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Your search keyword '"Topalov, Angel A."' showing total 33 results
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33 results on '"Topalov, Angel A."'

8. Design and implementation of an automated electrochemical flow system coupled with mass spectrometry for investigation of the dissolution behavior of platinum

Author

Topalov, Angel Angelov (M. Sc.) and Chemie

Subjects
Physikalische Chemie, Platin, Brennstoffzelle, Katalysator, Stabilität, ddc:540
Abstract

Kernthema dieser Dissertation ist die Untersuchung des elektrochemischen Auflösungsverhaltens von polykristallinem Platin, die durch die Verwendung gleichzeitiger Online-Elementaranalyse des Elektrolyten durchgeführt wurde. Zu diesem Zweck wurde eine neue mikroelektrochemische Durchflusszelle (\(\bf S\)canning \(\bf F\)low \(\bf C\)ell) entworfen und entwickelt, die durch ein induktiv gekoppeltes Plasma-Massenspektrometer ergänzt wurde. Um Hochdurchsatz- und kombinatorische Messungen zu ermöglichen, wurde das entwickelte System(-e) vollständig automatisiert. Erstmalig wurde ein zeitaufgelöstes Pt Konzentrationsprofil innerhalb eines zyklischen Voltammograms aufgedeckt. Die experimentellen Daten zeigen, dass die Auflösung während der Unter-Oberflächenoxidbildung (\(\textit {ca.}\) 1,1 V\(_{RHE}\)) wie bei einer Reduktion der Oxidschicht auftritt. Im Rahmen der neu gewonnenen Erkenntnisse werden die vorhandenen thermodynamischen Modelle der Auflösung hinterfragt und neue Mechanismen vorgeschlagen.

Published
2014

11. Rational design of the electrode morphology for oxygen evolution – enhancing the performance for catalytic water oxidation

Author

UCL - SST/IMMC/IMAP - Materials and process engineering, Zeradjanin, Aleksandar R., Topalov, Angel A., Van Overmeere, Quentin, Cherevko, Serhiy, Chen, Xingxing, Ventosa, Edgar, Schuhmann, Wolfgang, Mayrhofer, Karl Johann Jakob, UCL - SST/IMMC/IMAP - Materials and process engineering, Zeradjanin, Aleksandar R., Topalov, Angel A., Van Overmeere, Quentin, Cherevko, Serhiy, Chen, Xingxing, Ventosa, Edgar, Schuhmann, Wolfgang, and Mayrhofer, Karl Johann Jakob

Abstract

The fundamental understanding of the electrode/electrolyte interface is of pivotal importance for the efficient electrochemical conversion and storage. However, the reasons for the low rate of electrocatalytic oxygen evolution and issues of long-term material stability, which are central constrains for attaining desirable efficiency for sustainable technologies like water electrolysis or electrochemical CO2 reduction, are still not completely resolved. While a lot of attention has been directed towards the search for new materials with unique (electro)catalytic properties, experimental results accumulated during the last four decades and prediction from models suggest that RuO2 possesses superior activity for oxygen evolution under acidic conditions. Considering that RuO2 is a material of choice, we show that tailoring the surface morphology on the meso- and macroscale contains great potential for the improvement of the efficiency of this gas evolving reaction. Advanced analytical tools have been utilized for the combined investigation of both activity and stability. Namely, the potential dependent frequencies of gas-bubble evolution, an indicator for the activity of the electrode, were acquired by scanning electrochemical microscopy (SECM), while the dissolution of RuO2 was monitored using a micro electrochemical scanning flow cell combined with an inductively coupled plasma mass spectrometer (SFC-ICP-MS). The obtained fundamental insights will aid improving the design and thus performance of electrode materials for water oxidation.

Published
2014

15. Design criteria for stable Pt/C fuel cell catalysts

Author

Meier, Josef C, primary, Galeano, Carolina, additional, Katsounaros, Ioannis, additional, Witte, Jonathon, additional, Bongard, Hans J, additional, Topalov, Angel A, additional, Baldizzone, Claudio, additional, Mezzavilla, Stefano, additional, Schüth, Ferdi, additional, and Mayrhofer, Karl J J, additional

Published
2014
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22. Effect of Polarisation Mimicking Cathodic Electrodeposition Coating on Industrially Relevant Metal Substrates with ZrO2-Based Conversion Coatings.

Author

Sarfraz, Adnan, Posner, Ralf, Bashir, Asif, Topalov, Angel, Mayrhofer, Karl J. J., Lill, Kirsten, and Erbe, Andreas

Subjects
ELECTROPLATING, PHOTOLUMINESCENCE, RAMAN spectroscopy, COALESCENCE (Chemistry), CHEMICAL reactions
Abstract

Modern ZrO2-based conversion coatings were deposited on an aluminium alloy (AA6014), a cold-rolled steel, a zinc electrogalvanised steel and a Sendzimir zinc hot-dip galvanised steel. Pretreated substrates were subjected to galvanostatic polarisation in aqueous NaNO3 to mimic deposition conditions of cathodic electrodeposition coatings. No significant structural modification of the conversion coatings was found with Raman or photoluminescence (PL) spectroscopy. After treatment, increased PL indicated an increased number of point defects. Downstream monitoring of dissolved Zr indicated an insignificant totally dissolved fraction of 0.01 % after 5 s of polarisation, which may occur through vacancy-pair coalescence with concurrent oxide dissolution, as discussed for transpassive dissolution. Overall, the ZrO2 films remained intact after polarisation. [ABSTRACT FROM AUTHOR]

Published
2016
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28. Stability investigations of electrocatalysts on the nanoscale

Author

Meier, Josef C., primary, Katsounaros, Ioannis, additional, Galeano, Carolina, additional, Bongard, Hans J., additional, Topalov, Angel A., additional, Kostka, Aleksander, additional, Karschin, Arndt, additional, Schüth, Ferdi, additional, and Mayrhofer, Karl J. J., additional

Published
2012
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32. The influence of halides on the initial selective dissolution of Cu3Au (111)

Author

Ankah, Genesis N., Pareek, Aparna, Cherevko, Serhiy, Topalov, Angel A., Rohwerder, Michael, and Renner, Frank U.

Subjects
*HALIDES, *COPPER compounds, *DISSOLUTION (Chemistry), *CRYSTAL structure, *BROMIDES, *CUPROUS iodide, *ATOMIC force microscopy
Abstract

Abstract: We report an electrochemical in situ X-ray diffraction (XRD) and ex situ atomic force microscopy (AFM) study on the influence of the halide additives bromide and iodide in comparison to chloride in 0.1M H2SO4 solution on the selective dissolution of Cu3Au (111). Our results suggest that the addition of these halides have a pronounced effect on the dealloying process and lead to peculiar changes in the resulting surface morphologies. For an additive of bromide we observed (similar to an earlier study with chloride) a sequence of specific Au surface layers with an initial ultra-thin stacking-inverted Au-rich layer, subsequent pure Au islands, and finally substrate oriented nanometer-scale ligaments (nanoporosity). These structures occur with a negative shift in the transformation potentials compared to pure sulfuric acid solution. With an additive of iodide no stable passive Au film is formed and a porous surface was observed at relatively short times and low potentials. A precipitation of copper iodide (CuI) visible in the ex situ AFM images leads to the formation of surface porosity with bimodal length scales. [Copyright &y& Elsevier]

Published
2012
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33. Dissolution of platinum: limits for the deployment of electrochemical energy conversion?

Author

Topalov AA, Katsounaros I, Auinger M, Cherevko S, Meier JC, Klemm SO, and Mayrhofer KJ

Subjects
Catalysis, Electrochemical Techniques, Electrodes, Hydrogen chemistry, Energy-Generating Resources, Platinum chemistry
Abstract

Platinum stability: Dissolution of Pt, which is one major degradation mechanism in, for example, hydrogen/air fuel cells, was monitored under potentiodynamic and potentiostatic conditions. The highly sensitive and time-resolving dissolution monitoring enables the distinction between anodic and cathodic dissolution processes during potential transient and chronoamperometric experiments, and the precise quantification of the amount of dissolved Pt., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Published
2012
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