Fully Gravure-printed Gas Sensors Based On Tungsten Oxide Nanocomposite

Semiconductor gas sensors have been researched for many years, which are attracted considerable attention in a variety of fields such as industrial waste gas detection, civil life security and diagnosis of diseases. Despite many significant results have been obtained, many problems should be solved in the region of the gas sensors, such as relatively low response and selectivity and high operating temperature. Therefore, it is a hotspot to develop a new kind of gas-sensing materials for practical application. In this paper, with the target of improving the gas sensing properties of sensors at low operation temperature, we prepared nanocomposite sensor structures of WO3 mixed with PEDOT:PSS and RGO, respectively. Their gas sensing properties to NO2 and acetone were investigated, and the sensing mechanism was also explored. The main contents are as follows:1. Fully gravure-printed NO2 gas sensors based on WO3-PEDOT:PSS composites. Using the hydrothermal method for preparing g-WO3 nanoplates, and formed WO3-PEDOT:PSS nanocomposites by adding conductive polymer PEDOT:PSS. At last, we prepared the strip-patterned sensing layer for the first time by using gravure printing. Experimental results showed that, compared with pure WO3 nanoplates, the initial resistance of the WO3-PEDOT:PSS was decreased and their sensing properties in room temperature was also improved by adding proper amount of PEDOT:PSS. The p-n heterostructure between the n-type WO3 and p-type PEDOT:PSS would increase the depletion width in the WO3, resulting in an improved sensing performance. With the exposure to 50 ppb NO2, the response and recovery times were about 25 s and 53 s, which were quicker than the pure WO3 sensors. The WO3-PEDOT:PSS sensor also had less or no gas response to NH3, H2, methanol, ethanol, acetone, but good selectivity to NO2. Furthermore, the sensors based on the strip-patterned surface exhibit sensitivities distinctly higher than that based on the flat surface, the sensitivity of the sensors based on the strip-patterned surface is about 2.1 times as high as that based on the flat surface in the presence of 200 ppb NO2. Above all, we have achieved the detection of low NO2 concentration at room temperature.2. Fully gravure-printed acetone gas sensors based on h-WO3-RGO composites. Using the hydrothermal method for preparing h-WO3 nanorods assembled microspheres, and formed WO3-PEDOT:PSS nanocomposites by adding reduced graphene oxide(RGO). The microspheres of the h-WO3 have a diameter of 2–3 mm, which are randomly assembled by numerous nanorods of 10–20 nm size. The acentric O atoms in the(002) facet of h-WO3 can cause the non-uniform distribution of electron cloud, leading to local electric polarization to some extent. The dipole moment of acetone(2.88 D) is significantly larger than other gases; thus, the interaction between acetone molecules and the(002) facet of h-WO3 is considerably stronger. The optimization of the RGO loading modulate space charged layers at the interfaces between p-n WO3-PEDOT:PSS junction, thereby improving their sensing properties. Especially, the operating temperature was decreased from 300℃ to 200℃. With the exposure to 1 ppm acetone, the sensitivity was about 4.1, the response and recovery times were about 31 s and 10 s, respectively.In summary, the gravure-printed gas sensors based on tungsten oxide nocomposite can significantly improve the sensing performance towards NO2 and acetone at low operating temperature, which provide effective approachs and methods to solve the problems resulted from the thermal field.