Solid oxide fuel cell stack with floating cells

1. A planar fuel cell unit for use in a solid oxide fuel cell stack, stacked between upper and lower seal elements, the lower seal element having three distinct openings; a central cathode flow field opening which defines the peripheral boundary of a cathode flow field which includes an air intake portion and an air exhaust portion, a fuel intake manifold opening and a fuel exhaust manifold opening, the upper seal element having three distinct openings; a central anode flow field opening which defines the peripheral boundary of an anode flow field which includes a fuel intake portion and a fuel exhaust portion, an air intake manifold opening and an air exhaust manifold opening, said unit comprising:

(a) an upper cushion element and a lower cushion element wherein each of the upper and lower cushion elements define a central cell opening, air intake and exhaust manifold openings and fuel intake and exhaust manifold openings wherein the fuel intake manifold opening and the fuel exhaust manifold opening of the upper cushion element are positioned within the peripheral boundary of the anode flow field, aligned respectively with the fuel intake portion and the fuel exhaust portion of the anode flow field, and wherein the air intake manifold opening and the air exhaust manifold opening of the lower cushion element are positioned within the peripheral boundary of the cathode flow field, aligned respectively with the air intake portion and the air exhaust portion of the cathode flow field; and

(b) a cell holder plate having a central cell opening; and

(c) a fuel cell comprising upper electrode, a lower electrode and a central electrolyte and disposed within the cell holder plate cell opening;

(d) wherein the upper electrode is exposed through the upper cushion element opening, the lower electrode is exposed through the lower cushion element cell opening.

2. The fuel cell unit of claim 1 wherein one or both of the upper and lower cushion elements comprises a flexible, compressible seal material.

3. The fuel cell unit of claim 2 wherein the seal material comprises a porous composite material comprising ceramic fibres and ceramic particles.

4. A solid oxide fuel cell stack comprising a plurality of fuel cell units as claimed in claim 1 .

5. A solid oxide fuel cell stack comprising:

(a) a flow separator plate having air intake and exhaust manifold openings and fuel intake and exhaust manifold openings;

(b) a lower seal element having three distinct openings; a central cathode flow field opening defining the peripheral boundary of a cathode flow field combining an air intake portion and an air exhaust portion, and separate fuel intake and exhaust manifold openings;

(c) cathode contact media disposed within the cathode flow field;

(d) a fuel cell unit comprising:

i. an upper cushion element and a lower cushion element, the lower cushion element being adjacent to the lower seal element, wherein each of the upper and lower cushion elements define a central cell opening, air intake and exhaust manifold openings and fuel intake and exhaust manifold openings;

ii. a cell holder plate having a central cell opening, air intake and exhaust manifold openings and fuel intake and exhaust manifold openings;

iii. a fuel cell comprising an upper electrode, a lower electrode and a central electrolyte and disposed within the cell holder plate cell opening;

iv. wherein the upper electrode is exposed through the upper cushion element opening, the lower electrode is exposed through the lower cushion element cell opening;

(e) and an upper seal element adjacent to the upper cushion element, the upper seal element having three distinct openings; a central anode flow field opening defining the peripheral boundary of an anode flow field combining a fuel intake portion and a fuel exhaust portion, and separate air intake and exhaust manifold openings, and the upper seal element having anode contact media disposed within the anode flow field;

(f) wherein the fuel intake and exhaust manifold openings and the fuel intake portions and the fuel exhaust portions of the anode flow fields align vertically to form fuel intake and exhaust manifolds and the air intake and exhaust manifold openings and the air intake portions and air exhaust portions of the cathode flow fields align vertically to form air intake and exhaust manifolds; and

(g) wherein the fuel intake manifold opening and the fuel exhaust manifold opening of the upper cushion element are positioned within the peripheral boundary of the anode flow field and wherein the air intake manifold opening and the air exhaust manifold opening of the lower cushion element are positioned within the peripheral boundary of the cathode flow field.

6. The fuel stack of claim 5 wherein the cathode contact media comprises a lanced offset plate.