Yihua Gao

Solid-State High Performance Flexible Supercapacitors Based on Polypyrrole-MnO2-Carbon Fiber Hybrid Structure

A solid-state flexible supercapacitor (SC) based on organic-inorganic composite structure was fabricated through an “in situ growth for conductive wrapping” and an electrode material of polypyrrole (PPy)-MnO2 nanoflakes-carbon fiber (CF) hybrid structure was obtained. The conductive organic material of PPy greatly improved the electrochemical performance of the device. With a high specific capacitance of 69.3 F cm−3 at a discharge current density of 0.1 A cm−3 and an energy density of 6.16 × 10−3 Wh cm−3 at a power density of 0.04 W cm−3, the device can drive a commercial liquid crystal display (LCD) after being charged. The organic-inorganic composite active materials have enormous potential in energy management and the “in situ growth for conductive wrapping” method might be generalized to open up new strategies for designing next-generation energy storage devices.

Cable-type supercapacitors of three-dimensional cotton thread based multi-grade nanostructures for wearable energy storage.

A novel cable-type flexible supercapacitor with excellent performance is fabricated using 3D polypyrrole(PPy)-MnO2 -CNT-cotton thread multi-grade nanostructure-based electrodes. The multiple supercapacitors with a high areal capacitance 1.49 F cm(-2) at a scan rate of 1 mV s(-1) connected in series and in parallel can successfully drive a LED segment display. Such an excellent performance is attributed to the cumulative effect of conducting single-walled carbon nanotubes on cotton thread, active mesoporous flower-like MnO2 nanoplates, and PPy conductive wrapping layer improving the conductivity, and acting as pseudocapacitance material simultaneously.

Three-dimensional WO3 nanostructures on carbon paper: photoelectrochemical property and visible light driven photocatalysis.

Three-dimensional (3D) WO(3) nanostructures were grown on carbon paper by a catalyst-free high temperature reactive vapor deposition process, which exhibit a good photoelectrochemical property and visible light driven photocatalytic performance.

Synthesis, Raman scattering and defects of β-Ga2O3 nanorods

Large yield of β-Ga2O3 nanorods with metal Ga tip were efficiently synthesized. They were deposited on surface of amorphous C fibers by decomposition of Ga2O vapor at around 1000 °C, where Ga2O vapor was produced at 1360 °C by a reaction between pure Ga2O3 and active carbon powders. The nanorods had diameters ranging from 10 to 100 nm and lengths of up to several tens micrometers. Twins and edge dislocations having a Burgers vector of 0.0859 A [2.66, 3.66, 1] existed in the nanorods. A redshift of 4–23 cm−1 was found in the Raman scattering spectrum of nanorods compared with that of a pure Ga2O3 powder. This phenomenon was explained qualitatively in terms of the defects in the nanorods.

Highly Stretchable and Self-Healable Supercapacitor with Reduced Graphene Oxide Based Fiber Springs

In large-scale applications of portable and wearable electronic devices, high-performance supercapacitors are important energy supply sources. However, since the reliability and stability of supercapacitors are generally destroyed by mechanical deformation and damage during practical applications, the stretchability and self-healability must be exploited for the supercapacitors. Preparing the highly stretchable and self-healable electrodes is still a challenge. Here, we report reduced graphene oxide fiber based springs as electrodes for stretchable and self-healable supercapacitors. The fiber springs (diameters of 295 μm) are thick enough to reconnect the broken electrodes accurately by visual inspection. By wrapping fiber springs with a self-healing polymer outer shell, a stretchable and self-healable supercapacitor is successfully realized. The supercapacitor has 82.4% capacitance retention after a large stretch (100%), and 54.2% capacitance retention after the third healing. This work gave an essential strategy for designing and fabricating stretchable and self-healable supercapacitors in next-generation multifunctional electronic devices.

Tungsten oxide nanowires grown on carbon cloth as a flexible cold cathode.

Figure 1 . a) Optical images of the carbon cloth with TONWs, left-inset and right-inset show the optical images of a carbon cloth with TONWs under slight bending and severe bending, respectively. b,c) SEM images of the carbon cloth before and after growing TONWs, respectively. Inset [∗] X. H. Zhang , Y. Z. Cao , X. Xiao , W. M. Sun , Prof. Y. H. Gao , Prof. J. Zhou , Prof. Z. L. Wang Wuhan National Laboratory for Optoelectronics (WNLO) and College of Optoelectronic Science and Engineering Huazhong University of Science and Technology (HUST) Wuhan, 430074 (P. R. China) E-mail: jun.zhou@mail.hust.edu.cn; zhong.wang@mse.gatech.edu L. Gong , Prof. J. Chen Instrumental Analysis & Research Center Sun Yat-sen University Guangzhou, 510275 (P. R. China) K. Liu , Prof. X. J. Hu School of Power and Mechanical Engineering Wuhan University Wuhan, 430072 (P. R. China) Prof. Z. L. Wang School of Materials Science and Engineering Georgia Institute of Technology Atlanta, Georgia 30332-0245 (USA) Nanowire arrays for fi eld emission have attracted a lot of interest in the last few years because of numerous applications such as fl at-panel displays, X-ray radiotherapy, microwave amplifi ers, and vacuum microelectronic devices. [ 1 , 2 ] The growth of fi eld emitters on fl exible substrates may open up numerous fi elds of applications such as roll-up fi eld emission displays (FEDs), [ 3 ]

SiC nanorods prepared from SiO and activated carbon

SiC nanorods with 20–100 nm diameter and 10–100 μm length were synthesized by reaction between SiO and amorphous activated carbon (AAC) at 1380°C. Microstructural characterization of the SiC nanorods was carried out by high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS). The SiC nanorods grow on either a chain or from facets of SiC nanoparticles. They are usually straight and preferentially orientated along the [111] direction. Branching phenomenon exists for these nanorods. Typical SiC nanorod tip was analyzed by HRTEM image and EDS analysis. Based on an experimental analysis, a formation mechanism is proposed to explain the microstructural characterization of the SiC nanorods.

A wire-shaped flexible asymmetric supercapacitor based on carbon fiber coated with a metal oxide and a polymer

Due to high capacitance resulting from the redox character of the MnO2–PPy–carbon and V2O5–PANI–carbon fiber composites, a flexible wire-shaped fiber asymmetric supercapacitor (WFASC) was fabricated using these materials as the positive and negative electrodes, respectively. Especially, the large work function difference between MnO2 and V2O5 help the device to exhibit a wide potential window of 2.0 V and a high areal capacitance of 0.613 F cm−2. As a result, the WFASC showed a maximum energy density of 0.340 mW h cm−2 at a power density of 1.5 mW cm−2 and a maximum power density of 30 mW cm−2 at an energy density of 0.294 mW h cm−2. Furthermore, the device exhibited a perfect stability after 5000 cycles at a current density of 30 mA cm−2, meanwhile, it could withstand the bending test and drive a LED under bending states. All of the above results prove the potential application of WFASC devices.

Temperature measurement using a gallium-filled carbon nanotube nanothermometer

We report here temperature measurement by means of a Ga-filled C nanotube thermometer with diameter <150 nm and length ∼12 μm. The method relies on the initial identification and calibration of a nanothermometer in a transmission electron microscope (TEM), followed by placing it into an air-filled furnace whose temperature is to be measured, and final TEM reading of a postmeasurement gradation mark visible inside the tubular channel. The mark originates from the fact that, at high temperature, the Ga column tip exposed to the air through the open C nanotube end oxidizes, and a thin Ga oxide layer sticks to the nanotube walls upon cooling. The temperature according to this gradation mark coincides closely with nominal furnace temperature controlled by standard means. The method paves the way for practical temperature measurements using a C nanothermometer in air and within spatially localized regions (e.g., dimensions of tens of micrometers).

Inkjet printing of conductive patterns and supercapacitors using a multi-walled carbon nanotube/Ag nanoparticle based ink

A multi-walled carbon nanotube (MWCNT) and silver (Ag) nanoparticle ink for inkjet printing was prepared by dispersing MWCNTs and Ag nanoparticles in water with the assistance of sodium dodecylbenzenesulfonate (SDBS). Highly conductive patterns of Ag–MWCNTs were printed on paper using a HP Deskjet 1010 inkjet printer. The patterns showed good stability during the bending test and a low sheet resistance of ∼300 Ω sq−1 after being printed 50 times. By simply adding manganese dioxide (MnO2) nanoparticles with a diameter of 60–90 nm into the ink solution, patterned positive electrodes were prepared for asymmetric supercapacitors (ASCs) with filtrated MWCNT negative electrodes. The ASCs exhibit a wide operating potential window of 1.8 V and excellent electrochemical performances, e.g. a high energy density of 1.28 mW h cm−3 at a power density of 96 mW cm−3 and a high retention ratio of ∼96.9% of its initial capacitance after 3000 cycles. The inkjet-printing acting as a simple, low-cost, non-contact deposition method can be fully integrated with the fabrication process in current printed electronic devices and has potential applications in energy storage.