Separation plate for fuel cell with metal coating layer, and method for manufacturing the same.

Abstract

According to one aspect of the present invention, there is provided a method for manufacturing a metal separator for a fuel cell for a vehicle, the method comprising the steps of: preparing a base material; applying a coating agent containing platinum (Pt) and an electrolyte to the base material to form a discontinuous coating film; and heat treating the base material with the coating film.

Description

Technical Field

[0001] The present invention relates to a separator for a fuel cell with a metal coating layer and a method for manufacturing the same, and more particularly, to a separator for a fuel cell with a discontinuous coating layer utilizing platinum and noble metals and a method for manufacturing the same.

Background Art

[0002] A fuel cell used for hydrogen electricity is utilized as a power source for generating electricity through an electrochemical reaction between a reaction gas and a catalyst. The stack of the fuel cell has a structure in which components such as a membrane electrode assembly (MEA), a separator (bipolar plate), a gasket, a current collector, and an end plate are connected. Among them, the membrane electrode assembly (MEA) has a structure in which a gas diffusion electrode (GDE) composed of a catalyst layer and a gas diffusion layer (GDL) is in contact with both sides through a polymer electrolyte membrane.

[0003] The metal separator for a fuel cell is one of the components constituting the main body of the fuel cell, electrically contacts the hydrogen electrode of a unit cell and the air electrode of an adjacent cell, and hydrogen and air are supplied into the interior of each electrode through the fluid flow channels on both sides of the separator. Therefore, the metal separator of the fuel cell plays a central role in collecting and transmitting the electricity generated by the electrochemical reaction, conducting electricity, discharging the water formed by the electrochemical reaction, and heat management inside the battery.

[0004] While materials with excellent electrical conductivity, such as stainless steel, titanium alloy, aluminum alloy, or polymer composites, are used as the base material for the separator plate, due to the properties of metals, when the separator plate is exposed for a long period of time to the high temperature and humidity operating environment of a vehicle fuel cell, corrosion is accelerated, and the metal oxides formed on the surface act as an electrical insulator, leading to a decrease in conductivity or contamination of the catalyst, resulting in a reduction in the overall performance of the fuel cell.

[0005] To prevent such problems, research has been ongoing to ensure corrosion resistance and improve conductivity by forming discontinuous coating films containing various precious metal materials, including polymers, carbon, gold (Au), platinum (Pt), ruthenium (Ru), and iridium (Ir), on the surface of the base material of metal separation plates. In practice, coating films using gold (Au) nanocoating films are considered the mainstream. However, the persistent rise in the price of gold (Au) has created a need for the development of alternative coating films.

[0006] While experiments and studies have already shown that discontinuous platinum (Pt) coating films can be formed on the surface of the base material, the reality is that the results demonstrating process efficiency and significant implications for the application of platinum-based coating films are insufficient.

[0007] When discontinuous coating films are applied, a portion of the surface of the base material of the separator plate is directly exposed to the outside. However, for future fuel cell stacks that require high output and long durability, significant resources are needed to ensure performance through the uniformity of the coating material and to verify the stability of the plated electrode body. Despite this, there is a demand for coating technologies that possess excellent conductivity and chemical stability even when used in harsh environments.

[0008] Related technology is Korean Published Patent No. 10-2015-0138105 (Publication date: April 7, 2017, Title of invention: Coating composition for metal separation plate of solid oxide fuel cell, and method for manufacturing the same). [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The problem that this invention aims to solve is to provide a metal separation plate for a vehicle fuel cell that has excellent corrosion resistance, contact resistance, and production efficiency, as well as a method for manufacturing the same. [Means for solving the problem]

[0010] A method for manufacturing a metal separation plate for a vehicle fuel cell according to one aspect of the present invention may include the steps of: preparing a base material; applying a coating agent containing platinum (Pt) and further containing at least one selected from the group consisting of gold (Au), ruthenium (Ru), iridium (Ir), ruthenium oxide (RuO2), and iridium oxide (IrO2), and an electrolyte to the base material to form a discontinuous coating film; and heat-treating the base material with the coating film.

[0011] In one embodiment, the base material may be stainless steel plate, titanium, or aluminum.

[0012] In one embodiment, the coating film formation step may consist of one of the following: electrolytic plating, electroless plating, or PVD (photovoltaic coating) process.

[0013] In one embodiment, the platinum (Pt) contained in the coating agent may be chloroplatinic acid (H2PtCl6) or potassium chloroplatinate (K2PtCl6).

[0014] In one embodiment, the heat treatment step can be carried out in a temperature range of 80 to 600°C and a time range of 10 to 180 minutes.

[0015] In one embodiment, the heat treatment step can be carried out under any one of the following conditions: a vacuum, air, or an oxygen atmosphere.

[0016] The metal separator plate for a vehicle fuel cell according to another aspect of the present invention can be the metal separator plate for a vehicle fuel cell manufactured by the method described in any of the above embodiments.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a metal separator plate for a fuel cell that is excellent in corrosion resistance and contact resistance and is also excellent in production efficiency, and a method for manufacturing the same.

Brief Description of the Drawings

[0018] [Figure 1] It is a process flow diagram schematically showing a method for manufacturing a separator plate for a fuel cell according to a specific example of the present invention. [Figure 2] It is a diagram schematically showing a platinum coating step according to an embodiment and a comparative example of the present invention. [Figure 3] It is a diagram schematically showing a heat treatment step according to an embodiment and a comparative example of the present invention. [Figure 4] It is a schematic diagram for explaining a specimen and a measurement position for measuring the contact resistance of an embodiment and a comparative example of the present invention.

Modes for Carrying Out the Invention

[0019] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. The present invention can be embodied in various different forms and is not limited to the embodiments described in this specification. Throughout this specification, the same or similar components are denoted by the same reference numerals. Also, detailed descriptions of known functions and configurations that may obscure the gist of the present invention are omitted.

[0020] FIG. 1 is a flow diagram used in a method for manufacturing a metal separator plate for a vehicle fuel cell according to a specific example of the present invention. The manufacturing method according to the present invention includes a base material forming step S110, a coating layer forming step S120 on the surface of the base material, and a heat treatment step S130.

[0021] Base material formation step S110

[0022] The steel material of the metal separator plate of the vehicle fuel cell is not particularly limited as long as it is a metal or non-ferrous metal used for the metal separator plate, and stainless steel, titanium, aluminum, etc. can be used. For example, SUS300 series and 400 series stainless steels, and Grade 1 titanium are preferable in terms of elongation and durability.

[0023] Step S120: Forming a coating layer on the surface of the base material.

[0024] FIG. 2 is a diagram schematically showing the step of forming a coating film containing discontinuous platinum on the surface of the base material.

[0025] When the vehicle fuel cell is exposed to a high-temperature and high-humidity operating environment for a long time, metal oxides that gradually have an adverse effect on the conductivity of the fuel cell will be formed on the surface of the base material. Therefore, in the present invention, in order to provide a fuel cell that is excellent in both corrosion resistance and conductivity, a discontinuous coating layer is formed on the surface of the base material.

[0026] In order to form a coating layer that is excellent in both corrosion resistance and conductivity, various noble metals including gold (Au), platinum (Pt), ruthenium (Ru), and iridium (Ir) are usually used. However, in the present invention, according to the purpose, a coating layer containing platinum (Pt) is formed on the surface of the base material, so that a coating layer of the metal separator plate of the vehicle fuel cell that is excellent in corrosion resistance and conductivity can be formed.

[0027] Specifically, in the coating layer forming step, a coating film is formed by using a coating material and an electrolytic solution and applying a current at a certain coating temperature. The coating material can be used without particular limitation as long as it contains platinum (Pt) and can be used for the coating material. In particular, chloroplatinic acid (H2PtCl6) or potassium chloroplatinate (K2PtCl6) is desirable for a stable and efficient process.

[0028] Platinum (Pt) and additional precious metal series coatings used as coating materials may utilize nanoparticles having a size of 10 nm to 1 μm, and within this range, they can have a discontinuous coating film on the surface of the base material with reduced density.

[0029] As the electrolyte, an acidic electrolyte may be used, for example, a sulfuric acid-based or hydrochloric acid-based electrolyte may be used, and in particular, H2SO4 or HClO4 is preferred in terms of efficient chemical reaction during the platinum coating layer formation process.

[0030] The content of the coating material and electrolyte can be varied depending on the specific embodiment and the required amount of Pt deposition and coating density, but for example, chloroplatinic acid (H2PtCl6) or potassium chloroplatinate (K2PtCl6) can be used (1 × 10 -4 ~1) M and perchloric acid (HClO4) or sulfuric acid (H2SO4) (1 × 10 -2 ~1) It can be used in a mixture in the range of M, and in particular, when used with 2 mM to 0.1 M of chloroplatinic acid (H2PtCl6) or potassium chloroplatinate (K2PtCl6) and 0.1 M to 0.5 M of perchloric acid (HClO4) or sulfuric acid (H2SO4), excellent corrosion performance and contact resistance can be obtained. More preferably, it can be used with 10 mM to 0.05 M of chloroplatinic acid (H2PtCl6) or potassium chloroplatinate (K2PtCl6) and 0.2 M to 0.3 M of perchloric acid (HClO4) or sulfuric acid (H2SO4).

[0031] Within the above range, the relative content of the coating material to the electrolyte should be within the range of 1 to 10 times the unit molar content of the electrolyte to form a coating film with excellent corrosion resistance and contact resistance. Below this range, sufficient platinum (Pt) coating may not be achieved, and exceeding this range reduces the efficiency of the process.

[0032] As a coating material, 5 × 10¹⁴ chloroplatinic acid (H2PtCl6) or potassium chloroplatinate (K2PtCl6) -3When used in quantities less than 5 × 10, it becomes difficult to secure a sufficient amount of platinum (Pt) deposition, and the electrolyte is 5 × 10 -3 When used in amounts less than a certain limit, it becomes difficult to ensure sufficient returns.

[0033] In addition to the platinum-containing chloroplatinic acid or potassium chloroplatinate mentioned above, coating materials composed of noble metal series components such as gold (Au), ruthenium (Ru), iridium (Ir), ruthenium oxide (RuO2), and iridium oxide (IrO2) may be used as coating materials. When further coating materials are used, in addition to sulfuric acid-based or hydrochloric acid-based electrolytes, hydrofluoric acid-based or sulfuric acid-based electrolytes may also be used depending on the chemical properties of the added substances.

[0034] The coating step can be performed at room temperature, but heating improves reactivity, so it is carried out in the range of 25 to 80°C, for example. In particular, when carried out in the range of 40 to 60°C, the efficiency of the process is reconsidered, and excellent corrosion performance and contact resistance are achieved, especially in the range of 50 to 60°C.

[0035] During coating, the applied current is 5-60 mA / cm². 2 Performing the procedure within this range is preferable in order to suppress undercoating or overcoating of platinum (Pt) while preventing surface oxidation due to overcurrent, particularly 10-20 mA / cm². 2 Performing the procedure within this range is preferable in terms of surface stability of the base material and excellent performance of the coating film.

[0036] The surface coating process for the base material is not particularly limited as long as it is a commonly used method, but for example, it can be selected from electroplating, electroless plating, or PVD methods, and the efficiency of the process can be increased when these methods are used. In particular, electroplating is preferable in terms of uniform coating properties and mass production in the coating and manufacturing of both electrodes of the separator plate.

[0037] Heat treatment step S130

[0038] Figure 3 is a schematic diagram showing the step of heat-treating the base material with the coated film.

[0039] In the base material surface coating step, discontinuous platinum (Pt) and other material coating layers are formed on the surface of the base material, and a portion of the base material surface is exposed to the outside. Therefore, in order to ensure excellent corrosion current and contact resistance throughout the entire separation plate, an oxide film formation step S130 is performed through a heat treatment process.

[0040] Specifically, the temperature of the heat treatment process varies depending on the oxide film formation characteristics of the base material, but it can be performed in a temperature range of, for example, 80 to 600°C. In particular, for stainless steel base materials, the oxide film formation rate and efficiency are excellent in the temperature range of 170 to 230°C, and for titanium base materials, in the temperature range of 300 to 500°C.

[0041] The duration of the heat treatment process also varies depending on the properties of the base material, but it can be carried out for, for example, 10 to 180 minutes. In particular, when carried out for 30 to 60 minutes, the corrosion current and contact resistance performance of the oxide film are excellent.

[0042] While the heat treatment process can be carried out in general air, performing it in a low-oxygen, vacuum, or nitrogen atmosphere improves the efficiency of oxide film formation and the performance of the formed oxide film. In particular, performing the heat treatment process in a low-oxygen atmosphere prevents excessive oxide film formation, resulting in excellent contact resistance performance, which is preferable for maintaining coat adhesion performance.

[0043] Metal separator plate for vehicle fuel cells

[0044] According to the method for manufacturing the metal separator plate of the vehicle fuel cell, the metal separator plate of the fuel cell can maintain excellent corrosion resistance and electrical conductivity for a long period of time, even in a high-temperature and high-humidity operating environment.

[0045] Therefore, a metal separation plate for a vehicle fuel cell having excellent corrosion resistance and electrical conductivity can be completed as described above by going through a base material coating step using a platinum (Pt)-containing coating material and an electrolyte, and a heat treatment step, resulting in a base material, a discontinuous coating film on its surface, and an oxide film formed in the areas where the coating film is not formed. [Examples]

[0046] Examples and Comparative Examples

[0047] The base material forming step and coating step were performed using the base material, coating material and electrolyte component systems, applied current and temperature shown in Table 1 below. The discontinuous coated base material was then subjected to a heat treatment step under the conditions shown in Table 2 to produce specimens of the examples and comparative examples, respectively.

[0048] Specifically, in comparison with the embodiments of the present invention, in the coating material formation step, Comparative Example 1 differed in the amount of coating material, Comparative Example 5 differed in the amount of electrolyte, and Comparative Examples 2 and 6 differed in the applied current, as shown in Table 1. In the heat treatment step, Comparative Examples 3 and 6 differed in the heat treatment time, and Comparative Examples 4 and 8 differed in the heat treatment temperature, as shown in Table 2, to produce metal separation plate specimens.

[0049] [Table 1]

[0050] [Table 2]

[0051] Measurement of contact resistance

[0052] Interfacial contact resistance (ICR) measurements were performed on the examples and comparative examples. Figure 4 is a schematic diagram showing the structure of the test piece for measuring the contact resistance of the metal separation plate of the vehicle fuel cell according to the present invention, and the measurement position of the comparative test piece (dummy). Prior to the actual measurement, two gas diffusion layers (GDLs) 120 and one current collector 130 were formed on each side of the metal separation plate (bipolar plate, bp) 110 of each comparative example and example, and after the test pieces were fabricated, the contact resistance between the separation plate and the gas diffusion layer (GDL) was measured at two points R1 and R2, and the resistance between the separation plate and the gas diffusion layer was calculated using the following formula. To measure R2, a dummy specimen was fabricated by stacking three gas diffusion layers 120 with the metal separator removed, and then stacking current collectors 130 on both sides. When measuring the contact resistance, a pressure gauge (Instron 68SC5) was used on the dummy specimen to measure 50-100 N / cm². 2 The pressure was applied.

[0053]

number

[0054]

number

[0055]

number

[0056]

number

[0057] In the above formula, bp represents the metal separator, GDL represents the gas diffusion layer, cc represents the current collector, and S represents the separator-GDL reaction area.

[0058] Measurement of corrosion performance

[0059] Specimens were prepared from the metal separation films of the above examples and comparative examples, and short-term corrosion resistance evaluations of the base material and surface treatment layer were performed on each specimen. The potentiodynamic polarization method was used, and the test conditions are as shown in Table 3 below. HIOKI's 3541 precision resistance measuring equipment was used for current application and resistance measurement.

[0060] [Table 3]

[0061] The measured interfacial contact resistance and corrosion performance results are shown in Table 4 below.

[0062] [Table 4]

[0063] For the comparative examples and examples, steering rack bars were manufactured, cold draw tests were performed, and the presence or absence of cracks in the products was visually observed. The results are shown in Table 4.

[0064] Referring to Tables 1-4, it was found that in Examples 1-5 and Comparative Examples 1-4 using stainless steel base materials, and in Examples 6-10 and Comparative Examples 5-8 using titanium base materials, each example was superior to the comparative examples in terms of corrosion performance and interfacial contact resistance.

[0065] Specifically, when the amount of electrolyte or coating material falls outside the scope of the present invention, a noticeable decrease in performance was observed in both interfacial contact resistance and corrosion performance compared to other embodiments using the same base material. Furthermore, when the applied current and coating temperature deviate from a certain range, the performance of interfacial contact resistance decreases. This means that appropriate coating process conditions greatly influence the achievement of the objectives of the present invention.

[0066] In the heat treatment step, both the heat treatment temperature and heat treatment time were found to affect the interfacial contact resistance and corrosion performance, respectively. In particular, it was confirmed that the heat treatment time had a significant impact on the interfacial contact resistance, and the heat treatment temperature had a significant impact on the corrosion performance.

[0067] The above description has focused on embodiments of the present invention, but various modifications and variations can be made by those skilled in the art. Such modifications and variations can be considered to fall within the scope of the present invention as long as they do not depart from the scope of the present invention. Therefore, the scope of the rights of the present invention should be determined by the claims described below. [Industrial applicability]

[0068] This invention can be utilized in the fields of fuel cells and fuel cell separators, and can improve the reliability and competitiveness of products in those fields.

Claims

1. Steps to prepare the base material; The aforementioned base material, A step of applying a coating agent containing platinum (Pt) and an electrolyte to form a discontinuous coating film; and, A step of heat-treating a base material with a coated film; Includes, The heat treatment step is carried out in a temperature range of 80 to 600°C and a time range of 30 to 60 minutes. A method for manufacturing a metal separation plate for a vehicle fuel cell, characterized in that the platinum (Pt) contained in the coating agent is chloroplatinic acid (H₂PtCl₆) or potassium chloroplatinate (K₂PtCl₆).

2. The coating agent is gold (Au), ruthenium (Ru), iridium (Ir), ruthenium oxide (RuO ２ ), and iridium oxide (IrO ２ A method for manufacturing a metal separation plate for a vehicle fuel cell according to claim 1, further comprising at least one selected from the group consisting of ).

3. The method for manufacturing a metal separation plate for a vehicle fuel cell according to claim 1, wherein the base material is a stainless steel plate, titanium, or aluminum.

4. The method for manufacturing a metal separation plate for a vehicle fuel cell according to claim 1, wherein the coating film formation step is one of electrolytic plating, electroless plating, or a PVD process.

5. The method for manufacturing a metal separator plate for a fuel cell according to claim 1, characterized in that the heat treatment step is carried out under one of the following conditions: a vacuum, in air, or in an oxygen atmosphere.

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