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 Electrocatalysis     [SJR: 0.542]   [H-I: 7]    Follow        Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1868-2529 - ISSN (Online) 1868-5994    Published by Springer-Verlag  [2210 journals]
• Recent Advances in Heteroatom-Doped Metal-Free Electrocatalysts for Highly
Efficient Oxygen Reduction Reaction
• Abstract: Abstract Heteroatom-doped metal-free electrocatalysts for oxygen reduction reaction (ORR) represent one of the most prominent families of electrocatalysts for fuel cells. While nitrogen (N)-doped carbon electrocatalysts toward ORR have experienced great progress throughout the past decades and yielded promising material concepts, also other heteroatom-doped catalysts have gained the researchers’ tremendous interest recently. Boron (B)-doping on carbon has been extensively studied, and due to the contrary electronic properties between N and B, a synergetic effect between the codoped N and B on carbon has been found for ORR. The carbons doped with sulfur (S), phosphorus (P), silicon (Si), and halogen (fluorine (F), chlorine (Cl), bromine (Br), iodine (I)) have also been studied as metal-free electrocatalysts for ORR in both experimental and theoretical ways. It has been known that the difference in electronegativity and size between the heteroatoms (N, B, S, P, Si, Cl, Br, I) and carbon can polarize adjacent carbon atoms to facilitate the oxygen reduction process. Especially, our research group reported the first F-doped or N,F-codoped carbon black as highly efficient ORR electrocatalysts which possess one of the best price/performance ratio ever. In this feature article, we review the recent research progress in the development of heteroatom-doped carbon-based metal-free electrocatalysts for ORR. Graphical Abstract Heteroatom-doped metal-free electrocatalysts for oxygen reduction reaction represent one of the most prominent families of electrocatalysts that are used in fuel cells. In this feature article, we review the recent research progress in the development of heteroatom-doped carbon-based metal-free electrocatalysts for ORR.
PubDate: 2015-01-16

• CO 2 Electroreduction on Cu-Modified Platinum Single Crystal Electrodes in
Aprotic Media
• Abstract: Abstract Techniques of electrode modification by copper deposits are developed that allow obtaining compact bulk quasi-epitaxial deposits on basal Pt(hkl) single crystal faces. The issues of the deposit roughness and characterization are discussed. Problems of drying and transferring electrodes with copper deposits into other solutions are considered. The obtained deposits are used for CO2 electroreduction in propylene carbonate and acetonitrile solutions of 0.1 M TBAPF6, and the relationship between the electrode surface structure and its electrocatalytic activity in CO2 electroreduction is discussed. We also demonstrate that the restructuring of Cu deposits occurs upon CO2 electroreduction. Complementary reactivity studies are presented for bare Pt(hkl) and Cu(hkl) single crystal electrodes. Cu-modified Pt(hkl) electrodes display the highest activity as compared to bare Pt(hkl) and Cu(hkl). Particularly, the Cu/Pt(110) electrode shows the highest activity among the electrodes under study. Such high activity of Cu/Pt(hkl) electrodes can be explained not only by the increasing actual surface area but also by structural effects, namely by the presence of a large amount of specific defect sites (steps, kinks) on Cu crystallites.
PubDate: 2015-01-01

• On the Temperature Dependence of Hydrogen Evolution Reaction at Nickel
Foam and Pd-Modified Nickel Foam Catalysts
• Abstract: Abstract This communication reports on hydrogen evolution reaction (HER), studied at Ni foam and Pd-activated nickel foam materials in 0.1-M NaOH solution over the temperature range of 20–60 °C. Catalytic modification of Ni foam leads to significant facilitation of temperature-dependent HER kinetics, manifested through radically reduced values of charge-transfer resistance parameter, as well as substantially modified Tafel polarization curves. The presence of a catalytic additive (Pd) is evidenced through scanning electron microscopy (SEM) analysis.
PubDate: 2015-01-01

• Platinum Oxide Growth on Pt/C Fuel Cell Catalysts Using Asymmetric Scan
Electrochemical Quartz Crystal Nanogravimetry
• PubDate: 2015-01-01

• Electrocatalytic Oxidation of Formic Acid: Closing the Gap Between
Fundamental Study and Technical Applications
• Abstract: Abstract Electro-catalytic oxidation of formic acid has a significant importance in fundamental research of small organic molecule oxidation, as well as practical application to fuel cells. Notwithstanding intensive research efforts for last couple of decades, there are still fundamental questions in debate on the mechanistic origin. This perspective presents underlying issues in the electro-catalytic oxidation of formic acid. Until now, the oxidation mechanism of formic acid is not fully understood in spite of its importance of this work, since the role of adsorbed formate is not clearly identified. In addition, we will discuss on the role of Bi on Pt that unambiguously enhances the activity of Pt in fuel cell systems but is in debate with single crystal Pt surface. We finally accentuate the causes of the deactivation of Pd catalysts, because the utilization of non-Pt electrocatalysts could be one of the key researches for cost reduction of fuel cell systems. Thus, we intend to introduce different views toward formic acid oxidation proposed by the other researchers and provide perspectives on the further research to close the gap between fundamental study and technical applications.
PubDate: 2015-01-01

• Non-precious Metal Oxygen Reduction Nanocomposite Electrocatalysts Based
on Poly(phenylenediamines) with Cobalt
• Abstract: Abstract The unpyrolyzed non-precious metal-polymer nanocomposite electrocatalysts for the oxygen reduction reaction (ORR) based on amino-substituted analogues of polyaniline (poly-o-phenylenediamine—PoPDA, poly-m-phenylenediamine—PmPDA), cobalt and carbon black were obtained. Composition, morphology, structure and electrochemical properties of nanocomposite electrocatalysts were characterized by C,H,N-analysis, atomic absorption spectrometry, scanning electron microscopy, powder X-ray diffraction, FTIR spectroscopy and cyclic voltammetry. It was shown that differences in the structure of PoPDA and PmPDA caused by the position of the amino groups in the aromatic ring of the starting monomers, as well as conditions for their preparation, are responsible for the difference in the electrochemical properties of hybrid composites based on such polymers. It was found that nanocomposite electrocatalysts based on PmPDA (ORR onset potential, E onset up to 530 mV; ORR peak potential, E p up to 325 mV vs. reversible hydrogen electrode, RHE) were more active in 0.05 M H2SO4, compared with the analogue based on PoPDA. Moreover, the activity of PmPDA- or PoPDA-based metal-polymeric composites for the ORR was higher than that for previously reported similar polyaniline-based composite, which may be due to effective formation and/or increase the number of active sites for the ORR in electrocatalysts at the expense of the presence of additional nitrogen atoms in poly(phenylenediamines).
PubDate: 2015-01-01

• Insight into the Photocatalytical Activity of TiO 2 Nanoparticles Through
the Electrochemical Characterization of Carbon Paste Electrodes
• Abstract: Abstract We propose a methodology to study the behavior of semiconductor nanoparticles—especially TiO2 nanoparticles—in photoactivated processes via electrochemical studies, using solid electrodes instead of thin-film electrodes. This strategy allows the comparison of properties probed from freestanding nanoparticles with the results of electrochemical characterization, without grain growth or texturization effects, frequently observed in thin-film electrodes. In this study, solid electrodes prepared with homogenized carbon paste and TiO2 were characterized. The TiO2/carbon paste electrode showed lower currents than the carbon paste electrode under UVC illumination. The electrode containing 15 % TiO2/carbon paste showed better results for electroanalytical characterization. However, for electrolysis, the carbon paste electrode with 60 % TiO2 was used, as 15 to 45 % (w/w) TiO2 content was deemed insufficient for this purpose. In order to compare the electrochemical characterization with photocatalytical properties, the degradation of rhodamine B (Rhod-B) dye was used. The reaction order for the Rhod-B degradation was between first and second order, which suggests that the products of the reaction may interfere with the decomposition itself. The results will enhance the establishment of a valuable characterization route to support future research regarding the influence of different materials in photodegradation processes.
PubDate: 2015-01-01

• Electrochemical Growth of Surface Oxides on Nickel. Part 3: Formation of
β-NiOOH in Relation to the Polarization Potential, Polarization Time,
and Temperature
• Abstract: Abstract Electro-oxidation of surface β-Ni(OH)2 residing on metallic Ni to β-NiOOH was studied in 0.5 M aqueous KOH at 277 K ≤ T ≤ 318 K by means of cyclic voltammetry (CV) and chrono-amperometry (CA). The process is accompanied by a diffusion of H+ within the surface oxide phase. The formation of β-NiOOH gives rise to an anodic peak in CV profiles, the potential of which depends on the scan rate (s). An analysis of the relation between the anodic peak current density (j peak, AN) and s indicates that the growth of β-NiOOH is controlled by the diffusion of H+ and its modelling leads to the determination of the diffusion coefficient of H+ (D(H+)). In the case of 277 K ≤ T ≤ 318 K, the values of D(H+) are of the order of 10–11 cm2 s–1, when calculated with respect to the electrode’s geometric surface area (A geom), and of the order of 10–12 cm2 s–1, when calculated with respect to the electrochemically active surface area (A ecsa). The activation Gibbs energy of H+ diffusion (Δdiff G ≠(H+)) is in the 19.5–22.6 kJ mol–1 range. Chrono-amperometry transients for the formation of β-NiOOH are analyzed on the basis of finite-space diffusion, with the assumption that β-NiOOH can be formed through three mechanistic pathways. The values of D(H+) determined for both A geom and A ecsa using this approach are of the order of 10–12 cm2 s–1. They are smaller than the analogous values of D(H+) determined on the basis of CV measurements but the values of Δdiff G ≠(H+) obtained using these two experimental approaches are comparable.
PubDate: 2015-01-01

• Reactivity of Alcohols with Three-Carbon Atom Chain on Pt in Acidic Medium
• Abstract: Abstract n-Propanol, 2-propanol, 1,2-propanediol, 1,3-propanediol, and glycerol are all saturated alcohols with a three-carbon atom chain. The difference between them is the number of hydroxyl groups and their positions in these molecules. The interaction between alcohols with a three-carbon atom chain and model surfaces and the further reaction have been widely investigated in the last three decades. In this short review, we will concentrate our attention on the reactivity of n-propanol, 2-propanol, 1,2-propanediol, 1,3-propanediol, and glycerol on smooth Pt in acidic medium. We will present the most important results reported in the literature in this field, highlighting the main particularities related to their reactions, addressing key points such as the impact of the position of the OH group in the molecule, number of OH groups in the molecule, and presence of vicinal OH groups in the molecule on the reactivity of these alcohols over Pt. Finally, we will present some perspectives concerning the application of alcohols with a three-carbon atom chain, mainly glycerol, in fuel cells.
PubDate: 2015-01-01

• Electrochemical Behaviour of PSS-Functionalized Silica Films Prepared by
Electroassisted Deposition of Sol–Gel Precursors
• Abstract: Abstract Porous, electrically insulating SiO2 layers containing polystyrene sulfonate (PSS) were deposited on glassy carbon electrodes by an electrochemically assisted deposition method. The obtained material was characterized by microscopic, spectroscopic and thermal techniques. Silica-PSS films modify the electrochemical response of the glassy carbon electrodes against selected redox probes. Positively charged species show reduced diffusivities across the SiO2-PSS pores, which resulted in a concentration ratio higher than 1 for these species. The opposite behaviour was found for negatively charged redox probes. These observations can be interpreted in terms of the different affinity of the GC/SiO2-PSS-modified electrode for the electroactive species, as a consequence of the negatively charged porous silica.
PubDate: 2015-01-01

• A Simulation Study of Pt Particle Degradation During Potential Cycling
Using a Dissolution/Deposition Model
• Abstract: Abstract Polymer electrolyte fuel cells suffer from reduced lifetimes due to degradation of their Pt catalysts during operation. To understand the fundamental process of the Pt degradation, we proposed a model for the Pt particle growth based on the Gibbs-Thomson equation, which asserts that smaller particles tend to be dissolved in preference to the larger ones. We simulated the particle distribution changes during rectangular potential cycling between 0.6 and 1.0 V vs. the reversible hydrogen electrode at 25 °C under a N2 atmosphere. The parameters in our model were determined by fitting to the experimental data. The calculation results and experimental data for the changes in the particle distribution and electrochemically active surface area were in good agreement. Additionally, the particle distribution change under different conditions such as the potential range and the initial particle size distribution could be simulated by changing the parameters in the model. When the initial size standard deviation is low, particle growth does not readily occur because the differences in the particle size are small. When the initial standard deviation in the particle size is large, the particle growth is accelerated by the large difference in the particle sizes, because small particles more readily dissolve. Finally, the particle distribution becomes stable and the degradation levels off. It was suggested that the particle growth could be anticipated by using our model.
PubDate: 2015-01-01

• Preparation and Electrocatalytic Properties of Polydopamine Functionalized
Reduced Graphene Oxide-Silver Nanocomposites
• Abstract: Abstract Polydopamine functionalized reduced graphene oxide-silver nanoparticle (PDA-RGO/Ag NP) nanocomposites were successfully prepared by a simple and mild procedure. Graphene oxide (GO) sheets were firstly coated with PDA via a self-polymerization process which provided an excellent interface for in-situ growing silver nanoparticles. Fourier transform infrared spectroscopy (FTIR) confirmed the successful coating of PDA and informed the reduction of the surface functional groups of GO. The formation of reduced GO and silver NPs was further evidenced by UV-Vis and X-ray diffraction spectroscopy. The as-prepared PDA-RGO/Ag nanocomposites could greatly enhance the electrochemical reduction of hydrogen peroxide (H2O2). This excellent performance was attributed to the increased effective electrode surface area due to the deposition of nano-sized Ag particles and graphene. The PDA-RGO/Ag-based electrochemical sensor displayed a rapid amperometric response for H2O2 measurement with a wide linear range from 0.5 μM to 8 mM and a low detection limit of 2.07 μM.
PubDate: 2015-01-01

• Oxygen Electroreduction on Electrodeposited PdAu Nanoalloys
• Abstract: Abstract The electrocatalytic activity of electrodeposited palladium–gold (PdAu) alloys towards the oxygen reduction reaction (ORR) was studied in 0.05 M H2SO4 and 0.1 M KOH solutions using the rotating disc electrode (RDE) method. The electrochemical deposition was carried out at a constant potential and the ratio of concentrations of the precursors in the deposition bath was varied. The surface morphology of the deposits was studied using scanning electron microscopy (SEM), and the average particle size for PdAu alloys was determined to be about 6 nm. The X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) studies suggest that the resulting PdAu coatings are alloyed. The ORR activities of the electrodes were compared by calculating the specific activities on the basis of the real electroactive surface area of Pd. The specific activity did not depend on the composition of the alloy in sulphuric acid solution, but in alkaline medium it increased with decreasing Pd content.
PubDate: 2015-01-01

• Enhanced Electrooxidation of Ethanol Using Pd/C + TiO 2 Electrocatalysts
in Alkaline Media
• Abstract: Abstract This work describes the use of Pd nanoparticles synthetized by the borohydride process and supported on physical mixtures of C + TiO2 toward the ethanol electrooxidation reaction in alkaline media. In this study, the C/TiO2 ratios were studied by ranging the mass proportions of C/TiO2—100:0, 80:20, 60:40, 40:60, 20:80, and 0:100. X-ray diffraction patterns showed the presence of Pd face-centered cubic (fcc) structure, and carbon and TiO2 in rutile and anatase phases. Transmission electron micrographs showed metal nanoparticles with average particle size between 5.5 and 7.2 nm for all electrocatalysts. Cyclic voltammograms of Pd/C + TiO2 electrocatalysts showed a decrease of Pd surface area with the TiO2 increasing, while the linear sweep and chronoamperometric results showed the Pd/C + TiO2 (40:60) as the most promising electrocatalyst toward ethanol electrooxidation. The best results obtained with this catalyst were attributed to the presence of carbon and TiO2 in intermediate proportions since TiO2 supplies OH species and also changes the Pd d-band by a strong metal support interaction, increasing the alcohol oxidation without a significant decrease of conductivity and surface area.
PubDate: 2015-01-01

• Thermodynamics of the Under-Potential Deposition of Hydrogen on
Polycrystalline Platinum in Aqueous Trifluoromethanesulfonic Acid Solution

• Abstract: Abstract Understanding of the electrocatalytic behavior of the Pt/Nafion® ionomer interface is of great importance to fuel cell technology. Trifluoromethanesulfonic acid (CF3SO3H) is used as an electrolyte because it is the smallest fluorinated sulfonic acid and serves as a suitable molecular model mimicking the Nafion® ionomer. The under-potential deposition of H (UPD H) on polycrystalline Pt electrode in CF3SO3H is investigated using cyclic voltammetry in the 278–333 K temperature (T) range. The general electrochemical adsorption isotherm is used to determine the Gibbs energy (−13 ≤ Δ ec − ads G°(HUPD) ≤ −27 kJ mol−1), entropy (−59 ≤ Δ ec − ads S°(HUPD) ≤ +20 J mol−1 K−1), and enthalpy (−8 ≤ Δ ec − ads H°(HUPD) ≤ −43 kJ mol−1) of electro-adsorption, and the Pt–HUPD surface bond energy (+225 ≤  $${E}_{\mathrm{Pt}-{\mathrm{H}}_{\mathrm{UPD}}}$$  ≤ +261 kJ mol−1). The lateral interactions between the HUPD adatoms are repulsive; the energy of lateral interactions is T-dependent (ω(HUPD) = a − b T) and is in the +14 ≤ ω(HUPD) ≤ +22 kJ mol−1 range. The values of Δ ec − ads G°(HUPD), Δ ec − ads S°(HUPD), Δ ec − ads H°(HUPD), and $${E}_{\mathrm{Pt}-{\mathrm{H}}_{\mathrm{UPD}}}$$ for UPD H in CF3SO3H are very similar to the analogous values obtained in aqueous H2SO4 and HClO4 solutions. The anion present in the electrolyte has a small impact on UPD H and influences the values of Δ ec − ads G°(HUPD) only over a narrow HUPD coverage range. The anion nature has practically no impact on the values of Δ ec − ads S°(HUPD), Δ ec − ads H°(HUPD), or $${E}_{\mathrm{Pt}-{\mathrm{H}}_{\mathrm{UPD}}}$$ .
PubDate: 2015-01-01

• Electro-Oxidation of Nitrite Using an Oxidized Glassy Carbon Electrode as
Amperometric Sensor
• Abstract: Abstract In this work, a simple and innovative method is proposed to get an active glassy carbon electrode (GC) toward nitrite oxidation. The oxidation method was based on an anodic treatment, through a time- and potential-controlled electrolysis, in NaOH 0.1 M. This treatment increased the activity in all pH values that were studied, being the pH 8.0 as the best one. It was possible to calculate the kinetic parameters, where the number of transferred electrons calculated was one, and Tafel slope was 70 mV per decade. With these values, a reaction mechanism was postulated. At the best experimental conditions, the electrode has a good behavior as an amperometric sensor versus nitrite oxidation. The system follows linearity in all the range of concentrations and allowed the calculation of analytical parameters such as detection limit, quantification limit, accuracy, and exactitude. Good results were obtained at this point, so the system might be considered a good method for nitrite determination and quantification in aqueous solutions.
PubDate: 2014-12-30

• Infrared Reflection Absorption Spectroscopy of OH Adsorption on the Low
Index Planes of Pt
• Abstract: Abstract The adsorption of hydroxide (OHad) on Pt has been studied on the low index planes of Pt using infrared reflection absorption spectroscopy (IRAS) in electrochemical environments. We discuss the correlation between the integrated band intensity of the bending mode of OH of Pt–OH (δ PtOH) and the charge density of the oxide formation of Pt. The band of δ PtOH is observed around 1100 cm−1, and the onset potential depends on the surface structure. The onset potential of δ PtOH on Pt(110) and Pt(100) overlaps with the hydrogen adsorption/desorption potential region. The order of the integrated band intensity of δ PtOH at 0.9 V vs RHE is opposite to the order of the oxygen reduction reaction (ORR) activity. This finding supports that the OHad is one of the species deactivating the ORR.
PubDate: 2014-12-30

• Electrochemical Synthesis of Ammonia Based on Co 3 Mo 3 N Catalyst and
LiAlO 2 –(Li,Na,K) 2 CO 3 Composite Electrolyte
• Abstract: Abstract Cobalt molybdenum nitride (Co3Mo3N) catalyst was synthesised through ammonolysis of the corresponding precursors by flowing pure ammonia gas. The catalyst was characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ammonia was successfully synthesised from wet hydrogen and dry nitrogen at atmospheric pressure using Co3Mo3N–Ag composite as cathode, Ag–Pd alloy as anode and LiAlO2–(Li/Na/K)2CO3 composite as an electrolyte. Ammonia formation was investigated at 400, 425 and 450 °C, and the maximum observed ammonia formation rate was 3.27×10−10 mol s−1 cm−2 at 450 °C when applied at 0.8 V. The catalytic activity of Co3Mo3N for electrochemical ammonia synthesis is lower than that of Pd. The successful synthesis of ammonia demonstrates that LiAlO2–(Li/Na/K)2CO3 composite exhibits protonic or/and oxygen ion conduction.
PubDate: 2014-12-05

• The Effect of Reducing Agents on the Electronic, Magnetic and

• Abstract: Abstract The electronic, magnetic and electrocatalytic properties of bimetallic thiol-capped Pt/Co and Pt/Ni nanoparticles were synthesised using two reducing agents, NaBH4 and N2H4. X-ray diffraction analysis of the nanoparticles showed Pt lattice contraction upon the addition of Co or Ni to Pt indicating the formation of an alloy structure, more apparent when N2H4 was used. XPS data analysis revealed Pt metal and Pt(II) (assigned to PtO) and a higher concentration of surface metallic Ni and Co for the NaBH4-reduced samples. Both the NaBH4- and N2H4-reduced catalysts were active for the methanol oxidation reaction (MOR), with the Pt-Co-N2H4 catalyst revealing the highest activity. The N2H4 significantly affected the magnetic properties of Pt/Co and Pt/Ni particles by controlling the morphology and crystalline structure of the nanoparticles. In general, the type of reducing agent affected the final properties of the nanoparticles.
PubDate: 2014-11-21

• The Hydrogen Evolution Reaction on Rhenium Metallic Electrodes: A Selected
Review and New Experimental Evidence
• Abstract: Abstract The volcano plots reported in the field of electrocatalysis utilize data with a difference of three orders of magnitude between the worst and the best rhenium electrocatalytic activity toward the hydrogen evolution reaction (HER). However, the commonly used mean value of the exchange density current (j 0) of the HER on rhenium is log j 0 = −2.9 A cm−2, which is higher than the value used for platinum (log j 0 = −3.3 A cm−2). This fact seems to contradict Sabatier’s principle and points to the possibility that this value corresponds more to rhenized surfaces than to metallic rhenium. Rhenized surfaces are primarily composed of a mixture of oxides; therefore, the electrocatalytic behavior is attributed to these thin films rather than to metallic rhenium. In addition, a selected review of rhenized electrodes is included herein because these issues have not been considered in the electrocatalysis literature at the present time. We initially believed that the kinetic parameters might have been overestimated due to the formation of rhenide ion or rhenium hydride species; however, no evidence of the formation of these species was found. Our experimental mean value of the exchange current density of the HER on metallic rhenium is 7 × 10−5 A cm−2 in acidic solution. Therefore, our results are in accordance with Sabatier’s principle, which states that a weak adsorption energy of hydrogen on rhenium (energy, 6.9 kJ mol−1) results in a slow rate of reaction (log j 0 = −4.2 A cm−2), whereas an intermediate adsorption energy of hydrogen on platinum (12 kJ mol−1) produces a fast reaction (log j 0 = −3.3 A cm−2).
PubDate: 2014-11-18

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