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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  [2281 journals]
  • 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
           Electrooxidation
    • 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
       
  • Effect of Addition of Ru and/or Fe in the Stability of PtMo/C
           Electrocatalysts in Proton Exchange Membrane Fuel Cells
    • Abstract: Abstract In this work, the activity, stability, and CO tolerance of ternary and quaternary electrocatalysts formed by PtMo/C-PtFe/C, PtMo/C-PtRu/C, and PtMo/C-PtRuC-PtFe/C were studied in the anodes of proton exchange membrane fuel cells (PEMFCs). Cyclic voltammetry (CV) was used to study the surface characteristics and stability of the electrocatalysts and polarization curves were used to investigate the performance of PEMFC anodes supplied with pure hydrogen and hydrogen containing 100 ppm CO. Online mass spectrometry (OLMS) and CO stripping experiments were conducted to investigate the CO tolerance mechanism. The PtMo/C-PtRu/C-PtFe/C, PtMo/C-PtFe/C, and PtMo/C-PtRu/C electrocatalysts showed better performance for the oxidation of hydrogen in the presence of hydrogen containing 100 ppm CO as compared to the PtMo/C electrocatalyst. It was found that the partial dissolution of Mo, Ru, and Fe, and their migration/diffusion from the anode to the cathode occur during a CV cycling from 0.1 to 0.7 V vs. RHE at a scan rate of 50 mVs-1 up to total of 5,000 cycles. The results also showed that the stability of PtMo/C-PtRu/C-PtFe/C, PtMo/C-PtFe/C, and PtMo/C-PtRu/C are better than that of PtMo/C.
      PubDate: 2015-08-07
       
  • The Effects of a Low-Level Boron, Phosphorus, and Nitrogen Doping on the
           Oxygen Reduction Activity of Ordered Mesoporous Carbons
    • Abstract: Abstract In order to elucidate the role of B, N, and P dopants in carbon materials on the kinetics of oxygen reduction reaction (ORR) and to provide a fair comparison of the effects of each dopant, a series of ordered mesoporous carbons (OMCs) with low concentration of heteroatoms (<1 at%) has been prepared. Doped OMCs were characterized using X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES), Raman spectroscopy, X-ray powder diffraction (XRD), and N2 physisorption measurements. Comparative study of the ORR activity of these materials in alkaline solution was performed using rotating disk electrode voltammetry. The experiments evidenced that, compared to non-doped OMC, charge transfer kinetics was improved independently on the nature of the heteroatom. The decrease of the ORR overvoltage and the increase of the mass activity upon doping are similar for B and P and less prominent for N. On the other hand, OMCs doped with low levels of B and N were found to be selective for O2 reduction to peroxide, while for P-doped OMCs, the apparent number of electrons consumed per O2 molecule was up to 3.1. Experimental measurements were complemented by density functional theory (DFT) calculations.
      PubDate: 2015-08-07
       
  • The Formation of Surface Oxides on Nickel in Oxalate-Containing Alkaline
           Media
    • 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
           Chemicals
    • 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
       
  • Nickel Complexes Based on Thiophosphorylated Calix[4]Resorcinols as
           Effective Catalysts for Hydrogen Evolution
    • Abstract: Abstract Nickel complexes of thiophosphorylated calix[4]resorcinols showed high catalytic activity for hydrogen evolution from acidic solutions and stability in the electro-assisted catalysis at the surface of both glassy carbon and Hg-pool electrodes. The conformation of the macrocyclic ligand determines the dimensionality and shape of the catalytically active species generated on the electrode.
      PubDate: 2015-07-01
       
  • Electrochemical Fabrication of Well-Defined Spherical Iridium
           Nanoparticles and Electrocatalytic Activity towards Carbon Monoxide
           Adlayer Oxidation
    • Abstract: Abstract This study outlines the methodology to electrodeposit well-defined iridium nanospheres onto glassy carbon (GC) electrodes at room temperature, using a square wave potential (SWP) technique. Similar work has recently been carried out for other noble metal nanoparticles, in particular platinum and palladium. In this study, particle size and Ir loading can be controlled by altering two key parameters in the electrodeposition process; the nucleation potential and the growth duration. Ir nanoparticles were characterized using cyclic voltammetry (CV) and scanning electron microscopy (SEM). It was found that the nucleation potential and time influence not only the nucleation density but also the particle size. In addition, the electrochemical activity of the particles towards carbon monoxide (CO) adlayer oxidation was investigated as a surface test reaction. The results showed that surface morphology of the deposited particles, which could be altered using potential cycling, plays a pivotal role in determining the activity of the particles. Particles that were treated by potential cycling showed a significantly lower overpotential, in contrast to particles of similar size that were untreated. This indicates an enhancement in electrocatalytic activity due to the enrichment of surface defects.
      PubDate: 2015-07-01
       
  • Direct Electrochemistry of Glucose Oxidase on a Three-Dimensional Porous
           Zirconium Phosphate–Carbon Aerogel Composite
    • Abstract: Abstract Biocompatible materials with large specific surface areas can play a crucial role in direct electron transfer between redox proteins and an electrode surface. Here, we report zirconium phosphate–carbon aerogel (ZrP-CA) composites with a large specific surface area and uniform nanopore distributions as matrix for glucose oxidase immobilization. The immobilized glucose oxidase displays two stable, well-defined redox peaks with an electron transfer rate constant of 9.34 s−1 in nitrogen-saturated phosphate-buffered saline (PBS) solution (0.1 M, pH 7.0), at a scan rate of 100 mV s−1. The modified electrode was also used as a glucose biosensor, which was found to exhibit a linear calibration range of 0.12–2.0 mM, sensitivity of 5.56 μA mM−1 cm−2 at an applied potential of −0.5 V, and detection limit of 34 μM based on a signal-to-noise ratio of 3. After 80 scan cycles, the decreases in the peak current were less than 8 %, indicating good stability of the as-prepared ZrP-CA. The unique characteristics of the ZrP-CA nanocomposite make it a good matrix for protein immobilization and biosensor preparation.
      PubDate: 2015-07-01
       
  • 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
       
  • Electrocatalytic Reduction of Carbon Dioxide using Sol-gel Processed
           Copper Indium Sulfide (CIS) Immobilized on ITO-Coated Glass Electrode
    • Abstract: Abstract Sol-gel processed copper indium sulfide (CIS) films have been processed on glass and transparent indium doped tin oxide (ITO)-coated glass electrodes by a straightforward layer by layer spin coating route yielding excellent film qualities with subsequent thermal annealing. Resulting films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis spectroscopy. We apply these films in an electrochemical cell as a working electrode and take a view on the reduction of carbon dioxide (CO2) to its energy richer carbon monoxide (CO) in acetonitrile solution containing 0.1 M (C4H9)4NPF6 supporting electrolyte saturated with CO2. CIS films exhibit pronounced electrochemical and photoelectrochemical activities. Concomitantly, we quantify the generation of CO, which starts to evolve at a threshold potential of −0.60 V vs normal hydrogen electrode (NHE). The calculated faradaic efficiency of the electrochemical reduction of CO2 into CO exceeds 20 (±1) % in an optimized thin-film structure. Graphical Abstract Sol-gel processed copper indium sulfide (CIS) thin films have been processed on glass and indium doped tin oxide (ITO)-coated glass electrodes using layer by layer spin coating route yielding excellent film qualities with subsequent thermal annealing. Electrochemical and photoelectrochemical experiments performed in N2 and CO2 saturated acetonitrile solutions containing 0.1 M (C4H9)4NPF6 as an electrolyte and CIS-modified ITO as working electrode showed promising electrocatalytic and photoelectrocatalytic activity for the reduction of carbon dioxide (CO2) to its energy richer carbon monoxide (CO) with faradaic efficiency of about 20 (±1) %.
      PubDate: 2015-05-20
       
  • Electrochemical Quartz Crystal Microbalance Determination of Nickel Formal
           Partial Charge Number as a Function of the Electrode Potential upon Nickel
           Underpotential Deposition on Platinum in Sulfuric Medium
    • Abstract: Abstract Although nickel underpotential deposition (UPD) on platinum surfaces has been demonstrated in sodium sulfate media, there is no consensus regarding the value of nickel formal partial charge number (ι Ni) upon adsorption on platinum. Moreover, in most studies, nickel formal partial charge number is determined as an average, calculated on the whole Ni-UPD potential range (i.e., for NiUPD coverage values varying between approximately 0 and 1). In the present contribution, the electrochemical quartz crystal microbalance technique is employed to go beyond this average ι Ni determination. A simple method is proposed to evaluate the electrode-potential-dependent (i) variations of the surface coverages of the specifically adsorbed species and (ii) corresponding nickel formal partial charge number upon adsorption on platinum. From the values of the surface coverage of the adsorbing species, one can recalculate the current densities during the anodic sweep of the cyclic voltammogram. These recalculated current densities agree with the experimental data, which validates the method. The value of the nickel formal partial charge number (ι Ni) decreases upon electrode potential increase, suggesting enhanced sulfate co-adsorption at high Ni-UPD potential. This further enables to determine the potential of zero total charge (PZTC) of the platinum electrode in the considered sulfate-containing electrolyte solutions: The presence of nickel shifts the PZTC of platinum positively by ∼100 mV compared to supporting electrolyte, in agreement with the presence of specifically adsorbed cations.
      PubDate: 2015-04-17
       
  • One-Pot Hydrothermal Synthesis of Reduced Graphene Oxide–Multiwalled
           Carbon Nanotubes Composite Material on Nickel Foam for Efficient
           Supercapacitor Electrode
    • Abstract: Abstract The reduced graphene oxide/multiwalled carbon nanotubes deposited on nickel foam (rGO/MWCNTs/NF) composite material was successfully prepared using one-pot hydrothermal method. The prepared rGO/MWCNTs/NF composite material was characterized using scanning electron microscopy, electron dispersive spectroscopy, and Raman spectroscopy. The results show that MWCNTs were successfully incorporated into the graphene sheets uniformly. The rGO/MWCNTs/NF composite material was fabricated as electrode for supercapacitor application. The capacitive properties of the rGO/MWCNTs/NF composite material were studied using electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge/discharge in 1 M KOH aqueous electrolyte solution. The rGO/MWCNTs/NF electrode showed enhanced capacitance compared to rGO/NF, MWCNTs/NF, and bare NF electrodes due to high surface area and more accessibility of electrolyte after the addition of MWCNTs to the rGO/NF electrode. The rGO/MWCNTs/NF composite material shows specific capacitance of 81.14 F g−1 at current density of 1 A g−1 and excellent cycling stability with 83 % of its initial capacitance after 1000 charge/discharge cycles.
      PubDate: 2015-04-11
       
 
 
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