Fuel cell stack, fuel cell device and fuel cell vehicle

Abstract

The invention relates to a fuel cell stack (2) with a plurality of fuel cells and with an inlet header (4) for a first reactant and an inlet header (4) for a second reactant, wherein at least one of the inlet headers (4) has a dike-like siphon (5) to ensure a level of a water reservoir (7), and wherein a sponge element (8) is arranged in the inlet header (4) within the water reservoir (7). The invention further relates to a fuel cell device (1) and a fuel cell vehicle.

Description

[0001] The invention relates to a fuel cell stack comprising a plurality of fuel cells and having an inlet header for a first reactant and an inlet header for a second reactant. A dyke-like siphon is formed on at least one of the inlet headers to ensure a level of a water reservoir, and a sponge element is arranged in the inlet header within the water reservoir. The invention further relates to a fuel cell device and a fuel cell vehicle.

[0002] Fuel cell devices are used for the chemical conversion of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain the so-called membrane electrode assembly as their core component, which is a composite of a proton-conducting membrane and two electrodes, namely an anode and a cathode, arranged on either side of the membrane.

[0003] During operation of the fuel cell device with a plurality of fuel cells combined to form a fuel cell stack, the fuel, in particular hydrogen H2 or a hydrogen-containing gas mixture, is fed to the anode, where an electrochemical oxidation of H2 to H + with the release of electrons. The protons H are transported via the electrolyte or the membrane, which separates the reaction chambers from each other in a gas-tight manner and electrically insulates them. + from the anode compartment to the cathode compartment. The electrons provided at the anode are conducted to the cathode via an electrical conductor. Oxygen or an oxygen-containing gas mixture is supplied to the cathode, resulting in a reduction of O2 to O 2- with the absorption of electrons. At the same time, in the cathode compartment, these oxygen anions react with the protons transported across the membrane to form water.

[0004] Fuel cell devices require careful water management. On the one hand, it is necessary to prevent excessive water in the fuel cell or fuel cell stack, which would block the flow channels for the reactant supply. On the other hand, if there is too little water in the fuel cell, the proton conductivity of the membrane is limited, so it is important to ensure adequate humidity and water supply to the membrane.

[0005] For water management, it is known to use humidifiers to transfer moisture from two gaseous media with different moisture contents to the drier medium. Such gas / gas humidifiers are used in particular in fuel cell devices, where air is compressed with the oxygen it contains in the cathode circuit to supply the cathode chambers of the fuel cell stack. This results in relatively warm and dry compressed air whose humidity is insufficient for use in the fuel cell stack for the membrane electrode assembly. The dry air provided by the compressor for the fuel cell stack is humidified by passing it past a water vapor-permeable membrane, the other side of which is brushed with the moist exhaust air from the fuel cell stack.Humidifiers are large and material-intensive components that require a lot of space, so there is an incentive to enable humidification independently of a humidifier or to support a humidifier in order to be able to implement it with a smaller space requirement.

[0006] A fuel cell stack with elements for humidifying a reactant is described, for example, in the documents DE 10 2019 211 586 A1 and DE 103 04 657 A1.

[0007] DE 10 2014 018 846 A1 discloses a humidification unit for a fuel cell device, through which a flow channel for conveying a medium, in particular air, runs. A liquid tank or a porous, moist sponge is arranged in the humidification unit; alternatively, the use of a membrane humidifier is possible. US 2004 / 0110057 A1 discloses a fuel cell stack with an absorber arranged in a header, which can absorb droplets and release them to a drain to ensure sufficient space for a reactant gas.US 2004 / 0170878 A1 describes a fuel cell stack with integrated water management, in which water is transported internally from moist areas of the cathode side, where it is generated, to relatively dry areas by utilizing capillary forces in wick material that is arranged in the electrically active area and extends to the headers for supply and discharge.

[0008] The object of the present invention is therefore to reduce the installation space required for humidifying a fuel cell stack and to improve water management. A further object is to provide an improved fuel cell device and an improved fuel cell vehicle.

[0009] This object is achieved by a fuel cell stack having the features of claim 1, by a fuel cell device having the features of claim 9, and by a fuel cell vehicle having the features of claim 10. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0010] The fuel cell stack according to the invention offers the advantage of internal and intrinsic water management, which eliminates the need for an external humidifier or at least allows its significant reduction due to reduced power requirements. Humidification occurs as the reactant gas passes the sponge element, evaporating the water from the water reservoir. This occurs in the region of the reactant inlet header and thus upstream of the fuel cells, particularly their first zone, which is thus protected even from slight membrane moisture. The siphon maintains the fill level of the water reservoir at a desired target level, ensuring that the sponge element can protrude above the level of the water reservoir and that the reactant gas passes not only the surface of the water but also the sponge element.

[0011] The siphon can be assigned a water inlet through which the water reservoir is filled; a pipe connection can be used to drain the water from the reservoir in order to maintain the target level.

[0012] It is preferred if the inlet header having the water reservoir is assigned to the cathode as a cathode inlet header, but alternatively or additionally it is also possible for the inlet header having the water reservoir to be assigned to the anode as an anode inlet header, in which case the water reservoir can be used as a water separator.

[0013] It is further preferred if an inlet header for a coolant is provided, which is arranged between the cathode inlet header and the anode inlet header. This enables rapid warm-up after a cold start due to the short paths and good heat conduction.

[0014] If a horizontal arrangement is chosen for the fuel cell stack with a horizontal reactant inlet header, then the level of liquid water in the water reservoir can be more easily adjusted.

[0015] The above-mentioned advantages and effects also apply mutatis mutandis to a fuel cell device with such a fuel cell stack and to a fuel cell vehicle with such a fuel cell device, in which installation space and mass can be saved by completely omitting a humidifier or by significantly reducing its size, thereby increasing efficiency and range.

[0016] The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figure, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also considered to be encompassed and disclosed by the invention that are not explicitly shown or explained in the figure, but which emerge and can be produced through separate feature combinations from the explained embodiments.

[0017] Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the drawings. Herein: Fig. 1 a schematic, perspective view of a fuel cell stack in a horizontal arrangement with a horizontally extending reactant inlet header, Fig. 2 a front view of the reactant inlet header with a sponge element, Fig. 3 a side view of the reactant inlet header with an associated siphon and the sponge element, and Fig. 4 a schematic representation of a fuel cell device known from the prior art.

[0018] In the Fig. 4 schematically shows a fuel cell device 1 which can be used, for example, in a fuel cell vehicle, wherein said device comprises a humidifier 3 for regulating the humidity of a plurality of fuel cells combined in a fuel cell stack 2.

[0019] Each of the fuel cells comprises an anode, a cathode, and a proton-conducting membrane separating the anode from the cathode. The membrane is made of an ionomer, preferably a sulfonated polytetrafluoroethylene (PTFE) polymer or a perfluorinated sulfonic acid (PFSA) polymer. Alternatively, the membrane can also be formed as a sulfonated hydrocarbon membrane.

[0020] Fuel (e.g., hydrogen) from a fuel tank can be fed to the anode through an anode inlet header. In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules are split into protons and electrons at the anode. The PEM allows the protons to pass through but is impermeable to the electrons. For example, the reaction 2H2→4H occurs at the anode. + + 4e -(Oxidation / electron release). While the protons pass through the PEM to the cathode, the electrons are conducted via an external circuit to the cathode or to an energy storage device.

[0021] The cathode gas (for example oxygen or oxygen-containing air) can be supplied to the cathode via a cathode chamber through a cathode inlet header, so that the following reaction takes place on the cathode side: O2 + 4H + → 2H2O (reduction / electron uptake).

[0022] Since several fuel cells are combined in the fuel cell stack 2, a sufficiently large quantity of cathode gas must be provided, so that a compressor 6 provides a large cathode gas mass flow, whereby the compression of the cathode gas significantly increases its temperature. The conditioning of the cathode gas, i.e., its adjustment with regard to the desired temperature and humidity in the fuel cell stack 2, takes place in the humidifier 3 downstream of the compressor 6. This humidifier 3 causes moisture saturation of the fuel cell membranes to increase their efficiency, as this promotes proton transport. This humidifier 3 requires a relatively large installation space, which complicates the integration of the fuel cell device into a fuel cell vehicle.

[0023] For a fuel cell device with a significantly reduced humidifier 3 or even without a humidifier 3 as a humidifier-less system, a dyke-like siphon 5 ( Fig. 3) is designed to ensure a level of a water reservoir 7, wherein in the inlet header 4 a sponge element 8 is arranged within the water reservoir ( Fig. 2). The sponge element 8 can have a structure similar to a gas diffusion layer and absorb water from the water reservoir 7, with the sponge element 8 protruding above the level of the water reservoir 7. If, for example, the cathode gas flows through the cathode inlet header 9, which has the water reservoir 7, it passes the sponge element 8, which offers a large surface area, and causes increased evaporation. This evaporation is temperature-dependent, so that only slight humidification occurs under cold conditions, while at higher temperatures, increased evaporation with high humidification occurs, thus providing an intrinsic adaptation to the operating requirements of a fuel cell stack 2.

[0024] The siphon 5 is assigned a water inlet 10 through which liquid water drips into the water reservoir 7 and thus fills it; excess water can be drained from the siphon 5 through a pipe connection.

[0025] The inlet header 4 having the water reservoir 7 can alternatively or additionally be assigned to the anode as an anode inlet header, wherein the water reservoir 7 can additionally be used as a water separator.

[0026] As a rule, the fuel cell stack 2 is also assigned an inlet header for a coolant, which is preferably arranged between the cathode inlet header 9 and the anode inlet header.

[0027] Fig. 2 indicates that a horizontal arrangement has been chosen for the fuel cell stack 2, which is characterized by horizontally running reactant inlet headers. LIST OF REFERENCE SYMBOLS: 1 fuel cell device 2 fuel cell stacks 3 humidifiers 4 Entry header 5 siphon 6 compressors 7 Water reservoir 8 Sponge element 9 Cathode entry header 10 Water inlet

Claims

[1] Fuel cell stack (2) with a plurality of fuel cells and with an inlet header (4) for a first reactant and an inlet header (4) for a second reactant, characterized by that a dyke-like siphon (5) is formed on at least one of the inlet headers (4) to ensure a level of a water reservoir (7), and that in the inlet header (4) a sponge element (8) is arranged within the water reservoir (7). [2] Fuel cell stack (2) according to claim 1, characterized by that the sponge element (8) protrudes from the level of the water reservoir (7). [3] Fuel cell stack (2) according to claim 1 or 2, characterized by that a water inlet (10) is assigned to the siphon (5). [4] Fuel cell stack (2) according to one of claims 1 to 3, characterized by that the siphon (5) is assigned a pipe connection for draining the water from the water reservoir (7). [5] Fuel cell stack (2) according to one of claims 1 to 4, characterized by that the inlet header (4) having the water reservoir (7) is assigned to the cathode as a cathode inlet header (9). [6] Fuel cell stack (2) according to one of claims 1 to 5, characterized by that the inlet header (4) having the water reservoir is assigned to the anode as an anode inlet header, and that the water reservoir (7) can be used as a water separator. [7] Fuel cell stack (2) according to one of claims 1 to 6, characterized by that an inlet header (4) for a coolant is provided, which is arranged between the cathode inlet header (9) and the anode inlet header. [8] Fuel cell stack (2) according to one of claims 1 to 7, characterized by that a horizontal arrangement is selected with a horizontally running inlet header (4). [9] Fuel cell device (1) with a fuel cell stack (2) according to one of claims 1 to 8. [10] Fuel cell vehicle with a fuel cell device (1) according to claim 9.

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