WO2013042429A1 - Solid polymer fuel cell - Google Patents

Abstract

Provided is a solid polymer fuel cell which is capable of smoothly discharging produced water and capable of suppressing flooding even if a material other than a carbon material, for example, a metal material is used for a gas diffusion layer (GDL). Amorphous carbon films (C_G, C_B) are respectively formed on a gas diffusion layer (13c) and a separator (15c) that constitute a solid polymer fuel cell (1) so that the value (R_G) of the ratio (I_D/I_G) of the D-band peak intensity (I_D) to the G-band peak intensity (I_G) of the amorphous carbon film (C_G) as determined by Raman scattering spectroscopy, said amorphous carbon film (C_G) being formed on the gas diffusion layer (13c) side, is smaller than the value (R_B) of the similarly obtained ratio (I_D/I_G) of the amorphous carbon film (C_B), which is formed on the separator (15c) side.

Description

Polymer electrolyte fuel cell

The present invention relates to a polymer electrolyte fuel cell, and more particularly to a polymer electrolyte fuel cell having good drainage (flooding resistance) on the cathode side and excellent output characteristics particularly in a high current density region. It is.

Polymer electrolyte fuel cells using proton conducting polymer electrolyte membranes operate at lower temperatures compared to other types of fuel cells such as solid oxide fuel cells and molten carbonate fuel cells. It is also expected as a power source for moving bodies such as automobiles, and its practical use has also started.

Here, the power generation mechanism of the PEFC will be briefly described. During operation of the PEFC, a fuel gas such as hydrogen gas is supplied to the anode side of the single cell, while air such as oxygen or oxygen is supplied to the cathode side. Oxidant gas is supplied.
Thereby, in each of the anode and the cathode, an electrochemical reaction represented by the following reaction formula proceeds to generate electricity.
Anode side: H ₂ → 2H ⁺ + 2e ⁻
Cathode side: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O

Such a polymer electrolyte fuel cell (hereinafter sometimes abbreviated as “PEFC”) generally has a structure in which a plurality of single cells exhibiting a power generation function are stacked.
This single cell includes a polymer electrolyte membrane having proton conductivity (for example, a Nafion (registered trademark) membrane), an anode and a pair of electrode layers sandwiching the membrane (also referred to as an “electrode catalyst layer”), these A membrane electrode assembly including a pair of gas diffusion layers including an anode and a cathode sandwiching the electrolyte membrane and the electrode layer is provided. In general, carbon paper, carbon cloth, or the like is used as the gas diffusion layer (hereinafter sometimes abbreviated as “GDL”).

Membrane electrode assemblies (hereinafter, may be abbreviated as “MEA”) constituting individual single cells are electrically connected to MEAs of adjacent single cells via separators. The fuel cell stack is configured by stacking and connecting. Such a fuel cell stack is applied to various uses and functions as a power generation means.
In the fuel cell stack, the separator exhibits a function of electrically connecting adjacent single cells as described above. Further, a gas flow path is usually provided on the surface of the separator facing the MEA, and this gas flow path functions as a gas supply means for supplying fuel gas and oxidant gas to the anode and the cathode, respectively. .

As a material for such a fuel cell separator, metal, carbon, conductive resin, and the like are known because conductivity is required.
Of these, separators made of carbon or conductive resin require a relatively large thickness in order to ensure the strength after the formation of the gas flow path, which increases the overall size of the fuel cell stack. Therefore, it is not preferable as an in-vehicle power supply that is particularly required to be downsized.

On the other hand, since the metal separator has a relatively high strength, the thickness can be reduced and the conductivity is excellent, so that there is an advantage that the contact resistance with the MEA can be reduced.
On the other hand, in the case of a metal material, there may be a problem that the conductivity is reduced due to corrosion caused by, for example, generated water or a potential difference generated during operation, and the output of the stack is reduced accordingly. Accordingly, the metal separator is required to improve the corrosion resistance while ensuring its excellent conductivity.

On the other hand, in the polymer electrolyte fuel cell, as a result of the electrochemical reaction according to the above-described reaction formula, water is generated at the cathode. This water stays in the catalyst layer, GDL, separator, etc. Oxygen can hardly diffuse into the bed, and power generation cannot be continued. Such a phenomenon is called flooding.

As a countermeasure against such flooding, for example, in Patent Document 1, an amorphous carbon film is provided on the surface so that generated water does not stay as water droplets in the gas flow path of the separator and spreads. It has been proposed that the expanded metal is used as a gas flow path structure and the surface is hydrophilized so that the contact angle with attached water is 40 ° or less.

JP 2010-186578 A

However, the invention described in the above document is a technique related to the improvement of drainage of the separator, and in order to prevent battery flooding, the drainage path of generated water until reaching the separator must be taken into consideration. Don't be.
That is, the water generated by the battery reaction is generated at the portion of the air electrode surface that is in contact with the electrolyte membrane, and is discharged from the GDL through the separator to the outside, so that the generated water is smoothly discharged from the GDL to the separator. The separator is hydrophilic, whereas GDL needs to have water repellency.

As described above, carbon paper, carbon cloth, and the like are widely used for GDL, and these carbon materials exhibit water repellency. Therefore, the separator for fuel cells described in the above documents is carbon paper or carbon cloth. It can be said that this is effective when combined with a typical MEA using GDL as a GDL.
However, when other materials, such as metal materials, are applied to the GDL, surface treatment with amorphous carbon is required to reduce electrical resistance, resulting in hydrophilicity equivalent to that of the separator. Can not improve drainage. On the other hand, when the surface treatment is applied to impart water repellency to the GDL, the contact resistance with the separator increases, and the battery performance deteriorates.

The present invention has been made to solve such problems in conventional polymer electrolyte fuel cells, and the object of the present invention is to use materials other than carbon materials, for example, metal materials as GDL. It is another object of the present invention to provide a polymer electrolyte fuel cell that can smoothly discharge generated water and suppress flooding.

As a result of intensive studies to achieve the above object, the present inventors formed an amorphous carbon film on each of the GDL and the separator, and Raman scattering spectroscopic analysis of the amorphous carbon film formed on the GDL side. The intensity ratio (I _D / I _G ) between the D band peak intensity I _D and the G band peak intensity I _G measured by the above is made smaller than the intensity ratio of the amorphous carbon film formed on the separator side. Thus, the inventors have found that the above object can be achieved, and have completed the present invention.

The present invention is based on the above knowledge, and the solid polymer fuel cell of the present invention includes a polymer electrolyte membrane, an electrode layer sandwiching the polymer electrolyte membrane, and a gas diffusion sandwiching the polymer electrolyte membrane and the electrode layer. A membrane electrode assembly having a layer and a separator for forming a gas flow path between the membrane electrode assembly, and forming an amorphous carbon film on at least the gas flow path side surface of the gas diffusion layer and the separator, respectively The amorphous carbon film formed on the separator is more hydrophilic than the amorphous carbon film formed on the gas diffusion layer.

According to the present invention, the gas flow path surface of the separator can always be made hydrophilic with respect to the gas diffusion layer, the drainage of the generated water can be improved, and flooding in the polymer electrolyte fuel cell can be suppressed. it can.

It is sectional drawing which shows the structure of the polymer electrolyte fuel cell of this invention. It is a graph which shows the influence of the ( _ID / _IG ) value which acts on the static contact angle of the water droplet with respect to an amorphous carbon film. It is a graph which shows the electric power generation characteristic by the single cell obtained in the Example of this invention compared with the thing of a comparative example.

Hereinafter, the structure and production method of the polymer electrolyte fuel cell of the present invention will be described more specifically and in detail.

FIG. 1 is a cross-sectional view showing the structure of a solid polymer fuel cell according to the present invention. A polymer electrolyte fuel cell (PEFC) 1 shown in FIG. 1 has a polymer electrolyte membrane 11 and 1 sandwiching it. It has a pair of electrode layers (anode electrode layer 12a, cathode electrode layer 12c). The polymer electrolyte membrane 11 and the electrode layers 12a and 12c are further sandwiched by a pair of gas diffusion layers (anode GDL 13a and cathode GDL 13c), thereby forming a membrane electrode assembly (MEA) 10. In this example, as the GDLs 13a and 13c, those provided with microporous layers (MPLs 14a and 14c) on the electrode layer side are used respectively. However, the present invention is such a microporous layer (MPL). It is not limited only to the thing provided with.

Further, separators (anode separator 15a and cathode separator 15c) are disposed on the GDLs 13a and 13c side of the MEA 10, and gas flow paths 16a and 16c are formed between the GDLs 13a and 13c. In FIG. 1, only the cathode-side separator 15c is shown.
A fuel gas such as hydrogen is supplied to the anode-side gas flow path 16a, and an oxidant gas such as air is supplied to the cathode-side gas flow path 16c.

Further, in the PEFC of the present invention, the cathode side of the GDL13c and surfaces of the gas flow path 16c side of the separator 15c, the amorphous carbon layer _{C G} and _{C B} are respectively formed.

And, for the GDL13c and amorphous carbon layer _{C G} and _{C B} which are formed in the separator 15c, the intensity ratio of the D-band peak intensity _{I D} and G band peak intensity _{I G (I} D / _{I G)} is identified The film is formed so as to maintain this relationship.
That is, the the amorphous carbon layer C _G and C _B, carried out Raman scattering spectroscopy, as described below, to determine their D-band peak intensity I _D and G band peak intensity I _G. When the calculated these intensity ratio _(I D / I _G), towards the peak intensity ratio _{R G} in the amorphous carbon film _{C G} formed in GDL13c is, amorphous carbon formed on the separator 15c so that the value smaller than the peak intensity ratio R _B in the membrane C _B.

The amorphous carbon film is formed by a known method such as a PVD method, a CVD method, or a sputtering method. When such a carbon material is analyzed by Raman spectroscopy, it is usually around 1350 cm ⁻¹ and 1584 cm ⁻¹ . A peak occurs. Highly crystalline graphite has a single peak near 1584 cm ⁻¹ , and this peak is usually referred to as the “G band”.
On the other hand, a peak near 1350 cm ⁻¹ appears as the crystallinity decreases (crystal structure defects increase). This peak is usually referred to as the “D band” (note that the peak of diamond is strictly 1333 cm ⁻¹ and is distinct from the D band). D-band peak intensity _{(I D)} and the intensity ratio of the G-band peak intensity _{(I G) R (= I} D / I G) is disturbed degree (crystalline structural defects of) the graphite cluster size and graphite structure of the carbon material , And is used as an indicator such as sp2 bond ratio.

An increase in the D band peak intensity, that is, an increase in the intensity ratio R means an increase in crystal structure defects in the graphite structure. In other words, it means that the sp3 carbon increases in the highly crystalline graphite composed of almost only the sp2 carbon.

The R value (I _D / I _G ) is calculated by measuring the Raman spectrum of the carbon material using a microscopic Raman spectrometer. Specifically, the peak intensity of 1300 ~ 1400 cm ^-1 called the D band _{(I D),} the relative intensity ratio of the peak intensity of 1500 ~ 1600 cm ^-1 called the G band _{(I G)} (peak area ratio ( I _D / I _G )).

FIG. 2 shows the relationship between the R value (I _D / I _G ) in an amorphous carbon film and the static contact angle of water droplets on the carbon film, in other words, hydrophilicity. As the R value (I _D / I _G ) in the carbon film increases, the contact angle decreases, in other words, the hydrophilicity of the carbon film improves (increases).
Thus, the R value in the amorphous carbon film _{C G} formed GDL13c, i.e. R value in the amorphous carbon film _{C B} formed a _{R G} separator, if a value smaller than _{R B,} to GDL13c In contrast, the separator 15c is richer in hydrophilicity (higher hydrophilicity), the drainage performance of the entire cathode is improved, and flooding can be suppressed.

In order to obtain the result shown in FIG. 2, when an amorphous carbon film is formed on a metal substrate (SUS316L) by sputtering or the like, the bias voltage applied to the metal substrate is adjusted to adjust R. The value was changed. That is, the R value can be increased as the value of the negative bias voltage is increased.

The solid polymer fuel cell of the present invention has the above-described structure and characteristics, and the constituent elements of the cell will be described in more detail together with preferred forms thereof.

[Polymer electrolyte membrane]
The polymer electrolyte membrane has a function of selectively transmitting protons generated in the anode electrode layer during PEFC operation to the cathode electrode layer in the film thickness direction. The polymer electrolyte membrane also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

Polymer electrolyte membranes are roughly classified into fluorine-based polymer electrolyte membranes and hydrocarbon-based polymer electrolyte membranes depending on the type of ion exchange resin that is a constituent material.

Examples of ion exchange resins constituting the fluorine-based polymer electrolyte membrane 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 improving power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. A membrane is used.

Examples of hydrocarbon polymer electrolytes 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 membranes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the material selectivity is high. In addition, the ion exchange resin mentioned above can be used individually by 1 type, or can also use 2 or more types together. Moreover, it is not restricted only to the material mentioned above, You may use materials other than this.

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

(Electrode layer)
The electrode layer (anode electrode layer, cathode electrode layer) includes a catalyst component, a conductive catalyst carrier supporting the catalyst component, and an electrolyte, and is a layer in which a battery reaction actually proceeds. In the anode electrode layer, hydrogen oxidation The reaction proceeds, and the oxygen reduction reaction proceeds in the cathode electrode layer.

The catalyst component used for the anode electrode 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.
The catalyst component used for the cathode electrode layer is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a conventionally known catalyst can be applied.

Specific examples of these catalyst components include platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh), palladium (Pd), osmium (Os), tungsten (W), lead (Pb), iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni), manganese (Mn), vanadium (V), molybdenum (Mo), gallium (Ga), aluminum (Al) and other metals, An alloy etc. can be mentioned.

Among these, those containing at least platinum can be suitably used in order to improve catalyst activity, poisoning resistance to carbon monoxide, etc., heat resistance, and the like. The composition of such an alloy depends on the type of metal to be alloyed, but the platinum content is preferably 30 to 90 atomic%.
In general, an alloy is a generic term for an element obtained by adding one or more metal elements or non-metal elements to a metal element and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the constituent elements as separate crystals, a solid solution in which the constituent elements are completely dissolved, and an intermetallic compound or a compound of a metal and a nonmetal. In the present invention, any of them may be used.

The catalyst components used for the anode electrode layer and the cathode electrode layer are appropriately selected from the above, but the catalyst components of the anode electrode layer and the cathode electrode layer do not have to be the same, It can be selected appropriately.

The shape and size of the catalyst particles are not particularly limited, and the same shape and size as those of conventionally known catalysts are adopted, but the shape of the catalyst component is preferably granular.
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, it is possible to appropriately control the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading. The “average particle size” as used herein is measured as an average value of a crystallite size obtained from a half-value width of a diffraction peak of a catalyst component in X-ray diffraction or a particle size of a catalyst component examined from a transmission electron microscope image. can do.

The catalyst carrier is a carrier for supporting the catalyst component, and functions as an electron conduction path involved in the transfer of electrons between the catalyst component and other members.

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. If necessary, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. Further, “substantially consisting of carbon atoms” means that an impurity of about 2 to 3% by mass or less is allowed to be mixed.

The specific surface area of the catalyst support, the catalyst component may be a sufficient specific surface area to be highly dispersed supported but is preferably in the range of 20 ~ 1600m ² / g in BET specific surface area, 80 ~ 1200 m ² / More preferably, it is g.
When the specific surface area of the catalyst support is within such a range, the balance between the dispersibility of the catalyst component on the catalyst support and the effective utilization rate of the catalyst component becomes appropriate.

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

In the electrode catalyst in which the catalyst component is supported on the 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. By setting the amount of the catalyst component supported within the above 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 supported on the electrode catalyst can be measured by inductively coupled plasma emission spectroscopy (ICP).

The electrode layer contains an ion conductive polymer electrolyte in addition to the electrode catalyst. About this polymer electrolyte, it does not specifically limit and conventionally well-known knowledge can be referred suitably. For example, the ion exchange resin which comprises the polymer electrolyte membrane mentioned above can be added to a catalyst layer as a polymer electrolyte.

[Gas diffusion layer (GDL)]
The gas diffusion layers (anode GDL, cathode GDL) are supplied via a gas flow path (fuel gas flow path, oxidant gas flow path) formed between the separator (anode separator, cathode separator) ( In addition to promoting the diffusion of fuel gas, oxidant gas) to the electrode layers (anode electrode layer, cathode electrode layer), it functions as an electron conduction path.

In the polymer electrolyte fuel cell of the present invention, from the viewpoint of suppressing flooding, an amorphous carbon film is formed on at least the gas channel side surface of GDL as described above.
Characteristics of the amorphous carbon film, the ratio of the D-band peak intensity I _D and G band peak intensity I _G measured by Raman scattering spectroscopy (I D _{/ I G),} i.e. a separator which will be described later R _G value it is also the same as described above that is smaller than the amorphous carbon film peak intensity ratio _{(I D / I G) R} B value in the.

At this time, the difference in peak intensity ratio between the GDL and the amorphous carbon film formed on the separator (that is, R _B -R _G ) is desirably large to some extent, and the value of R _B -R _G is 0.5. The above is preferable.

The _RG value is preferably 1.3 or more from the viewpoint of reducing contact resistance with the amorphous carbon film formed on the separator. If the _RG value is less than 1.3, the sp3 property of the carbon film becomes high and the conductivity tends to deteriorate.
Furthermore, when the peak intensity ratio (I _D / I _G ) between the D band and the G band by the Raman scattering spectroscopic analysis of an amorphous carbon film having a static contact angle of a water droplet of 90 ° is R ₉₀ , it is formed in the GDL. in order to ensure the water repellency of the amorphous carbon film, it is desirable the R _G value is smaller than R _90. In addition, it can be read that the R ₉₀ value of the amorphous carbon film in which the contact angle of water is 90 ° is about 1.5 from the graph of FIG.

In the present invention, the thickness of the amorphous carbon film formed on the GDL is not particularly limited, but from the viewpoint of reliably exhibiting conductivity and corrosion resistance, and further water repellency according to the _RG value. It is desirable that the thickness be in the range of 1 to 1000 nm, more preferably 2 to 500 nm, and further 5 to 200 nm.

The amorphous carbon film only needs to be formed on the surface of the GDL on the gas flow path side. However, the device and process during film formation, workability, and simplicity during battery assembly (confirmation of the film formation surface) If unnecessary), the film may be formed on a surface other than the surface on the gas flow path side.
In the present invention, since the formation of the amorphous carbon film is a countermeasure against flooding, it is basically unnecessary to form such an amorphous carbon film on the anode-side GDL. However, it is also possible to apply GDL provided with an amorphous carbon film on the anode side from the viewpoint of sharing parts. The same applies to the separator described later.

The material constituting the GDL substrate is not particularly limited, and conventionally known materials can be applied.
In general, carbon-based materials such as carbon paper and carbon cloth are widely used, but metal materials such as stainless steel are used from the viewpoint of material cost, electrical conductivity, workability, and variety of types. It is desirable to apply a ferrous material typified by steel, felt, mesh, or foam metal made of aluminum or aluminum alloy, titanium or titanium alloy, or the like.

The thickness of the GDL substrate is appropriately determined in consideration of the characteristics of the obtained GDL, but is generally preferably about 30 to 500 μm. If the thickness of the GDL substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be made appropriate.

[Separator]
The separator (anode separator, cathode separator) is disposed between the MEAs, and forms a fuel gas flow path and an oxidant gas flow path between the anode GDL and the cathode GDL in the MEA, and electrically connects the MEAs. It has a function to connect to.

In the present invention, an amorphous carbon film is formed on at least the gas flow path side surface of the separator from the viewpoint of suppressing flooding as in the GDL.
This amorphous carbon film, the ratio of the D-band peak intensity was measured by Raman scattering spectroscopy _{I D} and G band peak intensity _{I G (I} D _{/ I} G), that is, the _{R B} value in the GDL It is necessary to make it larger than the _RG value of the formed amorphous carbon film.

The thickness of the amorphous carbon film formed on the separator, as in the GDL, but are not particularly limited, conductivity and corrosion resistance, furthermore reliably exhibit water repellency corresponding to R _B value Therefore, it is desirable that the thickness be in the range of 1 to 1000 nm, more preferably 2 to 500 nm, and further 5 to 200 nm.

It is sufficient that the amorphous carbon film is formed only on the surface of the separator on the gas flow path side. However, as in the case of GDL, the amorphous carbon film is formed on a surface other than the surface of the gas flow path side, for example, on the cooling water channel side. Even if a film is formed, there is no particular problem.
In addition, it is basically unnecessary to form an amorphous carbon film on the separator on the anode side. However, as in the case of GDL, even if a separator having an amorphous carbon film on the anode side is applied, there is no particular problem. There is no.

As a base material of this separator, as long as it contributes to ensuring electrical conductivity and mechanical strength, the material is not particularly limited, and the same metal material as GDL described above, for example, iron, titanium, aluminum, Mention may be made of alloys containing these metals.
These materials can be preferably used from the viewpoints of mechanical strength, versatility, cost performance, workability, and the like. Here, stainless steel can be mentioned as a typical example of an iron alloy.

In these, it is preferable to use stainless steel, aluminum, or an aluminum alloy.
As the stainless steel, any of austenite, martensite, ferrite, austenite / ferrite, and precipitation hardening can be applied without any problem. Examples of austenite include SUS301, SUS302, SUS303, SUS304, SUS305, SUS316 (L), and SUS317. Examples of the austenite / ferrite type include SUS329J1, and examples of the martensite type include SUS403 and SUS420. Further, examples of the ferrite system include SUS405, SUS430, and SUS430LX, and examples of the precipitation hardening system include SUS630.

In particular, 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 60 to 84% by mass, more preferably 65 to 72% by mass. Furthermore, the content of chromium (Cr) in the stainless steel is preferably 16 to 20% by mass, 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 are generally usable as an aluminum alloy. For example, copper (Cu), manganese (Mn), silicon (Si), magnesium (Mn ), Zinc (Zn), nickel, and the like may be included in the aluminum alloy.

Specific examples of the aluminum alloy include A1050 and A1050P as the pure aluminum system, A3003P and A3004P as the aluminum-manganese system, and A5052P and A5083P as the aluminum-magnesium system.
On the other hand, since the separator is also required to have mechanical strength and formability, it is possible to appropriately select the tempering of the alloy in addition to the above alloy types. When the separator substrate 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. That's it.

The thickness of the base material of the separator is not particularly limited, and is preferably 50 to 500 μm, and preferably 80 to 300 μm from the viewpoints of workability, mechanical strength, and improvement of battery energy density by thinning the separator itself. Is more preferable, and 80 to 200 μm is more preferable. In particular, the thickness when stainless steel is used is preferably 80 to 150 μm. On the other hand, the base material thickness when an aluminum-based material is used is preferably 100 to 300 μm.
When the base material thickness of the separator is within the above range, it has excellent workability and can achieve a suitable thickness while having sufficient strength as a separator.

The separator is preferably made of a material having a high gas barrier property. Since the separator of the fuel cell plays a role of partitioning cells, different gas flows on both sides of the separator. Therefore, from the viewpoint of eliminating the mixing of adjacent gases in each cell of each cell unit and the fluctuation of the gas flow rate, the metal base layer 31 is preferably as the gas barrier property is higher.

In the separator used in the present invention, an amorphous carbon film may be formed on the base material via an intermediate layer in order to improve the adhesion between the separator base material and the amorphous carbon layer. Such an intermediate layer also has a function of preventing elution of ions from the separator substrate.
Such an effect becomes more prominent when aluminum or an alloy thereof is used as the separator substrate. In the present invention, the intermediate layer may be formed as necessary and does not necessarily exist.

The material constituting the intermediate layer is not particularly limited as long as it provides adhesion as described above. For example, group 4 metals (titanium (Ti), zirconium (Zr), hafnium (Hf)), group 5 metals (vanadium (V), niobium (Nb), tantalum (Ta)) in the periodic table, Examples include Group 6 metals (chromium (Cr), molybdenum (Mo), tungsten (W)), carbides, nitrides, and carbonitrides thereof.

In particular, metals with low ion elution such as chromium, tungsten, titanium, molybdenum, niobium, and hafnium, or nitrides, carbides, or carbonitrides thereof can be preferably used. In particular, chromium, titanium, and carbides and nitrides thereof are preferable. When these are used, the role of the intermediate layer is to ensure adhesion with the upper amorphous carbon film and to prevent corrosion of the underlying separator substrate. In particular, when the separator base material is an aluminum-based material, corrosion proceeds due to moisture reaching the vicinity of the interface, and an aluminum oxide film is formed. As a result, the conductivity in the film thickness direction of the entire substrate is deteriorated.
Chromium, titanium, these carbides, and nitrides are particularly useful in that even if exposed portions are present due to the formation of a passive film, the elution itself is hardly observed. Especially, when the metal (especially chromium, titanium) with little ion elution mentioned above or its carbide | carbonized_material and nitride is used, it is excellent also in the point which can improve the corrosion resistance of a separator effectively. Thereby, the corrosion resistance of the separator can be maintained.

The thickness (film thickness) of the intermediate layer is not particularly limited. However, the thickness of the intermediate layer is preferably 0.01 to 10 μm from the viewpoint of making the separator thinner and thereby reducing the size of the fuel cell stack as much as possible. The thickness is more preferably 0.05 to 5 μm, further preferably 0.02 to 5 μm, and particularly preferably 0.1 to 1 μm.
If the thickness of the intermediate layer is 0.01 μm or more, a uniform layer is formed, and the corrosion resistance of the separator substrate can be effectively improved. On the other hand, if the thickness of the intermediate layer is 10 μm or less, an increase in the film stress of the intermediate layer can be suppressed, and a decrease in film followability with respect to the substrate and the accompanying peeling and cracking can be prevented.

In the polymer electrolyte fuel cell of the present invention, as shown in FIG. 1, as the need arises, the electric resistance between the GDL and the electrode layer is lowered and the intermediate layer for improving the gas flow is used. A microporous layer (hereinafter abbreviated as “MPL”) can be provided on the electrode layer side of the GDL substrate.
This MPL consists of an aggregate of carbon particles containing a water repellent.

The carbon particles constituting the MPL are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Of these, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are 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. Thereby, while being able to obtain the high drainage property by capillary force, the contact property with an electrode layer also improves.

The water repellent is not particularly limited. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP) ) And the like, polypropylene, polyethylene and the like.
In these, since it is excellent in water repellency, the corrosion resistance at the time of electrode reaction, etc., a fluorine-type polymeric material can be used preferably.

The mixing ratio of carbon particles and water repellent in MPL is about 90:10 to 40:60 (carbon particles: water repellent) in terms of mass ratio in consideration of the balance between water repellency and electron conductivity. preferable.
The thickness of the MPL is not particularly limited and is appropriately determined in consideration of the water repellency of the obtained GDL, but is preferably about 10 to 1000 μm, more preferably 50 to 500 μm.

Hereinafter, although the present invention will be specifically described based on examples, it is needless to say that the present invention is not limited to such examples.

(1) Production of Separator A stainless steel plate (SUS316L) having a plate thickness of 100 μm was formed into a predetermined separator shape to obtain a separator base material.
The obtained base material is ultrasonically cleaned in an aqueous ethanol solution for 3 minutes as a pretreatment, and the cleaned base material is stored in a vacuum chamber and subjected to ion bombardment treatment with Ar gas, and an oxide film on the surface of the base material. Was removed. In addition, these washing | cleaning and film removal processing were implemented with respect to both surfaces of the base material.

Next, using a sputtering apparatus (UBMS504, manufactured by Kobe Steel, Ltd.) by an unbalanced magnetron sputtering (UBMS) method, an intermediate layer is formed on the separator substrate using a Cr plate as a target, and then solid graphite is used as a target. As described above, an amorphous carbon film having a thickness of 0.2 μm was formed on both surfaces of the base material while applying a negative bias voltage to the base material.
At this time, the intensity ratio (I _D / I _G ) between the D band peak intensity I _D and the G band peak intensity I _G measured by Raman scattering spectroscopic analysis by changing the negative bias voltage applied to the substrate. , that were prepared five kinds of separators R _B values with different amorphous carbon film, respectively.

(2) Preparation of gas diffusion layer A 200 μm-thick mesh made of stainless steel wire (SUS316L) having a diameter of 100 μm was used as a GDL substrate, and the substrate was subjected to the same cleaning and film removal treatment as described above. By the same method, an amorphous carbon film having a thickness of 0.2 μm was formed on one surface of the substrate.
At this time, the intensity ratio (I _D / I _G ) between the D band peak intensity I _D and the G band peak intensity I _G measured by Raman scattering spectroscopic analysis by changing the negative bias voltage applied to the substrate. That is, three types of GDLs having amorphous carbon films having different _RG values were produced.

(3) the R value _(R B, _{R G)} for the separator and GDL obtained by measuring the above, the R value of amorphous carbon films formed on respectively, i.e. _{R B} values and _{R G} values were measured . Specifically, first, the Raman spectrum of the amorphous carbon film was measured using a microscopic Raman spectrometer. Then, 1300 ~ 1400 cm peak intensity of the bands (D-band) located ^-1 _{(I D),} the peak area ratio of the peak intensity _{(I G)} of band (G-band) located 1500 ~ 1600 cm ^-1 ( It calculates the _{I D} / I _G), to obtain a _{R B} values and _{R G} values, respectively.
As a result, were as shown in Table 1, R _B value of the amorphous carbon film formed on the separator is in the range 1.2 to 1.9, and the amorphous carbon film formed GDL R _G The value was confirmed to be in the range of 1.2 to 1.5.

(4) Manufacture of membrane electrode assembly (MEA) MEA was manufactured using each GDL obtained by the above.
That is, on both sides of a polymer electrolyte membrane made of a perfluorosulfonic acid electrolyte, an electrode layer made of platinum-supporting carbon and a perfluorosulfonic acid electrolyte similar to the above electrolyte membrane is formed, and both sides thereof are sandwiched by the GDL, An MEA (active area: 5 × 5 cm) having a GDL provided with amorphous carbon films having different _RG values was obtained.

(5) Assembly of fuel cell Each MEA obtained by the above and each separator obtained previously were combined, respectively, and the small unit cell of the polymer electrolyte fuel cell was produced.

(6) Evaluation of battery performance For each unit cell of each example and comparative example using a combination of each MEA and a separator, power generation output was measured (IV characteristics) under the following conditions.
The results are shown R _G value, with a combination of GDL and a separator having a R _B value is different amorphous carbon film in Table 2, FIG.
-Gas components: hydrogen (anode side), air (cathode side)
-Cell temperature: 80 ° C
・ Relative humidity: 100% (wet condition)

Table 2, as shown in FIG. 3, the peak intensity ratio of D band and G band in the amorphous carbon film formed in the separator, i.e. the peak intensity ratio of the amorphous carbon film R _B value is formed on the GDL R _G In the example larger than the value, especially in the example where the difference is somewhat large, it was confirmed that the output performance was particularly excellent on the high current density side. From this, it is considered that flooding can be substantially prevented in the battery of this example.
In contrast, in the comparative example R _B value in the amorphous carbon film of the separator is composed of a smaller combination than R _G value in the amorphous carbon film of the GDL, the voltage decreases as the current density increases Therefore, it is estimated that the water produced on the cathode side has not been smoothly discharged.

1 Polymer electrolyte fuel cell (PEFC)
10 Membrane electrode assembly (MEA)
11 Polymer electrolyte membrane 12a, 12c Electrode layer 13a, 13c Gas diffusion layer (GDL)
15c separator 16c gas channel C _{G, C B} amorphous carbon film

Claims (4)

1. A membrane electrode assembly having a polymer electrolyte membrane, an electrode layer sandwiching the polymer electrolyte membrane, and a gas diffusion layer sandwiching the polymer electrolyte membrane and the electrode layer;
   In a polymer electrolyte fuel cell comprising a separator that forms a gas flow path between the membrane electrode assembly,
   An amorphous carbon film is formed on at least the gas flow path side surface of the gas diffusion layer and the separator,
   A fuel cell, wherein the amorphous carbon film formed on the separator is more hydrophilic than the amorphous carbon film formed on the gas diffusion layer.
2. The intensity ratio (I _D / I _G ) between D band peak intensity I _D and G band peak intensity I _G measured by Raman scattering spectroscopic analysis of the amorphous carbon film formed in the gas diffusion layer is R _G , when the intensity ratio of the measured D-band peak intensity I _D and G band peak intensity I _G by Raman scattering spectroscopy of amorphous carbon film formed on the separator (I D _{/ I G)} and R _B the fuel cell according to claim 1, characterized in that the R G _{<R B.}
3. Amorphous carbon formed in the gas diffusion layer when the peak intensity ratio (I _D / I _G ) of the amorphous carbon film having a static contact angle of water droplets of 90 ° by Raman scattering spectroscopy is R ₉₀ the fuel cell according to claim 2 in which the peak intensity ratio R _G of the film is less than R _90, the peak intensity ratio R _B of the amorphous carbon film formed on the separator is equal to or greater than R _90.
4. The base material of the gas diffusion layer and the separator is any metal selected from the group consisting of iron, stainless steel, aluminum, an aluminum alloy, titanium, and a titanium alloy. A fuel cell according to one of the items.

Images