Urszula Dettlaff-Weglikowska

Hydrogen storage in carbon nanostructures

Abstract The paper gives a critical review of the literature on hydrogen storage in carbon nanostructures. Furthermore, the hydrogen storage of graphite, graphite nanofibers (GNFs), and single-walled carbon nanotubes (SWNTs) was measured by thermal desorption spectroscopy (TDS). The samples were ball milled under Ar or D2 atmosphere in order to modify the microstructure which was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. These investigations show a reversible hydrogen storage only for SWNTs and in addition indicate that an opening of the SWNTs is essential to reach high storage capacities.

Interconnection of carbon nanotubes by chemical functionalization

Intermolecular carbon nanotube junctions were formed by coupling chemically functionalized nanotubes with molecular linkers. An end-to-side or end-to-end heterojunction can be formed by reacting chloride terminated nanotubes with aliphatic diamine. The chemically modified nanotube mats were characterized by Raman spectroscopy. The peak shift in the tangential vibration mode reveals that the attached chemical functional groups can behave as either an electron donor or an acceptor, and facilitate charge transfer with the nanotube host. The charge transfer is also verified by transport measurements on individual end-to-side intermolecular junctions, which show diode-like behavior. The charge transfer can be attributed to amide functionality at the junction.

Are carbon nanostructures an efficient hydrogen storage medium

Literature data on the storage capacities of hydrogen in carbon nanostructures show a scatter over several orders of magnitude which cannot be solely explained by the limited quantity or purity of these novel nanoscale materials. With this in mind, this article revisits important experiments. Thermal desorption spectroscopy as a quantitative tool to measure the hydrogen storage capacity needs an appropriate calibration using a suitable hydride. Single-walled carbon nanotubes that have been treated by ultra-sonication show hydrogen uptake at room temperature. However, this storage can be assigned to metal particles incorporated during the sonication treatment. Reactive high-energy ball milling of graphite leads to a high hydrogen loading, however the temperatures for hydrogen release are far too high for application. In view of today’s knowledge, which is mainly based on experiments with small quantities and poorly characterised samples, carbon nanostructures at around room temperature cannot store the amount of hydrogen required for automotive applications.

Chemical functionalization of single walled carbon nanotubes

Abstract Chemical modification has been performed on purified single walled carbon nanotubes. XPS spectrum shows that the peak corresponding to C (1s) centered at 284.38 eV in pure nanotubes (graphitic C) is 0.4 eV downshifted in chlorinated sample. Subsequent coupling reactions were carried out with diamine molecules to form intertube connections. Tripropylentetramine and phenylendiamine have been chosen as a molecular linker. End-to-side and end-to-end nanotube interconnections are formed and then observed by atomic force microscopy (AFM). Statistical analysis made from AFM images shows around 30% junctions in functionalized and less than 2% in pristine material. Remarkable features can be observed in the Raman spectra at different functionalization steps. Simple conductance measurements on bucky papers prepared from prestine nanotubes and from nanotubes modified at various steps have been made and are discussed.

Growth and characterization of high-density mats of single-walled carbon nanotubes for interconnects

We grow high-density, aligned single wall carbon nanotube mats for use as interconnects in integrated circuits by remote plasma chemical vapor deposition from a Fe–Al2O3 thin film catalyst. We carry out extensive Raman characterization of the resulting mats, and find that this catalyst system gives rise to a broad range of nanotube diameters, with no preferential selectivity of semiconducting tubes, but with at least 1∕3 of metallic tubes.

High levels of electrochemical doping of carbon nanotubes: evidence for a transition from double-layer charging to intercalation and functionalization.

We studied the transition from the electrochemical double-layer charging regime to intercalative doping of bundled single-walled carbon nanotubes (SWNT) in KCl and HCl aqueous solution. For this purpose we used high doping levels by applying constant potentials above 1000 mV approaching and slightly exceeding the oxidation potential for Cl(-) ions. At each potential in situ Raman measurements of the radial breathing mode (RBM), the high-energy tangential mode (HEM), and the disorder-induced (D) mode were performed. Furthermore, the conductivity and reflectivity of a set of SWNT samples were measured as a function of doping and subsequently the samples were examined by X-ray photoelectron spectroscopy (XPS). From a comparative analysis of the results we conclude that above 1000 mV a significant penetration of chlorine species into the interstitial channels of the SWNT bundles and possible covalent functionalization take place.

Kohn anomaly and electron-phonon interaction at the K-derived point of the brillouin zone of metallic nanotubes.

We applied Raman spectroscopy to investigate the response to electrochemical doping of the second-order D* band in single-walled carbon nanotube (SWNT) bundles. Our study reveals a dramatic increase of the D* band sensitivity to doping upon moving the laser excitation to the red end of the visible spectrum and beyond. Using the double-resonance scattering model, we show that this phenomenon evidences a second Kohn anomaly in metallic SWNTs, located in the K-point-derived region of the Brillouin zone (BZ), which stems from the Kohn anomaly at the K-point of graphene. Our results will be compared to recent doping experiments on graphene with field-effect gating and can be used to investigate the wave-vector dependent electron-phonon coupling in the bulk of the BZ of metallic SWNTs.

Efficient SWCNT-Based Anode for DMFC Applications

Carbon Vulcan XC72 is still considered as the standard catalyst support in gas diffusion electrodes for low temperature polymer fuel cell applications. Because of its relatively low specific area and poor corrosion resistance, alternative materials such as carbon nanotubes (CNTs) are currently the focus of numerous investigations. This work reports on the test of single-walled carbon nanotubes (SWCNTSs) as Pt and PtRu catalyst support in the direct methanol fuel cell (DMFC) anode. After the treatment of the CNTs in air at 300°C or in a high concentrated nitric acid solution, power densities of 152 and 157 mW cm -2 have been reached under DMFC conditions at 2 bar abs , and 80°C. The anodic and cathodic Pt loadings amounted to 1 mg cm -2 . The performance of the membrane electrode assembly (MEA) with a PtRu-SWCNT anode was about 10-15% higher than that of the MEA with a conventional as-prepared PtRu-Vulcan XC72 system. This was principally ascribed to higher catalyst utilization, lower impedance, and methanol crossover of the carbon-nanotube-based electrodes compared to those of the carbon-Vulcan-based one.

RNA-Wrapped Carbon Nanotubes Aggregation Induced by Polymer Hybridization

The aggregation of poly(rA)-wrapped single-walled carbon nanotubes (SWNTs) induced by hybridization of the adsorbed polymer with free poly(rU) has been studied by differential UV absorption spectroscopy, NIR luminescence, and AFM. After the addition of poly(rU) into a poly(rA):SWNTs suspension, the double-stranded poly(rA)·poly(rU) was formed, which is evident from the characteristic S-like form of the melting curve for the polymer created. Hybridization of free poly(rU) with two complementary poly(rA), one of which was adsorbed to different individual nanotubes, links them together and causes the appearance of aggregates. The aggregation of nanotubes is accompanied with light scattering and can be monitored in an AFM image after the deposition of the suspension on a mica substrate. Molecular dynamic simulation demonstrates a possible structure of the SWNTs aggregate.

Neutral penta-coordinate derivatives of bis(O-dioxophenylene) silicon—crystal structure of Si(O2C6H4)2(OPPh3) and Si(O2C6H4)2{OP(NC5H10)3} · CH2Cl2

The reaction of Si(OMe) 4 with catechol (1,2-(HO) 2 C 6 H 4 ) in toluene at 70°C yields a colourless compound, which we believe to be Si(O 2 C 6 H 4 ) 2 (MeOH) 2 ( 1 ). Compound 1 reacts with excess OPR 3 (R Ph, NC 5 H 10 ) in CH 2 Cl 2 yielding the penta-coordinate complexes Si(O 2 C 6 H 4 ) 2 (OPPh 3 ) ( 2) and Si(O 2 C 6 H 4 ) 2 {OP(NC 5 H 10 ) 3 } · CH 2 Cl 2 ( 3 ). Crystal structure investigations of 2 and 3 reveal a distorted trigonal bipyramidal environment for the silicon atom in 2 , while 3 shows a nearly square pyramidal coordination. In the mass spectrum, 1 , 2 and 3 exhibit ion peaks for monomeric Si(O 2 C 6 H 4 ) 2 and the donor ligand at temperatures above the melting points.