In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

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A review of electrode materials for electrochemical supercapacitors

Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

Carbon properties and their role in supercapacitors

Graphene based materials: Past, present and future

In this review, the technologies and working principles of different materials used in supercapacitors are explained. The most important supercapacitor active materials are discussed from both research and application perspectives, together with brief explanations of their properties, such as specific surface area and capacitance values. A review of different supercapacitor electrolytes is given and their positive and negative features are discussed. Finally, cell configurations are considered, pointing out the advantages and drawbacks of each configuration.

Review on supercapacitors: Technologies and materials

Supercapacitors Using Single‐Walled Carbon Nanotube Electrodes

We have carried out systematic calculations for hydrogen-adsorption and -storage mechanism in carbon nanotubes at zero temperature. Hydrogen atoms first adsorb on the tube wall in an arch-type and zigzag-type up to a coverage of θ = 1.0 and are stored in the capillary as a form of H2 molecule at higher coverages. Hydrogen atoms can be stored dominantly through the tube wall by breaking the C−C midbond, while preserving the wall stability of a nanotube after complete hydrogen insertion, rather than by the capillarity effect through the ends of nanotubes. In the hydrogen-extraction processes, H2 molecule in the capillary of nanotubes first dissociates and adsorbs onto the inner wall and is further extracted to the outer wall by the flip-out mechanism. Our calculations describe suitably an electrochemical storage process of hydrogen, which is applicable for the secondary hydrogen battery.

A hydrogen storage mechanism in single-walled carbon nanotubes.

We have fabricated twisted nematic cells doped by carbon nanotubes (CNTs). The CNTs with a minute amount of doping did not perturb the liquid crystal orientation in the off and on state. The hysteresis studies of voltage-dependent transmittance and capacitance under ac and dc electric field showed that the residual dc, which is related to an image sticking problem in liquid crystal displays, was greatly reduced due to the ion trapping by CNTs.

Electrical-field effect on carbon nanotubes in a twisted nematic liquid crystal cell

High yield purification of multiwalled carbon nanotubes by selective oxidation during thermal annealing

Absorption and dispersion of singlewalled carbon nanotube films were measured using an optoelectronic THz beam system for THz time-domain spectroscopy. The anisotropically aligned nanotube films were prepared through simple mechanical squeezing with a bar coater. The angle-dependent absorption and dispersion values were then measured. Results indicate that the index of refraction decreases with increasing frequency (0.1–0.8 THz), whereas the real conductivity increases with increasing frequency. The real conductivity measured is not congruent with the simple Drude model, but it follows a Maxwell–Garnett model, where the nanotubes are embedded in a dielectric host.

Kay Hyeok An

Papers

Supercapacitors Using Single‐Walled Carbon Nanotube Electrodes

A hydrogen storage mechanism in single-walled carbon nanotubes.

Electrical-field effect on carbon nanotubes in a twisted nematic liquid crystal cell

High yield purification of multiwalled carbon nanotubes by selective oxidation during thermal annealing

Terahertz conductivity of anisotropic single walled carbon nanotube films