Coolant fluid distribution in PEM fuel cells

Abstract

Cooling a fuel cell utilises a water distribution cover 30 including a plurality of rivulets (800A-N, Fig 8A) which are fluidly connected to a plurality of fluid guides (700, Fig 7A-B) for passing coo

Description

TECHNICAL FIELD

[0001] The present disclosure relates to distribution of coolant in fuel cell stacks, and in particular to membrane-type fuel cells. BACKGROUND

[0002] 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.

[0003] Each fuel cell assembly 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.

[0004] 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.

[0005] In hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell. Such fuel cells normally include a proton exchange membrane (PEM) sandwiched between electrodes, together comprising the membrane-electrode assembly (MEA). The MEA itself is traditionally sandwiched between a cathode and anode side plate.

[0006] An important consideration in the operation of such fuel cells is the management of water within the system. 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 one or 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. Common ducts are often used to feed oxidant and fuel to the fuel cell in fuel cell assemblies forming a stack.

[0008] In a typical high power fuel cell arrangement, cooling fluid is injected into the anode or cathode face of a fuel cell and disperses. Uneven cooling is suboptimal and impacts uniformity of operation and reduces efficiency.

[0009] High efficiency PEM fuel cells (PEMFC) produce heat when operating and the removal or management of same from the fuel cell stack is a factor because it affects system efficiency. To keep a temperature within a nominal range while current is flowing, the heat must be reduced or be taken away. It is therefore desiderata to: (1) reduce uneven heat removal in fuel cells forming a stack and (2) reduce uneven cooling of fuel cells within a stack. DISCLOSURE

[0010] The following description of examples of implementations, reference is made to the accompanying drawings that form a part hereof, and which show, by way of illustration, specific implementations of the present disclosure that may be utilized. Other implementations may be utilized, and structural changes may be made without departing from the scope of the present disclosure.

[0011] Disclosed are aspects of exemplary implementations of reducing uneven heat removal in fuel cells forming a fuel cell stack.

[0012] Disclosed are aspects of exemplary implementations of providing for even cooling within a fuel cell stack.

[0013] Disclosed are exemplary aspects of implementations of devices and methods to distribute coolant for cooling a fuel cell including a cathode cover affixed to a bipolar plate with a plurality of fluid guides each having a diameter along the length of first cathode fluid passage in fluid communication with the cathode flow field and a water distribution cover having a fluid conduit in fluid communication with a plurality of rivulets. Each rivulet has a head connected to a fluid conduit and a tail end configured to align with the plurality of fluid guides affixed to at least a portion of the cathode cover. In some instances each rivulet has a body between the head and tail. In some instances at least two rivulet bodies are different lengths between the head and tail. In some instances each rivulet body is a different length between the head and tail.

[0014] Disclosed are exemplary aspects of implementations of devices and methods to distribute coolant for cooling a fuel cell including a cathode cover affixed to a bipolar plate with a plurality of fluid guides each having a diameter along the length of first cathode fluid passage in fluid communication with the cathode flow field and a water distribution cover having a fluid conduit in fluid communication with a plurality of rivulets. Each rivulet has a head connected to a fluid conduit and a tail end configured to align with the plurality of fluid guides affixed to at least a portion of the cathode cover. In some instances the rivulet bodies each have a width and at least two rivulets have different width bodies. In some instances the rivulet bodies have a depth and, at least two rivulets have different depths. In some instances at least two fluid guides are different diameters.

[0015] Disclosed are exemplary aspects of implementations of devices and methods to distribute coolant for cooling a fuel cell including controlling the flow of water into discreet portions of a cathode flow field by way of fluid guides aligned with each discreet portion and fluidly connecting a plurality of rivulets formed in a water distribution cover to a fluid conduit. Fluidly connecting one rivulet to one fluid guide whereby water is passed from the rivulet to the fluid guide and into the discreet portion of the cathode flow field. In some instances each rivulet further comprises a head connected to the fluid conduit and a tail end connected to a fluid guide. In some instances each rivulet has a body between the head and tail. In some instances at least two rivulet bodies are different lengths between the head and tail. In some instances each rivulet body is a different length between the head and tail.

[0016] Disclosed are exemplary aspects of implementations of devices and methods to distribute coolant for cooling a fuel cell including controlling the flow of water into discreet portions of a cathode flow field by way of fluid guides aligned with each discreet portion and fluidly connecting a plurality of rivulets formed in a water distribution cover to a fluid conduit. Fluidly connecting one rivulet to one fluid guide whereby water is passed from the rivulet to the fluid guide and into the discreet portion of the cathode flow field. In some instances each rivulet further comprises a head connected to the fluid conduit and a tail end connected to a fluid guide. In some instances the rivulet bodies each have a width and at least two rivulets have different width bodies. FIGURES

[0017] 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 of 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.

[0018] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.

[0019] Fig. 1 depicts aspects of a side exploded assembly view of a high efficiency fuel cell assembly.

[0020] Fig. 2 depicts aspects of a perspective exploded assembly view from anode side to cathode side of a high efficiency fuel cell assembly.

[0021] Fig. 3 depicts aspects of a top view of the anode side of a frame with anode flow fields of the high efficiency fuel cell assembly in Fig. 1.

[0022] Fig. 4A depicts aspects of a top component view of the cathode side of a frame with cathode flow fields of a high efficiency fuel cell assembly in Fig. 1.

[0023] Fig. 4B depicts aspects of a top view of the cathode side of a frame with cathode components assembled thereon of the high efficiency fuel cell assembly in Fig. 4A.

[0024] Fig. 5 depicts aspects of a top view of the cathode side of a high efficiency fuel cell assembly.

[0025] Fig. 6 depicts aspects of a fuel cell stack formed from a plurality of high efficiency fuel cell assemblies.

[0026] Figs. 7A and 7B show aspects of a cathode inlet cover plate formed to cooperate with a water distribution cover.

[0027] Fig. 8A is a water distribution cover configured to fit onto the cathode inlet cover of Fig. 7.

[0028] Fig 8B is a cut away view along line “A”- “A” in Fig. 8A within area “Z”.

[0029] Fig. 8C is a comparison view of two rivulet bodies of varying widths.

[0030] Fig. 9A shows the bottom of a cathode cover plate of Fig. 7A.

[0031] Fig. 9B shows an assembled portion of a bipolar plate cathode inlet region.

[0032] Fig. 10 is a graph of aspects of variable rivulet length.

[0033] All descriptions and callouts in the figures and all content therein are hereby incorporated by this reference as if fully set forth herein. All citations are hereby incorporated by this reference as if fully set forth herein. 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 DISCLOSURE

[0034] The present disclosure may be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that this disclosure is not limited to the specific devices, methods, applications, conditions, or parameters described and / or shown herein, and that the terminology used herein is for the purpose of describing particular exemplars by way of example only and is not intended to be limiting of the claimed disclosure.

[0035] Disclosed herein are aspects of methods and systems to provide for at least one of improved cooling and consistent compression of at least one of fluid flow plates, flow assemblies, fuel cells and fuel cells in a stack which improve efficiencies of electrical generation and reduce cost of production.

[0036] By right sizing cathode inlets and outlets to maintain pressure across a flow field and into a gas diffusion layer (GDL) from inlet to outlet on the cathode side of a fuel cell bottlenecks in fluid flow are at least one of eliminated and minimized. The expansion of air and addition of moisture as oxidant flows through the cathode side of a fuel cell assembly the volume expands by at least a factor of 5 or more times, in some instances it expands by a factor of 50 or more, in some instances it expands by a factor of 100 or more, in some instances it expands by a factor of 200 or more. The instance fuel cell assembly, fuel cells formed from such assembly, and stack formed from a plurality of such fuel cells are a more efficient fuel cell stack by way of minimizing the bottlenecks. More efficient refers to power density during operation compared to a traditional fuel cell or stack utilizing traditional fuel cell assembly outlet and inlets.

[0037] Figure 1 is a component overview of a fuel cell assembly and a fuel cell.

[0038] Two fuel cell assemblies 10 and 10’ each having bipolar plates providing fluid flow pathways cooperate when stacked together and compressed as part of a fuel cell stack and together function as a fuel cell 100 in that stack.

[0039] Figure 2 shows aspects of a fuel cell assembly viewed cathode side up. Figures 3-6 show aspects of the anode side of a bipolar plate, assembly of the cathode side of a bipolar plate of this disclosure, and the cathode side of a bipolar plate of this disclosure.

[0040] A membrane electrode assembly (MEA) containing a proton exchange membrane (also known as a polymer electrolyte membrane) is normally a multi-layer interface whereby protons from the anode side of a fuel cell cross the MEA and the stripped off electron travels around the MEA to generate electricity. On the cathode side oxygen is provided and the hydrogen protons eventually form water with some of the oxygen provided.

[0041] The MEA 12 in a fuel cell assembly (or a fuel cell) traditionally will have some gas diffusion layer or layers between the MEA and bipolar frame 13. On a first side of the MEA 12A which will be closest to the cathode face 14 of a bipolar frame 13 is a cathode gas diffusion layer (or layers) 15. On the opposite second side of the MEA 12B which will be closest to the anode face 16 of a bipolar frame 13 is an anode gas diffusion layer 17. The bipolar frame 13 has a first end 18 opposite a second end 19. disclosed herein is a bipolar frame configured wherein the anode face 16 is formed as part of the bipolar frame. Disclosed herein is a novel bipolar plate 200 wherein the cathode face has a separate cathode outlet cover 20 attached to the bipolar frame and a separate cathode inlet cover 22 attached to the bipolar frame. Configuring the bipolar frame 13 to affix separate cathode inlet and outlet covers eliminates the waste material caused by using a single cathode frame thus reducing at least one of carbon footprint, cost, and manufacturing cost. A separate water distribution cover 30 configured to affix over at least a portion of the cathode inlet cover may be attached. One or more gaskets are added to seal the fuel cell assembly when forming fuel cells within a fuel cell stack. At least a cathode gasket 40 and an anode gasket 42.

[0042] Figure 3 shows aspects of the anode side of a bipolar plate. At the first end 18 is an air inlet 300, a water inlet 310 and a hydrogen outlet 315. At the second end 19 is a cathode fluid outlet 320 and a hydrogen inlet 325. The hydrogen inlet is fluidly connected via a first anode fluid passage 330 to the anode face of the bipolar plate. The anode face is fluidly connected to a second anode fluid passage 335 that is fluidly connected to the hydrogen outlet 315. The water inlet 310 and air inlet 300 are fluidly connected to the cathode face of the bipolar plate.

[0043] Figure 4A shows aspects of the unassembled cathode side of a bipolar frame 13. The cathode inlet cover 22 attaches to the bipolar frame at its first end 18 aligning with the water inlet, air inlet 300 and hydrogen outlet 315 of the bipolar frame. A first cathode fluid passage 340 is formed at one edge of the cathode inlet cover 22. A separate cathode outlet cover 20 attached to the bipolar frame at its second end 19 aligning the cathode inlet 320 and hydrogen inlet of the bipolar frame. A second cathode fluid passage 345 is formed at one edge of the cathode outlet cover 20. Once the cathode covers are attached the bipolar plate is formed. Those of ordinary skill in the art and the skilled artisan will recognize that traditional bipolar plates utilizing multiple frames affixed together and bipolar plates with a single frame and no covers are within the scope of this disclosure. A separate water distribution cover is configured to affix over at least a portion of the cathode inlet cover. The air inlet 300 and the water inlet 310 are fluidly connected via a first cathode fluid passage 340 to the cathode face of the bipolar plate. The cathode face is fluidly connected to a second cathode fluid passage 345 which is fluidly connected to the cathode fluid outlet 320.

[0044] Figure 4B shows aspects of the assembled cathode side of a bipolar plate 200B including water distribution cover.

[0045] Figure 5 shows aspects of an assembled bipolar plate cathode face up with cathode gas diffusion layer 15 visible. Fluid 500 containing the air, water and water vapor from the air inlet 300 and the water inlet 310 fluidly pass through evenly spaced fluid guides 700 (shown in figures 7A and 7B) to the first cathode fluid passage 340 along the lines of arrow 500 through the cathode face 14 and the cathode gas diffusion layer 15 to the second cathode fluid passage 345 then to the cathode fluid (or exhaust) outlet 320.

[0046] Figure 6 shows an assembly view fuel cell stack 600 formed from a plurality of fuel cell assemblies 10(l-N) with the cathode gas diffusion layer 14, a first end plate 602 and a second end plate 604. A water outlet is also in fluid communication with the cathode fluid outlet.

[0047] Figures 7A through 9B illustrate aspects of methods and systems of exemplary implementations of controlled coolant distribution in a fuel cell.

[0048] Figure 7A shows a top view of aspects of a cathode inlet cover 22 having fluid guides 700 therein and Figure 7B shows a blow-up of section “Y” of Figure 7A. The cathode inlet cover has a top surface 701 and is configured to cooperate with the water distribution means to deliver water through an array of fluid guides 700A-700N. Welds or other connectors 702 may be added to affix the cathode inlet cover to the bipolar frame. A series of spacers 705 protrude from the bottom surface 703 of the cathode inlet cover to fluidly connect water flow into the cathode flow field 14 and cathode gas diffusion layer 15 of a bipolar plate. Fluid guides 700A - 700N may vary in diameter.

[0049] Figures 8A and 8B show aspects of rivulets 800A through 800N formed in the water distribution cover 30. The water distribution cover provides a fluid conduit 802 with a first end 803 and a second terminal end 804. Figure 8B shows the bottom face 805 of section “Z” of Figure 8 A of the water distribution cover, each rivulet has a depth “D” which when viewed from the top side appears as a height, therefore for purposes of this disclosure it is an out of plane bump or divot through which fluid may flow. Each rivulet has a head 807 fluidly connected to the fluid conduit 802. Water flows from the head end 807 through the indented rivulet body 809 and to the tail end 810 of the rivulet. The tail end of each rivulet is configured to align and fluidly connect with one of the fluid guides 700 on the cathode inlet cover. Figure 8C shows a portion of the body of rivulet 800B. By increasing the width of the rivulet body 809 to body 809’ the width “W” forms a larger pathway for water through rivulet body 809’ then through rivulet body 809, thus increasing the volume of water which can be delivered.

[0050] Figure 9A shows a portion of section “X” from Figure 4B. The cathode inlet cover is shown with its bottom surface 703 upward. The water distribution cover is affixed to the cathode inlet cover in this figure. The tail end 810 of the rivulet is visible through the fluid guide 700 and water 900 from the rivulet is directed out from under the bottom surface 707 of the cathode inlet cover to the cathode flow field 14 shown in Figure 9B. The water or coolant 900 is directed via fluid guides into different discreet portions “CFFA”, “CFFB” and “CFFN” of the cathode flow field 14. In some instances to even the fluid flow into the cathode flow field 14 through the cathode inlet cover the fluid guides 700A-700N are varied in diameter whereby the cross section of the guide will limit the fluid flow therethrough.

[0051] Figure 10 shows general aspects of how rivulet bodies 809 may vary over distance from the first end 803 of the fluid conduit 802 to even out the supply of coolant such as water to the water distribution cover. The varying of rivulet body length may also be combined with varying the fluid inlet sizing.

[0052] Figures 8A -10 illustrate another water distribution method to a fuel cell. Each of the rivulets 800(1) through 800(N) may be different sized. The rivulets are constructed in a wavelike form whereby if each rivulet has the same width, then varying the frequency and / or amplitude of the rivulet body will change the length of the wave or rivulet. By changing the length and keeping the diameter of each rivulet body 809 the same, the actual length of the body is lengthened or shortened. The fluid passing down the more circuitous (longer) body of rivulet 800A will travel a greater distance. The more tortuous path will also slow the rate of movement than fluid passing through the less tortured path body of rivulet 800N. The varying of length of bodies maintains even delivery of water to each rivulet. Generally, the rivulet closest to the first end 803 receives one of a greater volume of water and water under greater pressure _and the rivulet nearest the terminal end 804 receives one of a lesser volume of water and water under lower pressure. Maintaining the same water flow through each rivulet over time will deliver the same water quantity to each tail end for rivulets 800A-N which in turn will provide the same water quantity to each portion of the flow field 14 across the leading edge 811 of the water distribution cover.

[0053] It is also within the scope of this disclosure and those of ordinary skill in the art and the skilled artisan will recognize that the depth “D” of a rivulet body may be altered to further change the quantity or flow rate of water through the rivulet.

[0054] In some instances, any or all of the depth of the rivulet, the width of the rivulet, the amplitude of the rivulet and the frequency of the rivulet may be varied in rivulets 800A to 800N along the water distribution cover to deliver even quantities of water to all portions of the cathode flow field 14.

[0055] Returning to the cathode inlet cover 22, in Figure 8A the body of rivulet 800A compared to rivulet body 800B is a longer body. Both rivulets show a similar frequency but 800A is configured with greater amplitude in the body 809 compared to rivulet 800B. The greater amplitude in rivulet 800A corresponds to a greater length of the body 809 of rivulet 800A compared to the body of rivulet 800B. The contrast is even greater when comparing rivulet 800A body to rivulet 800N body. Rivulet 800N may have a similar contrast compared to rivulet 800B and even more pronounced compared to rivulet 800A.

[0056] 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 in stationary power systems. 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.

[0057] The components disclosed herein may utilize known materials that are used in the industry.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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

1. A fuel cell cooling system comprising;a cathode cover (22) affixed to a bipolar plate, said cathode cover (22) having a plurality of fluid guides (700A-700N) therein, each having a diameter and positioned along the length of first cathode fluid passage (340) in fluid communication with a cathode flow field (14);a water distribution cover (30) having a fluid conduit (802) in fluid communication with a plurality of rivulets (800A-800N) each of which has a head (807) connected to the fluid conduit (802), a body (809) and a tail (810) configured to align with a respective fluid guide of the plurality of fluid guides (700A-700N);wherein the cathode cover (22) partially covers one end of said bipolar plate; and,wherein the rivulet bodies each have a width (W) and a depth (D), and at least two rivulet bodies (809) have different widths or different depths.

2. The fuel cell cooling system of any preceding claim, wherein at least two rivulet bodies (809) are different lengths between the head (807) and tail (810).

3. The fuel cell cooling system of any preceding claim, wherein at least three rivulet bodies (809) are different lengths between the head (807) and tail (810).

4. The fuel cell cooling system of any preceding claim, wherein each rivulet body (809) is a different length between the head (807) and tail (810).

5. The fuel cell system of any preceding claim, wherein at least two fluid guides are different diameters.

6. A method of cooling a fuel cell, the method comprising:controlling the flow of water into discreet portions (CFFA, CFFB and CFFN) of a cathode flow field by way of a plurality of fluid guides (700A-700N), aligned with each discreet portion, wherein a cathode cover (22) is affixed to the bipolar plate, wherein said cathode cover (22) has the plurality of fluid guides (700A-700N) therein, and the cathode cover (22) partially covers one end of said bipolar plate;wherein each of the plurality of fluid guides (700A-700N) has a diameter and is positioned along the length of first cathode fluid passage (340) in fluid communication with a cathode flow field (14);fluidly connecting a plurality of rivulets (800A-800N) formed in a water distribution cover (30) to a fluid conduit (802) thereon, each of which has a head (807) connected to the fluid conduit (802), a body (809) and a tail (810) configured to align with a respective fluid guide of the plurality of fluid guides (700A-700N);fluidly connecting one rivulet to one of said plurality of fluid guides;whereby water is passed from the rivulet to the fluid guide and into the discreet portion of the cathode flow field (14); and,wherein the rivulet bodies (809) each have a width (W) and a depth (D), and at least two rivulet bodies (809) have different widths or different depths.

7. The method of cooling a fuel cell of Claim 6, wherein at least two rivulet bodies (809) are different lengths between the head (807) and tail (810).

8. The method of cooling a fuel cell of Claim 6 or 7, wherein at least three rivulet bodies (809) are different lengths between the head (807) and tail (810).

9. The method of cooling a fuel cell of any of Claims 6 to 8, where each rivulet body (809) is a different length between the head (807) and tail (810).

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