Thiolated Graphene – a New Platform for anchoring CdSe Quantum Dots for hybrid heterostructures

Effective organization of small CdSe quantum dots on graphene sheets has been achieved by a simple solution exchange with thiol terminated graphene prepared by diazonium salt chemistry. This generic methodology of CdSe nanoparticles attachment to any graphene surface has remarkable implications in designing hybrid heterostructure

Electric field induced transformation of carbon nanotube to graphene nanoribbons using Nafion as a solid polymer electrolyte

We report a remarkable transformation of multiwalled carbon nanotubes (MWCNTs, average diameter 40 nm) to graphene nanoribbons (GNRs) in response to a field gradient of 25 V/cm, in a sandwich configuration using a solid state proton conducting polymer electrolyte like a thin perfluorosulphonated membrane, Nafion. In response to the application of a constant voltage for a sustained period of about 24 h at both room temperature and elevated temperatures, an interesting transformation of MWCNTs to GNRs has been observed with reasonable yield. GNRs prepared by this way are believed to be better for energy storage applications due to their enhanced surface area with more active smooth edge planes. Moreover, possible morphological changes in CNTs under electric field can impact on the performance and long term stability of devices that use CNTs in their electronic circuitr

Tunable optical features from self-organized rhodium nanostructures

Manipulating the surface to tune plasmonic emission is an exciting fundamental challenge and here we report on the development of unique morphology-dependant optical features of Rh nanostructures prepared by an equilibrium procedure. The emergence of surface plasmon peaks at 375 nm and 474 nm, respectively, is ascribed to truncated and smooth surface of nanospheres in contrast to the absence of surface plasmon for bulk Rh(0) in the visible range. Smaller sized, high surface area domains with well developed, faceted organization are responsible for the promising characteristics of these Rh nanospheres which might be especially useful for potential catalytic, field emission and magnetic applications

Counter-ion Dependent, Longitudinal Unzipping of Multi-Walled Carbon Nanotubes to Highly Conductive and Transparent Graphene Nanoribbons

Here we report for the first time, a simple hydrothermal approach for the bulk production of highly conductive and transparent graphene nanoribbons (GNRs) using several counter ions from K2SO4, KNO3, KOH and H2SO4 in aqueous media, where, selective intercalation followed by exfoliation gives highly conducting GNRs with over 80% yield. In these experiments, sulfate and nitrate ions act as a co-intercalant along with potassium ions resulting into exfoliation of multi-walled carbon nanotubes (MWCNTs) in an effective manner. The striking similarity of experimental results in KOH and H2SO4 that demonstrates partially damaged MWCNTs, implies that no individual K1, SO422 ion plays a key role in unwrapping of MWCNTs, rather this process is largely effective in the presence of both cations and anions working in a cooperative manner. The GNRs can be used for preparing conductive 16 kVsq21, transparent (82%) and flexible thin films using low cost fabrication metho

Bio-inspired catalyst compositions for enhanced oxygen reduction using nanostructured Pt electrocatalysts in polymer electrolyte fuel cells

Composites of Nafion with a class of bio-molecules viz., plant hormones, are explored as potential polymer electrolytes for improving the proton transport inside the catalyst layer of a H2/O2 fuel cell. Specifically, four nitrogenous plant hormones, two each from the class of auxins and cytokinins have been investigated, following preliminary characterization of the composite dispersions and membranes. Interestingly, the use of indole-3-acetic acid (an auxin) in the catalyst layer reveals a 30% enhancement in Pt catalyst utilization and improved fuel cell performance by 150 mW /cm2. The effect of these bio-molecules on the kinetic and mass transport parameters has been analyzed systematically using a combination of electrochemical and spectroscopic techniques

Enhanced electrocatalytic performance of interconnected Rh nano-chains towards formic acid oxidation

A chain-like assembly of rhodium nanoparticles (5–7 nm mean diameter) has been synthesized from rhodium chloride with the help of polydentate molecules like tartaric and ascorbic acids (1 : 3 in mM scale) as capping agents at room temperature. Subsequent characterization using transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy reveals a unique inter-connected network like features, while their electrochemical behavior using cyclic voltammetry and current–time transient suggests potential applications as electrocatalysts in fuel cells. A significant negative shift in the onset potential as well as higher anodic peak current density for formic acid oxidation on Rh- tartaric acid (Rh-TA) as compared to that of bulk Rh metal confirms their higher electrocatalytic activity. Interestingly, the enhancement factor (R) with respect to that of bulk metallic Rh towards formic acid oxidation ranges up to 2000% for Rh-TA and 1200% for Rh-AA (Rh-ascorbic acid) respectively. The composition of Rh nano-chains has been further analyzed with thermogravimetry and Fourier transform infra-red spectroscopy to demonstrate the importance of controlling the chain topology using polyfunctional organic molecules. These findings open up new possibilities for tailoring nanostructured electrodes with potential benefits since the development of a better electrocatalysts for many fuel cell reactions continues to be an important challenge

Hydrous RuO2–carbon nanofiber electrodes with high mass and electrode-specific capacitance for efficient energy storage

We demonstrate a new strategy for the fabrication of supercapacitor electrodes possessing high mass and area-specific capacitance for efficient charge storage, which can be extremely useful for the development of light, compact and high performance supercapacitors for a variety of high power demanding applications. High mass and electrode area specific capacitances were attained by using Hydrous Ruthenium Oxide (HRO)–Carbon Nanofiber (CNF) hybrid electrodes prepared by the deposition of HRO (~31% Ru content) on both the outer and inner surfaces of a cylindrical hollow CNF having open tips. Electrochemical studies of the uniformly deposited HRO nanoparticles on the CNF surface showed a mass specific capacitance of 645 F/g and an electrode specific capacitance of 1.29 F/(cm.cm) with a HRO–CNF material loading of 2 mg /(cm.cm) in the supercapacitor electrodes. The mass specific capacitance of pure HRO is 301 F/g, whereas the mass specific capacitance of HRO in the HRO–CNF electrode is ~1300 F/g1, which is very close to the theoretical capacitance of HRO. This enhanced charge storage ability, high rate capability, better cyclic stability and low ESR of the HRO–CNF will be useful for the development of high performance supercapacitors

Synthesis of Rh–carbon nanotube based heterostructures and their enhanced field emission characteristics

Selective decoration of Rh nanospheres on acid functionalized carbon nanotubes has been demonstrated using Al as a sacrificial substrate. Remarkable field emission has been observed for this heterostructure as a high current density of 170 muA / cm2 is generated at an ultra-low threshold of 300 V/ mu m, compared to much smaller values for Rh nanospheres and carbon nanotubes separately

High Pt Utilization Electrodes for Polymer Electrolyte Membrane Fuel Cells by Dispersing Pt Particles Formed by a Preprecipitation Method on carbon “Polished” with Polypyrrole

Pt utilization on carbon black (CB) has been significantly improved by initially utilizing polypyrrole (PPy) as a moiety to “polish” the carbon surface and subsequently by dispersing Pt particles formed by a preprecipitation process to minimize their migration into the geometrically restricted areas of the carbon surface. This process strategy has helped to significantly extend the triple-phase boundary as a greater number of Pt particles comes in direct contact with Nafion, leading to a substantial improvement in the overall catalyst utilization. Preliminary analyses such as IR, thermogravimetric analysis, and N2 sorption confirmed the presence of PPy on the surface. Approximately 50% reduction in the surface area of CB after the controlled in situ polymerization of pyrrole monomer on the carbon surface indicated preferential filling and coverage of pores and other geometrically restricted pockets of carbon surface. On the other hand, by converting Pt into colloids in the preprecipitation method prior to their reduction, the platinum particles are forced to stay on the hybrid support; a major part of which otherwise would have been migrated into the surface pores and defect sites. Platinum particle size on these hybrid supports is 2 times higher than the catalyst prepared by polyol process. However, the electroactive surface area and mass activity are 2 times higher than that of the Pt particles prepared by polyol on hybrid material and are also significantly higher than that of the conventional electrocatalysts prepared by the polyol method. At 0.8 V, the kinetic current density (jk) of Pt/C-PPy-Pre obtained from the Koutecky-Levich plot is 1.5 and 2.5 times higher than that of catalysts prepared by the polyol method on PPy-coated carbon and Vulcan XC-72 carbon, respectively. Almost 210 and 160 mW cm-2 improvement for the maximum power density, respectively with oxygen and air, was obtained with the modified system in comparison to the conventional system when the single cell evaluations were carried out at 60 °C with a Pt loading of 0.5 mg cm-2 in the anode and cathode sides. This enhancement in the cell performance under the two different oxygen partial pressure conditions clearly emphasizes the improved oxygen reduction reaction (ORR) and mass-transfer characteristics of the hybrid electrode material compared to the other catalysts

Hysteresis and charge trapping in graphene quantum dots

We report current hysteresis in response to applied voltage in graphene quantum dots of average diameter 4.5±0.55 nm, synthesized electrochemically using multiwalled carbon nanotubes. In response to step voltages, transient current decay characteristic of deep and shallow level charge traps with time constants 186 ms and 6 s is observed. Discharging current transients indicate charge storage of the order of 100 µC. Trap states are believed to arise due to the fast physisorption of external adsorbates,which are found to havea significant effect on charge transport and changes the resistance of the prepared device by an order of 3