Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-11-08
2001-07-24
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S265000, C204S266000, C204S278500
Reexamination Certificate
active
06264807
ABSTRACT:
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
FIELD OF THE INVENTION
The present invention relates generally to ceramic oxygen generating systems and more particularly, to a novel oxygen generation system which uses a new ceramic ionic conducting material, known as copper-doped bismuth vanadate, or BICUVOX as an electrolyte.
BACKGROUND OF THE INVENTION
All ceramic oxygen-generating systems work in accordance with the same basic working principle. The ceramic electrolyte is bounded on either side by an electrode, that is, a cathode on one side (the air side) and anode on the other (the oxygen side). The ceramic electrolyte is preferably fabricated into a thin membrane in order to enhance oxygen flux and reduce internal resistance. Upon applying voltage across the electrolyte/electrode assembly oxygen molecules in the air side of the system are first ionized at the cathode/electrolyte interface (O
2
+4e
−
→2O
2−
). The negatively charged oxygen ions, driven by the potential gradient, then diffuse through the electrolyte via a large number of existing vacancies. At the opposite anode/electrolyte interface, oxygen molecules are reformed after releasing electrons (2O
2−
→O
2
+4e
31
). Since the ceramic electrolyte permits only O
2−
diffusion, pure oxygen is therefore generated on the oxygen side of the system.
Prior art ceramic oxygen generating systems typically use stabilized zirconia or ceria as an electrolyte material. Unfortunately, these ceramic oxygen-ion-conducting materials require a high temperature, in excess of 800° C., in order to achieve satisfactory conductivity. The need therefore exists for a cost-effective materials system for ceramic oxygen generating applications at lower operating temperatures (below 800° C.).
Recently, a new group of low-temperature ceramic ionic conductors has emerged, based on bismuth vanadate doped with metal cations. The highest conductivity has been exhibited by copper-doped bismuth vanadate, known by the generic name BICUVOX. BICUVOX generally has the following formula: Bi
2
V
0.9
Cu
0.1
O
5.35
.
BICUVOX has high potential for use in ceramic oxygen generating systems operating at temperatures below 600° C. One of the most significant benefits associated with the lowered working temperature is the availability of low-cost, machinable metals for use as electrodes.
SUMMARY OF THE INVENTION
In accordance with the foregoing background and unresolved needs, the system of the present invention is provided for oxygen generation applications at temperatures below 600° C.
In a first embodiment, an oxygen generation system is provided which comprises a pair of Inconel® electrodes placed in electrical contact with a BICUVOX electrolyte so as to produce a flow of oxygen ions there through. BICUVOX possesses superior oxygen mobility at the targeted working temperature. Inconel® is an inexpensive, machinable metal with similar thermal expansion behavior to that of BICUVOX. Gas flow channels are machined on the sides of the Inconel® electrodes. These gas flow channels are oriented so that oxygen gas flow and oxygen-depleted gas flow may be separated.
In a second embodiment, a plurality of electrolyte/electrode cells is arranged to form a stack of cells. Each BICUVOX electrolyte is comprised of a thin flat plate which is square in shape. The Inconel® electrodes are comprised of square plates having the same lengths and widths as the BICUVOX electrolytes. The electrode plates are machined with gas flow channels which are oriented so that oxygen flow and oxygen-depleted gas flow may be separated. A thin layer of gold paste is applied at each electrolyte/electrode interface. Electrical leads are attached to the electrodes. The stack of cells is enclosed in a tubular manifold which is composed of magnesium oxide and which has a diameter which is slightly larger than the diagonal length of the electrolyte and electrode plates. The stack is sealed at its four corners to the inside surface of the manifold, thereby creating four separate passages for flow of oxygen-containing gas, high purity oxygen gas, and oxygen-depleted gas. The tubular manifold is capped on the top and bottom with circular disks composed of Inconel®. Gas inlet and outlet tubes within the top cap supply oxygen containing gas to the system and remove oxygen gas and oxygen-depleted gas from the system. In operation, electrical power is supplied to the system through the lead wires. A source of oxygen-containing gas is supplied to the system through the inlet tube. Oxygen molecules are ionized at the cathode/electrolyte interface and reformed at the anode/electrolyte interface. High purity oxygen gas is collected from oxygen outlet tubes. Oxygen-depleted gas is released through another outlet tube.
REFERENCES:
patent: 4344832 (1982-08-01), Dahlberg
patent: 5332483 (1994-07-01), Gordon
patent: 5582710 (1996-12-01), Mairesse et al.
Dillon Nathan A.
Fenner Jerold E.
Wong Ming-Shih
Bell Bruce F.
Cole Tony Y.
Kundert Thomas L.
Scearce Bobby D.
The United States of America as represented by the Secretary of
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