METHOD FOR MINIMIZING CARBON CORROSION IN A FUEL CELL SYSTEM AND FUEL CELL SYSTEM DESIGNED FOR THIS PURPOSE

Abstract

Method for minimizing carbon corrosion in a fuel cell system (100), wherein the method comprises the steps that: a fuel cell stack (110) is provided with a plurality of fuel cells (112), each of the fuel cells (112) having an electrolyte membrane (12) arranged between an anode and a cathode; an anode supply distributor (118) and an anode discharge collector (120) are provided in fluid communication with the anodes of the fuel cells (112), wherein the anode supply distributor (118) is in fluid communication with a hydrogen gas source (132); a shutdown procedure is carried out in which hydrogen gas (119) is present in the anodes and the cathodes after shutdown; and a blower (124, 126, 128, 130) is provided in fluid communication with the anodes of the fuel cells (112) to generate a flow over the anodes after shutdown; characterized in that the blower (124, 126, 128, 130) is articulated to the anode supply distributor (118), an anode inlet line (134), the anode discharge collector (120) and / or an anode discharge line (142).

Description

FIELD OF THE INVENTION

[0001] The invention relates to hydrogen fuel cells. In particular, the invention relates to a fuel cell system according to the preamble of claim 5 and a method according to the preamble of claim 1 for minimizing carbon corrosion in the fuel cell system, as known, for example, from US Pat. No. 6,635,370 B2. A substantially similar fuel cell system is also disclosed in DE 10 2008 015 344 A1. BACKGROUND OF THE INVENTION

[0002] A fuel cell has been proposed as a clean, efficient, and environmentally friendly energy source for electric vehicles and various other applications. In particular, the fuel cell has been recognized as a potential alternative to the conventional internal combustion engine used in modern vehicles.

[0003] A typical fuel cell is known as a proton exchange membrane (PEM) fuel cell. The PEM fuel cell comprises three basic components: a cathode, an anode, and an electrolyte membrane. The cathode and anode typically comprise a finely divided catalyst, such as platinum, supported on carbon particles and mixed with an ionomer. The electrolyte membrane is sandwiched between the cathode and anode to form a membrane-electrolyte assembly (MEA). The MEA is often sandwiched between porous diffusion media (DM) that supports the delivery of gaseous reactants, typically hydrogen and oxygen from air, for an electrochemical fuel cell reaction. Individual fuel cells can be stacked in series to form a fuel cell stack. The fuel cell stack is capable of generating sufficient electricity to power a vehicle.

[0004] During periods of non-operation, a quantity of air accumulates in the anodes of the fuel cell stack. When the fuel cell stack is started up, hydrogen is delivered to the anodes. The hydrogen contacts the air, creating a "hydrogen-air front" that passes over the anodes. This hydrogen-air front is known to degrade fuel cell performance. In particular, the presence of both hydrogen and air at the anode causes a local short circuit between a portion of the anode exposed to hydrogen and a portion of the anode exposed to air. This local short circuit reverses current flow and increases the cathode interface potential, resulting in rapid corrosion of the fuel cell carbon substrates and catalyst supports.It has been found that the rate of carbon corrosion is proportional to a time period within which the hydrogen-air front is present and a magnitude of the local stress at the hydrogen-air front.

[0005] To prevent damage to the fuel cell system, the fuel cell system can be shut down using a hydrogen-hydrogen shutdown strategy, in which hydrogen is present at both electrodes (anode and cathode) after the shutdown procedure is completed. If the fuel cell system is restarted before air leaks into the cathode, no damaging carbon corrosion will occur. However, if air leaks into the cathode while hydrogen is still present, a stagnant hydrogen-air front can form at the anode, causing carbon corrosion at the cathode electrode.

[0006] Additionally, a freeze event can occur while the anode array is full of stagnant gas (hydrogen, air, or water vapor in any combination). As the temperature drops, the stagnant gas begins to condense across the anode array. Unfortunately, the gas can condense on valves and other critical moving parts and then freeze. The frozen condensation can render the valve (or other critical component) inoperable during startup, resulting in increased cell damage during startup and / or a failed freeze start.

[0007] The invention is based on the object of providing a fuel cell system and a method for minimizing carbon corrosion in the fuel cell system, wherein the system and the method maximize the durability of the fuel cell system while not dispensing with a hydrogen-hydrogen shutdown strategy. SUMMARY OF THE INVENTION

[0008] This object is achieved by a method having the features of claim 1 and by a fuel cell system having the features of claim 5. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above and other advantages of the present invention will be readily apparent to those skilled in the art from the following detailed description of the preferred embodiment with reference to the accompanying drawings, in which: Fig. 1 is a schematic exploded perspective view of a PEM fuel cell stack as is known in the art; Fig. Figure 2 is a schematic sectional view of a fuel cell system immediately after a hydrogen-hydrogen shutdown procedure; Fig. 3 a schematic sectional view of the fuel cell system of Fig. 2, which shows a decrease in hydrogen concentration when air leaks into the fuel cell system; and Fig. 4 a schematic sectional view of the fuel cell system of Fig. 2 is after air has filled one anode side of the fuel cell system. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

[0010] For simplicity, only a two-cell stack (i.e., a bipolar plate) is used in Fig. 1, it being understood that a typical fuel cell stack comprises many more such cells and bipolar plates.

[0011] Fig. Figure 1 shows a prior art PEM fuel cell stack 10. The fuel cell stack 10 includes a pair of membrane electrode assemblies (MEAs) 12, 14 separated by an electrically conductive bipolar plate 16. The MEAs 12, 14 and the bipolar plate 16 are stacked between a pair of clamping plates 18, 20 and a pair of unipolar end plates 22, 24. The clamping plates 18, 20 are electrically insulated from the end plates 22, 24 by a sealing element or dielectric coating (not shown). A working face 26, 28 of each of the unipolar end plates 22, 24 as well as the working faces 30, 32 of the bipolar plate 16 include a plurality of grooves or channels 34, 36, 38, 40 adapted to support the flow of a fuel, such as hydrogen, and an oxidizer, such as oxygen, therethrough.Non-conductive sealing elements 42, 44, 46, 48 provide seals as well as electrical insulation between the components of the fuel cell stack 10. Gas-permeable diffusion media 50, 52, 54, 56, such as carbon or graphite diffusion papers, are substantially adjacent to each of an anode side and a cathode side of the MEAs 12, 14. The end plates 22, 24 are disposed adjacent to the diffusion media 50, 56, respectively. The bipolar plate 16 is disposed adjacent to the diffusion media 52 on the anode side of the MEA 12. The bipolar plate 16 is further disposed adjacent to the diffusion media 54 on the cathode side of the MEA 14.

[0012] The fuel cell stack 10 further includes a cathode supply manifold 58 and a cathode exhaust manifold 60, a coolant supply manifold 62, a coolant exhaust manifold 64, an anode supply manifold 66, and an anode exhaust manifold 68. The supply manifolds 58, 62, 66 and the exhaust manifolds 60, 64, 68 are formed by aligning adjacent openings formed in the bipolar plate 16, openings formed in the sealing elements 42, 44, 46, 48, and openings formed in the end plates 22, 24. Hydrogen gas is supplied to the fuel cell stack 10 through the anode supply manifold 66 via an anode inlet conduit 70. An oxidizer gas is supplied to the fuel cell stack 10 through the cathode supply manifold 58 of the fuel cell stack 10 via a cathode inlet line 72. An anode outlet line 74 and a cathode outlet line 76 are provided for the anode exhaust manifold 68 and the cathode exhaust manifold 66, respectively.the cathode exhaust header 60. A coolant inlet conduit 78 and a coolant outlet conduit 80 are in fluid communication with the coolant supply manifold 62 and the coolant exhaust header 64 to provide a flow of liquid coolant therethrough. It should be understood that the configurations of the various inlets 70, 72, 78 and outlets 74, 76, 80 in . Fig. 1 are for illustrative purposes only and other configurations may be chosen if necessary.

[0013] The Fig. 2, Fig. 3 and Fig. 4 show an anode side of a fuel cell system 100 according to an embodiment of the invention. The fuel cell system 100 includes a fuel cell stack 110 having a plurality of fuel cells 112. Each of the fuel cells 112 has an anode (not shown) and a cathode (not shown) with an electrolyte membrane (not shown) disposed therebetween. The fuel cell stack 110 further includes a first end 114 and a second end 116. As described herein, the first end 114 is known as the "dry end" and the second end 116 is known as the "wet end."

[0014] In the embodiment shown, the fuel cell system 100 further includes an anode supply manifold 118, an anode exhaust header 120, a recirculation loop 122, and a plurality of fans 124, 126, 128, 130. It should be understood that additional components and systems may be included in the fuel cell system 100 as desired.

[0015] The anode supply manifold 118 is in fluid communication with the anodes of the fuel cells 112 and provides fluid communication between a hydrogen source 132 and the fuel cells 112. The anode supply manifold 118 receives a flow of gaseous hydrogen 119 through an anode inlet conduit 134 from the hydrogen source 132. The anode inlet conduit 134 defines a volume between the hydrogen source 132 and the anode supply manifold 118. It should be understood that the anode inlet conduit 134 may have any desired cross-sectional area and may further include, for example, a chamber.

[0016] The fuel cell system 100 further includes a fuel injector 136 and a jet pump 138 disposed between the hydrogen source 132 and the anode inlet line 134. The injector 136 and the jet pump 138 provide control for the hydrogen flow 119 into the anode inlet line 134. It should be understood that additional components may be in communication with the hydrogen source 132 and the anode inlet line 134, such as a pressure regulator and a recirculation pump. Optionally, other components or systems may be in communication with the anode inlet line 134.

[0017] An anode exhaust manifold 120 of the fuel cell system 100 provides fluid communication between the anodes of the fuel cells 112 and an exhaust system 140 and the recirculation loop 122. The anode exhaust manifold 120 receives a fluid flowing through the anodes of the fuel cells 112. As a non-limiting example, the fluid forced through the anodes may be gaseous hydrogen, air, or water. Other fluids may be used if desired. In the illustrated embodiment, the fuel cell system 100 includes an anode exhaust line 142 in fluid communication with the anode exhaust manifold 120. The anode exhaust line 142 defines a volume between the anode exhaust manifold 120 and the exhaust system 140 and / or the recirculation loop 122. It should be understood that the anode exhaust line 142 may have any desired cross-sectional area and may further include, for example, a chamber.

[0018] The recirculation loop 122 provides fluid communication between the anode exhaust header 120 and the anode supply manifold 118. In certain embodiments, the recirculation loop 112 includes at least a portion of the anode inlet line 134, at least a portion of the anode exhaust line 142, a recirculation line 144, a water separator 146, and a first valve 148. However, it should be understood that other components may be included, if desired.

[0019] The return line 144 defines a volume between the anode inlet line 134 and the anode exhaust line 142. It should be understood that the return line 144 may have any desired cross-sectional area and may further include, for example, a chamber. In the illustrated embodiment, the return line 144 is in fluid communication with the water separator 146 and the jet pump 138. It should be understood that the return line 144 may be in direct communication with the anode inlet line 134, the anode supply manifold 118, the anode exhaust header 120, and / or the anode exhaust line 142. It should further be understood that other components or systems may be disposed between the return line 144 and the anode inlet line 134, the anode supply manifold 118, the anode exhaust header 120, and / or the anode exhaust line 142, as appropriate.

[0020] The water separator 146 is disposed between the anode discharge line 142 and the return line 144 and is adapted to remove excess humidification or product water from the fluid received by the anode discharge line 142. The water separator 146 is further in fluid communication with the first valve 148. The first valve 148 is adapted to drain or discharge the product water collected in the water separator 146. As shown, the first valve 148 is further in fluid communication with the discharge system 140 and is adapted to discharge the product water into the discharge system 140. However, it should be understood that the first valve 148 may be adapted to discharge the product water to any system or device as desired. It should further be understood that additional valves and control devices may be included, if desired.

[0021] The fans 124, 126, 128, 130 may be any devices adapted to provide flow across the anode electrodes across the fuel cell stack 110. In the illustrated embodiment, the fuel cell system 100 includes four fans 124, 126, 128, 130. However, it should be understood that any number of fans may be used, if desired. It should further be understood that any of the characteristics and specifications of the fans 124, 126, 128, 130 may be modified as desired. In certain embodiments, the fans 124, 126, 128, 130 are low-power fans in a power range of 1-500 watts. However, other power ranges may be used. For example, favorable results have been achieved using fans with a power range of 10 - 50 watts.The fans 124, 126, 128, 130 may be in electrical communication with a dedicated electrical power system (not shown) and / or an electrical system of the fuel cell system 100 or vehicle. As shown, the first fan 124 is disposed adjacent the anode exhaust manifold 120 and is in fluid communication with the anode exhaust manifold 120 to provide flow within the anode exhaust manifold 120. The second fan 126 is disposed in the anode exhaust conduit 142 and is in fluid communication with the anode exhaust manifold 120 to provide flow within the anode exhaust manifold 120. The third fan 128 is disposed in the return conduit 144 and is adapted to provide flow through the return loop 122. The fourth fan 130 is arranged in the anode inlet line 134 and is pivotally coupled to the anode inlet line 134.The fourth fan 130 is positioned in the fluid flow path of the anode inlet conduit 134 and adapted to provide flow through the anode inlet conduit 134 and thereby through the anode supply manifold 118. When the fourth fan 130 is not in use, the fourth fan 130 can be selectively rotated out of the fluid flow path of the anode inlet conduit 134, as shown in FIGS. Fig. 2 to 4. It should be understood that the fans 124, 126, 128, 130, or a single fan, can be arranged at any location as desired. It should further be understood that any combination of fans 124, 126, 128, 130 and fan locations can be used as desired.

[0022] In use, the fuel cell system 100 is shut down such that hydrogen 119 is present at both the anodes and cathodes after the shutdown procedure is completed. It should be understood that any shutdown procedure, now known or later developed, may be used in which hydrogen 119 remains in both the anodes and cathodes after the shutdown procedure is completed. As a non-limiting example, at system shutdown, the cathode air flow is stopped and the cathode side of the fuel cell stack 110 is sealed. The flow of hydrogen 119 to the anode side of the fuel cell stack 110 continues, thus consuming any remaining oxygen in the stack.The anode side of the fuel cell stack 110 is sealed so that the hydrogen flow 119 only replaces the hydrogen that has been pumped to the cathode side of the fuel cell stack 110, thereby filling both the anode and cathode sides of the fuel cell stack with hydrogen. As shown in . Fig. As shown in Figure 2, the anode supply manifold 118, the anode exhaust manifold 120, and the fuel cells 112 of the fuel cell stack 110 have a substantially uniform hydrogen concentration 119 immediately after the shutdown procedure is completed. Over time, air 150 leaks into the cathodes of the fuel cell stack 110 and diffuses or leaks through the membrane or sealing elements into specific areas of the anodes. It should be understood that air 150 may also leak directly into specific areas of the anodes. Meanwhile, the fans 124, 126, 128, 130 create a flow to mix the air 150 and the hydrogen 119 in the anodes, thereby maintaining a substantially uniform hydrogen concentration between the anode supply manifold 118, the anode exhaust manifold 120, and the fuel cells 112.In certain embodiments, the fans 124, 126, 128, 130 have an intermittent duty cycle, such as 30 seconds on and 30 seconds off. However, it should be understood that the fans 124, 126, 128, 130 can be operated continuously or at any duty cycle as needed. Thus, mixing the air 150 and hydrogen 119 in the fuel cells 112 minimizes the possibility of a hydrogen-air front forming in the anode side of the fuel cell system 100. As shown in FIG. Fig. 3, the hydrogen concentration in the anode supply manifold 118, the anode exhaust collector 120, and the fuel cells 112 of the fuel cell stack 110 is reduced relative to the hydrogen concentration immediately after the shutdown procedure. As shown in Fig.4, the fans 124, 126, 128, 130 continue to mix the fluid flow within the fuel cells 112 as the air 150 continuously leaks slowly in from the cathodes, and the fuel cell stack 110 is returned to an environment in which air 150 is present at the cathodes and anodes (i.e., an air-to-air environment) of the fuel cell stack 110 without significant cathode damage. As a non-limiting example, the fans 124, 126, 128, 130 may also provide fluid flow over a "cold finger." A "cold finger" is a thermally conductive element in conjunction with ambient temperature conditions (outside the insulation and / or shroud) such that, in a freezing situation, the "cold finger" element is colder than any other part of the fuel cell stack 110.Thus, water vapor first condenses on the "cold finger," which is designed to allow condensed water to drain away from critical moving parts and / or freeze away. Fans 124, 126, 128, 130 can be operated until the temperature across fuel cell stack 110 is below freezing, while the "cold finger" element continues to condense and remove the water vapor. Eventually, the gas is quite dry, and no water condenses on the critical moving parts.

[0023] The fuel cell system 100 and method for minimizing carbon corrosion in the fuel cell system 100 provide a means for returning the fuel cell system 100 to an air-to-air environment. Accordingly, the fuel cell system 100 and method maximize the durability of the fuel cell system 100 while not sacrificing a hydrogen-to-hydrogen shutdown strategy. Furthermore, the fuel cell system 100 and method can support freeze-start / durability by enabling condensation (and subsequent freezing) of water at a specific location.

Claims

[1] A method for minimizing carbon corrosion in a fuel cell system (100), the method comprising the steps of: a fuel cell stack (110) having a plurality of fuel cells (112) is provided, each of the fuel cells (112) having an electrolyte membrane (12) arranged between an anode and a cathode; an anode supply manifold (118) and an anode exhaust manifold (120) are provided in fluid communication with the anodes of the fuel cells (112), the anode supply manifold (118) being in fluid communication with a hydrogen gas source (132); a shutdown procedure is carried out in which hydrogen gas (119) is present in the anodes and the cathodes after shutdown; and a fan (124, 126, 128, 130) is provided in fluid communication with the anodes of the fuel cells (112) for generating a flow over the anodes after shutdown; characterized by, that the blower (124, 126, 128, 130) is hingedly coupled to the anode supply manifold (118), an anode inlet line (134), the anode discharge header (120) and / or an anode discharge line (142). [2] The method of claim 1, wherein the blower (124, 126, 128, 130) has a power range of 1 to 500 watts. [3] The method of claim 1, wherein the anode inlet conduit (134) is adapted to provide fluid communication between the anode supply manifold (118) and the hydrogen source (132), and the anode exhaust conduit (142) is in fluid communication with the anode exhaust manifold (120). [4] The method of any one of claims 1, further comprising the step of: at least one of a jet pump (138) in fluid communication with the anode supply manifold (118), an injector (136) in fluid communication with the anode supply manifold (118) and a return loop (122) in fluid communication with the anode discharge collector (120) is provided, wherein the return loop (120) preferably comprises a blower, a water separator (146) and / or a valve (148). [5] Fuel cell system (100), comprising: a fuel cell stack (110) having a plurality of fuel cells (112), each of the fuel cells having an electrolyte membrane (12) arranged between an anode and a cathode; an anode supply manifold (118) in fluid communication with the anodes of the fuel cells (112), the anode supply manifold (118) providing fluid communication between a hydrogen source (132) and the anodes; an anode discharge collector (120) in fluid communication with the anodes of the fuel cells (112); and a blower (124, 126, 128, 130) in fluid communication with the anodes of the fuel cells (112), the blower (124, 126, 128, 130) controlling fluid flow through the anodes of the fuel cells (112) after the fuel cell system (110) is shut down; characterized by , that the blower (124, 126, 128, 130) is hingedly coupled to the anode supply manifold (118), an anode inlet line (134), the anode discharge header (120) and / or an anode discharge line (142). [6] Fuel cell system according to claim 5, wherein the blower (124, 126, 128, 130) has a power range of 1 to 500 watts. [7] The fuel cell system of claim 5, further comprising at least one of a jet pump (138) in fluid communication with the anode supply manifold (118), an injector (136) in fluid communication with the anode supply manifold (118), an anode inlet line in fluid communication with the anode supply manifold, and a recirculation loop (122) in fluid communication with the anode exhaust header (120), the recirculation loop (122) comprising a blower (124, 126, 128, 130), a water separator (146), and / or a valve (148).

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