Fuel cell manifold seal with rigid inner layer

A multi-layer seal system for a manifold (10) of a proton exchange membrane fuel cell includes a silicone rubber filler layer (22) between endplates (9) to compensate for the uneven edges of cell elements, an elastomer gasket (15) disposed within a groove (24) in the contact surfaces of a manifold (10), and a rigid dielectric strip (40) coplanar with the contact surfaces (17) of the endplates (9) interposed between the silicone rubber filler layer (22) and the gasket (15). The rigid dielectric strip (40) may be either angled (40a) for a corner seal, or flat (40b).

TECHNICAL FIELD

This invention relates to a multi-layer reactant gas manifold seal having a rigid inner layer for sealing a proton exchange membrane (PEM) fuel cell manifold to a fuel cell stack assembly.

BACKGROUND ART

A basic fuel cell comprises an anode electrode spaced apart from a cathode electrode with an electrolyte disposed between the two electrodes; each electrode includes a catalyst layer on the electrolyte side thereof. On the non-electrolyte side of the anode electrode is a reactant gas chamber for carrying a fuel, and on the non-electrolyte side of the cathode electrode is a reactant gas chamber for carrying an oxidant. The electrodes are constructed so that the gas diffuses therethrough and comes into contact with the electrolyte in the catalyst layer thereby causing a well-known electrochemical reaction whereby hydrogen ions and electrons are produced at the anode. The electrons travel from the anode electrode through an external circuit to the cathode electrode where they react with oxygen to produce heat and water. This flow of electrons is the electric current produced by the cell.

In a proton exchange membrane (PEM) fuel cell power plant, a number of fuel cells are connected electrically in series, forming a cell stack assembly (CSA). The cells of the CSA are sandwiched between end plates bolted together to hold the cells in tight contact with one another.

Cell stack assemblies that utilize gaseous reactants typically have opposed pairs of external manifolds which distribute the reactant gases to the cells in the stack, and gather reactant exhaust gases from the cells in the stack, as disclosed for example in commonly owned U.S. patent application Ser. No. 09/920,914, (PCT publication number US 2003-0027029) Typically, the pairs comprise a fuel inlet/exit manifold opposite a fuel turn manifold and an air inlet manifold opposite an air outlet manifold. Each manifold must be sealed to the cell stack assembly to prevent leakage of the reactant gases into the ambient environment. A manifold retention system may include load cables to provide a manifold-to-CSA sealing force.

Generally, the dimensional tolerances of the individual cells and the position tolerances of the cells within the cell stack assembly result in cell edge misalignment, known as an uneven “skyline”, within the PEM cell stack assembly.

Referring toFIG. 1, a typical prior art PEM fuel cell manifold-to-CSA seal arrangement, disclosed in commonly owned U.S. patent application Ser. No. 09/882,750, (PCT publication number US 2001-0055708-A1), is illustrated. Fuel cell elements8, which together form an uneven skyline, are sandwiched between endplates9bolted together so as to hold the individual cells8in tight contact with one another. A reactant gas manifold10(either oxygen containing oxidizing gas or hydrogen containing fuel gas) is positioned adjacent the cell elements8so as to provide a flow of reactant gas to and from the CSA35. The prior art seal system13includes one or more filler layers22of silicone liquid rubber applied to the skyline of the stack surface to form a flat relatively smooth surface above the elements8, overlapping the sealing surfaces17on the endplates9. A molded silicone rubber gasket15is bonded to a contact surface16of the manifold10. The gasket15is used in conjunction with a flat rubber strip20, typically a molded precast silicone rubber strip, interposed between the silicone rubber filler layer22and the gasket15.

When subject to a sealing force between the manifold10and CSA35, the layers of sealing materials,20,22and15, compress to form a tight seal. Even when compressed, however, the intervening layers of sealing materials result in a necessary clearance24between contact surfaces16and17of the manifold10and endplates9respectively.

Although well suited for stationary fuel cell power plant applications, such manifold-to-CSA seals disclosed in the prior art have certain limitations when used in automobiles or other vehicles subject to the stresses of acceleration and vibration. In particular, the seals may experience compressive creep over time, which reduces the sealing force exerted by the load cables, and can result in reactant leakage and slipping of the seals. Moreover, the rubber strip20, between the gasket15and the silicone rubber filler22transfers the compressive forces on the seal to the cell stack assembly non-uniformly and may result in cracked cell components8at the high spots in the skyline.

DISCLOSURE OF INVENTION

Objects of the invention include provision of:

a rigid, flat, level sealing surface between manifold and CSA to minimize leakage caused by compressive creep;

an even load distribution to the CSA seal area in order to reduce the loading concentration on skyline high spots that can cause cracking of the cell components; and

enhanced seal durability to meet vehicular CSA requirements.

According to the present invention, a manifold seal system for a fuel cell comprises at least three parts, including a first seal part of elastomer filler applied to the uneven skyline of the cell stack assembly between opposite endplates, the elastomer filler being any compatible elastomer such as a silicone rubber, a room temperature vulcanizing (RTV) rubber, and an ultraviolet curable elastomer, a second seal part comprising an elastomer gasket disposed within a groove in the contact surface of the manifold, and a third seal part comprising a rigid dielectric strip interposed between the first and second seal parts; the rigid strip being seated in a coplanar relationship with the contact surfaces of the endplates to form a sealing surface of the cell stack assembly, the three seal parts dimensioned so that facing surfaces of the manifold and the endplates (or coplanar rigid strip) are in direct contact with each other when the manifold is secured to the cell stack assembly under the proper design load.

Although it is preferable for the manifold seal system of the present invention to comprise at least three parts, it need not. In another aspect of the present invention, the manifold contact surface need only be in direct contact with a rigid sealing surface of a fuel cell stack assembly.

In yet another aspect of the present invention, the manifold seal system includes a rigid dielectric strip at the interface between a manifold contact surface and a corresponding sealing surface of a fuel cell stack assembly.

The cross section of the rigid dielectric strip may form a corresponding angle to enclose a corner of the cell stack assembly or, alternatively, the cross section of the rigid strip may be flat.

The present invention provides an effective seal between the manifold and the cell stack assembly, particularly for vehicular applications where the seal is subject to the forces of acceleration and vibration.

Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawings.

Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.

MODE(S) FOR CARRYING OUT THE INVENTION

Referring toFIG. 2, a reactant gas manifold10is positioned above a cell stack assembly35having an uneven skyline. At least one silicone rubber filler layer22, such as GE RTV 118, Shin Etsu KE3476T, or any compatible elastomer, is applied to the surface of the skyline to form a relatively flat, smooth surface above the cells8.

Endplate9of the present invention includes a notch27to receive an end portion of a rigid dielectric strip40coplanar with the contact surface17of the endplates9and extending over the CSA sealing area to spread the sealing load uniformly. The rigid strip40may be adhesively secured to the skyline silicone rubber filler layer22and on the notch surfaces of the endplates9. In order to prevent shorting of the cells8, the rigid strip40must be a dielectric, such as a NEMA G11 fiberglass reinforced plastic, or a polymer-coated metal. Other dielectric composite materials or metallic materials with a dielectric coating, known to those skilled in the art, may also be used to form the rigid strip40.

InFIG. 2, manifold10includes a groove24formed on the contact surface16thereof to hold a molded silicone rubber gasket15or equivalent compatible elastomer, that may be either pushed in place or molded into the groove24. It is an important aspect of the present invention that the groove24and the molded gasket15be dimensioned such that the contact surface16of the manifold10and the sealing surface of the CSA, (including the contact surface17of endplates9and coplanar surface of the rigid strip40) have a substantially zero clearance when the proper design load is applied by the load cables36, (seeFIG. 5) or other manifold attachment system. The elimination of a clearance between rigid surfaces16and17results in a much more stable seal and a constant sealing load that substantially reduces compressive creep. The multi-layer manifold seal of the present invention may be used advantageously with any PEM fuel cell manifold, including both fuel and oxidant inlet, exit and turn manifolds, in stationary, portable and vehicular PEM fuel cell applications.

In a first embodiment of the present invention, shown inFIGS. 3 and 4, molded elastomer gaskets15are partially recessed into grooves24in the contact surface of the manifold. Rigid strips40aand40bare adhesively secured to a layer of silicone rubber filler22and are coplanar with the surface17of endplates9such that when the proper design load on the load cables36(seeFIG. 5) is applied, contact surface16of the manifold is in direct contact with the corresponding sealing surface of the cell stack assembly. In this first embodiment, the rigid inner layer of the manifold seal at the corners37of the CSA is an angled strip40aenclosing the corner37. As used herein, “angled” means having a cross section conforming to the shape of the corner or other nonlinear edge of the cell stack assembly to be sealed. In this first embodiment the angled strip40ahas a generally L-shaped cross section as shown inFIG. 4. The angled strip40atends to force any fuel leakage from the fuel manifold30into the adjacent air manifolds31and32so that, advantageously, the fuel either reacts on the cathode catalyst or is vented in the high volume air exhaust stream.

In an alternative embodiment, illustrated inFIGS. 5 and 6, the rigid inner layer of the manifold seal at the corners37of the CSA comprise two flat strips40bat right angles to each other. The corner configuration using flat strips40bis shown in cross section inFIG. 6.

The aforementioned patent applications are incorporated herein by reference.

Thus, although the invention has been shown and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the invention.