Fuel cell pole plate structure with gradient hydrophilic wall surface

Abstract

The invention relates to a wall surface gradient hydrophilic fuel cell polar plate structure. A bipolar plate comprises an inlet distribution area, a flow field reaction area and an outlet distribution area, the integral surfaces of the inlet distribution area, the flow field reaction area and the outlet distribution area are hydrophilic (llt; liquid water is easily attached to the surface of the flow field, enough space is reserved for central airflow to pass through, gas-liquid two-phase flow in the flow field is induced to develop towards an annular flow state, the pushing effect of the airflow on discharging of the liquid water in the flow field is enhanced, and water logging in the flow field is avoided; the contact angle from the inlet to the outlet is gradually reduced, and the hydrophilicity of the flow field reaction area is gradually enhanced from the inlet to the outlet; the hydrophilicity of the outlet distribution area is slightly higher than that of the wall surface of the flow field reaction area; the wall surface hydrophilicity of the flow field reaction area is slightly higher than that of the inlet distribution area; the gradient contact angle can form additional driving force on the liquid drops. Compared with the prior art, the water drainage efficiency of the flow field reaction zone is enhanced, the internal water management of the fuel cell is optimized, and the cell performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field related to fuel cells, and in particular to a fuel cell plate structure with gradient hydrophilic wall surfaces. Background Art

[0002] Hydrogen energy is an efficient, clean, renewable energy source that has been widely explored and studied in recent years. Proton exchange membrane fuel cells are one of the most promising ways to utilize hydrogen energy. The monomer structure mainly includes bipolar plates and membrane electrode assemblies (gas diffusion layers, catalyst layers, and proton exchange membranes, etc.) sandwiched between the bipolar plates. It can directly convert the chemical energy in hydrogen and oxygen into electrical energy, is not restricted by the Carnot cycle, and has high energy conversion efficiency. The only reaction emission is water, with zero carbon emissions and no pollution. There is no mechanical transmission device inside the battery, almost no noise, and it can run quickly in a low-temperature environment. Therefore, it has great potential in the fields of new energy vehicles, fixed and distributed power generation, etc.

[0003] The bipolar plate is an important component of the proton exchange membrane fuel cell, and is mainly composed of an inlet and outlet, a flow field distribution area and a flow field reaction area. The inlet and outlet are responsible for introducing the reaction gas and coolant into the bipolar plate, and the distribution area is responsible for evenly distributing the reaction gas and coolant to the flow field of the reaction area. The reaction area is composed of grooves and ridges, and is in uniform contact with the membrane electrode. It is responsible for supplying the reaction gas and removing the reaction products, while transferring electrons and reaction heat.

[0004] However, the flow channel structure of today's fuel cells is usually fixed. In the flow field, the upstream gas flow rate is faster, the water in the flow field is easy to blow out, and it is not easy to block the gas channel. The fuel cell efficiency is high and the reaction is relatively rapid. However, as the gas flows, the gas flow rate decreases in the downstream of the flow field, and the water in the flow field is difficult to blow out, which can easily lead to gas channel blockage, thereby reducing the efficiency of the fuel cell. In severe cases, flooding may occur. The vast majority of existing fuel cell bipolar plates use the same physical parameters for each component, which can easily lead to the liquid water generated in the reaction zone being unable to be discharged smoothly through the distribution area. When optimizing the design of the distribution area, it is basically optimized only from the single perspective of the distribution area structure, and there is a lack of comprehensive consideration of the impact of other physical parameters on flow field drainage. Summary of the invention

[0005] The purpose of the present invention is to provide a fuel cell plate structure with gradient hydrophilicity on the wall in order to overcome the above-mentioned defects of the prior art, which has better drainage and gas transmission performance. By utilizing the design that the hydrophilicity of the reaction zone of the bipolar plate gradually increases from the inlet to the outlet, the liquid water distribution and two-phase flow pattern in the flow field are induced, and the gradient contact angle can form an additional driving force for the droplets. By utilizing the design that the outlet distribution zone is more hydrophilic than the reaction zone, liquid water is induced to leave the outlet reaction zone, reducing the effect of liquid water blockage on gas mass transfer. On the whole, the "flooding" effect in the flow field and gas diffusion layer is avoided, the mass transfer resistance is reduced, the internal water management of the fuel cell is improved, and the overall performance of the fuel cell is improved.

[0006] In the flow field, common gas-liquid two-phase flow patterns include bubbly flow, slug flow and annular flow. Generally speaking, when the gas content and flow velocity in the flow field are low, the flow state of the gas-liquid two-phase is bubbly flow. In this flow pattern, the liquid phase is the continuous phase, the gas phase is discontinuous, and the flow field will be flooded. As the gas flow rate gradually increases, the flow state of the gas-liquid two-phase in the flow field will change from bubbly flow to slug flow, and the gas content of the flow field is higher than that of the bubbly flow stage. When the gas flow rate is further increased, the flow state of the gas-liquid two-phase in the flow field will change to annular flow. In the annular flow state, the gas phase converges to form a gas core, which can flow smoothly in the center of the flow field, while the liquid phase will form a flowing liquid ring (film) along the wall of the flow field.

[0007] In the upstream of the bipolar plate flow field, the gas content in the flow field is high, the gas flow rate is fast, the gas-liquid two-phase is easy to form an annular flow, the water in the flow field is easy to be blown out, and it is not easy to block the gas channel. The fuel cell efficiency is high and the reaction is relatively rapid. However, as the gas flows, the gas content and gas flow rate in the flow field downstream of the flow field are significantly reduced, and the flow state of the gas-liquid two-phase tends to be a bubbling flow. The water in the flow field is difficult to be blown out, which easily leads to blockage of the flow field, thereby reducing the efficiency of the fuel cell. In severe cases, water flooding may occur.

[0008] The present invention provides a fuel cell plate structure with gradient hydrophilic wall surface, wherein the bipolar plate comprises: an inlet distribution area, a flow field reaction area, and an outlet distribution area;

[0009] The overall surface of the inlet distribution area, flow field reaction area, and outlet distribution area is hydrophilic (<90℃), which makes liquid water easily adhere to the flow field surface, leaving enough space for the central airflow to pass through, inducing the gas-liquid two-phase flow in the flow field to develop into an annular flow state, and strengthening the driving effect of the airflow on the discharge of liquid water in the flow field to avoid flooding in the flow field; the contact angle gradient decreases from the inlet to the outlet, and the hydrophilicity of the flow field reaction zone gradually increases from the inlet to the outlet; the hydrophilicity of the outlet distribution area is slightly stronger than that of the wall of the flow field reaction zone; the hydrophilicity of the wall of the flow field reaction zone is slightly stronger than that of the inlet distribution area.

[0010] The overall surface of the inlet distribution area, flow field reaction area, and outlet distribution area is hydrophilic, inducing liquid water to form an annular flow in the flow field grooves, and inhibiting the occurrence of water blockage in the flow channel. The hydrophilicity of the flow field reaction area gradually increases from the inlet to the outlet, optimizing the flow pattern of liquid water downstream of the flow field, so that the gradient contact angle can form an additional driving force for the droplets, and accelerate the discharge of liquid water in the reaction area. The wall of the flow field reaction area is more hydrophobic than that of the outlet distribution area, so that the liquid water that is about to leave the reaction area can quickly leave the reaction area, reducing the problem of liquid water blocking the gas mass transfer channel.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] (1) By designing the bipolar plate with a hydrophilic surface (<90°C) in the reaction zone and the distribution zone of the plate, liquid water can be induced to form an annular flow in the flow field groove, thereby suppressing the occurrence of water blockage in the flow channel.

[0013] (2) Through the bipolar plate design in which the hydrophilicity of the reaction zone gradually increases from the inlet to the outlet, the gradient contact angle can form an additional driving force for the droplets, accelerate the movement of liquid water in the reaction zone, and improve the drainage efficiency.

[0014] (3) By designing the reaction zone flow channel to be slightly more hydrophobic than the outlet distribution zone, liquid water can be induced to leave the reaction zone, reducing the problem of liquid water blocking the gas mass transfer channel.

[0015] (4) The present invention is applicable to electrode plate structures of all materials and can be used in combination with existing structural designs for enhanced drainage to improve water management of fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the plate structure;

[0017] Figure 2 This is a drainage simulation diagram of the reaction zone in Example 1;

[0018] Figure 3 This is the displacement diagram of drainage simulation in the reaction zone of Example 1;

[0019] Figure 4 This is a simulated drainage velocity diagram of the reaction zone in Example 1;

[0020] Figure 5 This is the drainage simulation pressure drop diagram of the reaction zone in Example 1;

[0021] Figure 6 This is a schematic diagram of drainage simulation from the reaction zone to the outlet distribution zone in Example 1;

[0022] Figure 7 This is a diagram showing the drainage simulation results from the reaction zone to the outlet distribution zone in Example 1;

[0023] Figure 8 This is the drainage simulation displacement diagram from the reaction zone to the outlet distribution zone in Example 1.

[0024] Figure numerals: 1. inlet distribution area; 2. flow field reaction area; 3. outlet distribution area. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms and other features not clearly described in this technical solution are all considered to be common technical features disclosed in the prior art.

[0026] Example 1

[0027] This embodiment provides a fuel cell plate structure with a gradient hydrophilic wall surface, such as Figure 1 As shown, the bipolar plate includes: an inlet distribution area 1, a flow field reaction area 2, and an outlet distribution area 3;

[0028] The overall surface of the inlet distribution area 1, the flow field reaction area 2, and the outlet distribution area 3 is hydrophilic (<90℃), so that liquid water can easily adhere to the surface of the flow field, leaving enough space for the central airflow to pass through, inducing the gas-liquid two-phase flow in the flow field to develop into an annular flow state, and strengthening the driving effect of the airflow on the discharge of liquid water in the flow field to avoid flooding in the flow field; the contact angle gradually decreases from the inlet to the outlet, and the hydrophobicity of the flow field reaction area 2 gradually decreases from the inlet to the outlet; the hydrophobicity of the inlet distribution area 1 is slightly stronger than that of the flow field reaction area 2, and the hydrophobicity of the wall of the flow field reaction area 2 is slightly stronger than that of the outlet distribution area 3.

[0029] The overall surface of the inlet distribution area 1, the flow field reaction area 2, and the outlet distribution area 3 is hydrophilic, inducing liquid water to form an annular flow in the flow field grooves, and inhibiting the occurrence of water blockage in the flow channel. The hydrophobicity of the flow field reaction area 2 gradually decreases from the inlet to the outlet, and the gradient contact angle can form an additional driving force for the droplets, accelerating the discharge of liquid water in the reaction area. The wall hydrophobicity of the flow field reaction area 2 is stronger than that of the outlet distribution area 3, so that the liquid water that is about to leave the reaction area can quickly leave the reaction area, reducing the problem of liquid water blocking the gas mass transfer channel.

[0030] In a specific embodiment, the outer dimensions of the bipolar plate are 350mm×120mm; the size of the flow field reaction zone 2 is 200mm×120mm; the inlet distribution area 1 and the outlet distribution area 3 are both trapezoidal with an upper width of 60mm, a lower width of 120mm, and a height of 25mm; the thickness of the bipolar plate is 0.6mm, and after deducting the thickness of the thin plate, the flow field height is 0.5mm; the contact angle of the flow field reaction zone 2 is 70-50 degrees; the contact angles of the inlet distribution area 1 and the outlet distribution area 3 are both 40 degrees.

[0031] The Comsol simulation platform was used to simulate the movement of liquid water in various parts of the bipolar plate of this embodiment, and the results are shown in the accompanying drawings.

[0032] The movement of droplets in the flow field with a contact angle of 60 degrees, a gradient contact angle of 70 to 50 degrees, and a gradient contact angle of 80 to 60 degrees are simulated respectively, such as Figure 2 shown. Figure 3 is the drainage simulation velocity diagram of the reaction zone, Figure 4 is the drainage simulation velocity diagram of the reaction zone, Figure 5 The simulated pressure drop diagram of drainage in the reaction zone. It can be seen from the figure that the movement of the droplet in the gradient contact angle wall flow field is better than that in the 60-degree contact angle wall flow field at the same time, and the larger the gradient range, the better the movement. The pressure drop in the gradient contact angle wall flow field is similar to that in the 60-degree contact angle wall flow field. Therefore, it can be determined that the gradient contact angle flow field design is conducive to promoting the detachment of liquid water from the gas diffusion layer surface and accelerating the movement of liquid water in the flow field.

[0033] The drainage simulation from flow field reaction zone 2 to outlet distribution zone is as follows Figure 6 As shown in the figure, the movement of liquid water in the downstream of the reaction zone flow field is simulated. In the simulation, the wall contact angle of the liquid water on the left side is 60 degrees, and the wall contact angle of the liquid water on the right side is 40 degrees. Figure 7 As shown in Figure 2, liquid water moves in the direction with a smaller contact angle without any other external force, and its movement speed curve is as follows: Figure 8 As shown, it can be concluded that the design in which the contact angle of the flow field reaction zone 2 of the bipolar plate is slightly larger than that of the outlet distribution zone 3 is conducive to the discharge of liquid water from the flow field reaction zone 2.

[0034] Therefore, this embodiment enhances the drainage efficiency of the flow field reaction zone 2, optimizes the internal water management of the fuel cell, and improves the battery performance.

[0035] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0036] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A fuel cell plate structure with gradient hydrophilic wall, characterized in that: The bipolar plate comprises: an inlet distribution area (1), a flow field reaction area (2), and an outlet distribution area (3); The entire surface of the inlet distribution area (1), the flow field reaction area (2), and the outlet distribution area (3) is hydrophilic; the contact angle gradually decreases from the inlet to the outlet, and the hydrophilicity of the flow field reaction area (2) gradually increases from the inlet to the outlet; the hydrophilicity of the outlet distribution area (3) is slightly stronger than the wall surface of the flow field reaction area (2); the hydrophilicity of the wall surface of the flow field reaction area (2) is slightly stronger than that of the inlet distribution area (1); the gradient contact angle can form an additional driving force for the droplets. The hydrophilicity of the inlet distribution area (1) and the outlet distribution area (3) is stronger than that of the flow field reaction area (2).

2. A fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The bipolar plate has an overall size of 350 mm×120 mm.

3. A fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The size of the flow field reaction zone (2) is 200 mm×120 mm.

4. A fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The inlet distribution area (1) and the outlet distribution area (3) are both trapezoidal in shape with an upper width of 60 mm, a lower width of 120 mm and a height of 25 mm.

5. A fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The bipolar plate has a thickness of 0.6 mm, and after deducting the thickness of the thin plate, the flow field height is 0.5 mm.

6. A fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The contact angle of the flow field reaction zone (2) is 70-50 degrees.

7. A fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The contact angle of the inlet distribution area (1) is 80 degrees, and the contact angle of the outlet distribution area (3) is 40 degrees.

8. The fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The entire surface of the inlet distribution area (1), the flow field reaction area (2) and the outlet distribution area (3) is hydrophilic, inducing liquid water to form an annular flow in the flow field grooves, thereby suppressing the occurrence of water blockage in the flow channel.

9. A fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The hydrophilicity of the flow field reaction zone (2) gradually increases from the inlet to the outlet, and the discharge effect on liquid water is enhanced through the influence of surface forces, thereby accelerating the discharge of liquid water in the reaction zone.

10. A fuel cell plate structure with gradient hydrophilic wall surface according to claim 1, characterized in that: The wall hydrophobicity of the flow field reaction zone (2) is stronger than that of the outlet distribution zone (3), so that liquid water that is about to leave the reaction zone can quickly leave the reaction zone, reducing the problem of liquid water blocking the gas mass transfer channel.

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