Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing nonmetal element
Patent
1997-01-29
1998-07-28
Bell, Bruce F.
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing nonmetal element
205636, 205687, 204252, 204257, 204265, 204266, 204291, 204421, 429 33, 429 40, 429193, C25B 102
Patent
active
057858390
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/FR95/00651 filed on May 18, 1995.
BACKGROUND OF THE INVENTION
(i) Field of the Invention
Various electrolyte/electrode couples can be used in the field of separating oxygen from air or from a mixture of gases containing it, by using an electrochemical cell with a solid electrolyte.
(ii) Description of Related Art
The operating principle of such an elementary cell is illustrated in FIG. 1. The oxygen molecules in the air are reduced at the cathode (C) into O.sup.2- ions which are then transported through the solid electrolyte (E) that is impermeable to the gases (stabilized zircon, cited by way of example in FIG. 1), under the effect of an electrical field; on the other face of the cell, these ions are oxidized at the anode (A) to generate the oxygen molecules. The performances of the cell thus depend on the ionic conductivity of the electrolyte and the capacity of the electrode materials to reduce the oxygen or to oxidize O.sup.2- ions at the working temperature.
The majority of solid electrolytes used for the separation of oxygen from air are stabilized zircons (for example, yttrium). These compounds make it possible to work between 700.degree. and 800.degree. C. (CERAMATEC INC., U.S. 4,879,016).
A new class of oxides, derived from Bi.sub.4 V.sub.2 O.sub.11, in which a variable portion of vanadium is replaced by an element, for example, an alkaline-earth metal, a transition metal, a rare earth element or an element of groups III to V, was described in international patent application PCT W091/01274. These oxides are conductors of O.sup.2- ions and their anionic conductivity at 300.degree. C. is on the same order of magnitude as that of stabilized zircon at 600.degree. C. These solid electrolytes can be used with different electrode couples. IHARADA, University of Grenoble, September 1991) are either gold, platinum or LSM (lanthanum manganite doped with strontium).
These derivatives are often labeled with the generic name of BIMEVOX (University of Sciences and Technologies of Lille).
The BIMEVOX derivatives will generally have the following formula (I): those that have an oxidation number of less than or equal to 3; those that have an oxidation number of less than or equal to 5; the substituent elements M and M', it being understood that at least one of the indices x and y is not zero.
In particular, the BIMEVOX derivatives can also have the following formula (II):
When it is present, M' is advantageously selected from among the alkaline metals, alkaline-earth metals, the transition metals, or the elements of groups III to V in the periodic table or among the rare earths.
But, while electrolytes based on BIMEVOX permit the transfer of O.sup.2- ions across their thickness at a low temperature (300.degree. C.), the metallic electrodes, with which they are currently associated (Au, Pt) are electrodes with a low flux that do not permit correct catalytic dissociation of the oxygen molecules that are placed in contact with them. Furthermore, the very structure of this type of electrode considerably reduces the surface developed by the electrode-electrolyte interface. It was furthermore possible to discover that these inconveniences can also be encountered when these electrodes are used with conventional electrodes, other than those based on BIMEVOX. These solid electrodes, for example, are zircon, stabilized by a doping agent, such as yttrium, or calcium; or oxides of bismuth Bi.sub.2 O.sub.3 doped or not doped by elements such as magnesium, calcium, yttrium, or erbium.
SUMMARY AND OBJECTIONS OF THE INVENTION
The object of the invention is to remedy these difficulties, in particular by developing new electrode-electrolyte systems that employ electrodes that are particularly adapted to BIMEVOX, at the same time having catalytic properties of O.sub.2 dissociation, properties of electronic conduction and a developed surface, permitting oxygen transport at a high flow rate from one side to the other of these systems, in particular at temperatures between 300.degree. and 700.deg
REFERENCES:
patent: 5573655 (1996-11-01), Mairesse et al.
patent: 5582710 (1996-12-01), Mairesse et al.
Boivin Jean-Claude
Kleitz Michel
Lagrance Gilles
Mairesse Gaetan
Bell Bruce F.
Ecole Nationale Superieure de Chimi de Lille, Universite des Sci
L'Air Liquide Societe Anonyme pour l'Etude et, l'Exploitation de
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