G Girishkumar

University of Notre Dame, Indiana, PA, United States

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Publications (7)30.17 Total impact

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    ABSTRACT: Comparison of the structure and activity of Pt nanoparticles anchored on two nanostructured carbon supports, C <sub>60</sub> and carbon nanotubes (CNTs) provides insight into their electrocatalytic activity in direct methanol fuel cells. The local structure of platinum atoms during the initial stages of the catalytic oxidation of methanol was probed using x-ray absorption spectroscopy. A large fraction of the Pt atoms in the Pt – C <sub>60</sub> nanocomposite continuously undergoes structural changes during the initial stages of methanol oxidation. The Pt-CNT system, however, proves to be more robust in maintaining its initial morphology and higher electrocatalytic activity. These observations reflect the importance of the carbon support in controlling the catalyst morphology and activity during methanol oxidation.
    Applied Physics Letters 03/2006; · 3.52 Impact Factor
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    ABSTRACT: Significant enhancement in the electrocatalytic activity of Pt particles toward oxygen reduction reaction (ORR) has been achieved by depositing them on a single wall carbon nanotubes (SWCNT) support. Compared to a commercial Pt/carbon black catalyst, Pt/SWCNT films cast on a rotating disk electrode exhibit a lower onset potential and a higher electron-transfer rate constant for oxygen reduction. Improved stability of the SWCNT support is also confirmed from the minimal change in the oxygen reduction current during repeated cycling over a period of 36 h. These studies open up ways to utilize SWCNT/Pt electrocatalyst as a cathode in the proton-exchange-membrane-based hydrogen and methanol fuel cells.
    Langmuir 03/2006; 22(5):2392-6. · 4.38 Impact Factor
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    ABSTRACT: Single-wall and multiwall carbon nanotubes are employed as carbon supports in direct methanol fuel cells (DMFC). The morphology and electrochemical activity of single-wall and multiwall carbon nanotubes obtained from different sources have been examined to probe the influence of carbon support on the overall performance of DMFC. The improved activity of the Pt-Ru catalyst dispersed on carbon nanotubes toward methanol oxidation is reflected as a shift in the onset potential and a lower charge transfer resistance at the electrode/electrolyte interface. The evaluation of carbon supports in a passive air breathing DMFC indicates that the observed power density depends on the nature and source of carbon nanostructures. The intrinsic property of the nanotubes, dispersion of the electrocatalyst and the electrochemically active surface area collectively influence the performance of the membrane electrode assembly (MEA). As compared to the commercial carbon black support, single wall carbon nanotubes when employed as the support for anchoring the electrocatalyst particles in the anode and cathode sides of MEA exhibited a approximately 30% enhancement in the power density of a single stack DMFC operating at 70 degrees C.
    The Journal of Physical Chemistry B 02/2006; 110(1):107-14. · 3.61 Impact Factor
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    ABSTRACT: A membrane electrode assembly (MEA) for hydrogen fuel cells has been fabricated using single-walled carbon nanotubes (SWCNTs) support and platinum catalyst. Films of SWCNTs and commercial platinum (Pt) black were sequentially cast on a carbon fiber electrode (CFE) using a simple electrophoretic deposition procedure. Scanning electron microscopy and Raman spectroscopy showed that the nanotubes and the platinum retained their nanostructure morphology on the carbon fiber surface. Electrochemical impedance spectroscopy (EIS) revealed that the carbon nanotube-based electrodes exhibited an order of magnitude lower charge-transfer reaction resistance (R(ct)) for the hydrogen evolution reaction (HER) than did the commercial carbon black (CB)-based electrodes. The proton exchange membrane (PEM) assembly fabricated using the CFE/SWCNT/Pt electrodes was evaluated using a fuel cell testing unit operating with H(2) and O(2) as input fuels at 25 and 60 degrees C. The maximum power density obtained using CFE/SWCNT/Pt electrodes as both the anode and the cathode was approximately 20% better than that using the CFE/CB/Pt electrodes.
    Langmuir 09/2005; 21(18):8487-94. · 4.38 Impact Factor
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    ABSTRACT: A hybrid carbon fiber electrode (CFE) consisting of TiO2 semiconductor photocatalyst and Pt-Ru catalyst has been developed to boost the performance of direct methanol fuel cells (DMFC). These two catalyst nanoparticles are deposited on opposite sides of the carbon fiber paper such that methanol oxidation is carried out catalytically on Pt-Ru and photocatalytically on TiO2 under UV-light irradiation. Since both catalysts carry out methanol oxidation independently, we observe an additive effect in the current generation. The carbon support fibers provide a large network to collect the electrons from both of these catalytic processes and thus assist in efficient current generation. In addition, TiO2 improves the performance of the Pt-Ru catalyst in dark, indicating possible surface area improvement or diminished poisoning effects. The concept of incorporating a photocatalyst provides new ways to minimize precious metal content and enhance the performance of DMFCs. At low catalyst loadings (0.15 mg/cm2) at 295 K, a 25% enhancement in the peak power density is observed upon illumination with light.
    The Journal of Physical Chemistry B 07/2005; 109(24):11851-7. · 3.61 Impact Factor
  • G. Girishkumar, K. Vinodgopal, Prashant V. Kamat
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    ABSTRACT: We show here, for the first time, a reproducible way to obtain films of varying amounts of single-walled carbon nanotubes (SWCNTs) on electrode surfaces using electrophoretic deposition. We deposit these nanotubes in a facile manner on an optically transparent electrode (OTE) and investigate its performance as an electrode material in the presence of platinum for methanol oxidation and oxygen reduction. Our focus here is on the deposition of the SWCNT on the electrodes, the characterization of the nanotubes on the electrode surface, and the cyclic voltammetry of methanol oxidation and oxygen reduction using these nanostructured carbon electrodes with platinum electrodeposited on them. The nanotubes retain their structure on the electrode surface, and we can obtain electrodes with relatively thick films of the CNTs. The high surface area and porosity of these films enable us to use relatively small amounts of platinum and yet obtain excellent currents. We see a remarkable enhancement in methanol oxidation current relative to unsupported platinum. Analysis of the electrode kinetics using Tafel plots suggests that the CNT support provides a strong electrocatalytic effect in both reactions arising from their unique electrical properties.
    Journal of Physical Chemistry B - J PHYS CHEM B. 12/2004; 108(52).
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    ABSTRACT: A one-step process of solubilization of single wall carbon nanotubes (SWCNT) in an organic solvent has enabled us to polarize them asymmetrically in a dc electric field. Quaternary ammonium ion-capped SWCNTs readily suspend in organic solvents; under the influence of a dc electric field, they assemble as stretched bundles anchored on the positive electrode. At low dc applied field (approximately 40 V), all of the SWCNTs from the suspension are deposited on the electrode, thus providing a simple methodology to design robust SWCNT films. At higher applied voltages (>100 V), the SWCNT bundles stretch out into the solution and orient themselves perpendicular to the electrode surface. The alignment of these bundles is responsive to the ON-OFF cycles of the applied electric field. The possibility of modulating the alignment of SWCNT in an electric field opens new ways to achieve electrical contacts in nano- to micro-devices.
    Journal of the American Chemical Society 09/2004; 126(34):10757-62. · 10.68 Impact Factor