received by the International Bureau on 14 February 2018 (14.02.2018)

1. A planar SOFC cell unit ( 1010, 3010, 4010) comprising:

a substantially planar spacer plate (1100) formed to enclose an open-ended cell chamber (1120, 1400);

a planar solid oxide fuel cell (2000, 2100, 2200), supported inside the cell chamber, configured for electro-chemical energy generation while operating at an SOFC operating temperature;

a substantially planar anode flow plate (1200) disposed adjacent to the spacer plate (1100) and opposed tp an anode surface (2020) of the solid oxide fuel cell (2000, 2100, 2200), wherein a planar surface of the substantially planar anode flovv plate extends entirely over a first open end of the open-ended chamber;

a substantially planar cathode flow plate (1300) disposed adjacent to the spacer plate (1100) and opposed a cathode surface (2040) of the solid oxide fuel cell (2000, 2100, 2200), wherein a planar surface of the substantially planar cathode flow plate extends entirely over a second open end of the open-ended chamber;

wherein each of the substantially planar spacer plate and the substantially planar cathode plate are thermally conductively coupled to each other across a planar boundary formed there between and together form a first substantially solid volume of plate material formed as a substantially continuous thermally conductive pathway extending from boundary surfaces of the cell chamber that are formed by the spacer plate and the cathode feed plate to outer perimeter edges of the first substantially solid volume; wherein the first substantially solid volume comprises one or more materials each having a coefficient of thermal conductivity of 100 W/mK or more; and,

wherein the first substantially solid volume comprises sufficient thermal mass to maintain the first substantially splid volume at a substantially constant temperature that is less than the SOFC operating temperature.

2. The planar SOFC cell unit of claim 1 wherein the first substantially solid volume comprises sufficient thermal mass to maintain the first substantially solid volume at 1Q00°C or less over an SOFC operating temperature range of 600 to 12Q0°C,

3. The planar SOFC cell unit of claim 2 wherein the first substantially solid volume comprises copper having a coefficient of thermal conductivity of 330 W/mK or greater.

4. The planar SOFC cell unit of claim 1 wherein the first substantially solid volume comprises sufficient thermal mass to maintain the first substantially solid volume at 50Q°C or less over an SOFC operating temperature range of 350 to 550°C.

5. The planar SOFC cell unit of claim 4 wherein the first substantially solid volume comprises aluminum having a coefficient of thermal conductivity of 165 W/mK or greater.

6. The planar SOFC cell unit of claim 1 wherein the planar solid oxide fuel cell comprises a planar solid electrolyte layer (2100) sandwiched between a planar solid anode electrode layer (2020) and a planar solid cathode electrode layer (2040) wherein each of the planar solid electrolyte layer and the planar solid cathode layer is in mating contact with opposing surfaces of the planar solid electrolyte layer.

7. The planar SOFC cell unit of claim 1 wherein the planar solid oxide fuel cell (2000) is compliantly supported inside the cell unit.

8. The planar SOFC cell unit of claim 1 wherein the cell chamber comprises;

an anode gas feed chamber (1420), bounded by an anode electrolyte surface layer supported by the planar solid oxide fuel cell and by a surface of the substantially planar anode flow plate;

a cathode gas feed chamber (1430) bounded by a cathode electrolyte surface layer supported by the planar solid oxide fuel cell and by a surface of the substantially planar cathode flow plate;

an anode gas inlet channel (1220) extending from an anode gas manifold (1620) for delivering an anode gas flow into the anode gas feed chamber;

a cathode gas inlet channel (1320) extending from a cathode gas manifold (1620) for delivering a cathode gas flow into the cathode gas feed chamber;

an anode gas outlet passageway (1230) extending from the anode gas feed chamber to an exhaust gas manifold (1650) for removing the flow of anode gas from the anode gas feed chamber;

a cathode gas outlet passageway (1330) extending from the cathode gas feed chamber to the exhaust gas manifold (1650) for removing the flow of cathode gas from the anode gas feed chamber

wherein each of the anode gas inlet channel, anode gas manifold, the anode gas outlet passageway, the cathode inlet channel, the cathode gas manifold, the cathode gas outlet passageway and the exhaust gas manifold pass through the first solid volume and the substantially planar anode gas feed plate.

9. The planar SOFC cell unit of claim 8 further comprising an exhaust gas combustion chamber (1340), formed inside the substantially planar cathode flow plate (1300) wherein the exhaust gas combustion chamber is in fluid communication with each of the cathode gas outlet passageway (1330) of a first cell unit, the anode gas outlet passageway (1230) of a second cell unit and the exhaust gas manifold (1650), wherein the exhaust gas combustion chamber receives the flow of cathode gas from the first unit cell and the flow of anode gas from the second unit cell.

10. The planar SOFC cell unit of claim 8 further comprising:

a first compliant annular seal element (1800), disposed inside the anode gas feed chamber between the substantially planar anode gas feed plate and the planar solid oxide fuel cell and formed to seal a perimeter edge of the anode gas feed chamber;

a second compliant annular seal element (1800), disposed inside the cathode gas feed chamber between the substantially planar cathode gas feed plate and the planar solid oxide fuel cell and formed to seal a perimeter edge of the cathode gas feed chamber;

wherein each of the first and second compliant seal elements support the planar solid oxide fuel inside the cell chamber without contact between surfaces of the planar SOFC unit cell and surfaces of the cell chamber.

11. The planar SOFC cell unit of claim 10 wherein each of the first and second compliant seal elements comprises a compliant non-woven fabric comprising matted ceramic wool having a modulus of elasticity of 0.3 MPa or less.

12. The planar SOFC cell unit of claim 8 further comprising:

a first compliant interconnect element disposed inside the anode feed chamber between the substantially planar anode flow plate and the anode electrolyte surface layer, wherein the first complaint element is configured to apply a compressive force directed orthogonal to the anode electrolyte surface layer and is further configured to provide an electrically and thermally conductive pathway extending from the anode electrolyte surface layer to the substantially planar anode flow plate;

a second complaint interconnect element disposed inside the cathode feed chamber between the substantially planar cathode flow plate and the cathode electrolyte surface layer, wherein the second complaint element is configured to apply a compressive force directed orthogonal to the cathode electrolyte surface layer and is further configured to provide an electrically and thermally conductive pathway extending from the cathode electrolyte surface layer to the substantially cathode anode flow plate,

13. The planar SOFC cell unit of claim 12 wherein each of the first and second compliant interconnect elements are substantially identical and each of the interconnect elements comprises: one of a porous mesh and a porous foam comprising copper; and a formed metal element (3532) formed from a planar metal sheet having a thickness of 0.002 to 0.09 inches and formed to include a planar base portion and a plurality of flexible tabs portions (3535) extending from the base portion, wherein the formed metal element comprises copper.

14. A planar SOFC stack comprising:

a plurality of the planar SOFC cell units of claim 12 stacked one above another:

an electrical insulation layer (1850) disposed between each substantially planar spacer plate and the substantially planar anode plate positioned adjacent thereto;

a first electrical terminal (7112) connected in series to the planar cathode feed plate of each unit cell; and,

a second electrical terminal (7114) connected in series to the planar anode plate of each unit cell.

15. The planar SOFC stack of claim 14 further comprising:

- a first substantially planer liner plate (4710) disposed in mating contact with a first planar surface of each substantially planar anode feed plate in the planar SOFC stack;

a second substantially planer liner plate (4720) disposed in mating contact with a second, planar surface of each substantially planar anode feed plate in the planar SOFC stack between the substantially planar anode feed plate and the substantially planar spacer plate corresponding therewith; and,

a third substantially planer liner plate (4730) disposed in mating contact with a first planar surface of each substantially planar cathode feed plate in the planar SOFC stack between the substantially planar cathode feed plate and the substantially planar spacer plate corresponding therewith; wherein each of the first, the second and the third substantially planer liner plates comprises a high temperature oxidation resistant alloy comprising nickel and copper or comprising nickel, molybdenum, chromium and iron.