Microjet reactant delivery system for use in fuel cells

Abstract

A new reactant delivery system for delivering reactants to the membrane electrode assembly of a fuel cell. The invention uses a plurality of small holes to propel high-velocity streams of reactant gases (“microjets”) against an impingement plate. The microjets assist in catalyzing the reactant gases and forcing them toward the proton exchange membrane. Reactant gas flow is primarily perpendicular to the orientation of the proton exchange membrane, thereby enhancing diffusion rates. In addition, each microjet acts like an expansion valve, which significantly cools the flowing gas and provides internal heat absorption. This internal heat absorption permits higher energy densities in the fuel cell.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view, showing a prior art fuel cell.

FIG. 2 is a detailed elevation view, showing a membrane electrode assembly.

FIG. 3 is an exploded perspective view, showing a simplified physical embodiment of a prior art fuel cell.

FIG. 4 is an exploded perspective view, showing the oxidant delivery system of a fuel cell made according to the present invention.

FIG. 4B is an exploded perspective view, showing the fuel cell of FIG. 4 with the fuel delivery system added.

FIG. 5 is a detail view, showing details of the microjet plate.

FIG. 6 is a hidden line view, showing the impingement plate laid over the microjet plate.

FIG. 6B is a hidden line view, showing details of how the microjets align with the webs in the impingement plate.

FIG. 7 is a perspective view with a cutaway, showing the interaction of the microjet plate with the impingement plate.

FIG. 7B is a section elevation view, showing the operation of the microjets.

FIG. 8 is an exploded perspective view, showing the stacking of the retaining plate, the impingement plate, and the microjet plate.

FIG. 8B is an exploded perspective view, showing the stacking of the retaining plate, the impingement plate, and the microjet plate from the opposite side.

FIG. 9 is an exploded perspective view, showing how to create a stacked fuel cell using the present invention.

FIG. 10 is an exploded perspective view, showing how to create a stacked fuel cell using the present invention.

FIG. 11 is an exploded perspective view, showing an alternate embodiment of the present invention.

FIG. 12 is a section view, showing an alternate embodiment of the present invention.

REFERENCE NUMERALS IN THE DRAWINGS
10	fuel cell	12	anode
14	proton exchange membrane	16	cathode
18	hydrogen inlet	20	oxygen inlet
22	electrical load	24	electron flow
26	membrane electrode assembly	30	hydrogen manifold
32	oxygen manifold	34	serpentine passage
36	retaining plate	38	impingement plate
41	waste product hole	40	microjet plate
42	mounting hole	43	conduit hole
44	oxygen stagnation chamber	45	end plate
46	microjet hole	47	hydrogen stagnation
			chamber
48	exhaust hole	49	center-to-center line
50	web	52	gas flow
54	impingement plate recess	61	thinned section
63	microjet	73	waste product channel
80	oxygen manifold	82	oxygen supply line
84	stagnation chamber	86	microjet plate
88	impingement plate	90	load
92	oxygen electrode	94	proton exchange membrane
96	hydrogen electrode	98	hydrogen manifold
100	hydrogen supply line	102	aqueous chamber
104	threaded connector	108	alkaline solution

DETAILED DESCRIPTION OF THE INVENTION

FIG. 4 shows a fuel cell incorporating the present invention. Membrane electrode assembly 26 is essentially the same as for the prior art. The example uses hydrogen (fuel) and oxygen (oxidizer) as the reactants. As for the prior art, the MEA must be sandwiched between two manifolds delivering ionized gaseous reactants. However, the method of delivering the reactants is substantially different.

FIG. 4 shows the MEA and the oxygen delivery components. The components are shown in an exploded view. When they are assembled they are all tightly clamped together using external clamping plates (not shown).

Retaining plate 36 clamps against the far side of the MEA. It retains impingement plate 38 in the correct position again microjet plate 40 when microjet plate 40 is clamped against the retaining plate. Oxygen manifold 32 is then clamped against the back side of the microjet plate. End plate 45 seals the far side of oxygen manifold 32 to form oxygen stagnation chamber 44. In operation, pressurized oxygen is fed in through oxygen inlet 20. The pressurized oxygen within oxygen stagnation chamber 44 is then forced through a plurality of microjet holes 46 in microjet plate 40.

The flow assumes the form of high velocity microjets. These impinge upon impingement plate 38, in an arrangement to be described in more detail subsequently. The gas flow then passes through exhaust holes in the impingement plate and then to the MEA. Once the oxygen leaves the oxygen stagnation chamber, it generally flows in a direction which is perpendicular to the plane of the proton exchange membrane.

The catalyst is evenly distributed on the outward-facing surfaces of the MEA. A gas diffusion layer (GDL) may also be included on the MEA, though the use of the microjet-based delivery approach will likely eliminate the need for this component.

Numerous additional components have been omitted for visual clarity. Each of the components includes a conduit hole 43 in the middle of each side and an exhaust hole 41 proximate each corner. The conduit holes house appropriately positioned electrical conductors which carry the electrical current to an external load (as well as possibly hooking up successive cells in a series connection). Waste product holes 41 house components for carrying away waste products.

Gaskets would be employed between the various layers to prevent gas leakage. Other hardware is needed to channel the water formed and to retain the proper saturation level for the MEA. All these components are well known to those skilled in the art and—accordingly—they have not been illustrated.

In FIG. 4B, the MEA and the oxygen delivery components have been clamped together. The hydrogen delivery components are shown in exploded form. The reader will observe that the hydrogen components are simply the oxygen components rotated 180 degrees and attached to the opposite side of the MEA. Hydrogen manifold 30 is closed by an end plate 45, which forms hydrogen stagnation chamber 47. The hydrogen manifold clamps against the back of microjet plate 40. The microjet plate clamps against impingement plate 38, which is retained in the proper position by retaining plate 36. All the hydrogen components are then clamped against the side of the MEA which faces the viewer. The result is a completed fuel cell having one set of electrodes. The fuel cell can be stacked to form a multi-cell unit as for the prior art. The type of stacking will be explained subsequently.

Of course, those skilled in the art will realize that the microjet sizes may need to be adjusted for different reactants. Thus, while the oxygen and hydrogen microjet plates may appear to be the same, the hole sizes and separations may in fact be different.

FIG. 5 shows a detail view of a portion of microjet plate 40. The reader will observe how the thinned section in the middle of the plate is pierced by many microjet holes 46. FIG. 6 is a hidden line view showing how impingement plate 38 lies over microjet plate 40. Impingement plate 38 includes a plurality of exhaust holes 48. The array of microjets 46 are positioned to be directly beneath the webs between the exhaust holes in the impingement plate. FIG. 6 clearly shows this alignment.

FIG. 6B shows the alignment in greater detail. The exhaust holes are preferably placed in a geometric pattern. Center-to-center line 49 connects the centers of adjacent exhaust holes (12 of these are shown as phantom lines in the view). Each microjet hole 46 preferably lies beneath the middle of a center-to-center line, which places each microjet hole in the center of a web 50 between adjacent exhaust holes. This alignment ensures that the microjet produced will strike a solid portion of the impingement plate, but that the “strike” will also be close to at least two exhaust holes.

FIG. 7 shows a perspective view of impingement plate 38 lying over microjet plate 40 with a cutaway added to show internal details. The cutaway is angled to pass through several microjet holes 46. Pressurized oxygen within oxygen stagnation chamber 44 is forced through these holes and against impingement plate 38. A gap exists between the microjet and impingement plates, since the microjet holes are formed in thinned section 61.

FIG. 7B shows a section view through two adjacent microjet holes 46. The pressurized oxygen flowing through each of these small holes creates a microjet 63. The microjet strikes the impingement plate and diffuses the gas at high velocity. Gas flow 52 then flows through exhaust holes 48 toward the membrane electrode assembly which lies adjacent to the impingement plate. The flowing gas then reacts with the catalyst on the MEA.

Each microjet hole acts like a small expansion valve. The gas within oxygen stagnation chamber 44 is essentially stagnant. As the gas flows through the microjet hole, it accelerates to high velocity. A pressure and temperature drop results from the Bernoulli effect. Thus, if the gas enters the stagnation chamber at room temperature, it will be substantially cooled by passing through the microjets. The temperature of the flowing gas recovers to near-ambient conditions after striking the impingement plate and then flowing into the MEA. Thus, the gas entering the MEA is back to near-ambient conditions. However, this near-ambient gas is flowing directly into the point of maximum heat generation (where the reaction is occurring in the outer regions of the MEA). This fact means that cooling is provided exactly where it is needed.

In addition, the cooling is provided in a very even and controlled manner across the entire face of the MEA. Localized “hot spots” are thereby minimized. This cooling phenomenon allows the operation of fuel cells having a higher energy density. This allows a faster reactant delivery (and more extracted power) without exceeding the fuel cell's temperature limit.

The cooling mechanism also allows inexpensive materials to be used for many of the components, since high temperatures will no longer be a problem. Some or all of the components in the reactant delivery systems can be made of relatively inexpensive thermoplastics.

The even gas distribution provided by the microjet delivery system also ensures a uniform gas distribution to the catalyst on the MEA. The catalyst is thereby uniformly consumed, which means that a lesser total amount of catalyst will be needed than for the prior art devices.

FIG. 8 shows an exploded view of retaining plate 36, impingement plate 38, and microjet plate 40. Many different geometric arrangements can be made between the microjet array and the impingement plate. The alignment of the microjet holes with the webs on the impingement plate is only one effective example. However, whatever alignment is chosen, it is significant that the alignment be maintained by fixing the position of the impingement plate relative to the microjet plate. In FIG. 8, the reader will observe that the side of the retaining plate which faces the impingement plate includes impingement plate recess 54. This fits around the perimeter of the impingement plate and secures it in position.

FIG. 8B shows the same assembly from the other side. Four waste product channels 73 are contained in the side of retaining plate 36 which faces the MEA. These can be used to carry waste products to the four waste product holes 41 which carry away water in the case of a hydrogen/oxygen fuel cell.

Those skilled in the art will know that PEM fuel cells produce a relatively low electrical potential across each individual membrane electrode assembly. Thus, prior art cells are typically stacked in series in order to increase the voltage which is ultimately extracted from the stacked cells. The assembly of several mated fuel cells is actually referred to as a “stack.” The nature of the prior art fuel cells, such as shown in FIG. 3, allows the stacking to proceed positive-negative-positive-negative by simply connecting adjoining cells together.

The structure of the present invention suggests a different arrangement. FIG. 9 shows a single oxygen manifold 32 being used to feed two microjet plates 40 (facing in opposite directions). Each microjet plate feeds through an impingement plate and to a membrane electrode assembly 26.

In FIG. 10, all the components shown in FIG. 9 have been clamped together into the unified “block” shown in the middle. The two MEAs 26 then form the outward facing portions. FIG. 10 shows a pair of exploded hydrogen supply components in position and ready to be clamped onto the central block.

Once all the components are clamped together, the pair of hydrogen manifolds 30 will feed hydrogen through microjet and impingement plates through to the two MEAs. The polarity of this assembly will then be negative-positive-positive-negative, so it is not possible to simply connect adjacent portions together in series. Instead, alternating bus bar arrangements must be made in order to create the positive-negative-positive-negative arrangement needed to obtain higher voltages. These bus bars are housed within the conduit holes.

Since the stack will not have the conventional positive-negative-positive-negative arrangement, it may be undesirable to use graphite for the manifolds (which would make the manifolds themselves act as the electrodes. Separate electrodes may be preferable. These will be porous components likely formed on the outer surfaces of the MEA itself. The bus bars will then be used to conduct the electricity out of each cell.

Of course, the stack shown in FIG. 10 is not limited to two cells. Two more microjet and MEA assemblies can be substituted for the end plates and the stack can be extended in both directions for many additional cells. These principles are well understood by those skilled in the art and are therefore not further illustrated.

Another embodiment of the present invention is illustrated in FIGS. 11 and 12. In this embodiment an electrolytic, alkaline solution is used on one side of the assembly to carry positively charged hydrogen protons to the proton exchange membrane. As illustrated in FIG. 11, the assembly includes oxygen manifold 80 having stagnation chamber 84 which is fluidly connected to oxygen supply line 82. Microjet plate 86, impingement plate 88, oxygen electrode 92, and proton exchange membrane 94 are arranged in the same configuration as previously described.

Hydrogen manifold 98 has aqueous chamber 102 which contains the electrolytic, alkaline solution. Hydrogen electrode 96 is attached to hydrogen supply line 100 by threaded connector 104. Hydrogen electrode 96 and oxygen electrode 92 are connected to an electrical circuit including load 90.

FIG. 12 illustrates the assembly of FIG. 11 in an assembled state. It is sectioned in half to aid visualization. Microjet plate 86, impingement plate 88, oxygen electrode 92 and proton exchange membrane 94 are sandwiched together between oxygen manifold 80 and hydrogen manifold 98 (as for the previously-described embodiments). Alkaline solution 108 fills the aqueous chamber. It is important that the alkaline solution have a pH of at least about 12.0 or greater for effective operation of the fuel cell. A 1 molar solution of potassium hydroxide in water is particularly effective.

Oxygen is fed to stagnation chamber 84 through oxygen supply line 82. The oxygen is forced through microjet holes in microjet plate 86 and diffused by impingement plate 88 as previously described.

Hydrogen is fed through hydrogen supply line 100 to hydrogen electrode 96. The hydrogen electrode includes a hollow interior which feeds the hydrogen gas out through perforations extending through its wall (shown best in FIG. 12). Electrons are stripped off of the hydrogen molecules and pass through the electrical circuit and load 90. The positively charged hydrogen protons are then able to pass through proton exchange membrane 94 where they react with oxygen to form water. The water is then transmitted out of the assembly through an exhaust port. Because the reaction occurs on the oxygen side of the membrane, the water does not dilute alkaline solution 108.

The readers should bear in mind that the structure shown for the hydrogen electrode is meant to be representative rather than an actual working version. In reality, the diameter of the perforations would likely be much smaller (and therefore harder to see in the illustrations). The size and shape of the hydrogen electrode might be substantially different as well. None of these modifications would alter the invention's structural nature.

The preceding description contains significant detail regarding the novel aspects of the present invention. It should not be construed, however, as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. As one example, new proton exchange membranes are being developed which do not require humidification in order to be effective. The present invention could function with these newer “dry” membranes just as well as for the “wet” membranes described in the examples. Accordingly, the scope of the invention should be fixed by the following claims, rather than by the examples given.

Claims

1. A fuel cell for reacting a first reactant with a second reactant comprising: a. an exchange membrane having a first side and a second side;b. a first input being configured to supply said first reactant to said fuel cell on said first side of said exchange membrane;c. a second input being configured to supply said second reactant to said fuel cell on said second side of said exchange membrane;d. a first stagnation chamber located on said first side of said exchange membrane, being configured to receive said first reactant from said first input;e. a first microjet plate located on said first side of said exchange membrane, said first microjet plate bounding said first stagnation chamber and comprising a plurality of microjet openings passing through said first microjet plate;f. a first impingement plate located on said first side of said exchange membrane and lying between said exchange membrane and said first microjet plate, said first impingement plate having a surface containing a plurality of exhaust openings and a plurality of webs lying between said plurality of exhaust openings; andg. wherein said plurality of microjet openings in said first microjet plate and said plurality of webs in said first impingement plate are positioned so that each gas microjet produced by each of said plurality of microjet openings strikes one of said plurality of webs, and the decelerated gas thereafter flows through said plurality of exhaust openings in said first impingement plate toward said exchange membrane.

2. A fuel cell as recited in claim 1, wherein said first reactant is oxygen and said second reactant is hydrogen.

3. A fuel cell as recited in claim 1, further comprising: a. a second stagnation chamber located on said second side of said exchange membrane, being configured to receive said second reactant from said second input;b. a second microjet plate located on said second side of said exchange membrane, said second microjet plate bounding said second stagnation chamber and comprising a plurality of microjet openings passing through said second microjet plate;c. a second impingement plate located on said second side of said exchange membrane and lying between said exchange membrane and said second microjet plate, said second impingement plate having a surface containing a plurality of exhaust openings and a plurality of webs lying between said plurality of exhaust openings; andd. wherein said plurality of microjet openings in said second microjet plate and said plurality of webs in said second impingement plate are positioned so that each gas microjet produced by each of said plurality of microjet openings strikes one of said plurality of webs, and the decelerated gas thereafter flows through said plurality of exhaust openings in said second impingement plate toward said exchange membrane.

4. A fuel cell as recited in claim 3, wherein said first reactant is oxygen and said second reactant is hydrogen.

5. A fuel cell as recited in claim 1, further comprising: a. an aqueous chamber located on said second side of said exchange membrane, said aqueous chamber configured to receive and contain an alkaline solution; andb. an electrode located within said aqueous chamber, being configured to diffuse said second reactant into said alkaline solution within said aqueous chamber.

6. A fuel cell as recited in claim 5, wherein said first reactant is oxygen and said second reactant is hydrogen.

7. A fuel cell as recited in claim I, further comprising: a. an aqueous chamber located on said second side of said exchange membrane;b. wherein said aqueous chamber is filled with an alkaline solution; andc. an electrode located within said aqueous chamber, being configured to diffuse said second reactant into said alkaline solution within said aqueous chamber.

8. A fuel cell as recited in claim 7, wherein said first reactant is oxygen and said second reactant is hydrogen.

9. A fuel cell as recited in claim 7, wherein said alkaline solution has a pH of at least about 12.0.

10. A fuel cell as recited in claim 7, wherein said alkaline solution is about a 1 molar solution.

11. A fuel cell as recited in claim 7, wherein said alkaline solution is potassium hydroxide.

12. A fuel cell as recited in claim 8, wherein said alkaline solution has a pH of at least about 12.0.

13. A fuel cell as recited in claim 8, wherein said alkaline solution is about a 1 molar solution.

14. A fuel cell as recited in claim 8, wherein said alkaline solution is potassium hydroxide.

15. A fuel cell for reacting a first reactant with a second reactant comprising: a. an exchange membrane having a first side and a second side;b. a first input being configured to supply said first reactant to said fuel cell on said first side of said exchange membrane;c. a second input being configured to supply said second reactant to said fuel cell on said second side of said exchange membrane;d. a first stagnation chamber located on said first side of said exchange membrane, being configured to receive said first reactant from said first input;e. a first microjet member located on said first side of said exchange membrane, said first microjet member being fluidly connected to said first stagnation chamber and comprising at least one microjet opening passing through said first microjet member;f. a first impingement member located on said first side of said exchange membrane and lying proximate said first microjet member, said first impingement member having a surface containing at least one exhaust opening and at least one solid portion; andg. wherein said at least one microjet opening in said first microjet member and said at least one solid portion in said first impingement member are positioned so that a gas microjet produced by said at least one microjet opening in said first microjet member strikes said at least one solid portion of said first impingement member, and the decelerated gas thereafter flows through said at least one exhaust opening in said first impingement member toward said exchange membrane.

16. A fuel cell as recited in claim 15, further comprising: a. a second stagnation chamber located on said second side of said exchange membrane, being configured to receive said second reactant from said second input;b. a second microjet member located on said second side of said exchange membrane, said second microjet member being fluidly connected to said second stagnation chamber and comprising at least one microjet opening passing through said second microjet member;c. a second impingement member located on said second side of said exchange membrane and lying proximate said second microjet member, said second impingement member having a surface containing at least one exhaust opening and at least one solid portion; andd. wherein said at least one microjet opening in said second microjet member and said at least one solid portion in said second impingement member are positioned so that a gas microjet produced by said at least one microjet opening in said second microjet member strikes said at least one solid portion of said second impingement member, and the decelerated gas thereafter flows through said at least one exhaust opening in said second impingement member toward said exchange membrane.

17. A fuel cell as recited in claim 15, further comprising: a. an aqueous chamber located on said second side of said exchange membrane, said aqueous chamber configured to receive and contain an alkaline solution; andb. an electrode located within said aqueous chamber, being configured to diffuse said second reactant into said alkaline solution within said aqueous chamber.

18. A fuel cell as recited in claim 17, wherein said first reactant is oxygen and said second reactant is hydrogen.

19. A fuel cell as recited in claim 15, further comprising: a. an aqueous chamber located on said second side of said exchange membrane;b. wherein said aqueous chamber is filled with an alkaline solution; andc. an electrode located within said aqueous chamber, being configured to diffuse said second reactant into said alkaline solution within said aqueous chamber.

20. A fuel cell as recited in claim 15, wherein said first reactant is oxygen and said second reactant is hydrogen.