No abstract

No abstract

The reduction of graphene oxide (GO) is a promising route to bulk produce graphene-based sheets. Different reduction processes result in reduced graphene oxide (RGO) with different properties. In this paper three reduction methods, chemical, thermal and electrochemical reduction, were compared on three aspects including morphology and structure, reduction degree and electrical conductivity by means of scanning electron microscopy (SEM), X-ray diffraction(XRD), the Fourier transform infrared spectroscopy (FT-IR) spectrum, X-ray photoelectron spectroscopy (XPS) and four-point probe conductivity measurement. Understanding the different characteristics of different RGO by preliminary comparison is helpful in tailoring the characteristics of graphene materials for diverse applications and developing a simple, green, and efficient method for the mass production of graphene.

No abstract

In this paper, we report the possibility of utilizing nitrogen-doped graphene (N-G) as a novel cathode material for Li-ion hybrid supercapacitors (Li-HSCs) applications. N-G was prepared by a simple one-pot hydrothermal method, followed by freeze-drying in a vacuum treatment. Li-ion hybrid supercapacitors was fabricated using N-G as the cathode along with lithium-ion intercalated compound LiMn 2 O 4 as the anode in an aqueous medium. The energy density of the Li-HSCs can increase up to 22.15Wh kg −1 when the power density reached was 132 W kg −1 , and still retained 13 Wh kg −1 at a power density of 2000 W/kg. The LiMn 2 O 4 / N-G Li-HSCs assembly also shows good cyclic performance with about 80% of the initial value retained after 2000 galvanostatic cycles under high rate cyclic conditions. This result clearly indicates that N-G is a promising candidate for future application in a Li-HSCs configuration.Energy storage has become a global concern in modern society, and high-performance energy storage devices are in great demand. Among various electrical energy storage devices, lithium ion batteries (LIBs) with high energy density and supercapacitors (SCs) with excellent power density are currently considered to be two excellent candidates as novel, environmentally friendly, low-cost, and high-performance energy storage devices to meet the increasing demand. The LIBs commonly can store a large amount of energy, as high as 150-200 Wh kg −1 , but are confined by their low power density (below 1000 W kg −1 ) and poor cycle life (usually less than 1000 cycles). In contrast, SCs can provide much higher power density (10 kW kg −1 ), long cycle life (exceeding 10 5 cycles), and fast charge-discharge processes (within seconds), but suffer from much lower energy density (only 5-10 Wh kg −1 ). 1 Therefore, there has been great and urgent demand for high-performance energy storage devices with both high energy density and high power density.With a combination of the fast charging rate of SCs and the high energy density of LIBs, a novel supercapacitor-battery energy storage system, also called lithium ion hybrid supercapacitors (Li-HSCs) has emerged, which is expected to possess the best features of both SCs and LIBs. 2-8 In principle, Li-HSCs are composed of a capacitor-type electrode and a lithium ion battery-type electrode in a Li + containing electrolyte. Therefore, compared with LIBs and SCs, Li-HSCs undergo different charge storage mechanism due to the unique reaction mechanisms of each electrode. Capacitor-type electrode store energy by a reversible adsorption/desorption of ions, while battery-type electrode store energy though a Li-ion insertion/extraction reaction. 9-11 It is possible to aim at much larger energy density without sacrificing power energy and cycle life. Because of its competitive characteristics it is expected to be useful power sources for hybrid electric vehicles and electric vehicles. [12][13][14] In Li-HSCs, adsorption/desorption of ions occurs on the surface of the capacitor-type electrode while t...