Rational design of WSe2/MWCNT composites with abundant edge-sites for highly selective and humidity-independent NO2 sensing

Abstract

Low-cost fabrication of heterostructures with micro/nanoscale dimensions remains the most challenging issue for high-performance gas sensors with humidity-independent detection. Such a process not only enables accurate detection and tracking of trace-level gas analytes, but also determines the commercial viability and practical utilization of the sensors in future multimodal systems. Tungsten diselenide (WSe2) nanosheets are promising for NO2 sensors but have low conductivity and high humidity fluctuation, limiting their practical application. We address these limitations by introducing edge-exposed WSe2/multi-walled carbon nanotube (MWCNT) composites prepared using a rapid, low-cost, sonication-assisted method as sensing elements for NO2 detection. Multiple characterizations were conducted to evaluate possible structural modification due to heterojunction formation. The combination of edge-exposed WSe2 and MWCNTs, with their high surface area and hydrophobic nature, not only increased the material conductivity, but also provided an ideal interfacial barrier structure and synergistic effect that enhances sensor performance. The optimal WSe2/MWCNT 1% composite sample exhibited excellent sensitivity, selectivity, and moisture resistance, resulting in a 1.85-fold improvement in response to 1 ppm of NO2 compared to pristine WSe2 at 100 °C. Gas-sensing kinetics and regression analyses revealed lower activation energy and a theoretical limit of detection of 2.8 ppb, implying greater sensitivity than various state-of-the-art WSe2-based gas sensors. Moreover, the sensors maintain excellent cyclic stability and long-term durability performance, even in extreme-humidity regimes (RH = 80%). The enhanced sensing performance was attributed to the formation of nanoscale p-p heterojunctions, numerous active sites, and defects, which improve charge transport and bring about a faster response time.