Fuel cell stack assembly

Abstract

The present invention is concerned with an improved fuel cell stack assembly (10) comprising a metal base plate (20) on which is mounted at least one fuel cell stack (30) and a metal end plate (40), each stack comprising at least one fuel cell stack layer (50) that comprises at least one fuel cell (101, 102) and at least one electrically insulating compression gasket (110), wherein a skirt (130) is attached to the base and end plates enclosing the stack and is under tension therebetween so as to maintain a compressive force through the stack, thereby obviating the need for tie-bars.

Claims

1. A metal supported solid oxide fuel cell stack assembly comprising: (i) a metal base plate; (ii) an at least one fuel cell stack mounted on the base plate; and (iii) a metal end plate; each at least one fuel cell stack arranged mounted between said base plate and said end plate, and comprising at least one fuel cell stack layer, each at least one fuel cell stack layer comprising at least one fuel cell and at least one electrically insulating compression gasket, characterised in that: a skirt is attached to and between the base plate and the end plate to enclose the at least one fuel cell stack and is under tension to and between the base plate and the end plate to maintain a compressive force through the at least one fuel cell stack; and at least one electrically insulating gasket is sandwiched between an outer side surface of said at least one fuel cell stack and an adjacent inner surface of said skirt, the insulating gasket preventing oxidant flow around the outside of the fuel cell stack.

2. A metal supported solid oxide fuel cell stack assembly according to claim 1, wherein the skirt has a coefficient of thermal expansion greater than the coefficient of thermal expansion of the at least one fuel cell stack, the solid oxide fuel cell stack assembly additionally comprising at least one expansion plate located between the base plate and the end plate, the at least one expansion plate having a coefficient of thermal expansion greater than that of the skirt.

3. A metal supported solid oxide fuel cell stack assembly according to claim 1, additionally comprising first and second end poles in electrical contact with said at least one fuel cell stack, and wherein said base plate and said end plate are electrically isolated from said at least one fuel cell stack.

4. A metal supported solid oxide fuel cell stack assembly according to claim 1, wherein the skirt is a metal skirt.

5. A metal supported solid oxide fuel cell stack assembly according to claim 1, wherein the skirt is attached to and between the base plate and the end plate by welding.

6. A method of forming a metal supported solid oxide fuel cell stack assembly according to claim 1, comprising the steps of: (a) assembling: (i) the metal base plate; (ii) the at least one fuel cell stack mounted on the base plate; and (iii) the metal end plate; (b) applying a compressive force through the at least one fuel cell stack; (c) attaching the skirt to and between the base plate and the end plate to enclose the at least one fuel cell stack, the skirt sandwiching the at least one electrically insulating gasket between the outer side surface of said at least one fuel cell stack and the adjacent inner surface of said skirt, the insulating gasket preventing oxidant flow around the outside of the fuel cell stack; and (d) removing the compressive force so that a compressive load on the at least one fuel cell stack is maintained through tensile forces in the skirt.

7. A method according to claim 6 wherein the skirt has a coefficient of thermal expansion greater than the coefficient of thermal expansion of the at least one fuel cell stack, the method further comprising locating at least one expansion plate between the base plate and the end plate, the at least one expansion plate having a coefficient of thermal expansion greater than that of the skirt.

8. A method according to claim 6, wherein said skirt comprises a plurality of skirt sections.

9. A method according to claim 8, wherein said skirt has only two skirt sections.

10. A method according to claim 6, wherein the skirt is a metal skirt.

11. A method according to claim 6, wherein the skirt is attached to and between the base plate and the end plate by welding.

12. A metal supported solid oxide fuel cell stack assembly according to claim 1, wherein a fuel flow path from a fuel inlet to an exhaust fuel outlet is internally manifolded such that it is manifolded within the at least one fuel cell stack.

13. A metal supported solid oxide fuel cell stack assembly according to claim 1, wherein an oxidant flow path is defined from an oxidant inlet to an exhaust oxidant outlet and is externally manifolded, such that it is manifolded external to the at least one fuel cell stack, and internal to the fuel cell stack assembly.

14. A metal supported solid oxide fuel cell stack assembly according to claim 13, wherein an oxidant manifolding volume is defined between the base plate, the end plate, the skirt, and the at least one fuel cell stack.

15. A metal supported solid oxide fuel cell stack assembly according to claim 14, wherein the skirt has been attached to and between the base plate and the end plate by welding, the welding forming a gas tight seal.

16. A metal supported solid oxide fuel cell stack assembly according to claim 1, having an oxidant inlet end and an exhaust oxidant outlet end.

Description

(1) An enabling disclosure of the present invention, to one of ordinary skill in the art, is provided herein. Reference now will be made in detail to embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. Of the figures:

(2) FIG. 1 shows a section through a solid oxide fuel cell stack assembly of Embodiment 1;

(3) FIG. 2 shows a section through a fuel cell stack layer of FIG. 1;

(4) FIG. 3 shows a section through a solid oxide fuel cell stack assembly of Embodiment 2;

(5) FIG. 4 shows a section through a solid oxide fuel cell stack assembly of Embodiment 3;

(6) FIG. 5 shows a section through a fuel cell stack layer of Embodiment 4;

(7) FIG. 6 shows a section through a solid oxide fuel cell stack assembly of Embodiment 4;

(8) FIG. 7 shows a section perpendicular to the section of FIG. 6 through a solid oxide fuel cell stack assembly of Embodiment 4;

(9) FIG. 8 shows a section through a solid oxide fuel cell stack assembly of Embodiment 5;

(10) FIG. 9 shows an exploded perspective view of a fuel cell stack layer with fuel and oxidant (air) flows;

(11) FIG. 10 shows an exploded perspective view of the fuel cell stack layer of FIG. 9;

(12) FIG. 11 illustrates a step in the manufacture of a fuel cell stack assembly;

(13) FIG. 12 illustrates a step in the manufacture of a fuel cell stack assembly;

(14) FIG. 13 illustrates a step in the manufacture of a fuel cell stack assembly;

(15) FIG. 14 illustrates a step in the manufacture of a fuel cell stack assembly; and

(16) FIG. 15 is a perspective view of a completed fuel cell stack assembly.

(17) A list of the reference signs used herein is given at the end of the specific embodiments. Repeat use of reference symbols in the present specification and drawings is intended to represent the same or analogous features or elements.

EMBODIMENT 1

(18) In this embodiment, solid oxide fuel cell stack assembly 10, as shown in FIG. 1, comprises metal base plate 20 on which is mounted fuel cell stack 30, and metal end plate 40. Fuel cell stack 30 comprises a plurality of fuel cell stack layers 50.

(19) Negative power take off plate 140 is located between base plate 20 and fuel cell stack 30, and positive power take off plate 150 is located between fuel cell stack 30 and end plate 40.

(20) Thermiculite gasket 160 (made of Thermiculite 866; an electrically insulating compression gasket) is located between negative power take off plate 140 and base plate 20. An additional Thermiculite gasket 160 is located between positive power take off plate 150 and end plate 40.

(21) Each fuel cell stack layer 50, as shown in FIG. 2, comprises metal interconnect plate 60 on which is mounted metal spacer 70, and metal substrate 80.

(22) Metal substrate 80 has laser-driller perforated (porous) regions 91, 92, and first and second fuel cells 101, 102 deposited over porous regions 91, 92 respectively.

(23) Each fuel cell 101, 102 comprises an anode layer deposited onto porous region 91, 92 (respectively), an electrolyte layer deposited over the anode layer, and a cathode layer deposited over the electrolyte layer.

(24) As shown in FIGS. 9 and 10, metal interconnect plate 60 is shaped to define fuel flow orifices 61, 62. Metal spacer 70 is shaped to define fuel flow orifices 71, 72. Metal substrate 80 is shaped to define fuel flow orifices 81, 82. Metal spacer 70 is further shaped to define fuel flow space 73, and to define openings 71a and 72a between fuel flow orifices 71, 72 and fuel flow space 73.

(25) With metal spacer 70 sandwiched between metal interconnect plate 60 and metal substrate 80, a fuel flow void 74 corresponding to fuel flow space 73 is thus defined between first (inner) surface 63 of metal interconnect plate 60, first (inner) surface 83 of metal substrate 80, and metal spacer 70. First (inner) surface 63 of metal interconnect plate 60 has dimples extending towards first (inner) surface 83 of metal substrate 80. These dimples in-use assist in fluid flow within fuel flow void 74 and in maintaining fuel flow void 74 when fuel cell stack 30 is under compressive load.

(26) Fuel cells 101, 102 are deposited onto the second (outer) surface 84 of metal substrate 80.

(27) Thermiculite gaskets (electrically insulating compression gaskets) 110 are positioned on second (outer) surface 84 of metal substrate 80 around fuel flow orifices 81, 82.

(28) Each fuel cell stack layer 50 thus defines a fuel flow path (a fluid flow path) between fuel flow orifices 61, 71, 81, openings 71a, fuel flow space 73, openings 72a, and fuel flow orifices 62, 72, 82.

(29) Orifices 61, 71, 71a and 81 are fuel inlet orifices/openings, and define a fuel inlet of fuel cell stack layer 50 and a fuel inlet side (or end) to fuel cell stack layer 50. Orifices 62, 72, 72a and 82 are exhaust fuel outlet orifices/openings, and define an exhaust fuel outlet of fuel cell stack layer 50 and an exhaust fuel outlet side (or end) to fuel cell stack layer 50.

(30) The light dashed arrows 700 in FIG. 9 illustrate a fuel fluid flow path. The heavy dashed lines 710 in FIG. 9 illustrate an oxidant (air) fluid flow path.

(31) Second (outer) surface 64 of metal interconnect plate 60 comprises a plurality of outwardly extending dimples 65. As fuel cell stack layers 50 are stacked together, the metal interconnect plate 60 of a first fuel cell stack layer contacts the Thermiculite gaskets 110 and (by way of outwardly extending dimples 65) the cathode layers of first fuel cell 101 and second fuel cell 102. The arrangement of Thermiculite gaskets 110 and outwardly extending dimples 65 results in an oxidant flow path being defined between the metal interconnect plate 60 of a first fuel cell stack layer 50 and the metal substrate 80 of an adjacent second fuel cell stack layer 50. This oxidant flow path is externally manifolded. Thus, each fuel cell stack layer 50 has an externally manifolded oxidant inlet and outlet.

(32) With fuel cell stack 30 arranged mounted between metal base plate 20 and metal end plate 40, compression means 600 (FIG. 12) is used to exert compressive force on fuel cell stack 30 between metal base plate 20 and metal end plate 40, i.e. they are compressed by compression means 600. Mica gaskets 120 (electrically insulating gaskets) are then placed along the sides of fuel cell stack 20. First skirt half 131 and second skirt half 132 are then placed around the base plate 20 (FIG. 13), fuel cell stack assembly 30, end plate 40, and mica gaskets 120. Each of first skirt half 131 and second skirt half 132 are then fillet welded using TIG welding to metal base plate 20 and metal end plate 40 at weld points 190. First skirt half 131 and second skirt half 132 are then fillet welded together to define skirt 130. Thus, a volume is defined between base plate 20, end plate 40 and skirt 130, within which is contained fuel cell stack 30.

(33) Compression means 600 is arranged such that it applies compressive force around the edges (i.e. around the perimeter) of metal base plate 20 and metal end plate 40 in order to reduce or minimise the bowing of fuel cell stack layers 50. With first skirt half 131 and second skirt half 132 welded to metal base plate 20 and metal end plate 40 (i.e. welded around metal base plate 20 and metal end plate 40), this compression around the edges is maintained when compression means 600 is removed.

(34) Compression means 600 is then removed (FIG. 14), and the compressive load on fuel cell stack 30 is maintained through the tensile forces in skirt 130. Thus, the use of tie-bars is not required to effect compression of the fuel cell stack assembly 10. This reduces thermal mass and improves performance of fuel cell stack assembly 10 as compared to a corresponding fuel cell stack assembly incorporating tie-bars. By not having tie-bars, the surface area of metal substrate 80 available onto which fuel cells can be deposited is increased, thus allowing for further increase in performance as compared to a corresponding fuel cell stack assembly incorporating tie-bars.

(35) In use, fuel cell stack assembly 10 can be readily configured to operate in a co-flow (FIG. 9) or counter-flow manner.

EMBODIMENT 2

(36) In this embodiment (see FIG. 3), construction and assembly of solid oxide fuel cell stack assembly 200 is generally as per the first embodiment. However, solid oxide fuel cell stack assembly 10 additionally comprises expansion plates 181, 182. A first expansion plate 181 is located between base plate 20 and Thermiculite gasket 160, and a second expansion plate 182 is located between end plate 40 and Thermiculite gasket 160.

(37) Materials used in the various embodiments detailed herein are shown in Table 1 below:

(38) TABLE-US-00001 TABLE 1 CTE @ 650 DegC. Element Material (μm/(m .Math. ° C.)) base plate 20 ferritic stainless steel 3CR12 11.9 end plate 40 ferritic stainless steel 3CR12 11.9 metal interconnect ferritic stainless steel, grade 441 10.5 plate 60 metal spacer 70 ferritic stainless steel, grade 441 10.5 metal substrate 80 Crofer 22 APU (VDM Metals 11.4 GmbH) Thermiculite gasket Thermiculite 866 (Flexitallic 8.04 110 Ltd., UK) mica gasket 120 mica 8.7 skirt 130 ferritic stainless steel, grade 441 10.5 Thermiculite gasket Thermiculite 866 8.04 160 expansion plate 181 austentic stainless steel 316 18 expansion plate 182 austentic stainless steel 316 18

(39) As can be seen from Table 1, the CTE (coefficient of thermal expansion) of the various components differs significantly. As a result of the at least one electrically insulating compression gasket (Thermiculite gasket 110) present in each fuel cell stack layer 50, the CTE value of skirt 130 is greater than that of fuel cell stack layer 50. The end result is that as the temperature of the fuel cell stack assembly increases, expansion of skirt 130 (between base plate 20 and end plate 40) is greater than expansion of fuel cell stack 30 and other components assembled between base plate 20 and end plate 40 (in particular Thermiculite gaskets 160 and Thermiculite gaskets 110), i.e. there is a differential in thermal expansion. This results in a decrease in compressive force exerted upon fuel cell stack 30 as the temperature of fuel cell stack assembly 10 increases.

(40) In this embodiment, expansion plates 181, 182 reduce this decrease in compressive force, and thus enhance performance of the fuel cell stack assembly 200.

(41) Expansion plates 181, 182 have a CTE greater than that of skirt 130 (and greater than that of base plate 20 and end plate 40), and are sized to compensate for the differential thermal expansion. Expansion plates 181, 182 are sized according to the number of fuel cell stack layers 50 in fuel cell stack assembly 200. This approach to sizing/dimensioning of expansion plates is generally applicable to all embodiments of the present invention.

EMBODIMENT 3

(42) In this embodiment (see FIG. 4), solid oxide fuel cell stack assembly 300 comprises a back-to-back arrangement of first and second fuel cell stacks 171, 172. Construction and assembly is generally as per the second embodiment. However, in the first embodiment positive power take off plate 150 contacts Thermiculite gasket 160, i.e. is sandwiched between: (a) first fuel cell 101, second fuel cell 102 and Thermiculite gaskets 110 of a fuel cell stack layer 50, and (b) Thermiculite gasket 160.

(43) Instead, in this second embodiment positive power take off plate 150 is sandwiched between: (a) first fuel cell stack 171, and (b) second fuel cell stack 172.

(44) Thus, positive power take off plate 150 is sandwiched between: (a) first fuel cell 101, second fuel cell 102 and Thermiculite gaskets 110 of a fuel cell stack layer 50 of first fuel cell stack 171, and (b) first fuel cell 101, second fuel cell 102 and Thermiculite gaskets 110 of a fuel cell stack layer 50 of second fuel cell stack 172.

(45) This arrangement provides the advantage of a larger power output within the same assembly design and compression process.

EMBODIMENT 4

(46) In this embodiment (see FIGS. 5-7), construction and assembly of solid oxide fuel cell stack assembly 400 is generally as per Embodiment 2. However, instead of each fuel cell stack layer 50a comprising first and second fuel cells (101, 102 respectively in Embodiment 2), each fuel cell stack layer 50a comprises a single fuel cell 410.

(47) FIG. 7 (illustrating this embodiment) shows mica gaskets 120 which are used to electrically insulate the side of fuel cell stacks (30, 171, 172) in the various embodiments of the present invention from the adjacent inner surface of skirt 130. Mica gaskets 120 are thus sandwiched between skirt 130 and the fuel cell stack (30, 171, 172) and limit (or block/prevent) fluid flow between them. This assists in the external manifolding of oxidant (air) flow within the fuel cell stack assembly, and assists in defining an oxidant inlet end to the fuel cell stack assembly which is manifolded external to the at least one fuel cell stack (30, 171, 172 etc.) and internal to the fuel cell stack assembly (10, 200, 300, 40, 500). Similarly, it assists in defining an exhaust oxidant outlet end to the fuel cell stack assembly which is manifolded external to the at least one fuel cell stack (30, 171, 172 etc.) and internal to the fuel cell stack assembly (10, 200, 300, 400, 500).

EMBODIMENT 5

(48) In this embodiment (see FIG. 8), construction and assembly of solid oxide fuel cell stack assembly 500 is generally as per Embodiment 3. However, as per Embodiment 4 each fuel cell stack layer 50a comprises a single fuel cell 410. Furthermore, only a single expansion plate 183 is provided, This expansion plate 183 is attached to metal end plate 40.

ALL EMBODIMENTS

(49) FIGS. 9 and 10 provided exploded perspective views of fuel cell stack layers 50 and 50a and illustrates the fluid flow paths within them and within stacks of them.

(50) Fuel fluid flow path 700 into fuel cell stack layer 50, 50a is via fuel flow orifice 81 in metal substrate 80, fuel flow orifice 71 and opening 71a in metal spacer 70 (i.e. on a fuel inlet side of the fuel cell stack layer 50, 50a) and into fuel flow void 74 defined in fuel flow space 73 between metal substrate 80, metal spacer 70 and metal interconnect plate 60, passing across first (inner) surface 83 of metal substrate 80 and first (inner) surface 63 of metal interconnect plate 60. The fuel cell/fuel cells 101, 102, 410 (depending on the embodiment) are located on second (outer) surface 84 of metal substrate 80 and fuel flow to (and the return of exhaust fuel from) the fuel cell/fuel cells is via laser-drilled perforated porous region 91, 92, 93 (depending on the embodiment).

(51) Exhaust fuel exits fuel cell stack layer 50, 50a via opening 72a and fuel flow orifice 72 in metal spacer 70, and fuel flow orifices 82 in metal substrate 80 (i.e. on an exhaust fuel outlet side of fuel cell stack layer 50, 50a).

(52) Orifices 61, 62 in metal interconnect plate 60 and Thermiculite gaskets 110 further extend the fluid flow path to adjacent fuel cell stack layers 50, 50a.

(53) Fuel fluid flow path 700 is internally manifolded.

(54) Oxidant flow path 710 is manifolded external to fuel cell stack layer 50, 50a and internal to fuel cell stack assembly 10, 200, 300, 400, 500. A volume is defined between metal base plate 20, metal end plate 40, skirt 130, and the fuel cell stack(s) 30, 171, 172 (depending on the embodiment). Oxidant flow from an oxidant inlet end of the fuel cell stack layer 50, 50a adjacent fuel flow orifices 81, 71, 61 (i.e. adjacent fuel inlet side) to an exhaust oxidant outlet end of the fuel cell stack layer 50, 50a adjacent fuel flow orifices 82, 72, 62 (i.e. adjacent exhaust fuel outlet side) is between adjacent fuel cell stack layers 50, 50a i.e. between metal interconnect plate 60 of a first fuel cell stack layer 50, 50a and metal substrate 80 of an adjacent second fuel cell stack layer 50, 50a.

(55) Oxidant flow from the oxidant inlet end to the exhaust oxidant outlet end around the outside of fuel cell stack 30, 171, 172 (i.e. other than between) fuel cell stack layers 50, 50a) is prevented by mica gasket 120 located sandwiched between skirt 130 and fuel cell stack 30, 171, 172 from the oxidant inlet end to the exhaust oxidant outlet end.

(56) FIG. 9 illustrates a co-flow operation of fuel and oxidant flows. Counter-flow operation is equally possible, i.e. oxidant flow is counter to fuel flow, with the oxidant inlet end of the fuel cell stack layer 50, 50a adjacent fuel flow orifices 82, 72, 62 (i.e. adjacent exhaust fuel outlet side) to an exhaust oxidant outlet end of the fuel cell stack layer 50, 50a adjacent fuel flow orifices 81, 71, 61 (i.e. adjacent fuel inlet side).

(57) Stack Assembly Method

(58) Fuel cell stack 30 is formed (FIG. 11) by assembling fuel cell stack layers 50 upon metal end plate 40. Metal base plate 20 is then placed on top of fuel cell stack 30.

(59) A removable compression means 600 is then used (FIG. 12) to exert compressive force 610 through end plate 40, fuel cell stack 30 and base plate 20.

(60) With compressive force 610 still being exerted through fuel cell stack 30 (FIG. 13), skirt first half 131 and skirt second half 132 are then placed around end plate 40, fuel cell stack 30 and base plate 20.

(61) Skirt first half 131 and skirt second half 132 are then attached to base plate 20, end plate 40 by TIG welding. Skirt first half 131 and skirt second half are also TIG welded to one another to form skirt 130 with fillet weld 133. Thus, fuel cell stack 30 is enclosed within a volume defined by base plate 20, end plate 40 and skirt 130. The TIG welding forms a gas tight seal between the skirt first half 131, skirt second half 132, base plate 20 and end plate 40.

(62) Compression means 600 is then removed (FIG. 14) and the compressive load 610 on fuel cell stack 30 is maintained through tensile forces 620 in skirt 130, i.e. fuel cell stack 30 is under tension to and between base plate 20 and end plate 40 to maintain a compressive force through fuel cell stack 30. Reference signs are incorporated in the claims solely to ease their understanding, and do not limit the scope of the claims. The present invention is not limited to the above embodiments only, and other embodiments will be readily apparent to one of ordinary skill in the art without departing from the scope of the appended claims.

REFERENCE SIGNS

(63) 10—solid oxide fuel cell stack assembly 20—metal base plate 30—fuel cell stack 40—metal end plate 50—fuel cell stack layer 50a—fuel cell stack layer 60—metal interconnect plate 61—fuel flow orifice 62—fuel flow orifice 63—first (inner) surface of metal interconnect plate 60 64—second (outer) surface of metal interconnect plate 60 65—outwardly extending dimples 70—metal spacer 71—fuel flow orifice 71a—opening 72—fuel flow orifice 72a—opening 73—fuel flow space 74—fuel flow void 80—metal substrate 81—fuel flow orifice 82—fuel flow orifice 83—first (inner) surface of metal substrate 80 84—second (outer) surface of metal substrate 80 91—laser-drilled perforated (porous) region 92—laser-drilled perforated (porous) region 93—laser-drilled perforated (porous) region 101—first fuel cell 102—second fuel cell 110—Thermiculite gasket 120—mica gasket 130—skirt 131—skirt first half 132—skirt second half 133—fillet weld 140—negative power take off plate 150—positive power take off plate 160—Thermiculite gasket 171—first fuel cell stack 172—second fuel cell stack 181—first expansion plate 182—second expansion plate 183—expansion plate 190—weld point 200—solid oxide fuel cell stack assembly 300—solid oxide fuel cell stack assembly 400—solid oxide fuel cell stack assembly 410—fuel cell 500—solid oxide fuel cell stack assembly 600—compression means 610—compressive forces 620—tensile forces 700—fuel fluid flow path 710—oxidant fluid flow path 720—fuel inlet side 730—exhaust fuel outlet side 740—oxidant inlet side 750—exhaust oxidant outlet side