EP3329536A1

EP3329536A1 - Bipolar plate and membrane electrode unit for a fuel cell arranged in a fuel cell stack, fuel cell and fuel cell stack

Info

Publication number: EP3329536A1
Application number: EP16742281.5A
Authority: EP
Inventors: Christian Martin ZILLICH
Original assignee: Audi AG; Volkswagen AG
Current assignee: Audi AG; Volkswagen AG
Priority date: 2015-07-30
Filing date: 2016-07-21
Publication date: 2018-06-06
Also published as: DE102015214517A1; US10879549B2; CN107925107B; WO2017016976A1; CN107925107A; US20180366752A1

Abstract

The invention relates to a bipolar plate (1) for a fuel cell (100), comprising a profiled anode plate (7) and a profiled cathode plate (8), each having an active region (6) and two distributor regions (2) for feeding and draining operating media to and from the active region (6), wherein the distributor regions (2) each have an anode gas main port (3) for supplying and discharging fuel, a cathode gas main port (4) for supplying and discharging oxidant, said cathode gas main port (4) being arranged such that, proceeding therefrom, cathode ducts (41) extend in a rectilinear manner at least over the distributor region (2) of the bipolar plate (1) and have a direction of flow which corresponds to a main direction of flow in the cathode ducts (41) in the active region, and a coolant main port (5) for supplying and discharging coolant. According to the invention, provision is made for the coolant main port (5) and the anode gas main port (3) to be arranged adjacent to one another, adjacent to the cathode gas main port (4) and away from an alignment of the active region.

Description

description

A bipolar plate and membrane electrode assembly for a fuel cell, fuel cell and fuel cell stack disposed in a fuel cell stack

The invention relates to a bipolar plate for a fuel cell comprising a profiled anode plate and a profiled cathode plate, each having an active area and two manifold areas for supply and discharge of operating media to or from the active area, wherein the manifold areas each have an anode gas main port for supply and discharge of fuel, a cathode gas main port for supply and removal of oxidant, which is arranged such that extending therefrom from this cathode channels at least over the distribution region of the bipolar plate straight and a

Have flow direction corresponding to a main flow direction in the cathode channels in the active region. Further, the manifold portions have a coolant main port for supplying and discharging coolant, the plates being formed and stacked on each other such that the bipolar plate has channels for the operating media connecting the main equipment ports of both manifold portions and wherein the manifold portions have a first intersecting portion in which Cathode channels and anode channels do not overlap each other fluidly, and have a second overlap portion, in the anode channels and coolant channels do not overlap each other fluidly connecting. Furthermore, the invention relates to a membrane electrode assembly having a quadrangular shape and a fuel cell comprising the bipolar plate and the membrane-electrode assembly.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as core component the so-called membrane electrode assembly (MEA for membrane electrode assembly), which is a composite of a proton-conducting membrane and in each case one on both sides of the membrane arranged electrode (anode and cathode). During operation of the fuel cell, the fuel, in particular hydrogen H ₂ or a hydrogen-containing gas mixture, is fed to the anode, where an electrochemical oxidation takes place with release of electrons (H ₂ -> 2 H ⁺ + 2 e ^" ) Separate reaction spaces gas-tight and electrically isolated, there is a (water-bound or anhydrous) transport of the protons H ⁺ from the anode compartment into the cathode compartment.The electrons provided at the anode are fed via an electrical line to the cathode. The cathode is supplied with oxygen or an oxygen-containing gas mixture, so that a reduction of the oxygen taking place of the electrons takes place (V2 0 ₂ + 2 e -> 0 ^{2 ~} ). At the same time react in the

In the cathode compartment, these oxygen anions are transported with the protons transported through the membrane to form water (2 H ⁺ + O ^{2 "} -> H ₂ O.) The direct conversion of chemical energy into electrical energy enables fuel cells to achieve better results than others

Electricity generators due to the bypass of Carnot factor improved efficiency. The cathode reaction is partly due to the opposite of

Hydrogen lower diffusion rate of oxygen the

Rate limiting member of the fuel cell reaction is.

In general, the fuel cell is formed by a plurality of stack (stack) arranged membrane electrode assemblies whose electrical power is added. Between two membrane-electrode units of a fuel cell stack, a bipolar plate is arranged in each case, on the one hand channels for supplying the process gases to the anode

or cathode of the adjacent membrane electrode units and cooling channels for the removal of heat. Bipolar plates also consist of an electrically conductive material to produce the electrical connection. They thus have the threefold function of the process gas supply to the membrane-electrode units, the cooling and the electrical connection.

Bipolar plates are known in different designs. Fundamental goals in the design of bipolar plates are the weight reduction, the reduction in space and the increase in power density. These criteria are particularly important for the mobile use of fuel cells, for example for the electromotive traction of vehicles.

US 2005/0058864 A1 (US Pat. No. 6,974,648 B2) and US 2006/0029840 A1 (US Pat. No. 7,601,452 B2) describe bipolar plates for fuel cells, which are constructed from two corrugated and nested plates. Each of the plates has a meander profiling, so that grooves are formed on both sides, which are bounded by wall-like elevations. In this case, the two plates on different widths of the trained gutters or surveys. In the nested structure of the plates closed channels are formed, which serve as cooling channels. The existing on both sides of the structure open channels (gutters) are in the assembled

Fuel cell stack on one side of the anode and on the other side of the cathode The adjacent MEA facing and serve their supply of air / oxygen or fuel / hydrogen.

The bipolar plate shown in WO 03/050905 A2 has a continuous side on one side

Recesses for the formation of anode channels and on the other side continuous recesses for the formation of cathode channels. Furthermore, the plate has enclosed coolant channels. All channels run parallel to each other.

The invention is based on the object to provide a fuel cell, which is characterized by a compact shape and increased power density.

This object is achieved by providing a bipolar plate and a membrane-electrode unit having the features of the independent claims and by a fuel cell having these components.

Thus, a first aspect of the invention relates to a bipolar plate for a fuel cell comprising a profiled anode plate and a profiled cathode plate, each having an active area and two manifold areas for supply and discharge of operating media to and from the active area, wherein the manifold areas each have a Anodengashauptport to Supply and discharge of fuel, a cathode gas main port for supply and removal of oxidant, as well as a coolant main port to supply and

Have discharge of coolant. In this case, the cathode gas main port is arranged in such a way that, starting from this, cathode channels extend in a straight line at least over the distributor region of the bipolar plate and have a flow direction which is one

Main flow direction of the cathode channels in the active area corresponds. Further, the plates are formed and stacked on each other such that the bipolar plate has channels for the operating media connecting the main body ports of both manifold regions, the manifold regions having a first intersecting portion in which cathode channels and anode channels do not intersect fluidly and have a second intersecting portion the anode channels and

Coolant channels do not overlap each other fluidly. According to the invention, it is provided that the main coolant port and the anode gas main port are arranged adjacent to one another, adjacent to the cathode gas main port and out of alignment with the active region. The advantage of the bipolar plate according to the invention is in particular in an elevated

Power density. This is achieved by virtue of the arrangement of the main ports in the distributor area, which has a larger area in which cathode channels and anode channels overlap. This area is already beneficial for the

Fuel cell reaction and thus used for energy production. Inactive areas are reduced in the distribution area.

In addition, the bipolar plate according to the invention has a very compact shape.

Instead of the known double T-shape with two legs per distribution region, the bipolar plate according to the invention preferably has a double-L shape and thus only one leg per distribution region. The length of the feeding flow channels in

Distributor area can also be reduced due to the arrangement of the main ports.

Thus, a fuel cell with a bipolar plate according to the invention can generate the same fuel cell performance with a smaller cell area as a fuel cell with a bipolar plate according to the prior art.

As a port are present openings in the bipolar plate to understand, which in one

Fuel cell stack resulting channels for the management of operating media.

A bipolar plate according to the invention also has the advantage that due to the straightness of the cathode channels a water discharge is favored and thus a blockage of

Cathode channels as a result of water accumulation as far as possible or completely

is prevented. Furthermore, the overlapping of anode and cathode channels according to the invention leads to a substantially homogeneous distribution of fuel and

Coolant over the overlap section. This, in turn, promotes a homogeneous distribution of the pressure of reactant fluids (since these are particularly gaseous, they are also referred to below as reactant gases) within the cathode channels over the entire area of the bipolar plate.

Channels are understood as meaning open (ie channel-shaped) and / or closed (ie tubular) fluid connections for transporting the equipment. They can be designed as discrete channels and / or as a flow field or flow field which allows a transverse flow. In the first overlap section are the cathode and

Anodenkanäle preferably arranged in discrete channels and parallel to each other. Furthermore, the cathode channels in the first overlap section are preferably at an angle in FIG Range from 0 ° to 70 ° in particular preferably in the range of 10 ° to 50 ° to each other, arranged.

In the present case, a bipolar plate is subdivided into three regions, comprising two distributor regions and one active region. A first distributor area serves for the supply of

Operating media to the active area of the bipolar plate, a second distribution area of the discharge of the operating media from the active area. Preferably, both distributor regions are designed the same and in particular can be converted into one another by rotational symmetry. In the distributor areas, in turn, the main equipment ports, ie anode gas main port, main coolant port and cathode gas main port, are arranged. Preferably, within a manifold region, the cathode gas main port and either the coolant gas main port or the anode gas main port are disposed along a first side edge of the bipolar plate. Further preferably, within a distributor region, the coolant gas main port and the anode gas main port are arranged along a second side edge adjacent to the first side edge. The first side edge is preferably at right angles to

Extension direction of the active area arranged.

Usually, the main equipment ports can be classified based on their training, in particular their size ratios. Thus, both in the prior art and in the present invention, the cathode gas main port of the three different

Equipment main ports always the largest clear area, the clear area of the

Anode gas main ports, on the other hand, are usually smaller than the areas of

Cathodengas main port and main coolant port. Thus, in the present invention, even in the passive state, the function of the respective resource main port can be clearly identified.

The active region, which is arranged between the two distributor regions, is characterized in that, in the assembled state of the fuel cell stack, this region faces an electrode of the membrane-electrode assembly. It is limited by the distributor areas and usually formed in a rectangular shape. That is, in the active area take place the chemical reactions, which are the basis for the energy production in a fuel cell.

The operating media in the present case are fluids, that is, liquid or gaseous substances, which are conducted through the respective main equipment ports via suitable feeds to the plate. These are two reactant fluids, in particular a cathode resource (oxidant) and an anode resource (Fuel) and a coolant, preferably water. Oxygen is preferred as

Oxidizing agent and hydrogen used as fuel.

In the present case, the cathode channels of a bipolar plate extend at least over the

Distribution area rectilinear or deflection-free, ie without change of direction. This is to be understood in the present case that the cathode channels in supervision on the

Cathode plate have no sweeping. Preferably, they are arranged parallel to each other. Such an arrangement is found at least in the distribution area. Also preferably, this arrangement over the entire length of the bipolar plate, ie also in the active region, continued. The straight-line course of the cathode channels has the advantage that a

Water accumulation and concomitant obstruction of the cathode channels can be prevented by improving the hydraulic cross section in the entire cathode channel area. Furthermore, bipolar plates according to the invention can be operated with a low-pressure strategy, that is to say an operating medium pressure of less than 2 bar.

The anode channels are preferably formed so that they extend over the entire width of a cathode flux field, wherein the cathode flux field of the sum of all

Cathode channels corresponds. As a result, it is advantageously achieved that the fuel is supplied to the flow field over the entire width with a substantially same initial pressure, whereas in conventional construction of a bipolar plate an inhomogeneous pressure distribution of the fuel is already generated in the distributor region.

An overlapping section in the sense of the invention is an area within one

Distribution area of the bipolar plate, in which at least two types of flow channels, so coolant channels, cathode channels and / or anode channels, not superimposed fluidly. It can be enclosed between two types of channels angle in the range of 0 ° to 180 °. If angles are included in the range of 0 ° to 89 °, the flow direction of the guided in the respective channels fluids is considered to be substantially equal, however, the included angle is in the range of 91 ° to 180 °, the flow direction is substantially opposite.

With particular advantage, anode channels and coolant channels run in the first

Intersecting section parallel to each other and close with the cathode channels an angle in the range of 10 ° to 90 °, in particular from 20 ° to 80 °, preferably from 25 ° to 75 °, particularly preferably from 35 ° to 55 °. In a preferred embodiment of the invention, it is preferred that the first intersecting section is arranged in the direction of extension of the active region in its alignment. This ensures that the cathode channels in the distributor region are rectilinear and also have the same flow direction as in the active region. More preferably, the sum of the width of all cathode channels emanating from the main cathode port substantially corresponds to the width of the active region. More preferably, the coolant gas main port and the Anodengashauptport au ßerhalb this escape, especially one-sided, arranged.

Advantageously, the first overlap section has the form of, in particular

right-angled, triangle up. This form is characterized by its simplicity.

In particular, by this embodiment, the first overlap portion of two mutually perpendicular sides, and thus completely and uniformly, is acted upon by the reaction gases. Thus, the first overlap section for the

Fuel cell reaction available.

This preferred form of the first overlap section is preferably achieved by having at least one of the main equipment ports, in particular the

Cathode gas main port, having a substantially triangular shape. Of the

Cathode gas main port is then advantageously arranged in the distributor area such that a corner, in particular the right angle, is arranged on a side of the distributor area facing away from the second overlap section, wherein the side edge of the triangle adjacent to the angle runs along the side edge of the bipolar plate which is adjacent to the angle

Extension direction of the bipolar plate is arranged vertically.

Furthermore, it is preferred that the first intersecting section is arranged such that a first side edge, in particular a catheter, of the first intersecting section extends in extension to an edge of the active region. The advantage of this embodiment lies in the optimal use of the available area. In connection with a membrane-electrode unit which is arranged on the bipolar plate, there is the advantage that the membrane can be coated over the entire surface, without areas of the electrodes, ie the catalytic coating, not being involved in the fuel cell reaction.

Advantageously, the first intersecting portion is further arranged such that a second side edge, in particular a catheter, of the first intersecting portion with a limiting boundary line of the active area runs. The boundary line runs perpendicular to the extension direction of the active region and delimits this from the distributor region.

The bipolar plate according to the invention also has a second one in the distributor region

Overlapping section on. In this run only the anode channels and the

Coolant channels, which intersect at an angle greater than 0 °, in particular at an angle in the range of 55 ° to 125 °, preferably in the range of 70 ° to 1 10 °. The second overlap section has no cathode channels and, according to a preferred embodiment, is located outside the alignment of the active area. This allows a maximum extension of the first overlap section and a compact form of the bipolar plate.

More preferably, the anode channels in the second overlap section extend in such a way that a flow direction extends in a direction away from the active region. That is, the anode gas flows in this section substantially opposite to a flow direction of the cathode gas in the cathode channels within the first

Overlap section. In other words, the anode channels in the second overlapping section extend at an angle in the range of 91 ° to 180 °, in particular in the range of 100 ° to 170 °, to the cathode channels in the first overlap section. The coolant channels in the second overlap section, however, preferably have an angle in the range of 0 ° to 90 °, in particular in the range of 20 ° to 80 °, relative to the cathode channels within the first overlap section. In this embodiment, the main coolant port of a distributor region has the largest possible diameter. In addition, the coolant channels are arranged such that the coolant is highly directed and distributed evenly distributed in the active area, without going through heavy bends, in which it could lead to an accumulation of sediment or ice.

Another aspect of the present invention relates to a membrane-electrode assembly comprising a membrane having a quadrangular shape with two parallel longitudinal sides and two opposite short sides, wherein at least one included by a short side and an adjacent longitudinal side angle of 90 ° is different. Furthermore, the membrane-electrode unit comprises two electrodes arranged on both sides of the membrane, wherein the electrode surface has the same shape as the membrane surface. According to the invention, the shape of the electrode surface corresponds to the shape of the membrane surface. In the present case, the included angle always means the smaller angle enclosed by the short and long sides, even if this is not the inner angle of the quadrangle corresponds. The membrane-electrode unit according to the invention is thus designed such that it can be arranged on the bipolar plate according to the invention.

The electrodes of a fuel cell are usually present as a catalytic coating on the gas diffusion layers, which are then referred to as gas diffusion electrodes. The

However, electrodes may also be present as a catalytic coating on the membrane. In this case one also speaks of catalytically coated membranes or CCM (for catalytic coated membrane). Various techniques are known to coat a membrane material with a catalytic material to produce a CCM, and so

To produce catalyst layers. These include printing processes,

Spray method, deposition method, brushing method. For mass production, low cost processes with high production rates are desirable.

The membrane according to the invention has the advantage over known membranes that a part of the active region extends functionally into the distribution area of the bipolar plate and thus the power density of the membrane-electrode unit is increased. The membrane of the invention is designed such that advantageously the entire membrane is activated for the production of a membrane-electrode unit, that is, coated with a catalytic material (catalytic coated membrane, CCM). Alternatively, a gas diffusion layer adjacent the membrane is coated with a catalytic material throughout the region adjacent the membrane, thereby maximizing the usable active area and increasing the power density of the membrane-electrode assembly.

The area of an MEA which is acted upon in the fuel cell stack with both reactant gases for the anode and cathode and on which the fuel cell reaction under

Generation of electricity is called the activated region. However, the activated area occupies only part of the total area of the MEA. The remaining areas, which may have a variable shape, serve to supply and distribute the operating media to the activated area and to seal and mechanically stabilize the MEA. These areas are called inactive or inactive areas. In conventional fuel cells, the activated region has the shape of the active region of the bipolar plate and thus usually a rectangular shape. In an effort to achieve a high space utilization for the activated area, are also recently

Arrangements with non-rectangular activated areas have been developed, for example with a regular or irregular hexagonal contour as shown in FIG. For reasons of cost is desirable in principle, only the activated area with the equip catalytic layer. The selective coating of the activated area is possible with printing processes, for example offset or screen printing. However, these methods are relatively time-consuming in the case of screen printing or require a cost-intensive machinery (offset printing). By contrast, continuous coating processes in which the membrane material is continuously coated with the catalytic material and the catalytically coated membrane is later cut out by a fabrication step are associated faster and with less effort. The disadvantage here is that in the case of non-rectangular activated areas, the coating of inactive areas of the membrane or the

Membranververschnitts is inevitable. If inactive areas are undesirable coated with catalytic material, these areas must be retrofitted, for example by

Application of diffusion barrier layers are blocked. In any case, the excess coating means a loss of catalytic material.

In a preferred embodiment, all internal angles of the quadrangle are different from 90 °. Thus, the membrane may have the shape of a trapezoid or a parallelogram. The advantage of this embodiment is that the membrane is individually adapted to the bipolar plate in such a way that a part of the membrane-electrode unit extends into the distributor region.

Furthermore, the opposite short sides are preferably parallel to one another. Thus, the membrane of the invention in this embodiment has the shape of a parallelogram, wherein the respective opposite angles are equal. If the membrane has the shape of a parallelogram, that is to say a regular rectangle, the manufacture is simplified compared to irregular geometric shapes.

Furthermore, the invention relates to a fuel cell, which comprises the bipolar plate according to the invention and the membrane-electrode unit according to the invention. The inventive

Fuel cell has an increased power density compared to the prior art.

Furthermore, the invention relates to a fuel cell stack comprising a plurality of alternately arranged with bipolar plates membrane electrode assemblies according to the invention. The fuel cell stack can be used in particular in a vehicle which has an electric motor drive, wherein the fuel cell stack of the

Electricity supply of the electric motor and / or a traction battery is used.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics. The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

The invention is described below in embodiments with reference to the associated

Drawings explained. Show it:

1 shows a schematic representation of a fuel cell stack,

FIG. 2 shows a schematic schematic diagram of a section of a bipolar plate in a first embodiment of the invention in a plan view,

FIG. 3 shows a schematic schematic diagram of a detail of a bipolar plate in a further embodiment of the invention in a plan view,

Figure 4A is a schematic representation of a membrane-electrode assembly according to the

State of the art,

4B is a schematic representation of a membrane-electrode assembly according to a preferred embodiment of the invention,

Figure 5 is a schematic representation of a membrane according to a preferred

Embodiment of the invention,

Figure 6A is a schematic representation of the cross section of a membrane according to the

State of the art, and

Figure 6B is a schematic representation of the cross section of a membrane in the

preferred embodiment of the invention.

FIG. 1 shows a schematic representation of a fuel cell stack 100. The fuel cell stack 100 comprises a first end plate 11 and a second end plate 12. Between the end plates 11 1, 12 a plurality of stacked stack elements are arranged, which bipolar plates 1 13 and 13 Include membrane electrode assemblies 1 14. The bipolar plates 1 13 are alternately stacked with the membrane electrode assemblies 1 14. The membrane-electrode units 1 14 each comprise a membrane and on both sides of the Membrane subsequent electrodes, namely an anode and a cathode (not shown). Adjacent to the membrane, the membrane-electrode assemblies 1 14 may also have gas diffusion layers (also not shown). Between the bipolar plates 1 13 and

Membrane electrode units 1 14 each sealing elements 1 15 are arranged, which seal the anode and cathode chambers gas-tight outward Shen. Between the end plates 1 1 1 and 1 12 of the fuel cell stack 100 by means of clamping elements 1 16, for example, tie rods or clamping plates, pressed.

In FIG. 1, only the narrow sides of the bipolar plates 13 and the membrane electrode units 14 are visible. The major surfaces of the bipolar plates 1 13 and the membrane electrode assemblies 1 14 abut each other. The representation in FIG. 1 is partly not dimensionally true. Typically, a thickness of a single cell, consisting of a bipolar plate 1 13 and a membrane electrode assembly 1 14, a few mm, the membrane electrode assembly 1 14 is the much thinner component. In addition, the number of

Single cells usually much larger than shown.

FIG. 2 shows a schematic schematic diagram of a section of a bipolar plate 1 in a first embodiment of the invention in a plan view of the bipolar plate 1. Shown is a distributor region 2 and the adjacent active region 6 of the bipolar plate 1. Der

Distributor area 2 is formed wider than the active area 6. He has three

Resource main ports, namely, a cathode gas main port 4, a main coolant port 5, and an anode gas main port 3. These are arranged such that the

Cathode gas main port 4 and the coolant main port 5 along a side edge of the

Bipolar plate 1 are positioned adjacent to each other. Furthermore, the cathode gas main port 4 is arranged in extension from the active region 6, that is to say in alignment therewith. Of the

Anodengashauptport 3, which is adjacent to the coolant main port 5, however, is au ßerhalb a flight of the active area 6. Thus, the bipolar plate 1 in the section shown an L-shape.

Starting from the main equipment ports 3, 4 and 5, flow channels 31, 41 and 51 lead via the distributor region 2 into the active region 6. At least two types of flow channels are superposed in regions. A first overlap section 9 and a second overlap section 10 are formed.

In the first overlap section 9, all the flow channels 31, 41 and 51 overlap, with anode channels 31 and coolant channels 51 extending substantially parallel to one another and intersect with the cathode channels 41 at an angle in the range of 10 ° to 45 °. The overlapping of the flow channels 31, 41 and 51 is not carried fluid, so there is no mixing or exchange of operating media. In the embodiment shown, the first intersecting section 9 extends beyond a width corresponding to the active region 6 and adjoins it via a borderline 12. A further side edge 11 of the first overlap section 9 forms an extension of a longitudinal edge 13 of the active region 6. Depending on the shape of the cathode main port 4, the first overlap section 9 has the shape of a, in particular right-angled, triangle. The cathode channels 41 extend in a straight line over the distributor region 2 and pass directly into the cathode channels of the active region 6.

The second intersecting portion 10 is arranged laterally adjacent to the first intersecting portion 9. He is also outside of an escape of the active area 6. He is also preferably triangular in shape and adjoins with a side edge, in particular a Hypotenuse, on the side edge 1 1 of the first overlap section 9, which forms the extension of the longitudinal edge 13 of the active area 6 , On the other sides of the second overlap section 10, the anode gas main port 3 and the

Main coolant port 5. The main coolant port 5 is preferably adjacent to

Cathode gas main port 4, so that the coolant channels 51 emanating from the main coolant port 5 meet the first overlap section 9 at an angle to the cathode channels 41 and have substantially the same flow direction as the cathode channels 41. They also run in a straight line over the second overlapping section 10

Anode flow channels 31, however, meet from the anode main port 3 at an angle greater than zero on the first overlap section 9 so that they undergo a flow reversal after their straight course over the second overlap section 10 to substantially rectified in the first overlap section 9, with respect to the flow direction of the anode gas to pass to the cathode channels 41.

The flow channels 31, 41 and 51 extend in the embodiment shown in the active region 6 parallel to each other and straight. Alternatively, at least one variety

Flow channels 31, 41 and / or 51 meander over the active area run.

Preferably, furthermore, the flow direction of the fluids in the flow channels 31, 41, and / or 51 is rectified, although embodiments in which two types, for example anode channels 31 and cathode channels 41, flow in opposite directions can also be selected. FIG. 3 shows a schematic sketch of a section of a bipolar plate in a further embodiment of the invention. The detail of the bipolar plate 1 is also shown in plan view and substantially corresponds to the structure of the embodiment in Figure 2. The difference of the second embodiment compared to that shown in Figure 2 consists in the arrangement of the anode gas main port 3 and the coolant main port 5. These are in Comparison with the first embodiment reversed. This affects the arrangement and the flow direction of coolant channels 51 and anode channels 31. While in the first embodiment, the anode channels 31 at the boundary between the second and first overlap section 9, 10 undergo a flow reversal, this is true in the embodiment shown in Figure 3 for the coolant channels. In return, the anode channels 31 extend in a straight line over the entire distributor region 2.

Since cathode channels 41 and anode channels 31 overlap in the first overlapping section 9, this region is already suitable for the fuel cell reaction since both a fuel and an oxidizing agent are available here and thus can be designated as an activatable region 28. In order to supply them to the fuel cell reaction, it is necessary that a suitable electrode surface is available in this area. This can be achieved by providing a membrane-electrode unit 20 according to the invention, as can be seen from the following figures.

FIG. 4A shows a membrane-electrode unit 20 according to the prior art in a plan view of one of its flat sides. The membrane-electrode unit 20 has the catalytically coated membrane 21. In the example shown, the catalytically coated membrane 21 has a hexagonal contour. Within this hexagonal contour, an active region 6 is arranged, which is indicated by a broken line. Outside the active region 6, the catalytically coated membrane 21 has activatable regions 28 and inactive regions 25. The active region 6 has the shape of the active region 6 of the bipolar plate 1. Depending on whether and how much of the activatable region 28 has a catalytic coating 22, the active region 6 and the activatable region 28 jointly form the activated region 29. In this activated region 29, the membrane electrode assembly 20 is inserted into a fuel cell stack 100, the fuel cell reactions take place at the anode and cathode and thus the generation of electricity. By contrast, the inactive regions 25 serve other functions, for example the supply of the operating media to the active region 6. Ideally, the polymer electrolyte membrane 21 is coated with the catalytic coatings 22 only in the active region 6. The membrane-electrode unit 20 comprises various passage openings 3 to 5, which serve to supply and discharge of the various operating media. These are preferably arranged in a protective and / or supporting layer 26 of the membrane. Thus, a first anode gas main port 3 serves to supply the anode working gas to the anodes of the fuel cell stack 100 and an opposite second anode gas main port 3 to exhaust the anode operating gas. Likewise, a first cathode gas main port 4 serves to supply a cathode working gas to the cathodes of the fuel cell stack 100 and an opposite second cathode gas main port 4 to discharge the gas

Cathode operating gas. Finally, a first coolant main port 5 serves to supply a coolant to the internal coolant passages 51 of the bipolar plates 1 and 1

The opposite main coolant port 5 of the discharge of the coolant 52. The bipolar plates 1, not shown in detail, have a substantially same blank as the membrane electrode assemblies 20 shown, in particular corresponding ports 3, 4 and 5. In this way, in the stacked state the membrane-electrode assemblies 20 and bipolar plates 1 main channels formed which the

Fuel cell stack 100 in its stacking direction S (see Figure 1) prevail. (These main operating media channels are not shown in Figure 1, which shows only a section through the active region 6 of the fuel cell stack.) The anode and

Kathodengashauptports 3 to 4 are open distribution channels in the stack 100th

adjacent bipolar plates 1 with the corresponding anode or

Cathode channels 31, 41 of the bipolar plates 1 fluidly connected. The coolant main ports 5 are connected to the internal coolant passages 51 of the bipolar plates 1. The ports 3, 4 and 5 and the anode and cathode channels 31, 41 of the active region 6

connecting distribution channel structures extend in the inactive regions 25.

For mechanical support, the membrane 21 is usually bordered on both sides by a respective support layer 26, which surrounds the membrane 21 at its edge regions.

Optionally, the membrane 21 may also extend over the entire surface of the membrane-electrode assembly 20 and be laminated with support layers 26 at its edge regions. Furthermore, in FIG. 4A, seals 27 can be seen, which surround the equipment passage openings 3, 4 and 5 as well as the catalytically coated membrane 21 in order to seal them to the outside. Optionally, the seals 27 may be disposed on the bipolar plates 1 or both instead of on the membrane-electrode unit 20.

As already stated, the fuel cell reaction takes place only in the activated region 29. It is therefore desirable, if possible, only in this area, the catalyst layers 22nd because the catalytic material is by far the most expensive single component of the fuel cell stack. On the other hand, the aim is to make the active region 6 as large as possible and the inactive regions 25 as small as possible in order to achieve the highest possible energy yield or to minimize the required installation space and the weight of the fuel cell. Corresponding to this endeavor, contours of the activated region 29 result, which may deviate from the conventional rectangular contour (as shown in FIG. 4A) and have an irregular contour.

The cost-effective and time-saving mass production of catalytically coated membranes 21 with a non-rectangular active region has so far been solved only unsatisfactorily. For example, the preparation can be carried out by selective coating methods, in which the catalytic material exclusively on the activated region 6 of a

Membrane material is applied, for example, by selective printing methods such as screen printing or offset printing. However, these procedures are slow

Production speed (screen printing) or by costly machines (offset printing). On the other hand, faster and more cost effective are continuous coating processes in which the catalytic material is applied to the membrane material to produce a constant coating width.

FIG. 4B shows a membrane-electrode unit 20 'according to the invention. The basic structure of the membrane electrode assembly 20 'according to the invention essentially corresponds to that shown in FIG. 4A. The difference is in the shape of the membrane 21 and the electrodes.

In the present case, the membrane 21 has a quadrangular shape with two parallel longitudinal sides. The short sides 23 are at an angle to the longitudinal sides 24, which is different from 90 °. In Figure 4B, the membrane has the shape of a parallelogram.

In the distributor area 2, the main equipment ports 3, 4 and 5 are arranged. The Kathodengashautport 4 is aligned in extension of the active area 6. Der

Coolant main port 5 and the anode gas main port 3 are arranged laterally of the diaphragm 21 in the distributor region 2.

Figure 5 shows a schematic representation of a membrane 21 according to the preferred embodiment of the invention in Figure 4B. The membrane 21 has a quadrangular shape in plan view, wherein the longitudinal sides 24 are arranged parallel to each other. The end points of the longitudinal sides 24 are connected by a short side 23 each. In this case, a first short side 23 with the two longitudinal sides 24 encloses an angle α and the second short side 23 with the longitudinal sides 24 an angle ß. At least one of the two angles α and / or β is different from 90 °. In addition, in the embodiment shown, the angles α and β are equal. Thus, the two short sides 23 are parallel to each other and the membrane 21 has the shape of a parallelogram. The largest possible rectangle within the membrane 21, which has the same width as the membrane 21, corresponds to the active region 6 of the bipolar plates 1 shown in the preceding figures.

For arrangement in a membrane-electrode unit 20 ', a catalytic material 22 is arranged on both sides of the membrane 21. This can be done, for example, by catalytic

Coating the membrane 21 or a gas diffusion layer (not shown) take place. The catalytic coating 22 is in the active region 6 and according to the invention additionally in the activatable region 28 and thus over the entire surface, with or without partial deactivation or only in some areas. The goal here is that all areas of the later membrane electrode unit 20 'in the areas have an active catalytic coating 22 in which fuel and oxidant are present simultaneously.

FIGS. 6A and 6B show the cross sections of a membrane 21 with adjacent catalytic coating 22 in two embodiments. The embodiment of FIG. 6A shows a partial catalytic coating 22 which adjoins the membrane only in the active region 6. This creates inactive areas 25 that are not available for the fuel cell reaction. In contrast, Figure 6B shows a preferred embodiment of the membrane 21 according to the invention in cross-section, which has a catalytic coating 22 over the entire surface. The arrangement of this membrane 21 in a membrane-electrode unit 20 for a bipolar plate 1 of the type described in FIGS. 2 and 3 increases the power density of the resulting fuel cell, since the regions in which the fuel cell reaction generates energy extend beyond the active region 6 walk.

Bipolar plate

distribution area

Anode gas main port

Cathode gas main port

Coolant main Gasport

active area

anode plate

cathode plate

first overlap section

second overlap section

Side edge of the first overlap section Boundary line

Longitudinal edge of the active area Membrane electrode unit

Membrane electrode assembly of the prior art membrane

catalytic coating

short side

long side

inactive area

backing

poetry

activatable area

activated area anode channels

cathode channels

Coolant channels

Coolant fuel cell stack

first end plate 1 12 second end plate

1 13 bipolar plate (prior art)

1 14 membrane electrode assembly

1 15 sealing element

1 16 clamping element

S stacking direction

Claims

claims

1 . A bipolar plate (1) for a fuel cell (100) comprising a profiled anode plate (7) and a profiled cathode plate (8), each having an active region (6) and two manifold regions (2) for supply and discharge of operating media to and from the active area (6), wherein the distributor areas (2) respectively

an anode gas main port (3) for supplying and discharging fuel,

a cathode gas main port (4) for the supply and removal of oxidizing agent,

which is arranged such that from this starting cathode channels (41) at least over the distributor region (2) of the bipolar plate (1) are rectilinear and have a flow direction corresponding to a main flow direction in the cathode channels (41) in the active region (6), and

a coolant main port (5) for the supply and discharge of coolant, wherein the plates (7, 8) are formed and arranged one above the other, that the bipolar plate (1) has channels (31, 41, 51) for the operating media, which Main body ports (3, 4, 5) of both manifold regions (2) connect, and wherein the manifold regions (2) overlap a first intersecting portion (9) in which cathode channels (41) and anode channels (31) do not fluidly overlap one another and a second intersecting portion (FIG. 10), in which anode channels (31) and coolant channels (51) do not overlap each other in a fluid-connecting manner,

characterized in that the main coolant port (5) and the

An anode gas main port (3) adjacent to each other, are disposed adjacent to the cathode gas main port (4) and out of alignment of the active area.

2. bipolar plate (1) according to claim 1, characterized in that the first

Intersecting section (9) in the extension direction of the active region (6) is arranged to escape.

3. bipolar plate (1) according to one of claims 1 and 2, characterized in that the first overlapping portion (9) has the shape of a, in particular rectangular, triangle.

4. bipolar plate (1) according to any one of the preceding claims, characterized in that the first intersecting portion (9) is arranged such that a first side edge (1 1) of the first intersecting portion (9) in extension to an edge of the active region (6 ) runs.

5. bipolar plate (1) according to any one of the preceding claims, characterized in that the first intersecting portion (9) is arranged such that a second side edge (1 1) of the first intersecting portion (9) with a boundary line (12) of the active region ( 6) is perpendicular to its direction of extension.

6. bipolar plate (1) according to any one of the preceding claims, characterized in that the second overlapping portion (10) is arranged outside a flight of the active region (6).

7. Bipolar plate (1) according to one of the preceding claims, characterized in that a flow direction of the anode gas in the anode flow channels (31) in the second overlap section (10) in one of the active region (6).

runs away.

8. membrane electrode assembly (20) comprising

a membrane (21) having a quadrangular shape with two parallel longitudinal sides (24) and two opposite short sides (23), wherein at least one by a short side (23) and an adjacent longitudinal side (24)

included angle (a) is different from 90 ° and

two electrodes arranged on both sides of the membrane (21),

characterized in that the shape of the electrode surface corresponds to the membrane surface.

9. membrane electrode assembly (20) according to claim 1, characterized in that all internal angles of the quadrilateral of the membrane (21) are different from 90 °.

10. Fuel cell (100) comprising a bipolar plate (1) according to any one of claims 1 to 7 and a membrane electrode assembly (20) according to any one of claims 8 and 9.