Carbon aerogels preparation

In other Pt-doped monolithic carbon aerogels, prepared by adding the Pt pre-cnrsor to the initial R/F mixture [41], the Pt particle size determined by H2 chemisorption was mnch higher than that determined by high-resolution transmission electron microscopy (HRTEM). This indicates that some Pt particles were encapsnlated by the carbon matrix and were consequently inaccessible to H2. This can be the main problem of this preparation method when the metal-doped carbon gel is to be used as catalyst, because part of the metal will not be accessible to the reactant molecules. 

Fung, A W P, Reynolds G A M, WangZ, Dresselhaus M, Dresselhaus G, Pekala R (1995) Relationship between particle size and magnetoiesistance in carbon aerogels prepared under different catalyst conditions. J Non-Cryst Solids 186 200-208. 

Fairen-Jimenez D, Carrasco-Marin F, Mraeno-Castilla C (2006) Porosity and surface area of monolithic carbon aerogels prepared using alkaline carbonates and organic acids as polymerization catalysts. Carbtm 44 ... 

Table 36.1. Types and characteristics of carbon aerogels prepared with different organic sources...

Carbonaceous resins, in hazardous waste management, 25 813 Carbon adsorbents, preparation, 1 586 Carbon adsorption, in hazardous waste management, 25 811-813 Carbon adsorption system, 26 681 Carbon adsorption units, 25 812 Carbon aerogels applications, 1 767 preparation, 1 752... 

M. Mirzaeian and P.J. Hall, Preparation of controlled porosity carbon aerogels for energy storage in rechargeable lithium oxygen batteries, Electrochim. Acta, 54(28) 7444-7451, December 2009. 

Carbon aerogels can be prepared from the organic gels mentioned above by supercritical drying with carbon dioxide and a subsequent heat-treating step in an inert atmosphere. 

A large variety of metal-containing carbon gels have already been prepared and characterized, including Na-, K-, Mg-, Zr-, Cr-, Mo-, W-, Mn-, Fe-, Ru-, Co-, Ni-, Pd-, Pt-, Cu-, Ag- Ce-, and Eu-containing carbon aerogels and xero-gels. The objective of these studies was to characterize these materials for then-use as supported catalysts, electrodes for electrical double-layer capacitors, and adsorbents in aqueous solutions. 

Using the same method, Cotet and co-workers [54] prepared high-content Ee-, Co-, Ni-, Cu-, and Pd-doped carbon aerogels. The metal content of these samples was around 20 wt%, except in the case of the Pd-containing sample, where it was as high as 46 wt%. Mean crystallite size ranged from 12 to 40 nm and the surface areas from 370 to 450 m /g. The presence of some graphitic nanoribbons was detected in some of the prepared samples, as reported previously by other authors [42,51,55]. 

Erkey and co-workers [59-61] prepared Pt- and Ru-doped carbon aerogels using a supercritical deposition method. This involved dissolution of an organometallic precursor in a supercritical fluid and the exposure of a solid substrate to this solution. After impregnation of the support with the metal precursor, it was converted to the metal form by different methods. Dimethyl(l,5-cyclooctadiene) platinum(ll) was used as a precursor for Pt [59,60], and two different Ru complexes, trisacetylacetonate Ru(lll) and Ru(cod)(tmhd)2, were used for Ru [61], Monolithic organic and carbon aerogels... 

Pt-doped carbon aerogels have been used successfully in the preparation of cathode catalyst layers for oxygen reduction reaction (ORR) in PEMFC systems [83-86]. Thus, different Pt-doped carbon aerogels with a Pt content of around 20 wt% were prepared by impregnation [83]. Results obtained with these Pt catalysts were compared with others supported on carbon blacks Vulcan XC-72 and BP2000, which are commonly used as electrocatalysts. The accessibility of the electrolyte to Pt surface atoms was lower than expected for high-surface-area... 

The effect of carbon aerogel pore texture and method of preparation of the supported Pt catalysts on their activity has recently been reported [85]. Two different Pt precursors were used H2[PtCl6] and [Pt(NH3)4](OH)2. For a given Pt precursor, the pore texture of carbon aerogels used had no influence in Pt surface area and ORR activity. The best ORR specific activity was obtained with catalysts prepared with H2[PtCl6]. By contrast, the activity of catalysts prepared from [Pt(NH3)4](OH)2 was low, despite the fact that the Pt dispersion value reached was the highest. These authors [85] indicate that this is probably due to the particle size effect on ORR activity, with a smaller Pt particle size showing a lower activity. 

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