Separator for fuel batteries and fuel battery

Abstract

Separator for fuel cell batteries, including: a metal base material; and a tin oxide film formed on the surface of the metal base material, where the tin oxide film is zirconium-encompassing tin oxide, an elemental ratio of zirconium to tin (Zr / Sn) in the range of 0.10 to 0.70, and where the zirconium content in the tin oxide film is 11.2 atomic % or more and 16.0 atomic % or less.

Description

Technical area

[0001] The present disclosure relates to a separator for fuel batteries and a fuel battery using the same. State of the art

[0002] A fuel battery cell of a polymer electrolyte fuel battery is provided with a membrane electrode assembly (MEA) comprising an ion-permeable electrolyte membrane; and an anode-side catalyst layer (electrode layer) and a cathode-side catalyst layer (electrode layer) sandwiching the electrolyte membrane. A gas diffusion layer (GDL) for supplying a fuel gas or an oxidizing gas and collecting electricity generated by an electrochemical reaction is formed on both sides of the membrane electrode assembly. The membrane electrode assembly with the GDL disposed on both sides is called a MEGA (Membrane Electrode and Gas Diffusion Layer Assembly), and the MEGA is sandwiched between a pair of separators. The MEGA is a power generation section of a fuel battery.When the gas diffusion layer does not exist, the membrane electrode assembly functions as a power generation section of a fuel battery.

[0003] ZB proposes a separator described below, as a separator for fuel cell batteries, in patent H08-185870 A. This separator comprises: a base substrate consisting of cermet, comprising a chromium-containing heat-resistant metal and a ceramic; and a protective film of a metal oxide covering an area of ​​the base substrate, the area being exposed to the cathode gas so that the area does not come into contact with the cathode gas. Furthermore, patent H08-185870 A discloses tin oxide as an example of this metal oxide. Citation listPatent literature

[0004] Patent Literature 1: JP H08-185870 A Summary of the inventionTechnical problem

[0005] According to the JP H08-185870 A fuel cell battery separator, the reduction in electrical power output of a fuel cell can be suppressed by reducing the diffusion of chromium to the cathode using a protective metal oxide film. Furthermore, tin oxide has relatively high electrical conductivity and can therefore reduce contact resistance. However, when tin oxide is used as the protective metal oxide film, it allows fluoride ions to penetrate. These fluoride ions, having penetrated the tin oxide film, form a complex with a metal in the base substrate, such as iron (Fe), and dissolve the metal in the base substrate. When the metal, such as Fe, is dissolved, it acts as a catalyst to produce hydrogen peroxide (Fenton reaction), and there is a possibility that a solid electrolyte membrane will decompose.If the solid electrolyte membrane decomposes, the electrical energy generation capacity of a fuel cell battery is naturally reduced.

[0006] Furthermore, in a fuel cell battery, a fluoride ion is produced from, for example, a solid electrolyte membrane containing a fluoride-based electrolyte resin, such as a perfluorosulfonic acid-based polymer or the like. Therefore, if, for example, Fe is dissolved from a base substrate due to the fluoride ion, an Fe ion acts as a catalyst to produce hydrogen peroxide, and this hydrogen peroxide further degrades the solid electrolyte membrane of the fluorine-based electrolyte resin. As the solid electrolyte membrane of a fluorine-based electrolyte resin degrades, a fluoride ion continues to be produced, and therefore, corrosion progresses.

[0007] Therefore, the present invention provides a separator for fuel cell batteries with low contact resistance and excellent corrosion resistance in highly corrosive environments, such as environments in the presence of a fluoride ion. Solution to the problem

[0008] Illustrative aspects of the present embodiment are as follows. (1) A separator for fuel batteries comprising: a metal base material; and an oxide film formed on the surface of the metal base material, wherein the tin oxide film is a zirconium-containing tin oxide film and the element ratio of zirconium to tin (Zr / Sn) is in a range of 0.10 to 0.70. (2) The separator for fuel batteries according to (1), wherein a content of zirconium in the tin oxide film is 3.0 atomic% or more and 16 atomic% or less. (3) A fuel battery comprising the fuel battery separator according to (1) or (2). (4) The fuel cell battery according to (3), further comprising a solid electrolyte membrane. (5) The fuel cell battery according to (4) wherein the solid electrolyte membrane comprises a fluorine-based electrolyte resin. Advantageous effects of the invention

[0009] The present disclosure can provide a separator for fuel cell batteries with low contact resistance and excellent corrosion resistance in highly corrosive environments, such as environments in the presence of a fluoride ion. Brief description of the drawings Fig. Figure 1 is a cross-sectional view of the main part of the fuel battery stack provided with the fuel battery separator according to the present embodiment; Fig.2 is an enlarged cross-sectional view near the surface of the separator for fuel batteries according to the present embodiment; and Fig. Figure 3 is a graph showing the relationship between the element ratio (Zr / Sn) (abscissa) and the contact resistance or the amount of dissolved Fe (ordinate) with respect to the results of Examples and Comparative Examples. Description of the embodiments

[0010] The present embodiment includes a fuel cell separator comprising: a metal base material; and an oxide film formed on the surface of the base material, wherein the tin oxide film is a zirconium-containing tin oxide film, and the elemental ratio of zirconium to tin (Zr / Sn) is in the range of 0.10 to 0.70. Furthermore, the present embodiment includes a fuel cell comprising the fuel cell separator according to the present embodiment.

[0011] The present embodiment is described below with reference to the accompanying drawings. As an example, a case is described below where the fuel cell battery separator according to the present embodiment is used in a fuel cell battery installed in fuel cell vehicles and the like. However, the present disclosure is not limited to such an example.

[0012] Fig. 1 is a diagram of a cross-sectional view of the main part of a fuel battery stack (fuel battery) 10. As shown in Fig.As illustrated in Figure 1, a plurality of cells (individual cells) 1, each representing a basic unit, are stacked in the fuel battery stack 10. Each cell 1 is a polymer electrolyte fuel battery that generates electromotive force through an electrochemical reaction between an oxidizing gas (e.g., air) and a fuel gas (e.g., hydrogen). The cell 1 is provided with: a MEGA 2; and separators (fuel battery separators) 3, each of which is in contact with the MEGA 2, so that the cell 1 separates the MEGA 2. Furthermore, in the present embodiment, the MEGA 2 is held between a pair of separators 3, 3.

[0013] The MEGA 2 is obtained by integrating a membrane electrode assembly (MEA) 4 and a gas diffusion layer 7, 7 arranged on both surfaces of the MEA 4. The MEA 4 comprises an electrolyte membrane 5 and a pair of electrodes 6, 6 connected to hold the electrolyte membrane 5 between them. The electrolyte membrane 5 comprises a proton-conducting ion-exchange membrane formed with a solid polymer material. The electrode 6 is formed with, for example, a porous carbon material on which a catalyst, such as platinum, is carried. The electrode 6 arranged on one surface of the electrolyte membrane 5 is an anode, and the electrode 6 on the other surface is a cathode. The gas diffusion layer 7 is formed with, for example, an electrically conductive element with gas permeability, the electrically conductive element comprising a carbon-porous body, such as...Carbon paper or carbon cloth, or metal-porous bodies, such as a metal grid or foam metal.

[0014] MEGA 2 is an energy generation section of the fuel battery 10, and separator 3 is in contact with the gas diffusion layer 7 of MEGA 2. Furthermore, if gas diffusion layer 7 is absent, the membrane electrode assembly 4 is an energy generation section, and in this case, separator 3 is in contact with the membrane electrode assembly 4. Accordingly, the energy generation section of the fuel battery 10 includes the membrane electrode assembly 4 and is in contact with separator 3.

[0015] The separator 3 is a plate-shaped member comprising, as a base material, a material excellent in electrical conductivity, gas impermeability, and the like. One surface of the separator 3 is adjacent to the gas diffusion layer 7 of the MEGA 2, and the other surface is adjacent to an adjacent separator 3.

[0016] Each separator 3 is formed in a wave shape. Regarding the shape of the separator 3, the wave shape forms an isosceles trapezoid, the apex portion of the wave is flat, and both ends of the apex portion have the same angle to be angular. That is, the shape of each separator 3 is approximately the same regardless of whether viewed from a surface side or a back side. The apex portion of the separator 3 is in surface contact with one of the gas diffusion layers 7 of the MEGA 2, and the apex portion of the other separator 3 is in surface contact with the other gas diffusion layer 7 of the MEGA 2.

[0017] A gas flow passage 21 defined between the gas diffusion layer 7 and the separator 3 on one side of the electrode (namely, the anode) 6 is a passage through which the fuel gas is circulated, and a gas flow passage 22 defined between the gas diffusion layer 7 and the separator 3 on the side of the other electrode (namely, the cathode) 6 is a passage through which the oxidant gas is circulated. When the fuel gas is supplied into the gas flow passage 21, which is one of the gas flow passages opposite each other through the cell 1, and the oxidant gas is supplied into the gas flow passage 22, the electrochemical reaction occurs in the cell 1 to generate electromotive force.

[0018] Furthermore, one cell 1 and another cell 1 are arranged adjacent to it such that electrode 6, acting as an anode, and electrode 6, acting as a cathode, are opposite each other. Additionally, an apex section on the back side of separator 3 is arranged along electrode 6 as the anode of one cell 1, and another apex section on the back side of separator 3 is arranged along electrode 6 as the cathode of another cell 1. The cells 1 are in surface contact with each other. Water is circulated as a cooling medium for cooling the cells 1 in a gap 23 defined between the separators 3 and 3, which are in surface contact between two adjacent cells 1.

[0019] As in Fig.As illustrated in Figure 2, the separator 3 includes a metal base material 31. Examples of the base material include titanium or stainless steel. Furthermore, both surfaces of the separator 3 (namely, the surface on the side in contact with the gas diffusion layer 7 and the surface on the side in contact with the adjacent separator 3) are covered with a tin oxide film 32.

[0020] The film thickness of the tin oxide film is in a range of 10 to 300 nm in some embodiments. When the film thickness of the tin oxide film is 10 nm or more, the effect induced by the tin oxide film can be sufficiently achieved. Furthermore, when the film thickness of the tin oxide film is 300 nm or less, the residual stress of the tin oxide film can be suppressed, and therefore, exfoliation of the tin oxide film from the base material can be suppressed.

[0021] In the present embodiment, the tin oxide film can be provided on at least one surface of the base material, but corrosion resistance is particularly required in the section where the gas diffusion layer and the separator are in contact with each other. Therefore, in some embodiments, the tin oxide film is formed on the surface of the base material on at least one section that is in contact with the gas diffusion layer.

[0022] The tin oxide film is tin oxide containing zirconium. Zirconium has the property of adsorbing fluoride ions, and therefore the permeation of fluoride ions through the tin oxide film can be suppressed by allowing the zirconium to be incorporated into the film. Furthermore, the elemental ratio of zirconium to tin (Zr / Sn) in the tin oxide film is in the range of 0.10 or more and 0.70 or less. If the elemental ratio (Zr / Sn) is less than 0.1, the dissolution of a metal (such as Fe) from the base material becomes significant, and therefore sufficient corrosion resistance cannot be achieved. Moreover, if the elemental ratio (Zr / Sn) exceeds 0.70, contact resistance becomes high, and therefore the electrical energy generation performance of the fuel cell is reduced.It is concluded that this is because an electrically conductive network structure of highly electrically conductive tin oxide is broken by zirconium when the element ratio (Zr / Sn) becomes high. In some embodiments, the element ratio (Zr / Sn) is 0.20 or more, 0.30 or more, or 0.40 or more from the perspective of corrosion resistance. In some embodiments, the element ratio (Zr / Sn) is 0.60 or less, or 0.50 or less from the perspective of contact resistance.

[0023] In some embodiments, the zirconium content in the tin oxide film is 3.0 atomic % or more and 16.0 atomic % or less, 8.0 atomic % or more and 14.0 atomic % or less, or 10.0 atomic % or more and 12.0 atomic % or less.

[0024] The tin oxide film can contain antimony (Sb) in addition to tin and zirconium. When the tin oxide film contains antimony, the pentavalent antimony is substituted by a quadrivalent tin facet in the tin oxide crystal lattice. Therefore, the concentration of the carrier material on the tin oxide facet is high, thus improving the electrical conductivity (specific electrical conductivity) of the tin oxide film. This can reduce the contact resistance of the separator on which the tin oxide film is formed, and the internal resistance of the fuel cell stack can be reduced. In some embodiments, the antimony content in the tin oxide film is 0.2 atomic percent or more and 10 atomic percent or less, 0.3 atomic percent or more and 5.0 atomic percent or less, or 0.4 atomic percent or more and 4.0 atomic percent or less.

[0025] The tin oxide film may comprise an additional element other than the above-described tin, zirconium, and antimony. Examples of the additional metal include bismuth and tellurium. In some embodiments, the content of the additional metal in the tin oxide film is 1.0 atomic % or less, 0.5 atomic % or less, or 0.1 atomic % or less.

[0026] Incidentally, the concentrations of metal elements in the base material can be measured by performing composition analysis using, for example, an X-ray photoelectron spectroscopy (XPS) device.

[0027] The process for forming a tin oxide film on a base material is not particularly limited. For example, the film can be formed by a physical vapor deposition (PVD) process using sputtering, vacuum vapor deposition, ion vapor deposition, ion plating, and the like. Alternatively, the tin oxide film can be formed on the surface of a base material by plasma sputtering and the like, using a calcined body obtained by calcining a mixture of tin oxide and zirconium oxide particles as a target. In this case, a tin oxide film with a desired element ratio (Zr / Sn) can be obtained by adjusting the amounts of tin oxide and zirconium oxide.

[0028] Furthermore, if the tin oxide film is formed by sputtering, the sputtering process can be carried out in an oxygen gas atmosphere, an inert gas atmosphere, or a vacuum atmosphere (in a pressure-reduced atmosphere). In some embodiments, the tin oxide film is formed in an inert gas atmosphere or in a vacuum atmosphere (in a pressure-reduced atmosphere).

[0029] As described above, the separator for fuel batteries according to the present embodiment has a low contact resistance, which is due to tin oxide with high electrical conductivity, and also has excellent corrosion resistance in highly corrosive environments, such as environments in the presence of a fluoride ion, because zirconium suppresses the passage of the fluoride ion.

[0030] In a fuel cell battery, a fluoride ion is easily produced from a fluorine-based electrolyte resin, such as a perfluorosulfonic acid-based polymer, as described above. Therefore, if a fuel cell battery uses a solid electrolyte membrane comprising a fluorine-based electrolyte resin, the fuel cell battery separator according to the present embodiment becomes particularly useful. Examples of fluorine-based electrolyte resins include perfluorosulfonic acid-based polymers, and specific examples include Nafion (trade name, manufactured by E.I. du Pont de Nermours and Company), Flemion (trade name, manufactured by AGC Inc.), and Aciplex (trade name, manufactured by Asahi Kasei Corp.). Among these, Nafion (trade name, manufactured by E.I. du Pont de Nermours and Company) can be used appropriately because it has excellent proton conductivity. Examples

[0031] The present embodiment is described below with reference to the examples. [Example 1]

[0032] A test piece corresponding to a separator was produced according to the method described below. First, a 0.1 mm thick SUS316 plate was fabricated as the metal base material for the separator. The metal base material was then placed in a vacuum chamber, argon gas was introduced into the chamber under vacuum conditions, and voltage was applied to generate argon ions. An oxide film on the surface of the metal base material was removed by the argon ions.

[0033] A calcined body, obtained by calcining a mixture of 89.1 parts by mass of tin oxide particles, 8.2 parts by mass of zirconium oxide particles, and 2.7 parts by mass of antimony oxide particles, was then positioned as a target in the vacuum chamber. Sputtering was performed using this calcined body as the target to form a tin oxide film on the surface of the metal base material. Specifically, the metal base material was first positioned facing the target, and the vacuum chamber was evacuated to create a vacuum atmosphere (a pressure-reduced atmosphere). Argon gas was then introduced into the vacuum chamber as the sputtering gas, and the target material was deposited onto the metal base material by applying a voltage in a state that heated the metal base material and allowing an argon ion to collide with the target.Furthermore, a preload was applied between the target and the metal base material. This resulted in the formation of a tin oxide film with a thickness of 100 nm on the surface of the metal base material. A test specimen E1 was thus produced. [Example 2]

[0034] A test piece E2 was produced in the same manner as in Example 1, except that a calcined body obtained by calcining a mixture of 80.8 parts by mass of the tin oxide particles, 16.8 parts by mass of the zirconium oxide particles and 2.4 parts by mass of the antimony oxide particles was used as the target. [Example 3]

[0035] A test piece E3 was produced in the same manner as in Example 1, except that a calcined body obtained by calcining a mixture of 72.2 parts by mass of the tin oxide particles, 25.7 parts by mass of the zirconium oxide particles and 2.2 parts by mass of the antimony oxide particles was used as the target. [Example 4]

[0036] A test piece E4 was prepared in the same manner as in Example 1, except that a calcined body obtained by calcining a mixture of 63.2 mass parts of the tin oxide particles, 34.9 mass parts of the zirconium oxide particles, and 1.9 mass parts of the antimony oxide particles was used as the target. [Comparison example 1]

[0037] A test piece C1 was prepared in the same manner as in Example 1, except that a calcined body obtained by calcining a mixture of 96.8 mass parts of the tin oxide particles and 3.2 mass parts of the antimony oxide particles (zirconium oxide particles were not included) was used as the target. [Comparative example 2]

[0038] A test piece C2 was prepared in the same manner as in Example 1, except that a calcined body obtained by calcining a mixture of 54.1 mass parts of the tin oxide particles, 44.3 mass parts of the zirconium oxide particles, and 1.6 mass parts of the antimony oxide particles was used as the target. <Messung des Elementverhältnisses (Zr / Sn)>

[0039] The contents of tin (Sn) and zirconium (Zr) were each measured using an X-ray spectroscopic instrument (QuanteraSXM manufactured by PHI) to calculate the element ratio of zirconium to tin (Zr / Sn) for the tin oxide films of specimens E1 to E4 and C1 to C2 prepared in Examples 1 to 4 and Comparative Examples 1 to 2. The results are shown in Table 1.

[0040] Furthermore, the levels of antimony (Sb) contained in the tin oxide film were measured using an X-ray spectroscopic device and it was found to be 3.0 atomic % for all test pieces. <Korrosionsbeständigkeitstest>

[0041] A corrosion resistance test (constant potential corrosion test) according to the procedure for high-temperature electrochemical corrosion tests of metallic materials in molten salts (JIS / Z2294) of Japanese Industrial Standards was performed on specimens E1 to E4 and C1 to C2 in Examples 1 to 4 and Comparative Examples 1 to 2. In an open atmospheric apparatus, each specimen was immersed in an aqueous sulfuric acid solution, the temperature of which was set to 80°C. NaF was dissolved in the solution to achieve a fluoride ion concentration of 3,000 ppm. Under these conditions, the specimen was subjected to corrosion by electrically connecting a counter electrode consisting of a platinum plate to the specimen (sample electrode), thereby generating a potential difference of 0.9 V between the counter electrode and the sample electrode.The potential of the test piece was kept constant using a reference electrode. The test time was set to 100 hours. Subsequently, the iron dissolved in the aqueous sulfuric acid solution was measured by ICP atomic emission spectroscopy (inductively coupled plasma atomic emission spectroscopy). The results are shown in Table 1. <kontaktwiderstandtest>

[0042] The contact resistance was measured for each test piece after the corrosion resistance test using the following method. Carbon paper (Toray Industries, Inc., TGP-H120, 0.5 mm thick) corresponding to a diffusion layer of a power generation section of a fuel battery was applied to the surface of the tin oxide film of each test piece, and a gold-plated copper plate was applied thereon to hold the carbon paper between the test piece and the copper plate. In addition, to measure only the contact resistance between the tin oxide film and the carbon paper, the other surface of the test piece (the surface where no film was formed) was also brought into contact with a gold-plated copper plate, so that contact resistance was not generated between these elements. Then, a constant load (0.98 MPa) was applied to the surface of the test piece using a measuring device.In this state, a current was applied from a power source, while the current was adjusted by an ammeter to maintain a constant current flowing in the test piece. The applied voltage to the test piece was measured by a voltmeter to calculate the contact resistance between the tin oxide film on the test piece and the carbon paper. The results are shown in Table 1. [Table 1] Amount of Zr (atomic %) Amount of Sn (atomic %) Element ratio (Zr / Sn) Amount of dissolved Fe (ng / ml) Contact resistance (mΩ·cm 2 ) Comparison example 1 0 30,2 0 210 11 Example 1 3,5 31,0 0,11 95 11 Example 2 7,2 28,5 0,25 23 11 Example 3 11,2 25,8 0,43 9 11 Example 4 15,5 23,0 0,68 <5 12 Comparison example 2 20,0 20,0 1,00 <5 23 <betrachtung>

[0043] Fig. Figure 3 illustrates a graph showing the relationship between the element ratio (Zr / Sn) (abscissa) and the contact resistance or the amount of dissolved Fe (ordinate). As in Fig. Figure 3 shows that when the elemental ratio (Zr / Sn) is small, i.e., when the amount of zirconium is low, the amount of dissolved Fe becomes large. This is assumed to be because the amount of zirconium in the tin oxide film was less than what is needed to prevent Fe from forming a complex in the metal base material due to the fluoride ion. Furthermore, when the elemental ratio (Zr / Sn) is large, i.e., when the amount of zirconium is high, the contact resistance becomes high. This is concluded to be because the electrically conductive network of highly conductive tin oxide, which is necessary for exhibiting high electrical conductivity, is disrupted by the zirconium.From the above description, it can be seen that a separator for fuel cell batteries with low contact resistance and corrosion resistance can be obtained if the element ratio (Zr / Sn) is 0.10 to 0.70.

[0044] A device for providing a fuel cell battery separator with low contact resistance and excellent corrosion resistance under highly corrosive environments, such as environments in the presence of fluorides, includes a fuel cell battery separator comprising a metal base material and a tin oxide film formed on the surface of the metal base material, wherein the tin oxide film is a zirconium-containing tin oxide and has an elemental ratio of zirconium to tin (Zr / Sn) in the range of 0.10 to 0.70. Description of the characters 1 cell 2 MEGA (power generation section) 3 Separator (separator for fuel batteries) 4 Membrane Electrode Unit (MEA) 6 electrode 7 Gas diffusion layer 10 fuel battery stacks (fuel battery) 21, 22 Gas flow passage 31 Metal base material 32 Tin oxide film< / betrachtung> < / kontaktwiderstandtest>

Claims

[1] Separator for fuel batteries, comprising: a metal base material; and a tin oxide film formed on the surface of the metal base material, wherein the tin oxide film is tin oxide comprising zirconium, an element ratio of zirconium to tin (Zr / Sn) is in a range of 0.10 to 0.70, and wherein a content of zirconium in the tin oxide film is 11.2 atomic% or more and 16.0 atomic% or less. [2] A fuel battery separator according to claim 1, wherein the tin oxide film additionally comprises antimony (Sb). [3] A fuel battery comprising the separator for fuel batteries according to claim 1 or 2. [4] The fuel battery according to claim 3, further comprising a solid electrolyte membrane. [5] The fuel battery according to claim 4, wherein the solid electrolyte membrane comprises a fluorine-based electrolyte resin.

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