JP2008198565A - Metal separator for fuel cell and polymer electrolyte fuel cell using the same - Google Patents

Abstract

A metal separator for a fuel cell in which water droplets are not generated in a concave groove which is a reaction gas flow path and gas clogging is hardly caused, and a solid polymer fuel cell using the same.
For example, a base plate 2 made of a thin metal plate such as stainless steel (SUS316L) and having a plurality of concave grooves 4 serving as a reaction gas flow path on at least one surface 3, and the plurality of the base plate 2 On the surface 3 having the concave grooves 4, the noble metal thin film layer 20 having a thickness of 1 to 100 nm covering at least the plural concave grooves 6 and the inside of the noble metal thin film layer 20 are dispersed, and at least the surface 3 of the plural concave grooves 4 A metal separator 1a for a fuel cell, comprising a fine powder 22 of a metal oxide (for example, SiO ₂ ) having a hydrophilic property with a water contact angle of 50 ° or less.
[Selection] Figure 4

Description

  The present invention relates to a fuel cell metal separator and a polymer electrolyte fuel cell using the same, in which gas clogging of a gas flow path through which a reaction gas flows hardly occurs.

A fuel cell metal separator is required to have corrosion resistance to a reaction gas and to have low contact resistance with an adjacent electrode.
For this reason, a stainless steel thin plate is press-molded to form a bulging molded portion having a large number of irregularities on its inner peripheral portion, and the tip end side surface (contact surface with the electrode) of the bulging molded portion has a thickness of 0. A fuel cell separator in which an Au plating layer of 0.01 to 0.02 μm is formed has been proposed (see, for example, Patent Document 1).
There has also been proposed a fuel cell separator in which the entire surface of a metal plate serving as a base material is coated with Ag, chromium nitride, a platinum group composite oxide, or the like by plating (see, for example, Patent Document 2).

JP-A-10-228914 (pages 1 to 4, FIGS. 1 to 3) Japanese Patent Laid-Open No. 11-162478 (pages 1 to 8, FIG. 1)

  However, as described in Patent Documents 1 and 2, when Au plating or Ag plating is applied to the metal separator, Au or Ag itself exhibits water repellency in the recessed groove of the press-formed reaction gas channel. After water adheres to the inner surface of the groove, the water gradually aggregates and eventually drops of water. When such water droplets become large, the above-mentioned concave groove is closed, which causes a gas blockage in which the reaction gas does not flow, and there is a problem that power generation may stop.

  MEANS TO SOLVE THE PROBLEM The present invention solves the problems described in the background art, a metal separator for a fuel cell in which water droplets are not generated in a concave groove as a reaction gas flow path, and gas clogging is difficult to occur, and a solid polymer fuel using the same It is an object to provide a battery.

Means for Solving the Problems and Effects of the Invention

In order to solve the above-mentioned problems, the present invention has been conceived in view of making the surface of the groove, which is a reaction gas flow path, hydrophilic, as a result of intensive studies by the inventors.
That is, the fuel cell metal separator of the present invention (Claim 1) is made of a thin metal plate, and has a base plate having a plurality of concave grooves serving as a reaction gas flow path on at least one surface, and the plurality of the base plate. On the surface having the groove, the noble metal thin film layer coated on at least the plurality of grooves and the hydrophilicity dispersed within the noble metal thin film layer so that the contact angle of water on the surface of at least the plurality of grooves is 50 degrees or less And a metal oxide fine powder having the following.

According to this, in the inside of the noble metal thin film layer, a fine powder of hydrophilic metal oxide having a water contact angle of 50 degrees or less on the surface of the groove is dispersed. For this reason, since the surfaces of the plurality of grooves are hydrophilic, even when a reaction gas flows through the grooves, the water adheres and aggregates, making it difficult to form water droplets. As a result, a situation in which water droplets block the plurality of concave grooves is less likely to occur, so that gas blockage in which the reaction gas does not flow can be reliably prevented or reduced. Therefore, it can contribute to providing a fuel cell capable of stable power generation.
If the contact angle of water exceeds 50 degrees, the hydrophilicity of the noble metal thin film layer coated on the surface of the groove is lowered and water repellency may be exhibited, so this range was excluded. Desirable water contact angle is 30 degrees or less, more desirably 25 degrees or less.

The metal thin plate is made of Fe, Ni, Ti, or an alloy based on any of these, and preferably made of an austenitic stainless steel (eg, SUS316L, SUS304) of an Fe-based alloy. Recommended.
The thickness of the thin metal plate is 0.2 mm or less, preferably 0.1 mm or less.
Further, the plurality of concave grooves in the base plate are provided in parallel to each other by, for example, press molding in the inner peripheral portion of the thin metal plate, and alternately reverse in the same direction (straight type) or adjacent to each other. A reactive gas is flowed in the direction (multi-serpentine type). A ridge is located between the adjacent grooves, and a U-turn groove, a diversion groove, or a merging groove for the reaction gas is disposed at the longitudinal ends of the plurality of grooves.
In addition, the noble metal thin film layer is coated by, for example, electrolytic metal plating or sputtering, and is coated not only on the inner surface of the groove by masking, but also includes a base plate including a ridge located between the adjacent grooves. You may coat | cover almost the whole surface of this, or the whole surface and back surface.

The present invention also includes a fuel cell metal separator (Claim 2) in which the noble metal thin film layer has a thickness of 1 to 100 nm.
According to this, it can be stably coated with a practical technique such as metal plating, the volume of the concave groove is not excessively pressed, the flow rate of the reaction gas can be appropriately secured, and the high cost can be avoided. Is possible.
In addition, if the thickness of the noble metal thin film layer is less than 1 nm, it is too thin to be stably coated with practical technology. On the other hand, if the thickness exceeds 100 nm, the volume of the concave groove is excessively increased. These ranges are excluded because they can be costly and costly. A desirable thickness of the noble metal thin film layer is 3 to 50 nm, and more desirably 5 to 20 nm.
In other words, the noble metal thin film layer is coated on the surface of the metal thin plate and then subjected to a compression process with a rolling reduction of 0.2 to 10%. A fuel cell metal separator is also included in the present invention. It is possible. A desirable rolling reduction is 1% or more, and more desirably 5% or more.

Further, according to the present invention, the noble metal thin film layer is made of any one of Au, Pt, Pd, and Ru, an alloy based on one of them, or an alloy of two or more of the above metal elements. Also included are metal separators (claim 3).
According to this, corrosion by the reaction gas can be surely prevented, and the precious metal thin film layer can be stably coated with a desired thickness by a practical technique such as metal plating or sputtering. Examples of the alloy include Au—Co.

In the present invention, the fine powder of the metal oxide having hydrophilicity is SiO ₂ , TiO ₂ , Al ₂ O ₃ , Bi ₂ O ₃ , CeO ₂ , CoO, CuO, Fe ₂ O ₃ , Ho _2. A fuel cell metal separator (Claim 4) comprising fine particles of O ₃ , ITO (indium tin oxide), Mn ₃ O ₄ , SnO ₂ , Y ₂ O ₃ , or ZnO is also included.
According to this, it becomes possible to make the noble metal thin film layer covering the surface of the concave groove hydrophilic at a low cost.
Furthermore, the present invention includes a fuel cell metal separator (Claim 5) in which the average particle size of the hydrophilic fine powder is 50% or less of the thickness of the noble metal thin film layer.
According to this, the hydrophilic fine powder can be dispersed relatively uniformly throughout the noble metal thin film layer, and the noble metal thin film layer can be reliably made hydrophilic.
When the average particle diameter of the fine powder exceeds 50% of the thickness of the noble metal thin film layer, the fine powder is difficult to be uniformly dispersed, and the hydrophilicity of the noble metal thin film layer may vary depending on the surface location. Therefore, this range was excluded. The desirable average particle diameter of the fine powder with respect to the thickness of the noble metal thin film layer is 25% or less, more desirably 20% or less.

  On the other hand, the polymer electrolyte fuel cell of the present invention (Claim 6) is characterized in that at least a pair of the metal separators are arranged in parallel with each other, and a polymer electrolyte membrane is sandwiched therebetween. According to this, at least a pair of the metal separators that hardly cause gas blockage is used. For this reason, the fuel gas, for example, hydrogen, which flows in the concave groove of one metal separator, comes into contact with the adjacent anode electrode of the solid polymer film and is decomposed into hydrogen ions and electrons, and these electrons pass through the external circuit. Then, after generating electricity, it is sent to the cathode electrode on the opposite side of the solid polymer membrane. On the other hand, when an oxidant gas, for example, air, flowing through the concave groove of the other metal separator contacts the cathode electrode, the oxygen contained therein reacts with the hydrogen ions penetrating the solid polymer film and the electrons. Water is formed and discharged. Therefore, stable power generation can be ensured.

In the following, the best mode for carrying out the present invention will be described.
FIG. 1 is a front view showing a fuel cell metal separator (hereinafter simply referred to as a metal separator) 1a according to an embodiment of the present invention.
The metal separator 1a is, for example, a thin metal plate made of stainless steel (SUS316L or the like) having a thickness of about 0.1 mm. As shown in FIG. A plurality of concave grooves 4 serving as reaction gas flow paths, which will be described later, are formed in parallel on the inner peripheral portion excluding the portion.

In FIG. 1, an independent elongated ridge 5 protrudes between the right and left concave grooves 4 and 4, and a diversion groove 6 or a merging groove is provided above and below the plurality of concave grooves 4. The grooves 6 are individually formed. A recess 7 having a supply hole 8 at its center is communicated with the upper left portion of the diversion groove 6 via a bottleneck, and a discharge hole 9 is provided at the center of the lower right of the merge groove 6 via a bottleneck. The recess 7 is in communication. The concave grooves 4, the ridges 5, the diversion / merging grooves 6, and the dents 7 are formed by press-molding the metal thin plate, for example. The width of the groove 4 and the width of the ridge 5 may be substantially the same.
As shown by the arrows in FIG. 1, the reaction gas introduced from the supply hole 8 of the upper left recess 7 flows through the joining groove 6, the plurality of recessed grooves 4, and the joining groove 6, and then the lower right It is discharged from the discharge hole 9 of the recess 7 to the outside. At least the surface of the merging groove 6, the plurality of concave grooves 4, and the merging groove 6 has a water contact angle of 50 degrees or less, as will be described later.

FIG. 2 shows a front view of a metal separator 1b of a different form, and on the surface 3 of a rectangular base plate 2 made of the same metal thin plate as described above, a reaction gas flow path, which will be described later, is provided on the inner peripheral portion excluding the peripheral portion. A plurality of concave grooves 14 are formed in parallel.
In FIG. 2, between the concave grooves 14, 14 adjacent to the left and right, elongated ridges 15 projecting forward are formed in parallel, and the top surfaces of the adjacent ridges 15, 15 alternately have upper ends or lower ends. It is connected with the flat part of the surface 3 of the base plate 2 as flush. As shown in FIG. 2, a substantially semicircular U-turn groove 16 is continuously formed at the upper end or lower end of the concave grooves 14 adjacent to the left and right.

A substantially semicircular groove end 12 is located at the upper end of the concave groove 14 located at the left end in FIG. 2, and a supply hole 18 is perforated at the center thereof. The concave groove 14 located at the right end in FIG. A substantially semicircular groove end 17 is located at the lower end of the tube, and a discharge hole 19 is formed in the center thereof. The width of the groove 14 and the width of the ridge 15 may be substantially the same.
As indicated by the arrows in FIG. 2, the reaction gas introduced from the supply hole 18 at the groove end 12 flows in a substantially zigzag manner through the plurality of concave grooves 14 and the plurality of U-turn grooves 16, and then the discharge hole at the groove end 17. 19 is discharged to the outside. At least the surfaces of the concave groove 14 and the U-turn groove 16 have a water contact angle of 50 degrees or less, as will be described later.

3 is a cross-sectional view taken along the line XX in FIG. 1 and along the line YY in FIG. As shown in FIG. 3, the plurality of concave grooves 4 (14) and the plurality of ridges 5 (15) are alternately formed on the surface 3 of the base plate 2. For this reason, the back surface (front surface) 3a of the base plate 2 has a groove 4a (14a) substantially similar to the groove 4 (14) and a groove 5a (similar to the protrusion 5 (15) ( 15) are located alternately.
The width of the groove 4 (14) and the width of the ridge 5 (15) may be substantially the same, and the groove 3 (14) and the convex of the cross section are formed on the back surface 3a of the base plate 2 in this form. The strips 4a (14a), the strips 5 (15), and the concave grooves 5a (15) having a substantially cross section are formed alternately.

FIG. 4 is a partially enlarged view of a one-dot chain line portion Z in FIG. As illustrated in FIG. 4, in the metal separator 1a (1b), at least the surface 3 of the concave groove 4 (14) is coated with a noble metal thin film layer 20 having a thickness t of 1 to 100 nm. The noble metal thin film layer 20 is made of any one of Au, Pt, Pd, and Ru, or an alloy based on one of them, such as an Au—Co alloy, or an alloy containing two or more of the above metal elements. The noble metal thin film layer 20 is coated with a substantially uniform thickness on the entire surface 3 of the base plate 2 or the surface 3 such as the recessed groove 4 (14) exposed by masking by electrolytic metal (Au) plating or sputtering. The
The noble metal thin film layer 20 is coated with metal plating or the like, and then subjected to compression processing with a reduction (processing) rate of 0.2 to 10%, whereby the adhesion to the base plate 2 is enhanced.

As shown in FIG. 4, a large number of fine powders 22 of hydrophilic metal oxide having a contact angle of water of 50 degrees or less on the surface are dispersed in the noble metal thin film layer 20.
The fine powder 22 is made of, for example, fine particles of SiO ₂ or TiO ₂ (metal oxide), and the average particle diameter thereof is 50% or less of the thickness t of the noble metal thin film layer 20, desirably 25% or less, and more desirably. 20% or less. By setting such an average particle size, the fine powder 22 is relatively uniformly dispersed inside the noble metal thin film layer 20, and the contact angle of water on the surface of the noble metal thin film layer 20 is 50 degrees or less, preferably 30. It is possible to set the angle to be equal to or less than 25 degrees, more desirably 25 degrees or less. The fine powder 22 is made of Al ₂ O ₃ , Bi ₂ O ₃ , CeO ₂ , CoO, CuO, Fe ₂ O ₃ , Ho ₂ O ₃ , ITO (indium tin oxide), Mn ₃ O ₄ , SnO ₂ , Either Y ₂ O ₃ or ZnO may be used.
As described above, when the contact angle of water on the surface of the metal thin film layer 20 is set to 50 degrees or less, the water in the vicinity hardly adheres and aggregates to form water droplets, and the reaction described below in the groove 4 (14) is as follows. Since gas flows smoothly, it is difficult to cause gas blockage.

FIG. 5 relates to the polymer electrolyte fuel cells (hereinafter simply referred to as fuel cells) 28 and 30 of the present invention.
As shown in the schematic diagram on the left side of FIG. 5, for example, an anode electrode 25 made of carbon fiber and a similar cathode electrode 26 are laminated on each side surface of the solid polymer film 24. The solid polymer film 24 is made of, for example, a fluororesin containing a sulfonic acid group.
On both sides of the solid polymer film 24, a pair of metal separators 1a (1b) facing the surface 3 having the concave grooves 4 (14) and the ridges 5 (15) are arranged symmetrically in the figure. As indicated by the arrows, the metal separator 1a (1b) is laminated on both sides of the solid polymer film 24 so as to cover the electrodes 25 and 26. In addition, these are fixed with the bolts and nuts, etc., not shown in the periphery thereof while maintaining the above-described laminated state.

As a result, as shown in the schematic diagram in the center of FIG. 5, both side surfaces of the solid polymer film 24 having the electrodes 25 and 26 are sandwiched between the surfaces 3 and 3 of the pair of metal separators 1a (1b). Stacked unit cell fuel cells 28 are formed.
Further, by stacking and fixing a plurality of the fuel cells 28 of the unit cell along the thickness direction, a stack type fuel cell 30 is formed as shown in the schematic diagram on the right side of FIG.
In addition, between the said recessed grooves 4 (14) of the adjacent metal separator 1a (1b) and between the recessed grooves 4 (14) of the metal separator 1a (1b) which pinched | interposed the solid polymer film 24, it is a detour which is not shown in figure. It communicates via a flow path. Further, in the metal separator 1a (1b) in which the width of the concave groove 4 (14) and the width of the ridge 5 (15) are substantially the same, the concave groove 5a (15a) on the back surface 3a side is also reactive gas. Therefore, it is possible to provide a stack type fuel cell 30 in which one metal separator 1a (1b) is sandwiched between adjacent solid polymer membranes 24, 24.

Here, the operation of the fuel cell 28 of the unit cell will be described as an example.
The fuel gas, for example, hydrogen flowing through the concave groove 4 (14) of the metal separator 1a (1b) on the left side in the center of FIG. 5 comes into contact with the adjacent anode electrode 25 on the solid polymer film 24 side, and hydrogen ions and electrons. And decomposed. Such electrons generate power when passing through an external circuit, and are then sent to the cathode electrode 26 on the opposite side of the solid polymer film 25.
On the other hand, when the oxidant gas, for example, air, flowing through the concave groove 4 (14) of the right metal separator 1a (1b) in the center of FIG. The hydrogen ions penetrating 24 and the electrons react to form water. Such water is immediately drained to the outside.

When the above reactive gas such as hydrogen or air flows through the concave groove 4 (14) of the metal separator 1a (1b), the inner surface of the concave groove 4 (14) has the fine particles 22 of SiO ₂ or TiO _2. By being uniformly dispersed inside, the contact angle of water on the surface of the metal thin film layer 20 is set to 50 degrees or less. For this reason, for example, even if nearby water adheres to the inner surface of the concave groove 4 (14), the water does not aggregate as spherical water droplets, and becomes flat adhering water. For this reason, reaction gas such as hydrogen can be smoothly fed and circulated in each concave groove 4 (14) without causing the conventional gas clogging. Therefore, according to the fuel cell 28, stable power generation can be performed. In this regard, the same applies to the stack type fuel cell 30.

Here, specific examples of the present invention will be described together with comparative examples.
A plurality of pairs of metal thin plates made of stainless steel (SUS316L) and having a thickness of 0.1 mm were prepared. With respect to the surface (3) of the thin metal plate, SiO ₂ or TiO ₂ (hydrophilic metal having different average particle diameters shown in Table 1 in Au plating solution, Pt plating solution, or Au—Co plating solution. With the oxide fine powder: 22) dispersed, electrolytic metal plating was applied individually to coat the noble metal thin film layer (20) having the thickness shown in Table 1. In addition, the said fine powder (22) was not used for a pair of metal thin plate.
Moreover, in the metal thin plate for each pair, the ratio of the average particle diameter of SiO ₂ or TiO ₂ to the thickness of the noble metal thin film layer (20) was calculated, and these are shown in Table 1.
Further, the contact angle on the surface of each of the pair of metal thin plates coated with the noble metal thin film layer (20) and the pair of metal thin plates not using the fine powder (22) was measured. It was shown in Table 1 as “Wettability”.

The plurality of pairs of metal thin plates coated with the noble metal thin film layer (20) are press-molded by the same press die, and a plurality of concave grooves having a depth of 0.5 mm and an average width of 0.9 mm and a substantially inverted trapezoidal cross section. A plurality of pairs of metal separators (1a) having a reaction gas flow path including (4) and a ridge (5) between them on the surface (3) of the base plate (2) were formed.
The pair of metal thin plates not using the fine powder (22) was also subjected to the same press forming as described above to form a pair of metal separators as Comparative Example 1.
Next, an anode electrode comprising a catalyst layer and a carbon fiber layer having the same thickness and size on both side surfaces of a plurality of solid polymer membranes (24) made of the same fluororesin containing sulfonic acid groups and having the same thickness ( 25) and the cathode electrode (26) were laminated.
Next, a plurality of pairs of metal separators (1a) are stacked and fixed on both sides of a plurality of solid polymer membranes (24) on which the electrodes (25, 26) are stacked, so that a plurality of single polymer films (24) are stacked. A cell fuel cell (28) was formed. Also, a pair of metal separators of Comparative Example 1 were laminated on both side surfaces of one solid polymer membrane (24) to form a single cell fuel cell of Comparative Example 1.

For the plurality of fuel cells (28) and the fuel cell of Comparative Example 1, fuel gas: hydrogen (utilization rate 70%), oxidant gas: air (utilization rate 40%), humidification temperature: anode side (25) A power generation test was performed on the cathode side (26) under the conditions of 80 ° C. and cell temperature: 80 ° C., and the IV characteristics at a sweep rate of 50 mA / sec were measured.
A plurality of the fuel cells (28) and the fuel cell of Comparative Example 1 are individually subjected to a power generation test to measure a cell voltage (V) at an output of 1 A / cm ² · hr, and during power generation The results of whether or not gas clogging occurred are shown in Table 1, respectively.
According to Table 1, according to the fuel cells 28 of Examples 1 to 10, the cell voltages were all about 0.49 V or more.

On the other hand, in all the fuel cells of Comparative Examples 1 to 5, the cell voltage was about 0.3 V or less.
In the fuel cells 28 of Examples 1 to 10, as shown in Table 1, the ratio of the average particle diameter of SiO ₂ or TiO _{2 with} respect to the thickness of the noble metal thin film layer 20 is relatively uniformly dispersed at 50% or less. Since the contact angle of water on the surface of the noble metal thin film layer 20 was hydrophilic of 30 degrees or less, it is presumed that no gas clogging occurred in the concave grooves 4 of the respective metal separators 1a.

On the other hand, in the fuel cells of Comparative Examples 1 to 5, as shown in Table 1, the ratio of the average particle diameter of SiO ₂ or TiO _{2 with} respect to the thickness of the noble metal thin film layer 20 is relatively non-uniform, both exceeding 50%. It was presumed that gas was blocked in the concave grooves 4 of each metal separator because the contact angle of water on the surface of the noble metal thin film layer 20 was water repellency of 60 degrees or more.
It is easily understood that the effects of the present invention are supported by the above Examples 1-10.

Obviously, the functions and effects of the above embodiment are almost the same when the metal separator 1b is used.
The metal separators 1a and 1b of the present invention can also be applied to fuel cells other than the solid polymer type (for example, phosphoric acid type fuel cells).

The front view which shows the metal separator of one form of this invention. The front view which shows the metal separator of a different form. Sectional drawing along the arrow of XX in FIG. 1, and the arrow of YY in FIG. The elements on larger scale of the dashed-dotted line part Z in FIG. Schematic which shows before and after the assembly of the polymer electrolyte fuel cell of this invention.

Explanation of symbols

1a, 1b ... Metal separator 2 ......... Base plate 3 ......... Surface 4,14 ... Concave groove 20 ......... Precious metal thin film layer 22 ......... Metal oxide fine powder t …… ......... Thickness of noble metal thin film layer 28,30 ... Solid polymer fuel cell

Claims (6)

A base plate made of a thin metal plate and having a plurality of concave grooves serving as reaction gas flow paths on at least one surface;
On the surface of the base plate having the plurality of grooves, a noble metal thin film layer covering at least the plurality of grooves,
A metal oxide fine powder having a hydrophilic property that is dispersed within the noble metal thin film layer and has a contact angle of water of at least 50 degrees on the surface of the plurality of grooves,
A metal separator for a fuel cell. The noble metal thin film layer has a thickness of 1 to 100 nm.
The metal separator for fuel cells according to claim 1. The noble metal thin film layer is made of any one of Au, Pt, Pd, Ru, an alloy based on one of these, or an alloy of two or more of the above metal elements.
The metal separator for fuel cells according to claim 1 or 2. The fine powder of metal oxide having _{hydrophilicity, SiO 2, TiO 2, Al} 2 O 3, Bi 2 O 3, CeO 2, CoO, CuO, Fe 2 O 3, Ho 2 O 3, ITO ( indium oxide Tin), Mn ₃ O ₄ , SnO ₂ , Y ₂ O ₃ , or ZnO fine particles,
The metal separator for a fuel cell according to any one of claims 1 to 3. The average particle diameter of the hydrophilic fine powder is 50% or less of the thickness of the noble metal thin film layer.
The metal separator for fuel cells according to any one of claims 1 to 4. At least a pair of the metal separators according to any one of claims 1 to 5 are arranged in parallel to each other, and a solid polymer film is sandwiched therebetween.
A polymer electrolyte fuel cell characterized by the above.

Images