Muhammad Sufyan Javed

High-performance flexible supercapacitors based on C/Na2Ti5O11 nanocomposite electrode materials

A new solution method to synthesize Na2Ti5O11 with titanium powder is presented, and the C/Na2Ti5O11 nanocomposite with high specific surface area and tunnel structure as the electrode material has excellent electrochemical performance. The single electrode composed of the C/Na2Ti5O11 nanocomposite based on carbon fiber fabric (CFF) has the highest area capacitance of 1066xa0mFxa0cm−2 at a current density of 2xa0mAxa0cm−2, which is superior to other titanates and Na-ion materials for supercapacitors (SCs). By scan-rate dependence cyclic voltammetry analysis, the capacity value shows both capacitive and faradaic intercalation processes, and the intercalation process contributed 81.7% of the total charge storage at the scan rate of 5xa0mVxa0s−1. The flexible symmetric solid-state SCs (C/Na2Ti5O11/CFF//C/Na2Ti5O11/CFF) based on different C/Na2Ti5O11 mass were fabricated, and 7xa0mg SCs show the best supercapacitive characteristics with an area capacitance of 309xa0mFxa0cm−2 and a specific capacitance of 441xa0Fxa0g−1, it has a maximum energy density of 22xa0Whxa0kg−1 and power density of 1286xa0Wxa0kg−1. As for practical application, three SCs in series can power 100 green light-emitting diodes (LEDs) to light up for 18xa0min, which is much longer than our previous work by Wang et al. lighting 100 LEDs for 8xa0min. Thus, the C/Na2Ti5O11 nanocomposite has promising potential application in energy storage devices.

Rational design of CuO nanostructures grown on carbon fiber fabrics with enhanced electrochemical performance for flexible supercapacitor

It is known that Faradaic redox reactions take place on the surface or inside of materials through ion insertion/extraction on the surface. Therefore, rational design of nanostructures to enlarge the specific surface of electrode materials is an effective way to achieve desirable electrochemical performance. In this paper, three kinds of copper oxide structures, including flower-like, particle-like and coral-like arrays grown on the carbon fiber fabrics, are prepared by the hydrothermal method under different conditions. These flowers, particles and corals are further assembled by nanoscale sheets, rods and porous networks, respectively. The flexible solid-state symmetric supercapacitor based on two electrodes of these CuO nanostructures is fabricated, and the electrochemical properties of these CuO nanostructures are investigated, from which we find that the supercapacitor based on the coral-like CuO nanostructure presents better performance than that of particle-like and flower-like CuO due to its higher specific area and suitable pores with rich reaction sites and ion diffusion channels. The specific capacitances of the flower-like, particle-like and coral-like CuO are 164.50, 309.65 and 481.76xa0Fxa0g−1, respectively, at scan rate of 5xa0mVxa0s−1. The specific capacitance of the coral-like nanostructure keeps 86.45% after 2000 cycles. These results indicate that the morphology influences the electrochemical properties greatly. Three supercapactiors connected in series can light up ten LEDs for 600xa0s.

High-Temperature Thermoelectric Properties of Ge-Substituted p -Type Nd-Filled Skutterudites

To clarify the influence of Ge substitution on the electrical transport properties of Nd-filled p-type skutterudites, a series of Nd0.9Fe2Co2Sb12−xGex compounds with compositions xxa0=xa00, 0.1, 0.2, 0.3, and 0.4 were synthesized by a solid-state reaction method followed by a spark plasma sintering process. The crystal structure of the prepared samples was characterized by x-ray diffraction analysis, revealing successful formation of skutterudites as main pure phase. The electrical and thermal transport properties were investigated as a function of Ge doping content for fixed Nd filler content. All samples possessed positive Seebeck coefficient, indicating effective p-type behavior. The lightly doped samples (xxa0=xa00.1 and 0.2) showed higher figure␣of merit over the entire temperature range, with the xxa0=xa00.2 sample showing the highest ZT value of 0.56 at 674xa0K, 40% higher than that of the Ge-free sample. The enhancement in ZT can be ascribed to the optimized carrier concentration and reduced thermal conductivity. However, further increase of the Ge content resulted in second phase in the matrix, lowering the overall ZT. The large enhancement of ZT through Ge doping indicates that these compounds may have great potential for application as p-type segments of thermoelectric devices.

WGUs sensor based on integrated wind-induced generating units for 360° wind energy harvesting and self-powered wind velocity sensing

Wind, as a natural power source, can be used to produce electricity using wind generators. However, detecting wind velocity has been challenging because wind always blows in a random direction. In this study, we design a self-powered wind velocity sensor based on integrated wind-induced generating units (WGUs) to harvest wind energy from all directions in a plane and as a self-powered wind velocity sensor (denoted as WGUs sensor). A wind-induced generating unit consists of two parallel plate Cu-electrodes (size 1.5 × 4 cm2, gap 0.5 cm) and a polytetrafluoroethylene (PTFE) thin film between them. The W-TGUs sensor can be effectively used to harvest wind energy from all directions in a plane by integrating the W-TGUs in circular and vertical directions. The output current and voltage of every WGU are 1–3.5 μA, and 13–20 V under a wind speed of 6–27 m s−1. The output rectified current of WGUs, with vertically integrated one to five WGUs, was 1.3–6.8 μA under a wind speed of 8 m s−1. Moreover, the W-TGUs sensor can detect a wind velocity from all directions on a plane with a resolution ratio of 0.13 (m s−1) Hz−1 and a response time of 0.15 s, which is a very important advantage as a self-powered wind velocity sensor. The output power of the WGUs sensor can be greatly enhanced by increasing the number of WGUs. This study provides a novel design for harvesting wind energy and sensing wind velocity from a random direction on a plane.