WO2007063257A1

WO2007063257A1 - Stackable integrated fuel cell

Info

Publication number: WO2007063257A1
Application number: PCT/FR2006/051263
Authority: WO
Inventors: Fabien Pierre; Mathieu Roy
Original assignee: Stmicroelectronics Sa
Priority date: 2005-11-30
Filing date: 2006-11-30
Publication date: 2007-06-07

Abstract

The invention relates to a multilayer fuel cell consisting of a layer stack (8) formed on the front face of a perforated substrate (21, 31), a first electrode corresponding to the stack external surface and a second electrode (27) corresponding to the stack bottom and connected to the rear face of the substrate by a conductor path extending along the perforated part of the substrate.

Description

EMPTY INTEGRATED FUEL CELL

Field of the invention

The present invention relates to a fuel cell and more particularly to a stackable integrated fuel cell structure. Presentation of the prior art

Figure 1 shows an example of an integrated fuel cell made using microelectronics techniques. This cell is formed on a support plate consisting of a silicon wafer 1 coated with a first insulating thin layer 2 and a second insulating layer 3 thicker. An opening is formed in a portion of the insulating layer 3. In this opening are successively deposited a support layer 4, a catalyst layer 5, an electrolyte layer 6 and a second catalyst layer 7. This set of layers constitutes a active stack 8. An electrode 10, placed on the first insulating layer 2, is in contact with the support layer 4 on the lower side of the cell side. An opening 11 in the second insulating layer 3 provides access to the electrode 10. An upper electrode 12 is in contact with the upper catalyst layer 7. The electrodes 10 and 12 are provided with openings, and channels 13 are formed in the silicon wafer 1 facing openings in the lower face metallization. The lower electrode 10 and the upper electrode 12 respectively constitute an anode collector and a cathode collector.

The electrolyte 6 is, for example, a polymeric acid such as Nafion in solid form and the catalyst layers are, for example, layers based on carbon and platinum. This is only an example of realization. Various types of fuel cells that can be made in the form illustrated in FIG. 1 are known in the art. To operate the fuel cell, hydrogen is injected according to the arrow H2 on the side of the lower face and air (oxygen carrier) is injected on the side of the upper face. Hydrogen is "broken" at the catalyst layer 5 to form a part of the H ⁺ protons which are moving towards the electrolyte 6 and the other elec trons ^¬ which are directed from the outside of the stack, to the anode collector 10. the H ⁺ protons pass through the electrolyte 6 to reach catalyst layer 7 where they recombi ^¬ NENT with oxygen and electrons arriving from outside of the stack by the cathode collector. In known manner, with such a structure, a positive potential is obtained on the cathode collector 12 (oxygen side) and a negative potential on the anode collector 10 (hydrogen side).

It should be emphasized that Figure 1 is not to scale. In particular, the support plate 1 typically has a thickness of the order of 250 to 700 μm while the active stack 8 of layers 4 to 7 typically has a thickness of the order of 30 to 50 μm.

The structure described in connection with Figure 1 poses many problems of manufacture and use.

One of the manufacturing problems lies in the fact that it is relatively difficult to form a thick insulating layer 3 that can serve as a housing for the active stack 8.

A difficulty in using the fuel cell cell shown in FIG. 1 lies in the fact that the two electrodes, anode and cathode, are accessible by the same face. On the other hand, it is conventional for stacks of any kind to make stacks for serial mounting, and it is then more convenient for the electrodes to be on opposite sides of the stack. Summary of the invention

An object of the present invention is to provide a fuel cell structure which overcomes at least some of the disadvantages of the structures of the prior art. Another object of the present invention is to provide such a simple structure fuel cell.

Another object of the present invention is to provide a fuel cell structure without a thick insulating layer. Another object of the present invention is to provide such a fuel cell which has an electrode on each of its opposite faces.

To achieve these objects, the present invention provides a multilayer fuel cell cell consisting of a stack of layers formed on the front face of a perforated substrate, a first electrode corresponding to the outer face of the stack, and a second electrode corresponding to the bottom of the stack and being connected to the rear face of the substrate by a conductive path extending along the perforated portion of the substrate.

According to one embodiment of the present invention, said stack of layers is formed in a recess of the front face of the perforated substrate.

According to one embodiment of the present invention, the substrate is made of silicon.

According to an embodiment of the present invention, said conductive path corresponds to a coating of a conductive material such as gold extending on the front face of the substrate at the location where said stack of layers, along the perforations and up to the back side of the substrate.

The present invention also provides a method of manufacturing a fuel cell, comprising the steps of forming a recess on the side of the front face of a support plate, forming channels through the support plate at the bottom of the fuel cell. the recess, forming an insulating layer on the front face of the plate and on the side walls of the recess, and forming a conductive coating at uncoated locations of the insulating layer.

According to an embodiment of the present invention, the method comprises, after the step of forming channels through the support plate, the formation of non-through channels from the front face, and the formation of a second recess from from the rear face facing the recess on the side of the front face, and to the bottom of said channels.

According to one embodiment of the present invention, the support plate is a silicon wafer, said recesses are formed by wet etching, the perforations are formed by plasma etching, the insulating layer is formed by thermal oxidation, and the conductive coating is formed by non-electrolytic deposition.

The present invention also provides an assembly of cells, consisting of stacking the cells on each other with the interposition of spacers arranged to allow a flow of gas between each spacer and the face opposite each cell. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features, and advantages of the present invention will be set forth in detail in the following description of particular embodiments in a non-limitative manner with reference to the accompanying figures in which: Figure 1 is a sectional view of a known fuel cell cell; Figure 2 is a schematic sectional view illus trating ^¬ a first embodiment of a fuel battery cell according to the present invention; Figure 3 is a schematic sectional view illus trating ^¬ a second embodiment of a fuel battery cell according to the present invention; Figs. 4A to 4C are sectional views illustrating steps of manufacturing a fuel cell according to the first embodiment of the present invention; Figs. 5A and 5B are sectional views illustrating steps of manufacturing a fuel cell according to the second embodiment of the present invention; FIG. 6 shows a fuel cell according to the first embodiment of the present invention associated with an interface module between cells; FIG. 7 shows a fuel cell according to the second embodiment of the present invention associated with an interface module between batteries; and Figure 8 shows a cell assembly according to the second embodiment of the present invention.

For the sake of clarity, as is usual in the representation of microcomponents, the elements of the various sectional and perspective views are not drawn to scale.

detailed description

Fig. 2 shows an example of a fuel cell according to a first embodiment of the present invention. This cell is formed from a support plate 21 comprising a perforated region 23. On the side of the upper face or front face of the wafer, in the region where the perforations or channels 23 are arranged, is formed a recess in which is disposed the stack 8 of active layers described in connection with Figure 1. The recess in the front face of the support 21 has a depth that corresponds substantially to the thickness necessary to house the stack 8. On the upper face of the stack, an anode electrode 24 is deposited.

According to one aspect of the invention, the contact with the lower cathode face of the stack 8 is carried on the lower face or rear face of the support plate 21. If the plate 21 is made of a highly conductive material, this Cathode contact report may be made by the material of the plate 21 itself. However, care must be taken to deposit an insulating layer 25 on the parts of the upper face of the plate 21 that may be in contact with the anode electrode 24 or insufficiently insulated from it. If the support plate 21 is insulating, the bottom of the recess formed on the side of the front face of the plate 21, the walls of the channels 23 and the rear face of the plate 21 of a highly conductive material 27, will be coated by example a layer of gold. In the case where the support plate 21 is a silicon wafer, which is a conductive but relatively resistive material, the insulating layer 25 and preferably the conducting layer 27 will be formed. This will be described later in various embodiments of the invention. In addition, if it is desired to prevent the material of the plate 21 from being at the cathode potential, an insulating thin layer (not shown) is deposited beneath the conductive layer 27. It will be noted that the structure illustrated in FIG. 2 incorporates two aspects of the invention:

- The formation of the stack 8 in a recess of the support plate;

- The postponement of contact with the rear face layer of the stack 8 to the rear face of the support plate.

The invention aims on the one hand each of these aspects, on the other hand the combination of these aspects. The second aspect of the present invention (transfer to the rear face of the support plate contact with the rear layer of the stack 8) could be implemented even with a conventional structure such as that of Figure 1 in which the opening 11 would be removed to resume contact with the electrode 10 from the front face. Nevertheless, the use of this structure could be poorly suited to an application according to the invention, described below, to the formation of cell stacks because then there would be a support on the thick insulating layer 3 which is usually not rigid.

Figure 3 is a schematic sectional illus trating ^¬ a second embodiment of the present invention constituting a variant embodiment shown in relation with Figure 2. In this figure, the same elements and layers are designated with the same 2. The support plate 31 is similar on its upper side to the plate 21 of Figure 2. It has a perforated zone 33 on the side of the lower face. In addition, facing the perforated zone 33 is provided a recess 35. As indicated above, the upper recess has a thickness of the order of 30 to 50 microns. The lower recess is as deep as possible to limit the thickness of the perforated area and simplify the perforations but must leave in place a sufficient thickness of the wafer to ensure sufficient mechanical strength of the wafer. For example, this recess will have a depth of the order of half the thickness of the support plate 31. In the case where the support plate is a silicon wafer with a thickness of 300 to 500 μm, the recess 35 may have a depth of the order of 150 to 300 microns.

FIGS. 4A to 4C are sectional views illustrating successive steps of manufacturing the stack structure of FIG. 2.

In a first step illustrated in FIG. 4A, an upper recess 22 is formed in a plate 21 and perforations 23 passing through the plate are made. In the case where the support plate 21 is a silicon wafer, the recess 22 may be formed by wet etching, for example by KOH, and etchings 23 may be formed by definition of a mask and then plasma etching.

In the step illustrated in FIG. 4B, an insulating layer 25 has been formed on the upper part of the support plate and on the sides of the recess 22 (as well as possibly on selected parts, not shown, of the rear face ).

This can be achieved by successively performing:

thermal oxidation to form a silicon oxide layer on all the exposed surfaces of the silicon wafer,

a masking of the areas that one wants to preserve, and

an elimination by chemical etching of the other parts of silicon oxide.

In the following steps illustrated in FIG. 4C, a conductive layer is deposited on the portions of the silicon wafer that are not protected by the silicon oxide layer 25. It will be possible, for example, to perform a non-electrolytic deposition of gold that hangs on the visible portions of silicon and not on the oxide layer 25. The conductive layer 27 is thus formed. After this, the active stack 8 is formed and the electrode is deposited. anode 24.

FIGS. 5A and 5B illustrate successive steps of manufacturing a fuel cell as illustrated in FIG. 3. Starting from a plate 31 comprising an upper recess 22 facing a lower recess 35, the part the wafer between the two recesses comprising channels or perforations 33. To obtain this structure, one proceeds for example following the following steps: - formation of the front face recess 22 by wet etching;

plasma attack piercing of non-through channels 33 extending only to the depth they will have after formation of a rear-face recess;

- oxidation of the structure; - forming the rear face recess 35 by wet etching; and

- deoxidation.

Then, on the front face of the wafer illustrated in FIG. 5A, the steps described previously in relation with FIGS. 4B and 4C are carried out to obtain the structure illustrated in FIG. 5B in which the same elements as in FIG. same references.

FIG. 6 is a sectional view illustrating a spacer associated with a cell as illustrated in FIG. 2 to allow stacking of cells. A cell 41 formed on a support plate 21 is disposed above a spacer 42 comprising a plate 44, possibly made of silicon or metal, surrounded by a ring 46 projecting upwards and downwards relative to the plate 44. It will be understood that this spacer can be supported on the lower face of the cell 41 and that the upper face of another cell 41 can be supported on the underside of the spacer. A stack of several cells can thus be constituted. A circulation of hydrogen between a lower face of the cell and a spacer may be conveniently made and between a top face of the cell and a spacer a circulation of air or oxygen.

The same spacers may be used in connection with cells of the type of those of Figure 3.

However, as illustrated in FIG. 7, a cell 51 of the type of that of FIG. 3, formed on a support plate 31 may be associated with a spacer 52 comprising a thin plate 54 surrounded by a ring 56 projecting only towards the bottom. Figure 8 shows a stack of cells and spacers according to the second embodiment of the present invention. One can see there first 61 and second 62 cells, a spacer 63 such as that of Figure 7 disposed between the cells 61 and 62, and a spacer 64 disposed under the cell 62. Of course, the stack can be repeat. The locations where hydrogen and air circulate respectively are marked by the indications "H2" and "O2". Various modes of electrical connection between the batteries can be provided. For example, if the spacers are conductive, there is provided a series circuit, the cathode terminal of a top cell being connected to the anode terminal of an NCI cell ^¬ higher.

It will be understood that several stacks such as that of FIG. 8 can be made side by side and that it will thus be possible to carry out series-parallel assemblies. Provision may also be various types of openings on the sides laté ^¬ ral struts or cells between two adjacent cells to permit circulation in the direction perpendi cular ^¬ in the figure or in the plane of FIG oxygen and / or of hydrogen.

Claims

1. A multi-layer fuel cell comprising a stack of layers (8) formed on the front face of a perforated substrate (21, 31), a first electrode corresponding to the outer face of the stack, and a second electrode corresponding to the bottom of the stack and being connected to the rear face of the substrate by a conductive path extending along the perforated portion of the substrate.

The fuel cell of claim 1, wherein said stack of layers (8) is formed in a recess in the front face of the perforated substrate (21, 31).

The fuel cell of claim 1 or 2, wherein the substrate is silicon.

A fuel cell cell according to any one of claims 1 to 3, wherein said conductive path corresponds to a coating of a conductive material such as gold extending on the front face of the substrate to the location where said stack of layer is deposited, along the perforations and up to the rear face of the substrate.

A method of manufacturing a fuel cell according to claim 1, comprising the steps of: forming a recess (22) on the front side of a support plate (21), forming channels (23) passing through the support plate at the bottom of the recess, forming an insulating layer (25) on the front face of the plate and on the side walls of the recess, and forming a conductive coating at uncoated locations of the insulating layer .

6. A method according to claim 5, comprising, after the step of forming channels through the support plate, the formation of non-through channels (33) from the front face, and the formation of a second recess (35). from the rear face facing the recess (22) on the side of the front face, and to the bottom of said channels.

7. The method of claim 5 or 6, wherein the support plate is a silicon wafer, said recesses are formed by wet etching, the perforations are formed by plasma etching, the insulating layer is formed by thermal oxidation, and the conductive coating. is formed by non-electrolytic deposition.

8. A cell assembly according to any one of claims 1 to 4, comprising stacking the cells on each other with the interposition of spacers arranged to allow a flow of gas between each spacer and the facing side of each cell.