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  • Methanol Electrooxidation on Nickel Nanoparticles Decorating Graphite Flakes Surface
    Electrocatalysis (IF 2.311) Pub Date : 2020-01-15
    Yunier Garcia-Basabe, Renan Gustavo Coelho De Souza Dos Reis, Rafael Otoniel Ribeiro Rodrigues da Cunha, Dunieskys Gonzalez Larrude, Kelly Daiane Sossmeier, Jose Ricardo Cezar Salgado

    In the present work, a simple approach was proposed to produce nanocomposites of nickel nanoparticles decorating graphite flake surface (Ni-NP/graphite) from a ball milling method for methanol electrooxidation reaction. Nickel nanoparticles (Ni-NPs) were obtained after milling for 40 h at 400 rpm. The nanocomposites were prepared blending Ni-NPs and graphite flakes and milling at different ball rotation speeds (100, 200, 300, and 400 rpm). Good agreement between scanning transmission electron microscopy and X-ray diffraction results was found, reporting average particle diameter size of 4.9 nm and average crystallite size of 5.5 nm for Ni-NPs. The methanol electrocatalytic activity and stability of Ni-NPs/graphite nanocomposites were evaluated using cyclic voltammetry and chronoamperometry techniques. The possible methanol electrooxidation mechanism in Ni-NP/graphite nanocomposites was established from deconvolution of the anodic parts of voltammetric curves. The more efficient electrocatalytic activity and stability was found for Ni-NPs/graphite nanocomposite prepared using lower rotation speed (100 rpm). This behavior is associated to the loss of graphite crystallinity and consequently decreasing of its electronic conductivity with the increase of the ball milling energy which is directly related to the rotation speed during decoration procedure.

    更新日期:2020-01-15
  • Preventing the Deactivation of Gold Cathodes During Electrocatalytic CO 2 Reduction While Avoiding Gold Dissolution
    Electrocatalysis (IF 2.311) Pub Date : 2019-10-26
    Hani Taleshi Ahangari, Aaron T. Marshall

    The electrochemical reduction of CO2 on gold cathodes was investigated, and the major products were found to be CO, H2 and formate, which is consistent with existing literature. The Faradaic efficiency for CO production decreased from around 60 to 10% over the course of 4 h when the electrolysis was performed at – 5 mA cm–2 in 0.2 M KHCO3 saturated with CO2. This deactivation was accompanied by an increase in the selectivity of the cathode towards H2 and formate production, which is normally attributed to the deposition of metals from trace impurities in the electrolyte or surface-bound species formed during the reaction. In this case, the deactivation was found to be due to the deposition of Cu, Zn and possibly Fe from the electrolyte, with the presence of Fe strongly enhancing H2 production, the Cu deposition increasing the formate production rate and Zn enhancing both H2 and formate production. While the accumulation of these poisons can be prevented with periodic anodic treatments (using methods previously described in the literature), these treatments lead to significant gold dissolution, with up to 450 ppb of gold found in the electrolyte after 4 h of electrolysis, and thus is unsuitable for use in long-term CO2 reduction systems. This dissolution is expected to alter the surface structure and thus selectivity of the cathode. Therefore, alternative electrochemical cleaning protocols (periodic cyclic voltammetry, open-circuit and low anodic current treatments) were investigated as methods to remove these poisons without significant gold corrosion occurring. The best approach to prevent the deactivation of gold cathodes during CO2 reduction is to cycle the potential between − 0.5 and 0.5 V vs Ag|AgCl every 15 min during long-term electrolysis. It is also shown that simply interrupting the CO2 reduction process every 15 min with 4 min at open circuit can also partially prevent the deactivation of the CO2 reduction reaction as will short anodic current pulses.

    更新日期:2020-01-14
  • Iodide as Terminating Agent for Platinum Electrodeposition
    Electrocatalysis (IF 2.311) Pub Date : 2019-10-25
    Sebastian Proch, Shuhei Yoshino, Juntaro Seki, Naoko Takahashi, Kousuke Kitazumi, Kensaku Kodama, Yu Morimoto

    “Approximate” Pt layers hold great promise to be highly active and durable oxygen reduction reaction (ORR) catalysts. Electrodeposition of such layers on relevant catalyst supports, for example TiOx, requires the application of a “Pt-on-Pt” deposition limiter to keep layers thin and leave no atom behind for catalysis. Classic Pt-on-Pt deposition limiting agents like CO and over-potential deposited hydrogen (Hopd) work reliably on gold but fail on TiOx substrates. Iodide, in contrast, is a new “Pt-on-Pt” deposition limiting agent that shows substantial Pt layer thickness reduction during electrodeposition on gold as well as TiOx substrates.

    更新日期:2020-01-14
  • The Modification of Electrochemical Properties of Pd by its Alloying with Ru, Rh, and Pt: the Study of Ternary Systems
    Electrocatalysis (IF 2.311) Pub Date : 2020-01-10
    Katarzyna Hubkowska, Suwaphid Themsirimongkon, Surin Saipanya, Mariusz Łukaszewski, Andrzej Czerwiński

    Abstract Pd-rich Pd-Pt-Ru alloys, obtained by electrodeposition, were characterized by microscopic and electrochemical techniques at room temperature (298 K). The influence of the electrode potential and bulk composition on the amount of electrosorbed hydrogen was studied in 0.5 M H2SO4 aqueous solutions and compared with the behavior of Pd-Rh-Ru alloys under identical experimental conditions. The maximum hydrogen absorption capacities gradually decreased with increasing total amounts of both Pt and Ru in the alloy bulk. The effects of both Pd bulk content and the relative proportions between other components in Pd-Pt-Ru and Pd-Rh-Ru electrodes are also responsible for the changes in maximum hydrogen absorption capacity, the decrease in the potential of the alpha-beta phase transition, and the decrease in the absorption/desorption hysteresis. During voltammetric cycling in 0.5 M H2SO4 in the potential range − 0.1÷1.5 V vs. RHE (scan rate 0.1 V/s), the freshly obtained deposits became enriched with Pt due to electrodissolution of Ru and Pd, and the electrode morphology was also altered due to hydrogen electrosorption and surface oxidation. Graphical Abstract

    更新日期:2020-01-11
  • Alkaline Ethanol Oxidation Reaction on Carbon Supported Ternary PdNiBi Nanocatalyst using Modified Instant Reduction Synthesis Method
    Electrocatalysis (IF 2.311) Pub Date : 2020-01-03
    Bernd Cermenek, Boštjan Genorio, Thomas Winter, Sigrid Wolf, Justin G. Connell, Michaela Roschger, Ilse Letofsky-Papst, Norbert Kienzl, Brigitte Bitschnau, Viktor Hacker

    Direct ethanol fuel cells (DEFC) still lack active and efficient electrocatalysts for the alkaline ethanol oxidation reaction (EOR). In this work, a new instant reduction synthesis method was developed to prepare carbon supported ternary PdNiBi nanocatalysts with improved EOR activity. Synthesized catalysts were characterized with a variety of structural and compositional analysis techniques in order to correlate their morphology and surface chemistry with electrochemical performance. The modified instant reduction synthesis results in well-dispersed, spherical Pd85Ni10Bi5 nanoparticles on Vulcan XC72R support (Pd85Ni10Bi5/C(II-III)), with sizes ranging from 3.7 ± 0.8 to 4.7 ± 0.7 nm. On the other hand, the common instant reduction synthesis method leads to significantly agglomerated nanoparticles (Pd85Ni10Bi5/C(I)). EOR activity and stability of these three different carbon supported PdNiBi anode catalysts with a nominal atomic ratio of 85:10:5 were probed via cyclic voltammetry and chronoamperometry using the rotating disk electrode method. Pd85Ni10Bi5/C(II) showed the highest electrocatalytic activity (150 mA⋅cm−2; 2678 mA⋅mg−1) with low onset potential (0.207 V) for EOR in alkaline medium, as compared to a commercial Pd/C and to the other synthesized ternary nanocatalysts Pd85Ni10Bi5/C(I) and Pd85Ni10Bi5/C(III). This new synthesis approach provides a new avenue to developing efficient, carbon supported ternary nanocatalysts for future energy conversion devices.

    更新日期:2020-01-04
  • Efficient Photoelectrocatalytic Degradation of BTEX Using TiO 2 /CuO/Cu 2 O Nanorod-Array Film as the Photoanode and MWCNT/GO/Graphite Felt as the Photocathode
    Electrocatalysis (IF 2.311) Pub Date : 2020-01-02
    Danial Safarvand, Iraj Naser, Mohammad Samipourgiri, Mehdi Arjmand

    Abstract Wastewater treatment challenges by conventional methods have necessitated the need for alternative/complementary methods that are environmentally safe and efficient especially towards recalcitrant organic pollutants. In this regard, a novel highly active visible-light responsive photoanode with the ternary hybrid CuO/Cu2O/TiO2 nanorods array film is proposed to enhance electron transfer in the photoelectrocatalytic (PEC) degradation of BTEX (benzene, toluene, ethyl benzene, and xylenes) by combining with MWCNT/GO/GF cathode. Structural, morphological, optical, electrochemical, and elemental analysis of proposed electrodes is investigated in detail. Response surface methodology (RSM) comprising of full-factorial central composite design (CCD) with five factors and five levels has been used to examine the effects of different operating parameters such as electrode distance, current density, treatment time (t), solution pH, and conductivity in a PEC batch reactor. BTEX mineralization in aqueous solution was examined with multiple responses such as chemical oxygen demand (COD) and specific energy consumption. During multiple response optimization, the desirability function approach was employed to concurrently maximize COD removal and minimize energy consumption. At the optimum condition, 81.3% COD removal and 9.5 kWh/kg of COD removed were observed. The photoelectrocatalytic oxidization mechanism of BTEX with proposed anode and cathode was discussed, then the possible degradation pathway of BTEX identified using GC–MS. Graphical abstract

    更新日期:2020-01-02
  • Electrocatalytic Behavior of Hydrogenated Pd-Metallic Glass Nanofilms: Butler-Volmer, Tafel, and Impedance Analyses
    Electrocatalysis (IF 2.311) Pub Date : 2019-12-21
    Baran Sarac, Tolga Karazehir, Marlene Mühlbacher, A. Sezai Sarac, Jürgen Eckert

    Electrocatalytic activity and sorption behavior of hydrogen in nanosized Pd–Si–(Cu) metallic glass thin film and Pd thin film electrodes sputtered on a Si/SiO2 substrate were investigated by linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrode MG4 (Pd69Si18Cu13) exhibits the best performance with the highest electrocatalytic activity in the hydrogen evolution region with less than half of the Tafel slope of Pd thin film of the same thickness and lowest overpotential at 10 mA cm−2. A new approach has been adopted by a nonlinear fitting of the entire region of the polarization curve (far- and near-equilibrium cathodic and anodic regions) to the Butler-Volmer model. α parameter is lowest for the MG2 electrode (Pd79Si16Cu5), marking that nonequilibrium conditions change the reaction kinetics. Together with MG2, MG4 shows the lowest Bode magnitude values for hydrogen sorption and evolution regions, indicating that the bonding and release of hydrogen atoms to the electrode is easier. MG4 electrode shows a dramatic decrease of the overpotential after 100 cycles, yielding an increase in hydrogen activity. Besides, MG4 exhibits the sharpest current density drop in the HER region in cyclic voltammetry compared with other MG and Pd electrodes, indicating higher electrocatalytic activity towards hydrogen evolution. The findings highlight the influence of the selected metallic glasses for the design and development of metal catalysts with higher sorption kinetics and/or electrocatalytic turnover.

    更新日期:2019-12-21
  • DFT Calculations of the Electrochemical Adsorption of Sulfuric Acid Anions on the Pt(110) and Pt(100) Surfaces
    Electrocatalysis (IF 2.311) Pub Date : 2019-12-14
    Juan A. Santana, Yasuyuki Ishikawa

    We have studied the electrochemical adsorption of sulfuric acid anions on the Pt(110) and Pt(100) surfaces employing calculations based on the density functional theory. Our results show that bisulfate, as well as hydronium–sulfate ion pairs, can be adsorbed on Pt(110) at electrode potentials below 0.4 V vs. the reversible hydrogen electrode (RHE). On the other hand, only bisulfate is stable on Pt(100) at potentials below 0.6 V (RHE). At a higher potential, the results indicate that only sulfate is stable on these surfaces. The sulfuric acid anions are two-fold coordinated on Pt(110) and Pt(100), which contrasts with the Pt(111) surface where the adsorbed conformation of the anions can change from a two-fold to three-fold coordination. These differences in the coordination of the adsorbed sulfuric acid anions on Pt(111), Pt(110), and Pt(100) could help rationalize the dissimilar voltammetric features of these surfaces in sulfuric acid solutions.

    更新日期:2019-12-17
  • Enhanced Photoelectrocatalytical Performance of Inorganic-Inorganic Hybrid Consisting BiVO 4 , V 2 O 5 , and Cobalt Hexacyanocobaltate as a Perspective Photoanode for Water Splitting
    Electrocatalysis (IF 2.311) Pub Date : 2019-12-10
    K. Trzciński, M. Szkoda, M. Sawczak, A. Lisowska-Oleksiak

    Thin layers of BiVO4/V2O5 were prepared on FTO substrates using pulsed laser deposition technique. The method of cobalt hexacyanocobaltate (Cohcc) synthesis on the BiVO4/V2O5 photoanodes consists of cobalt deposition followed by electrochemical oxidation of metallic Co in K3[Co(CN)6] aqueous electrolyte. The modified electrodes were tested as photoanodes for water oxidation under simulated sunlight irradiation. Deposited films were characterized using UV-Vis spectroscopy, Raman spectroscopy, and scanning electron microscopy. Since the V2O5 is characterized by a narrower energy bandgap than BiVO4, the presence of V2O5 shifts absorption edge (ΔE = ~0.25 eV) of modified films towards lower energies enabling the conversion of a wider range of solar radiation. The formation of heterojunction increases photocurrent of water oxidation measured at 1.2 V vs Ag/AgCl (3 M KCl) to over 1 mA cm-2, while bare BiVO4 and V2O5 exhibit 0.37 and 0.08 mA cm-2, respectively. On the other hand, the modification of obtained layers with Cohcc shifts onset potential of photocurrent generation into a cathodic direction. As a result, the photocurrent enhancement at a wide range of applied potential was achieved.

    更新日期:2019-12-11
  • Electrochemical Energy Conversion from Direct Oxidation of Glucose on Active Electrode Materials
    Electrocatalysis (IF 2.311) Pub Date : 2019-11-28
    Charly Lemoine, Lionel Dubois, Teko W. Napporn, Karine Servat, Kouakou B. Kokoh

    Electrochemical behavior of carbon-supported platinum and gold-based catalysts towards glucose oxidation and oxygen reduction reaction were investigated separately in alkaline medium before implementing the glucose/O2 fuel cell with the best anode and cathode catalysts. These electrode materials, prepared from a surfactant-free synthesis approach, were then used in low metal loadings in a fuel cell operating in alkaline medium which can be easily removed on resin for analyzing all the reaction products, as any toxic compound has to be avoided for the interest of this specific application. Pt/rGO is the most active anode towards the glucose oxidation. For all tested catalysts, this oxidation reaction leads mainly to gluconate without chromatographically detectable reaction products resulted from C–C bond cleavage.

    更新日期:2019-12-11
  • Electrochemical Impedance Spectroscopy Characterization of Silicon-Based Electrodes for Li-Ion Batteries
    Electrocatalysis (IF 2.311) Pub Date : 2019-11-28
    Maciej Ratynski, Bartosz Hamankiewiecz, Michał Krajewski, Maciej Boczar, Dominika A. Buchberger, Andrzej Czerwinski

    Lithium-ion cells are currently the most promising electrochemical power sources. New high-capacity electrodes made of silicon are presently under intensive study. Besides its high capacity, silicon undergoes a significant volume increase (up to 300%) during lithiation. The main research on the silicon-based electrodes is focused on the nanostructure development and capacity/life cycle measurements. Variations in other electrochemical parameters, SEI layer resistance and charge transfer resistance, are also important and give the information about structural changes and mechanisms of side processes that occur during an electrode lithiation/delithiation. This work presents electrochemical impedance spectroscopy measurements of three silicon–graphite composite electrodes, containing various silicon contents. A clear correlation between the SEI and charge transfer resistances and the active material lithiation level is presented. The effect of the cycle number on the measured parameters is also visible. We present possible mechanisms that lead to observed changes and highlight the requirement of the proper Si-based electrode formation and the correct estimation of operational parameters.

    更新日期:2019-12-11
  • Correlation between Precursor Properties and Performance in the Oxygen Reduction Reaction of Pt and Co “Core-shell” Carbon Nitride-Based Electrocatalysts
    Electrocatalysis (IF 2.311) Pub Date : 2019-11-21
    Vito Di Noto, Enrico Negro, Angeloclaudio Nale, Pawel J. Kulesza, Iwona A. Rutkowska, Keti Vezzù, Gioele Pagot

    This report shows the synthesis of a new family of “core-shell” carbon nitride (CN)-based electrocatalysts (ECs) for the oxygen reduction reaction (ORR) in acid medium. The ECs comprise “cores” of carbon black nanoparticles (NPs) that are covered by a CN “shell” embedding the active sites. The latter include Pt as the “active metal” and Co as the “co-catalyst.” The interplay between the synthesis parameters, the chemical composition, and the ORR performance of the final ECs is elucidated. In particular, the ORR performance and reaction mechanism are studied both in an: (i) “ex-situ” setup, by means of cyclic voltammetry with thin-film rotating ring-disk electrode (CV-TF-RRDE) measurements; and (ii) “in-situ” experiment, i.e., in single proton exchange membrane fuel cells (PEMFCs) tested under operating conditions. A structural hypothesis is proposed that explains both the “ex situ” and the “in situ” ORR results on the basis of: (i) the relative amounts of the reactants used in the precursor synthesis; and (ii) the main temperature of the pyrolysis process (Tf) adopted in the preparation of the ECs. It is shown that the understanding of the fundamental features of the physicochemical processes involved in the preparation of the ECs is crucial in order to improve the proposed synthesis route and to yield ORR ECs exhibiting a performance level beyond the state of the art.

    更新日期:2019-12-11
  • Facile Synthesis of a Carbon-Encapsulated Pd Catalyst for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells
    Electrocatalysis (IF 2.311) Pub Date : 2019-11-12
    Jeongsoo Hwang, Youngkwang Kim, Mohanraju Karuppnan, Taeho Lim, Oh Joong Kwon

    The key to popularizing proton exchange fuel cells is developing highly active, stable, and cost-effective catalysts for oxygen reduction reaction. Pd is considered as an alternative to Pt due to its high tolerance to poisoning and electronic similarity with Pt, which is a robust but expensive catalyst. However, its vulnerability to dissolving in acidic media prevents the use of Pd as an oxygen reduction reaction catalyst. In this study, a facile synthesis method was developed to prepare a carbon-encapsulated Pd catalyst using aniline. The oxidative polymerization of aniline with a Pd precursor formed Pd nanoparticles embedded in a rod-shaped polyaniline matrix. The polyaniline matrix was carbonized using heat treatment, which then acted as a source of N-containing carbon layer that protects Pd nanoparticles from dissolution and improves oxygen reduction reaction activity. The stability and oxygen reduction reaction activity of the synthesized Pd catalyst were strongly dependent on the heat treatment temperature. The Pd catalysts heat-treated at 300 °C and 500 °C exhibited improved activity and stability as compared to commercial Pd/C. We envision that this method is suitable for mass production of active and stable oxygen reduction reaction catalysts in proton exchange fuel cells.

    更新日期:2019-12-11
  • On the Influence of the Extent of Oxidation on the Kinetics of the Hydrogen Electrode Reactions on Polycrystalline Nickel
    Electrocatalysis (IF 2.311) Pub Date : 2019-11-12
    Alexandr G. Oshchepkov, Antoine Bonnefont, Elena R. Savinova

    The influence of the extent of oxidation of Ni electrodes on the kinetics of the hydrogen oxidation (HOR) and evolution (HER) reactions has been explored by combining an experimental cyclic voltammetry and chronoamperometry study with microkinetic modeling. The HOR/HER specific activity of the Ni/NiOx electrodes follows a volcano-type dependence with a maximum at 30% NiOx coverage corresponding to a 14-fold increase (nominally from 2.2 to 32.8 μA cm−2Ni) of the specific activity calculated as the exchange current density normalized by the electrochemical surface area of Ni active sites. The kinetic model suggests that the experimentally observed changes in the shape of current-potential curves as well as the HOR/HER specific activities are mostly due to the NiOx coverage–dependent strength of adsorption of hydrogen atoms. The latter is accompanied by an increase of the rate of the Volmer step and a decrease of the potential of OHad adsorption on Ni centers in the vicinity of surface Ni oxides.

    更新日期:2019-12-11
  • Biocompatible Palladium Telluride Quantum Dot-Amplified Biosensor for HIV Drug
    Electrocatalysis (IF 2.311) Pub Date : 2019-11-09
    Usisipho Feleni, Unathi Sidwaba, Nomaphelo Ntshongontshi, Lindsay Wilson, Emmanuel Iwuoha

    Indinavir (IDV) is a potent and well-tolerated protease inhibitor antiretroviral (ARV) drug used as a component of the highly active antiretroviral therapy (HAART) of human immunodeficiency virus (HIV). It undergoes hepatic first-pass metabolism that is catalysed by microsomal cytochrome P450-3A4 enzyme (CYP3A4), which results in pharmacokinetics that may be favourable or adverse. Therapeutic drug monitoring (TDM) of IDV during HIV treatment is therefore critical, in order to prevent the adverse effects of its first-pass metabolism and optimise an individual’s dosage regime. Biosensors are now the preferred diagnostic tools for TDM assessment at point-of-care, due to their high sensitivity and real-time response. An electrochemical biosensor for IDV was prepared by depositing a thin film of CYP3A4 (a thiolate enzyme) and thioglycolic acid-capped palladium telluride quantum dot (TGA-PdTeQD) on a cysteamine-functionalised gold disk electrode (Cyst|Au) using a combination of thiol and carbodiimide covalent bonding chemistries. The electrochemical signatures of the biosensor (CYP3A4|TGA-PdTeQD|Cyst|Au) were determined by cyclic voltammetry (CV) that was performed at a scan rate of 500 mV s−1, and the sensor responses at the characteristic reduction peak potential value of − 0.26 V were recorded. The sensitivity, linear range (LR) and limit of detection (LOD) values of the indinavir biosensor were 4.45 ± 0.11 μA nM−1 IDV, 0.5–1.0 nM IDV (i.e. 3.6 × 10−4–7.1 × 10−4 mg L−1 IDV) and 4.5 × 10−4 mg L−1 IDV, respectively. The values of the two analytical parameters (LR and LOD) of the biosensor were by up to four orders of magnitude lower than the maximum plasma concentration (Cmax) values of indinavir (0.13–8.6 mg L−1 IDV). The IDV biosensor was successfully used to detect IDV in human serum samples containing dissolved indinavir tablet. This, therefore, indicates the indinavir biosensor’s suitability for TDM applications, using samples obtained within 1–2 h of drug intake at point-of-care, for which very low levels of the drug are expected.

    更新日期:2019-12-11
  • Kelp-Derived Activated Porous Carbon for the Detection of Heavy Metal Ions via Square Wave Anodic Stripping Voltammetry
    Electrocatalysis (IF 2.311) Pub Date : 2019-11-09
    Jibiao Guan, Yini Fang, Ting Zhang, Lina Wang, Han Zhu, Mingliang Du, Ming Zhang

    Biomass-derived porous carbon materials with environmental adaptability and superior specific surface area have become one of the most promising materials in 21st era, especially in the electrochemical application. Herein, we proposed a kelp-derived carbon material (KPC) with a unique highly disordered graphite layer structure as an outstanding sensor via facile KOH activation method. The BET adsorption-desorption isotherm of KPC shows a typical IUPAC I type, and KPC possesses a high specific surface area with 2064 m2 g−1. Morphology observation and pore size analysis indicate that its porous-rich structure comprises countless micropores and mesopores. This unique structure of KPC not only provides massive active sites but exhibits high sensitivity in the detection of heavy metal by square wave anodic stripping voltammetry (SWASV), with Pb2+ at 53.4 μA μM−1 and Cd2+ at 26.5 μA μM−1 in simultaneous detection. This study reports a new strategy for the detection of heavy metal ions using porous metal-free carbon materials.

    更新日期:2019-12-11
  • Methanol Oxidation in Alkaline Media with Pt-Au/fMWCNTs and Pt-Pd/fMWCNTs Electrocatalysts on an Exfoliated Graphite Electrode
    Electrocatalysis (IF 2.311) Pub Date : 2019-10-14
    L. S. Mpeta, S. S. Gwebu, O. A. Arotiba, N. W. Maxakato

    The poisoning of pure platinum electrodes has propelled the improvement of platinum-based alloy catalysts. In this work, we report the application of exfoliated graphite electrode as an anode platform for binary platinum-based electrocatalysts for methanol oxidation in alkaline media. Platinum-based binary electrocatalysts comprising of Pt-Au and Pt-Pd nanoparticles on functionalized multi-walled carbon nanotubes (MWCNTs) support were synthesized via polyol process. The nanocomposite electrocatalysts (Pt-Au/fMWCNTs and Pt-Pd/fMWCNTs) were characterized by transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffractometer (XRD). The electrochemical activity of the Pt-Pd/fMWCNTs and the Pt-Au/fMWCNTs electrocatalysts was assessed utilizing cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in the presence of methanol. The nanoparticles were in the size regime of 3 to 5 nm and the XRD affirmed successful functionalization of the MWCNT and its impregnation with the binary Pt nanoparticles. The electrooxidation of methanol in alkaline conditions was seen with a high current density of about 26.1 mA cm−2 on Pt-Au/fMWCNTs and 13.52 mA cm−2 on Pt-Pd/fMWCNTs electrocatalysts deposited on exfoliated graphite working electrodes. The exfoliated graphite platform is a promising electrode for fuel cell application.

    更新日期:2019-12-11
  • Influence of Mixed 6-Thioguanine-Nonionic Surfactant Adsorption Layers on Kinetics and Mechanism of Bi(III) Ion Electroreduction
    Electrocatalysis (IF 2.311) Pub Date : 2019-08-18
    W. Kaliszczak, A. Nosal-Wiercińska

    The presence of mixed 6-thioguanine-nonionic surfactant adsorption layers affects the mechanism and kinetics of the irreversible Bi(III) ion electroreduction process in chlorates(VII). Tween 80 and Triton X-100 change the dynamics of the catalytic effects of 6-thioguanine on Bi(III) ion electroreduction with the tendency of inhibition. The mechanism of catalytic activity of 6-thioguanine is associated with formation of complexes under specific conditions which exist on the electrode surface. The effects of both 6TG and suitable surfactant mixture on the first electron transfer are much greater than those on the transition of other electrons. The Bi-6TG type complex plays the main role in the Bi-6-thioguanine-Tween 80 or Bi-6-thioguanine-Triton X-100 systems, as 6-thioguanine dominates in the formation of adsorption equilibria of the studied mixtures.

    更新日期:2019-12-11
  • Heterogeneous Electro-Fenton Process by MWCNT-Ce/WO 3 Nanocomposite Modified GF Cathode for Catalytic Degradation of BTEX: Process Optimization Using Response Surface Methodology
    Electrocatalysis (IF 2.311) Pub Date : 2019-08-07
    Mohammad Ranjbar, Nasrollah Majidian, Mohammad Samipourgiri

    This study investigates the degradation and mineralization of BTEX by heterogeneous electro-Fenton process using GO/MWCNT/Fe3O4 as a catalyst and MWCNT-Ce/WO3/GF as an electrode. The nanoscale MWCNT-Ce/WO3 composite catalyst was distributed more evenly on GF surface to form a catalyst layer with higher oxygen reduction reaction performance. After optimization of pH and time variables, the Box–Behnken experimental design (BBD) and response surface methodology (RSM) were used to design and optimize the performance of proposed system and energy consumption. Analysis of variance (ANOVA) revealed that the quadratic model was adequately fitted to the experimental data with R2 (0.98) and adj-R2 (0.97). The significance levels of linear and interaction effects of the reaction parameters on process efficiency were obtained. Then, the optimization of the working conditions for the design of a sustainable treatment system with optimum efficiency was carried out using a response surface methodology. The experiment carried out in the calculated optimal conditions for the electro-Fenton degradation process (current intensity 300 mA, catalyst dosage of 0.6 g, initial BTEX concentration of 100 ppm, and electrode distance of 1 cm) showed a BTEX removal of 73.2% and energy consumption of 12.3 (kWh/m3) close to the theoretical value predicted by the model 73. 2% and 11.8 (kWh/m3), respectively. Furthermore, the reusability test of GO/MWCNT/Fe3O4 nanocomposite after several cycles confirmed the high catalytic activities of adsorbent. Comparing the proposed system with conventional GF electrode and Fe2+ catalyst showed that modification of cathode and catalyst led to increasing COD removal efficiency by around 36.6 and 31.6%, respectively. The findings of present study revealed that the proposed heterogeneous electro-Fenton process can be utilized as pre-treatment technology to improve the biodegradability and reduce the organic load of wastewater by combine oxidation and coagulation.

    更新日期:2019-12-11
  • Effects of Crystallographic Structures of Metal-Phthalocyanine on Electrocatalytic Properties of Oxygen Reduction in Acidic Condition
    Electrocatalysis (IF 2.311) Pub Date : 2019-08-13
    Satoko Takase, Yuki Aoto, Daiki Ikeda, Hideaki Wakita, Youichi Shimizu

    Effects of the crystallographic structures of metal-phthalocyanines (metal: Co, Ni, Cu, Zn) between α and β phases on electrochemical oxygen reduction catalytic activities were investigated in acidic condition. As the distances of centered-metal in the structures of α and β phases are 3.8 Å and 4.8 Å, respectively, they were closed to the size of an oxygen molecule (3.6 Å). The phases of metal-phthalocyanines were conducted by an interface deposition method. The obtained catalyst powders were characterized by means of X-ray diffraction and X-ray photoelectron spectra analyses. Electrochemical oxygen reduction performances were mainly measured by using a gas diffusion type carbon electrode loaded with a metal-phthalocyanine. It was confirmed that the catalytic activities of cobalt- and copper-centered phthalocyanines were enhanced by the conversion from β to α phases. The effects of the distance between the metals in the crystallographic structures of metal-phthalocyanines should be explained by the adsorbed oxygen states that depend on the distance between the metals. The α phase has the distance which allows to form the bridge configuration of oxygen molecule which requires two adsorption sites and that eventually produces H2O by the direct 4-electron pathway. Analysis with the rotating disk electrode system showed that the α-phased metal-phthalocyanines enhance the 4-electron reduction pathway.

    更新日期:2019-12-11
  • Vulcan Carbon as Support for Sputtered Oxygen Evolution Electrocatalysts
    Electrocatalysis (IF 2.311) Pub Date : 2019-07-30
    D. Coertzen, R. J. Kriek, P. B. J. Levecque, A. Falch

    The development of support structures for electrocatalysts has received a great deal of attention over the last decade, with carbon structures (i.e. nanostructures, Vulcan carbon (VC)) having been studied extensively. Carbon support structures increase the surface area, stability and activity of electrocatalysts in most cases, and can be used to overcome the delamination of thin films. In an attempt to (i) obtain surface structures and areas on SiO2 wafer pads, for combinatorial high-throughput sputtering and screening, that are comparable to glassy carbon (GC), (ii) eliminate delamination of the electrocatalyst and (iii) increase activity and stability, this study focused on VC:Nafion support preparation techniques. Four VC inks were prepared and used as carbon support on GC electrode inserts to analyse their effect on the activity of sputtered Ni thin films (40 nm) towards the oxygen evolution reaction (OER) in alkaline media. Linear sweep voltammetry (LSV) and chronopotentiometry (CP) were employed to compare the catalytic activity and stability of these sputtered Ni thin films on the various VC supports. Results suggest that similar activity compared with IrO2 and RuO2 could be achieved by sputtered Ni on VC:Nafion support, indicating improved Ni utilisation as well as improved short-term stability of the Ni thin films. These results validate the use of VC:Nafion support as substrate for sputtered electrocatalysts.

    更新日期:2019-12-11
  • Over-Potential Deposited Hydrogen (H opd ) as Terminating Agent for Platinum and Gold Electro( co )Deposition
    Electrocatalysis (IF 2.311) Pub Date : 2019-07-31
    Sebastian Proch, Shuhei Yoshino, Kousuke Kitazumi, Juntaro Seki, Kensaku Kodama, Yu Morimoto

    An “approximate” Pt monolayer is a desirable morphology for oxygen reduction reaction (ORR) catalysts with high mass activity. Such structures can, reliably, be synthesized on gold by monolayer-limited CO- or over-potential deposited hydrogen (Hopd)-terminated Pt electrodeposition. On a more appropriate catalyst support for proton-exchange membrane fuel cells (PEMFCs), namely, the native oxide on metallic titanium (TiOx/Ti), the synthesis is disrupted by preadsorption of the monolayer-limiting agent. The role of auxiliary NaCl during Hopd-terminated Pt electrodeposition (chloride-assisted Hopd termination) on TiOx/Ti is investigated and discloses effects similar to CO observed previously.

    更新日期:2019-12-11
  • Characterization of Amorphous Ni-Nb-Y Nanoparticles for the Hydrogen Evolution Reaction Produced Through Surfactant-Assisted Ball Milling
    Electrocatalysis (IF 2.311) Pub Date : 2019-09-13
    S. Ghobrial, K. M. Cole, D. W. Kirk, S. J. Thorpe

    Amorphous Ni79.2Nb12.5Y8.3 and Ni81.3Nb6.3Y12.5 nanoparticles were synthesized using cryogenic mechanical alloying followed by surfactant-assisted high energy ball milling (SA-HEBM). These alloys were tested towards the hydrogen evolution reaction (HER) along with pure crystalline Ni and Ni5Y nanoparticles also produced through SA-HEBM. This two-stage ball milling process provided a novel processing route for the production of nanostructured/amorphous materials with a wide range of possible compositions not achievable through rapid solidification, electrodeposition, or chemical reduction techniques. The investigation of different surfactant and solvent concentrations resulted in improved nanoparticle yields whereby average particle sizes between 41 and 89 nm were obtained for crystalline and amorphous materials. Electrochemical testing showed that Ni81.3Nb6.3Y12.5 exhibited the lowest Tafel values and the fastest HER kinetics on both an electrochemically active surface area and on a mass loading basis. This investigation demonstrates their potential for use in anion exchange membrane water electrolysis.

    更新日期:2019-12-11
  • One-Pot Synthesis of Highly Efficient Carbon-Supported Polyhedral Pt 3 Ni Alloy Nanoparticles for Oxygen Reduction Reaction
    Electrocatalysis (IF 2.311) Pub Date : 2019-08-08
    Yongqiang Liu, Hongming Chen, Chongchong Tian, Dongsheng Geng, Dawei Wang, Siriguleng Bai

    The oxygen reduction reaction (ORR) properties were intensely affected by the facet of electrocatalysts. For example, (111) facet of Pt3Ni alloy has been proved to have excellent ORR electrocatalytic activity. Therefore, it could be very important to synthesize Pt3Ni nanocrystals with large proportion of (111) facet. However, most reported Pt3Ni polyhedron bound by (111) facets were synthesized using capping agents like oleylamine and oleic acid. These organic ligands will hinder the intrinsic ORR performance of catalyst and require tedious process to remove. Here, we report a one-pot synthesis of capping agents free for polyhedron Pt3Ni alloy nanoparticles on carbon (Pt3Ni/C) with large proportion of Pt3Ni (111) facets. The electrocatalysts achieved an enhancement of 224% in mass activity and 8.7-fold specific activity towards ORR in comparison with commercial Pt/C catalyst. The present study provides a simple method for designing highly efficient Pt alloy electrocatalysts.

    更新日期:2019-12-11
  • Iron Oxide Nanoflower–Based Screen Print Electrode for Enhancement Removal of Organic Dye Using Electrochemical Approach
    Electrocatalysis (IF 2.311) Pub Date : 2019-08-20
    Dalibor M. Stanković, Miloš Ognjanović, Ana Espinosa, Maria del Puerto Morales, Lotfi Bessais, Karim Zehani, Bratislav Antić, Biljana Dojcinović

    In this study, for the first time, we developed a novel platform for the removal of the synthetic organic dye Reactive Blue 52 based on a screen-printed electrode (SPCE). Additionally, SPCE was supported on a nanocomposite obtained by decoration of reduced graphene oxide (RGO) with iron oxide nanoflowers (IONFs), labeled as IONF@RGO/SPCE. IONFs were synthesized by polyol-mediated reduction of iron (III) chloride and characterized. Nanocomposite was prepared using a microwave hydrothermal-assisted procedure. The high stability (service life) of the IONF@RGO/SPCE electrode was measured, and it remained almost unchanged over time, achieving the same removal efficiency after 50 cycles of usage. Electrical impedance spectroscopy (EIS) tests indicated the synergetic effect of the used IONF@RGO by reducing resistivity of the system and improving its catalytic activity, which was confirmed with cyclic voltammetry (CV tests) where the great increase of the electrochemically active surface area sites was obvious. The results clearly indicate that with this approach, the optimum removal time of the selected pollutant was only 30 min, at a working potential of 3 V and with potassium chloride as the supporting electrolyte, with color removal efficiency of 99%, while chemical oxygen demand (COD) of more than 40%, total organic carbon (TOC) decrease of around 20%, and biochemical oxygen demand (BOD5), i.e., biodegradability (BOD5/COD ratio) significantly increased were measured after only 1 h of the treatment. Overall, the electrochemical removal procedure proposed in this study could be a reliable novel system, opening a new approach to using screen print–based electrodes.

    更新日期:2019-12-11
  • Voltammetric Determination of Pb(II) Ions at a Modified Kaolinite-Carbon Paste Electrode
    Electrocatalysis (IF 2.311) Pub Date : 2019-08-13
    Seyi P. Akanji, Omotayo A. Arotiba, Duduzile Nkosi

    We report a novel application of a carbon paste electrode modified with sodium dodecyl sulphate (SDS) intercalated kaolin clay for the electrochemical detection of Pb2+in aqueous medium using square wave voltammetry. SDS was used to modify a chemically purified kaolin clay via intercalation process to prepare a carbon paste electrode. The SDS kaolin clay was obtained by intercalation of SDS into the interlayer spaces of kaolinite in the presence of heat. The purified kaolinite and its SDS intercalate were characterised using techniques such as X-ray powder diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric analysis (TGA), attenuated total reflection Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM), BET and CHNS elemental analysis. These techniques proved the successful intercalation of SDS into the interlayer spaces of the clay adsorbent. Various parameters affecting the electrochemical detection of Pb2+ were optimised. A linear current response was obtained in the concentration range of 1–100 ppb. The limit of detection was found to be 2.48 ppb. The proposed sensor also demonstrates good reproducibility after series of 10 repetitive measurements with a relative standard deviation (RSD) of about 6.30%. The interfering effects of some ions on the detection of Pb2+ were evaluated. The proposed sensor was applied for the determination of Pb2+ in a real water sample.

    更新日期:2019-12-11
  • Cobalt-Pyrazolate-Derived N-Doped Porous Carbon with Embedded Cobalt Oxides for Enhanced Oxygen Evolution Reaction
    Electrocatalysis (IF 2.311) Pub Date : 2019-11-01
    Sumbal Farid, Weiwei Qiu, Jialin Zhao, Dandan Wu, Xuedan Song, Suzhen Ren, Ce Hao

    Developing highly competent and cost-effective electrocatalysts for oxygen evolution reaction (OER) is crucial for clean renewable energy technologies. To this end, the wise assimilation of transition metal compounds with carbon materials is a promising approach to prepare efficient electrocatalysts. Here, we report a facile and cost-effective solvothermal route to synthesize cobalt-pyrazolate framework (Co(pz)) followed by thermal treatment in the air to yield N-doped porous carbon encapsulating uniform cobalt oxides nanoparticles (Co3O4/N–C). The resulting composite material is evaluated as electrocatalyst for the OER in basic media with a low onset potential of ~ 1.52 V (vs. RHE), very small Tafel slope of 44 mV dec−1, and overpotential of only 390 mV to achieve a stable current density of 10 mA cm−2 in 1.0 M KOH. The achieved superior oxygen evolution activity in comparison with the state-of-the-art noble metal catalysts originates from in situ incorporation of metal oxides into highly porous carbon matrix, resulting in strong synergistic effects between Co3O4 and N-doped carbon with ordered mesoporous structure leading to the enhanced charge transport and conductivity, and high structural stability. The excellent electrocatalytic performance and superior stability make the Co3O4/N–C a promising non-precious electrode material for the OER.

    更新日期:2019-12-11
  • NiSe-Ni 3 Se 2 /Multiwalled Carbon Nanotube Composites as Efficient Electrocatalysts for the Oxygen Evolution Reaction in Alkaline Media
    Electrocatalysis (IF 2.311) Pub Date : 2019-10-31
    Oluwaseun A. Oyetade, Roelof J. Kriek

    The development of effective electrocatalysts for the oxygen evolution reaction (OER) is of great importance to combat energy-related concerns in the environment. Herein, we report a one-step solvothermal method employed for the fabrication of nickel selenide hybrids (NiSe-Ni3Se2) and a series of nickel selenide hybrid/multiwalled carbon nanotube composites (NiSe-Ni3Se2/MWCNT) as electrocatalysts for the OER in alkaline media. The catalytic activities of these electrocatalysts were investigated via several electrochemical characterization techniques, such as linear sweep voltammetry, chronoamperometric studies at constant potential, electrochemical surface area determination, and Tafel slope calculation, under alkaline conditions. Morphological observations demonstrated the agglomeration of non-uniform NiSe-Ni3Se2 microspheres around carbon nanotubes (CNTs), demonstrating the successful synthesis of NiSe-Ni3Se2/MWCNT nanocomposites. Among the tested electrocatalysts, the 20% NiSe-Ni3Se2/MWCNT nanocomposite demonstrated the highest activity, exhibiting an overpotential of 325 mV to achieve a current density of 10 mA.cm−2 in 0.1 mol.dm−3 KOH solution. The NiSe-Ni3Se2/MWCNT nanocomposites showed improved activity toward the OER compared to bare NiSe-Ni3Se2 hybrids and MWCNTs, exhibiting an overpotential of 528, 392, and 434 mV for 10%, 30%, and 50% NiSe-Ni3Se2/MWCNT nanocomposites, respectively. These results compare favorably to the overpotential of noble electrocatalysts, such as RuO2 and IrO2. Our results imply that the addition of MWCNTs increased the activity of NiSe-Ni3Se2 hybrids due to an increased number of catalytic sites, dispersion of NiSe-Ni3Se2 hybrid nanoparticles, and electronic conductivity of the nanocomposites. These nanocomposites also demonstrated better long-term stability compared to NiSe-Ni3Se2 hybrids and MWCNTs. Hence, NiSe-Ni3Se2/MWCNT nanocomposites possess the potential as effective electrocatalysts for the OER in alkaline media.

    更新日期:2019-12-11
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