Fuel cell hydrogen mitigation

Abstract

The present disclosure provides fuel cell hydrogen mitigation. A fuel cell includes an anode, a cathode, and a membrane separating the anode from the cathode. A controller injects hydrogen gas into the anode and draws oxygen from the cathode in response to expiration of a predetermined period of time starting with disconnection of the fuel cell from the electrical bus.

Description

[0001] Statement regarding federally sponsored research or development

[0002] This invention was made with government support under contract No. DE-EE0009858 granted by the Office of Energy Efficiency and Renewable Energy (EERE). The government holds certain rights to this invention. Technical Field

[0003] This disclosure relates to hydrogen mitigation in fuel cells. Background Technology

[0004] Systems requiring hydrogen mitigation are used in a variety of industrial applications. Proper management of hydrogen levels maintains system integrity and functionality, especially during extended periods of inactivity known as downtime. Traditionally, manual intervention is required to start and shut down such systems to ensure adequate hydrogen levels are maintained. Summary of the Invention

[0005] An automotive fuel system includes: a fuel cell having an anode, a cathode, and a membrane separating the anode and the cathode; and a controller. The controller, in response to the expiration of a predetermined time period beginning with the fuel cell being disconnected from an electrical bus, injects hydrogen into the anode and extracts oxygen from the cathode. The controller can also monitor the voltage of the fuel cell during hydrogen injection and oxygen extraction. The controller can terminate the hydrogen injection and oxygen extraction when the voltage reaches a predetermined threshold. The controller can perform the hydrogen injection and oxygen extraction without a contactor connecting the fuel cell to the electrical bus. The predetermined time period can be based on an estimated hydrogen depletion rate of the fuel cell. In some configurations, a hydrogen storage system is connected to the anode to supply hydrogen. In other embodiments, an air compressor may be present connected to the cathode for oxygen extraction.

[0006] A method for mitigation in a fuel cell system includes: injecting hydrogen into the inactive fuel cell system when the duration since the fuel cell system has been inactive exceeds a threshold time for hydrogen depletion across the fuel cell system; and depleting oxygen from the fuel cell system. In some configurations, the method may include monitoring the voltage of the fuel cell system during the hydrogen injection and oxygen depletion, and terminating the hydrogen injection and oxygen depletion when the voltage reaches a predetermined threshold. The threshold time may be determined based on the operating conditions of the fuel cell system before inactivation. The method may be performed periodically while the fuel cell system remains inactive for an extended period. The injected hydrogen may be supplied from a hydrogen storage system connected to the fuel cell system.

[0007] A method for maintaining the performance of an electrochemical cell includes: applying hydrogen to the inactive anode of the electrochemical cell to reactivate it when the time elapsed since the cell has been deactivated exceeds a predefined hydrogen depletion threshold; and removing oxygen from the cell to initiate an inactive state and reduce the residual voltage for subsequent reactivation. In some configurations, the method may include monitoring the voltage of the electrochemical cell during the hydrogen application and oxygen removal, and terminating the hydrogen application and oxygen removal when the voltage reaches a predetermined threshold. The predefined hydrogen depletion threshold may be based on the operating conditions of the electrochemical cell prior to deactivation. The method can be performed without connecting the electrochemical cell to an external load. A controller programmed to initiate these actions based on the time elapsed since deactivation can be used to perform the hydrogen application and oxygen removal. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of a traditional hydrogen decompression system;

[0009] Figure 2 This is a schematic diagram of a fuel cell system;

[0010] Figure 3 This is a schematic diagram of a hydrogen de-escalation system;

[0011] Figure 4 It is a diagram of the hydrogen decompression process; and

[0012] Figure 5 This is a flowchart of hydrogen mitigation. Detailed Implementation

[0013] This document describes embodiments. However, it should be understood that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The drawings are not necessarily drawn to scale. Some features may be enlarged or minimized to show details of specific components. Therefore, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching those skilled in the art.

[0014] The various features shown and described with reference to any of the accompanying drawings may be combined with features shown in one or more other drawings to produce embodiments not explicitly shown or described. The combinations of features shown provide representative embodiments for typical applications. However, for a particular application or implementation, various combinations and modifications of features consistent with the teachings of this disclosure may be desired.

[0015] Hydrogen (H2) protection is an aspect of fuel cell technology, particularly for systems such as those in vehicles that may experience extended periods of inactivity. The hydrogen protection process involves maintaining a hydrogen-rich environment within the fuel cell stack, effectively “coating” both the anode and cathode. The primary purpose of this H2 protection is to prevent catalyst degradation, which can affect fuel cell performance.

[0016] In the context of fuel cell powered vehicles, this protection allows for extended shutdowns during periods when the vehicle is inactive. Current technology has not yet effectively demonstrated the ability to maintain effective H2 protection for 90 hours or more. If the vehicle remains inactive for 90 hours or longer, or exceeds this threshold, hydrogen protection may be compromised. In such cases, when the fuel cell stack restarts, it will experience an "air / air start." This exposes both the anode and cathode to air, which can lead to faster degradation of the catalyst materials.

[0017] The effectiveness of hydrogen protection largely depends on the shutdown (SD) process, particularly the oxygen depletion SD that occurs when the vehicle is shut down. If this process is performed correctly, it prepares for an extended period of protection. However, if the oxygen depletion SD does not occur properly, hydrogen protection may only last a few minutes, leaving the fuel cell stack vulnerable to rapid degradation.

[0018] Figure 1 The operation and scavenging (SD) processes of a conventional fuel cell (FC) system are illustrated. During “Operating FC”, the FC has two compartments: the anode, labeled “Anode H2”, and the cathode, labeled “Cathode Air”. During normal operation, these compartments exchange protons only across the selective membrane between the anode and cathode. “FC Immediately Following O2 Depletion SD” shows the FC after oxygen depletion SD. After SD, oxygen is consumed, while the anode remains filled with H2. “FC Minutes After SD” shows the H2 within both the anode and cathode for proper storage to prevent catalyst degradation. If the FC is properly prepared, it can remain inactive for a longer period; however, if not prepared, catalyst degradation can begin within minutes of SD. In “FC After Loss of H2 Protection”, both the anode and cathode have been permeated with oxygen, indicating that hydrogen protection has been lost and air has entered both sides of the FC.

[0019] Figure 2This is a schematic diagram of an automotive FC system 10. The automotive FC system 10 includes an FC 12, which includes an anode 14, a cathode 16, and a separator 18 positioned between the anode 14 and the cathode 16. The separator 18 can be a proton exchange membrane made of a material such as a perfluorosulfonic acid polymer. This separator 18 allows protons to pass through while blocking electrons and gases, which allows electrochemical reactions in the FC 12. The anode 14 and cathode 16 can be made of a porous carbon material coated with a catalyst. For the anode 14, platinum or a platinum-ruthenium alloy can be used as a catalyst to promote the hydrogen oxidation reaction. The cathode 16 can use platinum or a platinum-cobalt alloy to catalyze the oxygen reduction reaction. The FC 12 is connected to a controller 20. The controller 20 manages the operation of the automotive FC system 10. The controller 20 is connected to the FC 12 via communication lines 22. These communication lines 22 enable the controller 20 to monitor various parameters of the FC 12, such as battery voltage, temperature, and gas pressure, and to control different aspects of the FC 12.

[0020] The controller 20 can be programmed to manage the operation of the FC system 10. These operations include injecting H2 into the anode 14 and extracting oxygen from the cathode 16 based on predetermined conditions or time periods. The controller 20 can monitor the voltage from the FC 12 during these processes and can terminate them when certain thresholds are reached to maintain the performance and lifespan of the FC 12. The FC system 10 may include additional components connected to the anode 14 to supply H2, such as an H2 storage system using a high-pressure tank or metal hydride. An air management system, including a compressor and possibly a humidifier, can be connected to the cathode 16 for oxygen supply and control. The configuration of the FC system 10 supports operation without external connection to the electrical bus during H2 maintenance procedures. This allows for greater flexibility in managing the state of the FC 12 during inactive periods, which maintains the integrity of the catalyst bed and extends the overall lifespan of the FC 12. The controller 20 can also be programmed to operate based on an estimated hydrogen depletion rate of the FC 12. This allows for adaptive management of the FC system 10, taking into account factors such as temperature, pressure, and previous usage patterns, to optimize the timing of the hydrogen injection and oxygen extraction procedures.

[0021] Figure 3This is a schematic diagram of the H2 mitigation system 24 for an FC. The H2 mitigation system 24 begins at stage 26, labeled “FC minutes after SD,” which shows the FC 12 immediately following the SD procedure. In this state, both anode 14 and cathode 16 are filled with H2. This state represents the initial hydrogen protection phase, where the FC is prepared for inactivity. The H2 mitigation system 24 has autonomous start (SU) and SD 28 processes to restore H2 protection in the FC 12. During the autonomous SU and SD 28 processes, operation 30, labeled “operating FC,” shows the FC 12 in its normal operating state. Anode 14 is filled with H2, while cathode 16 is filled with air, representing a typical reactant distribution during the operation of the FC 12. During SD operation 32, labeled “FC immediately following O2 depletion SD,” the FC 12 is shown after the oxygen depletion SD. Anode 14 remains filled with H2, while no oxygen remains in cathode 16. Following the autonomous SU and SD 28 processes, H2 from anode 14 permeates across separator 18 into cathode 16. In this stage 34, both anode 14 and cathode 16 are refilled with hydrogen for protection during inactivity. Depending on the length of the inactivity period, the autonomous SU and SD 28 processes can be repeated as needed to maintain the protection stage 34 of FC 12 during extended periods.

[0022] Figure 4 This is a process diagram for managing excessive downtime of an FC system, 36. The process begins with system shutdown 38, which initiates a management sequence. After shutdown, the system evaluates the downtime at decision point 40, thus querying "Too much downtime?" This step determines whether the FC has been inactive for a period that could impair its H2 protection. If the downtime is not excessive, the flowchart results in no action 42, indicating that the current H2 protection is sufficient and no intervention is required.

[0023] However, if the downtime is deemed excessive, the system proceeds to autonomous start 44. Autonomous start 44 initiates a series of automated procedures configured to refresh the H2 protection of the FC. Autonomous start 44 results in normal start procedure 46, in which the FC system undergoes its standard initialization process without closing any electrical contacts with any contact components. This is followed by a short operating period 48, during which the FC briefly runs to restore H2. After the short operating period, the system executes normal shutdown procedure 50. This controlled shutdown during normal shutdown procedure 50 establishes appropriate conditions for extended inactivity by depleting oxygen. The next step is to restore full H2 protection 52, indicating that a protective environment has been created for the FC components, particularly the catalyst layer. Finally, the process ends with a 90+ hour downtime preparation 54. This step sets the FC system for an extended period of inactivity, where the newly restored H2 protection is able to maintain the integrity of the FC for more than 90 hours. However, if the inactivity period is deemed excessive, the excessive downtime duration management system 36 can return to decision point 40 for repetition.

[0024] Figure 5 A flowchart of method 56 for mitigating degradation in an FC system during extended periods of inactivity is shown. A first step 58 involves injecting H2 into the inactive FC system when the duration since the FC system became inactive exceeds a threshold time for H2 depletion across the FC system. This step 58 maintains a protective H2 environment within the FC, thereby preventing catalyst degradation that can occur when the fuel cell is exposed to air during extended periods. A second step 60 involves depleting oxygen from the FC system. This oxygen depletion process creates an inert environment within the FC, further protecting its components from degradation. In further configurations, method 56 may involve monitoring the FC voltage, adjusting the threshold time based on previous operating conditions, and periodically performing method 56 during extended periods of inactivity. H2 injection may be accomplished using a connected storage system, while oxygen depletion may involve activating an air compressor to extract oxygen from the system. Method 56 can potentially be applied more broadly to various types of electrochemical cells in a wide range of applications.

[0025] The algorithms, methods, or processes disclosed herein may be delivered to or implemented by a computer, controller, or processing device, which may include any dedicated electronic control unit or programmable electronic control unit. Similarly, the algorithms, methods, or processes may be stored in many forms as data and instructions executable by a computer or controller, including but not limited to information permanently stored on non-writable storage media such as read-only memory devices and information reproducibly stored on writable storage media such as optical discs, random access memory devices, or other magnetic and optical media. The algorithms, methods, or processes may also be implemented as software executable objects. Alternatively, suitable hardware components, such as application-specific integrated circuits, field-programmable gate arrays, state machines, or other hardware components or devices, or firmware, combinations of hardware and software components, may be used to embody the algorithms, methods, or processes, in whole or in part.

[0026] While exemplary embodiments have been described above, these embodiments are not intended to describe all possible forms covered by the claims. Furthermore, the language used in this specification is descriptive rather than restrictive, and it should be understood that various changes may be made without departing from the spirit and scope of this disclosure. For example, the terms "controller" and "multiple controllers" may be used interchangeably herein, as the functionality of a controller may be distributed across several controllers / modules, all of which may communicate via standard technologies.

[0027] As previously described, features of various embodiments can be combined to form other embodiments of the invention that may not be explicitly described or shown. While various embodiments may have been described as offering advantages or preferences over other embodiments or prior art implementations in terms of one or more desired characteristics, those skilled in the art will recognize that one or more features or characteristics may be compromised to achieve desired overall system properties, depending on the specific application and implementation. These properties may include, but are not limited to, strength, durability, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. Therefore, embodiments described as less desirable than other embodiments or prior art implementations in terms of one or more characteristics are not outside the scope of this disclosure and may be desirable for a particular application.

[0028] According to the present invention, an automotive fuel cell system is provided, the automotive fuel cell system comprising: a fuel cell including an anode, a cathode and a membrane separating the anode and the cathode; and a controller programmed to inject hydrogen into the anode and extract oxygen from the cathode in response to the expiration of a predetermined time period beginning with the disconnection of the fuel cell from an electrical bus.

[0029] According to an embodiment, the controller is also programmed to monitor the voltage of the fuel cell during hydrogen injection and oxygen extraction.

[0030] According to an embodiment, the controller is programmed to terminate the hydrogen injection and oxygen extraction when the voltage reaches a predetermined threshold.

[0031] According to an embodiment, the controller is programmed to perform the hydrogen injection and oxygen extraction without a contactor connecting the fuel cell to the electrical bus engagement.

[0032] According to an embodiment, the predetermined time period is based on the estimated hydrogen depletion rate of the fuel cell.

[0033] According to an embodiment, the invention is further characterized by a hydrogen storage system connected to the anode to supply hydrogen.

[0034] According to an embodiment, the invention is further characterized by an air compressor connected to the cathode for oxygen extraction.

[0035] According to the present invention, a method for mitigation in a fuel cell system includes: injecting hydrogen into the inactive fuel cell system when the duration since the fuel cell system has been inactive exceeds a threshold time for hydrogen depletion across the fuel cell system; and depleting oxygen from the fuel cell system.

[0036] In one aspect of the invention, the method includes monitoring the voltage of the fuel cell system during the injection and the depletion.

[0037] In one aspect of the invention, the method includes terminating the injection and the depletion when the voltage reaches a predetermined threshold.

[0038] In one aspect of the invention, the threshold time is based on the operating conditions of the fuel cell system before activation.

[0039] In one aspect of the invention, the method includes periodically performing the injection and the depletion while the fuel cell system remains inactive for an extended period of time.

[0040] In one aspect of the invention, the injection includes supplying hydrogen from a hydrogen storage system connected to the fuel cell system.

[0041] In one aspect of the invention, the depletion includes activating an air compressor to extract oxygen from the fuel cell system.

[0042] According to the present invention, a method includes: supplying hydrogen to the anode of an inactive electrochemical cell to reactivate the electrochemical cell when the time elapsed since the corresponding electrochemical cell has been deactivated exceeds a predefined hydrogen depletion threshold; and removing oxygen from the electrochemical cell to initiate an inactive state and reduce the residual voltage for subsequent reactivation of the electrochemical cell.

[0043] In one aspect of the invention, the method includes monitoring the voltage of the electrochemical cell during the provisioning process.

[0044] In one aspect of the invention, the method includes terminating the supply and the removal when the voltage reaches a predetermined threshold.

[0045] In one aspect of the invention, the predefined hydrogen depletion threshold is based on the operating conditions of the electrochemical cell prior to the shutdown.

[0046] In one aspect of the invention, the method includes performing the provisioning and removal without connecting the electrochemical cell to an external load.

[0047] In one aspect of the invention, a controller is used to perform the provisioning and the removal, the controller being programmed to initiate the provisioning and the removal based on the time elapsed since the device was deactivated.

Claims

1. An automotive fuel cell system comprising: a fuel cell including an anode, a cathode, and a membrane separating the anode from the cathode; and a controller programmed to inject hydrogen into the anode and extract oxygen from the cathode in response to expiration of a predetermined time period beginning with the fuel cell being disconnected from an electrical bus.

2. The automotive fuel cell system of claim 1, wherein the controller is further programmed to monitor a voltage of the fuel cell during hydrogen injection and oxygen extraction.

3. The automotive fuel cell system of claim 2, wherein the controller is programmed to terminate the hydrogen injection and oxygen extraction when the voltage reaches a predetermined threshold.

4. The automotive fuel cell system of claim 1, wherein the controller is programmed to perform the hydrogen injection and oxygen extraction without a contactor engaging the fuel cell to the electrical bus.

5. The automotive fuel cell system of claim 1, wherein the predetermined time period is based on an estimated hydrogen depletion rate of the fuel cell.

6. The automotive fuel cell system of claim 1, further comprising a hydrogen storage system connected to the anode to supply the hydrogen.

7. The automotive fuel cell system of claim 1, further comprising an air compressor connected to the cathode for extracting oxygen.

8. A method for mitigation in a fuel cell system comprising: injecting hydrogen into an inactive fuel cell system when a duration since the fuel cell system was inactivated exceeds a threshold time for hydrogen depletion across the fuel cell system; and depleting oxygen from the fuel cell system.

9. The method of claim 8, further comprising monitoring a voltage of the fuel cell system during the injecting and the depleting.

10. The method of claim 9, further comprising terminating the injecting and the depleting when the voltage reaches a predetermined threshold.

11. The method of claim 8, wherein the threshold time is based on a duty cycle of the fuel cell system prior to being inactivated.

12. The method of claim 8, further comprising periodically performing the injecting and the depleting when the fuel cell system remains inactive for an extended period.

13. The method of claim 8, wherein the injecting includes supplying hydrogen from a hydrogen storage system connected to the fuel cell system.

14. The method of claim 8, wherein the depleting includes activating an air compressor to extract oxygen from the fuel cell system.

15. A method comprising: providing hydrogen to an anode of an inactive electrochemical cell when a time elapsed since deactivation of the corresponding electrochemical cell exceeds a predefined hydrogen depletion threshold, thereby reactivating the electrochemical cell; and removing oxygen from the electrochemical cell to initiate an inactive state and reduce a residual voltage for subsequent reactivation of the electrochemical cell.

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