Relative Humidity Detection in TiO₂ Quantum Dots and Multi-Walled Carbon Nanotubes Composite Sensors through Electrical Impedance Spectroscopy

Humidity sensors demonstrate significant sensitivity to changes in relative humidity (RH), which is essential for applications in various fields such as environmental monitoring, agriculture, and industrial processes. High sensitivity allows for more accurate and timely detection of humidity levels, which can be critical for maintaining optimal conditions in sensitive environments. This work investigates titanium dioxide quantum dots (TiO2 QDs) integrated with nitrogen-doped multiwalled carbon nanotubes (A-MWCNTs) for enhanced relative humidity (RH) sensing. Impedance spectroscopy revealed a six-order magnitude impedance drop from 5% to 85% RH, highlighting improved ionic conduction. The highest sensitivity achieved was 0.10 orders of magnitude per %RH at 100 Hz, while the lowest limit of detection (13% RH) and fastest recovery time (5.5 s) occurred at 15 kHz. In addition, the sensors exhibit different performance characteristics at various frequencies, allowing for tailored applications based on specific needs. For instance, higher frequencies may provide better stability and lower detection limits, while lower frequencies may enhance the sensitivity. This versatility can lead to improved sensor designs for specific operational contexts. These findings emphasize adsorption-driven mechanisms at low RH and proton conduction at high RH, positioning TiO2 QD/A-MWCNTS composites as promising candidates for advanced humidity sensors with adjustable performance and frequency flexibility.