Table of contents

Preparation of a new electrocatalyst for the anodic oxidation of methanol in sulfuric acid is described.The catalyst shows a high degree of passivity in hot sulfuric acid, and a modest electrocatalytic activity toward the methanol reaction.

The coenzyme dihydronicotinamide adenine dinucleotide (NADH) can be directly oxidized at ∼0.23 V at a bare silver electrode. Not only is the overpotential lower than that at the commonly used carbon or platinum electrodes, but the coenzyme gives a cathodic peak at ∼0.12 V which can be assigned to the reduction of the oxidized form. Since no mediator for the redox reaction of NAD⁺/NADH is present at the silver electrode surface, the working electrode is obviously stable and the reaction reported here is useful for electrochemical studies of the nicotinamide coenzyme.

Amorphous has been synthesized at ambient temperatures by a reduction of aqueous potassium molybdate solution with potassium borohydride. The sample has been characterized by x‐ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The amorphous exhibits excellent cyclability with a capacity of over 200 mAh/g in the range 3 to 1 V in lithium cells. The electrochemical behavior of amorphous is distinctly different from that of crystalline . Good cyclability at low enough voltage range makes amorphous an attractive candidate for anode hosts in rocking‐chair lithium cells.

Previous work performed in both sodium and lithium buffered chloroaluminate molten salts have shown that the addition of small amounts of promotes the reversible stripping behavior of lithium and sodium metal with cycling efficiencies between 80 and 90%. We have performed a series of optical studies in conjunction with electrochemical experiments at varying concentrations in both lithium and sodium chloride buffered melts. On investigation, the lithium deposit is dendritic in nature and does not form a uniform film on the tungsten electrode. After discharging at moderate current densities, disconnected lithium metal is observed at the electrode surface. In contrast, the sodium deposits as a uniform, flat film on the tungsten electrode with little or no dendritic growth. The sodium electrodeposits undergo complete stripping from the tungsten electrode without dendritic or disconnected sodium metal left on the electrode surface.

The nature of electronic interaction between noble metal and semiconducting oxide was investigated for Pd‐loaded sensor elements. It was shown that grains contacting to PdO were strongly depleted of electrons in air. This electronic interaction disappears on exposure not only to ‐containing air but also to He (inert gas). On the basis of these results, it was suggested that the adsorbed oxygen formed at the interface is responsible for the electronic interaction.

During our recent efforts to grow polycrystalline diamond thin films on glassy carbon substrates using microwave‐assisted chemical vapor deposition, we have reproducibly observed that a freestanding, polycrystalline diamond film is formed and can be lifted from the surface easily. The glassy carbon surface, on which the diamond films form, is gray in color (as opposed to the normal mirrorlike finish), rough, and hard as the surface is somewhat abrasion resistant after the growth. We postulate that growth of diamond on glassy carbon involves: (i) initial hydrogenation of the graphite edge plane sites forming a diamondlike surface, (ii) nucleation of diamond microparticles on the hydrogenated edge plane sites, and (iii) coalescence of the microparticles into a continuous film. The poor adhesion of diamond to the glassy carbon surface, as grown using our conditions, may result from a combination of growth condition and surface microstructural effects. Results from the characterization of a freestanding film by scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry are presented.

A zirconia‐based electrochemical device attached with an oxide electrode was developed for the detection of in air at elevated temperature. The sensing mechanism was confirmed to involve a mixed potential at the oxide sensing electrode. Among the oxides tested, ZnO was the best suited for the sensing electrode, giving a sharp selective response to 50 ∼ 500 ppm in air at 450 to 600°C.

A stable fluorosilicate glass (FSG) has been fabricated from the chemical vapor deposition of /tetraethylorthosilicate (TEOS)/ and . Films were subjected to a temperature and humidity stress for water absorption studies and were thermally stressed for fluorine diffusion studies. Fourier transform infrared spectrometry (FTIR) and secondary ion mass spectrometry (SIMS) indicate films produced from absorb less water and diffuse less fluorine into than films produced from . The activation energies of fluorine diffusion were calculated to be 1.00 and 0.82 eV for and FSG, respectively.

The electro‐oxidation of formic acid was studied in a direct‐oxidation polymer‐electrolyte fuel cell at 170°C using real‐time mass spectrometry. The results are compared with those obtained for methanol oxidation under the same conditions. Formic acid was electrochemically more active than methanol on both Pt‐black and Pt/Ru catalysts. The polarization potential of formic acid oxidation was ca. 90 to 100 mV lower than that of methanol. The oxidation of formic acid was dependent on the water/formic acid mole ratio. The best anode performance was obtained using a water/formic acid mole ratio of ∼2. In addition, Pt/Ru catalyst was more active than Pt‐black for formic acid oxidation. The mass spectrometric results showed that is the only reaction product of formic acid oxidation. The results are discussed in terms of possible formic acid oxidation mechanisms.

The main electrochemical characteristics of a new aluminum vanadium oxide synthesized via a sol‐gel process are reported. The kinetics of the electrochemical insertion of lithium into has been investigated using ac impedance spectroscopy and the pulse relaxation technique. These two methods, which involve basically different kinds of perturbation and measurement, provide similar data. The variation of the chemical diffusion coefficient _Li, in the range to , as a function of the Li content, is compared to that previously obtained for the parent oxide and tentatively correlated with previous structural data reported on and orthorhombic mixed oxides .

We have studied the behavior of phenol and 2‐naphthol on (111)Au during electro‐oxidation using atomic force microscopy (AFM) and surface Fourier transform infrared spectroscopy (FTIR). As oxidation begins, the AFM shows growth of amorphous features on the (111)Au surface. We observed different modes of nucleation and growth for the two molecules. We associate these features with poison formation as is also inferred from electrochemical measurements. FTIR spectra show an increase in the number and amplitude of absorbence bands as oxidation proceeds, indicating formation of new oxidation products and a thickening film on the (111)Au surface.

Graphite intercalation compounds of vanadium oxide fluoride, , were synthesized in a fluorine atmosphere. Fourier transform infrared spectroscopy, x‐ray photoelectron spectroscopy, and x‐ray diffraction measurements were used for their structural characterization. These experiments have suggested that cointercalation of fluorine and in the carbon occurs involving local structural modifications and that excess oxygen was present in the graphite layers. The study of electrochemical insertion of lithium was carried out at 25°C in a ‐propylene carbonate electrolyte by chronopotentiometry and ac impedance measurements. The interfacial charge‐transfer process, associated to the half‐reaction occurring during the intercalation, was found to be independent of the intercalation ratio of lithium cations, y. The chemical diffusion coefficient, D_Li, and the conductivity, σ_Li, obtained were deduced from impedance data by considering the geometric surface area. Both are roughly constant for all the y‐range: and for and for .

Supercritical drying of gels yields amorphous aerogels (ARG) that serve as reversible, high capacity hosts for lithium ion intercalation. We have found that ARG material consists of a highly interconnected solid network that has a surface area up to 450 m²/g and a specific pore volume of 2.3 cm³/g. The material hosts at least per mole of (ARG) as determined by both galvanostatic intermittent titration (GITT) and chemical lithiation (CL) techniques. The equilibrium voltage‐composition curve is identical for both GITT and CL techniques as well. (ARG) has a specific energy in excess of 1600 Wh/kg, the highest ever reported for any vanadium oxide host.

Electrodeposition of ion resulted in the growth of single‐crystal particles on an amorphous carbon electrode in solution. single crystals grow at potentials higher than −0.55 V vs. saturated calomel electrode (SCE) in (pH 7) as well as (pH 2.0) and HCl (pH 2.1) solutions. However, as well as Cu particles are formed simultaneously at potentials below −0.55 V vs. SCE. The oxygen in the may come from water via cuprous hydroxide intermediate. The effect of anions on the crystal habit of the particles was investigated by changing anions. Hexahedral single‐crystal particles were preferentially formed in solution, but in the presence of sulfate ion the particles grow in a polyhedral form. Y‐shape particles of were obtained in the presence of chloride ion, which may be due to the effect of stronger adsorption of on the surface of growing particles. Number density and average size of the particles grown on the electrode vs. the kind of anions and electrodeposition potential are discussed.

In this paper we report on the characteristics and performance of a new rechargeable 3 V battery system developed at Tadiran. The behavior of AA cells of an 800 to 750 mAh capacity is described in terms of charge‐discharge curves, cycle life, and low‐temperature and high‐current performance. At charging regimes around C/10, more than 350 cycles at 100% DOD could be obtained. These batteries have a unique cell chemistry based on /1,3‐dioxolane/tributyl amine electrolyte solutions which provide internal safety mechanisms that protect the cells from short circuit, overcharge, and thermal runaway upon heating up to 135°C. This behavior is due to the fact that the electrolyte solution is stable at low‐to‐medium temperatures but polymerizes at temperatures over 125°C.

Poly(5‐amino‐1‐naphthol) is a new conducting polymer, obtained by electropolymerization of 5‐amino‐1‐naphthol. Raman spectroscopy confirms the structure which consists of amine (‒NH‒C) and imine (‒N=C) links between naphthalene rings, characteristic of a polyaniline‐like structure. Its redox properties were investigated in aqueous acid (pH 0) by in situ Raman spectroscopy. Some amine units are reversibly transformed into imine groups on oxidation.

Voltammetric and coulometric results are described for the electrocatalytic oxidation of Cr(III) to Cr(VI) at the mixed bismuth(V)‐lead(IV) dioxide film electrodes (designated ) that are electrodeposited from acidic solutions of Pb(II) containing Bi(III). A current efficiency of 99.2% (σ = 1.1%, N = 12) is obtained for galvanostatic generation of Cr(VI) at a preconditioned film electrode. Preconditioning of the film merely involves the generation of Cr(VI) which, based on scanning electron micrographs, is concluded tentatively to achieve chemical stripping of noncatalytic portions of the films to produce films having greater electrocatalytic activity for the desired reaction. Electrochemical stripping of the electrode had a similar preconditioning effect. Based on wavelength dispersive spectroscopy, electrochemical stripping resulted in an increase in surface Bi concentration of 33% relative to Pb.

Electrochemical oxidation of zinc electrodes has been studied in 1.0 M KOH solutions employing cyclic voltammetric and in situ spectroelectrochemical techniques. The results indicate that three different processes, i.e., dissolution, prepassivation, and passivation, take place in different potential regions. Two optically different solution species absorbing at 250 and 290 nm, which are assigned to and , respectively, are produced initially during anodic oxidation of zinc at different potentials to different extents with different respective ratios. These species undergo a series of consecutive chemical reactions to eventually lead to passive films on the surface. The film compositions were identified to be ‐doped ZnO, and Zn‐doped ZnO depending on the potential regime and aging. Details of the electrochemistry and chemistry taking place during electrolysis in these three regions are discussed based on the cyclic voltammetric and spectroelectrochemical data.

A more comprehensive study than those previously reported in the literature was carried out on the electrochemical reduction of 10,10'‐dimethyl‐9,9'‐baicridinium ion (lucigenin) in aqueous solutions. Lucigenin exhibits one, two, or three irreversible voltammetric reduction peaks, depending on its concentration and the scan rate. The first peak is due to the reduction of the first monolayer of molecules adsorbed on the electrode. This process involves two simultaneous one‐electron transfers that yield a molecule (P), also immobilized at the electrode, which undergoes a conformational change to the form P'. In addition, the reagent molecules that reach the electrode by diffusion and the product (P) comproportionate to yield the intermediate radical R^⋅+. New reactant molecules can displace the product because the monolayer is reversibly adsorbed. The transfer coefficient of the process and the activation energy of the conformational change were determined. The second peak is due to the reduction of a second monolayer of adsorbed lucigenin molecules. This takes place via the first monolayer of product molecules adsorbed on the electrode. Finally, the third peak arises from reduction of lucigenin molecules adsorbed on the previous monolayers. The overvoltage required to reduce lucigenin increases with increasing number of monolayers formed. The formation of new insoluble monolayers blocks the faradaic process altogether in the second scan at more positive potentials than those for the second or third peak.

We studied lithium insertion in hydrogen‐containing carbons heated at temperatures near 700°C. High capacities with large hysteresis (lithium insertion into these carbons at nearly 0 V and removal at nearly 1 V) were shown to be proportional to the hydrogen content of the samples. It is believed that the lithium atoms may bind on hydrogen‐terminated edges of hexagonal carbon fragments, causing a change in the bond from sp² to sp³. We have carefully studied the electrochemical insertion of lithium in hydrogen‐containing carbons using a variety of charge‐discharge rates and cycling temperatures. These measurements allow the hysteresis to be quantified. A simple model, which treats the bonding change as an activated process, is used to model the hysteresis in the cells qualitatively.

The corrosion films on iron in aqueous carbonate/bicarbonate solutions were studied as a function of concentration, pH, and temperature by using the technique of surface‐enhanced Raman spectroscopy with electrodeposited silver. Both and were detected in the surface oxide film at prepassivation potentials. Iron carbonate (siderite) was observed in the corrosion film in a limited pH, temperature, and applied potential range. At lower carbonate/bicarbonate concentration (e.g., 0.01 M), passivation was lost, and continuous anodic dissolution of the iron occurred. The cathodic reduction of the corrosion film was enhanced at 75°C.

The effect of cobalt, platinum, and cobalt‐platinum, alloys on high surface area carbons for oxygen reduction in alkaline electrolyte was investigated. The Pt‐Co catalyst with ca. 1:3 atomic ratio was prepared by addition of solution to a mixture of methanol and a 5% surfactant in deionized water containing cobalt acetate and carbon suspension. This was followed by drying and heat‐treatment at 700 and 900°C in a flow of hydrogen and nitrogen gas mixtures. Polarization curves and kinetic parameters for Pt, Co, and Pt‐Co were conducted and compared in 6 M KOH and at 80°C. Higher activities were observed for the Pt‐Co alloy, that had been heat treated at 900°C. In addition to increased activity of this catalyst, the unalloyed base metal (Co) contributes to total performance improvement of the oxygen reduction process. Furthermore, surface, structural, and chemical characterizations of the catalysts were carried out using transmission electron microscopy, x‐ray diffraction, Brunauer, Emmett, and Teller method, and atomic absorption spectroscopy. Dissolution of cobalt from the electrodes, both from the single cobalt phase and Pt‐Co alloy catalysts, has been established. The x‐ray results demonstrated a shift to lower lattice parameters (3.618 Å) by the Pt‐Co alloys, prepared at 900°C, than the pure platinum catalyst (3.919 Å).

The characterization of electroless electrodes with heat‐treatment for oxygen evolution was investigated in 1 M KOH solution. The structures of the electrodes changed significantly with heat‐treatment, and the surface state was different from that of those without treatment. AC impedance measurements showed that the electrode prepared from bath possessed the best performance, as evaluated from the value of 1/R_ct. The electrochemical characteristics were found in relation to the morphology and the structure of the electrodes.

A mathematical model has been developed to describe the electrodeposition of Fe‐Ni alloys and composites under potentiostatic conditions. This model can be used to predict the polarization behavior, partial current densities, and alloy composition of each of the components as a function of the applied potential. samples were deposited on platinum rotating disk electrodes from sulfate electrolytes under potentiostatic conditions, and the results obtained were compared to the model. The model predictions were found to agree well with the experimental observations for the Fe‐Ni and systems.

Samples of with a wide composition range were prepared by electrodeposition from Cu(II), In(III), and Se(IV) precursors. According to the preparation conditions, sample groups were defined and characterized for their structural, optical, and photovoltaic properties. A postthermal treatment was carried out in order to improve the quality of the as‐deposited films. Strong correlations with the film composition are clearly evident with respect to the deposition conditions. Sample groups exhibit different properties, which are analyzed in terms of deviations from molecularity (Δm) and stoichiometry (Δs).

Based on the formula of ‐type glass‐ceramic ‐fast ionic conductors were successfully produced for a variety of rare‐earth ions, R, under the appropriate composition parameters. The possible combinations of x and y became more limited for the crystallization of the fast ionic conducting phase as the ionic radius of R increased, while the conduction properties were more enhanced in the glass‐ceramics of larger R. These results are discussed in view of the structure and the conduction mechanism. Also studied were the microstructural effects on the conduction properties, which were dependent upon the heating conditions of crystallization. These effects were understood in relation to the grain boundary conduction properties as well as the transmission electron microstructural morphology of grain boundaries.

X‐ray photoelectron spectroscopy and scanning electron microscopy methods were used for analysis of the surface layers of lithium deposited at various current densities from propylene carbonate containing and various amounts of HF, to investigate the effect of HF in electrolytes on the surface reaction of lithium during electrochemical deposition. Our analyses indicate that the surface state of lithium and the morphology of lithium deposits are influenced by both the concentration of HF and the electrodeposition current. The first parameter for the electrodeposition of lithium is related to the chemical reaction rate of the lithium surface with HF and second to the electrodeposition rate of lithium. These results suggest that surface modification is effective in suppressing lithium dendrite formation when the chemical reaction rate with HF is greater than the electrochemical deposition rate of lithium.

The solid solution compound represents a single‐phase derivative formally composed of 50 atom percent (a/o) and 50 a/o . It exhibits an ionic conductivity at 25°C. The total electronic conductivity in contact with elemental lithium or highly positively polarized electrodes is found to be around four orders of magnitude smaller. Detailed studies under different conditions and in different cell types are presented. In the asymmetric cell type (−) (+), the tantalum electrode served as an arbitrary positive electrode simulating different lithium activities due to the applied external voltage. Upon extreme polarization (E vs.) below 100°C, stable tarnishing layers were formed at the ‐electrode interfaces, thus resisting further decomposition, which makes a suitable electrolyte for investigating cathodes which exhibit very high positive voltages vs. lithium. Moreover, chemical stability experiments show this electrolyte to be inert against elemental lithium and up to at least 100 and 500°C, respectively. crystallizes in a monoclinic unit cell having the parameters a = 5.108(4) Å, b = 5.388(4) Å, c = 6.205(6) Å, and β = 90.40(9)°.

Dissolution of spinel manganese oxides and the concomitant cathodic capacity losses were examined in cells where PC is propylene carbonate and DME is dimethoxyethane. Dissolved contents in the electrolytes were analyzed as a function of cathode potential and carbon contents in the composite cathodes. Characteristically, manganese dissolution was notably high at the charged state (at >4.1 V vs.), in which potential range an electrochemical oxidation of the solvent molecules was also prominent. From this and another observation whereby the Mn dissolution increased with increasing carbon content in the composite cathodes, it was proposed that, at the charged state of the cathode the solvent molecules are electrochemically oxidized on carbon surfaces and an as‐generated species promotes the manganese dissolution. Results of an ac impedance study revealed that Mn dissolution brings about an increase in contact resistances at the Mn‐depleted spinel/carbon interface, and also in the electrode reaction resistances for intercalation/deintercalation. Thus, the Mn dissolution causes capacity losses in two different pathways; material loss of the loaded spinel and polarization loss due to a cell resistance increment. The former prevailed when cathodes contained excess amounts of carbon, while the latter became more of a problem as the carbon contents decreased.

Molecular dynamics simulations of lithium injection in lithium metasilicate‐ systems have been performed. Lithium ion penetration is more prevalent in amorphous in comparison to the crystalline form. Migration dynamics can be augmented through an increase in the simulation temperature or by decreasing the coulombic repulsion between the tungsten and lithium ions. For crystalline injection is dependent on the orientation of the crystal. Lithium penetration is more pronounced for the crystal with the (001) orientation than in the (110) oriented crystal, where there is only limited diffusion.

An impulse current response to a short laser pulse was measured using a current‐voltage converter with a zero input resistance, which enabled us to provide any band bending of a semiconductor electrode under a potentiostatic condition. The current transient can monitor a net charge‐transfer process across a semiconductor‐electrolyte interface because the external resistance is almost zero. The current transient was found to be characterized by a relaxation time where R_dl, R_sol, and C_sc are the diffuse double‐layer resistance, the solution resistance, and the depletion layer capacitance of the semiconductor. C_sc obtained from the analysis of the current transient gave an ideal Mott‐Schottky plot. By intentionally increasing the diffuse layer thickness with which R_dl and then τ increase, the dynamics of protons generated as an oxidation product of water was confirmed to be monitored from the current transient.

Titanium sheets coated with vacuum‐deposited tungsten films were oxidized at 1073 and 1173 K to form mixed oxide films. The mixed oxide films showed higher anodic photocurrents than pure films formed on Ti due to the oxidation of water. The photocurrent increased with the amount of W deposition on the Ti substrate and with oxidation temperature. From scanning electron microscopy, x‐ray diffraction, and x‐ray photoelectron spectroscopy, it is concluded that the film s containing larger amounts and uniformly distributed W in the depth direction of the film generate larger photocurrents. For films formed by thermal oxidation of W sheets, there was anodic dissolution of the underlying metal. This may be due to imperfections in the film. Such dissolution was not observed for the mixed oxide films, showing the electrochemical stability of these films.

The electrolyte decomposition during the first lithiation of graphite is reduced to 90 mAh/g in an electrolyte containing equal volumes of chloroethylene carbonate and a cosolvent of propylene carbonate, dimethyl carbonate, or diethyl carbonate. The volume fraction of chloroethylene carbonate can be further reduced to 0.05 in a trisolvent system with a cosolvent containing equal volumes of ethylene carbonate and propylene carbonate. A lithium‐ion cell containing chloroethylene carbonate and propylene carbonate shows a long cycle life. The capacity decreases by 20% from the initial value in over 800 cycles. The charging efficiency is 80 to 90%, is rate dependent, and is accompanied by a self‐discharge mechanism. A hypothesis of a chemical shuttle is suggested to explain the low charge efficiency and self‐discharge.

The electrochemical properties of new carbon materials obtained by the heat‐treatment of condensed polynuclear aromatic (COPNA) precursors have been investigated. The COPNA precursors were synthesized from an aromatic compound (pyrene, Py) and a cross‐linking agent, dimethyl‐p‐xylene glycol (DMPXG), with a series of DMPXG/Py molar ratios. The results indicate that the discharge capacities of the carbons heat‐treated at 800°C increased as the DMPXG/Py molar ratios increased. The discharge capacities of the carbons derived from them with molar ratios above 1.5 of DMPXG/Py were greater than , corresponding to the composition of stage 1 Li‐GIC, . Moreover, the discharge curves of these carbons showed two regions, one of which is the potential range of 0 to 1.0 vs., and the other, the plateau region around 1.0 V. The discharge capacity of the former was almost constant regardless of DMPXG/Py, whereas that of the latter increased as DMPXG/Py increased. However, the plateau region disappeared for carbon materials heat‐treated above 1000°C. These results suggest that "cavities" in the carbons heat‐treated below 800°C contribute to active charge‐discharge of lithium species for a high‐capacity carbon anode, while those in carbon materials heat‐treated above 1000°C do not. Furthermore, the observed charge capacities of those carbons heat‐treated in the range of 600 to 1600°C showed good agreement with the theoretical capacities calculated by using the structural parameters and the butanol displacement densities of the carbon materials. This result also supports the validity of our hypothesis, namely, that cavities in the carbon materials contribute to the charges of lithium species in lithium‐ion batteries.

The response of the electrochemical quartz crystal microbalance (EQCM) was studied in and KOH. The gold coating on the crystal served as the working electrode, and the frequency was determined as a function potential in the double‐layer region. Frequency shifts up to −5 Hz were observed, even though the ions of the electrolytes employed are not specifically adsorbed and there is no faradaic reaction which could lead to the formation of adsorbed species through charge‐transfer. The added weight which would cause a similar shift in frequency in our experimental setup is ca. 60 ng/cm², which is equivalent to about a monolayer of chlorine atoms adsorbed on the surface. Thus, elucidation of the origin of this effect is essential for the proper use of the EQCM in the submonolayer region. The effects observed are due to the surface excess of ions in the diffuse double layer. A model was developed in which the liquid in a thin layer near the surface has a higher viscosity than in the bulk, because of the high concentration of ions and the high electrical field in this region. The value of this viscosity can neither be calculated independently nor measured experimentally, since the liquid in this region is charged (electroneutrality is maintained across the interface but not on each side separately). Using the viscosity of the film as a parameter, we were able model the experimental behavior.

Effects of microstructure of carbon supports for platinum catalyst and of perfluorosulfonate‐ionomer (PFSI) distribution in the microstructure of the catalyst layer on the consequent performance of polymer‐electrolyte fuel cells, prepared by a new method based on the process of PFSI colloid formation, were investigated by electrochemical techniques, a mercury pore sizer, adsorption [Brunauer‐Emmett‐Teller and Barrett‐Joyner‐Halenda] methods, and CO adsorption. The microstructure of the catalyst layer and its effect on polymer‐electrolyte fuel cell performance were affected by the contents of PFSI and carbon supports. The PFSI were distributed in the distinctive pores of 0.04 to 1.00 μm. Pore volume and pore diameter were primarily affected by the carbon supports. Carbon supports had a large pore volume with pore diameters less than 8 nm on the surface of the primary particles. Polymer‐electrolyte fuel cell performance predominantly increased with the specific volume of pores covered with the PFSI in the catalyst layer and with a decrease of the specific volume of pores less than 8 nm without PFSI on the carbon surface.

The influence of convection and interfacial‐reaction resistance on the response of microsensors, including the effects of: (i) fluid flow rates; (ii) reactant (to be sensed) concentration and diffusion coefficient; (iii) fluid conduit and microsensor size; and (iv) sensor potential and interfacial‐reaction resistance, are clarified. For steady‐state convective diffusion to a microdisk sensor, it is shown that sensor response is a monotonic function of two dimensionless groups: the Péclet number Pe, which characterizes the magnitude of convective transport relative to that of diffusion, and the group tan (θ¯), which provides a measure of diffusive‐transport resistance relative to that of the interfacial charge‐transfer reaction. A singular‐perturbation solution provides the sensor response vs. Pe and θ¯ for small Pe, corresponding to slow fluid flows and small disks, and numerical calculations extend the analysis to higher Pe values. The analysis suggests a method for increasing the signal‐to‐noise ratio through altering the sensor bias potential.

The constant potential oxidation of iron in aqueous sulfuric acid solution induces a self‐sustained nonlinear oscillation of the current. Here, two independently controlled iron electrodes become synchronized to each other as the distance between the electrodes is reduced. The temporal pattern of the synchronization is a function of the potential difference between the electrodes. The oscillation frequency of the iron electrode can be changed by irradiation with visible light.

Room temperature molten salts consisting of 1,2‐dimethyl‐3‐propylimidazolium chloride and aluminum chloride have been examined as possible electrolytes for a room temperature design of the sodium/iron(II) chloride battery. This work examines the conditions which provide the most efficient reduction and oxidation of sodium from a sodium chloride buffered, neutral melt. Most work was performed on a tungsten substrate using cyclic voltammetry. Melts were treated with gaseous HCl using a closed electrochemical cell which allowed for quantification of the effect of HCl on the electrochemical behavior of sodium in the molten salt. The HCl threshold partial pressure was less than 1 kPa for sodium plating. This result was complicated by the slow equilibrium between gaseous HCl and that dissolved in the molten salt; the effect of HCl addition was found to last for months, demonstrating the slow equilibrium. Small amounts of water contamination were found to produce a similar effect. At elevated temperatures the melt had higher conductivity, an order of magnitude higher current densities, and higher coulombic efficiency.

The electrochemical characteristics of fullerenes and fluorinated fullerenes have been investigated by cyclic voltammetry and galvanostatic discharge using solid‐state lithium cells , and , MEP‐7 = a polyphosphazene derivative). In the cyclic voltammograms of and , the first half‐wave potential of is found to be 0.2 V more positive than that of , suggesting that the electron affinity of is slightly larger than that of . For the fluorinated fullerenes, cyclic voltammetry gives one irreversible reduction peak at a high potential, which has been verified to be due to the reduction of the C‒F bonds by x‐ray photoelectron spectroscopy. From the discharge curves of , and , a high utility of 90% is obtained. Changes in electronic structure of the cathode materials upon discharge are examined by x‐ray photoelectron spectroscopy and open‐circuit voltage dependence on cathode utilities, and the discharge reaction mechanism is deduced. The open‐circuit voltage dependence reveals that the electronic structure of fluorinated fullerenes changes continuously as a homogeneous electrochemical reduction proceeds.

The oxidation and passivation mechanism and the passive behavior of nickel in molten carbonate have been investigated with impedance measurements, quasi‐stationary polarization curve measurements, and scanning electron microscopy. The oxidation of nickel probably proceeds according to a dissolution and reprecipitation process. The slowest steps in the reaction sequence are probably dissociation of carbonate and diffusion of the formed NiO to the surface. In the passive range, it is most likely that dissolution of proceeds after diffusion of through the oxide layer. The is formed at the metal/oxide interface. The slowest process is the diffusion of bivalent nickel ions through the passive scale. If only one reaction path is assumed, the formation of trivalent nickel ions probably takes place at the oxide/melt interface. This reaction is accompanied by the incorporation of an oxygen ion and nickel vacancy in the NiO lattice. The trivalent nickel ions and the nickel vacancy diffuse to the bulk of the oxide scale. The slowest step in this sequence is likely the dissociation of the carbonate ions and the subsequent incorporation of the oxygen ion in the NiO lattice.

We studied the uniformity of chemical oxides formed on Si surfaces during wet chemical cleaning. The uniformity was determined by the surface morphology during the initial stage of photoexcited etching. Since photoexcited etches silicon 40 times faster than it etches silicon oxide, it highlights chemical oxides on silicon surfaces making them observable by scanning tunnel microscopy or atomic force microscopy. We found that the chemical oxides were not uniform, whereas oxides formed in gas phase were uniform. Boiling in (1:1:4 volume) or (1:1.4:4 volume) solutions formed 30 to 70 nm oxide islands. The island density was in the order of . Boiling in a solution also resulted in a chemical oxide which was composed of 25 nm diam dense islands and had pinholes at a density of . The island density was between 1 × 10¹¹ and . The chemical oxide nonuniformities were independent of both crystallographic orientation and substrate resistivity for the most part. It is possible that the nonuniformities may negatively influence subsequent processing.

In situ x‐ray absorption spectroscopy (XAS) in 1 M was used to examine the electronic and structural effects of hydrogen adsorption on carbon supported Pt (Pt/C) and Pt alloyed with first row transition metals (Cr, Mn, Fe, Co, and Ni). In the case of Pt/C, potential excursions from the double layer region (0.54 V vs. RHE) to 0.0 V caused significant changes in the XAS spectra whereas none was observed for the alloys. The and x‐ray absorption near edge structure indicated the generation of empty electronic states in the vicinity of the Fermi level due to adsorption of hydrogen, and the extended x‐ray absorption fine structure indicated an increase in the coordination number of the first Pt‐Pt shell from 9 to 11. The latter was attributed to a reversible surface restructuring process. Alloying of the Pt suppresses both the electronic and structural effects at 0.0 V. A comparison of the electrochemical kinetics for hydrogen oxidation by these electrocatalysts in a proton exchange membrane fuel cell indicated that alloying of the Pt had insignificant effects on the kinetics.

The electrochemical faceting and roughening of polycrystalline Ag and Cu electrodes in aqueous 0.01 MM at 25°C was investigated by applying a symmetric square wave potential reversal technique for 20 h between preset upper and lower potential values in the range 5 Hz < f < 5 kHz. The characteristics of treated specimens were followed by voltammetry, Pb underpotential deposition for Ag, and Tl underpotential deposition for Cu, and scanning electron microscopy. For f < 50 Hz, the net electrochemical reaction involves the metal electrodissolution in the oxidation half‐cycle and metal electrodeposition accompanied by the development of a branched metal topography in the reduction half‐cycle. In contrast, for f > 50 Hz, the metal electrodissolution/electrodeposition cycling produces local faceting at each metal grain. The amount of soluble species found in the solution after a 20 h potential reversal technique increases as f is decreased. Under comparable conditions, both metals behave in a rather similar way, although Cu deposits are always more compact than those resulting from the application of the potential reversal.

Shape evolution during through‐mask electrochemical micromachining was investigated to study the problem of island formation caused by loss of electrical contact. A mathematical model was developed to predict shape evolution. Laplace's equation for potential was solved using the boundary element method to determine current distribution at the anode. The current distribution was combined with a moving boundary algorithm to predict the shape of the evolving cavity. The influence of the photoresist artwork dimensions on current distribution at the surface of an evolving feature was investigated. The island formation problem was identified as most likely to occur with a combination of low aspect ratio and low film thickness ratio. Elimination of the island formation problem is discussed.

All‐solid‐state photoelectrochemical cells have been constructed using films of a conducting polymer, poly(3‐octylthiophene), and a polymer electrolyte, amorphous polyethylene oxide, complexed with the redox couple. An open‐circuit voltage of 250 mV and a short‐circuit current of 0.04 μA/cm² were obtained with white light illumination at approximately one sun. During illumination, a cathodic photocurrent was observed, indicating that the neutral poly(3‐octylthiophene) behaves as a p‐type semiconductor. From the spectral response, the junction responsible for the photocurrent generation is between the conducting polymer and the solid polymer electrolyte. The open‐circuit voltage and short‐circuit current dependence on intensity and variation of open‐circuit voltage with redox couple concentration have also been studied.

A spike peak superimposed on the oxygen reduction wave, which usually is not evident under atmospheric conditions, was observed on gold electrodes in both and eutectic melts under pressurized conditions. It has been analyzed by cyclic voltammetry as a function of carbonate composition, total oxidant gas pressure, oxidant gas composition and cathode electrode material. The spike peak appears distinctly in melts, because its peak potential in is located 30 mV more negative than in . The charge represented by the spike peak was found to be about 5.1 μC/cm², corresponding to less than a monolayer quantity (θ ∼ 1/100). The spike current was proportional to the scan rate, indicating a surface redox reaction associated with the oxygen reduction process. Considering the electron‐transfer mechanism of oxygen reduction, we discuss this phenomenon as an electrochemical adsorption/desorption step of an intermediate oxygen species adsorbed on a bare gold surface.

A mathematical model is presented for the galvanostatic deposition of films in stagnant solutions. The objective is to quantify the anomalous deposition behavior reported previously in which the utilization of the electrochemically generated species decreased drastically as the concentration of increased beyond 0.1 M. For example as the concentration increased from 0.1 to 2.0 M, the deposition rate decreased by a factor of ten at 2.5 mA/cm². At this high ratio of concentration to current density, a comparison with Faraday's law indicates that only 10% of the species generated at the surface led to deposition. It has been proposed that the inefficient use of electrochemically generated species is due to the presence of as an intermediate in the deposition process. As the bulk concentration increases, the concentration of at the electrode surface increases. A high concentration of the intermediate results in an increase in the diffusion rate of the species away from the electrode surface and thus a decrease in the deposition rate. Here, this hypothesis is tested by developing a model which includes the generation of from the electrochemical reduction of nitrate to ammonia and the diffusion and migration of , and . The model predictions agree well with previously reported mass deposition data collected using an electrochemical quartz crystal microbalance at different currents and over a range of concentrations. The present work confirms the role that plays in the deposition process and provides a fundamental framework for understanding the electrochemical impregnation of nickel electrodes.

The synthesis of highly efficient, green‐emitting SrS:Mn phosphors is described in detail. Cathodoluminescent efficiencies of 110% relative to the commercial TV phosphor, ZnS:Cu, Au, Al, were routinely achieved. Phosphors with the highest luminous efficiencies were obtained with a manganese concentration of 0.15 mole percent which resulted in a saturated emission with a chromaticity of x = 0.325, y = 0.650. The ZnS:Cu, Au, Al standard had x = 0.305, y = 0.615.

An investigation has been made on the chemical stability of the cathode‐interconnect interface in solid oxide fuel cells. Lanthanum calcium chromite and lanthanum strontium manganite (a dense 10% A‐site deficient manganite, a porous 10% A‐site deficient one or a dense 1% A‐site deficient one) were placed between air and fuel (hydrogen/water) at a selected electrical current density. The electrical conductivity across the interfaces was slightly increased for 300 h. Changes in morphology, chemical composition, and phases were examined by scanning electron microscopy/energy dispersive x‐ray and x‐ray diffractometry analysis. The dense 10% A‐site deficient cathode gave rise to the precipitation of manganese oxide at the air‐side surface as well as at the interface. The porous cathode enhanced chemical reactions between lanthanum calcium chromite and lanthanum strontium manganite. The dense 1% A‐site deficient cathode was most stable. These phenomena have been thermodynamically analyzed in terms of (i) irreversible mass transfer under an oxygen potential gradient, (ii) changes of the stable composition region of the perovskite phases as a function of oxygen potential, and (iii) an enhancing effect of the liquid formation on reactions at interfaces.

We investigated proton‐induced transmittance modulation in amorphous films with methods of analysis including variable angle spectroscopic ellipsometry (VASE) and atomic force microscopy (AFM). We induced optical transition from the clear to the colored state by injecting electrons and protons into the film. A decrease in the index of refraction, accompanied by an associated increase in the extinction coefficient in the visible range of the spectrum was measured with VASE upon the transition. Physical modulation in terms of a change in the surface morphology was characterized. AFM measurements showed enlargement of a characteristic domed surface structure as the transition took place from the clear to the colored state without significant change in the rms surface roughness value.

Absorption and photostimulation bands of the aggregates of F centers exist near 900 nm in the near infrared region for (X = Cl, Br) crystals. This study reveals that there is no response time difference of photostimulated luminescence (PSL) under stimulation either by a near infrared light beam of 1.06 μm on the aggregated F centers or by a visible light beam on the simple F centers for , and . Under stimulation of 1.06 μm, the response time of PSL is 8.0 μs for , 0.75 μs for , and about 19 μs for , respectively, which agrees with their photoluminescence lifetime. This kind of F center aggregate is of interest for applications using a solid‐state semiconductor laser in the field of information storage.

alloy films were annealed in flowing at temperatures of 450 to 700°C. Ti segregates to the free surface to form TiN, leaving nearly pure Cu in the remaining metal film. Elastic recoil detection and Auger electron spectroscopy were applied to investigate the chemistry of the as‐formed nitride as a function of anneal temperature. The use of these two techniques in tandem offers a combination of standardless compositional determination, excellent mass and depth resolution, and chemical bonding information. The Ti:N ratio is nearly 1.0 for T ⩾ 550°C, and the nitride contains ∼ 6 atom percent O. The amount of nitrogen incorporated increases with temperature with an activation energy of 0.6 eV. A native Ti oxide remaining at the TiN/Cu interface suggests Ti is the dominant diffusing species during nitridation.

Although TiN and films are widely used in silicon wafer fabs, the possibility of titanium contamination adversely affecting device characteristics remains a great concern. In this study, ion implantation was used to determine the critical level of titanium which significantly reduces carrier lifetime in a silicon substrate. Possible contamination vectors (wet etch solutions and hot processes), the diffusion of titanium in silicon, and the effect of oxidation and cleaning of substrates intentionally contaminated with Ti have been investigated. With reasonable safeguards, titanium contamination is not a critical problem.

Copper decoration followed by transmission electron microscopy (TEM) observation is proposed for identifying defects in the buried oxides of silicon‐on‐insulator (SOI) substrates. This method comprises Si surface layer etching (i.e., exposure of the buried‐oxide surface), oxide‐defect location detection with copper decoration, and sample thinning for TEM observation and analysis. The advantage of copper decoration is that the electronic current needed for defect detection is very small, so the influence of the electronic current on the original oxide‐defect structure can be minimized. Defects observed are categorized into four groups from the viewpoint of size and shape.

High‐pressure cleaning is proposed for precleaning wafers used in low‐temperature silicon epitaxial growth to remove such contaminants as oxygen and carbon at the interface between the epitaxial layer and the substrate in ultrahigh‐vacuum/chemical vapor deposition. Increasing the partial pressure up to 1300 Pa during cleaning at 850°C was found to produce a smooth surface with the contaminants perfectly removed. To investigate the effects of roughness and contaminants in the wafer surface on the crystallinity of the epitaxial layer, p‐n diodes were fabricated in the epitaxial layer and their characteristics were measured. Annealing at an partial pressure of 120 Pa produced roughness and contaminants in the wafer surface causing a leakage current. Annealing at 1300 Pa produced smooth clean surfaces and no leakage current was observed. These results suggest that the electronic properties of epitaxial layers are influenced by contaminants and roughness in the wafer surface. High pressure cleaning reduces roughness and removes contaminants in the surface, resulting in good electronic properties in the epitaxial layer.

Atomic force microscopy has been used to quantitatively determine the surface roughness of silicon substrates as a function of processing and limitations to direct wafer bonding ability. This data is conveniently converted into a power spectrum creating a description of the topography which contains information about the amplitude and frequency of the surface undulations. Following initial characterization, the wafers were subjected to typical device manufacturing processes resulting in various degrees of increased roughness. An empirical correlation was developed between the roughness spectrum and bondability of (100) silicon wafers. Data on the roughening of wafers due to various standard integrated circuit processing steps were obtained and used to identify processes which promote wafer‐to‐wafer direct bonding. The fractal dimensions of the surfaces have been calculated and are discussed.

A new kind of inorganic adhesive for Si bonding has been developed by mixing polypermethylcyclosilazane (PMSZ), polycarbosilane, and silicon powders with xylene. Chemically and thermally stable bonded materials with more than 100 MPa of bonding strength are formed after heating at 1200°C in Ar. Plasticizer effect of PMSZ and the formation of porous structures after firing may cause the crack‐free bonding. Metal ion impurities in the adhesives can be reduced to render the materials suitable for semiconductor processing tools.

After reactive ion etching (RIE) in the presence of photoresist, the thermal oxide grown on the etched silicon surface was found to be significantly thinner than the oxide of monitor wafers. X‐ray photospectroscopy analysis of the surface revealed contamination by carbon, forming carbide (with C‒Si bonding). It was concluded that the carbon from the photoresist mask formed C‒Si bonding on the etched surface and inhibited subsequent oxidation. After RIE, drastic oxidation impairment and a high level of carbon contamination were also detected. Regardless of the origin of the carbon, C‒Si bonding was identified as a cause of the oxidation impairment. Even a few atomic percent of C‒Si bonding introduced on the silicon surface slows down the subsequent oxidation rate of the etched surface. On consumption of the thin C‒Si containing surface region, the oxidation rate quickly returns to a normal value. Using rapid thermal oxidation (RTO), several physical characteristics of the impaired thin oxide films were investigated. Boron diffusivity and HF etching rate of the oxide indicate formation of a singular layer about 15 Å thick near the interface. Interface roughness is unchanged with the C‒Si bonding present. The singular layer is suspected to reduce availability of the oxidant at the interface, thus suppressing the oxidation.

Several groups have reported on the use of for in situ cleaning of the silicon surface prior to the epitaxial growth of silicon. However, questions remain as to the extent to which the surface oxide can be removed from the silicon surface by . We report here our results from the study of an in situ‐based clean in the temperature range of 500 to 700°C with 10 to 100 ppm in . For comparison, a bake in situ clean was also examined in the temperature range of 600 to 950°C. The results showed that surface oxide could not be removed by to an adequate level before excessive Ge deposits which causes epitaxial stacking fault. A 120 s bake at 850°C of an HF dipped surface results in no detectable oxygen based on secondary ion mass spectroscopy. Also, we demonstrate that the quality of the epitaxial layer grown after the clean is not necessarily a good indication of the effectiveness of the clean when the surface oxygen coverage is below a certain value. We conclude that due to the competition between the surface oxide removal and the Ge deposition, ‐based clean is not suitable for high quality Si epitaxial growth by chemical vapor deposition techniques.

Ohmic contacts on diamond were fabricated using a Ti/Pt/Au metallization scheme and two transmission line model masks. The double mask system is used to isolate the Ti by surrounding it with Pt. Pt is expected to prevent Ti diffusion either to the contact surface or along the diamond surface during annealing. In this study we found that this system of masks was successful in preventing the Ti diffusion as revealed by Auger analysis on the diamond and contact surfaces. An Auger depth profile revealed that the Ti was confined to the diamond/contact interfacial region, and was most likely combined with Pt.

Clarification of the complex chemical processes governing polarized wide‐range air‐to‐fuel‐ratio sensors should enable one to determine characteristics of the system geometry and physical properties necessary for successful sensor operation. To develop a mathematical description of these sensors, we have combined well‐established theories for electron, electron‐hole, and oxygen‐vacancy transport within yttria‐stabilized zirconia with transport equations that apply to gaseous diffusion within the dense, porous layer that covers the solid electrolyte. Along the interface between the solid electrolyte and the porous layer, a thin platinum electrode catalyzes various chemical reactions and an electrochemical charge‐transfer reaction. The model equations have been simplified using an asymptotic analysis which is valid over a broad range of conditions of practical interest; in particular, it is valid for all simulations presented in this work. Model calculations are shown to compare well with experimental data, and acceptable ranges for the four dimensionless groups that dictate sensor performance are considered.