CN114068948B - Fuel cell bipolar plate with bionic active water collecting and draining function and water collecting and draining method - Google Patents
Fuel cell bipolar plate with bionic active water collecting and draining function and water collecting and draining method Download PDFInfo
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- CN114068948B CN114068948B CN202111361187.4A CN202111361187A CN114068948B CN 114068948 B CN114068948 B CN 114068948B CN 202111361187 A CN202111361187 A CN 202111361187A CN 114068948 B CN114068948 B CN 114068948B
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H—ELECTRICITY
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- H01M8/10—Fuel cells with solid electrolytes
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Abstract
The invention discloses a fuel cell bipolar plate with bionic active water collecting and draining function and a water collecting and draining method. The invention etches the low surface energy film with low adhesion effect on the flow field wall to form hydrophilic pattern with periodic arrangement of hydrophilicity, which forms bionic surface of hydrophilic and hydrophobic coupling on the back of the simulated desert beetle; when the water yield of the fuel cell is smaller than the water demand, the product water can be effectively captured and collected and uniformly distributed, so that the proton conductivity of the proton exchange membrane is enhanced; when the water yield of the fuel cell is greater than the water demand, liquid drops accumulated on the surface of the gas diffusion layer can be sucked out and trapped on the bionic surface of the wall surface of the flow field, and the water draining speed of the flow field is accelerated, the mass transfer efficiency is enhanced, and the performance and the stability of the fuel cell are further improved through the synergistic effect of active water draining of the bionic surface and air flow dragging.
Description
Technical Field
The invention relates to a fuel cell technology, in particular to a fuel cell bipolar plate with a bionic active water collecting and draining function and a water collecting and draining method.
Background
The fuel cell is a power generation device for directly converting chemical energy of fuel into electric energy, the process is not limited by the Carnot cycle, and the fuel cell has the advantages of high energy conversion efficiency, zero emission and no pollution, and is regarded as the most promising power generation technology. The fuel cell represented by proton exchange membrane fuel cells (Proton Exchange Membrane Fuel Cell, PEMFC) has the outstanding advantages of modularized structural units, simple and convenient assembly, high specific power and reliability and the like, and is applied to the fields of traffic, energy sources, military, aerospace and the like. However, the water management problem of proton exchange membrane fuel cells has been one of the key issues limiting their life and performance. During normal operation of a proton exchange membrane fuel cell, the internal electrochemical reaction continues, and product water appears on the cathode side of the fuel cell. On the one hand, proton exchange membranes require a certain amount of water to increase their proton conductivity; on the other hand, excessive product water can accumulate in the cathode bipolar plate flow channels of the fuel cell to cause flooding. Therefore, it is necessary to maintain a stable and balanced water environment inside the fuel cell, which is related to whether the fuel cell can operate smoothly and efficiently.
The bipolar plate is one of important components for mass transfer and drainage of the fuel cell, and plays a very important role in maintaining the water balance inside the fuel cell. Currently, improvements in bipolar plates for fuel cell water management problems are mainly three: 1. the bipolar plate structure design, such as 3D flow field, composite flow field, etc. can strengthen the airflow speed in the flow field, change the airflow state and strengthen the drainage capacity. The defects are obvious, the design of the complex flow field clearly increases the processing difficulty and cost of the bipolar plate, and the bipolar plate is not beneficial to wide popularization and use; 2. the surface modification treatment of the bipolar plate is based on physical vapor deposition, chemical vapor deposition, electroplating and other technologies, hydrophilic and hydrophobic coatings are processed on the surface of the bipolar plate, and the water management problem of the fuel cell is improved by utilizing the wetting state of product water in different flow channels. The defect of the treatment mode cannot be ignored, no matter which coating processing technology is adopted, the treatment mode is still a flow channel with single wettability, passive drainage is carried out under the purging action of high-speed air flow in the flow channel, and the phenomena of flooding (hydrophilic coating) and drying (hydrophobic coating) of extreme phenomena of a battery are easy to occur, so that the treatment mode becomes the hidden trouble of the performance reduction and unstable operation of the battery.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a fuel cell bipolar plate with a bionic active water collecting and draining function and a water collecting and draining method, which are inspired by organisms in nature, and the functional surface with the characteristics of superhydrophobicity, low adhesion, thorn directional water transportation and high-efficiency water collection of the back of a beetle in a desert is processed in a flow field of the cell bipolar plate, so that the fuel cell bipolar plate has the functions of active water collection and drainage, the mass transfer capacity of the cell bipolar plate is improved, the water draining efficiency of the cell bipolar plate is enhanced, and the smooth progress of electrochemical reaction of the fuel cell is ensured, thereby improving the performance of the cell.
An object of the present invention is to provide a fuel cell bipolar plate with bionic active water collecting and draining function.
The fuel cell includes: bipolar plates, gas diffusion layers and catalyst layers and proton exchange membranes; the proton exchange membrane is positioned in the center, and two sides of the proton exchange membrane are respectively provided with a cathode catalyst layer, an anode catalyst layer, a cathode gas diffusion layer, an anode gas diffusion layer and a cathode bipolar plate and an anode bipolar plate which are symmetrically distributed from inside to outside.
The fuel cell bipolar plate with bionic active water collecting and draining function comprises: the bipolar plate comprises a bipolar plate main body, a main runner, an upper split runner, a lower converging runner, an air inlet and an air outlet; wherein the bipolar plate main body is a flat plate; a plurality of main flow channels which are periodically distributed are carved on the front surface of the bipolar plate main body; an upper flow dividing runner and a lower flow converging runner which are communicated with each main runner are respectively carved on the front surface of the bipolar plate main body and the upper end and the lower end of the main runner, and the main runners, the upper flow dividing runner and the lower flow converging runner jointly form a flow field; each of the main flow channel, the upper flow distributing channel and the lower flow distributing channel has a first side wall and a second side wall, the first side wall and the second side wall are vertical to the surface of the bipolar plate main body, and the bottom wall is parallel to the surface of the bipolar plate main body; an air inlet is formed in one end of the upper flow dividing channel, and an air outlet is formed in the other end of the lower flow dividing channel opposite to the air inlet; performing hydrophobic treatment on the first side wall, the second side wall and the bottom wall of each main runner, the upper flow dividing runner and the lower flow dividing runner to form a low surface energy film, wherein the film has the hydrophobic characteristic of imitating the low adhesion effect of the lotus leaf surface, so that the first side wall, the second side wall and the bottom wall form a hydrophobic surface with the hydrophobic characteristic; carrying out partial laser etching on the low-surface-energy film of the first side wall, etching away part of the low-surface-energy film to expose part of the surface of the bipolar plate main body, and forming micro-scale and nano-scale concave-convex structures on the surface to enable the etched area to have hydrophilic characteristics, forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, so that a hydrophobic surface and the vertical hydrophilic patterns are alternately arranged on the surface of the first side wall, wherein each vertical hydrophilic pattern is in a vertical trapezoid shape; the upper bottom and the lower bottom of the vertical trapezoid are both in the air flow transmission direction, the height of the upper bottom is in the horizontal direction and is consistent with the depth of the first side wall, the upper bottom is aligned with the front edge of the first side wall, the lower bottom is aligned with the bottom edge of the first side wall, the upper side waist is not larger than the lower side waist, and therefore the upper bottom is in an isosceles trapezoid shape or has downward inclination along the air flow transmission direction, and the arrangement period of a plurality of vertical hydrophilic patterns is longer than that of the lower bottom of the vertical trapezoid; carrying out partial laser etching on the low-surface-energy film of the second side wall, etching away part of the low-surface-energy film to expose part of the surface of the bipolar plate main body, and forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, and forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, so that the surface of the second side wall is provided with a plurality of vertical hydrophilic patterns, the hydrophobic surface and the vertical hydrophilic patterns are alternately arranged, the vertical hydrophilic patterns of each second side wall are identical to the vertical hydrophilic patterns of the first side wall, the arrangement period of the vertical hydrophilic patterns of the second side wall is identical to the arrangement period of the vertical hydrophilic patterns of the first side wall, and the corresponding vertical hydrophilic patterns of the first side wall and the second side wall are aligned or arranged in a staggered manner; carrying out partial laser etching on the low surface energy film of the bottom wall, etching away part of the low surface energy film to expose part of the surface of the bipolar plate main body, and forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, so as to form a plurality of horizontal hydrophilic patterns which are periodically arranged along the airflow transmission direction, and further form a plurality of hydrophobic surfaces which are alternately arranged with the horizontal hydrophilic patterns on the surface of the bottom wall, wherein each horizontal hydrophilic pattern is in a horizontal trapezoid shape; the upper bottom and the lower bottom of the horizontal trapezoid are perpendicular to the airflow transmission direction, the period of the horizontal hydrophilic pattern of the bottom wall is consistent with the height of the horizontal trapezoid along the airflow transmission direction, and the horizontal hydrophilic pattern is communicated so that drainage is smooth and product water is uniformly distributed on the bottom wall of the flow field; the etched vertical hydrophilic patterns and horizontal hydrophilic patterns are trapezoids imitating thorns of cactus, unbalanced Laplacian pressure can be generated on two sides of the upper bottom and the lower bottom of the trapezoids by liquid drops, the side of the upper bottom is higher than the side of the lower bottom, and the liquid drops can spontaneously move from the upper bottom to the lower bottom of the trapezoids, so that the device has the function of directional water transportation; further, periodic vertical hydrophilic patterns and horizontal hydrophilic patterns are etched on the side wall and the bottom wall of the flow field after the hydrophobic treatment, so that the hydrophobic characteristic and the hydrophilic characteristic are combined, hydrophilic and hydrophobic coupling bionic surfaces imitating the back of the beetles in the desert are formed on the surfaces of the side wall and the bottom wall of the flow field, and liquid drops on the lotus leaf-like low-adhesion hydrophobic surfaces are blown and rolled to the hydrophilic surfaces by airflow in the flow channels to be trapped, so that the efficient water collection function is realized;
When the fuel cell works, reaction gas enters the flow field through the gas inlet and is distributed on each main flow channel through the upper flow dividing flow channels, and the transmission direction of the reaction gas in the flow field is the air flow transmission direction; the reaction gas further passes through the gas diffusion layer to reach the catalyst layer to start electrochemical reaction, then product water enters the gas diffusion layer and accumulates on the surface of the gas diffusion layer facing to the flow field, the product water comprises liquid drops and also small fog drops, and then the liquid drops on the surface of the gas diffusion layer and the small fog drops carried by the air flow in the flow field are captured by the vertical hydrophilic patterns on the first side wall and the second side wall and the horizontal hydrophilic pattern on the bottom wall; when the water demand of the fuel cell is greater than the water yield, the trapped product water adheres to the vertical and horizontal hydrophilic patterns and is uniformly distributed and stored on the surfaces of the first side wall, the second side wall and the bottom wall of the flow field in the form of a water film, so that the water content of the fuel cell is kept, and the proton exchange membrane of the fuel cell is prevented from drying; when the water demand of the fuel cell is smaller than the water production, the trapped water accumulates on the vertical and horizontal hydrophilic patterns, which cause uneven surface tension of the water itself asymmetrically with respect to the air flow transmission direction, and the upper bottoms of the vertical and horizontal hydrophilic patterns are smaller than the lower bottoms, so that the laplace pressure of the droplets on the front side of the vertical and horizontal hydrophilic patterns is greater than the laplace pressure on the bottom side, thereby causing a laplace pressure difference; under the action of self uneven surface tension, laplace pressure difference and low surface slip resistance of a water film, product water starts to actively move in a directional manner along the air flow transmission direction; the product water trapped on the vertical and horizontal hydrophilic patterns in the flow field actively moves towards the air outlet and is simultaneously dragged by the shearing force of the air flow in the same direction in the flow field, so that the speed of discharging excessive product water from the flow field is further increased, the problem of flooding of the fuel cell is greatly relieved, the mass transfer efficiency of the fuel cell is enhanced, and the performance and stability of the fuel cell are improved.
The upper bottom of the trapezoid is smaller than the lower bottom.
Performing hydrophobic treatment on the first side wall, the second side wall and the bottom wall of the main runner by adopting a laser etching and chemical reagent soaking modification method to form a low-surface-energy film; firstly, performing laser etching to form micro-scale and nano-scale concave-convex structures, wherein the working parameters of the laser etching are that the scanning speed is 100mm/s-1000mm/s, the spot diameter is 10 mu m-50 mu m, the scanning interval is 10 mu m-50 mu m, and the processing power is 10w-30w; then carrying out chemical reagent soaking modification to form a low surface energy film on the concave-convex structure; the chemical agent is soaked into 0.5-2wt.% of ethanol solution of fluorosilane or stearic acid, and the low surface energy film is a fluorosilane or stearic acid film. Through hydrophobic treatment, the static contact angle of the two side walls and the bottom wall of the main runner is more than 135 degrees, and the rolling angle is less than 5 degrees.
The bipolar plate body is made of one of graphite, aluminum, nickel, titanium and stainless steel.
The flow field is one of a parallel flow field, a serpentine smooth flow field, an interdigital flow field, a composite flow field and a bionic flow field.
The cross sections of the main runner, the upper split runner and the lower combined runner are rectangular, the width is 0.5 mm-3.0 mm, and the depth is 0.5 mm-3.0 mm.
Processing the vertical hydrophilic patterns and the horizontal hydrophilic patterns on the two side walls and the bottom wall of the flow channel which are subjected to the hydrophobic treatment by using a laser etching method, and controlling the scanning area of laser according to the set patterns, wherein the working parameters of the laser are as follows: the scanning speed is 100mm/s-1000mm/s, the diameter of the light spot is 10 mu m-50 mu m, the scanning interval is 10 mu m-50 mu m, and the processing power is 10w-30w;
the static contact angle of the vertical hydrophilic pattern formed by etching is below 5 degrees; the static contact angle of the horizontal hydrophilic pattern is below 5 degrees; the length of the upper bottom of the vertical hydrophilic pattern is 0-3 mm, the length of the lower bottom is 1-3 mm, the period is 1-5 mm, and the wedge angle is 1-30 degrees; the upper bottom of the horizontal hydrophilic pattern has a length of 0-3 mm, the lower bottom of 1-3 mm, a height of 1-10 mm, and a wedge angle of 1-30 degrees.
Another object of the present invention is to provide a water collecting and draining method of a bipolar plate of a fuel cell with a bionic active water collecting and draining function.
The invention relates to a water collecting and draining method of a fuel cell bipolar plate with a bionic active water collecting and draining function, which comprises the following steps:
1) Preparing a fuel cell bipolar plate:
a) Providing a flat bipolar plate body;
b) A plurality of main flow channels which are periodically distributed are carved on the front surface of the bipolar plate main body; an upper flow dividing runner and a lower flow converging runner which are communicated with each main runner are respectively carved on the front surface of the bipolar plate main body and the upper end and the lower end of the main runner, and the main runners, the upper flow dividing runner and the lower flow converging runner jointly form a flow field; each of the main flow channel, the upper flow distributing channel and the lower flow distributing channel has a first side wall and a second side wall, the first side wall and the second side wall are vertical to the surface of the bipolar plate main body, and the bottom wall is parallel to the surface of the bipolar plate main body;
c) An air inlet is formed in one end of the upper flow dividing channel, and an air outlet is formed in the other end of the lower flow dividing channel opposite to the air inlet;
d) Performing hydrophobic treatment on the first side wall, the second side wall and the bottom wall of each main runner, the upper flow dividing runner and the lower flow dividing runner to form a low surface energy film, wherein the film has the hydrophobic characteristic of imitating the low adhesion effect of the lotus leaf surface, so that the first side wall, the second side wall and the bottom wall form a hydrophobic surface with the hydrophobic characteristic;
e) Carrying out partial laser etching on the low surface energy films of the first side walls of the main flow channel, the upper flow dividing flow channel and the lower flow dividing flow channel, etching away part of the low surface energy films to expose part of the surface of the bipolar plate main body, forming micro-scale and nano-scale concave-convex structures on the surface, enabling the etched area to have hydrophilic characteristics, forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, and forming alternate arrangement of the hydrophobic surface and the vertical hydrophilic patterns on the surface of the first side wall, wherein the shape of each vertical hydrophilic pattern is a vertical trapezoid; the upper bottom and the lower bottom of the vertical trapezoid are both in the air flow transmission direction, the height of the upper bottom is in the horizontal direction and is consistent with the depth of the first side wall, the upper bottom is aligned with the front edge of the first side wall, the lower bottom is aligned with the bottom edge of the first side wall, the upper side waist is not larger than the lower side waist, and therefore the upper bottom is in an isosceles trapezoid shape or has downward inclination along the air flow transmission direction, and the arrangement period of a plurality of vertical hydrophilic patterns is longer than that of the lower bottom of the vertical trapezoid; carrying out partial laser etching on the low-surface-energy film of the second side wall, etching away part of the low-surface-energy film to expose part of the surface of the bipolar plate main body, and forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, and forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, so that the surface of the second side wall is provided with a plurality of vertical hydrophilic patterns, the hydrophobic surface and the vertical hydrophilic patterns are alternately arranged, the vertical hydrophilic patterns of each second side wall are identical to the vertical hydrophilic patterns of the first side wall, the arrangement period of the vertical hydrophilic patterns of the second side wall is identical to the arrangement period of the vertical hydrophilic patterns of the first side wall, and the corresponding vertical hydrophilic patterns of the first side wall and the second side wall are aligned or arranged in a staggered manner; carrying out partial laser etching on the low surface energy film of the bottom wall, etching away part of the low surface energy film to expose part of the surface of the bipolar plate main body, and forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, so as to form a plurality of horizontal hydrophilic patterns which are periodically arranged along the airflow transmission direction, and further form a plurality of hydrophobic surfaces which are alternately arranged with the horizontal hydrophilic patterns on the surface of the bottom wall, wherein each horizontal hydrophilic pattern is in a horizontal trapezoid shape; the upper bottom and the lower bottom of the horizontal trapezoid are perpendicular to the airflow transmission direction, the period of the horizontal hydrophilic pattern of the bottom wall is consistent with the height of the horizontal trapezoid along the airflow transmission direction, and the horizontal hydrophilic pattern is communicated so that drainage is smooth and product water is uniformly distributed on the bottom wall of the flow field; the etched vertical hydrophilic patterns and horizontal hydrophilic patterns are trapezoids imitating thorns of cactus, unbalanced Laplacian pressure can be generated on two sides of the upper bottom and the lower bottom of the trapezoids by liquid drops, the side of the upper bottom is higher than the side of the lower bottom, and the liquid drops can spontaneously move from the upper bottom to the lower bottom of the trapezoids, so that the device has the function of directional water transportation;
f) The periodic vertical hydrophilic patterns and the horizontal hydrophilic patterns are etched on the side wall and the bottom wall of the flow field after the hydrophobic treatment, so that the hydrophobic characteristic and the hydrophilic characteristic are combined, hydrophilic and hydrophobic coupling bionic surfaces imitating the backs of the desert beetles are formed on the surfaces of the side wall and the bottom wall of the flow field, and liquid drops on the lotus leaf-imitating low-adhesion hydrophobic surfaces are swept and rolled to the hydrophilic surfaces by airflow in the flow channels to be trapped, so that the efficient water collection function is realized;
2) When the fuel cell works, reaction gas enters the flow field through the gas inlet and is distributed on each main flow channel through the upper flow dividing flow channels, and the transmission direction of the reaction gas in the flow field is the air flow transmission direction;
3) The reaction gas further passes through the gas diffusion layer to reach the catalyst layer to start electrochemical reaction, then product water enters the gas diffusion layer and accumulates on the surface of the gas diffusion layer facing to the flow field, the product water comprises liquid drops and also small fog drops, and then the liquid drops on the surface of the gas diffusion layer and the small fog drops carried by the air flow in the flow field are captured by the vertical hydrophilic patterns on the first side wall and the second side wall and the horizontal hydrophilic pattern on the bottom wall;
4) When the water demand of the fuel cell is greater than the water yield, the trapped product water adheres to the vertical and horizontal hydrophilic patterns and is uniformly distributed and stored on the surfaces of the first side wall, the second side wall and the bottom wall of the flow field in the form of a water film, so that the water content of the fuel cell is kept, and the proton exchange membrane of the fuel cell is prevented from drying;
5) When the water demand of the fuel cell is smaller than the water production, the trapped water accumulates on the vertical and horizontal hydrophilic patterns, which cause uneven surface tension of the water itself asymmetrically with respect to the air flow transmission direction, and the upper bottoms of the vertical and horizontal hydrophilic patterns are smaller than the lower bottoms, so that the laplace pressure of the droplets on the front side of the vertical and horizontal hydrophilic patterns is greater than the laplace pressure on the bottom side, thereby causing a laplace pressure difference; under the action of self uneven surface tension, laplace pressure difference and low surface slip resistance of a water film, product water starts to actively move in a directional manner along the air flow transmission direction; the product water trapped on the vertical and horizontal hydrophilic patterns in the flow field actively moves towards the air outlet and is simultaneously dragged by the shearing force of the air flow in the same direction in the flow field, so that the speed of discharging excessive product water from the flow field is further increased, the problem of flooding of the fuel cell is greatly relieved, the mass transfer efficiency of the fuel cell is enhanced, and the performance and stability of the fuel cell are improved.
Wherein, in step d) of step 1), the first and second side walls and a bottom wall of each main runner, the upper split runner and the lower split runner are subjected to hydrophobic treatment by adopting a laser etching and chemical reagent soaking modification method to form a low surface energy film, comprising the following steps: firstly, performing laser etching to form micro-scale and nano-scale concave-convex structures, wherein the working parameters of the laser etching are that the scanning speed is 100mm/s-1000mm/s, the spot diameter is 10 mu m-50 mu m, the scanning interval is 10 mu m-50 mu m, and the processing power is 10w-30w; then carrying out chemical reagent soaking modification to form a low surface energy film on the concave-convex structure; the chemical agent is soaked into 0.5-2wt.% of ethanol solution of fluorosilane or stearic acid, and the low surface energy film is fluorosilane or stearic acid. Through hydrophobic treatment, the static contact angle of the two side walls and the bottom wall of the main runner is more than 135 degrees, and the rolling angle is less than 5 degrees.
In step e), performing partial laser etching on the low surface energy thin films of the first and second sidewalls and the bottom wall of each of the main flow channel, the upper flow dividing flow channel and the lower flow dividing flow channel, and laser etching off a part of the low surface energy thin films so as to expose a part of the surface of the bipolar plate main body, and forming micro-scale and nano-scale concave-convex structures on the surface so that the etched region has hydrophilic characteristics, comprising the following steps: focusing the light spots of laser on the surfaces of the low surface energy films of the first side wall, the second side wall and the bottom wall respectively, then demarcating a laser etching range according to the set vertical hydrophilic pattern and the horizontal hydrophilic pattern, finally carrying out laser etching on the demarcating range, and operating parameters of the laser etching: the scanning speed is 100mm/s-1000mm/s, the diameter of the light spot is 10 mu m-50 mu m, the scanning interval is 10 mu m-50 mu m, and the processing power is 10w-30w; the static contact angle of the vertical hydrophilic pattern and the horizontal hydrophilic pattern is below 10 degrees after laser etching treatment.
The invention has the advantages that:
the invention has the capability of actively capturing and draining water; when the water yield of the fuel cell is smaller than the water demand, the bionic surface of the flow field wall surface can effectively capture the product water, and the product water is collected and uniformly distributed by utilizing the high adhesion effect of the hydrophilic surface and the product water, so that the phenomenon of water shortage of the proton exchange membrane of the fuel cell in the initial working stage is relieved, the proton conductivity of the proton exchange membrane is enhanced, and the performance of the fuel cell is improved; when the water yield of the fuel cell is greater than the water demand, liquid drops accumulated on the surface of the gas diffusion layer can be sucked out and trapped on the bionic surface of the wall surface of the flow field, and the water draining speed of the flow field is accelerated, the transmission resistance of reaction gas in the flow field is reduced, the mass transfer efficiency of the bipolar plate is enhanced, and the performance and stability of the fuel cell are further improved through the synergistic effect of active water draining of the bionic surface and air flow dragging.
Drawings
FIG. 1 is a schematic illustration of one embodiment of a fuel cell bipolar plate with bionic active water collection and drainage function of the present invention;
fig. 2 is a schematic view of a first sidewall of an embodiment of a fuel cell bipolar plate with bionic active water collecting and draining function according to the present invention, wherein (a) is a schematic view of an upper side waist being equal to a lower side waist, and (b) is a schematic view of an upper side waist being smaller than a lower side waist;
fig. 3 is a schematic view of the bottom wall of one embodiment of a fuel cell bipolar plate with bionic active water collecting and draining function of the present invention.
Detailed Description
The invention will be further elucidated by means of specific embodiments in conjunction with the accompanying drawings.
As shown in fig. 1, the fuel cell bipolar plate with bionic active water collecting and draining function and the water collecting and draining method of the embodiment include: the bipolar plate comprises a bipolar plate main body 1, a main runner 2, an upper split runner 3, a lower split runner 4, an air inlet 5 and an air outlet 6; wherein the bipolar plate main body 1 is a flat plate; a plurality of main channels 2 which are periodically and vertically arranged are carved on the front surface of the bipolar plate main body 1; an upper flow dividing flow passage 3 and a lower flow converging flow passage 4 which are communicated with each main flow passage 2 and are perpendicular to the main flow passages 2 are engraved on the front surface of the bipolar plate main body 1 and at the upper end and the lower end of the main flow passages 2 respectively, and each main flow passage 2, the upper flow dividing flow passage 3 and the lower flow converging flow passage 4 jointly form a flow field, and the flow field is of a parallel flow field type; each of the main flow channel 2, the upper flow-dividing flow channel 3 and the lower flow-converging flow channel 4 has first and second side walls perpendicular to the surface of the bipolar plate body 1 and a bottom wall parallel to the surface of the bipolar plate body 1; an air inlet 5 is arranged at one end of the upper flow dividing channel 3, and an air outlet 6 is arranged at the other end of the lower flow dividing channel 4 opposite to the air inlet; the first and second side walls and a bottom wall of each main runner 2, the upper split runner 3 and the lower split runner 4 are subjected to hydrophobic treatment to form a low surface energy film, and the film has the hydrophobic characteristic of imitating the low adhesion effect of the lotus leaf surface, so that the first and second side walls and the bottom wall form a hydrophobic surface with the hydrophobic characteristic; carrying out partial laser etching on the low surface energy film of the first side wall, etching away part of the low surface energy film to expose part of the surface of the high surface energy film of the bipolar plate main body 1, forming micro-scale and nano-scale concave-convex structures on the surface to enable the etched area to have hydrophilic characteristics, forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, and forming a hydrophobic surface and vertical hydrophilic patterns on the surface of the first side wall to be alternately arranged, wherein each vertical hydrophilic pattern is in a vertical trapezoid shape; the upper bottom and the lower bottom of the vertical trapezoid are both in the air flow transmission direction, the height of the vertical trapezoid is in the horizontal direction and is consistent with the depth of the first side wall, the upper bottom is aligned with the front edge of the first side wall, the lower bottom is aligned with the bottom edge of the first side wall, the upper side waist is equal to the lower side waist to form an isosceles trapezoid, namely, two bottom angles are equal, as shown in fig. 2 (a), or the upper side waist is smaller than the lower side waist so as to have downward inclination along the air flow transmission direction, as shown in fig. 2 (b), the upper bottom angle is 0-90 degrees larger than the lower bottom angle, and the arrangement period of a plurality of vertical hydrophilic patterns is longer than that of the lower bottom of the vertical trapezoid; carrying out partial laser etching on the low-surface-energy film of the second side wall, etching away part of the low-surface-energy film to expose part of the surface of the high-surface-energy film of the bipolar plate main body 1, forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, and forming a plurality of vertical hydrophilic patterns on the surface of the second side wall, wherein the hydrophobic surface and the vertical hydrophilic patterns are alternately arranged, the vertical hydrophilic pattern of each second side wall is identical to the vertical hydrophilic pattern of the first side wall, the arrangement period of the vertical hydrophilic patterns of the second side wall is identical to the arrangement period of the vertical hydrophilic patterns of the first side wall, and the corresponding vertical hydrophilic patterns of the first side wall and the second side wall are aligned or arranged in a staggered manner; carrying out partial laser etching on the low surface energy film of the bottom wall, etching away part of the low surface energy film to expose part of the surface of the high surface energy film of the bipolar plate main body 1, and forming micro-scale and nano-scale concave-convex structures on the surface to enable the etched area to have hydrophilic characteristics, so as to form a plurality of horizontal hydrophilic patterns which are periodically arranged along the airflow transmission direction, thereby forming alternate arrangement of the hydrophobic surface and the horizontal hydrophilic patterns on the surface of the bottom wall, wherein each horizontal hydrophilic pattern is in a horizontal trapezoid shape, as shown in fig. 3; the upper bottom and the lower bottom of the horizontal trapezoid are perpendicular to the airflow transmission direction, the period of the horizontal hydrophilic pattern of the bottom wall is consistent with the height of the horizontal trapezoid along the airflow transmission direction, and the horizontal hydrophilic pattern is communicated so that drainage is smooth and product water is uniformly distributed on the bottom wall of the flow field; the etched vertical hydrophilic patterns and horizontal hydrophilic patterns are trapezoids imitating thorns of cactus, unbalanced Laplacian pressure can be generated on two sides of the upper bottom and the lower bottom of the trapezoids by liquid drops, the side of the upper bottom is higher than the side of the lower bottom, and the liquid drops can spontaneously move from the upper bottom to the lower bottom of the trapezoids, so that the device has the function of directional water transportation; the periodic vertical hydrophilic patterns and the horizontal hydrophilic patterns are etched on the side wall and the bottom wall of the flow field after the hydrophobic treatment, so that the hydrophobic characteristic and the hydrophilic characteristic are combined, hydrophilic and hydrophobic coupling bionic surfaces imitating the backs of the desert beetles are formed on the surfaces of the side wall and the bottom wall of the flow field, and liquid drops are blown and rolled to the hydrophilic surfaces by air flow in the flow channel on the lotus leaf-imitating low-adhesion hydrophobic surfaces to be trapped, and the efficient water collection function is realized.
In this embodiment, the bipolar plate body is graphite; the type of flow field is a parallel flow field; the cross section of the main runner, the upper flow dividing runner and the lower flow converging runner is rectangular, the width is 2.0mm, and the depth is 2.0mm. The length of the upper bottom of the vertical hydrophilic pattern is 2mm, the length of the lower bottom is 2.4mm, and the wedge angle alpha is 5 degrees or 15 degrees; the upper bottom of the horizontal hydrophilic pattern has a length of 0.5mm, the lower bottom has a length of 1.9mm, the height is 8mm, and the wedge angle alpha is 5 DEG or 15 deg.
The water collecting and draining method of the fuel cell bipolar plate with the bionic active water collecting and draining function comprises the following steps:
1) Preparing a fuel cell bipolar plate:
a) Providing a flat bipolar plate main body, wherein the material is graphite;
b) A plurality of main flow channels which are periodically and vertically distributed are carved on the front surface of the bipolar plate main body; an upper flow dividing runner and a lower flow converging runner which are communicated with each main runner and are vertical to the main runner are engraved on the front surface of the bipolar plate main body respectively at the upper end and the lower end of the main runner, and the main runners, the upper flow dividing runner and the lower flow converging runner jointly form a flow field;
each of the main flow channel, the upper flow distributing channel and the lower flow distributing channel has a first side wall and a second side wall, the first side wall and the second side wall are vertical to the surface of the bipolar plate main body, and the bottom wall is parallel to the surface of the bipolar plate main body;
c) An air inlet is arranged at one end of the upper flow dividing channel, and an outlet is arranged at the other end of the lower flow dividing channel opposite to the air inlet
An air port;
d) The first and second side walls and a bottom wall of each main runner, upper split runner and lower split runner are subjected to hydrophobic treatment to form a low surface energy film, and the film has hydrophobic characteristics of imitating the low adhesion effect of the lotus leaf surface, so that the first and second side walls and the bottom wall form a hydrophobic surface with hydrophobic characteristics:
firstly, performing laser etching to form micro-scale and nano-scale concave-convex structures, wherein the working parameters of the laser etching are that the scanning speed is 500mm/s, the spot diameter is 10 mu m, the scanning interval is 10 mu m and the processing power is 10w; then carrying out chemical reagent soaking modification to form a low surface energy film on the concave-convex structure; the chemical agent is soaked to 1wt.%
The fluorosilane or stearic acid ethanol solution, the low surface energy film is fluorosilane or stearic acid, the two side walls and the bottom wall of the main flow channel are subjected to hydrophobic treatment, the static contact angle is 159 degrees, and the rolling angle is 2 degrees;
e) Carrying out partial laser etching on the low surface energy films of the first side wall, the second side wall and the bottom wall, etching away part of the low surface energy films to expose part of the surface of the high surface energy film of the bipolar plate main body, forming micro-scale and nano-scale concave-convex structures on the surface, enabling the etched area to have hydrophilic characteristics, and forming a plurality of vertical hydrophilic patterns and horizontal hydrophilic patterns which are periodically arranged along the airflow transmission direction: focusing light spots of laser on the hydrophobic surfaces of the first side wall, the second side wall and the bottom wall respectively, then calling the designed vertical hydrophilic patterns and the designed horizontal hydrophilic patterns to define a laser etching range, and finally etching the defined range, wherein the working parameters of the photoetching are that the scanning speed is 500mm/s, the diameter of the light spots is 10 mu m, the scanning interval is 10 mu m and the processing power is 10w;
The static contact angles of the vertical hydrophilic patterns and the horizontal hydrophilic patterns are 5 degrees after laser etching treatment;
2) When the fuel cell works, reaction gas enters the flow field through the gas inlet and is distributed on each main flow channel through the upper flow dividing flow channels, and the transmission direction of the reaction gas in the flow field is the air flow transmission direction;
3) The reaction gas further passes through the gas diffusion layer to reach the catalyst layer to start electrochemical reaction, then product water enters the gas diffusion layer and accumulates on the surface of the gas diffusion layer facing to the flow field, the product water comprises liquid drops and also small fog drops, and then the liquid drops on the surface of the gas diffusion layer and the small fog drops carried by the air flow in the flow field are captured by the vertical hydrophilic patterns on the first side wall and the second side wall and the horizontal hydrophilic pattern on the bottom wall;
4) When the water demand of the fuel cell is greater than the water yield, the trapped product water adheres to the vertical and horizontal hydrophilic patterns and is uniformly distributed and stored on the surfaces of the first side wall, the second side wall and the bottom wall of the flow field in the form of a water film, so that the fuel cell maintains a certain water content, and the proton exchange membrane of the fuel cell is prevented from drying;
5) When the water demand of the fuel cell is smaller than the water production, the trapped water accumulates on the vertical and horizontal hydrophilic patterns, which cause uneven surface tension of the water itself asymmetrically with respect to the air flow transmission direction, and the upper bottoms of the vertical and horizontal hydrophilic patterns are smaller than the lower bottoms, so that the laplace pressure of the droplets on the front side of the vertical and horizontal hydrophilic patterns is greater than the laplace pressure on the bottom side, thereby causing a laplace pressure difference; under the action of self uneven surface tension, laplace pressure difference and low surface slip resistance of a water film, product water starts to actively move in a directional manner along the air flow transmission direction; the product water trapped on the vertical and horizontal hydrophilic patterns in the flow field actively moves towards the air outlet and is simultaneously dragged by the shearing force of the air flow in the same direction in the flow field, so that the discharge speed of the excessive product water from the flow field is further accelerated, the flooding problem of the fuel cell is greatly relieved, the mass transfer efficiency of the fuel cell is enhanced,
The performance and stability of the fuel cell are improved.
Finally, it should be noted that the examples are disclosed for the purpose of aiding in the further understanding of the present invention, but those skilled in the art will appreciate that: various alternatives and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the disclosed embodiments, but rather the scope of the invention is defined by the appended claims.
Claims (10)
1. A fuel cell bipolar plate with bionic active water collecting and draining function, characterized in that the fuel cell bipolar plate comprises: the bipolar plate comprises a bipolar plate main body, a main runner, an upper split runner, a lower converging runner, an air inlet and an air outlet; wherein the bipolar plate main body is a flat plate; a plurality of main flow channels which are periodically distributed are carved on the front surface of the bipolar plate main body; an upper flow dividing runner and a lower flow converging runner which are communicated with each main runner are respectively carved on the front surface of the bipolar plate main body and the upper end and the lower end of the main runner, and the main runners, the upper flow dividing runner and the lower flow converging runner jointly form a flow field; each of the main flow channel, the upper flow distributing channel and the lower flow distributing channel has a first side wall and a second side wall, the first side wall and the second side wall are vertical to the surface of the bipolar plate main body, and the bottom wall is parallel to the surface of the bipolar plate main body; an air inlet is formed in one end of the upper flow dividing channel, and an air outlet is formed in the other end of the lower flow dividing channel opposite to the air inlet; the surfaces of the first side wall, the second side wall and the bottom wall of each main runner, the upper flow dividing runner and the lower flow dividing runner are subjected to hydrophobic treatment to form a low surface energy film, and the film has the hydrophobic characteristic of imitating the low adhesion effect of the lotus leaf surface, so that the first side wall, the second side wall and the bottom wall form a hydrophobic surface with the hydrophobic characteristic; carrying out partial laser etching on the low-surface-energy film of the first side wall, etching away part of the low-surface-energy film to expose part of the surface of the bipolar plate main body, and forming micro-scale and nano-scale concave-convex structures on the surface to enable the etched area to have hydrophilic characteristics, forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, so that a hydrophobic surface and the vertical hydrophilic patterns are alternately arranged on the surface of the first side wall, wherein each vertical hydrophilic pattern is in a vertical trapezoid shape; the upper bottom and the lower bottom of the vertical trapezoid are both in the air flow transmission direction, are vertical to the air flow transmission direction, are consistent with the depth of the first side wall in height, are aligned with the front edge of the first side wall, the lower bottom is aligned with the bottom edge of the first side wall, and the upper side waist is not larger than the lower side waist, so that the vertical trapezoid is an isosceles trapezoid or has downward inclination along the air flow transmission direction, and the arrangement period of a plurality of vertical hydrophilic patterns is longer than that of the lower bottom of the vertical trapezoid; carrying out partial laser etching on the low-surface-energy film of the second side wall, etching away part of the low-surface-energy film to expose part of the surface of the bipolar plate main body, and forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, and forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, so that the surface of the second side wall is provided with a plurality of vertical hydrophilic patterns, the hydrophobic surface and the vertical hydrophilic patterns are alternately arranged, the vertical hydrophilic patterns of each second side wall are identical to the vertical hydrophilic patterns of the first side wall, the arrangement period of the vertical hydrophilic patterns of the second side wall is identical to the arrangement period of the vertical hydrophilic patterns of the first side wall, and the corresponding vertical hydrophilic patterns of the first side wall and the second side wall are aligned or arranged in a staggered manner; carrying out partial laser etching on the low surface energy film of the bottom wall, etching away part of the low surface energy film to expose part of the surface of the bipolar plate main body, and forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, so as to form a plurality of horizontal hydrophilic patterns which are periodically arranged along the airflow transmission direction, and further form a plurality of hydrophobic surfaces which are alternately arranged with the horizontal hydrophilic patterns on the surface of the bottom wall, wherein each horizontal hydrophilic pattern is in a horizontal trapezoid shape; the upper bottom and the lower bottom of the horizontal trapezoid are perpendicular to the airflow transmission direction, the period of the horizontal hydrophilic pattern of the bottom wall is consistent with the height of the horizontal trapezoid along the airflow transmission direction, and the horizontal hydrophilic pattern is communicated so that drainage is smooth and product water is uniformly distributed on the bottom wall of the flow field; the etched vertical hydrophilic patterns and horizontal hydrophilic patterns are trapezoids imitating thorns of cactus, unbalanced Laplacian pressure can be generated on two sides of the upper bottom and the lower bottom of the trapezoids by liquid drops, the side of the upper bottom is higher than the side of the lower bottom, and the liquid drops can spontaneously move from the upper bottom to the lower bottom of the trapezoids, so that the device has the function of directional water transportation; further, periodic vertical hydrophilic patterns and horizontal hydrophilic patterns are etched on the side wall and the bottom wall of the flow field after the hydrophobic treatment, so that the hydrophobic characteristic and the hydrophilic characteristic are combined, hydrophilic and hydrophobic coupling bionic surfaces imitating the back of the beetles in the desert are formed on the surfaces of the side wall and the bottom wall of the flow field, and liquid drops on the lotus leaf-like low-adhesion hydrophobic surfaces are blown and rolled to the hydrophilic surfaces by airflow in the flow channels to be trapped, so that the efficient water collection function is realized;
When the fuel cell works, reaction gas enters the flow field through the gas inlet and is distributed on each main flow channel through the upper flow dividing flow channels, and the transmission direction of the reaction gas in the flow field is the air flow transmission direction; the reaction gas further passes through the gas diffusion layer to reach the catalyst layer to start electrochemical reaction, then product water enters the gas diffusion layer and accumulates on the surface of the gas diffusion layer facing to the flow field, the product water comprises liquid drops and small fog drops, and then the liquid drops on the surface of the gas diffusion layer and the small fog drops carried by the air flow in the flow field are captured by the vertical hydrophilic patterns on the first side wall and the second side wall and the horizontal hydrophilic pattern on the bottom wall; when the water demand of the fuel cell is greater than the water yield, the trapped product water adheres to the vertical and horizontal hydrophilic patterns and is uniformly distributed and stored on the surfaces of the first side wall, the second side wall and the bottom wall of the flow field in the form of a water film, so that the water content of the fuel cell is kept, and the proton exchange membrane of the fuel cell is prevented from drying; when the water demand of the fuel cell is smaller than the water production, the trapped water accumulates on the vertical and horizontal hydrophilic patterns, which cause uneven surface tension of the water itself asymmetrically with respect to the air flow transmission direction, and the upper bottoms of the vertical and horizontal hydrophilic patterns are smaller than the lower bottoms, so that the laplace pressure of the droplets on the front side of the vertical and horizontal hydrophilic patterns is greater than the laplace pressure on the bottom side, thereby causing a laplace pressure difference; under the action of self uneven surface tension, laplace pressure difference and low surface slip resistance of a water film, product water starts to actively move in a directional manner along the air flow transmission direction; the product water trapped on the vertical and horizontal hydrophilic patterns in the flow field actively moves towards the air outlet and is simultaneously dragged by the shearing force of the air flow in the same direction in the flow field, so that the discharge speed of the excessive product water from the flow field is further increased.
2. The fuel cell bipolar plate of claim 1 wherein the bipolar plate body is made of one of graphite, aluminum, nickel, titanium and stainless steel.
3. The fuel cell bipolar plate of claim 1 wherein the flow field is one of a parallel flow field, a serpentine flow, an alternating flow field, a compound flow field, and a biomimetic flow field.
4. The fuel cell bipolar plate of claim 1 wherein the vertical hydrophilic pattern has an upper base length of 0mm to 3mm, a lower base length of 1 μm to 3mm, a period of 1mm to 5mm, and a wedge angle of 1 ° to 30 °; the upper bottom of the horizontal hydrophilic pattern is 0 mm-3 mm in length, the lower bottom is 1 mu m-3 mm in height and 1 mm-10 mm in height, and the wedge angle is 1 DEG-30 deg.
5. A water collecting and draining method of a fuel cell bipolar plate with bionic active water collecting and draining function according to claim 1, characterized in that it comprises the steps of:
1) Preparing a fuel cell bipolar plate:
a) Providing a flat bipolar plate body;
b) A plurality of main flow channels which are periodically distributed are carved on the front surface of the bipolar plate main body; an upper flow dividing runner and a lower flow converging runner which are communicated with each main runner are respectively carved on the front surface of the bipolar plate main body and the upper end and the lower end of the main runner, and the main runners, the upper flow dividing runner and the lower flow converging runner jointly form a flow field; each of the main flow channel, the upper flow distributing channel and the lower flow distributing channel has a first side wall and a second side wall, the first side wall and the second side wall are vertical to the surface of the bipolar plate main body, and the bottom wall is parallel to the surface of the bipolar plate main body;
c) An air inlet is formed in one end of the upper flow dividing channel, and an air outlet is formed in the other end of the lower flow dividing channel opposite to the air inlet;
d) The surfaces of the first side wall, the second side wall and the bottom wall of each main runner, the upper flow dividing runner and the lower flow dividing runner are subjected to hydrophobic treatment to form a low surface energy film, and the film has the hydrophobic characteristic of imitating the low adhesion effect of the lotus leaf surface, so that the first side wall, the second side wall and the bottom wall form a hydrophobic surface with the hydrophobic characteristic;
e) Carrying out partial laser etching on the low surface energy films of the first side walls of the main flow channel, the upper flow dividing flow channel and the lower flow dividing flow channel, etching away part of the low surface energy films to expose part of the surface of the bipolar plate main body, forming micro-scale and nano-scale concave-convex structures on the surface, enabling the etched area to have hydrophilic characteristics, forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, and forming alternate arrangement of the hydrophobic surface and the vertical hydrophilic patterns on the surface of the first side wall, wherein the shape of each vertical hydrophilic pattern is a vertical trapezoid; the upper bottom and the lower bottom of the vertical trapezoid are both in the air flow transmission direction, are vertical to the air flow transmission direction, are consistent with the depth of the first side wall in height, are aligned with the front edge of the first side wall, the lower bottom is aligned with the bottom edge of the first side wall, and the upper side waist is not larger than the lower side waist, so that the vertical trapezoid is an isosceles trapezoid or has downward inclination along the air flow transmission direction, and the arrangement period of a plurality of vertical hydrophilic patterns is longer than that of the lower bottom of the vertical trapezoid; carrying out partial laser etching on the low-surface-energy film of the second side wall, etching away part of the low-surface-energy film to expose part of the surface of the bipolar plate main body, and forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, and forming a plurality of vertical hydrophilic patterns which are periodically arranged along the airflow transmission direction, so that the surface of the second side wall is provided with a plurality of vertical hydrophilic patterns, the hydrophobic surface and the vertical hydrophilic patterns are alternately arranged, the vertical hydrophilic patterns of each second side wall are identical to the vertical hydrophilic patterns of the first side wall, the arrangement period of the vertical hydrophilic patterns of the second side wall is identical to the arrangement period of the vertical hydrophilic patterns of the first side wall, and the corresponding vertical hydrophilic patterns of the first side wall and the second side wall are aligned or arranged in a staggered manner; carrying out partial laser etching on the low surface energy film of the bottom wall, etching away part of the low surface energy film to expose part of the surface of the bipolar plate main body, and forming a micro-scale and nano-scale concave-convex structure on the surface to enable the etched area to have hydrophilic characteristics, so as to form a plurality of horizontal hydrophilic patterns which are periodically arranged along the airflow transmission direction, and further form a plurality of hydrophobic surfaces which are alternately arranged with the horizontal hydrophilic patterns on the surface of the bottom wall, wherein each horizontal hydrophilic pattern is in a horizontal trapezoid shape; the upper bottom and the lower bottom of the horizontal trapezoid are perpendicular to the airflow transmission direction, the period of the horizontal hydrophilic pattern of the bottom wall is consistent with the height of the horizontal trapezoid along the airflow transmission direction, and the horizontal hydrophilic pattern is communicated so that drainage is smooth and product water is uniformly distributed on the bottom wall of the flow field; the etched vertical hydrophilic patterns and horizontal hydrophilic patterns are trapezoids imitating thorns of cactus, unbalanced Laplacian pressure can be generated on two sides of the upper bottom and the lower bottom of the trapezoids by liquid drops, the side of the upper bottom is higher than the side of the lower bottom, and the liquid drops can spontaneously move from the upper bottom to the lower bottom of the trapezoids, so that the device has the function of directional water transportation;
f) The periodic vertical hydrophilic patterns and the horizontal hydrophilic patterns are etched on the side wall and the bottom wall of the flow field after the hydrophobic treatment, so that the hydrophobic characteristic and the hydrophilic characteristic are combined, hydrophilic and hydrophobic coupling bionic surfaces imitating the backs of the desert beetles are formed on the surfaces of the side wall and the bottom wall of the flow field, and liquid drops on the lotus leaf-imitating low-adhesion hydrophobic surfaces are swept and rolled to the hydrophilic surfaces by airflow in the flow channels to be trapped, so that the efficient water collection function is realized;
2) When the fuel cell works, reaction gas enters the flow field through the gas inlet and is distributed on each main flow channel through the upper flow dividing flow channels, and the transmission direction of the reaction gas in the flow field is the air flow transmission direction;
3) The reaction gas further passes through the gas diffusion layer to reach the catalyst layer to start electrochemical reaction, then product water enters the gas diffusion layer and accumulates on the surface of the gas diffusion layer facing to the flow field, the product water comprises liquid drops and small fog drops, and then the liquid drops on the surface of the gas diffusion layer and the small fog drops carried by the air flow in the flow field are captured by the vertical hydrophilic patterns on the first side wall and the second side wall and the horizontal hydrophilic pattern on the bottom wall;
4) When the water demand of the fuel cell is greater than the water yield, the trapped product water adheres to the vertical and horizontal hydrophilic patterns and is uniformly distributed and stored on the surfaces of the first side wall, the second side wall and the bottom wall of the flow field in the form of a water film, so that the water content of the fuel cell is kept, and the proton exchange membrane of the fuel cell is prevented from drying;
5) When the water demand of the fuel cell is smaller than the water production, the trapped water accumulates on the vertical and horizontal hydrophilic patterns, which cause uneven surface tension of the water itself asymmetrically with respect to the air flow transmission direction, and the upper bottoms of the vertical and horizontal hydrophilic patterns are smaller than the lower bottoms, so that the laplace pressure of the droplets on the front side of the vertical and horizontal hydrophilic patterns is greater than the laplace pressure on the bottom side, thereby causing a laplace pressure difference; under the action of self uneven surface tension, laplace pressure difference and low surface slip resistance of a water film, product water starts to actively move in a directional manner along the air flow transmission direction; the product water trapped on the vertical and horizontal hydrophilic patterns in the flow field actively moves towards the air outlet and is simultaneously dragged by the shearing force of the air flow in the same direction in the flow field, so that the discharge speed of the excessive product water from the flow field is further increased.
6. The water collecting and draining method according to claim 5, wherein in the d) of the step 1), the surfaces of the first and second sidewalls and the bottom wall of each of the main flow path, the upper flow dividing flow path and the lower flow dividing flow path are subjected to hydrophobic treatment by means of laser etching and chemical agent soaking modification to form a low surface energy thin film, comprising the steps of: firstly, performing laser etching to form micro-scale and nano-scale concave-convex structures; then chemical reagent soaking modification is carried out to form a low surface energy film on the concave-convex structure.
7. The water collecting and draining method according to claim 6, wherein the working parameters of the laser etching are a scanning speed of 100mm/s-1000mm/s, a spot diameter of 10 μm-50 μm, a scanning interval of 10 μm-50 μm and a processing power of 10w-30w.
8. The water collecting and draining method according to claim 6, wherein the chemical agent is soaked in an ethanol solution of 0.5-2 wt.% fluorosilane or stearic acid.
9. The water collecting and draining method according to claim 5, wherein in e) of step 1), the low surface energy thin films of the first and second sidewalls and the bottom wall of the respective main flow channel, upper flow dividing flow channel and lower flow dividing flow channel are partially laser etched, and a part of the low surface energy thin films are laser etched so as to expose a part of the surface of the bipolar plate body, and micro-scale and nano-scale concave-convex structures are formed on the surface so that the etched region has hydrophilic characteristics, comprising the steps of: and respectively focusing the light spots of the laser on the surfaces of the low surface energy films of the first side wall, the second side wall and the bottom wall, then demarcating a laser etching range according to the set vertical hydrophilic pattern and the set horizontal hydrophilic pattern, and finally etching the demarcating range.
10. The water collecting and draining method of claim 9, wherein the operating parameters of the laser etching: the scanning speed is 100mm/s-1000mm/s, the light spot diameter is 10 μm-50 μm, the scanning interval is 10 μm-50 μm, and the processing power is 10w-30w.
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