JP5708455B2 - Manufacturing method of electrolyte membrane for fuel cell, fuel cell stack - Google Patents

Description

  The present invention relates to a method for producing an electrolyte membrane for a fuel cell, and more particularly to a technique for suppressing shrinkage of an electrolyte membrane during drying.

  Some fuel cells include a polymer electrolyte membrane that exhibits good proton conductivity in a wet state. It is known that the form of the electrolyte membrane changes as the wet state of the cell changes according to the operating conditions of the fuel cell. Since changes in the shape of the electrolyte membrane cause damage to the electrolyte membrane and damage to the membrane electrode assembly composed of the electrolyte membrane and the catalyst layer, a technique for suppressing the change in the shape of the electrolyte membrane due to changes in the wet state has been proposed. ing.

For example, there is a technique in which an electrolyte membrane is swollen in a humid atmosphere containing water as a main component, and a processing is performed in which the electrolyte membrane swollen on a support having a rotating aspect is dried in a state of being restrained and fixed. According to this technique, it is possible to suppress the deviation in thickness of the electrolyte membrane and the generation of wrinkles when the water content is increased.

JP 2007-26727 A JP 2005-166329 A JP 2009-176465 A JP 2007-165077 A

  However, in the conventional technique, since the electrolyte membrane is subjected to swelling treatment so as to have a desired area, the end in the planar direction is restrained and fixed, and the residual stress acts on the electrolyte membrane. . Therefore, during fuel cell power generation, when the water content of the electrolyte membrane increases, it is possible to suppress the occurrence of wrinkles and film thickness unevenness of the electrolyte membrane, but the residual stress of the electrolyte membrane is alleviated during swelling. When the water content of the membrane decreases, the tensile stress acting on the electrolyte membrane increases with drying, which may cause damage to the electrolyte membrane such as tearing or thinning of the electrolyte membrane.

  The present invention has been made in view of the above-described problems, and an object thereof is to suppress deterioration of an electrolyte membrane due to tensile stress resulting from drying of the electrolyte membrane.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A method for producing an electrolyte membrane for use in a fuel cell, comprising: a swelling step for swelling the electrolyte membrane in a humid atmosphere; and a drying step for fixing and drying an end of the electrolyte membrane after the swelling step The amount of the electrolyte membrane before the swelling step that shrinks and deforms in accordance with the dimensional change rate in humidity during power generation of the fuel cell is set as a predetermined shrinkage amount, and the drying step includes the electrolyte that is swollen A manufacturing method, in which a membrane is fixed by shrinking the predetermined shrinkage amount by an amount smaller than an initial size which is a size of the electrolyte membrane before the swelling step.

  According to the manufacturing method of the electrolyte membrane of Application Example 1, the humidity of the electrolyte membrane before the swelling step is equal to the shrinkage amount corresponding to the dimensional change rate in the humidity at the time of power generation of the fuel cell, and the initial dimension of the electrolyte membrane before the swelling step. Shrink more, fix and dry. In the present specification, the dimensional change rate represents the area change rate in the planar direction when the electrolyte membrane expands / contracts depending on the humidity (moisture content), and the humidity during power generation of the fuel cell is the fuel This is the humidity of the electrolyte membrane mounted on the fuel cell during battery power generation. The predetermined shrinkage amount is an area shrinkage amount corresponding to a dimensional change rate measured in advance when the electrolyte membrane before the swelling treatment is changed from a wet state to a dry state. Therefore, when the electrolyte membrane changes from a wet state to a dry state during power generation of the fuel cell, it is possible to suppress tensile stress from acting on the electrolyte membrane due to drying. Therefore, it is possible to suppress a change in shape due to shrinkage distortion of the electrolyte membrane.

[Application Example 2]
A method for producing a first electrolyte membrane used in a fuel cell, wherein a swelling step of swelling a second electrolyte membrane whose dimensional change rate in a plane direction changes according to a wet state in a humid atmosphere, and the swelling step A drying step of drying the second electrolyte membrane to produce the first electrolyte membrane, and the drying step includes supplying the swollen second electrolyte membrane to the fuel cell. The amount of contraction corresponding to the dimensional change rate according to the humidity of the second electrolyte membrane during power generation is contracted from the size of the second electrolyte membrane before the swelling step, and the second electrolyte membrane is contracted in the contracted state. The manufacturing method of fixing the edge part of 2 electrolyte membrane, and making it dry.

  According to the method for manufacturing an electrolyte membrane of Application Example 2, the swollen second electrolyte membrane is subjected to a shrinkage amount corresponding to a dimensional change rate according to the humidity of the second electrolyte membrane during power generation of the fuel cell, It is fixed and dried in a contracted state. Therefore, when the first electrolyte membrane changes from a wet state to a dry state during power generation of the fuel cell, it is possible to suppress the tensile stress from acting on the first electrolyte membrane due to drying. Therefore, it is possible to provide a first electrolyte membrane having a small form change, and to suppress a mechanical form change of the membrane / electrode assembly including the first electrolyte membrane and the electrode catalyst layer, and thus to include the membrane / electrode assembly. The durability of the fuel cell can be improved.

[Application Example 3]
In the method for manufacturing an electrolyte membrane according to Application Example 2, the amount of contraction of the second electrolyte membrane is a lower limit value in which the humidity of the second electrolyte membrane is defined based on the operating state of the fuel cell. A manufacturing method, which is a shrinkage amount corresponding to the dimensional change rate at the time.

  According to the method for manufacturing an electrolyte membrane of Application Example 3, the second electrolyte membrane has a lower limit value of the humidity of the second electrolyte membrane in which the humidity of the second electrolyte membrane is defined based on the operating state of the fuel cell. The amount of shrinkage corresponding to the dimensional change rate at this time is preliminarily contracted by drying. Therefore, when the first electrolyte membrane changes from a wet state to a dry state under the operating conditions of the fuel cell, it is possible to suppress the first electrolyte membrane from being contracted and deformed by a contraction amount that is contracted in advance. . Therefore, damage to the first electrolyte membrane can be suppressed, and a highly durable first electrolyte membrane can be provided.

[Application Example 4]
In the method for manufacturing an electrolyte membrane according to Application Example 2 or Application Example 3, the shrinkage amount of the second electrolyte membrane may be the same as that obtained when the end portion of the first electrolyte membrane is dried without being fixed. A manufacturing method, wherein the amount of contraction is smaller than the amount of contraction of the first electrolyte membrane corresponding to the dimensional change rate in the planar direction of one electrolyte membrane.

  When the end portion of the second electrolyte membrane is dried without being fixed, the produced electrolyte membrane has a large amount of contraction in the plane direction, the electrolyte membrane becomes thick, and proton conductivity decreases. Problems may arise. Moreover, when distortion (undulation) of the electrolyte membrane occurs, there is a possibility that the bonding property with the catalyst layer is lowered. For this reason, when the first electrolyte membrane is fabricated by processing the second electrolyte membrane, the thickness of the first electrolyte membrane is made as thin as possible within the range where tensile stress is unlikely to act on the first electrolyte membrane. It is preferable. According to the method of manufacturing the electrolyte membrane of Application Example 4, the second electrolyte membrane corresponding to the dimensional change rate in the planar direction of the second electrolyte membrane when the end portion of the second electrolyte membrane is dried without being fixed. A shrinkage amount smaller than the shrinkage amount of the electrolyte membrane is dried and contracted and deformed in advance. Therefore, when the first electrolyte membrane is changed from the wet state to the dry state, the strain of the first electrolyte membrane is reduced while suppressing the tensile stress from acting on the first electrolyte membrane due to the drying. It is possible to suppress the proton conductivity.

[Application Example 5]
A fuel cell stack configured by laminating a plurality of cells using the electrolyte membrane manufactured by any one of the application examples 2 to 4, wherein the wet state of the cell is the fuel cell stack in the fuel cell stack. The fuel cell stack, wherein the cell includes the first electrolyte membrane, which differs depending on a cell arrangement position, and the contraction amount is different depending on the cell arrangement position.

  Each cell constituting the fuel cell stack has a different wet state during power generation depending on various assembly conditions such as a stacking position and a fastening load. Therefore, according to the fuel cell stack of Application Example 5, the first electrolyte membrane that is contracted and deformed in advance with a different contraction amount can be assembled to the cell according to the arrangement position of the cell. Therefore, the cost can be suppressed as compared with the case where the first electrolyte membrane in which the shrinkage treatment is applied to all the cells is installed.

  In the present invention, the various aspects described above can be applied by appropriately combining or omitting some of them.

Explanatory drawing which illustrates schematic structure of the cell 110 in an Example. The schematic diagram explaining the dimensional change of the electrolyte membrane accompanying the change of a water-containing state. Explanatory drawing explaining the correlation of the humidity and dimensional change rate of the electrolyte membrane in an Example. The flowchart explaining the manufacturing method of the electrolyte membrane in an Example. A humidity-strain graph 700 showing the correlation between the shrinkage strain during drying of the electrolyte membrane and the humidity at which tensile stress acts. Explanatory drawing explaining the method for fixing in the state which contracted the electrolyte membrane in an Example. The dimensional change graph 800 which shows the comparative example about the relationship between the humidity of an electrolyte membrane, and a dimensional change. The schematic structure of the fuel cell in an Example. The flowchart explaining the selection method of the electrolyte membrane for every cell which comprises the fuel cell stack in an Example.

A. Example:
A1. Cell configuration:
FIG. 1 is an explanatory diagram illustrating a schematic configuration of the cell 110 in the embodiment. FIG. 1A is a schematic cross-sectional view of the cell 110, and FIG. 1B is an explanatory view illustrating a state in which the electrolyte membrane is fixed by a separator. The cell 110 includes a membrane electrode assembly (MEA) 120 and a separator 118 that holds the membrane electrode assembly 120 from both ends. Hereinafter, the membrane electrode assembly 120 is referred to as MEA 120. The MEA 120 includes an electrolyte membrane 112, an anode side catalyst layer (anode side catalyst electrode layer) 114 disposed on one side of the electrolyte membrane 112, and a cathode side catalyst layer (cathode side) disposed on the other side of the electrolyte membrane 112. Catalyst electrode layer) 116. In the following description, the anode side catalyst layer 114 and the cathode side catalyst layer 116 are also collectively referred to as “catalyst electrode layer” or “catalyst layer”.

  The electrolyte membrane 112 is a solid polymer electrolyte membrane (for example, Nafion (registered trademark) membrane: NRE212) formed of a fluorine-based sulfonic acid polymer as a solid polymer material, and has good proton conductivity in a wet state. Have. The electrolyte membrane 112 is not limited to Nafion, and other fluorine-based sulfonic acid membranes such as Aciplex (registered trademark) and Flemion (registered trademark) may be used. Further, as the electrolyte membrane 112, a fluorine-based phosphonic acid film, a fluorine-based carboxylic acid film, a fluorine-hydrocarbon-based graft film, a hydrocarbon-based graft film, an aromatic film, or the like may be used, or reinforcement such as PTFE or polyimide may be used. A composite polymer film having enhanced mechanical properties including a material may be used. The electrolyte membrane 112 has a characteristic that its dimensions change due to swelling and shrinkage accompanying changes in the water-containing state. In this specification, the dimension of the electrolyte membrane 112 represents the dimension in the planar direction of the electrolyte membrane 112, in other words, the area of the electrolyte membrane 112, and the dimensional change indicates a change in area. The electrolyte membrane 112 corresponds to the “first electrolyte membrane” in the claims.

FIG. 2 is a schematic diagram for explaining a dimensional change of the electrolyte membrane 112 accompanying a change in the water-containing state. FIG. 2A shows an initial state of the electrolyte membrane 50 before processing with respect to the electrolyte membrane 112 (hereinafter, the electrolyte membrane 50 before swelling treatment is referred to as “pre-processing electrolyte membrane 50”). FIG. 2B shows the wet pre-process electrolyte membrane 50a that has been humidified and swollen, and FIG. 2C shows the dry pre-process electrolyte membrane 50b after drying from the swollen state. The dimensions in the initial state in FIG. 2A correspond to “the initial dimension that is the dimension of the electrolyte membrane before the swelling process” and “the dimension of the second electrolyte membrane before the swelling process” in the claims. The unprocessed electrolyte membrane 50 corresponds to “second electrolyte membrane” and “electrolyte membrane before swelling treatment” in the claims. 2 (b) to FIG. 2 (c), the unprocessed electrolyte membranes 50 and 50a indicated by broken lines indicate the areas of the unprocessed electrolyte membranes 50 and 50a shown in FIG. 2 (a) to FIG. 2 (b), respectively. . When the pre-process electrolyte membrane 50 is humidified from the initial state shown in FIG. 2 (a), the area increases as shown by the arrow in FIG. 2 (b) to become the pre-process electrolyte membrane 50a. When dried from the state of the pre-processed electrolyte membrane 50a that swells and has an increased area size, it shrinks as shown by the arrow in FIG. 2C, and the area shrinks more than the pre-processed electrolyte membrane 50 of FIG. Thus, the unprocessed electrolyte membrane 50b is obtained. The correlation between the moisture content (humidity) of the electrolyte membrane 50 before processing and the dimensional change will be described in detail later.

  The unprocessed electrolyte membrane 50 is a sheet produced by applying a solvent containing an electrolyte on a water-repellent sheet and drying it. The initial state of the electrolyte membrane before processing represents a state where the swelling treatment and the drying treatment are not performed after the production.

  Returning to FIG. The catalyst layers 114 and 116 are layers that provide a catalyst that promotes an electrode reaction, and are formed of a material that includes a conductive carrier that supports the catalyst and an ionomer as an electrolyte. In addition, as a conductive support | carrier, carbon compounds represented by silicon carbide etc. other than carbon materials, such as carbon black, a carbon nanotube, and a carbon nanofiber, can be used, for example. Moreover, as a catalyst, platinum, a platinum alloy, palladium, rhodium, gold | metal | money, silver, osmium, iridium etc. can be used, for example. Examples of platinum alloys include platinum, aluminum, chromium, manganese, iron, cobalt, nickel, gallium, zirconium, molybdenum, ruthenium, rhodium, palladium, vanadium, tungsten, rhenium, osmium, iridium, titanium, and lead. An alloy with at least one of them can be used. Examples of the ionomer include perfluorosulfonic acid resin material (for example, Nafion), sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfone, sulfonated polysulfide, and sulfonated polyphenylene. Sulfonylated plastic electrolytes such as sulfoalkylated polyether ether ketone, sulfoalkylated polyethersulfone, sulfoalkylated polyetherethersulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, sulfoalkylated polyphenylene, etc. A plastic electrolyte or the like can be used.

  The separator 118 is formed of a dense material that does not transmit gas and has conductivity, such as dense carbon, metal, and conductive resin that are compression-molded. A fuel gas flow path is formed on the surface of the separator 118 on the side in contact with the anode side catalyst layer 114, and an oxidant gas flow path is formed on the surface on the side in contact with the cathode side catalyst layer 116.

FIG. 1B schematically shows a state in which the electrolyte membrane 112 is fixed by the separator 118. In FIG. 1B, the hatched portion indicates the outer edge contact portion between the pair of separators 118 and the electrolyte membrane 112. In FIG. 1A, for convenience of explanation, the electrolyte membrane 112 is described as having an area approximately the same as the area of the separator 118, but actually, as shown in FIG. Has a slightly smaller area than the separator 118, and the pair of separators 118 are arranged so as to sandwich the outer edge of the electrolyte membrane 112. By arranging the electrolyte membrane 112 and the separator 118 in this way, the electrolyte membrane 112 is fixed by the separator 118 and is dimensionally restricted in the planar direction.

  The cell 110 is also arranged on the anode side diffusion layer disposed on the side opposite to the side in contact with the electrolyte membrane 112 of the anode side catalyst layer 114 and on the side opposite to the side in contact with the electrolyte membrane 112 of the cathode side catalyst layer 116. And a cathode-side diffusion layer formed thereon. The cathode side diffusion layer and the anode side diffusion layer are layers that diffuse reaction gases (oxidant gas and fuel gas) used for the electrode reaction along the surface direction of the MEA 120, and are formed of, for example, carbon cloth or carbon paper. The water-repellent treatment may be performed with PTFE resin.

A2. Dimensional change rate of electrolyte membrane:
FIG. 3 is an explanatory diagram for explaining the correlation between the humidity and the dimensional change rate of the unprocessed electrolyte membrane 50 in the example. FIG. 3A is a dimensional change graph 600 showing the dimensional change rate of the pre-process electrolyte membrane 50 with respect to humidity. FIG. 3B schematically shows the dimensional change and the dimensional change rate associated with the expansion / contraction of the pre-processed electrolyte membrane 50 in the planar direction. In FIG. 3B, the unprocessed electrolyte membrane 50 shows the initial state shown in FIG. 2A, and the unprocessed electrolyte membrane 50a shows the swollen state shown in FIG. The pre-electrolyte membrane 50b shows the dry state shown in FIG.

The dimensional change graph 600 is obtained by repeatedly applying a humidification process and a drying process to the electrolyte membrane 50 before processing at a predetermined temperature (80 ° C. in the embodiment) to change from a wet state to a dry state, or from a dry state to a wet state. The result of having measured the dimensional change rate (area change rate) of the electrolyte membrane 50 before a process when a state transition is repeated is represented. In the dimensional change graph 600, the vertical axis represents the dimensional change rate (unit:%) of the unprocessed electrolyte membrane 50, and the horizontal axis represents the humidity (unit:% RH) of the unprocessed electrolyte membrane 50. The dimensional change curve 610 shows the dimensional change tendency of the pre-process electrolyte membrane 50 at the initial state transition, and the dimensional change curve 620 shows the dimensional change tendency of the pre-process electrolyte membrane 50 at the second and subsequent state transitions. In the embodiment, the dimensional change rate is the standard area when the area of the pre-processed electrolyte membrane 50 expands and contracts with the area of the pre-processed electrolyte membrane 50 as a reference (the dimensional change rate is 0%). The ratio of the area change with respect to is shown. When the area expands (expands), the dimensional change rate increases from 0%, and when the area contracts (shrinks), the dimensional change rate decreases from 0%. In the examples, the tensile stress acting on the pre-processing electrolyte membrane 50 was calculated using Equation 1. In Equation 1, E is the Young's modulus, β is the linear expansion coefficient with respect to humidity, and Δε corresponds to the minus part of the dimensional change in the plane direction. By reducing the minus amount, the tensile stress acting on the electrolyte membrane can be reduced.

  In the dimensional change graph 600, the state in which the dimensional change of the pre-processing electrolyte membrane 50 is 0% corresponds to the initial state shown in FIG. Since the pre-process electrolyte membrane 50 is manufactured to have a predetermined shape and size in a state where the humidity is 0%, the stress applied to the pre-process electrolyte membrane 50 during the manufacturing process is applied to the pre-process electrolyte membrane 50. Residual stress exists. Due to the residual stress, the molecular chains of the unprocessed electrolyte membrane 50 are fixed in an unbalanced state. In the experiment for measuring the dimensional change rate, the pre-processing electrolyte membrane 50 is soaked in liquid water and humidified until the water content of the pre-processing electrolyte membrane 50 is saturated at the time of the first humidification. The molecular chain of the film 50 is loosened and the residual stress is relaxed. Therefore, the dimensional change tendency of the electrolyte membrane 50 before processing when the residual stress is relaxed and dried from the humidified state is represented by the dimensional change curve 620. However, when the pre-process electrolyte membrane 50 is mounted on the fuel cell, the residual stress is gradually relieved while repeating the absorption and drying of the generated water by the power generation of the fuel cell. In this case, The dimensional change during the initial multiple state transitions is represented by a dimensional change curve 610. According to the dimensional change tendency represented by the dimensional change curve 610, the tensile change does not act on the pre-processed electrolyte membrane 50 because the dimensional change rate does not become less than 0% during the initial state transition.

  As shown in the dimensional change curve 610, when the pre-process electrolyte membrane 50 is humidified from the initial state, the humidity increases, and the area in the plane direction is increased as shown in the pre-process electrolyte membrane 50a of FIG. The dimensional change rate increases from 0%. The unprocessed electrolyte membrane 50a is saturated in moisture content when the humidity is 120% RH, and the dimensional change rate of the unprocessed electrolyte membrane 50a at this time is + 15.8% as shown in FIG. . That is, the area of the electrolyte membrane 50 before processing is expanded and expanded by 15.8% from the initial state.

  When the pre-process electrolyte membrane 50a is dried from the swollen state, as shown by the dimensional change curve 620, the area shrinks and the dimensional change rate of the pre-process electrolyte membrane 50a gradually decreases. Since the pre-process electrolyte membrane 50a has a loose molecular chain when the water content becomes saturated, when dried, as shown in the pre-process electrolyte membrane 50b of FIG. ) Further shrinks from the initial state, and the dimensional change rate becomes less than 0% (negative state). When excessively dried and the humidity becomes 0%, the dimensional change rate when the unprocessed electrolyte membrane 50 changes to the unprocessed electrolyte membrane 50b is −3.6% as shown in FIG. Become. That is, the area of the electrolyte membrane 50b before processing is contracted by 3.6% from the initial state (FIG. 2A).

  When an unprocessed electrolyte membrane is mounted on a cell of a fuel cell, the dimensional change rate is less than 0% because the end of the electrolyte membrane is fixed by a separator with a dimensional change rate of 0%. If it is attempted to shrink, tensile stress (drying stress) acts on the electrolyte membrane. Due to this tensile stress, the electrolyte membrane undergoes a shape change (such as tearing or thinning). That is, when it is dried excessively, tensile stress acts on the electrolyte membrane due to shrinkage due to drying. When tensile stress exceeding the allowable limit of the electrolyte membrane acts on the electrolyte membrane, the electrolyte membrane may be torn or thinned, which may cause deterioration of the electrolyte membrane.

  As shown in FIG. 3B, the electrolyte membrane 112 of the example is manufactured by subjecting the pre-processed electrolyte membrane 50 to a shrinking treatment that dries in a state in which a predetermined shrinkage amount is shrunk from the initial size. Is done. The predetermined shrinkage amount is a dimensional change rate in humidity at which the unprocessed electrolyte membrane 50 before the swelling treatment can be exposed during power generation of the fuel cell when the unprocessed electrolyte membrane 50 before the swelling treatment is mounted on the fuel cell. It is the amount of shrinkage deformation corresponding to, and in the example, it is the amount of shrinkage when the dimensional change rate is -1.6%. By doing so, damage to the electrolyte membrane 112 due to a change in the wet state is suppressed. The electrolyte membrane 112 is manufactured by the manufacturing method described below.

A3. Manufacturing process of electrolyte membrane:
FIG. 4 is a flowchart illustrating a method for manufacturing an electrolyte membrane in the example. First, an unprocessed electrolyte membrane 50 to be the electrolyte membrane 112 is prepared (step S10). The unprocessed electrolyte membrane 50 corresponds to the electrolyte membrane in the initial state in FIG.

  The pre-process electrolyte membrane 50 only needs to have proton conductivity and insulation. The electrolyte membrane 50 before processing is obtained by mixing a solution prepared by mixing a fluorine-based resin material (for example, perfluorosulfonic acid polymer) with a solvent such as water or alcohol into a water-repellent sheet (for example, Teflon (registered trademark)). It is prepared by coating on a sheet) and drying. It is preferable that the pre-process electrolyte membrane 50 is produced so that a film thickness may be 10 micrometers-50 micrometers. Note that the electrolyte membrane 50 before processing may be a commercially available electrolyte membrane such as Nafion NRE211.

  The pre-process electrolyte membrane 50 prepared in step S10 is immersed in a swelling treatment solution and swollen (step S12). Hereinafter, in this specification, the processing in step S12 is referred to as “swelling processing”.

  Examples of the swelling treatment solution in the examples include water; dimethyl sulfoxide; N-methyl-2-pyrrolidone; alcohols such as methanol, ethanol, propanol, ethylene glycol, propylene glycol; amides of dimethylacetamide and N-dimethylformamide; A mixture of these may be used. In particular, water and dimethyl sulfoxide are preferable. If water is used, even if the swelling treatment solution remains on the electrolyte membrane, there is an advantage that it does not affect other parts constituting the fuel cell and the operation of the fuel cell itself. Further, since dimethyl sulfoxide has a high permeation rate with respect to the pre-process electrolyte membrane 50 made of a fluororesin material, if dimethyl sulfoxide is used, the oriented molecular chain in the pre-process electrolyte membrane 50 is reduced. It becomes easy to loosen, and the pre-processing electrolyte membrane 50 can be reliably swollen. The swelling treatment solution is preferably hot water of 70 ° C. or higher. By so doing, the unprocessed electrolyte membrane 50 can be easily swollen.

  In the swelling treatment, in order to sufficiently swell the unprocessed electrolyte membrane 50, it is preferable to immerse the unprocessed electrolyte membrane 50 in the swelling treatment solution for at least about 10 minutes. The electrolyte membrane 50 before processing becomes a swollen state shown in FIG.

  The swollen pre-process electrolyte membrane 50 is fixed in a state of being loosened by a predetermined dimension (step S14). The shrinkage amount (deformation amount) of the shrinkage treatment with respect to the electrolyte membrane before processing is preferably adjusted based on the humidity to which the electrolyte membrane assembled in the cell can be exposed and the magnitude of the tensile stress acting on the electrolyte membrane. . The adjustment of the contraction amount will be described with reference to FIG.

FIG. 5 is a humidity-strain graph 700 showing the correlation between the shrinkage strain during drying of the electrolyte membrane and the humidity at which tensile stress acts. Humidity - In strain graph 700, the vertical axis represents the humidity [RH Unit%] acting tensile stress in the electrolyte membrane, and the horizontal axis, shrinkage tension (dimension change rate) during the drying process of the membrane [in%] Represents.

  As can be seen from the humidity curve 702 in which tensile stress acts on the pre-process electrolyte membrane 50 (Nafion NRE 211) of this example, when the humidity is less than 43% RH, shrinkage strain increases as the humidity decreases. Here, it is known that the pre-processing electrolyte membrane 50 is dried when the operating state of the fuel cell is changed from, for example, a high load to a low load. For example, it is experimentally known that the humidity of the film 50 is reduced to about 20% RH. Therefore, in the example, in the shrinkage treatment for the pre-processing electrolyte membrane 50, the pre-processing electrolyte membrane 50 was swollen and then relaxed by 1.6% compared to the area in the initial state (dimensional change rate = 0%). In this state, the outer peripheral end of the unprocessed electrolyte membrane 50 is fixed.

  FIG. 6 is an explanatory view illustrating a method for fixing the electrolyte membrane in a relaxed state in the example. In the embodiment, the fixture 200 is used to fix the dimensions of the electrolyte membrane 50 before processing. 6A is a top view of the fixture 200, and FIG. 6B is a cross-sectional view taken along the line AA in FIG. 6A. As shown in FIGS. 6A and 6B, the fixture 200 includes a pedestal 210 whose surface is water repellent and a frame jig 220 made of stainless steel that adjusts the dimensions of the electrolyte membrane 50 before processing. The frame-shaped jig 220 and the pressing jig 230 for fixing the pre-processing electrolyte membrane 50 to the pedestal 210 and a fastening member such as a bolt 240 are provided. The pedestal 210 has a thin Teflon sheet 214 disposed on a plate 212. The pedestal 210 may be constituted by a Teflon sheet or a plate whose surface is processed by Teflon, and the contact portion with the pre-processing electrolyte membrane 50 may be constituted by a water repellent material. In addition, it is preferable that the side surface 222 of the frame-shaped jig | tool 220 which contact | connects the electrolyte membrane 50 before a process, and the lower surface 232 of the press jig | tool 230 are also Teflon-processed. For example, a thin Teflon sheet may be attached to the side surface 222 and the lower surface 232. It is preferable that a plurality of bolts 240 are installed at predetermined intervals on each side of the frame-shaped jig 220 as well as the four corners of the frame-shaped jig 220. In this way, force can be applied evenly to the entire periphery of the pre-processed electrolyte membrane 50.

  In the embodiment, the frame-shaped jig 220 has a shrinkage amount corresponding to the dimensional change rate of the electrolyte membrane 50 before processing when the humidity of the electrolyte membrane is 20% RH (1.6 in the shrinking direction). %) To be smaller by the area corresponding to (%). By so doing, the pre-processing electrolyte membrane 50 in a swollen state is accommodated in the frame-shaped jig 220, so that the pre-processing electrolyte membrane 50 can be contracted to a desired dimension.

  The pre-process electrolyte membrane 50 fixed by the fixture 200 is dried (step S16). Various drying methods, such as a method using a dryer and a method using a heater, can be applied to dry the electrolyte membrane 50 before processing. In the embodiment, the electrolyte membrane 50 before processing is dried using a dryer. The fixture 200 to which the pre-process electrolyte membrane 50 is fixed is placed in a dryer, and the pre-process electrolyte membrane 50 is dried at a temperature in the range of 50 to 70 ° C. within a time range of 40 minutes to 1 hour. Apply. The drying temperature, the drying time, and the like are preferably selected by appropriately selecting appropriate values according to the manufacturing process of the pre-process electrolyte membrane 50 and the type of the swelling treatment solution. Hereinafter, in this specification, the processes in steps S14 and S16 are collectively referred to as “drying process”, and a series of processes of swelling process and drying process is referred to as “shrinking process”.

  In step S14, the pre-processing electrolyte membrane 50 in a swollen state is accommodated and fixed in the frame-shaped jig 220, so that the pre-processing electrolyte membrane 50 is loosened and wrinkled. However, in step S16, the pre-processing electrolyte membrane is formed. Sag is reduced or eliminated in the process of drying the membrane 50.

  As described above, the electrolyte membrane is manufactured. Hereinafter, a comparison of the dimensional change accompanying the humidity change between the electrolyte membrane manufactured in this way and the electrolyte membrane not subjected to the shrinkage treatment will be described.

A4. Comparison result:
FIG. 7 is a dimensional change graph 800 showing a comparative example of the relationship between the humidity and dimensional change of the electrolyte membrane. The dimensional change graph 800 represents a comparative example of the correlation between humidity and dimensional change between the electrolyte membrane that has undergone the shrinkage treatment and the electrolyte membrane that has not undergone the shrinkage treatment. The vertical axis and horizontal axis of the dimension change graph 800 are the same as those of the dimension change graph 600. A dimensional change curve 802 represents a dimensional change rate of an electrolyte membrane produced by subjecting the pre-processed electrolyte membrane 50 to a swelling treatment and then performing a drying treatment without fixing the end portion. A dimensional change curve 804 represents a dimensional change rate of the electrolyte membrane 112 manufactured by performing the shrinkage processing described with reference to FIG. A dimensional change curve 806 represents a dimensional change rate of an electrolyte membrane (that is, the pre-processed electrolyte membrane 50 itself) in which the pre-processed electrolyte membrane 50 has not been subjected to shrinkage treatment (swelling process, drying process). This is the same as the dimensional change curve 620. In the dimension change graph 800, the dimension after the drying process in the contraction process of the dimension change curve 802 is expressed as a dimension change rate = 0%.

  As shown in the dimensional change curve 802, the residual stress is removed from the electrolyte membrane produced by subjecting the electrolyte membrane 50 before processing to a swelling treatment and then subjecting it to a drying treatment without restraining the end portion. When the membrane is subjected to swelling treatment and drying treatment, the area increased by the swelling treatment returns to the initial state (dimensional change rate = 0%) by the drying treatment. That is, no tensile stress acts on the electrolyte membrane.

  However, when the electrolyte membrane is dried without fixing the end portion of the electrolyte membrane 50 before processing, the amount of shrinkage in the planar direction increases, the electrolyte membrane becomes thicker, or the electrolyte membrane is strained ( Undulation) may occur, which may cause a problem of a decrease in proton conductivity. For this reason, when producing an electrolyte membrane by performing shrinkage treatment on the pre-processed electrolyte membrane 50, it is preferable to make the thickness of the electrolyte membrane as thin as possible within a range in which tensile stress is unlikely to act on the electrolyte membrane.

  Further, as shown in the dimensional change curve 806, when the shrinkage treatment is not performed on the unprocessed electrolyte membrane 50, the electrolyte membrane (Nafion NRE211) of the example has an electrolyte membrane of less than 43% RH. The dimensional change rate is less than 0%, and tensile stress acts on the electrolyte membrane. As a result, the electrolyte membrane may be damaged due to the tensile stress, and the power generation performance of the fuel cell may be reduced.

  Therefore, as in the embodiment, by preliminarily deforming the electrolyte membrane by the amount of contraction corresponding to the dimensional change rate when the electrolyte membrane is exposed to the lower limit value of the humidity during fuel cell power generation, the electrolyte membrane 112 is produced. As indicated by a dimensional change curve 806, the electrolyte membrane 112 is pulled even when the humidity is assumed to be exposed to the lower limit (20% RH) under the operating conditions of the fuel cell. It can suppress that a stress acts. The lower limit value of the humidity to which the electrolyte membrane can be exposed during power generation of the fuel cell corresponds to the “lower limit value defined based on the operating state of the fuel cell” in the claims.

  In the embodiment, Nafion NRE211 is used as the pre-processing electrolyte membrane 50, and thus the shrinkage amount in the shrinkage treatment is set to 1.6% as described above. However, the shrinkage amount depends on the type of the electrolyte membrane and the electrolyte membrane. It is preferably determined as appropriate based on the humidity to which the material is exposed and the tensile stress acting on the electrolyte membrane.

  A fuel cell stack including a cell having an electrolyte membrane manufactured by the manufacturing method described above will be described below.

A5. Fuel cell schematic configuration:
FIG. 8 is a schematic configuration of the fuel cell in the example. The fuel cell stack 100 according to the embodiment is a polymer electrolyte fuel cell, and includes a plurality of cells 110 (described in FIG. 1), a terminal 124, an end plate 125, and a resistance measuring unit 130. In the fuel cell stack 100, a terminal 124 and an end plate 125 are arranged so as to sandwich a plurality of stacked cells 110 from both ends in the stacking direction.

  The resistance measurement unit 130 is connected to the terminal 124 and measures the resistance of the fuel cell stack 100. The resistance measurement unit 130 measures the alternating current impedance of the fuel cell stack 100 by detecting the alternating current flowing between both terminals 124.

  In the embodiment, since a fastening load is acting on each cell 110 in the stacking direction of the fuel cell stack 100, a binding force due to friction acts on the electrolyte membrane 112 disposed in each cell 110. Logically, it does not shrink in the plane direction. However, there is a portion where the binding force due to the fastening load does not sufficiently work due to the distribution of the surface pressure in the cell surface and the distribution of the thickness of the members constituting the cell. In such a portion, the electrolyte membrane 112 is likely to undergo a dimensional change in accordance with the moisture content, and as described above, the durability of the electrolyte membrane 112 may be reduced. Therefore, in the embodiment, the durability of the cell is improved by assembling the electrolyte membrane 112 manufactured by subjecting the pre-processed electrolyte membrane 50 to the cell considered to be easily dried.

A6. Selection process of electrolyte membrane to be installed in the cell:
FIG. 9 is a flowchart illustrating a method for selecting an electrolyte membrane for each cell constituting the fuel cell stack in the example. Power generation of the fuel cell stack is performed under the operating conditions of the vehicle on which the fuel cell stack is mounted, and cell resistance is measured for each of the plurality of cells constituting the fuel cell stack 100 (step S20).

In the fuel cell stack, when the load state of the fuel cell stack is changed from a high load to a low load, it is known that the mounted electrolyte membrane is easily dried. Therefore, in the embodiment, the in-plane resistance of each cell after the load state of the fuel cell stack is changed from a high load to a low load is measured, and a cell that is easily dried is specified based on the measurement result. The cell resistance is a local resistance value measured at a plurality of locations in the plane of each cell. A cell having a portion having a resistance value equal to or higher than a predetermined value is determined as a cell that is easily dried.

  For the local resistance value in each cell, various methods conventionally used can be used. For example, the terminal 124 is divided into a plurality of regions by an insulator, and the resistance measuring unit 130 is connected to each of the divided regions. The resistance measurement unit 130 measures a local current value flowing through each region, and calculates a local in-plane resistance value of each cell by dividing the cell voltage by the local current value. Each region is preferably divided on the basis of various conditions such as a position where it is easy to dry. For example, three regions may be provided in the vicinity of the oxidizing gas inlet, the fuel gas inlet, and the fuel gas outlet.

  For the cell determined to be easy to dry in step 20, the humidity of the electrolyte membrane provided in the cell is calculated based on the measured resistance value of the cell (step S22). Note that the humidity calculated at this time is a predicted value, and the humidity is calculated for each divided area.

  For each cell determined to be easy to dry, it is determined whether tensile stress acts on the electrolyte membrane included in the cell based on the calculated humidity and the dimensional change rate of the electrolyte membrane ( Step S24). Specifically, when the electrolyte membrane provided in the cell has at least one portion where the dimensional change rate of the electrolyte membrane corresponding to the calculated humidity is negative, the tensile stress is applied to the electrolyte membrane. Is determined to work.

  For a cell provided with an electrolyte membrane including a portion on which tensile stress acts, the electrolyte membrane provided in the cell is contracted in advance by a contraction amount corresponding to a lower limit value of humidity assumed in power generation of the fuel cell stack. It replaces | exchanges for the electrolyte membrane 112 to which the process was performed (step S26). In the embodiment, since NRE 211 is used as the electrolyte membrane, as described in FIG. 4, the electrolyte dried in a contracted state by 1.6% with respect to the initial size of the electrolyte membrane before processing. Replace with membrane 112. The fuel cell stack is manufactured by assembling the electrolyte membrane to the selected cell as described above and stacking a plurality of cells.

  According to the manufacturing method of the electrolyte membrane of the example, the amount of contraction of the electrolyte membrane before processing when the dimensional change rate in the plane direction of the electrolyte membrane before processing that changes according to the wet state is negative is a state in which the membrane is contracted and deformed beforehand It is fixed with and dried. Therefore, it is possible to suppress the tensile stress from acting on the electrolyte membrane due to drying when the electrolyte membrane provided in the fuel cell changes from a wet state to a dry state during power generation of the fuel cell. Therefore, it is possible to provide an electrolyte membrane that is unlikely to undergo morphological changes (such as tearing or thinning), and suppressing the mechanical morphological change of the membrane electrode assembly comprising the electrolyte membrane and the electrode catalyst layer, and thus the membrane electrode assembly. The durability of the fuel cell comprising

  In addition, according to the method for manufacturing an electrolyte membrane of the example, the pre-processed electrolyte membrane has a humidity when the pre-processed electrolyte membrane has a lower limit of the humidity of the pre-processed electrolyte membrane defined based on the operating state of the fuel cell. Only the amount of shrinkage corresponding to the dimensional change rate is dried in a deformed state. Therefore, when the electrolyte membrane changes from a wet state to a dry state under the operating conditions of the fuel cell, it is possible to suppress the electrolyte membrane from being deformed more than a previously deformed contraction amount. Therefore, damage to the electrolyte membrane can be suppressed, and a highly durable electrolyte membrane can be provided.

  Moreover, according to the manufacturing method of the electrolyte membrane by this invention, the shrinkage distortion of an electrolyte membrane can be adjusted according to the dimension of swelling and shrinkage | contraction processing. Therefore, according to the manufacturing method of the electrolyte membrane of the example, the electrolyte membrane before processing corresponding to the dimensional change rate in the planar direction of the electrolyte membrane before processing when the end portion of the electrolyte membrane before processing is dried without being fixed. The amount of contraction is smaller than the amount of contraction in advance. Therefore, when the electrolyte membrane is changed from a wet state to a dry state, it is possible to suppress the distortion of the electrolyte membrane while preventing the tensile stress from acting on the electrolyte membrane due to drying, and to ensure proton conductivity. .

In addition, under the operating conditions of the fuel cell, the electrolyte membrane can be manufactured by being contracted and deformed in advance by the amount of contraction at the lower limit of the humidity to which the electrolyte membrane can be exposed, and tensile stress is applied to the electrolyte membrane due to drying. Can be prevented from acting.

Further, according to the fuel cell stack of the embodiment, the electrolyte membrane that has been contracted and deformed in advance with different contraction amounts can be assembled to the cell according to the arrangement position of the cell. Therefore, the cost can be reduced as compared with the case where the electrolyte membrane subjected to the shrinkage treatment is installed for all the cells.

B. Variation:
B1. Modification 1:
The lower limit value of the humidity and the dimensional change rate of the pre-process electrolyte membrane used in the cells 110 constituting the fuel cell stack 100 are the power generation conditions of the fuel cell stack (operating conditions of the vehicle on which the fuel cell stack is mounted), It varies depending on various conditions such as the type of the electrolyte membrane before processing and the manufacturing method. Therefore, it is preferable to appropriately change the contraction amount in the contraction process of the electrolyte membrane before processing according to various conditions. In the embodiment, an electrolyte membrane that has been subjected to a shrinking treatment with a shrinkage amount of −1.6% is used, but the amount of deformation to shrink is the flat surface of the electrolyte membrane when the electrolyte membrane is in a predetermined wet state. It is preferable to cause shrinkage deformation by the amount of deformation of the electrolyte membrane corresponding to the dimensional change rate in the direction. The predetermined wet state is a state in which the humidity of the electrolyte membrane is a lower limit value of humidity defined based on the operating state of the fuel cell, and a lower limit value of humidity defined based on the operating state of the fuel cell Is the humidity of the electrolyte membrane after the load changes according to the operating state of the fuel cell. By carrying out like this, the electrolyte membrane which performed the contraction process according to the humidity lower limit of the electrolyte membrane which changes with materials and a manufacturing process can be assembled | attached to a cell.

B2. Modification 2:
In the examples, the electrolyte membrane subjected to the shrinkage treatment with the shrinkage amount of −1.6% is applied to all the cells judged to be easily dried, but the lower limit value of the humidity is specified for each cell. For each cell, an electrolyte membrane that has been subjected to shrinkage treatment with a shrinkage amount corresponding to the lower limit of humidity may be assembled. In this way, each cell can be provided with an electrolyte membrane that has been subjected to shrinkage treatment with an optimum shrinkage amount, and the power generation performance of the fuel cell can be improved.

  As mentioned above, although the various Example of this invention was described, this invention is not limited to these Examples, A various structure can be taken in the range which does not deviate from the meaning.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 50, 50a, 50b ... Pre-process electrolyte membrane 100 ... Fuel cell stack 110 ... Cell 112 ... Electrolyte membrane 114 ... Anode side catalyst layer 116 ... Cathode side catalyst layer 118 ... Separator 120 ... Membrane electrode assembly 124 ... Terminal 125 ... End plate 130 ... Resistance measurement part 200 ... Fixing tool 210 ... Base 212 ... Plate 214 ... Teflon sheet 220 ... Frame jig 230 ... Pressing jig 240 ... Bolt 600 ... Dimensional change graph 610 ... Dimensional change curve 620 ... Dimension Change curve 700: Humidity where tensile stress acts-Shrinkage strain graph when drying electrolyte membrane 702 ... Humidity curve where tensile stress acts 800 ... Dimensional change graph 802 ... Dimensional change curve 804 ... Dimensional change curve 806 ... Dimensional change curve

Claims (5)

A method for producing an electrolyte membrane used in a fuel cell,
A swelling step of swelling the electrolyte membrane in a humid atmosphere;
A drying step of fixing and drying the end of the electrolyte membrane after the swelling step,
The amount of the electrolyte membrane before the swelling step that shrinks and deforms in accordance with the dimensional change rate in humidity during power generation of the fuel cell is set as a predetermined shrinkage amount,
In the drying step, the swollen electrolyte membrane is loosened and fixed by the predetermined shrinkage amount from the initial size which is the size of the electrolyte membrane before the swelling step, and dried .
The manufacturing method is realized by loosening the electrolyte membrane by applying a force uniformly to the entire periphery of the electrolyte membrane . A method for producing a first electrolyte membrane used in a fuel cell, comprising:
A swelling step of swelling the second electrolyte membrane whose dimensional change rate in the planar direction changes according to the wet state in a wet atmosphere;
And after the swelling step, drying the second electrolyte membrane to produce the first electrolyte membrane, and
The drying step
The second electrolyte membrane being the swelling, by contraction amount corresponding to the dimensional change rate according to the humidity of the second electrolyte membrane during power generation of the fuel cell, wherein the swelling step prior to the second More slack than the electrolyte membrane dimensions,
Fixing the end of the second electrolyte membrane in the relaxed state, and drying ;
The loosening of the second electrolyte membrane is a manufacturing method realized by applying a force evenly to the entire periphery of the second electrolyte membrane . A method for producing a first electrolyte membrane used in a fuel cell, comprising:
A swelling step of swelling the second electrolyte membrane whose dimensional change rate in the planar direction changes according to the wet state in a wet atmosphere;
And after the swelling step, drying the second electrolyte membrane to produce the first electrolyte membrane, and
The drying step
The second electrolyte membrane being the swelling, by contraction amount corresponding to the dimensional change rate according to the humidity of the second electrolyte membrane during power generation of the fuel cell, wherein the swelling step prior to the second More slack than the electrolyte membrane dimensions,
Fixing the end of the second electrolyte membrane in the relaxed state, and drying ;
Contraction amount of the second electrolyte membrane humidity of the second electrolyte membrane, a contraction amount corresponding to the dimensional change rate when the lower limit is defined based on the operating state of the fuel cell,
Production method. A method for producing the first electrolyte membrane according to claim 2 or 3, wherein
The amount of contraction of the second electrolyte membrane corresponds to the dimensional change rate in the planar direction of the first electrolyte membrane when the end portion of the first electrolyte membrane is dried without being fixed. The amount of contraction is smaller than the amount of contraction of the electrolyte membrane of
Production method. A fuel cell stack configured by stacking a plurality of cells using the first electrolyte membrane manufactured by the manufacturing method according to claim 2,
The wet state of the cell depends on the position of the cell in the fuel cell stack,
The cell includes the first electrolyte membrane having a different amount of shrinkage depending on an arrangement position of the cell.
Fuel cell stack.

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