Highly Selective NO2 Sensors Based on Electrolytically Exfoliated Graphene/Flame-made WO3 Composite Films

Gas sensors based on flame-synthesized WO3 nanoparticles loaded with 0.2-5 wt% electrochemically exfoliated graphene were evaluated for NO2 detection at ppb levels. The characterizations by X-Ray diffraction, nitrogen adsorption, electron microscopy and Raman spectrometry verified that multi-layer graphene sheets were well dispersed within spheroidal WO3 nanoparticles. Sensing layers fabricated with different graphene loading levels were tested towards 50-5000 ppb NO2 with varying operating temperatures from 100 to 350 °C in dry air. From the test results, the graphene-loaded WO3 nanoparticles with the optimal graphene content of 2 wt% exhibited the highest sensor response of ~ 5061 to 5000 ppb NO2 at the optimum working temperature of 150 °C. Furthermore, the sensor based on graphene/WO3 composites displayed high NO2 selectivity against various environmental gases and volatile organic compounds at 150 °C. The mechanistic roles of graphene on NO2 gas-sensing performances were described based on reactive ohmic M-S heterointerfaces. Therefore, the combination of electrochemically exfoliated graphene and flame-made WO3 nanoparticles could be an attractive mean to achieve highly sensitive and selective NO2 sensors.