JP5691124B2 - Precious metal plating method on titanium substrate and separator for polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a method for plating a noble metal on a titanium or titanium alloy substrate having high adhesion without requiring a complicated operation. The present invention also relates to a polymer electrolyte fuel cell separator made of titanium or a titanium alloy base material plated with noble metal.

  Examples of the material for the separator of the polymer electrolyte fuel cell include graphite, a stainless steel material, a material obtained by plating a noble metal on the surface of a stainless steel substrate, and a material obtained by plating a noble metal on a titanium substrate. Properties required for the separator material include: a. High corrosion resistance, b. Low contact resistance, c. Light weight, d. The manufacturing cost is low. A material obtained by plating noble metal or the like on titanium or a titanium alloy satisfies the above-mentioned required characteristics and is suitable as a material for a fuel cell separator.

  Titanium or titanium alloy itself has a high contact resistance to form a stable oxide film on the surface, and cannot be used as a separator as it is.

  As a means for reducing the contact resistance of titanium or a titanium alloy, there is a method in which the surface of these materials is coated with a noble metal that does not easily corrode. However, electroplating on an active metal such as titanium is generally difficult and there is a problem that the plating is easily peeled off.

  Therefore, in Patent Document 1 below, if a noble metal of titanium or a titanium alloy substrate having irregularities on the surface is plated, and this plating surface is only the arithmetic average roughness (Ra) of the plating surface on the titanium or titanium alloy substrate, However, it is disclosed that when the surface area substitution value is in an appropriate range, the adhesion between the plating and the base material is improved, and the plating is difficult to peel off. Specifically, the arithmetic average roughness (Ra) of the surface obtained by enlarging the surface 1000 times with an electron beam three-dimensional roughness analyzer is in the range of 0.05 to 0.8 μm and (measurement) The surface area substitution value defined as (surface area of sample obtained from) / (longitudinal x lateral of measurement range) is disclosed as 1.003 to 1.08.

  By the way, it is known that gold is agglomerated in making ultra-thin gold plating on titanium. However, in this case, since gold is formed on the smooth base titanium, aggregation and dropping easily occur due to oxidation behavior. In the case where agglomeration and dropping occur, the internal resistance increases in the fuel cell, which greatly affects the power generation characteristics. If it tried to avoid it, there existed a problem which had to improve the adhesiveness of gold | metal | money by giving a fixed thickness to a plating layer, ie, the usage-amount of gold | metal | money had to be increased.

  Then, the aggregation / dropping caused by the oxidation behavior originates from the fact that titanium is an easily oxidizable material. In other words, even if titanium and gold are alloyed “temporarily” during the manufacturing process, they are energetically stabilized by some disturbance (such as high-temperature water mode). ) Had a problem in some cases.

JP 2007-103075 A

  It is an object of the present invention to provide a titanium or titanium alloy base material that is suitable for a metal plate material used for a separator of a polymer electrolyte fuel cell and is difficult to peel noble metal plating.

  The present inventors have found that the above problems can be solved by applying noble metal plating to a titanium or titanium alloy substrate by a specific simple method, and have reached the present invention.

  That is, first, the present invention is an invention of a method for plating a noble metal on a titanium or titanium alloy substrate, wherein the first step in which an easily oxidizable compound is present on the titanium or titanium alloy substrate, and the first step. A second step of plating a noble metal on the obtained titanium or titanium alloy substrate, and a noble metal-plated titanium or titanium alloy substrate obtained in the second step in an air atmosphere at 200 to 600 ° C., a rate of temperature increase; And a third step of baking at 10 to 20 ° C./min.

  By the steps of the present invention, fine irregularities are formed on the titanium or titanium alloy substrate. This uneven structure inhibits aggregation of noble metal particles such as gold. A strong oxide layer is formed before power generation evaluation, and changes after power generation evaluation are eliminated. The uneven structure improves hydrophilicity and is suitable as a fuel cell separator.

As the easily oxidizable compound used in the present invention, one or more selected from nitrogen compounds, boron compounds, and carbon compounds are preferably exemplified. These easily oxidizable compounds may be dispersed as a powder simultaneously with the introduction of N ₂ gas when rolling or annealing titanium or a titanium alloy, or used as a lubricating oil when rolling or annealing. It can be present on a titanium alloy substrate. In these cases, it is preferable in terms of the process in order not to increase the number of steps according to the present invention. Further, if a nitrogen compound, a carbon compound, or a boron compound is intentionally left on the surface layer during rolling / annealing, these easily oxidizable compounds can be present without going through the above-described method.

  The noble metal used in the present invention is not particularly limited, but one or more selected from gold, platinum, and palladium are preferably exemplified in consideration of the use as a fuel cell separator.

  The baking in the third step is performed in an air atmosphere, but is particularly preferably performed in a steam saturated air atmosphere.

  Secondly, the present invention is a polymer electrolyte fuel cell separator comprising a titanium or titanium alloy base material plated with a noble metal by the above method.

  According to the present invention, it is possible to obtain a titanium base material or a titanium alloy base material that is suitable for use as a separator for a polymer electrolyte fuel cell and in which noble metal plating hardly peels off.

The present invention is a noble metal plating technique on a titanium or titanium alloy substrate, and can be applied to gold plating and other noble metal plating. However, as a mandatory requirement,
1) A material that easily oxidizes exists on titanium. For example, metal nitride, metal boride, and metal carbide are exemplified, and metal nitride is particularly preferable.
2) The plated product is a noble metal that actively promotes oxidation of titanium. For example, Pt and Pd are preferably exemplified.
3) Baking is baking in a normal atmosphere (with air), and the temperature ranges from 200 ° C to 600 ° C. A steam saturated atmosphere is preferable, and it is particularly preferable to expose to the state when the temperature is 320 ° C. or higher. Moreover, the starting rate from normal temperature is 10-200 degreeC / min, Preferably, it is 20 degrees C / min or less.
These reasons are derived from the competitive reaction between gold aggregation and base oxidation.

  According to the present invention, the underlying titanium substrate forms a fine titanium relief structure having a width of 10 nm to 1000 nm and a depth of 10 to 100 nm. According to the conventional technology (patent) of titanium as far as the present inventors have investigated, there is no uneven processing method with such an aspect ratio in the 10 nm region.

  Inhibition of gold aggregation due to the uneven structure (gold anchor effect due to the uneven structure) occurs. A major feature of the present invention is that it exhibits inhibition of gold aggregation. For example, fuel cell power generation is exposed to high temperature corrosive liquid. In that case, when the adjacent gold itself tries to recombine with the underlying titanium, the movement is restricted by the uneven titanium. Moreover, even if it tends to drop out, it has an effect that it does not drop out easily because it is shaped like a sword mountain.

  An initial oxidation is formed by baking in a normal atmosphere. It is possible to form a strong oxide layer before power generation evaluation with nitrogen compounds and carbon compounds that are easily oxidized, and to eliminate changes after power generation evaluation.

  According to the present invention, an improvement in hydrophilicity due to the uneven structure is achieved. According to the Winzel equation, it is known that the hydrophilicity improves as the specific surface area increases. In this case, the surface area is increased by about 3.3 times when calculated using only the base titanium, and a significant improvement in hydrophilicity is expected. As a result, in the case of the conventional method described in, for example, the method described in JP-A-2006-97088, the contact angle of 50 degrees is 5.3 degrees, which is a significant improvement.

  The titanium or titanium alloy substrate used in the present invention is pure titanium or a titanium alloy or plate containing one or more alloy elements such as Ni, Al, Cr, V, Sn, and Ru. Since titanium or titanium alloy has good corrosion resistance, it is less likely to corrode inside the fuel cell in a corrosive atmosphere and is suitable as a separator material. Moreover, since it is lightweight, it is advantageous when the fuel cell is mounted on a vehicle.

  However, since titanium or titanium alloy has a high contact resistance, it is necessary to reduce the contact resistance in order to be used as a separator material for a polymer electrolyte fuel cell. Therefore, electroplating such as precious metal plating is applied to the titanium or titanium alloy base material. At that time, in order to ensure the adhesion of the plating, minute irregularities are formed on the surface of the base material, and "anchor effect" is achieved. Giving it is an effective means. According to the present invention, minute irregularities are formed on the surface of the titanium or titanium alloy base material, so that the plating film on the titanium or titanium alloy has sufficient adhesion.

  In a polymer electrolyte fuel cell separator material in which titanium or a titanium alloy substrate is plated, the thickness of the plating film is manufactured in the range of 0.005 to 1.50 μm. If the plating film is less than 0.005 μm, the corrosion resistance of the material is insufficient, and if it exceeds 1.50 μm, the effects such as corrosion resistance are saturated, while the manufacturing cost is increased, which is uneconomical. Furthermore, Preferably, it is 0.01-0.1 micrometer.

  The noble metal plating film formed on the surface of the titanium or titanium alloy substrate is one or more selected from Au, Pt, Pd, Rh, and Ru. These plating films are suitable for fuel cell separator materials because they do not corrode even in a corrosive atmosphere in the fuel cell and have low contact resistance. The plating film can be formed by electroplating using a known plating solution or a commercially available plating solution.

Examples of the present invention will be described below.
Using titanium material (Nippon Steel) rolled product (0.1 mm) as a base material,
1) Nitrogen annealing (1 Pa pressure) was performed at 800 ° C. for 10 minutes.
2) It was plated (before baking) by the method of JP-A-2006-97088.
3) Baking was performed at 200 ° C. (temperature increase rate: 20 ° C./min) in an air atmosphere.
4) Baking was performed at a temperature of 280 ° C. (temperature increase rate of 20 ° C./min) in an air atmosphere (the same applies to water vapor injection).
FIG. 1 shows a cross-sectional photograph.

  The titanium base material or titanium alloy base material obtained by the present invention from which noble metal plating is difficult to peel off is suitable for a separator of a polymer electrolyte fuel cell.

The cross-sectional photograph of a plating part is shown.

Claims (4)

A noble metal plating method to titanium or titanium alloy substrate, on the titanium or titanium alloy substrate, carbide titanium down or we selected to be formed by using titanium nitride emissions and lubricating oil is formed by nitrogen annealing A first step in which at least one kind is present, a second step of plating a noble metal on the titanium or titanium alloy substrate obtained in the first step, and a noble metal plated titanium or titanium obtained in the second step And a third step of baking the alloy substrate at 200 to 600 ° C. in a air atmosphere at a rate of temperature increase of 10 to 20 ° C./min.   The plating method according to claim 1, wherein the noble metal is at least one selected from gold, platinum, and palladium.   The plating method according to claim 1 or 2, wherein the air atmosphere in the third step is a steam saturated air atmosphere.   A separator for a polymer electrolyte fuel cell comprising a titanium or titanium alloy base material plated with a noble metal according to any one of claims 1 to 3.

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