Fuel cell unit

Abstract

A fuel cell unit (1) for electrochemically generating electrical energy, comprising: fuel cells (2) stacked into a fuel cell stack (40); a channel (12) for recirculating fuel integrated into the fuel cell stack (40); a recirculation system (65) with a recirculation line (15, 16.50) for recirculating the recirculated fuel discharged from the channel (12) back into the channel (12) so as to form a recirculation loop in the fuel cell unit; a drain valve (63) for discharging recirculated fuel from the recirculation system (65) into the environment; at least one fixing member for fixing the discharge valve; a seal (75) for sealing the flow path from the space (90) at the discharge valve (63) to the environment, the fuel cell unit (1) comprising an additional seal (77) for sealing the flow path from the environment to the seal (75) to prevent at least one component (79, 80) placed on the seal (75) from corrosion.

Description

Technical Field

[0001] The invention relates to a fuel cell unit according to the preamble of claim 1. Background Art

[0002] As an electric energy cell, the fuel cell unit converts the continuously supplied fuel and oxidant into electric energy by means of the redox reaction of the anode and the cathode. The fuel cell is applied to very different fixed and mobile references, such as houses without grid connection, or in motor vehicles, rail transportation, air travel, space travel and shipping. In the fuel cell unit, a large number of fuel cells are stacked into a fuel cell pile as a fuel cell group. In the fuel cell pile, a channel for passing through the recirculating fuel, a channel for passing through the oxidant and a channel for passing through the coolant are integrated. The recirculating fuel guided by the channel is not completely consumed after the passing, so after the recirculating fuel is derived from the channel of the recirculating fuel, the recirculating fuel will be supplied back to the channel of the recirculating fuel by means of the recirculating pipeline of the recirculating system. The fuel consumed according to the power required by the fuel cell unit is supplied to the recirculating pipeline by means of an injector. The greater the power of the fuel cell unit, the greater the fuel consumption, and the consumed fuel is supplied accordingly by means of an injector. The fuel (usually hydrogen) is stored in a compressed gas storage tank at high pressure. The recirculated fuel discharged from the fuel cell stack has a high water content, so the water is mechanically separated by means of a water separator in the recirculation system before the recirculated fuel reenters the fuel cell stack. The recirculation system includes a blower, a jet pump, a water separator and a discharge valve for the recirculated fuel as components.

[0003] The discharge valve for the recirculated fuel is fastened to a fixed component as a magnet valve. A seal is used to seal the space above the discharge valve from the environment. However, the fixed component is exposed to environmental influences and is therefore affected by moisture, water and electrolytes. For this reason, corrosion occurs on one or more components on which the seal is placed. Corrosion can cause pitting, cavitation or penetration of the seal. This can lead to leaks and uncontrolled escape of the recirculated fuel from the space at the discharge valve into the environment. This increases the demand for recirculated fuel and, if, for example, hydrogen escapes into the environment as a hydrogen-oxygen reaction, there is a risk of explosion.

[0004] DE 11 2004 001 483 B4 discloses a fuel cell system which reduces the hydrogen concentration in hydrogen exhaust gas discharged from a fuel cell and then discharges the hydrogen exhaust gas into the atmosphere, the fuel cell system comprising: a regulating valve for adjusting the flow rate of the hydrogen exhaust gas to a constant flow rate, wherein the regulating valve is arranged in an exhaust gas channel, through which the hydrogen exhaust gas is discharged from the fuel cell and directed to the outside of the fuel cell system; and a chamber for temporarily storing a gas containing the hydrogen exhaust gas, wherein the regulating valve is arranged downstream of the chamber in the exhaust gas channel.

[0005] US Pat. No. 7,655,336 B2 discloses a fuel cell system having a purge valve as a solenoid valve. Summary of the invention

[0006] Advantages of the present invention

[0007] According to the present invention, a fuel cell unit for electrochemically generating electrical energy includes: fuel cells arranged in a stack, and the stacked fuel cells form a fuel cell stack; a channel for recycled fuel integrated into the fuel cell stack; a recirculation system with a recirculation pipeline, for recycling the recycled fuel discharged from the channel for recycled fuel back into the channel for recycled fuel, thereby forming a recirculation loop with recycled recycled fuel in the fuel cell unit; a discharge valve for discharging the recycled fuel from the recirculation system into the environment; at least one fixed component for fixing the discharge valve; a seal for sealing a possible flow path from the space at the discharge valve to the environment, wherein the fuel cell unit includes an additional seal for sealing the flow path from the environment to the seal to prevent corrosion of at least one component placed on the seal.

[0008] In another embodiment, a seal is placed on the first member and the second member.

[0009] In a supplementary variant, the first component faces the discharge valve relative to the seal, while the second component faces away from the discharge valve relative to the seal.

[0010] In an additional configuration, the first component is constructed from a nobler metal than the second component.

[0011] Preferably, the seal is arranged at least partially, in particular completely, in the groove.

[0012] In another variant, the recess is formed in the first component and / or in the second component.

[0013] In another embodiment, the first component is formed by the sealing connection piece and / or the outlet valve, in particular the housing of the outlet valve. Preferably, the sealing connection piece is formed in one piece on the housing of the outlet valve or is a special component in addition to the housing of the outlet valve.

[0014] In a supplementary embodiment, the second component is formed by the base and / or the module housing.

[0015] Practically, the discharge valve is at least partially arranged in a bore of the fixed member.

[0016] In another variant, the fastening component is formed by the second component, in particular the module housing.

[0017] In a supplementary configuration, the additional seal is placed on the first additional component and on the second additional component.

[0018] In another variant, the first additional component faces the discharge valve relative to the additional seal, while the second additional component faces away from the discharge valve relative to the additional seal.

[0019] In a supplementary embodiment, the first additional component and the second additional component, in particular completely and / or on the contact surface with the additional seal, are made of metals having substantially (in particular with a deviation of less than 30%, 20%, 10%) the same negative potential and / or are made of stainless steel. The negative potential of a metal is a measure of the degree of inertness or non-inertness of a metal.

[0020] In a supplementary configuration, the recirculation system comprises a water separator integrated into the recirculation line for separating water from the recirculated fuel.

[0021] In particular, the recirculation system is mounted and / or inserted and / or integrated into the module housing, and preferably the module housing is fastened to the connecting plate of the fuel cell unit. Preferably, the module housing is constructed as a housing and / or frame structure and / or block structure and / or support structure and / or is constructed in one piece or in multiple pieces and / or has a functional geometry for components of the recirculation system. For example, the functional geometry is used to receive components of the recirculation system (for example, holes for receiving a discharge valve), and / or for constructing components of the recirculation system, such as at least one channel constructed in the module housing to construct a discharge line and / or supply line for the recirculated fuel. The module housing (for example as a support structure) preferably has any geometry and / or shape for the required function.

[0022] In a further embodiment, the additional seal is at least partially, in particular completely, arranged in the additional groove and / or recess and / or phase, in particular the additional groove and / or recess and / or phase is designed to completely surround the outlet valve.

[0023] In a supplementary embodiment, the first additional component is formed by the first component and / or the sealing flange and / or the sealing connection.

[0024] In a supplementary embodiment, the second additional component is formed by the second component and / or the module housing and / or the base.

[0025] Preferably, the base is structurally designed as a single piece on the rest of the module housing or as an additional component relative to the rest of the module housing.

[0026] In another embodiment, the first additional component and the second additional component are constructed of stainless steel.

[0027] In a further embodiment, the seal is designed to completely surround the space for the discharge valve and / or the opening in the module housing and / or the opening in the fastening component.

[0028] In a further embodiment, the additional seal is designed to completely surround the space for the discharge valve and / or the opening in the module housing or in the stationary component.

[0029] In a supplementary variant, the seal is loaded with pressure between the first component and the second component.

[0030] In a supplementary variant, the additional seal is loaded with pressure between the first additional component and the second additional component.

[0031] In another embodiment, when the discharge valve is open, the possible flow path from the space at the discharge valve to the environment is at least partially, in particular not at all, a flow path for recirculated fuel from the discharge valve to the environment. The function of the seal is to seal the space at the discharge valve to the environment so that when the discharge valve is closed, no recirculated fuel can escape from the space to the environment via the possible flow path.

[0032] In another embodiment, the space at the discharge valve is connected in a fluid-conducting manner to the recirculation line.

[0033] Preferably, the additional seal is placed only on at least one additional component.

[0034] In a supplementary embodiment, the additional seal is placed only on at least one additional component which has essentially the same negative potential and / or is made of stainless steel and / or has a contact surface relative to the additional seal, which is made of stainless steel and / or has a contact surface relative to the additional seal, which has essentially the same negative potential.

[0035] In a further embodiment, there is a distance between the seal and the additional seal, in particular in the axial direction of the bore for receiving the discharge valve.

[0036] Preferably, said distance between the seal and the additional seal is greater than 0.2 cm, 0.5 cm, 1 cm, 2 cm or 3 cm.

[0037] In a supplementary variant, the seal has no direct contact with the additional seal.

[0038] Practically, the seal and the additional seal are different components.

[0039] In an additional embodiment, the seal and / or the additional seal are designed in one piece.

[0040] In a supplementary variant, the seal and / or the additional seal are at least partially, in particular completely, constructed from an elastic material and / or an elastomer and / or a plastic, preferably HPU and / or PU and / or NBR and / or FPM and / or FKM and / or EPDM and / or silicone and / or PTFE and / or POM and / or PA and / or PA 6G and / or rubber.

[0041] Preferably, the elastic modulus of the seal and / or the additional seal material is between 0.001 GPa and 10 GPa, in particular between 0.01 GPa and 0.1 GPa.

[0042] In a further embodiment, the sealing flange and / or the base is designed flat and / or disk-shaped with an opening for receiving the outlet valve.

[0043] In particular, the sealing connection piece is designed essentially in the form of a cylindrical sleeve and preferably the cylindrical sleeve-shaped sealing connection piece surrounds the outlet valve.

[0044] Practically, the radial outer side of the sealing socket forms a groove for the seal.

[0045] Preferably, during operation of the fuel cell unit, the space at the outlet valve is charged with recirculating fuel and / or is at least partially flowed through.

[0046] In an additional embodiment, the space at the outlet valve is at least partially, in particular completely, delimited by the outlet valve and / or the module housing and / or the fastening component and / or the first component and / or the second component.

[0047] Preferably, the inlet of the discharge valve and / or the outlet of the discharge valve and / or the discharge line for the recirculated fuel and / or the supply line for the recirculated fuel open into the space at the discharge valve.

[0048] Preferably, the seal and / or the additional seal are constructed and / or arranged to completely surround the discharge valve.

[0049] In another variant, the additional seal serves to seal the flow path from the seal to the environment and vice versa.

[0050] In a supplementary embodiment, the fuel cell unit comprises a housing, in particular a housing with a connecting plate, and the fuel cell stack is preferably enclosed by the housing.

[0051] In a supplementary variant, the recirculation system comprises a conveying device, in particular a blower and / or a jet pump, for conveying the recirculated fuel through the recirculation circuit.

[0052] Preferably, the recirculation system is designed as a structural unit.

[0053] Preferably, the components of the fuel cell are ion exchange membranes, in particular proton exchange membranes, anodes, cathodes, gas diffusion layers and bipolar plates.

[0054] Preferably, the fuel cells each comprise layer-like components which are arranged in a stack.

[0055] In another embodiment, the recirculation system comprises at least one resistance heating element, in particular a plurality of resistance heating elements, for heating at least one component of the recirculation system and / or for heating the recirculation system. Thus, ice can be thawed into water by means of the at least one resistance heating element.

[0056] Practically, the components of the recirculation system are a recirculation line and / or a conveying device for the recirculated fuel, in particular a blower and / or a jet pump, and / or a water separator and / or at least one discharge valve and / or a drain valve for the recirculated fuel and / or an injector for the fuel and / or a module housing and / or a connecting plate and / or at least one connecting device.

[0057] Preferably, at least one component of the recirculation system, in particular all components of the recirculation system except the module housing, are inserted and / or installed and / or integrated into the module housing.

[0058] In a further embodiment, the fuel cell unit, in particular the recirculation system, comprises an injector for supplying fuel from a compressed gas reservoir for the fuel into the recirculation line and / or a compressed gas line for conducting fuel from the compressed gas reservoir into the injector.

[0059] In a supplementary variant, the separation of water from the recirculated fuel in the water separator as a mechanical water separator can be carried out by means of sedimentation and / or vortexes. For example, when separating by means of vortexes, the recirculated fuel can be subjected to a rotational movement in the discharge line as a cyclone separator, so that the water can be separated due to the centrifugal forces that occur.

[0060] The fuel cell system according to the present invention, in particular a fuel cell system for a motor vehicle, comprises a fuel cell unit, a compressed air storage device for storing gaseous fuel, and a gas delivery device for delivering a gaseous oxidant to the cathode of the fuel cell, wherein the fuel cell unit is constructed as the fuel cell unit described in the present patent application.

[0061] In another variant, a discharge valve is constructed in the recirculation line as a purge valve for discharging the recirculated fuel into the environment. If the fuel proportion in the recirculated fuel is low, i.e., other substances and / or gases other than fuel are accumulated in the recirculated fuel in large quantities, these substances and / or gases can be discharged into the environment. Therefore, in addition to the fuel as a pure substance, the recirculated fuel preferably also includes other substances and / or gases.

[0062] Preferably, the fuel is hydrogen, hydrogen-rich gas, reformed gas or natural gas.

[0063] Practically, the fuel cells and / or the components are of substantially flat and / or disk-shaped design.

[0064] In supplemental variations, the oxidant is oxygenated air or pure oxygen.

[0065] Preferably, the fuel cell unit is a PEM fuel cell unit having a PEM fuel cell, or a SOFC fuel cell unit having a SOFC fuel cell, or an alkaline fuel cell (AFC), or a solid oxide fuel cell (SOFC). BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The embodiments of the present invention are described in more detail below with reference to the accompanying drawings.

[0067] Figure 1 A strongly simplified exploded view of a fuel cell system with fuel cell components,

[0068] Figure 2 A perspective view of a portion of a fuel cell.

[0069] Figure 3 Longitudinal section of a fuel cell.

[0070] Figure 4 Perspective view of a fuel cell stack without the shell and recirculation system.

[0071] Figure 5 Cross-section of a fuel cell unit with housing and recirculation system,

[0072] Figure 6 Side view of a fuel cell unit with a recirculation system,

[0073] Figure 7 a longitudinal section through a portion of the discharge valve and the module housing, and

[0074] Figure 8 A perspective view of a portion of a drain valve and a portion of a module housing. DETAILED DESCRIPTION

[0075] Figures 1 to 3 The basic structure of a fuel cell 2 as a PEM fuel cell 3 (Polymerelektrolyt-Brennstoffzelle, polymer electrolyte fuel cell 3) is shown in the figure. The principle of the fuel cell 2 is to generate electrical energy or electric current by means of an electrochemical reaction. Hydrogen H2 is guided to the anode 7 as a gaseous recirculating fuel, and the anode 7 forms the negative electrode. The gaseous oxidant (i.e. air containing oxygen) is guided to the cathode 8, i.e. the oxygen in the air provides the required gaseous oxidant. Reduction (electron absorption) occurs at the cathode 8. Oxidation is carried out at the anode 7 in the form of released electrons.

[0076] The redox equation for the electrochemical process is as follows:

[0077] cathode:

[0078] O2+4H + +4e - →2H2O

[0079] anode:

[0080] 2H2→4H + +4e -

[0081] The total reaction equation of the cathode and anode is:

[0082] 2H2+O2→2H2O

[0083] Under standard conditions of the reversible fuel cell voltage or the no-load voltage of the unloaded fuel cell 2, the difference in the normal potential of the electrode pair is 1.23V. This theoretical voltage of 1.23V cannot be achieved in practice. In the idle state and at a small current, the voltage can reach more than 1.0V, and when running at a larger current, the voltage can reach between 0.5V and 1.0V. The series connection of multiple fuel cells 2, especially the fuel cell unit 1 with a fuel cell stack 40 composed of multiple superimposed fuel cells 2, has a higher voltage, which is equivalent to the number of fuel cells 2 multiplied by the individual voltage of each fuel cell 2.

[0084] The fuel cell 2 further includes a proton exchange membrane 5 (PEM), which is arranged between the anode 7 and the cathode 8. The anode 7 and the cathode 8 are constructed in layers or disks. The PEM 5 acts as a separator for the electrolyte, catalyst carrier and reaction gas. In addition, the PEM 5 acts as an electrical insulator and prevents electrical short circuits between the anode 7 and the cathode 8. A proton conducting membrane made of a perfluorinated and sulfonated polymer with a thickness of 12 μm to 150 μm is generally used. The PEM 5 conducts protons H + and essentially blocks all but the proton H +ions other than H, therefore, due to the PEM 5 proton + The permeability of the PEM 5 enables charge transport. The PEM 5 is substantially impermeable to the reactant gases oxygen O2 and hydrogen H2, that is, the flow of oxygen O2 and hydrogen H2 between the gas space 31 at the anode 7 (with recycled fuel hydrogen H2) and the gas space 32 at the cathode 8 (with air or oxygen O2 as an oxidant) is blocked. The proton conductivity of the PEM 5 increases with increasing temperature and water content.

[0085] The electrodes 7, 8 on both sides of the PEM 5 facing the gas chambers 31, 32 are respectively the anode 7 and the cathode 8. The unit composed of the PEM 5, the anode 7 and the cathode 8 is called a membrane electrode assembly (MEA). The electrodes 7, 8 are pressed together with the PEM 5. The electrodes 7, 8 are platinum-containing carbon particles bonded to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and / or PVA (polyvinyl alcohol), and are hot-pressed into microporous carbon fibers, glass fibers or plastic felts. On the electrodes 7, 8, a catalyst layer 30 (not shown) is usually applied on the side facing the gas chambers 31, 32, respectively. The catalyst layer 30 on the gas chamber 31 with recycled fuel on the anode 7 includes nano-dispersed platinum ruthenium on graphitized carbon black particles, and the carbon black particles are bound to a binder. The catalyst layer 3 on the gas chamber 32 with the oxidant on the cathode 8 includes similarly nano-dispersed platinum. For example, using Polytetrafluoroethylene emulsion or polyvinyl alcohol is used as a binder.

[0086] In contrast, the electrodes 7 and 8 are made of ion membranes (e.g. ), platinum-containing carbon particles and additives. These electrodes 7 and 8 with ion membranes are conductive because they contain carbon particles and can also conduct protons H + , and because the carbon particles contain platinum, they also additionally function as a catalyst layer 30. The membrane electrode assembly 6 with the electrodes 7, 8 including the ion membrane forms a membrane electrode assembly 6 as a CCM (catalyst coated membrane).

[0087] Gas diffusion layers 9 (GDL) are placed on the anode 7 and the cathode 8. The gas diffusion layer 9 on the anode 7 evenly distributes the recirculating fuel in the channel 12 for the recirculating fuel to the catalyst layer 30 on the anode 7. The gas diffusion layer 9 on the cathode 8 evenly distributes the oxidant from the channel 13 for the oxidant to the catalyst layer 30 on the cathode 8. In addition, the GDL 9 draws out the reaction water in a direction opposite to the flow direction of the reaction gas, that is, in a direction from the catalyst layer 30 to the channels 12, 13, respectively. In addition, the GDL 9 keeps the PEM 5 moist and conducts current. For example, the GDL 9 is composed of a hydrophobic carbon paper and a bonded carbon powder layer.

[0088] The bipolar plate 10 is placed on the GDL 9. The electrically conductive bipolar plate 10 is used as a current collector for conducting water and reactant gases through a channel structure 29 and / or a flow field 29, and for conducting waste heat, which occurs in particular when an exothermic electrochemical reaction occurs on the cathode 8. In order to conduct the waste heat, a channel 14 is installed in the bipolar plate 10 for passing through a liquid or gaseous coolant. The channel structure 29 on the gas chamber 31 for the recycled fuel is formed by channels 12. The channel structure 29 on the gas chamber 32 for the oxidant is formed by channels 13. For example, metal, conductive plastic and composite materials or graphite are used as materials for the bipolar plate 10. Therefore, the bipolar plate 10 includes three channel structures 29 formed by channels 12, 13 and 14 for separately passing through and conducting recycled fuel, oxidant and coolant. In a fuel cell unit 1 with a fuel cell stack 40 and / or a fuel cell group 40, a plurality of fuel cells 2 are arranged in an aligned stacked manner ( Figure 4 The fuel cell 2 and the components 5, 6, 7, 8, 9, 10 of the fuel cell 2 are constructed in layers and / or disks and span the imaginary plane 37 ( Figure 3 ). The components 5, 6, 7, 8, 9, 10 of the fuel cell 2 include a proton exchange membrane 5, an anode 7, a cathode 8, a gas diffusion layer 9 and a bipolar plate 10.

[0089] Figure 1 2 shows an exploded view of two stacked fuel cells 2. The seal 11 seals the gas chambers 31, 32 in a fluid-tight manner. Hydrogen H2 is stored as fuel in a compressed gas storage 21 at a pressure of, for example, 350 bar to 800 bar. Figure 1 The fuel is led from the compressed gas reservoir 21 via the high-pressure line 18 to the pressure reducer 20, which is used to reduce the pressure of the fuel in the medium-pressure line 17 by about 10 bar to 20 bar. From the medium-pressure line 17, the fuel is led to the injector 19. At the injector 19, the pressure of the fuel is reduced to an intake pressure of between 1 bar and 3 bar. Figure 5) indirectly delivers fuel from the injector 19 to the supply line 16 (shown in Figure 1 ) and is transported from the supply line 16 to the channel 12 for the recirculating fuel, which forms the channel structure 29 for the recirculating fuel. As a result, the recirculating fuel flows through the gas chamber 31 for the recirculating fuel. The gas chamber 31 for the recirculating fuel is formed by the channel 12 and the GDL 9 on the anode 7. After flowing through the channel 12, the fuel that is not consumed in the redox reaction at the anode 7 and the water generated by the controlled humidification of the anode 7 when necessary are discharged from the fuel cell 2 through the discharge pipe 15.

[0090] The gas delivery device 22, for example, is constructed as a blower 23 or a compressor 24, which delivers air from the environment as an oxidant to the oxidant supply line 25. The air is supplied from the supply line 25 to the oxidant channel 13, and the channel forms a channel structure 29 at the bipolar plate 10 of the oxidant, so that the oxidant flows through the oxidant air chamber 32. The oxidant air chamber 32 is composed of the channel 13 and the GDL 9 on the cathode 8. After flowing through the channel 13 or the oxidant air chamber 32, the oxidant that is not consumed at the cathode 8 and the reaction water produced by the electrochemical redox reaction at the cathode 8 are discharged from the fuel cell 2 through the discharge line 26. The oxidant discharge line 26 leads to the environment. The supply line 27 is used to supply coolant to the coolant channel 14, and the discharge line 28 is used to discharge the coolant guided through the channel 14. In Figure 1 In the figure, for the sake of simplicity, the supply and discharge lines 15, 16, 25, 26, 27, 28 are shown as separate lines, and are actually structurally configured as aligned fluid openings (not shown) at the end regions near the channels 12, 13, 14, and the fluid openings are at the end regions of the stacked membrane electrode assembly 6. Similarly, fluid openings (not shown) are also configured on the plate-shaped extensions (not shown) of the bipolar plates 10, and the fluid openings in the plate-shaped extensions of the bipolar plates 10 are aligned with the fluid openings (not shown) on the membrane electrode assembly 6 for partially configuring the supply and discharge lines 15, 16, 25, 26, 27, 28. The fuel cell unit 1 together with the compressed gas storage 21 and the gas delivery device 22 constitute the fuel cell system 4.

[0091] In the fuel cell unit 1, the fuel cells 2 are arranged between two clamping elements 33 as clamping plates 34. An upper clamping plate 35 is placed on the uppermost fuel cell 2, while a lower clamping plate 36 is placed on the lowermost fuel cell 2. The fuel cell unit 1 includes about 200 to 400 fuel cells 2, which are shown for clarity. Figures 4 to 5Not all fuel cells are shown. The clamping element 33 applies pressure to the fuel cells 2, i.e. the upper clamping plate 35 is placed under pressure on the uppermost fuel cell 2, and the lower clamping plate 36 is placed under pressure on the lowermost fuel cell 2. The fuel cell group 40 is thereby clamped to ensure the tightness of the fuel, oxidant and coolant (especially due to the effect of the elastic seal 11), and also to keep the electrical contact resistance within the fuel cell stack 40 as small as possible. In order to clamp the fuel cells 2 with the tensioning element 33, four connecting devices 38 are constructed on the fuel cell unit 1 as pins 39, which are subjected to tensile force. The four pins 39 are firmly connected to the clamping plate 34.

[0092] The fuel cell stack 40 is arranged in a housing 42 ( Figure 5 ). The shell 42 has an inner side 43 and an outer side 44. An intermediate space 41 is constructed between the fuel cell stack 40 and the shell 42. The shell 42 is also composed of a connecting plate 47 made of metal (especially steel). The rest of the shell 42 (excluding the connecting plate 47) is fastened to the connecting plate 47 by means of a fastening element 48 as a screw 49. An opening 45 is constructed in the connecting plate 47 and in the lower clamping plate 36 for introducing the recirculated fuel into the channel 12 of the recirculated fuel. In addition, an opening 46 for conducting the recirculated fuel from the channel 12 of the recirculated fuel is also constructed in the connecting plate 47 and in the lower clamping plate 36. In the connecting plate 47 and the lower clamping plate 36 as the clamping element 33, other openings not shown are also constructed for introducing an oxidant, conducting an oxidant, introducing a coolant and conducting a coolant. Therefore, a total of 6 openings are constructed in the connecting plate 47 and the lower clamping plate 36.

[0093] The recirculating fuel as the recirculating hydrogen is guided through the passage 12 for the recirculating fuel and further through the gas chamber 31 for the recirculating fuel. The recirculating line 50 is used to recirculate the recirculating fuel led out from the passage 12 for the recirculating fuel, i.e., the recirculating fuel led out from the passage 12 for the recirculating fuel is supplied back to the passage 12 for the recirculating fuel and further to the gas chamber 31 for the recirculating fuel by means of the recirculating line 50. Therefore, the discharge line 15 for the recirculating fuel and the supply line 16 for the recirculating fuel also play the role of the recirculating line 50. The water separator 51 is integrated into the recirculating pipe 50. The water separator 51 ( Figure 5 ) is therefore inserted into the recirculation line 50 and is also designed as a mechanical water separator 52 with a separation flow chamber 53. Figure 1The water separator 51 is not shown in the figure. The separation flow chamber 53 has a significantly larger flow cross-sectional area than the recirculation line 50, so the flow velocity of the recirculated fuel in the separation flow chamber 53 is significantly lower than the flow velocity in the recirculation line 50, and therefore the small water droplets in the recirculated fuel will be separated by sedimentation in the separation flow chamber 53, thereby forming a mechanical water separator 53. The separation flow chamber 53 is limited by the wall 54 of the water separator 51.

[0094] A water outlet opening 57 is provided in the separation flow chamber 53, so that the water separated in the separation flow chamber 53 can be discharged into the environment through the water outlet opening 57. The water outlet opening 57 is provided with a water discharge valve 91, so that the water separated can be collected in the separation flow chamber 53 and discharged into the environment in a targeted manner. For this purpose, a sensor (not shown) can optionally be provided on the water separator 51 for detecting the water level in the separation flow chamber 53, so that when a predetermined water level is reached in the separation flow chamber 53, the valve opening can be automatically and autonomously activated by means of the discharge valve 63 according to other parameters (e.g. the position of the motor vehicle). The water separator 51 is provided with an inlet opening 55 for introducing the recirculated fuel into the separation flow chamber 53 and a discharge opening 56 for discharging the recirculated fuel from the separation flow chamber 53. The recirculation line 50 leads to the inlet opening 55 and the discharge opening 56. The medium-pressure line 17 and the high-pressure line 18 are also referred to as a compressed gas line 59 of the fuel as a general term. The fuel is stored in a compressed gas storage 21 at an extremely high pressure of, for example, 400 or 800 bar.

[0095] Therefore, the recirculation system 65 of the fuel cell unit 1 includes a recirculation line 50 and a water separator 51. The recirculation system 65 also includes a delivery device 60 for the recirculation fuel as a blower 61. The recirculation fuel, that is, a mixture of recirculation fuel hydrogen, nitrogen, water vapor and liquid water, is circulated in the loop by means of the delivery device 60. The delivery device 60 as the blower 61 is driven by an electric motor not shown. In order to save the electrical energy used to drive the delivery device 60 as the blower 61 for electrical operation, the recirculation system 65 additionally includes a jet pump 62 as another delivery device 60. By means of the jet pump 62, the recirculation fuel is circulated by the high pressure of the recirculation fuel, and thus the electrical energy for the delivery device 60 as the blower 61 is saved. When the electrical power output of the electric fuel cell unit 1 is small, only a small volume flow of hydrogen is introduced into the recirculation line 50 by means of the injector 19 and the jet pump 62, so that only a small energy from the small volume flow of hydrogen can be used to deliver the recirculation fuel per unit time. Therefore, when the electric power output of the fuel cell unit 1 is small, it is necessary to additionally operate the delivery device 60 as a blower 61 with the help of electric energy. On the other hand, when the electric power output of the fuel cell unit 1 is large, the delivery device 60 as a blower 61 is not required and is turned off, because the volume flow of hydrogen is sufficient to deliver the recirculated fuel by means of the jet pump 62.

[0096] The water discharge valve 91 is configured on the water outlet opening 57 of the water separator 51. The water discharge valve 91 leads to the discharge line 64, and the discharge line 64 leads to the discharge line 26 of the oxidant and water. The discharge line 26 leads to the environment. Since condensed water can also accumulate at the conveying device 60 as a blower 61, a water discharge valve 91 with a discharge line 64 is also configured at the conveying device 60. The discharge line 64 of the water discharge valve 91 of the conveying device 60 as a blower 60 also leads to the discharge line 26 of the oxidant.

[0097] The resistance heating element 58 is arranged on the delivery device 60, the jet pump 62 and the water discharge valve 91. When the fuel cell unit 1 is started at a temperature below 0°C, the water on the delivery device 60, the jet pump 62 and the discharge valve 63 will freeze, so that the recirculation system 65 cannot work, and therefore the fuel cell unit 1 cannot be started. The drive system of the motor vehicle includes a battery as a buffer battery for storing electrical energy. When the fuel cell unit 1 is started at a temperature below 0°C, the resistance heating element 58 is operated with the help of electrical energy from the battery (not shown), thereby heating the delivery device 60 as the fan 61, the jet pump 62 and the water discharge valve 63, so that the frozen water contained therein as ice is thawed and exists in the form of liquid water. Then the fuel cell unit 1 can be started.

[0098] The recirculation system 65 comprises a connection plate 66 which is constructed from metal, in particular steel or aluminum, and / or plastic and is substantially flat and / or disk-shaped. The recirculation system 65 comprises a module housing 68 which is made of aluminum. Figure 5 The module housing 68 shown in the dashed line surrounds and / or integrates the components of the recirculation system 65 with the connecting plate 66. Therefore, the connecting plate 66 can also be optionally a component of the module housing 68 of the recirculation system 65. The connecting plate 66 is integrally formed with the module housing 68 or is a supplementary component relative to the module housing 68. The recirculation system 65 is mechanically connected and fastened to the remaining fuel cell unit 1, i.e., the fuel cell stack 40 with the housing 42, by means of the contact element 67.

[0099] The recirculation system 65 further comprises a discharge valve 63 as a purge valve 63 for discharging the recirculated fuel into the environment. The discharge valve 63 is fastened to the module housing 68, so that the module housing 68 forms a fixing component 73 for fixing and fastening the discharge valve 63 ( Figure 7 ). A hole 74 is formed in the module housing 68 and thus in the fixing member 73, and the discharge valve 63 is partially arranged in the hole 74. The discharge valve 63 includes an electromagnet, an elastic element (not shown) as a spring and a slide as a movable valve stem 70. The discharge valve 63 is provided with an electrical plug connector 69 ( Figure 7 and Figure 8 ) is used to energize the electromagnet (not shown). An annular groove 71 is formed on the valve stem 70, and a valve seal 72 (which is an O-ring seal) is arranged in the annular groove 71. Figure 7 ). A channel is constructed in the module housing 68, which partially forms the discharge line 15 and / or the supply line 16 of the recirculating fuel. The valve stem 70 can move between a closed position and an open position by means of a translational movement. In the closed position, the discharge valve 63 is closed, and in the open position, the discharge valve 63 is opened, so that the recirculating fuel can be discharged from the discharge line 15 and / or the supply line 16 to the environment through the discharge line, and the discharge line of the recirculating fuel preferably leads to the discharge line 26 of the oxidant. In the state where the discharge valve 63 is not energized, the valve stem 70 is held in the closed position by an elastic element not shown. When the electromagnet not shown of the discharge valve 63 is energized, the valve stem 70 moves from the closed position to the open position against the force applied to the valve stem 70 by the elastic element.

[0100] The discharge valve 63 is sealed with respect to the environment by means of a seal 75 which is an O-ring seal, i.e. Figure 7As shown, the space 90 between the discharge valve 63 and the module housing 68 is sealed relative to the environment under the seal 75. The seal 75 is constructed of an elastic material made of plastic. On the side facing the discharge valve 63, the seal 75 is placed on a first component 79 as a sealing connection 81. The sealing connection 81 is basically cylindrical. The seal 75 is placed on a second component 80 of the module housing 68 on the hole 74 on the side away from the discharge valve 63. The seal 75 is arranged in a groove 76 on the sealing connection 81. The sealing connection 81 is preferably a component of the discharge valve 63, especially the housing of the discharge valve 63. The first component 79 as a component of the discharge valve 63 is constructed of stainless steel, and the second component 80 as the module housing 68 is constructed of aluminum. Therefore, the first component 79 is constructed of a metal that is more inert than the second component 80. Corrosion depends on the position of the metal in the so-called stress series. The order is determined by the negative potential level of the metal. The higher the negative potential, the lower the inertness of the metal, and the more susceptible the metal is to corrosion. In the case of contact corrosion between a more noble metal and a less noble metal, corrosion occurs essentially only on the less noble metal.

[0101] The aluminum base 83 is fastened between the stainless steel sealing flange 82 and the module housing 68 by means of two fixing means 84. The base 83 and the module housing 68 can be constructed in one piece or as a separate component in addition to the module housing 68. When the base 83 is constructed as a supplementary component, a seal (not shown) between the base 83 and the module housing 68 is preferably required. In the case of a two-piece construction, the optional structural boundary between the base 83 and the module housing 68 is Figure 7 83 is shown as a dotted line. The term "module housing 68" preferably also includes a base 83. The base 83 is disc-shaped and has an opening, and the discharge valve 63 is partially arranged in the opening. A sealing flange 82 made of stainless steel is placed on the base 83 and is connected to the module housing 68 by means of two fixing devices 84 as screws 85. The sealing flange 82 is disc-shaped and has an opening, and the discharge valve 63 is partially arranged in the opening. The openings of the sealing flange 82 and the base 83 are aligned. Two through holes 86 are respectively constructed in the sealing flange 82 and the base 83. Two blind holes 87 with internal threads are constructed in the module housing 68. The through holes 86 are aligned with the blind holes 87, so that the fixing device 84 as the screw 85 is passed through the two through holes 86 and guided into the corresponding blind holes 87, so that the screw 85 is screwed into the internal thread on the blind hole 87. The head of the screw 85 is therefore placed on the upper side of the sealing flange 82 with pressure.

[0102] An additional groove 78 is constructed completely around the base 83, and an additional seal 77 as an O-ring seal is arranged in this additional groove 78. On the side facing the discharge valve 63, the additional seal 77 is placed on the sealing connection 81 and on the sealing flange 82 at the surrounding corner area. On the side facing away from the discharge valve 63, the additional seal 77 is placed on the base 83, that is, on the additional groove 78 on the base 83. The additional groove 78 is structurally constructed on the base 83 as a recessed portion 78 or phase 78, and is combined with the first additional component 88 to form the additional groove 78. Therefore, the sealing connection 81 and the sealing flange 82 form the first additional component 88. The first additional component 88 is constructed in two parts by the sealing connection 81 and the sealing flange 82. The base 83 forms a second additional component 89 for the additional seal 77, and the base 83 is preferably constructed of stainless steel. When both the first additional component 88 and the second additional component 89 are constructed of stainless steel, contact corrosion will not occur on the additional seal 77. The additional seal 77 prevents liquid or electrolyte from entering the seal 75 .

[0103] In general, the fuel cell unit 1 according to the invention has significant advantages. The additional seal 77 made of an elastic material (e.g. rubber) prevents moisture, liquid and electrolyte from penetrating into the seal 75. Contact corrosion of the seal 75 between the first component 79 and the second component 80 only occurs in the presence of moisture or electrolyte. The additional seal 77 thus prevents contact corrosion on the seal 75. Thus, even if the fuel cell unit 1, in particular the module housing 68, is frequently loaded with liquid and moisture from the external environment, the space 90 can be reliably sealed.

Claims

1. A fuel cell unit (1) for electrochemically generating electrical energy, comprising: - fuel cells (2) arranged in a stack, and the stacked fuel cells (2) form a fuel cell stack (40), - a channel (12) integrated into the fuel cell stack (40) for recycling the fuel, a recirculation system (65) having a recirculation line (15, 16, 50) for recirculating the recirculation fuel led out of the channel (12) for the recirculation fuel back into the channel (12) for the recirculation fuel, thereby forming a recirculation loop with the recirculated recirculation fuel in the fuel cell unit (1), - a discharge valve (63) for conducting the recirculated fuel from the recirculation system (65) into the environment, - at least one fixing member (73) for fixing the discharge valve (63), a seal (75) for sealing a possible flow path from the space (90) at the discharge valve (63) to the environment, It is characterized in that The fuel cell unit (1) comprises an additional seal (77) for sealing a flow path from the environment to the seal (75) to prevent corrosion of at least one component (79, 80) placed on the seal (75).

2. The fuel cell unit according to claim 1, It is characterized in that The seal (75) is placed on the first component (79) and the second component (80).

3. The fuel cell unit according to claim 2, It is characterized in that The first member (79) faces the discharge valve (63) relative to the seal (75), while the second member (80) faces away from the discharge valve (63) relative to the seal (75).

4. The fuel cell unit according to claim 2 or 3, It is characterized in that The first member (79) is constructed of a nobler metal than the second member (80).

5. A fuel cell unit according to one or more of the preceding claims, It is characterized in that The seal (75) is at least partially, in particular completely, arranged in the groove (76).

6. The fuel cell unit according to claim 5, It is characterized in that The recess (76) is formed in the first component (79) and / or the second component (80).

7. A fuel cell unit according to one or more of claims 2 to 6, It is characterized in that The first component (79) is formed by the sealing connection piece (81) and / or the outlet valve (63).

8. A fuel cell unit according to one or more of claims 2 to 7, It is characterized in that The second component (80) is formed by a base (83) and / or a module housing (68).

9. A fuel cell unit according to one or more of the preceding claims, It is characterized in that The discharge valve (63) is at least partially arranged in the hole (74) of the fixing member (73).

10. The fuel cell unit according to claim 9, It is characterized in that The fastening component (73) is formed by the second component (80), in particular the module housing (68).

11. A fuel cell unit according to one or more of the preceding claims, It is characterized in that The additional seal (77) is placed on the first additional component (88) and the second additional component (89).

12. The fuel cell unit according to claim 11, It is characterized in that The first additional component (88) faces the discharge valve (63) relative to the additional seal (77), while the second additional component (89) faces away from the discharge valve (63) relative to the additional seal (77).

13. The fuel cell unit according to claim 11 or 12, It is characterized in that The first additional member (88) and the second additional member (89) are constructed of metals having substantially the same negative potential.

14. A fuel cell unit according to one or more of the preceding claims, It is characterized in that The recirculation system (65) comprises a water separator (51) integrated into the recirculation line (15, 16, 50) for separating water from the recirculated fuel.

15. A fuel cell unit according to one or more of the preceding claims, It is characterized in that The recirculation system (65) is installed and / or inserted and / or integrated into the module housing (68), and preferably the module housing (68) is fastened to a connecting plate (47) of the fuel cell unit (1).

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