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

Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Role of nanomaterials in water treatment applications: a review.

Research progress on conducting polymer based supercapacitor electrode materials

Graphene-supported nanoelectrocatalysts for fuel cells: synthesis, properties, and applications.

Graphene oxide (GO) prepared by modified hummers method was used as adsorbent for removal of heavy metal ions. The oxygenous functional groups on the surface of GO were primarily responsible for the sorption of metal ions. The effects of the parameters of pH value, contact time, Cu(II) concentration, and adsorbent dosage on adsorption were examined. The sorption process conformed to the Freundlich isotherm, and the maximum sorption capacity of 117.5 mg g−1 was observed at an initial pH value of 5.3 after agitating for 150 min. It was also found that Cu-pretreated GO could be desorbed by HCl and the reusability of GO could still maintain above 90 % of its initial capability after ten cycles. The results suggest that GO is an effective adsorbent for copper ions removal in water treatment.

Highly Efficient Removal of Cu(II) from Aqueous Solution by Using Graphene Oxide

Supercapacitor based on electropolymerized polythiophene and multi-walled carbon nanotubes composites

A reduced graphene oxide–poly(p-phenylenediamine) (RGO–PPD) composite was prepared from p-phenylenediamine (PD) and chlorinated graphene oxide (GO–COCl) sheets through amidation and polymerization processes. Then the RGO–PPD composite was characterized by using scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The results show that PPD nanoparticles were wrapped within or on the surface of graphene sheets uniformly. The RGO–PPD composite displayed a layered-stacking structure and had a large surface area (674.22 m2 g−1) and a high pore volume (0.43 cm3 g−1). Capacitive properties of the RGO–PPD composite were studied using cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) in an electrolyte of 0.5 M H2SO4 aqueous solution. The RGO–PPD exhibits a high specific capacitance of 347 F g−1 at a discharge rate of 1 A g−1 and excellent cycling stability with 90.1% of its initial capacitance at a large current density of 10 A g−1 after 1000 charge/discharge cycles. The energy density and specific power density of the present supercapacitor are 48.2 W h kg−1 and 1.0 kW kg−1, respectively. The results suggest that the RGO–PPD is a promising material for high-performance supercapacitor applications.

Graphene covalently functionalized with poly(p-phenylenediamine) as high performance electrode material for supercapacitors

High-quality graphene scrolls (GSS) with a unique scrolled topography are designed using a microexplosion method. Their capacitance properties are investigated by cyclic voltammetry, galvanostatic charge–discharge and electrical impedance spectroscopy. Compared with the specific capacity of 110 F g−1 for graphene sheets, a remarkable capacity of 162.2 F g−1 is obtained at the current density of 1.0 A g−1 in 6 M KOH aqueous solution owing to the unique scrolled structure of GSS. The capacity value is increased by about 50% only because of the topological change of graphene sheets. Meanwhile, GSS exhibit excellent long-term cycling stability along with 96.8% retained after 1000 cycles at 1.0 A g−1. These encouraging results indicate that GSS based on the topological structure of graphene sheets are a kind of promising material for supercapacitors.

Yafei Kuang

Papers

Highly Efficient Removal of Cu(II) from Aqueous Solution by Using Graphene Oxide

Supercapacitor based on electropolymerized polythiophene and multi-walled carbon nanotubes composites

Graphene covalently functionalized with poly(p-phenylenediamine) as high performance electrode material for supercapacitors

Supercapacitors based on high-quality graphene scrolls

Preparation of Pd/MnO2-reduced graphene oxide nanocomposite for methanol electro-oxidation in alkaline media