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Journal Cover Electrocatalysis
  [SJR: 0.817]   [H-I: 17]   [2 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  [2350 journals]
  • Spinel Manganese Ferrites for Oxygen Electrocatalysis: Effect of Mn
           Valency and Occupation Site
    • Authors: Ye Zhou; Yonghua Du; Shibo Xi; Zhichuan J. Xu
      Pages: 287 - 292
      Abstract: Spinel catalysts have been widely explored for the electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). To consolidate the understanding on electrocatalysis by spinel family, intermediate spinels should be deliberately examined because most spinel oxides are of intermediate structure. Here, we report an investigation on the ORR and OER performance of intermediate spinel MnFe2O4. The modulation of cation oxidation state and inversion degree of spinel MnFe2O4 were achieved by a simple annealing process. X-ray absorption spectroscopy analysis reveals that the Mn occupancy in octahedral sites varied from 0.25 ~ 0.41 and Mn cations were oxidized from 2+ to 3+ with increasing temperature treatment. Convinced by the leading role of octahedral-geometric, we further reveal the role of Mn oxidation state through normalizing the activity to active Mn[Oh] site number. Our findings clearly indicate that Mn3+ was more catalytically active than Mn2+ in catalyzing ORR and OER. Graphical Both Mn occupancy in octahedral site and its oxidation state play dominant roles in determining the catalytic activities of spinel manganese ferrites toward oxygen electrocatalysis.
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0429-z
      Issue No: Vol. 9, No. 3 (2018)
       
  • Stability Testing of Pt x Sn 1 − x /C Anodic Catalyst for Renewable
           Hydrogen Production Via Electrochemical Reforming of Ethanol
    • Authors: Ana B. Calcerrada; Ana R. de la Osa; Holly A. E. Dole; Fernando Dorado; Elena A. Baranova; Antonio de Lucas-Consuegra
      Pages: 293 - 301
      Abstract: The stability testing of three different synthesized Pt x Sn1 − x /C anodic catalysts has been demonstrated for the renewable generation of hydrogen via the electrochemical reforming of ethanol in a proton exchange membrane (PEM) electrolysis cell. Three Pt-Sn anodic catalysts with different nominal Pt:Sn ratios of 60:40, 70:30, and 80:20 atomic (at.) % were synthetized and characterized by the means of electrochemical tests and XRD. Among them, the Pt-Sn anodic catalyst with 70:30 at. ratio showed the highest electrochemical active surface area (ECSA) and highest electrochemical reforming activity, which allowed the production of pure H2 with the lowest electrical energy requirement (below 23 kWh·kgH2 −1). The stability of the system was also demonstrated through a long-term chronopotentiometry experiment of 48 h in duration. The potential for practical use and coupling this technology with renewable solar energy, a number of cyclic voltammetry tests (with a low scan rate of 0.19 mV·s−1) were also carried out. These experiments were performed by simulating the electrical power produced by a photovoltaic cell. This test showed good stability/reproducibility of the MEA and, hence, a suitable integration between the two technologies for the sustainable energy storage in the form of hydrogen. ᅟ Graphical
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0428-0
      Issue No: Vol. 9, No. 3 (2018)
       
  • Catalyst Degradation Under Potential Cycling as an Accelerated Stress Test
           for PBI-Based High-Temperature PEM Fuel Cells—Effect of Humidification
    • Authors: Tonny Søndergaard; Lars Nilausen Cleemann; Lijie Zhong; Hans Becker; Thomas Steenberg; Hans Aage Hjuler; Larisa Seerup; Qingfeng Li; Jens Oluf Jensen
      Pages: 302 - 313
      Abstract: In the present work, high-temperature polymer electrolyte membrane fuel cells were subjected to accelerated stress tests of 30,000 potential cycles between 0.6 and 1.0 V at 160 °C (133 h cycling time). The effect that humidity has on the catalyst durability was studied by testing either with or without humidification of the nitrogen that was used as cathode gas during cycling segments. Pronounced degradation was seen from the polarization curves in both cases, though permanent only in the humidified case. In the unhumidified case, the performance loss was more or less recoverable following 24 h of operation at 200 mA cm−2. A difference in degradation behavior was verified with electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy. The strong effect of humidification is explained by drying of the phosphoric acid that is in the catalyst layer(s) versus maintaining humidification of this region. Catalyst degradation due to platinum dissolution, transport of its ions, and eventual recrystallization is reduced when this portion of the acid dries out. Consequently, catalyst particles are only mildly affected by the potential cycling in the unhumidified case. Graphical ᅟ
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0427-1
      Issue No: Vol. 9, No. 3 (2018)
       
  • The Contribution of Carbon Supports on the Activity of Pt for Glycerol
           Electrooxidation: the Importance of Investigating the Derivative
           Voltammogram and Arrhenius Plots
    • Authors: Brenda D. Ferreira; Leticia M. Alencar; Gabriel C. da Silva; Gilberto Maia; Cauê A. Martins
      Pages: 314 - 322
      Abstract: Glycerol electrooxidation was evaluated on Pt electrodeposited over carbon Vulcan (CV), multi-walled carbon nanotubes (MWCNTs), graphene oxide nanoribbons (GONRs), and graphene nanoribbons (GNRs). Different masses of Pt were deposited under the same conditions, producing different surface areas of Pt. The presence of GNRs slightly enhanced the specific activity of the catalyst. By investigating the derivative voltammetry of glycerol, we found that the supports did not shift the onset potential towards lower values. Moreover, we found that the apparent activation energy did not vary by changing the carbon support. In this sense, we rationalized the slight improvement in specific activity of Pt deposited on GNRs as a consequence of the frequency of collision factor due to the availability of Pt over the longitudinal flat surface of nanoribbons, as shown by the high active surface area/mass of electrodeposited Pt ratio.
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0431-5
      Issue No: Vol. 9, No. 3 (2018)
       
  • Electrodeposited Cu-Sn Alloy for Electrochemical CO 2 Reduction to CO/HCOO
           −
    • Authors: Masayuki Morimoto; Yoshiyuki Takatsuji; Ryota Yamasaki; Hikaru Hashimoto; Ikumi Nakata; Tatsuya Sakakura; Tetsuya Haruyama
      Pages: 323 - 332
      Abstract: Cu-Sn alloy electrodes were prepared by simple electrodeposition method for the electrochemical reduction of CO2 into CO and HCOO−. The alloy electrode surfaces provided good selectivity and efficiency in electrochemical CO2 conversion because they provided appropriate binding energies between the metal and the reactive species obtained through CO2 reduction. Therefore, product selectivity can be modulated by altering the Cu-Sn crystal structure of the electrode. Using the Cu-Sn alloy electrodes, electrochemical reduction was performed at applied potentials ranging from − 0.69 to − 1.09 V vs. reversible hydrogen electrode (RHE). During electrochemical CO2 reduction, all the prepared Cu-Sn alloy electrodes showed prominent suppression of hydrogen evolution. In contrast, Cu87Sn13 has high selectivity for CO formation at all the applied potentials, with maximum faradaic efficiency (FE) of 60% for CO at − 0.99 V vs. RHE. On the other hand, Cu55Sn45 obtained a similar selectivity for electrodeposition of Sn, with FE of 90% at − 1.09 V vs. RHE. Surface characterization results showed that the crystal structure of Cu87Sn13 comprised solid solutions that play an important role in increasing the selectivity for CO formation. Additionally, it suggests that the selectivity for HCOO− formation is affected by the surface oxidation state of Sn rather than by crystal structures like intermetallic compounds. Graphical The Cu-Sn alloy catalysts prepared by simple electrodeposition can control the selectivity for CO and HCOO− formation by tuning its crystal structure. Surface analyses revealed that solid solutions and the oxidation state of Sn play an important role in the formation of CO and HCOO− upon CO2 reduction, respectively.
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0434-2
      Issue No: Vol. 9, No. 3 (2018)
       
  • Electrochemical Investigation of the Hydrogen Evolution Reaction on
           Electrodeposited Films of Cr(OH) 3 and Cr 2 O 3 in Mild Alkaline Solutions
           
    • Authors: Adriano S. O. Gomes; Nina Simic; Mats Wildlock; Anna Martinelli; Elisabet Ahlberg
      Pages: 333 - 342
      Abstract: The hydrogen evolution reaction (HER) from water reduction is the main cathodic reaction in the sodium chlorate process. The reaction typically takes place on electrodes covered with a Cr(III) oxide-like film formed in situ by reduction of sodium dichromate in order to avoid reduction of hypochlorite and thereby increase the selectivity for the HER. However, the chemical structure of the Cr(III) oxide-like film is still under debate. In the present work, the kinetics of the HER were studied using titanium electrodes covered with electrodeposited Cr(OH)3 or Cr2O3, which were characterized by means of scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. A clear difference in the morphology of the deposited surfaces was obtained, and the structure could be revealed with Raman spectroscopy. The kinetics for the HER were investigated using potentiodynamic and potentiostatic techniques. The results show that the first electron transfer is rate limiting and that the activity decreases in the order Cr2O3@Ti > bare Ti > Cr(OH)3@Ti. The low activity obtained for Cr(OH)3@Ti is discussed in terms of the involvement of structural water in the HER and the slow ligand exchange rate for water in Cr(III) complexes, while the high activity obtained for Cr2O3@Ti is rationalized by a surface area effect in combination with reduction of surface water and water in solution. Graphical ᅟ
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0435-1
      Issue No: Vol. 9, No. 3 (2018)
       
  • Electrocatalytic Reduction of Nitrate and Nitrite at CuRh Nanoparticles/C
           Composite Electrodes
    • Authors: Peyman Mirzaei; Stéphane Bastide; Atieh Aghajani; Julie Bourgon; Claudia Zlotea; Michel Laurent; Michel Latroche; Christine Cachet-Vivier
      Pages: 343 - 351
      Abstract: Composites consisting of rhodium, copper, and copper-rhodium nanoparticles (2 nm in average diameter) dispersed in a high-surface area graphite powder (~ 10 wt.% of metal) have been synthesized by a wet chemical method. After characterization by ICP-OES and TEM, they have been tested for the electrochemical reduction of nitrates in alkaline media (10−1 mol L−1 KOH) using a cavity microelectrode. It is found that in the 0.02–0.5 V/RHE potential range, bimetallic composites exhibit a much higher electrocatalytic activity than single-metal composites. The peak current describes a volcano plot as a function of the composition, with a maximum for CuRh, which is 7.5 times higher than that obtained with pure rhodium (under identical metal wt.%). This synergistic effect can be rationalized directly from the electrochemical response of pure metals. It is then tentatively attributed to the fact that the first (rate determining) reduction step, corresponding to the formation of nitrites, takes place efficiently in copper-rich areas while the subsequent steps of nitrite reduction in ammonia (via hydroxylamine formation) occur in rhodium-rich areas. For the same mass of rhodium, the electrocatalytic conversion of nitrates to ammonia is 12 times more effective with CuRh than with pure rhodium. With the additional gain in active surface area due to the nanoparticle morphology compared to bulk or thin film forms, these results represent a step-forward in cost reduction of rhodium-based electrocatalysts for the conversion of nitrates to ammonia. Graphical Composites of copper-rhodium nanoparticles in graphite powder were tested for the electrochemical reduction of nitrates in alkaline media. They exhibit a much higher electrocatalytic activity for the conversion of nitrates to ammonia than composites with pure rhodium nanoparticles, up to 12 times more at a composition close to CuRh.
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0437-z
      Issue No: Vol. 9, No. 3 (2018)
       
  • Excellent Performances of Modified RuOs Bimetallic Materials as Anode
           Catalysts for Polymer Electrolyte Membrane Fuel Cells
    • Authors: Min Jeong Kim; Ok-Hee Kim; In-Su Park; Yong-Hun Cho; Yung-Eun Sung
      Pages: 352 - 358
      Abstract: Multicomponent catalysts such as RuOs/C binary electrocatalysts and Pt-modified RuOs/C (Pt-RuOs/C) ternary electrocatalysts were prepared using the sodium borohydride reduction method for use as anode materials in proton exchange membrane fuel cells (PEMFCs). The electrocatalyst particles, of size 3–4 nm, were uniformly dispersed on carbon supports and showed a similar performance to commercial Pt/C in single cell tests. In this study, we demonstrate the use of multicomponent materials with no Pt or a very low level of Pt as potential anode catalysts in an actual PEMFC device. The polarization test results showed that, when used in membrane-electrode assemblies (MEAs) within a PEMFC, the RuOs/C binary electrocatalysts exhibited a significantly enhanced electrochemical performance for hydrogen oxidation. In addition, Pt-RuOs/C revealed a similar performance to that of commercial Pt/C; the new electrocatalyst, in particular, showed excellent Pt mass activity. These results indicate that the RuOs/C catalyst is potentially an alternative anode electrocatalyst for PEMFCs. Graphical ᅟ
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0440-4
      Issue No: Vol. 9, No. 3 (2018)
       
  • Optimum Copper-Palladium Catalyst from a Combinatorial Library for
           Sensitive Non-Enzymatic Glucose Sensors
    • Authors: Isabella Pötzelberger; Cezarina Cela Mardare; Lisa Maria Uiberlacker; Sabine Hild; Achim Walter Hassel
      Pages: 359 - 369
      Abstract: The optimum activity for glucose electrocatalytic oxidation was found by screening along a large spread co-sputtered combinatorial copper-palladium library (2.6 at.% to 39.2 at.% Pd) in neutral media using flow-type scanning droplet cell microscopy (FT-SDCM). The elemental composition and the surface topography were characterized along the compositional spread using energy dispersive X-ray spectroscopy (EDX), as well as atomic force microscopy (AFM). The study proves that the entire range of alloys can be implemented in glucose detection. The highest catalytic effect was obtained at a Pd content of 8.2 at.% (E SHE = 0.58 V) with a current density value of 7.33 mA cm−2. The suitability for being used as quantitative and qualitative glucose sensor was demonstrated. The calibration performed in phosphate buffer solution containing different amounts of glucose revealed two linear regions with different sensitivities towards the quantitative glucose detection. The highest sensitivity was determined in the range of 0–25 mM glucose, which is indicated by an increase of 81.2 μA cm−2 mM−1, normalized to the stepwise increase of 1 mM glucose. Also, a good long-term stability, reproducibility (relative standard deviation ~ 5%), as well as the selective sensitivity to glucose oxidation were demonstrated by performing measurements in the presence of other compounds found in blood (e.g., ascorbic acid and uric acid). Graphical ᅟ
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0433-3
      Issue No: Vol. 9, No. 3 (2018)
       
  • Chemisorbed Oxygen at Pt(111): a DFT Study of Structural and Electronic
           Surface Properties
    • Authors: Ali Malek; Michael H. Eikerling
      Pages: 370 - 379
      Abstract: Simulations based on density functional theory are used to study the electronic and electrostatic properties of a Pt(111) surface covered by a layer of chemisorbed atomic oxygen. The impact of the oxygen surface coverage and orientationally ordered interfacial water layers is explored. The oxygen adsorption energy decreases as a function of oxygen coverage due to the lateral adsorbate repulsion. The surficial dipole moment density induced by the layer of chemisorbed oxygen causes a positive shift of the work function. In simulations with interfacial water layers, ordering and orientation of water molecules strongly affect the work function. It is found that the surficial dipole moment density and charge density are roughly linearly dependent on the oxygen surface coverage. Moreover, we found that water layers exert only a small impact on the surface charging behavior of the surface. Graphical Plane-averaged line charge density at the Pt(111)–Oad surface in the presence of one monolayer of water.
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0436-0
      Issue No: Vol. 9, No. 3 (2018)
       
  • Electrochemical Detection of Glucose in Beverage Samples Using
           Poly(3,4-ethylenedioxythiophene)-Modified Electrodes with Immobilized
           Glucose Oxidase
    • Authors: Paweł Krzyczmonik; Ewelina Socha; Sławomira Skrzypek
      Pages: 380 - 387
      Abstract: We developed two glucose biosensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) and polyacrylic acid (PAA) doped with poly(4-lithium styrenesulfonic acid) (PSSLi) or PEDOT and anthranilic acid (AA) doped with poly(4-styrenesulfonic acid) (PSSH). The first one was already mentioned in literature in similar configurations; however, the second one has not been described before. The glucose oxidase was immobilized by means of covalent bonding, which has been proved by spectrophotometric assay with o-dianisidine. Amperometric measurements were carried out for the determination of glucose in phosphate buffer. The prepared electrodes functioned as first-generation glucose biosensors at applied potential E = + 0.6 V during t = 30 s. The elaborated procedure was validated, and all of the statistical parameters met the requirements for biosensors. The presented method was successfully applied for determination of glucose concentration in food samples, such as grape juice and honey. The activity of the presented biosensors was also studied in the presence of ascorbic acid and uric acid, acting as interfering agents. Graphical ᅟ
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0442-2
      Issue No: Vol. 9, No. 3 (2018)
       
  • Microwave-Irradiation Polyol Synthesis of PVP-Protected Pt–Ni
           Electrocatalysts for Methanol Oxidation Reaction
    • Authors: Ntombizodwa R. Mathe; Manfred R. Scriba; Rirhandzu S. Rikhotso; Neil J. Coville
      Pages: 388 - 399
      Abstract: Bimetallic Pt–Ni nanoparticles were synthesized for use as electrocatalysts for the methanol oxidation reaction using a cost-effective microwave-irradiation synthesis procedure that offers precise temperature control. By varying the concentration of Ni in the Pt matrix, it was demonstrated that the electrocatalytic activity of the particles declined as the Ni content was increased, with a 50:50 Pt:Ni mixture giving the best performance. This in turn showed that the Pt electrocatalytically active surface area was affected by the incorporation of Ni atoms into the Pt lattice. No further calcination of the microwaved catalysts was required resulting in the synthesis of novel and highly active catalysts, which possessed higher activity than some commercially available Pt catalysts. The catalysts also exhibited good CO resistance and long-term stability behavior. Graphical ᅟ
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0441-3
      Issue No: Vol. 9, No. 3 (2018)
       
  • Oxygen Electroreduction in Alkaline Solution on Pd Coatings Prepared by
           Galvanic Exchange of Copper
    • Authors: Madis Lüsi; Heiki Erikson; Maido Merisalu; Aarne Kasikov; Leonard Matisen; Väino Sammelselg; Kaido Tammeveski
      Pages: 400 - 408
      Abstract: Thin Pd coatings were obtained on glassy carbon electrodes by galvanically replacing the electron beam-deposited copper layers with palladium. The prepared electrodes were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The electrodes were electrochemically tested for oxygen reduction reaction (ORR) employing the rotating disc electrode (RDE) method in alkaline solution. The remaining copper was detected for two of the thickest (5 and 10 nm) sacrificial Cu layers using energy-dispersive X-ray spectroscopy (EDX). SEM images of thin Pd films showed some larger particle growth for all the studied film thicknesses, but spherical particles such as those achieved for example by the electron beam evaporation method were not visible. Specific activity of the electrodes for O2 reduction did not depend on the thickness of the sacrificial copper layer. The O2 reduction reaction followed a four-electron pathway with a mechanism similar to that of commercial Pd/C, where the first electron transfer to the O2 molecule is the rate-determining step. Graphical ᅟ
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0445-z
      Issue No: Vol. 9, No. 3 (2018)
       
  • A Simple Method to Establish the Relationship Between the Equilibrium
           Polarization Resistance and the Elementary Kinetic Parameters of an
           Electrocatalysed Reaction
    • Authors: María A. Montero; Carlos A. Marozzi; María R. Gennero de Chialvo; Abel C. Chialvo
      Pages: 409 - 415
      Abstract: A simple and rigorous methodology to establish the relationship between the faradaic equilibrium polarization resistance of an electrocatalytic reaction with the elementary kinetic parameters involved in the reaction mechanism is proposed. It was derived through an alternative method, which avoided the differentiation of the corresponding current-overpotential dependence. This formalism includes the cases where both, reactants and products, exhibit diffusion contributions. It is demonstrated that the equilibrium polarization resistance is the sum of both, faradaic and diffusion, contributions. Each diffusion term has a linear variation with the inverse of the limiting diffusion current density of the species involved. This behavior was exemplified with two different experimental data sets for the hydrogen electrode reaction, obtained on a rotating disc and microelectrodes, respectively. Graphical Experimental equilibrium polarization resistance is the sum of faradaic ( \( {R}_p^o \) ) and diffusion ( \( {R}_p^d \) ) contributions. A simple and novel methodology is presented for the derivation of the relationship between \( {R}_p^o \) and the equilibrium reaction rates of the elementary steps ( \( {v}_i^e \) ). It is also demonstrated the linear variation of \( {R}_p^d \) with the inverse of the limiting diffusion current density.
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0443-1
      Issue No: Vol. 9, No. 3 (2018)
       
  • On the Corrosion Performance of Module-Mounting Assemblies for
           Ground-Mounted Photovoltaic Power Station
    • Authors: Boguslaw Pierozynski; Henryk Bialy
      Pages: 416 - 427
      Abstract: The present paper reports the corrosion performance results of construction materials employed for the manufacture of mounting assemblies for ground-mounted photovoltaic (PV) power stations. For this purpose, the corrosion behavior of industrial hot-dip Zn-coated steel sheets was compared with that of Magnelis® type steel coating. Experiments involved samples in continuous exposure in 3 wt% NaCl solution along with regular assessment of their corrosion parameters by means of major (impedance spectroscopy, linear and Tafel polarization plots) electrochemical techniques. Analyses of surface/cross-sectional morphology and elemental compositions of metal-coated samples were carried out by means of SEM and EDX spectroscopy techniques. Graphical ᅟ
      PubDate: 2018-05-01
      DOI: 10.1007/s12678-017-0446-y
      Issue No: Vol. 9, No. 3 (2018)
       
  • Graphitized Nitrogen-Doped Ordered Mesoporous Carbon Derived from Ionic
           Liquid; Catalytic Performance Toward ORR
    • Authors: Mohammad Rafiee; Babak Karimi; Hamidreza Shirmohammadi
      Abstract: Nitrogen-doped ordered mesoporous carbon (OMC) materials were fabricated by the carbonization of ionic liquid (1-methyl-3-phenethyl-1H-imidazolium hydrogen sulfate) and guanine using hard templating with ordered mesoporous silica SBA-15. Porosity, order of graphitization, and nitrogen content of as-synthesized OMCs were evaluated as the result of carbonization temperature and the content of guanine in precursors. Ionic liquid impregnated graphite electrode was used as simple and novel probe for the electrochemical characterization the resulted OMCs and their catalytic activity toward oxygen reduction reaction (ORR). The effects of structural characteristics of OMCs as the result of carbonization temperature and guanine contents were studied on ORR. This study gives both insights on the mechanism of ORR on different nitrogen functionalities in nitrogen-doped carbon nanostructures and how to treat samples to maximize the catalytic efficiency toward ORR. Graphical
      PubDate: 2018-04-19
      DOI: 10.1007/s12678-018-0472-4
       
  • Efficient and Cost-effective Photoelectrochemical Degradation of Dyes in
           Wastewater over an Exfoliated Graphite-MoO 3 Nanocomposite Electrode
    • Authors: Onoyivwe Monday Ama; Neeraj Kumar; Feyisayo Victoria Adams; Suprakas Sinha Ray
      Abstract: Herein, we prepared hexagonal MoO3 (h-MoO3) nanorods by homogenous co-precipitation and utilized them to fabricate a composite h-MoO3-exfoliated graphite (EG) electrode. The above composite was characterized by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, and UV-Vis spectroscopy, and used for the degradation of cationic (methylene blue, MB) and anionic (methyl red, MR) dyes in synthetic wastewater. The efficiency of this degradation was assessed by UV-Vis spectroscopy and electrochemical techniques. Good dispersion of h-MoO3 in EG decreased the electron-hole recombination rate and enhanced the photon absorption efficiency of the EG-MoO3 electrode, which therefore exhibited a higher dye photodegradation efficiency than the bare EG one. Specifically, the efficiencies of 180-min MB photodegradation over EG and EG-MoO3 electrodes were 66.9 and 88.55%, respectively, whereas the corresponding values for MR were 68.0 and 92.22%, respectively, i.e., MR was degraded more effectively than MB. Furthermore, photoelectrochemical oxidation was shown to be more efficient than purely photolytic and electrochemical oxidation, which, together with the ease of preparation, low cost, and high photoactivity/stability of the fabricated nanocomposite electrode makes it potentially suitable for industrial wastewater treatment. Graphical abstract ᅟ
      PubDate: 2018-04-16
      DOI: 10.1007/s12678-018-0471-5
       
  • The Native Oxide on Titanium Metal as a Conductive Model Substrate for
           Oxygen Reduction Reaction Studies
    • Authors: Sebastian Proch; Shuhei Yoshino; Naoko Takahashi; Juntaro Seki; Satoru Kosaka; Kensaku Kodama; Yu Morimoto
      Abstract: Very thin Pt layers on inexpensive substrates are promising oxygen reduction reaction (ORR) catalysts for polymer electrolyte fuel cells (PEFCs). TiOx is considered a suitable substrate but shows problems with conductivity, thus masking chemical effects by semiconductor effects (mismatch in energy states hindering electron transport). The native oxide on metallic Ti (TiOx/Ti) has been used as a novel and promising model substrate for ORR studies eliminating semiconductor effects. A high-coverage “particle” layer with high specific ORR activity was formed via electrodeposition from Ar-saturated solution. While high specific activities could be demonstrated, the concept could not be enhanced to high mass activities by limiting the Pt deposition amount. The approach to quench Pt deposition by introducing CO failed due to its adsorption to the TiOx/Ti substrate before metal deposition and thus the prevention of layer formation. A similar approach for the Pt/Au codeposition was also unsuccessful manifesting the TiOx/Ti-CO incompatibility even further. Graphical CO, blessing, and curse: Pt deposition from Ar-saturated solution leads to a “film”-like deposit with high specific ORR activity. In contrast, the corresponding CO-saturated solution leads to deposition termination but a smooth monolayer is not formed due to interaction of CO with the TiOx/Ti substrate and, consequently, very low ORR activity is obtained.
      PubDate: 2018-04-11
      DOI: 10.1007/s12678-018-0465-3
       
  • Electrocatalytic Cascade Reaction of Aldehydes and 4-Hydroxy-6-methyl-2 H
           -pyran-2-one
    • Authors: Michail N. Elinson; Olga O. Sokolova; Alexander D. Korshunov; Fructuoso Barba; Belen Batanero
      Abstract: The electrolysis of salicylaldehydes and 4-hydroxy-6-methyl-2H-pyran-2-one in an undivided cell in alcoholic media and in the presence of alkali metal halides results in rapid and efficient formation of the substituted 3-acetoacetylcoumarins in 85–93% product yields and 425–930% current efficiency. This novel chain electrocatalytic process reveals a “green” and advantageous route to functionalized 3-acetoacetylcoumarins having promising properties for the different biomedical and other practical applications. The analogous process with arylaldehydes leads to substituted 3,3′-(arylmethylene)bis(4-hydroxy-6-methyl-2H-pyran-2-ones). Thus, under mild conditions, this simple electrocatalytic system produces the electrochemically induced Knoevenagel condensation of aldehydes and 6-methyl-2H-pyran-2-one with either subsequent rearrangement in case of salicylaldehydes towards 3-acetoacetylcoumarins or further addition of 6-methyl-2H-pyran-2-one molecule in case of arylaldehydes, leading to substituted 3,3′-(arylmethylene)bis(4-hydroxy-6-methyl-2H-pyran-2-ones). Graphical abstract ᅟ
      PubDate: 2018-04-07
      DOI: 10.1007/s12678-018-0470-6
       
  • Silver/Nickel Oxide (Ag/NiO) Nanocomposites Produced Via a Citrate Sol-Gel
           Route as Electrocatalyst for the Oxygen Evolution Reaction (OER) in
           Alkaline Medium
    • Authors: M. Z. Iqbal; R. J. Kriek
      Abstract: A series of Ag/NiO nanocomposite electrocatalysts, with a general molecular formula of Ag x Ni1 − xO, was synthesised employing the citrate sol-gel route and tested for the oxygen evolution reaction (OER) in 0.1 M KOH solution. Crystal structure, morphology and stoichiometry of the catalysts were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The face-centred cubic (fcc) crystalline structure of NiO was revealed as being dominant, having an average crystallite size of 9.6 nm. SEM revealed a non-uniform, cotton-like surface for NiO showing aggregation of particles. Crystallinity of the different synthesised compounds decreased as the Ag content increased. The maximum OER activity was observed for pristine NiO, without any Ag additive, requiring an overpotential of only 263 mV to obtain a current density of 10 mA cm−2 at 25 °C. The addition of Ag inhibited the OER electrocatalytic activity, which might be due to Ag oxidation being observed at 1.431 V. Graphical ᅟ
      PubDate: 2018-01-22
      DOI: 10.1007/s12678-018-0455-5
       
 
 
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