Showing papers in "Journal of The Electrochemical Society in 1991"

Polymer Electrolyte Fuel Cell Model

Abstract: We present here an isothermal, one-dimensional, steady-state model for a complete polymer electrolyte fuel cell (PEFC) with a 117 Nation | membrane. In this model we employ water diffusion coefficients electro-osmotic drag coefficients, water sorption isotherms, and membrane conductivities, all measured in our laboratory as functions of membrane water content. The model pre.dicts a net-water-per-proton flux ratio of 0.2 H20/H § under typical operating conditions, which is much less than the measured electro-osmotic drag coefficient for a fully hydrated membrane. It also predicts an increase in membrane resistance with increased current density and demonstrates the great advantage of a thinner membrane in alleviating this resistance problem. Both of these predictions were verified experimentally under certain conditions.

Transition from “Supercapacitor” to “Battery” Behavior in Electrochemical Energy Storage

Abstract: The storage of electrochemical energy in battery, "supercapacitor," and double‐layer capacitor devices is considered. A comparison of the mechanisms and performance of such systems enables their essential features to be recognized and distinguished, and the conditions for transition between supercapacitor and "battery" behavior to be characterized. Supercapacitor systems based on two‐dimensional underpotential deposition reactions are highly reversible and their behavior arises from the pseudocapacitance associated with potential‐dependence of two‐dimensional coverage of electroactive adatoms on an electrode substrate surface. Such capacitance can be 10–100 times the double‐layer capacitance of the same electrode area. An essential fundamental difference from battery behavior arises because, in such systems, the chemical and associated electrode potentials are a continuous function of degree of charge, unlike the thermodynamic behavior of single‐phase battery reactants. Quasi‐two‐dimensional systems, such as hyperextended hydrous , also exhibit large pseudocapacitance which, in this case, is associated with a sequence of redox processes that are highly reversible. Such oxide redox systems give rise to the best supercapacitor behavior and capacitances of farads per gram can be achieved. Other examples are the conducting polymer electrodes and Li intercalate systems. These systems provide examples of the transition between battery and supercapacitor behavior arising from a range of degrees of oxidation/ reduction that arise over an appreciable range of potentials. The impedance behavior of an supercapacitor is illustrated but is far from that expected for an electrostatic capacitor.

The Spinel Phase of LiMn2 O 4 as a Cathode in Secondary Lithium Cells

Abstract: The electrochemical properties of and were studied for different conditions of sample preparation and different degrees of cation substitution . In the voltage range 3.5–4.5 V, cells of either spinel or (made by leaching the Li from ) reversibly insert 0.4 Li per Mn at an average voltage of 4.1 V, leading to an energy density of 480 Wh/kg of cathode. Cells cycled 50 times lost less than 10% of their initial capacity, suggesting that this material could be used instead of or as the cathode in the new generation of "rocking chair batteries." Replacing Mn with cations of valence 2 (Ni, Zn) or 3 (Fe) reduces the amount of Mn+3 and correspondingly reduces the capacity of the cells at 4.1 V, but does not affect their cycling performance.

Rechargeable LiNiO2 / Carbon Cells

Abstract: Rechargeable cells can be made using two different intercalation compounds, in which the chemical potential of the intercalant differs by several eV, for the electrodes. In this paper, the authors discuss the factors that play a role in the selection of appropriate lithium intercalation compounds for such cells. For ease of cell assembly the cathode should be stable in air when it is fully intercalated, like LiNiO{sub 2}. For the anode, the chemical potential of the intercalated Li should be close to that of Li metal, like it is in Li{sub x}C{sub 6}. The authors discuss the intercalation of Li in LiNiO{sub 2} and then in petroleum coke. Then, the authors show that LiNiO{sub 2}/coke cells have high energy density, long cycle life, excellent high-temperature performance, low self-discharge rates, can be repeatedly discharged to zero volts without damage, and are easily fabricated. In the authors' opinion this type of cell shows far more promise for widespread applications than traditional secondary Li cells using metallic Li anodes.

Chemical‐Mechanical Polishing for Fabricating Patterned W Metal Features as Chip Interconnects

Abstract: Interconnect features of W metal, recessed in an dielectric, can be formed using a novel chemical‐mechanical polish process. Mechanical action, to continually disrupt a surface passivating film on W, and chemical action, to remove W, appear to be requirements for workability of the process. A trial process chemistry using a ferricyanide etchant is described. Removal of the W is discussed in terms of competition between an etching reaction which dissolves W and a passivation reaction to reform on the surface of the W. This novel processing technology is compared with earlier methods of fabricating metal interconnect structures.

The Secondary Alkaline Zinc Electrode

Abstract: Zinc is the most commonly used battery electrode, and zinc primary batteries have found numerous applications. The zinc electrode is electrochemically reversible in alkaline electrolytes, and there is a strong incentive to develop a practical secondary battery based on this metal. However, secondary batteries that use zinc electrodes typically exhibit short lifetimes, because of problems with zinc material redistribution and undesirable zinc morphologies that form during recharge. There has been a worldwide effort to develop a long‐lived secondary alkaline zinc electrode, and marked improvements in cell lifetimes have resulted. This article reviews these efforts, paying particular attention to research and development during the period 1975–1990.

Li Metal‐Free Rechargeable Batteries Based on Li1 + x Mn2 O 4 Cathodes ( 0 ≤ x ≤ 1 ) and Carbon Anodes

Abstract: We show that the spinel , can also be used as the cathode in rechargeable rocking‐chair batteries based on lithium intercalation anodes (carbon, either graphite or petroleum coke). At room temperature, such cells show promising cycle life, an average open‐circuit voltage of 3.7 V and a specific energy of 250 Wh/kg of electrode materials . In addition, we report a novel easily reproducible solution technique for synthesizing , at low temperatures (<100°C), using as a mild reducing agent. The cycling behavior of rocking‐chair cells using this lithiated phase as the starting cathode is presented. appears to be a promising practical "air stable" Li‐bearing cathode for rocking‐chair‐type rechargeable cells.

Double-Phase Hydride Forming Compounds: A New Class of Highly Electrocatalytic Materials

Abstract: A new class of materials is proposed to improve the electrocatalytic activity of hydride forming intermetallic compounds of the ABs-type without making use of highly electrocatalytic precious metals like Pd or Pt. These materials, denoted as ABe.5, consist of two different crystallographic phases: the bulk phase, still responsible for hydrogen storage, is formed by the corrosion-resistant multicomponent "standard alloy" based on LaNis; and a second phase, homogeneously decorating the surface of the bulk-phase particles, provides for the extremely fast electrochemical hydrogen reaction. The composition of the second-phase alloy is such that synergism in the electrocatalysis occurs. A simple metallurgical method of producing double-phase materials is described. Various analytical techniques such as EPMA and x-ray diffraction are employed to characterize the solids produced. It is shown that the kinetics of the charge-transfer reaction can be characterized electrochemically by the overall exchange current. In accordance with the Brewer-Engel theory, MoCo3 precipitates are found to be highly electrocatalytic, which is reflected in an increase of the overall exchange current from 190 mA. g-1 for the single-phase AB5 compound to 588 mA. g-L As a consequence very high discharge efficiencies are accomplished with these MoCo3-based powder electrodes, even under extreme conditions: at 0~ the efficiency is improved from 34 to 90%.

Composite Polymer Electrolytes

Abstract: The characteristics of composite polymer electrolytes obtained by adding powders of a stable ceramic material having a regular spherical shape with a mean diameter of less than 1 μm, to a poly(ethylene oxide)‐lithium perchlorate complex, are described in terms recrystallization, conductivity, and ion transport number. The addition of the finely dispersed ceramic powder greatly improves the morphological and the electrochemical properties of the polymer electrolytes.

Copper Corrosion With and Without Inhibitors

Abstract: The utility of copper interconnects may ultimately depend on the ability to protect copper from corrosion. We have studied the capacity of lH-benzotriazole (1H-BTA) to provide a protective and stable surface film able to withstand harsh chemical and thermal environments. The film was characterized with electrochemical techniques, in situ ellipsometry, ex situ time-of-flight static secondary ion mass spectrometry, high-temperature mass spectrometry, and accelerated temperature and humidity tests. Several important passivating film properties (thickness, degree of polymerization, thermal stability, corrosion resistance) depend critically on the details of the film preparation conditions. The best corrosion protection is offered by the thin film formed on an oxidized Cu surface. This film has also shown the slowest growth kinetics and the highest degree of polymerization in the Cu-BTA structure. With more aggressive performance requirements for multilevel interconnections, higher conductivity metals, such as copper, are finding their way into a number of products. Copper is a relatively noble metal. Nevertheless, it reacts easily in ordinary, oxygen containing, environments (1). In view of the limited passivation offered by Cu-oxides, we have studied the effectiveness of organic azoles, such as lH-benzotriazole (1H-BTA), as a general method of controlling Cu degradation. For over 40 years 1H-BTA has been successfully used in the prevention of atmospheric Cu corrosion (2), in packaging, storage and transport, in the reduction of thermal oxidation and, in particular, in the protection of copper under immersed conditions (Ref. (3) and references within). The relevant literature is abundant but not unified in its teaching about bonding, thickness, composition and structure of the resulting film and the nature of its protection. Recent work from our laboratory, based on a combination of electrochemical, ellipsometric, and XPS data, has shown that the spontaneous reaction of Cu and 1H-BTA under a variety of conditions leads to the formation of Cu-BTA (4, 5), with copper being Cu +1 , as reported elsewhere (6-12). The formation of a Cu-N bond was clearly identified from the Cu LMM Auger lines. The film was formed both on an oxidized and an oxide-free Cu surface, in contrast to reports suggesting that the presence of Cu2O is a prerequisite for the buildup of CuBTA (8, 14). The thickness of the film was determined to be 0.5-4 nm in the pH range from 3 to 12, reaching 25 nm only under harsh conditions, i.e., in pH 2. Several recent studies of ultrahigh vacuum deposited 1H-BTA have indeed detected 1H-BTA adsorption on clean Cu metal (14-16). An electrochemical equivalent of such a film was formed in our laboratory at Cu 0 kept in

Application of Chemical Mechanical Polishing to the Fabrication of VLSI Circuit Interconnections

Abstract: Application of the chemical mechanical polishing of silicon dioxide used as the interlevel dielectric in the manufacture of VLSI chips has led to the development of a relatively simple process for fabrication of the device wiring on such chips. The polishing process is used to remove the interlevel dielectric from the tops of interconnect studs and produce a planarized surface ready for the next level of wiring. The characteristics of this polishing process were studied on both blanket films of oxide and on wafers with device topography. Empirical relationships were found, and the results applied to device manufacture, resulting in process simplification while increasing chip reliability and yield.

Quartz Crystal Microbalance Study: Ionic Motion Across Conducting Polymers

Abstract: In situ monitoring of mass change was performed during electrochemical growth and redox cycling of a conducting polymer(polypyrrole) on a quartz crystal microbalance. For the polypyrrole films grown with large polymeric anions(poly(4-styrenesulfonate) and polyvinylsulfonate), mostly cations and solvent molecules were inserted and removed to compensate charge in polypyrrole. The films formed with medium-sized anions (tosylate) showed both apparent anion and cation motion during the redox process. The films prepared in the presence of small anions (ClO 4 − and BF 4 − ) showed mostly anion motion, but apparent cation motion also became significant for higher oxidation and/or reduction state

Study of the Kinetics of Hydrogen Evolution Reaction on Nickel‐Zinc Alloy Electrodes

Abstract: The mechanism and kinetics of the hydrogen evolution reaction were studied in on nickel‐zinc alloy electrodes prepared by electrodeposition at controlled potential A series of electrodes containing 70 to 28% Ni was prepared Before the measurements, zinc was leached in alkaline solution Using the ac impedance technique, it was found that the reaction proceeds via the Volmer‐Heyrovsky mechanism, and the kinetic parameters of the process were determined With a decrease in the nickel content, the electrode becomes more active, and an increase in the real surface area is observed The surface morphology was studied using SEM and optical microscopy

Investigations of the O 2 Reduction Reaction at the Platinum/Nafion® Interface Using a Solid‐State Electrochemical Cell

Abstract: This paper reports on research in solid polymer electrolyte fuel cells gaining momentum because of the prospects of attaining high energy efficiencies and power densities essential for transportation and space applications. The most advanced solid polymer electrolytes for these fuel cells are the perfluorosulfonate ionomers (PFSIs), such as Du Pont's Nafion and the Dow PFSIs. The high oxygen solubility, chemical stability, proton conductivity and permselectivity exhibited by Nafion and the Dow PFSIs make them ideal candidates as electrolytes for fuel cells. Furthermore, the minimal anion adsorption on the Dow PFSIs make them ideal candidates as electrolytes for fuel cells. Furthermore, the minimal anion adsorption on electrodes from fluorinated acids enhances oxygen reduction kinetics. The objectives of this work were to determine the concentration and diffusion coefficient of oxygen in Nafion, and the electrode kinetic parameters for the reduction of oxygen at the Pt/Nafion interface under totally solid-state conditions (i.e., no contacting liquid electrolyte phase). Cyclic voltammetric and potentiostatic transient measurements were made at the Pt/Nafion interface. From cyclic voltammetric measurements, the purity of Nafion was ascertained and the roughness factor of the electrode was calculated. The slow sweep experiments yielded the Tafel parameters for oxygen reduction. From the two-section Tafelmore » plot, the calculated exchange current densities were found to be higher than those obtained at any other Pt/acid interface. From an analysis of the potentiostatic transients, the calculated values of oxygen solubility and diffusion coefficient in Nafion were higher than previously reported. These differences in mass-transfer data were attributed to differences in water content of the Nafion membrane.« less

Silicon‐On‐Insulator by Wafer Bonding: A Review

Abstract: Various approaches to wafer bonding technology are reviewed. Bonding kinetics are discussed as well as different mechanical and chemical thinning techniques. The structural and electrical qualities of state‐of‐the‐art bonded SOI silicon films and devices built in them are detailed. Problems faced by this technology are evaluated.

Electrochemical Reduction of CO 2 at Intentionally Oxidized Copper Electrodes

Abstract: We observed reduction to at various oxidized copper electrodes at 22°C. The electrode types included anodized Cu foil, Cu foil thermally oxidized in air, and air‐oxidized Cu electrodeposited on anodized or air‐oxidized Ti foil. The highest rates to date, (geometrical area), were found using anodized Cu in ,, and −1.9 V (SCE). Faradaic yields for depended on the current and reached about 240%. The onset potential for formation was near −0.4 V (SCE). Hydrogen gas and small amounts of were also formed. A mechanism is proposed involving chemical reduction steps up to , followed by three hydrogenation steps to . Absorption of oxygen by Cum is implied. The stability of semiconductor films is discussed in terms of breakdown currents due to band‐to‐band tunneling. The major impurities deposited on the Cu electrode during electrolysis are Zn and Fe at several atom percent each. An 8% level of Cl was found, originating from the etch used to remove the native oxide before thermal oxidation.

Design of Alloy Electrocatalysts for CO 2 Reduction III . The Selective and Reversible Reduction of on Cu Alloy Electrodes

Abstract: Many Cu alloys have been studied for electrocatalytic activity of reduction in aqueous solution. Anomalously low overpotentials with highly selective Cu alloy catalysts have been seen for the reduction of to, , or . Cu‐Ni alloys produce and selectively at reversible potentials and Cu‐Sn and Cu‐Pb produce and with an enhanced reaction rate at the reversible potentials of formation. Other alloy catalysts such as Cu‐Zn, Cu‐Cd, or Cu‐Ag also exhibit behaviors distinct from those of the elemental metals. The results reported here indicate further possibilities for the development of powerful new electrocatalysts for the reduction of .

The ZnGa2 O 4 Phosphor for Low‐Voltage Blue Cathodoluminescence

Abstract: This paper reports on the ZnCa{sub 2}O{sub 4} phosphor investigated for its application to vacuum fluorescent displays (VFDs) utilizing low-voltage cathodoluminescence. It is expected that this oxide phosphor does not cause damage to filaments in VFD's, while it is a serious problem for conventional sulfide phosphors. This phosphor shows blue luminescence with a spectral peak at with 470 nm and a chromaticity at X = 0.170 and Y = 0.130. A luminous efficiency of 0.7 lm/W has been obtained, when the VFD with this phosphor is operated at 30 V dc. The results of high-temperature operating life test have proven the excellent stability of VFDs utilizing this phosphor.

Scanning Electrochemical Microscopy VII . Effect of Heterogeneous Electron‐Transfer Rate at the Substrate on the Tip Feedback Current

Abstract: The dependence of the SECM feedback current on finite heterogeneous electron-transfer kinetics at the substrate electrode was examined by experimental studies of the reduction of Fe(III) in 1M H 2 SO 4 at a Pt tip over a biased glassy-carbon substrate

A Model of Silicon Carbide Chemical Vapor Deposition

Abstract: This paper presents a model describing the interacting gas phase and surface chemistry present during the steady-state chemical vapor deposition (CVD) of silicon carbide (SiC). In this work, the authors treat the case of steady-state deposition of SiC from silane (SiH{sub 4}) and propane (C{sub 3}H{sub 8}) mixtures in hydrogen carrier gas at one atmosphere pressure. Epitaxial deposition is assumed to occur on a pre-existing epitaxial silicon carbide crystal. Pyrolysis of SiH{sub 4} and C{sub 3}H{sub 8} is modeled by 83 elementary gas-phase reactions. A set of 36 reactions of gas- phase species with the surface is used to simulate the deposition process. Rates for the gas/surface reactions were obtained from experimental measurements of sticking coefficients in the literature and theoretical estimates. The authors' results represent the first simulation of a silicon carbide deposition process that includes detailed description of both the gas phase and surface reactions. The chemical reaction mechanism is also combined with a model of a rotating disk reactor (RDR), which is a convenient way to study the interaction of chemical reactions with fluid mechanics. Transport of species from the gas to the surface is accounted for using multicomponent transport properties. Predictions of deposition rates as amore » function of susceptor temperature, disk rotation rate, and reactant partial pressure are presented. In addition, velocity, temperature, and concentration profiles normal to the heated disk for 41 gas-phase species are determined using reactor conditions typical of epitaxial silicon carbide deposition on silicon substrates.« less

Direct In Situ Evidence for Proton/Anion Exchange in Polyaniline Films by Means of Probe Beam Deflection

Abstract: Probe beam deflection (PBD) was used to monitor the ion exchange between polymer film and bulk electrolyte during the redox reaction in polyaniline in aqueous electrolyte (HCl, HClO 4 , H 2 SO 4 ). The PBD results clearly show that protons as well as anions are exchanged during the first oxidation process

The Electrochemical Behavior of Calcium Electrodes in a Few Organic Electrolytes

Abstract: The electrochemical behavior of calcium electrodes in a few important organic electrolyte has been investigated. The solvents used included acetonitrile, tetrahydrofuran, γ‐butyrolactone, and propylene carbonate, and the salts included, , , and tetrabutyl ammonium salts (, ). Various techniques, including cyclic voltammetry, Fourier transform infrared spectroscopy, scanning electron microscopy, and x‐ray microanalysis were used in order to characterize discharge processes of calcium anodes in the various systems, and to correlate them with the surface chemistry and morphology of calcium in the electrolyte solutions. Some important surface species formed in the above systems were identified. It was found that, as with lithium, discharge of calcium anodes is surface film‐controlled. In contrast to lithium systems, however, calcium deposition in these solvent systems, either on calcium or noble metal electrodes, is impossible, due to the nature of the surface films formed.

In Situ Fourier‐Transform Electromodulated Infrared Study of Porous Silicon Formation: Evidence for Solvent Effects on the Vibrational Linewidths

Abstract: We report on an experimental investigation of porous silicon layer (PSL) formation and silicon/hydrofluoric acid interfaces, using internal‐reflection Fourier‐transform infrared spectroscopy and Fourier‐transform electrochemically modulated infrared spectroscopy. Low‐doping Si samples (, resistivity ≈4 Ω cm) have been used for PSL growing. The in situ electromodulated spectra during the formation of PSL and the transmission spectra of the PSL in contact with the electrolyte contain only a broad band at around 2100 cm−1, whereas the transmission spectra of the dried PSL give rise to three sharp peaks at around 2085, 2115, and 2140 cm−1. All these vibrational peaks are ascribed to chemical species. The broadening of the spectrum in the former cases has been found to be due to interaction of species with the solvent. Under cathodic conditions—either for n‐Si in the dark or for p‐Si with illumination—the spectrum of the Si/HF interface exhibits three sharp peaks, characteristic of a surface in contact with a gas phase. This is attributed to the presence of hydrogen gas bubbles on the Si surface. It is observed that the Si surface is covered with Si‒H bonds in solution at all the applied potentials and current densities. An attempt has been made to detect intermediate species such as in the process of anodic dissolution of Si in , and it is concluded that if these species exist at all, their lifetime is shorter than 0.3 ms.

Electrolytic ZrO2 Coatings I. Electrochemical Aspects

Abstract: coatings were deposited on graphite and titanium from an aqueous solution based on a water‐soluble precursor. A two‐step mechanism is suggested for the formation: generation of hydroxyl ions (OH−) at the cathodic substrate by reduction of and dissolved , and then reaction of the hydroxyl ions with zirconyl ions present in the solution to form the hydroxide , which in turn decomposes on drying to yield zirconia . Faradaic efficiencies of 20–50% were found, attributable to reduction reactions that do not produce hydroxyl ions, as well as to formation of the hydroxide at sites removed from the cathodic substrate due to diffusion of the hydroxyl ions. The effects of current density, time, and hydrodynamic conditions on coating weight, cell voltage, temperature, and pH of the solution were studied.

Reaction Kinetics and Microstructure of the Solid Oxide Fuel Cells Air Electrode La0.6Ca0.4MnO3 / YSZ

Abstract: This paper reports that in order to make clear the relationship between the microstructure of the porous oxide layer and electrochemical properties of air electrodes of solid oxide fuel cells, air/porous oxide/yttria stabilized zirconia, complex-impedance and cathodic polarization were measured on the air/La{sub 0.6}Ca{sub 0.4}MnO{sub 3}/YSZ electrodes at 900-1000{degrees} C with the porous La{sub 0.6}Ca{sub 0.4}MnO{sub 3} layers of different morphology prepared by different method and different firing temperatures. From the SEM images of the cross section of the interface, the length of the air/La{sub 0.6}Ca{sub 0.4}MnO{sub 3}/YSZ triple-phase boundary and the area of the closely contacted La{sub 0.6}Ca{sub 0.4}MnO{sub 3}-particles/YSZ interface were estimated. It was shown that the reaction rate was essentially proportional to the length of the triple-phase boundary, while the electrode capacitance was largely proportional to the closely contact area.

Application of Mixed Oxide Capacitor to the Selective Carbon Dioxide Sensor: I . Measurement of Carbon Dioxide Sensing Characteristics

Abstract: Oxide capacitors consisting of and an oxide are studied as a sensor for detection. Although the capacitance change of on exposure to was small, it was greatly enhanced by the combination with . Sensitivity to and optimum operating temperature were strongly dependent on the oxide combined with . The element which contains basic oxides such as and , is highly sensitive to , but the operating temperature exceeded 1073 K. Among the elements investigated in this study, exhibited the highest sensitivity to . selectively responded to , and this element could distinguish the concentrations up to 6%. On the other hand, the capacitance of decreased linearly with increasing concentration up to 20%. Mixed oxide capacitors of and , therefore, are suitable for sensing at the concentration range of hundreds of ppm, and at a percentage level, respectively.

Calibration of the Electrochemical Quartz Crystal Microbalance

Abstract: The quartz crystal microbalance seems to be a very usefui tool in electrochemical studies, but, up to now, no attempts have been made to calibrate the microbalance under electrochemical conditions. The aim of this paper is to determine not only the average sensitivity for different active areas but also the differential sensitivity as a function of the radial position of a localized change of mass. In this way, for homogeneous mass perturbation, it is possible to calculate the change of mass (Am) from the frequency shift (AJ) for different active areas by taking into account the average sensitivity value. In the case of localized Am, the differential sensitivity value allows one to calculate hm from hfif the position of the event is known. The calibration procedure was made for an AT-6 MHz quartz crystal. Quartz crystals are important sensing devices in liquid phase. They can be used to monitor changes in electrode mass (1-3) or changes in the liquid properties (4, 5). In an electrochemical process, a shift of the value of the quartz crystal resonance frequency (fo) can be attributed to a change in mass (Am) of the electrode, provided that the true relationship between hf and Am is known. The problem of the sensitivity of the quartz crystal microbalance (QCM) has been already dealt with in the air (6-8). The differential sensitivity of the QCM has been calculated from the local damage produced in a thin polymer film by an ion beam sputtering. In the liquid phase the distribution of the vibration amplitude of the quartz crystal has been investigated by putting a tungsten wire probe in contact with the quartz crystal to provoke a change in frequency (9, 10). The results obtained in both liquid and gas phases are rather similar, in spite of the properties of liquid phase which extend the vibration of the quartz crystal even beyond the active region defined by the metal deposit. These works show the complexity of the system and that the boundary conditions used for the derivation of Sauerbrey's equation (11, 12) are not always fulfilled. The problem of the QCM calibration has been extensively studied in air. on the contrary, despite the wide use of the QCM in electrochemistry, the calibration procedure of this technique in electrochemical conditions is not depicted in the literature. The aim of this work is to calibrate the electrochemical quartz crystal microbalance (EQCM), not only in the case where hm is uniformly spread on the active electrode surface, but also for localized mass changes. The last case is very relevant to all electrochemical phenomena which produce a change of mass on a small area, e.g., in localized corrosion or gaseous bubble evolution. The general case where the mass change is continuously but nonuniformly distributed across the surface is not addressed in the paper.

Novel Solid Redox Polymerization Electrodes All‐Solid‐State, Thin‐Film, Rechargeable Lithium Batteries

Abstract: This paper reports that lithium batteries using solid redox polymerization electrodes (SRPEs) maintain the inherent advantages of all-solid-state, thin-film systems while overcoming some of the limitations of using intercalation compounds as positive electrode. Laboratory Li/PEO/SRPE cells have demonstrated higher power capability, energy density, and capacity utilization than analogous Li/PEO/TiS{sub 2} cells. One of the Li/PEO/SRPE cells has achieved 350 cycles from 50 to 93{degrees} C with a sustained energy density of 160 Wh/kg (190 Wh/1, power density of 120 W/kg (140 W/1), and 40-75% capacity utilization of the polymerization electrode. At 100{degrees}C, power densities of over 1800 W/kg (2200 W/1) at energy densities of 140 Wh/kg (170 Wh/1) have been achieved with up to 96% utilization of cathode capacity. At ambient temperatures (35{degrees} C), the cells can be discharged at a current density of 250 {mu}a/cm{sup 2}, achieving a film capacity of 0.5 C/cm{sup 2}.