A fuel cell polar plate structure with a wall gradient hydrophilic

Abstract

The application relates to a fuel cell polar plate structure with gradient hydrophilic wall surface. The bipolar plate comprises an inlet distribution area, a flow field reaction area and an outlet distribution area. The surfaces of the inlet distribution area, the flow field reaction area and the outlet distribution area are hydrophilic. Along the direction of the reaction gas flowing from the inlet distribution area to the outlet distribution area, the wall surface contact angle gradually decreases. The hydrophilicity of the flow field reaction area gradually increases from the end close to the inlet distribution area to the end close to the outlet distribution area. The hydrophilicity of the outlet distribution area is stronger than that of the flow field reaction area. The hydrophilicity of the flow field reaction area is stronger than that of the inlet distribution area. The gradient change of the contact angle along the flow direction can generate an additional pushing force for the liquid drops towards the outlet direction. Compared with the prior art, the application enhances the water drainage efficiency of the flow field reaction area, optimizes the internal water management of the fuel cell and improves the cell performance.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a fuel cell electrode structure with gradient hydrophilic walls. Background Technology

[0002] Hydrogen energy is a highly efficient, clean, and renewable energy source that has been extensively explored and researched in recent years. Proton exchange membrane fuel cells (PEMFCs) are one of the most promising methods for utilizing hydrogen energy. The single-cell structure mainly consists of bipolar plates and membrane electrode assemblies (gas diffusion layer, catalyst layer, and proton exchange membrane, etc.) sandwiched between the bipolar plates. It can directly convert the chemical energy of hydrogen and oxygen into electrical energy, without being limited by the Carnot cycle, and boasts high energy conversion efficiency. The only emission is water, resulting in zero carbon emissions and no pollution. The battery has no internal mechanical transmission devices, produces almost no noise, and can operate rapidly in low-temperature environments. Therefore, it has enormous potential in fields such as new energy vehicles, stationary and distributed power generation.

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

[0004] However, the flow channel structure of current fuel cells is usually fixed. In the flow field, the upstream gas velocity is higher, making it easier for water to be blown out and less likely to clog gas channels, resulting in higher fuel cell efficiency and faster reactions. But as the gas flows downstream, the gas velocity decreases, making it difficult for water to be blown out, easily leading to gas channel blockage, reducing fuel cell efficiency, and in severe cases, causing flooding. Most existing fuel cell bipolar plates use the same physical properties for all components, which can easily prevent liquid water generated in the reaction zone from being smoothly discharged through the distribution zone. Optimization of the distribution zone design is also primarily based on the structural aspects of the distribution zone, lacking a comprehensive consideration of the impact of other physical properties on flow field drainage. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies by providing a hydrophilic fuel cell electrode structure with a gradient wall, resulting in superior drainage and gas transport performance. By utilizing the design of the bipolar plate reaction zone, which exhibits gradually increasing hydrophilicity from the inlet to the outlet, liquid water distribution and a two-phase flow pattern are induced within the flow field. The gradient change in the contact angle along the flow direction generates an additional driving force on the droplets towards the outlet. Furthermore, the outlet distribution zone, being more hydrophilic than the reaction zone, induces liquid water to leave the outlet reaction zone, reducing the impact of liquid water blockage on gas mass transfer. Overall, this avoids the "flooding" effect in the flow field and gas diffusion layer, reduces mass transfer resistance, improves internal water management of the fuel cell, and enhances the overall performance of the fuel cell.

[0006] In a flow field, common gas-liquid two-phase flow patterns include bubbly flow, slug flow, and annular flow. Generally, when the gas holdup and velocity in the flow field are low, the gas-liquid two-phase flow exhibits bubbly flow. In this flow pattern, the liquid phase is continuous, while the gas phase is discontinuous, and the flow field may experience flooding. As the gas velocity gradually increases, the flow state of the gas-liquid two-phase flow in the flow field changes from bubbly flow to slug flow, at which point the gas holdup of the flow field increases compared to the bubbly flow stage. When the gas velocity further increases, the flow state of the gas-liquid two-phase flow in the flow field will become annular flow. In annular flow, the gas phase converges to form a gas core, which can flow smoothly in the center of the flow field, while the liquid phase forms a flowing liquid ring (film) along the flow field wall.

[0007] Upstream of the bipolar plate flow field, the gas content is high, the gas velocity is fast, and the gas-liquid two-phase flow easily forms an annular flow. Water in the flow field is easily blown out, and the gas passages are not easily blocked, resulting in high fuel cell efficiency and rapid reaction. However, as the gas flows downstream, both the gas content and gas velocity decrease significantly. The flow state of the gas-liquid two-phase flow tends to be bubbly, making it difficult to blow out water and easily leading to flow field blockage. This reduces fuel cell efficiency and, in severe cases, can even cause flooding.

[0008] This invention provides a hydrophilic fuel cell bipolar plate structure with a gradient wall surface. The bipolar plate includes an inlet distribution region, a flow field reaction region, and an outlet distribution region. The surfaces of the inlet distribution zone, the flow field reaction zone, and the outlet distribution zone are hydrophilic (<90℃), making it easy for liquid water to adhere to the flow field surface. This provides sufficient space for the central airflow to pass through, inducing the gas-liquid two-phase flow within the flow field to develop into a ring flow state. It also strengthens the driving effect of the airflow on the discharge of liquid water within the flow field, preventing water flooding within the flow field. Along the direction of the reacting gas flow from the inlet distribution zone to the outlet distribution zone, the wall contact angle gradually decreases. The hydrophilicity of the flow field reaction zone gradually increases from the end closer to the inlet distribution zone to the end closer to the outlet distribution zone. The hydrophilicity of the outlet distribution zone is stronger than that of the flow field reaction zone wall. The hydrophilicity of the flow field reaction zone wall is stronger than that of the inlet distribution zone.

[0009] The surfaces of the inlet distribution zone, flow field reaction zone, and outlet distribution zone are hydrophilic, inducing liquid water to form a ring flow in the flow field channels and inhibiting channel blockage. The hydrophilicity of the flow field reaction zone gradually increases from the inlet to the outlet, optimizing the downstream liquid water flow pattern. The gradient change in the contact angle along the flow direction can generate an additional driving force on the droplets towards the outlet, accelerating the discharge of liquid water from the reaction zone. The walls of the flow field reaction zone are more hydrophobic than those of the outlet distribution zone, allowing liquid water about to leave the reaction zone to quickly detach, reducing the problem of liquid water blocking the gas mass transfer channels.

[0010] Compared with the prior art, the present invention has the following advantages: (1) By using a bipolar plate design with hydrophilic (<90℃) surfaces in the reaction zone and distribution zone of the electrode plate, liquid water can be induced to form a ring flow in the flow field groove, thus suppressing the phenomenon of water blockage in the flow channel.

[0011] (2) Through the bipolar plate design in the reaction zone where the hydrophilicity gradually increases from the inlet to the outlet, the gradient change of the contact angle along the flow direction can generate an additional driving force on the droplets toward the outlet direction, accelerating the movement of liquid water in the reaction zone and improving drainage efficiency.

[0012] (3) By designing the reaction zone channel to be 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.

[0013] (4) This invention is applicable to electrode structures of all materials and can be used in conjunction with existing reinforced drainage structural designs to improve water management of fuel cells. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the electrode structure; Figure 2 This is a simulation diagram of the drainage of the reaction zone in Example 1; Figure 3 This is a simulated displacement diagram of the drainage zone in Example 1; Figure 4 This is a simulated drainage velocity diagram of the reaction zone in Example 1; Figure 5 This is a simulated pressure drop diagram of the drainage zone in Example 1; Figure 6 This is a schematic diagram simulating the drainage from the reaction zone to the outlet distribution zone in Example 1; Figure 7 This is a simulation diagram of the drainage results from the reaction zone to the outlet distribution zone in Example 1; Figure 8 This is a simulated displacement diagram of drainage from the reaction zone to the outlet distribution zone in Example 1.

[0015] Attached diagram labels: 1. Inlet distribution zone; 2. Flow field reaction zone; 3. Outlet distribution zone. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0017] Example 1 This embodiment provides a fuel cell electrode structure with a gradient hydrophilic wall surface, such as... Figure 1 As shown, the bipolar plate includes: an inlet distribution zone 1, a flow field reaction zone 2, and an outlet distribution zone 3; The surfaces of the inlet distribution zone 1, the flow field reaction zone 2, and the outlet distribution zone 3 are hydrophilic (<90℃), which makes it easy for liquid water to 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 a ring flow state, strengthening the driving effect of the airflow on the discharge of liquid water in the flow field, and avoiding water flooding in the flow field; Along the direction of the reaction gas flowing from the inlet distribution zone 1 to the outlet distribution zone 3, the wall contact angle gradually decreases, and the hydrophilicity of the flow field reaction zone 2 gradually increases from the end near the inlet distribution zone 1 to the end near the outlet distribution zone 3; the hydrophobicity of the inlet distribution zone 1 is stronger than that of the flow field reaction zone 2, and the hydrophobicity of the wall of the flow field reaction zone 2 is stronger than that of the outlet distribution zone 3.

[0018] The surfaces of the inlet distribution zone 1, the flow field reaction zone 2, and the outlet distribution zone 3 are hydrophilic, inducing liquid water to form a ring flow in the flow field channels and inhibiting water blockage in the flow channels. The hydrophobicity of the flow field reaction zone 2 gradually decreases from the inlet to the outlet, and the gradient change in the contact angle along the flow direction can generate an additional driving force on the droplets towards the outlet, accelerating the discharge of liquid water from the reaction zone. The hydrophobicity of the wall of the flow field reaction zone 2 is stronger than that of the outlet distribution zone 3, allowing the liquid water about to leave the reaction zone to quickly detach from the reaction zone, reducing the problem of liquid water blocking the gas mass transfer channels.

[0019] In a specific embodiment, the bipolar plate has external dimensions of 350mm × 120mm; the flow field reaction zone 2 has dimensions of 200mm × 120mm; both the inlet distribution zone 1 and the outlet distribution zone 3 are trapezoids with an upper width of 60mm, a lower width of 120mm, and a height of 25mm; the bipolar plate has a thickness of 0.6mm, and after deducting the thickness of the thin plate skin, the flow field height is 0.5mm; the contact angle of the flow field reaction zone 2 is 70-50 degrees; and the contact angle of both the inlet distribution zone 1 and the outlet distribution zone 3 is 40 degrees.

[0020] The liquid water movement behavior of each part of the bipolar plate in this embodiment was simulated and tested using the Comsol simulation platform, and the results are shown in the attached figure.

[0021] The motion of droplets in flow fields with contact angles of 60 degrees, 70 to 50 degrees, and 80 to 40 degrees were simulated, respectively. Figure 2 As shown. Figure 3 This is a simulated drainage velocity diagram of the reaction zone. Figure 4 This is a simulated drainage velocity diagram of the reaction zone. Figure 5 The figure shows the pressure drop during drainage simulation in the reaction zone. It can be seen from the figure that, at the same time interval, the droplet motion within the gradient contact angle wall flow field is better than that within the 60-degree contact angle wall flow field, and the larger the gradient interval, the better the motion. The pressure drop within the gradient contact angle wall flow field is similar to that within the 60-degree contact angle wall flow field. Therefore, it can be concluded that the gradient contact angle flow field design is beneficial for promoting the detachment of liquid water from the gas diffusion layer surface and accelerating the movement of liquid water within the flow field.

[0022] The flow field reaction zone 2 to the outlet distribution zone drainage simulation is as follows: Figure 6 As shown, the motion of liquid water downstream of the reaction zone flow field was simulated. In the simulation, the contact angle between the liquid water and the wall on the left side was 60 degrees, and the contact angle on the wall on the right side was 40 degrees. The results are as follows. Figure 7 As shown, liquid water moves in the direction of smaller contact angle without any other external force, and its velocity curve is as follows. Figure 8 As shown. Therefore, it can be concluded that the design of the bipolar plate flow field reaction zone 2 having a slightly larger contact angle than the outlet distribution zone 3 is beneficial for the discharge of liquid water from the flow field reaction zone 2.

[0023] 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 battery performance.

[0024] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0025] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any 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 invention should be within the protection scope of the present invention.

Claims

1. A fuel cell electrode structure with gradient hydrophilic walls, characterized in that, The bipolar plate includes: an inlet distribution zone (1), a flow field reaction zone (2), and an outlet distribution zone (3); The surfaces of the inlet distribution zone (1), the flow field reaction zone (2), and the outlet distribution zone (3) are hydrophilic. From the end of the flow field reaction zone (2) near the inlet distribution zone (1) to the end near the outlet distribution zone (3), the wall contact angle gradually decreases. The hydrophilicity of the flow field reaction zone (2) gradually increases from the end near the inlet distribution zone (1) to the end near the outlet distribution zone (3). The hydrophilicity of the outlet distribution zone (3) is stronger than that of the wall of the flow field reaction zone (2). The hydrophilicity of the wall of the flow field reaction zone (2) is stronger than that of the inlet distribution zone (1). The gradient change of the contact angle of the flow field reaction zone (2) along the flow direction can generate an additional driving force for the droplets toward the outlet direction.

2. The fuel cell electrode structure with gradient wall hydrophilicity according to claim 1, characterized in that, The bipolar plate has external dimensions of 350mm × 120mm.

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

4. The fuel cell electrode structure with gradient hydrophilic walls according to claim 1, characterized in that, Both the import distribution area (1) and the export distribution area (3) are trapezoids with an upper width of 60mm, a lower width of 120mm, and a height of 25mm.

5. The fuel cell electrode structure with gradient wall hydrophilicity 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 skin, the flow field height is 0.5 mm.

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

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