Solid oxide electrolytic device

#1. Field of the Invention

#This application is related to U.S. provisional application No. 60/371,891. The present invention relates in general to solid oxide electrolytic devices, including solid oxide fuel cells (SOFC's) and oxygen generation systems (OGS′) and novel interconnect structures in such devices. In particular, the invention relates to the use of chrome-containing alloys in these devices, and the use of protective layers deposited to prevent corrosion, degradation, and/or increased electrical resistivity of the alloys.

#2. Description of the Related Art

#FIG. 1 is a cross-section of the dual-diffusion-barrier of present invention as incorporated within a typical solid oxide electrolytic device.

#FIG. 2 is a cross-section of the dual-diffusion-barrier in an alternative embodiment of the present invention.

#FIG. 3 is a perspective view of the disclosed electrode support structure, showing the sealing and active regions.

#The following description and FIGS. 1-11 of the drawings depict various embodiments of the present invention. The embodiments set forth herein are provided to convey the scope of the invention to those skilled in the art. While the invention will be described in conjunction with the preferred embodiments, various alternative embodiments to the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein. Like numerals are used for like and corresponding parts in the various drawings.

#FIG. 1 is a preferred embodiment of the present invention, wherein a chrome-containing metallic alloy structure (1) in a solid oxide electrolytic device is coated with the disclosed dual-layer interconnect structure (2). The component may be a bipolar connector plate used in solid oxide fuel cells and oxygen generators, or the supporting electrode disclosed in later figures. It may be noted from the preferred embodiments of FIG. 1 that a first CCCO layer (3) separates a second GDB layer (4) from the underlying chrome alloy structure (1). The CCCO layer may comprise various Cr-containing, electrically conducting manganites, manganates, cobaltites, chromites, molybdenates, or lanthanites. In the first preferred embodiment, the CCCO layer is composed of a LaSrCrMnO polycrystalline phase, and the GDB layer is platinum, though it may also comprise Ni metal or alloy in some applications. Without such a CCCO layer, at typical device operating temperatures, the Cr atoms will diffuse into the Pt to form such intermetallics as Cr3Pt and CrPt, which will subsequently result in an electrically insulating layer forming at the Pt surface, and eventual sublimation of Cr from the surface. The CCCO layer, however, provides sufficient binding energy to the Cr atoms, so that diffusion of Cr into the Pt is no longer chemically activated at device operating temperatures. At the same time, the Pt protects the CCCO layer from being degraded due to undesirable interfacial effects that would otherwise occur between the CCCO surface and the gaseous environment inside the device. These unwanted interfacial effects can include galvanic effects that activate reduction or otherwise effect the Cr—O bonding at the CCCO surface so that Cr sublimes or diffuses from the surface. Furthermore, when the gas media (6) of the device contains oxygen, the GDB layer prevents diffusion of oxygen from the gas media to the CCCO/alloy interface to form a low conductivity Cr2O3 layer.

#In the first preferred embodiment the CCCO layer is most easily formed by first depositing 100-10,000 nanometers of an electrically conducting manganate, such as (LaxSr1-x)MnO (LSM), on the surface of the Cr alloy component by such energetic deposition means as sputtering. Subsequently, the component is rapidly annealed with a first anneal to form an intermediate phase between the LSM coating and the Cr in the underlying alloy, thus producing a LaSrCrMnO (LSCM) CCCO layer. It is sufficient to perform the first anneal in air, with a fast ramp (typically less than 15 minutes) to 950° C., where the component is held for about fifteen minutes, depending on the composition and thickness, before cooling back down to room temperature in about fifteen minutes. This fast anneal allows for the LSCM CCCO layer to form without substantial formation of a Cr2O3 layer at the alloy—LSCM interface. Subsequently, the Pt GDB layer is deposited onto the LSCM layer, after which the resulting component is subjected to a second anneal similar to the first anneal. The second anneal is preferred to equilibrate the resulting heterostructure before subsequent processing, as well as to promote adhesion within the thin film stack. In the first preferred embodiment, both CCCO layer and Pt layer are less than one micrometer in thickness, with the Pt layer found most effective at thicknesses between 0.1 and 0.5 micrometers.