The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

Review on α-Fe 2 O 3 based negative electrode for high performance supercapacitors

Fe2O3 nanodots supported on nitrogen-doped graphene sheets (denoted as Fe2O3 NDs@NG) with different loading masses are prepared through a facile one-pot solvothermal method. The resulting Fe2O3 NDs@NG composites exhibit outstanding electrochemical properties in aqueous KOH electrolyte. Among them, with the optimal loading mass of Fe2O3 NDs, the corresponding Fe2O3 NDs@NG-0.75 sample is able to deliver a high specific capacitance of 274 F g–1 at 1 A g–1 and the capacitance is still as high as 140 F g–1 even at a ultrahigh current density of 50 A g–1, indicating excellent rate capability. More remarkably, it displays superior capacitance retention after 100 000 cycles (about 75.3% at 5 A g–1), providing the best reported long-term cycling stability for iron oxides in alkaline electrolytes to date. Such excellent electrochemical performance is attributed to the right combination of highly dispersed Fe2O3 NDs and appropriately nitrogen-doped graphene sheets, which enable the Fe2O3 NDs@NG-0.75 to offer plenty ...

Facile Synthesis of Fe2O3 Nano-Dots@Nitrogen-Doped Graphene for Supercapacitor Electrode with Ultralong Cycle Life in KOH Electrolyte.

One-pot synthesis of α-Fe2O3 nanoplates-reduced graphene oxide composites for supercapacitor application

Owing to the three different orbital hybridizations carbon can adopt, the existence of various carbon nanoallotropes differing also in dimensionality has been already affirmed with other structures predicted and expected to emerge in the future. Despite numerous unique features and applications of 2D graphene, 1D carbon nanotubes, or 0D fullerenes, nanodiamonds, and carbon quantum dots, which have been already heavily explored, any of the existing carbon allotropes do not offer competitive magnetic properties. For challenging applications, carbon nanoallotropes are functionalized with magnetic species, especially of iron oxide nature, due to their interesting magnetic properties (superparamagnetism and strong magnetic response under external magnetic fields), easy availability, biocompatibility, and low cost. In addition, combination of iron oxides (magnetite, maghemite, hematite) and carbon nanostructures brings enhanced electrochemical performance and (photo)catalytic capability due to synergetic and co...

Iron-oxide-supported nanocarbon in lithium-ion batteries, medical, catalytic, and environmental applications.

Facile hydrothermal fabrication of nitrogen-doped graphene/Fe2O3 composites as high performance electrode materials for supercapacitor

In order to investigate the temperature-dependent carrier transport property of the bilayer graphene, graphene films were synthesized on Cu foils by a home-built chemical vapor deposition (CVD) with C 2 H 2 . Samples regularity, transmittance ( T ) and layer number were analyzed by transmission electron microscope (TEM) images, transmittance spectra and Raman spectra. Van Der Pauw method was used for resistivity measurements and Hall measurements at different temperatures. The results indicated that the sheet resistance ( R s ), carrier density ( n ), and mobility ( μ ) were 1096.20 Ω/sq, 0.75×10 12  cm −2 , and 7579.66 cm 2  V −1  s −1 at room temperature, respectively. When the temperature increased from 0 °C to 240 °C, carrier density ( n ) increased from 0.66×10 12  cm −2 to 1.55×10 12  cm −2 , sheet resistance ( R s ) decreased from 1215.55 Ω/sq to 560.77 Ω/sq, and mobility ( μ ) oscillated around a constant value 7773.99 cm 2  V −1  s −1 . The decrease of the sheet resistance ( R s ) indicated that the conductive capability of the bilayer graphene film increased with the temperature. The significant cause of the increase of carrier density ( n ) was the thermal activation of carriers from defects and unconscious doping states. Because the main influence on the carrier mobility ( μ ) was the lattice defect scattering and a small amount of impurity scattering, the carrier mobility ( μ ) was temperature-independent for the bilayer graphene.

Study on temperature-dependent carrier transport for bilayer graphene

Unipolar induction phenomenon is a special kind of electromagnetic induction. There are two quite opposite theoretical explanations for this phenomenon, i.e., the N theory and the M theory. The research of unipolar induction has made significant progress, but there is no final conclusion by now. In this paper, an experiment of inversely rotating double Faraday disks and double magnets are designed, and the unipolar induction phenomenon is verified by means of theoretical calculation and experiment. Comparing and analyzing the theoretical calculation and experiment results, our experimental results support the N theory, that is to say, our experiment shows that the magnetic field does not rotate when the magnet rotates.

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An Experimental Study on Unipolar Induction

Partially depleted silicon-on-insulator (PDSOI) MOSFETs are widely used in 225 °C high-temperature electronic system applications with integrated circuits. But the process node stays at 0.5 µm for a long time and no further breakthrough can be achieved. This paper reports the high-temperature characteristics of 28 nm ultra-thin body and box fully depleted SOI (FDSOI) CMOS transistors with low threshold voltage (LVT) structure. Experimental results demonstrate that V t shift changes with temperature as low as 0.59 mV °C−1, the subthreshold slope (SS) is 145.35 mV dec−1 at 300 °C, and the related parameters are optimized by 3.7 times and 2.2 times respectively compared with 0.13 µm PDSOI. Combined with theoretical analysis, it is proved that the ultra-body FDSOI has an LVT drift rate and better SS than 0.13 µm PDSOI at high temperature. The advantage of this performance is mainly due to the difference between αVT α VT and β VT coefficients related to the back gate effect. Under negative back-gate bias, the I on/l off ratio can be increased by two orders of magnitude without affecting V t shift changes with temperature, this proves that the FDSOI is capable of high-temperature applications above 300 °C. This paper provides substantial support for future high-temperature system integrated circuits from the micro-scale to the nano-scale.

The low threshold-voltage shift with temperature and small subthreshold-slope in 28 nm UTBB FDSOI for 300 °C high-temperature application

Graphene is a two-dimensional material consisting of single atomic layers of graphite. Its quality is markedly different from conventional graphite and semiconductor material. In this paper, electrical conductivity and Hall Effect of the graphene were measured at room temperature by Var der Pauw method. An ohmic contact of the sample and the electrodes was constructed and tested before the measurement of Hall Effect. With the help of the Var der Pauw method, the Hall voltages of the samples were measured under the static magnetic field and different input currents. Sequentially, a series of Hall parameters of graphene were obtained. The results shown that the Hall coefficient RH is 7.00*10-7 m3/C; the carrier concentration n is 10.52*1024 m-3 that is fifteen orders of magnitude bigger than silicon; the Hall element production sensitivity KH is 6.87*102 m2/C and the carrier mobility was 1,882.54 cm2·V-1·s-1 which is much bigger than silicon. The measurement results in this paper can provide some reference for graphene’s research and application in related areas.

X. J. Li

Papers

Facile hydrothermal fabrication of nitrogen-doped graphene/Fe2O3 composites as high performance electrode materials for supercapacitor

Study on temperature-dependent carrier transport for bilayer graphene

An Experimental Study on Unipolar Induction

The low threshold-voltage shift with temperature and small subthreshold-slope in 28 nm UTBB FDSOI for 300 °C high-temperature application

Research on Hall Effect of Graphene by Var Der Pauw Method