Bipolar Plates for Fuel Cells

Abstract

A hydrogen fuel cell unit is fabricated from a plurality of identical bipolar plates, each of which is stamped from a single sheet of steel and coated with ta-C, the unit comprising, in order, (i) a first bipolar plate having a front and a back side, the back side being the anode of the unit, (ii) a first membrane electrode assembly, and (iii) a second bipolar plate having a front and a back side, the front side being the cathode of the unit and the back side being the anode of the unit, the first membrane electrode assembly being between the first and second bipolar plates, and a flow path being provided between the back side of the first bipolar plate and the first membrane electrode assembly for the flow of hydrogen. (iv) a second bipolar plate having a front surface and a flow path for oxygen flow between the front surface of the second bipolar plate and the first membrane electrode assembly; (v) a third bipolar plate having a front surface and a back surface, the front surface being the cathode of the unit, the second membrane electrode assembly being between the second bipolar plate and the third bipolar plate, a flow path for hydrogen flow between the back surface of the second bipolar plate and the second membrane electrode assembly, and a flow path for oxygen flow between the front surface of the third bipolar plate and the second membrane electrode assembly.

Description

[Technical field]

[0001] The present invention relates to a bipolar plate for use in hydrogen fuel cells, particularly PEM fuel cells, and a method for the manufacture thereof. [Background technology]

[0002] Growing awareness of the effects of climate change has led to increased research into alternative, "non-fossil" energy sources such as hydrogen. Hydrogen fuel cells have been developed that use the electrochemical, typically catalytic, oxidation of hydrogen to produce water to produce electricity.

[0003] A widely used hydrogen fuel cell is the proton exchange membrane (PEM) fuel cell, which contains a semi-permeable membrane that allows protons to pass through the membrane while acting as a barrier to electrons and reactants (e.g., hydrogen and oxygen gas). PEM fuel cells have many advantages, including high energy conversion rates, environmental friendliness, and low operating temperatures.

[0004] Because each cell in a PEM fuel cell produces a relatively low voltage, multiple PEM cells can be connected in series to increase the output voltage. This multi-cell assembly is sometimes called a fuel cell stack. Connecting adjacent PEM cells such that the cathode of one PEM cell is connected to the anode of the other effectively forms a bipolar plate that conducts electricity from one PEM cell to the adjacent PEM cell. Each of the cathode and anode plates, and therefore each half of the bipolar plate, also typically contains flow channels on its surface through which reactants or coolant can be delivered. As the core component of a hydrogen fuel cell, the bipolar plate has many important functions, including conducting electric current, supporting the membrane electrodes, uniformly transporting and separating reactant gases, and circulating coolant for rapid cooling.

[0005] When adjacent PEM cells are connected, a bipolar plate is formed from the two separate plates (anode and cathode) of these adjacent cells. These plates are usually welded together. There are many challenges associated with this. In particular, oxidation and corrosion at the weld sites can reduce the efficiency of the bipolar plate. Nevertheless, bipolar plates are common in the field when multiple cells are connected in series.

[0006] US 2020 / 212470 discloses a fuel cell unit having multiple flow plate assemblies arranged in a stacked configuration, with adjacent flow plate assemblies positioned at an offset angle relative to each other.

[0007] DE 10 2020 207353 discloses a bipolar plate for a fuel cell system, in which the plates are arranged such that the coolant flow through a first flow path structure is different from the coolant flow through a second flow path structure.

[0008] US 2015 / 325876 discloses a fuel cell including an anode / cathode stack having a first flow path structure and a second flow path structure with a first supply structure and a second supply structure, respectively.

[0009] US Pat. No. 4,292,379 discloses a fuel cell system for reducing reaction distribution bias.

[0010] US 2019 / 169759 discloses a stack of interconnected solid oxide electrochemical gas separator (SOEGS) cells separated by connecting tubes. Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to ameliorate problems associated with known fuel cell stacks or to provide an alternative to known fuel cell stacks and to bipolar plates between adjacent fuel cells. It is an object of certain embodiments to provide improved bipolar plates for fuel cell stacks, as well as fuel cell stacks incorporating one or more improved bipolar plates, and methods of manufacture thereof. [Means for solving the problem]

[0012] The present invention relates to a hydrogen fuel cell unit comprising, in order: (i) a first bipolar plate having a front and a back surface, the back surface being the anode of the unit; (ii) a first membrane electrode assembly; and (iii) a second bipolar plate having a front surface and a back surface, the front surface being the cathode of the unit and the back surface being the anode of the unit; a second bipolar plate, the first membrane electrode assembly being between the first bipolar plate and the second bipolar plate, with a flow passage between the back surface of the first bipolar plate and the first membrane electrode assembly for the flow of hydrogen, and a flow passage between the front surface of the second bipolar plate and the first membrane electrode assembly for the flow of oxygen; (iv) a second membrane electrode assembly; and (v) a third bipolar plate having a front and a back surface, the front surface being the cathode of the unit; a third bipolar plate, the second membrane electrode assembly being between the second bipolar plate and the third bipolar plate, with a flow path provided between the back surface of the second bipolar plate and the second membrane electrode assembly for the flow of hydrogen, and a flow path provided between the front surface of the third bipolar plate and the second membrane electrode assembly for the flow of oxygen.

[0013] Preferably, the bipolar plates include channels for the flow of oxygen, the oxygen channels of adjacent plates diverging and merging across the plates, for example in a crisscross pattern.

[0014] The present invention also provides a method for manufacturing a bipolar plate, comprising the steps of: (i) providing a sheet of a metal or alloy; (ii) punching the sheet to form a bipolar plate including a plurality of hydrogen channels and a plurality of oxygen channels; A method is provided by which the bipolar plates can be used to form a hydrogen fuel cell unit according to the present invention.

[0015] The present invention further provides a method for producing a hydrogen fuel cell, comprising the steps of: (i) providing a first bipolar plate having a front and a back surface, the back surface being an anode, and a second bipolar plate having a front and a back surface, the front surface being a cathode and the back surface being an anode; (ii) disposing a first membrane electrode assembly between the first bipolar plate and the second bipolar plate; when the first membrane electrode assembly is between the first bipolar plate and the second bipolar plate, a flow path is provided between the back surface of the first bipolar plate and the first membrane electrode assembly for the flow of hydrogen, and a flow path is provided between the front surface of the second bipolar plate and the first membrane electrode assembly for the flow of oxygen; (iv) providing a third bipolar plate having a front and a back surface, the front surface being a cathode; (v) disposing a second membrane electrode assembly between the second bipolar plate and the third bipolar plate; Including, wherein, when the second membrane electrode assembly is between the second bipolar plate and the third bipolar plate, a flow path is provided between the back surface of the second bipolar plate and the second membrane electrode assembly for flowing hydrogen, and a flow path is provided between the front surface of the third bipolar plate and the second membrane electrode assembly for flowing oxygen.

[0016] All of the plates may have the same design, with each plate stamped from a sheet of metal or alloy, with adjacent plates rotated 180 degrees with respect to each other. [Brief description of the drawings]

[0017] [Figure 1] 1 shows a known bipolar plate in a fuel cell stack. [Diagram 2] 1 shows known anode and cathode plate components that form a bipolar plate. [Diagram 3] FIG. 2 is a top and side view of a bipolar plate of the present invention. [Figure 4] FIG. 2 is a top plan view of one side of a bipolar plate of the present invention. [Diagram 5] FIG. 1 is a top view of the flow paths of two separate bipolar plates of the present invention, one plate stacked directly on top of the other, both plates having the same shape and configuration, with one bipolar plate rotated 180 degrees relative to the other. [Figure 6] FIG. 5 is a top view of the bipolar plate of FIG. 4, with the proton exchange membrane at the top, sealing the anode side of the bipolar plate. [Figure 7] FIG. 5 is a top view of the bipolar plate of FIG. 4 showing the anode gasket on the plate. [Figure 8] FIG. 5 is a top view of the bipolar plate of FIG. 4 showing the cathode gasket on the plate. [Figure 9]FIG. 2 is a top and side view of a portion of a stack of bipolar plates of the present invention, showing a cross section of the stack showing the air flow paths. [Figure 10] 10 shows a more detailed cross-section of the center of the fuel cell stack in the same direction as the portion of FIG. 9. [Figure 11] FIG. 11 is a cross-sectional view of the fuel cell stack taken in a direction perpendicular to FIGS. 9 and 10, showing the hydrogen flow paths. [Figure 12] 12 shows a more detailed cross-section of the edge of the fuel cell stack taken in the same direction as FIG. 11. [Figure 13] FIG. 13 is a top plan view of an alternative embodiment of a bipolar plate of the present invention. [Figure 14] FIG. 14 is a top view of the flow paths of two separate bipolar plates of the embodiment shown in FIG. 13, one plate stacked directly on top of the other, both plates having the same shape and configuration, with one bipolar plate rotated 180 degrees relative to the other. [Figure 15A] FIG. 13 is a top plan view of another embodiment of the bipolar plate of the present invention. [Figure 15B] FIG. 13 is a top plan view of another embodiment of the bipolar plate of the present invention. [Figure 16] FIG. 2 is a top plan view of another embodiment of a bipolar plate of the present invention having an enclosed cathode for use with an oxygen manifold. [Figure 17A] FIG. 2 is a top plan view of a further embodiment of a bipolar plate of the present invention having a closed cathode for use with an oxygen manifold. [Figure 17B] FIG. 2 is a top plan view of a further embodiment of a bipolar plate of the present invention having a closed cathode for use with an oxygen manifold. [Figure 18] FIG. 1 shows a top and side view of a fuel cell comprising a stack of bipolar plates according to the invention. [Figure 19] FIG. 19 is an exploded view of the fuel cell stack of FIG. [Figure 20] FIG. 20 is a top and side view of a cross section through the center of the fuel cell stack of FIGS. 18 and 19 showing the flow paths. [Figure 21] FIG. 21 shows a more detailed cross section in the same direction as FIG. 20, showing the conduits for connecting to the hydrogen manifold. [Figure 22] 20. A similar cross section in the same direction as FIG. 20, showing a cross section of a peripheral gasket. [Diagram 23] 20 to 22. FIG. 21 shows a more detailed partial cross-section of the peripheral gasket in the same direction as FIG. [Figure 24] 20 to 23, and shows a cross section passing through the center of the fuel cell stack in FIG. 18, viewed from above and to the side, illustrating the hydrogen flow path. [Diagram 25] 25 shows a cross section taken in a similar direction to FIG. 24, but from the side, with more detail showing the hydrogen flow paths and the surrounding gasket. [Figure 26] 25 is a similar cross section taken in the same direction as FIG. 24, but showing a further portion of the cathode gasket. [Figure 27] 27 is a more detailed partial cross-sectional view of a further portion of the cathode gasket taken in a similar direction to FIG. 26, but from the side. [Figure 28] FIG. 13 shows a further alternative embodiment of a bipolar plate of the present invention viewed from above and from the side. [Figure 29] FIG. 29 is a top plan view of the bipolar plate of FIG. 28. [Diagram 30] FIG. 29 is a top plan view of the anode side of the bipolar plate of FIG. 28 showing the anode gasket. [Diagram 31] FIG. 29 is a top plan view of the cathode side of the bipolar plate of FIG. 28 showing the cathode gasket. [Figure 32a] 32a, 32b, and 32c show the anode gasket, cathode gasket, and end plate gasket, respectively, of the embodiment of the invention shown in FIGS. 28-31. [Figure 32b]32a, 32b, and 32c show the anode gasket, cathode gasket, and end plate gasket, respectively, of the embodiment of the invention shown in FIGS. 28-31. [Fig. 32c] 32a, 32b, and 32c show the anode gasket, cathode gasket, and end plate gasket, respectively, of the embodiment of the invention shown in FIGS. 28-31. [Diagram 33] 29 shows a cross section (along line A in FIG. 29) of the bipolar anode gasket feature of FIG. 28. [Diagram 34] FIG. 29 is a view from the edge (parallel to line A in FIG. 29) of the stack of bipolar plates according to FIG. 28. [Diagram 35] 29 is a cross-section (along line B in FIG. 29) of the hydrogen inlet channel of the bipolar plate of FIG. 28. [Diagram 36] 29 is a cross section through the center of the bipolar plate of FIG. 28 (along line C in FIG. 29). [Figure 37] 37 to 40 are color diagrams of FIGS. 33 to 36, but are otherwise equivalent. [Figure 38] 37 to 40 are color diagrams of FIGS. 33 to 36, but are otherwise equivalent. [Figure 39] 37 to 40 are color diagrams of FIGS. 33 to 36, but are otherwise equivalent. [Diagram 40] 37 to 40 are color diagrams of FIGS. 33 to 36, but are otherwise equivalent. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The hydrogen fuel cell unit of the present invention therefore comprises, in order: (i) a first bipolar plate having a front and a back surface, the back surface being the anode of the unit; (ii) a first membrane electrode assembly; and (iii) a second bipolar plate having a front surface and a back surface, the front surface being the cathode of the unit and the back surface being the anode of the unit; a second bipolar plate, the first membrane electrode assembly being between the first bipolar plate and the second bipolar plate (e.g., between the back surface of the first bipolar plate and the front surface of the second bipolar plate), with channels provided between the back surface of the first bipolar plate and the first membrane electrode assembly for the flow of hydrogen, and channels provided between the front surface of the second bipolar plate and the first membrane electrode assembly for the flow of oxygen; (iv) a second membrane electrode assembly; and (v) a third bipolar plate having a front and a back surface, the front surface being the cathode of the unit; and a third bipolar plate, the second membrane electrode assembly being between the second bipolar plate and the third bipolar plate (e.g., between a back surface of the second bipolar plate and a front surface of the third bipolar plate), with a flow path provided between the back surface of the second bipolar plate and the second membrane electrode assembly for the flow of hydrogen, and a flow path provided between the front surface of the third bipolar plate and the second membrane electrode assembly for the flow of oxygen.

[0019] The plates contain channels for the flow of hydrogen (also called hydrogen channels), each channel having an inlet and an outlet. The inlets and outlets of the hydrogen channels of adjacent plates in a fuel cell unit can be preferably vertically aligned in a vertical stack of plates. This simplifies the design of gaskets between plates in a stack. For example, the same gasket can be used universally on the cathode side of each plate (e.g., sealing the hydrogen inlets and outlets on the cathode side of the plate to prevent hydrogen flow on the cathode side).

[0020] Each hydrogen flow path further includes a conduit between its inlet and outlet. The conduits or flow paths of adjacent plates in a fuel cell are preferably not vertically aligned along their entire length. Thus, when held, e.g., clamped, adjacent plates do not nest within a stack that is part of the fuel cell. The abutting portions of adjacent plates hold the membrane electrode assembly between the adjacent plates and help seal the hydrogen and oxygen flow paths, keeping the respective flow paths separated from each other. Also, the fact that the flow paths are not aligned along part of their length means that adjacent plates support each other in the stack and hold the membranes sealed between the plates.

[0021] As shown in the examples described in more detail below, the hydrogen flow channels of adjacent plates have their respective inlets vertically aligned, and then the hydrogen flow channels diverge and merge across the plate, eventually merging at a vertically aligned outlet. The hydrogen flow channels may repeatedly diverge and merge across the plate (whether or not the inlets and outlets of adjacent plates are vertically aligned), for example in a crisscross pattern. In a preferred embodiment, the hydrogen flow channels of adjacent plates may diverge and merge in a regular pattern.

[0022] The plates contain channels for the flow of oxygen (also referred to as oxygen channels), each channel having an inlet and an outlet. The inlets and outlets of the oxygen channels of adjacent plates in a fuel cell unit can be independently aligned, preferably vertically, in a vertical stack of plates. Again, the same gasket can be used on the anode side of each plate, simplifying the gasket design (e.g., sealing the oxygen inlets and outlets on the anode side of the plate to prevent oxygen flow on the anode side).

[0023] Each oxygen flow channel further includes a conduit between its inlet and outlet. The conduits of the oxygen flow channels of adjacent plates in a fuel cell are not vertically aligned along their entire length. Again, this prevents adjacent plates from nesting and helps to hold the membrane electrode assemblies securely in sealed engagement between the plates. Adjacent plates can better support each other in a stack as a result of this partial misalignment, and it is preferred that both a portion of the hydrogen flow channels and a portion of the oxygen flow channels are misaligned.

[0024] As shown in the examples described in more detail below, the oxygen channels of adjacent plates have their respective inlets vertically aligned, and then the oxygen channels diverge and merge across the plate, eventually merging into a vertically aligned outlet. The oxygen channels may repeatedly diverge and merge across the plate, for example in a crisscross pattern (regardless of whether the inlets and outlets of adjacent plates are vertically aligned). In a preferred embodiment, the oxygen channels of adjacent plates may diverge and merge in a regular (i.e., repeating) pattern.

[0025] With reference to the examples below, it will be appreciated that the hydrogen and oxygen flow paths may be defined by a combination of a recess in one plate and a membrane electrode assembly held between that plate and an adjacent plate.

[0026] As shown in more detail in the examples below, a bipolar plate may include hydrogen and oxygen flow paths that are substantially transverse to one another. For example, the hydrogen flow paths may extend substantially left to right across the plate, while the oxygen flow paths extend substantially back to front across the plate, or vice versa. Preferably, a majority of the hydrogen flow paths are substantially transverse to a majority of the oxygen flow paths. In a specific embodiment, all of the hydrogen flow paths are substantially transverse to all of the oxygen flow paths.

[0027] An advantage of the present invention is that each plate can be stamped from a single sheet and there is no need to weld or otherwise connect each anode and cathode side to actually form a bipolar plate. Instead, each stamped plate of the present invention forms a bipolar plate in its own right.

[0028] The hydrogen and oxygen flow paths are formed by the interface of one plate, preferably a stamped plate, with the membrane electrode assembly, where the membrane is held between the two plates. Protrusions on the plates are held in sealing engagement against the membrane, and recesses on the plates form flow paths between the recesses and the membrane.

[0029] According to an embodiment of the invention, for transverse flow, the hydrogen and oxygen channels cross each other. The oxygen channels can preferably be formed by indentations in the bipolar plate, and the transverse hydrogen channels can at the same time include a notch in the indentation forming the oxygen channel. The notch reduces the height of the oxygen channel at that point and forms a hydrogen channel on the opposite side between the notch and the membrane, or vice versa. Thus, the hydrogen channels can be formed by indentations in the bipolar plate, and the transverse oxygen channels can include a notch in the indentation forming the hydrogen channel.

[0030] One advantage of having intersecting hydrogen and oxygen flow paths in embodiments of the invention is that the bipolar plates can be stamped out of a single sheet of material, as described above. When the plates are stacked vertically one on top of the other, as shown in the examples below, a horizontal cross-section of the plates (i.e., a plane passing through the center of each plate and perpendicular to the vertical direction of the stack of plates) can be such that the cross-section passes through both the hydrogen and oxygen flow paths. This is not the case in known hydrogen fuel cell stacks.

[0031] In a preferred embodiment of the invention, all plates of the hydrogen fuel cell unit, e.g. each of the first, second and third bipolar plates, have the same design. This means that the plates can be produced by stamping, and only one stamping machine is required. Adjacent plates are conveniently arranged in a stack with adjacent plates rotated 180 degrees relative to each other (preferably about an axis perpendicular to the plane of the plates). The asymmetric plate design means that the plates can be effectively stacked to form the hydrogen and oxygen channels, while not nesting the channels of adjacent plates, and maintaining sufficient plate-to-plate contact to grip the membrane between the plates and form a seal channel that keeps the hydrogen and oxygen sides separated.

[0032] In such an embodiment, the bipolar plates are not rotationally symmetric about a line passing through the center of the plate in the stack normal (i.e., a line passing through the center of a plane perpendicular to the plane of the plate). Thus, by rotating adjacent bipolar plates 180 degrees relative to each other, the depressions in the plates will not align, meaning that the plates will not nest. In a preferred embodiment, the lack of rotational symmetry is due to the shape of the oxygen flow channels.

[0033] In embodiments where the bipolar plates are not rotationally symmetric overall, there may be rotational symmetry between certain features and elements of the plates. For example, the manifold openings of each plate may be rotationally symmetric. Preferably, the manifold openings of each bipolar plate are two-fold rotationally symmetric. That is, moving any bipolar plate from a first position to a second position by rotating it 180 degrees about a line passing through the center of the plate in the vertical direction of the stack of plates will map the location of the manifold openings in the first position to the location of the manifold openings in the second position. Such rotational symmetry allows the manifold openings of adjacent plates to be vertically aligned to form a manifold.

[0034] Regardless, the inlets and outlets of the hydrogen and / or oxygen channels on the bipolar plates may be rotationally symmetric (e.g., two-fold rotationally symmetric). Preferably, the inlets and outlets of the hydrogen and / or oxygen channels on each bipolar plate may be two-fold rotationally symmetric. That is, when any bipolar plate is moved from a first position to a second position by rotating it 180 degrees about a line passing through the center of the plate in the vertical direction of the stack of plates, the positions of the inlets and outlets of the hydrogen and / or oxygen channels of each bipolar plate in the first position map to the positions of the inlets and outlets in the second position. Such rotational symmetry allows the inlets and outlets of the hydrogen and / or oxygen channels to be vertically aligned in a plate stack in which adjacent plates are rotated 180 degrees relative to each other, as described above.

[0035] In alternative embodiments of the invention, different punches are used to form adjacent bipolar plates (e.g., the first and third bipolar plates are punched using the same punch and the second bipolar plate is punched using a different punch). When two (or more) punches are used, it is not necessary to rotate adjacent plates to prevent the flow channels of adjacent plates from nesting. In these embodiments, there is preferably a two bipolar plate design, where the hydrogen and / or oxygen flow channels of adjacent plates are not aligned along their entire length, thus preventing adjacent plates from nesting.

[0036] In such embodiments where there are two bipolar plate designs, certain features or elements are preferably maintained in the same location in both designs. For example, the manifold openings, and, independently, the inlets and outlets for the hydrogen and / or oxygen channels, are preferably in the same location in both designs.

[0037] There is also provided herein a bipolar plate for a fuel cell unit of the invention, which has no rotational symmetry about a line passing through the centre of the plate in the vertical direction of the stacking of the plates (i.e. perpendicular to the plane of the plates). Suitably, the bipolar plate is any of the first bipolar plate, the second bipolar plate and / or the third bipolar plate in the hydrogen fuel cell unit described above.

[0038] In preferred embodiments, the lack of rotational symmetry is due to the shape of the oxygen flow channels. As mentioned above, even in embodiments where the bipolar plate is not rotationally symmetric overall, there may be rotational symmetry between certain features and elements of the plate. For example, as mentioned above, there may be rotational symmetry between the manifold openings on the bipolar plate, or independently, between the inlets and outlets of the hydrogen flow channels and / or the oxygen flow channels. The rotational symmetry of a particular element may be two-fold rotationally symmetric; that is, an element maps onto itself twice for each 360 degree rotation. In preferred embodiments, the bipolar plate comprises two or more manifold openings, and the manifold openings are rotationally symmetric. It is particularly preferred that the rotational symmetry of the manifold openings is two-fold rotationally symmetric.

[0039] The bipolar plates are preferably stamped from a single sheet of metal or alloy, such as steel, titanium, or aluminum, or alloys thereof, which may be coated, for example, with ta-C. Preferably, the bipolar plates have no welded joints, i.e., there is no welding step in the formation of the bipolar plates.

[0040] There is now provided a method for manufacturing a bipolar plate, the method comprising: (i) providing a sheet of a metal or alloy; (ii) punching the sheet to form a bipolar plate including a plurality of hydrogen channels and a plurality of oxygen channels; Bipolar plates can be used to manufacture hydrogen fuel cell units according to the present invention, including any embodiment and combination of preferred embodiments or features.

[0041] The method preferably does not include a welding step.

[0042] Further according to the present invention there is provided a method for producing a hydrogen fuel cell, the method comprising the steps of: (i) providing a first bipolar plate having a front and a back surface, the back surface being an anode, and a second bipolar plate having a front and a back surface, the front surface being a cathode and the back surface being an anode; (ii) disposing a first membrane electrode assembly between the first bipolar plate and the second bipolar plate; when the first membrane electrode assembly is between the first bipolar plate and the second bipolar plate (e.g., between the back surface of the first bipolar plate and the front surface of the second bipolar plate), a flow path is provided between the back surface of the first bipolar plate and the first membrane electrode assembly for the flow of hydrogen, and a flow path is provided between the front surface of the second bipolar plate and the first membrane electrode assembly for the flow of oxygen; (iv) providing a third bipolar plate having a front and a back surface, the front surface being a cathode; (v) disposing a second membrane electrode assembly between the second bipolar plate and the third bipolar plate; Including, wherein when the second membrane electrode assembly is between the second bipolar plate and the third bipolar plate (e.g., between the back surface of the second bipolar plate and the front surface of the third bipolar plate), a flow path is provided between the back surface of the second bipolar plate and the second membrane electrode assembly for the flow of hydrogen, and a flow path is provided between the front surface of the third bipolar plate and the second membrane electrode assembly for the flow of oxygen.

[0043] A preferred method of manufacturing a hydrogen fuel cell includes one or more or all of the optional or preferred features of the present invention described elsewhere herein.

[0044] In these methods, the bipolar plates are preferably all of the same design, with adjacent plates rotated 180 degrees with respect to each other.

[0045] A method for manufacturing a hydrogen fuel cell unit includes: (i) providing a sheet of a metal or alloy; (ii) stamping the sheet to form a bipolar plate containing a plurality of hydrogen channels and a plurality of oxygen channels; (iii) repeating steps (i) and (ii) at least once to provide a plurality of similar bipolar plates; (iv) arranging a plurality of similar bipolar plates in a stack with adjacent plates rotated 180 degrees relative to each other.

[0046] A further method for producing a hydrogen fuel cell unit comprises: (i) providing a plurality of similar bipolar plates, each of which includes a plurality of hydrogen flow channels and a plurality of oxygen flow channels; (ii) arranging a plurality of similar bipolar plates in a stack with adjacent plates rotated 180 degrees relative to each other.

[0047] Thus, bipolar plates can be used to manufacture hydrogen fuel cell units according to the present invention, including any of the embodiments and combinations of preferred embodiments or features as described above. Exemplary stacks include 5 or more, particularly 10 or more, bipolar plates in the stack.

[0048] Gaskets are conventionally known in hydrogen fuel cells and are suitably used in the present invention between adjacent plates to prevent leakage between the hydrogen and oxygen sides of the fuel cell, to seal between the hydrogen channel inlets and outlets and the hydrogen manifold, and to seal the top and bottom plates of the stack to the current collectors, as conventionally known in hydrogen fuel cells. The inclusion of the oxygen manifold is optional, and if present, gaskets can be used to seal the oxygen channel inlets and outlets to the oxygen manifold.

[0049] In a preferred embodiment, a first gasket (referred to as a cathode gasket) may be used on the cathode side of all bipolar plates and a second gasket (referred to as an anode gasket) may be used on the anode side of all bipolar plates. Preferably, all cathode gaskets are the same (i.e., have the same shape) and all anode gaskets are the same (i.e., have the same shape). In some embodiments, a third gasket may be required for the anode current collector and a fourth gasket may be required for the cathode current collector. In other preferred embodiments, a first gasket (i.e., the gasket used on the cathode side of all plates) may be used for the cathode current collector and a second gasket (i.e., the gasket used on the anode side of all plates) may be used for the anode current collector. Separate gaskets may also be required for the end plates.

[0050] Thus, these methods preferably include the steps of adding a hydrogen manifold, adding a current collector, placing a gasket between each component, and fastening the plates, gasket, and other components together.

[0051] The single plate, bipolar plate of the present embodiment does not require welding between adjacent plates, thereby avoiding the oxidation and corrosion that occurs with conventional welded plates.

[0052] A single bipolar plate can be made thinner than conventional bipolar plates, requiring less material, reducing the overall size and / or weight of a hydrogen fuel cell stack with comparable power output to a welded stack.

[0053] A single bipolar plate can all have the same design, just with different orientations for each layer of the stack. Plate manufacturing and stack construction is less complicated. A single die-cutting machine can manufacture all the plates in a stack.

[0054] It has been found that the single plates used in embodiments of the present invention are easily and reliably sealed together using internal gaskets and MEAs.

[0055] The present invention will now be described with reference to the accompanying drawings.

[0056] For reference, referring to Figures 1 and 2, a known bipolar plate assembly includes alternating bipolar plates 1 and membrane electrode assemblies (MEAs) 2 spaced apart by gas diffusion layers 3. Each known bipolar plate 1 actually includes an anode sheet 5 of a first cell, a cathode sheet 6 of an adjacent cell, and a weld line 7 to form a bipolar plate. Thus, the anode sheet 5 and the cathode sheet 6 are welded together to form a bipolar plate, and gaskets 8 are provided on both sides of the bipolar plate.

[0057] 3 and 4, the bipolar plate 10 of the present invention is formed as a single stamped steel plate with two sides, one side forming and used as the anode side 11 in the middle of the fuel cell stack, and the other side forming and used as the cathode side 12. That is, the plates located at the top and bottom of the stack are either anodes or cathodes. The bipolar plate of the present invention further has through openings 14 at each end for sealing connection within the stack of plates to hydrogen manifolds (not shown here, shown in the figures below) at the top and bottom of the stack of plates. The openings allow H2 to flow from the inlet manifold (not shown) along the anode side of the plates in the stack to the outlet manifold (not shown) via H2 flow channels 16. Hydrogen flows vertically through the plate and leakage is prevented by gaskets (not shown here, shown in the figures below) and proton exchange membranes (not shown) between adjacent plates held in gasket channels 18. Hydrogen is prevented from flowing out of the H2 manifold openings 14 on the cathode side of the bipolar plate by an additional portion of the gasket (not shown here, but shown in the following figures) on the cathode side of the bipolar plate only. Thus, hydrogen can enter the anode side channels but not the cathode side channels. The bipolar plate of the present invention further includes air channels 17 on the cathode side 12 of the plate. Through the air channels 17, air flows laterally across the cathode side, across the width 20 of the plate. The (lateral) air flow is substantially perpendicular (transverse) to the (vertical) hydrogen flow. When looking at the plate alone (i.e., without the gasket or membrane), there is no difference (other than orientation) between the anode and cathode sides of the bipolar plate, but FIG. 4 has labeled it as the anode side 11 of the bipolar plate.

[0058] FIG. 5 shows two bipolar plates 10 of the present invention stacked on top of one another, with the top bipolar plate being partially transparent (for illustrative purposes only) to reveal the hydrogen channels (not numbered, see FIG. 4) and air channels 17a and 17b of the bottom plate. The plates are oriented in an alternating manner, i.e., adjacent bipolar plates in a fuel cell stack are rotated 180 degrees about the centerline of the plate, which is perpendicular to the surface of the plate. The channels are purposefully designed so that the air channels 17 of adjacent bipolar plates are not perfectly aligned, i.e., not aligned along their entire length, i.e., FIG. 5 shows that the air channel 17a of the top plate is vertically aligned at its edges, i.e., at the inlet and outlet, but then crosses in the opposite direction, its path repeatedly diverging and merging, and not perfectly aligned with the air channel 17b of the bottom plate. The plates are designed so that the air passages of adjacent plates (i.e., adjacent plates where one plate has been rotated relative to the next) are intentionally misaligned so that the passages of adjacent plates do not interdigitate or "nestate" with one another, thereby allowing a membrane (not shown) to be secured between adjacent plates where the underside of one plate meets the top of the other plate, eliminating the possibility of the membrane dropping or being pushed into the air passage 17, which could result in reduced airflow and / or a poor seal.

[0059] The shape of the curved flow channels is also important. The air flow channels are not straight to prevent partial shrinkage / collapse of the fuel cell stack. The bipolar plates arranged alternately in the fuel cell stack of the bipolar plates of the present invention are rotated 180 degrees. Therefore, the air flow channels on adjacent plates are not parallel, so the plates cannot nest. This is important to provide support from one plate to the next, and to prevent the air and hydrogen flow channels from being blocked by the channels on adjacent plates pressing against each other. The partially non-parallel flow channels between adjacent plates also allow the proton exchange membrane and both the anode and cathode gaskets to be tightly fixed between the adjacent plates, preventing H2 from leaking out of the cell and mixing of H2 with air in the fuel cell.

[0060] FIG. 6 shows a membrane 20 located on the anode side 11 of a bipolar plate of the present invention. The membrane extends across the width of the bipolar plate between the side gasket channels 18 (where gaskets are provided) and across the length of the bipolar plate between the H2 manifold openings 14 at either end of the bipolar plate. The membrane allows H2 to flow from the H2 manifold (not shown) longitudinally through the plate, out through the hydrogen channels (not shown), and into the H2 manifold opening at the other end of the bipolar plate without leaking out or into the cathode side of the adjacent bipolar plate.

[0061] 7 and 8 show gaskets on the anode and cathode sides, respectively, of a bipolar plate of the present invention. The anode gasket 22 runs through the outside of the bipolar plate in the gasket channels 18, preventing H2 leakage and allowing H2 to flow through the H2 channels. The cathode gasket 23 includes an additional portion 23a that prevents H2 from exiting the H2 manifold channels on the cathode side of the bipolar plate.

[0062] 9 and 10 show a cross section of a fuel cell stack taken along line A as shown in FIG. 4. Multiple bipolar plates 10 can be seen in the stack. On the underside of each is a cathode side 12 and on the upper side is an anode side 11. At the top of the stack, a membrane 20 can be seen attached to the anode side of each bipolar plate in the fuel cell stack. On the anode side of each plate, an anode gasket 22 prevents air flow, but on the cathode side of each plate, air channels 17 are open to allow air flow. It has been noted elsewhere that the air channels in adjacent bipolar plates of a fuel cell stack are not aligned along their entire length, but for ease of viewing, FIG. 9 shows a cross section where the channels are aligned.

[0063] 11 and 12 show cross sections of the fuel cell stack perpendicular to the cross section of FIG. 9, taken along line B shown in FIG. 4. A number of bipolar plates 10 can be seen in the stack, with the lower side of each being a cathode side 12 and the upper side being an anode side 11. At the top of the stack, a membrane 20 can be seen attached to the anode side of each bipolar plate in the fuel cell stack. A further portion 23a of the cathode gasket (along which the cross section is taken) prevents H2 flow at the cathode side of each plate, while the H2 flow channels 16 allow hydrogen flow at the anode side of each bipolar plate 10 in the stack. FIG. 12 further shows the anode gasket 22 in the gasket channel 18, which is to prevent air from flowing along the anode side 11 of the bipolar plates.

[0064] The H2 channels 16 in Figures 11 and 12 do not extend through the thickness of each bipolar plate 10. This is to prevent the H2 channels 16 from blocking the orthogonal air channels 17 (shown in Figures 9 and 10). The air channels 17 are punched into the bipolar plates with each channel having a depth d1, and then the orthogonal H2 channels are punched into the bipolar plates at a depth d2. The depth d2 of the H2 channels is less than the depth d1 of the air channels. At the location where the air and H2 channels intersect (on the opposing faces of the bipolar plates), the air channels are notched and narrow to a depth d1-d2. This arrangement allows air and hydrogen to flow simultaneously in mutually intersecting directions through their respective channels at the opposing faces of each bipolar plate in approximately orthogonal directions.

[0065] The bipolar plate shown in Figure 13 is an alternative embodiment of the present invention. Similar to the bipolar plates described above with reference to Figures 3-8, the bipolar plate 30 of Figure 13 is stamped and then rotated 180 degrees in alternating plates. This rotation prevents the air channels 38 from aligning and allows the cathode and anode gaskets (not shown) and proton exchange membranes (not shown) to be secured between adjacent plates. The bipolar plate of Figure 13 differs from the bipolar plate of Figures 3-8 in that the shapes of the stamped air channels are different. Otherwise, the features of the bipolar plate of Figure 13 are the same as or correspond to the features of the bipolar plate of Figures 3-8.

[0066] Figure 14 shows two bipolar plates 30 of the present invention stacked one on top of the other. The top bipolar plate is partially transparent (for illustration purposes only) so that the hydrogen channels (not numbered, see 36 in Figure 13) and air channels 38b of the bottom plate can be seen in the figure. The plate orientation is alternating, i.e. adjacent bipolar plates in a fuel cell stack are rotated 180 degrees about the centerline of the plate, which is perpendicular to the surface of the plate. The channels are purposely designed so that the air channels 38 of adjacent bipolar plates are not perfectly aligned, i.e., Figure 14 shows that the air channels 38a of the top plate are vertically aligned at their edges, i.e., at the inlet and outlet, but then cross in the opposite direction, their paths branching and merging repeatedly and not perfectly aligned with the air channels 38b of the bottom plate. The plates are designed so that the air passages of adjacent plates (i.e., one plate rotated relative to the next) are intentionally misaligned so that the passages of adjacent plates do not interdigitate or "nest" with one another. This allows a membrane (not shown) to be secured between adjacent plates where the underside of one plate meets the top of the other, eliminating the membrane from dropping or being pushed into the air passages 38, which could result in reduced airflow and / or a poor seal.

[0067] The bipolar plates shown in Figures 15a and 15b are an alternative embodiment of the invention. As described above (e.g., with reference to Figures 5 and 13), bipolar plates of the type described in Figures 3-8 and 13 are stamped and then rotated 180 degrees so that the air channels are not aligned. In the embodiment shown in Figures 15a and 15b, there is no need to rotate the bipolar plates when they are stacked. Different stamping machines were used to form bipolar plate 50 (shown in Figure 15a) and bipolar plate 60 (shown in Figure 15b). Thus, when bipolar plates 50 and 60 are alternated to form a fuel cell stack, there is no need to rotate any of the plates. Other than the pattern of air channels 57 and 67, these bipolar plates have flow channels according to the same principles as those shown in Figures 3-8. The top surface of each bipolar plate is the anode side 51, 61 and the bottom surface is the cathode side (not shown). Each bipolar plate 50, 60 has openings 54, 64 on either side connecting a hydrogen manifold (not shown) to hydrogen channels 56, 66 on the anode side of the plate. Additionally, in Figures 15a and 15b, gasket channels 58, 68 are provided to house anode gaskets 52, 62, respectively. Adjacent plates are not nested, allowing the MEA to be sealed and retained between adjacent plates.

[0068] The bipolar plate of FIG. 16 is a further alternative embodiment of the present invention. The bipolar plate 80 of FIG. 16 has a closed cathode, meaning that the cathode can be connected to an oxygen manifold. The bipolar plates of the present invention shown in FIGS. 3-8 and 13a-13b all have an open cathode, meaning that the air flow passages are not sealed. In FIG. 16, an embodiment with a closed cathode is shown. This means that the air flow passages 87 are sealed and air passes through them from openings 94 that connect to an air manifold (not shown). The closed cathode arrangement also allows for pure oxygen or air with added oxygen to pass through the air flow passages 87. In addition to the air openings 94, the bipolar plate 80 with the closed cathode arrangement also has a differently shaped gasket flow passages 88 to complement the differently shaped anode gasket 82 and cathode gasket (not shown) that the closed cathode arrangement requires. The anode gasket 82 and the cathode gasket have additional portions to seal the air openings 94 .

[0069] Figures 17a and 17b show an alternative arrangement of bipolar plates of the present invention with closed cathodes. Similar to bipolar plates 50 and 60 (shown in Figures 15a and 15b), bipolar plates 100 and 110 (shown in Figures 17a and 17b) do not need to be rotated during stacking. Instead, two separate punches are used to form the two bipolar plates 100 and 110. These bipolar plates are staggered to prevent the air channels 107 and 117 on adjacent plates from aligning when forming a fuel cell stack. Other than the shape of the air channels 107, 117, the bipolar plates 100 and 110 are identical and have the same features as the bipolar plate 80 shown in Figure 16.

[0070] 18 and 19, a fuel cell stack with bipolar plates of the present invention is shown. The fuel cell stack features a bipolar plate with an open cathode (e.g., as shown in Figs. 3-8, 13 and 15). The fuel cell stack includes a stack of bipolar plates 120 with current collector plates 123 and end plates 121 at either end of the bipolar plate staff. The fuel cell stack also features a number of different gaskets, specifically anode gasket 128 and cathode gasket (not shown) in the bipolar plate staff, current collector gasket 127, and end plate gaskets 129 at each end. Bolts 124 hold the two end plates 121 together and compress the staff to ensure a seal between the various gaskets 127, 128, and 129 and the bipolar plates / end plates in the staff to prevent gas leakage between the hydrogen and air flow paths. A hydrogen inlet 125 is shown. Through this, hydrogen is injected in a controlled manner into the hydrogen manifold and through openings (not shown) and hydrogen channels (not shown) in each bipolar plate. Additionally, an insulating layer 126 is provided between the collector plate and the end plate on each side of the staff.

[0071] 20 and 21 show a cross section through the center of the fuel cell stack of FIGS. 18 and 19 showing the air flow passages 130. In this cross section, one can see the hydrogen manifolds 131 and openings 132 in the bipolar plates 120 through which hydrogen enters and leaves the hydrogen flow passages on the anode side of the bipolar plates of the fuel cell stack. One can see the cathode gasket 136, which prevents hydrogen from leaking out of the fuel cell stack, as well as a further portion 136a of the cathode gasket, which prevents hydrogen from flowing along the cathode side of the bipolar plates in the staff. The anode gasket 137 also passes outside the hydrogen openings 132, preventing hydrogen from leaking out of the fuel cell stack while allowing hydrogen to pass through the hydrogen flow passages along the anode side of each bipolar plate.

[0072] Figures 22 and 23 show a further cross section of the fuel cell stack in the same direction as Figures 20 and 21, but through the perimeter gasket and not through the centre of the fuel cell stack. An anode gasket 135 prevents air from entering the anode side of the bipolar plates 120. Membrane and current collector gaskets 127 and 138 are provided between the stack of bipolar plates and the current collector plates 123 on each side of the stack to prevent hydrogen from leaking out of the stack of bipolar plates. Additionally, end plate gaskets 129 are provided between the current collectors 123 and the end plates 120 of the fuel cell stack.

[0073] 24 and 25 show cross sections through the center of the same fuel cell stack, taken orthogonally to the cross sections of FIGS. 20-23. Hydrogen flow paths 140 are shown through which hydrogen passes along the anode side of each bipolar plate in the fuel cell stack. Additionally, an anode gasket 128 can be seen which prevents air from entering the anode side 142 of the bipolar plates (top of these figures). Also visible is a cathode gasket 143 which prevents hydrogen from entering the cathode side of the bipolar plates (bottom of these figures). Additionally, there is a membrane between each bipolar plate which prevents hydrogen from flowing from the anode side of one bipolar plate to the cathode side of the adjacent bipolar plate.

[0074] Figures 26 and 27 show a further cross section of the fuel cell stack in the same direction as Figures 24 and 25, but through a further portion 136a of the cathode gasket adjacent the hydrogen opening. The further portion 136a of the cathode gasket prevents hydrogen from entering the cathode side of the bipolar plates. In addition, the anode gasket 135 can be seen, which prevents air from entering the anode side of the bipolar plates. These gaskets, in combination with the proton exchange membranes between each bipolar plate, are important in ensuring the separation of air and hydrogen within the fuel cell stack.

[0075] 28-40 show an alternative embodiment of the present invention. Referring first to FIGS. 28 and 29, a bipolar plate 200 is formed as a single stamped plate having two sides. As in the above embodiment, the first side is the anode side 211 and the other side is the cathode side 212. The bipolar plate has openings 214 at each end which form a hydrogen manifold when multiple plates are sealed and stacked. Hydrogen can flow from an inlet manifold (not shown) through hydrogen inlet channels 216a, via main hydrogen channels 216b (formed, for example, as notches in the air channels) and anode valleys 221 (formed as a result of the air channels on the cathode side of the plate), through hydrogen outlet channels 216c, and into an outlet manifold (not shown). While the hydrogen inlet and outlet channels in this embodiment are located on one side of the bipolar plate, they could be uniformly distributed along the width of the openings 214 instead of being located on one side of the bipolar plate. Hydrogen is only allowed to flow through the anode side of the plates due to a cathode gasket (not shown) that seals the hydrogen manifold on the cathode side of the bipolar plates.

[0076] The bipolar plate in this embodiment further includes air channels 217 through which air (and therefore oxygen) can flow on the cathode side 212 of the plate in a direction generally perpendicular to the hydrogen flow. The interaction of the anode gasket feature 220 with the anode gasket (not shown here, but shown in the following figures) prevents air flow on the anode side of the bipolar plate. The anode gasket feature is a stamped out portion of the bipolar plate that has a raised profile on the anode side of the bipolar plate. The anode gasket feature is not connected to the anode valley 221. Thus, when the anode gasket is compressed between the anode gasket feature 220 and the MEA (not shown), the anode side is sealed and air flow on the anode side of the bipolar plate is prevented.

[0077] During stacking, alternate plates are rotated 180 degrees to prevent stacking of air channels between adjacent plates and to allow the MEA (not shown) to be held between adjacent plates.

[0078] Figures 30 and 31 show anode and cathode gaskets located on the anode and cathode sides, respectively, of a bipolar plate of the present invention. These figures should be understood in conjunction with Figures 32a-c, which show the anode gasket, cathode gasket, and end plate gasket, in order. As mentioned above, the anode gasket 230 is sealed between the anode gasket feature (not shown here but shown in the figures above) on the anode side 211 of the plate and the MEA (not shown). The anode gasket is looped with a continuous thickness.

[0079] A cathode gasket 235 seals between the cathode side 212 of the plate and the MEA (not shown) to prevent hydrogen from flowing out of the openings 214 on the cathode side of the plate. The cathode gasket has a shape that complements the hydrogen inlet / outlet channels 216a, 216c. In the preferred embodiment as shown here, there is rotational symmetry between the hydrogen inlet channel 216a and the hydrogen outlet channel 216c. This allows the same cathode gasket 235 to be used for the openings 214 on both ends of the plate.

[0080] End plate gaskets 237 may be provided at one or both ends of the fuel cell stack (not shown) to seal the hydrogen manifold (not shown). For example, if the hydrogen manifold inlets and outlets are located on the same side of the fuel cell stack, then two end plate gaskets 237 would be required between the current collector plates and end plates on the same side of the fuel cell stack to seal the openings (not shown). In this example, no end plate gaskets are required between the current collector plates and end plates on opposite sides of the fuel cell stack. In another embodiment, it is envisioned that the hydrogen manifold inlets and outlets may be provided on opposite sides of the fuel cell stack, in which case one end plate gasket would be required between the current collector plates and end plates on both sides of the fuel cell stack to seal the openings.

[0081] FIG. 33 (and corresponding color diagram 37) shows a cross section of the anode gasket features of two adjacent bipolar plates 200 (the cross section is taken along line A in FIG. 29). In this view, the top side of each plate is the anode side 211 and the bottom side of each plate is the cathode side 212. Air channels 217 can be seen on the cathode side of each bipolar plate. The air channels border the cathode side of the bipolar plate and the MEA 238. Anode gasket features 220 are provided which provide a seal between the anode side 211 of each bipolar plate and the anode gasket 230, thus preventing air from entering the anode side of the bipolar plate.

[0082] Figure 34 (and corresponding color diagram 38) shows an edge view of the fuel cell stack from the same direction as the cross section of Figure 33, but without cutting through the anode gasket feature. Thus, it can be seen that the anode gasket feature 220 is not sealed and connected to the anode valleys 221, allowing the anode gasket feature to contact the anode gasket 230 and seal the anode side 211 (the top side of each plate in this view) from air. Air channels 217 can be seen on the cathode side 212 (the bottom side of each plate in this view) allowing oxygen-laden air to flow on the cathode side of each plate.

[0083] FIG. 35 (and corresponding color diagram 39) shows a cross section of the hydrogen inlet channels of two adjacent bipolar plates 200 (the cross section is taken along line B in FIG. 29). Hydrogen inlet channels 216a can be seen in each bipolar plate. The hydrogen inlet channels are formed between the anode side (top in this view) of each bipolar plate and the MEA 238. Hydrogen is prevented from entering the cathode side (bottom in this view) of each bipolar plate by a cathode gasket 235, which has a shape corresponding to the shape of the hydrogen inlet channels and is sealed between the cathode side of the plate and the MEA 238. Also visible are anode gasket features 220 in each bipolar plate and an anode gasket 230 between the two bipolar plates.

[0084] Figure 36 (and corresponding color diagram 40) shows a cross section taken along line C in Figure 29 through the center of two bipolar plates 200. Hydrogen flow channels 216b can be seen on the anode side (top of this diagram) of each bipolar plate. An MEA 238 can be seen disposed between the two bipolar plates. Because the cross section is taken through the edge of the bipolar plates, anode gasket features 220 and anode gasket 230 can be seen on each plate.

[0085] In use, hydrogen is pumped into the hydrogen manifold and then through an opening on one side of the fuel cell stack. It then flows through the H2 flow channels along the anode side of each bipolar plate in the stack. On the opposite side, there is an outlet manifold, allowing unused hydrogen to be recirculated. Hydrogen is prevented from entering the channels on the cathode side of each plate by the cathode gasket. During its passage through the anode, the H2 is converted to H2 over a catalyst (which may be part of or integrated into the MEA). + ions (protons). The protons then pass through the proton exchange membrane and combine with oxygen and electrons on the cathode catalyst to produce water. Hydrogen to H + The electrons produced by the conversion to ions travel through an external circuit (not shown) to a current collector where the electricity is collected. A current collector is provided at each end of the fuel cell stack.

[0086] The air flow can occur passively. Concurrent with the controlled hydrogen flow, a fan can force air through the approximately orthogonal air passages on the cathode side of each bipolar plate. Air is prevented from entering the anode side of each plate by the anode gasket. The air flow provides oxygen to the cathode, which converts oxygen to O by combining with electrons on the cathode catalyst (not shown). 2- It is converted to ions. 2- Ion is H + The water produced by combining with the ions exits the fuel cell as water vapor in the air flow path.

[0087] Between each bipolar plate of the fuel cell stack of the present invention, a membrane exchange assembly (MEA) is provided. MEAs are conventionally known in the art and typically include, in order, a first gas diffusion layer (GDL), an anode catalyst, a proton exchange membrane, a cathode catalyst, and a second gas diffusion layer (GDL). Each of these layers is conventionally known in the art. In the fuel cell stack of the present invention, the first GDL (adjacent to the anode catalyst of the MEA) will be adjacent to the anode side of the first bipolar plate 10, and the second GDL (adjacent to the cathode catalyst of the same MEA) will be adjacent to the cathode side of the second bipolar plate. Other configurations of MEAs are known and can be used with the bipolar plates of the present invention, for example, the GDL layer and the catalyst layer can be combined into one layer.

[0088] In making the plates and stacks, a single punch can be used to make multiple plates, rotate each adjacent plate 180 degrees relative to the previous plate, place the MEA between the adjacent plates, and seal the adjacent plates to each other with a gasket. Alternatively, two different punches can be used, with the bipolar plates made by each punch stacked on top of each other. Using two different punches eliminates the need to rotate adjacent plates. An additional advantage of using two different punches is that the cathode flow field can be made uniform, eliminating the unused space in the center of the bipolar plate that would be required if a single punch were used. The channels on the faces of the plates create sealed channels for hydrogen and oxygen, while the gasket and the MEA compressed between the plates keep the hydrogen and oxygen channels separated and the hydrogen channels sealed. This prevents leakage between the channels. The stack of plates is held tightly by clamps or the outer fuel stack body. Current collectors are attached to the anode and cathode ends of the stack, respectively. The hydrogen flow paths are sealed to provide one hydrogen inlet at one end of the stack and one hydrogen outlet at the other end. Hydrogen manifolds are attached and sealed to both the inlet and outlet to allow control of hydrogen flow through the hydrogen flow paths, as is conventionally known in fuel cells, but is not part of this invention.

[0089] In the illustrated embodiment, oxygen (contained in air) flows freely through and into the oxygen channels (air channels) on the cathode side of the plates, while access for hydrogen to the anode side is controlled via a manifold and gas flow control system such that the fuel cell operates to generate electricity. It will be understood that the hydrogen channels refer to gas channels that contain or consist of hydrogen, and the oxygen channels refer to gas channels that contain or consist of oxygen (particularly in air).

[0090] In another embodiment, an oxygen manifold (or air manifold) is also provided to control the inflow of oxygen (or air) and the outflow of water. In this alternative embodiment, both the oxygen manifold and the oxygen flow passages are sealed by manifolds, and the gas flows are controlled by valves at the respective gas inlets and outlets.

[0091] The present invention therefore provides a bipolar plate, a hydrogen fuel cell unit including the plate, and a method of manufacturing the same.

Claims

1. A hydrogen fuel cell unit comprising, in order: (i) a first bipolar plate having a front and a back surface, the back surface being the anode of the unit; (ii) a first membrane electrode assembly; and (iii) a second bipolar plate having a front surface and a back surface, the front surface being the cathode of the unit and the back surface being the anode of the unit; a second bipolar plate, the first membrane electrode assembly being between the first bipolar plate and the second bipolar plate, with a flow path for hydrogen flow between the back surface of the first bipolar plate and the first membrane electrode assembly, and a flow path for oxygen flow between the front surface of the second bipolar plate and the first membrane electrode assembly; (iv) a second membrane electrode assembly; and (v) a third bipolar plate having a front surface and a back surface, the front surface being the cathode of the unit; a third bipolar plate, the second membrane electrode assembly being between the second bipolar plate and the third bipolar plate, with a flow path for hydrogen flow provided between the back surface of the second bipolar plate and the second membrane electrode assembly, and a flow path for oxygen flow provided between the front surface of the third bipolar plate and the second membrane electrode assembly; The bipolar plates have oxygen flow paths for oxygen flow, and the oxygen flow paths of adjacent plates repeatedly branch and merge across the plates; the bipolar plate further comprises hydrogen flow paths for flowing hydrogen, the hydrogen flow paths and the oxygen flow paths substantially intersecting each other; A hydrogen fuel cell unit wherein the oxygen flow paths are formed by depressions in the bipolar plates and the crossing hydrogen flow paths include notches in the depressions that form the oxygen flow paths, or vice versa, wherein the hydrogen flow paths are formed by depressions in the bipolar plates and the crossing oxygen flow paths include notches in the depressions that form the hydrogen flow paths.

2. 10. The hydrogen fuel cell unit of claim 1, wherein the oxygen flow channels of adjacent plates diverge and converge in a crisscross pattern across the plates.

3. 3. The hydrogen fuel cell unit of claim 1 or 2, wherein the oxygen flow paths branch and merge in a regular pattern.

4. 4. A hydrogen fuel cell unit as described in any one of claims 1 to 3, wherein each oxygen flow path comprises an inlet and an outlet and a conduit between the inlet and the outlet, and the oxygen conduits of adjacent plates within the fuel cell are not aligned vertically along their entire length so that the adjacent plates do not nest when held in a stack that is part of the fuel cell unit.

5. 5. The hydrogen fuel cell unit of claim 4, wherein the membrane electrode assembly is fixed in position between the bipolar plates.

6. 6. A hydrogen fuel cell unit as described in any one of the preceding claims 1 to 5, wherein the plates are provided with channels for the flow of hydrogen, each channel having an inlet and an outlet, and the inlets and outlets of the hydrogen channels of adjacent plates of the fuel cell are vertically aligned.

7. 7. The hydrogen fuel cell unit of claim 1, wherein the hydrogen flow paths further comprise conduits between their inlets and outlets, the conduits of the flow paths of adjacent plates of the fuel cell not being vertically aligned along their entire lengths.

8. 8. The hydrogen fuel cell unit of claim 1, wherein each of the oxygen channels has an inlet and an outlet, and the inlets and outlets of the oxygen channels of adjacent plates of the fuel cell are vertically aligned.

9. 9. A hydrogen fuel cell unit according to any preceding claim, wherein when the plates are stacked vertically one above the other, a horizontal cross section of any plate passes through both a hydrogen flow path and an oxygen flow path.

10. 10. The hydrogen fuel cell unit according to claim 1, wherein the first bipolar plate and / or the second bipolar plate and / or the third bipolar plate are not rotationally symmetrical about a line passing through the center of the plates in the vertical direction of stacking the plates.

11. A hydrogen fuel cell unit as described in claim 10, wherein the first bipolar plate and / or the second bipolar plate and / or the third bipolar plate have two or more manifold openings, and the manifold openings on each plate are rotationally symmetric.

12. A hydrogen fuel cell unit as described in any one of claims 1 to 11, wherein each of the first bipolar plate, the second bipolar plate, and the third bipolar plate has the same design.

13. 13. The hydrogen fuel cell unit of claim 12, wherein adjacent bipolar plates are rotated 180 degrees relative to each other.

14. A bipolar plate having a plurality of hydrogen flow paths and a plurality of oxygen flow paths, said bipolar plate being usable in the manufacture of a hydrogen fuel cell unit as defined in any one of claims 1 to 13, and said bipolar plate being punched from a single sheet of metal or alloy.

15. A method for manufacturing a bipolar plate, comprising: (i) providing a sheet of metal or alloy; (ii) punching the sheet to form a bipolar plate having a plurality of hydrogen channels and a plurality of oxygen channels; Including, 14. A method in which the bipolar plate can be used to form a hydrogen fuel cell unit according to any one of claims 1 to 13.

16. 1. A method for manufacturing a hydrogen fuel cell, comprising: (i) providing a first bipolar plate having a front surface and a back surface, the back surface being an anode, and a second bipolar plate having a front surface and a back surface, the front surface being a cathode and the back surface being an anode; (ii) disposing a first membrane electrode assembly between the first bipolar plate and the second bipolar plate; When the first membrane electrode assembly is between the first bipolar plate and the second bipolar plate, a flow channel is provided between the back surface of the first bipolar plate and the first membrane electrode assembly for the flow of hydrogen, and a flow channel is provided between the front surface of the second bipolar plate and the first membrane electrode assembly for the flow of oxygen; (iii) providing a third bipolar plate having a front surface and a back surface, the front surface being a cathode; (iv) disposing a second membrane electrode assembly between the second bipolar plate and the third bipolar plate; Including, When the second membrane electrode assembly is between the second bipolar plate and the third bipolar plate: a flow path for hydrogen flow is provided between the back surface of the second bipolar plate and the second membrane electrode assembly; a flow path for oxygen flow is provided between the front face of the third bipolar plate and the second membrane electrode assembly; and the flow paths for the hydrogen flow and the flow paths for the oxygen flow substantially intersect each other; the bipolar plate has hydrogen flow paths for flowing hydrogen and oxygen flow paths for flowing oxygen, the hydrogen flow paths and the oxygen flow paths substantially intersecting each other; The method wherein the oxygen flow paths are formed by depressions in the bipolar plate and the crossing hydrogen flow paths include notches in the depressions that form the oxygen flow paths, or vice versa, wherein the hydrogen flow paths are formed by depressions in the bipolar plate and the crossing oxygen flow paths include notches in the depressions that form the hydrogen flow paths.

17. 17. The method of claim 16, wherein the bipolar plates all have the same design, with adjacent plates rotated 180 degrees relative to each other.

Images