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Electrocatalysis    Follow    
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1868-2529 - ISSN (Online) 1868-5994
     Published by Springer-Verlag Homepage  [2187 journals]   [SJR: 0.542]   [H-I: 7]
  • Addendum to Immobilization-Enabled Proton-Reduction Catalysis by a Di-iron
           Hydrogenase Mimic
    • PubDate: 2014-04-01
       
  • Accelerated Stress Tests of Pt/HSAC Electrocatalysts: an
           Identical-Location Transmission Electron Microscopy Study on the Influence
           of Intermediate Characterizations
    • Abstract: Abstract The influence of intermediate characterizations used in long-term accelerated stress tests (ASTs) to monitor the changes of the electrochemically active surface area of carbon-supported Pt nanoparticles (Pt/HSAC) was investigated. Our results indicate that, in the studied experimental protocol (potentiostatic polarization at E = 1.0 V vs. RHE during 96 h), the loss of the electrochemically active surface area is greatly exacerbated by intermediate characterizations such as cyclic voltammetry or stripping of a saturated COad surface layer. These results can be understood in view of the breakdown of the passivation layer formed on the Pt/HSAC electrocatalyst during the polarization at E = 1.0 V vs. RHE. By using identical location transmission electron microscopy, the structural modifications of the Pt/HSAC nanoparticles could be monitored. The migration/agglomeration of Pt nanocrystallites, the growth of Pt nanocrystallites by electrochemical Ostwald ripening, and the corrosion of the high surface area carbon support are more pronounced when cyclic or COad stripping voltammograms are implemented in the AST. A detailed analysis of the identical-location transmission electron microscopy images also indicates that adsorbed CO molecules minor the dissolution of Ptz+ ions into the electrolyte.
      PubDate: 2014-04-01
       
  • Electrochemical Growth of Surface Oxides on Nickel. Part 2: Formation of
           β-Ni(OH)2 and
           NiO in Relation to the Polarization Potential, Polarization Time, and
           Temperature
    • Abstract: Abstract Electro-oxidation of Ni(poly) in 0.5 M aqueous KOH solution is examined at various polarization potentials (E p), polarization times (t p), and temperatures (T) in the 0.7 ≤ E p ≤ 1.2 V versus RHE, 60 ≤ t p ≤ 10,800 s, and 288 ≤ T ≤ 318 K ranges. The oxide chemical composition is determined using X-ray photoelectron spectroscopy (XPS) and its thickness using XPS depth profiling. XPS measurements demonstrate that such formed oxide layers are multilayer in nature and contain both β-Ni(OH)2 and NiO, with β-Ni(OH)2 being the predominant, outermost species and NiO forming a thin layer sandwiches between metallic Ni and β-Ni(OH)2. An increase of E p, t p, and/or T results in an increase of the oxide thickness. XPS depth profiling measurements reveal that the thickness (d) of the β-Ni(OH)2 plus NiO layers is in the 2 ≤ d ≤ 11 nm range, depending on E p, t p, and T. The electrochemical formation of β-Ni(OH)2 plus NiO follows an inverse-logarithmic growth kinetic law with the escape of metal cation from the metal into the oxide at the inner metal/oxide interface being the rate-determining step. The oxide growth is treated mathematically using the Mott–Cabrera oxide growth theory.
      PubDate: 2014-04-01
       
  • Redox and Oxygen Evolution Electrocatalytic Properties of Nafion and
           Single-Walled Carbon Nanotube/Hydrous Iron Oxide Composite Films
    • Abstract: Abstract Novel Nafion and single-walled carbon nanotube composite hydrous iron oxide electrodes have been fabricated using a simple potential cycling methodology and are examined as oxygen evolution electrocatalyst films. Hydrous oxide materials prepared in this manner are typically quite amorphous in nature. Here, we show, using scanning electron microscopy and cyclic voltammetry, that a more uniform oxide growth can be achieved using a Nafion or carbon nanotube matrix as a template. This templated growth produces oxide films with unique surface morphologies and electrical properties. In particular, the composite films exhibit superior conductivity, as shown by electrochemical impedance spectroscopy, with up to eightfold decrease in charge transfer resistance. The ultimate result is an enhancement in the electrocatalytic performance of the hydrous Fe oxide film. Steady-state polarisation studies on the oxygen evolution reaction show a reduction in overpotential of up to 50 mV for the composite electrodes with a threefold increase in turnover frequency.
      PubDate: 2014-04-01
       
  • Obtaining Clean and Well-dispersed Pt NPs with a Microwave-assisted Method
    • Abstract: Abstract Carbon-supported platinum nanoparticles Pt/C (NPs) are used in many fields of science. These kinds of materials have been extensively studied in electrochemistry due to the fact that they are applied in fuel cell technology. Although there are a myriad of methods for Pt NP synthesis, the need for obtaining Pt/C NPs with a good dispersion (covering over the entire support), a narrow size distribution, and clean surface (among other parameters) is far to be overcome. On this sense herein we describe a very easy and quick method of synthesis of highly dispersed Pt NPs followed by a simple electrochemical cleaning step. The catalysts were electrochemically characterized by studying their behavior in 0.5 M H2SO4 and also by using CO as a probe during the CO electro-oxidation reaction (COEOR). This paper shows how to obtain highly dispersed and clean Pt/C NPs that produce very reproducible results. Besides, we demonstrate how the presence of impurities negatively affects the electrochemical reproducibility of Pt NPs with a clear impact on their catalytic activity. Figure ᅟ
      PubDate: 2014-03-20
       
  • Fabrication and Characterization of Graded Anodes for Anode-Supported
           Solid Oxide Fuel Cells by Tape Casting and Lamination
    • Abstract: Abstract Graded anodes for anode-supported solid oxide fuel cells (SOFCs) are fabricated by tape casting and subsequent cold lamination of plates using different compositions. Rheological parameters are adjusted to obtain stable suspensions for tape casting. The conditions for the tape casting and lamination will be described. Flexural strength of the reduced cermets measured using three-point bending configuration is 468 ± 37 MPa. The graded anode supports are characterized by scanning electron microscope observations, mercury porosimetry intrusion, and resistivity measurements, showing an adequate and homogeneous distribution of nickel, zirconia, and pores. The laminated samples showed a total porosity of 18.7 % (in vol%) and a bimodal pore size distribution centered in 20 and 150 nm, and the measured electrical resistivity of this sample was 120 ± 12 μΩ cm. The novelty of the present work is the lamination of tapes at room temperature without using plasticizers. This is made by the combination of two different binders with varying Tg (glass transition temperature) which resulted in plastic deformation at room temperature. Those results indicate that the proposed process is a cost-effective method to fabricate anode-supported SOFCs.
      PubDate: 2014-03-18
       
  • Mechanistic Principles of Platinum Oxide Formation and Reduction
    • Abstract: Abstract In polymer electrolyte fuel cells, the platinum catalyst in its active form is found predominantly in an oxidized state. Formation and reduction of surface oxide species determine both the electrocatalytic activity of the oxygen reduction reaction as well as the rate of corrosive Pt dissolution. Understanding of mechanisms and rates of oxide formation and reduction is therefore essential in view of both performance and durability. Pt(111) is the generic model system for fundamental studies in fuel cell electrochemistry and cyclic voltammetry at Pt(111) gives an unabated view of the oxide formation and reduction processes. The unresolved challenge is to develop an electrochemical kinetic model that allows the current response measured in cyclic voltammetry to be de-convoluted and interpreted in relation to independent spectroscopic, imaging and theoretical data. Accordingly, a kinetic model for Pt(111) oxide formation and reduction within the voltage range of 0.65–1.15 V is developed and evaluated against electrochemical, spectroscopic and computational studies. Considering the complexity of surface processes involved and the simplicity of the proposed model, the agreement with the extensive range of data is convincing. The model provides a comprehensive picture of surface electrochemical processes that occur at Pt(111) in the normal operational voltage range of the cathode catalyst for polymer electrolyte fuel cells in automotive applications.
      PubDate: 2014-03-07
       
  • Electrochemical Reduction of Oxygen and Nitric Oxide at Low Temperature on
           La1−       class="a-plus-plus">x Sr       class="a-plus-plus">        class="a-plus-plus">x FeO       class="a-plus-plus">3−δ Cathodes
    • Abstract: Abstract A series of six strontium-substituted lanthanum ferrites (La1−x Sr x FeO3−δ, x = 0.00, 0.05, 0.15, 0.25, 0.35, and 0.50) were synthesized using the glycine-nitrate process and evaluated as cathodes for the electrochemical reduction of oxygen and nitric oxide in the temperature range 200 to 400 °C, using cone-shaped electrodes and cyclic voltammetry. It was shown that the ferrites had a higher activity towards the electrochemical reduction of nitric oxide than towards the electrochemical reduction of oxygen, in the investigated temperature range. The highest activity towards the electrochemical reduction of nitric oxide was found for La0.95Sr0.05FeO3−δ at 400 °C. This compound also showed the highest activity towards the electrochemical reduction of oxygen at 400 °C. The highest apparent selectivity was found for the compound LaFeO3 at 200 °C. The materials showed ability to oxidize nitric oxide to nitrogen dioxide.
      PubDate: 2014-03-05
       
  • In Situ FT-IR Investigation of Methanol and CO Electrooxidation on Cubic
           and Octahedral/Tetrahedral Pt Nanoparticles Having Residual PVP
    • Abstract: Abstract The methanol oxidation reaction (MOR) and related carbon monoxide (CO) oxidation reaction (COR) activities on the synthesized cubic and octahedral/tetrahedral (O/T) Pt nanoparticles (NPs) still having residual polyvinylpyrrolidone (PVP) were investigated using electrochemical (EC) and in situ Fourier transform infrared (FT-IR) spectroscopic measurements in both 0.1 M HClO4 and 0.1 M H2SO4. While EC measurements confirmed the enhanced MOR activity on the O/T Pt NPs as observed previously (Susut et al., Phys. Chem. Chem. Phys. 10:3712, 6), the in situ IR measurements showed much improved data quality as compared to the previous studies and provided strong indications that the underlying reason for the observed MOR enhancement on the O/T Pt NPs was highly likely related to the enhanced no-CO-generating reaction pathway(s), as evidenced by much lower CO generation during the MOR on these Pt NPs.
      PubDate: 2014-03-01
       
  • Temperature-Dependent Dissolution of Polycrystalline Platinum in Sulfuric
           Acid Electrolyte
    • Abstract: Abstract Commercial proton exchange membrane (PEM) fuel cells, various types of water electrolyzers and recently proposed unified, regenerative fuel cells are usually operated at elevated temperatures. Higher-operation temperatures bring several advantages: (a) increase of the rate of slow oxygen reactions, (b) improved mass transport, and (c) minimization of the electrolyte (ionic conductor) resistance. However, at the same time, it is expected that degradation processes will be accelerated at such temperatures. In the current work, electrochemistry and in situ mass spectrometry are utilized to investigate how increased temperature affects the rate of (electro)chemical dissolution of platinum. The steady state dissolution rate during potentiostatic polarization decreases to a value below the detection limit after several minutes at all temperatures—dissolution thus remains a transient process controlled by oxide formation kinetics as reported previously for room temperature. Deconvolution of anodic and cathodic dissolution branches in potentiodynamic experiments reveals that the increase in temperature results in higher amounts of platinum being dissolved during oxide formation, while dissolution during oxide reduction decays with increasing temperature. In contrast to most literature reports, the total amount of dissolved platinum during 1 potential cycle is found to decrease with increasing temperature.
      PubDate: 2014-02-15
       
  • Hierarchically Structured Non-PGM Oxygen Reduction Electrocatalyst Based
           on Microemulsion-Templated Silica and Pyrolyzed Iron and Cyanamide
           Precursors
    • Abstract: Abstract Hierarchically structured electrocatalysts for oxygen reduction based on iron and cyanamide were synthesized using novel templating approach that leads to hierarchy of scales of pores and particles. Microemulsion process is used to generate silica template with multimodal pore distribution, which is impregnated with metal and nitrogen precursors, to create a large surface area openly structured active electrocatalysts for oxygen reduction in both acid and alkaline media. Extensive characterization using microscopic, spectroscopic, and electrochemical methods of electrocatalysts was done to understand the final catalysts structure obtained through this novel approach and its impact on activity.
      PubDate: 2014-02-07
       
  • Effect of TiO2
           Content on Ethanol Electrooxidation in Alkaline Media Using Pt
           Nanoparticles Supported on Physical Mixtures of Carbon and TiO       class="a-plus-plus">2 as Electrocatalysts
    • Abstract: Abstract Pt nanoparticles supported on physical mixtures of carbon and TiO2 (Pt/(C + TiO2) electrocatalyst) were tested for ethanol electrooxidation in alkaline media. The electrocatalysts were prepared with different C/TiO2 mass ratios using borohydride as reducing agent. X-ray diffraction patterns of the obtained materials showed the peak characteristic of Pt face-centered cubic (fcc) structure, carbon, and TiO2 phases. Transmission electron micrographs showed metal nanoparticles distributed preferentially over TiO2 support with average particle size between 5 and 7 nm for all electrocatalysts. The cyclic voltammograms of Pt/(C + TiO2) electrocatalysts in alkaline media showed a decrease of Pt surface area with the increase of TiO2 content. The electrooxidation of ethanol suggests the Pt/(C + TiO2) (40:60) as the most promising electrocatalyst for use in fuel cells since it presents almost the same current density value as that of the others and also slower current density decay in chronoamperometry. Moreover, TiO2 provides oxygen species to promote the CO oxidation, resulting in more activity.
      PubDate: 2014-01-24
       
  • Agglomeration and Cleaning of Carbon Supported Palladium Nanoparticles in
           Electrochemical Environment
    • Abstract: Abstract Here we investigate the electrochemical behavior of Pd/C synthesized by reduction with ethylene glycol in the presence of polyvinylpyrrolidone (EG-PVP). EG-PVP produces nanoparticles (NPs) with a narrow size distribution, but some of them remain covered by impurities after the synthesis. After successive voltammetric cycles, NPs become cleaner, but some agglomeration and structural modification occur; these effects affect the electrochemical behavior of Pd/C in different ways, so we used CO as a probe to better understand the processes taking place. CO stripping shows that the general features of the multiple oxidation peaks change with the number of cycles. Possibly, CO and OH from different NPs react when the particles agglomerate, contributing to CO stripping changes. Finally, different active areas are found when the charges involved in CO oxidation and PdO reduction are compared. Such differences are rationalized in terms of a balance between the increase of sites which promote the oxidation of CO and the loss of area provoked by the growing of the particles. Figure After successive voltammetric cycles, Pd/C NPs become cleaner with slightly agglomeration, which lead to increase of the electrochemically active surface area. The value of area reaches a maximum, after this point the agglomeration is the main effect and contributes to the surface area decay. The agglomeration facilitates the CO electrooxidation reaction among NPs
      PubDate: 2014-01-16
       
  • Electrochemical and In Situ FTIR Study of        class="a-plus-plus">o-Cresol on Platinum Electrode
           in Acid Medium
    • Abstract: Abstract The electrochemical behaviour of o-cresol in acidic medium on platinum electrode has been studied by cyclic voltammetry and in situ Fourier transform infrared spectroscopy. The o-cresol suffers hydrolysis during oxidation giving rise to the formation of methyl-p-benzoquinone. In situ FTIR spectroscopic studies also reveal the presence of CO2, formed as a consequence of the rupture of the aromatic ring. Moreover, the oxidation of o-cresol in acidic medium produces a polymeric film on the platinum surface that precludes further oxidation of o-cresol. The reduction of o-cresol at potentials below 0 V produces in the first step the partial reduction of the aromatic ring and when the potential goes to values below 0 V, methyl-cyclohexanone.
      PubDate: 2014-01-10
       
  • The Role of Electrodeposited Pd Catalyst Loading on the Mechanisms of
           Formic Acid Electro-Oxidation
    • Abstract: Abstract This work addresses the effects of Pd nanoparticle loading and dispersion on the mechanisms of formic acid (FA) electro-oxidation. For this purpose, different levels of Pd nanoparticle loading (0.10–0.98 mg cm−2) with similar size (∼10–13 nm) were electrodeposited on the carbon cloth via square wave pulse technique. The mechanisms of FA oxidation in 0.5 M HCOOH + 0.5 M H2SO4 solution were studied and identified using cyclic voltammetry (CV) together with Fourier transform infrared spectroscopy (FTIR). Based on the obtained results, it was found that the electrochemical active surface area and Tafel slopes are independent of Pd loading levels, but both the shape and peak potential of the voltammograms are significantly affected by the Pd loading levels. The results of CV and FTIR showed that the different levels of Pd loading changes the FA oxidation pathway, which is attributed to the fact that the higher Pd loading results in the closer distribution of Pd nanoparticles. It was suggested that, at high Pd loading, the Pd-HCOOads formation is not the only available pathway for FA oxidation process and the Pd-COads formation pathway also exists, which is oxidized to CO2 at more anodic potentials.
      PubDate: 2014-01-10
       
  • NiMnOx/C: A Non-noble
           Ethanol-Tolerant Catalyst for Oxygen Reduction in Alkaline Exchange
           Membrane DEFC
    • Abstract: Abstract A non-noble oxygen reduction catalyst based on nickel−manganese oxide supported on high-surface area carbon has been synthesized by a mild hydrothermal treatment, resulting in nanocrystalline needles. Cyclic voltammetry showed the electrochemical redox characteristics of this material, evidencing the appearance of peaks associated to consecutive reversible transitions involving Mn(IV)/Mn(III) and Mn(III)/Mn(II). The catalyst displayed a high activity for the oxygen reduction, despite that the complete reduction was not achieved, consuming less than three electrons of the four available in the oxygen molecule. More importantly, this activity did not decay under the presence of ethanol, revealing the high ethanol tolerance of this material. Finally, single-cell results have demonstrated the suitability of this material as cathode catalysts for alkaline DEFC: The open circuit voltage and the maximum power densities are close to those obtained by a standard Pt/C catalyst.
      PubDate: 2014-01-01
       
  • An Ultrahigh Selective and Sensitive Enzyme-Free Hydrogen Peroxide Sensor
           Based on Palladium Nanoparticles and Nafion-Modified Electrode
    • Abstract: Abstract An ultrahigh selective and sensitive hydrogen peroxide electrochemical sensor was developed based on palladium nanoparticles and nafion-modified electrode in enzyme-free conditions. The surface morphology of the fabricated electrode was characterized by using field emission scanning electron microscopy and electrochemical impedance spectroscopy. The fabricated sensor displayed an excellent electrocatalytic reduction of hydrogen peroxide (H2O2) at −0.2 V. The as-prepared-modified electrode displayed a very fast amperometric response (<2 s) of H2O2, indicating excellent electrocatalytic performance of the modified electrode. The sensor showed wide linear range response from 0.1 μM to 9 mM with a limit of detection of 0.018 μM for the determination of H2O2. In addition, the sensor displayed a high sensitivity of 0.766 μA μM−1 cm−2 with acceptable repeatability, reproducibility, and stability. The developed H2O2 sensor is highly selective even in the presence of higher concentrations of the potentially interfering species. The good practicality of the sensor indicates that it could be used as a good potential candidate for the real-time sensing of H2O2. Figure Schematic representation of the typical electrochemical reduction of H2O2 at Pd nanoparticles and nafion-modified glassy carbon electrode.
      PubDate: 2013-12-15
       
  • Molecular Modeling of Hydronium Ion and Water Distribution in Water-Filled
           Pt Nanochannels with Corrugated Walls
    • Abstract: Abstract Classical molecular dynamics was employed to study the impact of nanoconfinement and surface nanostructure on electrostatic phenomena and transport properties in catalyst layer pores of polymer electrolyte fuel cells. The porous structure of an ionomer-free ultrathin catalyst layer was represented by a water-filled nanochannel with corrugated and negatively charged Pt walls. The equilibrium hydronium ion distribution in the channel was used to assess local reaction conditions. We rationalized the effects of nanostructuring and metal surface charge on the electrostatic effectiveness factor of the channel. Furthermore, we investigated the water dynamics in the nanochannel, calculating the self-diffusion coefficients of surface and bulk-like water.
      PubDate: 2013-12-11
       
  • Non-platinum Carbon-Supported Oxygen Reduction Catalyst Ink Evaluation
           Based on Poly(sulfone) and Poly(phenylene)-Derived Ionomers in Alkaline
           Media
    • Abstract: Abstract Described in this work is an electrochemical evaluation of novel alkaline ionomers employed as catalyst binder for non-platinum group metal electrocatalysts based on cyanamide precursor. Electrochemical evaluation of the non-platinum group metal (non-PGM) catalyst bound with the featured alkaline ionomer classes over a range of conditions gives insight into how they behave, as well as provide information on how the varying functionalities enhance or inhibit the rate of oxygen reduction. We are showing that the polymer backbone structure has a larger influence on facilitating favorable reaction kinetics than ionomer to catalysts ratio. The poly(sulfone)-derived ionomers result in a worse activity than electrocatalysts with Nafion® and poly(phenylene)-derived ionomers. They also exhibited more peroxide desorption and greater limitation in the mass transport regime. The poly(phenylene)-derived polymers performed in line with the benchmark ionomer, Nafion®. The poly(phenylene)-derived ionomers show promise as fruitful line of research in establishing an anion-conducting ionomer for alkaline electrolyte fuel cells.
      PubDate: 2013-12-07
       
  • Lactose Electrooxidation on the Nickel Oxide Nanoparticles Electrocatalyst
           Prepared on the Multi-walled Carbon Nanotubes Modified Electrode
    • Abstract: Abstract The preparation of multi-walled carbon nanotubes–NiO nanoparticles composites (MWCNT–NiO) is presented and the composites were used for modification of glassy carbon electrode for lactose electrooxidation in NaOH. Nickel oxide (NiO) was accumulated on multi-walled carbon nanotubes (MWCNT) by pulsed potential electrodeposition. The structure and nature of the MWCNT–NiO were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that NiO nanoparticles were homogeneously electrodeposited on the surfaces of MWCNTs. Also, the electrochemical behaviour of MWCNT–NiO nanoparticles composite in an aqueous solution of alkaline of lactose was studied using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The peak on the voltammogram for MWCNT–NiO composite electrode in alkaline solutions of lactose was observed which was ascribed to the lactose oxidation in alkaline medium. The results obtained are discussed from the point of view of employment of the MWCNT–NiO composites for the catalytic electrodes of sugar-oxygen fuel cells.
      PubDate: 2013-12-07
       
 
 
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