Theoretical Insights into Effect of Surface Composition of Pt-Ru Bimetallic Catalysts on CH3OH Oxidation: Mechanistic Considerations

A deeper mechanistic understanding on CH3OH oxidation on Pt-Ru alloys with different Ru surface compositions is provided by DFT-based theoretical studies in this paper. The present results show that alloying and surface compositions of Ru can change CH3OH oxidation pathway and activity. The optimal surface composition of Ru is speculated to be ca. 50% since the higher Ru surface composition can lead to formation of carbonaceous species that can poison surface. Our present calculated Ru surface composition of ca. 50% exhibits excellent consistency with experimental studies. The origin of enhanced catalytic activity of Pt-Ru alloys is determined. The significantly decreased surface work functions after alloying suggest more electrons are transferred into adsorbates. The calculated lower electrode potentials after alloying imply that lower overpotentials are required for CH3OH oxidation. The excellent inconsistency with experimental study on decreased onset potentials after alloying further confirms accuracy of our present calculated results.

Performance Improvement of Gold Electrode towards Methanol Electrooxidation in Akaline Medium: Enhanced Current Density Achieved with Poly(aniline-co-2-hydroxyaniline) Coating at Low Overpotential

Electronically conducting poly (aniline-co-2-hydroxyaniline) (PACHA), a copolymer of aniline and 2-hydroxyaniline (2HA), was electrochemically coated on gold substrate for methanol electrooxidation in alkaline media. The electrochemical behavior of PACHA coated gold electrode towards methanol electrooxidation was investigated via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for application in an alkaline fuel cell. Methanol electrooxidation was observed at two different electrode potentials depending on the concentration of the base. At the PACHA coated gold electrode, the methanol oxidation peak was observed at lower overpotential (at 0.19 V) in a solution of high base concentration (1.8 M NaOH), which was 30 mV lower than the peak for the uncoated gold electrode. In addition, the Faradic current Imax obtained on the PACHA coated electrode (20 mA) was two times higher as compared to the Faradic current Imax of the un-modified gold electrode (10 mA). In solution of lower base concentration (0.06 M NaOH), the electrooxidation of methanol became sluggish on both electrodes, as indicated by peak shifting towards positive potential and with reduced faradaic current (at 0.74 V on PACHA coated electrode; Imax 10 mA). The electrooxidation of methanol at both lower and higher electrode potentials was analyzed mechanistically and discussed in light of the literature. EIS results were interpreted using Nyquist and Bode plots. The charge transfer resistance was decreased and pseudo-capacitive behavior changed to conductive behavior when external applied potential was increased from 0.1 V to 0.4 V.

Some thermodynamic and kinetic properties of H2SO4–H3PO4–H2O–Fe(III) system

The values of the electrode potentials of the redox couple Fe(III) / Fe(II) and the half-wave potentials of the reactions Fe3+ + e– = Fe2+ и Fe2+ — e– = Fe3+ on the cyclic voltammogram of a platinum electrode in acid solutions containing Fe(III) salts have been measured to characterize the oxidizing ability of the H2SO4—H3PO4—H2O—Fe(III) system. The values of these experimentally obtained parameters are close. A decrease in the oxidizing ability of H2SO4 and H3PO4 mixtures containing Fe(III) with an increase in the molar fraction of H3PO4 in them occurs due to the formation of Fe(III) complexes with phosphate anions which are inferior to their hydrate and sulfate complexes in the oxidizing ability. The temperature coefficients of the electrode potential (dE / dt) of the redox couple Fe(III) / Fe(II) in the H2SO4—H2O, H2SO4—H3PO4—H2O and H3PO4–H2O systems were determined experimentally. The diffusion coefficients of Fe(III) in the studied solutions were calculated based on the Randles—Shevchik equation. The temperature dependence of the diffusion coefficients of Fe(III) cations is satisfactorily described by the Arrhenius equation. The parameters of this equation are calculated.

Selection of rational electrochemical methods for controlling the efficiency of machining of corrosion-resistant steel

The article discusses methods of controlling the processes of mechanical processing based on electrochemical effects. The corresponding anodic polarization curves of 1X18H9T steel obtained in electrolyte solutions without and with stirring are presented. The article discusses methods of machining processes control based on electrochemical effects. Lubricating and cooling technological media (LCTM) used in machining are in most cases electrolytes, therefore, electrochemical processes and phenomena actively occur during contact dynamic machining. It is possible to control the processes of machining by acting on the system elements of the tool - LCTM- part, in particular by activating the LCTM and reducing the strength characteristics of the processed steel in the cutting zone. A reserve for increasing the efficiency of mechanical processing can be the composition selection of the applied LCTM, combined with the simultaneous electrochemical polarization of the treated surface of friction pair parts. It was found that when cutting, the efficiency of machining and the chip shapes are changed, which is explained by the influence of the current density on the strength of the processed steel. In the conditions of machining, complex dynamic processes occur due to the rotation of the work piece and/or tool, so it is necessary to take into account the hydrodynamic phenomena and processes that arise in this case. Electrode potentials are considered to be the most important characteristic of the metal cutting process. The potential of the system can regulate such processes and indicators as wear and surface micro hardness. Anodic polarization curves of the steel 1X18H9T obtained in various electrolyte solutions without stirring and with stirring on a rotating disk electrode are given. The study allowed determining the factors affecting the processes occurring in the cutting zone and to identify rational current densities due to simulating the conditions of real technological processes of the combined steel processing. The increase in the processing intensity of the steel 1X18H9T with the cutting zone polarization is associated with the action of factors activating the selective anodic dissolution of the processed alloy.

Electrodeposition of Ni–Fe alloy from solutions based on deep eutectic solvent ethaline

The kinetics of сodeposition of nickel and iron in an electrolyte based on a deep eutectic solvent (ethaline) was studied by voltammetry method. It was established that the partial voltammograms of iron ions reduction during alloy electrodeposition correspond to the region of electrode potentials, which is more than 100 mV positive in comparison with the electrodeposition potentials of pure iron. It was shown that the acceleration of iron ion electroreduction is associated with the gain in energy due to the alloy formation and a decrease in the overvoltage of iron electrodeposition during alloying. The change in the kinetics of iron electrodeposition can be explained by both a change in the mechanism of its electrodeposition in conjunction with nickel and a change in the state of the electrode surface in the potential region of the alloy formation. Comparison between the ratio of the content of the alloy components in the metal and the corresponding ions in the electrolyte showed that nickel and iron electrodeposit into the alloy in quantities that are proportional to their content in the electrolyte. Thus, electrodeposition of nickel-iron alloy from ethaline with a water content of up to 3% occurs by the so-called normal mechanism.

Control of the Optical and Physical Characteristics of Conjugated Polyelectrolytes in the Solution and Solid Phase

<p>Conjugated Polyelectrolytes (CPEs) are a branch of conducting polymers that combine the electronic and solution processability of conjugated polymers (CPs) with the ionic and self-assembling nature of polyelectrolytes. These systems have been shown to exhibit high sensitivity with changes in aggregation state and optical character dependant on the local environment. The ionic character of the CPEs can be used as scaffolds for post-synthetic alterations allowing for control of the optical and physical characteristics. In this thesis, the control of the optical and physical characteristics of the conjugated polyelectrolytes (CPEs) sodium poly[2-(3-thienyl)ethoxyl-4-butylsulfonate] (PTEBS) and poly(9,9-bis[6-(N,N,N-trimethylammonium)hexyl]fluorine-co-altphenylene] (FPQ-X, where X denotes the various counter-ions of the polymers) is investigated though the addition of various extrinsic ions to dilute solutions and concentrated solutions used for film casting, with the main focus being in the solution phase behavior. The CPE characteristics were studied primarily through UV/Vis absorption and fluorescence spectroscopy coupled with dynamic light scattering and surface tension techniques. Controlling the solution phase characteristics of the CPE was investigated through a study of through of solvent composition effects, monovalent and divalent ion addition, organic salt addition, and surfactant additions to dilute aqueous solutions of the CPEs. Solvent composition effects were shown to result in fluorescence enhancement with changes in the polarity of the solvent, while the addition of monovalent and divalent ions was shown to induce fluorescence quenching through ionic strength, ion condensation, and cross-linking of CPE molecules dependant on the concentration and valency of the metal ion. Organic salt additions of a range of concentrations were shown to result in both concentration and alkyl chain length dependant fluorescence intensity enhancements with little changes in the particle size of aggregates in solution. The lack of change in particle size suggested that the effects were localized to the aggregate surface with the size of the organic salt inducing a steric prying effect on the CPE aggregate. A proposed model of this was created to this effect. Large changes in the optical and physical characteristics of the CPEs were found with addition of surfactants to the CPE solutions. Fluorescence quenching and enhancements, particle size increases and decreases, and absorption hypsochromic shifts have been noted, with surfactant structure and concentration dependence. The resulting effects are shown to be hydrophobically, electrostatically, and self-assembly driven. Concentration control of the CPE aggregate size and optical characteristics is completed with surfactant micelles being noted at pre-CMC concentrations within the solutions. A model of interactions at the various concentration levels of surfactant has been developed explaining these results. Transferring this system to the solid state has been shown to exhibit both bathochromic and hypsochromic shifts in absorption and have two optically active phases. The dual phase absorption and emission was attributed to a CPE-surfactant complex where the CPE backbone and surfactant self assemblies result in lamellar type structures within the cast films. The optical overlap of the emission and absorption of the CPEs used was also shown to be favorable for FRET based transfer from FPQ-X to PTEBS. Films created by the layer-by-layer technique showed FRET based signal of PTEBS via excitation of FPQ-Br showing effective FRET based energy transfer between the two species. The absorption signatures of the films with multiple layer-by-layer processes showed that the films do not result in unique layers but rather interdigitated mixtures within the film. Proof of concept P3HT with DOD addition OFET devices were then created in the attempt to alter the electrode potentials using mobile ions. The devices were found to be less efficient than that of the controls due to the disruption of self assembled structures within the devices hampering electron movement.</p>

Control of the Optical and Physical Characteristics of Conjugated Polyelectrolytes in the Solution and Solid Phase

<p>Conjugated Polyelectrolytes (CPEs) are a branch of conducting polymers that combine the electronic and solution processability of conjugated polymers (CPs) with the ionic and self-assembling nature of polyelectrolytes. These systems have been shown to exhibit high sensitivity with changes in aggregation state and optical character dependant on the local environment. The ionic character of the CPEs can be used as scaffolds for post-synthetic alterations allowing for control of the optical and physical characteristics. In this thesis, the control of the optical and physical characteristics of the conjugated polyelectrolytes (CPEs) sodium poly[2-(3-thienyl)ethoxyl-4-butylsulfonate] (PTEBS) and poly(9,9-bis[6-(N,N,N-trimethylammonium)hexyl]fluorine-co-altphenylene] (FPQ-X, where X denotes the various counter-ions of the polymers) is investigated though the addition of various extrinsic ions to dilute solutions and concentrated solutions used for film casting, with the main focus being in the solution phase behavior. The CPE characteristics were studied primarily through UV/Vis absorption and fluorescence spectroscopy coupled with dynamic light scattering and surface tension techniques. Controlling the solution phase characteristics of the CPE was investigated through a study of through of solvent composition effects, monovalent and divalent ion addition, organic salt addition, and surfactant additions to dilute aqueous solutions of the CPEs. Solvent composition effects were shown to result in fluorescence enhancement with changes in the polarity of the solvent, while the addition of monovalent and divalent ions was shown to induce fluorescence quenching through ionic strength, ion condensation, and cross-linking of CPE molecules dependant on the concentration and valency of the metal ion. Organic salt additions of a range of concentrations were shown to result in both concentration and alkyl chain length dependant fluorescence intensity enhancements with little changes in the particle size of aggregates in solution. The lack of change in particle size suggested that the effects were localized to the aggregate surface with the size of the organic salt inducing a steric prying effect on the CPE aggregate. A proposed model of this was created to this effect. Large changes in the optical and physical characteristics of the CPEs were found with addition of surfactants to the CPE solutions. Fluorescence quenching and enhancements, particle size increases and decreases, and absorption hypsochromic shifts have been noted, with surfactant structure and concentration dependence. The resulting effects are shown to be hydrophobically, electrostatically, and self-assembly driven. Concentration control of the CPE aggregate size and optical characteristics is completed with surfactant micelles being noted at pre-CMC concentrations within the solutions. A model of interactions at the various concentration levels of surfactant has been developed explaining these results. Transferring this system to the solid state has been shown to exhibit both bathochromic and hypsochromic shifts in absorption and have two optically active phases. The dual phase absorption and emission was attributed to a CPE-surfactant complex where the CPE backbone and surfactant self assemblies result in lamellar type structures within the cast films. The optical overlap of the emission and absorption of the CPEs used was also shown to be favorable for FRET based transfer from FPQ-X to PTEBS. Films created by the layer-by-layer technique showed FRET based signal of PTEBS via excitation of FPQ-Br showing effective FRET based energy transfer between the two species. The absorption signatures of the films with multiple layer-by-layer processes showed that the films do not result in unique layers but rather interdigitated mixtures within the film. Proof of concept P3HT with DOD addition OFET devices were then created in the attempt to alter the electrode potentials using mobile ions. The devices were found to be less efficient than that of the controls due to the disruption of self assembled structures within the devices hampering electron movement.</p>

Combining pressure and electrochemistry to synthesize superhydrides

Recently, superhydrides have been computationally identified and subsequently synthesized with a variety of metals at very high pressures. In this work, we evaluate the possibility of synthesizing superhydrides by uniquely combining electrochemistry and applied pressure. We perform computational searches using density functional theory and particle swarm optimization calculations over a broad range of pressures and electrode potentials. Using a thermodynamic analysis, we construct pressure–potential phase diagrams and provide an alternate synthesis concept, pressure–potential (P2), to access phases having high hydrogen content. Palladium–hydrogen is a widely studied material system with the highest hydride phase being Pd3H4. Most strikingly for this system, at potentials above hydrogen evolution and ∼ 300 MPa pressure, we find the possibility to make palladium superhydrides (e.g., PdH10). We predict the generalizability of this approach for La-H, Y-H, and Mg-H with 10- to 100-fold reduction in required pressure for stabilizing phases. In addition, the P2 strategy allows stabilizing additional phases that cannot be done purely by either pressure or potential and is a general approach that is likely to work for synthesizing other hydrides at modest pressures.

Microcontroller Based High Voltage, High Speed Trigger Control Circuit for SMARTEX-C

Microcontroller based trigger control circuit for fast pulsing of electrode potentials on wide range of time scales has been designed, installed, and tested for electron plasma experiments which are carried out in partial toroidal trap SMall Aspect Ratio Toroidal Electron plasma EXperiment in C – shaped geometry (SMARTEX – C), a device to create and confine non-neutral plasma (electron plasma). The sequence of trap operation is inject-hold-dump for which electrodes need to be pulsed with applied voltages at a high switching speed of few nanoseconds. Also this sequence of operation needs to be controlled over a very wide range of time scales from few microseconds to few seconds. As the available COTS (Commercial-Off-The-Shelf) high voltage DC power supplies generally do not provide this feature of fast switching at nanosecond time scale, MOSFET based circuit is developed which provides fast switching in the range of 20 – 100 nanoseconds of high voltages (200Vdc - 500Vdc) of multiple electrodes. The timing pulse widths of these trigger pulses are controlled using a microcontroller-based circuit. This experimental set-up also requires the triggering of a high current dc power supply used for an Electro-magnet (Toroidal Field Coil) to generate a toroidal magnetic field, at the start of this experiment. For this purpose, a Silicon Controlled Rectifier (SCR) based circuit is used. The gate pulse to trigger the SCR circuit is also generated from this microcontroller-based circuit. National Instrument’s LabVIEW software based Graphical User Interface (GUI) is developed for triggering the SCR and electrodes with a programmable time period through the serial link.