Template synthesis of graphene-based nanocarbons as energy storage media
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba, Sendai,980-85770, Japan
Summary. So far various types of unique carbon materials have been synthesized using the template carbonization method. For example, we can prepare unique ordered microporous carbon by the template technique using zeolite [1, 2]. Moreover, very recently, we have synthesized “Graphene Mesosponge” carbon using alumina nanoparticles as a template . Here, in addition to our old attempt to produce a graphene sheet, we introduce the unique structures of the two types of carbons and demonstrate how such unique structures are useful for the energy applications.
Graphene synthesis using layered clay. In 1988, to synthesize a single sheet of carbon layer, we carbonized polyacrylonitrile between the lamellae of montmorillonite (layered clay) and liberated the resulting carbon from the clay. Since such layered clay provides the carbon precursor with an ideal two-dimensional space at the angstrom level, we expected the formation of a single sheet of carbon layer (graphene). However, it was not the case. Instead, highly orientated graphite was obtained .
Zeolite Templated Carbon (ZTC). ZTC consists of a buckybowl-like nanographene assembled into a three dimensional regular network. Both sides of the buckybowl-like unit are fully exposed, and, in addition, the narrow nanographene-based framework has a significant number of edge sites. Consequently, ZTC has a very large specific surface area close to 4000 m2/g. Due to such an extremely large surface area, ZTC shows as large a H2 storage capacity as 2.2 wt% under 34 MPa at room temperature . Moreover, the performance of ZTC as an electrochemical capacitor was evaluated in an organic electrolyte solution (1M Et4NBF4/propylene carbonate). Despite relatively small pore diameter in ZTC (ca. 1.2 nm), This carbon exhibits both of very high gravimetric (140~190 F/g) and volumetric (75~83 F/cm3) capacitances. In addition, such a high capacitance can be well retained even at a very high current up to 20 A/g. This finding clearly indicates that the three-dimensionally connected and regularly arranged micropores were very effective at reducing ion-transfer resistance . Furthermore, we examined the performance of ZTC in an aqueous electrolyte solution (1M H2SO4) and its details will be introduced in my talk.
Graphene Mesosponge (GMS). The carbon prepared using alumina nanoparticles as a template has a sponge-like mesoporous framework (mean pore size is 5.8 nm) consisting mostly of single-layer graphene walls (see its structure in Fig. 1), which realizes a high electric conductivity and a large surface area (1940 m2/g). Moreover, the graphene-based framework contains only a very small amount of edge sites, thereby achieving much higher stability against oxidation than conventional porous carbons such as carbon blacks and activated carbons. Thus, GMS can simultaneously possess seemingly incompatible properties; the advantages of graphitized carbon materials (high conductivity and high oxidation resistance) and porous carbons (large surface area). These unique features allow GMS to exhibit a sufﬁcient capacitance (125 F/g), wide potential window (4 V), and good rate capability as an electrode material for electric double-layer capacitors utilizing an organic electrolyte. Hence, GMS achieves a high energy density of 59.3 Wh/kg (material mass base), which is more than twice that of commercial activated carbon.
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Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
1977 B. Sc., Osaka City University, Osaka, Japan
1979 Ms. Sc.,Tohoku University, Sendai, Japan
1982 Dr. Sc., Tohoku University, Sendai, Japan
1982 Research Associate, Tohoku University, Sendai, Japan
1991 Associate Prof., Tohoku University, Sendai, Japan
2004 Prof., Tohoku University, Sendai, Japan
2005 The Chemical Society of Japan Award for Creative Work for 2005
2009 The Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology, Japan
2002-2013 Editor of Carbon journal
2003 - present Editorial Board Member of J. Porous Materials
2006 - present Editorial Board Member of New Carbon Materials
2011 – 2016 President of the Carbon Society of Japan
2014 - present Honorary Advisory Board of Carbon journal
2015 - present Editorial Board Member of Energy Storage Materials