Sundara Ramaprabhu

Platinum/carbon nanotubes (Pt/CNT) electrocatalysts are prepared. The CNTs are pre-treated in order to obtain reactive sites for the adherence of Pt metal particles. The electrocatalysts are characterized by scanning electron micrograph (SEM), transmission electron micrograph (TEM) and X-ray photoelectron spectrum (XPS) measurements. It is found that the catalysts contain both Pt(0) and Pt(IV) species. A high Pt loading of 32.5% on CNTs is obtained when the catalysts are prepared with ethylene glycol and Pt salt. The electrocatalysts are used for the oxygen reduction reaction in polymer electrolyte membrane fuel cells (PEMFCs) and the performance of PEMFC is analyzed with respect to catalyst synthesis and Pt loading. Cyclic voltammetric studies show that the Pt utilization in the fuel-cell electrodes is around 44%. Catalysts obtained with mild nitric acid-treated CNTs give a better performance of 680 mV at 500 mA cm-2 and 600 mV at 800 mA cm-2 than catalysts prepared with ethylene glycol and Pt salt. © 2004 Elsevier B.V. All rights reserved.

Functionalized graphene sheets have been investigated as catalyst supports for platinum electrocatalysts for use in PEMFC electrodes. Well-dispersed Pt nanoparticles with small particle size were impregnated on graphene sheets. The electrochemical tests showed that the Pt nanoparticles supported on graphene shows good electrochemical activity and much higher Electrochemical Surface Area (ECSA) of 24 m 2/g. The maximum current density was found to be 700 mA/cm 2 for electrodes having Pt/G catalysts on both electrodes, compared to electrodes where Pt/C is being used at the anode. This study reveals that Pt/G can be a good electro catalyst not only for oxygen reduction but also for hydrogen oxidation. The dispersion of the electrocatalyst on graphene has been found to be useful for achieving relatively better performance in fuel cells. Electrochemical experiments show that the Pt supported on graphene oxide have superior catalytic performance indicating that the graphene may have a splendid future as catalyst carrier in electrocatalyst and fuel cell. © 2012 American Scientific Publishers All rights reserved.

Pt-loaded multiwalled carbon nanotubes (Pt/MWCNTs) have been prepared by chemical reduction method using functionalized MWCNT synthesized by pyrolysis of acetylene over MmNi2 (Mm denotes misch metal) hydride catalyst. Composites of Pt/MWCNT and commercial Pt-loaded carbon black (Pt/C) have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC). Cathode catalyst with 50% Pt/MWCNT and 50% Pt/C showed best performance due to better dispersion and good accessibility of MWCNT support and Pt electrocatalysts for oxygen reduction reaction in PEMFC. A maximum performance of 540 mV at a current density of around 535 mA cm -2 has been obtained. © 2006 American Institute of Physics.

Graphene nanoplatelets have been synthesized by thermal exfoliation of graphitic oxide and nitrogen doped graphene nanoplatelets have been obtained by nitrogen plasma treatment. Graphene nanoplatelets and nitrogen doped graphene nanoplatelets have been used as a catalyst support for platinum nanoparticles for oxygen reduction reactions in proton exchange membrane fuel cells. Platinum nanoparticles were dispersed over these support materials using the conventional chemical reduction technique. The morphology and structure of the graphene based powder samples were studied using X-ray diffraction, Raman spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. A full cell was constructed with platinum loaded nitrogen doped graphene nanoplatelets and the results have been compared with platinum loaded graphene nanoplatelets. A maximum power density of 440 and 390 mW cm-2 has been obtained with platinum loaded nitrogen doped graphene and platinum loaded graphene nanoplatelets as ORR catalysts respectively. Nitrogen plasma treatment created pyrrolic nitrogen defects, which act as good anchoring sites for the deposition of platinum nanoparticles. The improved performance of fuel cells with N-G as catalyst supports can be attributed to the increased electrical conductivity and improved carbon-catalyst binding. © 2010 The Royal Society of Chemistry.

Multi-walled carbon nanotubes (MWNTs) have been synthesized by the pyrolysis of acetylene using hydrogen decrepitated Mischmetal (Mm) based AB3 alloy hydride catalyst. MWNTs have been characterized by SEM, TEM, Raman and XRD studies. Pt-supported MWNTs (Pt/MWNTs) have been prepared by chemical reduction method using functionalized MWNTs. Composites of Pt/MWNTs and Pt/C have been used as electrocatalysts for oxygen reduction reaction in Proton Exchange Membrane Fuel Cell (PEMFC). Cathode catalyst with 50 % Pt/MWNTs and 50 % Pt/C gives the best performance because of the better dispersion and good accessibility of MWNTs support and the Pt electrocatalysts in the mixture for the oxygen reduction reaction in PEMFC. The paper emphasizes that Pt/C and Pt/MWNTs composites have good potential as catalyst support material in PEMFC.

Multi-walled carbon nanotubes (MWNTs) have been synthesized by hemical vapour deposition technique using AB3 alloy hydride catalyst and platinum supported MWNT (Pt/MWNT) and platinum-ruthenium supported MWNT (Pt-Ru/MWNT) electrocatalysts have been prepared by chemical reduction method. MWNT 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 (EDX). The anode and cathode electrodes of direct methanol fuel cells (DMFC) have been fabricated using Pt-Ru/MWNT and 1:1 Pt / MWNT + Pt / C electrocatalyst, respectively. Performances of DMFC with these electrodes have been studied at different temperatures and the results have been discussed. A maximum power density of 39.3 mW / cm2 at a current density of 130 mA / cm2 has been obtained, which could be attributed to dispersion and accessibility of MWNT support and Pt-Ru in the electrocatalyst mixture for methanol oxidation reaction. © 2008 International Association for Hydrogen Energy.

The AB2 type Laves phase hydrogen absorbing alloys are being investigated as suitable electrode materials for Ni-MH batteries, because of their higher electrochemical capacity. The electrochemical properties like electrode potential, reversible electrochemical capacity and diffusion coefficient as a function of state of charge in the YxZr1-x MnmFenCopVoCr q(m+n+o+p+q=2) electrodes were investigated in an alkaline solution. The reversible electrochemical capacity of the electrode was found to be in excess of 450 mAh/g and hydrogen concentration was estimated as 3.5 hydrogens/formula unit. The process that occur in the electrode during charge and discharge, has been studied by Cyclic Voltammogram(CV) experiments, carried out at different sweep rates. It was found that at low sweep rates, the hydrogen concentration on the surface increases due to longer polarisation and the hydrogen concentration approaches a value which favours a metal hydride formation. The diffusion coefficients were also evaluated with respect to state of charge. The results will be presented in the paper.

Catalytic synthesis of multi-walled carbon nanotubes (MWNTs) by the pyrolysis of acetylene over mischmetal (Mm) based MmNi2 and MmFe 2 hydride catalysts is reported. The hydrogen decrepitation technique has been used to prepare the catalyst particles of these Mm based hydrogen storage alloys. Large hydrogen decrepitation and low cost make these hydrides potential catalysts for large-scale production of CNTs. The samples were purified by air oxidation and acid treatment and were characterized by XRD, SEM, TEM, HRTEM, Raman spectroscopy and XPS. The yield of MWNTs was estimated to be ∼60% and the purity of MWNTs thus obtained was more than 90%, as characterized by TGA. In addition, hydrogen adsorption measurements were carried out for as-prepared and purified MWNTs at 125 and 298 K using a high pressure hydrogen adsorption set-up. A maximum hydrogen storage capacity of 3.2 wt% at 60 bar is obtained at 125 K for purified CNTs prepared with MmFe2 hydride catalysts. © 2005 IOP Publishing Ltd.

We report a novel way of synthesizing graphene-carbon nanotube hybrid nanostructure as an anode for lithium (Li) ion batteries. For this, graphene was prepared by the solar exfoliation of graphite oxide, while multiwalled carbon nanotubes (MWNTs) were prepared by the chemical vapor deposition method. The graphene-MWNT hybrid nanostructure was synthesized by first modifying graphene surface using a cationic polyelectrolyte and MWNT surface with acid functionalization. The hybrid structure was obtained by homogeneous mixing of chemically modified graphene and MWNT constituents. This hybrid nanostructure exhibits higher specific capacity and cyclic stability. The strengthened electrostatic interaction between the positively charged surface of graphene sheets and the negatively charged surface of MWNTs prevents the restacking of graphene sheets that provides a highly accessible area and short diffusion path length for Li-ions. The higher electrical conductivity of MWNTs promotes an easier movement of the electrons within the electrode. The present synthesis scheme recommends a new pathway for large-scale production of novel hybrid carbon nanomaterials for energy storage applications and underlines the importance of preparation routes followed for synthesizing nanomaterials. © 2012 The Royal Society of Chemistry.

Multiwalled carbon nanotubes (MWNTs) have been synthesized by the pyrolysis of acetylene using hydrogen decrepitated Mischmetal based AB3 alloy hydride catalyst. Structural, morphological, and vibrational characterizations have been carried out using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) spectroscopy. Pt-supported MWNTs (Pt/MWNTs) have been prepared by chemical reduction method using functionalized MWNTs. Composites of Pt/MWNTs and Pt/C in different weight proportions have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC) and the performance on the accessibility of Pt electrocatalysts for the oxygen reduction reaction in PEMFC has been systematically studied. The cyclic voltammetric studies of the electrodes have been performed in order to understand the factors influencing the elecetrocatalytic activity and fuel cell performance and the results have been discussed. Copyright © 2010 by ASME.