Internal water separator in a fuel cell stack

Abstract

Disclosed herein are aspects of methods to separate water in a fuel cell system integrated into a fuel cell stack. A plurality of fuel cell assemblies are compressed together to form a fuel cell stack. By aligning the cathode exhaust outlets of the fuel cell assemblies a collection cavity is formed in the fuel cell stack fluidly connected to each fuel cells assembly. A water outlet is connected to collection cavity having a water collection means therein. The integrated water separator reduces the size of the fuel cell system.

Description

INTERNAL WATER SEPARATOR IN A FUEL CELL STACKRELATED APPLICATION

[0001] The present application is a PCT Application, which claims priority to UK Patent Application No. 2319829.4, filed on December 21, 2023, the disclosure of which is incorporated by reference herein in its entirety as is fully set forth herein.TECHNICAL FIELD

[0002] This disclosure generally relates to devices and methods for collecting and separating water from cathode exhaust of fuel cell stack.BACKGROUND

[0003] A typical fuel cell system includes a fuel cell stack for generating electricity, a hydrogen supply as a fuel to the fuel cell stack, an oxygen (air) supply system for supplying oxygen containing air as an oxidant for the electrochemical reaction and thermal management for removing reaction heat from the fuel cell stack and managing humidity in the stack and water removal. The fuel cell system generates heat and water as well as electricity.

[0004] In fuel cell assemblies, each unit , has an anode, a cathode and an electrolyte (electrolyte membrane). Hydrogen is supplied to the anode and oxygen containing air is supplied to the cathode. By way of a membrane electrode assembly (MEA) the hydrogen and oxygen produce electricity, heat and water.

[0005] A stack is formed from a number of such fuel cells arranged with separate anode and cathode fluid flow paths. Such a stack is typically in the form of a block comprising numerous individual fuel cell plates held together by end plates at either end of the stack. It is important that the polymeric ion transfer membrane remains hydrated for efficient operation. It is also important that the temperature of the stack is controlled. Thus, coolant may be supplied to the stack for cooling and / or hydration.

[0006] An important consideration in the operation of such fuel cells is the management of water within the MEA. During operation of a PEM fuel cell, product water from the reaction between hydrogen and oxygen is formed at catalytic sites of the MEA. This water is in oneor more phases of liquid, vapor and transitional depending on temperature and pressure when produced and it must be exhausted from the MEA via the cathode diffusion structure at the same time that oxygen is transported to the cathode face of the MEA. However, it is also important that the MEA remains suitably hydrated to ensure that the internal electrical resistance of the cell remains within tolerable limits. Failure to control the MEA humidification leads to hot spots and potential cell failure and / or poor electrical cell performance. The anode and cathode fluid flow field plates may each include a rigid, electrically conductive, material having fluid flow channels in the surface adjacent the respective diffusion structure for delivery of the reactant gases (for example, hydrogen and oxygen) and removal of the exhaust gases (for example, unused oxygen and water vapor).

[0007] Fuel cell stacks comprise a series of individual fuel cells built up layer by layer into a stack arrangement. Each fuel cell itself may include various layered components, such as a polymer electrolyte membrane, gas diffusion layers, fluid flow plates, and various sealing gaskets for maintaining fluid tightness and providing fluid fuel and oxidant distribution to the active surfaces of the membrane. The fluid inputs and fluid outputs are directed through flow fields and plates at the fuel cell level and through connected manifolds at the stack level.DISCLOSURE

[0008] This disclosure teaches of aspects of smaller footprint fuel cell stacks with evaporative cooling. Vehicle engine compartments tend to be space limited to minimize the size of the engine or power supply compartment. Traditional fuel cell stacks separate water produced during operation in a water separator device outside of the fuel cell stack and as part of the balance of plant.

[0009] The foregoing needs are met by the various aspects of integrated water separator for fuel cell systems, and methods of use disclosed throughout this application. According to some aspect of the disclosure a method of water separation in a manifold or duct in a fuel cell stack formed by way of fuel cell assembly frames aligning in a stack with common openings in fluid communication with inputs or outputs of fuel, air, water .

[0010] According to some aspect of the disclosure a system and method to adjust collected water and separate vapor from liquid with in a fuel cells system are disclosed including, a plurality of fuel cell assemblies configured to be compressed together to form a stack, having a top and bottom. Each fuel cell assembly has one or more frames configured to support a membrane electrode assembly (MEA), at least one hydrogen outlet configured to collect hydrogen from the anode side of the MEA, at least one cathode exhaust outlet configured tocollect at least air and water from the cathode side of the MEA and wherein the cathode exhaust outlets of the fuel cell assemblies are configured to form a collection cavity in the fuel cell stack fluidly connected to each fuel cells assembly. A water outlet is in fluid communication with the collection cavity and, a water collection means is configured to fit within the collection cavity.

[0011] In some instances, a cathode flow field is configured to distribute oxygen from at least one air inlet formed in each frame across the MEA. In some instances a anode flow field is configured to distribute hydrogen from one or more inlets formed in the frame across the MEA. In some instances there is at least one gas diffusion layer adjacent to at least one of the cathode and anode flow fields.1. In operation the above fuel cell system one or more inlets formed in each frame supply gaseous hydrogen to the anode side of the MEA and one or more inlets formed in each frame are configured to supply gaseous air to the cathode side of the MEA. Further one or more inlets formed in each frame are configured to supply water to at least the cathode side of the MEA and the water collection means further comprises a body portion having an outer surface configured to fit within the collection cavity and is configured to collect water from the cathode exhaust. In some instances the fuel cell system of claim 1 wherein the cathode exhaust outlet is bisected and the ramp is split to fit therein.

[0012] According to some aspects of the disclosure a system and method to adjust collected water and separate vapor from liquid with in a fuel cells system are disclosed including, a plurality of fuel cell assemblies configured to be compressed together to form a stack, having a top and bottom. Each fuel cell assembly has one or more frames configured to support a membrane electrode assembly (MEA), at least one hydrogen outlet configured to collect hydrogen from the anode side of the MEA, at least one cathode exhaust outlet configured to collect at least air and water from the cathode side of the MEA and wherein the cathode exhaust outlets of the fuel cell assemblies are configured to form a collection cavity in the fuel cell stack fluidly connected to each fuel cells assembly. A water outlet is in fluid communication with the collection cavity and, a water collection means is configured to have a body that fits within the collection cavity. In some instance the body portion has one or more of fins, bumps, protrusions, divots, channels and grooves. In some instances the body portion is multipart. In some instances the body portion has at least one of preselected surface lubricity and surface roughness. In some instances the body portion is one of hydrophobic and hydrophilic. In some instances the body portion has at least one regionwhich is more hydrophilic or more hydrophobic then other parts of the outer surface. In some. Instances the body portion has both hydrophilic and hydrophobic regions.

[0013] In some instances an exhaust outlet head is added and in fluid communication with the collection cavity. In some instances, a fan or stator is in fluid communication with the collection cavity.FIGURES

[0014] The present application is further understood when read in conjunction with the appended drawings. For the purpose of illustrating the subject matter, there are shown in the drawings exemplary aspects of the subject matter; however, the presently disclosed subject matter is not limited to the specific methods, devices, and systems disclosed. In the drawings:

[0015] Fig. 1 is a flow diagram of aspects of the operation of an internal water separator in a fuel cell stack.

[0016] Fig. 2 is a stack of fuel cell assemblies.

[0017] Fig. 3 is atop view of some aspects of a fuel cell assembly.

[0018] Fig. 4 is an exploded view of the assembly of a fuel cell system with an internal water separator.

[0019] Fig. 5 is an assembled view of a fuel cell system with an internal water separator.

[0020] Fig. 6 is a top view of the fuel cell system with an internal water separator of Fig. 5.

[0021] Figs. 7A and 7B illustrate some aspects of the internal water separator.

[0022] Aspects of the disclosure will now be described in detail with reference to the drawings, wherein like reference numbers refer to like elements throughout, unless specified otherwise.FURTHER DISCEOSURE

[0023] By integrating water separation of the exhausted water from the cathodes of the fuel cell assemblies in a fuel cell stack, this disclosure teaches the use or capture of previously lost manifold space to functional water separation. A smaller footprint fuel cell power system occupies less volume when mounted in a vehicle. In some instances the integrated water separator is less complex by way of utilizing the manifold as a portion of the encasement for the water separator.

[0024] Figure 1 illustrates a flow diagram of the operation of a fuel cell stack with integrated water separator 10. Fuel and air (oxidant) 12 are fed into the fuel cell stack 13 .As needed liquid coolant 14 such as water is feed into the fuel cell stack to be distributed to the fuel cells therein. The byproduct of the electrochemical reaction which takes place in the fuel cell is production of electricity (power) , heat , and water vapor and liquid 16. The water vapor and liquid are collected inside the fuel cell stack by way of flow channels or other fluid connection from each fuel cell forming the fuel cell stack to a stack collection location or manifold. The present disclosure teaches the integration of a water separation device or means to collect water and then separate 18 vapor from liquid. Water vapor and other cathode air is exhausted 20 from the stack. The collected liquid water 30 is one of distributed to the fuel cell stack 31 and stored 32 then distributed 33 to the fuel cell stack for humidification and cooling.

[0025] Figures 2-7B integrating water separation into a fuel cells stack. The fuel cell stack 100 is formed by stacking a plurality of fuel cell assemblies 115 / 115 (1-N) each supporting a membrane electrode assembly (MEA) 150 and having gaskets and bipolar plates. Normally flow fields (not shown) will be formed in the bipolar plates, and gas diffusion layers will be sandwiched between the MEA and cathodes and anodes. Not shown are gaskets and seals which are formed on the frame to seal the fuel cell assemblies into a stack with only predetermined manifolds and / or and fluid pathways.

[0026] Figure 3 shows a top view of a fuel cell assembly 115 showing inlets and outlets formed in the frame. At a first end of the fuel cell assembly there is at least one water inlet 160, at least one air inlet 162 and at least one hydrogen exhaust outlet 164. At a second end is at least one hydrogen inlet 166 and one or more air exhausts 168 from the cathodes. A water outlet is 170 also shown and it is in fluid contact with the air exhaust 168 region or manifold. The skilled artisan will recognize that there may be a plurality of water outlets in fluid communication with the collection cavity without departing from the scope of the disclosure. Optionally one or more additional manifolds 175 may be provided. One or more arrays of fluid pathways or connections 180 are formed at the first end and provide fluid communication to the flow fields below . One or more arrays of fluid pathways or connections 185 are formed at the second end and provide fluid communication with the flow fields below . Optionally, or in an optional exemplar the one or more cathode air exhausts 168 are shown bisected by a bridge 192 spanning from side to side whereby additional support across the opening is provided. Although the bridge appears flat in the figure, it is envisioned and therefore claimed that the bridge, if utilized, may be ribbed, dimpled or otherwise strengthened with indentations or outdents. In this exemplar the at least one airinlet 162 is shown bisected by a bridge 194 spanning from side to side whereby additional support across the opening is provided. Although the bridge appears flat in the figure, it is envisioned and therefore claimed that the bridge, if utilized, may be ribbed, dimpled or otherwise strengthened with indentations or outdents.

[0027] Figure 4 shows the assembly of the fuel cell stack into a fuel cell system 200 . The fuel cell stack 100, has a bottom 102 and a top 104. The fuel cell stack is shown compressed between a first end plate 201 covering the bottom 102 and a second end plate 210 covering the top 104. The designation of top and bottom is for convenience and is not a limitation. The plate can be side oriented and the top and bottom designation does not imply otherwise. The end plates and the fuel cell stack are configured to fit together. Fasteners are commonly used to further compress the fuel cell to assure all of the fuel cell assemblies seal together and do not leak. Fastening fuel cell stack and systems together is known in the art. Optionally, a bisecting region 240 may be formed as part of the second end plate . The extra region positioned between the large opening provides additional rigidity.

[0028] The second end plate 210 has passages which align with the water inlet, air inlet, hydrogen exhaust outlet, hydrogen inlet and exhaust from the cathodes. The water inlet passage 220 is fluidly connected to the at least one water inlet 160, the air inlet passage 222 is fluidly connected to the air inlet 162, the hydrogen outlet passage 226 is fluidly connected to the hydrogen outlet 164. The hydrogen inlet passage 236 is fluidly connected to the hydrogen inlet 166. The air exhaust 168 is fluidly connected to the exhaust passage 238. The water outlet 170 whereby liquid water is removed from the stack is also fluidly connected to the exhaust passage 238. The internal water separator 250 is configured with a collection portion 252 that fits into the air exhaust 168 and an outlet head 255 which is at least partially outside of the fuel cell stack. Those of ordinary skill in the art, and the skilled artisan will recognize that the entire water separator may also fit within the exhaust portion without departing from the scope of the disclosure.

[0029] Figures 5 and 6 show aspects of an assembled fuel cell system 200 with integrated water separator. Those of ordinary skill in the art and the skilled artisan will recognize that the dimensions of a fuel cell assembly may vary widely depending on the intended use and that the number of assemblies forming a stack may vary. However, these design variations will have common features that are within the scope of this invention. They will have a manifold of fluidly connected region through the plurality of fuel cell assemblies and that region will be configured for insertion of a water separation means. Fasteners 212 arecommonly used to compress or maintain a compressed state for the fuel cell assemblies in the fuel cell system.

[0030] In operation hydrogen inlet 166 receives a feed of gaseous hydrogen fuel which is distributed to the anodes of the bipolar plates of each fuel cell assembly and the unspent hydrogen exists at the hydrogen outlet 164 . Air is supplied through the air inlet 162 to the cathode side of the bipolar plates of each fuel cell assembly. Water is supplied to the fuel cell assemblies through the water inlet 160 and removed as liquid water and water vapor through the air exhaust 168. When stacked the fuel cell assemblies air exhausts form a collection cavity 300 for removing water and water vapor from the fuel cell stack. Collected liquid water may be removed via the water outlet 170 to be recycled to the fuel cell stack for cooling and humidification as needed.

[0031] Figures 7A and 7B illustrates aspects of an internal water separator 250 configured with a collection body portion 252 configured to fit into the collection cavity 300 formed by the plurality of air exhausts. In some instances the collection body portion 252 is homogeneous in thickness , width and height along its length. In some instances the collection body portion 252 is non homogeneous in at least one of thickness , width and height along its length. Variations in thickness , width and height along its length are used to tune the collection and flow.. The collection body at least one of cools, captures and redirects water existing in the cathode flow fields of each fuel cell assembly as cathode exhaust and urges condensation so that the water moves via gravity towards the bottom 102 of the fuel cell stack. The collection portion may be a plate or plates, it may be porous or textured to capture and move water. The collection portion may have surface features including but not limited to one or more of fins, bumps, protrusions, divots, channels or grooves to direct the water captured. The collection portion may be multi part and be constructed of non-homogeneous materials. The materials may be homogeneous in lubricity or roughness, or they may be non-homogeneous for same. In the optional system with bisection of the exhaust passage 238 and / or bridges added to the fuel cell assemblies the collection body portion is grooved or split along a substantially portion forming a gap to accommodate the bridge(s) and / or bisecting region 240.

[0032] The collection body portion may have regions of differing roughness or lubricity. In some instances the collection body portion is hydrophobic 253. In some instances the collection body portion is hydrophilic 254. In some instances the collection body portion has both hydrophilic 253 and hydrophobic 254 areas. It can act as a heat sink for the liquidwater and water vapor in the air exhaust to further urge condensation. A series of impact vanes 400 may be added to the inside of the body portion 252 to disrupt vapor and water flow out of the exhaust and collect / condense water in the fluid flow and redirect it back into the collection cavity. In some embodiments, a stator 400 (which optionally may be replaced by a fan) is shown and will impart radial momentum to the two phase flow.

[0033] The method disclosed herein is a method to repurpose wasted manifold spaces in a fuel cell stack to act as a containment for a water separator to reduce the footprint of the fuel cell system. Using the fuel cell as a containment also minimizes the cost and complexity of the water separator means.

[0034] The systems described throughout this disclosure can be utilized in a variety of applications for providing power generated by fuel cells. In some aspects, the systems disclosed throughout this application can be used in machine handling equipment (MHE), such as a forklift. In some aspects, the systems can be used in an unmanned aerial vehicle (UAV), such as a fixed wing or multi-rotor drones. In some aspects, the systems disclosed herein can be used in automotive, marine, or aerospace applications, such as in cars, trucks, marine vehicles, aircraft, or other stationary power applications. It will be appreciated that the systems can be used in a variety of other applications, and the certain functional and physical parameters, such as component sizes and quantities, may be varied for specific applications and may be dictated by requirements for specific uses. Additional advantages to those described above include being able to fit the systems and related components (such as fuel cannister cylinders) into smaller spaces and to arrange systems and related components more advantageously.

[0035] The components disclosed herein may utilized known materials that are used in the industry.

[0036] Throughout this specification, words are to be afforded their normal meaning as would be understood by those skilled in the relevant art. However, so as to avoid misunderstanding, the meanings of certain terms will be specifically defined or clarified.

[0037] While the disclosure has been described in connection with the various embodiments of the various figures, it will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this disclosure is not limited to the particular embodiments disclosed, and it is intended to cover modifications within the spirit and scope of the present disclosure as defined by the claims.

[0038] Features of the disclosure that are described above in the context of separate embodiments may be provided in combination in a single embodiment. Conversely, various features of the disclosure that are described in the context of a single embodiment may also be provided separately or in any sub-combination. Finally, while an embodiment may be described as part of a series of steps or part of a more general structure, each said step may also be considered an independent embodiment in itself, combinable with others.

[0039] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

Claims:

1. A fuel cell system comprising: a plurality of fuel cell assemblies configured to be compressed together to form a stack, having a top and bottom, each fuel cell assembly comprising; one or more frames configured to support a membrane electrode assembly (MEA); at least one hydrogen outlet configured to collect hydrogen from the anode side of the MEA; at least one cathode exhaust outlet configured to collect at least air and water from the cathode side of the MEA; wherein the cathode exhaust outlets of the fuel cell assemblies are configured to form a collection cavity in the fuel cell stack fluidly connected to each fuel cells assembly; a water outlet is in fluid communication with the collection cavity; and, a water collection means is configured to fit within the collection cavity.

2. The fuel cell system of claim 1 further comprising a cathode flow field configured to distribute oxygen from at least one air inlet formed in the frame across the MEA.

3. The fuel cell system of claim 1 further comprising a anode flow field configured to distribute hydrogen from one or more inlets formed in the frame across the MEA.

4. The fuel cell system of claim 1 further comprising at least one gas diffusion layer on or adjacent to at least one of the cathode and anode flow fields.

5. The fuel cell system of claim 1 further comprising one or more inlets formed in each frame configured to supply gaseous hydrogen to the anode side of the MEA.

6. The fuel cell system of claim 1 further comprising one or more inlets formed in each frame configured to supply gaseous air to the cathode side of the MEA.

7. The fuel cell system of claim 1 further comprising one or more inlets formed in each frame configured to supply water to at least the cathode side of the MEA.

8. The fuel cell system of claim 1 wherein the water collection means further comprises a body portion having an outer surface configured to fit within the collection cavity and is configured to collect water from the cathode exhaust.

9. The fuel cell system of claim 8 wherein the body portion has one or more of fins, bumps, protrusions, divots, channels and grooves.

10. The fuel cell system of claim 8 wherein the body portion is multipart.

11. The fuel cell system of claim 8 wherein the body portion has at least one of preselected surface lubricity and surface roughness.

12. The fuel cell system of claim 8 wherein the body portion is one of hydrophobic and hydrophilic.

13. The fuel cell system of claim 8 wherein the body portion has at least one region which is more hydrophilic or more hydrophobic then other parts of the outer surface.

14. The fuel cell system of claim 8 wherein the body portion has both hydrophilic and hydrophobic region.

15. The fuel cell system of claim 8 further comprising an exhaust outlet head in fluid communication with the collection cavity.

16. The fuel cell system of claim 8 further comprising a fan or stator in fluid communication with the collection cavity and within the water collection means.

17. A method to separate water in a fuel cell system integrated into a fuel cell stack, the method comprising: compressing a plurality of fuel cell assemblies together to form a fuel cell stack; aligning the cathode exhaust outlets of the fuel cell assemblies to form a collection cavity in the fuel cell stack fluidly connected to each fuel cells assembly; placing a water outlet in fluid communication with the collection cavity; and placing a water collection means in the collection cavity.

8. The method to separate water in a fuel cell system integrated into a fuel cell stack, of claim 17 wherein the cathode exhaust outlet is bisected and the water collection means is split.

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