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

• A thermoelectric—driven NO 2 gas sensor based on MWCNT/PPy was developed. • PPy plays a dual role: a gas-sensing material detecting NO 2 , and a thermoelectric material generating power to supply the sensor. • Incorporation of 0.375 wt% MWCNT boosts NO₂ adsorption capacity by 207% and increases the Seebeck coefficient by 42.05%. • The maximum response to 300 ppm NO₂ hits 55.50% at 0.375 wt% MWCNT doping, 5.35 times the undoped sample. Nitrogen dioxide (NO 2 ) 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 NO 2 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 NO 2 -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 NO 2 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 NO 2 , 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.