Electrochemical Properties of Nitrogen-Substituted Carbon and Organofluorine Compounds
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natural graphite(p,7pm) electrode in fluoroester-mixed 1 M LiCIO 4 -EC/DEC solutions. RESULTS Compositions, morphologies and crystallinity of CffN Table 1 shows the typical examples of compositions, morphologies and X-ray diffraction data of C,,N samples prepared at 800-11000 C with nickel catalyst in comparison with those of C.N prepared without catalyst and carbon prepared from benzene with nickel. C.N samples with compositions C 14N-C62 N were obtained in the temperature range of 800-1100'C. No hydrogen was detected by elemental analysis for all the samples prepared with nickel catalyst whereas less crystallized C14 NH 0 6. having hydrogen was obtained at 10009C in the absence of the catalyst. The products prepared 900cC and 10000 C had the highest nitrogen contents, as C14 N-C 21 N. Nitrogen concentrations were much less in the products deposited at the lower and higher temperatures, 800'C, 1050'C and 1100cC. The CfN samples prepared were apparently black powder. However, SEM and TEM observations revealed that the products obtained at 800'C were fibrous C.N with diameters of ca. 3 pm and 0.3 pm, those at 900'C were mixtures of fibrous C.N with diameters of ca. 0.5 pm and fine particles with diameters of 2-3 pm, and those at 1000'C were particles with diameters of 2-3 pm. The C.N samples exhibited the same diffraction lines as usual carbon materials. Table 1 shows that both d(002) values and half widths were smaller than those for C14NHo.6 prepared without nickel, indicating that the CQN samples synthesized using nickel have much higher crystallinity than that prepared without nickel. XPS analysis shows the existence of pyridine type nitrogen at the edge of graphene layer (398.8eV), nitrogen bonded to three carbon atoms (400.9eV), and pyridine-N-oxide (402.3eV) [6]. The peak at 400.9eV has higher intensity than other two peaks corresponding to nitrogen atoms existing at the edge of graphene layer when CfN is prepared with nickel catalyst, whereas CN prepared without nickel has a large amount of pyridine type nitrogens.
Table 1. Compositions,morphologies and XRD data of C.N and carbon samples. React. temp. Composition Morphology Diameter d(002) FWHM L,(002)
(C) 1100 1050 1000 900 800 1000 900
(pm) C 62N'
C33NG C20Na C21Ne
Particle Particle Particle Particle
-
2-,3 2,-,3
(nm)
(°)
(nm)
0.335 0.335 0.336 0.335
0.575 0.663 0.775 0.900
17 15 13 11
1.250 2.850 0.938
8 3 10
Fiber
;,0.5
C40 Na Fiber C14 NH0 .6 b -
;3,0.3
0.337
-
0.340
Cc
-
-
0.336
3
a Prepared from acetonitrile (partial pressure: 9.2 x 1O Pa) with Ni catalyst, b Prepared from acetonitrile (partial pressure: 9.2 x 10iPa) without catalyst, c Prepared from benzene (partial pressure: 9.2 x 10Pa) with Ni catalyst.
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Electrochemical behavior of CfN The potential of C=N electrodes gradually decreased and increased with lithium ion intercalation and deintercalation. Nitrogen incorporation in carbon induced the larger polarization for lithium ion deintercalation process and the slightly smaller one for the intercalation process a
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