Integrated seal for high-temperature electrochemical device (The Regents Of The University Of California)

CATEGORY: FUEL CELLS
PATENT
Integrated seal for high-temperature electrochemical device (The Regents Of The University Of California)
Publication number US8486580 B2
Application number US 12/988,297
PCT number
PCT/US2008/066737
Publication date Jul 16, 2013
Also published as CA2721455A1, 6 More »
Inventors
Michael C. Tucker, Craig P. Jacobson
Original Assignee
The Regents Of The University Of California
Abstract
The present invention provides electrochemical device structures having integrated seals, and methods of fabricating them. According to various embodiments the structures include a thin, supported electrolyte film with the electrolyte sealed to the support. The perimeter of the support is self-sealed during fabrication. The perimeter can then be independently sealed to a manifold or other device, e.g., via an external seal. According to various embodiments, the external seal does not contact the electrolyte, thereby eliminating the restrictions on the sealing method and materials imposed by sealing against the electrolyte.
STATEMENT OF GOVERNMENT SUPPORT
This invention was made with government support under Contract DE-AC02-05CH11231 awarded by the United States Department of Energy to The Regents of the University of California for the management and operation of the Lawrence Berkeley National Laboratory. The government has certain rights in this invention.
FIELD OF THE INVENTION
The present invention relates to sealing high-temperature electrochemical devices, such as solid oxide fuel cells.
BACKGROUND
Solid-state electrochemical devices are normally cells that include two porous electrodes, the anode and the cathode, and a dense solid electrolyte membrane disposed between the electrodes. In the case of a typical solid oxide fuel cell, the anode is exposed to fuel and the cathode is exposed to an oxidant in separate closed systems to avoid any mixing of the fuel and oxidants.
External seals are used to seal off the closed systems and prevent mixing. While no dominant seal technology exists, examples includes braze seals, compressive seals and glass seals. Seal-less designs, which allow mixing of the fuel and oxidant streams at the outlet of the device, have also been in development, though oxidant and fuel mixing is generally undesirable. Long-term performance of braze seals has not been demonstrated. In addition, braze seals can be costly and the coefficient of thermal expansion (“CTE”) must be modified to match the CTE of the electrolyte. Compressive seals are generally made with mica, display high leak rate and have poor thermal cycling capability. Glass seals can react with sealed surfaces and also have poor thermal cycling ability.
SUMMARY OF THE INVENTION
The present invention provides electrochemical device structures having integrated seals and methods of fabricating them. According to various embodiments, the structures include a thin, supported electrolyte film with the electrolyte sealed to the support. The perimeter of the support is self-sealed during fabrication. The perimeter can then be independently sealed to a manifold or other device, e.g., via an external seal. According to various embodiments, the external seal does not contact the electrolyte, thereby eliminating the restrictions on the sealing method and materials imposed by sealing against the electrolyte.
One aspect of the invention relates to electrochemical device structure having an integrated seal. The devices include first and second electrodes separated by a dense electrolyte and a support having dense and porous support regions. The dense and porous support regions share a dense support/porous support interface and are composed of the same material type (e.g., they are both metal or both cermet). The dense electrolyte is disposed on at least a portion of the dense support region to form an electrolyte/dense support interface. The electrolyte/dense support interface and dense support/porous support interface form a gas tight seal between the first electrode and the second electrode.
Another aspect of the invention relates to an electrochemical device structure having an integrated seal. The device includes first and second electrodes separated by a dense electrolyte; a porous support region cosintered to a dense support region to form a gas impermeable dense support/porous support interface; the dense electrolyte cosintered to at least a portion of the dense support region to form a gas impermeable electrolyte/dense support interface. The electrolyte/dense support interface and dense support/porous support interface forming a gas tight seal between the first electrode and the second electrode.
In certain embodiments, the dense support region provides a point of mechanical attachment to a housing, sheet, etc. For example, an external sealing member may be connected to the dense support region, to provide a further seal and/or to mount the device to a manifold, housing, another device, etc. This external sealing member is not in physical contact with the dense electrolyte. According to certain embodiments, the external sealing member is metal, and may be a brazed or welded joint. Also in certain embodiments, the dense support is fitted to a metal housing, e.g., by threading. In certain embodiments, the dense support region provides an electrical contact point for exchanging current or voltage with the device.
The porous support region may be an electrode or support an electrode. In certain embodiments, a ceramic or cermet interlayer is disposed between the porous support region and the dense electrolyte. This interlayer may function as an electrode. In certain embodiments, the porous and dense support regions are made of the same material (e.g., both are Ni—YSZ, or Cu—YSZ, or stainless steel). The device may be of any geometry, including planar and tubular geometries. In certain embodiments, solid oxide fuel cells are provided.
Another aspect of the invention relates to a method of fabricating an electrochemical device structure having an integrated seal. The method involves providing a support structure green body configured such that upon sintering, adjacent dense and porous support regions are formed; coating at least a portion of the support structure green body with a green electrolyte material; and cosintering the support structure green body and green electrolyte material such that a) a support having adjacent porous and dense support regions is formed, b) the dense support region and the electrolyte become substantially gas impermeable, and c) an integrated gas-tight seal is formed at an electrolyte/dense support region interface.
In certain embodiments, prior to coating a portion of the support structure green body with a green electrolyte material, green interlayer material is deposited on at least a portion of the support structure green body. The green electrolyte material is then deposited on the interlayer as well as a portion of the green support structure.
In certain embodiments, after sintering, the dense support region is attached to an external metal seal, housing, manifold or fitting such that the seal, housing, manifold or fitting does not contact the electrolyte. The external seal, etc. may also be sintered to the dense support region during the cosintering operation.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention.
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