Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CATHODE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources
PubMed2003

Theoretical calculation of product contents: battery and cathode ray tube examples.

Most product environmental assessments are based on manufacturer-supplied data on the material content of the product. This paper explores the potential for the material content of key components to be estimated with theoretical calculations. Two examples, the amount of cadmium in a nickel-cadmium battery and the amount of lead in a TV or computer CRT monitor, are developed. Both an upper and a lower limit on the amount of cadmium in a nickel-cadmium battery are calculated on the basis of the battery's chemical reaction. The amount of lead shielding needed in a TV or CRT computer monitor is estimated on the basis of the potential difference through which electrons are accelerated and the absorption length of photons in lead. Such calculations can be used as benchmarks in product environmental assessments, providing validation of manufacturer-supplied data and providing insight into the composition and design of products.

Benchmarking↗
PubMed2001

(2)H MAS NMR studies of the manganese dioxide tunnel structures and hydroxides used as cathode materials in primary batteries.

Variable-temperature (2)H MAS NMR spectroscopy was used to investigate the local environments and mobility of deuterons in the manganese dioxide tunnel structures. Five systems were investigated: electrolytic manganese dioxide (EMD), the model compounds groutite and manganite, and deuterium intercalated ramsdellite and pyrolusite. Ruetschi deuterons, located in the cation vacancy sites in EMD, were detected by NMR and give rise to a resonance at 150 ppm at room temperature. These deuterons are rigid on the (2)H MAS NMR time scale (i.e., the correlation time for motion, tau(c), is >10(-3) s) at room temperature, but start to become mobile above 150 degrees C. No Coleman protons (in the so-called 1 x 1 and 1 x 2 tunnels in EMD) were observed. Much larger (2)H NMR hyperfine shifts of approximately 300 and approximately 415 ppm were observed for the deuterons in the tunnel structures of manganite and groutite, which could be explained by considering the different bonding arrangements for deuterons in the 1 x 1 and 1 x 2 tunnels. The smaller shift of the EMD deuterons was primarily ascribed to the smaller number of manganese ions in the deuterium local coordination sphere. Experiments performed as a function of intercalation level for ramsdellite suggest that the 1 x 1 tunnels are more readily intercalated in highly defective structures. The almost identical shifts seen as a function of intercalation level for deuterons in both 1 x 1 and 1 x 2 tunnels are consistent with the localization of the e(g) electrons near the intercalated deuterium atoms. A Curie-Weiss-like temperature dependence for the hyperfine shifts of EMD and groutite was observed with temperature, but very little change in the shift of the manganite deuterons was observed, consistent with the strong antiferromagnetic correlations that exist above the Néel temperature for this compound. These different temperature dependences could be used to identify manganite-like domains within the sample of groutite, which could not be detected by X-ray diffraction.

Journal Article↗
PubMed2002

An oxygen cathode operating in a physiological solution.

We report the electroreduction of O(2) to water under physiological conditions (pH 7.4, 0.15 M NaCl, 37.5 degrees C) at a current density of 5 mA cm(-2) and at a potential only 0.18 V reducing versus that of the reversible O(2)/H(2)O electrode at pH 7.4. The immobilized electrocatalyst enabling the reduction is the electrostatic adduct of bilirubin oxidase from Myrothecium verrucaria, a polyanion at pH >4.1, and the polycationic redox copolymer of polyacrylamide and poly (N-vinylimidazole) complexed with [Os (4,4'-dichloro-2,2'-bipyridine)(2)Cl](+/2+), cross-linked on carbon cloth. The current density of the rotating electrodes was O(2) transport limited up to 8.8 mA cm(-2); their kinetic limit was reached at 9.1 mA cm(-2). The operational life of the electrodes depended on their angular velocity, which defined not only the current density but also the mechanical shear stress stripping the electrocatalyst. When the electrodes were rotated at 300 rpm and were poised at -256 mV versus the potential of the reversible O(2)/H(2)O electrode, their 2.4 mA cm(-2) initial current density decreased to 1.3 mA cm(-2) after 6 days of continuous operation at 37.5 degrees C.

Animals↗
PubMed2005

Microwave solid-state synthesis of LiV(3)O(8) as cathode material for lithium batteries.

A novel and economical microwave route has been developed for the synthesis of electrochemically active LiV(3)O(8) material by using a domestic microwave oven. The heating behavior of the designed reaction system guided the preparation of LiV(3)O(8) at a suitable irradiation power (i.e. heating rate), reaction time, and temperature. At the lowest irradiation power, the conversion fraction of reactants was mainly controlled by reaction temperature. Characterization results of X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy, scanning (SEM) and transmission (TEM) electron microscopy, and BET surface areas indicated that the phases of samples prepared by microwave and traditional methods were in good agreement. Nevertheless, the crystallinity, crystallite configuration, and morphology of the samples were different, and were affected by the irradiation time and power. A floppy superposition structure of nanosheets (the size of one nanosheet was about 4.5 microm x 1.2 microm x 3 nm) was preferentially grown at the lowest irradiation power, and this effect on structure was more in evidence as the nanorods formed at the highest irradiation power. Electrochemical studies on ionic conductivity, electrochemical impedance spectroscopy (EIS), and charge-discharge capacity were carried out. It was found that the conductivity, first discharge capacity, and cycle performances of the samples were affected by the crystal size, crystallinity, and crystal configuration and defection concentration. The sample L30 prepared at the lowest irradiation power and the shortest time (30 min) showed the highest discharge capacity (335 mAh/g), but its discharge capacity decreased rapidly. By comparison, the sample L100 had a floppy superposition structure of nanosheets and a high surface area, provided a good two-dimensional channel for the transition of Li(+) ions, and was stable during the intercalation/deintercalation process of Li(+) ions, therefore the high ionic conductivity, high discharge capacity, and good cycle performance were presented. The relationship between the electrochemical properties and the irradiation power was discussed.

Journal Article↗
PubMed2005

Madelung-Buckingham model as applied to the prediction of voltage, crystal volume changes, and ordering phenomena in spinel-type cathodes for lithium batteries.

Using a Madelung-Buckingham model, we study Li(x)()Mn(2)O(4) and its fluorine-substituted analogue to compute their voltages, lattice volume changes, and ordering phenomena during charge/discharge. The interactions included are the long-range Coulombic, short-range electron-electron repulsion, and the van der Waals. The voltage of the fluorine-substituted spinel is found to be slightly less than that of the unsubstituted. However, the former undergoes a greater crystal volume change than the latter during intercalation and de-intercalation. Investigations of lithium sublattice ordering in this system indicates that during intercalation lithium starts filling exclusively into one sublattice until x = 0.5, and only from x = 0.5 the other sublattice is filled up to x = 1. The models are compared with quantum ab initio and experimental results.

Journal Article↗
PubMed2005

Cathodic reduction of bisulfite and sulfur dioxide in aqueous solutions on copper electrodes: an electrochemical ESR study.

The electrochemical reduction of aqueous solutions of sulfite under acidic conditions on copper electrodes is reported, and a mechanism is proposed. Cyclic voltammetry at a copper disk suggests the operation of two reduction processes, the dominant process depending on solution pH. At very low pH (0-2), sulfur dioxide is reduced in a two-electron, two-proton reaction, but at higher pH (2-5), bisulfite is the electroactive species, being reduced by a single electron to ultimately yield the SO2*- radical anion. Simultaneous electrochemical electron spin resonance (ESR) measurements using a tubular flow cell support this proposal, and suggest that the radical anion is in equilibrium with dithionite, which is found to decay at low pH. Digisim modeling of the system is shown to be consistent with this mechanism over the experimental pH range.

Journal Article↗
PubMed2006

Environmentally friendly chemical route to vanadium oxide single-crystalline nanobelts as a cathode material for lithium-ion batteries.

Orthorhombic V(2)O(5) single-crystalline nanobelts with widths of 100-300 nm, thicknesses of 30-40 nm, and lengths up to tens of micrometers have been synthesized on a large scale in a hydrogen peroxide aqueous solution by an environmentally friendly chemical route. Such nanobelts grow along the direction of [010]. The influence of the reaction time on the crystal structures and morphologies of the resulting products are investigated. A probable dehydration-recrystallization-cleavage mechanism for the formation of V(2)O(5) nanobelts is proposed. The experiments demonstrate that the use of a nanosized belt-like structure can considerably enhance the specific discharge capacity in lithium-ion batteries.

Journal Article↗
PubMed2006

Elucidation of the redox behavior of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) at poly(3,4-ethylenedioxythiophene) (PEDOT)-modified electrodes and application of the DMcT-PEDOT composite cathodes to lithium/lithium ion batteries.

The redox reactions of DMcT at PEDOT-modified glassy carbon electrodes (GCEs) in acetonitrile (AN) have been investigated via cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM) in order to elucidate the redox reaction mechanism. A redox couple at -0.29 V versus Ag/Ag+ was assigned to the dimerization process of singly protonated DMcT (DMcT-1H), and a second couple observed at +0.42 V was assigned to the polymerization process of the protonated DMcT dimer. Our investigations revealed further that the anodic current response at +0.55 V (polymerization process) has a shoulder at +0.38 V ascribed to the dimerization process of doubly protonated DMcT (DMcT-2H), indicating that the redox couple at +0.42 V is the overlapping response of the polymerization of the protonated DMcT dimer and the dimerization of the DMcT-2H monomer. It was also confirmed that the dimerization process of DMcT-1H at -0.29 V proceeded not only at the surface of a PEDOT film but also inside the film as previously suggested. Moreover, the thermodynamics of these redox reactions at PEDOT-modified GCEs are dependent on the basicity (or acidity) of the solution, as anticipated and previously shown at unmodified GCEs. The oxidation of DMcT occurs at less positive potentials and the reduction occurs at more negative potentials in the presence of base. On the basis of the results obtained, the full redox reaction scheme for DMcT at a PEDOT-modified GCE is proposed.

Anions↗
PubMed1998

Direct formation of nanophase hydroxyapatite on cathodically polarized electrodes.

Ultrafine-grained, nanophase coatings of hydroxyapatite were synthesized by electrocrystallization from dilute electrolytes ([Ca]=6.1 x 10-4 M, [phosphate]=3.6 x 10-4 M) at pH values comparable with the biological pH. At these comparatively low supersaturations, hydroxyapatite is shown to be precipitated without the formation of a precursor phase. A description of the sequence of events occurring at the electrode-electrolyte interface is given to explain the mechanism involved in the direct formation of nanophase hydroxyapatite on polarized electrodes.

Journal Article↗