Applied Electrochemistry

Redox flow batteries (RFBs) are enjoying a renaissance due to their ability to store large amounts of electrical energy relatively cheaply and efficiently. In this review, we examine the components of RFBs with a focus on understanding the underlying physical processes. The various transport and kinetic phenomena are discussed along with the most common redox couples.

We report hydrothermal synthesis of single crystalline TiO(2) nanowire arrays with unprecedented small feature sizes of ~5 nm and lengths up to 4.4 μm on fluorine-doped tin oxide substrates. A substantial amount of nitrogen (up to 1.08 atomic %) can be incorporated into the TiO(2) lattice via nitridation in NH(3) flow at a relatively low temperature (500 °C) because of the small cross-section of the nanowires. The low-energy threshold of the incident photon to current efficiency (IPCE) spectra of N-modified TiO(2) samples is at ~520 nm, corresponding to 2.4 eV. We also report a simple cobalt treatment for improving the photoelectrochemical (PEC) performance of our N-modified TiO(2) nanowire arrays. With the cobalt treatment, the IPCE of N-modified TiO(2) samples in the ultraviolet region is restored to equal or higher values than those of the unmodified TiO(2) samples, and it remains as high as ~18% at 450 nm. We propose that the cobalt treatment enhances PEC performance via two mec...

Advances in electrochemical methods for pollutant remediation, recycling and sensing are reviewed. Additionally, applications of these methods in the drinking water industry, and for disinfection scenarios are discussed. Lastly, new electrode materials for environmental applications are described. In a companion review, photoelectrochemical methods will be discussed.

The inhibition effect of ceftobiprole against the corrosion of mild steel in 1 M HCl solution was studied by weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and atomic force microscopy techniques. Inhibition efficiency increased with inhibitor concentration where as decreased with acid concentration. Data obtained from EIS studies were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. The adsorption of ceftobiprole obeyed Langmuir adsorption isotherm. Both thermodynamic and activation parameters were calculated and discussed. Polarization curves indicated that they are mixed type of inhibitors. Polarization curves showed that ceftobiprole act as mixed-type inhibitor. The results obtained from weight loss, EIS and Potentiodynamic polarization are in good agreement.

The interfacial ohmic losses between the bipolar plate and the MEA can significantly reduce the overall power output from a SPFC. For graphitic bipolar plate materials, these losses are insignificant relative to stainless steel, where the existence of a passive film on the surface ...

Oxygen and hydrogen permeability through Nafion® 117 membrane and recast Nafion film has been studied by means of gas chromatography at different values of temperature and gas relative humidity. Water uptake from the vapour phase by Nafion® 117 membrane and recast film has been investigated. It has been shown that oxygen and hydrogen permeability increases both with temperature and relative humidity of the gas, but water vapour uptake by both Nafion® 117 membrane and recast film decreased with increasing temperature. SEM studies have been performed on the membrane-electrode assembly obtained by impregnation/hot-pressing and on carbon/Nafion® composite; these have indicated that the active catalyst layer is porous with channels for the gas transport.

ABSTRACT The hydrogen evolution reaction was studied in 1 M KOH at 25 °C on two types of electrodes:(i) pressed powders of Ni or NiMo with Al, heated at 700 °C; (ii) Ni—Al—Mo powders deposited by vacuum plasma spraying. These materials were treated with alkaline solution to leach out aluminum. Very active and stable Raney nickel—molybdenum electrodes were obtained from Al rich alloys. Adding molybdenum significantly improved catalytic activity. Electrochemical impedance spectroscopy was used to determine the apparent and intrinsic activities. Different ac models were tested and the appropriate one was selected. Intrinsic activities of these electrodes are smaller or equal to that of polycrystalline Ni and the origin of high apparent activities is related to the increase in real surface area.

... However, when wastewater contains organo-chlorinated compounds biological treatment may become ineffective ... K3, related to the mineralisation of aliphatic acids to CO2, does not ... in order to better match the op-erating parameters in real applications for waste water treatment. ...

4-aminoantipyrine (AAP) was tested as a corrosion inhibitor for mild steel in 2 M HCl solution using dierent techniques: weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that AAP is an inhibitor for mild steel in this medium. The inhibition was assumed to occur via adsorption of the inhibitor molecule on the metal surface. In the 20 to 60 C temperature range, the AAP adsorption follows the Flory±Huggins isotherm and/or the El-Awady et al. kinetic-thermodynamic model. The protection eciency increases with increasing inhibitor concentration (in the range 10 À3 ±10 À2 M) but decreases with increasing temperature. The thermodynamic functions of dissolution and adsorption processes were calculated.

This review concerns fundamental aspects of levelling and brightening in the electrodeposition of metals. The most important effects of additives, such as the grain refinement of the deposit, polarization of the cathode, incorporation of additives in the deposit, the change of the orientation of crystals and the synergism of additives are presented. The mechanisms proposed to explain the action of additives in metal electrodeposition are classified taking into account the rate determining step of the process. The main mechanisms are discussed.

The electrochemical behaviour of a Cu rotating disc electrode in neutral aerated NaC1 solution was investigated in the cathodic and anodic ranges and at the corrosion potential. In the cathodic range, where the reduction of oxygen takes place, reduction peaks allow the identification and quantitative evaluation of insoluble corrosion products (CuC1 and Cu20 ). In the anodic range Cu is dissolved, most likely as CuC12. A new mechanism for the anodic dissolution is proposed after comparing our data with previously published mechanisms. Corrosion currents were found to decrease with time and to be a function of the rotation rate of the electrode. Both the mixed kinetics of the anodic partial reaction and diffusion through a porous layer seem to be relevant in controlling/corr.

Two models of the cathode of the proton exchange membrane fuel cell, a pseudohomogeneous film model and an agglomerate model, have been compared. The influence of different parameters on the shape of the polarization curves has been shown. Curves simulated by use of the two models and different values of oxygen permeability, effective conductivity and thickness of the active layer as well as thickness of the Nafion® film surrounding agglomerates have been presented and compared with the experimental results. On the basis of the simulations and the SEM study of the structure of the active catalyst layer it has been concluded that the agglomerate model is a better representation of the active catalyst layer than the pseudohomogeneous film model.

Current efficiencies for the formation of CO2 during methanol oxidation at smooth polycrystalline platinum electrodes were determined by differential electrochemical mass spectrometry in a thin layer flow through cell. In all cases, the current efficiencies are below 60%; in particular, values as low as 16% were found in 0.1 M methanol solution at 0.6 V, which shows that a large

Reverse electrodialysis (RED) is a method for directly extracting electrical energy from salinity gradients, especially from sea and river water. For the commercial implementation of RED, the electrode system is a key component. In this paper, novel electrode systems for RED were compared with existing systems on safety, health, environment, technical feasibility and economics. Systems with inert DSA-type electrodes and a NaCl-HCl supporting electrolyte with the reversible Fe 2? /Fe 3? redox couple or the [Fe(CN) 6 ] 4-/Fe(CN) 6 ] 3couple achieved the highest ranking. Improvements of the electrode system are also discussed like the use of special stable metal electrodes, graphite electrodes, other reversible redox couples, capacitive electrodes and electrolytes with carbon particles.

The numerous theoretical and practical studies of the electrodeposition of nickel and its binary and selected ternary alloys with copper and cobalt over the last 10-15 years are reviewed. The reported mechanisms of the electrodeposition processes and accompanying evolution of hydrogen are considered. The complex influence of different bath compositions, pHs, current densities or potential ranges and temperature on the formation of single or multiple deposition layers are compared. The determination of the structure and morphology of the deposits on different substrates, including solid surfaces and particulate materials, using a range of analytical techniques are reported.

This article builds upon a companion review on electrochemical techniques [1] and discusses photocatalytic methods for the treatment and analysis of pollutants in water and air. Organic, inorganic and microbiological pollutants are considered. Areas wherein further research and development are needed are identified. Finally, perspectives on commercialization of this technology are presented.

The synthesis of various nanoscale materials, such as nanoparticles, nanowires of Au, Pt, Ni Co, Fe, Ag etc., by electrodeposition techniques have been demonstrated in this article. Both potentiostatic and galvanostatic methods were employed to carry out the electrodeposition process under different potential ranges, time durations, and current densities. The electrochemical behavior of the deposited nanoparticles on various substrates was investigated by cyclic voltammetric and chronoamperometric techniques. The synthesis of mono-dispersed gold (Au) nanoparticles on indium tin oxide (ITO) coated glass, preparation of Au nanorods on nanoporous anodic alumina oxide (AAO), formation of Au nanoclusters on polypyrrole-modified glassy carbon electrode and one-step electrodeposition of nickel nanoparticle chains embedded in TiO 2 etc. have been highlighted in this article. The potential applications of synthesized nanoparticles such as the role of maghemite (Fe 2 O 3) in arsenic remediation, higher electrocatalytic activity of Ag nanoclusters for the reduction of benzyl chloride, and the role of C 60 nanoparticle-doped carbon film in fabrication processes are also presented in this article.

A simple analytical expression to determine cell potential (i) against current density (i) behaviour in polymer electrolyte fuel cells (PEFCs) was derived. The equation describes experimental data over the whole range of current density taking into account possible mass transport limitations. The empirical equation was used to ®t experimental data obtained in a 50 cm 2 single cell in H 2 /air operation using electrodes with low Pt loading ($0.1 mg cm À2 ). A good agreement between theoretical and experimental data was found.

Several carbon blacks and graphite were investigated as candidates for diusion layer preparation in polymer electrolyte fuel cell electrodes (PEFC). Single cell electrochemical characterizations under dierent working cell conditions were carried out on the electrodes by varying the kind of carbon in the diusion layer. An improvement in cell performance was found by using Shawinigan Acetylene Black (SAB) as carbon, resulting in a measured power density of about 360 mW cm )2 in H 2 /air operation at 70°C and 1/1 bar. Pore size distribution and scanning electron microscopy analyses were carried out to help the understanding of the dierent behaviour of the investigated carbon diusion layers.

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 Bönnemann et al. [11], allowing easy variation of the atomic composition. These electrocatalysts were characterized by TEM, EDX and

The abundance of urea in the natural environment is dictated by the fact that it is one of the major products of mammalian protein metabolism. Due to the extensive use of urea in many branches of industry, it is produced in large quantities. Urea enters into the environment not only with wastewater from the production plants but also by leaching from the fields, agro-breeding farms, and the effluents from the plants using it as a raw material. There are many methods of urea removal, but most of them are still being developed or are very new. The methods themselves differ in terms of physicochemical nature and technological ingenuity. Many wastewater treatment methods include processes such as hydrolysis, enzymatic hydrolysis, decomposition in the biological bed, decomposition by strong oxidants, adsorption, catalytic decomposition, and electrochemical oxidation. In this work, methods of urea removal from aqueous solutions have been reviewed. Particular attention was paid to electrochemical methods.

A B S T R A C T Cellulose is the most abundant renewable material in nature. In this work, ordered cellulose nanocrystals (CNCs) have been transformed into porous carbon with an increased short-range ordered lattice and percolated carbon nanofiber at a relatively low carbonization temperature of 1000 °C. When evaluated as anode for sodium-ion batteries (SIBs), the CNC derived porous carbon shows superior performances including a high reversible capacity of 340 mA h/g at a current density of 100 mA/g, which is one of the highest capacity carbon anodes for SIBs. Moreover, the rate capability and cycling stability of the porous carbon are also excellent. The excellent electrochemical performance is attributed to the larger interlayer spacing, porous structure, and high electrical conductivity arising from the ordered carbon lattice and the percolated carbon nanofiber. The formation of nano-sized graphitic carbon from the ordered CNC at the low carbonization temperature of 1000 °C is supported by both molecular dynamic simulations and as well as in-situ TEM measurements. This study shed light on the fundamental understanding of converting hydrocarbon biopolymer from wood to high quality carbon with a large domain of ordered lattice.

Recent developments in the theory and applications of rotating cylinder electrodes are reviewed. Particular attention is paid to the mass transfer behaviour and the development of turbulent flow patterns, and its exploitation in electrochemical reactors for a variety of applications including metal deposition from waste and effluent liquors.

A sulfonated poly(sulfone) (S-Radel Ò ) membrane with high proton conductivity and low vanadium ion permeability showed high initial performance in a vanadium redox flow battery (VRFB) but suffered mechanical and chemical degradation during charge/discharge cycling. The S-Radel membrane showed different degradation behavior in flow cell cycling and ex-situ vanadium ion immersion tests. When the membrane was immersed in aqueous V 5? solution, the sample cracked into small pieces, but did not degrade to any measurable extent in V 4? solution. During charge/discharge cycling in the VRFB cell, the membrane underwent internal delamination, preferentially on the side of the membrane that faced the positive electrode. A vanadium-rich region was observed near the membrane surface that experienced delamination and Raman spectroscopic analysis of the degraded surface indicated a slightly depressed 1026 cm -1 band corresponding to a loss in the sulfonate SO 2 stretch intensity. Even though the S-Radel membrane underwent severe mechanical damage during the flow cell cycling, significant chemical degradation was not obvious from the spectroscopic analyses. For the VRFB containing an S-Radel membrane, an increase in membrane resistance caused an abnormal voltage depression during the discharge cycle. The reversible increase in membrane resistance and severe mechanical degradation of the membrane during cycling may be attributed to repeated formation and dissolution of particles inside the membrane. The mechanical stresses imposed by the particles coupled with a small amount of chemical degradation of the polymer by V 5? ions, are likely degradation mechanisms of the S-Radel membrane in VRFBs under high state-of-charge conditions.

The kinetics of the induced codischarge of Mo with Ni in citrate-ammonia electrolytes was investigated by means of polarization and a.c. impedance measurements. Three potential ranges were considered. At low polarization, hydrogen evolution resulting from citrate reduction is the main reaction. The impedance plots exhibit a large capacitive loop with a small high frequency inflection c:haracteristic of the development of a porous layer and a low frequency inductive feature. At intermediate polarization, the partial currents for Ni and Mo discharge increase in the same proportion; the hydrogen evolution is first constant and then rapidly decreases. Then a large lowfrequency capacitive feature is observed on the impedance plots, whose size decreases with increasing polarization. At still higher polarization, the Mo discharge becomes increasingly controlled by diffusion which generates an additional capacitive loop. A reaction scheme is proposed which accounts for the polarization data and the major impedance features.

This work studies the production of hydrogen peroxide through the cathodic reduction of oxygen in acidic medium, by comparing the results obtained using a commercial graphite and a gas diffusion electrode. A low pH was required to allow the application of hydrogen peroxide generation to an electro-Fenton process. The influence of applied potential and the gas flow composition were investigated. The gas diffusion electrode demonstrates a higher selectivity for hydrogen peroxide production, without significantly compromising the iron regeneration, thus making its successful application to a cathodic Fenton-like treatment, possible. Unlike the graphite cathode, the gas diffusion cathode also proved to be effective in the air flow.

Aqueous extracts of Roselle or Hibiscus sabdariffa L calyces have characteristic intense red colouration due to the presence of anthocyanins which could be utilised as colouring agent in pharmaceutical products. The aim of the current study was to evaluate the potential of aqueous extract of H. sabdariffa calyces as a colouring agent in three pediatric oral pharmaceutical formulations. The colour value of H. sabdariffa calyx extract was determined colorimetrically at λmax 540 nm to be within the BP range of ≥ 0.25. The colour value of H. sabdariffa (0.26) was lower than that of amaranth (0.46), a synthetic commercial pharmaceutical colourant. H. sabdariffa calyx extract retained its colour value within the BP standard for up to six months. The aqueous extract of H. sabdariffa calyces at 33 % w/v was used as colouring agent in paracetamol syrup, diphenhydramine syrup and pediatric cough linctus and the colour stability of the formulations against temperature, light and pH were determined. H. sabdariffa calyx extract was less stable than amaranth to temperature, light and pH when used as a colouring agent. H. sabdariffa calyx extract at 33 % w/v has potential as a colouring agent in pharmaceutical formulations when buffered at pH 5.0, packaged in amber bottles and stored at low temperatures (26-37 °C).

This paper describes the development of electrochemical processes for the oxidative degradation of toxic organic chemicals in waste waters. Doped bismuth lead dioxide anodes have been tested by the kinetic study of phenol anodic oxidation in aqueous solution. The main products ...

... and 70~ (Figs 6 and 8). In both cases it was possible to explain the experimental results assuming ... value of parameter b is not known it has been assumed that b = 1. The analysis of the ... Assuming that the surface roughness is that deter-mined by the BET technique (R = 2 x 10 4 ...

Dense, sintered samples of nickel ferrite/nickel oxide±copper cermets were produced and characterized. Three compositions were chosen, each with dierent NiO content. A new method of powder preparation involving no use of water as dispersant resulted in a well-dispersed ceramic phase with smaller metal grains than previously reported. The individual phases in the cermets were analysed quantitatively using energy-dispersive X-ray microanalysis, and signi®cant dierences between the materials were found. The electrical conductivity of the materials was measured, showing interesting properties not previously described. Reaction sintering was tried and found to lead to a microstructure dierent from that obtained with pre-calcined powder. The nickel contamination level in the electrolyte did not reach steady state after 4 h of electrolysis. Iron and copper did seem to reach steady state after some irregular behaviour early in the tests. The total contamination level of anode constituents in the deposited metal was as low as 0.116 wt%. These encouraging results seemed to be partly related to the cell con®guration giving very slow mass transfer from the electrolyte into the metal.

The structure, chemistry and morphology of commercially available carbon-supported and unsupported Pt±Ru catalysts are investigated by X-ray diffraction, energy-dispersive analysis by X-rays and electron microscopy. The catalytic activities of these materials towards electrooxidation of methanol in solid-polymer-electrolyte direct methanol fuel cells have been investigated at 90 C and 130 C with varying amounts of Na®on â ionomer in the catalytic layer. The unsupported Pt±Ru catalyst exhibits higher performance with lower activation-control and mass-polarization losses in relation to the carbon-supported catalyst.

Organic corrosion inhibitors have become competent alternatives to hazardous chrome conversion coatings due to their rapid adsorption over metal surfaces in corrosive environments. Literature suggests a wide range of organic corrosion inhibitors with high inhibition efficiency, barrier properties, and adsorption mechanisms. However, the long-term durability and protectiveness of an organic inhibitor film need to be understood with in-depth insights on its interaction with heterogenous alloy surfaces like AA6xxx, reduction of galvanic activities and time-resolved degradation due to ionic diffusion. The present article is focused on the time-resolved adsorption and degradation of 2-mercaptobenzimidazole (2-MBI)-induced inhibitor layer/film over AA6061 in 0.1 M NaCl solution. Electrochemical and surface analysis data indicate that the presence of 2-MBI drives the rapid formation of a 20–30 nm thick protective film comprised of constitutional elements of C, S, and N from 2-MBI upon the ...

In this work the products of the oxidation at BDD anode of chloride ions in aqueous solutions were identified during galvanostatic electrolyses performed in a filter-press reactor operating both in batch and continuous mode. A set of experiments were preformed in order to study the effect of operating conditions (current density, residence time, hydrodynamics and chloride concentration) on distribution and

A two-dimensional along-the-channel mass and heat transfer model for a proton exchange membrane fuel cell (PEMFC) is described. The model is used for calculation of cell performance (i.e., cell voltage against current density), ohmic resistance and water profile in the membrane, current distribution and variation of temperature along the gas channels. The following fuel cell regions are considered: gas channels, electrode backings and active layers at the anode and cathode side, and a proton exchange membrane. The model includes mass transfer in the gas channels and electrode gas backings, water transport in the membrane, electrode kinetics and heat transfer. Temperature in the cell is assumed to vary only along the gas channels, which means that it is the same at the anode and cathode and in the solid phase at a specified value of the channel coordinate. Electrode kinetics are considered only at the cathode, where major losses occur, whereas the anode potential is assumed to be equal to its equilibrium value. An agglomerate approach is used for the description of the active layer of the cathode. Simulations are carried out for different humidities of inlet gases, several different stoichiometric amounts of reactants and cooling media (air, water) with different heat transfer coefficients. Analysis of the results showed that the best performance of the PEMFC was obtained for well-humidified gases at conditions close to isothermal and at a stoichiometry of gases only somewhat higher than that corresponding to complete reactant consumption.

The application of rotating cylinder electrodes (RCEs) in electrochemistry has been reviewed for the period 1982±1995. Among the applications highlighted are the novel design of cell geometries and reactors for a range of electrochemical processes, voltammetry and analysis, electrodeposition and corrosion. This range amply indicates the widespread acceptance of the RCE for studies in a number of interdisciplinary ®elds.

The hydrogen evolution reaction (h.e.r) was studied in alkaline solutions on two types of electrodes: (i) obtained by alloying Raney nickel without or with nickel and (ii) by pressing Raney nickel and nickel powders at room temperature. The obtained electrodes are usually very active for the h.e.r. The most active electrode was obtained by pressing Raney nickel with nickel powder (50 wt %). It was characterized by a large roughness factor, R ~ 10 000 and a very low overpotential at the current density Of 250 mA cm -2, q250 : 56 mV. The mechanism of the h.e.r, was studied using a.c. impedance measurements. The high electrode activity is connected with the increase in the intrinsic activity of the porous electrode surface.

An equivalent circuit (EC) that reproduces the a.c. impedance of porous aluminium oxide films in a highly approximate manner is proposed. The results reveal that electrochemical impedance spectroscopy (EIS) is a powerful tool for obtaining detailed information on the electrochemical properties of both the porous and barrier layer on which the corrosion resistance of aluminium depends. The impedance at a given frequency can be used for accurate calculation of the electrochemical parameter for the oxide film represented by each element of the EC. In this way, the effects of any factor on sealing and ageing of anodized aluminium oxide films can be precisely analysed. The EIS technique provides an effective, advantageous alternative to existing seal quality control tests.

The stability of the electrolytes for all-vanadium redox flow battery was investigated with ex-situ heating/cooling treatment and in situ flow-battery testing methods. The effects of inorganic and organic additives have been studied. The additives containing the ions of potassium, phosphate, and polyphosphate are not suitable stabilizing agents because of their reactions with V(V) ions, forming precipitates of KVSO6 or VOPO4. Of the chemicals studied, polyacrylic acid and its mixture with CH3SO3H are the most promising stabilizing candidates which can stabilize all the four vanadium ions (V2+, V3+, VO2+, and VO2+) in electrolyte solutions up to 1.8 M. However, further effort is needed to obtain a stable electrolyte solution with >1.8 M V5+ at temperatures higher than 40 °C.

The surface roughness of porous Ni±Zn±P electrodes was studied in 1 M NaOH using in situ electrochemical techniques: ratio of the polarization current densities, electrochemical impedance spectroscopy, cyclic voltammetry, coulometric oxidation of the surface, and a new technique of a CO molecular probe. The obtained surface roughness was about 5X5 Â 10 3 . Good agreement was observed between the results obtained by all these techniques.

A new method for electrochemical characterization of composite electrode materials is reported. A paste of the catalytic material in Nafion® is coated on a rotating ring disc electrode (RRDE) to partially simulate the working environment of a proton exchange membrane (PEM)/electrode composite as used in, for example, water electrolysis or PEM fuel cell operation. This allows direct comparison of a wide range of candidate electrocatalysts in a reproducible manner. Problems specific to these volumic electrodes are accommodated satisfactorily by rational modification of the standard expressions used in RRDE analysis. The value of the method is illustrated in studies of various cobalt complexes which show promise in dioxygen reduction; namely, cobalt tetramethoxyphenylporphyrin (CoTMPP), cobalt phthalocyanine (CoPC), and cobalt cyclam (CoCy), supported on a range of particulate carbons BP2000, Printex XE 2 and Vulcan XC-72. Typical electrochemical parameters have been measured or estima...

Fine bubbles of the size required for many processes such as electroflotation can be generated by electrolysis. A large number of factors such as electrode material, electrode surface/morphological properties, pH and current density affect the gas bubble size distribution. This work is aimed at studies on the effect of interrupted current (pulsed) electrolysis on the generation of gas bubbles. A microcomputer-controlled current source designed to generate the required pulses is described along with typical results obtained with this system. It was observed that a decrease in duty cycle at a given pH and average current density causes an increase in fine sized bubbles and concomitant increase in bubble flux. A mechanism based on local potential gradients is proposed to explain this phenomenon.

NN AUNG1 and W. ZHOU2,* 1School of Mechanical and Production Engineering, Nanyang Technological University, Singapore 639798; 2Division of Engineering and Applied Sciences, Harvard University, 9 Oxford Street, Cambridge, MA 02138-2901, USA (*author ...

This paper concerns the preparation of cobalt oxides through anodic deposition from Co(NO 3 2 aqueous solutions on dierent substrates. The electroformed oxide ®lms exhibit good chemical stability and lower oxygen overvoltages, irrespective of the substrate material. Electrocatalytic properties are investigated through polarisation curves and impedance measurements, while the active surface area is estimated by cyclic voltammetry. Experimental data are analysed in terms of a possible reaction mechanism.

Iron(III) tetramethoxyphenylporphyrins (FeTMPP-Cl) adsorbed on high-area carbons were heat treated in an inert atmosphere at various temperatures ranging from 200±1000°C to produce catalysts for the electroreduction of oxygen in acid electrolytes. It was found that the speci®c surface area of the FeTMPP-Cl/C catalysts linearly decreases with increase of the FeTMPP-Cl loading on RB carbon. The electrical resistivity of the catalyst decreases with the increase of heat treatment temperature in the range of 200 to 800°C, then it increases beyond 800°C. The results obtained with elemental analysis, FTIR spectroscopy and XPS techniques indicate that the onset temperature for partial decomposition for the FeTMPP chelate occurs at temperatures of about 400±500°C. The surface concentrations of both iron and nitrogen on the carbon support increase as the heat treatment temperature increases, and the maximum occurs at 700°C. Some possibilities about the nature of active sites in the catalysts are discussed.

The cathodic deposition of copper from acid sulphate solution containing copper(I1) has been used to characterize the mass transport properties of reticulated vitreous carbon cathodes, operated in the flow-by mode. Current-potential curves recorded a t a rotating vitreous carbon disc electrode were used to determine the diffusion coefficient for copper(I1) under the conditions of the experiments and also to elucidate the effect of oxygen in the electrolyte stream. Pressure drop measurements have been used to separate the mass transport coefficient and real surface area effect for four grades of reticulated vitreous carbon, nominally having 10, 30, 60, 100 pores per inch.

This paper presents a fundamental study of the influence of carbon steel microstructure on the corrosion rate. Subsequently, the corrosion performance of various grades of carbon steels were evaluated in stirred autoclaves under elevated carbon dioxide and temperature conditions. Corrosion and penetration rates were determined via mass loss and optical microscopy, respectively. It was found that the corrosion rate of carbon steel line pipe is influenced by microstructure. More specifically, a relationship between localized corrosion susceptibility and the presence of pearlite bands in the steel microstructure was found. However, no correlation was evident between minor elemental concentrations (i.e., Ni, Cr, Mo) and corrosion resistance. It has been proposed that the corrosion stability of the various microstructures may arise from variations in the distribution of carbon bearing phases within the steel. In the banded ferrite/pearlite structure, the carbon-bearing phase (pearlite) is distributed in layers whereas in the other structures the carbon-bearing phases are much more evenly distributed. This study reports on the corrosion resistance of carbon steels in relation to their chemical and physical properties.

Ni-Mo nanocrystalline layers were electrodeposited using direct current from citrate-ammonia solutions. The quartz crystal microbalance investigation confirms that the discharge process starts with hydrogen evolution before the onset of the alloy deposition. The grain size was estimated from X-ray line broadening. It decreases when the molybdenum content is increased. It is smaller for layers deposited at pH 9.5 than 8.5. The microhardness exhibits a maximum close to 800 Vickers for s Mo around 17 wt%. For higher s Mo a softening is observed showing a deviation from Hall-Petch behaviour due to small grain size. In deaerated hydrochloric solutions, the layers show a large passivation domain without any pitting. The corrosion currents as well as the passivation currents, higher than for the bulk Hastelloy B alloy, decrease when s Mo is increased.

Low Pt loading electrodes have been obtained by the direct mixing of electrocatalyst and Na®on Ò ionomer (for catalyst layer) and by the introduction of an intermediate hydrophobic carbon layer to optimize gas distribution. The in¯uence of Te¯on Ò content in the carbon layer has been studied and an optimum content of 20 wt % has been found. The behaviour of the improved electrodes as a function of temperature (70±95°C) and gas (H 2 and air) pressure (1±5 bar) has been evaluated in a 50 cm 2 single cell. In air operation at 5 bar absolute pressure and 95°C a maximum in the power density of about 450 mW cm A2 has been obtained.