Showing papers in "Journal of Applied Electrochemistry in 1996"

Development and electrochemical studies of gas diffusion electrodes for polymer electrolyte fuel cells

Abstract: Electrochemical studies on low catalyst loading gas diffusion electrodes for polymer electrolyte fuel cells are reported. The best performance is obtained with an electrode formed from 20 wt% Pt/C, 0.4 mg Pt cm−2 and 1.1 mg Nafion® cm−2 in the catalyst layer and 15% PTFE in a diffusion layer of 50 µm thickness, for both the cathode and the anode. However, it is also observed that the platinum requirement can be diminished to values close to 0.2 mg Pt cm−2 in the cathode and 0.1 mg pt cm−2 in the anode, without appreciably affecting the good characteristics of the fuel cell response. The experimental fuel cell data were analysed using theoretical models of the electrode structure and of the fuel cell system. It is seen that most of the electrode systems present limiting currents and some also show linear diffusion components arising from diffusion limitations in the gas channels and/or in the thin film of electrolyte covering the catalyst particles.

A direct methanol fuel cell using acid-doped polybenzimidazole as polymer electrolyte

Abstract: A direct methanol/oxygen solid polymer electrolyte fuel cell was demonstrated. This fuel cell employed a 4 mg cm−2 Pt-Ru alloy electrode as an anode, a 4 mg cm−2 Pt black electrode as a cathode and an acid-doped polybenzimidazole membrane as the solid polymer electrolyte. The fuel cell is designed to operate at elevated temperature (200°C) to enhance the reaction kinetics and depress the electrode poisoning, and reduce the methanol crossover. This fuel cell demonstrated a maximum power density about 0.1 W cm−2 in the current density range of 275–500 mA cm−2 at 200°C with atmospheric pressure feed of methanol/water mixture and oxygen. Generally, increasing operating temperature and water/methanol mole ratio improves cell performance mainly due to the decrease of the methanol crossover. Using air instead of the pure oxygen results in approximately 120 mV voltage loss within the current density range of 200–400 mA cm−2 .

Capacitive deionization of NH4ClO4 solutions with carbon aerogel electrodes

Abstract: A process for the capacitive deionization of water with a stack of carbon aerogel electrodes has been developed by Lawrence Livermore National Laboratory (LLNL). Unlike ion exchange, one of the more conventional deionization processes, no chemicals are required for regeneration of the system. Electricity is used instead. An aqueous solution of NH4ClO4 is pumped through the electrochemical cell. After polarization, NH in4 su+ and ClO in4 su− ions are removed from the water by the imposed electric field and trapped in the extensive cathodic and anodic double layers. This process produces one stream of purified water and a second stream of concentrate. The effects of cell voltage, salt concentration, and cycling on electrosorption capacity have been studied in detail.

Influence of rib spacing in proton-exchange membrane electrode assemblies

Abstract: A two-dimensional design analysis of a membrane-electrode assembly for a proton-exchange membrane fuel cell is presented. Specifically, the ribs of the bipolar plates restrict the access of fuel and oxidant gases to the catalyst layer. The expected change in cell performance that results from the partial blocking of the substrate layer is studied by numerical simulation of the oxygen electrode and the membrane separator. The effects of rib sizing and the thickness of the gas-diffusion electrode on the current and water distributions within the cell are presented. For all of the cases considered, the two-dimensional effect only slightly alters the half-cell potential for a given applied current but has a significant influence on water management. Concentrated solution theory with variable transport properties is used in the membrane electrolyte to solve for the electrical potential and local water content. The Stefan-Maxwell equations are used in the gas-diffusion electrode to determine the local mole fractions of nitrogen, oxygen and water vapour. A control-volume formulation is used for the resolution of the coupled nonlinear differential equations. One advantage of the control-volume approach over finite-difference methods is the relative ease in which internal boundary points in fuel-cell and battery models are handled. This and other advantages are briefly discussed.

Electrochemical reduction of nitrates and nitrites in alkaline nuclear waste solutions

Abstract: Sodium nitrate and nitrite are major components of alkaline nuclear waste streams and contribute to environmental release hazards. The electrochemical reduction of these materials to gaseous products has been studied in a synthetic waste mixture. The effects of electrode materials, cell design, and other experimental parameters have been investigated. Lead was found to be the best cathode material in terms of current efficiency for the reduction of nitrate and nitrite in the synthetic mix. The current efficiency for nitrite and nitrate removal is improved in divided cells due to the elimination of anodic oxidation of nitrite. Operation of the divided cells at high current densities (300–600 mA cm−2) and high temperatures (80°C) provides more efficient reduction of nitrite and nitrate. Nearly complete reduction of nitrite and nitrate to nitrogen, ammonia, or nitrous oxide was demonstrated in 1000 h tests in a divided laboratory electrochemical flow cell using a lead cathode, Nafion® 417 cation exchange membrane, and oxygen evolving DSA® or platinum clad niobium anode at a current density of 500 mA cm−2 and a temperature of 70° C. Greater than 99% of the nitrite and nitrate was removed from the synthetic waste mix batch in the 1000 h tests at an overall destruction efficiency of 55%. The process developed shows promise for treating large volumes of waste.

Behaviour of poly(ethylene glycol) during electrodeposition of bright copper coatings in sulfuric acid electrolytes

Abstract: The interaction of poly(ethylene glycol) M n= 3000 with copper I and II ions in aqueous-acidic media was studied by investigation of the specific electrical conductivity, optical density and the cyclic voltamperometric curves in Cu+ and Cu2+ solutions. The results suggest the formation of complexes of the {Cu+(-EO-)3(x − 1)H2O} and {Cu2+(-EO-)4.(y − 1)(H2O)2} types. In the case when {−CH2CH2-O-} n and Cl− are simultaneously present in the copper electrolyte, the possibility of simultaneous complex formation between both copper ions and ethylene oxide units, and copper ions and chloride ions is considered. The strong increase in copper electrodeposition over-potential after the addition of polyethers to the electrolytes containing brighteners is explained by the formation of these complexes.

Electrocatalytic properties of ternary oxide mixtures of composition Ru0.3Ti(0.7−x)CexO2: oxygen evolution from acidic solution

Abstract: Mixed oxide electrodes of general composition Ru0.3Ti(0.7−x)Ce x O2 were prepared by thermal decomposition of the respective chlorides using Ti as a support. x was varied between 0 and 70 mol %. Oxygen evolution was used as a model reaction to investigate the dependence of the electrocatalytic properties on oxide composition. Kinetics was studied by quasistationary current-potential curves and reaction order determination. A minimum Tafel slope of about 30 mV has been found in the 10–30% CeO2 composition range. On the basis of a zero reaction order at constant overpotential, a reaction mechanism has been proposed accounting for the composition dependence of the Tafel slope. It has been concluded that the replacement of TiO2 with CeO2 brings about an increase in the electrocatalytic activity for oxygen evolution, while the layer becomes more prone to mechanical erosion.

Rate effect on lithium-ion graphite electrode performance

Abstract: The electrochemical performance of lithium-ion graphite electrodes with particle diameter in the range of 6–44 µm was evaluated at different discharge (intercalation)/charge (deintercalation) rates (C to C/60). The electrode capacity depends on both the average particle size and rate. With a simple rate programme, the electrode performance is dependent on the cycling rate. The capacity of small graphite particles (6 µm) at C/2 rate was 80% of that achieved at C/24 rate (∼372 mAh g−1). The capacity of large graphite particles (44 µm) obtained at fast rates (C/2) was only 25% of that obtained under near-equilibrium conditions (C/24). The electrode capacity, however, is nearly independent of the charge rate when the electrode is fully intercalated using a modified rate programme containing a constant-voltage hold at 0.005 V (vs Li+/Li) for several hours. The electrochemical behaviour is related to the physicochemical properties of the graphite particles.

Methanol permeability in perfluorosulfonate proton exchange membranes at elevated temperatures

Abstract: A simple electrochemical method for the measurement of the permeability of methanol in proton exchange membranes equilibrated with a supporting liquid electrolyte at elevated temperatures is proposed. Carbon supported platinum working electrodes are placed to both sides of the membrane sample and serve as concentration sensors. Methanol is added to one or both sides of the membrane and the permeability is calculated from the time responses of anodic peak currents on the two working electrodes. Experimental results are given for Nafion® 117 perfluorosulfonate membrane in 2.Om H2SO4 at 60 and 70°C.

Voltammetry in the presence of ultrasound: mass transport effects

Abstract: The voltammetry of various well-defined systems in acetonitrile solution has been studied using both micro and macroelectrodes in the presence of power ultrasound. A simple model is established which quantifies the mass transport observed under these conditions; this assumes that the effect of ultrasound is to promote mixing within the bulk of the solution up to within a certain distance of the electrode surface. Thus the ultrasound serves to thin the diffusion layer which would exist at the corresponding electrode under silent conditions. The relative enhancement of transport limited currents by ultrasound is dependent on the size of the electrode; for micrometre-sized electrodes the steady state limiting current observed tends to that predicted under silent conditions whereas for large electrodes a thin, steady-state diffusion layer is seen with a thickness which is power dependent. In addition to steady-state experiments, a.c. impedance measurements and potentials steps are used to verify the model proposed.

A comparison of the electrochromic properties of WO3 films intercalated with H+, Li+ and Na+

Abstract: The electrochromic response of W03 thin films under electrochemical insertion from nonaqueous electrolytes of one of the three different ions: protons, lithium and sodium cations is reported. In spite of the common belief that the nature of the ion does not change the electrochromic effect, we show that the sample colouring and bleaching are dependent on the intercalant ion and on the insertion rate. The facile insertion of protons is responsible for the highest optical contrast and the quickest response time of this intercalation electrode. Lithium and sodium-intercalated electrodes do not show large optical difference from the proton-intercalated tungsten trioxide unless large charging currents are used. Subtle changes in electrochromic efficiency and in the optical contrast in the red part of the spectrum can be detected; these are larger for the sodium than for the lithium intercalant. According to our analysis, the slow insertion kinetics of Na+ and the formation of a new MxWO3 (M=Li, Na) compound is responsible for most of the observed differences.

Electrochemical treatment of human wastes in a packed bed reactor

Abstract: There is an increasing interest in the use of electrochemical methods for dealing with pollution problems. This paper deals with the mass balance and the use of a packed bed reactor for the electrochemical incineration of human wastes. Parametric studies were carried out to determine the effect of: (i) anodic particle size, (ii) flow rate of faeces/urine mixture, (iii) height of packed bed, (iv) current density and (v) cathode to anode spacing arrangement, on the rate of oxidation of human waste. It is shown that particles of Ebonex™ (0.5–1.0 mm diam.) coated with a catalyst layer, comprising SnO2/Sb2O3, a solution flow rate of 0.9–1.4 cm s−1 through the packed bed based on the cross sectional area of the reactor, a bed height of 5–8 cm and a current density based on the geometric area of the particles of 5 mA cm−2 comprise an optimum set of parameters for the scale-up of a packed-bed electrochemical reactor system. A preliminary design for the further scale up of the process is also described.

Effect of coating thickness and surface treatment of titanium on the properties of IrO2-Ta2O5 anodes

Abstract: The effect of coating thickness and the effect of surface treatment of the titanium base metal on the surface morphology and electrochemical properties of IrO2-Ta2O5 anodes were investigated. It was observed that for an iridium content of 0.45–1.2 mg cm−2 the service life is proportional to the iridium content in the coating. During etching of titanium in 5% HF at 25 °C a surface with macroroughness is formed, while during etching in HCl at 30, 50 and 80°C a microrough surface with visible pitting is formed. The morphology of the IrO2-Ta2O5 active layer (0.32–0.39 mg Ir cm−2) depends strongly on the pretreatment of the titanium base metal. After etching of titanium in HF, the resulting IrO2-Ta2O5 layer is adherent to the macrorough surface of the titanium base metal. After etching of titanium in HCl the resulting surface of the IrO2-Ta2O5 layer is microrough with partly filled pitting holes. The service life of IrO2-Ta2O5 coating with different roughness does not differ and has a value of 1500 ± 400 h (0.5 M H2SO4, 25 °C and j = 2 A cm−2).

Pulse plating of Zn-Ni alloy coatings

Abstract: In this work the electrodeposition of Zn-Ni alloy coatings from a chloride-based electrolyte using a square-wave current pulse-plating technique was investigated. The effects of the pulse plating variables (peak current density, on-time and off-time) and some important bath conditions (ZnC12 and NiCl2.6H2O concentrations in the bath as well as bath temperature) on the chemical composition, surface morphology, grain size, phase distribution and preferred orientation of the deposits were studied. The bath temperature had a very strong effect on the composition of the deposits which, in turn, had very strong effects on the phases present, surface morphology and grain size. The peak current density was found to have little effect on the composition and phases present, but had considerable effect on grain size. The on-time and off-time had no significant influence on the characteristics of the deposits, except for slight grain refinement observed with increasing off-time. Only the η, γ and α crystal phases were found in the deposits while other intermediate phases such as β and δ were not found in any of the deposits produced in this work. Grain refinement of the deposits down to the nanocrystalline range can be achieved by increasing the Ni content of the deposits.

Influence of substituted benzothiazoles on corrosion in acid solution

Abstract: Compounds such as 2-aminobenzothiazole (ABT), 2-amino-6-chlorobenzothiazole (ACLBT), 2-amino-6-methyl benzothiazole (AMEBT) and 2-amino-6-methoxy benzothiazole (AMEOBT) have been synthesized and their inhibitive action on the corrosion of mild steel in 1 m HCl has been evaluated using weight loss, potentiodynamic polarization studies and hydrogen permeation measurements. Determination of inhibition efficiency in the presence of these compounds at different temperatures clearly indicates that ACLBT shows the best performance, even at a temperature as high as 60°C. Potentiodynamic polarization studies reveal the fact that ABT and its derivatives act as cathodic inhibitors. All these compounds are found to reduce the permeation of hydrogen through mild steel in HCl solution. The adsorption of these compounds on mild steel from HCl solutions obeys Temkin's adsorption isotherm. The adsorption of 2-amino benzothiazole on the mild steel has been substantiated by Auger electron spectroscopy.

Influence of anode material on current yields during ferrate(vi) production by anodic iron dissolution Part I: Current efficiency during anodic dissolution of grey cast iron to ferrate(vi) in concentrated alkali hydroxide solutions

Abstract: The dependence of the current efficiency for the oxidation of a pure iron (99.95%) anode to ferrate(vi) ions in 14m NaOH was measured in the region of bubble induced convection for the temperature range 20 to 50°C. The highest current yield obtained after 180min electrolysis was 60% at a current density of 2.3mAcm–2 and a temperature of 30°C. The same current yield was found at a current density of 4.5mAcm–2 and a temperature of 40°C. The dependence of the ferrate(vi) current yields on the NaOH concentration in the electrolyte solution was studied in the range 12 to 17m. The optimum concentration was found to be 16M. The quasistationary anodic polarization curve of pure iron in the transpassive potential region was measured. Apparent oxygen evolution starts at a potential 110mV higher than for white and grey cast iron anodes.

A synergistic effect between zinc salt and phosphonic acid for corrosion inhibition of a carbon steel

Abstract: This work is devoted to the corrosion inhibition of a carbon steel by a zinc salt/phosphonic acid association. Steady-state current-voltage curves and electrochemical impedance measurements carried out in the presence of each compound and for the mixture show a synergistic effect between the two molecules. The concentrations of the compounds in the mixture were lower than the concentrations used for each compound separately. Phosphonic acid was observed to act as an anodic inhibitor whereas cathodic action was shown for the zinc chloride. Electrochemical measurements and surface analysis (XPS and reflection-adsorption spectroscopy at grazing incidence) showed that the synergistic effect afforded by the mixture was attributable to the reaction of the phosphonic acid with the zinc salt. The inhibitor film acts as a protective layer impermeable to ionic or molecular diffusion. The film is very thin and homogeneous in composition. A chemical structure of the film is proposed.

Electrochemistry of room-temperature chloroaluminate molten salts at graphitic and nongraphitic electrodes

Abstract: The electrochemistry of unbuffered and buffered neutral AlCl3-EMIC-MC1 (EMIC =1-ethyl-3-methylimidazolium chloride and MC1= LiCl, NaCl or KCl) room-temperature molten salts was studied at graphitic and nongraphitic electrodes. In the case of the unbuffered 1 : 1 AlCl3 : EMIC molten salt, the organic cation reductive intercalation at about −1.6 V and the AlCl4 − anion oxidative intercalation at about +1.8 V were evaluated at porous graphite electrodes. It was determined that the instability of the organic cation in the graphite lattice limits the performance of a dual intercalating molten electrolyte (DIME) cell based on this electrolyte. In buffered neutral 1.1 :1.0:0.1 AIC13: EMIC : MCl (MC1= LiCl, NaCl and KCl) molten salts, the organic cation was intercalated into porous and nonporous graphite electrodes with similar cycling efficiencies as the unbuffered 1 : 1 melt; however, additional nonintercalating processes were also found to occur between 1 and −1.6 V in the LiCl and NaCl systems. A black electrodeposit, formed at −1.4 V in the LiCl buffered neutral melt, was analysed with X-ray photoelectron spectroscopy and X-ray diffraction and was found to be composed of LiCl, metallic phases containing lithium and aluminium, and an alumina phase formed from reaction with the atmosphere. A similar film appears to form in the NaCl buffered neutral melt, but at a much slower rate. These films are believed to form by reduction of the AlCl4 − anion, a process promoted by decreasing the ionic radius of the alkali metal cation in the molten salt. The partially insulating films may limit the usefulness of the LiCl and NaCl buffered neutral melts as electrolytes for rechargeable graphite intercalation anodes and may interfere with other electrochemical processes occurring negative of −1 V.

Oxygen electrocatalysis under fuel cell conditions: behaviour of cobalt porphyrins and tetraazaannulene analogues

Abstract: Under fuel cell conditions, using a protonic conductor Nafion® electrolyte, active cobalt porphyrins (TpOCH3PPCo or CoTMPP and derivatives) and cobalt tetraazaannulene (CoTAA) supported on an active charcoal were investigated towards oxygen reduction to test their activity and stability. Over a 200 h period, performances were found almost constant with CoTAA after an 800°C heat treatment (HT 800), whereas performances with different substituted phenyl porphyrins declined. XPS analyses were also carried out on these electrodes. On all samples they displayed a complete loss of cobalt within the measurement accuracy. Heat treatment temperature effects were visible on the Nls spectra for the CoTAA samples, the most stable and active samples presenting the lowest oxidation state after current drain application.

Paired electrooxidative degradation of phenol with in situ electrogenerated hydrogen peroxide and hypochlorite

Abstract: The oxidants, hydrogen peroxide and hypochlorite, were generated by the cathodic reduction of oxygen and anodic oxidation of chloride ion in a paired electrolysis process and used for phenol degradation. The degradation of phenol with electrogenerated hydrogen peroxide was slightly affected by pH and ferrous ion concentration. The oxidative degradation of phenol with paired electrogenerated hydrogen peroxide and hypochlorite was significantly affected by phenol concentration. In comparison with the cathodic and anodic degradation of phenol, the removal of phenol increased by 56.1 and 178.1%, respectively, in the case of paired electrooxidative phenol degradation. The COD decreased from 3222 and 3222 ppm to 2253 and 2746 ppm in the anodic and cathodic compartments when the charge passed increased from 0 to 2500C.

A study of RuO2 as an electrocatalyst for hydrogen evolution in alkaline solution

Abstract: The hydrogen evolution reaction (HER) on RuO2 coated nickel electrodes was investigated by d.c. polarization studies and a.c. impedance measurements in alkaline solution. The electroactive RuO2 coatings were prepared by thermal decomposition of a RuCl3 solution at 450°C in air. The real surface area of the cathodes was estimated from cyclic voltammetric measurements and from the double layer capacitance (evaluated by impedance measurements). A mechanism for the HER has been proposed involving two steps (Volmer and Heyrovsky reactions). The rate constants of the forward and backward reactions of these two steps have been estimated by a nonlinear fitting procedure.

Electrochemical properties of Ti/SnO2-Sb2O5 electrodes prepared by the spray pyrolysis technique

Abstract: Cyclic voltammetry for the ferri-ferrocyanide redox couple has been used to study the Ti/SnO2-Sb2O5 electrode prepared by spray-pyrolysis under different conditions. The obtained results shows that increasing the preparation temperature and the duration of coating deposition results in a decrease of ip and an increase of ΔEp for the ferri-ferrocyanide couple. This deviation from reversibility has been attributed to the formation of a titanium oxide layer at the Ti/coating interface. Concerning oxygen evolution at the Ti/SnO2-Sb2O5 anodes, a mechanism is proposed in which water is discharged at the anode forming hydroxyl radicals which are further oxidized to form dioxygen. Finally, a generalized mechanism for oxygen evolution at oxide electrodes has been proposed.

Chemical and morphological characterization of a direct methanol fuel cell based on a quaternary Pt-Ru-Sn-W)C anode

Abstract: Conventional and ‘paste process’ methods were investigated to fabricate the membrane/electrode assembly (M&E) for application in a vapour-feed direct methanol fuel cell. A quaternary Pt-RuSn-W/C and a Pt/C catalysts were employed for methanol oxidation and oxygen reduction, respectively. The structure and chemical composition of the catalysts were investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). A crystalline Pt f.c.c. phase was found to prevail in both catalysts. Agglomeration and twinned particles were frequently observed in the Pt-Ru-Sn-W/C catalyst. Electrochemical investigations were performed by a.c.-impedance spectroscopy and galvanostatic polarization. The ‘paste process’ based assembly showed a significantly lower uncompensated resistance and an approximately two-fold power density increase with respect to the conventional assembly. According to the scanning electron microscopy analysis the observed results were attributed to improved bonding between catalysts and perfluorosulfonic membrane and to a larger extension of the three-phase reaction zone in the ‘paste process’ based assembly.

Electrochemical generation of ferrate Part I: Dissolution of an iron wool bed anode

Abstract: The preparation of ferrate by the anodic dissolution of iron in 10m NaOH using a membrane cell with an iron wool anode is described. It is shown that the current efficiency drops from an initial value of 45–60% to ∼25% during a 2–3 h electrolysis. This is shown to be due to a change in the iron anode surface, probably the composition, structure and/or thickness of surface films. The influence of cell current as well as NaOH concentration and temperature on the current efficiency is described. The kinetics of the reactions of ferrate with water, alcohols and phenol have also been investigated and it is shown that some organics (methanol, ethanediol and phenol) undergo complete oxidation to CO2 and H2O even at room temperature.

Characterization of the efficiency of antiscale treatments of water. Part II: Physical processes

Abstract: The efficiency of physical antiscale treatments of water was evaluated by various techniques, such as chronoamperometry, electrochemical impedance and chronoelectrogravimetry. It was found that the antiscale electrolytic treatment is more efficient than magnetic treatment, at least for the commercial devices used here, and that it also has a longer lasting effect. The electrolytic process generates CaCO3 nuclei in suspension in the bulk water, which provokes homogeneous scaling rather than heterogeneous scaling on the walls which is to be avoided. If the small crystals generated in the bulk are eliminated by filtration, surface scaling is again observed.

Oxygen evolution and hypochlorite production on Ru−Pt binary oxides

Abstract: The electrocatalytic activities of Ru-Pt binary oxide electrodes prepared by thermal decomposition for both oxygen and chlorine evolution reactions (OER and CER) were investigated by cyclic voltammetry (CV) and log i/E relationships (Tafel study). Both CV and Tafel studies revealed that the electrodes from the coating solutions with 60 and 20 mol % Pt content possessed the maximum apparent activity for OER and optimal apparent activity for CER/hypochlorite production, respectively. The specific activity (i/q *) revealed that mixing of the RuO2 and PtO x had no synergistic effects for OER due to the occurrence of phase segregation, which was revealed by element mapping/surface morphologies and Auger electron spectroscopy. Lower current efficiencies for hypochlorite production were found on the freshly prepared binary electrodes (type I electrodes) than on those having been treated by repetitive CVs (type II electrodes). Stability testing of both type I and II electrodes was measured in 0.5 m NaCl solution at 300 mA cm−2 for 480 h, indicating that both type I and II electrodes are quite stable under the above conditions.

Impedance investigation of corrosion inhibition of armco iron by thiourea

Abstract: The inhibitive action of thiourea on the corrosive behaviour of ARMCO iron was investigated in deaerated 0.5 M H2SO4 solution, by means of electrochemical impedance spectroscopy. The inhibitor effectiveness increases with concentration, reaches a maximum (at about 1 mm) and then decreases. The adsorptive behaviour of thiourea on the electrode surface up to its peak follows a Frumkin-type isotherm with lateral repulsion, where the molecules are vertically adsorbed on the iron surface via the sulfur atom. Thiourea acts as a mixed inhibitor up to the critical concentration. It decreases the dissolution of iron and the hydrogen evolution reaction by blocking the electrode surface. The free energy of adsorption ΔGad = −39 kJ mol−1 and the attraction constant a = −4.4.

Characteristics of polypyrrole chemically synthesized by various oxidizing reagents

Abstract: Polypyrrole was chemically synthesized using various oxidizing reagents and examined as a positive electrode material. Physical properties, morphologies and electrochemical characteristics of polypyrrole were greatly influenced by the oxidizing reagent used for polymerization. In general, polypyrrole with a smaller particle size and a larger specific surface area showed better discharge performance than that with a larger particle size and a smaller specific surface area. Polypyrrole was also synthesized on various conducting and nonconducting substrates using Fe(C104)3 as an oxidizing reagent. By using PP nonwoven fabric as a substrate material, a high discharge capacity of 72 mA h g−1 was obtained. Polypyrrole synthesized on only one side of PP nonwoven fabric was able to be used as an electrode.

Pulse electroplating of rich-in-tungsten thin layers of amorphous Co-W alloys

Abstract: A combination of an improved plating bath and pulsed current was shown to lead to a substantial increase in tungsten content in amorphous Co-W alloys. This increase was associated with selective oxidation of cobalt during the rest times of the deposition process. The tungsten content reached 41.4 at % under the following conditions: current density 35 mA cm−2, ratio of pulse time to rest time 1/1, and pulse frequency 10 Hz. The alloy layers were of similar hardness and of much better smoothness, ductility, adhesion to the substrate, and resistance to corrosion compared to those plated according to the US 4 529 668 patent.

Effect of operational potential on performance decay rate in a phosphoric acid fuel cell

Abstract: The effect of operational potential on the cell voltage decay rate in a phosphoric acid fuel cell was estimated using the calculation of the platinum dissolution rate The voltage loss, due to deterioration in activation polarization, was used in calculating the cell voltage decay rate The voltage loss due to activation polarization was estimated using the relationship between the activation polarization and the platinum surface area The change in the Pt surface area, arising from the dissolution of platinum, was obtained under accelerated open circuit voltage (ocv) conditions The study was focused on typical voltage decay rates from 01 to 10 mV per 1000 h It was found that the cell voltage decay became significant even at low temperature during long-term operation (at ocv) and that the cell had to be operated below 840 mV (iR-free) at 200 mA cm−2) 200°C for a decay rate of 1 mV per 1000 h From the present estimation, operational conditions such as temperature, cathode potential, and holding time at a given potential, can be roughly determined for a given decay rate It was concluded that the voltage loss due to platinum dissolution may be negligible at a rated power operation