Carbon material structures

Recent advances on material s chemistiy have contributed to develop highly featured carbon nanostructures with unforeseen properties that offer unexpected opportunities in many fields. " The majority of these applications derives from the flexible coordination chemistiy of carbon atoms and their unique ability to bind other heteroatoms (either on the surface or inserted within the structural framework) or other carbon atoms, resulting in a wide spectrum of materials and allotropic forms, as shown in Fig. 1. The main carbon allotropes of interest in electrochemical applications and frequently used carbon electrodes are diamond, graphite, graphene and carbon nanotubes. A detailed review on carbon materials structure can be found in ref. 15,17 and 18, and below we summarize some important facts about their characteristics ... 

The activated carbon materials are produced by either thermal or chemical activation as granular, powdered, or shaped products. In addition to the form of the activated carbon, the final product can differ in both particle size and pore structure. The properties of the activated carbon will determine the type of application for which the carbon will be used. 

Chapter 1 contains a review of carbon materials, and emphasizes the stmeture and chemical bonding in the various forms of carbon, including the foui" allotropes diamond, graphite, carbynes, and the fullerenes. In addition, amorphous carbon and diamond fihns, carbon nanoparticles, and engineered carbons are discussed. The most recently discovered allotrope of carbon, i.e., the fullerenes, along with carbon nanotubes, are more fully discussed in Chapter 2, where their structure-property relations are reviewed in the context of advanced technologies for carbon based materials. The synthesis, structure, and properties of the fullerenes and... 

Chapter 11 reports the use of carbon materials in the fast growing consumer eleetronies applieation of lithium-ion batteries. The principles of operation of a lithium-ion battery and the mechanism of Li insertion are reviewed. The influence of the structure of carbon materials on anode performance is described. An extensive study of the behavior of various carbons as anodes in Li-ion batteries is reported. Carbons used in commereial Li-ion batteries are briefly reviewed. 

In addition to nanocapsules filled with metals and carbides, various exotic carbon materials with hollow structures, such as single-wall (SW) tubes[9,10], bamboo-shaped tubes, and nanochains[l 1], are produced by using transition metals as catalysts. 

Carbon materials which have the closest-packed hexagonal structures are used as the negative electrode for lithium-ion batteries carbon atoms on the (0 0 2) plane are linked by conjugated bonds, and these planes (graphite planes) are layered. The layer interdistance is more than 3.35 A and lithium ions can be intercalated and dein-tercalated. As the potential of carbon materials with intercalated lithium ions is low,... 

Solid carbon materials are available in a variety of crystallographic forms, typically classified as diamond, graphite, and amorphous carbon. More recently another structure of carbon was identified—namely the fullerenes which resemble a soccer ball... 

A similar, but highly porous, vitreous carbon material—reticulated vitreous carbon (RVC)—has found widespread application for flow analysis and spectro-electrochemistry (25). As shown in Figure 4-10, RVC is an open-pore ( spongelike ) material such a network combines the electrochemical properties of glassy carbon with many structural and hydrodynamic advantages. These include a very high surface area ( 66 cm2 cm-3 for the 100-ppi grade), 90-97% void volume, and a low resistance to fluid flow. 

Mesoporous carbon materials were prepared using ordered silica templates. The Pt catalysts supported on mesoporous carbons were prepared by an impregnation method for use in the methanol electro-oxidation. The Pt/MC catalysts retained highly dispersed Pt particles on the supports. In the methanol electro-oxidation, the Pt/MC catalysts exhibited better catalytic performance than the Pt/Vulcan catalyst. The enhanced catalytic performance of Pt/MC catalysts resulted from large active metal surface areas. The catalytic performance was in the following order Pt/CMK-1 > Pt/CMK-3 > Pt/Vulcan. It was also revealed that CMK-1 with 3-dimensional pore structure was more favorable for metal dispersion than CMK-3 with 2-dimensional pore arrangement. It is eoncluded that the metal dispersion was a critical factor determining the catalytic performance in the methanol electro-oxidation. 

Since the UV degraded C-PVC still contains substantial amounts of the initial CHC1-CHC1 structure, one can expect the chlorine radicals evolved to also initiate the zip-dehydrochlorination of these structures. The resulting chlorinated polyenes will then be further destroyed by the laser irradiation, so that finally all the C-PVC polymer is converted into a purely carbon material within a fraction of a second. 

Different types of activated carbon are among the most suitable materials for this purpose. For this reason specialists, involved in development of active materials for EC try to increase carbon s specific surface as much as possible and to optimize the internal structure of the carbon porous structure. 

A simple visual method to evaluate the rate of solvent/electrolyte migration through the porous electrode body has been developed. The method enables an express selection of carbon materials according to the mobility of electrolyte in their pore structure. 

The Li-Ion system was developed to eliminate problems of lithium metal deposition. On charge, lithium metal electrodes deposit moss-like or dendrite-like metallic lithium on the surface of the metal anode. Once such metallic lithium is deposited, the battery is vulnerable to internal shorting, which may cause dangerous thermal run away. The use of carbonaceous material as the anode active material can completely prevent such dangerous phenomenon. Carbon materials can intercalate lithium into their structure (up to LiCe). The intercalation reaction is very reversible and the intercalated carbons have a potential about 50mV from the lithium metal potential. As a result, no lithium metal is found in the Li-Ion cell. The electrochemical reactions at the surface insert the lithium atoms formed at the electrode surface directly into the carbon anode matrix (Li insertion). There is no lithium metal, only lithium ions in the cell (this is the reason why Li-Ion batteries are named). Therefore, carbonaceous material is the key material for Li-Ion batteries. Carbonaceous anode materials are the key to their ever-increasing capacity. No other proposed anode material has proven to perform as well. The carbon materials have demonstrated lower initial irreversible capacities, higher cycle-ability and faster mobility of Li in the solid phase. 

The replacement of an individual carbon material by a mixture (composite) in order to improve the electrode s performance seems promising [23], Discharging at low potentials (0-0.25 V vs Li/Li+) has been proven to be provided by the graphite-structure component while it is the non-graphitic one, which works above 0.25 V [4,9]. The present work deals... 

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