Westinghouse Electric Corporation

Siemens Westinghouse Power Corporation

Subhash C Singhal

Roswell J Ruka

Uday B Pal

George R Folser

Von L Richards

David M Moon

Li Baozhen

Frederick F Lange

Lewis J Kuo

William H McIntyre

Walter J Dollard

Sai-Kwing Lau

Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.

Solid oxide fuel cell operable over wide temperature range

Interfacial material for solid oxide fuel cell

An air electrode composition for a solid oxide fuel cell is disclosed. The air electrode material is based on lanthanum manganite having a perovskite-like crystal structure ABO.sub.3. The A-site of the air electrode composition comprises a mixed lanthanide in combination with rare earth and alkaline earth dopants. The B-site of the composition comprises Mn in combination with dopants such as Mg, Al, Cr and Ni. The mixed lanthanide comprises La, Ce, Pr and, optionally, Nd. The rare earth A-site dopants preferably comprise La, Nd or a combination thereof, while the alkaline earth A-site dopant preferably comprises Ca. The use of a mixed lanthanide substantially reduces raw material costs in comparison with compositions made from high purity lanthanum starting materials. The amount of the A-site and B-site dopants is controlled in order to provide an air electrode composition having a coefficient of thermal expansion which closely matches that of the other components of the solid oxide fuel cell.

Air electrode composition for solid oxide fuel cell

A highly sinterable powder consisting essentially of LaCrO.sub.3, containing from 5 weight % to 20 weight % of a chromite of dopant Ca, Sr, Co, Ba, or Mg and a coating of a chromate of dopant Ca, Sr, Co, Ba, or Mg; is made by (1) forming a solution of La, Cr, and dopant; (2) heating their solutions; (3) forming a combined solution having a desired ratio of La, Cr, and dopant and heating to reduce solvent; (4) forming a foamed mass under vacuum; (5) burning off organic components and forming a charred material; (6) grinding the charred material; (7) heating the char at from 590.degree. C. to 950 C. in inert gas containing up to 50,000 ppm O.sub.2 to provide high specific surface area particles; (8) adding that material to a mixture of a nitrate of Cr and dopant to form a slurry; (9) grinding the particles in the slurry; (10) freeze or spray drying the slurry to provide a coating of nitrates on the particles; and (11) heating the coated particles to convert the nitrate coating to a chromate coating and provide a highly sinterable material having a high specific surface area of over 7 m.sup.2 /g.

Method of making highly sinterable lanthanum chromite powder

A combustible polymer film, useful for application of an interconnection on an electrode is made by: (1) providing doped LaCro.sub.3 particles; (2) dispersing doped LaCrO.sub.3 particles in a solvent, to provide a dispersion; (3) screening the dispersion to provide particles in the range of from 30 micrometers to 80 micrometers; (4) admixing a fugitive polymer with the particles; (5) casting the dispersion to provide a film; (6) drying the film; and (7) stripping the film. The film can then be applied to a porous, preheated electrode top surface, and then electrochemical vapor depositing a dense skeletal LaCrO.sub.3 structure, between and around the doped LaCrO.sub.3 particles. Additional solid oxide electrolyte and fuel electrode layers can then be added to provide a fuel cell.

Tape method of forming a thin layer of doped lanthanum chromite

A method to form an electrochemical cell (12) is characterized by the steps of thermal spraying stabilized zirconia over a doped lanthanum manganite air electrode tube (14) to provide an electrolyte layer (15), coating conductive particles over the electrolyte, pressurizing the outside of the electrolyte layer, feeding halide vapors of yttrium and zirconium to the outside of the electrolyte layer and feeding a source of oxygen to the inside of the electrolyte layer, heating to cause oxygen reaction with the halide vapors to close electrolyte pores if there are any and to form a metal oxide coating on and between the particles and provide a fuel electrode (16).

Solid oxide electrochemical cell fabrication process

A dense, electronically conductive interconnection layer 26 is bonded on a porous, tubular, electronically conductive air electrode structure 16, optionally supported by a ceramic support 22, by (A) forming a layer of oxide particles of at least one of the metals Ca, Sr, Co, Ba or Mg on a part 24 of a first surface of the air electrode 16, (B) heating the electrode structure, (C) applying a halide vapor containing at least lanthanum halide and chromium halide to the first surface and applying a source of oxygen to a second opposite surface of the air electrode so that they contact at said first surface, to cause a reaction of the oxygen and halide and cause a dense lanthanum-chromium oxide structure to grow, from the first electrode surface, between and around the oxide particles, where the metal oxide particles get incoporated into the lanthanum-chromium oxide structure as it grows thicker with time, and the metal ions in the oxide particles diffuse into the bulk of the lanthamum-chromium oxide structure, to provide a dense, top, interconnection layer 26 on top of the air electrode 16. A solid electrolyte layer 18 can be applied to the uncovered portion of the air electrode, and a fuel electrode 20 can be applied to the solid electrolyte, to provide an electrochemical cell 10.

Method of doping interconnections for electrochemical cells

This is a process for producing an iron-boron-silicon-carbon composition for use in magnetic amorphous alloys. This process utilizes the carbon reduction of boric acid and avoids the use of expensive ferroboron as an ingredient. It also results in an alloy which is substantially free from aluminum. The process uses a mixture of iron-containing constituent, silicon-containing constituent, carbon-containing constituent and boric acid. Only 1-2 times the stoichiometric boron-containing amount of boric acid is required. The iron constituent is preferably selected from iron, ferrosilicon, carbon-containing iron, and mixtures thereof. The silicon content is preferably selected from the silicon, ferrosilicon, and mixtures thereof. The carbon constituent is preferably selected from the group consisting of carbon, carbon in iron, and mixtures thereof. The boric acid is lanced into the bottom of a molten pool which generally contains the other constituents. Preferably, carbon is mixed with the boric acid, and the combination lanced into the bottom of the molten pool such that the carbon reduction reaction can take place in the 1525.degree.-1575.degree. C. temperature range.

Production of an iron-boron-silicon-carbon composition utilizing carbon

This is a process for producing a ferroboron containing 0.5-20% silicon and up to 4.5% carbon. This process utilizes the silicon reduction of B.sub.2 O.sub.3 and avoids excessive losses due to volatilization of B.sub.2 O.sub.3. It also results in a ferroboron which is substantially free from aluminum impurity. The process uses a mixture, which includes an iron-containing constituent, a silicon containing constituent, and boric acid. Preferably a molten pool is prepared and controlled to a temperature of 1100-1550 (and preferably 1100.degree.-1450.degree. C.) prior to the addition of the boric acid. At least some of the silicon constituent can also be injected into the molten pool along with the boric acid.

Production of ferroboron by the silicon reduction of boric acid

This is a process for producing an iron-boron-silicon-carbon composition for a magnetic amorphous alloy. This process utilizes the silicon reduction of B.sub.2 O.sub.3 and avoids using expensive ferroboron as an ingredient. It also results in an alloy which is substantially free from aluminum impurity. The process uses a mixture of an iron containing constituent, a silicon containing constituent, a carbon-containing constituent and boric acid. Only 1-1.75 times the stoichiometric boron-containing amount of boric acid is required. The iron constituent is preferably selected from iron, iron oxide, ferrosilicon, carbon in iron and mixtures thereof. The silicon constituent is preferably selected from silicon, ferrosilicon, and mixtures thereof. The carbon constituent is preferably selected from the group consisting of carbon, carbon in iron and mixtures thereof. The reaction produces molten iron-3% boron-5% silicon alloy with up to 1% carbon. The reaction also produces a silicon dioxide containing slag.

Production of iron-boron-silicon composition for an amorphous alloy

The invention provides both preferred material alloys and electrode lead wire configurations for electrically connecting the solid electrolyte cell in a gas sensing probe to a remote measuring circuit.

Gas measuring probe

Dense, ceramic compositions fabricated within the Si.sub.3 N.sub.4 -Si.sub.2 N.sub.2 O-Y.sub.2 Si.sub.2 O.sub.7 compatibility triangle in the Si.sub.3 N.sub.4 -SiO.sub.2 -Y.sub.2 O.sub.3 system are extremely stable in oxidizing environments and particularly suited for use as a high temperature structural material. In addition, the hot-pressed, densified articles fabricated from compositions within the compatibility triangle exhibit improved strength and creep resistance at elevated temperatures relative to commercial Si.sub.3 N.sub.4.

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Murrysville, PA, United States of America

Subhash C Singhal