WO2023219625A1

WO2023219625A1 - Preventing fuel cell degradation with reverse cathode flow

Info

Publication number: WO2023219625A1
Application number: PCT/US2022/029060
Authority: WO
Inventors: Daniel Orlowski
Original assignee: Us Hybrid Corporation
Priority date: 2022-05-12
Filing date: 2022-05-12
Publication date: 2023-11-16

Abstract

Preventing fuel cell degradation with reverse cathode flow is provided. An example fuel cell has a degradation mitigation mode that directs the hydrogen gas used as fuel to both sides of the polymer electrolyte membrane (PEM) during cool-down periods. Instead of its conventional isolation to the anode side, the hydrogen gas that is directed to the cathode side while the cell stack is still hot reverses accumulated polarizations in both the polymer electrolyte membrane (PEM) and the surface of the cathode, thereby preventing the usual rate of degradation that a fuel cell undergoes before rejuvenation is needed. In an implementation, a controller operates valves in the fuel cell to create a channel for the hydrogen gas to flow to the cathode compartment and then runs the air blower in reverse at a carefully controlled flow rate to pull the hydrogen gas into the cathode compartment.

Description

PREVENTING FUEL CELL DEGRADATION WITH

REVERSE CATHODE FLOW

BACKGROUND

[0001] In routine operation, a fuel cell has a cell stack that generates electric power during fuel cell operation. The fuel, such as hydrogen gas, releases electrons on the anode side of the fuel cell thereby creating an electron flow for an electrical circuit. The resulting hydrogen ions travel through the polymer electrolyte membrane (PEM) of the fuel cell to the cathode side of the fuel cell to combine with oxide anions being formed by reduction of oxygen from air at the cathode. The reduction of the oxygen is accomplished by the electrons that were generated at the anode and have flowed through an electrical circuit in a vehicle hosting the fuel cell, for example.

[0002] Although the polymer electrolyte membranes (PEMs) used in fuel cells are very efficient and the anode and cathode electrodes are coated with finely divided noble metals such as platinum that do not easily corrode, there are still some cumulative polarizations and oxidations on and around the electrode surfaces and in the PEM that create resistance to operation and degradation of performance over long periods of accumulated use. These cumulative polarizations and oxidations are sometimes reversible to a degree, or preventable.

SUMMARY

[0003] Preventing fuel cell degradation with reverse cathode flow is provided. An example fuel cell has a degradation mitigation mode that directs the hydrogen gas used as fuel to both sides of the polymer electrolyte membrane (PEM) during cool-down periods. Instead of its conventional isolation to the anode side, the hydrogen gas that is directed to the cathode side while the cell stack is still hot reverses accumulated polarizations in both the polymer electrolyte membrane (PEM) and the surface of the cathode, thereby preventing the usual rate of degradation that a fuel cell undergoes before rejuvenation is needed. In an implementation, a controller operates valves in the fuel cell to create a channel for the hydrogen gas to flow to the cathode compartment and then runs the air blower in reverse at a carefully controlled flow rate to pull the hydrogen gas into the cathode compartment.

[0004] This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The detailed description is set forth with reference to the accompanying figures. The use of the same reference numbers in different figures indicates similar or identical items or features.

[0006] Fig. 1 is a diagram of a fuel cell electric vehicle hosting an example fuel cell engine capable of mitigating a degradation process of the cell stack.

[0007] Fig. 2 is a block diagram of the example fuel cell engine of Fig. 1 in greater detail. [0008] Fig. 3 is a diagram of the example fuel cell engine of Fig. 2 in a configuration for mitigating a degradation process of the cell stack.

[0009] Fig. 4 is a flow diagram of an example method of preventing fuel cell degradation with reverse cathode flow

DETAILED DESCRIPTION

[0010] This disclosure describes preventing fuel cell degradation with reverse cathode flow. Fuel cells that have a polymer electrolyte membrane (PEM) can degrade slightly over long term use due to accumulated polarizations in the PEM and around the anode and cathode electrodes. Introducing hydrogen gas, the fuel of the fuel cell, into both the anode and cathode compartments of the fuel cell during cool-down periods, while the cell stack of the fuel cell is still hot, can mitigate the rate at which this slight long-term degradation occurs. The hydrogen gas used to mitigate the degradation in this manner contacts both sides of the polymer electrolyte membrane (PEM) and the surface of the cathode. By contrast, the hydrogen gas fuel is conventionally isolated to the anode compartment.

[0011] In this description, the term “fuel cell” also includes “fuel cell engines” that can be used to power an electric vehicle or to power other industrial applications. The term “anode” as used herein also represents multiple “anodes” in the cell stack of a fuel cell or fuel cell engine, and the term “cathode” may represent multiple “cathodes” in the cell stack of a fuel cell or fuel cell engine.

[0012] In an implementation, an example fuel cell has an electronic controller (“controller”) that can apply a degradation mitigation process during cool-down of the fuel cell to prevent degradation processes in the cell stack by applying a reverse cathode flow of the hydrogen gas. The term “prevents” as used herein is used roughly to refer to a degree of mitigation of the expected degradation of fuel cells over time.

[0013] To initiate the degradation mitigation process, the controller closes an exhaust valve or backpressure control valve of the fuel cell and opens a fuel purge valve to establish a continuous channel for fluid flow of the hydrogen gas from the anode compartment to the cathode compartment. The purge valve normally removes a buildup of gases (e.g., nitrogen, trace atmospheric gases) from the anode compartment, channeling these unwanted gases to the cathode exhaust output. This configuration for gas flow of the hydrogen fuel from anode compartment to cathode compartment is normally forbidden during normal operation of the fuel cell producing electric power.

[0014] In an implementation, the controller runs the air blower of the fuel cell in a carefully controlled reverse direction to pull the hydrogen gas into the cathode compartment and into contact with the cathode surfaces and the cathode side of the polymer electrolyte membrane (PEM). The air blower is conventionally used only to pump oxygen (from air) to the cathode for producing the electric power.

[0015] The controller may variably control the exhaust valve, the purge valve, and the air blower in concert with each other to transfer a quantitatively determined amount of the hydrogen gas to the cathode compartment during cool-down. Likewise the controller may variably control the exhaust valve, the purge valve, and the air blower in concert with each other to transfer the hydrogen gas to the cathode compartment during cool-down at a quantitatively determined flow rate.

In an implementation, the controller may base its variable control on the current temperature of the cell stack, applying variable control to the openness of the purge valve in relation to the speed and flow rate of the air blower variably running in a reverse direction in relation to the current temperature of the cell stack. The amount of hydrogen gas transferred to the cathode compartment may taper down as the temperature decreases. Alternatively, the controller may transfer hydrogen gas to the cathode compartment for a set period of time during cool-down of the fuel cell, and then stop.

Example Systems

[0016] The example fuel cells and fuel cell engines described herein generate electricity for an electric vehicle or for industrial applications, while including components for preventing fuel cell degradation with reverse cathode flow. In some implementations, the fuel cell engine makes use of components that are already present in the fuel cell engine, saving manufacturing costs.

[0017] Fig. 1 shows a fuel cell engine 100 in an example electric vehicle 102, manufactured with the ability to perform the example degradation mitigation process for fuel cells described herein. The example vehicle 102 has a high-pressure supply of hydrogen gas 104 used as fuel for the fuel cell engine 100. One or more high-voltage batteries 106 store energy from the fuel cell engine 100 and may sometimes reclaim energy generated from braking as electrical energy for battery storage. The one or more high-voltage batteries 106 may provide supplemental power to the electric (traction) motor 108 via the power distribution unit 110 of the vehicle 102. The main source of electric power for the electric motor 108 powering propulsion of the vehicle 102 is the fuel cell engine 100. The power distribution unit 110 of the vehicle 102 directs various high-voltage electric currents of the fuel cell engine 100, high-voltage batteries 106, and electric motor 108 via a high-voltage power bus 112.

[0018] The layout of components in the example vehicle 102 of Fig. 1 is only one example for the sake of description. The various components of the example vehicle 102 may be arranged in numerous different layouts and may have many more incidental components not shown in Fig. 1. For example, the vehicle 102 may have a low voltage battery (e.g., 12 volts) to power conventional automotive functions. The low voltage battery (not shown) may be charged by a DC/DC step down transformer from the fuel cell engine 100 and/or from the high- voltage batteries 106. The supply of high-pressure hydrogen gas 104 (the “gas tank”) may have a filler port / high-pressure interface on the outside of the vehicle 102 to replenish the supply of hydrogen gas 104.

[0019] Each of the major components shown in Fig. 1 may have numerous subcomponents. For example, the fuel cell engine 100 has its own inherent electrical system, and may have its own electronics, including one or more DC/DC converters or a “power conditioning system” to modify the voltage and/or current of the electricity it generates for the power distribution unit 110, for the electric motor 108, and for the high-voltage batteries 106. The DC/DC converter(s) of the fuel cell engine 100 may be physically separate from the power distribution unit 110 of the vehicle 102. The power distribution unit 110 of the vehicle 102 may be in communication with the DC/DC converters of the fuel cell engine 100 and call for specific voltages and currents from the fuel cell engine 100 depending on the state of the vehicle: starting, accelerating, maintaining highway speed, braking, decelerating, idling, stopping, and so forth.

[0020] Fig. 2 shows the example fuel cell engine 100 of Fig. 1 in greater detail. The fuel cell engine 100 of Fig. 2 is only diagrammatic for purposes of description and does not portray actual dimensions, geometry, and complete components of a fuel cell engine 100. Each individual cell in a cell stack 200 of the fuel cell engine 100 has an anode 202 and a cathode 204 on either side of a layer of intervening polymer electrolyte membrane (PEM) 206. A fuel processing system of the fuel cell engine 100 provides the hydrogen gas 104 to the anode compartment 208 of the cell stack 200 as the fuel to be consumed for electrochemically producing electric power at each cell of the cell stack 200. An air processing system with air blower 210 provides oxygen 212 to the cathode compartment 214 of the cell stack 200 for producing the electric power.

[0021] The fuel cell engine 100 may have one or more electronically controlled fuel valves (not shown) and also has other valves capable of assuming a valve configuration suitable for executing the example degradation mitigation process. During normal operation producing electric power, an exhaust backpressure valve 216 intervenes in the flow of exhaust through an exhaust outlet 218 to maintain an optimal backpressure of the oxygen-containing air in the cathode compartment 214 against the cathodes 204, for producing electric power optimally. The exhaust of the fuel cell engine 100 generally contains air and water vapor at an elevated temperature. The exhaust backpressure valve 216 may be under variable control of the electronic controller 114 in order to optimize the backpressure in light of current conditions of pressure, temperature, and electrical demand in the fuel cell engine 100.

[0022] During normal operation while producing electricity, an anode compartment purge valve 220 of the cell stack 200 is normally closed. The hydrogen gas fuel 104 is ideally completely consumed at the anodes 202 in the production of electric power, with no leftover hydrogen gas 104 to be discarded as exhaust. The controller 114 of the fuel cell engine 100 tries to maintain a near-ideal stoichiometry between the hydrogen gas 104 as fuel and the oxygen in the air 212 as oxidant via a carefully maintained pressure balance at the anodes 202 and cathodes 204 as implemented by the one or more electronically controlled fuel valves, for example, and the air blower 210.

[0023] The electronic controller 114 of the fuel cell engine 100 manages and supervises all the operations of the cell stack 200 and fuel cell engine 100 in general during routine operation. The electronic controller 114 includes the mitigation unit 116 for performing the example degradation mitigation process described herein.

[0024] Fig. 3 shows the fuel cell engine 100 during a cool-down period after a session of producing electric power. The electronic controller 114 may receive a signal from the vehicle 102 or from an operator in an industrial setting, when the fuel cell engine 100 is fulfilling an industrial use, the signal indicating to turn off and shut down the fuel cell engine 100. The mitigation unit 116 of the electronic controller 114 may check or monitor a temperature sensor 302 of the cell stack 200 to verify that the temperature is high enough for the degradation mitigation process to be beneficial. A low-temperature PEM fuel cell may operate at 60-80 °C while a high-temperature PEM fuel cell may operate at over 100 °C. The favorable conditioning imparted by the hydrogen gas 104 on the cathode-side materials of the PEM 206 and on the cathodes 204 works better at higher temperatures. The mitigation unit 116 may also check that the power production circuit(s) 304 of the cell stack 200 have been disconnected from electric power production.

[0025] After checking the above factors for determining that a cool-down period is to start, the mitigation unit 116 begins a mitigation cycle by closing the exhaust backpressure valve 216. The mitigation unit 116 opens the anode compartment purge valve 220 to some degree, depending on implementation. The configuration of these two valves 216, 220 creates a continuous channel for the hydrogen gas 104 to flow from the anode compartment 208 to the cathode compartment 214. In an implementation, the mitigation unit 116 actuates the air blower 210 of the fuel cell engine 100 to pull the hydrogen gas 104 from the anode compartment 208 into contact with the cathodes 204 in the cathode compartment 214 and into contact with the cathode-side polymer electrolyte membrane (PEM) 206 in the cathode compartment 214.

[0026] In an implementation, the blower 210 for pulling the hydrogen gas 104 into the cathode compartment 214 from the anode compartment 208 may be the same air blower 210 operating to pump air into the cathode compartment 214 during production of electric power, except running in a reverse flow direction to the pull hydrogen gas 104 rather than to push air containing oxygen gas 212 into the cathode compartment 214, as it does when running in a forward direction. The air blower 210 may be capable of running in the reverse direction at a slower speed or at a lower flow rate under control of the mitigation unit 116, compared to its normal operation of running in the forward direction for pushing air and oxygen 212 to the cathodes 204 at a significant pressure for producing the electric power.

[0027] In an implementation, an auxiliary gas blower or pump that is separate from the main air blower 210 of the fuel cell engine 100 is used to pull the hydrogen gas 104 into the cathode compartment 214 in order to execute the degradation mitigation process. When an auxiliary gas blower is used it may be smaller and operate at a lower pressure than the main air blower 210 of the fuel cell engine 100. However, when the main air blower 210 is used to draw the hydrogen gas 104 by running in a reverse flow direction, this may save parts and costs during manufacture.

[0028] In an implementation, the fuel cell engine 100 may have a closing valve or a simple physical cap 306 to cover the air inlet of the air blower 210 when the air blower 210 is turned off after pulling the hydrogen gas 104 from the anode compartment 208 into contact with the cathodes 204 and the polymer electrolyte membrane (PEM) 206 in the cathode compartment 214. The closing valve or cap 306 stops a flow of the hydrogen gas 104 in the cathode compartment 214 and holds the hydrogen gas 104 in contact with the cathodes 204 and the polymer electrolyte membrane (PEM) 206.

[0029] In an implementation, the mitigation unit 116 variably controls the anode compartment purge valve 220 and the air blower 210. The variable control may move a measured quantity of the hydrogen gas into contact with the cathodes 204 and the polymer electrolyte membrane (PEM) 206 in the cathode compartment 214 at a measured flow rate. It may be desirable to transfer a calculated quantity of the hydrogen gas 104 depending on the geometry and spatial volume of the cathode compartment 214, for purposes of optimizing the conditioning imparted by the hydrogen gas 104.

[0030] The mitigation unit 116 may also variably control the anode compartment purge valve 220 and the air blower 210 in relation to each other. The concerted variable control may allow the mitigation unit 116 to move a quantitative amount of the hydrogen gas 104 into the cathode compartment 214, or to move the hydrogen gas 104 into the cathode compartment 214 at a quantitative flow rate with very precise control. In other words, the mitigation unit 116 may base the variable control of the air blower 210 on the variable control of the anode compartment purge valve 220, and vice versa, for greater control of the quantity and flow rate of the hydrogen gas 104.

[0031] In an implementation, the mitigation unit 116 variably controls the anode compartment purge valve 220 and the air blower 210 in relation to each other based on a current temperature of the cell stack from the temperature sensor 302, for example, wherein the quantitative amount of the hydrogen gas 104 per unit time decreases to zero when the current temperature of the cell stack reaches an ambient temperature, for example. [0032] In the same or another implementation, the mitigation unit 116 may open the anode compartment purge valve 220 and drive the air blower 210 in a reverse flow direction to pull the hydrogen gas 104 from the anode compartment 208 to the cathode compartment 214 for a set period of time after initiating the cool-down period.

Example Process

[0033] Fig. 4 shows an example method 400 for preventing degradation of a fuel cell. In the flow diagram of Fig. 4, operations of the example method 400 are shown in individual blocks. The order in which the operations are described in the example method 400 is not intended to be construed as a limitation, and any number of the described blocks can be combined in any order and/or in parallel to implement the example process.

[0034] At block 402, the method 400 includes initiating a cool-down period in a fuel cell for producing electric power from a hydrogen gas, the fuel cell comprising a cell stack, an anode of the cell stack in an anode compartment, and a cathode of the cell stack in a cathode compartment.

[0035] At block 404, the method 400 includes closing an exhaust valve of the fuel cell, the exhaust valve opening and closing an exhaust outlet of the cathode compartment of the cell stack.

[0036] At block 406, the method 400 includes opening a purge valve of the anode compartment to create a continuous channel for the hydrogen gas to flow from the anode compartment to the cathode compartment.

[0037] At block 408, the method 400 includes driving a blower to pull the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment. [0038] The example method 400 may further include initiating the cool-down period after sensing a signal to terminate production of electric power and after sensing a sufficiently high temperature of the cell stack for the preventative mitigation to be effective.

[0039] The blower for pulling the hydrogen gas may be an air blower of the fuel cell that is used for pushing air through the cathode compartment when producing electric power. The air blower is operated in a reverse flow direction to pull the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment.

[0040] The blower for pulling hydrogen gas 104 may also be a secondary blower separate from the main air blower of the fuel cell. The secondary blower may be dedicated solely to pulling the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment.

[0041] The method 400 may also include shutting a closing valve or a cap on an air inlet of the blower when the blower is turned off after pulling the hydrogen gas from the anode compartment to the cathode compartment. The closing valve or cap stops a flow of the hydrogen gas in the cathode compartment and holds the hydrogen gas in the cathode compartment in contact with the cathode and the polymer electrolyte membrane (PEM).

[0042] The method 400 may also include variably controlling the purge valve and the blower. The variable control may be used to move a measured quantity of the hydrogen gas into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment at a measured flow rate. The method 400 may include variably controlling the purge valve and the blower in relation to each other to move a quantitative amount of the hydrogen gas into the cathode compartment and into contact with the cathode and the polymer electrolyte membrane (PEM) or to move the hydrogen gas at a quantitative flow rate. [0043] The method 400 may further include variably controlling the purge valve and the blower in relation to each other based on a current temperature of the cell stack, or based on some other parameter, or combination of parameters, of the cell stack. In one scenario, the quantitative amount of the hydrogen gas being transferred per unit time decreases to zero when the temperature of the cell stack reaches an ambient temperature.

[0044] The method 400 may include opening the purge valve and driving the blower to pull the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment for a set or predetermined period of time after initiating the cool-down period. [0045] In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The sole and exclusive indicator of the scope of the invention, and what is intended by the applicants to be the scope of the invention, is the literal and equivalent scope of the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction.

Claims

CLAIMS What is claimed is:

1. An apparatus, comprising: a fuel cell for producing electric power from a fuel comprising hydrogen gas; a cell stack of the fuel cell; an anode of the cell stack in an anode compartment; a cathode of the cell stack in a cathode compartment; an exhaust outlet of the cathode compartment with an exhaust valve; a purge valve of the anode compartment for removing gases from the anode compartment through the exhaust outlet; a blower for pushing air through the cathode compartment to produce the electric power, the blower capable of pulling the hydrogen gas from the anode compartment into contact with the cathode and a polymer electrolyte membrane (PEM) in the cathode compartment; and a controller for mitigating a degradation of the fuel cell, capable of: initiating a cool-down period after sensing a signal to terminate the production of the electric power and after sensing a high temperature of the cell stack; closing the exhaust valve; opening the purge valve to create a continuous channel for the hydrogen gas to flow from the anode compartment to the cathode compartment; and driving the blower to pull the hydrogen gas from the anode compartment into contact with the cathode and a polymer electrolyte membrane (PEM) in the cathode compartment.

2. The apparatus of claim 1, wherein the blower comprises a first blower for pushing the air through the cathode compartment to make the electric power and a second blower for pulling the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment.

3. The apparatus of claim 1, wherein the blower comprises a single blower, the single blower capable of running in a forward direction to push the air through the cathode compartment to make the electric power and capable of running in a reverse direction to pull the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM).

4. The apparatus of claim 3, wherein the single blower is capable of running in the reverse direction at a slower speed or at a lower flow rate than when running in a forward direction for pushing the air through the cathode compartment to make the electric power.

5. The apparatus of claim 1, further comprising a closing valve on an air inlet of the at least one blower; wherein the closing valve shuts when the at least one blower is turned off after pulling the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment; wherein the closing valve stops a flow of the hydrogen gas in the cathode compartment; and wherein the closing valve holds the hydrogen gas in the cathode compartment in contact with the cathode and the polymer electrolyte membrane (PEM).

6. The apparatus of claim 1, wherein the controller is capable of variable control of the purge valve and variable control of the blower, the variable controls for moving a measured quantity of the hydrogen gas into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment at a measured flow rate.

7. The apparatus of claim 6, wherein the controller is capable of variably opening and closing the purge valve and variably speeding up and slowing down the blower in relation to each other, wherein the purge valve and the blower are controlled in concert with each other to move a quantitative amount of the hydrogen gas into the cathode compartment and into contact with the cathode and the polymer electrolyte membrane (PEM) or to move the hydrogen gas into the cathode compartment and into contact with the cathode and the polymer electrolyte membrane (PEM) at a quantitative flow rate.

8. The apparatus of claim 6, wherein the controller is capable of variably opening and closing the purge valve and variably speeding up and slowing down the blower in relation to each other based on a current temperature of the cell stack.

9. The apparatus of claim 8, wherein the controller directs the purge valve and the blower to move a quantitative amount of the hydrogen gas per unit time proportional to the current temperature of the cell stack, wherein the quantitative amount of the hydrogen gas per unit time decreases to zero when the current temperature of the cell stack reaches an ambient temperature.

10. The apparatus of claim 1, wherein the controller opens the purge valve and drives the blower to pull the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment for a set period of time after initiating the cool-down period.

11. A method, comprising: initiating a cool-down period in a fuel cell for producing electric power from a hydrogen gas, the fuel cell comprising a cell stack, an anode of the cell stack in an anode compartment, and a cathode of the cell stack in a cathode compartment; closing an exhaust valve of the fuel cell, the exhaust valve opening and closing an exhaust outlet of the cathode compartment of the cell stack; opening a purge valve of the anode compartment to create a continuous channel for the hydrogen gas to flow from the anode compartment to the cathode compartment; and driving a blower to pull the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment.

12. The method of claim 11, further comprising initiating the cool-down period after sensing a signal to terminate production of the electric power and after sensing a high temperature of the cell stack.

13. The method of claim 11, wherein the blower comprises an air blower of the fuel cell for pushing the air through the cathode compartment to produce the electric power, and wherein driving the blower to pull the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment comprises running the air blower in a reverse direction.

14. The method of claim 13, wherein the air blower is capable of running in the reverse direction at a slower speed or at a lower flow rate than when running in a forward direction for pushing the air through the cathode compartment to produce the electric power.

15. The method of claim 11, wherein the blower is dedicated solely to pulling the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment and the blower is separate from an air blower of the fuel cell for pushing the air through the cathode compartment to produce the electric power.

16. The method of claim 11, further comprising shutting a closing valve on an air inlet of the blower when the blower is turned off after pulling the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment; and wherein the closing valve stops a flow of the hydrogen gas in the cathode compartment and holds the hydrogen gas in the cathode compartment in contact with the cathode and the polymer electrolyte membrane (PEM).

17. The method of claim 11, further comprising variably controlling the purge valve and the blower, the variable control for moving a measured quantity of the hydrogen gas into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment at a measured flow rate.

18. The method of claim 17, further comprising variably controlling the purge valve and the blower in relation to each other to move a quantitative amount of the hydrogen gas into the cathode compartment and into contact with the cathode and the polymer electrolyte membrane (PEM), or to move the hydrogen gas into the cathode compartment and into contact with the cathode and the polymer electrolyte membrane (PEM) at a quantitative flow rate.

19. The method of claim 18, further comprising variably controlling the purge valve and the blower in relation to each other based on a current temperature of the cell stack, wherein the quantitative amount of the hydrogen gas per unit time decreases to zero when the current temperature of the cell stack reaches an ambient temperature.

20. The method of claim 1, further comprising opening the purge valve and driving the blower to pull the hydrogen gas from the anode compartment into contact with the cathode and the polymer electrolyte membrane (PEM) in the cathode compartment for a set period of time after initiating the cool-down period.