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Journal Cover Electrocatalysis
  [SJR: 0.883]   [H-I: 10]   [1 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  [2281 journals]
  • Atomistic Mechanism of Pt Extraction at Oxidized Surfaces: Insights from
    • Abstract: Abstract In this article, we propose a novel mechanism for the atomic-level processes that lead to oxide formation and eventually Pt dissolution at an oxidized Pt(111) surface. The mechanism involves a Pt extraction step followed by the substitution of chemisorbed oxygen to the subsurface. The energy diagrams of these processes have been generated using density functional theory and were analyzed to determine the critical coverages of chemisorbed oxygen for the Pt extraction and Oads substitution steps. The Pt extraction process depends on two essential conditions: (1) the local coordination of a Pt surface atom by three chemisorbed oxygen atoms at nearest-neighboring fcc adsorption sites; (2) the interaction of the buckled Pt atom with surface water molecules. Results are discussed in terms of surface charging effects caused by oxygen coverage, surface strain effects, as well the contribution from electronic interaction effects. The utility of the proposed mechanism for the understanding of Pt stability at bimetallic surfaces will be demonstrated by evaluating the energy diagram of a CuML/Pt(111) near-surface alloy. Graphical Abstract Atomistic mechanism of Pt extraction at oxidized surfaces
      PubDate: 2016-05-11
  • 3,8-Diaminobenzo[ c ]Cinnoline Derivatived Graphene Oxide Modified
           Graphene Oxide Sensor for the Voltammetric Determination of Cd 2+ and Pb
    • Abstract: Abstract Highly sensitive 3,8-diaminobenzo[c]cinnoline (3,8-DABCC) modified graphene oxide (GO) electrode was prepared, and it was denoted as pGO-DABCC. The electrode material was characterized with infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). pGO-DABCC on glassy carbon (GC/pGO-DABCC) electrode was investigated for simultaneous determination of Cd2+ and Pb2+ in aqueous media by differential pulse anodic stripping voltammetry (DPASV). Optimum conditions of the electrode were determined with some parameters such as constant potential, incubation time, pH, and volume of suspension on the electrode. The calibration equations for Cd2+ and Pb2+ determination were calculated as Ip(μA) = 0.3606[Cd2+] + 0.4346 with a correlation coefficient of 0.9972 and Ip(μA) = 0.2496[Pb2+] + 0.2878 with a correlation coefficient of 0.9968 (N = 5), respectively. The detection limits (LODs) for Cd2+ and Pb2+ were calculated as 0.12 and 0.21 μg/L, respectively. The remarkable results, such as good selectivity, repeatability, and reproducibility were obtained with the modified electrode. Application of the sensors to milk samples produced recovery values in the range 95 to 102 %.
      PubDate: 2016-05-01
  • Influence of Halide Ions on Anodic Oxidation of Ethanol on Palladium
    • Abstract: Abstract Ethanol oxidation on polycrystalline palladium electrodes in alkaline media was studied in the presence of halide ions. Addition of halide ions decreased the ethanol oxidation peak current monotonically as a function of increasing halide concentration. The extent of poisoning was found to be in the order I− > Br− > Cl−. Thus, Cl− ions show appreciable inhibition of ethanol oxidation peak current at [Cl−] ~ 10−3 M, whereas Br− and I− inhibit ethanol oxidation even at [Br−] or [I−] ~ 10−6 M. The potential of the ethanol oxidation peak shifted positive with increasing halide ion concentration. The extent of the shift was found to be in the order I− > Br− > Cl−. This study is relevant due to the widespread use of palladium halide complexes in the production of Pd electrocatalysts for ethanol oxidation and other electrocatalytic reactions.
      PubDate: 2016-05-01
  • Electrochemistry Investigation of the Monolacunary and Their Transition
           Metal Substituent Keggin-Type Polyoxometalates
    • Abstract: Abstract The electrochemical and electrocatalytic behaviors of [XW11O39] n− and [XW11M(H2O)O39] m− (X = B, Si, and P; MII = Mn, Co, and Ni) polyoxometalates were studied with specific emphasis on the tungsten centers by cyclic voltammetry in aqueous solution. Electrochemical studies show the two or three stepwise cathodic/anodic peaks corresponding to the redox processes of WVI centers. The reversibility of redox peaks increases for [SiW11M(H2O)O39]6− and [PW11M(H2O)O39]5− polyoxometalates; however, that of [BW11M(H2O)O39]7− maintains quasi-reversible. The redox waves of the W-O framework for all polyoxometalates are pH- and scan rate-dependent. The tungsten-centered waves for these compound show a classical potential shift as a function of acidity at pH = 2.2–4.2. The electrocatalysis behaviors of these compounds toward the reduction of nitrite ions have been studied in details. The plots of catalytic efficiency versus γ for [XW11O39] n− and [XW11M(H2O)O39] m− (X = B, Si, P; MII = Mn, Co, Ni) show the catalytic efficiency of [BW11O39]9− and [BW11M(H2O)O39]7− (M = Mn, Co, Ni) more than that of the other compounds which are mentioned in this article. Graphical Abstract The electrochemical behavior of the XW11 and XW11M (X = B, Si and P; MII = Mn, Co and Ni) polyoxometalates has been investigated systematically in aqueous solution by cyclic voltammetry. Electrocatalytical reductions of nitrite ion by these compounds were investigated in detail
      PubDate: 2016-05-01
  • Study of Hypochlorite Reduction Related to the Sodium Chlorate Process
    • Abstract: Abstract Reduction of hypochlorite is the most important side reaction in the sodium chlorate reactor leading to high energy losses. Today chromate is added to the reactor solution to minimize the hypochlorite reduction but a replacement is necessary due to health and environmental risks with chromate. In order to understand the effect of different substrates on the hypochlorite reduction, α-FeOOH, γ-FeOOH, Cr2O3 and CrOH3 were electrodeposited on titanium and subjected to electrochemical investigations. These substances are commonly found on cathodes in the chlorate process and can serve as model substances for the experimental investigation. The mechanism of hypochlorite reduction was also studied using DFT calculations in which the reaction at Fe(III) and Cr(III) surface sites were considered in order to single out the electrocatalytic properties. The experimental results clearly demonstrated that the chromium films completely block the reduction of hypochlorite, while for the iron oxyhydroxides the process can readily occur. Since the electrocatalytic properties per se were shown by the DFT calculations to be very similar for Fe(III) and Cr(III) sites in the oxide matrix, other explanations for the blocking ability of chromium films are addressed and discussed in the context of surface charging, reduction of anions and conduction in the deposited films. The main conclusion is that the combined effect of electronic properties and reduction of negatively charged ions can explain the reduction kinetics of hypochlorite and the effect of chromate in the chlorate process. Graphical Abstract Two dimensional test rig for hypochlorite reduction on transition metal sites embedded in an oxy-hydroxide matrix. The adsorption of Cl is used as descriptor for the reaction.
      PubDate: 2016-04-21
  • Carbon-Supported Pt Hollow Nanospheres as a Highly Efficient
           Electrocatalyst for the Oxygen Reduction Reaction
    • Abstract: Abstract In this study, carbon black Vulcan XC-72R (VC)-supported Pt hollow nanospheres (HNSs) were prepared through a simple synthesis strategy using VC-supported Co nanoparticles (NPs) as the template combined with the replacement of Co by PtCl6 2− ions. The new modified synthesis method results in improved Pt distribution and performance compared to the previously reported conventional synthesis method. The as-developed Pt(20 wt%)HNS/VC catalyst has a homogenous Pt HNS particle size of ca. 18 nm and a uniform particle distribution on the VC support. Furthermore, the Pt HNSs are found to be composed of discrete Pt NPs with a crystallite size of ca. 2–3 nm. Due to the unique nanostructure and alloying with Co of the Pt HNS, the Pt(20 wt%)HNS/VC outperforms significantly a state-of-the-art Pt(20 wt%)NP/VC for the oxygen reduction reaction. Graphical Abstract Carbon black Vulcan XC-72R (VC) supported Pt hollow nanospheres (HNSs) were prepared through a simple synthesis strategy. Due to the unique nanostructure of the Pt HNS, the Pt(20 wt%) HNS/VC outperforms significantly a state-of-the-art Pt(20 wt%) NP/VC for the oxygen reduction reaction.
      PubDate: 2016-04-21
  • Synthesis of Pt/C Fuel Cell Electrocatalysts: Residual Content of Chloride
           and Activity in Oxygen Reduction
    • Abstract: Graphical Abstract Transmission electron micrographs (TEM), the corresponding Pt particle size distribution histograms, and chemical analysis for residual Cl content by instrumental neutron activation analysis (INAA) and X-ray photoelectron spectroscopy (XPS) of selected representative Pt/C fuel cell catalysts.
      PubDate: 2016-04-12
  • Evaluation of Oxygen Reduction Activity by the Thin-Film Rotating Disk
           Electrode Methodology: the Effects of Potentiodynamic Parameters
    • Abstract: Abstract An accurate and efficient assessment of activity is critical for the research and development of electrocatalysts for oxygen reduction reaction (ORR). Currently, the methodology combining the thin-film rotating disk electrode (TF-RDE) and potentiodynamic polarization is the most commonly used to pre-evaluate ORR activity, acquire kinetic data (i.e., kinetic current, Tafel slope, etc.), and gain understanding of the ORR mechanism. However, it is often neglected that appropriate potentiodynamic parameters have to be chosen to obtain reliable results. We first evaluate the potentiodynamic and potentiostatic polarization measurements with TF-RDE to examine the ORR activity of Pt nanoelectrocatalyst. Furthermore, our results demonstrate that besides depending on the nature of electrocatalyst, the apparent ORR kinetics also strongly depends on the associated potentiodynamic parameters, such as scan rate and scan region, which have a great effect on the coverage of adsorbed OHad/Oad on Pt surface, thereby affecting the ORR activities of both nanosized and bulk Pt. However, the apparent Tafel slopes remained nearly the same, indicating that the ORR mechanism in all the measurements was not affected by different potentiodynamic parameters. Graphical Abstract CV response of bulk Pt under a programmed potential scan
      PubDate: 2016-04-11
  • 3D π-Conjugated Poly(amic) Acid Polymer as Support Matrices for
           Ethanol Electro-Oxidation on Palladium and Platinum Catalysts
    • Abstract: Abstract The search for new catalyst support matrices to replace the conventional carbon black support has been an important research field for decades. Aromatic conducting polymer (ACP)-based matrices have been found as prospective candidates. Poly(amic) acid (PAA) is one such polymer. We hereby present the catalytic activity and stability of electrodeposited palladium (PdNPs) and platinum (PtNPs) nanoparticles stabilized with PAA. We fabricated four electrodes: Pd/GCE, PAA/Pd/GCE, Pt/GCE, and PAA/Pt/GCE. Cyclic voltammetry and chronoamperometry were employed to assess the ethanol oxidation reaction using PAA as support matrix. PAA was used as support to enhance the stability of PdNPs and PtNPs in basic and acidic media, respectively. The synthesized PAA was characterized using NMR and FTIR. Scanning electron microscopy and X-ray diffraction (XRD) were used for nanoparticle characterization. Test results revealed that the presence of PAA layer on the catalysts leads to sluggish electron transfer kinetics as deduced from higher forward and reverse current densities (5 and 11 mA/cm2) for PdNPs on glassy carbon (Pd/GCE) electrode compared to PAA-stabilized PdNPs (PAA/Pd/GCE) (0.6 and 1.2 mA/cm2), respectively. A similar trend was reported for PtNPs. However, in presence of PAA, both PtNPs and PdNPs were observed to provide stability at up to 900 and 150 cycles, respectively. Chronoamperometric results reinforced the catalyst stabilization effect of the polymer, with findings revealing that the steady-state current density of PAA/Pd/GCE was ∼2.5 times higher than the bare Pd/GCE. Graphical Abstract Poly (amic) acid (PAA)- a biodegradable, electroactive, conductive and π-conjugated polymer- was spin coated onto electrodeposited Pd and Pt nanoparticles and subsequently used for ethanol oxidation reaction in basic and acidic conditions respectively. The catalytic activity of Pd and Pt nanoparticles was retained and the catalyst stability enhanced in presence of PAA film.
      PubDate: 2016-04-11
  • In Situ ATR-FTIR Studies of Ethanol Electro-oxidation in Alkaline Medium
           on PtRh/C Electrocatalyst Prepared by an Alcohol Reduction Process
    • Abstract: Abstract Anion exchange membrane fuel cell is a new chance to produce a functional and portable fuel cell; however, the studies are still at an early stage with few reports regarding the AEMFC. PtRh/C electrocatalysts with different Pt:Rh atomic ratios were prepared by an alcohol reduction process. X-ray diffraction patterns for all PtRh/C materials indicated no shift in Pt(fcc) peaks showing that Rh did not incorporated into Pt lattice; however, the analysis of lattice parameter showed that some Pt atoms are added to Rh(fcc) structure. The mean particle sizes were in the range of 4–5 nm. Electrochemical experiments showed that PtRh/C electrocatalyst with Pt:Rh atomic ratio of 70:30 had superior performance exhibiting a current density of 5.0 mA mgmetal −1. From in situ ATR-FTIR experiments, it was observed that PtRh/C electrocatalyst with Pt:Rh atomic ratio of 70:30 produced more acetate ions than other ones, while the material prepared with Pt:Rh atomic ratio of 50:50 was more selective to CO2 as observed in acid media. Graphical Abstract Integrated acetaldehyde, carbonate, acetate, and CO2 band intensity as a function of the electrode potential for Pt/C, Rh/C, and PtRh/C electrocatalysts
      PubDate: 2016-03-22
  • The Effect of Platinum Loading and Surface Morphology on Oxygen Reduction
    • Abstract: Abstract The catalytic activity of Pt catalysts towards the oxygen reduction reaction (ORR) was investigated on a catalyst system developed by thermally induced chemical deposition of Pt on carbon. The use of this deposition method made it possible to prepare a practical catalyst system with various Pt loadings on the support. Increasing the Pt loading caused a change in the Pt surface morphology which was confirmed by transmission electron microscopy (TEM) and CO stripping voltammetry measurements. The occurrence of a low and high-potential CO oxidation peak suggested the presence of Pt agglomerates and Pt nanoparticles, respectively. An increase in Pt loading lead to a subsequent decrease in the electrochemical surface area (ECSA, m2 Pt/gPt) as the platinum surface transitioned from isolated platinum nanoparticles to platinum agglomerates. The specific activity was found to increase with increasing Pt loadings, while the mass activity decreased with loading. The mass and specific activity data from this study was found to follow a ‘master curve’ obtained by the comparison of normalised activities from various different studies in the literature. Pt selectivity was also affected by Pt loading and hence Pt surface morphology. At low Pt loadings, i.e. large interparticle distances, the amount of H2O2 produced was significantly higher than for high Pt loadings. This confirms the presence of a ‘series reaction pathway’ and highlights the importance of the H2O2 desorption-readsorption mechanism on Pt nanoparticles and the ultimate role of Pt interparticle distance on the ORR mechanism. Graphical Abstract Effect of platinum loading and surface morphology on oxygen reduction activity
      PubDate: 2016-03-16
  • Comparison of FePt and Pt Nanostructures for Oxygen Reduction Reaction in
           Basic Medium
    • Abstract: Abstract FePt nanoparticles (NPs) and colloidal nanoparticle clusters (CNCs) have been synthesized by the reduction of platinum acetylacetonate (Pt(acac)2) combined with thermal decomposition of iron pentacarbonyl (Fe(CO)5) and compared to pure Pt NPs and CNCs for the catalytic activity of the oxygen reduction (ORR). The formation of NPs and CNCs has been carried out controlling injection temperature of the precursors and the surfactants during the synthesis. The size of the NPs and the CNCs formed is around 3 and 38 nm, respectively. High electrocatalytic performance of the FePt CNCs in comparison with that of nanoparticles and nanocluster of platinum has been obtained for the reduction reaction (ORR) in basic medium. The ORR is carried out by a four-electron charge transfer. The increase in the activity of the CNC structures formed by FePt nanoparticles can be attributed to the alloy formation that produces surface and electronic changes of the Pt atoms and to the structure of the CNCs obtained. Graphical Abstract Polarization curves of (a) CNCs FePt, (b) NPs FePt, (c) CNCs Pt, and (d) NPs Pt and their morphology.
      PubDate: 2016-03-14
  • Investigation of Electrochemical Properties of Model Lanthanum Strontium
           Cobalt Ferrite-Based Cathodes for Proton Ceramic Fuel Cells
    • Abstract: The electrochemical properties of La0.6Sr0.4Co0.2Fe0.8O3-δ-based cathodes are studied as model electrodes for proton ceramic fuel cells. The electrochemical performance of symmetric cells with porous cathodes (La0.6Sr0.4Co0.2Fe0.8O3-δ, La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ, and La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ), investigated as a function of oxygen and water partial pressures, follows the order La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ ≥ La0.6Sr0.4Co0.2Fe0.8O3-δ >> La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ. The results indicate that the cathode performance of La0.6Sr0.4Co0.2Fe0.8O3-δ–BaCe0.9Y0.1O3-δ is enhanced mainly due to the extension of the effective triple phase boundary, whereas that of La0.6Sr0.4Co0.2Fe0.8O3-δ–BaZr0.8Y0.2O3-δ is lowered due to the poor proton conductivity along the percolated BaZr0.8Y0.2O3-δ particles. From the observed oxygen partial pressure dependence, the rate-determining step of the above cathode polarization reaction is principally ascribed to the oxygen reduction reaction. Graphical abstract Schematics of the cathode reaction mechanism at the surface of the LSCF, LSCF-BCY, and LSCFBZY cathodes
      PubDate: 2016-03-14
  • Enhanced Catalytic Performance of Bimetallic Nickel–Cobalt Loaded
           Low-Content Au Catalyst Toward Ethanol Electro-Oxidation
    • Abstract: Abstract Low-content Au nanoparticles loaded over nickel–cobalt bimetallic nanoflakes on a FTO substrate electrode (Au/NiCo) were obtained by an electrodeposition-replacement precipitation method. The as-prepared catalysts were characterized by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), and their catalytic performances for ethanol electro-oxidation were investigated by multi-cyclic voltammetry, current-time curve, Tafel curve, and electrochemical impedance spectroscopy (EIS). The result showed that Au/NiCo catalysts exhibited higher electrocatalytic activity toward ethanol electro-oxidation compared to Au nanoparticles loaded on nickel (Au/Ni) and cobalt (Au/Co), respectively, due to the enhanced anti-poisoning tolerance by Co, and the bifunctional effect of NiCo and Au. Moreover, the ratio of Ni and Co had a great effect on the activity of the nanocomposite catalyst; Au/Ni0.04 prepared from the electrolyte of 0.04 mol/L Ni(NO3)2 + 0.005 mol/L Co(NO3)2 showed the highest performance for ethanol electro-oxidation. The result from this work suggests a new route for rational design of low-cost and high-performance electrocatalysts in direct ethanol fuel cells. Graphical Abstract Au/Ni0.04 with porous spherical flower-like structure showed higher electrocatalyitc activity toward ethanol electro-oxidation
      PubDate: 2016-03-05
  • Membrane Electrolysis of Toluene Hydrogenation with Water Decomposition
           for Energy Carrier Synthesis
    • Abstract: Abstract Large-scale technology for energy storage and transportation is needed to increase renewable energies which unevenly distribute with fluctuations, such as wind and solar power. The organic hydride of the toluene/methylcyclohexane system is one of the best energy carriers. In order to improve the energy conversion efficiency of the hydrogenation of toluene using electric power, a membrane electrolyzer, which consists of a carbon-supported precious metal-coated porous carbon cathode, perfluorosulfonic acid (PFSA) membrane separator, and DSE® anode for the oxygen evolution reaction, has been designed and evaluated. The activity of the PtRu/C catalyst layer for the electrohydrogenation of toluene was higher than that of Pt/C. Hydrophilization of the anode side of the PFSA effectively discharged oxygen gas from the anode compartment. The electrohydrogenation of toluene without hydrogen evolution has been successfully up to a 450 mA cm−2 current density with 100 % toluene feed at ca. 2 V cell voltage. In order to evaluate the conversion ratio for the hydrogenation, the current efficiency as a function of the current density was evaluated at various concentrations of toluene. Significant hydrogen was generated above 100 mA cm−2 of current density for 10 times the stoichiometry of a 5 % toluene feed. During the electrolysis, by-products were hardly detected except for hydrogen. Although the improvement of the mass transport in the catalyst layer occurred, more than 95 % of the toluene conversion with a high energy efficiency should be feasible based on these experiments.
      PubDate: 2016-03-01
  • Novel Noble-Metal-Free Electrocatalyst for Oxygen Evolution Reaction in
           Acidic and Alkaline Media
    • Abstract: Abstract This study focuses on the feasibility of using TMTiP (where TM is a 3d transition metal or a mixture of 3d transition metals, Cr, Mn, Fe, Co, and Ni; TiP denotes titanium phosphide) as the electrode material for the oxygen evolution reaction (OER) by systematic modification to the atomic ratio of the constituent metals. The catalytic activity of the electrode materials is expected to be governed by the d electrons of the transition metals; the electrical conductivity is provided by TiP even under highly acidic conditions. The OER activity followed a “volcano plot” as the TM was changed from Cr to Ni and assumed the maximum value for the composition cobalt titanium phosphide (CoTiP). The CoTiP electrode also exhibited excellent corrosion resistance and metallic conductivity (on the order of 10−6 Ω m) over the pH range 0–14. The OER activity of CoTiP was comparable to that of Pt but inferior to that of state-of-the-art IrO2 and RuO2.
      PubDate: 2016-03-01
  • The “Particle Proximity Effect” in Three Dimensions: a Case
           Study on Vulcan XC 72R
    • Abstract: Abstract The “particle proximity effect” is a hypothesis claiming that Pt nanoparticles have higher ORR activity when they get closer to one another. In order to put this hypothesis under scrutiny, the “tool-box” approach was investigated in each process step by electron microscopy, ICP, and surface science methods. It is shown that particle size stability is brought about by a NaCl shell which can effectively be removed by washing with water. I.e., the “tool-box” synthesis with an additional washing step produces clean, closely spaced, and well-separated particles with interparticle distances necessary for the effect to occur. Despite this powerful synthesis route, a conclusive proof of the “proximity effect” could not be obtained. This is due to difficulties with catalyst film formation at higher platinum loadings on Vulcan XC 72R, suggesting that film deposition and drying methods have to be optimized for each catalyst loading separately and that a holistic approach is not very realistic. Graphical Abstract Sometimes less is more: Oxygen reduction catalysts on Vulcan XC 72R with high Pt loading (> 10 %) show unfavorable film qualities on glassy carbon tips and cannot be evaluated for their kinetic current and specitic activities (extensive coffee ring formation) while for lower loadings reliable values can be obtained.
      PubDate: 2016-02-24
  • Adsorption of Acetonitrile on Platinum and its Effects on Oxygen Reduction
           Reaction in Acidic Aqueous Solutions—Combined Theoretical and
           Experimental Study
    • Abstract: Abstract Combined theoretical and experimental study of acetonitrile (AcN) adsorption on platinum was performed and its effects on the kinetics of oxygen reduction reaction in HClO4 and H2SO4 solutions were examined. Using periodic density functional theory calculations, it was shown that AcN molecule can interact with Pt surface either through the unsaturated π electron system or via lone electron pair of nitrogen atom. In both cases, adsorption energy decreases upon increasing coverage, while the modification of electronic structure of Pt surface is localized to the adsorption site. By combining the results of the DFT calculations with the results of blank cyclic voltammetry and rotating disk electrode voltammetry in O2-saturated solutions, it was concluded that the effects of AcN on Pt surface chemistry and ORR kinetics are primarily steric in nature. Resulting measured ORR activities of polycrystalline platinum in the presence of AcN are due to the combination of (i) suppression of (bi)sulfate adsorption (in H2SO4 solution), (ii) suppression of surface oxidation (in both H2SO4 an HClO4 solution), and (iii) site blockage by adsorbed AcN (or products of its electrochemical transformations). Graphical Abstract ᅟ
      PubDate: 2016-02-11
  • Spontaneous Deposition of Iridium onto Nickel Substrates for the Oxygen
           Evolution Reaction
    • Abstract: Abstract Spontaneous deposition of Ir onto Ni substrates was investigated as a method to produce electrocatalytic layers for the oxygen evolution reaction in 30 % KOH solution. UV/Vis spectroscopy, cyclic voltammetry and other electrochemical methods are used to investigate the deposition process and the activity of the electrocatalytic coating towards the oxygen evolution reaction. From three solutions (IrCl3+HCl, H2IrCl6+HCl and H2IrCl6), H2IrCl6 is shown to give the most active and stable coating, with deposition times of 45 min at 60∘C enough to increase the activity of the Ni substrate for the oxygen evolution reaction. It is proposed that Ir deposition can occur via the reduction of the Ir precursor coupled to Ni oxidation, as well as the hydrolysis and localised precipitation of the Ir precursor due to the increase in surface pH during Ni dissolution.
      PubDate: 2016-02-05
  • Ammonia Oxidation at Electrochemically Platinum-Modified Microcrystalline
           and Polycrystalline Boron-Doped Diamond Electrodes
    • Abstract: Abstract The electrochemical oxidation of ammonia was done at electrochemically Pt-modified microcrystalline and polycrystalline boron-doped diamond (BDD) thin films from sp3 Diamond Technologies and Element Six. The Pt electrodepositions were done by chronoamperometry and cyclic voltammetry using a 1 mM K2PtCl6 solution in 0.5 M H2SO4. The Pt-BDD electrodes were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, and cyclic voltammetry. The Pt-BDD electrodes were compared by SEM and ammonia oxidation. At BDD electrodes, cyclic voltammetry depositions favors the formation of cubic and cauliflower Pt nanostructures at microcrystalline and polycrystalline BDD electrodes, respectively. On the other hand, chronoamperometry electrodeposition favors dendrite formation structures in both BDD electrodes. Platinum electrodeposited by chronoamperometry favors the formation of platinum (100) facets, which enhances ammonia oxidation. Pt-microcrystalline BDD showed the highest ammonia oxidation peak current densities when compared to Pt-polycrystalline BDD.
      PubDate: 2016-01-08
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