Elena A. Baranova

Electrochemical Promotion of Ethylene Oxidation over Rh Catalyst Thin Films Sputtered on YSZ and TiO2 / YSZ Supports

The effect of electrochem. promotion of catalysis or nonfaradaic electrochem. modification of catalytic activity or electropromotion was studied for the model reaction of ethylene oxidn. on sputter-coated Rh films. The thin (40 nm) Rh films were deposited on Y2O3-stabilized-ZrO2 (YSZ) and on YSZ coated with a thin porous TiO2 layer. The catalytic activity of Rh for C2H4 oxidn. can be reversibly enhanced via anodic current or potential application by up to a factor of 80 and the increase in the oxidn. rate is up to 2000 times larger than the rate of supply of O2- to the Rh catalyst-electrode. Smaller anodic currents cause periodic catalytic rate and potential oscillations. The TiO2 layer was found to enhance the open-circuit catalytic activity and to stabilize the electrochem. promoted catalyst state. The obsd. pronounced electrochem. promotion behavior is due to the anodically controlled migration (back spillover) of O2- species from YSZ to the Rh/gas interface and the concomitant destabilization, via repulsive lateral interactions, of the formation of surface Rh2O3. The electropromotion of such thin metal catalyst films with metal dispersion near 10% is of significant importance for the practical use of the electrochem. promotion of catalysis. [on SciFinder (R)]

Mechanism of Electrodeposition of Lead Dioxide from Nitrate Solutions

The lead dioxide electrodeposition (LDE) from nitrate electrolytes is studied by the rotating disk electrode, cyclic voltammetry, and electrode impedance methods. A four-stage kinetic scheme of the LDE reaction is proposed: (1) the electron transfer and generation of oxygen-containing species on the electrode surface; (2) the species interact with lead ions, forming an oxygen-containing intermediate product of Pb(III) of the type Pb(OH)2+, which is not fixed on the electrode surface; (3) the product is oxidized, with the transfer of the second electron, forming compounds of Pb(IV) associated with oxygen (of the type Pb(OH)2+2); and (4) the latter decomposes via a chemical mechanism to form PbO2. The rate-determining stage of the LDE process is essentially dependent on the potential and state of the electrode surface, concentration of Pb(II) ions in solution, and hydrodynamic conditions of experiment. The proposed scheme explains within a unified mechanism of the LDE reaction all the experimental data obtained both in this work and in the literature.

Atomic Layer Deposition of Pd Nanoparticles on TiO2 Nanotubes for Ethanol Electrooxidation: Synthesis and Electrochemical Properties

Palladium nanoparticles are grown on TiO2 nanotubes by atomic layer deposition (ALD), and the resulting three-dimensional nanostructured catalysts are studied for ethanol electrooxidation in alkaline media. The morphology, the crystal structure, and the chemical composition of the Pd particles are fully characterized using scanning and transmission electron microscopies, X-ray diffraction, and X-ray photoelectron spectroscopy. The characterization revealed that the deposition proceeds onto the entire surface of the TiO2 nanotubes leading to the formation of well-defined and highly dispersed Pd nanoparticles. The electrooxidation of ethanol on Pd clusters deposited on TiO2 nanotubes shows not only a direct correlation between the catalytic activity and the particle size but also a steep increase of the response due to the enhancement of the metal-support interaction when the crystal structure of the TiO2 nanotubes is modified by annealing at 450 °C in air.

3D-nanoarchitectured Pd/Ni catalysts prepared by atomic layer deposition for the electrooxidation of formic acid

Summary Three-dimensionally (3D) nanoarchitectured palladium/nickel (Pd/Ni) catalysts, which were prepared by atomic layer deposition (ALD) on high-aspect-ratio nanoporous alumina templates are investigated with regard to the electrooxidation of formic acid in an acidic medium (0.5 M H2SO4). Both deposition processes, Ni and Pd, with various mass content ratios have been continuously monitored by using a quartz crystal microbalance. The morphology of the Pd/Ni systems has been studied by electron microscopy and shows a homogeneous deposition of granularly structured Pd onto the Ni substrate. X-ray diffraction analysis performed on Ni and NiO substrates revealed an amorphous structure, while the Pd coating crystallized into a fcc lattice with a preferential orientation along the [220]-direction. Surface chemistry analysis by X-ray photoelectron spectroscopy showed both metallic and oxide contributions for the Ni and Pd deposits. Cyclic voltammetry of the Pd/Ni nanocatalysts revealed that the electrooxidation of HCOOH proceeds through the direct dehydrogenation mechanism with the formation of active intermediates. High catalytic activities are measured for low masses of Pd coatings that were generated by a low number of ALD cycles, probably because of the cluster size effect, electronic interactions between Pd and Ni, or diffusion effects.

Kinetic study of electro-Fenton oxidation of azo dyes on boron-doped diamond electrode

The present work compares electrochemical degradation of red and blue azo textile dyes in single- and two-compartment electrochemical cells in the presence of Fenton reagent (Fe2+) and using a boron-doped diamond anode. Degradation of both dyes was related to the concentration of dye, applied current density and the concentration of FeSO4 catalyst. Complete colour removal and approximately 91% of organic matter oxidation was achieved in a two-compartment electrochemical cell at an applied current density of 20 mA·cm −2, pH of 3 and Fe2+ ion concentration of 0.02 mM. Higher current density and reaction time were required to achieve the same removals in a one-compartment electrochemical cell. Dye degradation kinetics as well as chemical oxygen demand removal rate were successfully modelled to pseudo first-order kinetics. The apparent first-order rate constants (k o) for degradation of red dye with an initial concentration of 20, 40 and 60 ppm were found to be 2.67±0.16, 2.19±0.09 and 1.5±0.03 min−1, and for blue dye at the same initial concentrations were 1.99±0.2, 0.95±0.02 and 0.71±0.030 min−1, respectively.

Oxygen evolution on lead dioxide modified with fluorine and iron

In the oxygen evolution reaction in a sulfuric acid solution, the electrocatalytic activity of lead dioxide doped with fluorine or iron changes. At low and elevated dopant concentrations, the reaction rate is limited by the transfer of the second and first electrons, respectively.

Ethylene Oxidation in an Oxygen‐Deficient Environment: Why Ceria is an Active Support?

Pt/CeO2, Ru/CeO2, Ir/CeO2 and the corresponding unsupported nanoparticles (Pt, Ru and Ir) were evaluated for their performance in the complete oxidation of ethylene in the presence and absence of oxygen. The lattice oxygen and oxygen storage capacity (OSC) of CeO2 had a significant influence on the interaction with the supported metal nanoparticles, which caused different catalytic behaviours in the absence of oxygen. Overall, Ru/CeO2 was more stable than Ir/CeO2 and Pt/CeO2, which results in transient promotional rate enhancement ratio (ρMSI; MSI=metal–support interaction) values that reach 200 in the first 25 min. These results were attributed to the corresponding interaction with CeO2 and negligible carbon deposition. A proposed relationship between ρMSI and the O2− consumed from CeO2 is discussed, which was suggested as a possible tool to estimate the extent of the MSI. In general, an increase in ρMSI corresponded to an increase in O2− consumed from ceria.

Copper and nickel nanoparticles: synthesis by electrochemical discharges

The unique optical, electronic, chemical and biological properties of metal nanoparticles have stimulated a large research activity into manufacturing methods of these nano-structures. An example of copper and nickel nanoparticle synthesis using electrochemical discharges in aqueous solutions is described. This low-cost template technique is a facile procedure to fabricate large quantities of metallic nano-sized particles. The resulting particles are characterized using an electrochemical method (cyclic voltammetry), Energy Dispersive X-ray Spectroscopy (EDS) analysis and Transmission Electron Microscopy (TEM).

Electro-oxidation of two reactive azo dyes on boron-doped diamond electrode

Electrochemical oxidation (decolorization/degradation) of blue and red commercial reactive azo dyes was carried out on boron-doped diamond (BDD) electrode. The effect of various quantities of FeSO(4) was investigated in the electro-Fenton reaction on BDD. Progress of dyes degradation during the electrolysis and electro-Fenton reaction was monitored by UV-visible absorption and by estimation of the chemical oxygen demand (COD). Direct electrolysis showed a limiting capacity for red and blue dye removal even at high current densities, e.g. maximum red color and COD removal were 70 and 20%, respectively at 30 mA cm(-2) after 300 min. Higher red and blue color removal efficiencies were achieved by electro-Fenton oxidation. Current density of 30 mA cm(-2) in the presence of 0.05 mmol/L of FeSO(4) resulted in the red color and COD removal of 98 and 96%, respectively. The optimum FeSO(4) concentration for the electro-Fenton reaction was determined to be 0.05 mmol/L. Instantaneous current efficiency (ICE) in the presence of FeSO(4) was almost three times higher than for experiments carried out without FeSO(4).

Pt7Sn3 catalysts for ethanol electro-oxidation: correlation between surface structure and catalytic activity

Ethanol electro-oxidation has attracted great attention in the fuel cell technology for direct ethanol fuel cells (DEFCs). Active and inexpensive electrocatalysts are required to efficiently break C-C bond and completely convert ethanol to CO2. Recent studies showed that PtxSn1-x catalysts have promising catalytic activity for ethanol electro-oxidation in both acidic and alkaline solutions [1, 2]. Despite the numerous studies on PtSn catalysts, several issues regarding their catalytic activity and stability remain to be addressed. Surface composition and chemistry of bimetallic catalyst is complex and may be influenced by several parameters, e.g., synthesis method, particle size, catalyst structure, surface chemistry, therefore investigation of the surface structure of bimetallic catalysts and its correlation to the catalytic performance is an important task. In the present work PtSn nanostructured catalysts with the atomic ratio of Pt to Sn of 70:30 at. % were synthesized and tested for ethanol electro-oxidation in alkaline and acidic solutions. X-ray photoelectron spectroscopy has been chosen to study the surface chemistry of carbon-supported Pt7Sn3 catalysts and correlate it with electrocatalytic activity. The ability to discriminate between different chemical environments, not just elemental compositions, is one of the primary advantages of XPS in the characterization of catalysts. Synthesis of the bimetallic Pt7Sn3 catalysts supported on carbon (Vulcan XC-72) is described in details elsewhere [4]. Table 1 summarizes the synthesis conditions and some characteristics of Pt7Sn3 nanoparticles. Carbon-supported Pt7Sn3 catalysts were analyzed by KRATOS Axis Ultra DLD X-ray Photoelectron Spectrometer. The XPS analysis was conducted at 140 W and at pass energy of 20 eV. The peak positions were corrected for sample charging by setting the maximum of C 1s peak to binding energy of 284.7 eV. Data analysis and quantification was performed using CasaXPS software. Correlation of XPS structural information with catalytic performance for ethanol electro-oxidation in acidic and alkaline solutions, particle size and structural characteristics is accomplished by application of Multivariate statistical methods of data analysis (MVA). [3] Principal Component Analysis (PCA) and Partial Least Squares Discriminant Analysis (PLSDA) are used herein as an analysis tools to find samples which are globally correlated or anti-correlated, and to facilitate visualization of the variables responsible for the correlations and to highlight differences between two categories of structures of catalysts obtained. Several observations were found from the structureto-property correlations for the carbon-supported Pt7Sn3 catalysts : 1. Best performing catalysts for ethanol electrooxidation in acidic solution do not have largest absolute amounts of Pt and Sn on the surface, whereas samples with largest amount of total Pt and Sn have the worst catalytic activity (current density, i) and largest electrochemical active surface area (EASA). 2. Relative distribution of types of Pt and Sn is more important than the absolute amounts. Best performing samples have small amounts of both metals, but have largest relative amount of both metallic Pt and metallic Sn. The same best performing samples have fewest amounts of all types of oxides, i.e. PtO, PtO2 and SnOx. Ongoing electrochemical evaluations of Pt7Sn3 catalysts for ethanol oxidation in alkaline media will be correlated to XPS structural information and discussed along with their catalytic activities.