Clamping system for fuel cell stacks and fuel cell stacks with such a

Abstract

A clamping system (10) for a fuel cell stack (100), comprising a first end plate (11) arranged on one side of the fuel cell stack (100), a second end plate (12) arranged on the opposite side of the fuel cell stack (100), and a plurality of clamping elements for clamping the fuel cell stack (100) to one another via the first and second end plates (11, 12), characterized in that the first and second end plates (11, 12) each consist of a first and a second partial end plate (14, 15) configured to correspond to one another, wherein the first partial end plates (14) are arranged on the fuel cell stack (100), that the clamping elements encompass the fuel cell stack (100) and the two first partial end plates (14), and that the edges (16) of the two first partial end plates (14) are rounded at least in the region over which the clamping elements are guided,and that the second partial end plates (15) are each arranged on the first partial end plates (14).,

Description

The invention relates to a clamping system for a fuel cell stack comprising a first end plate arranged on one side of the fuel cell stack, a second end plate arranged on the opposite side of the fuel cell stack and a plurality of clamping elements for clamping the fuel cell stack to one another via the first and the second end plate. The invention further relates to a fuel cell system having the clamping device.Fuel cells utilize the chemical reaction of a fuel with oxygen to form water to generate electrical energy. For this purpose, fuel cells contain as core component the so-called membrane electrode assembly (MEA), which is a structure of an ion-conducting (mostly proton-conducting) membrane and a catalytic electrode (anode and cathode) arranged on both sides of the membrane. The latter usually comprise supported noble metals, in particular platinum. In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane electrode arrangement on the sides of the electrodes facing away from the membrane. As a rule, the fuel cell is formed by a plurality of MEAs arranged in the stack (fuel cell stack), the electrical powers of which are added together. Bipolar plates (also called flow field or separator plates) are generally arranged between the individual membrane electrode arrangements, which bipolar plates ensure a supply of the individual cells with the operating media, i.e. the reactants, and usually also serve for cooling. In addition, the bipolar plates provide for an electrically conductive contact to the membrane electrode arrangements.During operation of the fuel cell, the fuel (anode operating medium), in particular hydrogen H 2 or a hydrogen-containing gas mixture, is supplied to the anode via an anode-side open flow field of the bipolar plate, where electrochemical oxidation of H 2 to protons H + takes place with emission of electrons (H 2→2H ++ 2 e -). Via the electrolyte or the membrane, which separates the reaction spaces from one another in a gas-tight manner and electrically isolates them, the protons are transported (water-bound or water-free) from the anode space into the cathode space. The electrons provided at the anode are supplied to the cathode via an electrical line. Oxygen or an oxygen-containing gas mixture (for example air) is supplied to the cathode as cathode operating medium via a cathode-side open flow field of the bipolar plate, so that a reduction from O 2 to O 2- takes place with the absorption of the electrons (1⁄2 O 2+ 2 e - → O 2-). At the same time, in the cathode space, the oxygen anions react with the protons transported via the membrane to form water (O 2-+ 2 H + → H 2 O).The fuel cell stack typically has end plates at its opposite stack ends, which are connected to one another by means of clamping devices as part of a clamping system. By means of the clamping devices, tensile forces are transmitted which pull the end plates towards each other and press the individual cells arranged therebetween, i.e. press them against each other. As the jigs, belts, belts or the like are usually used. The compressive pressure helps seal the stack also during operation thereof and ensures adequate electrical contact between the stack components.DE 10 2008 026 858 A1 discloses a fuel cell system which is provided with a belt mechanism in order to maintain compression. The belt mechanism is secured to opposing end plates, each of which has a curvature facing away from the fuel cell stack. Alternatively, the straps may encircle the fuel cell stack with the two end plates.DE 10 2004 027 694 A1 discloses a fuel cell system having a clamping system in which end plates of the fuel cell stack are surrounded by clamping bands. The clamping straps are each fixed to a means for clamping which rests on the end plates and with which the clamping straps are guided in a convex shape around the edges of the fuel cell.DE 10 2012 000 266 A1 describes a fuel cell stack which is compressed with the aid of clamping bands which are guided over curved end plates, as a result of which a pressure on the fuel cell stack is equalized. One end plate has a curvature facing away from the stack and the opposite end plate has a curvature facing the stack.The above-mentioned fuel cell systems with clamping devices have the disadvantage overall that the configuration has a relatively large requirement for installation space which is available to a very limited extent as a rule in automotive applications. In addition, these embodiments usually require additional structural measures in order to provide a flat platform as possible. In addition, the tension of the device generally decreases over time.The object of the invention is now to provide a clamping system for a fuel cell stack which solves or at least weakens the problems of the prior art. Another object of the present invention is to provide a fuel cell system which is optimized in terms of a mass / yield ratio.This object is achieved by a clamping system and a fuel cell stack having the features of the independent claims. Advantageous embodiments of the invention are characterized in the dependent claims.According to the present invention, there is provided a clamping system for a fuel cell stack, including a first end plate disposed on one side of the fuel cell stack and a second end plate disposed on the opposite side of the fuel cell stack. Both end plates are connected to one another via a plurality of clamping elements, by means of which the fuel cell stack can be pressed or clamped. The first and the second end plate each consist of a first and a second partial end plate formed correspondingly to one another, i.e. the adjoining surfaces of the first and the second partial end plate of an end plate are designed like a positive and negative shape. The first partial end plate of the first or second end plate is arranged on the fuel cell stack and abuts against the latter, wherein the clamping elements encompass the fuel cell stack and the two first partial end plates and press them together. The edges of the two first partial end plates are rounded at least in the region over which the clamping elements are guided. These edges are opposite the edges which directly adjoin the fuel cell stack, that is to say are located on the side of the first partial end plate which is opposite the fuel cell stack. The two first partial end plates are covered by the correspondingly formed second partial end plates.Preferably, means are also provided for fixing the first and second end plates in relation to each other.The second partial end plate advantageously brings about a stiffening of the respective end plate.The configuration of the clamping system according to the invention enables the guiding of clamping elements, in particular clamping bands, around the edges of the fuel cell stack with an optimized, i.e. larger, radius, so that a decreasing tension or compression due to an elongation of the material of the clamping elements or a decrease of the spring force can be reduced.Further advantages of the clamping system according to the invention are given below.Preferably, the edges are rounded not only in the region of the clamping elements but over their entire length, so that the production thereof is advantageously simplified.According to a particularly preferred embodiment of the invention, the region between the completely or partially rounded edges is not planar but is curved (convex) away from the fuel cell stack. The second partial end plate is accordingly "trough-shaped" (concave).Advantageously, this preferred embodiment of the first and second partial end plates allows the radius of curvature to be further increased and, in addition, the compression in the central region of the two end plates is optimized as a result.It is likewise particularly preferred that the first and the second partial end plate are joined together in a cuboid shape or form a cuboid shape.This offers the advantage that the fuel cell stack also has an essentially cuboidal configuration and in particular a planar footprint. This simplifies the arrangement of the fuel cell stack in the available installation space in a vehicle, for example.Other configurations of the second partial end plate with respect to the surface facing away from the fuel cell stack can be provided in order to adapt to specific circumstances in the available installation space, which require a different geometry. Preferably, it should be noted that the region between the edges protrudes in order to ensure improved compression.The clamping elements are preferably clamping bands which are particularly easy to handle, have a small space requirement and can additionally withstand high loads or with which a high compression can be achieved.Within the scope of the invention, clamping elements can also be selected in which clamping bands are used only in the region of the end plates, which clamping bands can be combined with other clamping elements, which are fundamentally known to the person skilled in the art.The clamping elements and / or the clamping bands are preferably manufactured from a polymeric and / or a metallic material. Corresponding configurations are known to the person skilled in the art.As polymeric material, for example, polyester can be used, which can consist of polymer fibers woven together. The metallic material is preferably made of steel, which is preferably stainless or galvanized. This is preferably used as a solid strip.For simple assembly of the clamping elements, these preferably have closure means which are preferably provided outside the region spanning over the end plates in order to keep the design of the end plates as simple as possible.The clamping elements preferably have means for clamping, so that the clamping or compression can advantageously also be varied at any desired times after production. With regard to the arrangement of the means for tensioning, the explanations given apply to the closure means.The invention also relates to a fuel cell stack which has a clamping system described above.By using the clamping system according to the invention in a fuel cell stack, the power density is advantageously improved by optimized compression, based on the weight of the fuel cell system.The configuration thereby offers the advantage that the force which is transmitted to the fuel cells by the clamping elements of the clamping device, for example, when used in a fuel cell stack, is distributed over the base surface of the fuel cell stack in a more homogeneous manner, i.e. in particular not only the edge region.Due to the larger radii of the clamping elements in the edge region of the partial end plates compared to the prior art, a loss of the clamping can also advantageously be significantly reduced, since the clamping elements do not have to be guided at an angle of 90°. In addition, the clamping elements can distribute this over the entire circumference of the fuel cell stack when the spring force is released.Thus, maintenance intervals can be significantly extended.A further aspect of the invention is a fuel cell stack and a fuel cell system which has a clamping system according to the invention in one of the described embodiments. Such fuel cell stacks or fuel systems have a better ratio of weight to yield and are also more stable to breakage.The various embodiments of the invention mentioned in this application can be combined with one another with advantage unless stated otherwise in the individual case.The invention is explained below in exemplary embodiments with reference to the associated drawings. The following are shown: FIG. 1 shows a perspective view of a fuel cell stack with a clamping device according to the invention; FIG. 2 is a cross-sectional perspective view of the fuel cell stack of FIG. 1 ; FIG. 3 shows a perspective view of a first partial end plate of the clamping device according to the invention; and FIG. 4 shows a perspective view of a second partial end plate of the clamping device according to the invention.FIGS. 1 and 2 schematically show a fuel cell stack, generally designated 100, according to a preferred embodiment of the present invention. The fuel cell stack 100 is part of a vehicle, not shown in any more detail, in particular an electric vehicle, which has an electric traction motor which is supplied with electrical energy by the fuel cell stack 100.The fuel cell stack 100 comprises a plurality of membrane electrode arrangements arranged in an alternating manner on their flat sides (stacked), and polar plates, which are not shown here in any more detail. Thus, a plurality of stacked single cells altogether form the fuel cell stack 100. The aforementioned components, not shown, of the fuel cell stack 100 have, inter alia, anode and cathode spaces, not shown, which are bounded by seals, likewise not shown.Inter alia, in order to produce the sealing function of the seals, the fuel cell stack 100 is compressed (pressed) in the stacking direction S by means of the clamping system 10 according to the invention.The clamping system 10 includes a first end plate 11 disposed on one side of the fuel cell stack 100, a second end plate 12 disposed on the opposite side of the fuel cell stack 100, and a plurality of clamping bands 13 as clamping members for clamping the fuel cell stack 100 via the first and second end plates 11, 12.The first and the second end plates 11, 12 each consist of a first and a second partial end plate 14, 15 which are shaped correspondingly to one another and are shown separately in FIGS. 3 and 4.The first partial end plates 14 bear directly against the fuel cell stack 100 and are surrounded by the clamping bands 13. The second partial end plates 15 are arranged and fixed on the first partial end plates 14 and the tightening straps 13, resulting in a gapless cuboid dressing, which represents the first and the second end plates 11, 12.By configuring the first partial end plate 14 with rounded edges 16, over which the clamping bands 13 are guided, and a curvature formed between the edges 16, which curvature extends completely over the fuel cell stack 100, a tension can advantageously be kept largely the same over time and a compression can be ensured over the entire surface, in particular in the central region of the fuel cells.Other components of the clamping device 10 according to the invention, such as closure means or the like, are not shown.List of reference characters100 Fuel cell stack 10 Clamping device 11 First end plate 12 Second end plate 13 Clamping band 14 First partial end plate 15 Second partial end plate 16 Edge S Stacking direction

Claims

Clamping system (10) for a fuel cell stack (100) comprising a first end plate (11) arranged on one side of the fuel cell stack (100), a second end plate (12) arranged on the opposite side of the fuel cell stack (100) and a plurality of clamping elements for clamping the fuel cell stack (100) to one another via the first and the second end plate (11, 12), characterized in that the first and the second end plate (11, 12) each consist of a first and a second partial end plate (14, 15) formed correspondingly to one another, wherein the first partial end plates (14) are arranged on the fuel cell stack (100), in that the clamping elements comprise the fuel cell stack (100) and the two first partial end plates (14), and the edges (16) of the two first partial end plates (14) are formed rounded at least in the region over which the clamping elements are guided, and in that the second partial end plates (15) are arranged on the first partial end plates (14), respectively.Clamping system (10) according to claim 1, characterised in that the edges (16) over which the clamping elements are guided are rounded over their entire length.Clamping system (10) according to Claim 1 or 2, characterized in that the region between the completely or partially rounded edges (16) of the first partial end plates (14) is shaped in a curved manner.Clamping system (10) according to one of the preceding claims, characterized in that the first and the second partial end plate (14, 15) of the first and the second end plate (11, 12) are cuboidal in the assembled state.Clamping system (10) according to one of the preceding claims, characterized in that the clamping elements are clamping bands (13).Clamping system (10) according to one of the preceding claims, characterized in that the clamping elements or the clamping bands (13) consist of a polymeric and / or a metallic material.Clamping system (10) according to one of the preceding claims, characterized in that the clamping elements or the clamping bands (13) each have a closure means.Clamping system (10) according to one of the preceding claims, characterized in that the clamping elements or clamping bands (13) have a means for clamping.Clamping system (10) according to one of the preceding claims, characterized in that the end plates (11, 12) consist of a polymeric material, a metallic material or a mixture of both materials.Fuel cell stack (100) comprising a clamping system (10) according to one of the preceding claims.

Images