Structure for improving laminating efficiency of metal-separator for fuel cell

Disclosed is a structure for improving a laminating efficiency of a metal-separator for a fuel cell stack, the metal-separator comprising an embossed structure that has an indentation and a projection alternately formed along at least one edge thereof so as to enable a plurality of the metal-separators to be stably laminated in a honeycomb shape.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2006-0086441 filed in the Korean Intellectual Property Office on Sep. 7, 2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a metal-separator for a fuel cell stack, and more particularly to a structure for improving laminating efficiency of a metal-separator for a fuel cell stack in which an edge of the separator comprises an embossed structure so that a plurality of the separators can be stably laminated in a honeycomb structure.

FIG. 1is an exploded perspective view of a conventional polymer electrolyte fuel cell, andFIG. 2AandFIG. 2Bare top plan views thereof.

As shown inFIG. 1, a polymer electrolyte fuel cell stack1includes a membrane electrode assembly (MEA)3which is comprised of a polymer electrolyte membrane and electrodes formed on both sides of the polymer electrolyte membrane. It also includes a pair of gas diffusion layers4which are coupled to the membrane electrode assembly3and deliver reaction gases to the electrodes. It also includes a pair of conductive separators6which adhere to outer surfaces of the respective gas diffusion layers4so as to supply reaction gases. It also includes a gasket5which is interposed between the membrane electrode assembly3and the separator6so as to prevent the reaction gases from being leaked and to seal a gap. In addition, current collectors7and connecting plates (end plates)8are coupled to the outside of the separator6, thereby forming the fuel cell stack1.

The separator6separates hydrogen and oxygen, electrically connects the membrane electrode assembly3, and supports the membrane electrode assembly3to maintain the shape of the fuel cell stack1.

Accordingly, the separator should have a rigid structure for preventing the two gases from being mixed, an excellent electrical conductivity for serving an electrical conductor, and a high strength for serving a support member.

However, since voltage generated by one unit cell (basic unit of a fuel cell which is formed by coupling the membrane electrode assembly, the gasket, and the separator) is small, tens or hundreds of unit cells should be laminated in order to produce a desired electric power.

In the case that a lot of unit cells are laminated, if the separator cannot maintain a constant surface pressure, the separator may be locally deformed so that the sealing cannot be maintained. There have been many structures suggested to overcome this problem. Such structures, however, have a complicated sealing structure, causing the forming process to be complicated and limiting the degree of freedom in the development of design.

There is thus a need for an improved structure that can overcome the problems.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a structure for improving laminating efficiency of a metal-separator for a fuel cell stack in which at least one edge of the separator comprises an embossed structure so that a plurality of the separators can be stably laminated in a honeycomb structure.

In a preferred embodiment, the present invention provides a structure for improving a laminating efficiency of a metal-separator for a fuel cell stack which includes: a unit cell having a membrane electrode assembly; a gas diffusion layer moving reaction gases to the membrane electrode assembly; a metal-separator coupled to an outside of the gas diffusion layer so as to support the membrane electrode assembly; a gasket interposed between the membrane electrode assembly and the metal-separator so as to prevent reaction gas from being leaked; and a connecting plate having a plurality of manifolds and coupled to an outside of the unit cell so as to support the unit cell, wherein the metal-separator comprises an embossed structure that has a plurality of indentations and a plurality of projections alternatively formed at least one edge thereof so as to enable a plurality of the metal-separators to be stably laminated in a honeycomb shape.

Preferably, the metal-separator may comprise at one or more longitudinal end thereof a plurality of separator manifolds corresponding to the manifolds of the connecting plate.

The metal-separator may further include a reaction surface on its front surface and a cooling surface on its rear surface.

The reaction surface, preferably, is coupled to the gas diffusion layer so as to allow the reaction gas to be supplied and to be discharged.

The metal-separator may further include a reaction gas inlet hole in the vicinity of the separator manifolds provided at one end portion of the separator, and a reaction gas out let hole in the vicinity of the separator manifolds provided at the end portion opposite to the reaction gas inlet hole.

In a preferred embodiment, the gasket may be disposed along the edge of the metal-separator having the embossed structure and along the surrounding of the separator manifold so as to seal the area between the membrane electrode assembly and the metal-separator.

Preferably, the gasket may have a shape that fits the corresponding shape of the separator manifold.

Also preferably, a separate embossed structure may be further provided to the space between the respective separator manifolds for contributing to precisely determine the installation position of the gasket.

In another aspect, motor vehicles are provided that comprise a described structure.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like. The present structures will be particularly useful with a wide variety of motor vehicles.

Other aspects of the invention are discussed infra.

10: fuel cell stack100: unit cell

130a: reaction gas inlet hole130b: reaction gas outlet hole

DETAILED DESCRIPTION

FIG. 3Ais a perspective view of a fuel cell to which a metal-separator according to an exemplary embodiment of the present invention is applied,FIG. 3Bis an exploded view showing a laminating sequence of a metal-separator ofFIG. 3A,FIG. 4is a cross sectional view showing a laminating state of a metal-separator according to an exemplary embodiment of the present invention,FIG. 5Ais a top plan showing a reaction surface of a metal-separator according to an exemplary embodiment of the present invention,FIG. 5Bis a top plan view showing a cooling surface of a metal-separator according to an exemplary embodiment of the present invention, andFIG. 6is a drawing showing a structure in which a plurality of metal-separators according to an exemplary embodiment of the present invention are laminated.

As shown inFIG. 3AandFIG. 3B, a metal-separator130is sequentially laminated in an inside of a fuel cell stack10.

As shown inFIG. 3B, the metal-separators130are respectively coupled to both sides of a membrane electrode assembly (MEA) which is comprised of a polymer electrolyte membrane and electrodes formed on both sides of the polymer electrolyte membrane, and is integrated with a gas diffusion layer (not shown) which delivers the gas to the electrode. A gasket120is interposed between a membrane electrode assembly110and the metal-separator130for preventing leakage of reaction gas and for sealing gaps between them. Tens or hundreds of unit cells100formed by coupling the membrane electrode assembly110, the gasket120, and the metal-separator130are laminated, and a current collector (not shown) and a connecting plate (end plate)200are coupled to the laminated unit cells100so as to support the same, thereby forming the fuel cell stack10. A plurality of manifolds210is formed on the connecting plate200for supplying reaction gas and coolant to the unit cell100.

As shown inFIG. 4, in the unit cell100, the gasket120and the metal-separator130are sequentially disposed on both sides of the membrane electrode assembly110, and adhere closely to the membrane electrode assembly110. Coolant, air, and hydrogen are not mixed with one another by the flow passages formed in the metal-separator130and the gasket120. They are supplied to the membrane electrode assembly110through the metal-separator130and are discharged (detailed explanation for this will be made later).

As shown inFIG. 5AandFIG. 5B, the metal-separator130includes an embossed structure132which is formed along an edge of the plate surface. It also includes a plurality of separator manifolds134which are formed at both ends in the length direction of the plate surface corresponding to the manifolds210formed in the connecting plate200. In addition, a reaction surface136which is coupled to a gas diffusion layer so as to allow reaction gas to be supplied and to be discharged is formed on a front surface of the metal-separator130, and a cooling surface138which is a passage of coolant for cooling the unit cell100is formed on a rear surface of the metal-separator130(since flow passages which are formed in a metal-separator and are passages of air, hydrogen, and coolant are typically used in a metal-separator, detailed explanation for the same will be omitted).

As shown inFIG. 5A, a reaction gas inlet hole130afor supplying hydrogen gas to the unit cell100is formed at an inward portion from the separator manifold134which is formed at one end of the metal-separator130. In addition, a reaction gas outlet hole130bthrough which hydrogen gas is discharged is formed at an inward portion from the separator manifold134which is formed at the other end of the metal-separator130.

The reaction gas inlet hole130aand the reaction gas outlet hole130ballow reaction gases to be supplied and discharged therethrough, and make it easy to design a sealing structure of the reaction surface.

As shown inFIG. 5AandFIG. 5B, the embossed structure132has an indentation132awhich is inwardly indented and a projection132bwhich is outwardly protruded. The indentation and the projection are alternately formed along an edge of the metal-separator130.

The metal-separator130may be made by forming a metal plate with a thickness of 0.1 to 0.2 mm using a stamping process (forming process in which a metal plate is mounted on a solid member and is being stamped so as to form) to produce a sealing structure having a linear shape and a curve shape. Although a metal plate may be twisted after the forming, the metal-separator130has a high strength against deformation since the embossed structure132is formed along the edge of the metal-separator130.

In addition, since an edge of the metal-separator130is formed to have the embossed structure132, a plurality of the metal-separators130is laminated so as to form a honeycomb structure. This structure helps the fuel cell stack10to be evenly laminated, and serves to increase the connecting pressure, thereby tightly and stably connecting the unit cells of the fuel cell stack10(referring toFIG. 4andFIG. 6).

In addition, the embossed structure132serves to enable the gasket120to be easily coupled.

Typically, a gasket groove may be formed on both sides of a graphite separator. However, with the stamping process, it is not possible to form grooves for coupling a gasket at the same positions of both sides of the metal-separator130which is used for connecting the fuel cell stack10in an exemplary embodiment of the present invention.

A position where the gasket120is located can be precisely determined by the embossed structure132according to an exemplary embodiment of the present invention.

As shown inFIG. 5AandFIG. 5B, the gasket120is coupled along an edge of the metal-separator130and the surrounding of the separator manifold134, so the gasket120seals the area between the metal-separator130and the membrane electrode assembly110when the metal-separator130is coupled to the membrane electrode assembly110.

For this, the gasket120should be coupled at the substantially same positions on the reaction surface136and the cooling surface138, and since the embossed structure132is formed along the edge of the metal-separator130, the gasket120can be coupled to the substantially same positions on both sides of the metal-separator130even without a guide groove if the gasket120is positioned between the embossed structure132and the edge.

In addition, since the gasket120should seal the surrounding of the separator manifold134, the gasket120is coupled along the surrounding of the separator manifold134. It is preferable that the gasket120coupled to the reaction surface136is coupled to be disposed between the separator manifold134, the reaction gas inlet hole130aand the reaction gas outlet hole130b, so as not to close the reaction gas inlet hole130aand the reaction gas outlet hole130b.

However, it is preferable that the gasket120coupled to the cooling surface138is coupled to be disposed outside the reaction gas inlet hole130aand the reaction gas outlet hole130b, i.e., inside the metal-separator so as prevent reaction gas from being leaked to the cooling surface138through the reaction gas inlet hole130aand the reaction gas outlet hole130b.

Although the gasket120can be formed in a shape corresponding to the shape of the separator manifold134, an embossed structure may be added to the space between respective separator manifolds134in order to fix an installation location (referring to regions A ofFIG. 5AandFIG. 5B). Accordingly, an installation position of the gasket120can be precisely determined even without a separate guide groove.

As described above, in a metal-separator for a fuel cell stack according to an exemplary embodiment of the present invention, an edge of a metal-separator contacting a gasket is formed in an embossed structure so that the metal-separator can be laminated in a stable honeycomb structure that can reduce the frequency of laminating error and increasing the connecting pressures, thereby enhancing laminating characteristics.

Furthermore, even when a linear shape and a curve shape are mixed in the forming of the metal-separator, edge portion(s) of the metal-separator may maintain a high strength against the deformation by the embossed structure, thereby preventing the metal-separator from being deformed and enhancing the stability of a fuel cell stack.