No abstract

The structure of graphite fluoride, (C2F)n has been investigated by X‐ray analyses, solid state 19F‐n.m.r., and electron microscopy for well characterized and crystallized samples obtained from natural graphite or HOPG (highly oriented pyrolytic graphite). On the basis of the present results and structural properties derived from previous works, (C2F)n has a layered structure of stage‐2 which belongs hexagonal to the system with C3h symmetry. Detailed discussions on the symmetry both for (CF)n and (C2F)n have led to possible stacking sequences each unit cell of graphite fluoride should require. The ideal structure of (C2F)n is a hexagonal crystal lattice with a = b = 2.5 Å; c = 16.2 Å, and a plausible stacking sequence of AB/B′A′/ with Ic (identity period) = 8.09 Å. The layered structure of (CF)n is of stage‐1 with A/A′/ stacking sequence.

An ordered microporous carbon, which was prepared with zeolite as a template, was used as a model material to understand the ion storage/transfer behavior in electrical double-layer capacitor (EDLC). Several types of such zeolite-templated carbons (ZTCs) with different structures (framework regularity, particle size and pore diameter) were prepared and their EDLC performances were evaluated in an organic electrolyte solution (1 M Et(4)NBF(4)/propylene carbonate). Moreover, a simple method to evaluate a degree of wettability of microporous carbon with propylene carbonate was developed. It was found that the capacitance was almost proportional to the surface area and this linearity was retained even for the carbons with very high surface areas (>2000 m(2) g(-1)). It has often been pointed out that thin pore walls limit capacitance and this usually gives rise to the deviation from linearity, but such a limitation was not observed in ZTCs, despite their very thin pore walls (a single graphene, ca. 0.34 nm). The present study clearly indicates that three-dimensionally connected and regularly arranged micropores were very effective at reducing ion-transfer resistance. Despite relatively small pore diameter ZTCs (ca. 1.2 nm), their power density remained almost unchanged even though the particle size was increased up to several microns. However, when the pore diameter became smaller than 1.2 nm, the power density was decreased due to the difficulty of smooth ion-transfer in such small micropores.

The chemical bonding and the electronic structures of C 60 F x and C 70 F x were investigated by near edge X-ray absorption fine structure (NEXAFS) spectroscopy and UV photoemission spectroscopy (UPS), which are useful methods for examining the unoccupied and the occupied states, respectively. With these results and XPS measurements, we derived the electronic energy diagram of C 60 F x and discussed the change of the electronic structure from that of C 60 by fluorination. The energies of the LUMO and the Fermi level of solid C 60 F 48 were estimated to be -5.0 and -5.4 eV below the vacuum level, indicating that highly doped C 60 F x is a strong electron acceptor. The electronic absorption spectra of C 60 F x solutions deep into the vacuumultraviolet region were also measured, and the isomerism of C 60 F x was discussed by comparing the observed results with theoretical simulations.

No abstract