Nitrogen dioxide (NO2) is a gas species that plays an important role in certain industrial, farming, and healthcare sectors. However, there are still significant challenges for NO2 sensing at low detection limits, especially in the presence of other interfering gases. The NO2 selectivity of current gas-sensing technologies is significantly traded-off with their sensitivity and reversibility as well as fabrication and operating costs. In this work, we present an important progress for selective and reversible NO2 sensing by demonstrating an economical sensing platform based on the charge transfer between physisorbed NO2 gas molecules and two-dimensional (2D) tin disulfide (SnS2) flakes at low operating temperatures. The device shows high sensitivity and superior selectivity to NO2 at operating temperatures of less than 160 °C, which are well below those of chemisorptive and ion conductive NO2 sensors with much poorer selectivity. At the same time, excellent reversibility of the sensor is demonstrated, which has rarely been observed in other 2D material counterparts. Such impressive features originate from the planar morphology of 2D SnS2 as well as unique physical affinity and favorable electronic band positions of this material that facilitate the NO2 physisorption and charge transfer at parts per billion levels. The 2D SnS2-based sensor provides a real solution for low-cost and selective NO2 gas sensing.

Relaxor ferroelectric (FE) ceramic capacitors have attracted increasing attention for their excellent energy-storage performance. However, it is extremely difficult to achieve desirable comprehensive energy-storage features required for industrial applications. In this work, very high recoverable energy density W rec ≈ 8.73 J cm -3 , high efficiency η ≈ 80.1%, ultrafast discharge rate of <85 ns, and temperature-insensitive high W rec and η (W rec ≈ 5.73 ± 4% J cm -3 , η ≈ 75 ± 6%, 25-200 °C) are simultaneously obtained in 0.68NaNbO 3 -0.32(Bi 0.5 Li 0.5 )TiO 3 relaxor FE ceramics by introducing various polarization configurations in combination with microstructure modification. The structure mechanism for the excellent energy-storage performance is disclosed by analyzing in situ structure evolution on multiple scales during loading/unloading by means of transmission electron microscopy and Raman spectroscopy. Both local regions consisting of different-scale polar nanodomains and a nonpolar matrix, and local orthorhombic symmetry remaining with electric fields ensure a linearlike polarization response within a wide field and temperature range owing to significantly delayed polarization saturation. The stabilization of orthorhombic FE phases rather than antiferroelectric orthorhombic phases in NaNbO 3 after adding (Bi 0.5 Li 0.5 )TiO 3 is also explored by means of X-ray diffraction, dielectric properties, and selected area electron diffraction. In comparison with antiferroelectric ceramics, NaNbO 3 -based relaxor FE ceramics provide a new solution to successfully design next-generation pulsed power capacitors.

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