A metal bipolar plate with variable cross-section stepped flow channel for fuel cell

Abstract

The present invention relates to a metal bipolar plate with a variable cross-section and step-shaped flow channel for a fuel cell. In order to solve the problems of low gas diffusion efficiency, poor drainage, and uneven current density distribution of the linear flow channel of the metal bipolar plate, a metal bipolar plate structure with a variable cross-section and step-shaped flow channel for a fuel cell is proposed. The bottom of the oxygen flow channel and the hydrogen flow channel are both stepped, and each of the oxygen flow channel and the hydrogen flow channel includes m steps; the depth of each oxygen flow channel is gradually increased from the outer flow channel of the cathode monopolar plate to the middle flow channel, and the depth of each hydrogen flow channel is gradually reduced from the outer flow channel of the anode monopolar plate to the middle flow channel; from the flow channel inlet to the outlet direction, the depth of each step of the oxygen and hydrogen flow channels is gradually reduced, and the difference in the depth of the two adjacent steps is the same; the sizes of the cross sections of the oxygen and hydrogen flow channels perpendicular to the gas flow direction are different. The present invention can effectively improve the gas diffusivity and the uniformity of the current density of the rear section flow channel, and improve the drainage performance.

Description

Technical Field

[0001] The invention relates to a metal bipolar plate with a variable-section step-shaped flow channel of a fuel cell, and belongs to the technical field of fuel cells. Background Art

[0002] As a power generation device that directly converts hydrogen chemical energy into electrical energy, the metal bipolar plate proton exchange membrane fuel cell has a power generation efficiency of more than 50%, and the only product of fuel reaction power generation is water. It is an environmentally friendly energy supply device. At the same time, it has the characteristics of fast start-up, low operating temperature, and low noise, and is an ideal functional device for future automotive and other industries. As a core component of fuel cells, bipolar plates account for a large proportion of the quality and cost of the entire stack. The function of the bipolar plate is to isolate and distribute the reaction gas, collect and export current, connect each single cell in series, and support the entire stack structure. Therefore, there are certain requirements for the thermal conductivity, electrical conductivity, corrosion resistance, mechanical strength, cost and processing difficulty of the bipolar plate. The structure of the cathode flow field and the anode flow field formed on the metal bipolar plate directly affects the distribution of the reaction gas, while the structure of the cooling medium flow field formed on the metal bipolar plate directly affects the distribution of the cooling medium. Most existing flow channels are linear flow channels, such as the linear gradient flow channels disclosed in patent authorization publication number CN106571472B. This type of flow channel has the advantages of good processing and manufacturing performance and consistent reaction performance in each flow channel. However, compared with other complex flow channel forms, there are problems such as insufficient flow rate and low reaction gas diffusion efficiency, which are not conducive to the current density of the battery and affect the battery performance. If the reaction gas is unevenly distributed, it will lead to insufficient local gas supply and may also cause reduced battery performance; and the uneven distribution of the cooling medium will cause local overheating of the battery and even damage the battery stack. Therefore, it is necessary to invent a new type of flow channel that can not only have the advantages of a linear flow channel, but also increase the proportion of the contact area between the gas flow channel and the membrane electrode to improve battery performance. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and propose a metal bipolar plate structure with a variable-section stepped flow channel of a fuel cell, including a metal cathode plate and a metal anode plate, which can effectively improve the gas diffusion and uniformity of the current density in the rear section of the flow channel and improve the drainage performance.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A metal bipolar plate with variable cross-section step-shaped flow channels for a fuel cell, comprising an anode monopolar plate and a cathode monopolar plate, wherein a hydrogen flow channel is arranged on the outer side of the anode monopolar plate, and an oxygen flow channel is arranged on the outer side of the cathode monopolar plate, wherein the hydrogen flow channel and the oxygen flow channel both comprise n parallel straight-line flow channels, and the cathode monopolar plate and the anode monopolar plate are symmetrical in convex and concave directions, wherein the bottoms of the oxygen flow channel and the hydrogen flow channel are both step-shaped, and each oxygen flow channel and the hydrogen flow channel comprises m steps; the depth of each oxygen flow channel is characterized by gradually increasing from the outer flow channel of the cathode monopolar plate to the middle flow channel, while the depth of each hydrogen flow channel is characterized by gradually decreasing from the outer flow channel of the anode monopolar plate to the middle flow channel; from the flow channel inlet to the outlet direction, the depth of each step of the oxygen flow channel and the hydrogen flow channel decreases step by step, and the depth of two adjacent steps is gradually reduced. The difference in step depth is the same; the oxygen flow channel characteristics also include: oxygen flow channel depth, oxygen flow channel groove bottom width, oxygen flow channel step draft angle, oxygen flow channel wall and oxygen flow channel groove bottom projection on the vertical yoz coordinate plane formed by the angle, the oxygen flow channel wall and the oxygen flow channel top projection on the vertical yoz coordinate plane formed by the angle, the hydrogen flow channel characteristics also include: hydrogen flow channel depth, hydrogen flow channel groove bottom width, hydrogen flow channel step draft angle, hydrogen flow channel wall and hydrogen flow channel groove bottom projection on the vertical YOZ coordinate plane formed by the angle, the hydrogen flow channel wall and the hydrogen flow channel top projection on the vertical YOZ coordinate plane formed by the angle, the oxygen, hydrogen flow channels perpendicular to the gas flow direction of each cross-sectional size is different, the above characteristics are determined according to the following model:

[0006] 1) Oxygen channel depth y i (x,z) is determined according to the following model:

[0007]

[0008] In formula (1): h i1 is the channel depth of the i-th oxygen channel in the cathode flow field at coordinate (x, z) (0, 0); Δh is the difference between the oxygen channel depths at coordinate x = 0 and x = l in the same oxygen channel; l is the length of each step, ranging from 50mm to 100mm; i is the oxygen channel number, there are n oxygen channels in the cathode flow field, numbered from 1 to n, n≤100, and the channels numbered 1 and n are located at the outermost sides of the cathode flow field; j is the step number, the steps of each oxygen channel are numbered from 1 to m, m>3, the step numbered 1 is located at the entrance of the oxygen channel, and the step numbered m is located at the exit of the oxygen channel. The relationship between j and x can be expressed by the floor function Indicates that j is not greater than The maximum integer; a and b are the amplitude coefficients of each step, a∈[-1,1], b∈[0,0.3], independent variable x∈[0,L], L is the total length of the flow channel, L = 1m, w 2(x) is the width of the bottom of the oxygen channel at a distance x from the oxygen channel inlet;

[0009] 2) The width w of the bottom of the oxygen channel at the distance x from the oxygen channel inlet 2 (x) is determined according to the following model:

[0010]

[0011] In formula (2): w 2 is the width of the bottom of the oxygen channel at the inlet, and its value range is 0.9 mm to 1.8 mm; θ is the angle formed by the intersection line of the bottom of the oxygen channel and the wall of the oxygen channel;

[0012] 3) Draft angle α of each step of oxygen flow channel i (x), the angle γ formed by the projection of the oxygen channel wall and the bottom of the oxygen channel groove on the vertical yoz coordinate plane i (x), the angle β formed by the projection of the oxygen channel wall and the top of the oxygen channel on the vertical yoz coordinate plane i (x) is determined according to the following model:

[0013]

[0014] In formula (3): w 1 is the top width of the oxygen channel entrance, w 1 =w 2 +0.2;y i (x,w 2 (x)) is the coordinate of the i-th oxygen flow channel (x,w 2 The depth of the flow channel at (x));

[0015] 4) Hydrogen flow channel depth Y p (X,Z) is determined according to the following model:

[0016]

[0017] In formula (4): H p1 is the depth of the pth hydrogen flow channel in the anode flow field at the coordinate (X, Z) of (0,0); ΔH is the difference between the depth of the hydrogen flow channel at the coordinate X = 0 and the coordinate X = l of the same hydrogen flow channel, ΔH is equal to Δh; l is the length of each step; p is the hydrogen flow channel number, the hydrogen flow channels in the anode flow field are numbered from 1 to p, and the channels numbered 1 and p are located at the outermost sides of the anode flow field; q is the step number, and the steps of each hydrogen flow channel are numbered from 1 to q, q>3, the step numbered 1 is located at the entrance of the hydrogen flow channel, and the step numbered q is located at the exit of the hydrogen flow channel. The relationship between q and X can be expressed by the floor function It means that q is not greater than The largest integer; a and b are the amplitude coefficients of each step, the independent variable X∈[0,L], L is the total length of the flow channel, w 2 (X) is the width of the bottom of the hydrogen flow channel at a distance X from the hydrogen flow channel inlet;

[0018] The bottom width w of the hydrogen flow channel at a distance X from the hydrogen flow channel inlet 2 The calculation formula of (X) and the width w of the bottom of the oxygen channel at the distance x from the oxygen channel inlet 2 The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel;

[0019] The draft angle of each step of the hydrogen flow channel is α p The calculation formula of (X) and the draft angle α of each step of the oxygen flow channel i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel;

[0020] The angle γ formed by the projection of the hydrogen flow channel wall and the hydrogen flow channel bottom on the vertical YOZ coordinate plane p The calculation formula of (X) and the angle γ formed by the projection of the oxygen channel wall and the bottom of the oxygen channel groove on the vertical yoz coordinate plane i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel;

[0021] The angle β formed by the projection of the hydrogen flow channel wall and the top of the hydrogen flow channel on the vertical YOZ coordinate plane p The calculation formula of (X) and the angle β formed by the projection of the oxygen channel wall and the top of the oxygen channel on the vertical yoz coordinate plane i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel.

[0022] Furthermore, the channel depth h of the i-th oxygen channel of the cathode flow field at the coordinate (x, z) of (0,0) is i1 Determined according to the following model:

[0023]

[0024]

[0025] When the oxygen flow channel n is an odd number and When n is an odd number and When n is an even number and When n is an even number and When , the formula (8) is used for calculation;

[0026] In formula (5): k 1 The coordinates (x, z) of the first oxygen flow channel are (0,0) and The ratio of the oxygen flow channel coordinate (x, z) to the flow channel depth at (0, 0) ranges from 0.5 to 0.8; For the The depth of the oxygen flow channel at the coordinate (x, z) of (0,0) ranges from 0.2mm to 0.6mm, where In Indicates the cathode monopolar plate oxygen flow channel, 1 represents the first step at the entrance of the oxygen flow channel;

[0027] In formula (6): k 2 The coordinates (x, z) of the nth oxygen flow channel are (0,0) and The ratio of the depth of the oxygen channel at coordinate (x, z) (0, 0), k 2 With k 1 The value range of is equal;

[0028] In formula (7): k 3 The coordinates (x, z) of the first oxygen flow channel are (0,0) and The ratio of the oxygen flow channel coordinate (x, z) to the flow channel depth at (0, 0) ranges from 0.5 to 0.8; For the The depth of the oxygen flow channel at the coordinate (x, z) of (0,0) ranges from 0.2mm to 0.6mm;

[0029] In formula (8): k 4 The coordinates (x, z) of the nth oxygen flow channel are (0,0) and The ratio of the depth of the oxygen channel at coordinate (x, z) (0, 0), k 4 With k 3 The value range of is equal.

[0030] Furthermore, the difference Δh between the depths of the oxygen flow channel at x=0 and x=1 of the same oxygen flow channel is determined according to the following model:

[0031]

[0032]

[0033] When the oxygen flow channel n is an odd number, the calculation is performed using formula (9); when the oxygen flow channel n is an even number, the calculation is performed using formula (10);

[0034] In formula (9): k 5 For the The ratio of the depth of the oxygen flow channel at coordinate (x, z) (L, 0) to the depth of the flow channel at coordinate (x, z) (0, 0) ranges from 0.5 to 0.8;

[0035] In formula (10): k 6 For the The ratio of the depth of the oxygen flow channel at coordinate (x, z) (L, 0) to the depth of the flow channel at coordinate (x, z) (0, 0), k 6 With k 5 The value range of is equal.

[0036] Furthermore, the flow channel depth H at the coordinate (X, Z) of the pth hydrogen flow channel is (0,0) p1 Determined according to the following model:

[0037]

[0038]

[0039] When the hydrogen flow channel n is an odd number, the calculation is performed using formula (11); when the hydrogen flow channel n is an even number, the calculation is performed using formula (12);

[0040] In formula (11): K 5 For the The ratio of the depth of the hydrogen flow channel at coordinate (X, Z) (L, 0) to the depth of the flow channel at coordinate (X, Z) (0, 0), K 5 With k 5 The value range of is equal; For the The depth of the hydrogen flow channel at coordinate (X, Z) (0,0) is and The value range of H is equal; (n+1-p)m is the depth of the flow channel at the coordinate (X, Z) of the (n+1-p)th hydrogen flow channel (L, 0), ranging from 0.2 mm to 0.6 mm, where H (n+1-p)m The (n+1-p) in the figure represents the (n+1-p)th hydrogen flow channel of the anode monopolar plate, and m represents the mth step at the entrance of the hydrogen flow channel;

[0041] In formula (12): K 6 For the The ratio of the depth of the hydrogen flow channel at coordinate (X, Z) (L, 0) to the depth of the flow channel at coordinate (X, Z) (0, 0), K6 With K 5 The value range of is equal; For the The depth of the hydrogen flow channel at coordinate (X, Z) (0,0) is and The value range of is equal.

[0042] The beneficial effects of the present invention are:

[0043] The variable-section step-shaped flow channel promotes the reaction gas diffusion efficiency of the rear section of the flow channel and improves the uniformity of the current density of the step-shaped rear section of the flow channel. The variable-section flow channel can disturb the flow of the reaction gas, causing turbulence in the gas flowing through the flow channel and enhancing the diffusion capacity of the gas. The cathode monopolar plate adopts a structure in which the depth of the middle flow channel is greater than the depth of the outer flow channel, which can eliminate the uneven flow velocity distribution caused by the different paths of oxygen being transmitted from the oxygen inlet through the transition zone to the flow channel inlet, improve the uniformity of power density in each area of ​​the plate, and enhance the drainage of the flow channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a structural diagram of a metal bipolar plate of the present invention;

[0045] Figure 2 This is a structural diagram of the hydrogen flow field of the anode monopolar plate of the present invention;

[0046] Figure 3 This is a structural diagram of the oxygen flow field of the cathode monopolar plate of the present invention;

[0047] Figure 4 It is a schematic diagram of the flow direction of hydrogen, oxygen and cooling water in the flow channel area of ​​the metal bipolar plate of the present invention, taken along the CC and DD sections perpendicular to the two ends of the flow channel, including the local area of ​​the middle flow channel and the flow channels on the left and right sides, and when the bottom of the step groove is a curved surface;

[0048] Figure 5 It is a schematic structural diagram of a metal bipolar plate flow channel region of the present invention, cut along the CC and DD sections perpendicular to the two ends of the flow channel, including a local area of ​​the middle flow channel and the flow channels on the left and right sides, and the bottom of the step groove is a curved surface;

[0049] Figure 6 It is a schematic diagram of the structure of the hydrogen flow channel on the anode monopolar plate of the present invention, taken along the CC and DD sections perpendicular to the two ends of the flow channel, including the local area of ​​the middle flow channel and the left and right flow channels, and when the bottom of the step groove is a curved surface;

[0050] Figure 7 It is a schematic diagram of the structure of the oxygen flow channel on the cathode monopolar plate of the present invention, taken along the CC and DD sections perpendicular to the two ends of the flow channel, including the local area of ​​the middle flow channel and the left and right flow channels, and when the bottom of the step groove is a curved surface;

[0051] Figure 8 It is a schematic diagram of the inner wall of a single flow channel of the hydrogen flow channel of the present invention, wherein the bottom of the step groove is a curved surface;

[0052] Fig. 9 It is a schematic diagram of the inner wall of a single flow channel of the oxygen flow channel of the present invention, wherein the bottom of the step groove is a curved surface;

[0053] Fig.10 A top view of a single hydrogen flow channel in which the bottom of the step groove of the anode monopolar plate of the present invention is a curved surface;

[0054] Fig.11 It is a top view of a single oxygen flow channel with a curved bottom of the cathode monopolar plate step groove of the present invention;

[0055] Fig.12 The metal bipolar plate flow channel region of the present invention is cut along the CC and DD sections perpendicular to the flow channels, and contains two cooling medium flow channels, and when the bottom of the step groove is a curved surface, the hydrogen flow channel inlet ( Fig.10 A cross-sectional view along the hydrogen flow channel inlet direction when the mid-coordinate X=0;

[0056] Fig.13 The metal bipolar plate flow channel region of the present invention is cut along the CC and DD sections perpendicular to the flow channels, and contains two cooling medium flow channels, and when the step groove bottom is a curved surface, the distance from the hydrogen flow channel inlet is X ( Fig.10 (EE section when the middle coordinate X=X), a cross-sectional view along the direction of the hydrogen flow channel inlet;

[0057] Fig.14 The metal bipolar plate flow channel region of the present invention is cut along the CC and DD sections perpendicular to the flow channels, and contains two cooling medium flow channels, and when the bottom of the step groove is a curved surface, the distance from the oxygen flow channel inlet ( Fig.11 (x=0) section, a cross-sectional view along the oxygen flow channel inlet direction;

[0058] Fig.15 The metal bipolar plate platform flow channel region of the present invention is cut along the CC and DD sections perpendicular to the flow channels, and contains two cooling medium flow channels, and when the bottom of the step groove is a curved surface, the distance from the oxygen flow channel inlet is x ( Fig.11 (FF section when the middle coordinate x=x), a cross-sectional view along the oxygen flow channel inlet direction;

[0059] Fig.16 It is a schematic diagram of the flow direction of hydrogen, oxygen and cooling water on the flow channel area of ​​the metal bipolar plate of the present invention, taken along the CC and DD sections perpendicular to the two ends of the flow channel, including the local area of ​​the middle flow channel and the flow channels on the left and right sides, and when the bottom of the step groove is a plane;

[0060] Fig.17It is a structural schematic diagram of a metal bipolar plate flow channel region of the present invention, cut along the CC and DD sections perpendicular to the two ends of the flow channel, including a local area of ​​the middle flow channel and the flow channels on the left and right sides, and the bottom of the step groove is a plane;

[0061] Fig.18 It is a schematic diagram of the structure of the hydrogen flow channel on the anode monopolar plate of the present invention, taken along the CC and DD sections perpendicular to the two ends of the flow channel, including the local area of ​​the middle flow channel and the left and right flow channels, and when the bottom of the step groove is a plane;

[0062] Fig.19 It is a schematic diagram of the oxygen flow channel structure on the cathode monopolar plate of the present invention, taken along the CC and DD sections perpendicular to the two ends of the flow channel, including the local area of ​​the middle flow channel and the left and right flow channels, and when the bottom of the step groove is a plane;

[0063] Fig. 20 It is a schematic diagram of the inner wall of a single flow channel of the hydrogen flow channel of the present invention, wherein the bottom of the step groove is a plane;

[0064] Fig.21 It is a schematic diagram of the inner wall of a single flow channel of the oxygen flow channel of the present invention, wherein the bottom of the step groove is a plane;

[0065] Fig. 22 A top view of a single hydrogen flow channel of the anode monopolar plate of the present invention with a flat bottom of the step groove;

[0066] Fig.23 A top view of a single oxygen flow channel in which the bottom of the step groove of the cathode monopolar plate of the present invention is a plane;

[0067] Fig.24 The metal bipolar plate flow channel region of the present invention is cut along the CC and DD sections perpendicular to the flow channels, and contains two cooling medium flow channels, and the bottom of the step groove is a plane, and the distance from the hydrogen flow channel inlet ( Fig. 22 A cross-sectional view along the hydrogen flow channel inlet direction when the mid-coordinate X=0;

[0068] Fig.25 The metal bipolar plate flow channel region of the present invention is cut along the CC and DD sections perpendicular to the flow channels, and contains two cooling medium flow channels, and when the bottom of the step groove is a plane, the distance from the hydrogen flow channel inlet is X ( Fig. 22 (When the middle coordinate X=X) GG section, a cross-sectional view along the inlet direction of the hydrogen flow channel;

[0069] Fig.26 The metal bipolar plate flow channel region of the present invention is cut along the CC and DD sections perpendicular to the flow channels, and contains two cooling medium flow channels, and when the bottom of the step groove is a plane, the distance from the oxygen flow channel inlet ( Fig.23 (x=0) section, a cross-sectional view along the oxygen flow channel inlet direction;

[0070] Fig. 27 The metal bipolar plate flow channel region of the present invention is cut along the CC and DD sections perpendicular to the flow channels, and contains two cooling medium flow channels, and when the step groove bottom is a curved surface, the distance from the oxygen flow channel inlet is x ( Fig.23 HH section when the middle coordinate x=x), a cross-sectional view along the oxygen flow channel inlet direction;

[0071] In the figure, A-cathode monopolar plate, B-anode monopolar plate, 1-oxygen flow field inlet, 2-cooling medium flow field inlet, 3-hydrogen flow field outlet, 4-hydrogen outlet, 5-oxygen flow field outlet, 6-cooling medium flow field outlet, 7-hydrogen flow field inlet, 8-hydrogen inlet, 9-hydrogen flow channel, 10-oxygen inlet, 11-oxygen outlet, 12-oxygen flow channel, 13-cooling medium flow channel, 14-oxygen flow channel groove bottom, 15-oxygen flow channel wall, 16-oxygen flow channel top, 17-hydrogen flow channel groove bottom, 18-hydrogen flow channel wall, 19-hydrogen flow channel top. DETAILED DESCRIPTION

[0072] Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

[0073] like Figure 1 to Figure 3 As shown, a metal bipolar plate with a variable cross-section stepped flow channel for a fuel cell includes an anode monopolar plate B and a cathode monopolar plate A. A hydrogen flow channel 9 is provided on the outside of the anode monopolar plate B, and an oxygen flow channel 12 is provided on the outside of the cathode monopolar plate A. The hydrogen flow channel 9 and the oxygen flow channel 12 each include n parallel linear flow channels, and the cathode monopolar plate A and the anode monopolar plate B are symmetrical in convex and concave directions; wherein, as Figure 8-Figure 9 , Figure 20-21 As shown, the oxygen flow channel bottom 14 and the hydrogen flow channel bottom 17 are both step-shaped, and each oxygen flow channel 12 and hydrogen flow channel 9 includes m steps; Figure 7 , Fig.19 As shown, the depth of each oxygen flow channel 12 gradually increases from the outer flow channel to the middle flow channel of the cathode monopolar plate, as shown in FIG. Figure 6 , Fig.18 As shown, the depth of each hydrogen flow channel 9 gradually decreases from the outer flow channel to the middle flow channel of the anode monopolar plate; Figure 8-Figure 9 , Figure 20-21 As shown, from the flow channel inlet to the outlet direction, the depth of each step of the oxygen flow channel and the hydrogen flow channel decreases step by step, and the difference between the depths of two adjacent steps is the same; Figure 14-15 , Figure 26-27 As shown, the oxygen flow channel features also include: the width of the oxygen flow channel groove bottom, the draft angle of each step of the oxygen flow channel, the angle formed by the projection of the oxygen flow channel wall and the oxygen flow channel groove bottom on the vertical yoz coordinate plane, and the angle formed by the projection of the oxygen flow channel wall and the oxygen flow channel top on the vertical yoz coordinate plane; as shown Figure 12-13, Figure 24-25 As shown, the hydrogen flow channel features also include: hydrogen flow channel groove bottom width, hydrogen flow channel step draft angles, hydrogen flow channel wall and hydrogen flow channel groove bottom projection on the vertical YOZ coordinate plane formed by the angle formed by the hydrogen flow channel wall and the hydrogen flow channel top projection on the vertical YOZ coordinate plane, the above features are determined according to the following model:

[0074] 1) Oxygen channel depth y i (x,z) is determined according to the following model:

[0075]

[0076] In formula (1): h i1 is the channel depth of the i-th oxygen channel in the cathode flow field at coordinate (x, z) (0, 0); Δh is the difference between the oxygen channel depths at coordinate x = 0 and x = l in the same oxygen channel; l is the length of each step, ranging from 50mm to 100mm; i is the oxygen channel number, there are n oxygen channels in the cathode flow field, numbered from 1 to n, n≤100, and the channels numbered 1 and n are located at the outermost sides of the cathode flow field; j is the step number, the steps of each oxygen channel are numbered from 1 to m, m>3, the step numbered 1 is located at the entrance of the oxygen channel, and the step numbered m is located at the exit of the oxygen channel. The relationship between j and x can be expressed by the floor function Indicates that j is not greater than The maximum integer; a and b are the amplitude coefficients of each step, a∈[-1,1], b∈[0,0.3], independent variable x∈[0,L], L is the total length of the flow channel, L = 1m, w 2 (x) is the width of the bottom of the oxygen channel at a distance x from the oxygen channel inlet;

[0077] 2) The width w of the bottom of the oxygen channel at the distance x from the oxygen channel inlet 2 (x) is determined according to the following model:

[0078]

[0079] In formula (2): w 2 is the width of the bottom of the oxygen channel at the entrance, and its value range is 0.9mm to 1.8mm; θ is the angle between the bottom of the oxygen channel and the wall of the oxygen channel

[0080] 3) Draft angle α of each step of oxygen flow channel i (x), the angle γ formed by the projection of the oxygen channel wall and the bottom of the oxygen channel groove on the vertical yoz coordinate plane i (x), the angle β formed by the projection of the oxygen channel wall and the top of the oxygen channel on the vertical yoz coordinate plane i(x) is determined according to the following model:

[0081]

[0082] In formula (3): w 1 is the top width of the oxygen channel entrance, w 1 =w 2 +0.2;y i (x,w 2 (x)) is the coordinate of the i-th oxygen flow channel (x,w 2 The depth of the flow channel at (x));

[0083] 4) Hydrogen flow channel depth Y p (X,Z) is determined according to the following model:

[0084]

[0085] In formula (4): H p1 is the depth of the pth hydrogen flow channel in the anode flow field at the coordinate (X, Z) of (0,0); ΔH is the difference between the depth of the hydrogen flow channel at the coordinate X = 0 and the coordinate X = l of the same hydrogen flow channel, ΔH is equal to Δh; l is the length of each step; p is the hydrogen flow channel number, the hydrogen flow channels in the anode flow field are numbered from 1 to p, and the channels numbered 1 and p are located at the outermost sides of the anode flow field; q is the step number, and the steps of each hydrogen flow channel are numbered from 1 to q, q>3, the step numbered 1 is located at the entrance of the hydrogen flow channel, and the step numbered q is located at the exit of the hydrogen flow channel. The relationship between q and X can be expressed by the floor function It means that q is not greater than The largest integer; a and b are the amplitude coefficients of each step, the independent variable X∈[0,L], L is the total length of the flow channel, w 2 (X) is the width of the bottom of the hydrogen flow channel at a distance X from the hydrogen flow channel inlet;

[0086] The bottom width w of the hydrogen flow channel at a distance X from the hydrogen flow channel inlet 2 The calculation formula of (X) and the width w of the bottom of the oxygen channel at the distance x from the oxygen channel inlet 2 The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel;

[0087] The draft angle of each step of the hydrogen flow channel is α p The calculation formula of (X) and the draft angle α of each step of the oxygen flow channel i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel;

[0088] The angle γ formed by the projection of the hydrogen flow channel wall and the hydrogen flow channel bottom on the vertical YOZ coordinate plane p The calculation formula of (X) and the angle γ formed by the projection of the oxygen channel wall and the bottom of the oxygen channel groove on the vertical yoz coordinate plane i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel;

[0089] The angle β formed by the projection of the hydrogen flow channel wall and the top of the hydrogen flow channel on the vertical YOZ coordinate plane p The calculation formula of (X) and the angle β formed by the projection of the oxygen channel wall and the top of the oxygen channel on the vertical yoz coordinate plane i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel.

[0090] The depth h of the i-th oxygen flow channel of the cathode flow field at the coordinate (x, z) of (0,0) is i1 Determined according to the following model:

[0091]

[0092]

[0093] When the oxygen flow channel n is an odd number and When n is an odd number and When n is an even number and When n is an even number and When , the formula (8) is used for calculation;

[0094] In formula (5): k 1 The coordinates (x, z) of the first oxygen flow channel are (0,0) and The ratio of the oxygen flow channel coordinate (x, z) to the flow channel depth at (0, 0) ranges from 0.5 to 0.8; For the The depth of the oxygen flow channel at the coordinate (x, z) of (0,0) ranges from 0.2mm to 0.6mm, where In Indicates the cathode monopolar plate oxygen flow channel, 1 represents the first step at the entrance of the oxygen flow channel;

[0095] In formula (6): k 2The coordinates (x, z) of the nth oxygen flow channel are (0,0) and The ratio of the depth of the oxygen channel at coordinate (x, z) (0, 0), k 2 With k 1 The value range of is equal;

[0096] In formula (7): k 3 The coordinates (x, z) of the first oxygen flow channel are (0,0) and The ratio of the oxygen flow channel coordinate (x, z) to the flow channel depth at (0, 0) ranges from 0.5 to 0.8; For the The depth of the oxygen flow channel at the coordinate (x, z) of (0,0) ranges from 0.2mm to 0.6mm;

[0097] In formula (8): k 4 The coordinates (x, z) of the nth oxygen flow channel are (0,0) and The ratio of the depth of the oxygen channel at coordinate (x, z) (0, 0), k 4 With k 3 The value range of is equal.

[0098] The difference Δh between the depths of the oxygen flow channel at x=0 and x=1 of the same oxygen flow channel is determined according to the following model:

[0099]

[0100]

[0101] When the oxygen flow channel n is an odd number, the calculation is performed using formula (9); when the oxygen flow channel n is an even number, the calculation is performed using formula (10);

[0102] In formula (9): k 5 For the The ratio of the depth of the oxygen flow channel at coordinate (x, z) (L, 0) to the depth of the flow channel at coordinate (x, z) (0, 0) ranges from 0.5 to 0.8;

[0103] In formula (10): k 6 For the The ratio of the depth of the oxygen flow channel at coordinate (x, z) (L, 0) to the depth of the flow channel at coordinate (x, z) (0, 0), k 6 With k 5 The value range of is equal.

[0104] The depth H of the pth hydrogen flow channel at coordinate (X, Z) (0, 0) p1 Determined according to the following model:

[0105]

[0106]

[0107] When the hydrogen flow channel n is an odd number, the calculation is performed using formula (11); when the hydrogen flow channel n is an even number, the calculation is performed using formula (12);

[0108] In formula (11): K 5 For the The ratio of the depth of the hydrogen flow channel at coordinate (X, Z) (L, 0) to the depth of the flow channel at coordinate (X, Z) (0, 0), K 5 With k 5 The value range of is equal; For the The depth of the hydrogen flow channel at coordinate (X, Z) (0,0) is and The value range of H is equal; (n+1-p)m is the depth of the flow channel at the coordinate (X, Z) of the (n+1-p)th hydrogen flow channel (L, 0), ranging from 0.2 mm to 0.6 mm, where H (n+1-p)m The (n+1-p) in the figure represents the (n+1-p)th hydrogen flow channel of the anode monopolar plate, and m represents the mth step at the entrance of the hydrogen flow channel;

[0109] In formula (12): K 6 For the The ratio of the depth of the hydrogen flow channel at coordinate (X, Z) (L, 0) to the depth of the flow channel at coordinate (X, Z) (0, 0), K 6 With K 5 The value range of is equal; For the The depth of the hydrogen flow channel at coordinate (X, Z) (0,0) is and The value range of is equal.

[0110] The hydrogen flow channel bottom 17 and the oxygen flow channel bottom 14 both include two forms of changes: one is as follows Figure 6 to Figure 9 As shown, when a and b are not 0 at the same time, the bottom 17 of the hydrogen flow channel and the bottom 14 of the oxygen flow channel are both curved structures; the other is as follows Figure 18 to Figure 21 As shown, when a=0 and b=0, the bottom 17 of the hydrogen flow channel and the bottom 14 of the oxygen flow channel are both planar structures.

[0111] When the number of hydrogen flow channels on the anode monopolar plate is 50, the number of oxygen flow channels on the cathode monopolar plate is 50, the flow channel depth is 0.4 mm, the flow channel width is 1.5 mm, the angle between the flow channel wall and the flow channel bottom is 15°, each oxygen flow channel and hydrogen flow channel includes 4 steps, and the length of each step is 50 mm, the metal bipolar plate structure is as follows: Figure 1 to Figure 3 shown.

[0112] Figure 1 The metal bipolar plate shown is composed of a cathode monopolar plate A and an anode monopolar plate B. The cathode monopolar plate A includes an oxygen flow field inlet 1 and an oxygen inlet hole 10 located at the lower right corner of the plate, a group of oxygen flow channels 12 located in the middle of the plate, an oxygen flow field outlet 5 and an oxygen outlet hole 11 located at the upper left corner of the plate, Figure 3 The anode monopolar plate B includes a hydrogen flow field inlet 7 and a hydrogen inlet hole 8 located at the upper left corner of the plate, a group of hydrogen flow channels 9 located in the middle of the plate, a hydrogen outlet hole 4 and a hydrogen flow field outlet 3 located at the lower right corner of the plate, see Figure 2 .

[0113] When a=0 and b=0 in formula (1), along the direction from the inlet to the outlet of the oxygen flow channel, the bottom 14 of the oxygen flow channel of the cathode monopolar plate is a step-like structure, and the depth of each step of the oxygen flow channel 12 decreases step by step, the difference between the depths of two adjacent steps is the same, and the depth of the flow channel of each step body remains unchanged, the bottom of each step surface is a plane, the left and right walls of the oxygen flow channel are inclined surfaces, and the top 16 of the oxygen flow channel is a plane, such as Fig.16 , 19 21; the cross-sectional area of ​​the oxygen flow channel 12 along the direction perpendicular to the x-axis gradually decreases. Under the condition of constant flow rate, the oxygen flow rate increases and the pressure decreases along the direction from the oxygen flow channel inlet to the outlet, which can effectively improve the drainage performance of the flow channel. Fig.19 The structure of the middle flow channel and the flow channels on the left and right sides of the cathode monopolar plate is shown. The depth of each oxygen flow channel gradually increases from the outer flow channel of the cathode monopolar plate to the middle flow channel, and the increase in the depth of the flow channels between adjacent flow channels is the same. This structure can eliminate the uneven flow velocity distribution caused by the different paths of oxygen being transmitted from the oxygen inlet through the transition zone to the flow channel inlet, and improve the uniformity of power density in each area of ​​the plate. The intersection line of the oxygen flow channel groove bottom 14 and the oxygen flow channel wall forms a contraction angle θ, and the contraction angle θ of each step body is unchanged. From the oxygen flow channel inlet to the outlet, the contraction angle θ of each step is different and gradually decreases. Fig.23 As shown; the draft angle of each step of each channel of the cathode monopolar plate is α i (x) gradually increases from the oxygen channel inlet to the outlet, and the angle γ formed by the projection of the oxygen channel wall and the bottom of the oxygen channel groove on the vertical yoz coordinate plane i (x) With step draft angle α i(x) increases with the increase of the angle β formed by the projection of the oxygen channel wall and the top of the oxygen channel on the vertical yoz coordinate plane i (x), the angle β i (x) follows the γ i (x) increases and decreases, such as Figure 26-27 As shown; the runner contraction angle θ, the draft angle α i (x), angle β i (x), angle γ i The change of (x) and the gradual reduction of the step depth at each level make the flow channel cross section along the direction perpendicular to the x-axis change continuously. The sizes of the cross sections of the oxygen flow channel perpendicular to the airflow direction are different, so that the oxygen in the flow channel is disturbed, effectively enhancing the gas diffusion capacity.

[0114] When a=0 and b=0 in formula (4), from the inlet to the outlet of the hydrogen flow channel, the bottom 17 of the hydrogen flow channel of the anode monopolar plate is a step-shaped structure, and the depth of each step of the hydrogen flow channel decreases step by step, the difference between the depths of two adjacent steps is the same, and the depth of the flow channel of each step body remains unchanged, the bottom of each step surface is a plane, the left and right walls of the hydrogen flow channel are inclined surfaces, and the top 19 of the hydrogen flow channel is a plane. The above structural features are the same as those of the cathode monopolar plate. Fig.16 , 18 20; the cross-sectional area of ​​the hydrogen flow channel along the direction perpendicular to the X-axis gradually decreases. Under the condition of constant flow rate, the pressure decreases and the hydrogen flow rate increases along the direction from the inlet to the outlet of the hydrogen flow channel. Fig.18 The structure of the middle flow channel and the flow channels on the left and right sides of the anode monopolar plate is shown. The depth of each hydrogen flow channel gradually decreases from the outer flow channel of the anode monopolar plate to the middle flow channel, and the depth reduction between adjacent flow channels is the same. This structure can eliminate the uneven flow velocity distribution caused by the different paths of hydrogen being transmitted from the hydrogen inlet through the transition zone to the flow channel inlet, and improve the uniformity of power density in each area of ​​the plate. The intersection line of the hydrogen flow channel groove bottom 17 and the hydrogen flow channel wall forms a contraction angle θ. The contraction angle θ of each step body is unchanged. From the hydrogen flow channel inlet to the outlet, the contraction angle θ of each step is different and gradually decreases. Fig. 22 As shown; the draft angle of each step of each flow channel of the anode monopolar plate is α p (X) gradually increases from the hydrogen flow channel inlet to the outlet, and the angle γ formed by the projection of the hydrogen flow channel wall and the hydrogen flow channel bottom on the vertical YOZ coordinate plane p (X) With step draft angle α p (X) increases with the increase of the angle β formed by the projection of the hydrogen flow channel wall and the top of the hydrogen flow channel on the vertical YOZ coordinate plane p (X), the angle β p (X) as described γ p (X) increases and decreases, such as Figure 24-25 The runner contraction angle θ and the draft angle α p (X), angle β p (X), angle γ p The change of (X) and the reduction of the step depth at each level make the cross section of the flow channel along the direction perpendicular to the X-axis change continuously. The cross sections of the hydrogen flow channel perpendicular to the gas flow direction are of different sizes, thereby disturbing the hydrogen in the flow channel and effectively enhancing the gas diffusivity.

[0115] When a and b in formula (1) are not 0 at the same time, from the oxygen flow channel inlet to the outlet, the bottom 14 of the oxygen flow channel of the cathode monopolar plate is a step-like structure, and the depth of each step of the oxygen flow channel decreases step by step, and the difference in the depth of two adjacent steps is the same. The bottom of each step groove is a curved surface, and the left and right walls of the flow channel are curved surfaces. The flow channel depth of each step body changes in the form of a sine function along the x-axis direction, and the flow channel depth changes in the form of a parabola along the z-axis direction, such as Figure 4 , 7 , 9; the flow channel characteristics make the oxygen pressure gradually decrease from the middle of the flow channel to the two sides of the flow channel, and the oxygen flow rate gradually increases from the middle of the flow channel to the two sides of the flow channel. This increases the gas turbulence characteristics in the flow channel, effectively promotes gas diffusion, and improves oxygen utilization. Figure 7 The structure of the middle flow channel and some of the flow channels on the left and right sides of the cathode monopolar plate is shown. The depth of each oxygen flow channel gradually increases from the outer flow channel to the middle flow channel of the cathode monopolar plate, and the increase in the depth of the flow channels between adjacent flow channels is the same. This structure can eliminate the uneven flow velocity distribution caused by the different paths of oxygen being transmitted from the oxygen inlet through the transition zone to the flow channel inlet, and improve the uniformity of power density in each area of ​​the plate. The intersection of the bottom of the oxygen flow channel groove and the oxygen flow channel wall forms a contraction angle θ. The contraction angle θ of each step body first increases, then decreases, and then increases again along the x-axis direction. From the oxygen flow channel inlet to the outlet, the contraction angle θ of each step is different and decreases as a whole. Fig.14 As shown; the draft angle of each step of each flow channel of the cathode monopolar plate is α i (x) gradually increases along the direction from the oxygen channel inlet to the outlet, and the angle γ formed by the projection of the oxygen channel wall and the bottom of the oxygen channel groove on the vertical yoz coordinate plane i (x) With the step draft angle α i (x) increases with the increase of the angle β formed by the projection of the oxygen channel wall and the top of the oxygen channel on the vertical yoz coordinate plane i (x), the angle β i (x) follows the γ i (x) increases and decreases, such as Figure 14-15 The oxygen flow channel has different cross-sectional sizes perpendicular to the airflow direction, and the flow channel contraction angle θ and draft angle α i (x), angle β i(x), angle γ i The change of (x) and the reduction of step depth at each level cause the flow channel cross section along the oxygen flow channel inlet to outlet to change continuously, thereby disturbing the oxygen in the flow channel and effectively increasing the gas diffusion capacity.

[0116] When a and b in formula (4) are not 0 at the same time, from the hydrogen flow channel inlet to the outlet direction, the bottom 17 of the hydrogen flow channel of the anode monopolar plate is a step-like structure, and the depth of each step of the hydrogen flow channel decreases step by step, and the difference in the depth of two adjacent steps is the same. The bottom of each step groove is a curved surface, and the left and right walls of the flow channel are curved surfaces. The flow channel depth of each step body changes along the X-axis direction in the form of a sine function corresponding to the cathode plate, and the flow channel depth changes along the Z-axis direction in a parabolic form, such as Figure 4 , 6 , as shown in 8; the flow channel characteristics make the hydrogen pressure gradually decrease from the middle of the flow channel to the two sides of the flow channel, and the hydrogen flow rate gradually increases from the middle of the flow channel to the two sides of the flow channel, so that the diffusion of the gas in the flow channel to the area corresponding to the flow channel ridge is enhanced, thereby improving the uniformity of the current density distribution. Figure 6 The structure of the middle flow channel and some of the flow channels on the left and right sides of the anode monopolar plate is shown. The depth of each hydrogen flow channel gradually decreases from the outer flow channel to the middle flow channel of the anode monopolar plate, and the depth reduction between adjacent flow channels is the same. This structure can eliminate the uneven flow velocity distribution caused by the different paths of hydrogen being transmitted from the hydrogen inlet through the transition zone to the flow channel inlet, and improve the uniformity of power density in each area of ​​the plate. The intersection of the bottom of the hydrogen flow channel groove and the wall of the hydrogen flow channel forms a contraction angle θ. The contraction angle θ of each step body first increases, then decreases, and then increases again along the X-axis direction. From the hydrogen flow channel inlet to the outlet, the contraction angle θ of each step is different and decreases as a whole, such as Fig.10 As shown; the draft angle of each step of each flow channel of the anode monopolar plate is α p (X) gradually increases along the direction from the hydrogen flow channel inlet to the outlet, and the angle γ formed by the projection of the hydrogen flow channel wall and the bottom of the hydrogen flow channel groove on the vertical YOZ coordinate plane p (X) With step draft angle α p (X) increases with the increase of the angle β formed by the projection of the hydrogen flow channel wall and the top of the hydrogen flow channel on the vertical YOZ coordinate plane p (X), the angle β p (X) as described γ p (X) increases and decreases, such as Figure 12-13 The cross-sections of the hydrogen flow channel perpendicular to the direction of the gas flow have different sizes, and the flow channel contraction angle θ and draft angle α p (X), angle β p (X), angle γ pThe change of (X) and the reduction of step depth at each level cause the flow channel cross section along the hydrogen flow channel inlet to outlet to change continuously, thereby disturbing the oxygen in the flow channel and effectively increasing the gas diffusion capacity.

[0117] The different flow channel structures proposed in the present invention are simulated, and the basic structural parameters of the flow channel are: the number of flow channels is 50, the flow channel depth is 0.4 mm, the flow channel width is 1.5 mm, and the angle between the flow channel wall and the flow channel groove bottom is 15°. Compared with the straight flow channel and the straight gradient flow channel, the simulation results are shown in Table 1.

[0118] Table 1 Different effects achieved by different flow channel designs of metal bipolar plates

[0119] Current density (A / cm^2) Maximum flow rate (m / s) Oxygen concentration change (mol / m^3) Straight channel 1.2 36.2 1.4 Straight gradient flow channel 1.21 54.5 1.6 Stepped flow channel 1.23 81.9 2.7

[0120] As shown in Table 1, when the metal bipolar plate adopts the variable cross-section step-shaped flow channel design of the present invention, under the same conditions, the variable cross-section step-shaped flow channel can disturb the flow of the reaction gas, causing turbulence in the gas flowing through the flow channel, and enhancing the gas diffusion efficiency of the step flow channel. It can be seen from Table 1 that the flow velocity of the step-shaped flow channel is significantly greater than the flow velocity of the straight-line flow channel, and the maximum flow velocity is more than twice the flow velocity of the straight-line flow channel, proving that the variable cross-section step-shaped flow channel has achieved good results in improving the drainage performance of the flow channel; the variable cross-section step-shaped flow channel promotes the reaction gas diffusion efficiency of the rear section flow channel, so that the current density of the step-shaped rear section flow channel is increased by about 1.5% relative to the current density of the straight-line gradient flow channel, and is increased by 2% to 5% relative to the current density of the straight-line flow channel; thereby proving the superiority of the variable cross-section step-shaped flow channel structure of the present invention in improving battery performance.

Claims

1. A metal bipolar plate with variable cross-section stepped flow channels for a fuel cell, comprising an anode monopolar plate and a cathode monopolar plate, wherein a hydrogen flow channel is disposed on the outer side of the anode monopolar plate, and an oxygen flow channel is disposed on the outer side of the cathode monopolar plate, wherein the hydrogen flow channel and the oxygen flow channel both comprise n parallel linear flow channels, and the cathode monopolar plate and the anode monopolar plate are symmetrical in convex and concave directions, and characterized in that: The bottoms of the oxygen flow channel and the hydrogen flow channel are both step-shaped, and each of the oxygen flow channel and the hydrogen flow channel includes m steps; the depth of each oxygen flow channel gradually increases from the outer flow channel of the cathode monopolar plate to the middle flow channel, and the depth of each hydrogen flow channel gradually decreases from the outer flow channel of the anode monopolar plate to the middle flow channel; From the flow channel inlet to the outlet direction, the depth of each step of the oxygen flow channel and the hydrogen flow channel decreases step by step, and the difference in the depth of two adjacent steps is the same; the oxygen flow channel characteristics also include: the oxygen flow channel depth, the oxygen flow channel groove bottom width, the oxygen flow channel step draft angle, the oxygen flow channel wall and the oxygen flow channel groove bottom projection on the vertical yoz coordinate plane formed by the angle, the oxygen flow channel wall and the oxygen flow channel top projection on the vertical yoz coordinate plane formed by the angle, the hydrogen flow channel characteristics also include: the hydrogen flow channel depth, the hydrogen flow channel groove bottom width, the hydrogen flow channel step draft angle, the hydrogen flow channel wall and the hydrogen flow channel groove bottom projection on the vertical YOZ coordinate plane formed by the angle, the hydrogen flow channel wall and the hydrogen flow channel top projection on the vertical YOZ coordinate plane formed by the angle, the oxygen and hydrogen flow channels are different in size in cross section perpendicular to the gas flow direction, and the above characteristics are determined according to the following model: 1) Oxygen channel depth y i (x,z) is determined according to the following model: ， In formula (1): h i1 is the channel depth of the i-th oxygen channel in the cathode flow field at coordinate (x, z) (0, 0); Δh is the difference between the oxygen channel depths at coordinate x = 0 and x = l of the same oxygen channel; l is the length of each step, ranging from 50 mm to 100 mm; i is the oxygen channel number, and the oxygen channels in the cathode flow field are numbered from 1 to n, and the channels numbered 1 and n are located at the outermost sides of the cathode flow field; j is the step number, and the steps of each oxygen channel are numbered from 1 to m, m>3, the step numbered 1 is located at the entrance of the oxygen channel, and the step numbered m is located at the exit of the oxygen channel. The relationship between j and x is expressed by the floor function Indicates that j is not greater than The maximum integer; a and b are the amplitude coefficients of each step, a∈[-1,1], b∈[0,0.3], independent variable x∈[0,L], , L is the total length of the flow channel, L=1m, w2(x) is the width of the bottom of the oxygen flow channel at a distance x from the oxygen flow channel inlet; 2) The width w2(x) of the bottom of the oxygen channel at a distance x from the oxygen channel inlet is determined according to the following model: ， In formula (2): w2 is the width of the bottom of the oxygen channel at the inlet, and its value range is 0.9 mm to 1.8 mm; θ is the angle between the intersection of the bottom of the oxygen channel and the wall of the oxygen channel; 3) Draft angle α of each step of oxygen flow channel i (x), the angle γ formed by the projection of the oxygen channel wall and the bottom of the oxygen channel groove on the vertical yoz coordinate plane i (x), the angle β formed by the projection of the oxygen channel wall and the top of the oxygen channel on the vertical yoz coordinate plane i (x) is determined according to the following model: ， In formula (3), w1 is the top width at the entrance of the oxygen flow channel, w1=w2+0.2; y i (x,w2(x)) is the depth of the i-th oxygen flow channel at the coordinate (x,w2(x)); 4) Hydrogen flow channel depth Y p (X,Z) is determined according to the following model: ， In formula (4): H p1 is the depth of the pth hydrogen flow channel in the anode flow field at the coordinate (X, Z) of (0,0); ΔH is the difference between the depth of the hydrogen flow channel at the coordinate X = 0 and the coordinate X = l of the same hydrogen flow channel, ΔH is equal to Δh; l is the length of each step; p is the hydrogen flow channel number, the hydrogen flow channels in the anode flow field are numbered from 1 to p, and the channels numbered 1 and p are located at the outermost sides of the anode flow field; q is the step number, and the steps of each hydrogen flow channel are numbered from 1 to q, q>3, the step numbered 1 is located at the entrance of the hydrogen flow channel, and the step numbered q is located at the exit of the hydrogen flow channel. The relationship between q and X is expressed by the floor function It means that q is not greater than The maximum integer of ; a and b are the amplitude coefficients of each step, the independent variable X∈[0,L], , L is the total length of the flow channel, w2(X) is the bottom width of the hydrogen flow channel at a distance X from the hydrogen flow channel inlet; The calculation formula for the bottom width w2(x) of the hydrogen flow channel at a distance x from the hydrogen flow channel inlet and the calculation formula for the bottom width w2(x) of the oxygen flow channel at a distance x from the oxygen flow channel inlet are the same except for the independent variables, wherein the meaning of the independent variables in the hydrogen flow channel is correspondingly the same as that in the oxygen flow channel; The draft angle of each step of the hydrogen flow channel is α p The calculation formula of (X) and the draft angle α of each step of the oxygen flow channel i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel; The angle γ formed by the projection of the hydrogen flow channel wall and the hydrogen flow channel bottom on the vertical YOZ coordinate plane p The calculation formula of (X) and the angle γ formed by the projection of the oxygen channel wall and the bottom of the oxygen channel groove on the vertical yoz coordinate plane i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel; The angle β formed by the projection of the hydrogen flow channel wall and the top of the hydrogen flow channel on the vertical YOZ coordinate plane p The calculation formula of (X) and the angle β formed by the projection of the oxygen channel wall and the top of the oxygen channel on the vertical yoz coordinate plane i The calculation formula of (x) is the same except for the independent variable, wherein the independent variable has the same meaning as that in the oxygen flow channel; The depth h of the i-th oxygen flow channel of the cathode flow field at the coordinate (x, z) of (0,0) is i1 Determined according to the following model: ， When the oxygen flow channel n is an odd number and When n is an odd number and When n is an even number and When n is an even number and When , the formula (8) is used for calculation; In formula (5), k1 is the distance between the first oxygen flow channel at coordinate (x, z) (0,0) and the first The ratio of the oxygen flow channel coordinate (x, z) to the flow channel depth at (0, 0) ranges from 0.5 to 0.8; For the The depth of the oxygen flow channel at the coordinate (x, z) of (0,0) ranges from 0.2mm to 0.6mm, where In Indicates the cathode monopolar plate oxygen flow channel, 1 represents the first step at the entrance of the oxygen flow channel; In formula (6): k2 is the distance between the nth oxygen flow channel at coordinate (x, z) (0,0) and the nth oxygen flow channel at coordinate (x, z) (0,0). The coordinates (x, z) of the oxygen flow channel are the ratio of the flow channel depth at (0, 0), and the value ranges of k2 and k1 are equal; In formula (7): k3 is the distance between the first oxygen flow channel at coordinate (x, z) (0,0) and the first The ratio of the oxygen flow channel coordinate (x, z) to the flow channel depth at (0, 0) ranges from 0.5 to 0.8; For the The depth of the oxygen flow channel at the coordinate (x, z) of (0,0) ranges from 0.2mm to 0.6mm; In formula (8): k4 is the distance between the nth oxygen flow channel at coordinate (x, z) (0,0) and the nth oxygen flow channel at coordinate (x, z) (0,0). The coordinates (x, z) of the oxygen flow channel are the ratio of the flow channel depth at (0, 0), and the value ranges of k4 and k3 are equal; The difference Δh between the depths of the oxygen flow channel at x=0 and x=1 of the same oxygen flow channel is determined according to the following model: ， When the oxygen flow channel n is an odd number, the calculation is performed using formula (9); when the oxygen flow channel n is an even number, the calculation is performed using formula (10); In formula (9): k5 is the The ratio of the depth of the oxygen flow channel at coordinate (x, z) (L, 0) to the depth of the flow channel at coordinate (x, z) (0, 0) ranges from 0.5 to 0.8; In formula (10): k6 is the The ratio of the depth of the oxygen flow channel at the coordinate (x, z) (L, 0) to the depth of the flow channel at the coordinate (x, z) (0, 0), the value range of k6 is equal to that of k5.

2. A metal bipolar plate with a variable cross-section stepped flow channel for a fuel cell according to claim 1, characterized in that: The depth H of the pth hydrogen flow channel at coordinate (X, Z) (0, 0) p1 Determined according to the following model: ， When the hydrogen flow channel n is an odd number, the calculation is performed using formula (11); when the hydrogen flow channel n is an even number, the calculation is performed using formula (12); In formula (11): K5 is the The ratio of the depth of the hydrogen flow channel at the coordinate (X, Z) (L, 0) to the depth of the flow channel at the coordinate (X, Z) (0, 0), the value range of K5 and k5 is equal; For the The depth of the hydrogen flow channel at coordinate (X, Z) (0,0) is and The value range of H is equal; (n+1-p)m is the depth of the flow channel at the coordinate (X, Z) of the (n+1-p)th hydrogen flow channel (L, 0), ranging from 0.2 mm to 0.6 mm, where H (n+1-p)m The (n+1-p) in the figure represents the (n+1-p)th hydrogen flow channel of the anode monopolar plate, and m represents the mth step at the entrance of the hydrogen flow channel; In formula (12): K6 is the The ratio of the depth of the hydrogen flow channel at the coordinate (X, Z) (L, 0) to the depth of the flow channel at the coordinate (X, Z) (0, 0), the value range of K6 and K5 is equal; For the The depth of the hydrogen flow channel at coordinate (X, Z) (0,0) is and The value range of is equal.

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