Extrusion-Printed CNT–Graphene Sensor Array with Embedded MXene/PEDOT:PSS Heater for Enhanced NO₂ Sensing at Low Temperature

Abstract

Wearable sensors are currently one of the top emerging areas with enormous growth potential. Low-cost fabrication techniques using simple and scalable printing technologies are making a significant impact on their development. Recent advances in high-performance gas/vapor sensors based on carbon nanomaterials have shown potential applications ranging from disease diagnostics to environmental monitoring and defences. Herein, a hybrid sensing material of 1D carbon nanotubes (CNTs) and 2D graphene is developed, and a conductive ink is formulated, which is applied for fabricating a nitrogen dioxide (NO2) gas sensor array within a compact design utilizing extrusion printing. To improve NO2-sensing performance and optimal operating temperature, a reverse-side layer is designed, which combines MXene and poly(3,4-ethylenedioxythiophene)-doped poly(styrene sulfonate) (PEDOT:PSS), and functions as a Joule heater. The printed CNT–graphenebased sensor with an embedded MXene/PEDOT:PSS heater is capable of detecting trace amounts of NO2 gas (1 ppm) at 65 °C. The sensor is able to distinguish between various gases/volatile organic compounds and target NO2 gas based on their chemical affinities. The printed CNT–graphene sensor array also demonstrates a high-level of recoverability, satisfied stability, durability, and reproducibility, which render this sensor a suitable candidate for practical applications.