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Electronic and transport properties of Bi2O2Se under strain are calculated using Tran–Blaha modified Becke–Johnson (TB-mBJGGA) potential and semiclassical Boltzmann transport theories. The electronic band gap decreases with tensile and compressive in-plane strain. We predict that the n-type Seebeck coefficient can be increased under compressive in-plane strain, while the p-type Seebeck coefficient can be increased under tensile in-plane strain. Further, the power factor of n-type doping Bi2O2Se can be increased under compressive in-plane strain, while that of p-type doping Bi2O2Se can be increased under tensile in-plane strain. For p-type doping Bi2O2Se, large thermoelectric figure of merit (ZT ≈ 1.42) could be obtained under tensile strain (2.3%) at 800 K. Moreover, a higher ZT ≈ 1.76 could be achieved along the ZZ direction. This study demonstrates that the electronic and thermoelectric properties can be controlled by strain engineering in thermoelectric material.

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The exploration of high Faradic redox active materials with the advantages of low cost and low toxicity has been attracting great attention for producing high energy storage supercapacitors. Here, the high Faradic redox active material of Cu7S4-NWs coated on a carbon fiber fabric (CFF) is directly used as a binder-free electrode for a high performance flexible solid state supercapacitor. The Cu7S4-NW-CFF supercapacitor exhibits excellent electrochemical performance such as a high specific capacitance of 400 F g(-1) at the scan rate of 10 mV s(-1) and a high energy density of 35 Wh kg(-1) at a power density of 200 W kg(-1), with the advantages of a light weight, high flexibility and long term cycling stability by retaining 95% after 5000 charge-discharge cycles at a constant current of 10 mA. The high Faradic redox activity and high conductance behavior of the Cu7S4-NWs result in a high pseudocapacitive performance with a relatively high specific energy and specific power. Such a new type of pseudocapacitive material of Cu7S4-NWs with its low cost is very promising for actual application in supercapacitors.

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