JP2009238497A - Fuel cell separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell separator having a high conductivity, corrosion resistance, and adhesion. <P>SOLUTION: This is the fuel cell separator 5 which has a metal substrate layer and a carbon layer containing conductive carbon and metal particles. The separator 5 includes the metal substrate layer 6 and the carbon layer 9 containing metal particles 7 and conductive carbon 8. Then, the carbon layer 9 is formed on the metal substrate layer 6. Since the metal particles 7 which tend to be easily oxidized exist in the carbon layer 9 together with the conductive carbon 8, the metal particles 7 are oxidized earlier than metal atoms to constitute the metal substrate layer 6. Thereby, formation of an oxide film on the surface of the metal substrate layer 6 is suppressed, and increase of contact resistance as a separator can be suppressed. Furthermore, since the metal particles 7 and the conductive carbon 8 exist in mixed state in the carbon layer 9, internal stress of the carbon layer 9 itself is alleviated, and as a result, high adhesion with the metal substrate layer 6 being a foundation layer can be obtained, and reduction of resistance value of the battery and a long term stability can be obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell separator.

  The polymer electrolyte fuel cell has a structure in which one cell (single cell) is laminated. Further, the single cell is composed of a solid polymer electrolyte layer, (electrode) catalyst layers provided on both sides thereof, a gas diffusion layer for dispersing supply gas on both sides thereof, and a separator provided on the outside thereof. .

  In the unit cell, fuel gas (for example, hydrogen gas) is supplied to the anode, oxidant gas (for example, air or oxygen) is supplied to the cathode, and electricity is generated by causing the following electrochemical reaction in each of the anode and the cathode. Producing.

  The separator used in such an environment must have good conductivity and high corrosion resistance. Conventionally, carbon materials such as cutting graphite and a mixture of carbon and resin have been mainly used for fuel cell separators. However, since the mechanical strength is not excellent, it is difficult to reduce the thickness, and a relatively thick separator has to be used, resulting in a problem that the size of the fuel cell stack increases.

  In view of this, metal separators are being studied as a substitute for carbon materials, and corrosion resistance to metal substrates and surface treatment without using expensive metals are being promoted. Among them, several metal separators have been proposed in which a metal substrate is coated with a carbon layer and have both good conductivity and corrosion resistance.

  For example, a composite metal material separator in which a film made of conductive graphite is formed on the surface of a metal substrate is disclosed (Patent Document 1). Conductive graphite is deposited on the metal substrate by gas flow sputtering, and has a low resistance value and high adhesion (result of cross-cut peel test).

  Further, it is disclosed that an increase in contact resistance on the separator surface due to corrosion can be suppressed by coating an arbitrary separator base material with a conductive hard carbon film having excellent corrosion resistance (Patent Document 2).

Moreover, although the carbon layer is formed with respect to the base material, it is disclosed that the carbon layer is formed on the surface of the separator base material by a dry film forming method while applying a negative high voltage to the separator base material. (Patent Document 3). According to such a method, even the inside of the carbon layer can be reliably graphitized, and the obtained separator can have high conductivity as well as high chemical stability.
JP 2004-235091 A International Publication No. 01/006585 Pamphlet JP 2006-286457 A

  However, cracks and pins may be applied to the carbon layer formed on the metal base layer (metal substrate) when subjected to a load due to stacking when the cells are stacked or during press molding to form a gas flow path or the like. Defects such as holes may occur. In such a case, while the corrosion resistance of the carbon layer itself is maintained, there is a problem that corrosion due to oxidation occurs on the surface of the metal base layer due to the penetration of acidic water, and the contact resistance as a separator deteriorates (increases).

  Moreover, even if the carbon layer itself has high corrosion resistance, metals such as stainless steel and aluminum used as the metal base layer are easily oxidized. Therefore, although the obtained separator shows low contact resistance in the initial stage, there is a problem that an oxide film is gradually formed on the surface of the metal base layer, resulting in an increase in contact resistance.

  Therefore, an object of the present invention is to provide a fuel cell separator having high conductivity, corrosion resistance and adhesion.

  The present invention for achieving the above object provides a fuel cell separator including a metal base layer and a carbon layer containing conductive carbon and metal particles in a mixed state.

  According to the present invention, the metal particles that are easily oxidized are dispersed in the carbon layer in advance so that the oxide of the metal particles is easily formed before the acidic water reaches the metal base layer. Thus, formation of an oxide film on the surface of the metal substrate layer can be suppressed. Further, by introducing metal particles into the carbon layer, the film stress is relaxed, and the adhesion between the carbon layer and the metal substrate layer is improved. As a result, high conductivity, corrosion resistance, and adhesion can be obtained by using the fuel cell separator of the present invention.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments to which the invention is applied will be described with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) among fuel cells according to an embodiment of the present invention. A catalyst layer 3 (anode catalyst layer and cathode catalyst layer) is disposed on both surfaces of the solid polymer electrolyte layer 2, and a gas diffusion layer (GDL) 4 (anode side gas diffusion layer and cathode side gas diffusion layer) is sandwiched therebetween. ) To form a membrane electrode assembly (MEA). The MEA is finally sandwiched between a pair of conductive separators 5 to form a PEFC single cell. Actually, a gas seal is disposed between the separator 5 and the electrolyte layer 2 and between the battery 1 and another battery adjacent to the battery 1, but is omitted in this schematic diagram. The separator 5 is obtained by forming a thin plate of 0.5 mm or less into a corrugated shape by pressing, and a reaction gas or cooling water is allowed to flow there. As described above, the separator 5 includes a gas flow path and a manifold through which different fluids such as a fuel gas, an oxidant gas, and a refrigerant flow in addition to the function of electrically connecting the MEAs in series. It also has the function of maintaining the desired strength.

  FIG. 2 is a cross-sectional view showing a schematic configuration of the separator 5 in FIG. The separator 5 includes a metal base layer 6 and a carbon layer 9 containing metal particles 7 and conductive carbon 8. The carbon layer 9 is formed on the metal base layer 6. The presence of the metal particles 7 that are relatively easily oxidized together with the conductive carbon 8 in the carbon layer 9 causes the metal particles 7 to be oxidized earlier than the metal atoms constituting the metal base layer 6. Thereby, the production | generation of the oxide film in the metal base material layer 6 surface can be suppressed, and the increase in the contact resistance as a separator can be suppressed. Further, in the carbon layer 9, since the metal particles 7 and the conductive carbon 8 exist in a mixed state, the internal stress of the carbon layer 9 itself is alleviated. Performance, and a reduction in battery resistance and long-term stability. Hereinafter, each component of the separator 5 will be described in detail.

  First, although the material (element) which comprises the metal base material layer 6 is not specifically limited, It is preferable to select in relation with the metal particle 7 mentioned later. Specifically, in terms of easy oxidation, the material is preferably made of a metal element that is equivalent to or less easily oxidized than the metal particles 7. Furthermore, the material is more preferably composed of at least one of the same metal element as the metal particles 7 and a noble metal element. Examples of such a material include aluminum (Al) or an alloy thereof, stainless steel, titanium, or magnesium. Among these, stainless steel, aluminum or an alloy thereof, titanium, more preferably aluminum or an alloy thereof, or stainless steel is preferable. The purity of aluminum is preferably 97% or more, and more preferably 99% or more. About elements other than aluminum in an aluminum alloy, it is more preferable to consist of at least 1 sort (s) of the same metal element as the metal particle 7, and a more noble metal element like the above-mentioned. Specific examples include copper, manganese, silicon, magnesium, zinc and nickel. Moreover, the content rate of iron (Fe) in stainless steel becomes like this. Preferably it is 60-84 mass%, More preferably, it is 65-72 mass%. Furthermore, the chromium (Cr) content in the stainless steel is preferably 16 to 20% by mass, more preferably 16 to 18% by mass.

  Examples of the stainless steel include austenite, martensite, ferrite, austenite / ferrite, and precipitation hardening. Examples of the austenitic system include SUS201, SUS202, SUS301, SUS302, SUS303, SUS304, SUS305, SUS316, and SUS317. Examples of the austenite-ferrite type include SUS329J1. Examples of the martensite system include SUS403 and SUS420. Examples of the ferrite type include SUS405, SUS430, and SUS430LX. Examples of the precipitation hardening system include SUS630. Among these, it is more preferable to use austenitic stainless steel such as SUS304 and SUS316.

  Examples of the aluminum alloy include pure aluminum, aluminum / manganese, and aluminum / magnesium. Examples of the pure aluminum system include A1050P, examples of the aluminum / manganese system include A3003P and A3004P, and examples of the aluminum / magnesium system include A5052P and A5083P. Among these, it is more preferable to use an A1050P pure aluminum-based aluminum alloy.

  Moreover, it is preferable that it is 50-500 micrometers from the viewpoint of workability and mechanical strength, and, as for the thickness of the metal base material layer 6, it is more preferable that it is 80-200 micrometers.

  Subsequently, the element constituting the metal particle 7 is not particularly limited, but is preferably selected in relation to the material (metal atom) constituting the metal base layer 6 as described above. Specifically, in terms of easy oxidation, the metal particles 7 are preferably made of metal atoms that are equivalent to or more easily oxidized than the metal atoms constituting the metal base layer 6. Furthermore, it is preferable that the metal particle 7 consists of at least 1 sort (s) of the same metal element as the element which comprises the metal base material layer 6, and a base metal element. In such a case, the metal particles 7 are oxidized in preference to the material (metal atoms) constituting the metal base layer 6. Thereby, the production | generation of the oxide film in the metal base material layer 6 surface can be suppressed, and the increase in the contact resistance as a separator can be suppressed.

  Further, from the viewpoint of the magnitude relationship of the ionization tendency, regarding the combination of the elements constituting the metal particles 7 and the elements constituting the metal substrate layer 6, the metal particles 7 are aluminum and / or titanium and the metal group. The material layer 6 is preferably made of stainless steel. Or it is preferable that the metal particle 7 is aluminum and / or magnesium, and the metal base material layer 6 consists of aluminum or an aluminum alloy. In such a combination, the increase in the contact resistance can be suppressed more remarkably.

  The above two types of combinations will be specifically described below. First, according to the former combination, when the mechanical strength such as the load in the fuel cell stack, press molding, and the cost are taken into consideration, the above-mentioned stainless steel is used as the material of the metal base layer 6 in the separator. Moreover, aluminum (Al) and / or titanium (Ti) is mentioned as a metal which is a base metal than stainless steel and forms a stable oxide. By making the metal particles 7 Al and / or Ti, the oxidation of the metal particles 7 is performed in preference to the oxidation on the surface of the metal base layer 6. Thereby, an increase in contact resistance can be suppressed while maintaining a low initial contact resistance, and corrosion resistance can be improved. On the other hand, in the latter combination, when the above-mentioned aluminum or aluminum alloy is used as the material of the metal base layer 6, the above-mentioned Al is used as the same metal or a base metal to form a stable oxide. And / or magnesium (Mg). By making the metal particles 7 Al and / or Mg, the metal particles 7 are oxidized in preference to the oxidation on the surface of the metal base layer 6. In particular, Al (or an alloy thereof) is a material of the metal base layer 6 because it is highly convenient due to its light weight and high malleability among metals, and has excellent electrical conductivity. The merit to use as is very large. Thereby, an increase in contact resistance can be suppressed while maintaining a low initial contact resistance, and corrosion resistance can be improved.

  Thus, it is preferable that the metal particles 7 are dispersed in the carbon layer 9 as a base metal, that is, a metal having a lower standard electrode potential, than the metal constituting the metal base layer 6 serving as a base. In such a case, the metal particles 7 in the carbon layer 9 form oxides preferentially over the formation of the surface oxide film of the metal constituting the metal base layer 6 that is the base. On the other hand, a noble metal is not preferable because it promotes oxidation of the metal constituting the metal base layer 6 serving as a base. However, by dispersing and mixing the metal particles 7 that are easily oxidized in the carbon layer 9 in advance, the metal particles 7 in the carbon easily form oxides before the oxygen reaches the metal base layer 6. can do. Thereby, the increase in the whole resistance from the metal base material layer 6 to the surface layer part of the carbon layer 9 can be suppressed. Further, since the metal particles 7 also have an effect of relieving the internal stress of the carbon layer 9, it is possible to improve the adhesion with the metal base layer 6 as a base, and the contact resistance as a separator is remarkably reduced. it can.

  In addition, as another advantage of using the metal particles 7, when the metal particles 7 and the conductive carbon 8 exist in a mixed state in the carbon layer 9, the internal stress of the carbon layer 9 itself is relaxed as a result. High adhesion to a certain metal substrate layer 6 is obtained, and a reduction in battery resistance and long-term stability are obtained.

  Moreover, it is preferable that the average particle diameter of the metal particle 7 is 0.2-20 nm, It is more preferable that it is 0.5-10 nm, It is further more preferable that it is 0.5-5 nm. When the average particle diameter is 0.2 nm or more, sacrificial oxidation of the metal particles 7 is likely to occur, and generation of an oxide film on the surface of the metal base layer 6 can be more effectively suppressed. It can be improved further. On the other hand, when the average particle diameter is 20 nm or less, even if the metal particles 7 generate an oxide, there is a high possibility that an oxide film is formed not only outside but also inside the metal particles 7. 7 can be utilized more efficiently and without waste. In the present specification, “particle diameter” means the maximum distance among the distances between any two points on the particle outline. In addition, as the value of “average particle size”, the average value of the particle size of particles 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). The value calculated as is assumed to be adopted.

  About the content rate of the metal particle 7 in the carbon layer 9, it is preferable that it is 1-50 mass%, and it is more preferable that it is 5-20 mass%. When the content of the metal particles 7 is 1% by mass or more, sacrificial oxidation of the metal particles 7 takes precedence over the oxidation at the interface between the carbon layer 9 and the metal base layer 6, and the contact resistance of the separator is reduced. The increase can be effectively suppressed. On the other hand, when the content of the metal particles 7 is 50% by mass or less, the oxide of the metal particles 7 can be formed in the carbon layer 9 without inhibiting the conductivity of the carbon layer 9 itself.

  Subsequently, the carbon material usable as the conductive carbon 8 is not particularly limited as long as the contact resistance as a separator is not increased. When the intensity ratio of the carbon layer 9 measured by Raman scattering spectroscopy is within a predetermined range, an increase in the contact resistance can be remarkably suppressed. Therefore, the carbon material used as the conductive carbon 8 is preferably selected so that the carbon layer 9 has an intensity ratio within the predetermined range.

Raman spectroscopy is a method for analyzing the structure of a sample by analyzing Raman scattered light, and this analysis method is called Raman scattering spectroscopy. When the carbon material is analyzed by Raman spectroscopy, peaks are usually generated around 1350 cm ⁻¹ and 1584 cm ⁻¹ . Graphite with high crystallinity has a single peak in the vicinity of 1584 cm ⁻¹ , and this peak is usually referred to as G-band. On the other hand, as crystallinity decreases (crystal structure defects increase), a peak near 1350 cm ⁻¹ , which is usually called a D-band, appears (strictly, the peak of diamond is 1333 cm ⁻¹ , and the D-band Are distinct). The intensity ratio R (I _D / I _G ) of the _D -band and G-band indicates the graphite cluster size of the carbon material, the disorder of the graphite structure (crystal structure defect), and the sp ² bond ratio. Yes. That is, it can be used as an index of contact resistance as a separator, and can be used as a film quality parameter for controlling the conductivity of the carbon layer 9.

The R value is calculated by measuring the Raman spectrum of the carbon material using a microscopic Raman spectrometer. Specifically, the relative intensity ratio between the peak intensity (I _D ) of 1300 to 1400 cm ⁻¹ called D-band and the peak intensity (I _G ) of 1500 to 1600 cm ⁻¹ called G-band, that is, the peak It is calculated | required by calculating an area ratio ( _ID / _IG ). And I _D is D- band peak intensity, _{I G} is a G- band peak intensity, also referred to, respectively. That is, by increasing the ratio of the D-band, the ratio of sp ² bonds of carbon atoms increases, and the contact resistance as a separator can be further reduced. The peak area can be determined by the following Raman spectroscopic measurement.

(Raman spectroscopy measurement)
The Raman spectrum was measured using a Holo Lab 5000R (manufactured by Kaiser Optical System Inc.) as a measuring apparatus under the following conditions at room temperature, exposure 30 seconds × total 5 times.

Solid graphite was used as a raw material for the conductive carbon 8. Then, the acceleration voltage (V) was changed to determine the contact resistance as a separator at various R values (I _D / I _G ). The contact resistance measurement method will be described. The voltage value when a constant current is passed between the two opposing copper electrode rods sandwiched between the gas diffusion base material-metal base material-gas diffusion base material, The penetration resistance is calculated. At this time, since there are two contact portions between the base material and the gas diffusion base material, 1/2 of the measured value is set as the contact resistance (the bulk resistance of the gas diffusion base material and the metal base material is included, but the bulk The value of the resistance is very small and can be ignored, so it is ignored here).

The results are shown in FIG. The vertical axis in FIG. 3 indicates the ratio of the relative contact resistance value to the minimum contact resistance value. From FIG. 3, the present inventors show that when the strength ratio (R value) of the carbon layer 9 is within a predetermined range, the ratio of sp ² bonds of carbon atoms in the carbon layer 9 increases. It has been found that the electrical conductivity is improved and the contact resistance can be further reduced. The predetermined range for the R value (I _D / I _G ) of the carbon layer 9 is preferably 1.4 or more, and more preferably 1.4 to 2.0. In the case of 1.4 or more, the carbon layer 9 having high conductivity is obtained. In addition, the critical point of the graph in FIG. 3 is about 1.4. On the other hand, in the case of 2.0 or less, the reduction of the graphite component can be suppressed and the increase of the internal stress of the carbon layer 9 itself can be suppressed, and the adhesiveness with the metal base material layer 6 as the base is further improved. Can be made.

  Examples of the conductive carbon 8 include carbon black, graphite, fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, and carbon fibril. Specific examples of carbon black include ketjen black, acetylene black, channel black, lamp black, oil furnace black, or thermal black. Carbon black may be subjected to a graphitization treatment. From the viewpoint of reducing the contact resistance between the carbon layer 9 and the metal base layer 6 due to the structure and shape of the conductive carbon 8, graphite or carbon nanotubes are preferable. Moreover, the said carbon material may be used individually by 1 type, and may use 2 or more types together.

  Moreover, the average particle diameter when the material of the conductive carbon 8 is particulate is not particularly limited, but is preferably 1 to 100 nm, more preferably 5 to 20 nm from the viewpoint of suppressing the thickness of the carbon layer 9.

  The diameter when the material of the conductive carbon 8 is in the form of a fiber such as a carbon nanotube is not particularly limited, but is preferably 0.4 to 100 nm, more preferably 1 to 20 nm. On the other hand, although the length in the case of the said fibrous form is not specifically limited, 5-200 nm, More preferably, it is 10-100 nm. And the aspect ratio in the case of the said fibrous form is although it does not specifically limit, It is 1-500 nm, More preferably, it is 2-100 nm. When it exists in the above-mentioned range, the thickness of the carbon layer 9 can be suppressed suitably. Moreover, about the content rate of the electroconductive carbon 8 in the carbon layer 9, it is preferable that it is 50-99 mass%, it is more preferable that it is 80-98 mass%, and it is especially 80-95 mass%. preferable. When it exists in an above-described range, the obtained separator can have electroconductivity, corrosion resistance, and adhesiveness with a high value and a good balance.

  Next, the carbon layer 9 will be described. The preferred range of the intensity ratio measured by Raman scattering spectroscopy in the carbon layer 9 is as described above.

  The carbon layer 9 may be present on at least one surface of the metal base layer 6, but is preferably present on both surfaces in order to achieve the desired effect of the present invention higher.

  The film thickness of the carbon layer 9 is preferably 0.005 to 1 μm, more preferably 0.01 to 0.2 μm. When it exists in the said range, while having low initial contact resistance, the increase in contact resistance can also be suppressed and corrosion resistance can improve. More specifically, in the case of 0.005 μm or more, the surface coverage of the carbon layer 9 with respect to the metal substrate layer 6 increases, and the carbon layer 9 can be formed as a uniform and continuous layer. Generation of undulations such as irregularities on the surface of the layer 6 can be suppressed. Moreover, it can prevent that the metal particle 7 contained in the carbon layer 9 is exposed to the outermost surface of the carbon layer 9, and can suppress that an oxide film forms on the surface of the metal base material layer 6. . Therefore, the conductive path in the entire carbon layer 9 is reduced, and as a result, the contact resistance can be further reduced. On the other hand, when the thickness is 1 μm or less, generation of film stress (internal stress) of the carbon layer 9 can be prevented, and adhesion to the metal base layer 6 can be remarkably improved. In addition, the initial resistance in the thickness direction itself can be reduced, and the occurrence of cracks and the like can be prevented without causing internal stress of the carbon layer 9 due to the thin film effect, resulting in contact resistance. Can be reduced.

  As described above, the carbon layer 9 mainly includes the metal particles 7 and the conductive carbon 8, but may include other materials. Examples of the other materials include water-repellent substances such as PTFE.

  Further, an intermediate layer composed of one or more selected from the group consisting of metal, metal nitride, and metal carbide may be provided between the metal base layer 6 and the carbon layer 9. By providing the intermediate layer between the metal substrate layer 6 and the carbon layer 9, the adhesion of the carbon layer 9 can be improved. If the carbon layer 9 is coated directly on the metal base layer 6, good adhesion may not be obtained. Specifically, when the R value exceeds the upper limit of the preferable range described above, the metal base material layer 6 and the carbon layer 9 as the base may not be suitably adhered. In such a case, the metal base layer 6 and the carbon layer 9 can be suitably adhered by inserting the intermediate layer. The material constituting the intermediate layer is not particularly limited as long as it provides the above adhesion. For example, metals with low ion elution such as chromium (Cr), tungsten (W), titanium (Ti), molybdenum (Mo), niobium (Nb), hafnium (Hf), their metal nitrides and their metal carbides, And carbonitride. Preferred are metals with low ion elution such as chromium (Cr) and titanium, their metal nitrides and their metal carbides. In particular, when the metal with little ion elution (and its metal nitride and metal carbide) is used, the corrosion resistance of the separator can be improved. The thickness of the intermediate layer is not particularly limited, but from the viewpoint of reducing the size of the fuel cell stack as much as possible by reducing the thickness of the separator, it is 5 to 1,000 nm. It is preferable that it is 10 to 200 nm. Furthermore, since the intermediate layer exists between the metal base layer 6 and the carbon layer 9, the material constituting the intermediate layer is also the material constituting the intermediate layer (like the metal particles 7 in the carbon layer 9). The oxidation of (metal) is preferably performed in preference to the oxidation on the surface of the metal base layer 6. Therefore, the material (metal) constituting the intermediate layer is composed of at least one of the same metal element as the element constituting the metal base layer 6 and the base metal element, and the same metal element as that of the metal particle 7; And at least one of noble metal elements. For example, a preferable combination of an element constituting the metal particle 7, an element constituting the intermediate layer, and an element constituting the metal substrate layer 6 will be described. It is preferable that the metal particles 7 are aluminum and / or titanium, the intermediate layer is made of chromium (Cr), titanium (Ti) aluminum (Al), and the metal base layer 6 is made of stainless steel. Alternatively, the metal particles 7 are aluminum and / or magnesium, the intermediate layer is made of chromium (Cr), titanium (Ti), aluminum (Al), magnesium (Mg), and the metal base layer 6 is aluminum or an aluminum alloy. Preferably it consists of.

  The intermediate layer may be present on at least one surface of the metal base layer 6, but is preferably present on both surfaces in order to achieve the desired effect of the present invention at a higher level. In addition, when an intermediate | middle layer exists on both surfaces of the metal base material layer 6, the carbon layer 9 will be further provided on the surface of each intermediate | middle layer.

The carbon layer 9 can be formed by forming a film on the metal substrate layer 6 using the metal particles 7 and the conductive carbon 8 as targets. At that time, it is preferable to use a physical vapor deposition (PVD) method such as a sputtering method or an arc ion plating method, or an ion beam vapor deposition 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, and a dual magnetron sputtering method. By using such a method for forming the carbon layer 9, the carbon layer 9 having a low hydrogen content can be formed. Therefore, the ratio of bonds (sp ² ) between carbon atoms can be increased, and excellent conductivity can be obtained.

Second Embodiment
According to one embodiment of the present invention, a method for manufacturing a fuel cell separator is obtained. Since various conditions such as the material of each component of the fuel cell separator are as described in the first embodiment, description thereof is omitted here. Although the said manufacturing method is not specifically limited, Several examples of a processing procedure are described below.

  First, as a first example, the surface of the metal base layer 6 is degreased and washed using an appropriate solvent (for example, ethanol, ether, acetone, isopropyl alcohol, trichloroethylene, and a caustic alkali agent). Examples of the treatment include ultrasonic cleaning. The ultrasonic cleaning conditions may be 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 sides) of the metal base layer 6 is removed. As a method for removing the oxide film, there may be a cleaning treatment with an acid, a dissolution treatment applying a potential, or an ion bombardment treatment.

  Next, the carbon layer 9 is formed using the sputtering method described in the first embodiment. For example, the conductive carbon 8 such as solid graphite and the metal particles 7 such as Al are used as targets, and a negative bias voltage is preferably applied to the substrate at 50 to 300 V while the both sides of the metal substrate layer 6 are applied. A carbon layer 9 having a desired film thickness in which Al particles are dispersed is formed. In this way, the fuel cell separator of the present invention is obtained.

  The separator for a fuel cell according to the present invention is characterized by the relationship between the carbon layer 9 and the metal base layer 6 as constituent elements. After removing the oxide film and impurities from the surface of the metal base layer 6 in advance as described above, the conductive carbon 8 and the metal particles 7 are deposited on the metal base layer 6 at the atomic level in a vacuum. Then, the carbon layer 9 is formed. As a result, the interface between the carbon layer 9 and the metal substrate layer 6 directly attached and the vicinity thereof exerts an adhesive force by intermolecular force or a slight carbon atom intrusion, and further provides adhesion over a long period of time. Can be held.

  When the carbon layer 9 is directly formed on the metal base layer 6, if the carbon layer 9 having extremely high hardness as compared with the metal base layer 6 serving as a base is coated, internal stress is generated in the carbon layer 9. Further, peeling may easily occur between the carbon layer 9 and the metal base layer 6. Therefore, it is preferable to coat the carbon layer 9 having a hardness relatively close to the metal element constituting the metal base layer 6.

  Next, as a second example, the surface of the metal base layer 6 is degreased and washed, and the oxide film is removed as in the first example. Subsequently, metals with low ion elution such as chromium (Cr), tungsten (W), titanium (Ti), molybdenum (Mo), niobium (Nb), hafnium (Hf), their metal nitrides and their metal carbides Target. A film of an intermediate layer is formed on the surface of the metal base layer 6 using the above target by magnetron sputtering, UBMS, or the like. Further, a carbon layer 9 is formed on the intermediate layer as in the first example. In this way, a fuel cell separator having the intermediate layer of the present invention is obtained.

<Third Embodiment>
According to one embodiment of the present invention, a fuel cell is obtained using the fuel cell separator of the first embodiment or the fuel cell separator obtained by the manufacturing method of the second embodiment. The fuel cell separator according to the present invention includes various fuel cells such as a solid polymer type (PEFC), a phosphoric acid type (PAFC), a molten carbonate type (MCFC), a solid electrolyte type (SOFC), and an alkaline type (AFC). Can be used. Preferably, it is a polymer electrolyte (PEFC) fuel cell that can be suitably used for a vehicle described later.

  Hereinafter, the configuration of the fuel cell other than the fuel cell separator will be described in detail. However, the present invention has a feature in the separator, and members other than the separator constituting the fuel cell are conventionally known ones. Can do.

[Electrolyte layer]
As the electrolyte layer, a conventionally known electrolyte layer can be used, and a polymer electrolyte layer is preferable. The polymer electrolyte layer is roughly classified into a fluorine-based polymer electrolyte layer and a hydrocarbon-based polymer electrolyte layer depending on the type of ion exchange resin that is a constituent material. Examples of ion exchange resins constituting the fluorine-based polymer electrolyte layer include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), 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- Examples include perfluorocarbon sulfonic acid polymers. From the viewpoint of power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte layers are preferably used, and particularly preferably fluorine-based polymer electrolyte layers composed of perfluorocarbon sulfonic acid polymers are used. It is done.

  Specific examples of the hydrocarbon 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). These hydrocarbon polymer electrolyte layers are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the selectivity of the material is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

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

[Catalyst layer]
The catalyst layer includes a catalyst component, a conductive catalyst carrier that supports the catalyst component, and an electrolyte.

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

  Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. The composition of the alloy is preferably 30 to 90 atomic% for platinum and 10 to 70 atomic% for the metal to be alloyed, depending on the type of metal to be alloyed. The composition of the alloy when the alloy is used as the cathode catalyst varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art, but platinum is 30 to 90 atomic%, and other metals to be alloyed are 10 to 70. It is preferable to use atomic%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the anode catalyst layer and the catalyst component used for the cathode catalyst layer can be appropriately selected from the above. In the following description, unless otherwise specified, the descriptions of the catalyst components for the anode catalyst layer and the cathode catalyst layer have the same definition for both, and are collectively referred to as “catalyst components”. However, the catalyst components of the anode catalyst layer and the cathode catalyst layer do not have to be the same, and are appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be used, but 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 diameter 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 ease of loading can be appropriately controlled. The “average particle diameter of catalyst particles” in the present invention is the average of the crystallite diameter determined from the half-value 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 an electron conduction path involved in the exchange of electrons with the catalyst component.

  Any catalyst carrier may be used as long as it has a specific surface area for supporting the catalyst component in a desired dispersion state and sufficient electron conductivity, and the main component is preferably carbon. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. Note that “substantially consisting of carbon atoms” means that contamination of about 2 to 3 mass% or less of impurities can be allowed.

The BET specific surface area of the catalyst carrier may be a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. When the specific surface area of the catalyst carrier is in 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.

  The size of the catalyst carrier is not particularly limited, but from the viewpoints of easy loading, catalyst utilization, and (electrode) catalyst layer thickness control within an appropriate range, the average particle size is 5 to 200 nm, preferably It may be about 10 to 100 nm.

  In the electrode catalyst in which the catalyst component is supported on the catalyst carrier, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 70% by mass with respect to 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 support and the catalyst performance can be appropriately controlled. The supported amount of the catalyst component can be measured by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst layer includes an ion conductive polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. For example, an ion exchange resin constituting the polymer electrolyte layer can be added to the catalyst layer as the polymer electrolyte.

[Gas diffusion layer]
Each electrode in the anode and the cathode may have a gas diffusion layer in addition to the above-mentioned (electrode) catalyst layer. The gas diffusion layer is disposed on a surface opposite to the surface of the (electrode) catalyst layer that is in contact with the electrolyte layer.

  In the electrode having the (electrode) catalyst layer and the gas diffusion layer, the (electrode) catalyst layer may be formed on the gas diffusion layer, or the (electrode) catalyst layer is formed in a part of the gas diffusion layer. Also good. In the case of the latter, the thing which the electrode catalyst and the electrolyte material were impregnated to the site | part which the gas diffusion base material mentioned later mentions is mentioned.

  The gas diffusion layer is not particularly limited, and known ones can be used in the same manner, for example, a sheet-like gas diffusion group having conductivity and porosity such as carbon woven fabric, paper-like paper body, felt, and non-woven fabric. The thing which consists of materials is mentioned.

  The thickness of the gas diffusion base material may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm.

  The gas diffusion base material may contain a water repellent for the purpose of further improving water repellency and preventing a flooding phenomenon. Although it does not specifically limit as said water repellent, Fluorine-type, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), etc. Examples thereof include polymer materials, polypropylene, and polyethylene.

  In order to further improve water repellency, the gas diffusion layer may have a carbon particle layer made of an aggregate of carbon particles containing a water repellent on the gas diffusion base material.

  The carbon particles are not particularly limited, and may be conventional ones such as carbon black, graphite, and expanded graphite. Of these, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are preferred because of their excellent electron conductivity and large specific surface area.

  Examples of the water repellent used for the carbon particle layer include the same water repellents as those described above used for the gas diffusion base material. Of these, fluorine-based polymer materials are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction.

  The mixing ratio between the carbon particles and the water repellent in the carbon particle layer may be insufficient to obtain water repellency as expected when there are too many carbon particles. If there are too many water repellents, sufficient electron conductivity may be obtained. There is a risk that it will not be obtained. Considering these, the mixing ratio of the carbon particles and the water repellent in the carbon layer is preferably about 90:10 to 40:60 in terms of mass ratio.

  The thickness of the carbon particle layer may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer, but is preferably 10 to 1000 μm, more preferably 50 to 500 μm.

  The method for producing the fuel cell of the present invention is not particularly limited, and can be produced by appropriately referring to conventionally known knowledge in the field of fuel cells.

  The fuel type of the fuel cell is not particularly limited, and is hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol. Can be used. Of these, hydrogen and methanol are preferred because they can increase the output.

  Furthermore, a stack in which a plurality of membrane electrode assemblies are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

<Fourth embodiment>
According to one embodiment of the present invention, the fuel cell separator of the first embodiment, the fuel cell separator obtained by the manufacturing method of the second embodiment, or the fuel cell of the third embodiment is used. A vehicle is obtained. Although it does not restrict | limit especially as a use of the fuel cell of this invention, Since it is excellent in electric power generation performance, it is preferable to use as a drive power supply in vehicles, such as a motor vehicle.

[Example 1]
A separator plate (metal substrate layer) made of stainless steel (SUS316L) and having a film thickness of 100 μm was subjected to ultrasonic cleaning in ethanol solution for 3 minutes as a pretreatment. Then, the metal base material layer was further installed in the vacuum chamber, the ion bombardment process by Ar gas was performed, and the surface oxide film was removed. The pretreatment and the ion bombardment treatment were both performed on both surfaces of the metal base layer.

Next, by using unbalanced magnetron sputtering (UBMS), solid graphite and Al are used as targets, and a negative bias voltage of 150 V is applied to the metal substrate layer. While applying the voltage, a carbon layer having a film thickness of 0.2 μm formed by dispersing Al particles (average particle diameter: 10 nm) was formed on both surfaces of the metal substrate layer. In addition, the R value (I _D / I _G ) of the carbon layer was 1.5. The content rate of the metal particles in the carbon layer was 10% by mass, and the content rate of conductive carbon was 90% by mass. In all examples and comparative examples, the same solid graphite was used.

[Example 2]
Pretreatment and ion bombardment treatment were performed in the same manner as in Example 1 using a separator plate (metal substrate layer) having a thickness of 100 μm made of stainless steel (SUS316L).

Next, Cr was used as a target by the UBMS method, and a 0.2 μm-thick Cr film (intermediate layer) was formed on both surfaces of the metal substrate layer. Further, a carbon layer having a thickness of 0.2 μm was formed on the intermediate layer in the same manner as in Example 1. The carbon layer had an R value (I _D / I _G ) of 1.5. The content rate of the metal particles in the carbon layer was 10% by mass, and the content rate of conductive carbon was 90% by mass.

[Example 3]
Pretreatment and ion bombardment treatment were performed in the same manner as in Example 1 using a separator plate (metal substrate layer) having a film thickness of 200 μm made of an Al alloy (A1050).

Next, by UBMS method, using solid graphite and Mg as targets, while applying a negative bias voltage of 150 V to the metal substrate layer, Mg particles (average particle diameter of 15 nm) are formed on both surfaces of the metal substrate layer. A carbon layer having a thickness of 0.2 μm formed by dispersion was formed. The carbon layer had an R value (I _D / I _G ) of 1.4. The content rate of the metal particles in the carbon layer was 10% by mass, and the content rate of conductive carbon was 90% by mass.

[Example 4]
Pretreatment and ion bombardment treatment were performed in the same manner as in Example 1 using a separator plate (metal substrate layer) having a film thickness of 200 μm made of an Al alloy (A1050).

Next, a carbon layer having a thickness of 0.2 μm was formed in the same manner as in Example 1. The carbon layer had an R value (I _D / I _G ) of 1.5. The content rate of the metal particles in the carbon layer was 10% by mass, and the content rate of conductive carbon was 90% by mass.

[Example 5]
Pretreatment and ion bombardment treatment were performed in the same manner as in Example 1 using a separator plate (metal substrate layer) having a film thickness of 200 μm made of an Al alloy (A1050).

Next, a Cr film (intermediate layer) having a thickness of 0.2 μm and a carbon layer having a thickness of 0.2 μm were formed in the same manner as in Example 2. The carbon layer had an R value (I _D / I _G ) of 1.5. The content rate of the metal particles in the carbon layer was 10% by mass, and the content rate of conductive carbon was 90% by mass.

[Comparative Example 1]
Pretreatment and ion bombardment treatment were performed in the same manner as in Example 1 using a separator plate (metal substrate layer) having a thickness of 100 μm made of stainless steel (SUS316L).

Next, a carbon layer having a thickness of 0.2 μm was formed in the same manner as in Example 1 except that only solid graphite was used as a target. The carbon layer had an R value (I _D / I _G ) of 1.5.

[Comparative Example 2]
Pretreatment and ion bombardment treatment were performed in the same manner as in Example 1 using a separator plate (metal substrate layer) having a film thickness of 200 μm made of an Al alloy (A1050).

  Next, a carbon layer having a thickness of 0.2 μm was formed in the same manner as in Example 1 except that only solid graphite was used as a target.

<Contact resistance measurement>
As shown in FIG. 4, gas diffusion layers are provided on both sides of the separators formed in the above examples and comparative examples, and both sides are sandwiched by electrodes, and contact is made based on the energization amount and voltage value when a load of 1 MPa is applied. The resistance value was calculated. The results are shown in FIGS.

<Corrosion resistance test>
The separator formed into a film in the said Example was cut out to 30 mm x 30 mm size, and it immersed in 80 degreeC acidic water always maintained at pH 4 or less for 100 hours, and measured the contact resistance value before and behind an immersion test. The results are summarized in FIGS. 5 and 7 show the ratio of the contact resistance values of the separators obtained in Examples 1 and 2 when the contact resistance value of the separator obtained in Comparative Example 1 is 1.0. 6 and 8 show the ratio of the contact resistance values of the separators obtained in Examples 3 to 5 when the contact resistance value of the separator obtained in Comparative Example 2 is 1.0.

  From the above results, it has been clarified that the separator containing the predetermined metal particles in the carbon layer according to the present invention is extremely excellent in at least corrosion resistance and conductivity as compared with the conventional separator. This result will be described in detail.

  In the case of a conventional separator (for example, Comparative Examples 1 and 2), a conductive carbon film (carbon layer) is directly formed on a metal substrate (metal base layer). However, good adhesion between the metal substrate and the conductive carbon film cannot be obtained, the initial contact resistance value is high, and corrosion at the interface between the metal substrate and the conductive carbon film tends to proceed.

  In addition, an intermediate layer made of a conductive material such as Cr may be provided on the conventional separator in order to improve the adhesion between the metal substrate and the conductive carbon film. However, although the adhesion is improved, corrosion due to oxidation on the surface of the metal substrate proceeds due to cracks generated due to the load caused by stacking and the penetration of acidic water from the pinhole, and the contact resistance increases.

  After all, in the case of conventional separators, when cracks or scratches occur during stacking loads or press molding, the corrosion of metal substrate surfaces due to the penetration of acidic water in the cell causes deterioration of contact resistance as a separator ( Increase) was difficult to avoid.

  On the other hand, the fuel cell separator of the present invention has a configuration in which predetermined metal particles are included in the carbon layer. Due to the above-described configuration, even if cracks or scratches occur during stacking load or press molding, the `` acidic component '' that has penetrated into the cell is in the carbon layer before reaching the metal substrate layer. It reacts with the predetermined metal particles to form an oxide. Thus, the acidic component is so-called “trapped”. Therefore, according to the present invention, it is possible to effectively increase the resistance from the metal substrate layer to the surface layer of the separator without causing the problem that the acidic component reaches the surface of the metal substrate layer to form an oxide film. Can be suppressed.

It is the schematic which shows the structure of the fuel cell which is one Embodiment of this invention. It is sectional drawing which shows schematic structure of the separator part of FIG. Is a graph showing the relationship between the contact resistance and the I _{D /} I _G of the carbon layer. It is a figure which shows schematic structure of the measuring method of contact resistance. It is a graph which shows the relationship between the separator obtained by each Example and the comparative example, and a contact resistance value. It is a graph which shows the relationship between the separator obtained by each Example and the comparative example, and a contact resistance value. It is a graph which shows the relationship between the separator obtained by each Example and the comparative example, and a contact resistance value. It is a graph which shows the relationship between the separator obtained by each Example and the comparative example, and a contact resistance value.

Explanation of symbols

1 fuel cell unit,
2 electrolyte layer,
3 catalyst layer,
4 Gas diffusion layer,
5 separator,
6 metal substrate layer,
7 metal particles,
8 conductive carbon,
9 Carbon layer.

Claims (11)

A metal substrate layer;
A fuel cell separator comprising a carbon layer containing metal particles and conductive carbon.   2. The fuel cell separator according to claim 1, wherein the metal particles are composed of at least one of the same metal element as the element constituting the metal base layer and a base metal element.   The fuel cell separator according to claim 1 or 2, wherein the metal particles are aluminum and / or titanium, and the metal base layer is made of stainless steel.   The fuel cell separator according to claim 1 or 2, wherein the metal particles are aluminum and / or magnesium, and the metal base layer is made of aluminum or an aluminum alloy. In the carbon layer is the intensity ratio _{R =} I D / _{I G} of the Raman scattering D- band peak intensity was measured spectrophotometrically _{I D} and G- band peak intensity _{I G} is 1.4 or more, claim 1 5. The fuel cell separator according to claim 4.   6. The fuel cell separator according to claim 1, wherein the carbon layer has a thickness of 0.005 to 1 μm.   The intermediate layer comprised by 1 or more types selected from the group which consists of a metal, a metal nitride, and a metal carbide between the said metal base material layer and the said carbon layer is provided. A separator for a fuel cell as described in 1.   The carbon layer is formed on the metal substrate layer by sputtering, arc ion plating, or filtered cathodic vacuum arc (FCVA) using the metal particles and the conductive carbon as targets. The fuel cell separator according to claim 1, wherein the separator is a layer.   The fuel cell separator according to any one of claims 1 to 8, wherein the metal particles have an average particle diameter of 0.2 to 20 nm.   A fuel cell comprising the fuel cell separator according to claim 1.   A vehicle comprising the fuel cell according to claim 10.

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