Fuel cell separator

Abstract

Fuel cell separator comprising a metal substrate and a surface layer formed on a surface of the substrate, wherein the surface layer comprises an antimony-containing tin oxide film in an outermost surface of the same, the antimony-containing tin oxide film has a value (%) which represents the orientation of the (200) plane and is calculated according to expression (1): [Mathematical expression 1] Peak intensity (200) − level 21 Peak intensity (110) − level 100 + peak intensity (101) − level 75 + peak intensity (200) − level 21 × 100 where the values ​​of the respective peak intensities are obtained by means of X-ray diffraction, has a value of 35 or greater, the antimony-containing tin oxide film comprises a first layer of a tin oxide film or an antimony-containing tin oxide film, which is formed relatively close to the surface of the substrate, and a second layer of an antimony-containing tin oxide film on the first layer, and wherein, if both the first layer and the second layer comprise an antimony-containing tin oxide film, the first layer is produced at a lower temperature at which the oxidation of the substrate is suppressed, and the second layer is produced at a higher temperature at which the crystallinity is improved.

Description

BACKGROUND Technical area

[0001] The invention relates to a fuel cell separator and a manufacturing process for the separator. State of the art

[0002] A fuel cell is a battery cell in which a flammable chemical substance such as hydrogen, carbon monoxide, or hydrocarbons, or a fuel containing such a substance, is used as the active material. An oxidation reaction of the chemical substance or fuel is carried out electrochemically to directly convert the energy change from the oxidation process into electrical energy. High energy conversion efficiency can be expected.

[0003] For example, Japanese patent publication (Kokai) JP H08-185870A (1996) describes a fuel cell separator formed by applying a protective film of Sb-doped tin oxide to a separator substrate consisting of a cermet, a refractory metal, and a ceramic. According to the patent publication (Japanese patent publication (Kokai) JP H08-185870A (1996)), the separator exhibits high density, high strength, satisfactory electrical conductivity, excellent heat resistance, and corrosion resistance. Furthermore, it possesses satisfactory separator properties, such as adjustable coefficients of thermal expansion and no negative effect on the cathode. However, the fuel cell separator has the following problem: Since the contact resistance of the intermediate layer, for example,If the conductivity of a carbon material is not satisfactorily reduced, its conductivity is insufficient.

[0004] Japanese patent publication (Kokai) JP 2013-077436A describes a separator consisting of a substrate formed from a metallic material and a thin film of a conductive metal oxide formed on the surface of the substrate. According to the patent publication (Japanese patent publication (Kokai) JP 2013-077436A), the conductive metal oxide preferably contains at least one element selected from the group consisting of tin, tantalum, niobium, titanium, tungsten, and zirconium. The separator formed from a metallic material (metal separator) presents the following problem: Metal ions are released from the metal separator by corrosion, flow into an electrolyte film, and react with a peroxide produced within the fuel cell to generate radicals that damage the electrolyte film, thereby accelerating its degradation.The patent publication (Japanese patent publication (Kokai) JP 2013 - 077 436 A) describes how the dissolution of metal ions can be suppressed by the separator. According to the patent publication (Japanese patent publication (Kokai) JP 2013 - 077 436 A), the thin film layer can be formed by a physical vapor deposition process (sputtering, ion plating) or a chemical vapor deposition process. However, the physical vapor deposition process has problems: a long processing time and the use of expensive equipment, as the processing is carried out under reduced atmospheric pressure. The chemical vapor deposition process has the following problem: high raw material costs, as the raw material must be vaporized under normal or reduced pressure.

[0005] The Japanese patent publication (Kokai) JP H10 - 53 418 A (1998) describes that its tin oxide film (TO), which is selectively formed in the (200) plane, is formed on a glass substrate by a thermal spray decomposition technique using a solution of an organic solvent (dibutyltin diacetate); and furthermore, a tin oxide film (ATO or FTO) containing an element such as antimony or fluorine, wherein the number of outermost shell electrons of the same is one greater than that of tin or oxygen, is formed by a thermal spray decomposition technique using a solution of an organic solvent containing an element such as antimony or fluorine, wherein the number of outermost shell electrons of the same is one greater than that of tin or oxygen.According to the patent publication (Japanese patent publication (Kokai) JP H10 - 53 418 A (1998)), the thin tin oxide film exhibits high alignment, low resistance, and excellent transparency. However, the thin tin oxide film suffers from high raw material costs, as dibutyltin diacetate, used as a raw material in the thermal spray decomposition process, is expensive.

[0006] Furthermore, the published patent applications JP 2017 - 199 535 A and US 2009 / 0 181 306 A1 disclose fuel cell separators from the prior art.

[0007] As described above, a separator must also be suitable for use in fuel cells and exhibit sufficiently high conductivity. Furthermore, a fuel cell separator with excellent conductivity and an economical manufacturing process are required. SUMMARY

[0008] The invention provides a fuel cell separator which has excellent conductivity and a manufacturing method for the separator.

[0009] The present inventors carried out investigations for the purpose of solving the aforementioned problems. Consequently, they found that the conductivity of the separator to be obtained can be improved by forming a surface layer on a metal substrate, wherein the surface layer has an antimony-containing tin oxide film on its outermost surface, in which the value representing the orientation of the (200) plane, calculated in accordance with expression (1), is a predetermined value or more. The present inventors also found that the antimony-containing tin oxide film can be formed by using a solution containing inexpensive raw materials, e.g., tin chloride and antimony chloride, by specifically adjusting the conditions.

[0010] In particular, the invention is summarized as follows: [1] A fuel cell separator comprises a metal substrate and a surface layer formed on a surface of the substrate, wherein the surface layer contains an antimony-containing tin oxide film in its outermost surface, the antimony-containing tin oxide film has a value (%) which represents the orientation of the (200) plane and is calculated according to expression (1): [Mathematical expression 1] Peak intensity of the (200) level 21 Peak intensity of the (110) level 100 + Peak intensity of the (101) level 75 + Peak intensity of the (200) level 21 × 100 where the respective peak intensity values ​​are obtained by means of X-ray diffraction, has a value of 35 or greater, the antimony-containing tin oxide film comprises a first layer of a tin oxide film or an antimony-containing tin oxide film, which is formed relatively close to the surface of the substrate, and a second layer of an antimony-containing tin oxide film on the first layer, and wherein, if both the first layer and the second layer comprise an antimony-containing tin oxide film, the first layer is produced at a lower temperature at which the oxidation of the substrate is suppressed, and the second layer is produced at a higher temperature at which the crystallinity is improved. [2] The fuel cell separator according to point [1], wherein the value (%) representing the orientation of the (200) plane and calculated according to expression (1) is 70 or greater. [3] The fuel cell separator according to point [1] or [2], wherein the antimony content in the first layer is 0 atomic %, or 0.2 atomic % to 10 atomic %, and the antimony content in the second layer is 0.2 atomic % to 10 atomic %. [4] The fuel cell separator according to one of points [1] to [3], wherein the film thickness of the first layer is 10 nm to 100 nm and the film thickness of the second layer is 40 nm to 250 nm. [5] A method for producing the fuel cell separator according to any one of points [1] to [4], comprising atomizing or atomizing a solution containing tin chloride and antimony chloride by ultrasonic waves and applying the resulting mist-like solution to a substrate heated to 300 °C to 600 °C in order to form an antimony-containing tin oxide film, wherein, if both the first layer and the second layer comprise an antimony-containing tin oxide film, the first layer is produced at a lower temperature at which the oxidation of the substrate is suppressed, and the second layer is produced at a higher temperature at which the crystallinity is improved.

[0011] The fuel cell separator of the invention exhibits excellent conductivity. According to the invention's method for manufacturing a fuel cell separator, the fuel cell separator can be produced cost-effectively. BRIEF DESCRIPTION OF THE DRAWING Fig. Figure 1 is a graph showing the results of a conductivity evaluation test. DETAILED DESCRIPTION

[0012] The invention relates to a fuel cell separator comprising a metal substrate and a surface layer formed on a surface of the substrate, characterized in that the surface layer contains an antimony-containing tin oxide film in its outermost surface, and the antimony-containing tin oxide film has a value (%) which represents the orientation of the (200) plane and is calculated according to expression (1): [Mathematical expression 2] Peak intensity of the (200) level 21 Peak intensity of the (110) level 100 + Peak intensity of the (101) level 75 + Peak intensity of the (200) level 21 × 100 wherein the respective peak intensities obtained by X-ray diffraction are 35 or greater (hereinafter also referred to as the separator of the invention). With regard to the separator of the invention, the surface layer of the same comprises an antimony-containing tin oxide film in which a value (%) representing the orientation of the (200) plane is a predetermined value or greater, and therefore the contact resistance of the intermediate layer with, for example, a carbon material is reduced.

[0013] The metal substrate is not particularly limited as long as it is conventionally used in fuel cell separators. Examples of metal substrates include titanium, iron, and aluminum; austenitic stainless steels such as SUS304, SUS305, SUS310, SUS316, and SUSMX7; and ferritic stainless steels such as SUS430. Titanium is used in some embodiments for its pitting corrosion resistance and resistance to metal solutions.

[0014] The separator of the invention comprises a surface layer formed on the surface of a metal substrate. This surface layer contains a specific antimony-containing tin oxide film on its outermost surface. The specific antimony-containing tin oxide film consists of a tin oxide film or an antimony-containing tin oxide film (a first layer) formed relatively close to the surface of the substrate, and an antimony-containing tin oxide film (a second layer) on top of the first layer. Alternatively, the specific antimony-containing tin oxide film can consist of a single antimony-containing tin oxide film (not part of the invention).The former case is preferred insofar as the alignment of the (200) plane can be improved by the presence of the first layer, which thereby improves performance; whereas the latter case is preferred insofar as the manufacturing can be carried out in a number of few steps and production costs and time can be reduced.

[0015] In some embodiments, the antimony-containing tin oxide film, which is contained in the outermost surface of the surface layer, has a value (%) representing the orientation of the (200) plane, calculated according to expression (1), of 35 or greater to obtain high conductivity. In some embodiments, the antimony-containing tin oxide film, which is contained in the outermost surface of the surface layer, has a value (%) representing the orientation of the (200) plane, calculated according to expression (1), of 70 or greater to obtain high conductivity. The upper limit of the value (%) representing the orientation of the (200) plane, which is not specifically restricted, may, for example, be 95 or less, or 90 or less. The separator of the invention has low contact resistance due to the high orientation of the (200) plane and possesses high conductivity.In contrast, for example, if the crystal of the antimony-containing tin oxide film is randomly aligned or oriented, the (110) plane and the (101) plane exhibit high contact resistance, resulting in degraded electrical properties. The value representing the orientation of the (200) plane can be measured by the method described, for example, in the following section.<Auswertungsverfahren für den Film> , “(3) XRD analysis” is described.

[0016] In expression (1), the peak intensity values ​​of the (200) plane, (110) plane, and (101) plane are obtained by X-ray diffraction. The values ​​by which the peak intensity values ​​are divided correspond to the I(f) values ​​of the respective surfaces of JCPDS map no. 41-1445. Similarly, the values ​​(%) representing the orientation of the (110) plane and the (101) plane are calculated according to expressions (2) and (3) below: [Mathematical expression 3] Peak intensity of the (110) level 100 Peak intensity of the (110) level 100 + Peak intensity of the (101) level 75 + Peak intensity of the (200) level 21 × 100 Peak intensity of the (101) level 75 Peak intensity of the (110) level 100 + Peak intensity of the (101) level 75 + Peak intensity of the (200) level 21 × 100

[0017] In some embodiments, the antimony-containing tin oxide film, which is present in the outermost surface of the aforementioned surface layer, has an antimony content of 0.2 atomic percent to 10 atomic percent, with regard to improving the electrical properties by increasing the carrier concentration. In some embodiments, the antimony-containing tin oxide film, which is present in the outermost surface of the aforementioned surface layer, has an antimony content of 0.2 atomic percent to 5 atomic percent, with regard to improving the electrical properties by increasing the carrier concentration.In some embodiments, the antimony-containing tin oxide film, which is contained in the outermost surface of the aforementioned surface layer, has an antimony content of 0.2 atomic percent to 3 atomic percent, with regard to improving the electrical properties by increasing the carrier concentration.

[0018] If antimony is present in excessive amounts, a trivalent antimony oxide is produced, which can degrade the electrical properties. In some embodiments, if the specific antimony-containing tin oxide film consists of a tin oxide film or of an antimony-containing tin oxide film (the first layer) formed relatively close to the surface of the substrate, and an antimony-containing tin oxide film (the second layer) on top of the first layer, the antimony content in the first layer is 0 atomic percent, or 0.2 to 10 atomic percent, or 0.2 to 5 atomic percent, or 0.2 to 3 atomic percent; and the antimony content in the second layer is 0.2 to 10 atomic percent, or 0.2 to 5 atomic percent, or 0.2 to 3 atomic percent.The antimony content in the antimony-containing tin oxide film can be determined using the method described, for example, in the section below.<Auswertungsverfahren für den Film> , “(2) Measurement of the antimony content in the film” described procedure.

[0019] In some embodiments, the thickness of the antimony-containing tin oxide film present in the outermost surface of the aforementioned surface layer is 50 nm or more to achieve excellent corrosion resistance. In some embodiments, the thickness of the antimony-containing tin oxide film present in the outermost surface of the aforementioned surface layer is 60 nm to 400 nm to achieve excellent corrosion resistance. In some embodiments, the thickness of the antimony-containing tin oxide film present in the outermost surface of the aforementioned surface layer is 80 nm to 380 nm to achieve excellent corrosion resistance.In some embodiments, when the antimony-containing tin oxide film is formed from a single layer, the thickness of the antimony-containing tin oxide film is 50 nm or more to achieve excellent corrosion resistance. In other embodiments, when the antimony-containing tin oxide film is formed from a single layer, the thickness of the antimony-containing tin oxide film is 80 nm to 400 nm to achieve excellent corrosion resistance.In some embodiments, when the specified antimony-containing tin oxide film is formed from a tin oxide film or from an antimony-containing tin oxide film (a first layer) formed relatively close to the surface of the substrate, and an antimony-containing tin oxide film (a second layer) on top of the first layer, the total film thickness of the first and second layers is 50 nm or more. In some embodiments, the film thickness of the first layer is 10 nm to 100 nm to produce original crystal grains oriented in the (200) plane; and the film thickness of the second layer is 40 nm to 250 nm to obtain excellent corrosion resistance.In some embodiments, the film thickness of the first layer is 10 nm to 100 nm to produce original crystal grains aligned in the (200) plane; and the film thickness of the second layer is 80 nm to 200 nm to obtain excellent corrosion resistance. The thickness of the antimony-containing tin oxide film can be adjusted by means of the method described, for example, in the section below.<Auswertungsverfahren für den Film> , “(5) Measurement of film thickness” described in the procedure. Since a SEM or TEM is used, for example a scanning electron microscope JSM-7100F, manufactured by JEOL Ltd.

[0020] The separator of the invention exhibits excellent conductivity. In some embodiments, when the contact resistance of the intermediate layer is measured with, for example, a carbon material, it can reach 30 mΩ·cm. 2or less. In some embodiments, when the contact resistance of the intermediate layer is measured with, for example, a carbon material, it can be 10 mΩ·cm. 2 or less. The contact resistance can be determined using, for example, the method described in section<Auswertungsverfahren für den Film> , “(1) Evaluation of conductivity” described in the method. The separator of the invention can exhibit excellent corrosion resistance. If the amounts of the metal components of a dissolved substrate are measured using the method described, for example, in the following section<Auswertungsverfahren für den Film> , “(4) Evaluation of corrosion resistance” described in the procedure, they may be below the detection limit or below (for example, less than 5 ng / mL).

[0021] The invention also relates to a method for manufacturing a fuel cell separator (hereinafter also referred to as the manufacturing method of the invention). The manufacturing method of the invention is suitable for manufacturing the separator of the invention. The manufacturing method of the invention is characterized by atomizing a solution containing tin chloride and antimony chloride by means of ultrasonic waves and applying or feeding the resulting mist-like solution onto a substrate heated to 300 °C to 600 °C in order to form an antimony-containing tin oxide film (hereinafter referred to as step (a)). Without wishing to be bound to a specific theory, it is assumed that if a solution containing tin chloride and antimony chloride is atomized or fed by means of an ultrasonic vibration process,When the liquid is atomized to obtain fog droplets of uniform size and applied to a heated metal substrate, the droplets evaporate before contacting the substrate, and local chemical vapor deposition can be performed. In this way, it is assumed that a highly crystalline film can be obtained and the conductivity improved. If the liquid droplets are large, or if the temperature of a metal substrate is low, the liquid droplets will fall onto the substrate before evaporating. In this case, components other than tin and antimony will be present in the liquid droplets within the film, resulting in deterioration of the crystallinity and a decrease in conductivity. The film formation process of step (a) corresponds to a fog CVD process. For the implementation of the fog CVD process, reference can be made, for example, to the scientific publication (JG Lu et al.Reference is made to the publications “Zno-based thin films synthesized by atmospheric pressure mist chemical vapor deposition”, Journal of Crystal Growth 299 (2007) 1-10) and the scientific publication (Takahiro Shirahata et al., “Transparent conductive zinc-oxide-based films grown at low temperature by mist chemical vapor deposition”, Thin Solid Films 597 (2015) 30-38). Conditions other than those mentioned above for carrying out the manufacturing process of the invention can be appropriately adjusted by a person skilled in the art.

[0022] In step (a), a solution containing tin chloride and antimony chloride is used. Since tin chloride (SnCl₂ or SnCl₄) and antimony chloride (SbCl₃ or SbCl₃) are inexpensive (the cost of tin chloride is approximately 1 / 10 that of dibutyltin diacetate), the preparation method of the invention is economically preferred. In some embodiments, the concentration of tin chloride in the solution is 0.001 mol / L to 1 mol / L, and the concentration of antimony chloride is 0.000002 mol / L to 0.1 mol / L. An organic solvent and water are specified as the solvent for the solution. These can be used as a mixture. The organic solvent is not particularly limited as long as it is conventionally used in the fog CVD process and can dissolve tin chloride and antimony chloride.At least one solvent, selected from monohydric alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, and octanol, may be used individually or as a mixture (two types or more). In some embodiments, when a water-containing solvent is used, an acid, such as hydrochloric acid or nitric acid, is added to the solution to dissolve stannous chloride and antimony chloride. In some embodiments, the concentration of the acid in the stannous chloride and antimony chloride-containing solution is 0.0001 mol / L to 0.07 mol / L to achieve the desired orientation.

[0023] In step (a), a solution containing tin chloride and antimony chloride is atomized or atomized using ultrasonic waves. In some embodiments, the frequency of the ultrasonic waves is 100 kHz to 5 MHz to obtain liquid droplets of a sufficiently small size to be vaporized before coming into contact with a metal substrate. In some embodiments, the frequency of the ultrasonic waves is 2.4 MHz to obtain liquid droplets of a sufficiently small size to be vaporized before coming into contact with a metal substrate.

[0024] In step (a), the mist-like solution obtained by atomization is applied to a substrate heated to 300 °C to 600 °C to form an antimony-containing tin oxide film. When a metal substrate is heated to the aforementioned temperature, the liquid droplets can be evaporated before they come into contact with the metal substrate, resulting in a film with high crystallinity. From this perspective, in some embodiments, the substrate is heated to 400 °C to 500 °C. Step (a) is carried out continuously until an antimony-containing tin oxide film of a predetermined thickness is formed, and then the heating of the substrate is stopped. In this way, a desired separator can be obtained.If the specified antimony-containing tin oxide film consists of a tin oxide film or an antimony-containing tin oxide film (a first layer) formed relatively close to the surface of the substrate, and an antimony-containing tin oxide film (a second layer) on the first layer, the method of the invention may further comprise, prior to step (a), a step (b) of atomizing a tin chloride and optionally antimony chloride-containing solution by means of ultrasonic waves and applying the resulting mist-like solution to a substrate heated to 300 °C to 600 °C in order to form the tin oxide film or the antimony-containing tin oxide film. Reference may also be made to the descriptions of step (a) and the first layer of the separator of the invention for the embodiment of step (b).

[0025] Note that when an antimony-containing tin oxide film is formed by thermal spray decomposition without atomization using ultrasonic waves or heating of a substrate, the film's crystallinity and conductivity are considered low because tin chloride is hardly decomposed. If a film is formed by thermal spray decomposition at a temperature where the oxidation of the metal substrate itself is suppressed, the film contains impurities and its crystallinity decreases, resulting in unsatisfactory electrical properties and likely an increase in contact resistance. Conversely, increasing the film formation temperature to improve crystallinity promotes the growth of the oxide film on the metal substrate, resulting in an increase in contact resistance.Alternatively, if a tin oxide-containing film is formed using a sputtering process, the orientation of the crystals becomes random or arbitrary, with the result that the (110) and (101) planes, which degrade the electrical properties, are present in a large proportion. Therefore, the conductivity of the film is presumably reduced. EXAMPLES

[0026] The invention is described in more detail by means of the examples. However, the technical scope of the invention is not limited by the examples. <substrat>

[0027] A pure titanium plate (thickness: 0.1 mm) was used as a metal substrate. <Rohstoff für den Antimon-enthaltenden Zinnoxid-Film oder einen Zinnoxid-Film> Material A:

[0028] An aqueous solution containing SnCl2 (the concentration of Sn in the aqueous solution obtained is 0.01 mol / L), SbCl3 (the concentration of Sb in the solution obtained is 0.0005 mol / L), 0.3 mol / L hydrochloric acid (1 vol%) and 0.2 mol / L nitric acid (1 vol%). Material B:

[0029] An aqueous solution containing SnCl2 (the concentration of Sn in the obtained aqueous solution is 0.01 mol / L), 0.3 mol / L hydrochloric acid (1 vol%) and 0.2 mol / L nitric acid (1 vol%). Material C:

[0030] An aqueous solution containing SnCl2 (the concentration of Sn in the aqueous solution obtained is 0.01 mol / L), SbCl3 (the concentration of Sb in the aqueous solution obtained is 0.0005 mol / L), 1.6 mol / L hydrochloric acid (5 vol%), and 0.2 mol / L nitric acid (1 vol%). <Verfahren zur Filmbildung>

[0031] A surface layer was formed on a substrate using a fine channel system fog CVD apparatus and according to the fog CVD process. (1) The substrate was placed on a warm plate. (2) A mist-like material obtained by atomization or atomization was introduced onto a surface of the substrate, which was heated to the film formation temperature shown in Table 1 below. The material was atomized using an ultrasonic transducer at 2.4 MHz. (3) The mist was evaporated on the substrate surface, allowing it to undergo a chemical reaction to form an antimony-containing tin oxide film or a tin oxide film. Care was taken to ensure that the mist did not fall onto the substrate in the form of liquid droplets. (4) When film growth progressed and a desired film thickness, as shown in Table 1 below, was achieved, the raw material feed was stopped. The substrate was maintained at a predetermined temperature in steps (2) and (3). (5) When forming the second layer, the substrate temperature was controlled to be the temperature shown in Table 1 below, and then steps (2) to (4) were carried out. (6) Once the temperature of the substrate had dropped to 50°C or less, the substrate was removed from the hot plate. <Auswertungsverfahren für den Film>(1) Evaluation of conductivity

[0032] To measure the contact resistance, a gold-plated copper plate was stacked onto the film-forming surface of a metal substrate with a carbon paper (TGP-H-120, manufactured by Toray Industries Inc.) between them. A pressure of 0.98 MPa per unit area was applied, and a continuous current was applied between the metal substrate and the copper plate. The voltage value at this time was measured. (2) Measurement of the antimony content in the film

[0033] The detection intensity of the Sb binding energy 540 eV was measured using X-ray photoemission spectroscopy (QuanteraSXM, manufactured by PHI) and converted into a content. (3) XRD analysis

[0034] The measurement was performed using an X-ray diffraction device (SmartLab, Rigaku).

[0035] The values ​​(%) representing the orientation of the (200) level, (110) level, and (101) level were each calculated according to the following (Expression 1), (Expression 2), and (Expression 3). Numerical values ​​of 21, 100, and 75, by which the peak intensity values ​​in (Expression 1), (Expression 2), and (Expression 3) are divided, are I(f) values ​​of individual levels of JCPDS Map No. 41-1445. [Mathematical expression 4] Peak intensity of the (200) level 21 Peak intensity of the (110) level 100 + Peak intensity of the (101) level 75 + Peak intensity of the (200) level 21 × 100 Peak intensity of the (110) level 100 Peak intensity of the (110) level 100 + Peak intensity of the (101) level 75 + Peak intensity of the (200) level 21 × 100 Peak intensity of the (101) level 75 Peak intensity of the (110) level 100 + Peak intensity of the (101) level 75 + Peak intensity of the (200) level 21 × 100 (4) Evaluation of corrosion resistance

[0036] A constant-potential corrosion test was performed according to the procedure for electrochemical high-temperature corrosion tests of metallic materials (Japanese Industrial Standards, JIS Z2294). A test piece was immersed in an aqueous sulfuric acid solution maintained at 80 °C. In this state, 0.9 V was maintained against the potential of SHE. NaF was dissolved in the aqueous sulfuric acid solution to achieve a fluoride ion concentration of 3000 ppm. The test time was set to 100 hours. After the corrosion resistance test, the amount of dissolved titanium (Ti) in the metal substrate was evaluated. If the amount of dissolved Ti was at or below the detection limit (less than 5 ng / mL), a "good" rating was given. (5) Measurement of film thickness

[0037] A test sample was embedded in a resin and polished. The section of the test piece was observed (using SEM or TEM) to measure the film thickness.

[0038] The results of the preceding evaluation tests on the separators obtained in Examples 1 to 7, Comparative Example 1, and Reference Examples 1 and 2 are shown in Table 1 below. Examples 1 to 3 are not part of the invention. [Table 1] First shift Second shift alignment raw material Film thickness Film formation temperature Film composition raw material Film thickness Film formation temperature Film composition (110) (101) (200) Contact resistance (mΩ·cm 2 ) Corrosion resistance evaluation results Example 1 A 210 nm 450 °C SnO2Sb - - - - 64 1 36 22 Good Example 2 A 352 nm 450 °C SnO2Sb - - - - 40 0 60 22 Good Example 3 A 100 nm 400 °C SnO2Sb - - - - 23 13 64 24 Good Example 4 A 10 nm 350 °C SnO2Sb A 90 nm 450 °C SnO2Sb 24 5 71 7 Good Example 5 B 10 nm 450 °C SnO2 A 190 nm 450 °C SnO2Sb 22 1 77 8 Good Example 6 A 10 nm 350 °C SnO2Sb A 190 nm 450 °C SnO2Sb 9 7 84 6 Good Example 7 B 10 nm 450 °C SnO2 A 30 nm 450 °C SnO2Sb 18 7 75 9 5 ng / mL or more Comparative example 1 C 100 nm 450 °C SnO2Sb - - - - 75 4 21 35 Good Reference example 1 A 50 nm 450 °C SnO2Sb - - - - - - - 32 Good Reference example 2 A 70 nm 450 °C SnO2Sb - - - - - - - 25 Good

[0039] Regarding the separators obtained in Examples 1 to 4, 6, Comparative Example 1, and Reference Examples 1 and 2, the Sb concentration of the antimony-containing tin oxide film was 2 atomic percent. Regarding the separators obtained in Examples 5 and 7, the Sb concentration of the antimony-containing tin oxide film (formed from the first layer and the second layer) was 0.2 atomic percent.

[0040] From the foregoing results, it is found that the separators obtained in Examples 1 to 7, whose values ​​(%), which represents the orientation of the (200) plane and which is calculated according to expression (1), are high (35 or more), have a low contact resistance (30 mΩ·cm). 2 or less). It was also found that in cases where the value (%) representing the orientation of the (200) plane, calculated according to expression (1), is 70 or more, there is a further reduction in the contact resistance (10 mΩ·cm). 2 or less) and exhibit excellent conductivity. It is further found that the separators obtained in Examples 1 to 6 have an antimony-containing tin oxide film thickness of 50 nm or more and show satisfactory corrosion resistance evaluation results.

[0041] From Example 1 and Example 2, it is found that the value representing the orientation of the (200) plane increases, since the (200) plane preferentially grows as the thickness of the antimony-containing tin oxide film increases; and that the contact resistance in Comparative Example 1 is high, with the value representing the orientation of the (200) plane being low ( Fig. 1) Since the film formation temperature in Example 3 is low, it is assumed that the value representing the orientation of the (200) plane increases.

[0042] In the conductivity evaluation, the area (actual contact area) actually in contact with an antimony-containing tin oxide (ATO) is estimated to be approximately 1% of the area (apparent contact area) in contact with carbon paper. This area (approximately 1%) is estimated to consist of contact points with a diameter of 200 to 300 nm. The ATO film, which is 50 nm or thick and produced using a fog CVC process, is estimated to consist of columnar crystals with a diameter of 10 to 50 nm. Based on this, the number of columnar ATO crystals in point contact with the carbon paper is assumed to be approximately 4 to 30. The contact resistance is generated within this area. This is because the actual contact area is small compared to the apparent contact area, and therefore current converges to the contact point near the surface.Therefore, it is assumed that as the number of contact points increases, the resistance decreases. Pillar-like ATO crystals aligned in the (110) and (101) planes exhibit poor electrical properties at their outermost surface. It is therefore hypothesized that the current flows selectively through the low-resistance, pillar-like crystals aligned in the (200) plane. Based on this, it is assumed that as the number of pillar-like crystals aligned in the (200) plane, which exhibit satisfactory electrical properties, increases, the contact resistance decreases.If the value (%) representing the orientation in the (200) plane, calculated according to expression (1), becomes 35 or greater, the columnar crystals aligned in the (200) plane will appear at almost all contact points, presumably resulting in a state where the contact resistance is sufficiently reduced. Furthermore, it is assumed that if the value (%) representing the orientation in the (200) plane, calculated according to expression (1), becomes 70 or greater, the columnar crystals aligned in the (200) plane will come into contact with each other and be connected along the horizontal direction of the substrate across the entire film.Therefore, since the current flows through the column-like crystals, which are aligned in the (200) plane and connected over the entire ATO film and distributed in the horizontal direction to the substrate, the resistance produced by converging the current near the contact points is reduced.< / substrat>

Claims

[1] Fuel cell separator comprising a metal substrate and a surface layer formed on a surface of the substrate, wherein the surface layer comprises an antimony-containing tin oxide film in an outermost surface of the same, the antimony-containing tin oxide film has a value (%) which represents the orientation of the (200) plane and is calculated according to expression (1): [Mathematical expression 1] Peak intensity of the (200) level 21 Peak intensity of the (110) level 100 + Peak intensity of the (101) level 75 + Peak intensity of the (200) level 21 × 100 where the values ​​of the respective peak intensities are obtained by means of X-ray diffraction, has a value of 35 or greater, the antimony-containing tin oxide film comprises a first layer of a tin oxide film or an antimony-containing tin oxide film, which is formed relatively close to the surface of the substrate, and a second layer of an antimony-containing tin oxide film on the first layer, and wherein, if both the first layer and the second layer comprise an antimony-containing tin oxide film, the first layer is produced at a lower temperature at which the oxidation of the substrate is suppressed, and the second layer is produced at a higher temperature at which the crystallinity is improved. [2] Fuel cell separator according to claim 1, wherein the value (%) representing the orientation of the (200) plane and calculated according to expression (1) is 70 or greater. [3] Fuel cell separator according to claim 1 or 2, wherein the antimony content in the first layer is 0 atomic %, or 0.2 atomic % to 10 atomic %, and the antimony content in the second layer is 0.2 atomic % to 10 atomic %. [4] Fuel cell separator according to one of claims 1 to 3, wherein the film thickness of the first layer is 10 nm to 100 nm and the film thickness of the second layer is 40 nm to 250 nm. [5] A method for producing the fuel cell separator according to any one of claims 1 to 4, comprising atomizing a tin chloride or antimony chloride-containing solution by means of ultrasonic waves, and applying the resulting mist-like solution to a substrate heated to 300 °C to 600 °C in order to form the first layer and the second layer of the antimony-containing tin oxide film, wherein, if both the first layer and the second layer comprise an antimony-containing tin oxide film, the first layer is produced at a lower temperature at which the oxidation of the substrate is suppressed, and the second layer is produced at a higher temperature at which the crystallinity is improved.

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