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

To enhance the long stability of sulfur cathode for a high energy lithium–sulfur battery system, a sulfur–carbon sphere composite was prepared by encapsulating sulfur into micropores of carbon spheres by thermal treatment of a mixture of sublimed sulfur and carbon spheres. The elemental sulfur exists as a highly dispersed state inside the micropores of carbon spheres with a large surface area and a narrow pore distribution, based on the analyses of the X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), thermogravimetry (TG) and local element line-scanning. It is demonstrated from galvanostatic discharge–charge process, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) that the sulfur–carbon sphere composite has a large reversible capacity and an excellent high rate discharge capability as cathode materials. In particular, the sulfur–carbon sphere composite with 42 wt% sulfur presents a long electrochemical stability up to 500 cycles, based on the constrained electrochemical reaction inside the narrow micropores of carbon spheres due to strong adsorption. Therefore, the electrochemical reaction constrained inside the micropores proposed here would be the dominant factor for the enhanced long stability of the sulfur cathode. The knowledge acquired in this study is important not only for the design of efficient new electrode materials, but also for understanding the effect of the micropores on the electrochemical cycle stability.

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Enhancement of long stability of sulfur cathode by encapsulating sulfur into micropores of carbon spheres

Waste materials for activated carbon preparation and its use in aqueous-phase treatment: a review.

Fractal characterization of adsorption-pores of coals from North China: An investigation on CH4 adsorption capacity of coals

Cork is a natural, renewable, sustainable raw material that has been used for many centuries. As a result of this very long term interest, the scientific literature on cork is extensive. The present review focuses on the chemical composition, physical and mechanical properties of cork and on its products and sub-products. The substantial efforts to fully characterise cork, as well as new developments and evolving research, are reviewed, beginning with its histology, growth and morphology (at macro- and microscales). The chemical structure is analysed in detail, covering both the materials that form the wall structure and the low molecular weight, extractable components. The unique properties of cork are discussed and correlated with current knowledge on morphology and chemical structure. Finally, the important industrial applications of cork are reviewed, in the context of research to provide cork with novel, high added-value applications.

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M.A. Díaz-Díez

Papers

Application of the Rosin–Rammler and Gates–Gaudin–Schuhmann models to the particle size distribution analysis of agglomerated cork

Porous texture of activated carbons prepared by phosphoric acid activation of woods

Preparation of activated carbons from bituminous coal pitches

Preparation and characterization of activated carbons from impregnation pitch by ZnCl2

Study of the pore size distribution and fractal dimension of HNO3-treated activated carbons