Porous carbons applications

Porous carbon fiber-carbon bmder composites are a class of matenals that are not widely known, yet they fulfill a vital role in the RTG space power systems, and show considerable potential for other uses in light absorption or gas adsorption applications. These applications are enabled through the unique combmation of physical properties exhibited by the porous carbon fiber-carbon binder composites Perhaps the most significant of its physical attributes is the open, yet rugged, form of the material which contributes significantly to its utility m the fields of... 

Detailed accounts of fibers and carbon-carbon composites can be found in several recently published books [1-5]. Here, details of novel carbon fibers and their composites are reported. The manufacture and applications of adsorbent carbon fibers are discussed in Chapter 3. Active carbon fibers are an attractive adsorbent because their small diameters (typically 6-20 pm) offer a kinetic advantage over granular activated carbons whose dimensions are typically 1-5 mm. Moreover, active carbon fibers contain a large volume of mesopores and micropores. Current and emerging applications of active carbon fibers are discussed. The manufacture, structure and properties of high performance fibers are reviewed in Chapter 4, whereas the manufacture and properties of vapor grown fibers and their composites are reported in Chapter 5. Low density (porous) carbon fiber composites have novel properties that make them uniquely suited for certain applications. The properties and applications of novel low density composites developed at Oak Ridge National Laboratory are reported in Chapter 6. 

A recently developed adsorbent version of ORNL s porous carbon fiber-carbon binder composite is named carbon fiber composite molecular sieve (CFCMS). The CFCMS monoliths were the product of a collaborative research program between ORNL and the University of Kentucky, Center for Applied Energy Research (UKCAER) [19-21]. The monoliths are manufactured in the manner described in Section 2 from P200 isotropic pitch derived fibers. While development of these materials is in its early stages, a number of potential applications can be identified. 

In practical application, it was reported that the platinum particles dispersed in highly porous carbonized polyacrylonitrile (PAN) microcellular foam used as fuel-cell electrocatalyst160 have the partially active property. The fractal dimension of the platinum particles was determined to be smaller than 2.0 by using the potentiostatic current transient technique in oxygen-saturated solutions, and it was considered to be a reaction dimension, indicating that not all of the platinum particle surface sites are accessible to the incoming oxygen molecules. 

This concept later evolved into the Ucarsep membrane made of a layer of nonsintered ceramic oxide (including Zr02) deposited on a porous carbon or ceramic support, which was patented by Union Carbide in 1973 (Trulson and Litz 1973). Apparently, the prospects for a significant industrial development of these membranes were at the time rather limited. In 1978, Union Carbide sold to SPEC the worldwide licence for these membranes, except for a number of applications in the textile industry in the U.S. At that time, SPEC recognized the potential of inorganic membranes, but declassification of the inorganic membrane technology it had itself developed for uranium enrichment was not possible. 

Phosphoric acid fuel cells (PAFC) use liquid phosphoric acid as an electrolyte - the acid is contained in a Teflon-bonded silicon carbide matrix - and porous carbon electrodes containing a platinum catalyst. The PAFC is considered the "first generation" of modern fuel cells. It is one of the most mature cell types, the first to be used commercially, and features the most proven track record in terms of commercial applications with over 200 units currently in use. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses. 

The resorcinol-formaldehyde polymers have been used to prepare highly porous carbon materials, by controlled pyrolysis in an inert atmosphere [144,154], The microstructure of the carbon is an exact copy of the porous polymer precursor. Poly(methacrylonitrile) (PM AN) PolyHIPE polymers have also been used for this purpose. These monolithic, highly porous carbons are potentially useful in electrochemical applications, particularly re-chargeable batteries and super-capacitors. The RF materials, with their very high surface areas, are particularly attractive for the latter systems. 

One energy application of methanol in its early stages of development is the direct methanol fuel cell (DMFC). A fuel cell is essentially a battery in which the chemicals are continuously supplied from an external source. A common fuel cell consists of a polymer electrolyte sandwiched between a cathode and anode. The electrodes are porous carbon rods with platinum... 

Thus, although the CAVE process has definite value in its ability to fluorinate smoothly certain organic compounds which are not particularly amenable to other methods of fluorination, for example, by the ECF Simons process, its general application is obviously severely limited by the combined requirements that substrates be only slightly soluble in hydrogen fluoride and sufficiently volatile at the temperature of the cell ( 100 °C) to permit diffusion though the porous carbon matrix of the anode. 

Metallic NPs are most widely used in catalytic applications due to their inherent properties. Several examples of platinum and gold NPs are apparent in the literature. For example, electrodeposited platinum NPs on porous carbon substrates exhibit electrocatalytic activity for the oxidation of methanol.60 In another example, gold NPs catalyze the electrochemical oxidation of nitric oxide on modified electrodes.61 In general, catalytic NPs provide two distinct functions enhancing an electrochemical reaction and/or increasing electron transfer to an electrode. 

In this respect, this review provides a comprehensive survey of synthetic methods and physicochemical properties of the porous carbon materials. Furthermore, as electrochemical applications of the porous carbons to electrode materials for supercapacitor, the effects of geometric heterogeneity and surface inhomogeneity on ion penetration into the pores during double-layer charging/ discharging are discussed in detail by using ac-impedance spectroscopy, current transient technique, and cyclic voltammetry. 

Because of their biocompatibility, chemical stability, high thermal and electrical conductivity, sorption ability, tuneable surfaces area, pore-size distribution and straightforward functionalization chemistry, porous carbons have found application in diverse topical areas such as sensors, fuel cells, hydrogen storage, and sorption.39 11 One particular property that distinguishes porous carbon from porous silica materials is the electrical conductivity of the former that has no counterpart in siliceous-based scaffoldings. This feature opens the route for certain applications... 

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