniques for ammonia detection are extremely needed, especially if on soft substrates Nowadays, a wide range of gas sensors based on single-walled carbon nanotubes (SWCNTs) has been reported. Nevertheless, most of the reported solutions (mostly on rigid substrates) suffer from non-linear responses and low sensitivity. In this work, we report flexible gas sensors based on spray-coated SWCNTs for the detection of (NH3) in a range of concentrations from 15 ppm to 90 ppm. The performance of fabricated devices was evaluated by comparing two different measurement methods, i.e. conventional resistance (CR) and impedance spectroscopy (IS). The calibration curve of the fabricated SWCNT gas sensor using CR showed a linear detection range with a 97.56% coefficient of determination and a sensitivity of 0.27 (% normalized response/ppm to NH3). By using IS instead of CR on the same detection range, the extracted coefficient of determination was 99.56% and the sensitivity 1.26, almost five times higher than the former value. This difference in the sensitivity shows that it is possible to perform a much more sensitive measurement by employing IS.