Hermann Kronberger

Molecular dynamics simulations of the adsorption of industrial relevant silane molecules at a zinc oxide surface

The physical behavior of different adsorbed silane molecules (octyltrihydroxysilane, aminopropyltrihydroxysilane, and thiolpropyltrihydroxysilane) at a ZnO surface (0001) dissolved in isopropanol are studied via constant temperature (298 K) molecular dynamics simulations. The adsorbed silane molecules exhibit a different behavior depending on the chemical nature of their tail. Octyltrihydroxysilane molecules with their rather unpolar tail show two distinct, energetic different orientations at the polar metal oxide surface. Mostly the three polar hydroxy groups of the head are in contact with ZnO the unpolar tail remaining in the isopropanol phase. Occasionally only two hydroxy groups interact with the surface the whole tail simultaneously being attached. On the contrary, due to their highly polar tail aminopropyltrihydroxysilane molecules have only one favorite orientation at the surface: Apart from some minor fluctuations two hydroxy groups as well as the amino group of the tail are in contact with the ...

Development of high performance cathodes for hydrogen production from alkaline solutions

Abstract Ni-based mixed catalysts were tested as hydrogen generating cathodes in alkaline solutions. Low activation energies and low overvoltage was found on binary Ni/TiH catalysts indicating high catalytic activity. The best results under technical operating conditions were obtained on activated plasma-sprayed Raney-alloy coatings and sintered ternary Ni/B/TiH, and are rather a consequence of optimized surface structure parameters and a possible change of mechanism of the H2-evolution reaction than of a further increase of catalytic activity.

Reduction of oxygen from electrolyte emulsions with high oxygen contents

The kinetics of oxygen reduction from electrolyte emulsions containing oxygen carriers was studied with respect to fuel cell applications. Electrochemical experiments including stationary and nonstationary measurements under defined hydrodynamic conditions at a rotating platinum disk electrode revealed that diffusion-controlled limiting currents can be increased significantly at high oxygen concentrations. Additionally, the limiting currents show a strong correlation with the composition and the structure of the emulsions. In particular, the average droplet size of the organic phase and its distribution depends on the nature of the emulsifying agents used for stabilisation. The complex hydrodynamic behaviour of two-phase electrolyte emulsions and the influence of different surfactants seem to outweigh the effect of the total oxygen concentration on the transport kinetics of oxygen.

Nanocrystalline hydrogen storage alloys for rechargeable batteries

Copyright (c) 1997 Elsevier Science S.A. All rights reserved.AB 5 -type intermetallic compounds were prepared by the melt spinning method. Structure analysis was carried out by X-ray diffractometry, SEM and high resolution electron microscopy. The hydrogen storage capacity was determined by isothermic mass controlled absorption of hydrogen and by electrochemical charge/discharge cycles. A variation of the preparation parameters showed that a nanocrystalline structure was achieved at high cooling rates. Nanocrystalline AB 5 -compounds show improved electrochemical properties.

Mapping the chemistry in nanostructured materials by energy-filtering transmission electron microscopy (EFTEM)

Energy-filtered transmission electron microscopy (EFTEM) can be used to acquire elemental distribution maps at high lateral resolution within short acquisition times, which makes it quite efficient for a detailed characterization of nanostructures, as illustrated with examples concerning a nanostructured substituted La-based cermet compound and a nanoscale multilayer. In the first example, we show how phases in a rapidly cooled substituted LaNi5 can be visualized by recording jump ratio images. Secondly, EFTEM was capable of imaging individual nanoscale layers in a magnetic multilayer consisting of 2 nm terbium and 3 nm iron.

Effect of PEG 400 on Zn–Cr Alloy Electrodeposition

The effect of poly(ethylene glycol) (PEG) with molecular mass 400 (PEG 400) on the hydrogen evolution reaction (HER) and on the Zn reaction in a Na 2 SO 4 solution and a Zn 2+ -containing electrolyte was investigated by electrochemical methods. The major effect of PEG 400 on the cathode process was in the range of HER from H 2 O and bulk deposition of Zn. In the electrolyte for Zn-Cr alloy deposition, the polarization effect of PEG 400 is not sufficiently strong in the potential range of Cr codeposition with Zn, as a result of which the average amount of Cr incorporated in the coatings is relatively low, up to 6 mass %. Based on X-ray photoelectron spectroscopy and X-ray diffraction analysis, it is assumed that Cr is present as metallic Cr in the coatings under the surface hydroxide oxides. Major constituents of the Zn-Cr coatings are two hexagonal phases: η-(Zn,Cr) and 8-Zn,Cr). Also considering experiments under the industrial conditions of high electrolyte flow and high current density, it is concluded that PEG 400 is not a suitable additive for the electrodeposition of Zn-Cr alloy coatings.

Electrochemistry of Titanium Tetrachloride in 1-Butyl-2,3-dimethyl Imidazolium Tetrafluoroborate

The electrochemistry of titanium tetrachloride has been examined in trialkyl-substituted imidazolium tetrafluoroborate at 65 °C. Ti(IV) reduction was studied with chronopotentiometry and cyclic voltammetry in melts with different concentrations of TiCl4. The diffusion coefficient of Ti(IV) ranged between 1.1·10−7 and 7·10−8 cm2 s−1. The electroreduction of Ti(IV) was found to proceed via the sequence of one-electron steps, the relative stability of the low valence intermediates being dependent on the concentration of TiCl4 in the electrolyte. The kinetics of an overlapping disproportionation reaction of Ti(II) was examined and its rate constant at low concentration (0.025 mol/l) of TiCl- was found to be k = 2 · 106 cm3 mol−1 s−1, Ti(0) being the final product of the stepwise reduction process at higher concentrations (0.03 - 0.14 mol/l).

Untersuchungen über die selektive Katalyse der Elektrodenreaktionen im Aasserstoff-Brom-Speichersystem

SummaryConsiderable rates are obtained for the hydrogen electrode reactions using WC-gas-diffusion electrodes which are not impaired by active Br2 in the solution. Tafel-lines withb-values of appr. 30 mV for both, anodic and cathodic current density potential curves, can be attributed to the Tafel-reaction as the rate controlling step. High reversibility (very low polarization) of the Br2/2 Br− redox couple is observed at activated carbon plastic composite material. The presence of H2 does not influence the electrode behavior. The use of both substrates in the H2/Br2 storage system provides definite advantages of the conceptual design and operation due to their electrocatalytic selectivity.

Effizienz von Fahrzeugen mit innovativem Brennstoffzellendesign

ZusammenfassungBrennstoffzellenfahrzeuge zählen zu den großen Hoffnungen für eine nachhaltige und emissionsfreie Mobilität. Die hohen Effizienzen des Energiewandlers Brennstoffzelle werden im Betrieb aber durch die Versorgung der Nebenaggregate, vor allem durch die Luftversorgung, gemindert. Durch den Entwurf eines neuen dreidimensionalen Brennstoffzellendesigns konnten jedoch die Strömungs- und Druckverluste in den Zellen drastisch verringert werden. Simulationen des Kraftstoffverbrauchs des Gesamtfahrzeugs zeigen Einsparungspotentiale durch den Einsatz der fortschrittlichen Zellenarchitektur auf allen simulierten Strecken. Zusätzliche Vorteile könnten durch diese Entwicklung in Zukunft auch bei der Kühlung der Zellen erreicht werden.SummaryFuel-cell vehicles represent a major chance for future sustainable zero-emission mobility. The high efficiencies of the energy converter fuel cell are lowered by the supportive system, especially by the air supply system during operation. By developing innovative three dimensional fuel cell architecture the pressure drops and losses in the cells could be mitigated dramatically. Simulation runs done for different real world cycles and test cycles revealed reduction potential in fuel consumption on all simulated routes. In future steps additional advantages in cooling system simplification can be expected, too.

Brennstoffzellen — Stand der Entwicklung

ZusammenfassungNeben den wichtigsten Grundlagen werden historischer Hintergrund und aktuelle Entwicklungstrends einzelner Brennstoffzellensysteme beschrieben. Einen Schwerpunkt bilden dabei die Niedertemperatur-Brennstoffzellen.AbstractThis review gives a general view on the state of the art of fuel cell development. Apart from some basic information on the electrochemical mechanisms, historical background and current technology trends of the most important fuel cell systems are described. A special focus is set on low temperature fuel cell systems.