A facile method to prepare flexible n-type Ag 2 Se/Se/polypyrrole (PPy) composite films is developed. First, Ag 2 Se nanostructures (NSs) are wet chemically synthesized; PPy is then in situ polymerized at the surface of the Ag 2 Se NSs; and finally, the Ag 2 Se/Se/PPy composite film on a porous nylon membrane is fabricated by a vacuum-assisted filtration process followed by hot pressing. An optimal composite film shows an exceptionally high power factor of ≈2240 µW m −1 K −2 at 300 K, mainly because of the synergistic effect between well-developed crystalline Ag 2 Se grains and a small amount of Se and PPy. The film also possesses outstanding flexibility (only about 6.5% decrease in electrical conductivity after 1000 times bending along a rod with a radius of 4 mm). Moreover, a flexible thermoelectric generator composed of six legs of the film outputs a voltage of 21.2 mV and a maximum power of 4.04 µW (corresponding power density of 37.6 W m −2 ) at a temperature difference of 34.1 K, verifying exceptionally high thermoelectric properties. This work shows the promise of the as-prepared composite film for practical applications in wearable devices and will surely promote the research and development of flexible TE generators.

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Bi2S3‐based thermoelectric materials without toxic and expensive elements have a high Seebeck coefficient and intrinsic low thermal conductivity. However, Bi2S3 suffers from low electrical conductivity, which makes it a less‐than‐perfect thermoelectric material. In this work, halogen elements F, Cl, and Br from halogen acid are successfully introduced into the Bi2S3 lattice using a hydrothermal procedure to efficiently improve the carrier concentration. Compared with the pure sample, the electron concentration of the Bi2S3 sample treated with HCl is increased by two orders of magnitude. An optimal power factor of 470 µW m−1 K−2 for the Bi2S2.96Cl0.04 sample at 673 K is obtained. Density functional theory calculations reveal that an effective delocalized electron conductive network forms after Cl doping, which raises the Fermi level into the conduction bands, thus generating more free electrons and improving the conductivity of the Bi2S3‐based materials. Ultimately, an excellent ZT of ≈0.8 is achieved at 673 K for the Bi2S2.96Cl0.04 sample, which is one of the highest values reported for a state‐of‐the‐art Bi2S3 system. The energy conversion efficiency of the module reaches 2.3% at 673 K with a temperature difference of 373 K. This study offers a new method for enhancing the thermoelectric properties of Bi2S3 by adding halogen acid in the hydrothermal process for powder synthesis.

The recent growing energy crisis draws considerable attention to high-performance thermoelectric materials. n-type bismuth telluride is still irreplaceable at near room temperature for commercial application, and therefore, is worthy of further investigation. In this work, nanostructured Bi 2 Te 3 polycrystalline materials with highly enhanced thermoelectric properties are obtained by alkali metal Na solid solution. Na is chosen as the cation site dopant for n-type polycrystalline Bi 2 Te 3 . Na enters the Bi site, introducing holes in the Bi 2 Te 3 matrix and rendering the electrical conductivity tunable from 300 to 1800 Scm -1 . The solid solution limit of Na in Bi 2 Te 3 exceeds 0.3 wt%. Owing to the effective solid solution, the Fermi level of Bi 2 Te 3 is properly regulated, leading to an improved Seebeck coefficient. In addition, the scattering of both charge carriers and phonons is modulated, which ensured a high-power factor and low lattice thermal conductivity. Benefitting from the synergistic optimization of both electrical and thermal transport properties, a maximum figure of merit (ZT) of 1.03 is achieved at 303 K when the doping content is 0.25 wt%, which is 70% higher than that of the pristine sample. This work disclosed an effective strategy for enhancing the performance of n-type bismuth telluride-based alloy materials.

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Various micro surface-modification approaches including photolithography, dip-pen lithography and ink-jet systems have been developed and used to extend the functionalities of solid surfaces. While those approaches work in the "open space", push-pull systems which work in solutions have recently drawn considerable attention. However, the confining flows performed by push-pull systems have realized only the dispense process, while microscale, region-selective chemical reactions have remained unattainable. This study reports a microchemical pen that enables region-selective chemical reactions for the micro surface modification/patterning. The chemical pen is based on the principle of microfluidic laminar flows and the resulting mixing of reagents by the mutual diffusion. The tiny diffusion layer performs as the working region. This report represents the first demonstration of an open microreactor in which two different reagents react on a real solid sample. The multifunctional characteristics of the microchemical pen are confirmed by different types of reactions in many research areas, including inorganic chemistry, polymer science, electrochemistry and biological sample treatment.