JP2010170817A - Method for manufacturing solid polymer fuel cell stack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce total contact resistance while securing corrosion resistance of a metal base material constituting a separator in a solid polymer fuel cell stack. <P>SOLUTION: A method for manufacturing the solid polymer fuel cell stack comprises using, as a base material, stainless steel having a roughened surface with a surface area not less than twice the projection area and with a surface roughness SRa of 2 μm or less, arranging MEAs (membrane electrode assemblies) and separators alternately on the roughened surface of the base material to form a laminated structure, using the separators having conductive coating films with an average thickness of 3-50 μm formed by solidifying conductive carbon particles with thermosetting resin. The laminated structure is fixed so that the average surface pressure at a contact part between the electrode surface of the MEA and the conductive coating film surface of the separator is 0.5-5 MPa, and then in the fixed state, heat treatment is applied so that the conductive coating film of each separator is held for 10 minutes or longer at 90-200°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a polymer electrolyte fuel cell stack having a plurality of cells.

  In a polymer electrolyte fuel cell, one cell is formed by a solid polymer membrane, which is an ion exchange membrane, electrodes on both sides (positive electrode and negative electrode), and a gas flow channel facing each electrode. In order to obtain a large electromotive force, each cell is separated by a separator and used as a stacked “stack”. As members of the electrode and the ion exchange membrane, MEA (membrane electrode assembly) in which an electrode sheet such as carbon paper is joined to both sides of the ion exchange membrane is generally used. The separator has a role of isolating each cell and electrically connecting the positive and negative electrodes of adjacent cells. Therefore, the MEA electrode surface (for example, carbon paper surface) and the separator surface are in partial contact with each other, and a gap serving as a gas flow path is provided between the two. Usually, a contact portion between the gas flow path and the electrode is formed by forming a plurality of grooves on the surface of the separator.

  Conventionally, separators made of carbon have been used for various practical tests and the like, but recently, development of applying a metal material that is resistant to vibration and impact and is inexpensive is underway. However, to apply a metal separator, it is necessary to clear the problem of corrosion. That is, in a general polymer electrolyte fuel cell using a fluororesin or the like as an ion exchange membrane, an acidic substance is generated by the decomposition of the ion exchange membrane, which becomes a major factor that corrodes the metal separator. When the metal separator corrodes, not only does the contact resistance between the separator and electrode increase and the battery output decreases, but also the metal ions eluted due to corrosion enter the ion exchange membrane, the ion conductivity decreases. Decomposition of the ion exchange membrane may be promoted by ions.

  As a relatively inexpensive high corrosion resistance material, there is stainless steel, and its corrosion resistance is secured by a passive film as is well known. However, since the passive film is inferior in conductivity, the contact resistance between the separator and the electrode increases if stainless steel is used as it is for the separator. Even if a stainless steel type with high corrosion resistance is selected, it does not always show satisfactory corrosion resistance when exposed to the internal environment of a solid polymer fuel cell that is in an acidic environment. On the other hand, noble metal materials such as gold and platinum exhibit good corrosion resistance and conductivity, but are expensive and difficult to adopt in order to popularize solid polymer fuel cells.

  Therefore, a method of providing a conductive coating layer on the surface of stainless steel has been proposed (Patent Documents 1 and 2).

JP-A-11-345618 JP 2001-283880 A Japanese Patent No. 3818723

  Patent Document 1 describes a separator material in which a graphite (graphite) -containing resin coating layer having a thickness of 3 to 20 μm is formed on the surface of austenitic stainless steel. In this material, the strong passive film on the surface of the base material is removed by the pickling treatment, and it is considered that the contact resistance due to the passive film is reduced. However, in this separator material, the content of graphite is limited in securing the adhesion of the coating layer, and as a result, the contact resistance of the substrate / coating layer, the electrical resistance of the coating layer itself, and the coating layer / The resistance taking into account all the contact resistances between the carbon electrodes (total contact resistance) has not necessarily been reduced to a satisfactory level. That is, the total contact resistance increases due to the provision of the coating layer.

  Patent Document 2 describes a separator material in which a carbon-containing resin coating layer is formed on the surface of a roughened stainless steel substrate. In this case, the adhesion of the coating layer is improved. However, according to subsequent investigations, it was found that the resin-coated stainless steel material produced by the method of Patent Document 2 does not necessarily have satisfactory characteristics in corrosion resistance. It is conceivable that the coating layer thickness is as thin as about 1 μm. Then, it tried to increase the coating layer thickness using the technique of the cited reference 2. FIG. However, since the amount of carbon in the coating layer is small, increasing the coating layer thickness also increases the total contact resistance.

  By applying the techniques of these documents, the surface of the stainless steel substrate is roughened to improve the adhesion of the coating layer, and the amount of carbon in the coating layer is increased, thereby increasing the coating layer thickness. It was thought that the improvement of the total contact resistance when thickened and the improvement of the corrosion resistance in the polymer electrolyte fuel cell environment could be realized at the same time. However, it turned out that it was not always the case.

  The present invention secures the corrosion resistance of a metal substrate constituting a separator in a stack of polymer electrolyte fuel cells in which a separator based on a metal and a general MEA having an electrode such as carbon paper are combined. However, it is intended to provide a technique for reducing the total contact resistance.

The above purpose is to construct a polymer electrolyte fuel cell stack having a plurality of cells by alternately arranging MEAs (membrane / electrode assemblies) and separators.
As the MEA, an electrode sheet composed of fibrous carbon is joined to the surface of the ion exchange membrane,
As a separator, a stainless steel having a rough surface with a surface area of 2 times or more of the projected area and a surface roughness SRa of 2 μm or less is used as a base material. Using a conductive coating film having an average thickness of 3 to 50 μm obtained by solidifying the carbon particles with a thermosetting resin,
The MEA and the separator are alternately arranged to form a laminated structure, and after fixing the laminated structure so that the average surface pressure at the contact point between the electrode surface of the MEA and the conductive coating surface of the separator is 0.5 to 5 MPa, This is achieved by a method for producing a polymer electrolyte fuel cell stack in which heat treatment is performed so that the conductive coating film of each separator is held at 90 to 200 ° C. for 10 minutes or longer in the fixed state.

  Here, the projected area of the base material is an area of a certain measurement region (microscope field of view) as seen from a direction perpendicular to the plate surface of the stainless steel base material (thickness direction of the steel plate). That the surface area is more than twice the projected area means that the actual surface area in the measurement region is more than twice the projected area of the measurement region. The surface roughness SRa means the average roughness (three-dimensional average surface roughness) in the center plane (reference plane) when the surface roughness curve is approximated by a sine curve, and each point obtained using a laser microscope or the like It is calculated | required by measuring the height of these and performing three-dimensional surface roughness analysis about those measurement data. The measurement area may be, for example, a rectangular area (for example, 50 μm × 50 μm) having a side of 40 μm or more. As the actual surface area and the surface roughness SRa, values measured using a scanning confocal laser microscope are employed. The average thickness of the conductive coating film is the average thickness including the coating layer portion that has entered the recesses on the roughened surface of the base material. If the relationship between the coating amount and the coating film thickness is known, The average thickness of the conductive coating film can be calculated from the coating amount per unit projected area on the material surface.

  The conductive coating film preferably contains 30 to 300 parts by mass of graphite as conductive carbon particles with respect to 100 parts by mass of the thermosetting resin, and further contains carbon black in a range of 100 parts by mass or less. It doesn't matter. An example of the thermosetting resin of the conductive coating film is a phenol resin. The roughened surface of the substrate is preferably formed by chemical removal means. The heat treatment can be performed by flowing a gas of 90 to 200 ° C. through the gas flow path of each cell, or by placing each cell in an atmosphere of 90 to 200 ° C. in the fixed state. While each cell is placed in an atmosphere of 90 to 200 ° C. in the fixed state, a gas of 90 to 200 ° C. may be allowed to flow through the gas flow path of each cell.

  According to the present invention, in a polymer electrolyte fuel cell using stainless steel as a separator material, the contact resistance between the separator and the MEA can be significantly reduced by a simple method. In addition, corrosion of stainless steel can be sufficiently prevented in an acidic environment inside the fuel cell. Therefore, the present invention can contribute to the spread of solid polymer fuel cells.

The cross-sectional SEM photograph of the surface vicinity of the separator used as the object of this invention. SEM photograph of carbon paper surface. The cross-sectional SEM photograph of the contact location of the separator and the carbon fiber of an electrode after heat processing. The graph which showed the relationship between heat processing temperature and the total contact resistance between a separator / electrode. The graph which showed the time-dependent change of the total contact resistance at the time of performing a temperature fluctuation for 6 cycles.

  The total contact resistance (total contact resistance between separator / electrode) between a separator having a conductive coating film formed on the surface of a stainless steel substrate and an electrode using fibrous carbon such as carbon paper is “stainless steel base It greatly depends on “contact resistance of material / conductive coating film”, “internal resistance of conductive coating film” and “contact resistance of conductive coating film / electrode”.

As a result of detailed studies, the inventors have obtained the following findings.
(I) In order to reduce the “contact resistance of the stainless steel substrate / conductive coating film”, it is extremely effective to make the surface of the stainless steel substrate have a specific roughened form. It is also effective to perform a heat treatment described later. Further, it is advantageous that the conductive coating film covering the roughened surface of the stainless steel contains a large amount of conductive carbon particles having a large particle diameter such as flake graphite.
(Ii) In order to reduce “internal resistance of the conductive coating film”, it is effective to increase the content of conductive carbon particles in the coating film, and it is particularly advantageous to contain flake graphite. .
(Iii) In order to reduce the “contact resistance of the conductive coating film / electrode”, it is important to create a state where the conductive carbon particles in the coating film and the carbon fibers constituting the electrode are in sufficient contact. For this purpose, it is extremely effective to perform the heat treatment described later. In particular, it is advantageous to contain a large amount of flake graphite in the conductive coating film.
The present invention has been completed based on such findings. Hereinafter, matters for specifying the present invention will be described.

[Stainless steel substrate]
The surface of stainless steel as a base material needs to have a specific roughened form. As a result of various studies, when the surface is a roughened surface having a surface area of 2 times or more than the projected area and a surface roughness SRa of 2 μm or less, “contact resistance of stainless steel substrate / conductive coating film” is remarkable. To reduce. Although the mechanism is not necessarily clear, the resin of the coating film is deformed by heat treatment in a state where a surface pressure is applied as described below. It is presumed that the contact opportunity between the filler and the stainless steel base material may be greatly increased. In particular, in the case of a coating film containing a large amount of flake graphite particles, the graphite particles have a remarkably large particle size and a flake shape compared to commonly used conductive carbon fillers such as carbon black. Therefore, it is considered that the chance of contact between the projections and the graphite particles on the roughened surface of the base material is greatly increased, and is particularly effective in reducing the “contact resistance of the stainless steel base material / conductive coating film”. Become.

  However, it is important that the pits constituting the roughened surface of the substrate are not excessively large. Specifically, when the surface roughness SRa is larger than 2 μm, the “contact of stainless steel substrate / conductive coating film” may be used even if the substrate has an uneven shape such that the surface area is twice or more the projected area. The “resistance” may not decrease sufficiently. As one of the causes, it can be considered that the number of contact portions between the convex portions on the roughened surface and the conductive filler particles is reduced.

  The size of the surface area with respect to the projected area needs to be twice or more, but according to the alternating electrolysis treatment in ferric chloride aqueous solution (see Patent Document 3), it is possible to produce a thing close to 8 times. it can. It has been confirmed that even such a thing can reduce the “contact resistance of the stainless steel substrate / conductive coating film”. Therefore, the size of the surface area relative to the projected area may be adjusted in the range of about 2 to 8 times. On the other hand, the surface roughness SRa is specified to be 2 μm or less, but the lower limit is not particularly required because it is restricted by specifying the ratio of the surface area to the projected area to be twice or more. A particularly preferable SRa range is 0.5 to 2 μm.

  As the stainless steel used for the base material, it is not necessary to apply a steel type with particularly improved corrosion resistance. “Stainless steel” is steel having a Cr content of 10.5% or more as described in JIS G0203: 2000, number 4201, and various steel types are applicable. For austenite, Cr: 10.5 to 40% by mass, preferably 11 to 30% by mass, Ni: about 5 to 30% by mass, and for ferrite, Cr: about 10.5 to 40% by mass, preferably 15 to A steel grade of about 30% by mass can be adopted. For example, SUS304, SUS316, SUS310S etc. are mentioned in the austenite type if the steel types specified in JIS G4305: 2005 are exemplified, and SUS430, SUS436L, SUS444, SUS445J1, SUS445J2, SUS447J1, etc. are mentioned in the ferrite type.

  For example, the base stainless steel plate having a thickness of about 0.1 to 0.6 mm can be used. In order to form a gas flow path in the cell, the shape is generally processed into a corrugated plate shape. What is necessary is just to give the roughening process by a chemical removal means in the state of a flat plate, and shape | mold it in a predetermined shape after that. The coating for forming the coating film described later may be performed in a state of a flat plate before processing (pre-coating) or after processing (post-coating).

[Conductive coating]
A separator applicable to the present invention is obtained by forming a conductive coating film in which carbon particles, which are conductive fillers, are hardened with a thermosetting resin as a binder on the roughened surface of the stainless steel substrate. .

  As the resin that is a constituent material of the coating film, thermosetting resins such as phenol resins and epoxy resins are effective. The thermosetting resin is not excessively softened in the heat treatment described later, and the surface pressure between the separator and the electrode is maintained sufficiently high even after the heat treatment, and thus is excellent in the effect of reducing the total contact resistance. Phenol resins and epoxy resins are also suitable for solid polymer fuel cell applications because of their excellent water resistance.

  It is desirable to use graphite particles as the conductive carbon particles. In particular, flake graphite particles are effective in reducing resistance. When the coating is applied, the wide surface of the graphite particles (the plane perpendicular to the thickness direction) is easily oriented at an angle close to the parallel to the substrate surface when the paint is applied. Since it becomes easy to line up in the state which overlapped, when surface pressure is given between a substrate and MEA, conduction by contact of each graphite particle becomes easy to be secured. As the flake graphite, it is desirable to use flake graphite powder having an average particle diameter D50 of 1 to 20 μm by a laser diffraction particle size distribution analyzer. Such flake graphite powder is composed of particles having an average thickness of 1 to 5 μm and an average diameter (major axis) of about 5 to 100 μm.

  It is desirable to add 30 parts by mass or more of graphite to 100 parts by mass of the thermosetting resin, and it is more preferable to add 45 parts by mass or more. By solidifying a large amount of graphite with a thermosetting resin in this manner, the “internal resistance of the conductive coating film” can be kept low. It is also advantageous to reduce “stainless steel substrate / conductive coating contact resistance” and “conductive coating / electrode contact resistance”. However, if the graphite content is excessively high, the kneadability with the resin is lowered, so the graphite content needs to be adjusted within a range where the paint can be prepared. For example, it is desirable that the amount of graphite blended with respect to 100 parts by mass of the thermosetting resin is 300 parts by mass or less.

  Carbon fibers can be used as the conductive carbon particles other than graphite. In particular, short fibers obtained by cutting carbon fibers having a diameter of about 2 to 20 μm into lengths of about 5 to 100 μm can be used as the conductive carbon particles.

  In order to further improve the conductivity of the coating film, it is more preferable to further contain carbon black. In that case, it is more effective to add 10 parts by mass or more of carbon black to 100 parts by mass of the thermosetting resin, and it is more effective to add 20 parts by mass or more. However, when it is excessively contained, kneadability is lowered and it becomes difficult to prepare a uniform paint. Therefore, when carbon black is blended, it is performed in a range of 100 parts by mass or less relative to 100 parts by mass of the thermosetting resin. It is desirable.

  The average thickness of the conductive coating film (the average thickness of the cured coating film formed on the substrate surface before application of surface pressure) is preferably 3 to 50 μm. If the thickness is less than 3 μm, the number of graphite contained in the film thickness decreases, and the deformation of the coating film due to heating becomes difficult to occur, so that the total contact resistance is unlikely to decrease. Moreover, corrosion resistance also falls. If it exceeds 50 μm, the deformation of the coating film becomes large in the heat treatment under pressure described later, and the surface pressure tends to decrease. In that case, the effect of reducing the total contact resistance is reduced.

  FIG. 1 illustrates a cross-sectional SEM photograph near the surface of a separator that is the subject of the present invention. In this example, the surface area of SUS445J1 having a roughened surface with a surface area of about 5.5 times the projected area and a surface roughness SRa of 1.1 μm is applied to 100 parts by mass of phenol resin. A conductive coating film is formed by blending 110 parts by mass of flake graphite powder and further blending 40 parts by mass of carbon black. It can be seen that the graphite particles (portions that appear bright in the coating film) are oriented so that their wide surfaces (planes perpendicular to the thickness direction) are at angles close to parallel to the substrate surface.

[MEA]
MEA (Membrane Electrode Assembly) can be applied to various commercially available materials, but those having a sheet-like electrode composed of carbon fiber such as carbon paper on the surface thereof. Is preferred.

  FIG. 2 illustrates an SEM photograph of the carbon paper surface. Carbon paper is composed of carbon fibers and has a high porosity of about 80%, for example. For this reason, when it is made to contact with the separator coating film surface, the contact pressure at the contact point between the carbon fiber and the conductive coating film increases, which is advantageous in reducing the contact resistance.

〔stack〕
As the separator that is a constituent member of the polymer electrolyte fuel cell stack, a separator in which the conductive coating film is formed on the surface of the roughened stainless steel plate is used. A separator with a conductive coating on both sides of a corrugated stainless steel substrate, and two corrugated stainless steel substrates are welded, brazed, pressed, etc., and a cooling water flow path is formed inside A separator of a type provided with a conductive coating on the outer surfaces on both sides can be applied. MEAs and separators are alternately arranged to form a laminated structure. Usually, current collectors having the same structure as the separator are disposed at both ends of the laminated structure. By applying a compressive load between the current collectors at both ends and fixing the laminated structure in a state where the average surface pressure at the contact portion between each MEA and the separator is 0.5 to 5 MPa, the solid polymer fuel cell A stack is built. It is sufficient that the surface pressure at the time of actual use is applied, but if the average surface pressure is too low, the contact resistance increases. On the other hand, if the average surface pressure is too high, the MEA and the separator may be carelessly deformed and the predetermined structure may not be maintained. In particular, when carbon paper is used for the MEA electrode, the structure of the carbon paper may buckle, and the contact resistance with the conductive coating may not be sufficiently improved. The average surface pressure is more preferably in the range of 1 to 3 MPa.

〔Heat treatment〕
In the present invention, the conductive coating film of each separator is 10 minutes or more at 90 to 200 ° C. with respect to the stack in a state where the average surface pressure at the contact point between each MEA and the separator is 0.5 to 5 MPa. Heat treatment is performed so that it is maintained. The inventors have found that this heat treatment significantly reduces the total contact resistance between the separator / electrode and maintains a low contact resistance even in subsequent use. Usually, the use temperature (gas temperature) of the polymer electrolyte fuel cell is often set to about 20 to 90 ° C., but it is considered that it can be set to a higher temperature depending on the type of the ion exchange membrane. When the actual use temperature is between 90 and 200 ° C., the initial heating in the actual use may be used as the heat treatment. There are many unclear points about the mechanism by which the total contact resistance is significantly reduced by this heat treatment, but the conductive coating resin is slightly deformed by heating under pressure, and conductive carbon particles, especially particles, are conductive fillers. This is due to the fact that flake graphite and carbon short fibers having a large diameter are reoriented so as to be more in contact with the base material, electrodes (carbon fibers in the case of carbon paper) and adjacent conductive carbon particles. It is guessed that there is.

  If the heat treatment temperature is less than 90 ° C., it is considered that the degree of reorientation tends to be insufficient, and the effect of reducing the total contact resistance is actually small. On the other hand, when heated to a high temperature exceeding 200 ° C., the ion exchange membrane tends to deteriorate. In addition, if the time of holding between 90 and 200 ° C. is less than 10 minutes, the heat treatment often ends with much room for resistance reduction in the course of reorientation, which is not preferable. Usually, the optimum time can be found in the range of 10 minutes to 3 hours. You may set in the range of 0.5 to 2 hours.

  In FIG. 3, the cross-sectional SEM photograph of the contact location of the separator and the carbon fiber of an electrode after heat processing is illustrated. It can be seen that the roughened surface of the stainless steel substrate (SUS445J1), the carbon fibers of the electrode, and the conductive coating film are in contact with the tight under pressure.

  The heat treatment may be performed by charging the entire stack into a heating furnace, or after constructing an actual power generation system for a polymer electrolyte fuel cell, in an initial stage, 90 to 90 gas flow paths in each cell. You may carry out by flowing 200 degreeC gas. The stack subjected to the heat treatment is directly applied to the polymer electrolyte fuel cell system without being disassembled.

  Simulating the contact structure between the separator and MEA in a polymer electrolyte fuel cell stack, forming a contact structure consisting of “stainless steel substrate / conductive coating / carbon paper”, and examining the effect of reducing the total contact resistance by heat treatment An experimental example is shown.

As the stainless steel plate for the base material, a SUS445J1 plate having a thickness of 0.2 mm and a No. 2D finishing material having the following chemical composition is prepared. A stainless steel substrate having a roughened surface having a surface roughness SRa of about 6.2 μm and a surface roughness SRa of 1.1 μm was prepared.
[Chemical composition]
In mass%, C: 0.006%, Si: 0.24%, Mn: 0.19%, Ni: 0.14%, Cr: 21.94%, P: 0.034%, S: 0.0. 001%, Cu: 0.07%, Mo: 1.12%, balance Fe and inevitable impurities [electrolytic surface roughening treatment conditions]
12 mass% FeCl ₃ aqueous solution, 50 ° C., anode current density 3.0 kA / m ² , cathode current density 0.5 kA / m ² , alternating electrolysis cycle 2.5 Hz, treatment time 60 seconds

The following is prepared as a conductive paint, applied on the roughened surface of the substrate by the bar coater method, and heated at 150 ° C. for 30 minutes to cure the resin, thereby curing the average coating after curing. A coating film having a film thickness of 15 μm was formed as a separator sample.
[Conductive paint]
Resin; phenol resin; conductive carbon particles;
・ Flake graphite: Average particle diameter D50 by laser diffraction particle size distribution analyzer: 5 μm
・ Carbon black: Ketjen Black International Co., Ltd., trade name “Ketjen Black EC”
Compounding: 110 parts by mass of flake graphite and 40 parts by mass of carbon black with respect to 100 parts by mass of resin

On the other hand, carbon paper (manufactured by Toray Industries, Inc .; TGP-H-120) was prepared as an electrode material.
A disk having a diameter of 50 mm is cut out from the separator sample, carbon paper is placed on the surface of the conductive coating film, and a current density is applied between the base material and the carbon paper with a compressive load applied so that the average surface pressure is 1 MPa. In a state where a direct current of 0.3 A / cm ² was passed, the sample was placed in a furnace set at various temperatures of 80 to 130 ° C., and the potential difference between the base material and the carbon paper was monitored by the four-terminal method. Thus, the change in contact resistance (mΩ · cm ² ) was examined.

FIG. 4 shows the total contact resistance when the holding time at a predetermined temperature is 10 minutes and when 24 hours have elapsed. If this contact resistance value is 10 mΩ · cm ² or less, it is evaluated that practical performance can be obtained as a polymer electrolyte fuel cell stack. As can be seen from FIG. 4, the contact resistance is reduced by the heat treatment, and particularly when heated at 90 ° C. or more for 10 minutes or more, a contact resistance of 10 mΩ · cm ² or less can be stably obtained.
When a stainless steel substrate having no roughened surface was used, a contact resistance of 10 mΩ · cm ² or less could not be obtained under each heat treatment condition.

  FIG. 5 shows a change with time of the total contact resistance when the temperature variation is performed 6 cycles by the above heating method. The lower limit temperature of the temperature variation pattern is 25 ° C., and the upper limit temperature is various temperatures of 80 to 130 ° C. As can be seen from FIG. 5, the contact resistance rapidly decreases at the initial stage of the heat treatment, and thereafter, the contact resistance is kept low even if the temperature variation is repeated.

Claims (8)

When constructing a stack of polymer electrolyte fuel cells having a plurality of cells by alternately arranging MEAs (membrane / electrode assemblies) and separators,
As the MEA, an electrode sheet composed of fibrous carbon is joined to the surface of the ion exchange membrane,
As a separator, a stainless steel having a rough surface with a surface area of 2 times or more of the projected area and a surface roughness SRa of 2 μm or less is used as a base material. Using a conductive coating film having an average thickness of 3 to 50 μm obtained by solidifying carbonaceous particles with a thermosetting resin,
The MEA and the separator are alternately arranged to form a laminated structure, and after fixing the laminated structure so that the average surface pressure at the contact point between the electrode surface of the MEA and the conductive coating surface of the separator is 0.5 to 5 MPa, A method for producing a polymer electrolyte fuel cell stack, in which heat treatment is performed so that the conductive coating film of each separator is maintained at 90 to 200 ° C. for 10 minutes or more in the fixed state.   The method for producing a polymer electrolyte fuel cell stack according to claim 1, wherein the conductive coating film contains 30 to 300 parts by mass of graphite as conductive carbon particles with respect to 100 parts by mass of the thermosetting resin.   The method for producing a polymer electrolyte fuel cell stack according to claim 2, wherein the conductive coating film further contains carbon black as conductive carbon particles in a range of 100 parts by mass or less.   The method for producing a polymer electrolyte fuel cell stack according to any one of claims 1 to 3, wherein the thermosetting resin of the conductive coating film is a phenol resin.   The method for producing a polymer electrolyte fuel cell stack according to any one of claims 1 to 4, wherein the roughened surface of the substrate is formed by chemical removal means.   The method for producing a polymer electrolyte fuel cell stack according to any one of claims 1 to 5, wherein the heat treatment is performed by flowing a gas of 90 to 200 ° C through a gas flow path of each cell.   The method for producing a polymer electrolyte fuel cell stack according to any one of claims 1 to 5, wherein the heat treatment is performed by placing each cell in an atmosphere of 90 to 200 ° C in the fixed state.   The heat treatment is performed by placing each cell in an atmosphere of 90 to 200 ° C in the fixed state and flowing a gas of 90 to 200 ° C through a gas flow path of each cell. The manufacturing method of the polymer electrolyte fuel cell stack of description.