Low-Cost Gas Sensing: Dynamic Self-Compensation of Humidity in CNT-Based Devices

Solid-state gas sensors are a cost-effective and well-spread alternative to conventional gas sensing, employable in most environments, ranging from homes and offices to harsh industrial scenarios. The emergence of carbon nanotubes (CNTs) as sensing material in solid-state gas sensors paved the way to a new class of devices, which are semitransparent, flexible, and with a remarkably low environmental impact. These devices, however, lack selectivity to other gases and concurring physical phenomena, such as temperature and pressure changes. In this contribution, we show how by measuring the impedance of CNT-based gas sensors at different frequencies, it is possible to evaluate sensitivity coefficient for the immediate compensation of moisture content in the air, while still preserving in the considered ranges of average sensitivities as high as 0.045, 0.112, 7.842 × 10^-5, and 0.041 % Z/ppm for ammonia, carbon dioxide, carbon monoxide and ethanol gas, respectively. With this simple approach, it will be possible to develop simple sensor read-out systems, with reduced external electronic, simplifying the route to low-cost and low-power sensor nodes for the internet of things.