Energy-efficient NO₂ sensors based on two-dimensional layered 2H-WS₂ nanosheets

Layered transition metal dichalcogenides (TMDCs) are considered among the next-generation materials for gas sensing. Here, we report exfoliated 2 H-WS₂ nanosheets for the fabrication of highly performing NO₂ sensors. Thermal annealing at several temperatures was performed to investigate the oxidation of WS₂. The long-term stability of 2 H-WS₂ bulk was verified. Using droplet variation method, three batches of conductometric sensors from 2 H-WS₂ dispersions were fabricated on electrical transducers, namely two layers (2 L), five layers (5 L) and ten layers (10 L) WS₂ nanosheets. These sensors were tested towards low NO₂ concentrations at different temperatures (Room Temperature (20 ℃), 50 ℃ and 100 ℃) and relative humidity (RH) levels (20%, 40%, 60%, 80% and 90% RH). 2 L-WS₂ based sensor showed the highest response at room temperature (RT). Excellent repeatability (4 cycles) towards 1 ppm NO₂ and long-term stability (more than two months) were achieved. Full selectivity towards NO₂ (1 ppm) at RT was observed over NH₃ (15 ppm), H₂S (15 ppm), ethanol (30 ppm) and acetone (30 ppm). Our results confirm that low-power consumption devices with high sensitivity (even at high RH), long-term stability and excellent selectivity towards NO₂ were fabricated using 2 H-WS₂ nanosheets.