Synthesis of Cnt-Metal Oxide Nano-Composite Electrode Materials for Supercapacitator by Low-Pressure MOCVD
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SYNTHESIS OF CNT-METAL OXIDE NANO-COMPOSITE ELECTRODE MATERIALS FOR SUPERCAPACITATOR BY LOW-PRESSURE MOCVD Pallavi Arod1 and S.A. Shivashankar1,2 Materials Research Centre, 2Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560012, India 1
ABSTRACT Homogeneous composite thin films of Fe2O3-carbon nanotube were synthesized in a novel, single-step process by metalorganic chemical vapor deposition (MOCVD) using ferric acetyl acetonate as precursor. The deposition of composite takes place in a narrow range of CVD conditions, beyond which the deposition either multiwall carbon nanotubes (MWNTs) only or hematite (Į-Fe2O3) only takes place. The composite film formed on stainless steel substrates were tested for their supercapacitive properties in various aqueous electrolytes. INTRODUCTION Metal oxide-carbon nanotube (CNT) composites have attracted significant research attention in recent years owing to their potential applications in catalysis, chemical sensors, energy storage devices, magnetic data storage etc. [1-5]. Haematite , or Į-Fe2O3, a highly stable semiconducting, antiferromagnetic oxide has been investigated as photocatalyst, pigment, energy storage devices etc.[6,7]. Recently, Į-Fe2O3-MWNT composites have been investigated as electrode material for lithium ion batteries.[8] In general, most of the methods used to prepare metal oxide-CNT composite are multi-step processes, which involve the synthesis of the oxide by a chemical route followed by the addition of pre-synthesized carbon nanotubes, or the catalytic growth of CNTs on the oxide nanoparticles. Homogeneous mixing, interfacial adhesion, and size-control of the constituents are the main concerns in the synthesis of these composites by such multi-step methods. In the present effort, homogeneous composite thin films of Fe2O3 and carbon nanotubes have been synthesized in a novel, single-step process by metal-organic chemical vapor deposition (MOCVD), using ferric acetyl acetonate - Fe(acac)3 - as precursor. Such metal ȕdiketonate complexes contain direct metal-oxygen bonds, together with hydrocarbon or other organic moieties. The formation of carbonaceous metal oxide from such metalorganic complexes, through the simultaneous deposition of a metal oxide and elemental carbon, has been predicted theoretically through equilibrium thermodynamic analysis of the decomposition of precursor in the CVD chamber under different reaction conditions, and “CVD phase stability diagrams” have been constructed to represent the possibility.[9] The deposition of carbon in the form of multi-walled nanotubes in copious amounts is, however, a surprise. To date, Fe(acac)3 does not appear to have been employed as both catalyst and carbon source in the synthesis of carbon nanotubes. EXPERIMENT The deposition of iron oxide/carbon nanotube thin films was carried out in a hot-wall, low-pressure CVD reactor built in house [10], employing a fused quartz tube reactor chamber. High purity argon was used as the carrier gas, the gas flow rate being regulated by e
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