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Jafri R.I.,Nano Functional Materials Technology Center | Rajalakshmi N.,Indian Institute of Technology Madras | Ramaprabhu S.,Nano Functional Materials Technology Center
Journal of Power Sources | Year: 2010

Multi-walled carbon nanocoils (MWNCs) are synthesized by chemical vapour deposition and nitrogen-doped MWNCs (N-MWNCs) are obtained by nitrogen plasma treatment. MWNCs and N-MWNCs are used as catalyst supports for platinum nanoparticles. Pt nanoparticles are dispersed over these support materials using the conventional chemical reduction technique and then used for the oxygen reduction reaction in proton-exchange membrane fuel cells. The morphology and structure of the MWNC-based powder samples are studied by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Full cells are constructed with Pt-loaded MWNC/N-MWNC and the results are discussed. A maximum power density of 550 and 490 mW cm -2 is obtained with Pt/N-MWNC and Pt/MWNC as the ORR catalyst, respectively. The improved performance of a fuel cell with a N-MWNC catalyst support can be attributed to the creation of pyrrolic nitrogen defects due to the nitrogen plasma treatment. These defects act as good anchoring sites for the deposition of Pt nanoparticles and to the increased electrical conductivity and improved carbon-catalyst binding. © 2010 Elsevier B.V. All rights reserved.


Jafri R.I.,Nano Functional Materials Technology Center | Ramaprabhu S.,Nano Functional Materials Technology Center
International Journal of Hydrogen Energy | Year: 2010

Multi walled carbon nanotubes (MWNTs) have been synthesized by chemical vapour deposition technique using AB3 alloy hydride catalyst. Platinum supported MWNTs (Pt/MWNTs) and platinum-tin supported MWNTs (Pt-Sn/MWNTs) electrocatalysts have been prepared by chemical reduction method. MWNTs and electrocatalysts have been characterized by powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), high resolution TEM (HRTEM) and Energy dispersive X-ray analysis (EDAX). The anode and cathode electrodes for DEFC have been fabricated using Pt-Sn/MWNTs and 1:1 Pt/MWNTs + Pt/C electrocatalyst respectively. Performances of Direct Ethanol Fuel Cell (DEFC) with these electrodes have been studied at different temperatures of the membrane electrode assembly at ambient fuel conditions and the results have been discussed. A maximum power density of 38.6 mW/cm2 at a current density of 130 mA/cm2 is obtained. A six cell planar Micro Direct Ethanol Fuel Cell (μ-DEFC) stack was also constructed using these electrocatalysts and etched printed circuit boards as anode and cathode current collectors. A maximum power density of 2 mW/cm2 was achieved when the μ-DEFC was operated in air breathing mode at room temperature. This enhancement of the performance may be attributed to dispersion and accessibility of MWNTs support and Pt-Sn in the electrocatalyst mixture for ethanol oxidation reaction. © 2009 Professor T. Nejat Veziroglu.


Kaniyoor A.,Nano Functional Materials Technology Center | Baby T.T.,Nano Functional Materials Technology Center | Ramaprabhu S.,Nano Functional Materials Technology Center
Journal of Materials Chemistry | Year: 2010

A novel and facile technique for the rapid synthesis of few layered graphene sheets via hydrogen induced reduction-exfoliation of graphite oxide at a low temperature of ∼200 °C is reported. © 2010 The Royal Society of Chemistry.


Jha N.,Nano Functional Materials Technology Center | Jafri R.I.,Nano Functional Materials Technology Center | Rajalakshmi N.,Center for Fuel Cell Technology of India | Ramaprabhu S.,Nano Functional Materials Technology Center
International Journal of Hydrogen Energy | Year: 2011

Nanostructured PtRu and Pt dispersed functionalized graphene-functionalized multi walled carbon nanotubes (PtRu/(f-G-f-MWNT)), (Pt/(f-G-f-MWNT)) nanocomposites have been prepared. Electrochemical studies have been performed for the methanol oxidation using cyclic voltammetry (CV) and chronoamperometry technique. Full cell measurements have been performed using PtRu nanoparticles dispersed on the mixture of functionalized graphene (f-G) and functionalized multi walled carbon nanotubes (f-MWNT) in different ratios as anode electrocatalyst for methanol oxidation and Pt/f-MWNT as cathode catalyst for oxygen reduction reaction in direct methanol fuel cell (DMFC). In addition, full cell measurements have been performed with PtRu/(50 wt% f-MWNT + 50 wt% f-G) and Pt/(50 wt% f-MWNT + 50 wt% f-G) as anode and cathode electrocatalyst respectively. With PtRu/(50 wt% f-MWNT + 50 wt% f-G) as anode electrocatalyst, a high power density of about 40 mW/cm2 has been obtained, in accordance with cyclic voltammetry studies. Further enhancement in the power density of about 68 mW/cm2 has been observed with PtRu/(50 wt% f-MWNT + 50 wt% f-G) and Pt/(50 wt% f-MWNT + 50 wt% f-G) as electrocatalyst at anode and cathode respectively. These results have been discussed based on the change in the morphology of the f-G sheets due to the addition of f-MWNT. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Mishra A.K.,Nano Functional Materials Technology Center | Ramaprabhu S.,Nano Functional Materials Technology Center
Journal of Materials Chemistry | Year: 2012

The current scientific community is extensively involved in developing novel materials for energy and environmental applications. Capture of CO 2 to remove it from the atmosphere is one of the most important applications among them. In the present work, we have demonstrated for the first time, to the best of our knowledge, a polyaniline-graphene nanocomposite as a CO 2 capture candidate. Graphene was prepared by hydrogen induced thermal exfoliation of graphite oxide and was further coated with polyaniline using a chemical method. The nanocomposite was characterized by different techniques and the capture capacity was measured using a high pressure Sievert's apparatus. FTIR spectroscopy was used to confirm the possible CO 2 capture mechanism in the nanocomposite. CO 2 adsorption capacities at a pressure of 11 bar and different temperatures of 25, 50 and 100°C were experimentally found to be 75, 47 and 31 mmol g -1, respectively. This nanocomposite shows much higher CO 2 capture capacity compared to pure graphene and shows a high degree of recyclability. © 2012 The Royal Society of Chemistry.


Kaniyoor A.,Nano Functional Materials Technology Center | Ramaprabhu S.,Nano Functional Materials Technology Center
Journal of Materials Chemistry | Year: 2012

Anchoring functional moieties on the surface of graphene is an important step in the processing of graphene for numerous applications. In this article, the effects of two different functionalization methods on graphene viz. the conventional method involving ultrasonication in acids and a novel polyelectrolyte based method are systematically investigated. While the conventional acid treatment method makes graphene highly hydrophilic, it also causes severe damage to the graphene sheets and leads to disordered restacking. In contrast, the soft functionalization method based on polyelectrolytes preserves the morphology to a significant extent. Moreover, the presence of charges on the surface of polyelectrolyte modified graphene causes mutual repulsion between the sheets, thereby assisting in the fabrication of optically transparent films. The presence of charges also affects the electrochemical behaviour towards tri-iodide reduction, which is investigated via electrochemical impedance spectroscopy. New equivalent circuits are proposed to interpret the observed response. © The Royal Society of Chemistry 2012.


Vinayan B.P.,Nano Functional Materials Technology Center | Nagar R.,Nano Functional Materials Technology Center | Rajalakshmi N.,International Advanced Research Center for Powder Metallurgy And New Materials | Ramaprabhu S.,Nano Functional Materials Technology Center
Advanced Functional Materials | Year: 2012

A novel synthesis procedure is devised to obtain nitrogen-doping in hydrogen-exfoliated graphene (HEG) sheets. An anionic polyelectrolyte-conducting polymer duo is used to form a uniform coating of the polymer over graphene sheets. Pyrolysis of graphene coated with polypyrrole, a nitrogen-containing polymer, in an inert environment leads to the incorporation of nitrogen atoms in the graphene network with simultaneous removal of the polymer. These nitrogen-doped graphene (N-HEG) sheets are used as catalyst support for dispersing platinum and platinum-cobalt alloy nanoparticles synthesized by the modified-polyol reduction method, yielding a uniform dispersion of the catalyst nanoparticles. Compared to commercial Pt/C electrocatalyst, Pt-Co/N-HEG cathode electrocatalyst exhibits four times higher power density in proton exchange membrane fuel cells, which is attributed to the excellent dispersion of Pt-Co alloy nanoparticles on the N-HEG support, the alloying effect of Pt-Co, and the high electrocatalytic activity of the N-HEG support. A stability study shows that Pt/N-HEG and Pt-Co/N-HEG cathode electrocatalysts are highly stable in acidic media. The study shows two promising electrocatalysts for proton exchange membrane fuel cells, which on the basis of performance and stability present the possibility of replacing contemporary electrocatalysts. A novel method for the synthesis of Pt-Co alloy nanoparticles dispersed on nitrogen-doped graphene is developed. The as-prepared electrocatalysts show excellent oxygen reduction reaction (ORR) activity and stability in acidic medium for proton exchange membrane fuel cell (PEMFC) applications due to the high dispersion and alloying effect of Pt-Co, along with the inherent electrocatalytic activity of nitrogen-doped graphene as the supporting material. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Jaidev,Nano Functional Materials Technology Center | Jafri R.I.,Nano Functional Materials Technology Center | Mishra A.K.,Nano Functional Materials Technology Center | Ramaprabhu S.,Nano Functional Materials Technology Center
Journal of Materials Chemistry | Year: 2011

Herein, we report a preparation method of a novel binary hybrid nanocomposite based on polyaniline (PANI) and α-MnO 2 nanotubes (MNTs) by in situ polymerization. The polymerization is carried out in acidic medium using α-MnO 2 nanotubes as oxidant. A symmetrical supercapacitor is fabricated and the electrochemical performance of the supercapacitor is investigated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) techniques using 1.0 M H 2SO 4 as electrolyte. The nanocomposite shows maximum specific capacitance of 626 F g -1 and corresponding energy density of 17.8 W h kg -1, as calculated from the charge-discharge curve at a specific current density of 2 A g -1 in the potential range 0-0.7 V. © 2011 The Royal Society of Chemistry.


Baby T.T.,Nano Functional Materials Technology Center | Ramaprabhu S.,Nano Functional Materials Technology Center
Journal of Materials Chemistry | Year: 2011

In the present work we describe a novel synthesis procedure for silver decorated functionalized hydrogen induced exfoliated graphene (Ag/HEG) and preparation of nanofluids using this material. Further, thermal conductivity and convective heat transfer studies are carried out for these nanofluids. A simple chemical reduction method is implemented to synthesize uniformly coated Ag/HEG and characterized by different experimental techniques. Ag/HEG is used for making nanofluids considering the high thermal conductivity of graphene and silver nanoparticles. Ag/HEG has been dispersed in deionized water and ethylene glycol using ultrasonic agitation and proper dispersion is achieved without any surfactant. Thermal conductivity and heat transfer studies on Ag/HEG dispersed nanofluids show an enhancement in the corresponding values compared to the base fluid. The level of enhancement depends on the volume fraction and temperature at which the measurement is performed. Ag/HEG dispersed deionized water based nanofluid shows an enhancement of ∼25% for 0.05% volume fraction at 25°C. Similarly, the heat transfer coefficient of Ag/HEG based nanofluids also shows a large enhancement compared to the base fluid. The synthesized nanofluid is stable for more than three months. © 2011 The Royal Society of Chemistry.


Baby T.T.,Nano Functional Materials Technology Center | Ramaprabhu S.,Nano Functional Materials Technology Center
Talanta | Year: 2010

A new type of amperometric glucose biosensor based on silicon dioxide coated magnetic nanoparticle decorated multiwalled carbon nanotubes (Fe3O4@SiO2/MWNTs) on a glassy carbon electrode (GCE) has been developed. MWNTs have been synthesized by catalytic chemical vapour decomposition (CCVD) of acetylene over rare earth (RE) based AB3 alloy hydride catalyst. The as-grown MWNTs have been purified and further functionlized. Functionalized MWNTs have been decorated with magnetic Fe3O4 nanoparticles which have been uniformly coated with biocompatible SiO2 using a simple chemical reduction method. The characterization of magnetic nanoparticle modified MWNTs have been done by X-ray diffraction (XRD), Fourier transform infra red spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM), energy dispersive X-ray analysis (EDX) and UV-vis spectroscopy. Amperometric biosensor has been fabricated by the deposition of glucose oxidase (GOD) over Nafion-solubilized Fe3O4@SiO2/MWNTs electrode. The resultant bioelectrode retains its biocatalytic activity and offers fast and sensitive glucose quantification. The performance of the biosensor has been studied using cyclic voltammetry and amperometry and the results have been discussed. The fabricated glucose biosensor exhibits a linear response from 1 μM to 30 mM with an excellent detection limit of 800 nM indicating the potential applications in food industries. © 2009 Elsevier B.V. All rights reserved.

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