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An oxidation-resistant and elastic mesoporous carbon, graphene mesosponge (GMS), is prepared. GMS has a sponge-like mesoporous framework (mean pore size is 5.8 nm) consisting mostly of single-layer graphene walls, which realizes a high electric conductivity and a large surface area (1940 m 2 g −1 ). Moreover, the graphene-based framework includes 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 suffi cient capacitance (125 F g −1 ), 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 −1 (material mass base), which is more than twice that of commercial materials. Moreover, the continuous graphene framework makes GMS mechanically tough and extremely elastic, and its mean pore size (5.8 nm) can be reversibly compressed down to 0.7 nm by simply applying mechanical force. The sponge-like elastic property enables an advanced force-induced adsorption control.

Analytical techniques were investigated for examining the influence of the ionomer network structure on proton transport in the catalyst layers of a polymer electrolyte fuel cell. Two samples were made with and without a pseudocatalyst layer (PCL) consisting of a carbon black support and an ionomer between two membranes. The overall resistance of the samples was evaluated with a hydrogen pump technique. The difference in resistance between them was mainly due to the proton-transport resistance of the PCL. Another technique of subtracting high frequency resistance from the overall resistance was also examined. Almost the same characteristics were obtained with both techniques. Using the former technique, the effective proton conductivity of PCLs with different carbon supports was investigated. The effective proton conductivities differed. An analysis of the difference revealed the following two possible causes. One is that the Bruggeman factor of the samples might have been affected by the state of ionomer coverage. Another is that the proton conductivities of the ionomer as bulk differed, which might have been due to a difference in water content attributable to the carbon supports.

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The influence of the ionomer content on proton transport phenomena in the catalyst layers of a fuel cell was examined using pseudo catalyst layers (PCLs) consisting of the carbon support and the ionomer. Effective proton conductivity r eff of the PCL increased with increasing ionomer content in both graphitized ketjen black (GKB) and ketjen black (KB) systems. It was found that the ionomer coverage h and the Bruggeman factor c, which is related to the tortuosity of the proton path in the PCL, did not depend on the ionomer content appreciably. In the GKB system, the volume fraction of the ionomer e ion was the dominant factor of the difference in r eff . However, the results of a water adsorption analysis with a heterogeneous Do-Do model suggested that the proton conductivity of the ionomer as bulk r bulk probably differs depending on the ionomer content in the KB system, though it was independent of the ionomer content in the GKB system. It was inferred that the interaction between functional groups on the KB surface and the ionomer weaken its water adsorbability. Consequently, the ionomer content would appear to affect not only structural parameters (i.e. c and e ion ) but also r bulk in the KB system.

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