Highly porous carbon

Kierzek K., Frackowiak E., Lota G., Gryglewicz G., Machnikowski J. Electrochemical capacitors based on highly porous carbons prepared by KOH activation Electrochim Acta 2004 49 515-23. 

The activation with KOH of selected parent materials under appropriate process conditions (temperature, time, reagent ratio) can provide highly porous carbons of controlled pore size distribution and surface chemistry, also suitable for use as electrode materials in supercapacitors. 

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. 

Laszlo K, Czakkel O, Dobos G, Lodewyckx P, Rochas C, Geissler E (2010) Water vapour adsorption in highly porous carbons as seen by small and wide angle X-ray scattering. Carbon 48 1038-1048... 

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. 

Highly porous carbons can serve as electrodes in -> super (EDL = electric double layer) capacitors. Their very wide electrochemical window allows their use in nonaqueous (relative) high energy-high power density super (EDL) capacitors. 

There is no precise definition of an active carbon , but it is generally understood to be a carbonaceous material of appreciable specific surface area. If it is to be an effective adsorbent, an active carbon must have a surface area of at least 5 m2 g1. Active carbons used as industrial adsorbents have much larger BET-areas, which may extend well above 2000 m2 g1. In accordance with this broad definition, an active carbon may be porous or non-porous. The term activated carbon has a more specific connotation, however, since it is reserved for a highly porous carbon produced from a carbon-rich material by some form of chemical or physical activation. 

It was not long before the first activated carbon fibres (ACFs) were developed. In the work of Economy and Lin (1971, 1976) highly porous carbon fibres were prepared from Kynol, a fibrous phenolic precursor. Carbonization was carried out in nitrogen at 800°C and activation occurred in steam at 750-1000°C. The products appeared to be predominantly microporous and were found to be effective for the removal of low levels of certain pollutants (e.g. phenol and pesticides) from air or aqueous solutions. 

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. 

Shiraishi, S. Kurihara, H. Tsubota, H. Oya, A. Soneda, Y. Yamada, Y. Electric double layer capacitance of highly porous carbon derived from lithium metal and PTFE. Electrochem. Solid-State Lett. 2001, 4, A5-A8. 

Highly porous carbons can be produced from a variety of natural and synthetic precursors [11, 12]. Relatively inexpensive activated carbons are useful adsorbents, but generally their surface and pore structures are exceedingly complex [11, 13]. However, it is now possible to prepare a number of more uniform carbonaceous adsorbents. For example, molecular sieve carbons (MSCs) are available with narrow distributions of ultramicropores, which exhibit well-defined molecular selectivity [11], and carbon nanotubes, aerogels, and membranes are also amongst the most interesting advanced materials for research and development [12, 14]. 

Wasa et al. (1984a) developed a chemically modified enzyme electrode for ascorbic acid. The enzyme was attached to impregnated highly porous carbon together with BSA by glutaraldehyde. In intensively stirred solution the response time of the sensor was only 3 s. The sensitivity dropped to 80% within 3 months. 

Physisorption and Chemisorption The phenomena of adsorption on solid surfaces are much more varied than those on liquid surfaces. A good example for observing these phenomena is activated carbon, a highly porous carbon with a large specific surface (300 to 2,000 m g carbon) and possessing excellent adsorption capacity (Experiment 15.6). 

On one side of the membrane is pressed the Gas Diffusion Layer (GDL) which is normally made of highly porous carbon paper or carbon cloth. The GDL has many functions, the more important ones are to uniformly distribute the gasses and to adsorb the product water. The GDL is porous and has good electrons conductibility. The membrane or the GDL are coated with a catalyst to support the RED-OX... 

Ye S, Vijh AK, Dao LH (1996) A new fuel cell electrocatalyst based on highly porous carbonized polyacrylonitrile foam with very low platinum loading. J Electrochem Soc 143 (1) L7-L9... 

Amount of iodine adsorbed from aqueous solution as a measure for the specific surface area not applicable for oxidized or highly porous carbon blacks... 

Modern gas-diffusion medium in low-temperature fuel cells is typically a highly porous carbon paper with porosity in the range of sgdl = 0.6-0.8 and with the mean pore radius in the order of 10 pm (10 cm). By the order of magnitude, the mean free path of molecules in atmospheric pressure air is = l/(A LO-fci ), where Nl = 2.686 10 cm is the Loschmidt number (number of molecules in a cubic centimetre of atmospheric pressure gas at standard temperature) and akin — 10 cm is the molecular cross-section for kinetic collisions. With this data we get 3 10 cm, or 3 10 pm. Obviously, mean pore radius in the GDL is nearly 3 orders of magnitude greater than I f and the physical mechanism of molecule transport is binary molecular diffusion. 

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