TREATMENT OF HYDROGEN-CONTAINING AND OXYGEN-CONTAINING RESIDUAL GASES FROM FUEL CELLS

Description

[0001] The invention relates to a fuel cell arrangement with fuel cells and a residual gas treatment device for hydrogen-containing and oxygen-containing residual gases from the fuel cells and to a method for treating hydrogen-containing and oxygen-containing residual gases from fuel cells.

[0002] Fuel cells, fuel cell assemblies comprising a plurality of fuel cells, and methods for their operation are extensively known in the prior art. Fuel cells are galvanic cells that provide the energy released during a chemical reaction, particularly an exergonic one, of at least two reaction gases, at least partially as electrical energy. Fuel cells thus serve, among other things, to supply electrical energy, but under certain circumstances also thermal energy.

[0003] Fuel cells are used, among other things, in stationary applications to provide uninterruptible power supplies, island grids, and / or similar applications. Furthermore, fuel cells can also be used to provide thermal energy for heating purposes.

[0004] Furthermore, the use of fuel cells is also planned for vehicles, for example watercraft such as ferries or submarines, aircraft, but also for motor vehicles, in particular for electrically powered vehicles such as electric vehicles, hybrid vehicles or the like.

[0005] It is also often intended that the range of electrically powered vehicles should be improved by using fuel cells, in which fuel cells are provided in addition to or as an alternative to the use of a respective vehicle battery to supply electrical energy to an electric drive device of the vehicle.

[0006] A frequently used type of fuel cell is the hydrogen-oxygen fuel cell, in which electrical energy and heat are usually generated through an electrochemical reaction between hydrogen and oxygen. The oxygen supply can also be replaced or supplemented by air, depending on the design of the fuel cell. One of the reaction products is water. Furthermore, residual gases must be removed from the fuel cell in the area of ​​each electrode, for example, a hydrogen-containing residual gas at the anode electrode and an oxygen-containing residual gas at the cathode electrode.

[0007] During normal operation of a hydrogen-oxygen fuel cell, hydrogen is supplied to the anode, while oxygen is supplied to the cathode. The electrodes interact electrochemically with each other via an electrolyte, which can be formed, for example, by a polymer electrolyte membrane or the like. The hydrogen can be supplied either by pure hydrogen gas or by a hydrogen-containing fuel gas. Likewise, the oxygen can be supplied by pure oxygen gas or, for example, in the form of air.

[0008] In such a hydrogen-oxygen fuel cell, a direct voltage is typically provided between the electrodes, which may, for example, be approximately 1 V or less. Therefore, a plurality of fuel cells are typically operated electrically in series and can be combined to form a fuel cell stack of a fuel cell assembly.

[0009] During operation of fuel cells, unconverted residual gases are produced at the outlet. These are normally released into the environment. In the case of a polymer electrolyte fuel cell, these are hydrogen-containing residual gases and oxygen-containing residual gases. If the fuel cell is required to operate in a closed system, the residual gases must be stored. To enable safe storage, the hydrogen content in the residual gases must be reduced below the explosion limit, ideally eliminated entirely.

[0010] Non-operating modules may also have hydrogen on the oxygen side, for example if the gas spaces have been charged with hydrogen to prevent corrosion and oxidation.

[0011] Although the fuel cell is first purged with nitrogen before it is put into operation, "new oxygen" can still meet "old hydrogen" on the oxygen side and react with it, releasing thermal energy in quantities that can damage the fuel cell(s).

[0012] Excess hydrogen can therefore often be removed downstream using so-called catalytic burners or recombiners with the help of available oxygen. These catalytic burners or recombiners are separate components.

[0013] Such recombinators are described, for example, in US 2008 / 248369 or EP 1750321.

[0014] WO 2020 / 038907 A1, for example, discloses a method for treating hydrogen-containing and oxygen-containing residual gases from fuel cells, as well as a residual gas treatment system. The teaching of WO 2020 / 038907 A1 is particularly suitable for essentially closed operation of a fuel cell arrangement, in which the residual gases are not to be readily released into an environment, for example, an ambient atmosphere or the like. Even though this teaching has proven successful, disadvantages still arise. Particularly during changes in the operating state of the fuel cell, in particular during a switch-on or switch-off process of the fuel cell, an undesirable gas composition of the residual gas mixture can arise in the residual gas circuit, which can influence optimal utilization according to the teaching of WO 2020 / 038907 A1.

[0015] The invention is therefore based on the object of providing a fuel cell arrangement with fuel cells and a residual gas treatment device for hydrogen-containing and oxygen-containing residual gases of the fuel cells, as well as a method for treating hydrogen-containing and oxygen-containing residual gases from fuel cells in order to be able to realize a largely optimal residual gas treatment.

[0016] As a solution, the invention proposes a fuel cell arrangement with fuel cells and a residual gas treatment device for hydrogen-containing and oxygen-containing residual gases from the fuel cells, as well as a method for treating hydrogen-containing and oxygen-containing residual gases from fuel cells according to the independent claims.

[0017] Advantageous further training results from features of the dependent claims.

[0018] The invention solves the problem directed to a fuel cell arrangement by providing that in such a fuel cell arrangement, comprising a plurality of fuel cells electrically and mechanically combined in a fuel cell stack, further comprising a residual gas treatment device for hydrogen-containing and oxygen-containing residual gases of the fuel cells, the residual gas treatment device comprises a recombinant fuel cell with catalyst and membrane, which is conducted via an electrical circuit separate from the fuel cells.

[0019] The structure of the fuel cell assembly is expanded by one or more so-called recombinant fuel cells. These fuel cells are conventional cells with a catalyst and membrane, as used in fuel cell arrays. The resulting residual gases are fed into the recombinant fuel cell, where they are electrochemically converted into water. The recombinant fuel cell is powered by an electrical circuit separate from the other fuel cells.

[0020] In an advantageous embodiment of the invention, the recombinant fuel cell is arranged directly downstream of the fuel cells in the fuel cell stack, which enables a compact design.

[0021] In an alternative embodiment, the recombinant fuel cell is located outside the fuel cell stack. In this case, the existing fuel cell stack can remain unchanged.

[0022] According to the invention, a voltage and / or current measuring device is integrated into the recombinant fuel cell or connected to the recombinant fuel cell. This allows the conversion of hydrogen in the residual gas to be measured and, ideally, provides information about the amount of hydrogen at the outlet of the recombinant fuel cell.

[0023] In a further advantageous embodiment of the invention, a sheet metal recombination cell is arranged between the fuel cells and the recombinant fuel cell, wherein in the sheet metal recombination cell, the membrane of the recombinant fuel cell is replaced by a sheet metal. The sheet metal in the center of the cell makes this sheet metal recombination cell more mechanically and thermally stable. Due to the direct reaction of reactant mixtures from the fuel cells in the fuel cell stack in the mechanically more stable sheet metal recombination cell, potential damage to the subsequent membrane recombinant fuel cell can be prevented.

[0024] The object, which is directed to a method for treating hydrogen-containing and oxygen-containing residual gases from fuel cells, is achieved by a method in which the residual gases from fuel cells electrically and mechanically combined in a fuel cell stack are fed to a recombinant fuel cell which is conducted via an electrical circuit separate from the fuel cells.

[0025] Advantageously, the residual gases within the fuel cell stack are fed to the recombinant fuel cell.

[0026] Alternatively, it may be advantageous if the residual gases are led out of the fuel cell stack and fed to a recombinant fuel cell arranged outside the stack.

[0027] It is useful to measure the voltage and / or current of the recombinant fuel cell.

[0028] Advantageously, residual gases first flow through a sheet metal recombination cell in which a membrane of the recombination fuel cell is replaced by a sheet metal before being fed into the recombination fuel cell.

[0029] With the invention, the recombination of residual gases can be integrated directly into the structure of the fuel cell stack. The reactivity of the recombination cell can be measured using voltage and / or current measurements, eliminating the need for additional gas sensors. Integration into the fuel cell stack offers a significant geometric advantage. Due to its design, the recombination system can be optimally cooled. In certain cases, energy recovery from the reactants would also be possible.

[0030] The invention is explained in more detail by way of example with reference to the drawings. They show schematically and not to scale: Figure 1 shows a first fuel cell arrangement according to the invention, Figure 2 shows a basic structure of a PEM fuel cell, Figure 3 shows a second fuel cell arrangement according to the invention and Figure 4 shows a third fuel cell arrangement according to the invention.

[0031] FIG 1 shows a simplified representation of a fuel cell arrangement 1 comprising a fuel cell stack 2 and an operating part 13. The fuel cell stack 2 consists of several individual fuel cells 3, here PEM fuel cells, stacked on top of one another and thus electrically connected in series.

[0032] Furthermore, the Figure 1a residual gas treatment device 4 according to the invention for hydrogen-containing and oxygen-containing residual gases from the fuel cells 3 of the fuel cell stack 2. This residual gas treatment device 4 comprises a recombinant fuel cell 5, the basic structure of which does not differ from that of a fuel cell 3 of the fuel cell stack 2. The recombinant fuel cell 5 is connected downstream of the fuel cells 3 with respect to a flow direction 9 of the reactants, but is not electrically connected in series with them, but is guided via an electrical circuit 8 separate from the fuel cells 3.

[0033] Figure 2shows a simplified cross-sectional view of the fuel cell structure. Each of the fuel cells 3 or recombinant fuel cells 5 has a membrane 7 and, on either side thereof, a catalyst layer 6 and a gas diffusion layer 14. The gas diffusion layer 14 and the catalyst layer 6 together form a gas diffusion electrode 24. This is followed by a bipolar plate 15, which establishes the electrical connection to the next fuel cell 3 and in which gas distribution structures 16 are incorporated, through which gas spaces 17 and 18 are formed for the reactants hydrogen and oxygen. The electrode 24 adjacent to a gas space 17 for hydrogen is also called the anode, and the electrode 24 adjacent to a gas space 18 for oxygen is also called the cathode. Channels for supplying and removing the reactants to and from the fuel cells, seals, etc. are not shown to simplify the illustration.

[0034] The operating part 13 of the fuel cell assembly 1 comprises connection technology, sensors, valves, water separators, etc. Therefore, there are connections for the hydrogen supply 19 and discharge 20 and connections for the oxygen supply 21 and discharge 22. Furthermore, at the end of the fuel cell assembly 1 on the operating part side, electrical load connections 23 are led outwards, to which a load (not shown) to be supplied with current from the fuel cell assembly 1 can be connected. In the embodiment of the Figure 1 the recombination fuel cell 5 is arranged directly downstream of the fuel cells 3 in the fuel cell stack 2 in the flow direction 9 of the reactants, so that a compact structure is achieved.

[0035] Figure 3shows an alternative embodiment of a fuel cell arrangement 1 according to the invention, in which the recombination fuel cell 5 is arranged outside the fuel cell stack 2 downstream of the fuel cells 3 in the flow direction 9 of the reactants.

[0036] According to the invention, a voltage and / or current measuring device 10 is integrated into the recombinant fuel cell 5 (see Figure 2 ). In the examples of the Figure 1 and 4 The corresponding connections to circuit 8 are located in the area of ​​the other connections. Figure 3 Corresponding connections are found on the external recombination fuel cell 5.

[0037] The fuel cell arrangement of the Figure 4 is compared to the embodiment of the Figure 1modified in that a sheet metal recombination cell 11 is arranged between the fuel cells 3 and the recombinant fuel cell 5. The structure of such a sheet metal recombination cell 11 differs from that of the recombinant fuel cell 5 in that the membrane 7 of the recombinant fuel cell 5 is replaced by a sheet metal 12, whereby the mechanical stability is increased compared to the recombinant fuel cell 5 and the mechanical or thermal stress resulting from the reaction of hydrogen with oxygen can already occur in this cell without damaging it, and thus possible damage to the subsequent recombinant fuel cell 5 can be prevented.

Claims

1. Fuel cell assembly (1) comprising a plurality of fuel cells (3) amalgamated electrically and mechanically in a fuel cell stack (2), further comprising a residual gas treatment device (4) for hydrogen-containing and oxygen-containing residual gases of the fuel cells (3), wherein the residual gas treatment device (4) comprises a recombination fuel cell (5) with catalyst (6) and membrane (7) that is led via a power circuit (8) separate from the fuel cells (3), characterized in that a measuring device (10) for voltage and / or current is integrated into the recombination fuel cell (5) or connected to the recombination fuel cell (5).

2. Fuel cell assembly (1) according to Claim 1, wherein the recombination fuel cell (5), in the flow direction (9) of the reactants, is directly downstream of the fuel cells (3) in the fuel cell stack (2).

3. Fuel cell assembly (1) according to Claim 1, wherein the recombination fuel cell (5), in the flow direction (9) of the reactants, is downstream of the fuel cells (3) outside the fuel cell stack (2).

4. Fuel cell assembly (1) according to any of the preceding claims, wherein a metal-sheet recombination cell (11) is arranged between the fuel cells (3) and the recombination fuel cell (5), the membrane (7) of the recombination fuel cell (5) being replaced in the metal-sheet recombination cell (11) by a metal sheet (12).

5. Method for treating hydrogen-containing and oxygen-containing residual gases from fuel cells (3), in which the residual gases from fuel cells (3) amalgamated electrically and mechanically in a fuel cell stack (2) are supplied to a recombination fuel cell (5) which is led via a power circuit (8) separate from the fuel cells (3), characterized in that voltage and / or current strength of the recombination fuel cell (5) is measured.

6. Method according to Claim 5, wherein the residual gases within the fuel cell stack (2) are supplied to the recombination fuel cell (5).

7. Method according to Claim 5, wherein the residual gases are led out of the fuel cell stack (2) and supplied to the recombination fuel cell (5).

8. Method according to any of Claims 5 to 7, wherein residual gases flow first through a metal-sheet recombination cell (11) in which instead of a membrane (7), as in the recombination fuel cell (5), a metal sheet (12) is arranged, before they are led into the recombination fuel cell (5).