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52. Pt-Ag catalysts as cathode material for oxygen-depolarized electrodes in hydrochloric acid electrolysis

Author

Maljusch, Artjom, Nagaiah, Tharamani Chikka, Schwamborn, Stefanie, Bron, Michael, and Schuhmann, Wolfgang

Subjects
Hydrochloric acid -- Chemical properties, Hydrochloric acid -- Composition, Electrochemistry -- Research, Catalysts -- Chemical properties, Catalysts -- Composition, Catalysts -- Usage, Electrodes -- Chemical properties, Electrodes -- Composition, Electrolysis -- Methods, Oxygen -- Chemical properties, Oxygen -- Control, Chemistry
Abstract

Pt-Ag nanoparticles were prepared on a glassy carbon (GC) surface by pulsed electrodeposition and tested using cyclic voitammetry and scanning electrochemical microscopy (SECM) with respect to their possible use as catalyst material for oxygen reduction in 400 mM HCl solution. For comparison, a Pt catalyst was investigated under similar conditions. The redox competition mode of scanning electrochemical microscopy (RC-SECM) was adapted to the specific conditions caused by the presence of CI ions and used to visualize the local catalytic activity of the Pt-Ag deposits. Similarly prepared Pt deposits were shown to dissolve underneath the SECM tip. Pt-Ag composites showed improved long-term stability toward oxygen reduction as compared with Pt even under multiple switching off to open-circuit potential in 400 mM HCl. 10.1021/ac902620g

Published
2010

53. Electrocatalytic activity of spots of electrodeposited noble-metal catalysts on carbon nanotubes modified glassy carbon

Author

Chen, Xingxing, Eckhard, Kathrin, Zhou, Min, Bron, Michael, and Schuhmann, Wolfgang

Subjects
Electrochemical reactions -- Observations, Nanotubes -- Chemical properties, Nanotubes -- Electric properties, Precious metals -- Chemical properties, Precious metals -- Electric properties, Metal catalysts -- Usage, Chemistry
Abstract

A strategy for the screening of the electrocatalytic activity of electrocatalysts for possible application in fuel cells and other devices is presented. In this approach, metal nanoclusters (Pt, Au, Ru, and Rh and their codeposits) were prepared using a capillary-based droplet-cell by pulsed electrodeposition in a diffusion-restricted viscous solution. A glassy carbon surface was modified with carbon nanotubes (CNTs) by electrophoretic accumulation and was used as substrate for metal nanoparticle deposition. The formed catalyst spots on the CNT-modified glassy carbon surface were investigated toward their catalytic activity for oxygen reduction as a test reaction employing the redox competition mode of scanning electrochemical microscopy (RC-SECM). Qualitative information on the electrocatalytic activity of the catalysts was obtained by varying the potential applied to the substrate; semiquantitative evaluation was based on the determination of the electrochemically deposited catalyst loading by means of the charge transferred during the metal nanoparticle deposition. Qualitatively, Au showed the highest electrocatalytic activity toward the oxygen reduction reaction (ORR) in phosphate buffer among all investigated single metal catalysts which was attributed to the much higher loading of Au achieved during electrodeposition. Coelectrodeposited Au-Pt catalysts showed a more positive onset potential (-150 mV in RC-SECM experiments) of the ORR in phosphate buffer at pH 6.7. After normalizing the SECM image by the charge during the metal nanocluster deposition which represents the mass loading of the catalyst, Ru showed a higher electrocatalytic activity toward the ORR than Au.

Published
2009

72. BaTiO3 –CoFe2O4 –BaTiO3 trilayer composite thin films prepared by chemical solution deposition

Author

Walther, Till, Quandt, Norman, Köferstein, Roberto, Roth, Robert, Steimecke, Matthias, Bron, Michael, Dörr, Kathrin, Ebbinghaus, Stefan, Martin-Luther-Universität Halle Wittenberg (MLU), Martin-Luther University Halle-Wittenberg, Institut für Kernphysik, and Technische Universität Darmstadt (TU Darmstadt)

Subjects
Materials science, spinel, Multiferroics, Thin films, CoFe2O4, Analytical chemistry, 02 engineering and technology, Thermal treatment, engineering.material, [CHIM.INOR]Chemical Sciences/Inorganic chemistry, 01 natural sciences, Spin Coating, symbols.namesake, 0103 physical sciences, Materials Chemistry, composite, Thin film, perovskite, Perovskite (structure), 010302 applied physics, Spin coating, Spinel, [CHIM.MATE]Chemical Sciences/Material chemistry, Chemical Solution Deposition, 021001 nanoscience & nanotechnology, Hysteresis, BaTiO3, Ceramics and Composites, symbols, engineering, 0210 nano-technology, Raman spectroscopy
Abstract

International audience; Multiferroic BaTiO3-CoFe2O4-BaTiO3 thin films were synthesized by spin coating of Co(NO3) 2-Fe(NO3)3 and Ba(OAc)2-Ti(i-OPr)4 solutions in a solvent mixture of acetic acid and dimethylformamide. Subsequent stepwise thermal treatment at 200, 400 and 800 °C leads to the desired ferroelectric and ferrimagnetic phases. The phase formation process was monitored by thermogravimetric, XRD, IR and Raman measurements. SEM was used to characterize the layered sandwich structure and the thickness of each layer. Two samples with different thicknesses of the perovskite and spinel layers are discussed. Sample 1 consists of a 120 nm layer of CoFe2O4 between two 70 nm thick BaTiO3 layers. For sample 2 the 90 nm 2 thick top and bottom layers of BaTiO3 are enclosing a 220 nm CoFe2O4 layer. The quality of the samples surfaces was determined by AFM leading to root mean square roughness values of about 4 nm. Magnetic investigations reveal a slightly anisotropic behavior for in-plane and out-of-plane magnetizations and coercivities. Polarization measurements show hysteresis loops (maximum Ps = 29 µC cm-2 ; maximum Pr = 17 µC cm-2) with pronounced switching peaks at the corresponding coercive fields of 200 and 360 kV cm-1 , respectively.

Published
2015

74. In SituCharacterization of Ni and Ni/Fe Thin Film Electrodes for Oxygen Evolution in Alkaline Media by a Raman-Coupled Scanning Electrochemical Microscope Setup

Author

Steimecke, Matthias, Seiffarth, Gerda, and Bron, Michael

Abstract

We present a spectroelectrochemical setup, in which Raman microscopy is combined with scanning electrochemical microscopy (SECM) in order to provide both spectroscopic and electrochemical information on the very same location of an electrode at the same time. The setup is applied to a subject of high academic and practical interest, namely, the oxygen evolution reaction at Ni and Ni/Fe electrodes. It comprises a transparent substrate electrode, onto which Ni and Ni/Fe thin films are deposited. An ultramicroelectrode (UME) is placed closely above the substrate to obtain electrochemical information, while a Raman microscope probes the same sample spot from below. To obtain information on oxygen evolution activity and structural changes, increasingly positive potentials from 0.1 up to 0.7 V vs Hg|HgO|1 M KOH were applied to the Ni/Fe-electrodes in 0.1 M KOH solution. Evolved oxygen is detected by reduction at a Pt UME, allowing for the determination of onsetpotentials, while the substrate current, which is recorded in parallel, is due to both overlapping oxygen evolution and the oxidation of Ni(OH)2to NiOOH. An optimum of 15% Fe in Ni/Fe films with respect to oxygen evolution activity was determined. At the same time, the potential-dependent formation of γ-NiOOH characterized by the Raman double band at 475 and 557 cm–1allows for the conclusion that a certain amount of disorder introduced by Fe atoms is necessary to obtain high oxygen evolution reaction (OER) activity.

Published
2024
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76. Back Cover: Chemical Leaching of Pt-Cu/C Catalysts for Electrochemical Oxygen Reduction: Activity, Particle Structure, and Relation to Electrochemical Leaching (ChemElectroChem 11/2016)

Author

Petrova, Olga, primary, Kulp, Christian, additional, Pohl, Marga-Martina, additional, ter Veen, Rik, additional, Veith, Lothar, additional, Grehl, Thomas, additional, van den Berg, Maurits W. E., additional, Brongersma, Hidde, additional, Bron, Michael, additional, and Grünert, Wolfgang, additional

Published
2016
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78. Chemical Leaching of Pt–Cu/C Catalysts for Electrochemical Oxygen Reduction: Activity, Particle Structure, and Relation to Electrochemical Leaching

Author

Petrova, Olga, primary, Kulp, Christian, additional, Pohl, Marga‐Martina, additional, ter Veen, Rik, additional, Veith, Lothar, additional, Grehl, Thomas, additional, van den Berg, Maurits W. E., additional, Brongersma, Hidde, additional, Bron, Michael, additional, and Grünert, Wolfgang, additional

Published
2016
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85. A Comparative Study of Functionalized High-Purity Carbon Nanotubes towards the V(IV)/V(V) Redox Reaction Using Cyclic Voltammetry and Scanning Electrochemical Microscopy.

Author

Steimecke, Matthias, Rümmler, Stefan, Schuhmacher, Nils‐Frederik, Lindenberg, Titus, Hartmann, Mark, and Bron, Michael

Subjects
CARBON nanotubes, OXIDATION-reduction reaction, CYCLIC voltammetry, SCANNING electrochemical microscopy, OXYGEN, FUNCTIONAL groups
Abstract

Functionalized high purity carbon nanotubes (CNTs) with various amounts of oxygen containing surface groups were investigated towards the relevant redox reactions of the all-vanadium redox flow battery. The quinone/hydroquinone redox peaks between 0.0 and 0.7 V vs. Ag|AgCl|KClsat. were used to quantifying the degree of functionalization and correlated to XPS results. Cyclic voltammetry in vanadyl sulfate-containing 3 M H2SO4 as a common supporting electrolyte showed no influence of the amount of surface groups on the V(IV)/V(V) redox system. In contrast, the reactions occurring at the negative electrode (V(II)/V(III) and V(III)/V(IV)) are strongly affected by oxygen surface groups. However, under modified experimental conditions, SECM experiments detecting the consumption of VO2+ molecules by CNT thin films in pH=2 solution show improved onset potentials with increased surface oxygen content up to ∼ 3 at%. Further increase in surface oxygen up to 8 at% led to minor improvement. These dissimilar results under different experimental conditions are rationalized by suggesting that oxygen functional groups do not form the active site for the V(IV)/V(V) reaction but wetting of the catalyst layer is of high importance. [ABSTRACT FROM AUTHOR]

Published
2017
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91. A Linear Sweep Voltammetric Procedure Applied to Scanning Electrochemical Microscopy for the Characterization of Carbon Materials towards the Vanadium(IV)/(V) Redox System.

Author

Steimecke, Matthias, Rümmler, Stefan, Kühhirt, Mathias, and Bron, Michael

Subjects
VANADIUM, VOLTAMMETRY, CATALYTIC activity, ULTRAMICROELECTRODES, ELECTROCHEMICAL analysis, SCANNING electrochemical microscopy
Abstract

A linear sweep voltammetric procedure applied to scanning electrochemical microscopy is presented to investigate carbon materials towards their activity for vanadium redox reactions of relevance for redox flow batteries. A linear sweep voltammetric experiment is performed at an ultramicroelectrode (UME) in close distance to an electrocatalytically active material, triggering a competition situation where both the UME and the material compete for the same molecule (VO2+). Depending on the redox activity of the catalytic material at the applied potential and thus the consumption of VO2+, a decreased current in the detection sweep at the UME is observed. After evaluating relevant experimental parameters using a glassy carbon electrode as substrate, the mode is applied to a commercial carbon material where its redox behavior was examined and compared with results from cyclic voltammetry. Finally, it is shown that the presented linear sweep voltammetry-scanning electrochemical microscopy (LSV-SECM) method can be used to visualize catalytic activity. [ABSTRACT FROM AUTHOR]

Published
2016
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