Method for controlling fuel cell performance and fuel cell system

Abstract

To provide a technology for controlling the pressure applied to a fuel cell stack in accordance with the state of the fuel cell stack, thereby controlling deterioration in fuel cell performance.SOLUTION: In order to control the performance of a fuel cell stack pressurized by a binding member, the deterioration of the fuel cell stack is evaluated, and when deterioration of the fuel cell stack is confirmed, the pressure applied by the binding members is reduced, thereby suppressing performance deterioration of the fuel cell stack and extending its lifespan.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses a method for controlling the performance of a fuel cell and a fuel cell system. [Background technology]

[0002] Fuel cells are configured as a stack of multiple cells. Fuel cell stacks are sometimes equipped with disc springs to apply pressure evenly to the stacked cells to ensure efficient performance. It has been disclosed that a decrease in fuel cell performance can be prevented by suppressing the misalignment of these disc springs and maintaining uniformity of in-plane pressure (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-062425 Summary of the Invention [Problem to be solved by the invention]

[0004] During fuel cell operation, carbon and other substances contained in the catalyst layer may oxidize, reducing the strength of the catalyst layer. Depending on the applied pressure, this may cause the catalyst layer to collapse, resulting in a decrease in fuel cell performance. The pressure initially intended to improve fuel cell performance may instead accelerate the deterioration of fuel cell performance and shorten its operating life.

[0005] This specification provides a technology for controlling the pressure applied to a fuel cell stack in accordance with the state of the fuel cell stack, thereby preventing the deterioration of fuel cell performance. [Means for solving the problem]

[0006] The technology disclosed herein is embodied in a method for controlling the performance of a fuel cell stack, in which the fuel cell stack is pressurized by a restraining member, and the method evaluates deterioration of the fuel cell stack and, if deterioration of the fuel cell stack is confirmed, reduces the pressurizing force applied by the restraining member.

[0007] According to this method, when deterioration of the fuel cell stack is confirmed, the pressure applied to the fuel cell stack by the restraining member is reduced, thereby suppressing the crushing of the catalyst layer due to the pressure, slowing the rate at which the performance of the fuel cell stack deteriorates, and extending its operating life.

[0008] The technology disclosed herein may also be embodied in a fuel cell system including a fuel cell stack pressurized by a restraining member and a processor that evaluates deterioration of the fuel cell stack and, when the deterioration of the fuel cell stack is confirmed, executes a notification process regarding a decrease in the pressurizing force applied by the restraining member.

[0009] This system notifies the maintenance personnel of the need to reduce the pressure applied by the restraining members by notifying them of the reduction in the pressure applied by the restraining members. By reducing the pressure, it is possible to prevent the catalyst layer from collapsing, slow down the rate at which the performance of the fuel cell stack deteriorates, and extend its operating life. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 10 is a diagram showing the influence of the fastening surface pressure of the stack on the relationship between the operation time of the fuel cell stack and the fuel cell performance. [Figure 2] FIG. 1 is a cross-sectional view showing an example of a fuel cell stack provided with a restraining member. [Figure 3] FIG. 10 is a diagram illustrating steps of a control method. [Figure 4] FIG. 1 is a diagram showing an overview of a fuel cell system. [Figure 5] FIG. 4 is a flowchart showing a process executed by the fuel cell system. DETAILED DESCRIPTION OF THE INVENTION

[0011] One embodiment of the method for controlling the performance of a fuel cell stack disclosed in this specification (hereinafter also simply referred to as the control method) is a method in which the fuel cell stack is pressurized by a restraining member, deterioration of the fuel cell stack is evaluated, and when deterioration of the fuel cell stack can be confirmed, the pressurizing force by the restraining member is reduced.

[0012] The control method is based on the inventors' discovery that the thickness and porosity of the cathode catalyst layer decrease over the operation time of the stack due to oxidation of carbon in the catalyst layer, particularly the cathode catalyst layer. The inventors also discovered that such changes in the catalyst layer shape lead to a decrease in catalytic reaction and ultimately to a decrease in cell performance. Furthermore, the inventors discovered that reducing the pressure applied to the stack can suppress the decrease in cell performance and extend the life of the stack.

[0013] Figure 1 shows the effect of the fastening surface pressure on the stack on the relationship between stack operation time and fuel cell performance. As shown in Figure 1, by reducing the pressure on the stack at a timing when stack degradation can be confirmed, the rate of stack performance degradation can be slowed and the stack lifespan can be extended.

[0014] Another embodiment of the control method includes evaluating the deterioration of the fuel cell stack based on whether an output value of the fuel cell stack satisfies a predetermined condition. According to this embodiment, the deterioration of the fuel cell stack can be easily evaluated.

[0015] Another embodiment of the control method includes evaluating the deterioration of the fuel cell stack based on whether the rate of decrease in the output value of the fuel cell stack satisfies a predetermined condition, which may enable early or highly reliable confirmation of the deterioration of the fuel cell stack.

[0016] Another embodiment of the control method includes evaluating the deterioration of the fuel cell stack based on whether a gas diffusion resistance value of the fuel cell stack satisfies a predetermined condition, which may enable early or highly reliable confirmation of the deterioration of the fuel cell stack.

[0017] One embodiment of the fuel cell system disclosed in this specification includes a fuel cell system (hereinafter simply referred to as a system) including a fuel cell stack pressurized by a restraining member, and a processor that evaluates deterioration of the fuel cell stack and, when deterioration of the fuel cell stack is confirmed, executes a notification process regarding a decrease in the pressurizing force applied by the restraining member. The processor of this system can perform the evaluations specified in the various embodiments of the control method described above.

[0018] The control method and system will be described below with reference to the drawings as appropriate. The type of fuel cell is not particularly limited in this specification, but it may be meaningful to apply it to, for example, a polymer electrolyte fuel cell (PEFC). The fuel cell is also not particularly limited, but it may be used as a power source for driving a mobile body such as a vehicle, or may be used as a stationary type. For convenience of explanation, a fuel cell stack will be described below, followed by a description of the control method and system.

[0019] (Fuel cell stack) As shown in FIG. 1, a fuel cell stack (hereinafter simply referred to as a stack) 2 is configured by stacking a plurality of fuel cell units (hereinafter simply referred to as cells) 4. The cells 4 are not particularly limited and may have a known configuration. In the stack 2, the cells 4 are stacked with separators (not shown) sandwiched between them, and a terminal 6 and an insulating sheet 8 are disposed at each end of the cells.

[0020] The stack 2 is accommodated in an accommodation space Z formed by the stack case 10 and the end plate 12. In the accommodation space Z, a restraining member 20 is arranged between the stack 2 and a ceiling portion 10a of the stack case 10.

[0021] The restraining member 20 is not particularly limited as long as it can bias the stack 2 against the end plate 12 and apply uniform pressure to the entire cell 4. For example, as shown in FIG. 1, the restraining member 20 is composed of a pair of pressure plates 20a, 20b and a spring 22 as a biasing member. The pressure plates 20a, 20b are only required to have a size and rigidity sufficient to allow the biasing force of the spring 22 to be applied to the entire surface of the cell 4.

[0022] The springs 22 are arranged so that the pressure plates 20a, 20b can pressurize the stack 2 in the stacking direction of the cells 4 in the stack 2. For example, disc springs can be used as shown in FIG. 1. The springs 22 are arranged in a number and pattern that can apply a sufficient pressure to the stack 2. In addition to various types of springs, elastic bodies such as rubber can also be used as the biasing members.

[0023] In the stack 2, the restraining member 20 is provided, so that the cells 4 stacked in the stack 2 are uniformly pressurized. As a result, in the stack 2, gas diffusion and catalytic reaction are homogenized within the cells 4, enabling the stack 2 to perform efficiently.

[0024] Next, a method for controlling the cell performance of the stack 2 will be described with reference to Figures 1 and 3. The control method is carried out during maintenance of the stack 2. In the following description, a case where the stack 2 is mounted on a fuel cell electric vehicle (FCEV) will be taken as an example, and the control method executed during vehicle maintenance will be described.

[0025] (Deterioration evaluation process) The deterioration evaluation step S10 evaluates the deterioration of the stack 2. Here, deterioration includes deterioration of the cell performance of the stack 2. For the deterioration evaluation, a suitable index (hereinafter also referred to as a deterioration index) can be appropriately set based on a durability test of the stack 2 or the like.

[0026] The deterioration index is not particularly limited, but may be, for example, the output value of the stack 2 or the rate of decrease thereof. Deterioration can be easily detected by evaluating it based on the output value (e.g., P(kw)). Furthermore, evaluation based on the rate of decrease in the output value allows for highly accurate detection of deterioration or early detection of signs of deterioration. The deterioration index may also be, for example, the gas diffusion resistance value (e.g., R(s / m)) or the rate of increase thereof. Evaluation based on the gas diffusion resistance value allows for detection of deterioration due to a decrease in the porosity of the catalyst layer. Furthermore, evaluation based on the rate of decrease in the gas diffusion resistance value allows for highly accurate detection of deterioration or early detection of signs of deterioration. It may be preferable to use the resistance value of the cathode electrode as the gas diffusion resistance value. For example, the difference in performance of the stack 2 when air is supplied at a sufficiently high stoichiometric ratio and when air is supplied at a stoichiometric ratio of 1 may be used.

[0027] Such an evaluation can be performed by operating the stack 2 or, in addition, by using a known inspection device for fuel cells. In addition, the evaluation of the deterioration of the stack 2 can be performed using the above-mentioned deterioration indicators alone or in combination.

[0028] (Deterioration determination process) The deterioration determination step S20 is a step of determining whether deterioration of the stack 2 can be confirmed based on the deterioration index. To confirm deterioration of the stack 2, it is determined whether the above-mentioned index satisfies a predetermined condition related to deterioration that has been set in advance. The condition is set appropriately in an operational durability test or the like on the stack 2. If deterioration of the stack 2 can be confirmed, the pressure reduction step S30 is performed, and if not, the control method is terminated.

[0029] (Pressure reduction process) The pressure reducing step S30 is a step of reducing the pressure applied by the restraining members 20 when it is determined that the stack 2 has deteriorated. The reduction in the pressure applied by the restraining members 20 to the stack 2 is not particularly limited, and examples of the reduction in the biasing force of the springs 22 include reducing the number of springs 22, changing to springs 22 with weaker biasing force, reducing the thickness of the restraining members 20 themselves, changing the restraining members 20, or eliminating the restraining members 20.

[0030] The degree of reduction in the pressure force is not particularly limited and can be determined appropriately depending on the results of a durability test or the like of the stack 2. The inventors have found that reduction in the pressure force by the restraining member 20 is effective regardless of the degree. They have also found that a decrease in cell performance and an increase in gas diffusion resistance can be suppressed depending on the degree of reduction in the pressure force applied to the stack 2.

[0031] According to this control method, the deterioration of the cell performance of the stack 2 can be suppressed, and the life of the stack 2 can be extended.

[0032] The control method can also be implemented as a control method executed by a fuel cell system, for example. Figure 4 shows an overview of an example of a fuel cell system 30, and Figure 5 shows a flowchart of the processing executed by the system 30. Note that in Figure 4, supply paths for gases and the like are simply shown.

[0033] The system 30 includes the stack 2 and a control device 40 that controls power generation in the stack 2. The control device 40 is an example of a processor in this specification. The control device 40 monitors the output value of the stack 2 using output values ​​acquired from an output meter (not shown) or the like provided in the stack 2. The control device 40 also controls the supply, discharge, and circulation of hydrogen, which is a fuel gas, and oxygen, which is an oxidizer gas. The control device 40 is also configured to be able to output information to an output device such as a display provided outside the system 30. The control device 40 has an executable program stored therein that determines deterioration of the stack 2 and issues an alarm regarding a drop in pressurization caused by the restraining member 20.

[0034] Next, a description will be given of a control method executed by the system 30. In the following description, the characteristic features of the control method executed by the system 30 will be mainly described.

[0035] (Deterioration evaluation process) In the deterioration evaluation step S40, the deterioration of the stack 2 is evaluated. Since the control device 40 monitors the output value of the stack 2, the output value of the stack 2 is used as the deterioration index.

[0036] (Deterioration determination process) In the deterioration determination step S50, it is determined whether the monitored output value has fallen below a preset output value. If the control device 40 can confirm that the stack 2 is deteriorated, it executes the alarm notification step S60. If it cannot confirm this, it ends the control method.

[0037] (Alarm notification process) The pressure reduction step S30 is a step in which, when the control device 40 can confirm that the stack 2 has deteriorated, it issues an alarm requesting a reduction in the pressure applied by the restraining members 20. The alarm notification step is an example of a notification process related to a reduction in pressure applied by the control device 40, as disclosed in this specification. The control device 40 outputs to an external display of the system 30 or a higher-level control device that the time has come to reduce the pressure applied by the restraining members 20, and then ends the control method.

[0038] According to this system 30 and control method, the system 30 detects deterioration of the stack 2 and issues an alarm regarding a decrease in the pressure applied by the restraining member 20. This allows the worker to reduce the pressure applied to the stack 2 even when not performing regular maintenance of the stack 2. Furthermore, even during regular maintenance of the stack 2, the worker can easily understand the need to reduce the pressure applied to the stack 2.

[0039] The above system 30 may be a system 30 including a stack 2 mounted on a vehicle and a control device 40 mounted on the vehicle, or a system 30 including a stack 2 mounted on a vehicle and a control device 40 located outside the vehicle. Alternatively, the system 30 may be a system 30 including a stationary stack 2 and a control device 40.

[0040] In the above system 30, the output value of stack 2 is used as the deterioration index, but this is not limited to this. By providing a device that can detect other deterioration indexes and acquiring index data from the device, it is possible to evaluate and determine the deterioration of stack 2 using other deterioration indexes alone or in combination.

[0041] In the above embodiment, the stack 2 and the restraining member 20 shown in Fig. 2 have been described as an example, but the stack and the restraining member disclosed in this specification are not limited to these. The present invention is widely applicable to known fuel cell stacks and restraining members for pressurizing the cells of the stack.

[0042] Specific examples of the technology disclosed in this specification have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above, such as a fuel cell control method. The technical elements described in this specification or in the drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. The technology exemplified in this specification or in the drawings can achieve multiple objectives simultaneously, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0043] 2 fuel cell stack, 4 cell, 6 terminal, 8 insulating sheet, 10 stack case, 12 end plate, 20 restraint member, 20a, 20b pressure plate, 22 spring, 30 fuel cell system, 40 control device

Claims

1. 1. A method for controlling performance of a fuel cell stack, comprising: the fuel cell stack is pressurized by a restraining member; assessing degradation of the fuel cell stack; The method further comprises reducing the pressure applied by the restraining member when it is determined that the fuel cell stack has deteriorated.

2. The method according to claim 1 , wherein the deterioration of the fuel cell stack is evaluated based on whether an output value of the fuel cell stack satisfies a predetermined condition.

3. The method according to claim 1 , wherein the deterioration of the fuel cell stack is evaluated based on whether a rate of decrease in an output value of the fuel cell stack satisfies a predetermined condition.

4. The method according to claim 1 , wherein the deterioration of the fuel cell stack is evaluated based on whether a gas diffusion resistance value of the fuel cell stack satisfies a predetermined condition.

5. 1. A fuel cell system, comprising: a fuel cell stack pressurized by a restraining member; a processor that evaluates deterioration of the fuel cell stack and, when it is determined that the fuel cell stack has deteriorated, executes a notification process regarding a decrease in the pressure applied by the restraining member; A fuel cell system comprising:

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