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  Electrochemical oxygen separator cellUSPTO Application #: 20070034507Title: Electrochemical oxygen separator cell Abstract: An electrochemical oxygen separator cell including an electrode based on lanthanum strontium manganese oxide or lanthanum strontium cobalt iron oxide; and an electrolyte membrane of doped ceria. (end of abstract) Agent: Finnegan, Henderson, Farabow, Garrett & Dunner LLP - Washington, DC, US Inventors: Xicola Agustin Sin, Antonio Zaopo, Vicenzo Antonucci, Antonino Salvatore Arico USPTO Applicaton #: 20070034507 - Class: 204290100 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Elements, Electrodes, Laminated Or Coated (i.e., Composite Having Two Or More Layers), Rare Earth Metal (i.e., Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Or Lu) Or Compound Containing The Patent Description & Claims data below is from USPTO Patent Application 20070034507. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to electrochemical cells for separating oxygen from other gases to produce an oxygen-enriched stream or an oxygen-depleted stream. [0002] A large number of commercial processes needs oxygen, oxygen-enriched or oxygen-depleted stream. Examples of industrial processes requiring oxygen enriched stream uses include glass production, petrochemical industry, paper industry, metallurgical industry, aerospace and medical applications. Oxygen depleted streams can be advantageous for lowering the emission of nitrogen oxides (NO.sub.x) by diesel engines. [0003] There are many differing methods and apparatus used for separating oxygen from other fluids, such as cryogenic cycles, non-cryogenic air separation plants, including the use of molecular sieves. [0004] One of such methods uses an electrochemical process where an oxygen-containing gaseous mixture, such as air, is fed to one side of a ceramic membrane with an electrical potential applied across the membrane. The oxygen molecules are reduced to oxygen ions at the interface between the cathode and the electrolyte membrane and the oxygen ions can selectively pass through the electrolyte. [0005] After passing through the electrolyte, a further reaction takes place at the interface between the electrolyte and the anode where the oxygen ions are oxidized to reform oxygen molecules. By using of particular electrolyte membranes, only the oxygen ions are allowed to pass through the cell and thus the overall process is very selective for producing a stream with high concentration of oxygen. [0006] In further detail, when an electrical potential is applied across an oxygen ion electrolyte membrane via electrodes, oxygen is dissociated and reduced at the cathode according to the following reaction O.sub.2.fwdarw.4e.sup.-.fwdarw.2O.sup.-2 [0007] Oxygen ions migrate through the electrolyte, and are oxidised and recombined at the anode to produce oxygen. An external electrical connection allows the transfer of electrons from the anode to the cathode. The flux of oxygen produced by an electrically driven force is directly proportional to the current passing through the electrolyte membrane according to the Faraday law, mols .times. .times. O 2 = I .times. t 4 .times. F wherein I is the electrical current (A), [0008] t is time (sec), [0009] F is the Faraday constant (i.e. 96485.3 C/eq) and [0010] 4 is the number of electrons exchanged in the electrochemical reaction 2O.sup.-2.fwdarw.4e.sup.-+O.sub.2, eq/mol. [0011] This means that the flux of oxygen for an applied potential is governed by the electrochemical resistance of the cell (the sum of the electrolyte and electrode polarisation resistance). The O.sub.2 flux can be increased by either raising the potential of the electrochemical cell or reducing the resistance of the membrane. [0012] U.S. Pat. No. 5,021,137 (in the name of Ceramatec Inc.) relates to a ceramic solid electrolyte based electrochemical oxygen concentrator cell. The cell is based on a doped cerium oxide ceramic solid electrolyte and lanthanum strontium cobaltite (LSCO) ceramic electrodes. Preferably, cerium oxide is doped with calcium oxide, strontium oxide or yttrium oxide. This cell exhibits a current density of 450 mA/cm.sup.2 at 800.degree. C. and 1.0V dc operating voltage. [0013] D. Waller et al. Steele, Electrochemical Society Proceedings Vol. 95-24 (1997) pp. 48-64 disclose oxygen separation using dense gadolinia doped ceria membranes. More specifically, Ce.sub.0.9Gd.sub.0.1O.sub.1.95 (ceria doped with 10% of gadolinia, hereinafter referred to as CGO-10) as electrolyte is screen printed or painted with lanthanum strontium cobalt iron oxide (LSFCO) as electrodes. The X-ray diffraction (XRD) data of the LSFCO electrodes show a polyphase pattern. The current density provided by this construction is of almost 350 mA/cm.sup.2 at 800.degree. C. and 0.6V dc operating voltage. [0014] This paper reports that for achieving a production of 1 ml of oxygen per minute and per cm.sup.2, it is necessary a separator showing a current density of at least 287 mA/cm.sup.2. It is established that the electrode resistance is the predominant factor in limiting the oxygen flux through the cell. Reducing the electrode resistance is the key factor in increasing the performance of the cell. The electrolyte resistance constitutes only a small proportion of the overall resistance of the cell; therefore the thickness of the electrolyte may be increased (e.g. from 100 to 250 .mu.m) to improve the mechanical strength of the cell without giving rise to a large increase in the overall resistance of the cell. [0015] Applicant faced the problem of providing an electrochemical oxygen separator cell with higher performance, in term of current density and, as a consequence, of oxygen separation, with respect to those known in the art. [0016] This problem is solved by providing an electrochemical oxygen separator cell with a specific combination of material for electrolyte membrane and electrodes which yields surprisingly high performances also in the presence of a cell architecture wherein the supporting element is one of the electrode, thus having a thickness greater than that of the electrolyte membrane. [0017] Therefore the present invention relates to an electrochemical oxygen separator cell including [0018] a cathode comprising a material selected from lanthanum strontium manganese oxide/doped ceria in a ratio ranging between about 85:15 and about 75:25 by weight; and lanthanum strontium cobalt iron oxide; [0019] an electrolyte membrane comprising ceria doped from about 15 to about 25% by mole; [0020] an anode comprising a material selected from lanthanum strontium manganese oxide/doped ceria in a ratio ranging between about 85:15 and about 75:25 by weight; and lanthanum strontium cobalt iron oxide. [0021] Unless otherwise indicated, in the following of the description lanthanum strontium cobalt iron oxide will be referred to as LSFCO, and lanthanum strontium manganese oxide will be referred to as LSMO. [0022] In the following of the description, cathode and anode could also be referred to as "electrode". [0023] Examples of doped ceria useful in the present invention are gadolinia doped ceria and samaria doped ceria. [0024] The doped ceria is used as electrolyte membrane material is preferably doped in an amount of about 20% by mole. Preferred in this connection is Ce.sub.0.8Gd.sub.0.2O.sub.1.90 (hereinafter referred to as CGO-20). [0025] Cathode and anode of the present invention can have the same or different composition and morphology. [0026] Preferably, lanthanum strontium manganese oxide/doped ceria ratio is from about 80:20 to about 70:30 by weight. [0027] Preferably La.sub.1-xSr.sub.xMnO.sub.3-.delta. is La.sub.0.8Sr.sub.0.2MnO.sub.3 (hereinafter referred to as LSMO-80). [0028] Preferred material for electrode is La.sub.1-xSr.sub.xFe.sub.1-yCo.sub.yO.sub.3-.delta., wherein x and y are independently equal to a value comprised between 0 and 1 included and 8 is from stoichiometry, more preferably La.sub.0.6Sr.sub.0.4Fe.sub.0.8Co.sub.0.2O.sub.3-.delta. (hereinafter referred to as LSFCO-80). Preferably, LSFCO is in single phase belonging to the perovskite family, i.e. a group of compounds of the general formula ABX.sub.3 with X most frequently oxygen. Optionally, LSFCO can be added with doped ceria. [0029] Both cathode and anode preferably show a porosity at least of about 20% (measured by SEM). [0030] In a preferred embodiment, electrochemical oxygen separator cell of the invention shows one electrode (supporting electrode) being substantially thicker than the electrolyte membrane. Preferably the supporting electrode is the anode. Continue reading... Full patent description for Electrochemical oxygen separator cell Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electrochemical oxygen separator cell patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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