Nanocarbons for electrochemical capacitor electrode materials

Abstract

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.