The behavior of exfoliated carbon fibers, carbon-coated tungsten carbides and MgO-templated mesoporous carbons as an electrochemical capacitor electrode is summarized in relation with their nanostructures. Exfoliated carbon fibers which are composed of a bundle of nano-fibrils composed of exfoliated graphene layers showed pseudocapacitive characteristics in a sulfuric acid electrolyte. Due to the lack of carbon layer stacking in exfoliated carbon fibers, the cyclic voltammograms showed no redox reaction peaks as a result of staging, but an intercalation-like charge-transfer reaction could be considered. In the case of carbon-coated nano-size tungsten carbides, the first polarization cycle in sulfuric acid caused a complete transformation of the carbon-coated tungsten carbide nano-particles from carbides to oxyhydrides which showed a pseudocapacitive response in the cyclic voltammograms. MgO-templated mesoporous carbons with a large mesopore contribution and a surface area greater than 2000 m² g⁻¹ provided superior characteristics as capacitor electrode materials with a high rate capability and good low temperature performance with a variety of electrolytes.

Graphite-like layer materials composed of boron/carbon (B/C) and boron/carbon/nitrogen (B/C/N) have been prepared by chemical vapor deposition (CVD). In order to evaluate the electronic states of these materials, the X-ray absorption near-edge structures (XANES) of the materials have been measured and analyzed by first-principle calculation using the “discrete variational (DV)-Xα molecular orbital method”. Absorption intensities of the CK-edge XANES spectra for B/C and B/C/N materials started to increase at energies 1.1 eV lower than that of graphite, which suggests that the energy levels of the conduction bands of B/C and B/C/N materials were lower than that of graphite by 1.1 eV. DV-Xα calculation suggests that covalent bonds between boron and carbon atoms lower the bottoms of the conduction bands of these materials, compared with that of graphite. Since electron affinity is defined to be the difference between the vacuum level and the bottom of the conduction band, these results indicate that B/C and B/C/N materials have larger electron affinities than that of graphite. Consequently, the present study supports the experimental results which have been reported for the donor-type intercalation of Na, Mg and Ca into B/C and B/C/N materials.

Trends in research and the development of activated carbons is surveyed from information on patent application publications using international patent classification (IPC) (C01B 31/08, B01J 20/20, and so on) and Japan platform for patent information (J-PlatPat). The number of application publications which relates to electric double-layer capacitors (EDLCs) or lithium ion capacitors (LICs) was about 500 between 1989 to 2017. It is found that the important issue for EDLCs or LICs was to increase their capacitance, and the number of patent applications relating to alkali activation is 20∼30%, or more.