A Thermoelectric-Driven nitrogen dioxide gas sensor based on Multiwall carbon Nanotube/Polypyrrole composites

Abstract

Nitrogen dioxide (NO₂) gas sensors commonly suffer from high operating temperatures, complex sensing systems, and excessive energy consumption, hindering large-scale deployment in sensor networks. Herein, we reported a NO₂ gas sensor by integrating thermoelectric and gas-sensing functions. Pure polypyrrole (PPy) and multi-walled carbon nanotube/ polypyrrole (MWCNT/PPy) composites were synthesized via in-situ polymerization. Specifically, PPy functions dually as a NO₂-sensitive material and a thermoelectric element, harnessing thermoelectric effects to enable sensor operation. First-principles calculations based on density functional theory (DFT) was employed to investigate the electronic transport properties of the conductive polymer PPy. Both characterization and computational studies demonstrate that the MWCNT/PPy composite simultaneously enhances gas chemisorption capacity and thermoelectric response. Notably, an incorporation of MWCNT contributes to a gain of 207 % in adsorbing NO₂ molecules. A MWCNT doping content of 0.375 wt% leads to a 42.05 % enhancement in Seebeck coefficient and an optimal responsivity (55.50 %) toward 300 ppm NO₂, which is 5.35 times that of the undoped version. This work presents a novel research paradigm for thermoelectric-driven gas sensors, and lays a theoretical foundation for future applications in monitoring automotive exhaust and oceanic vessel gas leaks.