Showing papers in "Journal of Applied Electrochemistry in 2003"

Electroless Ni-P composite coatings

Abstract: This review outlines the development of electroless Ni–P composite coatings. It highlights the method of formation, mechanism of particle incorporation, factors influencing particle incorporation, effect of particle incorporation on the structure, hardness, friction, wear and abrasion resistance, corrosion resistance, high temperature oxidation resistance of electroless Ni–P composite coatings as well as their applications. The improvement in surface properties offered by such composite coatings will have a significant impact on numerous industrial applications and in the future they will secure a more prominent place in the surface engineering of metals and alloys.

Effects of process conditions and electrode material on reaction pathways for carbon dioxide electroreduction with particular reference to formate formation

Abstract: This paper reviews the most common reaction pathways for CO2 electroreduction proposed by various workers in recent years. Each pathway involves certain intermediate compounds and certain end products and thus the pathways promoted, within a specific process, can be deduced from which of these have been detected. There are considered to be four principal pathways, each based on one of the following reactions: (1) CO(g) formation via disproportionation, (2) •CO2− radical formation, (3) COOH(ad) formation and (4) the formation of reduced COxy−(ad) species giving a range of reduced CO2 end products. This paper places particular emphasis on the formation of HCOOH. The effects of electrocatalyst and process conditions on reaction pathways is also reviewed.

Electrochemical oxidation of water on synthetic boron-doped diamond thin film anodes

Abstract: Electrolysis in aqueous 1 M HClO4 and 1 M H2SO4 solutions has been carried out under galvanostatic conditions using boron-doped diamond electrodes (BDD). Analyses of the oxidation products have shown that in 1 M HClO4 the main reaction is oxygen evolution, while in H2SO4 the main reaction is the formation of H2S2O8. In both electrolytes small amounts of O3 and H2O2 are formed. Finally, a simplified mechanism involving hydroxyl radicals formed by water discharge has been proposed for water oxidation on boron-doped diamond anodes.

A nonlinear kinetic model introduced for the corrosion inhibitive properties of some organic inhibitors

Abstract: Corrosion kinetics of low-carbon steel in hydrochloric acid was studied at various concentrations of mimosa tannin inhibitor. This system was subjected to impedance spectroscopy and quasi steady-state polarization. The inhibition efficiency, η was derived from the corrosion current, icorr and charge transfer resistance, Rct data. The fractional surface coverage as a function of the inhibitor concentration was calculated from the rate of hydrogen evolution reaction (h.e.r.) at constant cathodic potential. Based on the theoretical model and the observed experimental relationship between the ratio of the corrosion current densities in the uninhibited and the inhibited systems and the surface coverage, the relative influences of the geometric blocking action and the energy effect of the inhibitor on the corrosion process were estimated. Fitting of the nonlinear model to the experimental data was carried out by the Levnberg–Marquardt nonlinear fit method implemented into the programming system Mathematica®. Restructuring of the adsorbed layer and change in the orientation of adsorbed inhibitor molecules upon the increase of surface coverage was assumed on the basis of the experimentally observed functional relationship of the double layer capacitance and the surface coverage. The results were explained with respect to the molecular properties of the inhibitor – geometry and size of the molecule, electronic orbital structure and dipole moment.

Corrosion inhibition of mild steel by benzotriazole derivatives in acidic medium

Abstract: Benzotriazole derivatives, namely, N-[1-(benzotriazolo-1-yl)alkyl] aryl amine (BTMA), N-[1-(benzotriazolo-1-yl)aryl] aryl amine (BTBA), and 1-hydroxy methyl benzotriazole (HBTA), were synthesized and their inhibition behaviour on mild steel in 0.5 M H2SO4 at room temperature was investigated by various techniques. Preliminary screening of the inhibition efficiency (IE) was carried out using weight-loss measurements. Potentiodynamic polarization and AC impedance studies were used to investigate the inhibitor mechanism. Benzotriazole derivatives were found to act as mixed type inhibitors. Among the compounds studied, HBTA exhibited the best performance giving more than 95% IE in H2SO4 solutions. The passive film characterization was done using FTIR spectrum.

Electrooxidation of methanol at platinum-Ruthenium catalysts prepared from colloidal precursors : Atomic composition and temperature effects

Abstract: The electrocatalytic oxidation of methanol was investigated on PtRu electrodes of different atomic compositions at several temperatures (from 25 to 110 °C) Very active catalyst nanoparticles supported on active carbon (Vulcan XC 72) were obtained using the colloidal synthesis developed by Bonnemann et al [11], allowing easy variation of the atomic composition These electrocatalysts were characterized by TEM, EDX and XRD; results indicate that they consist of platinum nanoparticles decorated by ruthenium Methanol oxidation was studied as a function of composition, temperature and methanol concentration Two effects were investigated: the effect of the working temperature and the effect of the atomic composition It appeared that for lower methanol electrooxidation overvoltages, the best catalysts are ruthenium-rich, whereas at higher overvoltages the best one is the Pt + Ru (80:20)/C composition, irrespective of the working temperature, either in half-cell or in a single DMFC

Electrochemical oxidation of several chlorophenols on diamond electrodes Part I. Reaction mechanism

Abstract: The electrochemical oxidation of 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol aqueous wastes using boron-doped diamond electrodes was studied. This treatment led to complete mineralization of the wastes regardless of the operating conditions. A simple mechanistic model is consistent with the voltammetric and electrolysis results. According to this model, the electrochemical treatment of chlorophenol aqueous wastes involves the anodic and cathodic release of chlorine followed by the formation of non-chlorinated aromatic intermediates. Subsequent cleavage of the aromatic ring gives rise to non-chlorinated carboxylic acids. Chlorine atoms arising from the hydrodehalogenation of the chlorophenols are converted into more oxidized molecules at the anode. These molecules react with unsaturated C4 carboxylic acid to finally yield trichloroacetic acid through a haloform reaction. The non-chlorinated organic acids are ultimately oxidized to carbon dioxide and the trichloroacetic acid into carbon dioxide and volatile organo-chlorinated molecules. Both direct and mediated electrochemical oxidation processes are involved in the electrochemical treatment of chlorophenols.

Synergistic effect of 2-mercapto benzimidazole and KI on copper corrosion inhibition in aerated sulfuric acid solution

Abstract: 2-Mercapto benzimidazole (MBI) was used as a copper corrosion inhibitor in aerated 0.5 mol L−1 H2SO4 solutions. The inhibition efficiency (IE) increased with increasing MBI concentration to 74.2% at the 1 mM level. A synergistic effect existed when MBI and iodide ions were used together to prevent copper corrosion in sulfuric acid. It was found that IE reached 95.3% in 0.5 mol L−1 H2SO4 solutions containing 0.75 mmol L−1 MBI and 0.25 mmol L−1 KI. X-ray photoelectron spectroscopy (XPS) analysis of the copper samples showed that a (Cu+MBI) complex film formed on the surface to inhibit the copper corrosion and the iodide ions did not participate in the formation of the inhibitor film. The synergistic effect was attributed to the adsorption of iodide anions on the copper surface, which then facilitated the adsorption of protonated MBI and the formation of an inhibitive film.

Electropolymerization of aniline on carbonized polyacrylonitrile aerogel electrodes: applications for supercapacitors

Abstract: Polyaniline was electrochemically synthesized on carbon polyacrylonitrile aerogel electrodes for use as active material in supercapacitor devices. Electrochemical characterization was performed by cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and charge–discharge experiments in aqueous medium. Two types of electrochemical phenomenon were observed; the first is based on electrostatic energy storage in the double layer at the interface solution/carbon polyacrylonitrile (PAN) aerogel, the other is associated with the redox processes in polyaniline, for which the faradaic charge depends on the potential range. The performance of the supercapacitor was tested for capacity, energy and power density and self-discharge. Specific capacitance as high as 230 F g−1 was reached. A symmetrical supercapacitor showed good cyclability (over 3000 cycles) during repeated charge–discharge cycles. The results are very promising and demonstrate the viability of a symmetric supercapacitor based on carbon PAN aerogel covered by an electronically conducting polymer.

The effect of current density on properties of electrodeposited nanocrystalline nickel

Abstract: Nanocrystalline nickel electrodeposits were fabricated at 18, 25 and 50 mA cm−2 using a sulfamate-based electrolyte. The crystallite size of the deposits was evaluated by XRD technique and their mechanical properties were characterized by tensile testing. The results of this study confirmed that increasing the current density results in an increase in the grain size of nickel deposits. The strength of the deposits decreased consistently with increasing the crystallite size. However, the deposit fabricated at 50 mA cm−2, in comparison to nickel with conventional grain size (>1 μm), showed a relatively low strength and a surprisingly low tensile elongation. It is suggested that the enhanced evolution of hydrogen at high current densities is responsible for the formation of larger crystals and the unusual low tensile elongation.

Electrochemical treatment of wastewater containing phenolic compounds: oxidation at boron-doped diamond electrodes

Abstract: This work investigates the performance of BDD electrodes during oxidation of aqueous solutions of phenol. The main reaction intermediates are identified, the effect of operating conditions on the faradic yield of the process, and the degree of mineralization achievable under different experimental conditions are evaluated. Due to the crucial role of mass transfer in the process, an impinging jet cell is used for the experiments. The results indicate that if a minimum value of current density is imposed, suitable initial conditions can be set at which the removal of the reactant is always under mass transfer control and the process is carried out at a faradic yield of about unity, up to the near-complete disappearance of total organic load. High current density and high mass transfer coefficient must be used in order to carry out the process with high space-time yield. The performance of BDD is compared to that obtained at Ti/RuO2 anodes.

Electrochemical reduction of carbon dioxide at ruthenium dioxide deposited on boron-doped diamond

Abstract: Study of carbon dioxide reduction at RuO2-coated diamond electrodes showed that conductive metallic oxides are promising electrocatalysts for this process and allow higher reduction products to be obtained. The main reduction products obtained in acidic and neutral media were formic acid and methanol, with product efficiencies as high as 40 and 7.7%, respectively. It was observed that conductive diamond is a very well suited material for studying the electrocatalytic properties of conductive metallic oxides, because its use resulted in a negligible substrate effect. This feature will greatly enhance the ability to understand the relationships between the intrinsic electrochemical behavior and the electrocatalytic behavior, in view of developing new effective electrocatalysts. The use of conductive diamond could also allow better utilization of the electrocatalyst by avoiding the need for thick films.

An electrochemical study of the dissolution of gold in thiosulfate solutions Part I: Alkaline solutions

Abstract: The anodic dissolution of gold in alkaline thiosulfate solutions has been studied by using a rotating gold disc. Experimental results have shown that the gold dissolves at measurable rates in thiosulfate solutions at potentials above 0.2 V. It has been confirmed that dissolution occurs in parallel with oxidation of thiosulfate with a dissolution current efficiency that varies with time and with the experimental conditions and which is generally in the range of 0.3 to 0.6. Although oxygen could be used as an oxidant for gold in the thiosulfate system, the rate of the cathodic reduction of oxygen in the relevant potential region is too slow for practical purposes. It was found that in the potential region investigated, thiosulfate ions undergo oxidative decomposition leaving a sulfur-like film on the surface of gold, which inhibits the rate of dissolution of gold and results in a low anodic current efficiency for the dissolution of gold. The factors (temperature, pH, thiosulfate concentration and ammonia) have been found to have positive effects on the kinetics of gold dissolution. The rates of gold dissolution in oxygenated alkaline thiosulfate solutions have been estimated to be much lower than in the copper–ammonia–thiosulfate and cyanide systems.

Chemical and electrochemical considerations on the removal process of hexavalent chromium from aqueous media

Abstract: Two methods were used to remove Cr(VI) from industrial wastewater Although both are based in the same general reaction: 3Fe(II)(aq) + Cr(VI)(aq) ⇌; 3Fe(III)(aq) + Cr(III)(aq) the way in which the required amount of Fe(II) is added to the wastewater is different for each method In the chemical method, Fe(II)(aq) is supplied by dissolving FeSO4 · 7(H2O)(s) into the wastewater, while in the electrochemical process Fe(II)(aq) ions are formed directly in solution by anodic dissolution of an steel electrode After this reduction process, the resulting Cr(III)(aq) and Fe(III)(aq) ions are precipitated as insoluble hydroxide species, in both cases, changing the pH (ie, adding Ca(OH)2(s)) Based on the chemical and thermodynamic characteristics of the systems Cr(VI)–Cr(III)–H2O–e− and Fe(III)–Fe(II)–H2O–e− both processes were optimized However we show that the electrochemical option, apart from providing a better form of control, generates significantly less sludge as compared with the chemical process Furthermore, it is also shown that sludge ageing promotes the formation of soluble polynuclear species of Cr(III) Therefore, it is recommended to separate the chromium and iron-bearing phases once they are formed We propose the optimum hydraulic conditions for the continuous reduction of Cr(VI) present in the aqueous media treated in a plug-flow reactor

Degradation kinetics of ascorbic acid during ohmic heating with stainless steel electrodes

Abstract: Ascorbic acid degradation experiments were performed in buffer solution at pH 3.5 using a batch ohmic heater with uncoated stainless steel electrodes. The electrical conductivity of the buffer solution was adjusted using sodium chloride. The concentration of ascorbic acid was found using an HPLC technique. Kinetics of degradation can be described adequately by a first order model for both conventional and ohmic treatments, but unlike conventional heating, the temperature dependence of degradation for some ohmic treatments cannot be represented by the Arrhenius relation. During ohmic heating, power, temperature and NaCl content affect the degradation rate. A number of reactions, including electrode reactions, electrolysis of the solution, as well as reactions between electrode materials and electrolysis products may influence the reaction mechanism as well as kinetic parameters. At the highest power and salt content, citrate complexation and a significant loss of buffering capacity were noted, resulting in an increase in pH. The results underline the importance of inert electrode coatings, or the use of high frequency power for control of electrochemical reactions.

Electrochemical oxidation of p-chlorophenol on SnO2–Sb2O5 based anodes for wastewater treatment

Abstract: The influence of an IrO2 interlayer between the Ti substrate and the SnO2–Sb2O5 coating on the electrode service life and on the efficiency of p-chlorophenol (p-CP) oxidation for wastewater treatment has been investigated. The results have shown that if the loading of the SnO2–Sb2O5 coating relative to the IrO2 interlayer loading (γ ratio defined by Equation 1) is high (γ = 20–30) the service life of the electrode can be increased without modification of the ability of this electrode to perform p-CP oxidation. This suggests that the oxidation of p-CP using a Ti/IrO2/SnO2–Sb2O5 electrode with high γ ratio (γ > 20) occurs only through the SnO2–Sb2O5 component of the electrode, with no interference of the IrO2 interlayer. However, the electrode potential at a given current density is considerably lower in the case of the Ti/IrO2/SnO2–Sb2O5 electrode. In order to explain this decrease in electrode potential we speculate that water is firstly discharged on IrO2, which is present in small amounts on the surface, forming hydroxyl radicals at a relatively low potential. These active hydroxyl radicals then migrate (spill over) towards the SnO2–Sb2O5 coating, where they are physiosorbed and react with p-CP leading to complete combustion.

Inhibition of acid corrosion of steel using cetylpyridinium chloride

Abstract: The cationic surfactant cetylpyridinium chloride (CPC) showed high inhibition efficiency for the corrosion of low carbon steel in 1 M H2SO4. Electrochemical measurements were dedicated to test the performance of CPC at different concentrations and temperatures. CPC has a significant inhibiting effect on the corrosion of steel and protection efficiencies up to 97% were measured. The inhibitor shifted the corrosion potential in the cathodic direction. It was found that adsorption is consistent with the Bockris–Swinkels isotherm in the studied temperature range (30–60 °C). The negative values of the free energy of adsorption and the decrease in apparent activation energy in the presence of the inhibitor suggest chemisorption of the CPC molecule on the steel surface.

Hector bases – a new class of heterocyclic corrosion inhibitors for mild steel in acid solutions

Abstract: Three heterocyclic compounds namely 3-anilino-5-imino-4-phenyl-1, 2,4-thiadiazoline (AIPT), 3-anilino-5-imino-4-tolyl-1, 2,4-thiadiazoline (AITT), and 3-anilino-5-imino-4-chlorophenyl-1, 2,4-thiadiazoline (AICT) were synthesized and their influence on the inhibition of corrosion of mild steel in 1 M HCl and 0.5 M H2SO4 was investigated by weight loss and potentiodynamic polarization techniques. The values of activation energy and free energy of adsorption of these compounds were also calculated. Potentiodynamic polarization studies were carried out at room temperature, and showed that all the compounds were mixed type inhibitors causing blocking of active sites on the metal. The inhibition efficiency of the compounds was found to vary with concentration, temperature and immersion time. Good inhibition efficiency was evidenced in both acid solutions. The adsorption of the compounds on mild steel for both acids was found to obey the Langmuir adsorption isotherm. Electrochemical impedance spectroscopy was also used to investigate the mechanism of corrosion inhibition.

Effect of ambient conditions on performance and current distribution of a polymer electrolyte membrane fuel cell

Abstract: The performance and current distribution of a free-breathing polymer electrolyte membrane fuel cell (PEMFC) was studied experimentally in a climate chamber, in which temperature and relative humidity were controlled. The performance was studied by simulating ambient conditions in the temperature range 10 to 40 °C. The current distribution was measured with a segmented current collector. The results indicated that the operating conditions have a significant effect on the performance of the fuel cell. It was observed that a temperature gradient between the fuel cell and air is needed to achieve efficient oxygen transport to the electrode. Furthermore, varying the air humidity resulted in major changes in the mass diffusion overpotential at higher temperatures.

Electrochemical synthesis and structural studies of polypyrroles, poly(3,4-ethylene- dioxythiophene)s and copolymers of pyrrole and 3,4-ethylenedioxythiophene on carbon fibre microelectrodes

Abstract: Polypyrrole, poly(3,4-ethylenedioxythiophene) and the copolymer of pyrrole and 3,4-ethylenedioxythiophene films were synthesized electrochemically on carbon fibre microelectrodes (CFME). Deposition conditions on the carbon fibre and the influence of monomer concentrations on the copolymerization, as well as the electrochemistry of the resulting polymers and copolymers, were studied. Structural studies of the polymers were conducted using different techniques such as cyclic voltammetry, in situ spectroelectrochemistry, FTIR and scanning electron microscopy. The effect of the monomer ratio on the formation of copolymer is reported. A high level of stability to overoxidation was also observed for poly(3,4-ethylenedioxythiophene) as the polymer on this CFME substrate shows limited degradation of its electroactivity at potentials 1.2 V above its half-wave potential.

Effect of nucleation mode on the morphology and texture of electrodeposited zinc

Abstract: The effect of temperature, pH and current density on the morphology and texture of electrodeposited zinc on mechanically polished steel was studied. The electrodeposited zinc had mostly basal (0 0 0 2) and low angle planes (1014, 1013, 1012) parallel to the surface. At pH 2, increasing overvoltage (i.e., increasing current density or decreasing temperature) reduced the percentage of basal plane and increased the percentage of low angle planes parallel to the substrate surface. Increasing overvoltage decreased the zinc crystal size. At pH 4, increasing current density increased the percentage of both basal and low angle planes parallel to the surface, but increased the zinc crystal size. This variation of behaviour at pH 4 was explained by a change in nucleation mode due to hydroxide adsorption. The nucleation mode was determined by comparing dimensionless (i/im)2 vs (t/tm) potentiostatic current–time transient graphs with models for instantaneous and progressive nucleation. It was shown that at pH 2, instantaneous nucleation was predominant, whereas at pH 4, it was close to progressive.

Electrodeposition of copper–zinc alloys in pyrophosphate-based electrolytes

Abstract: Copper–zinc alloy coatings were deposited on mild steel substrates using pyrophosphate-based electrolytes at room temperature and under continuous current The use of polyligand electrolytes was also investigated, as well as the influence of organic additives on the composition, morphology and electrochemical properties of the coatings The results showed that good quality copper–zinc alloy deposits could be produced in pyrophosphate-based polyligand electrolytes, especially with the addition of allyl alcohol

Operating characteristics of aqueous magnetite electrochemical capacitors

Abstract: Operating characteristics, including capacitance, leakage current, operating potential range, cycling stability and open-circuit self-discharge behaviours, of the magnetite (Fe3O4) supercapacitor, containing 10 wt % carbon black as conductive additive, in aqueous electrolytes of Na2SO3, KOH and Na2SO4 were investigated. Although the capacitance of the oxide was found to depend heavily on electrolyte composition, the self-discharge mechanism in these electrolytes appeared to be the same. Reduction in the dissolved oxygen content (DOC) of the electrolyte reduced the leakage current and profoundly improved the cycling stability. In particular, Na2SO3(aq) gives the highest capacitance, nearly 30 F (g-Fe3O4)−1 or 80 μF cm−2 of actual surface area, with an operation range of 1.1 V based on a leakage current less than 0.1 mA F−1, and the electrode showed no deterioration after 104 cycles under a DOC < 0.1 ppm.

Electrochemical remediation of acid mine drainage

Abstract: Acid mine drainage (AMD), which has long been a significant environmental problem, results from the microbial oxidation of iron pyrite in the presence of water and air, affording an acidic solution that contains toxic metal ions. Electrochemical treatment of AMD offers possible advantages in terms of operating costs and the opportunity to recover metals, along with cathodic reduction of protons to elemental hydrogen. This work describes the electrolysis of synthetic AMD solutions containing iron, copper and nickel and mixtures of these metals using a flow-through cell divided with an ion exchange membrane. Iron was successfully removed from a synthetic AMD solution composed of FeSO4/H2SO4 via Fe(OH)3 precipitation outside the electrochemical cell by sparging the electrolysed catholyte with air. The work was extended to acidic solutions of Fe2+, Cu2+, and Ni2+, both singly and in combination, and to an authentic AMD sample containing principally iron and nickel.

Electrodeposition of noncrystalline cobalt–tungsten alloys from citrate electrolytes

Abstract: Induced electrodeposition of Co–W alloys onto steel substrates from acid citrate baths has been investigated. The effects of some plating parameters, such as current density, pH and temperature on the potentiodynamic cathodic polarization curves, cathodic current efficiency of the alloy and the percentage tungsten in the alloy were studied. Highly adherent and compact Co–W alloys codeposited from citrate baths containing up to 28 mass % tungsten were obtained. The percentage W (w/w) in the alloy increases with increasing pH, bath temperature and Co2+ ion concentration. On the other hand, the percentage W in the alloy decreases with increasing current density. Anodic linear stripping voltammetry (ALSV) indicated that the alloy might consist of one phase solid solution. These alloys were determined to be noncrystalline by X-ray diffraction analysis.

Protection of copper corrosion by carbazole and N-vinylcarbazole self-assembled films in NaCl solution

Abstract: Self-assembled films of carbazole (CZ) and N-vinylcarbazole (NVC) were prepared on copper surfaces. The corrosion protection abilities of the films were evaluated in an air-saturated 0.5 mol dm(-3) NaCl solution using electrochemical impedance spectroscopy ( EIS), polarization and cyclic voltammetry. The results indicate that CZ and NVC form dense protective films on copper. Fourier transform infrared ( FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the film. It was found that the NVC molecules are tilted at an angle to the copper surface. The theoretical ab initio calculations support the experimental results.

Electrolytic decomposition of amaranth dyestuff using diamond electrodes

Abstract: The electrolytic decomposition of an amaranth dyestuff solution using several combinations of electrodes with diamond and platinum is reported. It is observed that a portion of the amaranth is decomposed on the cathode surface while the other portion is decomposed to lower molecular weight components on the anode surface. The decolourizing rate is higher at diamond electrodes used as the anode and the cathode than with other combinations. This electrode combination also shows a rapid decrease in total organic carbon concentration. Acetic acid and oxalic acid are detected as the intermediate substances, and CO2 gas is generated as a final product corresponding to the decrease in the oxalic acid concentration.

Influence of electrolyte additives on safety and cycle life of rechargeable lithium cells

Abstract: The influence of electrolyte additives on the safety and cycle life of 4V-class lithium cells is examined. The electrolyte solution employed was 1 M LiClO4-propylene carbonate, the most widely used electrolyte in lithium battery research. The additives studied were ten organic aromatic compounds including biphenyl, cyclohexylbenzene and hydrogenated diphenyleneoxide. For safety, focus was given to the overcharging tolerance of the lithium cells. Biphenyl is well-known as an overcharge protection additive. The purpose of this work was to find additives with a higher oxidation potential and longer charge–discharge cycle life than biphenyl. The oxidation potentials and currents of the additives were measured to determine whether or not these compounds work as overcharge protection additives. Charge–discharge cycling efficiencies were examined for lithium metal anodes. The results showed that cyclohexylbenzene and hydrogenated diphenyleneoxide have a higher oxidation potential and a higher lithium cycling efficiency than biphenyl.

Electrolytic reduction of trichloroethylene and chloroform at a Pt- or Pd-coated ceramic cathode

Abstract: Trichloroethylene (TCE) and chloroform (CF) were electrolytically dechlorinated in a two-compartment cell in which the working electrode (cathode) consisted of an Ebonex ceramic sheet plated with platinum (Pt) or palladium (Pd). The halogenated targets were not reduced using a cathode of untreated Ebonex. Under typical experimental conditions (e.g., cathode potentials EC = −0.3 V to −1.4 V vs SHE, pH 7.0), transformations were first order in TCE and CF. Reaction kinetics were mass transport limited at EC < −1.4 V. Transport-limited rate constants were 0.45 cm min−1 for TCE reduction and 0.42 cm min−1 for CF. The primary products of CF reduction were methane and hydrochloric acid. For TCE reduction, major products were ethane, ethylene and hydrochloric acid. Carbon and chlorine mass balances were within 5–10%. Current efficiencies ranged from nearly 100% at EC = −0.5 V (both reactants) to 24.4% for TCE and 16.6% for CF at EC = −1.4 V. Rate constants for TCE and CF transformations were inversely related to pH in the range 2 < pH < 11. Pt–Ebonex resisted sulfate and chloride poisoning. The Pd–Ebonex electrode quickly lost activity (50% loss in 5–10 min) in 0.1 M K2SO4 electrolyte (cathode potential, EC = −1.15 to −1.4 V vs SHE).