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Progress in Solid Acid Fuel Cell Electrodes
Issue: Volume 2, Issue 6-1, December 2014
Pages: 61-65
Received: 15 November 2014
Accepted: 23 December 2014
Published: 23 December 2014
DOI:
10.11648/j.nano.s.2014020601.18
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Abstract: Solid acid fuel cells represent a relatively new technology with the advantage of an intermediate operating temperature of 240°C and a solid state proton conducting electrolyte (CsH2PO4). Widespread commercial application has been hindered mainly by low performance and costly electrodes containing a high Pt loading. Here we review the recent progress and current status of solid acid fuel cell electrodes. Major efforts include creating nanostructured composites leading to much reduced Pt loadings while maintaining or even increasing performance. Furthermore, fundamental studies on Pt thin films, as geometrically controlled electrodes, have recently revealed the possibility of an electrochemical pathway through the two-phase boundary in addition to the classic three-phase boundary. Carbon nanotubes as electronic interconnects have been shown to dramatically improve Pt catalyst utilization and hence electrode performance. Major efforts are spent to search for alternative, non-precious metal catalysts.
Abstract: Solid acid fuel cells represent a relatively new technology with the advantage of an intermediate operating temperature of 240°C and a solid state proton conducting electrolyte (CsH2PO4). Widespread commercial application has been hindered mainly by low performance and costly electrodes containing a high Pt loading. Here we review the recent progre...
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Investigations on the Hydrothermal Synthesis of Pure and Mg-Doped Nano-CuCrO2
Issue: Volume 2, Issue 6-1, December 2014
Pages: 53-60
Received: 16 November 2014
Accepted: 19 November 2014
Published: 23 December 2014
DOI:
10.11648/j.nano.s.2014020601.17
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Abstract: This paper presents some investigations on the hydrothermal synthesis of nano-CuCrO2. Several successively altered synthesis protocols are used to investigate effects of changing the mineralizer amount, lowering reaction temperature and addition of a reducing agent. As a result modified protocols for the hydrothermal synthesis of pure and Mg-doped CuCrO2 are presented. Different washing and annealing steps are used to perform a comparative XRD-study on these materials.
Abstract: This paper presents some investigations on the hydrothermal synthesis of nano-CuCrO2. Several successively altered synthesis protocols are used to investigate effects of changing the mineralizer amount, lowering reaction temperature and addition of a reducing agent. As a result modified protocols for the hydrothermal synthesis of pure and Mg-doped ...
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Optical Switching of Azophenol Derivatives in Solution and in Polymer Thin Films: The Role of Chemical Substitution and Environment
Yasser M. Riyad
,
Sergej Naumov
,
Jan Griebel
,
Christian Elsner
,
Ralf Hermann
,
Katrin R. Siefermann
,
Bernd Abel
Issue: Volume 2, Issue 6-1, December 2014
Pages: 39-52
Received: 16 November 2014
Accepted: 19 November 2014
Published: 23 December 2014
DOI:
10.11648/j.nano.s.2014020601.16
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Abstract: Design of polymer materials whose properties can be reversibly changed by illumination with light is a technology of particular scientific interest. Such materials contain molecular chromophors, which change their geometry and/or polarity upon absorption of light of a specific wavelength. The most prominent chromophores are azobenzene derivatives. Here, we present a systematic study on azobenzene derivatives in order to quantify the impact of chemical substitution and chemical environment on the dynamics of light-induced trans-cis isomerization (at 368 nm and 355 nm), thermal cis-trans relaxation, and light-induced cis-trans isomerization (at 434 nm). Systems under investigation were 4-hydroxyazobenzene (4-HAB) in acetonitrile (MeCN) solution and in a poly(methylmethacrylate) (PMMA) matrix. These two systems are compared to systems in which 4-HAB is esterified, namely 4-hydroxyazobenzene covalently bound (esterified) to PMMA matrix, and N-(tert-butoxycarbonyl)glycine-4- hydroxyazobenzene (Boc-Gly-4-HAB) in MeCN and in PMMA. Photoisomerization and thermal relaxation kinetics are monitored with UV-vis absorption spectroscopy and accompanied by quantum chemical calculations to shed light into the molecular origin of observed differences in switching properties. We find that the chemical environment (MeCN vs. PMMA) only has minor impacts (~10%) on trans to cis photoisomerization rates. Also, the impact of chemical environment on thermal cis to trans relaxation is small; with relaxation rates in PMMA beeing < 35% smaller compared to rates in MeCN solution. However, the thermal cis to trans relaxation rates of 4-HAB are clearly faster (factor > 400) than the rates of esterified systems. This difference is a clear result of the different substituents on the azobenzene moiety. Quantum chemical calculations suggest that the cis-configuration in the esterified systems is stabilized by an intramolecular H-bond between a carbonyl oxygen on the substituent and an H atom on the phenyl ring. In all systems, the cis to trans isomerization can be significantly accelerated by illumination with 434 nm light. For esterified systems, accelerations by factors of about 5700 – 15500 are observed. In the case of 4-hydroxyazobenzene covalently bound (esterified) to the PMMA matrix, complete light induced transfer from cis to trans is possible. In addition, it features a low thermal cis to trans isomerization rate and acceptable photoinduced trans to cis isomerization properties. With this, the material fulfills the basic requirements of a functional polymer material whose properties can be reversibly changed by illumination with light.
Abstract: Design of polymer materials whose properties can be reversibly changed by illumination with light is a technology of particular scientific interest. Such materials contain molecular chromophors, which change their geometry and/or polarity upon absorption of light of a specific wavelength. The most prominent chromophores are azobenzene derivatives. ...
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A Flexible Research Reactor for Atomic Layer Deposition with a Sample-Transport Chamber for in Vacuo Analytics
Axel Sobottka
,
Lutz Drößler
,
C. Hossbach
,
Bernd Abel
,
Ulrike Helmstedt
Issue: Volume 2, Issue 6-1, December 2014
Pages: 34-38
Received: 16 November 2014
Accepted: 19 November 2014
Published: 23 December 2014
DOI:
10.11648/j.nano.s.2014020601.15
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Abstract: A modular reactor for thermal atomic layer deposition (ALD) was designed, which allows changes of all reactor components in order to obtain a flexible set-up for research purpose. A sample transport chamber is included for dual purpose. It allows for in vacuo transport of samples to analytical devices such as an XPS instrument. Surface activation of the samples is possible in the same chamber via an irradiation-induced approach.
Abstract: A modular reactor for thermal atomic layer deposition (ALD) was designed, which allows changes of all reactor components in order to obtain a flexible set-up for research purpose. A sample transport chamber is included for dual purpose. It allows for in vacuo transport of samples to analytical devices such as an XPS instrument. Surface activation o...
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High Resolution Imaging of a Multi-Walled Carbon Nanotube with Energy-Filtered Photoemission Electron Microscopy
Andreas Neff
,
Olga Naumov
,
Timna-Josua Kühn
,
Nils Weber
,
Michael Merkel
,
Bernd Abel
,
Aron Varga
,
Katrin R. Siefermann
Issue: Volume 2, Issue 6-1, December 2014
Pages: 27-33
Received: 15 November 2014
Accepted: 19 November 2014
Published: 23 December 2014
DOI:
10.11648/j.nano.s.2014020601.14
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Abstract: Photoemission electron microscopy (PEEM) is a powerful and well established tool in surface science. In recent years, PEEM has been increasingly applied to new terrain, such as imaging of complex nano-objects and functional molecular materials, as well as time-resolved experiments. When applying PEEM to such new terrain, information on the mechanisms causing contrast in the PEEM image is particularly valuable. Here, we present a PEEM study on a complex nano-object – an individual multi-walled carbon nanotube (CNT) – to shed light on the origin of PEEM contrast. The presented PEEM images of the nanotube are of unsurpassed resolution and feature intensity variations along the nanotube. Complementary scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements on the same nanotube reveal topography as the dominant cause for the contrast observed along the nanotube. Energy-filtered PEEM measurements demonstrate that the contrast between nanotube and substrate mainly originates from their different electronic structures. The measurements further demonstrate that energy-filtered PEEM has the potential to image electronic structure variations of complex nano-objects and materials on nanometer length scales.
Abstract: Photoemission electron microscopy (PEEM) is a powerful and well established tool in surface science. In recent years, PEEM has been increasingly applied to new terrain, such as imaging of complex nano-objects and functional molecular materials, as well as time-resolved experiments. When applying PEEM to such new terrain, information on the mechanis...
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Comparison of Four Ionic Liquid Force Fields to an Ab Initio Molecular Dynamics Simulation
Stefan Zahn
,
Richard Cybik
Issue: Volume 2, Issue 6-1, December 2014
Pages: 19-26
Received: 10 November 2014
Accepted: 25 November 2014
Published: 23 December 2014
DOI:
10.11648/j.nano.s.2014020601.13
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Abstract: The reliability of four force fields developed for 1-alkyl-3-methylimidazolium bis¬(tri¬fluoro¬methylsulfonyl)imide ionic liquids are compared to an ab inito molecular dynamics simulation regarding structural properties. Except the hydrogen bond structure between the most acidic hydrogen atom of the imidazolium ring and the nitrogen atom of the anion as well as the intramolecular potential surface of the anion in solution, structural properties are reproduced very well by all investigated force fields. Most recommended can be the force field developed by Canongia Lopes and Pádua because it reproduces best the hydrogen bond structure between the most acidic hydrogen atom of the imidazolium ring and the nitrogen atom of the anion.
Abstract: The reliability of four force fields developed for 1-alkyl-3-methylimidazolium bis¬(tri¬fluoro¬methylsulfonyl)imide ionic liquids are compared to an ab inito molecular dynamics simulation regarding structural properties. Except the hydrogen bond structure between the most acidic hydrogen atom of the imidazolium ring and the nitrogen atom of the ani...
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Efficient Route to High-Quality Graphene Materials: Kinetically Controlled Electron Beam Induced Reduction of Graphene Oxide in Aqueous Dispersion
Roman Flyunt
,
Wolfgang Knolle
,
Axel Kahnt
,
Siegfried Eigler
,
Andriy Lotnyk
,
Tilmann Häupl
,
Andrea Prager
,
Dirk Guldi
,
Bernd Abel
Issue: Volume 2, Issue 6-1, December 2014
Pages: 9-18
Received: 2 November 2014
Accepted: 4 November 2014
Published: 23 December 2014
DOI:
10.11648/j.nano.s.2014020601.12
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Abstract: This work is presenting a highly efficient, cost-efficient and environmentally friendly method for the production of graphene materials (reduced graphene oxide, RedGO) via electron beam (EB) irradiation of aqueous dispersions of graphene oxide (GO). Our strategy here is based on a reduction of GO via EB irradiation under optimally controlled conditions, i.e. dose and dose rate, reducing species, and taking the environmental impact of educt and product into account. The preparation of highly conductive RedGO under these conditions takes only 10-20 minutes at ambient temperature. After our first approach [1], a somewhat similar study was reported by Jung et al. [2] for GO dispersions in H2O/EtOH (50:50). However, the latter route [2], although being similar in spirit, has serious drawbacks for large-scale production because of the formation of acetaldehyde, a very toxic compound, derived from the ethanol in the solvent. The advantages of the present approach compared to [2] are: (i) the use of water as a solvent with only a small content (0.03 - 2 wt.-%) of 2-PrOH allows the scaling-up, since neither 2-PrOH nor its final product acetone are of high technological or environmental concerns; (ii) a much lower dose is required for GO reduction (about 20 vs. 200 kGy, corresponding to only 1/10 of energy consumed); (iii) the conductivity of RedGO is over 60 times higher. Based on the XPS and conductivity measurements, it was established that the EB treatment is leading also to a more efficient reduction of GO compared to the hydrazine method. The highest conductivity in our systems is identical to the best known value of 3 x 104 S/m for RedGO obtained via HI / acetic acid treatment which takes, however, 40 h at 40 ºC.
Abstract: This work is presenting a highly efficient, cost-efficient and environmentally friendly method for the production of graphene materials (reduced graphene oxide, RedGO) via electron beam (EB) irradiation of aqueous dispersions of graphene oxide (GO). Our strategy here is based on a reduction of GO via EB irradiation under optimally controlled condit...
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Tailored Nano- and Micrometer Sized Structures of Gold-Nanoparticles at Polymeric Surfaces Via Photochemical and Kinetic Control of the Synthesis and Deposition Process
Christian Elsner
,
Andrea Prager
,
Ulrich Decker
,
Sergej Naumov
,
Bernd Abel
Issue: Volume 2, Issue 6-1, December 2014
Pages: 1-8
Received: 2 November 2014
Accepted: 4 November 2014
Published: 23 December 2014
DOI:
10.11648/j.nano.s.2014020601.11
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Abstract: The goal of the present work is to elucidate complex nano- and micrometer surface modification of soft materials via photochemical and kinetic control of the synthesis and deposition process of gold-nanoparticles. The key to this technology is the synthesis of gold-nanoparticles from different HAuCl4 precursor solutions with photons of a defined short wavelength emitted by Xe2* (172 nm) and XeCl* (308 nm) vacuum UV and UV-C excimer lamps. The size and plasmonic properties of the spherical nanoparticles are tailored by the application of different irradiation conditions. Additionally, with 172 nm irradiation porous nanomembranes are generated. Furthermore, the spatial and density controlled immobilization of nanoparticles on to solid supports such as paper and PES membranes is demonstrated leading to defined 2-dimensional structures in the micrometer range. The synthesis of high gold content structures on paper substrates allows for the rapid and simple generation of conductive paths in electronic circuits. The generated micro– and nanosystems are characterized by scanning electron and light microscopy, photoelectron spectroscopy, dynamic light scattering and UV/VIS spectroscopy. In order to shed light into the kinetic mechanism quantum chemical calculations are employed that help to identify preferred reaction paths of the photo-induced reduction of Au(III) to Au(0).
Abstract: The goal of the present work is to elucidate complex nano- and micrometer surface modification of soft materials via photochemical and kinetic control of the synthesis and deposition process of gold-nanoparticles. The key to this technology is the synthesis of gold-nanoparticles from different HAuCl4 precursor solutions with photons of a defined sh...
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