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Journal Cover Electrocatalysis
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1868-2529 - ISSN (Online) 1868-5994
     Published by Springer-Verlag Homepage  [2210 journals]   [SJR: 0.542]   [H-I: 7]
  • The Effect of Reducing Agents on the Electronic, Magnetic and
           
    • Abstract: Abstract The electronic, magnetic and electrocatalytic properties of bimetallic thiol-capped Pt/Co and Pt/Ni nanoparticles were synthesised using two reducing agents, NaBH4 and N2H4. X-ray diffraction analysis of the nanoparticles showed Pt lattice contraction upon the addition of Co or Ni to Pt indicating the formation of an alloy structure, more apparent when N2H4 was used. XPS data analysis revealed Pt metal and Pt(II) (assigned to PtO) and a higher concentration of surface metallic Ni and Co for the NaBH4-reduced samples. Both the NaBH4- and N2H4-reduced catalysts were active for the methanol oxidation reaction (MOR), with the Pt-Co-N2H4 catalyst revealing the highest activity. The N2H4 significantly affected the magnetic properties of Pt/Co and Pt/Ni particles by controlling the morphology and crystalline structure of the nanoparticles. In general, the type of reducing agent affected the final properties of the nanoparticles.
      PubDate: 2014-11-21
       
  • The Hydrogen Evolution Reaction on Rhenium Metallic Electrodes: A Selected
           Review and New Experimental Evidence
    • Abstract: Abstract The volcano plots reported in the field of electrocatalysis utilize data with a difference of three orders of magnitude between the worst and the best rhenium electrocatalytic activity toward the hydrogen evolution reaction (HER). However, the commonly used mean value of the exchange density current (j 0) of the HER on rhenium is log j 0 = −2.9 A cm−2, which is higher than the value used for platinum (log j 0 = −3.3 A cm−2). This fact seems to contradict Sabatier’s principle and points to the possibility that this value corresponds more to rhenized surfaces than to metallic rhenium. Rhenized surfaces are primarily composed of a mixture of oxides; therefore, the electrocatalytic behavior is attributed to these thin films rather than to metallic rhenium. In addition, a selected review of rhenized electrodes is included herein because these issues have not been considered in the electrocatalysis literature at the present time. We initially believed that the kinetic parameters might have been overestimated due to the formation of rhenide ion or rhenium hydride species; however, no evidence of the formation of these species was found. Our experimental mean value of the exchange current density of the HER on metallic rhenium is 7 × 10−5 A cm−2 in acidic solution. Therefore, our results are in accordance with Sabatier’s principle, which states that a weak adsorption energy of hydrogen on rhenium (energy, 6.9 kJ mol−1) results in a slow rate of reaction (log j 0 = −4.2 A cm−2), whereas an intermediate adsorption energy of hydrogen on platinum (12 kJ mol−1) produces a fast reaction (log j 0 = −3.3 A cm−2).
      PubDate: 2014-11-18
       
  • CeO 2 Nanotubes Supported Pd Electrocatalysts for Formic Acid Oxidation
    • Abstract: Abstract CeO2 nanotubes with well-defined hollow interiors are employed as support material for Pd electrocatalysts towards formic acid oxidation (FAO). Pd nanoparticles are deposited both on the outer surfaces and inside interiors of CeO2 nanotubes. The as-prepared Pd catalysts possess a large electrochemical surface area (ESA) and exhibit improved electrocatalytic performance towards FAO in comparison with the Vulcan XC-72 carbon black and the commercial CeO2 powder supported Pd catalysts.
      PubDate: 2014-11-08
       
  • High-Throughput Screening for Acid-Stable Oxygen Evolution
           Electrocatalysts in the (Mn–Co–Ta–Sb)O x Composition
           Space
    • Abstract: Abstract Solar generation of fuel is a promising future energy technology, and strong acidic conditions are highly desirable for integrated solar hydrogen generators. In particular, water splitting near pH 0 is attractive due to the availability of high theoretical efficiency, high performance hydrogen evolution catalysts, and robust ion exchange membranes. The lack of a stable, earth-abundant oxygen evolution catalyst inhibits deployment of this technology, and development of such a material is hampered by the strong anti-correlation between electrochemical stability and catalytic activity of non-precious metal oxides. High-throughput screening of mixed metal oxides offers a promising route to the identification of new stable catalysts and requires careful design of experiments to combine the concepts of rapid experimentation and long-term stability. By combining serial and parallel measurement techniques, we have created a high-throughput platform to assess the catalytic activity of material libraries in the as-prepared state and after 2 h of operation. By screening the entire (Mn–Co–Ta–Sb)O x composition space, we observe that the compositions with highest initial activity comprised cobalt and manganese oxides, but combinations with antimony and tantalum offer improved stability. By combining the desired properties of catalytic activity and stability, the optimal composition regions are readily identified, demonstrating the success and fidelity of this novel high-throughput screening platform.
      PubDate: 2014-11-07
       
  • Effect of Platinum Nanoparticle Loading on Oxygen Reduction at a Pt
           Nanocluster-Activated Microporous–Mesoporous Carbon Support
    • Abstract: Abstract Very high surface area carbon-supported Pt nanoparticle catalysts have been applied to the oxygen reduction reaction in alkaline solution. The distribution effect of deposited Pt nanoparticles onto the carbon support on the oxygen reduction reaction kinetics has been established by comparing the various carbon-supported Pt (20 and 60 wt% metal) catalysts. The various Pt catalysts were prepared by using a sodium borohydride reduction method. All the catalysts showed a face-centered cubic crystal structure as determined by X-ray diffraction method; the average platinum particle sizes were ∼4.2, ∼4.8, ∼5.4, and ∼27.2 nm for 20 wt% Pt–C(Mo2C), 60 wt% Pt–C(Mo2C)-I, 60 wt% Pt–Vulcan XC72, and 60 wt% Pt–C(Mo2C)-II catalysts, respectively. The X-ray photoelectron spectra for all the catalysts indicated that most of the platinum nanoparticles have an oxidation state of 0. The low-temperature N2 sorption, time-of-flight mass spectrometry, scanning electron microscopy, and transmission electron microscopy experiments have been carried out to characterize the structure of prepared materials. The cyclic voltammetry and rotating disk electrode techniques were used to study the oxygen electroreduction kinetics.
      PubDate: 2014-11-07
       
  • An Easy Method for Calculating Kinetic Parameters of Electrochemical
           Mechanisms: Temkin’s Formalism
    • PubDate: 2014-10-31
       
  • Electrodeposition of Pt Nanoparticles on New Porous Graphitic Carbon
           Nanostructures Prepared from Biomass for Fuel Cell and Methanol Sensing
           Applications
    • Abstract: Abstract We investigate the performance of an iron-doped porous graphitic carbon nanostructure (GCN) prepared from biomass for application in fuel cells and electrochemical sensors. By using cyclic voltammetry (CV), we show that these GCNs have appropriate electrochemical properties and exhibit a significantly high catalytic activity toward oxygen reduction without Pt catalyst. The GCNs were also used as a substrate for electrodeposition of Pt nanoparticles (Pt-NPs) to study electro-oxidation and sensing of methanol. The composition of Pt-NPs and GCNs show high catalytic affinity toward electro-oxidation of methanol in an acidic medium. The modified electrode with Pt-NPs and GCNs also could act as an effective sensor for determination of methanol concentration in natural pH. This sensor enables determination of methanol with a wide linear range (0.05–21.73 mM), low detection limit (20 μM, at S/N of 3), high sensitivity (11.49 μA cm−2 mM−1), and long-term stability (over 40 days). The present sensor also has low working potential (0.17 V) making it less prone to an interference effect. The resulting electrodes were characterized by using scanning electron microscopy, energy dispersive X-ray spectroscopy, and CV.
      PubDate: 2014-10-28
       
  • Self-adsorption of an Ultrathin Bismuth Layer in the Size of Ions on an Au
           Surface
    • Abstract: Abstract Molecular self-assembly is an important aspect of bottom-up approaches for the nanofabrication of functional materials. The self-assembly of smaller-size units like ions has yet to be studied further. The self-adsorption of BiIII without applied potential and electrochemical deposition of Bi/BiIII were studied and compared through cyclic voltammetry. Both of them exhibit two pairs of redox peaks assigned to the (2 × 2)-Bi adlayer and incommensurate (p × √3)-2 Bi adlayer. The adsorption of two Bi surface phases is related with the Bi salt concentration and adsorption time. Within a certain concentration or time range, the adsorption approaches to be saturated due to the surface limitation of self-adsorbed surface layers. The (2 × 2)-Bi adlayer firstly adsorbs to the active sites of Au where there is strong interaction between Bi and Au. With the increase of time, more Bi adsorbs onto the unoccupied sites of Au with a relatively weak interaction force to form a denser (p × √3)-2 Bi layer. A new pair of redox peaks appears for the electrodeposition of the Bi/BiIII bulky layer which is easily stripped from the Au surface through a consecutive potential scan. Comparatively speaking, the adsorbed (2 × 2) and (p × √3)-2 Bi adlayers are stable in the same potential scanning condition due to the strong interaction between the two surface Bi layers and the below Au atoms. Such a controllable self-adsorption of the BiIII ultrathin layer on foreign substrates exhibits a potential for the modification of materials in the size of ions.
      PubDate: 2014-10-24
       
  • Selectivity of Nanocrystalline IrO 2 -Based Catalysts in Parallel Chlorine
           and Oxygen Evolution
    • Abstract: Abstract Nanocrystalline electrocatalysts with chemical composition corresponding to Ir1 − x M x O2 (M = Co, Ni, and Zn, 0.05 ≤ x ≤ 0.2) were prepared by the hydrolysis of H2IrCl6·4H2O solutions combined with nitrates and acetates of Ni, Zn, and Co. X-ray diffraction (XRD) analysis indicates that the dopant Co, Ni, and Zn cations substitute the Ir atoms in the rutile lattice. The prepared materials contain small inclusions of iridium metal on the level comparable with the detection of the XRD technique. The local environment of Co and Zn in the doped IrO2 materials conforms to a rutile model with a homogeneous distribution of the doping elements in the rutile lattice. The incorporated Ni is distributed in the rutile lattice non-homogeneously and tends to form clusters within rutile structure. The incorporation of Ni and Co enhances the activity of the prepared electrocatalysts in oxygen evolution. The modification of the IrO2 via doping process alters also the material’s selectivity in the parallel oxygen and chlorine evolution. Incorporation of Co and Zn cations shifts the selectivity of the catalysts toward oxygen evolution in chloride-containing media; the Ni incorporation leads to an enhancement of the selectivity toward chlorine evolution. Chlorine evolution is apparently limited by the number of the active catalytic sites on the electrode surface.
      PubDate: 2014-10-18
       
  • Using the Alkynyl-Substituted Rhenium(I) Complex
           (4,4′-Bisphenyl-Ethynyl-2,2′-Bipyridyl)Re(CO) 3 Cl as Catalyst
           for CO 2 Reduction—Synthesis, Characterization, and Application
    • Abstract: Abstract The synthesis, structure, photophysics, and spectroscopic characterization of an organometallic rhenium multichromophore compound carrying a central 2,2′-bipyridyl acceptor moiety with additional phenylethynyl substituents conjugated at the 4,4′-positions of the acceptor ligands and its effect on the electron density of the central rhenium atom as metal center for CO2 reduction is reported. The results were compared to fac-(2,2′-bipyridyl)Re(CO)3Cl and fac-(5,5′-bisphenylethynyl-2,2′-bipyridyl)Re(CO)3Cl. Cyclovoltammetric studies and rotating disk electrochemistry were performed for electrochemical characterization. Ultraviolet and visible (UV-vis) absorption, Fourier transform infrared (FTIR), and luminescence measurements were carried out for a spectroscopic characterization and compared to theoretical calculations at the density functional theory (DFT) level. In addition, the rhenium complex fac-(4,4′-bisphenyl-ethynyl-2,2′-bipyridyl)-Re(CO)3Cl was used as a novel catalyst for the electrochemical reduction of CO2 in homogeneous solution. Results showed an 11-fold increase in the current density under CO2 saturation and a catalytic second-order rate constant for CO formation of about 560 M−1 s−1 on a Pt working electrode. For further characterization of the CO2 reduction capabilities, bulk controlled potential electrolysis experiments were performed using a CO2-saturated acetonitrile electrolyte solution. The headspace product gas analysis yields CO as main reduction product with faradaic efficiencies of about 12 % over 5-h electrolysis time. Graphical Abstract
      PubDate: 2014-10-15
       
  • In Situ Analysis of Scan Rate Effects on Pt Dissolution Under Potential
           Cycling Using a Channel Flow Double Electrode
    • Abstract: Abstract To investigate the effect of scan rate (ν), the instantaneous dissolution of Pt under potential cycling 0.5–200 mV/s was studied using a channel flow double electrode. In an anodic scan, ν affects the initiation and inhibition of Pt dissolution during oxide formation. Slow scans induce Pt dissolution earlier, but soon suppress it. The extent of dissolution, however, did not show significant changes like the oxide development does when changing the ν. In a cathodic scan, the electrochemical dissolution of Pt2+ during oxide reduction speeds up with ν. The trivial chemical dissolution of unstable PtO2 into Pt4+ also occurs and increases with increasing ν.
      PubDate: 2014-10-11
       
  • On the Temperature Performance of Ethanol Oxidation Reaction at
           Palladium-Activated Nickel Foam
    • Abstract: Abstract The present paper reports on ethanol oxidation reaction (EOR) investigated at catalytically modified nickel foam material. The EOR was studied in 0.1 M NaOH supporting electrolyte on Pd-activated nickel foam catalyst material, obtained by a spontaneous deposition method. Catalytic modification of Ni foam resulted in a composite material having superior EOR kinetics, as elucidated through corresponding values of a.c. impedance-derived charge-transfer resistance parameter (including temperature-dependence of the EOR over the temperature range 20–60 °C). The presence of a catalytic additive was disclosed from SEM and XRD analyses.
      PubDate: 2014-10-01
       
  • Photoelectrocatalytic Degradation of Ofloxacin Using Highly Ordered
           
    • Abstract: Abstract Ofloxacin has been widely used as a form of quinolone antibiotics. However, it has the potential to exert biological effects on aquatic organisms and cause surface water pollution. It is necessary to find an efficient way to remove ofloxacin. This study reports on the degradation of ofloxacin in solution using TiO2 nanotubes (TiO2 NTs) as photocatalyst. The TiO2 NTs were synthesized through anodization. The morphology, elemental composition and state, crystalline phase, and photocatalytic activity of this photocatalyst were characterized by a variety of surface analysis techniques. The obtained TiO2 NTs were applied to ofloxacin degradation by photoelectrocatalysis. The degradation efficiency was assessed by in situ monitoring the UV-vis absorbance spectrum of ofloxacin solution during the degradation process. The effects of initial pH, bias potential, and initial concentration of ofloxacin were investigated systematically. Moreover, the toxicity of ofloxacin during the photoelectrocatalytic degradation process was evaluated using the growth inhibition test with Microcystis aeruginosa. The TiO2 NT-based photoelectrocatalytic method provided a high degradation rate for ofloxacin removal.
      PubDate: 2014-10-01
       
  • The Influence of Pt Oxide Film on the Activity for the Oxygen Reduction
           Reaction on Pt Single Crystal Electrodes
    • Abstract: Abstract Correlation between Pt oxide and the activity for the oxygen reduction reaction (ORR) has been investigated on the low index planes of Pt (Pt(111), Pt(100), and Pt(110)) using voltammogram and rotating disk electrode (RDE). Pt oxide is formed by holding the potential at 1.0 V vs. RHE. The ORR activity decreases with the increase of the time of Pt oxide formation. The order of the ORR activity is Pt(100) < Pt(111) < Pt(110) in 0.1 M HClO4 after the formation of Pt oxide. This order is identical with that without Pt oxides. Formation of hardly reducible Pt oxide deactivates the ORR activity on Pt(111) remarkably. The amount of Pt oxides (PtOH, PtO and hardly reducible Pt oxide) increases as Pt(100) < Pt(111) < Pt(110) at 1.0 V.
      PubDate: 2014-10-01
       
  • The Effect of TiO2 on
           the Catalytic Activity of a PtRu/C Catalyst for Methanol Oxidation
    • Abstract: Abstract In this work, the effect of the addition of different amounts of TiO2 nanotubes to a PtRu catalyst supported on Vulcan XC-72R carbon black for methanol oxidation was studied. Two approaches were used for the catalyst preparation. In the first case, Pt and Ru metal ions were impregnated onto the support (C-TiO2) and subsequently reduced with NaBH4. In the second case, the metal ions were first reduced and then impregnated, in order to obtain a catalyst with metal loading of 30 % of PtRu (50:50 at.% composition of Pt/Ru) and varying concentrations of TiO2 (5–15 wt%); the actual composition was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) analysis. The electrochemical properties were studied via cyclic voltammetry and chronoamperometry in 0.5 M H2SO4 solution. X-ray diffraction analyses indicated the formation of PtRu alloy with different degrees of alloying. The CO-stripping voltammetry studies showed that both the onset potential and the peak potential are dependent on the catalyst composition; the PtRu/C-TiO2(10) exhibited a relatively higher CO oxidation current compared to those exhibited by the other catalysts. Both the linear sweep voltammetry and the chronoamperometric results also demonstrated that the PtRu/C-TiO2(10) catalyst exhibited a higher methanol oxidation current and a lower poisoning rate among the investigated catalysts with various TiO2 nanotube contents (i.e., 0, 5, and 15 % TiO2). The prepared catalysts revealed essentially the same catalytic performance independently of the procedure used for their preparation.
      PubDate: 2014-10-01
       
  • Electrocatalytic Properties of Co-Mo Alloys Electrodeposited from a
           Citrate-Pyrophosphate Electrolyte
    • Abstract: Abstract The electrocatalytic activity of electrodeposits of cobalt and Co-Mo alloys in the electroreduction reaction of hydrogen evolution in an acid, neutral and alkaline media has been studied in this work. To deposit coatings, a nontoxic citrate-pyrophosphate electrolyte was used, which was proposed earlier. It has been found that the alloys having the same chemical composition but a different phase composition can exhibit different electrocatalytic activity. The best electrolyte for the making of catalytically active Co-Mo alloys, for which the decrease in hydrogen evolution overpotential as compared with pure cobalt is about 400 mV at 30 mA cm−2 in alkaline solution, is solution with the cobalt and molybdenum concentration ratio 10:1.
      PubDate: 2014-10-01
       
  • Investigation of a Polyaniline-Coated Copper Hexacyanoferrate Modified
           Glassy Carbon Electrode as a Sulfite Sensor
    • Abstract: Abstract A polyaniline-coated copper hexacyanoferrate modified glassy carbon electrode (PANI/CuHCF/GC) was successfully prepared by cyclic voltammetry, which had higher electrocatalytic activity and good stability toward the oxidation of sulfite. The mechanism and main factors of influencing the electrocatalytic activity for the preparation of PANI/CuHCF/GC were investigated. The results indicated that the optimal concentration of K3Fe(CN)6–CuCl2 (molar ratio of 1:1) and aniline, scanning number of CuHCF particles deposition, and aniline polymerization were 0.6 μmol·L−1, 13, and 15, respectively. The PANI/CuHCF/GC surface properties were characterized by scanning electron microscopy and AC impedance spectra, whose results indicated that CuHCF particles evenly attached to GC surface and the electron transfer impedance was significantly reduced. Sulfite was detected by an amperometric-time (i–t) method, whose linear equation, linear range, and detection limit were Δi (μA) = 0.0624 + 46.42c mmol·L−1 (n = 15, R = 0.9978), 4.3 × 10−6 to 3.9 × 10−4 mol·L−1 and 0.6 μmol·L−1 (S/N = 3), respectively. The response time was less than 1 s. The interference of some common potential substances toward sulfite determination was studied, whose results indicated that PANI/CuHCF/GC electrode had strong anti-interference ability. The PANI/CuHCF/GC was successfully applied to the detection of sulfite in real samples with satisfactory results.
      PubDate: 2014-10-01
       
  • Impedance Spectroscopy and Catalytic Activity Characterization of a
           La0.85Sr       class="a-plus-plus">0.15MnO       class="a-plus-plus">3/Ce       class="a-plus-plus">0.9Gd       class="a-plus-plus">0.1O       class="a-plus-plus">1.95 Electrochemical Reactor
           for the Oxidation of Propene
    • Abstract: Abstract This study aims to characterize the catalytic and electrochemical behavior of a La0.85Sr0.15MnO3/Ce0.9Gd0.1O1.95 porous reactor for the oxidation of propene in the presence of oxygen. The application of anodic polarization strongly increased the propene oxidation rate up to 71 %, although the current efficiency remained low. The effect of prolonged polarization on the reactor catalytic activity was evaluated. Prolonged polarization enhanced both the reactor intrinsic catalytic activity and the electrode performance due to the formation of oxygen vacancies on the electrode surface. Electrochemical impedance spectroscopy was used to investigate the effect of propene introduction on the reactor impedance response. The introduction of propene into reactive system caused a strong increase of electrode resistance, mainly located in the low-frequency region of the impedance spectrum. This effect was caused by the strong adsorption of propene on electrode surfaces inhibiting the adsorption and dissociation of oxygen.
      PubDate: 2014-10-01
       
  • Non-precious Metal Oxygen Reduction Reaction Catalysts Synthesized Via
           Cyanuric Chloride and        class="a-plus-plus">N-Ethylamine
    • Abstract: Abstract Non-precious metal oxygen reduction reaction catalysts were synthesized in this study using novel and cheap nitrogen sources, cyanuric chloride, and N-ethylamine. These materials presented a promising catalytic activity toward the oxygen reduction reaction (ORR) in acid media, which is the most challenging. For the catalyst based on N-ethylamine, the onset potential for ORR is 0.803 V vs reversible hydrogen electrode (RHE) or 0.703 V at 0.1 mA cm−2. The nitrogen source is shown to be extremely important in the final morphology and ORR activity of the catalyst. Steady state ORR polarizations evidenced that the final morphology of the catalysts play a major rule on mass transport in this class of catalysts, with a lamella-like structure being detrimental. Physical characterizations of the catalysts revealed that cyanuric chloride promotes morphology alterations to the carbon support toward a lamella-like structure, while the catalysts synthesized from N-ethylamine retained the nanoparticle structure of the carbon precursor. This catalyst exhibited a Tafel slope of 66 mV per current decade in the lower potential region, with promising four-electron selectivity in a polymer electrolyte fuel cell (PEFC) operational potential.
      PubDate: 2014-10-01
       
  • 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
       
 
 
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