CN111384414A

CN111384414A - Bipolar plate of fuel cell and manufacturing method thereof

Info

Publication number: CN111384414A
Application number: CN201811622591.0A
Authority: CN
Inventors: 刘燕妮; 王鸿彬
Original assignee: Industrial Technology Research Institute ITRI
Current assignee: Industrial Technology Research Institute ITRI
Priority date: 2018-12-28
Filing date: 2018-12-28
Publication date: 2020-07-07
Anticipated expiration: 2038-12-28
Also published as: CN111384414B

Abstract

The invention discloses a bipolar plate of a fuel cell and a manufacturing method thereof, wherein the bipolar plate of the fuel cell comprises a base material and an anti-corrosion layer. The substrate has a plurality of flow channels. A resist layer overlying the substrate. The surface roughness of the substrate is less than or equal to 1.2 μm. The bipolar plate of the fuel cell and the manufacturing method thereof can improve the corrosion resistance and the service life of the bipolar plate of the fuel cell.

Description

Bipolar plate of fuel cell and manufacturing method thereof

Technical Field

The present invention relates to a fuel cell and a method for fabricating the same, and more particularly, to a bipolar plate of a fuel cell and a method for fabricating the same.

Background

The fuel cell has the advantages of high energy conversion efficiency, cleanness, low pollution, high energy density, quick start, long continuous power supply time and the like, so the fuel cell is considered to be an ideal power generation device with energy and environmental requirements and a strategic option of energy autonomy in the future. The fuel cell can increase the flow channel density of the bipolar plate by manufacturing the bipolar plate using an ultra-thin metal plate for increasing the energy density of the cell. However, in the process of stamping the ultrathin metal bipolar plate, high deformation is likely to occur at the contact part with the die, so that the surface of the ultrathin metal bipolar plate becomes rough, and local corrosion and fracture are likely to occur.

Disclosure of Invention

The invention aims to provide a bipolar plate of a fuel cell and a manufacturing method thereof, which can improve the corrosion resistance and the service life of the bipolar plate of the fuel cell.

The embodiment of the invention provides a bipolar plate of a fuel cell, which comprises a substrate and an anti-corrosion layer. The substrate has a plurality of flow channels. A resist layer overlying the substrate. The surface roughness of the substrate is less than or equal to 1.2 μm.

The embodiment of the invention also provides a manufacturing method of the bipolar plate of the fuel cell, which comprises the steps of providing a plate and carrying out a rolling manufacturing process on the plate. And tempering the plate. And carrying out a stamping manufacturing process on the plate through a stamping die to form a base material, wherein the base material is provided with a plurality of flow channels. And (5) carrying out a demolding manufacturing process.

Based on the above, the bipolar plate of the fuel cell and the manufacturing method thereof of the embodiment of the invention can improve the corrosion resistance and the service life of the bipolar plate of the fuel cell.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.

Drawings

Fig. 1A to 1F are cross-sectional flow views of a method of manufacturing a bipolar plate for a fuel cell according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a mold of an embodiment of the present invention;

FIG. 3 is a cross-sectional view of a substrate having a flow channel in accordance with an embodiment of the present invention;

fig. 4A is a schematic sectional view of a fuel cell of an embodiment of the invention;

FIG. 4B is a schematic cross-sectional view of a fuel cell having flow channels of a bipolar plate according to an embodiment of the present invention;

FIG. 5A is a schematic cross-sectional view of a fuel cell with parallel bipolar plate flow channels according to an embodiment of the invention;

FIG. 5B is a schematic cross-sectional view of a fuel cell with the bipolar plates in a flow channel orientation perpendicular according to an embodiment of the invention;

fig. 6 is a schematic cross-sectional view of a fuel cell stack according to an embodiment of the present invention;

FIG. 7A is an SEM image of the grains of stainless steel of example 1;

FIG. 7B is an SEM image of the grains of stainless steel of comparative example 1;

FIG. 8A is a schematic of surface roughness analysis of a stainless steel substrate of example 1;

FIG. 8B is a surface roughness analysis chart of the stainless steel base material of comparative example 1;

fig. 9A is an image of an Optical Microscope (OM) of the stainless steel substrate obtained after stamping with a die having a draft angle of 45 degrees of example 2;

fig. 9B is an image of an optical microscope of the stainless steel substrate obtained after stamping with a die having a draft angle of 70 degrees of example 1;

FIG. 10A is an SEM image of titanium grains of example 4;

FIG. 10B is an SEM image of titanium grains of comparative example 3;

FIG. 11A is a surface roughness analysis chart of the titanium substrate of example 4;

FIG. 11B is a graph showing the surface roughness analysis of the titanium substrate of comparative example 3;

FIG. 12A is an image taken by an optical microscope of a titanium substrate obtained after stamping with a die having a 45 degree draft angle runner pattern of example 5;

fig. 12B is an image taken by an optical microscope of the titanium substrate of example 4 after stamping with a die having a 70 degree draft angle runner pattern.

Detailed Description

The ultrathin metal bipolar plate can be used for improving the flow channel density of a fuel cell bipolar plate and improving the energy density of a cell, but the increase of the flow channel density of the ultrathin metal plate causes the coating uniformity of a coating film to be seriously challenged, particularly, the original crystal grains of the ultrathin metal plate are thick after rolling forming, obvious crystal grains can be seen after the high-density flow channel is punched and formed, the surface of the flow channel is rough, the uniformity of the coating film is poor, the corrosion resistance of the bipolar plate is reduced, and the service life is influenced. The present invention provides an ultra-thin metal bipolar plate having excellent plating uniformity, improved corrosion resistance and improved lifetime.

Fig. 1A to 1F are cross-sectional flow views illustrating a method of manufacturing a bipolar plate for a fuel cell according to an embodiment of the present invention.

Referring to fig. 1A, a plate 10 is provided. The plate material 10 is, for example, a flat plate-like conductive material. The conductive material comprises a metal, a derivative of a metal, a metalloid, or a combination thereof. The metal is, for example, stainless steel, titanium alloy, nickel alloy, aluminum alloy, or a combination thereof. The stainless steel may be 430 or moreStainless steel, 304 stainless steel, 316 stainless steel, or combinations thereof; the titanium alloy comprises pure titanium and titanium-aluminum-vanadium (Ti)₆Al₄V), titanium palladium alloys or related alloys; the nickel alloy comprises pure nickel, nickel-chromium alloy, nickel-molybdenum alloy or relative alloy; the aluminum alloy comprises pure aluminum, aluminum-magnesium-silicon alloy, aluminum-copper-magnesium alloy or related alloys. Derivatives may include carbides, nitrides, oxynitrides, or cyanides. In embodiments where the sheet 10 is a derivative of a conductive material, the sheet 10 is, for example, a carbide, nitride, oxynitride or cyanide of titanium or aluminum. In the embodiment where the plate 10 is a conductive intermetallic material, the plate 10 is, for example, an intermetallic material of titanium nickel or titanium aluminum. The thickness of the sheet 10 ranges, for example, from 100 micrometers (μm) to 1000 micrometers. The grain size of the crystal grains of the plate 10 is, for example, 0.5 μm to 200 μm. The average grain size of the plate 10 is, for example, in the range of 1 μm to 100. mu.m. The thickness of the plate 10 is, for example, 50 μm to 500 μm.

Referring to fig. 1B, a rolling process 13 is performed on the sheet 10 to thin the sheet 10 by rolling and dynamically recrystallize the sheet 10 to refine grains, so as to form a sheet 10 a. The calender forming process 13 may be processed by a calender. The calender may be a two roll calender, a 3 roll former, or a roll former. In some embodiments, the calendering process is performed at a pressure in a range of 100MPa to 3000 MPa. In some embodiments, the calendering process is performed at a pressure in a range of 100MPa to 1500 MPa. In other embodiments, the calendering process is performed at a pressure in a range of 200MPa to 1000 MPa. In still other embodiments, the pressure at which the rolling process is performed is maintained at a constant value, such as 300MPa, 600MPa, or 800 MPa. The temperature range in which the rolling process is performed is, for example, 20 degrees celsius to 900 degrees celsius.

The thickness of the rolled sheet material 10a may be 1/20 to 1/2 of the thickness of the sheet material 10 before rolling. The thickness of the rolled sheet material 10a may be 200 μm or less. In some embodiments, the thickness of the sheet 10a is 20 μm to 300 μm. The crystal grains of the plate material 10a have a grain size in a range of, for example, 5 μm to 100 μm, 1 μm to 50 μm, or 1 μm to 20 μm. The average grain size of the plate material 10a is, for example, in the range of 5 μm to 50 μm, 1 μm to 20 μm, or 0.5 μm to 10 μm.

In some embodiments, a trace amount of precipitates is also added to the sheet material 10. The precipitates are added into the grain boundaries to avoid the phenomenon of over-growth of local grains due to recrystallization during the rolling process, thereby limiting the size of the grains. The precipitates are, for example, metal carbides, alloys or metal borides. Metal carbides are, for example, M (Fe, Cr, Mo.)₂₃C₆、Fe₃C、Cr₃C or Mo₃C. The alloy being, for example, Ti₂Pd or Ti₃And Al. The metal boride being, for example, Ti₃B、Zr₃B, and the like.

Referring to fig. 1C, after the rolling process, the rolled sheet material 10a is heat treated (heat treatment process) 14 to change the microstructure of the sheet material 10 a. the heat treatment 14 may be a tempering process or an annealing heat treatment, more specifically, the heat treatment 14 may regenerate and reform the crystal grains of the sheet material 10a, convert the strain energy after rolling into kinetic energy of the regenerated crystal grains to refine the crystal grains, so that the grain size of the crystal grains of the heat treated sheet material 10b is controlled within a certain range, the heat treatment 14 is performed in a vacuum environment, for example, the degree of vacuum of the heat treatment 14 is less than 1 × 10, for example^-2In some implementations, the vacuum of the heat treatment 14 is, for example, 1 × 10^-5torr to 1 × 10^-2torr. The temperature of the heat treatment 14 is, for example, a low temperature tempering of less than 600 degrees celsius. In some implementations, the temperature range of the heat treatment 14 is, for example, 300 degrees celsius to 550 degrees celsius. In still other implementations, the temperature range of the heat treatment is, for example, 300 degrees celsius to 400 degrees celsius. The time range of the heat treatment 14 is, for example, 1 hour to 6 hours. The heat treatment 14 may be performed by a continuous furnace, a heat treatment furnace, or the like.

In some embodiments, the grain size of the grains of the heat treated sheet material 10b is about 1/50 to 1/2 of the grain size of the grains of the sheet material 10 prior to rolling. Further, the grain size of the crystal grains of the plate material 10b after the heat treatment is about 1/30 to 1/2 of the grain size of the crystal grains of the plate material 10a before the treatment (after rolling). The grain size of the crystal grains of the heat-treated plate material 10b is, for example, in the range of 1 μm to 7 μm, 1 μm to 5 μm, or 0.1 μm to 3 μm. The average grain size of the plate material 10b is, for example, in the range of 1 μm to 6 μm, 2 μm to 4 μm, or 0.1 μm to 1 μm.

Referring to fig. 1D and fig. 2, after the heat treatment, a stamping process is performed on the plate 10 b. The stamping fabrication process may be performed by using a stamping die. The stamping die includes an upper die (not shown) and a lower die 12. The shape of the upper die is corresponding to that of the lower die. The lower mold 12 includes a main body 12B and a plurality of projections 12P. The convex portion 12P protrudes from the body portion 12B. Since the convex portions 12P are provided at intervals on the main body portion 12B, the convex and concave surfaces 12T are formed with the main body portion 12B. The side wall 12S of the projection 12P is connected to the surface of the body 12B.

Referring to fig. 1D and 2, top surface 12Pt of protrusion 12P may be a single or multiple flat surface, curved surface, or a combination thereof, corner α 'of protrusion 12P may be a chamfer, obtuse angle or rounded obtuse angle, in an embodiment where corner α' of protrusion 12P is rounded obtuse angle, top surface 12Pt of protrusion 12P includes a plane Ft 'between two corners α', plane Ft 'has a width of, for example, 0.2mm to 3mm, corner α' is rounded obtuse angle, and has a radius of curvature in a range of 0.01mm to 0.5mm, for example, 0.1mm, 0.2mm, or 0.25 mm.

In the cross-sectional view, the sidewalls 12S of the convex portions 12P are inclined straight lines, arcs, or parabolic lines. In other words, the side wall 12S of the convex portion 12P may be an inclined surface, a curved surface, or a paraboloid. The height H' of the projections 12P, i.e., the distance between the top surface 12Pt of the projections 12P and the surface 12Bb of the body 12B, may range from 0.2mm to 3mm, from 0.2mm to 2mm, or from 0.2mm to 0.8mm, for example, from 0.35mm, 0.45mm, or 0.55 mm. In some embodiments, the height H' of the protrusion 12P is also referred to as the height of the sidewall 12S of the protrusion 12P.

The bottom corners β ' of the recesses 12B may be chamfered, the chamfer being either an obtuse angle or a rounded obtuse angle, the angular range of the bottom corners β ' of the recesses 12B is, for example, 90 to 150 degrees, in embodiments where the bottom corners β ' of the recesses 12B are rounded obtuse angles, the bottom sides 12Bb of the recesses 12B include a plane Fb ' located between two bottom corners β ', the width of the plane Fb ' may range from 0.2 to 3mm, for example, 0.5mm, 1mm, or 2mm, the bottom corners β ' are rounded obtuse angles, the radius of curvature of which may range from 0.01 to 0.5mm, for example, 0.1mm, 0.2mm, or 0.25mm, the bottom corners β ' and the top corners α ' may be the same or different in radius.

The bottom angle γ ' of the protrusion 12P of the lower mold 12, i.e., the angle between the sidewall 12S of the protrusion 12P and the extension line of the surface of the main body 12B, may be referred to as a draft angle γ ', or draft angle γ '. In some embodiments of the present invention, the draft angle γ' ranges, for example, from greater than or equal to 30 degrees, or greater than or equal to 40 degrees. In some examples, the draft angle γ' is between 40 degrees and 90 degrees, for example. In still other examples, the draft angle γ' may be between 40 and 80 degrees. The draft angle γ' is, for example, 70 degrees, 60 degrees, 45 degrees.

Further, the pitch P' of two adjacent projections 12P may be less than or equal to 3 mm. In some embodiments, the pitch P' of two adjacent protrusions 12P is, for example, 1mm to 2.4 mm. In other embodiments, the pitch P 'of two adjacent protrusions 12P' is, for example, 1.2mm to 2 mm.

In some embodiments, the stamping die is mounted on a stamping press. In the punching, the punch presses the sheet material 10 to plastically deform the sheet material 10. The stamping press may be a mechanical press or a hydraulic press. The pressure applied to the sheet material 10 is, for example, 100MPa to 1000 MPa. The stamping process may be performed at room temperature or higher. More specifically, the temperature at which the stamping process is performed is, for example, 20 to 300 degrees celsius.

Since the crystal grains of the plate material 10b are refined and uniform in size, the high curvature portion of the plate material 10b, such as the die-drawing portion, is not easily broken during the punching process, and thus plastic deformation can be generated, thereby forming the base material 11 having a flow channel pattern and a uniform thickness.

The thickness of the substrate 11 may be, for example, 200 μm or less. In some embodiments, the substrate 11 has a thickness ranging from 40 μm to 200 μm. In other embodiments, the substrate 11 has a thickness in a range from 150 μm to 200 μm. In still other embodiments, the substrate 11 has a thickness in the range of 50 μm to 100 μm. The grain size of the substrate 11 ranges, for example, from 0.3 μm to 15 μm, from 1 μm to 6 μm, or from 0.1 μm to 8 μm. The average grain size of the crystal grains of the base material 11 is, for example, in the range of 0.3 μm to 5 μm. The surface roughness Ra of the substrate 11 is, for example, 1.2 μm or less. In some embodiments, the surface roughness Ra of the substrate 11 ranges, for example, from 0.156 μm to 1.171 μm, from 0.242 μm to 0.739 μm, or from 0.1 μm to 1.2 μm.

Next, referring to FIG. 1E, after the stamping process, in some embodiments, a resist layer 20 is further formed on the surface of the substrate 11. the resist layer 20 has a conductivity of, for example, 1 × 10³S/cm to 1 × 10⁵S/cm. The material of the resist layer 20 is, for example, carbon, a metal carbon compound, a metal nitride, or a carbon-nitrogen mixture of metals. The resist layer 20 may be formed by dry plating or wet plating. For example, the dry coating can be physical vapor deposition such as evaporation or sputtering, or chemical vapor deposition such as plasma enhanced chemical vapor deposition. The wet plating method may be an electrochemical method such as a chemical plating method, an electroless plating method, a molten salt method, or the like.

In some embodiments, the thickness of the resist layer 20 ranges from 0.1 μm to 5 μm, for example. Since the crystal grains and the surface roughness of the substrate 11 are small, the step coverage of the resist layer 20 is high, and the surface of the substrate 11 can be effectively covered. Therefore, the resist layer 20 does not need to be so thick as to cover the substrate 11. In some embodiments, the thickness of the resist layer 20 is, for example, less than or equal to 3 μm. The thickness of the resist layer 20 ranges from 3 μm to 0.2 μm, for example. In some embodiments, the thickness of the resist layer 20 is less than 0.5 μm.

The mold stripping process is performed to remove the substrate 11 covered with the resist layer 20 from the stamping mold to form the bipolar plate 30 with flow channels.

In an embodiment of the present invention, the stamping is performed using a stamping die having a large draft angle θ, so that the flow channels 16 of the bipolar plate 30 can be formed with a small spacing therebetween after the die is removed.

Referring to fig. 3, more specifically, the base material 11 of the bipolar plate 30 has protrusions 11P and recesses 11R. The concave portion 11R and the convex portion 11P share the side wall 11S. That is, the side wall 11S connects the bottom surface 11Rb of the concave portion 11R and the top surface 11Pt of the convex portion 11P.

In embodiments where the apex angle α of the projection 11P is a rounded obtuse angle, the top surface 11Pt of the projection 11P includes a flat surface Ft. between two apex α corners, the width of the flat surface Ft is, for example, 0.2mm to 3mm, the apex angle α is a rounded obtuse angle, and the radius of curvature may range from 0.01mm to 0.5mm, for example, 0.1mm, 0.2mm, or 0.25 mm.

The sidewall 11S may be a smooth surface. More specifically, the side wall 11S may be a single or a plurality of slopes, curved surfaces, or a combination thereof. The height H of the side wall 11S, i.e., the vertical distance between the bottom surface 11Rb of the recess 11R and the top surface 11Pt of the projection 11P, may be 0.2mm to 3mm, for example, 0.35mm, 0.45mm, or 0.55 mm.

The bottom corners β of the pockets 11R can be chamfered, obtuse or rounded obtuse, the bottom corners β of the pockets 11R can have an angular range of, for example, 90 to 150 degrees, in embodiments where the bottom corners β of the pockets 11R are rounded obtuse, the width of the bottom corners 11Rb of the pockets 11R, including the plane Fb. between the two bottom corners β, can be in the range of 0.2 to 3mm, such as 0.5mm, 1mm or 2mm, the bottom corners β can be rounded obtuse, and have a radius of curvature in the range of 0.01 to 0.5mm, such as 0.1mm, 0.2mm or 0.25mm, the bottom corners β can be the same as or different from the radius of curvature of the top corners α.

In addition, an angle between a horizontal extending line of the bottom surface 11Rb of the recess (runner) 11R and the side wall 11S is also referred to as a draft angle γ. In some embodiments, the draft angle γ ranges from greater than or equal to 30 degrees, or greater than or equal to 40 degrees, for example. In some examples, the draft angle γ is, for example, between 40 degrees and 90 degrees. In still other examples, the draft angle γ is, for example, between 40 degrees and 80 degrees. The draft angle γ is, for example, 70 degrees, 60 degrees, or 45 degrees.

Further, the pitch P of the adjacent two projections 11P may be less than or equal to 3 mm. In some embodiments, the pitch P of two adjacent projections 11P is, for example, 1mm to 2.4 mm. In other embodiments, the pitch P of two adjacent projections 11P is, for example, 1.2mm to 2 mm. When the bipolar plate 30 is used in a fuel cell, the reduced spacing between the flow channels 16 helps to increase the current density of the cell.

Fig. 4A is a schematic cross-sectional view of a fuel cell unit according to an embodiment of the present invention. Referring to fig. 4A, a fuel cell 100 includes a Membrane Electrode Assembly (MEA) 102 and a pair of bipolar plate sets 130a and 130 b. The mea 102 includes a Proton Exchange Membrane (PEM) 104 and

gas diffusion layers

106a and 106 b. The proton exchange membrane 104 may be a perfluorosulfonic acid ion membrane (Nafion). The

gas diffusion layers

106a and 106b are disposed on two sides of the proton exchange membrane 104.

Gas diffusion layers

106a and 106b may be graphite fibers, titanium metal fibers, or noble metal (e.g., Ag, Au, Pt) fibers. The

bipolar plate groups

130a and 130b are disposed outside the

gas diffusion layers

106a and 106b, respectively.

The bipolar plate group 130a includes

bipolar plates

131a and 132 a. The

bipolar plates

131a and 132a may employ the bipolar plate 30 of the above-described embodiment. The bipolar plate 131a is located between the gas diffusion layer 106a and the bipolar plate 132 a. The

bipolar plates

131a and 132a have a first cooling flow channel 116a and a first gas flow channel 118 a. The first cooling channels 116a and the first gas channels 118a are disposed in a staggered manner. Specifically, the protrusions 131P1 of the bipolar plate 131a and the recesses 132R of the bipolar plate 132a₁Disposed correspondingly, and between the protrusions 131P1 of the bipolar plate 131a and the gas diffusion layer 106a as the first gas flow channels 118 a. Recesses 131R of bipolar plate 131a₁Corresponding to the protrusions 132P1 of the bipolar plate 132a, and the space formed by the protrusions serves as the first cooling channel 116 a.

Likewise, bipolar plate set 130b includes

bipolar plates

131b and 132 b. The bipolar plate 131b is located between the gas diffusion layer 106b and the bipolar plate 132 b. The

bipolar plates

131b and 132b have a second cooling flow channel 116b and a second gas flow channel 118 b. The second cooling channels 116b and the second gas channels 118b are, for example, arranged in a staggered manner. In particular, it relates toRecesses 131R of bipolar plate 131b₂Disposed corresponding to the protrusions 132P2 of the bipolar plate 132b, and the recesses 131R of the bipolar plate 131b₂And the gas diffusion layer 106b as second gas flow paths 118 b. The convex portion 131P2 of the bipolar plate 131b and the concave portion 132R of the bipolar plate 132b₂And the corresponding space is used as the second cooling channel 116 b.

Referring to fig. 5A and 5B, in some embodiments, the extending direction of the flow channels Ca of the bipolar plate set (only the bipolar plate 131a is shown) may be the same as the extending direction of the flow channels Cb of the bipolar plate set (only the bipolar plate 131B is shown), as shown in fig. 5A. In the present embodiment, the extending direction of the flow channel Ca/Cb refers to the extending direction of the first cooling flow channel 116 a/the second cooling flow channel 116b and/or the first gas flow channel 118 a/the second gas flow channel 118 b. In fig. 5A, the flow channels Ca of the bipolar plate 131a and the flow channels Cb of the bipolar plate 131b extend along a first direction D1. Further, the first cooling flow passage 116a and the second cooling flow passage 116b are arranged in upper and lower phase alignment; the first gas channel 118a and the second gas channel 118b are also disposed in a vertically corresponding and aligned manner, however, the embodiment of the invention is not limited thereto.

In other embodiments, the flow channels of the bipolar plate 131a and the flow channels of the bipolar plate 131b may both extend along the first direction D1. However, the first cooling flow channel 116a and the second cooling flow channel 116b are arranged in parallel in the vertical direction but shifted from each other; the first gas flow path 118a and the second gas flow path 118b are also arranged in a vertically parallel manner but offset.

In other embodiments, the flow channels Ca 'of the bipolar plate set (only bipolar plate 131a is shown) may extend in a direction different from the flow channels Cb' of the bipolar plate set (only bipolar plate 131B is shown), as shown in fig. 5B. In fig. 5B, the flow channels Ca' of the bipolar plate 131a extend along the first direction D1; and the flow channels Cb' of the bipolar plate 131b extend along the second direction D2. The first direction D1 is different from the second direction D2. In some embodiments, the first direction D1 is perpendicular to the second direction D2, however, the present invention is not limited thereto.

In addition, referring to fig. 4B, the spacing Pc1 of the first cooling channels 116a of the bipolar plate set 130a may be the same as or different from the spacing Pc2 of the second cooling channels 116B of the bipolar plate set 130B. The pitch Pg1 of the first gas flow channels 118a of bipolar plate set 130a may be the same as or different from the pitch Pg2 of the second gas flow channels 118b of bipolar plate set 130 b.

Additionally, fig. 6 is a schematic cross-sectional view of a fuel cell stack according to some embodiments of the invention. In fig. 6, the fuel cell stack includes a plurality of fuel cells 200 stacked. Further, structures such as a unipolar plate, a collector plate (collector plate), an end plate (end plate), and the like may be provided outside the fuel cell stack of the third embodiment, but the present invention is not limited thereto.

The following examples are given to confirm the efficacy of the present invention, but the scope of the present invention is not limited to the following.

< example 1>

Providing a 316L stainless steel plate with the size of 25cm × 60cm and the thickness of 200 microns, wherein the range of original crystal grains of the stainless steel plate is 25-60 microns, the range of average crystal grains of the original crystal grains is 30-50 microns, rolling the stainless steel plate to the thickness of 100 microns under the force of 1350MPa in the environment of 900 ℃, then cooling the stainless steel plate to room temperature in a furnace, taking out the plate, measuring the range of average crystal grains of the rolled plate to be 20-45 microns, taking the partially rolled plate, and performing vacuum processing at 35550 ℃ under the vacuum degree of 1 × 10^-2the stainless steel plate after rolling and annealing is subjected to runner press forming at 20 degrees celsius and 225MPa using an oil press for 3 hours, and a runner press forming is performed under conditions of 225MPa, as shown in fig. 2, a lower mold of the mold is used in this example, like the convex portion 12P of the lower mold 12, the height (i.e., the depth of the runner) H ' is 0.5mm, the apex angle α ' of the convex portion (runner) 12P is a rounded obtuse angle, the radius of curvature is 0.25mm, the width of the plane (or flat surface) Fb ' of the main portion 12B between two adjacent convex portions 12P is 1mm, the mold has a plurality of patterns having different pitches P ' and draft angles γ ', and the draft angles γ '/pitches P ' of example 1 are 70 degrees/2.36 mm, respectively, and thereafterThe grain size was measured, and surface roughness analysis was performed using a contact probe measuring instrument (α -stepper, manufactured by Kosaka Laboratory Ltd., model ET-4000A).

< example 2>

Providing a 316L stainless steel plate with the size of 25cm × 60cm and the thickness of 200 microns, wherein the range of original crystal grains of the stainless steel plate is 25-60 microns, the range of average crystal grains of the original crystal grains is 30-50 microns, rolling the stainless steel plate to the thickness of 100 microns under the force of 1350MPa in the environment of 900 ℃, then cooling the stainless steel plate to room temperature in a furnace, taking out the plate, measuring the range of average crystal grains of the rolled plate to be 20-45 microns, taking the partially rolled plate, and performing vacuum processing at 35550 ℃ under the vacuum degree of 1 × 10^-2the stainless steel sheet after rolling and annealing is subjected to runner press forming at 20 degrees celsius and 225MPa using an oil press for 3 hours, and the stainless steel sheet is subjected to runner press forming under a pressure of 225MPa, referring to fig. 2, a die is used in this example, like the convex portion 12P of the die 12, the height (i.e., the depth of the runner) H ' is 0.5mm, the apex angle α ' of the convex portion (runner) 12P is a rounded obtuse angle, the radius of curvature is 0.25mm, the width of the flat surface (or called flat surface) Fb ' of the main body portion 12B between two adjacent convex portions 12P is 1mm, the die is used with a plurality of sets of patterns having different pitches P ' and draft angles γ ', the draft angles γ '/pitches P ' of example 2 are 45 degrees/3 mm, respectively, thereafter, the grain sizes are measured, and surface roughness analysis is performed using a contact probe (α -step, Laboratory, koet-4000 ET).

< comparative example 1>

Similar to example 1, but without annealing after rolling and before pressing, the rolled and annealed stainless steel sheet of example 1 was subjected to runner press forming using an oil press at 20 degrees celsius and a pressure of 225MPa, to form a stainless steel substrate having runners, a die used for pressing was shown in fig. 2, and in this example, like the convex portion 12P of the die 12, the height (i.e., the depth of the runner) H ' was 0.5mm, the apex angle α ' of the convex portion (runner) 12P was a rounded obtuse angle with a radius of curvature of 0.25mm, the width of the flat surface Fb ' of the main body portion 12B between two adjacent convex portions 12P was 1mm, and the die used had a plurality of sets of patterns having different pitches P ' and draft angles γ ', the draft angles γ '/pitches P ' of example 1 were 70 degrees/2.36 mm, respectively, and thereafter, the grain size was measured using a contact type tester (α -sample), kosaet model No. 4000 kosaet.

< example 3>

A3 μ M carbon film was formed on the stainless steel sheet of example 1 by a salt bath method in carbonate at 350 ℃ to serve as a resist film, and an electrochemical corrosion test was conducted to estimate the corrosion life, the electrochemical corrosion test was conducted in a potassium hydroxide solution having a concentration of 1M at 80 ℃ and the surface roughness analysis was conducted using a contact probe tester (α -stepper, manufactured by Kosaka Laboratory Ltd., model ET-4000A) and the results are shown in Table 2.

< comparative example 2>

Similar to example 3, but the stainless steel sheet of comparative example 1, which was not heat-treated, was substituted for the stainless steel sheet of example 1, which was heat-treated. The results are shown in Table 2.

TABLE 1

	Comparative example 1	Example 1	Example 2
				Sheet materialMaterial	Stainless steel	Stainless steel	Stainless steel
Sheet thickness (μm)	100	100	100
				Calendering	Is provided with	Is provided with	Is provided with
Thermal treatment	Is free of	Is provided with	Is provided with
				Average particle diameter (μm)	30	3.7	3.7
Surface roughness (Ra, mum)	1.171	0.156	0.156
				Stamping	Is provided with	Is provided with	Is provided with
Draft angle	70 degree	70 degree	45 degree
				Spacing (mm)	2.36	2.36	3
Continuity of a substrate with flow channels	Jia	Jia	Jia
				Uniformity of substrate with flow channel	Jia	Jia	Jia

TABLE 2

Fig. 7A is an image of an SEM of the stainless steel grains of example 1. FIG. 7B is an SEM image of the grains of stainless steel of comparative example 1. The results of fig. 7A and 7B show that the grain size of the stainless steel grains of example 1 subjected to heat treatment after rolling is much smaller than that of the stainless steel grains of comparative example 1 not subjected to heat treatment after rolling.

Fig. 8A is a surface roughness analysis of the stainless steel substrate of example 1. Fig. 8B is a surface roughness analysis of the stainless steel plate material of comparative example 1. It is shown from the results of fig. 8A and 8B that the surface roughness of the stainless steel substrate of example 1 subjected to the heat treatment after rolling is much smaller than that of the stainless steel substrate of comparative example 1 not subjected to the heat treatment after rolling.

Fig. 9A is an image of an Optical Microscope (OM) of the stainless steel substrate obtained after stamping with a die having a draft angle of 45 degrees of example 2. Fig. 9B is an image of an optical microscope of the stainless steel substrate obtained after stamping with a die having a draft angle of 70 degrees of example 1. The results of fig. 9A and 9B show that the stainless steel substrate after stamping is continuous and uniform in thickness.

In addition, the electrochemical corrosion results and the life prediction results of table 2 show that: the electrochemical corrosion rate of example 3, which was heat-treated after rolling, was lower than that of comparative example 2, which was not heat-treated after rolling, and the lifetime thereof could be improved by about 33.1%. The reason for this increase is presumed to be that the grains of the stainless steel are refined after the heat treatment, the surface roughness is reduced, and the electrochemical corrosion rate is decreased.

<Example 4>Taking a titanium plate with the thickness of 100 micrometers, wherein the range of original crystal grains is 6 micrometers to 20 micrometers, the average range of the crystal grains of the original crystal grains is 9 micrometers to 15 micrometers, and taking the part of the titanium plate at 350 ℃ and the vacuum degree of 1 × 10^-2the average grain size of the formed grains was in the range of 0.1 to 3 μm when annealing was performed in an environment of torr for 1 hour, the die used for the stamping was as shown in fig. 2, in this example, the die was similar to the convex portion 12P of the die 12, the height (i.e., the depth of the runner) H ' was 0.5mm, the apex angle α ' of the convex portion (runner) 12P was a rounded obtuse angle, the radius of curvature was 0.25mm, the width of the plane (or flat surface) Fb ' of the main body portion 12B between two adjacent convex portions 12P was 1mm, the die used had a plurality of patterns having different pitches P ' and draft angles γ ', the draft angles γ '/pitches P ' of example 1 were 70 degrees/2.36 mm, respectively, and the results are shown in table 3.

< example 5>

Taking a titanium plate with the thickness of 100 micrometers, wherein the range of original crystal grains is 6 micrometers to 20 micrometers, the average range of the crystal grains of the original crystal grains is 9 micrometers to 15 micrometers, and taking the part of the titanium plate at 350 ℃ and the vacuum degree of 1 × 10^-2Annealing for 1 hour in a torr environment to form crystal grains with average grain size of 0.1-3 micronsReferring to fig. 2, a die used for stamping is shown in fig. 2, in this example, the die is similar to the protrusion 12P of the die 12, the height (i.e., the depth of the runner) H ' is 0.5mm, the apex angle α ' of the protrusion (runner) 12P is a rounded obtuse angle, the radius of curvature is 0.25mm, the width of the plane (or called flat surface) Fb ' of the main body 12B between two adjacent protrusions 12P is 1mm, the die has a plurality of sets of patterns having different pitches P ' and draft angles γ ', the draft angles γ '/pitches P ' of example 2 are 45 degrees/3 mm, respectively, thereafter, the grain size is measured, and surface roughness analysis is performed using a contact probe tester (α -stepper, Kosaka laboratory ltd., model ET-4000A).

< comparative example 3> similar to example 4, but the titanium plate was not annealed, the results are shown in table 3. a die used for the press is shown in fig. 2. referring to fig. 2, in this example, a die similar to the convex portion 12P of the die 12 having a height (i.e., a depth of the runner) H ' of 0.5mm, a vertex angle α ' of the convex portion (runner) 12P is a rounded obtuse angle having a radius of curvature of 0.25mm, and further, a plane (or referred to as a flat plane) Fb ' of the main body portion 12B between adjacent two convex portions 12P is 1mm, and further, the die used has a plurality of sets of patterns having different pitches P ' and draft angles γ ', and thereafter, the draft angles γ '/pitches P ' of example 1 are 70 degrees/2.36 mm, respectively, and thereafter, the grain diameters are measured, and surface roughness analysis is performed using a contact probe (α -stepper, Kosaka Laboratory ltd.

< example 6>

The other part of the titanium plate of example 4 was subjected to the process of forming a resist film in the manner described in example 3, and an electrochemical corrosion test was performed to estimate the corrosion life. The results are shown in Table 4.

< comparative example 4>

Similar to example 6, but the example 4 sheet was replaced with the untreated sheet of comparative example 3. The results are shown in Table 4.

TABLE 3

	Comparative example 3	Example 4	Example 5
				Sheet material	Titanium (IV)	Titanium (IV)	Titanium (IV)
Sheet thickness (μm)	100	100	100
				Calendering	Is free of	Is free of	Is free of
Thermal treatment	Is free of	Is provided with	Is provided with
				Average particle diameter (μm)	11	0.3	0.3
Surface roughness (Ra, mum)	0.793	0.242	0.242
				Stamping	Is provided with	Is provided with	Is provided with
Draft angle	70 degree	70 degree	45 degree
				Spacing (mm)	2.36	2.36	3
Continuity of a substrate with flow channels	Jia	Jia	Jia
				Uniformity of substrate with flow channel	Jia	Jia	Jia

TABLE 4

	Example 6	Comparative example 4
			Sheet material	Titanium (IV)	Titanium (IV)
Sheet thickness (μm)	100	100
			Thermal treatment	Is provided with	Is free of
Carbon-coated film	Is provided with	Is provided with
			Corrosion potential (Ecorr)	0.11	0.12
Corrosion current density (. mu.A/cm)²)	3.15	3.74
			Corrosion Rate (. mu.m/year)	36.2	43
Estimated lifetime (year)	2.76	1.87
			Life (%)	147.6	100

Fig. 10A is an SEM image of the titanium grains of example 4. FIG. 10B is an SEM image of titanium grains of comparative example 3. It is shown from the results of fig. 10A and 10B that the grain size of the titanium crystal grains of example 4 subjected to the heat treatment after rolling is much smaller than that of comparative example 3 which is not subjected to the heat treatment.

Fig. 11A is a surface roughness analysis of the titanium substrate of example 4. Fig. 11B is a surface roughness analysis of the titanium substrate of comparative example 3. The results of fig. 11A and 11B show that the surface roughness of the titanium substrate of example 4 subjected to the heat treatment is much smaller than that of the titanium substrate of comparative example 3 not subjected to the heat treatment.

Fig. 12A is an image of an Optical Microscope (OM) of the titanium substrate of example 5 after stamping with a die having a 45 degree draft angle runner pattern. Fig. 12B is an image taken by an optical microscope of the titanium substrate of example 4 after stamping with a die having a 70 degree draft angle runner pattern. The results in fig. 12A and 12B show that the titanium substrate after stamping is continuous and uniform in thickness.

In addition, the electrochemical corrosion results and the life prediction results of table 4 show: the electrochemical corrosion rate of example 6 with heat treatment is lower than that of comparative example 4 without heat treatment, and the lifetime can be improved by about 47.6%. The reason for this increase is presumed to be that the titanium crystal grains are refined after the heat treatment, the surface roughness is reduced, and the electrochemical corrosion rate is decreased.

In summary, the fuel cell according to the embodiment of the invention can improve the corrosion resistance and the service life of the bipolar plate. In some embodiments, the fuel cell of the present invention can be applied to an ultra-thin metal bipolar plate set with a thickness of 200 μm or less, and the surface roughness after stamping the flow channel is reduced (Ra <1.2um) by refining the metal plate grains (grain <15 μm), and the coating layer material is selected to promote higher coverage (coverage) of the resist coating when the flow channel draft angle is greater than or equal to 40 degrees, so as to be more corrosion-resistant.

Although the present invention has been described with reference to the above embodiments, it should be understood that the invention is not limited thereto, and that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A bipolar plate for a fuel cell, comprising:

a substrate having a plurality of flow channels; and

a resist layer overlying the substrate,

wherein the surface roughness of the substrate is less than or equal to 1.2 μm.

2. The bipolar plate for a fuel cell according to claim 1, wherein the average particle diameter of the crystal grains of the substrate ranges from 0.3 μm to 15 μm.

3. The bipolar plate of a fuel cell according to claim 1, wherein a pitch of the flow channels is less than or equal to 3 mm.

4. The bipolar plate of a fuel cell according to claim 1, wherein the substrate comprises stainless steel, titanium, nickel, chromium, derivatives thereof, intermetallics thereof, or combinations thereof.

5. The bipolar plate of a fuel cell according to claim 1, wherein the substrate comprises a carbide, nitride, oxynitride, cyanide, titanium-nickel intermetallic or titanium-aluminum intermetallic of titanium or chromium.

6. The bipolar plate of a fuel cell according to claim 1, wherein a draft angle of the flow channel of the substrate is greater than 40 degrees.

7. The bipolar plate for a fuel cell according to claim 1, wherein the etch-resistant layer has an electrical conductivity of 1 × 10³S/cm to 1 × 10⁵S/cm。

8. The fuel cell bipolar plate of claim 1, wherein the etch-resistant layer has a thickness of less than or equal to 3 μm.

9. A method of manufacturing a bipolar plate for a fuel cell, comprising:

providing a plate;

carrying out a rolling manufacturing process on the plate;

carrying out a heat treatment manufacturing process on the plate; and

and carrying out a stamping manufacturing process on the plate through a stamping die to form a base material, wherein the base material is provided with a plurality of flow channels, and the draft angle of the stamping die is more than 40 degrees.

10. The method for manufacturing a bipolar plate for a fuel cell according to claim 9, wherein the pressure of the calendaring process is 100MPa to 1500 MPa.

11. The method for manufacturing a bipolar plate for a fuel cell according to claim 9, wherein the temperature of the heat treatment process is 300 to 600 degrees celsius.

12. The method of manufacturing a bipolar plate for a fuel cell according to claim 9, further comprising performing a de-molding process.

13. The method of manufacturing a bipolar plate for a fuel cell according to claim 12, further comprising forming a resist layer on the substrate before the de-molding process is performed.