HUMIDIFIER, FUEL CELL DEVICE WITH HUMIDIFIER AND MOTOR VEHICLE

Abstract

A humidifier for a fuel cell device is provided which includes a water vapor permeable membrane and at least one flow field arranged on one side of the membrane, in which flow channels are separated by flow field webs. The flow field webs are designed as hollow webs for integration into a coolant circuit. A fuel cell device with a humidifier as well as to a motor vehicle with such a fuel cell device are also provided.

Claims

1. A humidifier for a fuel cell device, the humidifier comprising: a water vapor permeable membrane; and at least one flow field arranged on one side of the membrane; wherein the flow field includes flow channels separated by flow field webs; wherein the flow field webs are hollow and configured for integration into a coolant circuit; wherein the flow field webs have respective cross-sectional shapes comprising polygons; wherein the flow field webs have respective water reservoirs on respective external sides of the flow field webs; and wherein the water reservoirs are formed of a hydroscopic material.

2. (canceled)

3. The humidifier according to claim 1, wherein the flow field webs are formed of a heat-conducting material.

4-5. (canceled)

6. The humidifier according to claim 1, wherein the flow field webs have respective porous structures.

7. The humidifier according to claim 1, wherein the flow field is arranged in a heat insulating frame.

8. The humidifier according to claim 1, wherein on the side of the membrane opposite the flow field, there is a second, similarly formed flow field for the passage of a gas to be humidified.

9. A fuel cell device, comprising: a fuel cell stack including a cooling circuit; and a humidifier including: a water vapor permeable membrane; and at least one flow field arranged on one side of the membrane; wherein the flow field includes flow channels separated by flow field webs; wherein the flow field webs are hollow; wherein the flow field webs have respective cross-sectional shapes comprising polygons; wherein the flow field webs have respective water reservoirs on respective external sides of the flow field webs; and wherein the water reservoirs are formed of a hydroscopic material; wherein the cooling circuit is routed through the flow field webs of the humidifier; and wherein the flow channels are flow-connected with a separator of the fuel cell stack.

10. A motor vehicle, comprising: a fuel cell device including: a fuel cell stack including a cooling circuit; and a humidifier including: a water vapor permeable membrane; and at least one flow field arranged on one side of the membrane; wherein the flow field includes flow channels separated by flow field webs; wherein the flow field webs are hollow; wherein the flow field webs have respective cross-sectional shapes comprising polygons; wherein the flow field webs have respective water reservoirs on respective external sides of the flow field webs; and wherein the water reservoirs are formed of a hydroscopic material; wherein the cooling circuit is routed through the flow field webs of the humidifier; and wherein the flow channels are flow-connected with a separator of the fuel cell stack.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016] Further advantages, features and details are apparent from the claims, the following description, and the drawings.

[0017] FIG. 1 shows a schematic representation of a fuel cell device comprising a humidifier.

[0018] FIG. 2 shows a schematic representation of a flow field of a humidifier with coolant channels separated by webs, with water reservoirs associated with the webs and depicted while empty.

[0019] FIG. 3 shows a cross-section through the flow field from FIG. 2.

[0020] FIG. 4 shows a representation corresponding to FIG. 2 with the water reservoir when full.

[0021] FIG. 5 shows a representation corresponding to FIG. 3 for the flow field from FIG. 4.

[0022] FIG. 6 shows a representation corresponding to FIG. 3 of an alternative embodiment with modified webs.

[0023] FIG. 7 shows a representation corresponding to FIG. 5 of the alternative embodiment from FIG. 6.

DETAILED DESCRIPTION

[0024] FIG. 1 schematically shows a fuel cell device 1 comprising a humidifier 2 for regulating the humidity of a plurality of fuel cells 4 combined in a fuel cell stack 3.

[0025] Each of the fuel cells 4 comprises an anode, a cathode, as well as a proton-conductive membrane separating the anode from the cathode. The membrane is formed from an ionomer, such as a sulfonated polytetrafluoroethylene (PTFE) polymer or a perfluorinated sulfonic acid (PFSA) polymer. Alternatively, the membrane may be formed as a sulfonated hydrocarbon membrane.

[0026] The anodes and/or the cathodes may additionally be admixed to a catalyst, wherein the membranes may be coated on their first side and/or on their second side with a catalyst layer of a noble metal or a mixture comprising noble metals such as platinum, palladium, ruthenium or the like, which serve as reaction accelerators in the reaction of the respective fuel cell.

[0027] The anode fuel (for example, hydrogen) can be supplied to the anode via an anode compartment. 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. At the anode, for example, the following reaction takes place: 2H.sub.2.fwdarw.4H.sup.++4e.sup.− (oxidation/electron release). Whereas the protons pass through the PEM to the cathode, the electrons are directed to the cathode or to an energy storage device via an external power circuit.

[0028] The cathode gas (for example, oxygen or oxygen-containing air) can be supplied to the cathode via a cathode chamber, such that the following reaction takes place on the cathode side: O.sub.2+4H.sup.++4e.sup.−.fwdarw.2H.sub.2O (reduction/electron capture).

[0029] Since several fuel cells 4 are combined in the fuel cell stack 3, a sufficiently large amount of cathode gas must be provided, so that a large cathode gas mass flow or fresh gas flow is provided by a compressor 5, wherein as a result of the compression of the cathode gas, its temperature increases greatly. The conditioning of the cathode gas or of the fresh air gas stream, which is to say its adjustment with regard to the temperature and humidity desired in the fuel cell stack 3, takes place in an intercooler, not shown in more detail, downstream of the compressor 5, as well as in the humidifier 2, which causes moisture saturation of the membranes of the fuel cells 4 to increase their efficiency, since this promotes proton transport.

[0030] On the anode side, the fuel cell stack 3 is fluid-mechanically connected to an anode supply line 6, such that fuel contained in the schematically shown fuel storage 7 can be supplied to the fuel cell stack 3. A valve or even a suction jet pump can be suitable to realize the desired partial pressure of fresh fuel within the anode circuit, which is created by the anode recirculation line 8. With such an anode recirculation line 8, the fuel not consumed in the fuel cell stack 3 can be supplied once again to the anode chambers upstream of the fuel cell stack 3, such that the anode recirculation line 8 once again opens out into the anode supply line 6. To remove the liquid from the anode circuit, a separator 9 is integrated in the anode recirculation line 8. This is fluid-mechanically connected to the cathode side of the fuel cell device 1, such that the liquid accumulating on the anode side is introduced, for example, into the cathode exhaust line 10 provided downstream of the fuel cell stack 3, in order to convey the liquid, for example, out from the fuel cell device 1. Alternatively or additionally, the liquid accumulating on the anode side can also discharge from the separator 9 into a cathode supply line 11 upstream of the humidifier 2, such that the liquid is introduced there into the fresh cathode gas before it enters the humidifier 2. This has the advantage that the humidifier 2 can be designed to be smaller overall, since the fresh gas, which has been dried by compression using the compressor 5, no longer needs to be humidified to such an extent in order to ensure the required humidity of the membranes in the fuel cell stack 3.

[0031] In order to be able to regulate the mass flow of the cathode gas through the fuel cell stack 3, a bypass 12 is provided which has an actuating element, in particular a pressure regulating valve. This bypass 12 connects the cathode supply line 11 with the cathode exhaust line 10.

[0032] In the embodiment shown in FIG. 1, the humidifier 2 is constructed as a planar humidifier with several humidifier modules 13 (FIG. 2), each of which is formed with a water vapor permeable membrane and a flow field 14 arranged on one side of the membrane and a second flow field 14 arranged on the opposite side of the membrane, which are arranged in a heat-insulating frame 15, which is to say, that poorly conducts heat. Flow channels 16 are separated by flow field webs 17 in the flow fields 14, wherein the flow field webs 17 are designed as hollow webs (FIG. 3) for integration into a coolant circuit 18, namely into the coolant circuit 18 of the fuel cell stack 3 of the fuel cell device 1, which has a cooler 19 and a coolant pump 20, which in the embodiment example shown in FIG. 1 are arranged downstream of the humidifier 2 in the coolant circuit 18. The heat dissipated with the coolant from the fuel cell stack 3 is thus used to heat the gas flowing in the flow channels 16 and to counteract the cooling that occurs due to the evaporation of the liquid water. This heat supply is also associated with a higher liquid water conversion. This is achieved by designing the hollow webs as a cross-sectional polygon 21 to increase the surface area and by forming them from a heat-conducting material.

[0033] This heat utilization upstream of the cooler 19 also means that the cooler is required to extract less heat from the coolant and can therefore optionally be made smaller.

[0034] Furthermore, the liquid water accumulated in the fuel cell stack 3 and collected in the separator 9 is utilized in that the flow channels 16 are flow-connected to the separator 9 of the fuel cell stack 9. On the fresh gas side, this leads to humidification, such that less water transfer through the membrane is required and therefore the membrane area and consequently the size of the humidifier 2 can be reduced. On the cathode exhaust side, this leads to the humidification of the cathode exhaust.

[0035] Since the flow field web 17 has a water reservoir 22 on its outside, it is possible to fill this water reservoir 22 when liquid water is available and to release the stored water when less liquid water is available from the separator 9. The water reservoir 22 is formed by a hygroscopic material which is placed, glued or pressed onto the flow field webs 17. It is also possible for the flow field webs 17 to have a porous structure.

[0036] In a motor vehicle with a fuel cell device 1 and a humidifier 2 of this type, less installation space is required for the humidifier 2, which can be manufactured more compactly and accordingly with less material.

[0037] Aspects of the various embodiments described above can be combined to provide further embodiments. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.