P. Murugan

Carbon-supported Pd–Co as cathode catalyst for APEMFCs and validation by DFT

Carbon supported PdCo catalysts in varying atomic ratios of Pd to Co, namely 1 : 1, 2 : 1 and 3 : 1, were prepared. The oxygen reduction reaction (ORR) was studied on commercial carbon-supported Pd and carbon-supported PdCo nanocatalysts in aqueous 0.1 M KOH solution with and without methanol. The structure, dispersion, electrochemical characterization and surface area of PdCo/C were determined by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Cyclic Voltammetry (CV), respectively. The electrochemical activity for ORR was evaluated from Linear Sweep Voltammograms (LSV) obtained using a rotating ring disk electrode. The catalysts were evaluated for their electrocatalytic activity towards oxygen reduction reaction (ORR) in Alkaline Polymer Electrolyte Membrane Fuel Cells (APEMFCs). PdCo(3 : 1)/C gives higher performance (85 mW cm(-2)) than PdCo(1 : 1)/C, PdCo(2 : 1)/C and Pd/C. The maximum electrocatalytic activity for ORR in the presence of methanol was observed for PdCo(3 : 1)/C. First principles calculations within the framework of density functional theory were performed to understand the origin of its catalytic activity based on the energy of adsorption of an O(2) molecule on the cluster, structural variation and charge transfer mechanism.

Au–Pt graded nano-alloy formation and its manifestation in small organics oxidation reaction

A graded nano-alloy of Au100−xPtx (x = 7, 15, 23, 32, 40, 51, 62, 73 and 86) nanoparticles (NPs) formed by co-reduction of HAuCl4 and H2PtCl6 and the details are presented in this work. Au100−xPtx NPs were characterized using surface plasmon resonance (SPR) absorption spectroscopy and transmission electron microscopy (TEM). The NPs were dispersed in Vulcan carbon (Au100−xPtx/C) and annealed at 250, 400, 600 and 800 °C. The as-formed and annealed materials were characterized using TEM, high resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (XRD), cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The CV studies indicate excess Pt on the surface, which is corroborated by XPS and HR-TEM results. The XRD data show that Vegards law is obeyed by the as-formed material and the materials annealed at 250 and 400 °C, indicating that these materials are not nano-alloys. The studies clearly indicate that the formation of Au100−xPtx NPs is kinetically controlled rather than being controlled by the thermodynamic stability. The results demonstrate the formation of graded alloys of Au100−xPtx NPs. Pt excess in the graded nano-alloy is reflected favourably in the electrochemical oxidation of small organics. In the methanol oxidation reaction (MOR), the peak current value per mg of Pt increases as a function of x, reaches a maximum value at x = 23 and the ratio of forward current to reverse current for MOR reached an unprecedented value of 6.7, which shows the catalyst’s stability against poisoning by carbonaceous intermediates.

Nanoscale functionalization of surfaces by graft-through Sonogashira polymerization

Graft through Sonogashira polymerization was used to functionalize various surfaces with conjugate polymers in a dimension of less than 100 nm. Atomic force microscopy measurement revealed a dense surface coverage with several closely packed islands. UV-vis spectroscopy and cyclic voltammetry measurements suggested a moderate band gap, which is important for various applications in material science. A device was fabricated using polymer functionalized ITO and deposited aluminium as cathode to determine the current–voltage (I–V) characteristics and charge carrier mobility. Space charge limited current method indicated moderate charge carrier mobility while I–V characteristic data indicated a behaviour as semiconducting material.

Lithiated assemblies of metal chalcogenide nanowires

We study hexagonal assemblies of M6X6 (M=Mo and W and X=S, Se, and Te) nanowires from first-principles calculations to understand their structural stability, electronic properties, and the effects of Li intercalation. It is shown that due to van der Waals interactions between the nanowires, the intercalation is achieved without a significant change in their atomic structure. With an increase in Li concentration, we predict a new phase for Li3Mo6S6 compound, in which the hexagonal assembly transforms to a monoclinic structure by a change in the orientation of nanowires. The LixMo6S6 assemblies are electrically conductive and can be potentially used as cathode materials in Li-ion batteries for nanoscale applications. The voltage of such a battery, calculated to be 1.7V, can be manipulated such as by iodine doping without a significant change in the atomic structure.

Structural and magnetic stabilities of cubic and orthorhombic phases of CeMnNi4

First-principles density functional calculations have been carried out on cubic and orthorhombic phases of CeMnNi4, in order to understand their structural and magnetic stabilities. The calculations show the orthorhombic phase to be energetically favorable as compared to the cubic phase reported experimentally by Singh et al. [Appl. Phys. Lett. 88, 022506 (2005)]. Ferromagnetic state turns out to be more stable for both cubic and orthorhombic phases, the latter having lower total magnetic moment. The moment is mainly localized on Mn atoms, and their alignment is mediated via the indirect exchange interaction. Half-metallic nature as proposed experimentally is elusive for the pure compound which shows metallic behavior.Using first-principles density functional calculations, we study the possible phases of CeMnNi

Initial Stage of the Adsorption of Fluorofullerene Molecules on Si Surface

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Calculations of spin-induced transport in ferromagnets

and show that the ground state is ferromagnetic. We observed the hexagonal phase to be lowest in energy whereas experimentally observed cubic phase lies slightly higher in energy. We optimized the structure in both phases and in all different magnetic states to explore the possibility of the structural and magnetic phase transitions at ground state. We do not find any phase transitions between the magnetic and non-magnetic phases. The calculated structural, magnetic properties of cubic phase are in excellent agreement with experiments. Further, we do not observe half metallic behavior in any of the phases. However, the cubic phase does have fewer density of states for down-spin component giving a possibility of forming half metallic phase artificially, introducing vacancies, and disorder in lattice.

Electronic and magnetic properties of double-impurities-doped TiO2 (rutile): First-principles calculations

Spatially resolved images of an individual C60F18 fluorofullerene molecule on Si(100) − 2 × 1 surface have been obtained using scanning tunneling microscopy. Scanning tunneling microscopy results and ab initio calculations show that the fluorofullerene molecules interact with the Si(100) − 2 × 1 surface with F atoms pointing down towards the surface. The adsorption energy of a C60F18 molecule on Si(100) − 2 × 1 surface is ∼12.1 eV, which is much higher than the adsorption energy of the same molecule on Si(111) − 7 × 7 surface (6.65 eV). C60F18 molecules are located in the troughs in-between the dimer rows occupying the four-dimer site on Si(100) − 2 × 1 surface.

TiO2 (rutile) doped with double impurities for fabricating spintronic devices—a combinatorial computational approach

Based on first-principles density functional calculations, a general approach for determining and analyzing the degree of spin polarization

AB INITIO STUDY OF MAGNETISM IN PALLADIUM CLUSTERS SUPPORTED ON (110) SURFACE OF TiO2 RUTILE

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