Use of sulfur-containing fuels for direct oxidation fuel cells

Abstract

The invention relates to a solid oxide fuel cell which comprises a solid electrolyte comprised of an electronic insulator which allows transfer of anions, a ceramic-metal composite anode and, a cathode. The fuel cell also comprises a sulfur-containing hydrocarbon fuel having a sulfur content of from about 1 ppm to about 5000 ppm and an oxygen source. The invention further relates to a process of producing electrical energy with the fuel cell and a process of restoring the operability of a fuel cell that was deactivated by sulfur poisoning. The invention also relates to a method for preparation of a porous cermet as a direct-oxidation anode with supported electrolyte structure for a solid-oxide fuel cell using a nickel cermet. The nickel cermet is leached to remove at least part of the nickel, thereby producing a porous oxide. The resulting porous oxide is then impregnated, preferably with a salt of copper, which is calcined to CuO, then reduced to elemental copper. The resulting copper cermet or copper-nickel alloy cermet can be used as the direct-oxidation anode. The starting material for the nickel cermet is preferably a tape formed from a slurry comprising NiO and a ceramic powder comprising YSZ. This tape is combined into an assemblage with one or two additional tapes cast from a slurry comprising a ceramic powder. The invention further relates to a solid-oxide fuel cell comprising an anode material with supported electrolyte structure made by this method and a process for producing electrical energy using this fuel cell.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This patent application claims the benefit of pending U.S. Provisional Patent Application No. 60 / 247,444 filed Nov. 9, 2000, U.S. Provisional Patent Application No. 60 / 269,525 filed Feb. 19, 2001, and U.S. Provisional Patent Application No. 60 / 308,313, filed Jul. 27, 2001, the entire disclosures of which are incorporated by reference herein.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates to fuel cell technology and more particularly to a solid oxide fuel cell capable of being operated with a sulfur-containing hydrocarbon fuel, as well as methods of fabrication of such fuel cells and their use for producing electric energy. [0004] 2. Description of Prior Art [0005] Solid-oxide fuel cells (SOFCs) have grown in recognition as a viable, high temperature source of electric energy. As the operating temperatures of these fuel cells typically exceed 600° C. and may be as high as 1,000° C., the material...

AI Technical Summary

Benefits of technology

[0014] It is an objective of this invention to overcome the problems associated with the presence of complex organic sulfur compounds in a hydrocarbon fuel stream for use in a fuel cell, without increasing fuel-processing complexity.

[0016] It is another objective of this invention to provide a fuel cell that can operate with fuel that does not have to undergo prior treatment to remove complex organic sulfur compounds.

[0017] It is yet a further objective of this invention to provide a process by which a fuel cell that is contaminated by sulfur can be restored to full performance after being deactivated by sulfur poisoning.

[0019] It is another objective of this invention to provide a method for preparing a layered ceramic structure comprising a direct oxidation anode with a supported electrolyte, which may incorporate an additional layer to impart greater strength to the structure.

[0021] It is yet another objective of this invention to provide a solid-oxide fuel cell, having a ceramic-metal alloy composite anode, which operates efficiently using a dry hydrocarbon fuel containing sulfur.

[0027] The present invention further provides a method of fabricating a porous copper cermet or copper-nickel alloy cermet from a sintered nickel cermet with nickel content between about 10% and about 60% for use as a direct-oxidation anode. The method comprises leaching at least a part of the nickel from the cermet, thereby increasing the cermet's porosity. Cu is then added back into the pore structure to obtain a Cu cermet. In one embodiment, the porous structure is impregnated with a soluble, copper-containing impregnant, preferably a copper salt. The impregnated cermet is subjected to a temperature sufficient to convert the copper-containing impregnant to copper oxide which, in turn is reduced to elemental copper, resulting in the formation of a copper cermet or copper-nickel alloy cermet, depending on the amount of nickel removed during the leaching step.

Problems solved by technology

As the operating temperatures of these fuel cells typically exceed 600° C. and may be as high as 1,000° C., the materials used for the cell components are limited to those that are stable at such temperatures.

Steam reforming is costly and adds significant complexity to the system.

It has been proposed to use dry methane; however, Ni catalyzes the formation of carbon fibers in dry methane, resulting in carbon formation on the anode.

Such raw fuels are not currently in use as a fuel source suitable for a fuel cell because these fuels contain relatively high levels of sulfur, often as naturally-occurring complex organic sulfur compounds.

Oxidation in the presence of sulfur results in a poisoning effect on catalysts used in the hydrogen generation system, often including the fuel cell anode catalyst.

While this system can be used in large stationary applications, it adds significant complexity to the systems.

According to U.S. Pat. No. 6,159,256, when using an autothermal reformer to process raw fuels containing complex organic sulfur compounds, the result is a loss of autothermal reformer catalyst effectiveness and useful catalyst life of the remainder of the fuel-processing system.

Images