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Journal Cover   Electrocatalysis
  [SJR: 0.883]   [H-I: 10]   [0 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1868-2529 - ISSN (Online) 1868-5994
   Published by Springer-Verlag Homepage  [2280 journals]
  • Polymer of Intrinsic Microporosity Induces Host-Guest Substrate
           Selectivity in Heterogeneous 4-Benzoyloxy-TEMPO-Catalysed Alcohol
    • Abstract: Abstract The free radical 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4B-TEMPO) is active as an electrocatalyst for primary alcohol oxidations when immobilised at an electrode surface and immersed into an aqueous carbonate buffer solution. In order to improve the catalytic process, a composite film electrode is developed based on (i) carbon microparticles of 2–12 μm diameter to enhance charge transport and (ii) a polymer of intrinsic microporosity (here PIM-EA-TB with a BET surface area of 1027 m2 g−1). The latter acts as a highly rigid molecular framework for the embedded free radical catalyst with simultaneous access to aqueous phase and substrate. The resulting mechanism for the oxidation of primary alcohols is shown to switch in reaction order from first to zeroth with increasing substrate concentration consistent with a kinetically limited process with competing diffusion of charge at the polymer layer-electrode interface (here the “LEk” case in Albery-Hillman notation). Reactivity optimisation and screening for a wider range of primary alcohols in conjunction with DFT-based relative reactivity correlation reveals substrate hydrophobicity as an important factor for enhancing catalytic currents. The PIM-EA-TB host matrix is proposed to control substrate partitioning and thereby catalyst reactivity and selectivity. Graphical Abstract The water-insoluble molecular alcohol oxidation catalyst 4-benzoyloxy-TEMPO is employed here embedded in a nano-composite film based on a hydrophobic polymer of intrinsic microporosity (PIM)
      PubDate: 2015-09-29
  • Surface and Catalytical effects on Treated Carbon Materials for Hydrogen
           Peroxide Electrogeneration
    • Abstract: Abstract This work focuses on the catalytic activity and surface modification of Vulcan XC 72R and Printex L6 toward the oxygen reduction reaction (ORR) after the carbon supports were subjected to a pre-treatment with nitric acid or ammonia. The results indicated that acid-treated Printex L6 was the best-suited material toward the two-electron pathway of the ORR. This material contained the largest concentration of oxygenated acid species and hydrogen, as determined by XPS, the Boehm method, and elemental analysis. The enhanced formation of H2O2 for acid-treated Printex L6 can be explained by the presence of oxygenated acid species increasing the hydrophilic character of the carbon support. The hydrophilicity of the material was investigated by contact angle measurements. However, the changes of the surface area, porosity, and the aliphatic chains of the carbons induced by the pre-treatments and the contributions of these factors to H2O2 production cannot be disregarded.
      PubDate: 2015-09-28
  • Evaluation of Polycrystalline Platinum and Rhodium Surfaces for the
           Electro-Oxidation of Aqueous Sulfur Dioxide
    • Abstract: Abstract Polycrystalline Rh and Pt were studied to ascertain their electrocatalytic activity for the electro-oxidation of SO2, an important reaction in sulfur dioxide depolarized electrolyzers used to produce hydrogen. Cyclic voltammetry and linear polarization methods were employed to evaluate the catalytic activity of these surfaces. Rh exhibited 25-fold lower catalytic activity than Pt and was more susceptible to poisoning by adsorbed intermediate sulfur species. Koutecky-Levich analysis indicated a two-electron transfer reaction on the Pt surface, which corresponded to the most commonly accepted SO2 electro-oxidation reaction mechanism. The Tafel slopes in the low potential region (near the onset potential), in conjunction with an analysis of well-known reaction mechanisms, suggested that the step leading to the oxidation of water to form adsorbed hydroxyl species was the rate-determining step (RDS). This mechanistic model predicts a decrease in Tafel slope with increasing coverage of catalyst active surface sites by adsorbed sulfur species. For Pt, we estimate a surface sulfur coverage of 4 % based on the experimentally measured Tafel slope. In the case of Rh, the sulfur coverage was calculated to be approximately 1 %. The Tafel slopes obtained changed from 106 mV decade−1 for Rh and 80 mV decade−1 for Pt at potentials below 0.7 V vs. standard hydrogen electrode (SHE) to 210 mV decade−1 for Rh and 162 mV decade−1 for Pt at potentials above 0.7 V vs. SHE, suggesting a change in the reaction mechanism corresponding to a change in the surface of the electrocatalyst.
      PubDate: 2015-09-23
  • Study of 2-Propanol, 1-Propanol, and Acetone Electrochemical Oxidation on
           Pt in Gelled Phosphoric Acid at 170 °C
    • Abstract: Abstract Electrochemical oxidation of acetone, 2-propanol, and 1-propanol on Pt was studied by slow scan rate voltammetry at 170 °C using fuel cell with the membrane of the H3PO4 doped polybenzimidazole. Reaction rate orders with respect to partial pressures of the aliphatic compounds and water vapors were determined at E = 0.5 V and at E = 0.9 V, which correspond to low and high surface oxide coverages on Pt. At E = 0.5 V close to zero reaction rate orders in respect to vapor pressures of aliphatic reactants were found. At E = 0.5 V reaction, rate orders with respect to water vapor pressure were slightly higher than unity in all cases. At E = 0.9 V oxidation, reaction rate orders with respect to aliphatic reactant vapor pressure ranged within 0.6–1. Close to zero reaction rate orders with respect to water vapor pressure were found in all cases at E = 0.9 V.
      PubDate: 2015-09-10
  • The Effect of Rapid Thermal Annealing on Sputtered Pt and Pt 3 Pd 2 Thin
           Film Electrocatalysts for Aqueous SO 2 Electro-Oxidation
    • Abstract: Abstract Insight into the effect that rapid thermal annealing (RTA) has on the structural and electrochemical characteristics of sputtered Pt and Pt3Pd2 thin film electrocatalysts is communicated. The DC magnetron sputtered thin films were rapidly annealed at temperatures ranging from 600 to 900 °C under an Ar atmosphere. The microstructural changes and electrochemical properties (onset potential, current density and stability) induced by rapid thermal annealing were investigated towards the electro-oxidation of aqueous SO2. An increase in annealing temperature induced different degrees of crystallinity, and the surfaces changed from being smooth and granular to surfaces exhibiting defined grain boundaries. Electrochemical characterisation, employing linear polarisation (LP) and cyclic voltammetry (CV), revealed improved catalytic activity for the Pt3Pd2 thin film catalysts (compared to Pt) exhibiting lower onset potentials, competitive currents and acceptable stability. The Pt3Pd2 thin film, annealed at 800 °C, proved to be a promising contender in competing with pure Pt towards the electro-oxidation of aqueous SO2.
      PubDate: 2015-09-10
  • Effect of the OH − /Pt Ratio During Polyol Synthesis on Metal
           Loading and Particle Size in DMFC Catalysts
    • Abstract: Abstract A systematic variation of the molar ratio between hydroxide ions and platinum during polyol synthesis of Pt electrocatalysts supported on carbon nanotubes was conducted. The resulting materials were physically characterized by transmission electron microscopy, thermogravimetric analysis, and X-ray diffraction. It could be shown that precise control of the OH−/Pt ratio is necessary for achieving small-sized uniformly distributed Pt nanoparticles at high chemical yield. Simple adjustment of the pH value is not sufficient to control the reduction conditions since even small pH variations give rise to significant changes of the catalyst properties. The optimal OH−/Pt molar ratio was found to be 5:1 resulting in small particle size (ca. 2.5 nm in diameter) and high platinum loading (ca. 39 wt% at a nominal loading of 40 wt%). Moreover, we have shown that the developed electrocatalyst exhibits a high activity toward the oxygen reduction reaction which is confirmed by half-cell experiments in a rotating disk electrode and in single-cell experiments in direct methanol fuel cells.
      PubDate: 2015-09-03
  • PtAu Electrocatalyst for Glycerol Oxidation Reaction Using a
           ATR-FTIR/Single Direct Alkaline Glycerol/Air Cell In Situ Study
    • Abstract: Abstract Different ratios of PtAu/C electrocatalysts were synthesized and assessed for their capability by glycerol electrooxidation. Electrocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), chronoamperometry, and direct glycerol/air fuel cell coupled with a ATR-FTIR setup. XRD of PtAu/C electrocatalysts showed the presence of Pt (fcc), Au (fcc), and PtAu (fcc) phases, and TEM images for PtAu/C electrocatalysts showed particle size between 5.4 and 5.8 nm. PtAu/C (50:50) presented the best result for glycerol electrooxidation by cyclic voltammetry and chronoamperommetry measurements in comparison with other electrocatalysts prepared. All PtAu/C showed better performance in comparison with Pt/C and Au/C. Moreover, the addition of gold to platinum favored glycerol by electronic effect and bifunctional mechanism. Through ATR-FTIR/direct alkaline glycerol/air cell in-situ study, it was possible to identify glycerate and tartronate as main products formed during the electrochemical glycerol oxidation.
      PubDate: 2015-09-03
  • Photoelectrochemical Treatment of α,β-Unsaturated Ketones on TiO
           2 -RuO 2 /Ti Electrode
    • Abstract: Abstract The photoelectrochemical degradation of structurally similar α,β-unsaturated ketones such as 4-phenyl-3-buten-2-one (benzylideneacetone), 1-(p-totyl)-1-penten-3-one, 4-(p-totyl)-3-buten-2-one, and 4-mesityl-3-buten-2-one has been investigated. Their susceptibility to oxidation and reduction was determined on the basis of voltammetric measurements. It was found that the more methyl groups are attached to the aromatic ring, the oxidation and reduction occurs easier. Among electrodes with different molar ratio of TiO2 and RuO2 (also modified with transition metals oxides: Nb2O5, ZrO2, and Y2O3), TiO2 (70 %)-RuO2 (30 %)/Ti electrode was selected for photoelectrochemical reaction as the optimum one. The photocatalytic activity of the analyzed materials has been determined on the basis of the photocurrent generated in KCl and NaClO4 solutions. The highest mineralization was achieved for benzylideneacetone while the lowest was for 4-mesityl-3-buten-2-one using current intensity of 0.3 A and UV radiation with the wavelength of 254 nm during 120 min.
      PubDate: 2015-09-02
  • Achievements and Trends in Photoelectrocatalysis: from Environmental to
           Energy Applications
    • Abstract: Abstract The great versatility of semiconductor materials and the possibility of generation of electrons, holes, hydroxyl radicals, and/or superoxide radicals have increased the applicability of photoelectrocatalysis dramatically in the contemporary world. Photoelectrocatalysis takes advantage of the heterogeneous photocatalytic process by applying a biased potential on a photoelectrode in which the catalyst is supported. This configuration allows more effectiveness of the separation of photogenerated charges due to light irradiation with energy being higher compared to that of the band gap energy of the semiconductor, which thereby leads to an increase in the lifetime of the electron-hole pairs. This work presents a compiled and critical review of photoelectrocatalysis, trends and future prospects of the technique applied in environmental protection studies, hydrogen generation, and water disinfection. Special attention will be focused on the applications of TiO2 and the production of nanometric morphologies with a great improvement in the photocatalyst properties useful for the degradation of organic pollutants, the reduction of inorganic contaminants, the conversion of CO2, microorganism inactivation, and water splitting for hydrogen generation.
      PubDate: 2015-09-01
  • PdAu/C Electrocatalysts as Anodes for Direct Formate Fuel Cell
    • Abstract: Abstract PdAu/C electrocatalysts in different atomic ratios (90:10, 80:20, 70:30, and 50:50) supported on Vulcan XC72 carbon were evaluated toward formate oxidation in alkaline media. The materials were prepared by the borohydride process. X-ray diffraction (XRD) patterns of PdAu materials showed peak characteristic of Pd and Au face-centered-cubic (fcc) structures while transmission electron micrographs (TEM) showed the nanoparticles with particle size between 4 and 10 nm for all electrocatalysts. Experiments considering single cell suggested the PdAu/C (90:10) and PdAu/C (80:20) as promisors for formate oxidation. The best result obtained was attributed to the presence of Au in small quantities that contributes to the formate adsorption.
      PubDate: 2015-09-01
  • Overlayer Au-on-W Near-Surface Alloy for the Selective Electrochemical
           Reduction of CO 2 to Methanol: Empirical (DEMS) Corroboration of a
           Computational (DFT) Prediction
    • PubDate: 2015-08-27
  • The Synthesis of Metallic β-Sn Nanostructures for Use as a Novel Pt
           Catalyst Support and Evaluation of Their Activity Toward Methanol
    • Abstract: Abstract This study offers a unique insight into the use of high surface area metallic tin as support material for platinum catalysts for fuel cell application. We have synthesized high surface area metallic β-tin nanostructures (TNSs) in aqueous solutions by novel one-pot process and used it as a platinum catalyst support in methanol electrooxidation reaction. Rigorous study of parameters controlling the size and shape of TNSs was performed, including selected surfactant molecules at various concentrations, tin salts, and the addition of sodium citrate. Rod-shaped particles with a 50-nm diameter and 500-nm length were obtained from solutions of selected surfactant in concentrations of 1–20 mM by sodium borohydride reduction. These particles had a β-Sn crystalline core with a main lattice plane of (101) and were covered by a 4-nm oxide shell. A maximal surface area of 170 m2 g−1 was measured from a sample prepared by using low concentration of sodium dodecyl sulfate (SDS) (1 mM). This sample is composed of nanorods and nano semi-spherical shape tin particles. Addition of sodium citrate, which acts as a Sn2+ ion ligand, yields longer rods. Electrochemical oxidation of methanol on platinum catalyst, supported on metallic Sn nanostructure, exhibits a high activity, which is comparable to commercial carbon-supported platinum catalysts. In situ surface-enhanced Raman (SER), emphasizing the role of surface oxides on the methanol oxidation activity, further studied methanol oxidation on Pt/TNS, Pt/C, and Pt-Sn alloy catalyst.
      PubDate: 2015-08-27
  • NiO/MWCNT Catalysts for Electrochemical Reduction of CO 2
    • Abstract: Abstract This communication reports the electrochemical reduction of CO2 on high surface area NiO/multi-walled carbon nanotube (MWCNT) catalysts. The catalysts are prepared by an incipient wetness technique with different NiO loadings. The prepared catalysts are characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) techniques. A conventional two compartments half-cell and a reverse fuel cell are employed to establish the effects of variation of NiO loading on MWCNT. The characterization results indicate that high surface area of MWCNT provides good NiO dispersion on the catalyst surface. The NiO on MWCNT also shows high electrical conductivity in the fuel cells. In CO2 reduction, the catalysts demonstrate good CO2 conversion activity and produce high-pressure effects even at ambient conditions. The reduction product mainly contains syngas (CO and H2). In half-cell evaluation, an increase in current is observed with increasing NiO content up to 20 wt%. Further increase of NiO loading shows no significant increase in current density. Among the studied catalysts, NiO (20 wt%)/MWCNT displays optimum activity in both the half-cell and reverse fuel cell evaluations. With this catalyst, the total faradaic efficiency of 35.2 % is obtained at the potential of −1.7 V versus normal hydrogen electrode (NHE).
      PubDate: 2015-08-14
  • Electrochemical Hydrogen Oxidation on Pt(100): a Combined Direct Molecular
           Dynamics/Density Functional Theory Study
    • Abstract: Abstract We have studied the hydrogen oxidation reaction on various catalytic sites at the water/Pt(100) interface with first-principles direct molecular dynamics and minimum energy pathway calculations. The calculations indicate that the mechanism for electro-oxidation of H2 on terrace sites of the Pt(100) surface depends on the concentration of inactive adsorbed hydrogen on the electrode surface. Near the reversible potential, the electro-oxidation follows the Tafel-Volmer homolytic cleavage of H2 at low coverage of adsorbed hydrogen. If the surface is covered with ca. 1 monolayer of hydrogen, however, the oxidation proceeds by the Heyrovsky-Volmer mechanism. We found good agreement between measured and predicted Tafel plots, indicating that hydrogen oxidation/reduction reaction on Pt(100) takes place via the Heyrovsky-Volmer mechanism under ca. 1 monolayer coverage of inactive adsorbed hydrogen.
      PubDate: 2015-08-09
  • First Insight into Fluorinated Pt/Carbon Aerogels as More
           Corrosion-Resistant Electrocatalysts for Proton Exchange Membrane Fuel
           Cell Cathodes
    • Abstract: Abstract This study evaluates the fluorination of a carbon aerogel and gives first insights into its durability when used as platinum electrocatalyst substrate for proton exchange membrane fuel cell (PEMFC) cathodes. Fluorine has been introduced before or after platinum deposition. The different electrocatalysts are physico-chemically and electrochemically characterized, and the results discussed by comparison with commercial Pt/XC72 from E-Tek. The results demonstrate that the level of fluorination of the carbon aerogel can be controlled. The fluorination modifies the texture of the carbons by increasing the pore size and decreasing the specific surface area, but the textures remain appropriate for PEMFC applications. Two fluorination sites are observed, leading to both high covalent C-F bonds and weakened ones, the quantity of which depends on whether the treatment is done before or after platinum deposition. The order of the different treatments is very important. Indeed, the presence of platinum contributes to the fluorination mechanism, but leads to amorphous platinum, which is demonstrated rather inactive towards the oxygen reduction reaction. On the contrary, a better durability was demonstrated for the fluorinated and then platinized catalyst compared both to the same but not fluorinated catalyst and to the reference commercial material (based on the loss of the electrochemical real surface area after accelerated stress tests).
      PubDate: 2015-08-08
  • The Formation of Surface Oxides on Nickel in Oxalate-Containing Alkaline
    • Abstract: Abstract The electrochemical formation of α-Ni(OH)2 and NiOOH in the presence of adsorbed oxalate in alkaline media is studied under well-controlled experimental conditions that include the variation of the system temperature (T = −10 to 20 °C), the scan rate (v = 20, 150, and 200 mV s−1), and the concentration of supporting electrolyte (0.10 and 0.50 M KOH). The studies are carried out using cyclic voltammetry (CV) with polycrystalline bulk nickel and nickel foams. In situ infrared spectroscopy with voltammetry confirms the adsorption of oxalate to the surface of nickel in the 0.10 to 0.30 V potential window, concurrent with the formation of the α-Ni(OH)2 species. The presence of oxalate in the system increases the charge density (Q) for the formation of both the α-Ni(OH)2 and NiOOH surface oxides. The Q values calculated under various conditions indicate that the presence of oxalate in the system encourages the formation of a full single monolayer (ML) of NiOOH in the first CV scan. Measurements carried out at room temperature demonstrate that an increase in v decreases the Q values for NiOOH in the presence of oxalate to minimum values achieved at v ≥150 mV s−1. An increase of KOH concentration results in the formation of a thicker layer of NiOOH both in the presence and absence of oxalate. The Q values of NiOOH reduction in conditions that favor the formation of one complete monolayer of NiOOH are used to calculate the specific surface areas of open-cell nickel foams. The calculation of electrochemical surface area using this method is discussed and evaluated with respect to calculations based on the charge of α-Ni(OH)2 formation.
      PubDate: 2015-07-30
  • Ordered Intermetallic Nanostructured PtSb/C for Production of Energy and
    • Abstract: Abstract This paper has evaluated ordered intermetallic nanostructured PtSb/C as anode for glycerol electrochemical oxidation in both acidic and alkaline media. Nanostructured PtSb/C performed as well as and 50 % better than commercially available Pt/C nanoparticles in acidic and basic media, respectively. The presence of Sb atoms in the material structure enhanced C-C bond cleavage activation in alkaline medium. Spectroelectrochemical studies confirmed that the reactions conducted in acidic and alkaline solutions produced high-value chemicals. Depending on the nature of the employed electrolyte, the nanostructured PtSb/C material can potentially afford interesting compounds for the chemical industry or even generate electrical energy.
      PubDate: 2015-07-28
  • Enhanced Oxygen Reduction Reaction Activity with Electrodeposited Ag on
           Manganese Oxide–Graphene Supported Electrocatalyst
    • Abstract: Abstract Manganese oxide-modified graphene nanosheet-supported silver nanocatalyst (Ag-MnOx/G) was prepared via two-step chemical and electrochemical deposition. Surface characterization of the prepared Ag-MnOx/G catalyst was performed by X-ray photoelectron spectroscopy, scanning electron microscopy, as well as X-ray fluorescence techniques, and the electrocatalytic activity toward the oxygen reduction reaction (ORR) in alkaline media was studied using cyclic voltammetry and the rotating disk electrode (RDE) method. The onset potential of the ORR of the prepared catalyst material shifted positive about 40 mV, and the half-wave potential 20 mV compared to those of the bulk Ag electrode. After 1000 potential cycles between 0.05 and 1.1 V for accelerated aging tests, high stability of the Ag-MnOx/G catalyst in the ORR was observed with the half-wave potential of the ORR shifting negatively only about 0.04 V. RDE studies displayed unconditional improvement of electrochemical activity and long-term durability for the Ag-MnOx/G composite material.
      PubDate: 2015-07-23
  • Influence of Vanadium Ions on the Degradation Behavior of Platinum
           Catalysts for Oxygen Reduction Reaction
    • Abstract: Abstract The vanadium air redox flow battery is a combination of a redox flow battery and a reversible fuel cell. For the oxygen reduction during discharge, platinum (Pt) catalysts are common. During operation, vanadium (V) cations can penetrate through a proton exchange membrane into the water/air half-cell. The aim of the present work is to study whether V compounds are deposited on the Pt surface under operation conditions or whether the V ions influence the stability of Pt in any other way. Thereby, bulk platinum electrodes are compared as a simple model system to carbon-supported Pt nanoparticles via cyclic voltammetry. In the case of bulk platinum, electrochemical quartz crystal microbalance measurements showed no deposition of vanadium compounds but indicated the decrease of the (hydr)oxide layer on Pt above V3+ and VO2+ redox potentials. Cycling 100 times between oxygen reduction and oxygen evolution potentials with and without a heavy V contamination did not lead to significant degradation of the model catalyst and shows no influence of V ions. On the contrary, the nanoparticle-based catalyst significantly degraded during the same stability protocol. The V contamination lowered the degradation in this case.
      PubDate: 2015-07-15
  • Kinetic Investigations of Glycerol Oxidation Reaction on Ni/C
    • Abstract: Abstract This study evaluates the electrochemical oxidation of glycerol using a nickel-supported catalyst under several well-defined experimental conditions. The influence of scan rate, temperature, glycerol, and NaOH concentrations were systematically investigated. The slope of the log-log relationship of the anodic peak current for glycerol oxidation as a function of the scan rate indicates that the electrochemical glycerol oxidation is a complex mechanism partially limited by diffusion-controlled process. This is in agreement with the temperature effect on glycerol oxidation, since the slope value associated with the relationship between the logarithm of the current density of the anodic peak and the inverse of temperature also indicates a diffusion process. When the glycerol concentration increases, the peak associated to its oxidation also increases, but it seems to reach a limit. This behavior was associated with two main effects, i.e., the saturation of the active catalytic sites on the electrode surface and the change in the glycerol oxidation mechanism as demonstrated by FTIR spectroscopic measurements.
      PubDate: 2015-06-05
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