Free radical and isomerisation processes during the electrochemical fluorination of n-butyryl chloride, i-butyryl chloride and pivaloyl chloride in anhydrous hydrogen fluoride

Electrochemical perfluorination (ECPF) of the title compounds containing primary, secondary and tertiary carbon atoms was carried out in anhydrous hydrofluoric acid (AHF). Detailed analysis of major and minor products suggest that carbon chain isomerisation involving cyclo-propane intermediate is more prevalent during ECPF of i-butyryl chloride when compared to n-butyryl chloride. Simple statistical probability involving free radical intermediates also support this observation. ECPF involving cyclo-propane intermediate is even more prevalent in pivaloyl chloride containing three methyl substituents. In this case, perfluorinated cyclo-propane intermediates were also observed in the product sample. Distribution of minor perfluorinated and partially fluorinated products also suggest the predominant role of normal free radical pathway involving single-electron transfer.     

Surface fluorination and electrochemical behavior of petroleum cokes graphitized at medium and high temperatures for secondary lithium battery

The surface structure and electrochemical performance have been investigated of petroleum cokes heat-treated at 2100 and 2600 °C (abbreviated to PC2100 and PC2600) and those fluorinated by elemental fluorine at 200 and 300 °C. XPS study indicated that surface fluorine was covalently bonded to carbon and surface fluorine contents were in the range of 4.9-17.8 at.%. Surface oxygen was reduced by fluorination. BET surface areas were nearly the same before and after fluorination. Fluorination enhanced D-band intensity in two Raman shifts observed at 1580 cm⁻¹ (G-band) and 1360 cm⁻¹ (D-band), indicating the increase in the surface disordering. At a high current density of 150 mA/g, the capacity increase was observed for PC2100 fluorinated at 200 °C and for PC2600 fluorinated at 200 and 300 °C. The most interesting result was the increase in first coulombic efficiencies by surface fluorination. First columbic efficiencies for PC2600 fluorinated at 300 °C were increased by 12.1% at 60 mA/g and by 25.8% at 150 mA/g, respectively. The impedance measurements showed that the resistances of surface films on carbon electrodes were increased by fluorination, however, the charge transfer resistances were decreased by 12.3% for PC2100 fluorinated at 200 °C, and by 27.5 and 6.4% for PC2600 fluorinated at 200 and 300 °C, respectively. The reduction of the charge transfer resistances was consistent with increase in the charge capacities for PC2100 fluorinated at 200 °C and PC2600 fluorinated at 200 and 300 °C.     

Prevention of anode fouling during the electrochemical perfluorination of aromatic carboxylic acid chlorides

The electrochemical perfluorination of benzoyl chloride, p-substituted benzoyl chlorides and cyclo-hexane carboxylic acid chloride in anhydrous hydrogen fluoride (AHF) medium on nickel electrode is reported. Experimental conditions suppressing polymeric film formation on the electrode are optimized. Addition of 1 wt.% dimethyl sulfide based on the volume of AHF in the initial stage of electrochemical fluorination and maintenance of the reactant and intermediate concentrations below a critical level ensured electrochemical fluorination of all the reactants without fouling of the electrode surface. Presence of p-substituents in the benzene ring improved the selectivity of alicyclic perfluoro carboxylic acid. GC/MS and ¹⁹F NMR data for the major perfluorinated products are reported.     

Fluorinated carbon nanofibres for high energy and high power densities primary lithium batteries

The electrochemical performances of fluorinated carbon nanofibres have been tested for a use as cathode material in primary lithium battery using LiBF₄ PC:DME 1M as electrolyte. For a very narrow fluorination range (420–450 °C), the fluorine content in the carbon nanofibres increases up to CF_0.78 and so do both the energy and the power densities. A maximum of 8057 W kg⁻¹ power density has been reached. Moreover, a current density of 6C can be used for such fluorinated carbon nanofibres. Such high electrochemical values can be correlated to the amount of unfluorinated carbon located in the core of the carbon nanofibres. Owing to solid state ¹³C NMR which can accurately evaluated this fraction, a minimum of 10% of unfluorinated carbon nanofibre is necessary in order to insure a good conducting behaviour.     

Electro-catalytic performance of Pt-supported poly (o-phenylenediamine) microrods for methanol oxidation reaction

Poly (o-phenylenediamine) (PoPD) microrods were obtained by interfacial polymerization using ferric chloride as oxidant and without any template or functional dopant. Pt/PoPD nanocatalysts were prepared by the reduction of chloroplatinic acid with sodium borohydride, and the composite catalysts formed were characterized by X-ray diffraction and electrochemical methods. The nanocomposite of Pt/PoPD microrods has been explored for their electro-catalytic performance towards oxidation of methanol. The electro-catalytic activity of Pt/PoPD was found to be much higher (current density 1.96?mA/cm² at 0.70?V) in comparison to Pt/Vulcan electrodes (the current density values of 1.56?mA/cm² at 0.71?V) which may be attributed to the microrod morphology of PoPD that facilitate the effective dispersion of Pt particles and easier access of methanol towards the catalytic sites.     

Effect of sodium cation on the electrochemical reduction of CO<Subscript>2</Subscript> at a copper electrode in methanol

The electrochemical reduction of CO₂ with a Cu electrode in methanol was investigated with sodium hydroxide supporting salt. A divided H-type cell was employed; the supporting electrolytes were 80 mmol dm⁻³ sodium hydroxide in methanol (catholyte) and 300 mmol dm⁻³ potassium hydroxide in methanol (anolyte). The main products from CO₂ were methane, ethylene, carbon monoxide, and formic acid. The maximum current efficiency for hydrocarbons (methane and ethylene) was 80.6%, at −4.0 V vs Ag/AgCl, saturated KCl. The ratio of current efficiency for methane/ethylene, r _f(CH₄)/r _f(C₂H₄), was similar to those obtained in LiOH/methanol-based electrolyte and larger relative to those in methanol using KOH, RbOH, and CsOH supporting salts. In NaOH/methanol-based electrolyte, the efficiency of hydrogen formation, a competing reaction of CO₂ reduction, was suppressed to below 4%. The electrochemical CO₂ reduction to methane may be able to proceed efficiently in a hydrophilic environment near the electrode surface provided by sodium cation.     

Effect of surface fluorination on the electrochemical behavior of petroleum cokes for lithium ion battery

Surface structure change and electrochemical behavior of fluorinated petroleum coke samples (petroleum cokes: petroleum coke and those heat-treated at 1860 °C, 2300 °C and 2800 °C, abbreviated to PC, PC1860, PC2300 and PC2800, respectively) have been investigated. Surface oxygen of petroleum coke was decreased by the fluorination using elemental fluorine. Raman and EPR spectroscopies revealed that surface fluorination increased surface disorder and lattice defects. ¹⁹F NMR spectrum suggests that distribution of fluorine atoms in PC fluorinated 300 °C was similar to that in graphite fluoride with covalent CF bonds. Surface areas of fluorinated petroleum cokes were nearly the same as those of non-fluorinated ones or only slightly increased by fluorination, except PC fluorinated at 300 °C. It is noted that first coulombic efficiencies of PC2300 and PC2800 were highly increased to 80-84% by the fluorination at 300 °C. These values of 80-84% were 12-18% higher than those of non-fluorinated PC2300 and PC2800.     

Ionic interactions in aqueous electrolyte-polyelectrolyte mixtures: Comparisons with mixtures of sodium chloride and the model electrolyte benzyltrimethyl-ammonium chloride at 25°C

Osmotic coefficients for aqueous mixtures of sodium chloride with benzyltrimethylammonium chloride, BzMe₃NCl, obtained by the gravimetric isopiestic vapor pressure comparison method are interpreted with the McKay-Perring transform, with the Scatchard neutral electrolyte treatment, and with the Pitzer ion-component equations. Molal ionic and mean ionic activity coefficients for Na⁺ and Cl^– ions and for NaCl, respectively, in these mixtures at unit total ionic strength also were determined with an electrochemical cell. The excess free energy chenges G^ex on mixing NaCl with BzMe₃NCl were estimated and employed to gain an insight into the relative importance of like and unlike cation-cation interactions.     

Surface and bulk properties of severely fluorinated carbon fibres

The development of ultra-inert composites using fluorinated carbon fibres as the reinforcement requires fluorinated carbon fibres with a durable surface composition. Here we report the effect of direct fluorination using an F₂/N₂ mixture at 653 K on the surface and bulk properties of two types of high strength carbon fibres. These were treated up to a surface fluorine content of ∼64 at.% and a bulk fluorine content of ∼15 mass%. A colour change was observed after fluorination caused by the changes in the graphitic band structure of the carbon fibres by the introduction of carbon sp³ hybridisation. The tensile strength and Young's modulus decrease after fluorination by up to 33 and 22%, respectively. XRD shows marginal changes in the interlayer distance but the crystallite size increases. Changes in the electrical conductivity of the fluorinated carbon fibres indicate that the modification is confined to the near surface volume. Predominantly covalent C-F bonds are formed as shown by X-ray photoelectron spectroscopy (XPS) and measured zeta (ζ)-potentials. Hence the fluorinated fibres are hydrophobic and have low surface tensions. This and the large increase in fibre surface area, as determined by nitrogen adsorption, is expected to facilitate interfacial interaction between fluorinated carbon fibres and fluoropolymers.     

Enhancement of Methanol Tolerance in DMFC Cathode: Addition of Chloride Ions

In the operation of a direct methanol fuel cell, the modification by chloride ions on the surface of a Pt cathode can facilitate the extraordinary increase of power performance and long‐term stability. Analyzing the results of cyclic voltammograms and electrochemical impedance spectroscopy, the positive shift of Pt oxidation onset potential and the depression of oxidation current are observed, which results from the role of chloride as surface inhibitor. In addition, O₂ temperature‐programmed desorption and X‐ray photoelectron spectroscopy also reveal that the suppression of Pt surface oxide can be best understood in terms of lower binding of oxygen species by the alteration of electronic state of Pt atoms. Such a reduced surface oxide formation not only provides more efficient proton adsorption sites with high selectivity but also decreases the mixed potential by crossover methanol, resulting in higher performance and stability even under high voltage long‐term operation.     

Carbon Dioxide Measurements with and without Barium Peroxide in Electrolytic Studies with and without a Supporting Electrolyte

Abstract

This research deals with the quantitative formation of carbon dioxide in electrolytic oxidation reactions. The electrolytic reactions were run with barium peroxide to generate the superoxide anion at the anode. With the organic compounds used in these electrolytic studies we needed to develop a method where we could determine the amount of carbon dioxide liberated from these compounds with the superoxide anion. This method degasses an acidified solution with dry nitrogen, which carries the carbon dioxide to a standard solution of sodium hydroxide. Titration of the sodium hydroxide solution with standardized hydrochloric acid revealed the amount of carbon dioxide formed in the reaction after precipitation of the carbonate ions with barium chloride. Blank runs with the apparatus using anhydrous sodium carbonate produced 99% plus results of recovered carbon dioxide from the sodium carbonate.     

Uptake of liquid alcohols by the flexible Fe(III) metal-organic framework MIL-53 observed by time-resolved in situ X-ray diffraction

A comprehensive, time‐resolved, energy‐dispersive X‐ray diffraction study of the uptake of liquid alcohols (methanol, ethanol, propan‐1‐ol and propan‐2‐ol) by the flexible metal‐organic framework solid MIL‐53(Fe)[H₂O] is reported. In the case of the primary alcohols, a fluorinated version of the MIL‐53(Fe) host (C2/c symmetry V ca. 1000 ų), in which a fraction of framework hydroxides are replaced by fluoride, shows uptake of alcohols to give initially a partially expanded phase (C2/c symmetry, V ca. 1200 ų) followed by an expanded form of the material (either Imcm or Pnam symmetry, V ca. 1600 ų). In the case of methanol–water mixtures, the EDXRD data show that the partially open intermediate phase undergoes volume expansion during its existence, before switching to a fully open structure if concentrated methanol is used; analogous behaviour is seen if the initial guest is propan‐2‐ol, which then is replaced by pyridine, where a continuous shift of Bragg peaks within C2/c symmetry is observed. In contrast to the partially fluorinated materials, the purely hydroxylated host materials show little tendency to stabilise partially open forms of MIL‐53(Fe) with primary alcohols and the kinetics of guest introduction are markedly slower without the framework fluorination: this is exemplified by the exchange of water by propan‐2‐ol, where a partially open C2/c phase is formed in a step‐wise manner. Our study defines the various possible pathways of liquid‐phase uptake of molecular guests by flexible solid MIL‐53(Fe).     

Utilization of Solutions after the Electrosynthesis of 4-Aminodiphenylamine

The electroreduction of technological solutions of a sodium salt of 4-nitrosodiphenylamine with a continuous extraction of formed 4-aminodiphenylamine into a water-immiscible solvent and a separation of the latter, leaves a solution containing alkali, sodium chloride, methanol, and admixtures of the initial and target compounds. Freed from the methanol, the solution may serve as anolyte in the salt electroreduction, instead of an alkali solution used for the purpose. The most suitable anode material is titanium covered with platinum or iridium. Anodically treated solutions are colorless and contain no initial and target substances but include oxygen compounds of chlorine. The formation of the compounds may be avoided by introducing 10^–4 M Co²⁺ into solution. The ions may be used repeatedly.     

Total organochloride and organobromide determinations in aqueous samples by microwave induced plasma-optical emission spectrometry

The element specific detection of the adsorbable organic halogen (AOX) parameter in waters has been investigated by adsorption of the halogenated analytes on activated carbon, incineration to yield carbon dioxide and hydrogen halide, trapping of the halide on a 0.01 M sodium hydroxide solution and online introduction of the halogen formed by continuous oxidation into a microwave induced plasma (MIP). Detection has been carried out by optical emission spectrometry (OES) in the visible spectral region.The performance of three microwave cavities for MIP-OES running at atmospheric pressure (Beenakker, Surfatron and Microwave Plasma Torch) as well as a reduced pressure Surfatron were investigated for halide analysis. The Surfatron device operated at 30 torr provided the best detection limits: 3ng.ml^–1 for chloride and 8 ng.ml^–1 for bromide; consequently, it was the plasma chosen for AOX analysis.On-line continuous oxidation of organic compounds using KMnO₄ in H₂SO₄ medium and in batch catalytic dechlorination with a Fe/Pd system were investigated as alternatives to the incineration method for the destruction of organic halogens to render inorganic halides are also investigated.Finally, the optimized method has been applied successfully to the determination of organochloride and organobromide in spiked river waters, being the recoveries in the interval 92–105%.     

Facile one-pot synthesis of fluorinated graphene oxide for electrochemical sensing of heavy metal ions

Doping and functionalization could significantly assist in the improvement of the electrochemical properties of graphene derivatives. Herein, we report a one-pot synthesis of fluorinated graphene oxide (FGO) from graphite. The surface morphology, functionalities and composition of the resulting FGO have been studied using various surface characterization techniques, revealing that layer-structured nanosheets with ~ 1.0 at.% F were formed. The carbon bound F exhibited semi-ionic bonding characteristic and significantly increased the capacitance of FGO compared to GO. Further, the FGO has been employed for the simultaneous detection of heavy metal ions Cd^2 +, Pb^2 +, Cu^2 + and Hg^2 + using square wave anodic stripping voltammetry; and a substantial improvement in the electrochemical sensing performance is achieved in comparison with GO.     

High Sensitive Sensor Based on Carbon Nanotube Electrode for Determination of Lanthanum in the Presence of Calcon Carboxylic Acid

In this paper we have investigated the electrochemical activity of lanthanum chloride (La (III)) in the presence of calcon carboxylic acid (CCA) using a multi-walled carbon nano tube/carbon paste electrode (CNT/CPE). The peak current increases linearly with increasing of the La (III) concentration. For this purpose, a few electrochemical methods such as cyclic, differential pulse voltammetry, linear sweep and hydrodynamic voltammetry, and chronoamperometry were used. The results show that calcon carboxylic acid as a ligand was useful for determination of La (III) and was able to improve its sensitivity. Cyclic voltammetry was used for study of reduction reaction of La (III) at the surface of modified electrode. The electrochemical parameters for La (III) at the surface of CNT/CPE, such as diffusion coefficient (D/ cm² s ^?1 = 5.26 × 10^?6), the electron transfer coefficient, (α = 0. 43), and the reduction rate constant, (k/ M s^?1 = 2.33 (±0.015) × 10²), were determined using voltammetry methods, which with the detection limit of La (III) by differential pulse voltammetry was found to be 1.3 nM. The combination of CCA with CNT as mediators in carbon paste electrode showed that this electrode is capable, sensitive, and simple to quantify La (III) in real samples with an average recovery of 97.64%.     

Application of the Pitzer Model to a Weakly Associated Uni-univalent Electrolyte in Mixed Solvents: Solubility of Thallium(I) Chloride in the System TlCl + NaCl + Methanol + Water at 25°C

The solubility of thallium(I) chloride has been measured in methanol + water mixtures (10, 20, 30, and 40%, w/w methanol) containing added sodium chloride at concentrations up to 1 mol-kg^–1 at 25°C. The data were analyzed using Pitzer's equations, without making an explicit assumption of association of Tl⁺ and Cl^– ions to ion pairs, by assuming that is 3 instead of 2, the value used by Pitzer for strong electrolytes in aqueous solutions. It is found that reasonable fits of the experimental solubility data could be obtained without the need to introduce a formal association constant. This implies that the ⁽¹⁾ parameter plays the role of an association constant. ⁽⁰⁾ and ⁽¹⁾ values are derived in addition to the mixture parameters, _Tl,Na and _TlNaCl. Application of the higher-order limiting-law correction for symmetrical mixing in the manner proposed by Pitzer led to perceptibly, although insignificantly, worse fits of the experimental data, so that this correction in its present form appears to be more of theoretical than practical interest.     

A facile synthesis of fluorinated alkoxytrimethylsilanes using 1-methylimidazole as an acid scavenger

Fluorinated alkoxytrimethylsilanes (R_fCH₂OSiMe₃), potential candidates for the third-generation cleaning agents, were synthesized in high yields over 95% from the reaction of chlorotrimethylsilane and fluorinated alcohol (R_fCH₂OH) in the presence of 1-methylimidazole. Elemental and ¹H NMR spectroscopic analysis showed that the reaction proceeds through the formation of an intermediate, 3-methyl-1-trimethylsilylimidazolium chloride.     

Electrocatalytic oxidation of methanol on Pt-Pd nanoparticles supported on honeycomb-like porous carbons in alkaline media

Honeycomb-like porous carbons (PCs) were synthesized using a facile self-assembly method with phenolic resin as the carbon source and tetraethyl orthosilicate (TEOS) as the silica source. The PCs were found to have a large BET surface area of 458 m² g^?1 and a partially graphitized structure. The obtained PCs were used as a support for various Pt-Pd bimetallic alloy catalysts employed for methanol oxidation in alkaline media. Compared with Pt supported on commercial Vulcan XC-72R carbon (Pt/C) and with the other Pt-Pd bimetallic alloy catalysts on PCs, Pt₃Pd₁ on PCs displayed the most negative onset potential for methanol oxidation and the highest steady-state current (2.04 mA cm^?2). This may be because the Pt₃Pd₁/PCs catalyst has the largest electrochemical active surface area (ESA), and because adding Pd to the catalyst improves the ability of the intermediate species to tolerate oxidation. The results show that the prepared Pt-Pd/PCs is a potential candidate for application as a catalyst in alkaline direct methanol fuel cells.     

FTIR spectroscopy study of the electrochemical reduction of CO2 on various metal electrodes in methanol

The electrochemical reduction of CO₂ on Sn, Cu, Au, In, Ni, Ru and Pt electrodes in methanol containing 0.1 M sodium perchlorate was studied by cyclic voltammetry and in-situ FTIR spectroscopy. Dissolved CO₂ increases the cathodic current at potentials below −1.3 V vs. Ag|0.01 M Ag⁺ with Sn, Au, Cu, In and Ni electrodes. It is concluded from the FTIR spectra obtained that there is no reduction of CO₂ on any of the metals studied, and that the only reaction product detected by Fourier transform (FT) IR spectroscopy, i.e. CO²⁻₃, is formed by reaction of CO₂ with hydroxyl anions produced in the electroreduction of residual water.In order to identify the electroreduction products of CO₂ it was necessary to obtain the FTIR spectra of sodium oxalate and sodium carbonate in methanol. They were obtained by the electroreduction of oxalic acid and the alkalinization of CO₂-saturated methanol respectively. It could be proved that the electroreduction of carboxylic acids to carboxylate anions in organic solvents does not require either a H-chemisorbing metal electrode, or the presence of water in the solvent.