Electrochemical capacitors (ECs) are characterized by their much higher power density as well as longer cyclability than those of secondary batteries. However, ECs have a fatal drawback of limited energy density, compared to the secondary batteries. Thus, the development of new electrode materials for ECs is significantly important to realize next-generation ECs that satisfy both of high energy and power density. In this talk, a unique ordered microporous carbon, zeolite-templated carbon (ZTC), will be introduced as a new type of high-performance electrode material for ECs.

From their excellent electrical conductivity and relatively high surface areas, single-walled carbon nanotubes (SWCNTs) and graphenes are often mentioned as promising electrode materials for ECs. Their building unit, a graphene sheet, has a large theoretical surface area (2630 m2 g–1), and thereby a large capacitance could be potentially expected. However, the actual BET surface areas of SWCNTs and graphenes are usually much lower than the aforementioned theoretical value, because of the aggregations/stacking of the graphene sheets by a strong van der Waals interaction. Accordingly, their capacitances actually does not reach to the level of high-surface activated carbons. In order to expose the entire surface, a graphene sheet has to be formed into a self-standing three dimensional network. Our group has demonstrated that it is indeed possible to synthesize a graphene-based architecture having 3D topology inside a confined nanospace-network of a zeolite crystal. The material thus obtained is called as zeolite-templated carbon (ZTC), and it is made up of a buckybowl-like nanographene assembled into a three-dimensional regular network. The both sides of the buckybowl-like unit are fully exposed, and in addition, the narrow nanographene-based framework has a significant amount of edge sites. 

The extraordinary structure of ZTC gives rise to extremely unique electrochemical behavior that is distinguishable from any other carbonaceous materials. The mutually connected 1.2-nm nanopores realize a remarkably high rate capability even in an organic electrolyte (1M Et4N-BF4), compared to other micro/mesoporous activated carbons. In addition, we have discovered that appropriate polarization of ZTC in the same electrolyte greatly enhances its pseudocapacitance up to 330 F g–1. Such enhancement is much more remarkable in 1M H2SO4: the edge sites of ZTC framework are very easily oxidized in this case, and a large amount of quinone-type functional groups are introduced as a result. The quinone groups thus introduced give rise to the occurrence of a very large pseudocapacitance, and the resulting total capacitance reaches up to ca. 500 F g–1, which is much larger than any of carbonaceous materials reported so far, and is even comparable to conductive polymers and metal oxides, or their composites.

Electrochemical capacitors (ECs) are characterized by their much higher power density as well as longer cyclability than those of secondary batteries. However, ECs have a fatal drawback of limited energy density, compared to the secondary batteries. Thus, the development of new electrode materials for ECs is significantly important to realize next-generation ECs that satisfy both of high energy and power density. In this talk, a unique ordered microporous carbon, zeolite-templated carbon (ZTC), will be introduced as a new type of high-performance electrode material for ECs.

From their excellent electrical conductivity and relatively high surface areas, single-walled carbon nanotubes (SWCNTs) and graphenes are often mentioned as promising electrode materials for ECs. Their building unit, a graphene sheet, has a large theoretical surface area (2630 m2 g–1), and thereby a large capacitance could be potentially expected. However, the actual BET surface areas of SWCNTs and graphenes are usually much lower than the aforementioned theoretical value, because of the aggregations/stacking of the graphene sheets by a strong van der Waals interaction. Accordingly, their capacitances actually does not reach to the level of high-surface activated carbons. In order to expose the entire surface, a graphene sheet has to be formed into a self-standing three dimensional network. Our group has demonstrated that it is indeed possible to synthesize a graphene-based architecture having 3D topology inside a confined nanospace-network of a zeolite crystal. The material thus obtained is called as zeolite-templated carbon (ZTC), and it is made up of a buckybowl-like nanographene assembled into a three-dimensional regular network. The both sides of the buckybowl-like unit are fully exposed, and in addition, the narrow nanographene-based framework has a significant amount of edge sites. 

The extraordinary structure of ZTC gives rise to extremely unique electrochemical behavior that is distinguishable from any other carbonaceous materials. The mutually connected 1.2-nm nanopores realize a remarkably high rate capability even in an organic electrolyte (1M Et4N-BF4), compared to other micro/mesoporous activated carbons. In addition, we have discovered that appropriate polarization of ZTC in the same electrolyte greatly enhances its pseudocapacitance up to 330 F g–1. Such enhancement is much more remarkable in 1M H2SO4: the edge sites of ZTC framework are very easily oxidized in this case, and a large amount of quinone-type functional groups are introduced as a result. The quinone groups thus introduced give rise to the occurrence of a very large pseudocapacitance, and the resulting total capacitance reaches up to ca. 500 F g–1, which is much larger than any of carbonaceous materials reported so far, and is even comparable to conductive polymers and metal oxides, or their composites.