Fuel cell device and fuel cell vehicle

Abstract

Fuel cell device (1) with a fuel cell stack (2) having at least one fuel cell (3), with a cathode fresh gas line (4) opening into the fuel cell stack (2), an anode fresh gas line (10) opening into the fuel cell stack (2), and a recirculation line (13), wherein the recirculation line (13) is arranged on the side of the fuel cell stack (2) opposite the side with the anode fresh gas line (10) and its opening into the fuel cell stack (2), wherein a cathode fresh gas header (18), an anode fresh gas header (12), a cathode exhaust gas header, and anode exhaust gas header are arranged in the fuel cell stack (2), characterized in that the recirculation line (13) is led from the anode exhaust gas header to the anode fresh gas header (12), and that in the anode fresh gas header (12) a mixing element (16) is arranged,into which the recirculation line (13) opens and which is at least partially permeable to the recirculated anode exhaust gas.,

Description

The invention relates to a fuel cell device having a fuel cell stack having at least one fuel cell, having a cathode fresh gas line which opens into the fuel cell stack, an anode fresh gas line which opens into the fuel cell stack and an anode gas recirculation line, wherein the recirculation line is arranged on the side of the fuel cell stack which is opposite the side having the anode fresh gas line and the orifice thereof into the fuel cell stack. The invention also relates to a fuel cell vehicle.Fuel cell devices are used for the chemical reaction of a fuel with oxygen to form water in order to generate electrical energy. For this purpose, fuel cells contain, as core component, the so-called membrane electrode unit which is a composite of a proton-conducting membrane and in each case one electrode (anode and cathode) arranged on both sides of the membrane. In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane electrode unit on the sides of the electrodes facing away from the membrane. During operation of the fuel cell device having a plurality of fuel cells combined to form a fuel cell stack, the fuel, in particular hydrogen (H 2) or a hydrogen-containing gas mixture, is fed to the anode, where electrochemical oxidation of H 2 to H + takes place with emission of electrons. Via the membrane, which separates the reaction spaces from one another in a gas-tight manner and electrically isolates them, the protons H + 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 is supplied to the cathode, so that a reduction from O 2 to O 2- takes place with the absorption of the electrons. At the same time, these oxygen anions react in the cathode space with the protons transported via the membrane to form water.On the anode side, the fuel is usually provided from a fuel reservoir. The fuel cells are supplied with the fuel and also the oxidizing agent in superstoichiometric amounts in order to maximize their efficiency. Unreacted fuel at the fuel cells is recirculated for resource conservation, i.e. is fed back to the fuel cells. Here, the recirculated fuel is introduced into the fuel cell stack after mixing with the fresh fuel, wherein very many components are installed along the fuel cell stack, in competition with components for supplying other operating media. The interaction impairs the uniform distribution of the fuel along the fuel cell stack and results in pressure losses which are not in the optimum range. If use in a fuel cell vehicle is also sought, further boundary conditions are produced which make it difficult to achieve good accessibility and cost efficiency.DE 10 2013 005 802 A1 discloses a device for the treatment of supply air flowing to a fuel cell. A humidifier and a bypass line bypassing the humidifier are assigned to the supply air line, wherein a mixer is arranged downstream of the humidifier and upstream of the opening of the bypass line into the supply air line, by means of which mixer the humidified supply air stream is mixed and homogenized. DE 10 2021116 953 A1 describes a processing module for a fuel cell device, which has a module housing in which one or more components of a hydrogen recirculation path, an oxygen supply path and / or a temperature control circuit are integrated.A fuel cell device according to the preamble of claim 1 is known from DE 103 04 657 A1.It is therefore the object of the present invention to provide a fuel cell device which alleviates the disadvantages mentioned at the beginning. It is a further object to provide an improved fuel cell vehicle.This object is achieved by a fuel cell device having the features of claim 1 and by a fuel cell vehicle having the features of claim 8. Advantageous embodiments with expedient developments of the invention are specified in the dependent claims.The recirculation line is formed by an anode gas recirculation line. When using the recirculation line for the anode gas, the advantage results that the fuel section as a whole can be made very compact with the feed line and the recirculation, with efficiency advantages resulting from lower and more uniform pressure losses in the fuel cell stack. Since there are fewer connections on one side of the fuel cell stack, there are also more structural freedoms in the region of the line arrangement. Also, operating conditions may be shifted towards improved, lower stoichiometry.In this case, headers for the cathode fresh gas, the anode fresh gas, the cathode off-gas and the anode off-gas can be arranged in the fuel cell stack, wherein the recirculation line is guided from the header for the anode off-gas to the header for the anode fresh gas; that is to say a minimum distance is required along the fuel cell stack without having to guide the recirculation line in the direction of the fuel tank.According to the invention, it is provided that a mixing element is arranged in the header for the anode fresh gas, in which mixing element the recirculation line opens out and which is at least partially permeable to the recirculated anode exhaust gas.As a result, the recirculation can take place directly in the header for the anode fresh gas, wherein the mixing element can be of hollow design and can have at least one opening.It is advantageous if the at least one opening is oriented radially on the mixing element, since the recirculated fuel can be supplied again to the fuel cells located there in a targeted manner in a region of the fuel cell stack, that is to say upstream consumption of the fuel can be compensated for at least partially.In this case, it is possible for the opening to be provided multiple times, and for the openings to be arranged in a row in the longitudinal direction of the mixing element and / or to be situated opposite one another with respect to the longitudinal direction of the mixing element. This configuration has the advantage that the mentioned compensation can be carried out multiple times distributed over the height extension of the fuel cell stack.It is advantageous here if the openings lined up in the longitudinal direction of the mixing element have an opening width varying with the distance from the opening of the recirculation line into the mixing element, since a variation of the discharge of the recirculated fuel can thus take place in the region of the longitudinal extent of the anode fresh gas header.In this case, there is the possibility that the mixing element is configured statically. Alternatively, however, the mixing element can have an active region at least over a partial region of its extent, which changes its shape variably as a function of an external parameter, since an adaptation to changed boundary conditions can thus take place.The aforementioned effects and advantages also apply to a fuel cell vehicle having an aforementioned fuel cell device, which can be operated more efficiently and thus leads to a longer range.The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figure can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of the invention. Therefore, embodiments are also to be considered included and disclosed by the invention which are not explicitly shown or explained in the figure, but which emerge from the explained embodiments and can be generated by separate combinations of features.Further advantages, features and details of the invention are evident from the claims, the following description of preferred embodiments, and with reference to the drawings. The following shows: FIG. 1 shows a schematic illustration of a fuel cell device, FIG. 2 shows a schematic illustration of a hydrogen header, having a mixing element, of a fuel cell stack constructed from a plurality of fuel cells, FIG. 3 shows schematic representations of the structure of the mixing element with a) a terminal singular opening, b) a central singular opening, c) a plurality of openings, d) a plurality of openings of different sizes, FIG. 4 shows a plan view of a fuel cell stack having the hydrogen header, the coolant header and the oxygen header, and FIG. 5 shows cross-sectional representations of the hydrogen header with a mixing element positioned therein, with a) an opening pointing downward in the cross-sectional plane, b) two opposite openings pointing downward and upward, c) an opening pointing to the right.FIG. 1 shows the part required for explaining the invention, in particular a fuel cell stack 2 having a plurality of fuel cells 3, of a fuel cell device 1 which can be used, for example, in a fuel cell vehicle. The membrane is formed from an ionomer, preferably a sulfonated tetrafluoroethylene polymer (PTFE) or a perfluorinated sulfonic acid polymer (PFSA). Alternatively, the membrane may be formed as a sulfonated hydrocarbon membrane.A catalyst can additionally be mixed with the anodes and / or the cathodes, wherein the membranes are preferably coated on their first side and / or on their second side with a catalyst layer made of a noble metal or of mixtures comprising noble metals such as platinum, palladium, ruthenium or the like, which serve as reaction accelerators in the reaction of the respective fuel cell 3.Fuel (for example hydrogen) is supplied to the anodes via anode spaces within the fuel cell stack 2. In a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules are split into protons and electrons at the anode. The membrane allows the protons (for example H +) to pass through, but is impermeable to the electrons (e -). The following reaction takes place at the anode: 2H 2 →4H ++ 4 e -( oxidation / electron emission). As the protons pass through the membrane to the cathode, the electrons are conducted to the cathode or to an energy store via an external circuit. Cathode gas (for example, air containing oxygen or oxygen) can be supplied to the cathodes via cathode spaces within the fuel cell stack 2, so that the following reaction takes place on the cathode side: O 2+ 4 H ++ 4 e -→2H 2 O (reduction / electron uptake).To supply the fuel cell stack 2 with the reactants, the fuel cell device 1 has a cathode fresh gas line 4 with a compressor 5, a charge air cooler 6 and a humidifier 7; the cathode fresh gas line 4 opens into the fuel cell stack 2, from which a cathode exhaust gas line 8 is led to the humidifier 7; a turbine 9 supporting the drive of the compressor 5 is also arranged in the cathode exhaust gas line 8.It can also be seen from FIG. 1 that an anode fresh gas line 10 opens into the fuel cell stack 2 on the same side of the fuel cell stack 2 as the cathode fresh gas line 4 for the further reactant provided in a fuel tank 11. Furthermore, the fuel cell stack 2 contains headers cathode fresh gas header 18, anode fresh gas header 12, cathode exhaust gas header and anode exhaust gas header, which can be supplemented by a coolant circuit header 19.Since the reactants are provided in a fuel cell 3 in a superstoichiometric manner, in the exemplary embodiment shown a recirculation fan 14 is incorporated into a recirculation line 13 in order to feed the fuel, which has not been converted in the fuel cell stack 2 with a plurality of fuel cells 3, in the anode off-gas once again to the fuel cell stack 2 as anode fresh gas, and thus to "recirculate". The recirculation line 13 is led from the anode exhaust gas header to the anode fresh gas header 12. In principle, in this arrangement the recirculation line 13 for the cathode gas can be present, supplemented by an additional air compressor.An anode separator 15 can be associated with the recirculation line 13 in order to remove excess liquid from the anode circuit. Optionally, a purge valve is arranged in the recirculation line 13 downstream or alternatively upstream of the recirculation fan 14 in order to purge the anode circuit, should the fuel concentration present in the anode circuit fall below a critical value or should the proportion of inert gases therein become too high.The recirculation line 13 is arranged on the side of the fuel cell stack 2 opposite the side with the anode fresh gas line 10 and its mouth into the fuel cell stack 2 (FIG. 1 ), whereby a very compact anode circuit is realized, which results in more freedom in the arrangement of the plurality of lines and package advantages.A mixing element 16 is arranged in the anode fresh gas header 12 (FIG. 2 ) with a connecting end for connection to the recirculation line 13, so that the recirculation line 13 opens into the mixing element 16, which is at least partially permeable to the recirculated anode exhaust gas.The mixing element 16 is of hollow design and has at least one opening 17, wherein in the exemplary embodiments shown the at least one opening 17 is oriented radially on the mixing element 16 (FIGS. 3 a) to 3 d)).FIGS. 3 c ) and 3 d) show that the opening 17 is provided multiple times, wherein the openings 17 are arranged in a row in the longitudinal direction of the mixing element 16 and can be opposite each other with respect to the longitudinal direction of the mixing element 16 (FIG. 5 b )).FIG. 3 d ) refers to the fact that the openings 17 lined up in the longitudinal direction of the mixing element 16 have an opening width varying with the distance from the opening of the recirculation line 13 into the mixing element 16, as a result of which a varying proportion of the recirculated anode off-gas can be discharged to the fuel cells 3, that is to say more anode gas can be supplied to specific fuel cells 3 than others and thus the consumption of the anode gas can be at least partially compensated for when the anode fresh gas header 12 flows through.In the exemplary embodiments shown, the mixing element 16 is of static design, that is to say with a constant shape. However, the mixing element 16 can have an active region at least over a partial region of its extent, which region changes its shape variably as a function of an external parameter, such that the discharge of the anode gas also changes. This can be realized by a material with shape memory structures which change their shape variably as a function of an external parameter such as temperature, pressure or relative humidity.LIST OF REFERENCE CHARACTERS:1 Fuel cell device 2 Fuel cell stack 3 Fuel cell 4 Cathode fresh gas line 5 Compressor 6 Charge air cooler 7 Humidifier 8 Cathode exhaust gas line 9 Turbine 10 Anode fresh gas line 11 Fuel tank 12 Anode fresh gas header 13 Recirculation line 14 Recirculation blower 15 Anode exhaust gas conductor 16 Mixing element 17 Opening 18 Cathode fresh gas header 19 Coolant circuit header

Claims

Fuel cell device (1) having a fuel cell stack (2) having at least one fuel cell (3), having a cathode fresh gas line (4) which opens into the fuel cell stack (2), an anode fresh gas line (10) which opens into the fuel cell stack (2) and a recirculation line (13), wherein the recirculation line (13) is arranged on the side of the fuel cell stack (2) which is opposite the side having the anode fresh gas line (10) and the mouth thereof into the fuel cell stack (2), wherein cathode fresh gas headers (18), anode fresh gas headers (12), cathode off-gas headers and anode off-gas headers are arranged in the fuel cell stack (2), characterized in that the recirculation line (13) is guided from the anode off-gas header to the anode fresh gas header (12), and in that a mixing element (16) is arranged in the anode fresh gas header (12), in which mixing element the recirculation line (13) opens and which is at least partially permeable to the recirculated anode exhaust gas.Fuel cell device (1) according to Claim 1, characterized in that the mixing element (16) is of hollow design and has at least one opening (17).Fuel cell device (1) according to Claim 2, characterized in that the at least one opening (17) is oriented radially on the mixing element (16).Fuel cell device (1) according to Claim 3, characterized in that the opening (17) is provided a plurality of times, and in that the openings are arranged in a row in the longitudinal direction of the mixing element (16) and / or are opposite one another with respect to the longitudinal direction of the mixing element (16).Fuel cell device (1) according to Claim 4, characterized in that the openings (17) which are lined up in the longitudinal direction of the mixing element (16) have an opening width which varies with the distance from the orifice of the recirculation line (13) into the mixing element (16).Fuel cell device (1) according to one of Claims 1 to 5, characterized in that the mixing element (16) is of static design.Fuel cell device (1) according to one of Claims 1 to 5, characterized in that the mixing element (16) has an active region at least over a partial region of its extent, which active region changes its shape variably as a function of an external parameter.Fuel cell vehicle having a fuel cell device (1) according to one of Claims 1 to 7.

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