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Journal Cover Electrocatalysis
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1868-2529 - ISSN (Online) 1868-5994
     Published by Springer-Verlag Homepage  [2208 journals]   [SJR: 0.542]   [H-I: 7]
  • Electrochemical Growth of Surface Oxides on Nickel. Part 3: Formation of
           β-NiOOH in Relation to the Polarization Potential, Polarization Time,
           and Temperature
    • Abstract: Abstract Electro-oxidation of surface β-Ni(OH)2 residing on metallic Ni to β-NiOOH was studied in 0.5 M aqueous KOH at 277 K ≤ T ≤ 318 K by means of cyclic voltammetry (CV) and chrono-amperometry (CA). The process is accompanied by a diffusion of H+ within the surface oxide phase. The formation of β-NiOOH gives rise to an anodic peak in CV profiles, the potential of which depends on the scan rate (s). An analysis of the relation between the anodic peak current density (j peak, AN) and s indicates that the growth of β-NiOOH is controlled by the diffusion of H+ and its modelling leads to the determination of the diffusion coefficient of H+ (D(H+)). In the case of 277 K ≤ T ≤ 318 K, the values of D(H+) are of the order of 10–11 cm2 s–1, when calculated with respect to the electrode’s geometric surface area (A geom), and of the order of 10–12 cm2 s–1, when calculated with respect to the electrochemically active surface area (A ecsa). The activation Gibbs energy of H+ diffusion (Δdiff G ≠(H+)) is in the 19.5–22.6 kJ mol–1 range. Chrono-amperometry transients for the formation of β-NiOOH are analyzed on the basis of finite-space diffusion, with the assumption that β-NiOOH can be formed through three mechanistic pathways. The values of D(H+) determined for both A geom and A ecsa using this approach are of the order of 10–12 cm2 s–1. They are smaller than the analogous values of D(H+) determined on the basis of CV measurements but the values of Δdiff G ≠(H+) obtained using these two experimental approaches are comparable.
      PubDate: 2014-07-20
  • On the Temperature Dependence of Hydrogen Evolution Reaction at Nickel
           Foam and Pd-Modified Nickel Foam Catalysts
    • Abstract: Abstract This communication reports on hydrogen evolution reaction (HER), studied at Ni foam and Pd-activated nickel foam materials in 0.1-M NaOH solution over the temperature range of 20–60 °C. Catalytic modification of Ni foam leads to significant facilitation of temperature-dependent HER kinetics, manifested through radically reduced values of charge-transfer resistance parameter, as well as substantially modified Tafel polarization curves. The presence of a catalytic additive (Pd) is evidenced through scanning electron microscopy (SEM) analysis.
      PubDate: 2014-07-17
  • CO2 Electroreduction
           on Cu-Modified Platinum Single Crystal Electrodes in Aprotic Media
    • Abstract: Abstract Techniques of electrode modification by copper deposits are developed that allow obtaining compact bulk quasi-epitaxial deposits on basal Pt(hkl) single crystal faces. The issues of the deposit roughness and characterization are discussed. Problems of drying and transferring electrodes with copper deposits into other solutions are considered. The obtained deposits are used for CO2 electroreduction in propylene carbonate and acetonitrile solutions of 0.1 M TBAPF6, and the relationship between the electrode surface structure and its electrocatalytic activity in CO2 electroreduction is discussed. We also demonstrate that the restructuring of Cu deposits occurs upon CO2 electroreduction. Complementary reactivity studies are presented for bare Pt(hkl) and Cu(hkl) single crystal electrodes. Cu-modified Pt(hkl) electrodes display the highest activity as compared to bare Pt(hkl) and Cu(hkl). Particularly, the Cu/Pt(110) electrode shows the highest activity among the electrodes under study. Such high activity of Cu/Pt(hkl) electrodes can be explained not only by the increasing actual surface area but also by structural effects, namely by the presence of a large amount of specific defect sites (steps, kinks) on Cu crystallites.
      PubDate: 2014-07-16
  • Electrochemical Behaviour of PSS-Functionalized Silica Films Prepared by
           Electroassisted Deposition of Sol–Gel Precursors
    • Abstract: Abstract Porous, electrically insulating SiO2 layers containing polystyrene sulfonate (PSS) were deposited on glassy carbon electrodes by an electrochemically assisted deposition method. The obtained material was characterized by microscopic, spectroscopic and thermal techniques. Silica-PSS films modify the electrochemical response of the glassy carbon electrodes against selected redox probes. Positively charged species show reduced diffusivities across the SiO2-PSS pores, which resulted in a concentration ratio higher than 1 for these species. The opposite behaviour was found for negatively charged redox probes. These observations can be interpreted in terms of the different affinity of the GC/SiO2-PSS-modified electrode for the electroactive species, as a consequence of the negatively charged porous silica.
      PubDate: 2014-07-04
  • 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: 2014-07-01
  • 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: 2014-07-01
  • Hierarchically Structured Non-PGM Oxygen Reduction Electrocatalyst Based
           on Microemulsion-Templated Silica and Pyrolyzed Iron and Cyanamide
    • 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: 2014-07-01
  • 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: 2014-07-01
  • Electrooxidation of NaBH       class="a-plus-plus">4 in Alkaline Medium on
           Well-defined Pt Nanoparticles Deposited onto Flat Glassy Carbon Substrate:
           Evaluation of the Effects of Pt Nanoparticle Size, Inter-Particle
           Distance, and Loading
    • Abstract: Abstract Well-defined Pt nanoparticles deposited at smooth glassy-carbon (GC) surfaces were elaborated and thoroughly characterized. Using such model Pt/GC surfaces enabled demonstrating that the borohydride oxidation reaction (BOR) is subjected to nanoparticle size and ensemble effects: larger particle diameter and shorter inter-particle distance yield faster BOR kinetics and larger faradaic efficiency. As previously noted for smooth Pt (and Au) surfaces, the Pt/GC nanoparticles are self-poisoned in the course of the BOR; surprisingly, such poisoning also proceeds in open-circuit conditions. The adsorbed intermediates formed in the course of the step-wise electrooxidation and heterogeneous hydrolysis processes are most likely yielding the Pt surface blocking below E = 0.6 V vs. Reversible Hydrogen Electrode (RHE). This blocking is, however, reversible, since incursions to potentials E > 0.6 V vs. RHE enable cleaning the Pt surface. Finally, comparing smooth Pt/GC surfaces to volumic active layers composed of Pt/carbon black (CB) demonstrates that the intrinsic activity/faradaic efficiency of the Pt nanoparticles may strongly be biased by mass-transport effects within the active layer. Larger (apparent) faradaic efficiency and lower BOR onset potential are observed for thick active layers, whereas the specific activity in these is artificially lowered following effectiveness factor well below unity in that case. As a result, the determination of the intrinsic activity of an electrocatalytic material should only be done with tremendous care and with a perfect control of the electrode/surface morphology, texture and structure.
      PubDate: 2014-07-01
  • 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: 2014-07-01
  • 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: 2014-07-01
  • 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: 2014-07-01
  • Electrocatalytic Oxygen Evolution on Electrochemically Deposited Cobalt
           Oxide Films: Comparison with Thermally Deposited Films and Effect of
           Thermal Treatment
    • Abstract: Abstract Electrocatalytic cobalt oxide layers have been prepared on nickel substrates using thermal decomposition and electrochemical deposition methods. Importantly, it was confirmed that the electrochemical deposition method could be applied to nickel foam substrates for use in zero-gap alkaline water electrolysis cells. The oxide layers produced were then investigated for their activity towards the oxygen evolution reaction in 30 wt % KOH solution and found to be superior compared with the uncoated nickel substrate. Layers produced by both methods had similar electrochemical behaviour, provided that the layers were annealed at temperatures ≥350 ∘C. This thermal treatment was required to mechanically stabilise the electrochemically deposited cobalt oxide layer. Due to this finding, the effect of annealing temperature was investigated for the electrochemically deposited layer, and it was found that the overpotential for oxygen evolution increased with increasing annealing temperature. Using cyclic voltammetry and impedance spectroscopy, it is concluded that the decrease in performance with increasing annealing temperature is largely caused by the corresponding decrease in active surface area. However, for annealing temperatures ≥400 ∘C, additional resistances are introduced that cause lower performance. The impedance data suggest that these additional resistances are caused by either a decrease in the conductivity of the cobalt oxide layer itself, or the formation of a passivating-like nickel oxide layer between the active cobalt oxide and the nickel substrate, or both. The resistances’ dependence on potential suggests that they originate from a semi-conducting material and these additional resistances ultimately give rise to non-linear Tafel behaviour.
      PubDate: 2014-06-22
  • Electrochemical and Fuel Cell Evaluation of PtIr/C Electrocatalysts for
           Ethanol Electrooxidation in Alkaline Medium
    • Abstract: Abstract PtIr/C electrocatalysts prepared by borohydride reduction process were characterized by X-ray diffraction, transmission electron microscopy, and cyclic voltammetry. The X-ray diffraction measurements suggested the PtIr alloy formation; furthermore, peaks of IrO2 were not observed; nevertheless, the presence of Ir oxides in small amounts and amorphous forms cannot be discarded. The transmission electron microscopy showed the average particle diameter between 4.0 and 6.0 nm for all compositions prepared. The catalytic activity for ethanol electrooxidation in alkaline medium at room temperature (cyclic voltammetry and chronoamperometry results) showed that PtIr/C (70:30) and PtIr (90:10) exhibited higher performance toward ethanol oxidation than the other electrocatalysts. Experiments using direct ethanol alkaline fuel cell at 75 °C showed PtIr (90:10) as the best electrocatalyst and Ir/C as virtually inactive for ethanol oxidation in real conditions. The best result obtained using PtIr/C may be associated to the electronic effect between Pt and Ir that could decrease the poisoning on catalyst surface and also by the occurrence of bifunctional mechanism.
      PubDate: 2014-06-21
  • In Search of the Best Iron N       class="a-plus-plus">4-Macrocyclic Catalysts
           Adsorbed on Graphite Electrodes and on Multi-walled Carbon Nanotubes for
           the Oxidation of        type-small-caps">l-Cysteine by Adjusting the
           Fe(II)/(I) Formal Potential of the Complex
    • Abstract: Abstract The redox potential of macrocyclic complexes is a very predictive reactivity index for the electrocatalytic activity of these molecules, and it can be easily measured under the same conditions of the catalysis experiments. It reflects directly the activity of a given complex. We have investigated the effect of the Fe(II)/(I) formal potential on the catalytic activity of a series of Fe porphyrins and Fe phthalocyanines for the electrooxidation of l-cysteine, with the complexes directly adsorbed on ordinary pyrolytic graphite or adsorbed on multi-walled carbon nanotubes (MWCNTs) deposited on graphite. A correlation of log j (at constant potential) versus the Fe(II)/(I) formal potential of the catalysts gives a volcano curve for both systems without and with MWCNTs with higher activities in the latter case. Our results clearly show that the highest catalytic activity is achieved in a rather narrow potential window of Fe(II)/(I) formal potentials of N4-macrocyclic complexes. The use of MWCNTs as supporting material for the catalysts does not change the reactivity trends of the Fe complexes.
      PubDate: 2014-06-18
  • Fabrication of Nanostructured Palladium Within Tridentate
           Schiff-Base-Ligand Coordination Architecture: Enhancement of
           Electrocatalytic Activity Toward CO       class="a-plus-plus">2 Electroreduction
    • PubDate: 2014-05-22
  • Heterogenization of a Water-Insoluble Molecular Complex for Catalysis of
           the Proton-Reduction Reaction in Highly Acidic Aqueous Solutions
    • PubDate: 2014-04-26
  • Direct Dimethyl Ether Fuel Cell with Much Improved Performance
    • Abstract: Abstract Due to several apparent advantages over methanol, dimethyl ether (DME) has been viewed as a promising alternative fuel for direct fuel cell technology. Similar to methanol, DME oxidation requires a surface oxidant, such as OH, for the removal of adsorbed CO. Consequently, the reaction occurs at much faster rates on binary PtRu catalysts than Pt alone. In this work, PtRu catalysts with a wide variety of Pt-to-Ru ratios were systematically studied in the direct DME fuel cell (DDMEFC) operating at 80 °C. A Pt50Ru50 catalyst was found to perform the best at high and middle voltages, while a Pt80Ru20 catalyst performed best at low voltages. DDMEFC operation conditions, such as DME flow rate, anode back pressure, DME-to-water molar ratio, and membrane thickness, were also studied in order to maximize the cell performance. A maximum power density of 0.12 W cm−2 obtained in this work exceeds the highest reported DME performance. In comparison with the direct methanol fuel cell (DMFC), the optimized DDMEFC performs better at cell voltages higher than 0.55 and 0.49 V with feed concentrations of methanol of 0.5 and 1.0 M, respectively.
      PubDate: 2014-04-04
  • Understanding Catalyst Layer Degradation in PEM Fuel Cell Through
           Polarization Curve Fitting
    • PubDate: 2014-04-04
  • New Electrocatalysts with Pyrolyzed Siloxane Matrix
    • Abstract: Abstract In a first screening, platinum nanoparticles in pyrolyzed siloxane matrices with additional carbon fillers were developed and tested for their use as electrocatalysts. The influence of various parameters - type of carbon filler, carbon content, pyrolysis temperature, and siloxane composition - on structural properties and on electrochemical activity was investigated. Homogeneous distributions of platinum nanoparticles could be obtained for most of these electrocatalysts. Uniform platinum particles were generated with average particle sizes of 2.5–4.7 nm. At a temperature of 300 °C, the siloxane-based electrocatalysts exhibit high thermal stabilities with maximum weight losses of around 8 wt% after 20 h. The electrochemical behavior of the siloxane-based electrocatalysts in contact with 0.1 M H2SO4 was studied by cyclic voltammetry. Electrocatalytic activities were studied by CO adlayer oxidation, which also served for determining the electrochemical active surface area. High electrochemically active surface areas with up to 50 m2 g−1 Pt were obtained, which are in the same range as carbon-based electrocatalysts. Interestingly, some siloxane-based electrocatalysts showed a slightly higher catalytic activity for CO adlayer oxidation than carbon-based materials.
      PubDate: 2014-04-03
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