Carbon/transition metal oxide composites

Although a majority of these composite thermistors are based upon carbon black as the conductive filler, it is difficult to control in terms of particle size, distribution, and morphology. One alternative is to use transition metal oxides such as TiO, VO2, and V2O3 as the filler. An advantage of using a ceramic material is that it is possible to easily control critical parameters such as particle size and shape. Typical polymer matrix materials include poly(methyl methacrylate) PMMA, epoxy, silicone elastomer, polyurethane, polycarbonate, and polystyrene. 

Isolation and identification of surface-bonded acetone enolate on Ni(l 11) surfaces show that metal enolate complexes are key intermediates in carbon-carbon bond-forming reactions in both organometaUic chemistry and heterogeneous catalysis. Based on studies on powdered samples of defined surface structure and composition, most of the results were reported for acetone condensation over transition-metal oxide catalysts, as surface intermediate in industrially important processes. With the exception of a preoxidized silver surface, all other metal single-crystal surfaces have suggested that the main adsorption occurs via oxygen lone-pair electrons or di-a bonding of both the carbonyl C and O atoms. 

The DIN definition of the term colorant includes both dyes and pigments. In contrast to dyes, pigments are practically insoluble in the binder. They consi.st of solid particles generally with a uniform chemical composition and are mainly transition metal oxides, oxide hydrates, sulfides, silicates, sulfates or carbonates (.see Table 5.9-1). 

The history of mesoporous material synthesis is unintentionally or intentionally duplicating the development of zeolites and microporous molecular sieve. It starts from silicate and aluminosilicate, through heteroatom substitution, to other oxide compounds and sulfides. It is worth mentioning that many unavailable compositions for zeolite (e.g., certain transition metal oxides, even pure metals and carbon) can be made in mesoporous material form. 

In three-phase reactors, one of the main problems is often the mass transport limitations, which may reflect internal as well as external mass transfer resistances. The use of filamentous catalytic materials for multiphase reactions may help reduce or even avoid mass transfer limitations [63,132,133]. Filamentous woven cloths made of glass, composite mixed oxides, metallic alloys, or activated carbon (Figure 18) can be used as supports for active components such as platinum, palladium, or transition metal oxides. The diameters of the filaments are of the order of several micrometers and correspond to the typical diameters of catalysts that are suspended in the reaction medium. By using such small diameters, internal mass transfer limitations can be avoided. 

Mesoporous molecular sieves having chemical compositions different from silicates and alumina including aluminum phosphates, various transition-metal oxides, chalcogenide and nitridic framework, metals, and carbons were recently nicely reviewed by Schiith [79]. 

Efforts to enhance the conductivity of transition metal oxide electrodes have included the preparation of composites of the oxide with a conductive material, such as carbon black. Traditional composite electrodes, however, are characterized by aggregation of the carbon black particles [23]. These aggregates are typically on the order of hundreds of nanometers in diameter and may occlude the oxide aerogel surface. Work to enhance the conductivity of the transition metal oxide... 

After being demonstrated for the first time for transition metal oxides [POI 00], the conversion reaction (equation [1.3]) has since been expanded to a number of other elements (X = O, S, P, F, Sb...). This profound transformation of the initial material MaXb into a composite electrode made up of metallic nanoparticles and a Li X matrix enables high energy densities to be reached. Moreover, it involves redox reactions very different from those of the insertion mechanisms, which only involve the transition metal, whereas here the transition metal and post-transitional element are simultaneously reduced or oxidized. These conversion reactions thus enable more than 1 Li (le ) to be exchanged per metallic atom, and result in gravimetric and volumetric capacities that can reach 1,000 mAh/g, and 7,000 mAh/cm, respectively, which is nearly 10 times that of graphitic carbon (800 mAh/cm ). Until recently, these materials were only a laboratory curiosity since the conversion reaction, although reversible, did... 

Carbon nanotubes can serve as a three-dimensional support of materials with pseudocapacitive properties, for example, electrically conducting polymers (PANl, PPy, PEDOT) or transition metal oxides, for example, Mn02. CNTs play a perfect conducting role in these composites. 

In this chapter we deal with four major electrode surfaces active metals, carbons, non-active metals (e.g., noble metals), and composite electrodes comprising lithiated transition metal oxide powders as the active mass, plus polymeric binder and conductive additives (usually carbon black or graphite powders at low percentage). In terms of general surface chemistry, we find that the surface reactions on lithium, lithiated carbons, carbon, and noble metals polarized to low potentials in non-aqueous Li salt solutions are very similar. All of these electrodes are covered by surface films comprising insoluble Li salts, which are formed by reduction of solution species. Upon anodic polarization of carbon or noble metal electrodes in non-aqueous solutions, solution species are oxidized. Here, the impact of the cations is negligible. It seems that the species that determine the anodic stability of non-aqueous solutions are the solvents. For instance, ether may be oxidized at potentials below 4 V, while alkyl carbonates may apparently be stable up to 5 V (Li/Li ). However, it should be noted that some minor oxidation reactions of alkyl carbonate solvents on noble metal electrodes (e.g., Pt, Au) can be detected even at a potential below 4 V. The... 

As shown by Eqs. 1 and 5, the ORRs in the aqueous alkaline electrolyte and in the non-aqueous electrolyte share the same two-electron reduction. This means that all catalysts showing the catalytic activity towards the ORR in alkaline fuel cells and metal-air batteries are theoretically suitable for the non-aqueous electrolyte Li-air batteries. Base on the chemical composition of the materials, these catalysts can be briefly classified into the following categories (1) porous carbon and doped carbon materials, (2) transition metal oxides, nitrides, and sulfides, (3) marcocyclic transition metal complexes, (4) non-precious metals and alloys, (5) precious metals and alloys, (6) organic redox mediators. 

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