bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Characterization of Monolayer Bimetallic Surfaces: A Synchrotron NEXAFS and XPS Study
Authors: Rettew Robert E. , Guthrie James W. , Jaye Cherno , Fischer Daniel , Alamgir Faisal
Published: December 2009

Surface limited redox replacement (SLRR) is a potentially powerful tool for atomic monolayer-scale model catalyst fabrication for a plethora of spectroscopic techniques. This paper compares overpotential Ni deposition as an intermediary for SLRR with the traditional Cu intermediary method. It also presents the use of SLRR to fabricate samples for study using near-edge x-ray absorption fine structure (NEXAFS.) We present the use of NEXAFS spectroscopy to study adsorbate bonding strengths on this type of bimetallic model catalyst. We report a correlation between the strength of the adsorbate-Pt bond as a function of the thickness of Pt overlayers. Deposition of Pt on polycrystalline and single crystalline Au has been conducted via Ni and Cu replacement, respectively. The growth of Pt overlayers has been characterized by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV).
Understanding the Oxygen Reduction Reaction on Pd-Based Alloys (Pd-M, M=Ni, Co) Surfaces Using Density Functional Theory Calculations
Authors: Li Bing , Greeley Jeffrey , Prakash Jai
Published: December 2009

A periodic model of the close-packed (111) surfaces of Pd-based alloys, based on (2x2x4) or (4x2x4) unit cell, was constructed with various possible atomic configurations. Two alloying elements, Ni and Co, with compositions of 25 and 50 atomic %, respectively, were considered in this study. The first two or three atomic layer compositions were systematically permuted to model the surface segregation phenomena of Pd and to find the most stable structures. The Density Functional Theory (DFT) calculations were used to obtain the oxygen binding energy on these Pd-based alloys' surfaces. Oxygen binding energy, an important descriptor for the oxygen reduction reaction (ORR) catalytic activity on the transition metals, was used to estimate trends in the activities of these alloys' surfaces.
Nanostructured Mesoporous NbRuyOz as a Catalytic Support for Fuel Cells
Authors: Konopka Daniel , Pylypenko Svitlana , Ward Timothy , Atanassov Plamen
Published: December 2009

An electrically conductive NbRu (8:1 by weight) support with high surface area of ~170m2/g has been synthesized by using the spray pyrolysis technique. The support is a highly stable phase equivalent to conductive Nb(IV), thanks to intrinsic alteration of the niobia by the ruthenium in an inter-metallic phase. Platinum deposited by various methods onto the NbRuyOz support is initially electrochemically deactivated until its surface can be re-activated under argon at a scanning rate of 250 mV/s.
Polyaniline Coated Active Carbon as Binary Catalysts Support for Direct Methanol Fuel Cell
Authors: Lee H.Y. , Vogel W. , Chu Peter P.
Published: December 2009

Conducting polymer coated graphitized active carbon as fuel cell catalysts support improves both the catalytic performance and stability. The PANi coating prevent aggregation and the loss of particles and shows improved long-term stability. X-ray diffraction indicated the Pt/Ru alloy is homogeneous and lacks Pt-core Ru-shell structure. The superior fuel cell performance and better electrocatalytic stability observed for Pt-Ru/P1ACg are attributed from its high degree of Pt-Ru alloy, and high active surface area. This study unveils a new design of durable catalysts by coating a layer of conducting polymer on carbon support which improves catalytical activity, CO tolerance and stability over other catalysts based on the current art.
Effect of Doping Concentration on the Proton Conductivity of Y-doped BaZrO3 Thin Films
Authors: Kosasang Onthida , Somroop Kittichai , Chindaudom Pongpan , Pornprasertsuk Rojana
Published: December 2009

Y-doped BaZrO3 (BYZ) pellets and thin films were fabricated by solid state reaction and co-sputtering technique, respectively. The conductivity of BYZ samples was measured using electrochemical impedance spectroscopy technique in the atmospheres of air, dry H2, and wet H2. As Y content increases from 6 at.% to 20 at.%, the increase of bulk and grain boundary conductivity is observed, while at 30 at.%, the conductivity starts to degrade. The activation energies in bulk and grain boundary are in the range of 0.28-0.40 eV and 0.91-0.96 eV, respectively. BYZ pellets have the highest proton conductivity at the Y doping concentration of 20 at.%. Furthermore, the dense and uniform BYZ thin films of 130-140 nm in thickness were obtained by co-sputtering technique. The conductivities of the BYZ thin films are about 10^3 - 10^4 times those of the pellet samples. The reason of the observed high conductivity is still under further investigation.
Metal Oxide Nano-particles and Nano-composite Polymer Electrolytes - Electrodes and Electrolytes in Solar and Galvanic Cells of the Second Generation
Authors: Turkovic Aleksandra
Published: December 2009

Nanocomposite polymer electrolytes and nanophased metal oxide films are tailored and used as electrodes and electrolytes in galvanic and solar cells of second generation. Nano-composites were prepared using PEO γ-irradiated to selected doses and TiO2 nanograins, which treatments largely enhanced the conductivity of these polymer Zn2+-ion conducting electrolytes. Metal oxide nanostructured films based on titanium, cerium and vanadium were investigated as possible working electrodes in solar or galvanic cells of second generation. As the most promissing and complete methods for investigation of morphology and structure of nanosize ordered materials, synchrotron small-angle X-ray scattering (SAXS) methods were applied to study both type of nano-materials.
A Simple Alternative to the Expression of Finite Warburg Diffusion Impedance in Porous Electrodes by Considering Oxygen Consumption Along the Air Channel
Authors: Mainka Julia , Maranzana Gaël , Dillet Jérôme , Didierjean Sophie , Lottin Olivier
Published: December 2009

The classical expression of the finite Warburg element used for analysing electrochemical impedance spectroscopy (EIS) spectra is obtained assuming that the reaction occurs at the electrode/membrane interface and that the oxygen concentration at the gas channel/gas diffusion layer interface is constant. An alternative to this expression is proposed: it takes into account the variation in oxygen concentration along the gas channel due to the oxygen-reduction reaction (ORR). This pseudo-2D approach is well suited for investigating mass transfer limitations in the fuel cell membrane-electrode assemblies (MEA). Simple numerical applications starting from data already published by different authors show that with this new expression, conclusions about the mass transfer limiting layer and its main characteristics can be significantly modified. This improvement to the usual Warburg impedance could contribute to a better understanding of mass transfer limitation in fuel cells and eventually, to the design of MEAs in which diffusion losses are minimal.
The Apparent Capacitance of the Electrode "Charging" Process
Authors: Villa Marco , Nelli Paolo , Salvi Paolo , Kiros Yohannes , Zangari Giovanni
Published: December 2009

We investigate simple models of the electrode charging (discharging) at constant current i, where the potential (E) is recorded as a function of time, or charge,q=i.t. Our goal is to assess the advantages of a representation in terms of capacitance,C=dq/dE ,vs. E. Such a plot is related with cyclic voltammetry (c.v.) plot (i(c.v.) vs E) at a constant rate (b=dE/dt) since, under appropriate circumstances, we should have C=i(c.v.)/b=dq/dE . We will discuss the following items: a) origins and suppression of the singularities in the capacitance plots, b) effects of the finite charging currents, c) comparison between c.v. and electrode charging experiments.
Electrochemical Impedance Spectroscopy (EIS) Used as a Diagnostic Tool of Oxygen Sensors for Molten Lead - Bismuth Eutectic Alloy (44.5% Pb - 55.5% Bi)
Authors: Colominas Sergi , Verdaguer Ariadna , Abella Jordi
Published: December 2009

One of the coolants proposed for accelerator drive systems (ADS) and Generation IV nuclear reactors is molten lead. A key parameter in the use of molten lead as a coolant is the oxygen activity in the liquid alloy. Potentiometric oxygen sensors for molten metals have been developed in the Electrochemistry Laboratory at Institut Quimic de Sarria since 1998. In this paper we used Electrochemical Impedance Spectroscopy as a diagnostic tool to evaluate the sensor status in service operations. The following parameters have been evaluated: sensor impedance at different temperatures and the effect of using a reductive and a low oxygen content as covering gases, effect of metal oxides accumulation at the ceramic element of the sensor and measurement of the impedance of a short-circuited sensor.
Effect of Bending Energy on the Self-Spreading Lipid Bilayer
Authors: Nabika Hideki , Yamamoto Takuya , Murakoshi Kei
Published: December 2009

Self-spreading dynamics of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) on a glass substrate was studied in order to make clear the effect of bending energy. We show that PE bilayer spread with lower velocity compared with PC bilayer at the same experimental condition. The observed difference between PC and PE was qualitatively explained by the structural dependence on the bending energy that cost for both lipids to form planar lipid bilayer.
Application of TiO2 Modified Boron Doped Diamond (BDD) Electrode for As(III) Determination in Natural Waters
Authors: Zlatev Roumen , Stoytcheva Margarita , Magnin Jean-Pierre , Valdez Benjamin , Argüelles Mafalda , Valera José
Published: December 2009

Activated by Au nanoparticles, Boron Doped Diamond (BDD) electrode was modified electrochemically by TiO2 and applied for As(III) determination in natural ground waters. The modification with TiO2 results in up to 49.7% sensitivity increase compared with the non modified electrode achieved at the maximum TiO2 coverage percentage of about 73% of the BDD surface.
Tuning the Formal Potential of Metallomacrocyclics for Maximum Catalytic Activity For the Oxidation of Thiols and Hydrazine
Authors: Ochoa Gonzalo , Geraldo Daniela , Linares Cristian , Nyokong Tebello , Bedioui Fethi , Zagal Jose H.
Published: December 2009

The electrocatalytic activity of a series of Co macrocyclic complexes confined on graphite electrodes for the oxidation of thiols : 2mercaptoethanol, 2-mercaptoacetate, 2-aminoethanethiol and l-cysteine give volcano correlations between catalytic activity of the metallo complexes and the formal potential of the complex. The formal potential that gives the maximum activity correlates linearly with the pKa of the thiol. We have extended previous studies for the oxidation of hydrazine using Co and Fe macrocyclics and obtain volcano correlations for this reaction as well. The slope of the rising region of the volcano (where the catalytic activity increases with the driving force of the catalyst) gives values of ca. +0.120 V/decade which is the theoretical value when using a Langmuir isotherm for the adsorbed thiol or hydrazine molecule on the reacting site. These results indicate that is possible to "tune" the redox potential of the complexes to attain maximum activity.
Electrochemistry of Scorpionates Complexes - Towards an Electrochemical Molecular Switch
Authors: Vachon Jason , Mayoral Margarita , Ayme-Perrot David , Schougaard Steen B.
Published: December 2009

Poly(pyrazolyl)borate complexes, otherwise known as scorpionate complexes, display molecular switch-like properties. Herein we attempt to establish the relation between structure change and electrochemical properties. Cyclic voltammetry studies showed that bis(pyrazolyl)borate nickel(II) complexes are oxidized irreversibly, while tris(pyrazolyl)borate nickel(II) complexes exhibit pseudo-reversible behaviour. Preliminary DFT calculations suggest that this change in behaviour may be related to differences in the charge distribution of the HOMO/SOMO orbital involved in the oxidation process
Effect of Temperature on Oxygen Solubility in Molten Pb - Bi Eutectic Alloy (44.5% Pb - 55.5% Bi)
Authors: Verdaguer Ariadna , Colominas Sergi , Abella Jordi
Published: December 2009

One of the coolants proposed for accelerator drive systems (ADS) is lead - bismuth eutectic alloy, LBE (44.5%Pb - 55.5%Bi). One of the disadvantages of using this alloy is that it is highly corrosive for structural steels. Then, it is important to maintain a passivation layer of Fe3O4 on the structural material. In order to maintain this passivation layer stable avoiding PbO formation, it is necessary to control and monitor oxygen content in LBE. ADS reactors will operate in a wide temperature range: from 300ºC to 600ºC. For that, the goal of this work is to determine the effect of temperature on oxygen solubility in molten LBE. The proposed method is based on the following electrochemical cell: O2 (reference mixture), Pt // YSZ // O2 (LBE) Results for oxygen solubility in LBE at 460, 500 and 540ºC have been obtained.
Potentiometric Behavior of Diverse Polypyrrole-sulphate Films Electro Synthesized on Graphite - Epoxy Resin Composite
Authors: De J. Licona-Sánchez Teresa , Álvarez-Romero Giaan A. , Palomar-Pardavé Manuel , Galán-Vidal Carlos A. , Páez Hernández María E.
Published: December 2009

In this work, polypyrrole films are electrosynthesized in aqueous media over graphite-epoxy resin composite; sulphate ions used to dope the polymer are obtained from different salts (Na2SO4, Li2SO4, (NH4)2SO4 and K2SO4). Potentiostatic techniques are used to induce the polymerization. Potentiometric response of Ppy-SO4-2 films was evaluated by calibration curves. Analyzing the slope sign, behavior of the different films can be classified in three responses: anionic, cationic and anionic-cationic. These behaviors were observed for all synthesized films, independently of the sulphate salt used. When analyzing the transients obtained for the different salts, similarities where found for those with the same potentiometric behavior, but significative differences where observed when comparing transients of different potentiometric response. It was determined that the cation size of the sulphate salt influences the Ppy-SO4-2 film response. Boundaries on the potentiostatic synthesis parameters are suggested to induce a specific potentiometric response.
Quantification of Hydrogen Peroxide using Poly Fe (III)-5-amino 1, 10 Phenanthroline
Authors: Lozano Maria Luisa C. , Galicia Luis Laura , Rodriguez Marcela , Rivas Gustavo A.
Published: December 2009

In this work, the results obtained by using a composite (dispersing multiple- wall carbon nanotubes in mineral oil) (CNTPE) and modified with a polymeric matrix of poly Fe (III)-5-amino 1,10 phenanthroline (MCNTPE) thus to develop a sensor for quantifying hydrogen peroxide based on the polymer electrocatalytic effects are presented. By means of hydrodynamic voltamperometry, it was possible to determine the ox-red potentials of hydrogen peroxide by using the MCNTPE. The amperometric response to H2O2 by using the CNTPE and MCNTPE was evaluated at -0,100 and 0,700 V vs Ag/AgCl. At -0,100 V, the sensibility of the MCNTPE was increased by a factor of 200 in comparison with the CNTPE. At 700 mV, the sensibility of the MCNTPE was increased by a factor of 268 respected to the CNTPE one. These results show that a new composite with electrocatalytic properties can be proposed to develop electrochemical sensors for the quantification of hydrogen peroxide.
Modeling and Simulation of a Rotating Cylinder Electrode Reactor for Metal Recovering
Authors: Granados Paola , Rivera Fernando F. , Gonzalez Ignacio , Rivero Eligio P.
Published: December 2009

In the present work, numerical simulations of the behavior of a laboratory scale rotating cylinder electrode (RCE) reactor are shown. The influence of the geometry of counter electrodes on the primary current distribution along the cathode is examined. Laminar and turbulent hydrodynamic properties are studied for a RCE reactor using a concentric cylinder as counter electrode. A turbulent mass transport study is presented using copper electrodeposition from a CuSO4-H2SO4 electrolyte as a test system. The calculated concentration of Cu(II) versus time is compared with the reported experimental data.
Electrochemical Paired Convergent Production of ClO2 from NaClO2 and NaClO3
Authors: Gomez-Gonzalez Alejandro , Ibanez Jorge G. , Vasquez-Medrano Ruben , Zavala-Araiza Daniel , Paramo-Garcia Ulises
Published: December 2009

The paired production of ClO2 by reduction of ClO3- and oxidation of ClO2- is achieved in a divided cell. The highly acidic nature of the catholyte and the neutral conditions at the anolyte require an intermediate compartment to prevent their interaction, since passage of H3O+ from the former to the later would chemically produce ClO2. An anionic exchange membrane, AEM/fritted glass/AEM set up was effective in preventing proton migration. The production of ClO2 was spectroelectrochemically monitored in situ and in real time at its characteristic absorption wavelength (359 nm) by adapting a normal rectangular spectrophotometer quartz cell as the electrolytic cell inside a spectrophotometer. The corresponding yields are highly dependent on the applied potential: the cathodic production is favored as the potential approaches the rest potential of the catholyte, whereas the anodic production behaves the opposite. The highest overall yield after 30 min of reaction was ca. 10%.
Computational Fluid Dynamics of an Electrolytic Cell FM01-LC
Authors: Enciso-Pérez Rubi , Velasco-Martínez Guillermo , Delgadillo Gómez Jose A. , Rodríguez- Torres Israel
Published: December 2009

Due to the complexity of an Electrochemical Reactor, the knowledge of the kinetics, thermodynamics, process engineering and fluid hydrodynamics is needed to achieve an optimum operation. The availability of electrolytic reactor FM01-LC has been studied lately with great interest. The fluid mechanics of the electrolyte in this type of reactors is essential to be studied because its effect modifies the mass transport to the electrodes. Computational fluid dynamics (CFD) is a novel tool to compute and understand the fluid mechanics in great detail, the software FLUENT TM 6.3.26 was used to solve the governing equations. The velocity profiles and flow paths were predicted using the k-epsilon model for turbulence closure and compared with experimental results. k-epsilon model has shown to be an adequate model to describe the flow in parallel plate reactors FM01-LC type.
Electrochemical Characterization of Quercetin in Aqueous Solution
Authors: Álvarez-Diduk Ruslan , Ramirez-Silva Maria Teresa , Alarcón-Angeles Georgina , Galano Annia , Rojas-Hernández Alberto , Romero-Romo Mario Alberto , Palomar-Pardavé Manuel
Published: December 2009

The low solubility of quercetin in water and the lack of information in the literature on this substance in this solvent were the main reasons to warrant the analysis of the electrochemical behavior of the molecule and the determination of its acidity constants by an spectrophotometric method, due to inconsistencies in the literature. Cyclic voltammetry was performed to analyze the response to different pH values, and also differential pulse voltammetry to analyze the change of these signals in terms of concentration, using β-CD to modify a carbon paste electrode aiming to increase the intensity of the current significantly to extend further the detection limit. In this way, it is easier to study this system given the low water solubility of the quercetin and to contribute by discussing its properties.
Theoretical Study of pH Stability of Azomethine Based on Hardness Calculations
Authors: Cuan Angeles , Palomar-Pardavé Manuel , Ramirez-Silva Maria Teresa , Corona-Avendaño Silvia , Cortés-Romero Carlos , Romero-Romo Mario Alberto
Published: December 2009

The behavior of neutral and protonated azomethine has been investigated by means of quantum-chemical calculations of its structural and electronic properties. The most stable structural configuration has been optimized at the B3LYP/6311G (d,p) level of theory where a dihedrical angle of 24 degrees from the molecule base C-C-N-C has been obtained. The distribution of the HOMO and LUMO isosurface of both neutral and protonated azomethine molecules was also obtained and discussed. Hardness values of the species involved show that protonated azomethine is more reactive than neutral since its softness value is higher than the latter species which indicates protonated species is more susceptible to chemical transformation or self-decomposition. Furthermore, the IR spectra of the species aforementioned were successfully calculated and reproduced in order to compare both chemical systems in detail.
Dopamine Electrochemical Behavior onto an Electrode Modified with a β-cyclodextrin Polymer
Authors: Ramirez-Silva Maria Teresa , Corona-Avendaño Silvia , Alarcón-Angeles Georgina , Rojas-Hernández Alberto , Romero-Romo Mario Alberto , Palomar-Pardavé Manuel
Published: December 2009

Because dopamine can form inclusion complexes with cyclodextrin, a selectivity advantage is achieved through the formation of such complexes, thereby changing the charge transfer properties and stability of dopamine. This work studied the interaction of dopamine-cyclodextrin on a carbon paste electrode formed with different membranes at different experimental conditions such as concentrations of perchloric acid and b-cyclodextrin. The electrochemical response of dopamine shows that as the concentration of perchloric acid increases in the system, the heterogeneous rate constant increases, aside that when the concentration increased to 2M, the process became controlled by adsorption, unlike others that were diffusion-controlled processes.
Study of SDS-Curcumin Interaction by Micelar Electrokinetic Chromatography (MEKC)
Authors: Rodríguez-Barrientos Damaris , Rojas-Hernández Alberto , Ramirez-Silva Maria Teresa
Published: December 2009

The study of the SDS-curcumin system was made by Micelar Electrokinetic Chromatograpy (MEKC). It was done by changing the surfactant concentration from10 to 40 mM, on 5 mM phosphate buffer. Each, the curcumin mobility and absorption spectra, were followed in order to prove that it was solubilized into the micelle on its neutral form. It was observed that mobility and absorption spectra reaches its maximum value for a 25 mM SDS concentration. Additionally the determination of SDS critical micellar concentration (cmc) was made under conditions of buffer concentration and pH (pH 6.8, [PO4'] 5 mM).
The Effect of the SDS Concentration on the Electrochemical Response of Adrenaline at Acid pH
Authors: Espinoza-Castañeda Marisol , Corona-Avendaño Silvia , Romero-Romo Mario Alberto , Ramirez-Silva Maria Teresa , Palomar-Pardavé Manuel
Published: December 2009

The effect that micellar aggregates have on the electrochemical response of some compounds is indeed interesting, because adsorption and solubility of electrochemically active compounds may induce changes in the redox potential, in the charge transfer and on the diffusion coefficients of the species predominating in solution. This work studies the behavior of adrenaline in the presence of different SDS concentrations on carbon paste electrodes, CPE, with particular reference to its diffusion-controlled redox mechanism, which has an associated chemical reaction step. On consideration of its heterogeneous reaction constant, ko, the overall process is said to be quasi-reversible with one electron transferred. Therefore, it is rightly interpreted that the adrenaline's oxidation mechanism changes drastically in the presence of SDS, whereby the latter favors oxidation of the former, also becoming adsorption-controlled. These results indeed support the applicability of an analytical procedure for the neurotransmitter's quantification
Electrochemical Study on the Kinetic Behavior of the Immobilized Acetylcholinesterase
Authors: Stoytcheva Margarita , Zlatev Roumen , Velkova Zdravka , Valdez Benjamin , Ovalle Marcela
Published: December 2009

In this work are reported new results on the type of the immobilized acetylcholinesterase inhibition by specific and non-specific inhibitors, as well as the values of the characteristic enzyme reaction kinetic parameters in the absence and in the presence of inhibitors, identified applying an electrochemical approach. It was found that: -The kinetics of the process of acetylthiocholine hydrolysis catalyzed by the immobilized acetylcholinesterase is complicated by mass transfer constraints, at low substrate concentrations; -The inhibition of the immobilized acetylcholinesterase by specific inhibitors (trichlorfon, oxophosphol, galantamine, caffeine, atropine, nicotinic acid, and eserine) is of a competitive type, while quinine and thiamine acts as non-competitive inhibitors; -The character of acetylcholinesterase inhibition in heterogeneous phase by non-specific inhibitors (Hg2+, Cu2+, Cd2+, Mn2+, Fe3+, and AsO33-) is reversible and non-competitive. The reactivity of the inhibitors decreases in the order: Hg2+ → Cu2+ → Cd2+ → AsO33- → Fe3+ → Mn2+.
Electrochemical Synthesis of Ni(II) and Al(III) Metalloporphyrins Assisted by Ultrasound
Authors: Aguilera Elsa N. , Blanco Leonor M. , Alonso Jorge L.
Published: December 2009

The electrochemical synthesis of Ni(II) and Al(III) metalloporphyrins by the reaction of the radical dianion of the 5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin (TPPOH) with Ni(II) and Al(III) ions is reported. The electrosynthesis conditions were stablished by cyclic voltammetry of TPPOH. The electrosynthesis process was carried out in an undivided cell at the potential corresponding to the formation of the porphyrin dianion radical. A sacrificial anode of Ni or Al was used to electrogenerate the ions. The experiments were carried out in aprotic and protic solvents to evaluate the effect of the solvent. The effect of the application of 20 kHz ultrasound on the electrochemical process was also evaluated. The electrosynthesis products were characterized by spectroscopy and electrochemical techniques. The results indicate the formation of metalloporphyrins in the different solvents in silent conditions and with ultrasound. The application of 20 kHz ultrasound and protic solvents enhance the reaction yields without affecting the electrochemical reaction mechanism.
Study of the Electrocatalytic Oxygen Reduction Reaction in Acid Medium on PdPtSn
Authors: Salvador-Pascual José J. , Solorza-Feria Omar
Published: December 2009

The synthesis of compound PdPtSn nanoparticles prepared the reduction of PdCl2, H2PtCl6 on SnCl2 and NaBH4 in THF at 0 {degree sign}C. The synthesized powders were characterized with X-ray diffraction, transmission electron microscopy, scanning electron microscopy and electron dispersion spectroscopy. Studies were conducted to determine the electrochemical activity and electrocatalytic properties of the material for the oxygen reduction reaction, using cyclic voltammetry and rotating disc electrode in H2SO4 0.5 M. The kinetic results showed that the reaction comes through 4 electrons and determining the stage of the cathodic reaction is the transfer of the first electron. Apparent activation enthalpy determined from the Arrhenius equation was ΔE ≠ = 42.54 {plus minus} 1 kJ mol-1, a value much lower than that reported for nanometric PdSn synthesized by the same route, but higher than those reported for Pt and Ru nanostructured for the same under the same experimental conditions.
Oxidation of the Borohydride Ion at Silver Nanoparticles on a Glassy Carbon Electrode (GCE) Using Pulsed Potential Techniques
Authors: Hernández-Ramírez Vianey , Alatorre-Ordaz Alejandro , Yépez-Murrieta Ma. de Lourdes , Ibanez Jorge G. , Ponce-de-León Carlos , Walsh Franck C.
Published: December 2009

Direct oxidation borohydride fuel cells are very attractive energy conversion devices. Silver has been reported as one of the few materials which can catalyze an 8-electron oxidation. Potential step amperometric pulse techniques to synthesize nanostructured silver material on flat glassy carbon electrodes is reported and significant differences with bulk silver deposit have been observed. The oxidation of borohydride ion on the silver particles occurs at -0.025 V vs. SCE and the potential decreases towards negative values at longer cycle times. The oxidation current also decreases with the number of cycles, suggesting that the silver active sites become partially blocked by oxidation products of borohydride. The electroactive area per unit electrode area of silver was relatively low for particles deposited using potential step amperometric techniques on glassy carbon (0.002 cm2 per cm-2) compared with the area found at a polycrystalline silver electrode (0.103 cm2 per cm-2).
Electrochemical Evaluation of Electrocatalytic Materials for Water Oxidation
Authors: Perez-Garcia Rosalina , Gonzalez-Martinez Ignacio , Oropeza-Guzmán Mercedes T.
Published: December 2009

This paper presents an easy electrochemical evaluation of the charge transfer controlling steps in the mechanism of water oxidation on Ti/IrO2, Ti/IrO2/SnO2/Sb2O3 and Ti/IrO2/Ta2O5. Current density vs. polarization curves (j-Δ plots) were obtained for each electrocatalyst taking the reached current density for specific polarization values at 0.25 s from an oxidation chronoamperometric series in 0.5M H2SO4. Tafel model was used to compare and determinate which material improves the oxygen bubbles evolution, looking forward to use those electrodes in electroflotation processes. The electrodes were comparated vs. Pt to show their remarkable electrocatalytic behavior. Ti/IrO2 (100%) and Ti/IrO2/Ta2O5, seemed to be the more suitable materials for oxygen evolution due to their low electric energy consumption. However Ti/IrO2/SnO2/Sb2O3 were selected as the more convenient electrode, since its great oxidation kinetic was showing no pseudostationary state for charge transfer after water adsorption on electrode vacancies.
Electrocatalysis of Oxygen Reduction on Au Nanoparticles
Authors: Vázquez-Huerta Gerardo , Ramos-Sanchez Guadalupe , Antaño-López René , Solorza-Feria Omar
Published: December 2009

The Oxygen Reduction Reaction (ORR) on synthesized Au nanoparticles was investigated. The reduction of AuCl3 with NaBH4 in THF forms highly crystalline Au particles with a face-centered cubic structure and approximate size of ~5nm. From RDE measurements the kinetic parameters were obtained, i.e. Tafel slope of -0.110 Vdec-1 and charge transfer coefficient, a =0.54. The Nyquist and Bode spectra of Au nanoparticles for E > 0.38 V vs NHE show one loop which may be associated to the reduction process of O2 to generate H2O2. The impedance spectra for E<0.38 V show a second time constant, which may be associated to a second process, ie. the reduction of H2O2 to H2O.
Electrochemical Characterization of Palladium Supported in Thermally Treated Carbon for Oxygen Reduction Reaction in Acid Media
Authors: González Rosa D. , Luna-Martínez Mónica L. , Solorza-Feria Omar
Published: December 2009

In proton exchange membrane fuel cell (PEMFC), the low interaction between the electrocatalyst and the support has been subjected of an intensive research in last years. The low interaction arises by a decreased contact between the support and the nano sized catalyst. In this paper the palladium supported in thermally treated carbon (Pd/TTC) was synthesized via the NaBH4 reduction of the PdCl2 precursor at 60{degree sign}C. The supporting carbon was thermally treated at 200oC, 400{degree sign}C, 600{degree sign}C and 800{degree sign}C. Structural characterization of the TTC was examined by Raman spectroscopy and the Pd/TTC morphology by SEM. Electrocatalyst activity for the oxygen reduction reaction was investigated by cyclic and linear voltammetry in 0.5M H2SO4 at 25{degree sign}C. The resulted Pd/TTC at 400{degree sign}C and 600{degree sign}C showed significantly higher activity following kinetics of four electrons transfer to water formation. This behavior is attributed to structural properties and superficial conditions of the supporting carbon.
Decolorization of Synthetic Azo Dyes by Electrochemically Generated •OH Radicals in Acidic Medium using Boron Doped Diamond (BDD) Electrodes
Authors: Rodríguez De León Norma , Cruz-González Karla , Torres-López Omar , Hernandez Ramírez Aracely , Guzmán-Mar Jorge , Martínez-Huitle Carlos , Peralta-Hernández Juan Manuel
Published: December 2009

In this work, a comparative study of electrochemical degradation of Acidic yellow 36 (Ay-36) and Methyl orange (MO) aqueous solutions using direct electrochemical oxidation (DEO) and electro-Fenton system (EF) processes are reported. For both processes, Boron Doped Diamond (BDD) electrodes were used as anode and cathode. The electrochemical decolorization of azo dye compounds was followed by UV-Vis spectrophotometry. Decolorization kinetics of the azo dyes by electrochemically generated hydroxyl radicals followed a pseudo-first order model. The DEO-EF combined process generally resulted in higher oxidation rate than DEO process during the first minutes of electrolysis, due to the oxidizing power of H2O2 was enhanced in the presence of Fe2+ via Fenton's reaction.
Electrochemical Oxidation of Wastewaters from the Instant Coffee Industry Using a Dimensionally Stable RuIrCoOx Anode
Authors: Cárdenas Angélica , Zayas Teresa , Morales Ulises , Salgado Leonardo
Published: December 2009

The electrochemical oxidation of wastewater from an industrial plant producing instant coffee was studied using a dimensionally stable anode comprised of titanium with a film of ruthenium, iridium and cobalt oxides, Ti/Ru(40%)Ir(40%)Co(20%)Ox. Prior to the electrochemical treatment, the wastewater was subjected to a flocculation process. The anodic oxidation was performed at a controlled potential and monitored as a function of electrolysis time. HCl or NaCl was used as a support electrolyte. The efficiency of the wastewater purification process was evaluated through measurements of the chemical oxygen demand (COD), color, turbidity and UV-vis spectra. The flocculation process reduced the COD by 32% with respect to the initial value. The reductions in COD, color and turbidity induced by anodic oxidation depended on the electrolysis time and the support electrolyte used. NaCl was a more effective than HCl for reducing the COD. It is hypothesized that the oxidation of organic compounds proceeds indirectly via active chlorine species.
Selection of the Electrolyte Solution by Applying Electro-kinetic Treatment of Lead Contaminated Soil
Authors: Guerrero Oscar X. , Oropeza-Guzmán Mercedes T. , Sumbarda Emigdia G.
Published: December 2009

In electrokinetic treatment of contaminated soils three transport phenomena are induced in soil solution: electroosmosis, electrophoresis and (1). These help in the extraction of contaminants and can be optimized by modifying conditions of the soil solution. Of the most important factors to consider are: soil type, electrolytic medium composition and current values. In this work first a model soil (sand A100) was characterized and its zeta potential (pZ) was measured varying electrolytes, pH and intensity of current. This in order to select the most appropriate parameters to be used in electrokinetic treatment. Since when the pZ is in the range of -30 to +30 mV colloidal particles (soil dispersion) tend to agglomerate hampering electrokinetic treatment it is recommended to work with pZ values outside this range. It was observed that dispersion using NH4AcO as electrolyte introduced a lower pZ value, so it is best to be used in electrokinetic treatment.
Characterization for EIS of a Modified Graphite Electrode in a Hexane/CTAB- (CTA)4[Fe(CN)6]-Butanol/Water Microemultion
Authors: Carreon Gutierrez Carlos A. , Estrada Vargas Arturo , Barcena Soto Maximiliano , Casillas Santana Norberto
Published: December 2009

The present work show the results of the characterization of the hexane/CTAB-(CTA)4[Fe(CN)6]-butanol/water system by electrochemical impedance spectroscopy (EIS). This system has the singularity to form an adsorbed surfactant layer on the graphite surface that modifies the electrode properties. The modified electrode has been applied in Fe(CN)6-3 standard solution. Ferrocyanide molecules spread it out presumably through the adsorbed CTAB's tails even catching up with the surface of the carbon electrode, exposing an electrochemical answer of oxide-reduction. The electrochemical answer system uses a series of elements harbored the equivalent circuit agrees with the transit of ions through the adsorbed tensoactive, the range of the errors during the adjustment is small, therefore the data remains reliable; according to the Kramers-Kronig transformed (to the one were the simulations gotten out).
Palladium Electrodeposition on Carbon Black Films in an Acid Environment
Authors: Sánchez-Peña Aldo H. , Miranda-Hernández Margarita
Published: December 2009

Electrochemical deposition of palladium on nanostructured carbon black films electrodes (nCBFE) supported in glassy carbon (GC) was studied by cyclic voltammetry of reversal potential (E lambda), chronoamperometry and the anodic stripping voltammetry techniques in the electrolytic system 10-3M PdCl2; 1M NH4Cl pH=0. The cyclic voltammetry studies allowed us to characterize the electrochemical response of nCBFE and establish that it can be used as an electrode material for palladium electrodeposition. The chronoamperometry and anodic stripping voltammetry studies allowed us to define a specific potential range for palladium deposition without hydrogen evolution (-0.09 to -0.19 V vs. SCE). It should be noted that the hydrogen discharge takes place at more negative potentials. Moreover, it was possible to evaluate the corresponding mass of metallic palladium in a wide potential range with and without hydrogen discharge influence.
Kinetics of Polypyrrole Films Doped with Sulphate Ions Electrodeposited Over Graphite - Epoxy Resin Electrode
Authors: De J. Licona-Sánchez Teresa , Álvarez-Romero Giaan A. , Mendoza-Huizar Luis H. , Palomar Manuel E. , Galán-Vidal Carlos A.
Published: December 2009

A kinetic study for the electrosynthesis of polypyrrole (Ppy) doped with SO4-2 ions is presented. Ppy films are electrochemically polymerized over graphite - epoxy resin electrode. Cyclic voltammetry shows a non-reversible process and the charge density increases as the number of cycles increases too. Current transients are obtained for three different potentiometric behaviors: anionic, cationic and a combination of both. Experimental data was statistically fitted to theoretical models to determine the nucleation and growth processes governing the polymer synthesis. Statistical fit suggests that the mechanism involved in the electropolimerization process is 3D nucleation limited by diffusion of the electroactive specie. The anionic-response polymer displays the lowest diffusion coefficient, while the cationic-response polymer displays the highest one. In all cases, both the active-sites number and the nucleation rate have considerably high values.
Study of Activation Losses and Ohmic Resistance in a PEM Fuel Cell using Computational Fluid Dynamics
Authors: Sierra Juan M. , Pathiyamattom Sebastian J. , Gamboa Sergio
Published: December 2009

Study of activation losses and ohmic resistance in a PEM fuel cell using computational fluid dynamics In the present work a 3D model of a proton exchange membrane fuel cell (PEMFC) was developed using a computational fluid dynamics (CFD) code (Fluent 6.3.26). The model is based on the experimental fuel cell with serpentine channel configuration. The effect of operating conditions such as pressure, temperature and humidity on the performance of fuel cell was investigated. The results showed that pressure has more impact on the pattern of overpotential distribution and temperature on its magnitude. The analysis showed good agreement with the literature data by polarization curves. The 3D fuel cell model provided a clear understanding over the influence of operating conditions in the irreversibility's that take place in PEM fuel cells with serpentine flow-field.
Preparation of Particulate Fuel Cell Electrodes by Electrodeposition Method
Authors: Guzman Carlos , Verde Ysmael , Bustos Erika , Manriquez Federico , Terol Ivan , Arriaga Luis G. , Orozco German
Published: December 2009

In this investigation we used pulse electrodeposition to prepare electrodes suitable for membrane electrode assemblies (MEA) in PEM fuel-cell applications. Platinum can be deposited directly onto a Nafion-bonded carbon electrode from an aqueous solution consisting of hydrogen dinitrosulfatoplatinate (II). The average platinum particle diameter is considerably larger than desired. Further work is needed to optimize the Pt particle size. We studied the durability of Pt/C and Pt/MWCNT using an accelerated durability test (ADT). In this test we observed Pt particle dissolution. Multi-wall carbon nanotubes used as the Pt support exhibit excellent performance in corrosion tests.
Anodic Alloys Degradation Exposed to Different Flow Conditions in Natural Seawater
Authors: Orozco-Cruz Ricardo , Meza José M. , Galván-Martínez Ricardo , Fernández-Gómez Imelda , Martínez Enrique A.
Published: December 2009

Flow conditions can be harmful to the performance of the sacrificial anodes exposed to the marine environment. The anodic alloy used for protection to the metal structures in this environment, can be affected by the high chloride concentration and other substances that accelerate the electrochemical corrosion phenomenon. The anodic alloys used in the marine environment are zinc and aluminium based alloy. Different tests to evaluate the electrochemical performance of three alloys, Zn, Al-Zn-Mg and Al-Zn-In, were carried out. A rotating cylinder electrode (RCE) was used in order to control the hydrodynamic conditions. The electrochemical techniques used in the corrosion studies were: corrosion potential (Ecorr), linear polarization resistance (Rp), potentiodynamic polarization curves and Electrochemical Impedance Spectroscopy (EIS) and natural seawater was used as the test solution. Cathodic kinetics information was obtained in the electrochemical analysis results where, it shows the effect of the Rp values versus rotational speed, as the rotational speed increased the Rp values decreased. In addition, a localized corrosion form was found in the corrosion process.
EIS Monitoring of Cathodic Protection of Steel Reinforced Concrete Enhanced by Humectants
Authors: Del Valle-Moreno Angelica , Genesca-Llongueras Joan , Torres-Acosta Andres A. , Martinez Miguel
Published: December 2009

The Galvanic Cathodic Protection system problem lies in its capacity to drive an adequate protective protection current from the galvanic anode to the embedded steel reinforcement. This study investigates the reaction mechanism, based on Electrochemical Impedance Spectroscopy (EIS), of the cathodic protection system by thermo sprayed zinc anodes to which LiBr and H2O have been added as humectants. Six reinforced slabs were tested. The specimens were placed in two different Relative Humidity cells. Electrochemical Impedance Spectroscopy and conventional electrochemical properties such as potential, galvanic current and polarization decay of the anode were routinely measured over a 150 days after the humectants addition. It was found that the LiBr notably improved the protective galvanic current; however this improvement was only temporary. Relative humidity had a greater impact than the LiBr addition on the concrete's resistivity.
Efficiency of Supplementary Materials Against Steel Corrosion in Concrete with Recycled Aggregate Exposed to Sulfates
Authors: Arredondo Rea Susana P. , Corral Higuera Ramón , Almaral Sánchez Jorge L. , Castorena González José H. , Neri Flores Miguel &. , Martínez Villafañe Alberto , Almeraya Calderón Facundo
Published: December 2009

Reinforced concrete was fabricated using recycled concrete coarse aggregate and replacing partially Portland cement with supplementary materials as fly ash, ground granulated blast furnace slag and silica fume. On test specimens, partially immersed in 3.5% Na2SO4 aqueous solution, the efficiency of the supplementary materials against corrosion was evaluated. For such aim, corrosion potentials and corrosion current density of reinforcement were determined by means of electrochemical techniques as Open Circuit Potential (OCP) and Linear Polarization Resistance (LPR), respectively. The results show that the silica fume addition was the best efficiency against steel corrosion.
A Semiempirical PM6 Study of Some Aminopyrimidine Derivatives and their Interaction with an Iron Surface
Authors: Mendoza-Huizar Luis H. , Rios-Reyes Clara H. , Palomar-Pardavé Manuel
Published: December 2009

At present work we analyzed at PM6 level, the electronic properties of 2-aminopirimidyne, 2,4-diaminopirimidyne and 2,4,6-triaminopyrimidine corrosion inhibitors. The results indicated that the HOMO's energy and HOMA index may be related with the inhibition efficiency reported for these compounds. The HOMO's energy values and HOMA indexes indicated that the corrosion inhibition efficiency order is 2,4,6-triaminopyrimidine > 2,4-diaminopirimidyne > 2-aminopirimidyne. The less aromatic compounds showed better corrosion inhibition efficiency. The analysis of the adsorption process of aminopirimidynes on an iron surface indicated that the surface reactivity diminishes in function of the number of amine groups presents in the compound. Thus, the 2,4,6-triaminopyrimidine deactivates the iron surface more efficiently than the 2-aminopirimidyne. Also, it was found that the adsorption process may be done through carbon atoms and not exclusively through Nitrogen atoms.
Microwave-Assisted Preparation of 2-(Benzylthio)imidazole and 2-(Benzylthio)benzimidazole and its Comparative Corrosion Inhibiting Performance with 2-Mercaptoimidazole and 2-Mercaptobenzimidazole
Authors: Cruz Deysi Y. , Negrón Guillermo , Romero-Romo Mario Alberto , Herrera-Hernández H. , Palomar-Pardavé Manuel
Published: December 2009

In this paper, the anticorrosive performance of four inhibitive organic heterocyclic compounds [2-Mercaptoimidazole (2MI), 2-Mercaptobenzimidazole (2MBI), 2-(Benzylthio)imidazole (2BZMI) and 2-(Benzylthio)benzimidazole (2BZMBI)] were investigated using pipeline steel in hydrochloric acid media (1M HCl) and compared using electrochemical impedance spectroscopy, EIS. The last two organic compounds were obtained through non-conventional synthesis using microwaves. As the inhibitors concentration increased from 5-200 ppm, Z're also increased continuously, thereby suggesting inhibitor adsorption onto the metal surface. Also, all the organic inhibitors studied showed acceptable corrosion inhibiting efficiency, IE, of about 94-96% after adding 30 ppm to the acid system. Furthermore, at this concentration the better protection efficiency was attained for the inhibitor 2BZMBI. The four inhibitive organic compounds were classified as mixed inhibitors, in accordance with the corrosion mixed potential theory.