Porous carbon materials

Note that for metal nanoparticles supported on porous carbon materials, it is even more difficult to establish the mechanism of the ORR. Indeed, for the above-described thin layer or porous RRDE (Section 15.3), H2O2 has very little chance to escape from the CL and be detected at the ring. H2O2 can readsorb either on Pt particles or on the carbon support, and undergo chemical decomposition or further electrochemical reduction, while diffusing out of the CL. This implies great difficulties in establishing the detailed ORR mechanism on nanometer-sized metal nanoparticles. 

Jurewicz K., Vix C., Frackowiak E., Saadallach S., Reda M., Parmentier J., Patarin J., Beguin F. Capacitance properties of ordered porous carbon materials prepared by a templating procedure. J Phys Chem Solids (2004) in press. 

Figure 7 illustrates the dynamics of fluid migration through porous carbon electrodes to obey the Hagen-Poiseuille equation that is normally used to describe the transport through membranes having the pores of cylinder-like shape. Therefore, this method can probably be used for express analysis of the electrolyte dynamics in different porous carbon materials. 

This work was supported by the Science-and-Technology Center in Ukraine (project STCU 1830). Financial support was also provided within the framework of INTAS 00-761 research project. Porous carbon materials derived from various carbides in accordance with methods, which were developed by Skeleton Technologies, were received from Central Research Institute for Materials (St. Petersburg, Russia). 

Recent reports describe the use of various porous carbon materials for protein adsorption. For example, Hyeon and coworkers summarized the recent development of porous carbon materials in their review [163], where the successful use of mesoporous carbons as adsorbents for bulky pollutants, as electrodes for supercapacitors and fuel cells, and as hosts for protein immobilization are described. Gogotsi and coworkers synthesized novel mesoporous carbon materials using ternary MAX-phase carbides that can be optimized for efficient adsorption of large inflammatory proteins [164]. The synthesized carbons possess tunable pore size with a large volume of slit-shaped mesopores. They demonstrated that not only micropores (0.4—2 nm) but also mesopores (2-50 nm) can be tuned in a controlled way by extraction of metals from carbides, providing a mechanism for the optimization of adsorption systems for selective adsorption of a large variety of biomolecules. Furthermore, Vinu and coworkers have successfully developed the synthesis of... 

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. 

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. 

Whereas nanodiamond can be considered as an analog to solid nanoparticles, meso-porous carbon materials such as the CMK materials24 introduced in Chapter 2 are... 

Vix-Guterl, C., Frackowiak, E., Jurewicz, K., Friebe, M., Parmentier, J., and Beguin, F. Electrochemical energy storage in ordered porous carbon materials. Carbon 43, 2005 1293-1302. 

Leis, J., Arulepp, M., and Perkson, A. Method to modify the pore characteristics of porous carbon and porous carbon materials produced by this method. European Patent WO/2004/094307, 2004. 

Porous carbon materials mostly consist of carbon and exhibit appreciable apparent surface area and micropore volume (MPV) [1-3], They are solids with a wide variety of pore size distributions (PSDs), which can be prepared in different forms, such as powders, granules, pellets, fibers, cloths,... 

FIGURE 4.4 High-resolution N2 adsorption-desorption isotherms at 77 K (a) normal and (b) semilogarith-mic scale, for three porous carbon materials. Open symbols adsorption full symbols desorption. ACF1 ACF prepared from Nomex aramid fiber by physical activation with C02 [29] AC1 and AC2 activated carbons prepared from Spanish Anthracite by chemical activation with KOH [21]. 

FIGURE 4.5 C02 adsorption isotherms at 273 K for four porous carbon materials (a) subatmospheric and... 

This is very likely due to their very high reactivity, making deposition difficult and unwanted side reactions probable. Because the walls have uniform thickness (<1 nm), zeolites have been used as a template for the synthesis of ordered micro porous carbon materials [127-130] and they are tested for hydrogen physisorption [131]. 

A considerable number of different techniques has been employed in the past to characterize the porosity and surface chemistry of porous carbon materials. These include gas adsorption (mostly N2 and CO2) [9-14], immersion calorimetry [9], small-angle X-ray [11,15] and neutron [14] scattering, inverse gas chromatography [12,13], differential thermal analysis [12], Fourier transform infrared [12], Raman [16] and X-ray photoelectron [17] spectroscopies and electron spin resonance [16]. It is worth mentioning that the information about the porous structure of the material provided by this array of techniques is only indirect... 

As can be seen from Figure 2 the adsorption branch of this isotherm exhibits two distinct steps that reflect the capillary condensation inside smaller or larger mesopores at relative pressures about 0.79 and 0.9, respectively. The condensation in the relative pressure range of 0.9S-0.99S reflects condensation in secondary mesopores or small macropores, which resulted from the imprinting of agglomerates of colloidal particles. To our knowledge, this kind of isotherm has not been reported for porous carbon materials. The pore size distribution for this mesoporous carbon shown in Figure 3 exhibits two distinct peaks located about 11 nm and 24 nm, which correspond to the particle size of Bindzil 30/360 and Ludox AS-40 colloidal silicas, respectively. 

The use of Positron Annihilation Lifetime Spectroscopy (PALS) technique to characterize porous carbon materials has been analyzed. Positron annihilation lifetimes have been measured in two series of petroleum pitch-based activated carbon fibers (ACF) prepared by CO2 and steam activation. Two lifetime components were found a short-lived component, Ti from 375 to 393 ps and a long-lived component, 1 2 from 1247 to 1898 ps. The results have been compared to those obtained by Small Angle X-Ray Scattering (SAXS) and N2 and CO2 adsorption at 77K and 273K respectively The correlation found demonstrates the usefulness of PALS to get complementary information on the porous structure of microporous carbons. 

In the present work, positron annihilation lifetime spectroscopy has been applied to characterize the porosity of activated carbons fibers. These materials are essentially microporous [16], with slit shaped pores and with a homogeneous pore size distribution. Because of that, they seem to be the most appropriate materials to analyze the application of PALS technique to the characterization of porous carbon materials. 

A number of different methods exist for the production of catalyst layers [97-102]. They use variations in composition (contents of carbon, Pt, PFSI, PTFE), particle sizes and pds of highly porous carbon, material properties (e.g., the equivalent weight of the PFSI) as well as production techniques (sintering, hot pressing, application of the catalyst layer to the membrane or to the gas-diffusion layer, GDL) in order to improve the performance. The major goal of electrode development is the reduction of Pt and PFSI contents, which account for substantial contributions to the overall costs of a PEFC system. Remarkable progress in this direction has been achieved during the last decade [99, 100], At least on a laboratory scale, the reduction of the Pt content from 4.0 to 0.1 mg cm-2 has been successfully demonstrated. 

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