Polymer electrolyte membrane, fuel cell stack, single cell voltage acquisition means, and single cell voltage abnormality detection method

Abstract

The objective of this invention is to provide a polymeric electrolyte membrane capable of improving the accuracy of anomaly detection. To achieve this objective, the polymeric electrolyte membrane (50) is used in a fuel cell and comprises: a reinforcing material (22) comprising a material having PTC properties; and ionomer layers (24, 26) coated on both surfaces of the reinforcing material (22).

Description

Technical Field

[0001] This invention relates to a polymer electrolyte membrane for fuel cells, a fuel cell stack, a means of acquiring cell voltage, and a method for detecting abnormal cell voltage. Background Technology

[0002] In recent years, research and development related to fuel cells have been underway to help improve energy efficiency, in order to ensure that more people have access to affordable, practical, sustainable and advanced energy.

[0003] The challenge in fuel cell development lies in suppressing cell degradation caused by the obstruction of hydrogen or air supply, which leads to a negative voltage in the individual cells. Regarding this degradation suppression, Patent Document 1 discloses a technique: when the lowest voltage of a power-generating cell in the fuel cell stack is in the negative voltage region, current extraction from the fuel cell stack is stopped.

[0004] [Existing Technical Documents]

[0005] (Patent Documents)

[0006] Patent Document 1: Japanese Patent Application Publication No. 2009-283138 Summary of the Invention

[0007] [The problem the invention aims to solve]

[0008] Furthermore, in fuel cell-related technologies, a structure is considered for setting up a voltage detection circuit for multiple cells to reduce costs. However, this structure has the following problem: it cannot sufficiently ensure the margin between the voltage value determined to be abnormal and the voltage value determined to be normal, resulting in low anomaly detection accuracy.

[0009] Therefore, the present invention aims to provide a polymeric electrolyte membrane that can improve the accuracy of anomaly detection, thereby solving the above-mentioned problems and contributing to improved energy efficiency.

[0010] [Technical means to solve the problem]

[0011] <1> A polymeric electrolyte membrane for use in fuel cells, the polymeric electrolyte membrane comprising: a reinforcing material comprising a material having PTC properties; and an ionomer coated on both surfaces of the reinforcing material.

[0012] Based on the aforementioned polymeric electrolyte membrane, since it possesses PTC characteristics, the membrane resistance increases due to the temperature rise when the monomer voltage decreases. Therefore, excessive current can be suppressed, thus protecting the polymeric electrolyte membrane.

[0013] <2> according to <1> The aforementioned polymeric electrolyte membrane, wherein the aforementioned PTC characteristic refers to,

[0014] It is conductive in a first temperature region below a specified temperature and substantially non-conductive in a second temperature region above a specified temperature. The aforementioned specified temperature corresponds to the temperature at which the aforementioned polymer electrolyte membrane begins to break down.

[0015] According to the above-described polymeric electrolyte membrane, the polymeric electrolyte membrane has the following characteristic: its resistance increases above a temperature at which membrane rupture begins, or at a temperature below but near the stated temperature. Therefore, it can improve the protective effect of the polymeric electrolyte membrane.

[0016] <3> according to <1> or <2> The aforementioned polymeric electrolyte membrane, wherein the reinforcing material comprises a composite material of PVDF and Ni.

[0017] Based on the above-mentioned polymer electrolyte membrane, it is easy to achieve <2> The aforementioned PTC characteristics.

[0018] <4> A fuel cell stack is formed by stacking multiple layers of power generation cells having an electrolyte membrane, electrode structures, and a separator. The electrolyte membrane comprises... <1> to <3> The polymer electrolyte membrane described in any one of the following statements.

[0019] Based on the above fuel cell stack, a fuel cell stack that is not prone to membrane rupture due to polarity reversal can be obtained.

[0020] <5> A method for obtaining single-cell voltage, <4> The voltage of the aforementioned power generation unit,

[0021] The aforementioned method for obtaining the voltage of a single unit is set up for each of the aforementioned generating units.

[0022] Based on the aforementioned methods for obtaining cell voltage, the number of methods for obtaining cell voltage can be reduced, thereby lowering costs. Furthermore, it simplifies the structure of the fuel cell system.

[0023] <6> according to <5> The aforementioned single-unit voltage acquisition method acquires the sum of the single-unit voltages of multiple aforementioned power generation units.

[0024] Based on the aforementioned methods for obtaining individual unit voltages, simple calculations can be used to determine abnormalities in the generating units.

[0025] <7> A method for detecting anomalies in single-cell voltage, using <5> or <6> The aforementioned single-cell voltage acquisition method determines that one of the power generation cells is abnormal when the single-cell voltage value acquired by the aforementioned single-cell voltage acquisition method is less than the voltage value when one of the aforementioned power generation cells is abnormal and the other aforementioned power generation cells are normal. The voltage threshold for a power generation cell to be abnormal is set as follows: at the voltage, when the polymer electrolyte membrane of the power generation cell is a material with PTC characteristics, membrane rupture does not occur, but when the polymer electrolyte membrane of the power generation cell is a material without PTC characteristics, membrane rupture occurs.

[0026] Based on the above-mentioned method for detecting abnormalities in individual cell voltages, a large margin between abnormalities and normal conditions can be ensured during abnormality detection.

[0027] (The effect of the invention)

[0028] According to the present invention, a polymeric electrolyte membrane that can improve the accuracy of anomaly detection can be provided. Attached Figure Description

[0029] Figure 1 This is a cross-sectional view of the polymer electrolyte membrane according to an embodiment of the present invention.

[0030] Figure 2 This is a block diagram illustrating the structure of a fuel cell system according to an embodiment of the present invention.

[0031] Figure 3 This is a graph showing the relationship between the voltage of a single power generation cell and the temperature of the electrolyte membrane.

[0032] Figure 4 It is a graph showing the change of the lowest single-cell voltage over time during an abnormal event. Detailed Implementation

[0033] (Polymer electrolyte membrane)

[0034] Reference Figure 1 The polymer electrolyte membrane 50 of the present invention will be described in detail. Figure 1 This is a cross-sectional view of the polymer electrolyte membrane 50. The polymer electrolyte membrane 50 is the electrolyte membrane present in the power generation unit 11 constituting the fuel cell stack 10. The polymer electrolyte membrane 50 is an electrolyte membrane used in fuel cells. The fuel cell stack 10 and the power generation unit 11 will be referred to below. Figure 2 This will be explained. In addition, sometimes polymeric electrolyte membranes are simply referred to as electrolyte membranes.

[0035] The polymer electrolyte membrane 50 comprises a reinforcing material 22, an ionomer layer 24, and an ionomer layer 26. The reinforcing material 22 is sandwiched between the ionomer layer 24 and the ionomer layer 26. The ionomer layer is also called a proton exchange layer or an electrolyte layer.

[0036] (Temperature characteristics of the resistivity of the enhanced material)

[0037] In the polymer electrolyte membrane 50 of this embodiment, the reinforcing material 22 comprises a material having PTC characteristics. The positive temperature coefficient (PTC) characteristic refers to the temperature characteristic where resistance increases with increasing temperature. In the polymer electrolyte membrane 50 of this embodiment, the reinforcing material 22 comprises a material having PTC characteristics. Therefore, the resistance of the reinforcing material 22 increases due to the temperature rise when the monomer voltage decreases, thereby increasing the resistance of the polymer electrolyte membrane 50. This suppresses excessive current flow, resulting in the protection of the polymer electrolyte membrane 50.

[0038] (First temperature zone and second temperature zone)

[0039] The PTC characteristics of the reinforcing material 22 are preferably as follows: it is conductive in a first temperature region below a specified temperature, and substantially non-conductive in a second temperature region above the specified temperature. The specified temperature is the temperature corresponding to the temperature at which the polymer electrolyte membrane 50 begins to rupture. The temperature corresponding to the temperature at which the polymer electrolyte membrane 50 begins to rupture refers to the temperature at which the polymer electrolyte membrane 50 begins to rupture, and temperatures near but below the specified temperature.

[0040] The PTC properties of the reinforcing material 22 include the following characteristics: the resistance value increases at or above the temperature at which the polymer electrolyte membrane 50 begins to crack, thereby more effectively protecting the polymer electrolyte membrane 50.

[0041] Typically, as the monomer voltage decreases, the temperature of the polymer electrolyte membrane 50 will rise. At this time, if the resistance of the reinforcing material 22 increases from the point before the polymer electrolyte membrane 50 reaches the temperature at which it begins to rupture, the polymer electrolyte membrane 50 can be protected more effectively.

[0042] By suppressing further temperature rise before reaching the temperature at which cracking begins, it is more effective to prevent the temperature from reaching the point where cracking begins.

[0043] (Materials for reinforcing materials)

[0044] The reinforcing material 22 may also include, for example, a composite material of polyvinylidene fluoride (PVDF) and Ni. PVDF serves as the base polymer in the conductive composite material forming the reinforcing material 22. Ni acts as a conductive filler. A method for producing the conductive composite material from PVDF and Ni may be as follows: First, PVDF particles are thermally melted, and then Ni filler is added thereto. Subsequently, the mixture is kneaded and hot-pressed using a mold. Afterward, it is naturally cooled along with the mold, thereby obtaining the reinforcing material 22 comprising the composite material of PVDF and Ni.

[0045] By setting the material of the reinforcing material 22 to be a composite material of PVDF and Ni, the reinforcing material 22 with the desired PTC properties can be easily obtained.

[0046] (Manufacturing method of polymer electrolyte membrane)

[0047] The manufacturing method of the polymer electrolyte membrane 50 will be described. The polymer electrolyte membrane 50 can be made by coating both surfaces of the reinforcing material 22 with an ionomer. The layers containing the coated ionomer are designated as ionomer layer 24 and ionomer layer 26. Examples of ionomers include perfluorosulfonic acid ionomers and hydrocarbon ionomers. Alternatively, the coating of the ionomer onto the reinforcing material 22 can be performed using conventional methods.

[0048] (Structure of a fuel cell system)

[0049] Reference Figure 2 The fuel cell system 1 of this embodiment will be described. Figure 2 This is a block diagram showing the general structure of a fuel cell system 1. The fuel cell system 1 includes a fuel cell stack 10, a cell voltage acquisition means 15, an anode system 20, a cathode system 30, a power consumption system 40, and a control device 60.

[0050] (Fuel cell stack)

[0051] The fuel cell stack 10 is constructed by stacking multiple power generation cells 11. The power generation cells 11 can be so-called solid polymer monomers. Multiple power generation cells 11 are electrically connected in series. The number of power generation cells 11 stacked in a fuel cell stack 10 can be, for example, more than 200 and less than 400.

[0052] (Power generation unit)

[0053] The power generation unit 11 includes a membrane electrode assembly (not shown), an anode diaphragm (not shown), and a cathode diaphragm (not shown). The anode diaphragm and cathode diaphragm are configured to hold the membrane electrode assembly in place. Both the anode diaphragm and cathode diaphragm are conductive. The anode diaphragm and cathode diaphragm are collectively referred to as diaphragms.

[0054] (Membrane electrode assembly)

[0055] The membrane electrode assembly includes a polymer electrolyte membrane 50 (illustrated in...) Figure 1 (middle) and electrode structure (not shown). The polymer electrolyte membrane 50 includes a solid polymer membrane. The electrode structure has an anode and a cathode.

[0056] (Polymer electrolyte membrane)

[0057] The polymer electrolyte membrane 50 of this embodiment is as previously referred to. Figure 1 As described, it comprises reinforcing material 22, ionomer layer 24, and ionomer layer 26. Furthermore, reinforcing material 22 includes a material with PTC properties.

[0058] (Electrode structure)

[0059] In addition to the anode and cathode, the electrode structure also includes a catalyst for initiating the electrode reactions in the anode and cathode. The catalyst may be, for example, Pt or Ru. Furthermore, the electrode structure may also include a gas diffusion layer.

[0060] (Anode diaphragm)

[0061] An anode flow path 12 is formed on the anode diaphragm. The anode flow path 12 functions as a fuel gas flow path.

[0062] (Cathode diaphragm)

[0063] A cathode flow path 13 is formed on the cathode diaphragm. The cathode flow path 13 functions as an oxidant gas flow path.

[0064] As described above, the polymeric electrolyte membrane of this embodiment comprises: a reinforcing material, including a material with PTC properties; and an ionomer coated on both surfaces of the reinforcing material. Furthermore, the fuel cell stack 10 of this embodiment is composed of multiple stacked power generation cells having an electrolyte membrane, electrode structures, and a separator, wherein the electrolyte membrane includes the aforementioned polymeric electrolyte membrane. Therefore, in the fuel cell stack 10 of this embodiment, a fuel cell stack that is less prone to membrane rupture due to polarity reversal can be obtained. Membrane rupture will be explained below.

[0065] (Anode system)

[0066] The system that supplies and discharges hydrogen to the anode is called the anode system 20. The anode system 20 includes a hydrogen storage tank 21 and an anode piping 25. The anode piping 25 is connected to the anode flow path 12.

[0067] (Cathode system)

[0068] The system that supplies and discharges oxygen to and from the cathode is called the cathode system 30. The cathode system 30 includes a compressor 32 and a cathode piping 35. Air 31 is supplied to the cathode piping 35 via the compressor 32. The cathode piping 35 is connected to the cathode flow path 13.

[0069] (Electricity consumption system)

[0070] The system that consumes the generated electricity from the fuel cell stack 10 is called the power consumption system 40. The power consumption system 40 may include, for example, power consumption devices 41 such as vehicle motors and batteries. The current drawn from the fuel cell stack 10 to the power consumption system 40 is defined as the command current.

[0071] (Control device)

[0072] The control device 60 is a device for controlling the operation of the fuel cell system 1. The control device 60 can control the overall operation of the fuel cell system 1 based on the individual cell voltages acquired by the individual cell voltage acquisition means 15 described below. The control device 60 can execute various processes according to its internally stored programs to control the various devices included in the fuel cell system 1.

[0073] The control device 60 may, for example, determine whether the lowest single-cell voltage is in a negative voltage region or whether it has left the negative voltage region based on the lowest single-cell voltage input from the single-cell voltage acquisition means 15. Furthermore, various devices of the fuel cell system 1 can be controlled based on the determination result. Additionally, the lowest single-cell voltage refers to the lowest single-cell voltage among the single-cell voltages acquired in the fuel cell stack 10.

[0074] (Methods for obtaining individual cell voltage)

[0075] The cell voltage acquisition means 15 is a device for acquiring the cell voltages of the plurality of power generation cells 11 constituting the fuel cell stack 10. The cell voltage acquisition means 15 scans the power generation cells 11 at a predetermined period, for example. Furthermore, it can acquire the cell voltage of each power generation cell 11 and calculate the lowest cell voltage. In addition, the cell voltage acquisition means 15 can output the calculated lowest cell voltage to the control device 60.

[0076] The following describes the reactions in the power generation unit 11. When hydrogen is supplied to each anode via the anode flow path 12, the electrode reaction of formula (1) occurs. Furthermore, when air is supplied to each cathode via the cathode flow path 13, the electrode reaction of formula (2) occurs. As a result, a potential difference is generated in each power generation unit 11.

[0077] 2H₂→4H⁺+4e - (1)

[0078] O2 + 4H+ + 4e- - →2H₂O(2)

[0079] When the fuel cell stack 10 is electrically connected to the power consumption system 40 such as the walking motor and extracts current, the fuel cell stack 10 will continuously generate electricity.

[0080] (Insufficient hydrogen)

[0081] Here, for example, moisture may prevent the supply of the required hydrogen to the anode. In other words, the power generation unit 11 may experience a hydrogen shortage. Once a hydrogen shortage occurs, the voltage of the power generation unit 11, i.e., the unit voltage, will show a downward trend.

[0082] (Individual voltage drop)

[0083] When the voltage of a portion of the generating cells 11 drops while the generating cells 11 on either side of it remain normal, voltage is applied to the generating cell 11 with the dropped voltage from the normal generating cells 11 on either side. As a result, the voltage of the generating cell 11 drops, and sometimes becomes a negative voltage.

[0084] If the voltage drop of the monomer causes an excessive current to flow in the polymer electrolyte membrane 50, the heat generated during the current flow will cause the temperature of the polymer electrolyte membrane 50 to rise, which may lead to the rupture of the polymer electrolyte membrane 50.

[0085] Furthermore, in the absence of hydrogen, the reaction described in (1) will not occur at the anode; instead, water electrolysis will take place. This may result in the decomposition of the anode catalyst, impairing the anode's function.

[0086] Therefore, the cell voltage acquisition means 15 detects a decrease in cell voltage. Furthermore, the control device 60 performs current control on the fuel cell system 1 based on the lowest cell voltage acquired by the cell voltage acquisition means 15.

[0087] Current control can be performed in multiple stages, for example. The following illustrates an example of current control performed in two stages. A first voltage value and a second voltage value are preset as the minimum single-cell voltage to begin specifying current control.

[0088] (First voltage value and current limit)

[0089] When the minimum single-cell voltage drops below the specified voltage, it is determined that the minimum single-cell voltage is in a negative voltage region, and the voltage at which the command current should be 0 A is defined as the first voltage value. Furthermore, the negative voltage region refers to a region where the anode potential of the power generation cell 11, which should normally be reduced, is higher than the cathode potential. When the minimum single-cell voltage obtained by the single-cell voltage acquisition means 15 drops to the first voltage value, the control device 60 sets the command current to 0 A. That is, no power is supplied to the power-consuming device 41. Thus, when the minimum single-cell voltage drops to the first voltage value, the current to the external load is limited.

[0090] (Second voltage value and power generation stop)

[0091] When the minimum cell voltage drops below the specified voltage, the voltage at which the electrolyte membrane of the power generation cell 11 decomposes is defined as the second voltage value. This second voltage value is lower than the first voltage value. The second voltage value is also called the breakdown voltage. When the minimum cell voltage acquired by the cell voltage acquisition means 15 is determined to have dropped to the second voltage value, the control device 60 disconnects the electrical connection between the fuel cell stack 10 and the power consumption system 40. For example, the power consumption device 41, such as a walking motor, which serves as an external load, is disconnected from the fuel cell stack 10. In other words, power generation is stopped when the minimum cell voltage drops to the second voltage value, or more precisely, before the minimum cell voltage drops to the second voltage value.

[0092] (Thermal decomposition of electrolyte membrane and monomer voltage)

[0093] Figure 3 This is a graph showing the relationship between the voltage of the power generation cell 11 and the temperature of the electrolyte membrane. Figure 3 The horizontal axis of the graph shown represents the cell voltage (-V). The vertical axis represents the temperature of the electrolyte membrane (°C). The temperature characteristic of the electrolyte membrane in this embodiment is defined as the first temperature characteristic 301. The temperature characteristic of a conventional electrolyte membrane is defined as the second temperature characteristic 302. Figure 3 The first temperature characteristic 301 and the second temperature characteristic 302 are shown.

[0094] The region where the electrolyte membrane undergoes thermal decomposition is defined as thermal decomposition region 320. Thermal decomposition region 320 is the temperature region above the thermal decomposition temperature of the electrolyte membrane. Figure 3 The thermal decomposition region 320 is shown. Figure 3 In the example shown, the thermal decomposition temperature of the electrolyte membrane is T1. T1, as the thermal decomposition temperature, is the temperature at which the ionomer layer 24 or ionomer layer 26 in the electrolyte membrane ruptures due to thermal decomposition.

[0095] As shown in the first temperature characteristic 301, in the electrolyte membrane of this embodiment, the monomer voltage when the temperature of the electrolyte membrane reaches the thermal decomposition temperature, i.e., T1, is -V1. The monomer voltage when the temperature of the electrolyte membrane of this embodiment reaches the thermal decomposition temperature is defined as the first membrane rupture limit voltage 311.

[0096] In contrast, as shown in the second temperature characteristic 302, in conventional electrolyte membranes, the monomer voltage when the temperature of the electrolyte membrane reaches T1 is -V2. The monomer voltage when the temperature of the conventional electrolyte membrane reaches the thermal decomposition temperature is defined as the second membrane rupture limit voltage 312.

[0097] In the electrolyte membrane of this embodiment, the reinforcing material includes a material with PTC characteristics. Therefore, in the electrolyte membrane of this embodiment, even if the monomer voltage decreases and the temperature of the electrolyte membrane rises, excessive current will not flow because the overall resistance of the electrolyte membrane increases. As a result, the temperature of the electrolyte membrane does not easily rise even if the monomer voltage decreases. In other words, compared with the conventional electrolyte membrane shown in the second temperature characteristic 302, the temperature rise of the electrolyte membrane caused by the decrease in monomer voltage is less. Therefore, in the electrolyte membrane of this embodiment, the monomer voltage at which the temperature of the electrolyte membrane reaches the thermal decomposition temperature is lower than that of the conventional electrolyte membrane.

[0098] In contrast, in conventional electrolyte membranes, the temperature rise of the electrolyte membrane is more rapid when the monomer voltage decreases than in the electrolyte membrane of this embodiment. This is because the reinforcing material does not possess PTC properties. Therefore, in conventional electrolyte membranes, the temperature of the electrolyte membrane only reaches the thermal decomposition temperature at a higher monomer voltage than that of the electrolyte membrane of this embodiment.

[0099] As described above, in the electrolyte membrane of this embodiment, by using an electrolyte membrane with a PTC characteristic material that increases in resistance as temperature rises, the membrane rupture temperature will not be reached even if the monomer voltage is below -V2.

[0100] Reference Figure 4 Explaining anomaly detection and prevention of electrolyte membrane rupture. Figure 4 It is a graph showing the change of the lowest single-cell voltage over time during an abnormal event. Figure 4 The horizontal axis of the graph shows the elapsed time (msec). The vertical axis shows the lowest single-cell voltage (-V) during an abnormal event.

[0101] First, let's explain our past methods for anomaly detection and handling. Anomaly detection primarily involves identifying anomalies based on factors such as individual cell voltage, while anomaly determination mainly involves assessing whether a condition is abnormal based on factors such as individual cell voltage. (Refer to previous...) Figure 3 As explained, the monomer voltage at which the electrolyte membrane reaches its thermal decomposition temperature is the membrane rupture limit voltage. Previously, the membrane rupture limit voltage of electrolyte membranes was the second membrane rupture limit voltage, 312. In the following explanation, if... Figure 3 The second membrane rupture limit voltage 312 is set to -V2.

[0102] Figure 4 In the example shown, for safety reasons under the second membrane rupture limit voltage 312 (-V2), the unit voltage at which power generation is stopped is set to -V3.

[0103] There is a time lag between detecting an anomaly or abnormal signs and initiating or stopping power generation. In other words, there is a time delay between detecting an anomaly or abnormal signs and issuing a power generation stop command and initiating or stopping power generation.

[0104] During the time lag, the individual cell voltage decreases. Therefore, the individual cell voltage for detecting anomalies needs to be a value that takes into account the decrease in individual cell voltage during the time lag. The individual cell voltage for detecting anomalies is defined as the threshold voltage. The previous threshold voltage is defined as the second threshold voltage 422. Figure 4 In this context, -V4 represents the second threshold voltage 422.

[0105] (Current limitation and power generation shutdown)

[0106] This section provides a more detailed explanation of the process from anomaly detection to anomaly response. Anomaly response includes current limiting and power generation shutdown. The details of current limiting and power generation shutdown are as previously explained. Current limiting and power generation shutdown are performed sequentially.

[0107] Figure 4 In the previous example shown, the time from the start of current limit detection to the activation of current limit is T1. That is, the current limit determination time is T1. During this period, the cell voltage decreases at a slope of S1.

[0108] also, Figure 4 In the previous example shown, the time from the start of power generation stop detection to the start of power generation stop is T1. That is, the power generation stop determination time is T1. During the time that overlaps with the current limit determination time during the power generation stop determination time, the individual cell voltage decreases at a slope of S1. During the time that ends after the current limit determination time during the power generation stop determination time, the individual cell voltage decreases at a slope of S2.

[0109] exist Figure 4 In the example shown, the start of power generation shutdown detection is at time T2, which is the time since the start of current limit detection. Furthermore, the start of power generation shutdown is at time T3, which is the time since the start of current limit detection. Therefore, during the period from current limit start T1 to power generation shutdown start T3, the individual cell voltage will decrease at a slope of S2.

[0110] Figure 4 The drop in the aforementioned individual cell voltage is represented by the second voltage drop line 402. The individual cell voltage at the start of current limit detection is determined by tracing back along the second voltage drop line 402 from the start of power generation shutdown. Figure 4 In the example shown, the cell voltage at the start of current limit detection is -V4. The cell voltage at the start of current limit detection is the second threshold voltage 422. Furthermore, in Figure 4 In the example shown, the individual cell voltage at the start of the power generation shutdown detection is -V5.

[0111] As mentioned above, in conventional electrolyte membranes, in order to ensure that the cell voltage at the start of current limiting detection is not lower than -V2, the cell voltage, i.e., the threshold voltage, is set to -V4.

[0112] Next, the threshold voltage of the electrolyte membrane in this embodiment will be explained. In the following description, the differences from the threshold voltage of the conventional electrolyte membrane will be emphasized.

[0113] The membrane rupture limit voltage of the electrolyte membrane in this embodiment is the first membrane rupture limit voltage 311, as previously stated. Figure 3 The value shown is set to -V1.

[0114] Figure 4 In the example shown, for safety reasons regarding the first membrane rupture limit voltage 311, i.e. -V1, the unit voltage at which power generation is stopped is set to a voltage higher than -V1.

[0115] In this embodiment, the time from anomaly detection to power generation shutdown, and the rate of decrease in the individual cell voltage during this period, are the same as in the case of conventional electrolyte membranes. Figure 4 In this embodiment, the decrease in the cell voltage of the electrolyte membrane is shown as the first voltage drop line 401. The changing trend of the first voltage drop line 401 is the same as that of the second voltage drop line 402.

[0116] The cell voltage at the start of current limiting detection is determined, similar to the conventional electrolyte membrane voltage, by tracing back along the first voltage drop line 401 from the start of power generation shutdown. Figure 4 In the example shown, the cell voltage at the start of current limit detection is -V6. This cell voltage at the start of current limit detection becomes the first threshold voltage 421.

[0117] As described above, in the electrolyte membrane of this embodiment, in order to ensure that the cell voltage when power generation stops is not lower than -V1, the cell voltage, i.e., the threshold voltage, at the start of current limiting detection is set to -V6.

[0118] In the polymer electrolyte membrane 50 of this embodiment, the reinforcing material 22 includes a material with PTC properties. Therefore, the first membrane rupture limit voltage 311 is reduced. Furthermore, by reducing the first membrane rupture limit voltage 311, the first threshold voltage 421 is also reduced. Thus, in the anomaly determination of the fuel cell system 1 based on the acquisition results of the cell voltage acquisition means 15, particularly the lowest cell voltage, the occurrence of false determinations can be suppressed. This is especially true in structures where one cell voltage acquisition means 15 is provided for multiple power generation cells, where false determinations can be effectively suppressed. A detailed explanation follows.

[0119] First, let's explain the voltage detection in the power generation cell, which has a conventional electrolyte membrane. (Refer to...) Figure 4 As explained, the threshold voltage for voltage detection, i.e., the second threshold voltage 422, was previously set to -V4.

[0120] This describes the scenario where a single voltage acquisition method is set up for each generator unit. The voltage value acquired by this method is set to a negative value. Because the voltage value is negative, it can be determined that the generator unit is malfunctioning. Setting up a single voltage acquisition method for each generator unit allows for correct determination because the acquired voltage value is specific to the generator unit being acquired. Even if the acquired voltage value is higher than -V4, the negative value still indicates that the generator unit is malfunctioning.

[0121] Next, we will explain the case where a single voltage acquisition method is used for two generator cells. The average value of the voltages acquired by the single-cell voltage acquisition method is set to negative. In this case, since the voltage values ​​are negative, it can be determined that at least one of the two generator cells is abnormal. For example, suppose one generator cell is normal and the other is abnormal. If the absolute value of the normal generator cell voltage is less than the absolute value of the abnormal generator cell voltage, then the sum of the voltages of the two generator cells is negative. Furthermore, the average value of the single-cell voltages is also negative. As described above, when a single voltage acquisition method is used for two generator cells, a correct determination can be made by either the sum of the single-cell voltages being negative or the average value of the single-cell voltages being negative.

[0122] Next, we will explain the scenario where three generator cells are equipped with a single-cell voltage acquisition method. The average value of the cell voltages acquired by the single-cell voltage acquisition method is set to positive. In this case, since the voltage values ​​are positive, it is determined that all three generator cells are functioning normally.

[0123] However, at this point, there may be two normal generating units and one abnormal generating unit among the three generating units. When the absolute value of the voltage of the normal generating units is greater than the absolute value of the voltage of the abnormal generating unit, the sum of the voltages of the three generating units is positive. Furthermore, the average value of the individual unit voltages is also positive. As mentioned above, when a single method for obtaining the voltage of each of the three generating units is used, it is impossible to make a correct determination based on whether the sum of the individual unit voltages is negative or the average value is negative. This is because even if an abnormal generating unit is included, the sum and average values ​​of the individual unit voltages are still positive.

[0124] As mentioned above, in the past, for the purpose of reducing costs, a single voltage acquisition method was set up for multiple power generation units. When scanning multiple power generation units, if more power generation units were added, the anomaly detection threshold needed to be increased to prevent false positives. However, the anomaly detection threshold can only be increased to a range that does not overlap with the voltage of normal power generation units. Therefore, there is a limit to reducing the number of voltage acquisition methods by setting up a single voltage acquisition method for multiple power generation units.

[0125] In contrast, in voltage detection of a power generation cell equipped with the electrolyte membrane of this embodiment, false detections can be suppressed.

[0126] The following explanation uses the case where one individual voltage acquisition method is set up for three power generation cells as an example. In the electrolyte membrane of this embodiment, the individual voltage of abnormal power generation cells is lower compared to the conventional electrolyte membrane. In this embodiment, because the threshold voltage is lower, even when one individual voltage acquisition method is set up for three power generation cells, it is easy to make a correct anomaly determination by the fact that the total value of the individual voltages is negative or the average value of the individual voltages is negative.

[0127] Thus, for a single power generation cell equipped with the electrolyte membrane of this embodiment, even when one cell voltage acquisition method is provided for three power generation cells, the total and average values ​​of the cell voltages remain negative. In other words, false detections caused by the overlap of abnormal negative voltages and normal positive voltages can be suppressed. As a result, the number of power generation cells that can be detected using a single cell voltage acquisition method can be increased.

[0128] As described above, the single-unit voltage acquisition means 15 of this embodiment is a single-unit voltage acquisition means 15 for acquiring the voltage of a power generation unit 11, and one single-unit voltage acquisition means 15 can be set for multiple power generation units 11.

[0129] The individual voltage acquisition means 15 can acquire the sum of the individual voltages of multiple power generation cells 11. Furthermore, the individual voltage acquisition means 15 can also acquire the average value of the individual voltages of multiple power generation cells 11.

[0130] (Methods for detecting abnormalities in single-cell voltage)

[0131] This embodiment describes a method for detecting anomalies in the individual cell voltage. The method uses an individual cell voltage acquisition means 15. When the individual cell voltage value acquired by the individual cell voltage acquisition means 15 is less than the sum of the voltages of multiple generating cells 11 when one of them is abnormal and the other generating cells 11 are normal, it is determined that one of the generating cells 11 is abnormal. The voltage threshold for an abnormal generating cell 11 is set to a voltage at which the polymer electrolyte membrane 50 of the generating cell 11 does not rupture when it is a material with PTC characteristics, but ruptures when it is a material without PTC characteristics. This will be explained below.

[0132] As described above, the single-unit voltage acquisition means 15 of this embodiment can be provided for multiple power generation units 11. Furthermore, when the single-unit voltage value acquired by the single-unit voltage acquisition means 15 is less than the total voltage of the multiple power generation units 11 when one of them is abnormal while the others are normal, it can be determined that one of the power generation units 11 is abnormal. For example, as previously explained, when the acquired single-unit voltage is less than the single-unit voltage value when one of the three power generation units 11 is abnormal while the other two are normal, it can be determined that at least one of the power generation units 11 is abnormal.

[0133] Here, the voltage threshold for determining an abnormality in a single power generation unit 11 can be set based on a previous reference. Figure 4 The first threshold voltage 421 and the second threshold voltage 422 are described. The range above the second threshold voltage 422 and below the first threshold voltage 421 is defined as the threshold setting range 450. Figure 4 The threshold setting range is shown as 450. The voltage threshold for determining an abnormality in a single power generation unit 11 can be set within the threshold setting range of 450.

[0134] The threshold setting range 450 can be explained as follows: The threshold setting range 450 is the voltage at which membrane rupture will not occur when the polymer electrolyte membrane 50 of the power generation cell 11 is a material with PTC characteristics, and the voltage at which membrane rupture will occur when the polymer electrolyte membrane 50 of the power generation cell 11 is a material without PTC characteristics.

[0135] This is because the second threshold voltage 422 and the first threshold voltage 421 can be expressed as follows: That is, when the polymer electrolyte membrane 50 of the power generation cell 11 is a material with PTC characteristics, the voltage at which membrane rupture does not occur is a voltage higher than the second threshold voltage 422. Furthermore, when the polymer electrolyte membrane 50 of the power generation cell 11 is a material without PTC characteristics, the voltage at which membrane rupture occurs is a voltage lower than the first threshold voltage 421.

[0136] In summary, the threshold setting range 450 can be described as the following voltage range: within this voltage range, the polymer electrolyte membrane 50 will not rupture when it has PTC characteristics, but will rupture when it does not have PTC characteristics.

[0137] The single-cell voltage anomaly detection method of this embodiment can ensure a large margin between the abnormal and normal during anomaly detection.

[0138] As described above, this embodiment uses an electrolyte membrane with PTC characteristics. By using a PTC-characteristic material, even if the voltage decreases, the material's resistance increases, thus suppressing excessive current flow. Furthermore, by using a PTC-characteristic material in the electrolyte membrane, the threshold for anomaly detection is lowered, and the individual cell voltage detection circuit integrating multiple cells is also lowered. The PTC-characteristic material has a low resistance at the temperature where the membrane does not rupture, and its resistance increases at the temperature where the membrane ruptures. Therefore, in this embodiment, the voltage value reaching the membrane rupture temperature can be reduced, resulting in sufficient margin for anomaly detection even when the voltage detection circuit is integrated.

[0139] The embodiments of the present invention have been described above. The present invention is not limited to the foregoing embodiments, and various modifications, variations, and combinations are possible.

[0140] Figure Labels

[0141] 1: Fuel Cell System

[0142] 10: Fuel Cell Stack

[0143] 11: Individual power generation unit

[0144] 15: Methods for Obtaining Individual Cell Voltage

[0145] 22: Reinforcing materials

[0146] 24: Isopolymer layer

[0147] 26: Isopolymer layer

[0148] 40: Power Consumption System

[0149] 41: Electrical power consumption equipment

[0150] 50: Polymer electrolyte membrane.

Claims

1. A polymeric electrolyte membrane for use in fuel cells. The polymer electrolyte membrane is composed of a reinforcing material and an ionomer. The reinforcing material contains a material with PTC properties, and the ionomer is coated on both surfaces of the reinforcing material.

2. The polymeric electrolyte membrane according to claim 1, wherein, The PTC characteristic refers to, It exhibits electrical conductivity in the first temperature region below the specified temperature. In the second temperature region above the specified temperature, it essentially becomes a non-conductor. The specified temperature corresponds to the temperature at which the polymer electrolyte membrane begins to break down.

3. The polymeric electrolyte membrane according to claim 2, wherein, The reinforcing material comprises a composite material of PVDF and Ni.

4. A fuel cell stack is formed by stacking multiple power generation cells having an electrolyte membrane, an electrode structure, and a separator, wherein the electrolyte membrane comprises a polymer electrolyte membrane according to claim 1 or 2.

5. A method for obtaining the voltage of a single power generation unit according to claim 4. The method for obtaining the voltage of a single unit is set up for each of the multiple power generation units.

6. The single-cell voltage acquisition method according to claim 5, wherein, The single-unit voltage acquisition method acquires the sum of the single-unit voltages of multiple power generation units.

7. A method for detecting anomalies in a single cell voltage, comprising using the single cell voltage acquisition means according to claim 5. When the voltage value of a single unit acquired by the single unit voltage acquisition means is less than the voltage value when one of the multiple power generation units is abnormal and the other power generation units are normal, it is determined that one of the power generation units has become abnormal. The voltage threshold for an abnormality in a power generation cell is set as follows: at the voltage specified, no membrane rupture occurs when the polymer electrolyte membrane of the power generation cell is a material with PTC characteristics, while membrane rupture occurs when the polymer electrolyte membrane of the power generation cell is a material without PTC characteristics.

Images