Recently, thermoelectric lead-free selenides have attracted great attention due to their earth-abundant, low-cost and environment-friendly characteristics. Here we report a new strategy to simultaneously enhance the electronic transport properties and reduce the thermal conductivity of polycrystalline SnSe2. By combining weak van der Waals bonding with the mobile behavior of Ag+ ions, the carrier concentration is optimized over a wide temperature range, which can be attributed to the dynamic Ag+-intercalation into the van der Waals gap from the Ag+ ion reservoir AgSnSe2. On account of additional electrical bridges between interlayers contributed by the intercalated Ag+ ions and weak anisotropy, an exciting high power factor of up to ∼7.46 μW cm−1 K−2 at 789 K is achieved along the pressing direction. In addition, the thermal conductivity is simultaneously reduced to ∼0.57 W m−1 K−1 at 789 K, owing to numerous line defects, phase interfaces, twin boundaries, dislocations and intercalated atomic layers generated after Ag introduction, as well as the anharmonic vibration of Ag+ ions. As a result, a record peak ZT of ∼1.03 at 789 K is realized along the pressing direction, which is ∼1.6 times larger than the highest reported value (0.63) of polycrystalline SnSe2 and even comparable to that of p-type polycrystalline SnSe. This study opens a new way to achieve ultra-high thermoelectric performance, especially in layered materials.
Nitrogen dioxide (NO 2 ) is a common gas that can cause irreversible damage to human health, emphasizing the essentiality of developing highly sensitive NO 2 sensors with good selectivity and low consumption. Here, a facile in–situ cation exchange method was employed to successfully synthesize interlayer expansion Ag intercalated SnS 2 with S vacancies for NO 2 gas sensing. The presence of S vacancies strongly improves the electronic structure of SnS 2 and significantly facilitates the interaction of NO 2 with the sensor. Moreover, the interlayer spacing of SnS 2 is expanded by 0.48 Å after Ag intercalation, prompting diffusion behavior of NO 2 molecules between the interlayers. Benefiting from the factors above, SnS 2 –Ag exhibited excellent gas sensing performance for NO 2 with a high response to 5 ppm NO 2 (response value = 8.37) and detection limits as low as 200 ppb at a low temperature of 100 °C. This work combines defect engineering with interlayer engineering to provide a new perspective for extending the application of SnS 2 gas sensors.
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