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.
SourceAvailable from: Mihkel Koel[Show abstract] [Hide abstract]
ABSTRACT: Carbon aerogels are nanostructured porous carbon materials, which can be produced from locally available phenolic compounds. A method for the preparation of metal-doped carbon aerogels from oil shale processing by-products 5-methylresorcinol and 2,6-dihydroxy-4-methyl-benzoic acid was developed. Aerogels doped with Ni, Co and Cu were characterized by atomic absorption spectroscopy, nitrogen adsorption, transmission electron microscopy and X-ray diffraction. The resulting materials exhibited pore diameters in microporous and mesoporous regions, high surface areas and pore volumes. The metal content in aerogels was found to be dependent on the amount of ion-exchange moiety and metal content as high as 14.5 wt% was achieved in carbon aerogels, where also metal nanoparticles had formed.Oil Shale 01/2014; 31(2-4):185-194. DOI:10.3176/oil.2014.2.08 · 0.84 Impact Factor
[Show abstract] [Hide abstract]
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
[Show abstract] [Hide abstract]
ABSTRACT: Resorcinol–formaldehyde (RF) hydrogel and RF–nickel–palladium (RF–Ni–Pd) hydrogel were synthesized by sol–gel polycondensation followed by ambient drying. Carbon gel and carbon–nickel–palladium doped gels were prepared by carbonizing the RF and RF–Ni–Pd gels at 900 °C under a nitrogen atmosphere. The goal of this study was to determine the effect of oxidative thermal treatment on the electrochemical activity of nickel–palladium doped carbon gels (C–Ni–Pd). The scanning electron microscopy analysis, adsorption and X-ray diffraction measurements showed that the admixture of Ni and Pd to carbon matrix resulted in the modification of morphological, porous and crystalline features. It has been demonstrated that composite C–Ni–Pd composed of sphere-like granules incrusted with well-crystalline nickel and palladium particles exhibits electrochemical activity in 6 M KOH aqueous solution. Thermal treatment of the composite carried out in air at 450 °C brought about the improvement of electrochemical activity in the potential range of the hydrogen sorption/desorption reaction.Journal of Sol-Gel Science and Technology 07/2014; 71(1):109-117. DOI:10.1007/s10971-014-3338-0 · 1.55 Impact Factor