WO2008154984A1

WO2008154984A1 - Fuel cell arrangement with a ventilated fuel cell housing

Info

Publication number: WO2008154984A1
Application number: PCT/EP2008/003492
Authority: WO
Inventors: Markus Pabst; Erwin WÜCHNER
Original assignee: Daimler AG; Ford Global Technologies LLC
Current assignee: Mercedes Benz Group AG; Ford Global Technologies LLC
Priority date: 2007-06-20
Filing date: 2008-04-30
Publication date: 2008-12-24
Anticipated expiration: 2009-12-20
Also published as: DE102007028299A1

Abstract

The object of the present invention is to propose a fuel cell arrangement which is operationally reliable. A fuel cell arrangement (1) is proposed having a fuel cell stack (4), having a housing (2), with the fuel cell stack (4) being arranged in the housing (2), and having a filling material (11), (12) which is open for hydrogen and moisture diffusion and is arranged in an intermediate space (5) between the fuel cell stack (4) and the housing (2), in which the filling material (11, 12) fills the intermediate space (5) completely and/or essentially completely, and/or the filling material (11, 12) surrounds the fuel cell stack (4) completely and/or essentially completely.

Description

Fuel cell arrangement with a ventilated fuel cell housing

The invention relates to a fuel cell arrangement having a fuel cell stack and having a housing, with the fuel cell stack being arranged in the housing, and having a filling material which is open for hydrogen diffusion and is arranged in an intermediate space between the fuel cell stack and the housing.

Fuel cell arrangements are energy sources which use an electrochemical process to combine a fuel, generally hydrogen, and an oxidant, generally surrounding air, with one another in order to generate electrical energy. The operational reliability of fuel cell arrangements is a fundamental condition, particularly for mobile use, for the financial viability of this future-oriented technology for energy generation for vehicles. Care must be taken particularly during the development of fuel cell arrangements to ensure that any possible risk of explosion resulting from the fuel that is used is precluded, even when the fuel emerges from the closed gas system in the event of a fault and could form an explosive mixture with the surrounding air in that case.

The document DE 103 42 493 Al actually forms the closest prior art and describes a fuel cell module having a multiplicity of fuel cells which are arranged in a stack and are accommodated in a housing so that a permanent external purging with surrounding air around the connecting stubs of the fuel cells in the housing not only allows cooling but also makes it possible to tolerate slight leaks during operation from the connecting stubs, and hydrogen emerging as a consequence of this. Another section of this document mentions that filling material can be used between the anode and cathode plates, for example in the form of a metallic foam or a metallic felt. This filling material is used to make electrical contact between the opposite connecting ends of the anode and cathode plates.

The object of the present invention is to propose a fuel cell arrangement which is operationally more reliable.

This object is achieved by a fuel cell arrangement having the features of Claim 1. Preferred or advantageous embodiments of the invention result from the dependent claims, the following description and/or the attached figures.

According to the invention, a fuel cell arrangement is proposed which is designed and/or suitable for mobile and stationary use, preferably in vehicles, with the fuel cell arrangement being used to generate the propulsion energy, for example in the drive train of the vehicle. The fuel cell arrangement has a plurality of fuel cells which are preferably arranged in one or more stacks. In particular, more than 100 such fuel cells are combined in one stack. The fuel cells have a cathode area and an anode area which are separated from one another by a membrane (PEM) , with the electrochemical process taking place in these electrode areas, in which hydrogen is combined with an oxidant, preferably surrounding air, in order to generate electrical energy, or to convert it from the chemical energy in the hydrogen. The hydrogen is either made available from a replenishable tank in the fuel cell arrangement or is produced by means of a mobile reform installation which is carried in the vehicle.

The at least one fuel cell stack is arranged in a housing which is sealed in a gas-tight manner from the surrounding area except for supply lines and outlet lines which, for example, are required for supplying the fuel cell stack. The gas-tightness of the housing not least achieves the object of protecting the fuel cell stack or stacks against contamination. The design means that an intermediate space is formed between the fuel cell stack or stacks and the housing and is initially in the form of an empty space or empty volume .

The invention proposes that this intermediate space be filled with a filling material, in which case, according to version a) of the invention, the filling material fills the entire intermediate space completely and/or essentially completely and/or, according to version b) of the invention the filling material surrounds the fuel cell stack completely and/or essentially completely.

The invention is based on the idea that the active positive purging of the housing which is known from the prior art appears to be technically complex because of the fans and compressors that are used. Furthermore, the fan noise that occurs can have a disturbing effect during operation. A further possible disadvantage is that, once the fan has been switched off, hydrogen can accumulate in the housing, possibly until an explosive mixture is produced. In contrast, the invention proposes that the fuel cell stack be filled with filling material, with the filling material being open for hydrogen diffusion and optionally additionally being open for diffusion of moisture, and that in this way the fuel cell stack be surrounded by means of the filling material. The filling material preferably ensures that any remaining free residual spaces between the fuel cell stack or the fuel cell stacks and the housing are sufficiently small that no explosion would occur even if an explosive mixture were to be formed in them. The material characteristic of the diffusion openness for hydrogen additionally means that any hydrogen and air humidity which may be present can diffuse over time through the filling material to an output from the housing, and are therefore dissipated safely. For practical implementation of the explosion protection, it is advantageous that the moisture which is produced can also diffuse out of the housing at the same time as the hydrogen. Without a fan, there would otherwise be a risk of water condensing in the intermediate space, decreasing the insulation resistance of the stack.

The first version of the invention therefore provides for the entire intermediate space - except for residual spaces resulting from the design - to be completely filled with the filling material. At least 90%, probably at least 95% and in particular at least 98% of the intermediate space is preferably filled with the filling material. Alternatively or additionally, the invention provides for the free remaining residual spaces to form cavities which are separated from one another by the filling material, with each individual cavity being less than 10 cubic centimetres, preferably less than 5 cubic centimetres, and in particular less than 1 cubic centimetre . Another version of the invention requires the filling material to surround the complete area of the fuel cell stack or stacks - possibly leaving free less than 10%, preferably less than 5% and in particular less than 3% of the total area. In this version, it is possible to provide a disposal gap or gas line system for any hydrogens that emerge, connected for flow purposes to the filling material.

In one preferred embodiment of the invention, the material characteristic of diffusion openness is formed by the filling material being porous and/or fibrous, for example being in the form of a glass wool, or porous ceramic (as a pourable material or as a plate configuration) . In the case of a porous material, the hydrogen can diffuse through the material itself. In the case of a fibrous material, the hydrogen can diffuse through the fibres, which are in the form of hollow fibres with channels, or through the intermediate spaces between the fibres. In this case, it is particularly preferable for the filling material to be difficult to ignite and/or to be non-combustible, and optionally to be electrically insulating.

In one preferred embodiment of the invention, the filling material is a pourable material, for example in the form of particles. This embodiment has the advantage that, once the fuel cell stack has been stored in the housing, the intermediate spaces can be completely filled in a simple manner .

Another embodiment of the invention provides for the filling material to be a mesh or a mat, in particular multilayer mesh or mat. This embodiment makes it particularly simple to completely encapsulate the fuel cell stack during assembly. Furthermore, the filling material can be removed more easily if the fuel cell arrangement has to be dismantled, for example for repair reasons.

The filling material may have homogeneous and/or isotropic material characteristics. In modified embodiments, for example, the filling material has a plurality of layers, and in particular is a multilayer mesh, with the plurality of layers preferably differing in the degree of diffusion openness and/or their insulation coefficient, so that sections of the filling material with different diffusion openness are connected in series for flow purposes, with the porous layer adjacent to the stack preferably being electrically insulating. In further, modified embodiments of the invention, the filling material is designed and/or arranged such that sections of different diffusion openness are connected in parallel for flow purposes, so that part of the hydrogen which emerges is stored in less diffusion-open filling material sections, and a further part is passed on through sections of the filling material which are more diffusion open.

One physical embodiment provides for the filling material or a layer of it to be formed and/or supported by a metal mesh. This embodiment results in the filling material envelope being particularly robust. One particularly preferred embodiment has a first electrically insulating layer (or filling material) which directly surrounds the fuel cell stack and possibly has low diffusion openness, and which is surrounded by a second layer of filling material, which is in the form of a metal mesh or has at least one metal mesh, and has great diffusion openness. This embodiment makes it possible for any hydrogen that emerges to diffuse quickly through the second layer. One embodiment of the invention preferably provides for the housing to have a ventilation apparatus for ventilation of the intermediate space, with hydrogen and moisture which emerge being transported away out of the housing through the ventilation apparatus.

In this case, it is particularly preferable for the ventilation apparatus to be a passive vent line which, for example, opens into the outlet line or into the supply line of the fuel cell stack, in particular of the cathode section of the fuel cell stack.

In one embodiment, which is particularly advantageous with regard to the energy budget of the fuel cell arrangement, the vent line leads into the cathode-supply line of the fuel cell stack, to be precise upstream of a pumping device. This results in the actual ventilation apparatus being passive, although the pumping device for the fuel cell stack is used in a duplicated form, by being used at the same time for forced ventilation of the housing.

Further features, advantages and effects of the inventions will become evident from the following description of preferred exemplary embodiments.

In the figures:

Figure 1 shows a schematic illustration of a first exemplary embodiment of the invention; and

Figure 2 shows the same illustration of a second exemplary embodiment of the invention. Mutually corresponding parts or variables are each annotated with the same reference symbols in both figures.

Figure 1 shows a schematic block diagram of a fuel cell arrangement 1 as a first exemplary embodiment of the invention. The fuel cell arrangement 1 is used as a mobile energy generating unit in a vehicle, which is not illustrated.

The fuel cell arrangement 1 has a gas-tight housing 2 in which a plurality of fuel cells 3 are joined together, for example in the form of a fuel cell stack 4. An intermediate space 5 is located between the fuel cell stack 4 and the inner walls of the housing 2 and is a result of the housing 2 being somewhat larger than the fuel cell stack 4.

In order to supply an oxidant and a fuel to the fuel cell stack 4, the fuel cell arrangement 1 has an air inlet line 6 which sucks the surrounding air in - for example cleaned by a filter - with the aid of a compressor 7 and passes it to the fuel cell stack 4 through the walls of the housing 2 and via the intermediate space 5. For the fuel supply, the fuel cell arrangement 1 has a hydrogen supply line 8 which is arranged in parallel with the air inlet line 6 and likewise passes through the housing 2 and the intermediate space 5, and, insulated therefrom, passes hydrogen into the fuel cell stack 4.

In order to transport the consumed or partially consumed working gases away, the fuel cell arrangement 1 has an outlet line 9 which carries the off-gases into the surrounding area, for example, via an exhaust installation 10. During operation of the fuel cell arrangement 1, it is impossible to prevent hydrogen and moisture diffusing out of the fuel cells 3 and therefore out of the fuel cell stack 4 into the intermediate space 5. The diffusion direction is indicated by small arrows in the figures. In order to provide protection against the formation of the explosive mixtures and in order to dissipate any moisture that occurs out of the stack and therefore to prevent not only the risk of explosion but also short circuits being formed by condensed water, the fuel cell stack 4 is surrounded by a porous insulation layer 11 which surrounds the fuel cell stack 4 like a casing and/or completely. The aperture areas for the air inlet line 6, the hydrogen supply line 8 and the exhaust gas line 9 are, of course, cut out. This porous insulation layer 11 is provided, for example, by a mesh and has the object of allowing the hydrogen to be absorbed in the porous cavities and to diffuse through the insulation layer 11. By way of example, the insulation layer 11 is formed from a high-temperature material such as silicate fibre.

An optional second protective layer 12 is arranged for flow purposes in series with and connected to the porous insulation layer 11, and surrounds it. The second protective layer 12 is, for example, a porous material or a metal mesh. In contrast to the porous insulation layer 11, the second protective layer 12 may have greater diffusion openness or less flow resistance, and may also be in the form of a metallic mesh, thus allowing adequate venting of the intermediate space 5.

In order to vent the intermediate space 5, the fuel cell arrangement shown in Figure 1 has a housing vent line 13 which connects the intermediate space 5 to the exhaust installation 10, for flow purposes. Figure 2 shows a second embodiment of the invention which essentially matches Figure 1 but, in contrast to Figure 1, has a housing vent line 13 which connects the intermediate space 5 via this vent line to the air inlet line 6 upstream of the compressor 7. This flow circuitry makes use of the fact that the arrangement formed by the housing vent line 13 on the inlet side of the compressor 7 actively sucks away any hydrogen and air moisture which may be present in the intermediate space 5, through the compressor 7. Furthermore, the hydrogen that has been sucked out can be combined in the cathode areas of the fuel cells 3 safely by means of a catalytic reaction with the oxidant to form water, it can advantageously be used at this position to moisturize the sensitive membranes and therefore to reduce the hydrogen emission into the environment.

Additionally, vent openings can optionally be provided, which allow gas to circulate in the intermediate space 5 so that clean air, for example filtered by vent openings which are not illustrated in Figures 1 and 2, flows in, flows through the intermediate space 5 and is then sucked out again through the housing vent line 13. In order to further improve the operational reliability, a hydrogen sensor may be integrated, that monitors the hydrogen concentration in the intermediate space 5.

Finally, additional non-porous insulation layers may be fitted between the fuel cell stack 4 and the stack housing 2 in order to prevent moisture from condensing in the intermediate space 5 on the inner face of the stack housing.

Claims

Patent Claims

1. Fuel cell arrangement (1) having a fuel cell stack (4), having a housing (2), with the fuel cell stack (4) being arranged in the housing (2), and having a filling material (11, 12) which is open for hydrogen diffusion and is arranged in an intermediate space (5) between the fuel cell stack (4) and the housing (2 ) , characterized in that a) the filling material (5) fills the intermediate space (11, 12) completely and/or essentially completely, and/or b) the filling material (5) surrounds the fuel cell stack (4) completely and/or essentially completely.

2. Fuel cell arrangement (1) according to Claim 1, characterized in that the filling material (11, 12) is porous or fibrous .

3. Fuel cell arrangement (1) according to Claim 1 or 2, characterized in that the filling material (11, 12) is non- combustible .

4. Fuel cell arrangement (1) according to one of the preceding claims, characterized in that the filling material

(11, 12) is a pourable material.

5. Fuel cell arrangement (1) according to one of the preceding claims, characterized in that the filling material

(11, 12) is a mesh, in particular a multilayer mesh, with the filling material or mesh which rests on the fuel cell stack (4) preferably being electrically insulating.

6. Fuel cell arrangement (1) according to one of the preceding claims, characterized in that the filling material comprises a first layer (11) with a first diffusion openness, and a second layer (12) with a second diffusion openness which is greater than the first diffusion openness.

7. Fuel cell arrangement according to Claim 6, characterized in that the second layer (12) surrounds the first layer (11) and the fuel cell stack (4).

8. Fuel cell arrangement (1) according to one of the preceding claims, characterized in that the filling material

(11, 12) or a layer (11, 12) of it, in particular the second layer (12), is formed and/or supported by a metal mesh.

9. Fuel cell arrangement (1) according to one of the preceding claims, characterized in that the filling material

(11, 12) is composed of a high-temperature material, in particular of silicate fibre.

10. Fuel cell arrangement (1) according to one of the preceding claims, characterized in that the housing (2) has a ventilation apparatus (13) for ventilation of the intermediate space (5).

11. Fuel cell apparatus (1) according to one of the preceding claims, characterized in that the ventilation apparatus (13) is a passive vent line.

12. Fuel cell apparatus (1) according to Claim 12, characterized in that the vent line (13) opens into the outlet line (9) or into the supply line to the fuel cell stack ( 6) .

13. Fuel cell apparatus (1) according to Claim 13, characterized in that the vent line (13) opens into the cathode-side supply line (13) of the fuel cell stack, upstream of a pumping device.

14. Fuel cell apparatus (1) according to Claim 13, characterized in that the vent line (13) carries away not only hydrogen that has been released but at the same time moisture in the intermediate space (5) .

15. Fuel cell apparatus (1) according to Claim 14, characterized in that additional non-porous insulation layers are fitted to the inner face of the housing (2) in the intermediate space (5), in order to prevent condensation of moisture in the intermediate space (5) .