JP6856871B2 - Manufacturing method of separator parts for polymer electrolyte fuel cells and separator parts for polymer electrolyte fuel cells - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention relates to a separator material used mainly for vehicles such as vehicles, ships, and aircraft, or used in companies and general households, particularly a polymer electrolyte fuel cell, and a solid height using the material. The present invention relates to a method for manufacturing a separator component for a molecular fuel cell and a separator component for a polymer electrolyte fuel cell.

In recent years, most of the fuel cells mounted as a power source for automobiles and buses and the fuel cells provided as a power source for general households are polymer electrolyte fuel cells (PEFC or PEMFC). Polymer electrolyte fuel cells are smaller and lighter than other fuel cells such as phosphoric acid fuel cells, and are relatively easy to operate at startup, so they are widely used in various industrial fields. It's progressing. Therefore, the separator constituting the polymer electrolyte fuel cell is required to have various properties such as corrosion resistance in acid and moldability during processing, in addition to good electrical conductivity.

For example, Patent Document 1 discloses an austenitic stainless steel sheet having an average crystal grain size in the range of 1 to 40 μm as a stainless steel fuel cell separator. It is explained that by defining the average crystal grain size of the austenitic stainless steel sheet within a certain range, appropriate dimensional accuracy and moldability can be ensured.

Further, Patent Document 2 also discloses a chemical composition of an austenitic stainless steel material as a separator material for a fuel cell as in Patent Document 1. In particular, the oxygen (O) concentration in the steel material is required to be relatively low from the viewpoint of suppressing the formation of oxides, and in particular, preventing the bond with sulfur (S) in the steel material. It is explained that this makes it possible to realize the oxidation resistance and electrical conductivity of the fuel cell separator material in a high temperature atmosphere.

Japanese Unexamined Patent Publication No. 2004-339569 Japanese Unexamined Patent Publication No. 11-293941

However, in the stainless steel separator for PEFC (solid polymer fuel cell) disclosed in Patent Document 1, only the corrosion resistance of stainless steel in a simulated PEFC environment (low pH or atmosphere of fluoride ions) is disclosed. What about the influence of inclusions (oxides and sulfides) in steel, which is the starting point of corrosion of ordinary stainless steel, the oxygen concentration in steel, and the corrosion resistance of stainless steel separators in the actual PEFC environment? Not disclosed.

Further, in the stainless steel separator for PEFC (solid polymer fuel cell) disclosed in Patent Document 2, the influence of oxides and sulfides in the steel, which is the starting point of corrosion, has a high temperature oxidation atmosphere of 873 K or more. It is limited to the corrosion resistance of the stainless steel in the above, and the corrosion resistance of the stainless steel near the operating temperature of PEFC of 353 K and the strength and workability when the stainless steel is thinned are not disclosed at all.

Therefore, an object of the present invention is to provide a fuel cell separator component having desired electrical conductivity and corrosion resistance required as a separator for a fuel cell application.

In order to solve the above-mentioned problems, the present inventor is a separator component for a polymer electrolyte fuel cell made of stainless steel, and the crystal grain size of the stainless steel is 3.0 μm or less with respect to the whole. The ratio shall be 60% or more. When the stainless steel is an austenitic stainless steel, it is used as a separator component for a polymer electrolyte fuel cell in which the amount of oxygen contained in the stainless steel is 30 ppm or less in mass%.

Further, a polymer electrolyte fuel cell in which styrene-butadiene rubber (hereinafter referred to as “SBR”) containing titanium nitride particles (hereinafter referred to as “TiN”) is adhered to the surface of the separator component for the polymer electrolyte fuel cell described above. It can also be used as a separator.

As a method for manufacturing a separator component for a polymer electrolyte fuel cell, SBR containing TiN particles may be brought into close contact with the surface of stainless steel heated in a temperature range of 80 ° C. or higher and 220 ° C. or lower in an atmosphere of normal pressure. it can. Further, the surface of the stainless steel may be heated stepwise by heating the surface of the stainless steel in a temperature range of 80 ° C. or higher and 100 ° C. or lower and then raising the temperature to a temperature range of 150 ° C. or higher and 220 ° C. or lower. Absent.

By using the separator component for a polymer electrolyte fuel cell according to the present invention, it is possible to achieve both the desired electrical conductivity and corrosion resistance required as a separator for a fuel cell application. Further, in the method for manufacturing a separator component for a polymer electrolyte fuel cell of the present invention, SBR containing TiN particles adheres to a material (stainless steel) in a normal pressure atmosphere and at a heating temperature of about 200 ° C., so that comparison is made. It has the effect of being able to manufacture separator parts at low cost.

It is a power generation test result up to 500 hours in each cell which separately incorporated the materials 1 and 2 of the present invention and the materials 1 to 3 of the comparative materials in Example 1. It is an SEM photograph which shows the state which SBR containing TiN particles is attached to the surface of stainless steel. It is a power generation test result up to 500 hours in each cell which separately incorporated the materials 1 to 4 of the present invention and the resin impregnated graphite material (comparative material 4) as a comparative material in Example 2.

An example of an embodiment of the present invention will be described. The separator component for the polymer electrolyte fuel cell of the present invention is made of stainless steel, and as the steel type, for example, austenitic stainless steel or ferritic stainless steel can be applied.

Regarding the crystal grain size of stainless steel, the ratio of the crystal grain size of 3.0 μm or less to the whole is set to 60% or more. The reason for specifying the ratio of the crystal grain size of stainless steel is that when the ratio of the crystal grain size of 3.0 μm or less to the whole is less than 60%, the characteristics of processing the raw material stainless steel into a separator are improved ( This is because it becomes easier to process), but the strength of the material as a material for the separator parts decreases, or it is necessary to design the mold in consideration of springback in the processing process.

Further, when the steel grade of the stainless steel is austenitic stainless steel, the amount of oxygen (O) contained in the stainless steel is 30 ppm or less in mass%. The reason why the upper limit of the amount of oxygen contained in austenitic stainless steel is set to 30 ppm is that when the amount of oxygen in the austenitic stainless steel exceeds 30 ppm, oxide-based inclusions in the austenitic stainless steel increase, so that the separator component This is because the corrosion resistance of the stainless steel is lowered, which in turn leads to a decrease in the power generation efficiency of the separator.

As a method of modifying the surface of stainless steel, which is the material (raw material) of the separator parts, carbon or nitride coating by a noble metal plating method such as gold plating, a CVD method or a PVD method, and chromium nitride by a thermal nitriding method are precipitated. There is a way to make it. However, since the apparatus and process used for modifying the surface are complicated, in the present invention, SBR containing (containing) TiN particles is attached to the surface of stainless steel by a simple electrophoretic electrodeposition method. ..

As a result, it is possible to reduce the contact resistance with the gas diffusion layer (hereinafter referred to as "GDL") serving as the electrode substrate. Here, the electrophoretic electrodeposition method is a state in which two electrodes are immersed in a dispersion bath in which conductive particles are dispersed, and a voltage is applied between these two electrodes to make them conductive on one of the electrodes. It refers to a method of adsorbing and depositing particles.

For the dispersion bath used in the above-mentioned electrophoresis electrodeposition method, for example, 2-propanol can be selected as the dispersion medium, TiN particles having an average particle size of 50 nm as the conductive particles, and SBR as the rubber-based binder. .. After adding TiN particles at a ratio of 0.050 wt% and SBR at a ratio of 0.074 wt% to the dispersion medium, the dispersion bath is a mixture of TiN particles and SBR sufficiently dispersed in the dispersion medium by ultrasonic vibration. can do.

Since the material of the present invention (2nd level) and the comparative material (3rd level) were incorporated into separate cells to perform a power generation test as a separator, the test results will be described with reference to the drawings. As the test material used in this test, first, as the material of the present invention, a material in which crystal grains were finely divided with respect to SUS316L steel in which the amount of oxygen contained in the stainless steel was 30 ppm or less in weight% was used (the material of the present invention). The amount of oxygen in 1-2 is 22 ppm). As a result of refining the crystal grains of the material 1 of the present invention as shown in Table 2, the ratio of the crystal grains having an average crystal grain size of 1.5 μm and a crystal grain size of 3.0 μm or less to the total crystal grains is occupied. Is 96% of the test material. The material 2 of the present invention is a test material having an average crystal grain size of 2.9 μm and a ratio of crystal grains having a crystal grain size of 3.0 μm or less to 63% of all crystal grains.

On the other hand, the crystal grains are finer than that of the SUS316L steel in which the amount of oxygen contained in the test material (hereinafter referred to as "comparative material 1") and the stainless steel, which are not refined, is 30 ppm or more in weight%. The test materials that were not converted (hereinafter referred to as "comparative material 2") and the test materials in which the crystal grains were refined (hereinafter referred to as "comparative material 3") were designated as comparative materials 1 to 3. Table 1 shows the chemical composition (unit: weight%) of the test material used in this test, Table 2 shows the average crystal grain size of the test material, and Table 3 shows the specifications and test conditions of the test material. ..

The thickness (plate thickness) of the test material was 0.07 mm for the materials 1 and 2 of the present invention and the comparative material 3, and 0.10 mm for the materials 1 and 2.

The groove depth of the separator component for any of the materials 1 and 2 of the present invention and the comparative materials 1 to 3 is the groove depth of the flow path bottom plate so that the groove depth of the flow path forming material and the flow path bottom plate is 0.5 mm. A serpentine flow path was formed on the bottom plate of the flow path by machining. Further, in this power generation test, the surface where the flow path forming material and the flow path bottom plate are in contact with each other is gold-plated on the flow path forming material side to reduce the contact resistance.

FIG. 1 shows the results of a power generation test up to 500 hours in each cell in which the materials 1 and 2 of the present invention and the materials 1 and 3 of the comparative materials were separately incorporated. The change over time of the cell voltage during the power generation test during this test is linearly approximated from the graph shown in FIG. 1, and the cell voltage and average cell voltage decrease rate at the start of power generation of the materials 1 and 2 of the present invention and the comparative materials 1 to 3 Asked. As a result, the cell voltage at the start of power generation is about 0.64 V for the material 1 of the present invention, about 0.67 V for the material 2 of the present invention, about 0.62 V for the materials 1 and 2, and about 0.65 V for the material 3. there were. Comparing the average cell voltage reduction rates, the material 1 of the present invention was 0.23 × 10 ^-4 Vh ^-1 , the material 2 of the present invention was 0.25 × 10 ^-4 Vh ^-1 , and the material 1 was 0.19. × 10 ^-4 Vh ^-1 , the comparative material 2 was 0.29 × 10 ^-4 Vh ^-1 , and the comparative material 3 was 0.46 × 10 ^-4 Vh ^-1 .

Comparing the voltage reduction rates of Comparative Materials 1 and 2, Comparative Material 1 subjected to the oxygen reduction treatment was superior to Comparative Material 2 not subjected to the oxygen reduction treatment. The materials 1 and 2 of the present invention, which have been subjected to oxygen reduction treatment and crystal grain microfabrication on the comparative material 1 and the comparative material 2 for the purpose of making the stack compact by thinning the separator, have not been subjected to the oxygen reduction treatment. The voltage reduction rate was superior to that of the comparative material 3.

Further, after the power generation test, each cell was disassembled, and the surfaces of the separators of the materials 1 and 2 of the present invention and the materials 1 to 3 were observed with an optical microscope. As a result, no corrosion marks were observed on the surface of the separator component of the materials 1 and 2 of the present invention on both the anode side and the cathode side. Similarly, no corrosion marks were observed on the surfaces of the separator components on the anode side of Comparative Materials 1 to 3. On the other hand, the entire surface of the separator component on the cathode side of the comparative materials 2 and 3 was uniformly corroded.

This is considered to be one of the causes due to the influence of oxide-based inclusions in the stainless steel material. That is, the oxygen-reducing treatment of the materials 1 and 2 of the present invention and the comparative material 1 reduced the oxide-based inclusions in the stainless steel, which is the starting point of corrosion, to about 50% of that of the comparative material 2. As a result, it is considered that the elution of impurities in the stainless steel was suppressed during the power generation test, and the corrosion resistance of the materials 1 and 2 of the present invention and the comparative materials 1 and the comparative materials 2 and 3 were different.

From the above, the material of the present invention (plate thickness = 0.07 mm) can obtain the same power generation efficiency while maintaining the corrosion resistance even if the plate thickness is thinner than that of the comparative material (plate thickness = 0.10 mm). , A larger number of separators can be accommodated in a cell stack of a predetermined capacity. As a result, it becomes possible to output a high voltage as a fuel cell. Alternatively, the capacity of the fuel cell stack for outputting the same voltage can be reduced.

Next, the test materials (hereinafter referred to as “materials 3 and 4”) obtained by subjecting the surfaces of the materials 1 and 2 of the present invention to electrodeposition treatment were incorporated into separate cells to perform a power generation test. At the same time, a power generation test of a cell in which a resin-impregnated graphite material (comparative material 4) was incorporated as a separator was also performed, and the test results will be described with reference to the drawings.

The materials 3 and 4 of the present invention have improved contact resistance with GDL by adhering SBR containing TiN particles to the surface of stainless steel by an electrophoretic electrodeposition method as a surface treatment. Specifically, an SBR dispersion bath containing TiN particles with respect to the materials 1 and 2 of the present invention (dispersion medium: 2-propanol, conductive particles: TiN (average particle size is 50 nm) 0.050 wt%, rubber binder: A predetermined voltage was applied to the counter electrode using SUS304 steel while being immersed in the SBR binder (0.074 wt%).

Next, the materials 1 and 2 of the present invention are heated in the air at a temperature of 353 K (80 ° C.), then heated to 453 K (180 ° C.) and heated again to be dried. 4 was prepared. FIG. 2 shows an example (SEM photograph) of a state in which SBR containing TiN particles is attached to the surface of stainless steel.

The test conditions of this example were the same as those of Example 1 under the conditions shown in Table 2. FIG. 3 shows the results of power generation tests up to 500 hours in each cell in which the materials 1 to 4 of the present invention and the comparative material 4 were separately incorporated.

As a result of linearly approximating the change with time of the cell voltage during the present power generation test from the graph shown in FIG. 3 and comparing the cell voltage at the start of power generation of the cell incorporating the materials 1 to 4 of the present invention and the comparison material 4 as separators. The material 1 of the present invention was about 0.64 V, the material 2 of the present invention was about 0.67 V, the material 3 of the present invention was about 0.66 V, the material 4 of the present invention was about 0.66 V, and the comparative material 4 was 0.66 V. ..

By surface-treating the materials 1 and 2 of the present invention, the cell voltage at the start of power generation became equivalent to that of the comparative material 4 (resin-impregnated graphite material) as a benchmark. After the power generation test, each cell was disassembled and the surface of the separator was observed with an optical microscope. As a result, the SBR having TiN particles on the surfaces of the materials 3 and 4 of the present invention did not peel off during the power generation test, and no corrosion on the surface of the stainless steel was confirmed.

Claims (3)

Solid height of austenitic stainless steel in which the amount of oxygen contained is 30 ppm or less in mass% and the ratio of crystal grains having a crystal grain size of 3.0 μm or less is 60% or more with respect to all crystal grains. Separator component for polymer electrolyte fuel cell, characterized in that styrene butadiene rubber containing titanium nitride particles is provided on the surface of the separator material for molecular electrolyte fuel cell. The method for manufacturing a separator component for a polymer electrolyte fuel cell according to claim 1, wherein the surface of the austenitic stainless steel is heated in a temperature range of 80 ° C. or higher and 220 ° C. or lower in an atmosphere of normal pressure. , A method for manufacturing a separator component for a polymer electrolyte fuel cell, which comprises adhering the styrene butadiene rubber to the surface of the austenitic stainless steel. The surface of the austenitic stainless steel is heated in a temperature range of 80 ° C. or higher and 100 ° C. or lower, and then the surface of the austenitic stainless steel is heated stepwise by raising the temperature to a temperature range of 150 ° C. or higher and 220 ° C. or lower. The method for manufacturing a separator component for a polymer electrolyte fuel cell according to claim 2, wherein the separator component is for a solid polymer fuel cell.

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