JP6649675B2 - Conductive member, method for producing the same, fuel cell separator and polymer electrolyte fuel cell using the same - Google Patents

Description

  The present invention relates to a conductive member, a method for producing the same, a fuel cell separator using the same, and a polymer electrolyte fuel cell. In particular, in a separator having an intermediate layer having high potential corrosion resistance and a surface carbon layer on a metal substrate, it is possible to improve the adhesion between the intermediate layer and the conductive carbon layer while ensuring high potential corrosion resistance. The present invention relates to a method for manufacturing a conductive member.

  A polymer electrolyte fuel cell (PEFC) has a structure in which a plurality of single cells exhibiting a power generation function are stacked. Each of the single cells includes a polymer electrolyte membrane, a pair of (anode and cathode) catalyst layers sandwiching the polymer electrolyte membrane, and a pair of (anode and cathode) gas diffusion layers for dispersing a supply gas sandwiching these. Including a membrane electrode assembly. The MEA of each unit cell is electrically connected to the MEA of the adjacent unit cell via a separator. By stacking and connecting the single cells in this manner, a fuel cell stack is formed. Then, this fuel cell stack can function as power generation means that can be used for various applications. In such a fuel cell stack, the separator exerts a function of electrically connecting adjacent single cells as described above. In addition, a gas channel is usually provided on the surface of the separator facing the MEA. The gas flow path functions as a gas supply unit for supplying a fuel gas and an oxidizing gas to the anode and the cathode, respectively.

  To briefly explain the power generation mechanism of the PEFC, during the operation of the PEFC, a fuel gas (for example, hydrogen gas) is supplied to the anode side of the single cell, and an oxidant gas (for example, atmosphere or oxygen) is supplied to the cathode side. As a result, at each of the anode and the cathode, an electrochemical reaction represented by the following reaction formula proceeds, and electricity is generated.

  As a separator for a fuel cell requiring conductivity, a conventional carbon separator or a conductive resin separator is being replaced with a metal separator. This is because the stack can be miniaturized by the metal separator having excellent strength and conductivity. In recent years, separators in which a layer having corrosion resistance is laminated on a metal base material have been developed in order to prevent a decrease in conductivity due to corrosion, which is a problem of the metal separator, and a reduction in output of the stack due to the corrosion. For example, a technique has been proposed in which a negative bias voltage is changed from a low value to a high value on a metal substrate to form an intermediate layer by a dry film formation method, and a conductive carbon layer is formed on the intermediate layer. (For example, see Patent Document 1). In this document, at the initial stage of forming an intermediate layer by a dry film forming method, film formation is started with a low bias voltage to reduce the roughness of the interface with the substrate, and thereafter, the bias voltage is shifted to a high value. The columnar crystals grow thick. Here, the conductive carbon film grows with the column diameter of the columnar crystal in the intermediate layer. As described above, by increasing the column diameter of the columnar crystals in the intermediate layer, the gaps in the intermediate layer and the defects of the conductive carbon film existing thereon are reduced, and the penetration of water is prevented, so that oxidation at each interface is prevented. And an increase in contact resistance can be suppressed.

JP 2010-287542 A

  However, if the intermediate layer is formed of titanium nitride, carbide, or carbonitride having excellent high-potential corrosion resistance, the adhesion to the conductive carbon layer is not sufficient. For this reason, further improvement in the corrosion resistance of the separator and further reduction in the increase in the contact resistance have been required.

  Therefore, the present invention has been made in view of the above prior art, and is a conductive member having a high adhesion between an intermediate layer having excellent high-potential corrosion resistance and a conductive carbon layer, and having sufficient conductivity. It is an object of the present invention to provide a method for manufacturing a conductive member capable of suppressing an increase in contact resistance while ensuring the above.

  The present inventors have studied the cause of the low adhesion between the conventional conductive carbon layer and an intermediate layer such as a titanium nitride having excellent high potential corrosion resistance. Since the conventional conductive carbon layer is formed under a high bias voltage, the carbon layer rebounds due to an intermediate layer such as hard titanium nitride, which makes the film difficult to form. The method was examined. As a result, the inventors have found that the above problem can be solved by changing the bias voltage from a low value to a high value in the conductive carbon layer forming step, and have completed the present invention.

  That is, the method for manufacturing a conductive member according to the present invention is characterized in that the conductive carbon layer is formed on the intermediate layer by changing the negative bias voltage from a low value to a high value.

According to the method of the present invention, the adhesion between the intermediate layer and the conductive carbon layer can be improved. Therefore, the conductive member manufactured according to the method of the present invention can suppress an increase in contact resistance while sufficiently securing its excellent conductivity, and has a small contact resistance with another member (eg, MEA). (Separator 5) can be provided. Here, the mechanism by which the method of the present invention can improve the adhesion between the intermediate layer and the conductive carbon layer is unknown, but is presumed as follows. Note that the present invention is not limited to the following assumption. That is, if the film is formed at a low bias voltage, a flexible DLC carbon film containing a large amount of sp ³ carbon is formed on an intermediate layer of a hard titanium nitride, carbide, carbonitride, etc., and the surface layer is formed at a high bias voltage. In this case, the collision of carbon is reduced, and a stable film can be manufactured. Further, when the bias voltage is low, the rotation of carbon to the irregularities of the titanium nitride can be improved, and a dense film can be obtained. On the other hand, if the bias voltage is high, it is difficult to contribute to the adhesion to the intermediate layer due to the rebound due to collision and the graphitization. Therefore, according to the method of the present invention, it is possible to obtain a conductive member having low contact resistance and good adhesion between the intermediate layer and the conductive carbon layer.

1 is a schematic cross-sectional view showing a basic configuration of a cell unit of a polymer electrolyte fuel cell (PEFC) using a separator to which a conductive member according to the present invention is applied. 1. It is sectional drawing which shows another form of the schematic structure of the part of a separator in FIG. 1, and has an intermediate | middle layer and a boundary layer on both surfaces of the metal base material of the separator used for the fuel cell unit of FIG. FIG. 2 is a schematic cross-sectional view schematically showing a configuration provided with a conductive carbon layer. FIG. 2 is a schematic diagram showing a fuel cell (stack) including a current collector plate of a fuel cell to which the conductive member of the present invention is applied. FIG. 4 is a perspective view of the fuel cell (stack) of FIG. 3. 5A to 5D are diagrams showing various patterns obtained by changing a negative bias voltage from a low value to a high value at the time of forming an intermediate layer in a dry film formation method. FIG. 5A shows the bias voltage. FIG. 5 is a diagram showing an example of a pattern in which is changed in one step from a low value to a high value. FIG. 5B is a diagram showing an example of a pattern in which the negative bias voltage during the formation of the intermediate layer is continuously changed from a low value to a high value in the dry film formation method. FIG. 5C is a diagram showing an example of a pattern in which the negative bias voltage during the formation of the intermediate layer is changed from a low value to a high value in multiple stages in the dry film formation method. FIG. 5D is a drawing showing an example of a pattern in which the negative bias voltage during the formation of the intermediate layer is changed continuously from a low value to a high value in a multi-step manner in the dry film forming method. The conductive member according to the present invention, in particular, at least one layer of each of the intermediate layer and the conductive carbon layer, preferably, each of these layers is sequentially formed by sputtering (for example, unbalanced magnetron sputtering (UBMS)). FIG. 2 is a schematic plan view of a manufacturing apparatus for forming (an example in which an existing disk-shaped wafer is set in place of a flat metal separator before pressing the unevenness). A manufacturing apparatus for forming a film of the conductive member of the present invention, in particular, at least one of the layers of the intermediate layer and the conductive carbon layer, preferably using the arc ion plating (AIP) method. (However, it is the example which set the existing disk-shaped wafer instead of the flat metal separator before uneven | corrugated press, and shows the example). 3 is an external appearance photograph of the conductive member shown in Example 1 of the present invention. 4 is an external appearance photograph of a conductive member shown in Comparative Example 1 of the present invention. 3 is a surface SEM observation photograph of the conductive member shown in Example 1 of the present invention. 5 is a SEM observation photograph of the surface of the conductive member shown in Comparative Example 1. It is a schematic diagram which shows the outline | summary of the measuring device used for measuring the contact resistance in an Example.

(Method of manufacturing conductive member)
In the method for producing a conductive member according to the present invention, a metal of Group 4 of the periodic table (for example, Ti, Zr, Nf), a metal of Group 5 (for example, V, Nb, Ta), Forming an intermediate layer of at least one selected from the group consisting of carbides, nitrides, and carbonitrides of Group 6 metals (for example, Cr, Mo, W); and forming a conductive layer on the intermediate layer. Forming a conductive carbon layer on the intermediate layer, the step of forming a conductive carbon layer on the intermediate layer includes changing a negative bias voltage from a low value to a high value. is there. As a method for manufacturing a conductive member according to the present invention, a simple method of simply changing a set value of an apparatus of a dry film forming method (sputtering or the like) used at the time of film formation, while sufficiently securing its excellent conductivity, A conductive member capable of suppressing an increase in contact resistance can be realized.

  The present embodiment is characterized in that a negative bias voltage at the time of forming a conductive carbon layer is changed from a low value to a high value in a dry film formation method.

  Here, changing the bias voltage in the dry film forming method from a low value to a high value does not include a process of changing the bias voltage from a high value to a low value on the way, for example, a pattern shown in FIGS. 5A to 5D or the like. Is mentioned. Specifically, it is changed in one step from a low value to a high value (FIG. 5A), continuously changed from a low value to a high value (FIG. 5B), or changed in multiple steps from a low value to a high value. Pattern (FIG. 5C). Alternatively, the value may be continuously changed from a low value to a high value in multiple steps (FIG. 5D). As described above, in the present specification, “change the negative bias voltage from a low value to a high value” means that the bias voltage is continuously or stepwise changed from a low value to a high value within a predetermined range. Should be changed to Therefore, the process of changing the bias voltage may include a steady state (a state in which the bias voltage is held) in the middle. However, the change in the bias voltage always rises or takes a steady state, and the process of changing the bias voltage does not include a state in which the bias voltage decreases.

When the film is formed with a low bias voltage, a DLC carbon film containing a large amount of soft sp ³ carbon is formed on the hard intermediate layer, and the collision of carbon when forming the surface layer portion with a high bias voltage is reduced, and the film is formed. It will be easier. In addition, when the bias voltage is low, the rotation of the intermediate layer to the unevenness can be improved. On the other hand, if a high bias voltage such as 200 V or more is used from the beginning, a film cannot be formed due to rebound due to collision, or it is difficult to contribute to adhesion to the intermediate layer due to graphite.

  Therefore, in the conductive carbon layer film thickness, the vicinity of the intermediate layer is formed at a low bias voltage to suppress the formation of the graphite structure, thereby improving the adhesion to the intermediate layer. The initial bias voltage in the conductive carbon layer forming step may be a voltage higher than 0 V, and is usually higher than 0 V and 50 V or less, in order to improve the adhesion between the intermediate layer and the conductive carbon layer. The effect is obtained.

  Methods for obtaining a conductive carbon layer in the vicinity of the intermediate layer, which is denser and has high adhesion to the intermediate layer, include a method for forming the conductive carbon layer after the formation of the intermediate layer and a method for forming the conductive carbon layer during the formation of the conductive carbon layer. Controlling the material temperature within a certain range can be mentioned. Here, the carbon film is graphitized at about 400 ° C. or higher, and it is difficult or impossible to maintain the form as a film. For this reason, it is preferable to keep the temperature during the film formation process from the start of the formation of the intermediate layer to the end of the film formation below the above-mentioned temperature. Further, the surface layer temperature during film formation may increase due to collision between carbons. In consideration of the above points, the substrate temperature during the film formation step is preferably lower than 350 ° C, more preferably 300 ° C or lower, and further preferably 270 ° C or lower. In addition, the lower limit of the said temperature range is not specifically limited, For example, 100 degreeC or more is preferable and 150 degreeC or more is more preferable. Within such a temperature range, it can be suppressed that the conductive carbon layer formed on the intermediate layer is graphitized by the temperature.

  When the conductive carbon layer is formed as described above, a conductive carbon layer region showing good adhesion to the intermediate layer is formed between the surface layer of the conductive carbon layer and the intermediate layer. This region is referred to as a “boundary layer” in the present application.

As the boundary layer of the conductive carbon layer of the present invention, the R value (= I _D / I _G ) is preferably less than 1.3, more preferably 1.2 or less, further preferably 1 or less. .1 or less. The lower limit of the R value of the boundary layer in the conductive carbon layer is not particularly limited, but is preferably, for example, 0.6 or more, and more preferably 0.7 or more. When the R value is in such a range, it is preferable from the viewpoint that the inhibition of adhesion due to the formation of the graphite structure can be sufficiently suppressed. Here, the “boundary layer in the conductive carbon layer” intends a layer formed by applying a low bias voltage, and the thickness thereof is not particularly limited, and the thickness is not limited to the adhesiveness between the intermediate layer and the conductive carbon layer. It can be appropriately prepared according to the requirements. In this specification, the R value (= _ID / _IG ) means a value measured in the following examples.

  From the viewpoint of ensuring high adhesion between the intermediate layer and the conductive carbon layer, the R value of the conductive carbon layer preferably gradually increases from the outermost surface of the intermediate layer to the surface layer. The R value of the surface layer portion is preferably 1.3 or more, more preferably 1.4 or more, and even more preferably 1.5 or more. When the R value of the surface layer is 1.3 or more, the conductivity of the surface layer can be ensured, and the contact resistance can be sufficiently reduced. In addition, the upper limit of the R value of the surface layer portion in the conductive carbon layer is not particularly limited, but is, for example, preferably 2.0 or less, more preferably 1.9 or less. Here, the “surface layer portion in the conductive carbon layer” intends a layer formed by applying a high bias voltage. The thickness of the surface layer portion in the conductive carbon layer is not particularly limited, as in the case of the boundary layer, and can be appropriately adjusted according to conductivity, adhesion to the intermediate layer, and the like.

  The above is the description of the main features of the method for manufacturing a conductive member according to the present invention. Other manufacturing methods (steps and the like) can be manufactured by appropriately referring to conventionally known methods. . Hereinafter, a preferred embodiment for manufacturing a conductive member will be described, but the technical scope of the present invention is not limited to only the following embodiments. In addition, since various conditions such as the material of each component of the conductive member forming the separator will be described in the section of the conductive member described later, the description is omitted here.

  First, an aluminum plate, a titanium plate, a stainless steel plate, or the like having a desired thickness is prepared as a constituent material of the metal base 31. Next, the surface of the prepared constituent material of the metal base material 31 is degreased and cleaned using an appropriate solvent (for example, ethanol, ether, acetone, isopropyl alcohol, trichloroethylene, and a caustic agent). Examples of the treatment include ultrasonic cleaning. The conditions of the ultrasonic cleaning include a processing time of about 1 to 10 minutes, a frequency of about 30 to 50 kHz, and a power of about 30 to 50 W.

  Subsequently, the oxide film formed on the surface (both surfaces) of the constituent material of the metal base material 31 is removed. Examples of a technique for removing the oxide film include a washing treatment with an acid, a dissolution treatment by applying an electric potential, and an ion bombardment treatment.

  Next, in the present invention, in order to manufacture the conductive member (separator 5) having the conductive carbon layer 33 in the form shown in FIG. A step of forming the intermediate layer 32 on at least one main surface, preferably both surfaces, of the substrate 31 is performed. At this time, as a method of forming the intermediate layer 32, a method similar to that described later for forming the conductive carbon layer 33, preferably a dry film forming method can be adopted. However, it is necessary to change the target to the constituent material of the intermediate layer 32. Particularly preferably, the intermediate layer 32 is preferably formed according to the method described in JP-A-2010-287542. The intermediate layer formed by the method has excellent corrosion resistance and can suppress an increase in contact resistance.

  In particular, in the present invention, the negative bias voltage at the time of forming the conductive carbon layer 33 by the dry film forming method is changed from a low value to a high value. Thereby, the R value of the conductive carbon layer 33 can be controlled, a boundary layer having an R value of less than 1.3 is formed near the intermediate layer, and the R value is 1.3 or more on the opposite side to the intermediate layer. Is formed. The initial low bias voltage may be a voltage higher than 0 V as described above, and may be a range usually higher than 0 V and 50 V or less. The high bias voltage is preferably 200 V or more, more preferably 200 or more and 500 V or less, and still more preferably 200 V or more and 300 V or less. That is, it is preferable to change the negative bias voltage at the time of forming the conductive carbon layer from 50 V or less to 200 V or more. Within such a range, a surface layer portion having a sufficiently high R value can be obtained, and a conductive member having low contact resistance can be obtained. By changing the bias voltage from a low value to a high value in this manner, a conductive carbon layer 33 whose R value gradually changes from a low value to a high value from the vicinity of the intermediate layer toward the surface layer is obtained.

  The lower the bias voltage is, the smaller the pushing effect during film formation by Ar + ions is, and the lower the collision energy of carbon atoms is. Therefore, carbon atoms can be laminated on the hard and chemically stable intermediate layer 32 of titanium nitride, carbide, carbonitride, or the like, and the form as a film can be maintained. When the bias voltage is increased, the energy of carbon due to Ar + ions increases, and the carbon atoms bounce off instead of being stacked on the film, so that the shape of the film cannot be maintained, and the film becomes powdery and remains on the surface. Alternatively, even if the form of the film can be maintained, a poorly-formed film structure having a gap at a grain boundary or the like may cause poor adhesion.

  Therefore, by forming a film in the vicinity of the intermediate layer 32 while controlling the bias voltage to a low value, it is possible to suppress the change to graphite that does not contribute to the adhesion to the intermediate layer. Layers can be obtained.

  Then, in the subsequent film formation, a high bias voltage is applied as approaching the surface layer, and a surface layer having a highly conductive graphite structure is formed, thereby having high adhesion to the intermediate layer and high conductivity. A conductive carbon layer can be obtained.

  After the above-described polishing process is performed on the surface of the metal base material 31, or in the step of forming the intermediate layer 32 using a method of changing a negative bias voltage from a low value to a high value, the intermediate layer 32 is formed by sputtering. It is preferable to perform a method of forming by a method (coating treatment for forming a film). In order to form a conductive member composed of the metal base material 31, the intermediate layer 32, and the conductive carbon layer 33 having the structure of the present invention, the conductive carbon layer 33 is preferably formed by a sputtering method. This is because the formation of the intermediate layer 32 to be performed is desirably performed by a similar dry process, particularly, a sputtering method. The intermediate layer 32 allows the conductive carbon layer 33 to be formed without poor adhesion, so that high conductivity and corrosion resistance can be obtained. In addition, since the film can be formed in the same manner as the conductive carbon film, the manufacturing process cost can be reduced.

  In the case where a step of forming the intermediate layer 32 by changing the negative bias voltage from a low value to a high value is included, the surface of the metal substrate 31 is subjected to a pre-treatment such as polishing, It is desirable to perform a coating treatment for forming a film on the surface of the film by a sputtering method. This is because, when the intermediate layer 32 is made of a columnar crystal or the like, the number of nucleation sites of the columnar crystal is reduced and the individual columnar crystal can be thickened if the substrate roughness is reduced by the polishing treatment. By using such an intermediate layer, contact between the metal substrate and the acidic solution can be prevented, and the corrosion resistance can be improved. Here, as the pre-treatment, items generally performed can be widely adopted in addition to the polishing treatment. For example, electropolishing, lapping, micro shot processing, and the like can be applied.

  Next, an intermediate layer 32 and a conductive carbon layer 33 are sequentially formed on the surface of the constituent material of the metal substrate 31 that has been subjected to the above processing. As a target to be used, for example, the above-described constituent material of the intermediate layer 32 (for example, titanium metal) and the constituent material of the conductive carbon layer 33 (for example, solid graphite) can be used. First, using a titanium metal as a target, sputtering is performed by applying a negative bias voltage to the metal substrate while introducing a nitrogen gas into the system, so that a titanium nitride film is formed on both surfaces of the metal substrate 31. Formed. Next, the conductive carbon layer 33 having the boundary layer 33a and the surface layer portion 33b can be obtained by using solid graphite as a target and changing the bias voltage from a low value to a high value. Thus, the intermediate layer 32 and the conductive carbon layer 33 can be sequentially formed on the metal substrate 31.

  As a method preferably used for laminating (forming a film) the intermediate layer 32 and the conductive carbon layer 33, a physical vapor deposition (PVD) such as a sputtering method or an ion plating method may be used as a dry film forming method. Or an ion beam evaporation method such as a filtered cathodic vacuum arc (FCVA) method. Examples of the sputtering method include a magnetron sputtering method, an unbalanced magnetron sputtering (UBMS) method, a dual magnetron sputtering method, and an ECR sputtering method. In addition, examples of the ion plating method include an arc ion plating method. Among them, it is preferable to use a sputtering method and an ion plating method which are dry film forming methods. According to such a method, a graphite structure having a turbostratic structure with a small hydrogen content can be formed as a surface layer portion. As a result, the R value of the surface layer can be increased, and excellent conductivity can be achieved. In addition to this, there is an advantage that film formation can be performed at a relatively low temperature, and damage to the metal base material 31 can be minimized. Further, according to the sputtering method, there is an advantage that the crystal structure of the intermediate layer 32 can be controlled and the quality of each layer to be formed can be controlled by controlling the bias voltage and the like.

  Here, when forming the intermediate layer 32 and the conductive carbon layer 33 by a sputtering method which is a dry film forming method, as described above, a negative bias voltage is applied to the metal base 31 at the time of sputtering. Good. According to such an embodiment, the crystal structure can be controlled as in the above-described intermediate layer 32 by the ion irradiation effect, and the structure of the conductive carbon layer 33 can be changed between the boundary layer and the surface layer. As a result, it is possible to form an intermediate layer that contributes to the improvement of corrosion resistance, and to obtain a conductive carbon layer that can achieve both high adhesion and low contact resistance like the conductive carbon layer in the present invention.

  The intermediate layer 32 can enhance the anticorrosion effect of the metal base material 31 as described above, and can be applied as the metal base material 31 of the separator even in the case of a corrosive metal such as aluminum. In this embodiment, the magnitude (absolute value) of the applied negative bias voltage is not particularly limited, and a voltage that can form the intermediate layer 32 can be adopted. As an example, the magnitude of the applied voltage is preferably 50-500V, more preferably 100-300V.

  The conductive carbon layer 33 according to the present invention has high adhesion to the intermediate layer due to the boundary layer, and the surface layer portion can exhibit excellent conductivity. A conductive member (separator 5) having small contact resistance can be provided. As described above, in the conductive carbon layer 33, a method of changing the negative bias voltage at the time of forming the conductive carbon layer 33 from a low value to a high value is used. More specifically, in the initial stage of the formation of the conductive carbon layer 33 as in the example described later, a low bias voltage (higher than 0 V, 0 V The film formation may be started at an ultra-high voltage of 50 V, and then the bias voltage may be shifted to a high value (usually 200 to 500 V, preferably 200 to 300 V) to change the graphite into a highly conductive graphite having a turbostratic structure.

  It should be noted that specific conditions such as other conditions at the time of forming the intermediate layer 32 and the conductive carbon layer 33 are not particularly limited, and conventionally known knowledge can be appropriately referred to. When the conductive carbon layer 33 is formed by the UBMS method, it is preferable that the intermediate layer 32 is formed in advance by a similar apparatus and manufacturing method, and the conductive carbon layer 33 is formed thereon. Thereby, the intermediate layer 32 and the conductive carbon layer 33 having excellent adhesion to the underlayer can be formed. However, the intermediate layer 32 may be formed by another method, and the conductive carbon layer 33 may be formed by a different apparatus or manufacturing method. Even in this case, the intermediate layer 32 having excellent adhesion to the metal substrate 31 and the conductive carbon layer 33 can be formed.

  According to the above-described method, a conductive member having the intermediate layer 32 and the conductive carbon layer 33 formed on both surfaces of the metal base 31 can be manufactured. In order to manufacture a conductive member in which the intermediate layer 32 and the conductive carbon layer 33 are formed on both surfaces of the metal base material 31, a commercially available appropriate film forming apparatus (a double-sided simultaneous sputtering film forming apparatus and the same) was used. Sputtering method) may be used, or a sputtering device or a sputtering device capable of forming the intermediate layer 32 and further the conductive carbon layer 33 on both surfaces of the metal substrate 31 may be separately formed. It is not particularly limited. Although not advantageous in terms of cost, an intermediate layer 32 and further a conductive carbon layer 33 are formed on one main surface of the metal base material 31, and then the other main surface of the metal base material 31 is formed. On the other hand, the intermediate layer 32 and the conductive carbon layer 33 may be sequentially formed by the same method as described above. Alternatively, first, the intermediate layer 32 is formed on one main surface of the metal substrate 31 in an apparatus targeting a metal material such as chromium, and then, the intermediate layer 32 is opposed to the intermediate layer 32 formed in the above-described process. The step of forming the intermediate layer 32 on a main surface different from the main surface to be performed is performed. Subsequently, the target is switched to carbon, and a conductive carbon layer 33 is formed on the intermediate layer 32 formed on one main surface of the metal base material 31 in the same apparatus. A step of forming the conductive carbon layer 33 on a main surface different from the main surface opposite to the main surface opposite to the formed conductive carbon layer 33 may be performed. As described above, as a method of forming the intermediate layer 32 on both surfaces of the metal substrate 31 and a method of forming the conductive carbon layer 33 on the surface of the intermediate layer 32, the intermediate layer 32 may be formed on one surface of the metal substrate 31. The method for forming the layer 32 and the conductive carbon layer 33 is not particularly limited, for example, a method similar to that described above (however, the number of steps can be reduced by half) can be adopted.

(Conductive member)
The conductive member of the present invention is provided with a metal substrate and an intermediate layer containing metal nitride, carbide, or carbonitride on the metal substrate, and a conductive carbon layer is coated on the intermediate layer. Conductive member. The conductive carbon layer is characterized in that the step of forming the conductive carbon layer includes a step of changing from a low bias voltage to a high bias voltage. By this step, a boundary layer having good adhesion to the intermediate layer is formed near the intermediate layer, and the outermost layer has high conductivity. The use of titanium nitride and other Group 4 metals, Group 5 metals, Group 6 metals carbides, nitrides and carbonitrides as the material of the intermediate layer improves the corrosion resistance of the conductive member. Valid from.

  However, when a conductive carbon layer is formed on the intermediate layer to reduce contact resistance with other members, it has been difficult to secure adhesion between the intermediate layer and the conductive carbon layer. . The reason is that a constant high bias voltage was applied in the conventional conductive carbon layer forming process. The conductive carbon layer manufactured by such a method has a high R value due to a large ratio of graphite having a turbostratic structure, and cannot obtain high adhesion to the above-mentioned materials such as titanium nitride.

Therefore, the present invention includes a step of changing the bias voltage from a low value to a high value in the conductive carbon layer forming step. In the process of forming the conductive carbon layer in this manner, if the process is performed at an initial low bias voltage, a conductive carbon layer in which a large amount of sp ³ carbon remains is obtained, and the collision energy is small, so that the rotation of the intermediate layer to unevenness is reduced. Become well dense. By stacking a surface layer having a low contact resistance with a high bias voltage on such a soft carbon layer containing a large amount of sp ³ carbon, a collision of carbon is reduced and a stable film can be manufactured. Therefore, a conductive member having low contact resistance and good adhesion between the intermediate layer and the conductive carbon layer can be obtained. Observation of the surface of the conductive member according to the present invention by SEM reveals that there are very few gaps at the grain boundary portion of the intermediate layer as shown in FIG. 9A. On the other hand, in the conventional manufacturing method, when the intermediate layer is made of a material such as hard titanium nitride, the conductive carbon layer is graphitized, so that a dense film cannot be formed on the surface of the intermediate layer. As a result, a gap is generated between the intermediate layer and the conductive carbon layer as shown in FIG. 9B.

  As described above, according to the configuration of the conductive member of the present invention, by providing the boundary layer having good adhesion between the intermediate layer and the surface layer of the conductive carbon layer, the intermediate layer and the conductive layer Gaps and defects formed between the carbon layers can be reduced. Further, a function of suppressing intrusion of water can be provided by suppressing peeling of the conductive carbon layer and generation of gaps. As a result, the anticorrosion effect of the metal base can be enhanced. By having such anticorrosive performance, the conductive member according to the present invention can be used stably as a separator for a long period of time even when a lightweight and inexpensive metal such as aluminum is used as a metal substrate, even when a corrosive metal is used as a metal substrate. . That is, by providing the boundary layer between the intermediate layer and the surface layer of the conductive carbon layer, it is possible to obtain high adhesion between the intermediate layer and the conductive carbon layer while having high conductivity of the surface layer. . Furthermore, by suppressing the generation of gaps and defects between the intermediate layer and the conductive carbon layer, it is possible to prevent water from entering, suppress oxidation of each member, and suppress an increase in contact resistance.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to only the following embodiments. In addition, the dimensional ratios in the drawings are exaggerated for convenience of description, and may be different from the actual ratios.

FIG. 1 shows a basic configuration of a fuel cell using a metal separator, which is a typical embodiment of a conductive member according to the present invention, specifically, only a basic configuration of a cell unit of a polymer electrolyte fuel cell (PEFC). In a cell unit 1 of a fuel cell (PEFC) shown in FIG. 1, catalyst layers 3 (anode 3a and cathode 3b) are arranged on both surfaces of a solid polymer electrolyte membrane 2. I have. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layer 3 (3a, 3b) is further provided with a gas diffusion layer 4 (anode 4a and cathode 4b) so as to sandwich them. A membrane electrode assembly (MEA) 9 is formed. An MEA (Membrane Electrode Assembly) 9 is finally sandwiched by a pair of conductive metal separators 5 (anode 5a and cathode 5b) to form a single cell unit 1 of PEFC. In FIG. 1, the metal separators 5 (anode 5a and cathode 5b) are illustrated as being located on both sides (both sides) of the MEA 9. However, in a fuel cell stack in which a plurality of MEAs 9 are stacked, the metal separator 5 is generally also used as the metal separator 5 for the adjacent PEFC cell unit 1 (see FIG. 3). In other words, in the fuel cell stack, the MEAs 9 are sequentially stacked with the metal separator 5 interposed therebetween to form a stack. In an actual fuel cell stack, between a metal separator (5a, 5b) and a solid polymer electrolyte membrane 2, or between a cell unit 1 of PEFC and a cell unit 1 of another PEFC adjacent thereto. Although a gas seal portion is provided, these descriptions are omitted in FIG. 1 (see FIGS. 3 and 4).

The convex portions of the metal separator 5 (5a, 5b) viewed from the MEA 9 side are in contact with the MEA 9. Thereby, an electrical connection with the MEA 9 is ensured. The concave portion (the space between the metal separator 5 and the MEA 9 generated due to the uneven shape of the metal separator 5) seen from the MEA 9 side of the metal separator 5 (5a, 5b) is a gas when the PEFC 1 is operated. Function as a gas flow path for flowing the gas. Specifically, a fuel gas 5ag (for example, hydrogen or a hydrogen-containing gas) flows through the gas flow path 5aa of the anode separator 5a, and an oxidant gas 5bg (for example, air) flows through the gas flow path 5bb of the cathode separator 5b. and such as O ₂ containing gas) circulating.

  On the other hand, the concave portion viewed from the side opposite to the MEA 9 side of the metal separator 5 (5a, 5b) is a refrigerant for flowing the refrigerant 8w (for example, cooling water, water) for cooling the PEFC during the operation of the PEFC1. Channel 8 is provided. Further, the metal separator 5 (5a, 5b) is usually provided with a manifold (not shown). This manifold functions as connecting means for connecting each cell (unit 1) of the PEFC when forming a stack. With such a configuration, the mechanical strength of the fuel cell stack 200 can be ensured (see FIGS. 3 and 4).

In an actual fuel cell (PEFC), a gas seal is formed between the metal separator 5 and the periphery (peripheral edge) of the end of the electrolyte membrane 2 and between the cell unit 1 of the fuel cell and another cell unit 1 adjacent thereto. Although they are arranged, they are omitted in this schematic diagram. The fuel cell separator 5 is a metal separator 5 which is an embodiment of the conductive member according to the present invention. For example, by performing a pressing process on a thin plate having a thickness of 0.5 mm or less, the unevenness as shown in FIG. Shaped (corrugated) gas flow paths 5aa, 5bb and refrigerant flow path 8 are formed (gas flow paths 5aa, 5bb) into fuel gas 5ag (hydrogen or hydrogen-containing gas) or oxidizing gas 5bg (air or O2). ₂ containing gas) and 8 w of cooling water.

  As described above, in addition to the function of electrically connecting the respective MEAs 9 in series, the metal separator 5 has the gas flow paths 5aa, 5bb and the coolant flow path for flowing different fluids such as the fuel gas 5ag, the oxidant 5bg gas, and the coolant 8w. It has a path 8 and a manifold, and further has a function of maintaining the mechanical strength of the stack. In addition, since a perfluorosulfonic acid type membrane is usually used for the electrolyte membrane 2, various acidic ions eluted from the membrane and a humidifying gas are supplied to the battery, so that the inside of the battery has a weak acidic corrosion. Under the environment.

  In the present embodiment shown in FIG. 2, the conductive member constituting the metal separator 5 has a configuration in which an intermediate layer 32 and a conductive carbon layer 33 are sequentially laminated on a metal base material 31. The conductive carbon layer includes a boundary layer 33a near the intermediate layer and a surface layer 33b. In the PEFC cell unit 1, the metal separator 5 is arranged such that the conductive carbon layer 31 is located on the MEA 9 side (see FIGS. 2, 3, and 4).

  As shown in FIG. 2, the sectional configuration of the metal separator 5 of the fuel cell (PEFC), which is a typical embodiment of the conductive member according to the present invention, includes two main surfaces ( The intermediate layer 32 and the outermost conductive carbon layer 33 are disposed on the surface. When stainless steel having excellent corrosion resistance, such as SUS316L, is used for the metal base 31, the main purpose is to prevent corrosion by acid, because the metal base 31 itself can withstand the acidic environment in the fuel cell. Then, the requirements of the intermediate layer 32 are not so severe. However, a high potential may be locally generated in the cell when the fuel cell is started or stopped. Considering the corrosion resistance to high potentials, the above materials such as titanium nitride are more suitable than the conventional intermediate layer made of metal.

  However, when a material such as titanium nitride having excellent high-potential corrosion resistance is used as the intermediate layer, the adhesion to the conductive carbon layer formed on the intermediate layer becomes poor to reduce contact resistance and the like. It is considered that the cause is that graphite having a turbostratic structure, which is often contained in the conventional conductive carbon layer having a high R value, does not contribute to the adhesion to the intermediate layer.

  Therefore, in the present invention, by controlling the R value of the conductive carbon layer near the intermediate layer to be lower than that of the surface layer, a boundary layer having high adhesion to the intermediate layer material such as titanium nitride is formed. I have.

  Thus, a conductive member having low contact resistance and high adhesion to the intermediate layer can be obtained. Further, the conductive member according to the present invention can suppress the peeling of the conductive carbon layer, and can suppress the permeation of water into the inside of the separator, which leads to an increase in the contact resistance of the conductive carbon layer and corrosion of the metal base material. As a result, the desired excellent battery performance can be stably developed, maintained for a long period of time.

  Hereinafter, each component of the metal separator 5 of the present embodiment will be described in detail.

[Metal base material]
The metal base material 31 is a main layer of a conductive member constituting the metal separator 5, and contributes to securing conductivity and mechanical strength.

  The metal constituting the metal base 31 is not particularly limited, and any metal conventionally used as a constituent material of the metal separator 5 can be appropriately used. Examples of the constituent material of the metal base material 31 include iron, titanium, aluminum, and alloys thereof. These materials can be preferably used from the viewpoint of mechanical strength, versatility, cost performance, ease of processing, and the like. Here, stainless steel is included in the iron alloy. In particular, the metal base 31 is preferably made of stainless steel, aluminum, or an aluminum alloy. When stainless steel is used as the metal substrate 31, the conductivity of the contact surface with the gas diffusion substrate, which is a constituent material of the gas diffusion layer (GDL) 4, can be sufficiently ensured. As a result, even if moisture penetrates into the gap between the films at the rib shoulders, the durability can be maintained by the corrosion resistance of the oxide film generated on the metal base material 31 made of stainless steel itself. Here, the GDL 4 is composed of a portion where the surface pressure is directly applied to the GDL 4 (4a, 4b) (a contact portion with the metal separator 5; a rib portion) and a portion not directly applied (a portion not in contact; a flow channel portion), The rib shoulder portion refers to a portion in contact with the metal separator 5; a shoulder portion (corner portion) of the rib portion.

  Examples of stainless steel include austenitic, martensitic, ferritic, austenitic / ferritic, and precipitation hardening stainless steels. Examples of the austenitic system include SUS201, SUS202, SUS301, SUS302, SUS303, SUS304, SUS305, SUS316 (L), and SUS317. SUS329J1 is mentioned as an austenitic ferrite type | system | group. SUS403 and SUS420 are mentioned as a martensite system. SUS405, SUS430, and SUS430LX are examples of ferrite. As the precipitation hardening system, SUS630 is given. Among them, it is more preferable to use austenitic stainless steel such as SUS304 and SUS316. The content of iron (Fe) in the stainless steel is preferably from 60 to 84% by mass, and more preferably from 65 to 72% by mass. Further, the content of chromium (Cr) in stainless steel is preferably 16 to 20% by mass, and more preferably 16 to 18% by mass.

  On the other hand, examples of the aluminum alloy include pure aluminum, aluminum-manganese, and aluminum-magnesium. Elements other than aluminum in the aluminum alloy are not particularly limited as long as they can be generally used as an aluminum alloy. For example, copper, manganese, silicon, magnesium, zinc and nickel may be included in the aluminum alloy. Specific examples of aluminum alloys include A1050 and A1050P as pure aluminum-based alloys, A3003P and A3004P as aluminum-manganese-based alloys, and A5052P and A5083P as aluminum-magnesium-based alloys. On the other hand, since the metal separator 5 is also required to have mechanical strength and formability, the tempering of the alloy can be appropriately selected in addition to the above-mentioned alloy types. When the metal substrate 31 is composed of a simple substance of titanium or aluminum, the purity of the titanium or aluminum is preferably 95% by mass or more, more preferably 97% by mass or more, and further preferably 99% by mass. % Or more.

  The thickness of the metal substrate 31 is not particularly limited. It is preferably 50 to 500 μm, more preferably 80 to 300 μm, and still more preferably 80 to 300 μm, from the viewpoints of ease of processing and mechanical strength, and improvement of the energy density of the battery by making the separator 5 itself thinner. ２００200 μm. In particular, when stainless steel is used as a constituent material, the thickness of the metal base 31 is preferably 80 to 150 μm. On the other hand, when aluminum is used as a constituent material, the thickness of the metal base 31 is preferably 100 to 300 μm. When the thickness is in the above range, the metal separator 5 has sufficient strength, but is excellent in workability and can achieve a suitable thickness.

  In addition, for example, from the viewpoint of providing sufficient strength as a constituent material of the fuel cell separator 5 and the like, the metal base material 31 is preferably made of a material having high gas barrier properties. Since the separator 5 of the fuel cell plays a role of separating cells from each other, different gas flows on both sides of the separator 5 (see FIG. 3). Therefore, from the viewpoint of eliminating the mixing of the gas adjacent to each cell of the cell unit 1 of the PEFC and the fluctuation of the gas flow rate, the higher the gas barrier property of the metal substrate 31, the more preferable.

[Conductive carbon layer]
The conductive carbon layer 33 is a layer containing conductive carbon. Due to the presence of this layer, the corrosion resistance can be improved as compared with the case where only the metal base material 31 is used, while ensuring the conductivity of the conductive member constituting the metal separator 5. In the present invention, a boundary layer having good adhesion with the intermediate layer is formed at the interface of the intermediate layer by changing the bias voltage from a low value to a high value during the formation of the conductive carbon layer. Can form a highly conductive surface layer.

Conductive carbon layer 33 is measured by a Raman scattering spectroscopic analysis is defined by the intensity ratio of the D-band peak intensity _{(I D)} and G-band peak intensity _{(I G) R (I D} / I G). By controlling the R value of the boundary layer and the surface layer to a certain region, effects such as improvement in adhesion between the intermediate layer and the conductive carbon layer, reduction in contact resistance, and corrosion resistance are increased. Hereinafter, this will be described in more detail.

When a carbon material is analyzed by Raman spectroscopy, peaks usually occur around 1350 cm ^{-1 and} around 1584 cm ^-1 . Highly crystalline graphite has a single peak around 1584 cm ⁻¹ , which peak is commonly referred to as the “G band”. On the other hand, as the crystallinity decreases (crystal structure defects increase), a peak around 1350 cm ⁻¹ appears. This peak is usually referred to as "D band" (the diamond peak is strictly at 1333 cm < ^-1 > and is distinguished from the D band). The intensity ratio R ( _ID / _IG ) between the D-band peak intensity ( _ID ) and the G-band peak intensity ( _IG ) is determined by the graphite cluster size of the carbon material, the degree of disorder of the graphite structure (crystal structure defect), It used as an index, such as sp ² bond ratio. That is, in the present invention, it can be used as an index of the contact resistance of the conductive carbon layer 33, and can be used as a film quality parameter for controlling the conductivity of the conductive carbon layer 33.

R _(I D / I _G) value, using a microscopic Raman spectrometer, is calculated by measuring the Raman spectra of the carbon material. Specifically, the relative intensity ratio (peak area ratio (peak area ratio (I _G )) of a peak intensity ( _ID ) of 1300 to 1400 cm ⁻¹ called D band and a peak intensity (IG) of 1500 to 1600 cm ⁻¹ called G band. I _D / I _G )).

  As described above, in the present embodiment, the R value of the surface portion is preferably 1.3 or more, more preferably 1.4 to 2.0, and still more preferably 1.4 to 1.9. Yes, particularly preferably 1.5 to 1.8. When the R value is 1.3 or more, a surface layer portion having sufficient conductivity can be obtained. Further, when the R value is 2.0 or less, the decrease in the graphite component can be suppressed. Further, an increase in the internal stress of the conductive carbon layer 33 itself can be suppressed, and the adhesion with the boundary layer can be further improved.

Further, the R value of the boundary layer is preferably less than 1.3, more preferably 1.2 or less, and still more preferably 1.1 or less. When the R value is less than 1.3, a boundary layer containing a large amount of sp ³ carbon can be obtained, and the surface layer can be formed on the boundary layer with a high bias voltage.

  The mechanism by which the above-described effects can be obtained by setting the R value of the surface layer portion to 1.3 or more or the R value of the boundary layer to less than 1.3 as in the present embodiment is estimated as follows. I have. However, the following estimation mechanism does not limit the technical scope of the present invention in any way.

In polycrystalline graphite, since the graphene surface is formed by bonding of sp ² carbon atoms constituting the graphite cluster, conductivity is ensured in the surface direction of the graphene surface. Therefore, the conductive carbon layer according to the present invention has high adhesion between the intermediate layer and the conductive carbon layer while ensuring low contact resistance.

  Here, the size of the graphite cluster constituting the polycrystalline graphite which is the surface portion of the conductive carbon layer according to the present invention is not particularly limited. For example, the average diameter of the graphite cluster is preferably about 1 to 50 nm, more preferably 2 to 10 nm. When the average diameter of the graphite cluster is within such a range, it is possible to prevent the conductive carbon layer 33 from being thickened while maintaining the crystal structure of the polycrystalline graphite. Here, the “diameter” of the graphite cluster means the largest distance among the distances between any two points on the contour line of the cluster. The average diameter value of the graphite cluster is calculated as an average value of the diameter of the cluster observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It can be calculated.

  In the present embodiment, the conductive carbon layer 33 may be composed of only polycrystalline graphite, but the conductive carbon layer 33 may include a material other than polycrystalline graphite. Examples of carbon materials other than polycrystalline graphite that can be included in the conductive carbon layer 33 include carbon black, fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, and carbon fibril. Further, specific examples of carbon black include, but are not limited to, Ketjen black, acetylene black, channel black, lamp black, oil furnace black, and thermal black. The carbon black may be subjected to a graphitization treatment. Materials other than the carbon material that can be included in the conductive carbon layer 33 include gold (Au), silver (Ag), platinum (Pt), ruthenium (Ru), palladium (Pd), rhodium (Rh), and indium. A noble metal such as (In); a water-repellent substance such as polytetrafluoroethylene (PTFE); and a conductive oxide. As the material other than polycrystalline graphite, only one kind may be used, or two or more kinds may be used in combination.

  The thickness of the conductive carbon layer 33 (however, excluding the protruding particles 33a; average value) is not particularly limited. However, it is preferably from 1 to 1000 nm, more preferably from 2 to 500 nm, and still more preferably from 5 to 200 nm. If the thickness of the conductive carbon layer 33 is within such a range, sufficient conductivity between the gas diffusion base material and the separator 5 can be ensured. In addition, the metal substrate 31 can have an advantageous effect of having a high corrosion resistance function. In the present embodiment, the conductive carbon layer 33 may be present only on one main surface of the conductive member (separator 5), but preferably, as shown in FIG. It is preferable that the conductive carbon layer 33 be present on other main surfaces (that is, on both surfaces of the conductive member). This is because, on both surfaces of the conductive member (conductive carbon layer 33), the metal substrate 31 and the conductive carbon layer 33 are kept in close contact with each other via the intermediate layer 32, and the anticorrosion effect of the substrate is improved. This is because it can be further maintained.

  In the present embodiment, the entirety of the metal substrate 31 is covered with the conductive carbon layer 33 via the intermediate layer 32. In other words, in the present embodiment, the ratio (coverage) of the area where the metal substrate 31 is covered with the conductive carbon layer 33 is 100%. However, it is not limited only to such a form, and the coverage may be less than 100%. The coverage of the metal substrate 31 with the conductive carbon layer 33 is preferably 50% or more, more preferably 80% or more, further preferably 90% or more, and most preferably 100%. With such a configuration, a decrease in conductivity and corrosion resistance due to formation of an oxide film on an exposed portion of the metal substrate 31 that is not covered with the conductive carbon layer 33 can be effectively suppressed. In the case where the intermediate layer 32 is interposed between the metal base material 31 and the conductive carbon layer 33 as in the present embodiment, the above-mentioned coverage is determined when the conductive member (metal separator 5) is viewed from the laminating direction. Means the ratio of the area of the metal substrate 31 overlapping the conductive carbon layer 33.

[Intermediate layer]
As shown in FIG. 2, in the present embodiment, the conductive member forming the separator 5 has an intermediate layer 32. The intermediate layer 32 has a function of preventing contact between the acidic aqueous solution and the metal base material and preventing elution of ions from the metal base material 31. In particular, when the R value of the conductive carbon layer exceeds the upper limit of the preferable range described above, the effect of providing the intermediate layer 32 is remarkably exhibited. However, it goes without saying that the intermediate layer 32 can be provided even when the R value is within the above-described preferred range. In other respects, the above-described operation and effect provided by the provision of the intermediate layer 32 are more remarkably exhibited when the metal substrate 31 is made of a material having low corrosion resistance under acidic conditions such as aluminum or an alloy thereof. Hereinafter, a preferred embodiment in the case where the intermediate layer 32 is provided on the conductive member will be described.

  The material forming the intermediate layer 32 is not particularly limited as long as it provides the above-mentioned adhesion. For example, carbides, nitrides, and metals of Group 4 metals (Ti, Zr, Nf), Group 5 metals (V, Nb, Ta), and Group 6 metals (Cr, Mo, W) of the periodic table. And carbonitrides. Of these, nitrides, carbides, or carbonitrides of metals such as tungsten (W), titanium (Ti), molybdenum (Mo), niobium (Nb), and hafnium (Hf) with low ion elution are preferably used. More preferably, in addition to the anticorrosion effect of the underlying metal base material, titanium nitride, carbide, or carbonitride having high high-potential corrosion resistance is used. By using these materials, the conductive member can be protected from a local high potential or the like generated at the time of starting and stopping. Further, these metal materials are particularly useful in that even if an exposed portion is present due to the formation of a passivation film, elution of the metal material itself is hardly observed. In particular, when the metal base is a metal base 31 made of a metal having low corrosion resistance, such as aluminum or an alloy thereof, corrosion proceeds due to moisture that has reached near the interface. As a result, the conductivity of the entire metal substrate 31 in the thickness direction is deteriorated. For this reason, providing an intermediate layer is effective for imparting corrosion resistance to the conductive member.

  The thickness of the intermediate layer 32 is not particularly limited. However, from the viewpoint of making the size of the fuel cell stack as small as possible by making the separator 5 thinner, the thickness of the intermediate layer 32 is preferably 0.01 to 10 μm, more preferably 0 to 10 μm. 0.05-5 μm, more preferably 0.02-5 μm, especially 0.1-1 μm. If the thickness of the intermediate layer 32 is 0.01 μm or more, a uniform layer is formed, and the corrosion resistance of the metal base 31 can be effectively improved. On the other hand, if the thickness of the intermediate layer 32 is 10 μm or less, an increase in the film stress of the intermediate layer 32 is suppressed, and a decrease in film followability to the metal base material 31 and the occurrence of peeling and cracks due to this can be prevented. .

  It is preferable that the surface of the intermediate layer 32 on the side of the conductive carbon layer 33 is roughened at the nano level. According to such an embodiment, the adhesion between the boundary layer formed densely on the intermediate layer 32 and the intermediate layer 32 can be further improved. Examples of such an intermediate layer include an intermediate layer having a columnar crystal structure.

Further, when the coefficient of thermal expansion of the intermediate layer 32 is close to the coefficient of thermal expansion of the metal constituting the metal substrate 31, the adhesion between the intermediate layer 32 and the metal substrate 31 is improved. However, in such a form, the adhesion between the intermediate layer 32 and the conductive carbon layer 33 may be reduced. Similarly, if the coefficient of thermal expansion of the intermediate layer 32 is close to the coefficient of thermal expansion of the conductive carbon layer 33, the adhesion between the intermediate layer 32 and the metal base 31 may be reduced. In consideration of these, the coefficient of thermal expansion (α _mid ) of the intermediate layer 32, the coefficient of thermal expansion (α _sub ) of the metal substrate 31, and the coefficient of thermal expansion (α _c ) of the conductive carbon layer 33 are represented by α _sub. > Α _mid > α _c is preferably satisfied.

  It is desirable that the intermediate layer 32 be present on both surfaces of the metal base material 31. However, in the case where the intermediate layer 32 is used for an application location that does not impair the intended effect of the present invention, the intermediate layer 32 is provided on one of the surfaces. There may be only one. However, when the conductive carbon layer 33 exists only on one main surface of the metal base material 31, the intermediate layer 32 exists between the metal base material 31 and the conductive carbon layer 33. Further, the conductive carbon layer 33 may be present on both surfaces of the metal base 31 as described above. In such a case, it is preferable that the intermediate layer 32 be interposed between the metal base material 31 and both conductive carbon layers 33, respectively. When the intermediate layer 32 exists only between the metal substrate 31 and any one of the conductive carbon layers 33, the intermediate layer 32 is a conductive carbon layer to be disposed on the MEA 9 side in the PEFC1. It is preferably present between 33 and the metal substrate 31 (see FIGS. 1, 3 and 4).

  FIG. 6 shows a manufacturing apparatus for forming (forming) at least one layer of the conductive member of the present invention, in particular, the intermediate layer 32 and the conductive carbon layer 33, and preferably these layers in order by sputtering. FIG. Here, as the sputtering apparatus, an apparatus applicable to the unbalanced magnetron sputtering (UBMS) method used in the embodiment is shown.

  FIG. 7 shows the conductive member of the present invention, in particular, at least one layer of each of the intermediate layer 32 and the conductive carbon layer 33, and preferably, each of these layers is sequentially formed (formed) by an arc ion plating (AIP) method. FIG. 2 is a schematic plan view of a manufacturing apparatus for performing the above steps. However, FIGS. 6 and 7 show an example in which an existing disk-shaped wafer is set in place of the flat metal separator 5 before the uneven pressing.

  When sputtering is performed using the apparatuses 300 and 400 shown in FIGS. 6 and 7, one or a plurality of metal separators 5 are arranged on the rotating tables 301 and 401, respectively. Also, each metal separator 5 itself also rotates in a direction perpendicular to the rotation surface (rotation axis) of the rotating table. The arrow method of each of the metal separators 5 of the rotating tables 301 and 401 indicates the direction of rotation where the rotating surfaces (axes) are perpendicular to each other.

The inside of the vacuum chambers 303 and 403 shown in FIGS. 6 and 7 is maintained at a level of 10 ^-1 to 10 ^-2 Torr, and as needed. Gases (not shown) such as N ₂ and Ar can be introduced from the air supply ports 305 and 405. Unnecessary atmosphere gases and extra gas sources are appropriately exhausted from exhaust ports 307 and 407 in order to control a predetermined pressure (vacuum pressure or the like) in the vacuum chambers 303 and 403.

  Temperature control equipment is connected to the vacuum chambers 303 and 403 and the tables 301 and 401 that hold the metal separators 5, and the temperature can be adjusted.

  First, the surface of each metal separator 5 shown in FIGS. 6 and 7 is subjected to Ar ion bombardment (reverse sputtering) to remove an oxide film present on the surface of the metal separator 5. Since the oxide film is formed with a thickness of several angstroms, the removal time may be several seconds to several minutes. In this embodiment, a titanium nitride is disposed as the intermediate layer 32 before the conductive carbon layer 33 is formed. Therefore, Ti targets (sputtering targets (Ti)) 309 and 409 are arranged in the chambers 301 and 401, and sputtering is performed in a nitrogen atmosphere. After the formation of the intermediate layer 32 made of titanium nitride, the conductive carbon layer 33 is subsequently formed using carbon (targets (sputtering targets (C))) 311, 411 disposed in the same chambers 301, 401. In forming the conductive carbon layer 33, as shown in FIG. 6, various patterns may be used in which the negative bias voltage during the formation of the conductive carbon layer is changed from a low value to a high value. In addition, the metal separators 5 can be continuously formed by changing the bias voltage, temperature, degree of vacuum, and the like. Also in the formation of the intermediate layer 32, the bias voltage or the like may be constant without changing the bias voltage or the like at a predetermined value, or may be changed twice or more (although it may be changed continuously). good. In addition, the metal separators 5 can be continuously formed by changing the bias voltage, temperature, degree of vacuum, and the like.

  When the conductive carbon layer 33 is formed by arc ion plating (AIP) using the apparatus shown in FIG. 7, the target (sputtering target (C)) 411 should be used as in FIG. However, by arranging another evaporation source 413 for arc discharge, it is possible to form a film in the same chamber 401 without reducing the degree of vacuum. Also in forming the conductive carbon layer 33 by the AIP method using the apparatus shown in FIG. 7, in order to obtain the conductive carbon layer 33 having predetermined characteristics, the conditions (voltage / current) of the arc power supply 415, the degree of vacuum, The temperature, the bias voltage, and the like may be constant without changing a predetermined value, or the temperature, the bias voltage, and the like may be changed appropriately.

  The conductive carbon layer 33 is formed, for example, by using the apparatus shown in FIGS. 6 and 7 and after replacing the target after the deposition of the intermediate layer 32, by applying a bias (voltage), a temperature, a degree of vacuum, and a supply gas amount (minute). It is desirable to form at least one of the pressures in the same batch or process using the same apparatus and method. This is because the conductive carbon layer 33 can be formed continuously after the formation of the intermediate layer 32 and can be formed on the same film formation process, which is advantageous in that the cost is reduced.

  In the present invention, the intermediate layer 32 and the conductive carbon layer 33 are formed by sputtering using the apparatus shown in FIG. 6 or formed by AIP or ECR sputtering using the apparatus shown in FIG. desirable. This is because a conductive path from one surface of the conductive carbon layer 33 to the other surface is secured by using a sputtering method or an AIP method, which is a dry film forming method, for the intermediate layer 32 and the conductive carbon layer 33. This is excellent in that a conductive member with further improved corrosion resistance can be provided while sufficiently ensuring excellent conductivity. Further, in the conductive member having the intermediate layer 32 between the metal base material 31 and the conductive carbon layer 33, a means for suppressing an increase in contact resistance while sufficiently securing excellent conductivity can be provided. Is excellent.

  In forming the intermediate layer 32 and the conductive carbon layer 33, a solid source (for example, graphite carbon) is desirable. With gas sources, it is difficult to produce good ones with currently used gas types. This is because hydrogen enters the film (as a result, conductivity decreases).

  In addition, the size and the number of the targets 309, 311, 409, 411, and 413 can be appropriately adjusted according to the size of the metal separator 5, the throughput, and the like.

  In the present invention, the present invention is applicable not only to the metal separator 5 but also to any surface of a component requiring conductivity and corrosion resistance. For example, current collecting plates 30 and 40 (see FIG. 3) disposed at both ends of a stack 20 in which a plurality of cells are stacked, a gas diffusion layer (GDL) 4, and a terminal connection portion (not shown) for monitoring a voltage. 4 (see output terminals 37 and 47).

  In the present embodiment, when the intermediate layer is formed on the metal substrate in the dry film forming method, the dry film forming method is preferably a sputtering method or an ion plating method. However, the present invention is not limited thereto, and various conventionally known film forming techniques described above can be used.

  Hereinafter, with reference to FIGS. 1 to 4 and the like, the components of the PEFC using the separator composed of the conductive member of the present embodiment will be described. However, the present invention is characterized by a conductive member constituting the separator. Therefore, the specific form such as the shape of the separator in the PEFC and the specific form of the members other than the separator constituting the fuel cell can be appropriately modified with reference to conventionally known knowledge. 3 is a schematic cross-sectional view illustrating an example of a fuel cell stack configuration in which a plurality of unit cell configurations of the fuel cell in FIG. 1 are stacked, and FIG. 4 is a perspective view of the fuel cell stack configuration in FIG. It is.

[Electrolyte layer]
The electrolyte layer is composed of, for example, a solid polymer electrolyte membrane 2 as shown in FIGS. 1 and 3. The solid polymer electrolyte membrane 2 has a function of selectively transmitting protons generated in the anode catalyst layer 3a to the cathode catalyst layer 3b along the film thickness direction during the operation of the PEFC including the plurality of cell units 1 and the like. Having. Further, the solid polymer electrolyte membrane 2 also has a function as a partition wall for preventing the fuel gas 5ag supplied to the anode side and the oxidant gas 5bg supplied to the cathode side from being mixed.

  The solid polymer electrolyte membrane 2 is roughly classified into a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane depending on the type of ion exchange resin as a constituent material. Examples of the ion exchange resin constituting the fluorine-based polymer electrolyte membrane include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride Perfluorocarbon sulfonic acid-based polymers and the like can be mentioned. From the viewpoint of improving power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably a fluorine-based polymer electrolyte composed of a perfluorocarbonsulfonic acid-based polymer. A membrane is used.

  Specific examples of the hydrocarbon-based electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). From the viewpoint of manufacturing that raw materials are inexpensive, the manufacturing process is simple, and material selectivity is high, these hydrocarbon-based polymer electrolyte membranes are preferably used. In addition, only one kind of the above-mentioned ion exchange resin may be used alone, or two or more kinds may be used in combination. Further, the present invention is not limited to only the above-described materials, and other materials may be used.

  The thickness of the electrolyte layer may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte layer is usually about 5 to 300 μm. When the thickness of the electrolyte layer is within such a range, the balance between the strength during film formation, the durability during use, and the output characteristics during use can be appropriately controlled.

[Catalyst layer]
The catalyst layers 3 (anode catalyst layer 3a and cathode catalyst layer 3b) shown in FIGS. 1 and 3 are layers in which a battery reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer 3a, and the reduction reaction of oxygen proceeds in the cathode catalyst layer 3b.

  The catalyst layer 3 includes a catalyst component, a conductive catalyst carrier supporting the catalyst component, and an electrolyte. Hereinafter, a composite in which a catalyst component is supported on a catalyst carrier is also referred to as an “electrode catalyst”.

  The catalyst component used for the anode catalyst layer 3a is not particularly limited as long as it has a catalytic action on the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. The catalyst component used in the cathode catalyst layer 3b is not particularly limited as long as it has a catalytic action on the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specifically, it can be selected from metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof. .

  Among them, those containing at least platinum are preferably used in order to improve catalytic activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. Although the composition of the alloy depends on the type of the metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. Note that an alloy is generally a metal element obtained by adding one or more metal elements or non-metal elements, and is a general term for an alloy having metallic properties. The alloy structure includes eutectic alloys, which are so-called mixtures in which the component elements are separate crystals, those in which the component elements are completely dissolved and in solid solution, and those in which the component elements are intermetallic compounds or compounds of metals and nonmetals. Some of them are formed, and any of them may be used in the present application. At this time, the catalyst component used for the anode catalyst layer 3a and the catalyst component used for the cathode catalyst layer 3b can be appropriately selected from the above. In the present specification, unless otherwise specified, the description of the catalyst components for the anode catalyst layer and the cathode catalyst layer has the same definition for both. Therefore, they are collectively referred to as “catalyst components”. However, the catalyst components of the anode catalyst layer 3a and the cathode catalyst layer 3b do not need to be the same, and can be appropriately selected so as to exert the above-described desired action.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as those of known catalyst components can be adopted. However, the shape of the catalyst component is preferably granular. At this time, the average particle diameter of the catalyst particles is preferably 1 to 30 nm. When the average particle size of the catalyst particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the simplicity of the loading can be appropriately controlled. In the present invention, the “average particle diameter of the catalyst particles” refers to the crystallite diameter determined from the half width of the diffraction peak of the catalyst component in X-ray diffraction, or the average particle diameter of the catalyst component determined from a transmission electron microscope image. It can be measured as a value.

  The catalyst carrier functions as a carrier for supporting the above-described catalyst component and as an electron conduction path involved in transfer of electrons between the catalyst component and another member.

  The catalyst carrier has only to have a specific surface area for supporting the catalyst component in a desired dispersed state and have sufficient electron conductivity, and it is preferable that the main component is carbon. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite, and the like. Here, “the main component is carbon” means that a carbon atom is contained as a main component, and is a concept that includes both of a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, "consisting substantially of carbon atoms" means that mixing of impurities of about 2 to 3% by mass or less is permissible.

The BET specific surface area of the catalyst carrier may be any specific surface area sufficient to highly disperse and support the catalyst component, but is preferably 20 to 1600 m ² / g, and more preferably 80 to 1200 m ² / g. When the specific surface area of the catalyst carrier is within such a range, the balance between the dispersibility of the catalyst component on the catalyst carrier and the effective utilization rate of the catalyst component can be appropriately controlled.

  Although the size of the catalyst carrier is not particularly limited, the average particle diameter is about 5 to 200 nm, preferably 10 to 10 from the viewpoint of simplicity of loading, catalyst utilization, and controlling the thickness of the catalyst layer in an appropriate range. The thickness is preferably about 100 nm.

  In an electrode catalyst in which a catalyst component is supported on a catalyst carrier, the amount of the catalyst component supported is preferably 10 to 80% by mass, more preferably 30 to 70% by mass, based on the total amount of the electrode catalyst. When the supported amount of the catalyst component is within such a range, the balance between the degree of dispersion of the catalyst component on the catalyst carrier and the catalyst performance can be appropriately controlled. The amount of the catalyst component carried on the electrode catalyst can be measured by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst layer 3 contains an ion-conductive polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, the ion exchange resin constituting the electrolyte layer 2 described above can be added to the catalyst layer 3 as a polymer electrolyte.

[Gas diffusion layer (GDL)]
The gas diffusion layer 4 (gas diffusion layer 4a, cathode gas diffusion layer 4b) shown in FIG. 31 is formed of a gas flow path (fuel gas flow path 5aa, oxidant gas flow path) of the metal separator 5 (anode separator 5a, cathode separator 5b). 5bb) has a function of promoting the diffusion of the gas (fuel gas or oxidizing gas) supplied to the catalyst layer 3 (anode catalyst layer 3a, cathode catalyst layer 3b) and a function as an electron conduction path.

  The material constituting the base material of the gas diffusion layer 4 (4a, 4b) is not particularly limited, and conventionally known knowledge can be appropriately referred to. For example, a conductive and porous sheet material such as a carbon woven fabric, a paper-like paper body, a felt, and a nonwoven fabric may be used. The thickness of the base material of the gas diffusion layer 4 may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, and may be about 30 to 500 μm. If the thickness of the base material of the gas diffusion layer 4 is within such a range, the balance between the mechanical strength and the diffusivity of gas, water, and the like can be appropriately controlled.

  The gas diffusion layer 4 preferably contains a water repellent for the purpose of further increasing the water repellency and preventing the flooding phenomenon and the like. Examples of the water repellent include, but are not particularly limited to, fluorine-based high-molecular compounds such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples include a molecular material, polypropylene, and polyethylene.

  In order to further improve the water repellency, the gas diffusion layer 4 is provided with a carbon particle layer (microporous layer; MLP, not shown) made of an aggregate of carbon particles containing a water repellent on the catalyst layer side of the substrate. May be provided.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately used. Among them, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black can be preferably used because of their excellent electron conductivity and large specific surface area. The average particle diameter of the carbon particles is preferably about 10 to 100 nm. This makes it possible to obtain a high drainage property due to the capillary force, and also to improve the contact property with the catalyst layer 4.

  Examples of the water repellent used in the carbon particle layer include the same water repellents as described above. Among them, a fluorine-based polymer material can be preferably used because it is excellent in water repellency, corrosion resistance during an electrode reaction, and the like.

  The mixing ratio between the carbon particles and the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) in mass ratio in consideration of the balance between water repellency and electron conductivity. Is good. The thickness of the carbon particle layer is not particularly limited and may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer, but is preferably 10 to 1000 μm, and more preferably 50 to 500 μm. Good.

[Separator]
The metal separator 5 shown in FIGS. 1 and 3 is as described in the embodiments described later.

The conductive member of the present embodiment can be used for various applications. A typical example is the PEFC separator 5 shown in FIG. However, the application of the conductive member of the present embodiment is not limited to this. For example, in addition to PEFC, various fuel cell separators such as a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid electrolyte fuel cell (SOFC), and an alkaline fuel cell (AFC) It can also be used as In addition to the fuel cell separator, it can be used for various applications in which both conductivity and corrosion resistance are required. Applications other than the fuel cell separator in which the conductive member of the present embodiment can be used include, for example, other fuel cell components (current collectors, bus bars, gas diffusion base materials, MEAs), and contacts of electronic components. . In another preferred embodiment, the conductive member of the present embodiment is used in a wet environment and an energized environment. When used in such an environment, the function and effect of the present invention of achieving both conductivity and corrosion resistance can be remarkably exhibited.
[Basic configuration of cell unit]
1 and 3, the basic structure of a single cell (cell unit) 1 of the polymer electrolyte fuel cell is such that a fuel electrode side electrode catalyst layer 3a and a fuel electrode side gas are provided on both sides of a polymer electrolyte membrane 2. The fuel cell includes the MEA 9 in which the fuel electrode including the diffusion layer 4a and the oxygen electrode including the oxygen electrode-side electrode catalyst layer 3b and the oxygen electrode-side gas diffusion layer 4b are arranged to face each other. It is sandwiched between the fuel electrode side separator 5a and the oxygen electrode side separator 5b. Further, the fuel gas 5ag (hydrogen-containing gas) and the oxidizing gas 5bg (air) supplied to the MEA are supplied to the fuel electrode side electrode catalyst layer 3a and the oxygen electrode side electrode 5a on the fuel electrode side separator 5a and the oxygen electrode side separator 5b. The fuel gas is supplied via a fuel gas flow path 5aa and an oxidizing gas flow path 5bb formed at a plurality of locations on the surface facing the catalyst layer 3b.

  In order to use the cell unit (single cell) 1 for a fuel cell (stack) 20, a stack (laminated stack) in which the single cells 1 are singly or two or more stacked is further added in the thickness direction of the single cell 1 or the stacked stack. Are used by fastening a pair of end plates from both sides (both ends), that is, a fuel electrode side end plate 70 and an oxygen electrode side end plate 80 (see FIG. 4).

  More specifically, as a configuration of the fuel cell stack 20 (a portion sandwiched between the current collecting plates 30 and 40), as shown in FIG. 3, a single cell (cell unit) 1 of a plurality of fuel cells is stacked. It has a stack unit 20 and is used as a power supply. The use of the power source is, for example, for stationary use, for consumer portable devices such as mobile phones, for emergency use, for outdoor use such as a power source for leisure and construction, and for mobile objects such as automobiles with limited installation space. In particular, the power supply for a mobile body is preferably applied since a high output voltage is required after a relatively long operation stop. Further, in the vehicle equipped with the fuel cell of the present invention, the thickness and cost can be reduced through the components (conductive members) such as the metal separator 5 and the current collectors 30 and 40 of the fuel cell (PEFC or the like). This can contribute to improvement of the output density of the fuel cell. Therefore, the weight of the vehicle and the cost of the vehicle can be reduced, and when a fuel cell of the same volume is mounted, a longer mileage can be run, and the acceleration performance is also improved.

  In the single cell (cell unit) 1 of the fuel cell according to the present invention, the thickness and cost can be reduced through the components (conductive members) such as the metal separator 5 and the current collectors 30 and 40 of the fuel cell (PEFC), and the stack is reduced. When the fuel cell stack 20 is formed, the power density of the fuel cell stack 20 can be improved. In addition, the components (conductive members) such as the metal separator 5 and the current collectors 30 and 40 of the fuel cell are excellent in corrosion resistance, and the durability (extended life) of the fuel cell stack 20 can be achieved.

  Current collecting plates 30, 40, insulating plates 50, 60 and end plates 70, 80 are arranged on both sides of the stack section 20. The current collector plates 30 and 40 are formed of a gas-impermeable conductive member such as dense carbon, a copper plate, or an aluminum plate, and are provided with output terminals 37 and 47 for outputting an electromotive force generated in the stack unit 20. Have been. The insulating plates 50 and 60 are formed from an insulating member such as rubber or resin.

  Here, instead of the above-mentioned carbon and the like, the current collector plates 30 and 40 are made of a copper plate or an aluminum plate which is thinner and lighter than stainless steel, but has poor corrosion resistance, from the viewpoint of thinning and cost reduction. When used for the electric plates 30, 40, the configuration of the present invention can be adopted. With such a configuration, it is possible to form a conductive member in which resistance is reduced on the outermost surface of the conductive carbon layer 33 while preventing corrosion of the base material 31 due to intrusion of droplets in the intermediate layer 32. As a result, the chemical stability can be maintained even when the metal current collector plates 30 and 40 are exposed to an acidic atmosphere while maintaining the conductivity. Specifically, a surface treatment capable of effectively suppressing ion elution against defects such as pinholes without increasing the electrical resistance (here, as shown in FIG. 3, the contact resistance with the separator 5). The provided current collector plates 30 and 40 can be provided.

  Further, as shown in FIGS. 1 and 4, the end plates 70 and 80 are formed of a rigid material, for example, a metal material such as steel. The end plates 70 and 80 are provided with a fuel gas flow path (hydrogen-containing gas flow path) 5aa and a oxidizing gas for flowing the fuel gas 5ag (eg, hydrogen), the oxidizing gas 5bg (eg, oxygen), and the cooling water 8w. A fuel gas inlet 71, a fuel gas outlet 72, an oxidizing gas inlet 74, and an oxidizing gas outlet, which communicate with the gas flow path (oxygen gas flow path) 5bb and the cooling water flow path (refrigerant flow path) 8. 75, a cooling water inlet 77, and a cooling water outlet 78.

  As shown in FIG. 4, through holes through which tie rods 90 are inserted are arranged at four corners of the stack section 20, the current collecting plates 30 and 40, the insulating plates 50 and 60, and the end plates 70 and 80. The tie rod 90 has a nut (not shown) screwed into a male screw portion formed at the end thereof, and fastens the inside of the fuel cell stack 200 (the stack portion 20) with the end plates 70 and 80. The load for forming the stack acts in the stacking direction of the single fuel cell (cell unit) 1 (MEA 9), and holds the single fuel cell (cell unit) 1 in a pressed state.

As shown in FIG. 4, the tie rod 90 is formed of a rigid material, for example, a metal material such as steel, and has an insulated surface to prevent an electric short circuit between the fuel cell single cells 201. Having a part. The number of tie rods 90 to be installed is not limited to four (four corners). The fastening mechanism of the tie rod 90 is not limited to screwing, and other means can be applied. As shown in FIGS. 1 and 3, the single fuel cell (cell unit) 1 is , MEA 9, separators 5a and 5b, and a gasket (not shown). The MEA 9 includes the electrolyte membrane 2, and a fuel electrode side electrode (catalyst layer 3 a and gas diffusion layer 4 a) and an oxygen electrode side electrode (catalyst layer 3 b and gas diffusion layer 4 b) which are arranged with the electrolyte membrane 2 interposed therebetween. The separators 5a and 5b are arranged on the outer surface of the MEA 9. The separator 5a has a flow path 5aa through which the fuel gas 5ag flows, and is connected to the fuel gas inlet 71 and the fuel gas outlet 72 arranged on the end plate 70. The separator 5b has a flow path 5bb through which the oxidizing gas 5bg flows, and is connected to the oxidizing gas inlet 74 and the oxidizing gas outlet 75 arranged on the end plate 80.

  As shown in FIGS. 1 and 3, the separators 5 a and 5 b have a flow path 8 for flowing the cooling water 8 w, and the cooling water introduction ports 77 and The cooling water outlet 78 is connected.

  Next, the gasket is a sealing member disposed so as to surround the outer periphery of the electrode located on the surface of the MEA 9 and is fixed to the outer surface of the electrolyte membrane 2 of the MEA 9 via an adhesive layer (not shown). It may have a configuration. The gasket has a function of ensuring a sealing property between the separator 5 and the MEA 9. In addition, it is preferable that the adhesive layer used as necessary corresponds to the shape of the gasket and is arranged in a frame shape on the entire periphery of the electrolyte membrane in consideration of securing the adhesiveness.

  As shown in FIG. 4, in the fuel cell stack 200 using the conductive member of the present invention, a manifold (anode (fuel gas 5ag), a cathode (oxidation gas) formed so as to penetrate the current collector plates 30 and 40 is formed. In a preferred embodiment, the intermediate layer 32 is also formed on the inner wall of the penetrating portion of each of the agent gas 5bg) and the cooling water 8w, one at the inlet and one at the outlet. That is, since conductivity is not required on the inner wall of the through portion of the manifold, it is preferable to form the intermediate layer 32 without providing a surface treatment layer such as gold plating. This is extremely effective in that corrosion of the base material in the through portion of the manifold can be effectively prevented.

  The above is the outline of the configuration of the fuel cell stack 200 using the conductive member of the present invention. In addition to the metal separator 5 and the current collectors 30 and 40, the components of the fuel cell that require conductivity and corrosion resistance As for the (conductive member), the configuration of the present invention can be adopted. This makes it possible to reduce the thickness and weight of the components (conductive members) of the fuel cell and the fuel cell stack, thereby contributing to improving the output density. Furthermore, it is also useful as a battery element technology to be mounted on a fuel cell vehicle, for which cost reduction is strongly required, because it leads to cost reduction.

  The method for manufacturing the fuel cell of the present invention is not particularly limited, except for the metal separator 5 (especially except for the above-described method for manufacturing the intermediate layer 32), and can be manufactured by appropriately referring to conventionally known knowledge in the field of fuel cells. It is.

  Although the type of the fuel gas 5ag (hydrogen-containing gas) used when operating the fuel cell has been described using hydrogen as an example in the above description, it is not particularly limited. In addition to hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, and diethylene glycol can be used. Among them, hydrogen and methanol are preferred because high output can be achieved.

  Further, a fuel cell stack 200 having a structure in which a plurality of membrane electrode assemblies (MEA 9) are stacked via a metal separator 5 and connected in series may be formed so that a desired voltage or the like can be obtained by the fuel cell. 3 and 4). The shape and the like of the fuel cell are not particularly limited, and may be appropriately determined so as to obtain desired cell characteristics such as a desired voltage.

  Although the use of the fuel cell of the present invention is not particularly limited, it is preferably used as a driving power source in a vehicle such as an automobile because of its excellent power generation performance.

  The above-described PEFC cell unit 1 and fuel cell stack 200 use the metal separator 5 composed of a conductive member having excellent conductivity and corrosion resistance. Therefore, the PEFC cell unit 1 and the fuel cell stack 200 are excellent in output characteristics and durability, and can maintain good power generation performance for a long period of time. In the cell unit 1 of the PEFC shown in FIG. 1, the metal separator 5 is formed into an uneven shape by performing a pressing process on a flat conductive member. However, it is not limited only to such a form. For example, by performing a cutting process on a flat metal plate (metal base material 31), irregularities forming the gas flow paths 5ag and 5bg and the refrigerant flow path 8 are formed in advance, and the above-described method is applied to the surface thereof. By forming the conductive carbon layer 33 (and the intermediate layer 32 as necessary), the metal separator 5 may be formed.

  The PEFC cell unit 1 of the present embodiment and the fuel cell stack 200 using the same can be mounted, for example, as a drive power supply in a vehicle.

  In order to mount the fuel cell stack 200 on a vehicle such as a fuel cell vehicle, for example, the fuel cell stack 200 may be mounted under a seat in the center of the vehicle body of the fuel cell vehicle. If installed under the seat, the interior space and trunk room can be widened. In some cases, the place where the fuel cell stack 200 is mounted is not limited to below the seat, but may be below the rear trunk room or in the engine room in front of the vehicle. Thus, the vehicle on which the above-described PEFC cell unit 1 and fuel cell stack 200 are mounted is also included in the technical scope of the present invention. The above-described PEFC cell unit 1 and fuel cell stack 200 are excellent in output characteristics and durability. Therefore, a highly reliable fuel cell vehicle can be provided for a long period of time.

  Hereinafter, the effects of the present invention will be described using examples and comparative examples, but the technical scope of the present invention is not limited to these examples.

[Example 1]
Using a separator plate made of austenitic stainless steel and having a thickness of 100 μm, after ultrasonic cleaning in an ethanol solution for 3 minutes as a pretreatment, further installing a metal substrate in a vacuum chamber, performing ion bombardment treatment with Ar gas, and performing surface treatment. The oxide film of was removed. Both the pretreatment and the ion bombardment treatment were performed on both surfaces of the metal substrate.

  Next, a negative bias voltage is applied to the metal substrate while introducing nitrogen gas by using a Ti as a target by an arc ion plating method (or a sputtering method) to form a TiN film having a thickness of 0.5 μm. An intermediate layer was formed on both sides of the metal substrate. The temperature during the formation of the intermediate layer is 200 ° C., and the voltage application pattern is constant at 50 V.

  Next, while applying a negative bias voltage to the metal substrate by the sputtering method on the intermediate layer, using solid graphite as a target, the film thickness is formed on both surfaces of the metal substrate on which the intermediate layer is formed. A conductive carbon layer having a thickness of 0.02 μm was formed. The temperature and voltage application pattern at the time of forming the conductive carbon layer were maintained at the initial value of the bias voltage of 50 V for 5 minutes, then increased to a final voltage of 200 V for 7 minutes, and maintained at the final voltage of 200 V for 3 minutes. The values of the peel test and the contact resistance are shown in Table 1 below.

  In this example, as is clear from the appearance photograph shown in FIG. 8A, the front surface of the conductive member has gloss and the entire surface can be formed. Further, as shown in Table 1, it can be understood that the obtained conductive carbon layer has high adhesion to the intermediate layer while having low contact resistance.

  In addition, as is clear from the surface SEM observation photograph shown in FIG. 9A, it is understood that there is no gap in the grain boundaries and the like, and the film has a dense film form.

[Example 2]
In the step of forming the conductive carbon layer in Example 1, the holding time at the initial value of the bias voltage of 50 V was 15 minutes, the boosting time to the final voltage of 200 V was 10 minutes, and the holding time at the final voltage of 200 V was 5 minutes. A conductive member was prepared in the same manner, except that the amount was changed.

  As in this embodiment, by increasing the film formation time at a low voltage and increasing the pressure, it is possible to improve the adhesion to the intermediate layer while maintaining a low contact resistance of the conductive carbon layer.

[Example 3]
A conductive member was produced in the same manner as in Example 1, except that the final voltage was set to 300 V in the step of forming the conductive carbon layer.

  By setting the final voltage high as in this embodiment, the degree of graphitization of the surface layer can be increased, which is advantageous from the viewpoint of reducing the contact resistance of the surface layer.

[Comparative Example 1]
A conductive member was manufactured in the same manner as in Example 1 except that the bias application pattern when forming the conductive carbon layer was set to 150 V for 15 minutes.

  In this comparative example, as is clear from the appearance photograph of FIG. This is probably because the value of the bias voltage is too high to form the boundary layer.

  Further, as is clear from FIG. 9B which shows a surface SEM observation photograph of a portion that is not in a powder form in FIG. 8B, it is understood that the film has a dense film form with no gaps in the grain boundaries and the like.

[Comparative Example 2]
A conductive member was produced in the same manner as in Comparative Example 1, except that the substrate temperature immediately before forming the conductive carbon layer was 350 ° C. and the bias voltage was 50 V.

  The value of the bias voltage in this comparative example is preferable for forming a carbon layer as a boundary layer having a low R value and good adhesion to the intermediate layer. However, the graphitization proceeds due to the high temperature, and the adhesion between the intermediate layer and the conductive carbon layer cannot be ensured.

[Comparative Example 3]
A conductive member was produced in the same manner as in Comparative Example 1, except that the bias application pattern when forming the conductive carbon layer was 50 V.

  In this comparative example, a carbon layer having a low R value and capable of functioning as a boundary layer having good adhesion to the intermediate layer can be formed on the intermediate layer. However, such a carbon layer has a high degree of contact resistance due to a low degree of graphitization.

[Measurement of contact resistance]
With respect to the conductive members manufactured in Examples 1 to 3 and Comparative Example 3, the contact resistance in the stacking direction of the conductive members was measured. Specifically, as shown in FIG. 10, both sides of the conductive member (metal separator 5) formed in Examples 1 to 3 and Comparative Example 3 are paired with a gas diffusion base material (gas diffusion layer 4 a). , 4b), the both sides of the obtained laminate are further sandwiched by a pair of electrodes (catalyst layers 3a, 3b), a power source is connected to both ends thereof, and a load of 1 MPa is applied to the entire laminate including the electrodes. While holding, a measuring device was configured. A constant current of 1 A was passed through this measuring device, and the contact resistance value of the laminate was calculated from the amount of current and the voltage value when a load of 1 MPa was applied.

As shown in Table 1, the contact resistances of the conductive members manufactured in Examples 1 to 3 were all 1 mΩ · cm ² . On the other hand, in Comparative Example 3, it was 5 mΩ · cm ² .

[Measurement of R value]
The R value of the conductive carbon layer 33 was measured for the surface layer portion and the intermediate layer for the conductive members prepared in the above Examples 1 to 3 and Comparative Example 3 in which the conductive carbon layer could be formed. Specifically, first, the Raman spectrum of the conductive carbon layer 33 was measured using a microscopic Raman spectrometer. Then, the peak intensity of the bands (D-band) located 1300~1400cm ^-1 _{(I D),} the peak area ratio of the peak intensity _{(I G)} of band (G-band) located 1500~1600cm ^-1 ( I _D / I _G ) was calculated and used as the R value. The results obtained are shown in Table 1 below.

  As shown in Table 1, the R value of the surface layer portion 33b in the conductive members produced in Examples 1 to 3 was 1.3 or more. The R values of the boundary layers of Examples 1 to 3 and Comparative Example 3 were all less than 1.3.

1,201 Single cell (unit cell) of polymer electrolyte fuel cell (PEFC),
2 electrolyte membrane (solid polymer electrolyte membrane),
3 catalyst layer,
3a anode catalyst layer (fuel electrode side electrode catalyst layer),
3b cathode catalyst layer (oxygen electrode side electrode catalyst layer),
4 gas diffusion layer (GDL),
4a anode gas diffusion layer (fuel electrode side gas diffusion layer),
4b cathode gas diffusion layer (oxygen electrode side gas diffusion layer),
5 separator (metal separator),
5a anode separator (fuel electrode side separator),
5b cathode separator (oxygen electrode side separator),
5aa anode side gas flow path,
5bb cathode side gas flow path,
5ag fuel gas,
5bg oxidant gas,
8 cooling water flow path (refrigerant flow path),
8w cooling water (refrigerant),
9 membrane-electrode assembly (MEA),
20 stack part (laminated stack),
30, 40 current collector,
31 metal substrate,
32 middle layers,
33 conductive carbon layer,
33a boundary layer,
33b surface layer,
37, 47 output terminals,
50, 60 insulating plate,
70 fuel electrode side end plate,
80 oxygen electrode side end plate,
71 fuel gas inlet,
72 fuel gas outlet,
74 oxidant gas inlet,
75 oxidant gas outlet,
77 cooling water inlet,
78 cooling water outlet,
90 tie rods,
200 Fuel cell (stack).

Claims (4)

In the dry film forming method,
An intermediate made of at least one selected from the group consisting of carbides, nitrides and carbonitrides of metals belonging to Group 4 of the periodic table, metals of Group 5 and metals of Group 6 on a metal substrate. Forming a layer;
Forming a conductive carbon layer on the intermediate layer,
The step of forming a conductive carbon layer on the intermediate layer,
Changing the negative bias voltage from a low value to a high value,
In the step of forming the conductive carbon layer, the negative bias voltage applied to the metal base material is continuously or stepwise increased from 50 V or less to 200 V or more while continuing to form the conductive carbon layer. A method for producing a fuel cell separator, comprising a step of changing the fuel cell separator.   The step of forming the conductive carbon layer, wherein the intermediate layer is made of titanium nitride, comprises applying a negative bias voltage of 50 V to 200 V to the metal base while continuing to form the conductive carbon layer. The manufacturing method according to claim 1, further comprising a step of continuously or stepwise changing the above. A fuel cell separator in which a metal substrate and an intermediate layer made of titanium nitride are provided on the metal substrate, and a conductive carbon layer is coated on the intermediate layer, wherein the conductive carbon layer Consists of only the boundary layer in contact with the intermediate layer and the surface layer ,
The _I D / _{I G} bordering Sakaiso has an area of 0.7 to 1.1, however, _I D / _{I G} of the boundary layer is 0.7 or more and less than 1.3,
Table layer part _is I D / _{I G} is 1.3 or more, the fuel cell separator. The surface portion of the conductive carbon layer _is I D / _{I G} is 1.5 to 1.9, a separator for the fuel cell according to claim 3.