Formation of graphitic structures in cobalt- and nickel-doped carbon aerogels.
ABSTRACT We have prepared carbon aerogels (CAs) doped with cobalt or nickel through sol-gel polymerization of formaldehyde with the potassium salt of 2,4-dihydroxybenzoic acid, followed by ion exchange with M(NO3)2 (where M = Co2+ or Ni2+), supercritical drying with liquid CO2, and carbonization at temperatures between 400 and 1050 degrees C under a N2 atmosphere. The nanostructures of these metal-doped carbon aerogels were characterized by elemental analysis, nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Metallic nickel and cobalt nanoparticles are generated during the carbonization process at about 400 and 450 degrees C, respectively, forming nanoparticles that are approximately 4 nm in diameter. The sizes and size dispersion of the metal particles increase with increasing carbonization temperatures for both materials. The carbon frameworks of the Ni- and Co-doped aerogels carbonized below 600 degrees C mainly consist of interconnected carbon particles with a size of 15-30 nm. When the samples are pyrolyzed at 1050 degrees C, the growth of graphitic nanoribbons with different curvatures is observed in the Ni- and Co-doped carbon aerogel materials. The distance of graphite layers in the nanoribbons is approximately 0.38 nm. These metal-doped CAs retain the overall open cell structure of metal-free CAs, exhibiting high surface areas and pore diameters in the micro- and mesoporic region.
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ABSTRACT: CNTs were grown on iron-modified mesoporous graphitized carbon aerogel (GCA) at 700 °C, 800 °C and 900 °C using catalytic CVD method. Resultant CNT/GCA materials composition, morphology and structure were studied to understand their electrochemical stability and performance for oxygen reduction reaction (ORR) in acidic medium. CNT growth was increased from 700 °C to 800 °C, dominated by MWCNTs formation. In the temperature range from 800 °C to 900 °C, the growth was reduced by forming nanofiber/nanoribbon structures accompanied by MWCNTs. Mesoporosity of CNT/GCA composites declined at 700 °C and 800 °C due to MWCNT formation. However, CNT/GCA growth at 900 °C improved mesoporosity with substantial increase in pore volume (∼3 times of GCA) due to formation of nanofibers and nanoribbons. The structure of CNT/GCA materials revealed nitrogen doping and dispersion of FeNx phase. A synergistic contribution of CNT/GCA material structure and morphology to ORR activity was noticed. Among CNT/GCA materials, CNT-800 °C/GCA material showed ORR activity at lowest onset potential of 0.5 V. However, CNT-900 °C/GCA exhibits the highest ORR mass activity, with a half-wave onset potential difference of 120 mV with Pt (40 wt.%)/C. Moreover, CNT-900 °C/GCA demonstrates high selectivity (>3.97) to 4 electron ORR path, excellent methanol tolerance and electrochemical durability which makes it a potential DMFC cathode candidate.Carbon 09/2014; 79:518-528. DOI:10.1016/j.carbon.2014.08.010 · 6.16 Impact Factor
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ABSTRACT: An easy co-gelation route has been developed to synthesize porous graphitic carbons with high surface areas by using teraethylorthosilicate (TEOS), furfuryl alcohol (FA), and metal nitrates as precursors. Using a one-pot co-gelation process, a polyfurfuryl alcohol–silica interpenetrating framework with metal ions uniformly dispersed was formed during the polymerization of FA and the hydrolysis of TEOS within an ethanol solution of the three precursors. This synthesis process is simple and time-saving in comparison with the conventional preparation methods. During the heat treatment, Fe7Co3 alloy nanoparticles were produced by carbothermal reduction and they then catalyzed the graphitization of the amorphous carbon. The graphitic carbons obtained have a high crystallinity as shown by X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy analysis. The degree of graphitization can be controlled by the varying the loading amount of catalyst. The porous texture of the carbons combines miropores and bimodal mesopores, mainly originating from the silica template formed with different sizes and the loose packing of the graphite sheets. The carbons have large surface areas (up to 909 m2/g) and exhibit excellent electrochemical performance.Graphical abstractResearch highlights► An easy co-gelation route has been developed to synthesize porous graphitic carbons. ► This methods is simple and time-saving in comparison with the conventional ones. ► Fe7Co3 were produced by carbothermal reduction and then catalyzed the graphitization. ► The degree of graphitization can be controlled by varying the amount of catalyst. ► The carbons have large surface areas and exhibit excellent electrochemical performance.Carbon 01/2011; 49(1):161-169. DOI:10.1016/j.carbon.2010.08.056 · 6.16 Impact Factor