Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing nonmetal element
Patent
1994-05-16
1996-12-10
Tung, T.
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing nonmetal element
204421, 204424, 204427, 205687, 429 33, 429193, C25B 102
Patent
active
055827101
DESCRIPTION:
BRIEF SUMMARY
The present invention has for its object an electrochemical cell comprised of a solid electrolyte, an anode and a cathode as well the use of this electrochemical cell with a view towards the electrochemical separation of gases from a mixture of at least one gas and of oxygen or with a view towards the extraction of oxygen from a molecule containing oxygen.
It is known that some solid electrolytes, classically comprising, for example, compositions derived from oxides of zirconium, yttrium, bismuth or cerium, containing or not containing dopants such as ytterbium or calcium, can be used as conductors of O.sup.2- ions, when they are subject to an electric field and/or a difference of partial pressure of oxygen. These solid electrolytes typically possess the same base structure, derived from the so-called structure of fluorine type possessing oxygenated gaps. They permit a conduction of O.sup.2- ions which is essentially tri-dimensional.
Besides, solid electrolyte conductors for O.sup.2- ions have been described in patent application WO91/01274 the teachings of which are totally incorporated herein by reference. These electrolytes are comprised of a composition derived from Bi.sub.4 V.sub.2 O.sub.11 and of which at least one of the constituent elements is substituted by one or several substituting elements chosen of the kind such that the structural type of the gamma phase of Bi.sub.4 V.sub.2 O.sub.11 is maintained, as well as the equilibrium of the charges. This type of solid electrolyte presents a lamellar structure in which the mechanism of conduction of the ions O.sup.2- is essentially hi-dimensional.
Thus, the solid electrolytes comprised of a composition derived from Bi.sub.4 V.sub.2 O.sub.11 can be distinguished from classical solid electrolytes, by their chemical composition, their crystalline structure and their mode of conduction of O.sup.2- ions.
Some solid electrolytes comprised of compositions derived from Bi.sub.4 V.sub.2 O.sub.11 possess the remarkable property of permitting an anionic conductivity of 10.sup.-3 .psi..sup.-1 cm.sup.-1 at 200.degree. C., which is of the order of one hundred times superior to the performances of materials currently on the market. Such classical materials are even inoperative at temperatures less than 300.degree. C. In order to attain an anionic conductivity of the order of 10.sup.-3 .psi..sup.-1 cm.sup.-1, it is necessary to take them to temperatures greater than about 600.degree. C.
It, however, has been observed by the Applicants that classical electrodes, essentially based on silver or gold, deposit, for example, under the form of a lacquer on the solid electrolyte, lead, when they are associated with a solid electrolyte comprised of a composition derived from Bi.sub.4 V.sub.2 O.sub.11, to a rapid deactivation of the electrochemical cell. Such a deactivation is not produced when the solid electrolyte is comprised, for example, of a classical stabilized zirconium. It is well understood that such a deactivation of the electrochemical cell is not compatible with exploitation on an industrial scale. Without being bound to a theoretical explanation, the Applicants were able to attribute the deactivation to a chemical reaction between one or several of the constituent elements of the electrolyte derived from Bi.sub.4 V.sub.2 O.sub.11 and of the electrode based on silver. In the case of gold, its diffusion in the electrolytic material often leads to a very strong increase in the surface resistivity, which is prejudicial to good distribution of the density of the current, being capable of leading to the phenomena of craterization which leads to the deterioration of the cell.
The Applicants pursued their research and have developed an electrochemical cell whose solid electrolyte is comprised of a composition derived from Bi.sub.4 V.sub.2 O.sub.11 and is not rapidly deactivated. An object of the present invention thus consists of an electrochemical cell comprised of such a solid electrolyte, an anode and a cathode permitting use over long duration, even on an industrial s
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patent: 4789561 (1988-12-01), Schafer et al.
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patent: 5378345 (1995-01-01), Taylor et al.
Boivin Jean-Claude
Cocolios Panayotis
Lagrange Gilles
Mairesse Gaetan
Ecole Nationale Superieure de Chimie de Lille
L'Air Liquide Societe Anonyme pour l'Etude et, l'Exploitation de
Tung T.
Universite des Science et Technologies de Lille Cite Scientifiqu
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