Fuel cell membrane electrode and fuel cell and electrical device having the membrane electrode

Abstract

The present disclosure relates to fuel cell membrane electrodes and fuel cell systems and electrical devices having the membrane electrodes. The fuel cell membrane electrode includes a proton exchange membrane, a cathode catalyst layer disposed on a cathodic side of the proton exchange membrane. The fuel cell membrane electrode also includes a cathode gas diffusion layer disposed on an outer side of the cathode catalyst layer, an outer surface of the cathode gas diffusion layer having a first region in contact with a bipolar plate and a second region not in contact with the bipolar plate. Further, the fuel cell membrane electrode further comprises a hydrophobic layer disposed on an outer side of the cathode gas diffusion layer, wherein the hydrophobic layer has hydrophobic properties and the hydrophobic layer covers at least a portion of a region in the second region. This approach preserves moisture in the membrane electrodes, improves the performance and lifespan of fuel cells, and provides cost savings.

Description

[0001] Fuel Cell Membrane Electrode and Fuel Cell and Electrical Device Having the Membrane Electrode

[0002] Technical Field

[0003] The present disclosure relates to fuel cell systems, and more particularly to fuel cell membrane electrodes and fuel cell systems and electrical devices having the membrane electrodes.

[0004] Background Art

[0005] A membrane electrode assembly (MEA) is a core component of a fuel cell that achieves an electrochemical reaction at the membrane electrode and generates an electrical current. The membrane electrode typically consists of a proton exchange membrane, an anode catalyst layer, a cathode catalyst layer, an anode gas diffusion layer, and a cathode gas diffusion layer. A proton exchange membrane (PEM) is a high molecular proton conductor membrane that, while allowing a proton to pass, does not permit the passage of electrons and other substances, with a function to separate the anode and cathode and allow the protons to move from the anode to the cathode.

[0006] A catalyst layer is present on each of two sides of the proton exchange membrane and the role thereof is to accelerate the electrochemical reaction of hydrogen and oxygen. The gas diffusion layer (GDL) is a microporous carbon paper or carbon cloth material that can ensure that the reactants can be effectively diffused to the catalyst layer while guiding products such as water to be discharged. The performance of the proton exchange membrane can directly affect the productivity and lifespan of the entire fuel cell system.

[0007] Summary of Invention

[0008] In a first aspect of an embodiment of the present disclosure, a fuel cell membrane electrode is provided. The fuel cell membrane electrode includes a proton exchange membrane. The fuel cell membrane electrode also includes a cathode catalyst layer disposed on a cathodic side of the proton exchange membrane. The fuel cell membrane electrode also includes a cathode gas diffusion layer disposed on an outer side of the cathode catalyst layer, an outer surface of the cathode gas diffusion layer having a first region in contact with a bipolar plate and a second region not in contact with the bipolar plate. Further, the fuel cell membrane electrode further comprises a hydrophobic layer disposed on an outer side of the cathode gas diffusion layer, wherein the hydrophobic layer has hydrophobic properties and the hydrophobic layer covers at least a portion of a region in the second region.

[0009] In a second aspect of an embodiment of the present disclosure, a fuel cell system that includes a fuel cell membrane electrode is provided. The fuel cell membrane electrode includes a proton exchange membrane. The fuel cell membrane electrode also includes a cathode catalyst layer disposed on the cathodic side of the proton exchange membrane. The fuel cell membrane electrode also includes a cathode gas diffusion layer disposed on an outer side of the cathode catalyst layer, an outer surface of the cathode gas diffusion layer having a first region in contact with the bipolar plate and a second region not in contact with the bipolar plate. Further, the fuel cell membrane electrode further comprises a hydrophobic layer disposed on an outer side of the cathode gas diffusion layer, wherein the hydrophobic layer has hydrophobic properties and the hydrophobic layer covers at least a portion of a region in the second region.

[0010] In a third aspect of an embodiment of the present disclosure, an electrical device is provided, the electrical device including a fuel cell system that includes a fuel cell membrane electrode. The fuel cell membrane electrode includes a proton exchange membrane. The fuel cell membrane electrode also includes a cathode catalyst layer disposed on the cathodic side of the proton exchange membrane. The fuel cell membrane electrode also includes a cathode gas diffusion layer disposed on an outer side of the cathode catalyst layer, an outer surface of the cathode gas diffusion layer having a first region in contact with a bipolar plate and a second region not in contact with the bipolar plate. Further, the fuel cell membrane electrode further comprises a hydrophobic layer disposed on an outer side of the cathode gas diffusion layer, wherein the hydrophobic layer has hydrophobic properties and the hydrophobic layer covers at least a portion of a region in the second region.

[0011] It will be understood that the content described in the Summary of the Invention is not intended to limit key or important features of the examples of the present disclosure, nor is it intended to limit the scope of the present disclosure. Other features of the present disclosure will become readily understood by the following description.

[0012] Description of Accompanying Drawings

[0013] Above and other features, advantages and aspects of various examples of the present disclosure will become more apparent in combination with the accompanying drawings and with reference to the following detailed description. In the accompanying drawings, like or similar accompanying drawings designate like or similar elements, wherein:

[0014] FIG. 1 shows a schematic view of a wet augmentation principle for a fuel cell membrane electrode, consistent with some embodiments of the present disclosure;

[0015] FIG. 2 shows a schematic view of an example fuel cell membrane electrode having a hydrophobic layer, consistent with some embodiments of the present disclosure;

[0016] FIG. 3 shows a schematic view of an example fuel cell membrane electrode having a hydrophobic layer in a case where a bipolar plate has a channel, consistent with some embodiments of the present disclosure;

[0017] FIGS. 4A to 4B show a schematic view of an example fuel cell membrane electrode with a hydrophobic layer in a case where a bipolar plate has a window, consistent with some embodiments of the present disclosure;

[0018] FIG. 5 shows a schematic view of an example fuel cell membrane electrode having a porous hydrophobic layer, consistent with some embodiments of the present disclosure;

[0019] FIG. 6 shows a schematic view of an example fuel cell membrane electrode having a porous hydrophobic layer in a case where a bipolar plate has a channel, consistent with some embodiments of the present disclosure;

[0020] FIGS. 7A to 7B show a schematic view of an example fuel cell membrane electrode having a porous hydrophobic layer in a case where a bipolar plate has a window, consistent with some embodiments of the present disclosure;

[0021] FIG. 8 shows a schematic diagram of an example process for determining the pore size of a porous hydrophobic layer, consistent with some embodiments of the present disclosure; and

[0022] FIG. 9 shows a schematic view of an example process for determining a thickness of a porous hydrophobic layer, consistent with some embodiments of the present disclosure.

[0023] Specific Embodiments

[0024] The examples of the present disclosure will be described in further detail below with reference to the accompanying drawings. While certain examples of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure may be implemented in various forms and should not be construed as being limited to the examples set forth herein, rather these examples are provided for a more thorough and complete understanding of the present disclosure. It will be understood that the accompanying drawings and examples of the present disclosure are for exemplary purposes only and are not intended to limit the scope of protection of the present disclosure, and the examples of the present disclosure that are described below with reference to the accompanying drawings are for exemplary purposes only.

[0025] In a fuel cell, hydrogen at an anode is oxidized to positive ions (i.e., protons) and electrons under the action of a catalyst, wherein the electrons are released and flow along an external circuit, and the positive ions are transmitted from the anode through a proton exchange membrane (PEM) to the cathode. At the cathode, the positive ions, oxygen, and the electrons transmitted by the external circuit are bound to produce water under the action of the catalyst, where the electrons are derived to form a current, and the water is discharged from the fuel cell. In the proton exchange membrane, the water molecules can assist in the intra-membrane transmission of the protons, promoting the diffusion and conduction of the protons. Thus, the proton exchange membrane needs to be held to a certain extent wet to achieve its optimal proton transfer performance.

[0026] In some liquid-cooled fuel cells, in order to maintain the humidity of the proton exchange membrane, an external humidifier may be utilized to humidify the air, and the humidified air is then fed to the fuel cell, which may increase the humidity of the proton exchange membrane. However, the external humidifier has such drawbacks as being costly, occupying space, and further complicating the fuel cell system.

[0027] In some air-cooled fuel cells, air replaces liquid coolant while acting as a reactant and a coolant. Where air acts as a coolant, the membrane electrode needs to be exposed to the environment and be continuously blown by high flow air, resulting in a rapid loss of moisture on the surface of the membrane electrode. The drying of the membrane electrode surface increases the moisture concentration difference between the membrane electrode surface and the proton exchange membrane, resulting in moisture in the proton exchange membrane being transferred to the membrane electrode surface at an accelerated rate and rapidly lost under the action of high flow air. Thus, in an aircooled fuel cell, the proton exchange membrane is more likely to be in a dry state, thereby reducing the performance and lifespan of the fuel cell.

[0028] To this end, embodiments of the present disclosure provide for a fuel cell membrane electrode comprising a proton exchange membrane, a cathode catalyst layer, a cathode gas diffusion layer, and a hydrophobic layer. The cathode catalyst layer is disposed on the cathodic side of the proton exchange membrane, the cathode gas diffusion layer is disposed on an outer side of the cathode catalyst layer, and an outer surface of the cathode gas diffusion layer has a region in contact with a bipolar plate and a region not in contact with the bipolar plate. Further, the hydrophobic layer is disposed on an outer side of the cathode gas diffusion layer, wherein the hydrophobic layer has hydrophobic properties, and the hydrophobic layer covers at least a portion of the region that is not in contact with the bipolar plate.

[0029] In this way, the hydrophobic layer with hydrophobic properties may hinder the loss of water from the surface of the cathode gas diffusion layer, thereby enabling the water produced at the cathode to remain in the membrane electrode. In this way, the proton exchange membrane can be wetted using water generated at the cathode, which can improve the performance of the fuel cell. Moreover, there is no need for an external humidifier, which enables cost and space savings, reduces the complexity of fuel cells, and improves the stability of fuel cells.

[0030] FIG. 1 shows a schematic diagram illustrating self-wetting principles for a fuel cell membrane electrode (referred to as a membrane electrode) 100, consistent with some embodiments of the present disclosure. As shown in FIG. 1 , the membrane electrode 100 includes a proton exchange membrane 102, a cathode catalyst layer 104, an anode catalyst layer 106, a cathode gas diffusion layer 108, an anode gas diffusion layer 110, and a hydrophobic layer 112. The hydrogen gas enters the membrane electrode 100 as one of the reactants from the anode gas diffusion layer 110, and the anode gas diffusion layer 110 provides a channel for transmission of hydrogen gas so that hydrogen gas can evenly enter the anode catalyst layer 106. At the anode catalyst layer 106, hydrogen gas is oxidized to positive ions (i.e., protons) and electrons (i.e., H2^2H+2e under the action of the catalyst, where the electrons are released and flow along an external circuit, and the positive ions are transmitted to the cathode through the proton exchange membrane 102. Water is present at the proton exchange membrane 102, and the water molecules may assist in transmitting the positive ions from the anode catalyst layer 106 to the cathode catalyst layer 104. At the cathode catalyst layer 104, the positive ions, oxygen, and the electrons transmitted by the external circuit are bound by the catalyst to produce water (i.e., O2+4H+4e’— >2H2O), where the electrons are derived to form a current via the cathode gas diffusion layer 108, and water is transmitted to the outer side of the membrane electrode 100 via the cathode gas diffusion layer 108.

[0031] In a related technique, in the absence of the hydrophobic layer 112, air is blown to the outer surface of the cathode gas diffusion layer 108 to allow oxygen in the air to enter the cathode as a reactant to participate in chemical reaction. With air in effect, moisture at the cathode gas diffusion layer 108 is rapidly lost such that the water concentration difference between the proton exchange membrane 102 and the cathode gas diffusion layer 108 increases, thereby accelerating the transfer of water at the proton exchange membrane 102 to the cathode gas diffusion layer 108, which results in a drop in humidity or even dryness at the proton exchange membrane 102. This phenomenon has become more pronounced in air-cooled fuel cells. In an air-cooled fuel cell, the cathode gas diffusion layer 108 is blown off with greater flow of air to function as cooling, but greater flow of air will cause more moisture loss, thereby accelerating moisture loss at the proton exchange membrane 102 and reducing the performance and lifespan of the fuel cell.

[0032] In the membrane electrode 100 shown in FIG. 1 , a hydrophobic layer 112 is provided on the outer surface of the cathode gas diffusion layer 108. The hydrophobic layer 112 is made of a hydrophobic material, thus possessing hydrophobic properties, i.e., the surface of the hydrophobic layer 112 is water exclusive such that the water produced at the cathode does not easily pass through the hydrophobic layer 112, but is retained inside the membrane electrode 100, thereby enabling self-wetting of the membrane electrode 100, reducing moisture loss at the proton exchange membrane 102, improving the performance of the membrane electrode 100, and extending the lifespan of the membrane electrode 100.

[0033] In some embodiments, the fuel cell membrane electrode includes a proton exchange membrane, a cathode catalyst layer disposed on the cathodic side of the proton exchange membrane, a cathode gas diffusion layer disposed on an outer side of the cathode gas diffusion layer, and a hydrophobic layer disposed on the outer side of the cathode gas diffusion layer, wherein an outer surface of the cathode gas diffusion layer has a region in contact with a bipolar plate (also referred to as a first region) and a region not in contact with the bipolar plate (also referred to as a second region), the hydrophobic layer having hydrophobic properties and covering at least a portion of the region in contact with the bipolar plate.

[0034] FIG. 2 shows a schematic view of an example fuel cell membrane electrode 200 having a hydrophobic layer, consistent with some embodiments of the present disclosure. The membrane electrode 200 may be, for example, a membrane electrode of air-cooled fuel cells. As shown in FIG. 2, the membrane electrode 200 includes a proton exchange membrane 202, a cathode catalyst layer 204, an anode catalyst layer 206, a cathode gas diffusion layer 208, an anode gas diffusion layer 210, and a hydrophobic layer 212, wherein the cathode catalyst layer 204 is disposed on the cathodic side of the proton exchange membrane 202, the cathode gas diffusion layer 208 is disposed on the outer side of the cathode catalyst layer 204, and the hydrophobic layer 212 is disposed on an outer surface of the cathode gas diffusion layer 208.

[0035] As shown in FIG. 2, the bipolar plate 214 is in close contact with the cathode gas diffusion layer 208 for supporting the membrane electrode 200. The outer surface of the cathode gas diffusion layer 208 has regions 216-1 , 216-2 and 216-3 (collectively referred to as region 216, also referred to as the first region) in contact with the bipolar plate 214. Further, the outer surface of the cathode gas diffusion layer 208 also has regions 218-1 , 218-2, and 218-3 (collectively referred to as region 218, also referred to as the second region) that are not in contact with the bipolar plate 214. The region 216 in which the bipolar plate 214 is in contact with the cathode gas diffusion layer 208, in addition to supporting the membrane electrode 200, may also export electrons to an external circuit to form a current. Because the hydrophobic material is not conductive, the hydrophobic layer 212 may be set to bypass or avoid the region 216 in which the bipolar plate 214 contacts the cathode gas diffusion layer 208 (i.e., no hydrophobic layer 212 is provided within the region 216 of the cathode gas diffusion layer 208 surface) in order to enable the electrons to be derived by the bipolar plate 214. In this way, the electrons may be conductive to the bipolar plate 214 via the region 216 without being influenced by the hydrophobic layer 212.

[0036] As shown in FIG. 2, the hydrophobic layer 212 with hydrophobic properties may cover at least a portion of the region 218 in which the cathode gas diffusion layer 208 is not in contact with the bipolar plate 214. Because the hydrophobic layer 212 is made of a hydrophobic material, the hydrophobic layer 212 may reduce moisture loss due to air blowing, thereby enabling water generated at the cathode to be retained inside the membrane electrode 200. In some implementations, the inner side of the cathode gas diffusion layer 208 (i.e., near the cathodic side of the cathode catalyst layer 204) has a microporous layer, the material that makes the microporous layer may include hydrophobic materials. However, due to the small proportion of hydrophobic material in the microporous layer (e.g., around 5%) and the large pore size of the microporous layer, the microporous layer is primarily used to facilitate the discharge of water generated at the cathode catalyst layer 204. With respect to the microporous layer inside the cathode gas diffusion layer 208, the hydrophobic layer 212 may consist almost entirely of hydrophobic materials to prevent moisture from flowing through the hydrophobic layer 212 and being lost. Considering that the hydrophobic layer 212 may include other functional materials in some possible implementations, in some embodiments, the proportion of hydrophobic materials included in the hydrophobic layer 212 may be greater than a predetermined proportional threshold. For example, the proportion of hydrophobic materials included in the hydrophobic layer 212 may be greater than 80%, 90%, etc., which can ensure that the hydrophobic layer 212 impedes moisture from passing through, thereby retaining a portion of moisture in the membrane electrode 200.

[0037] In some embodiments, the hydrophobic layer 212 may cover only a portion of the region 218 in which the cathode gas diffusion layer 208 is not in contact with the bipolar plate 214. In other words, the hydrophobic layer 212 may not completely cover the region 218. In this way, air as a reactant may be allowed to enter the cathode catalyst layer 204 of the membrane electrode 200 through a portion of the region 218 where the hydrophobic layer 212 is not provided to react with positive ions to generate water. In some embodiments, the area of the region 218 where the hydrophobic layer 212 is not provided is determined based on the desired air mass flow and moisture loss velocity. In this way, a balance can be struck between chemical reaction efficiency and moisture loss to maximize the performance of the membrane electrode 200.

[0038] In some embodiments, the hydrophobic layer 212 may also have a porous structure to allow air to pass through the holes of the hydrophobic layer 212 into the membrane electrode 200 and excess moisture to drain from the membrane electrode 200 through these holes. Such embodiments will be described in detail elsewhere herein.

[0039] In this way, the hydrophobic layer 212 with hydrophobic properties may hinder the loss of water from the surface of the cathode gas diffusion layer 208, thereby enabling the water produced at the cathode to remain in the membrane electrode 200. In this way, the proton exchange membrane 202 can be wetted using water generated at the cathode, thereby improving the fuel cell performance. Moreover, there is no need for an external humidifier, which enables cost and space saving, reduces the complexity of fuel cells, and improves the stability of fuel cells.

[0040] In some embodiments, the bipolar plate has a ridge for conducting electricity and a channel for transmitting gas, the region where the cathode gas diffusion layer is in contact with the bipolar plate is a region where an outer surface of the cathode gas diffusion layer is in contact with the ridge of the bipolar plate, and the region where the cathode gas diffusion layer is not in contact with the bipolar plate is a region where the outer surface of the cathode gas diffusion layer corresponds to the channel of the bipolar plate.

[0041] FIG. 3 shows a schematic view of an example fuel cell membrane electrode 300 having a hydrophobic layer where the bipolar plate has a channel, consistent with some embodiments of the present disclosure. As shown in FIG. 3, the membrane electrode 300 includes a proton exchange membrane 202, a cathode catalyst layer 204, an anode catalyst layer 206, a cathode gas diffusion layer 208, an anode gas diffusion layer 210, and a hydrophobic layer 212, wherein the cathode catalyst layer 204 is disposed on the cathodic side of the proton exchange membrane 202, the cathode gas diffusion layer 208 is disposed on an outer side of the cathode catalyst layer 204, and the hydrophobic layer 312 is disposed on an outer side of the cathode gas diffusion layer 208.

[0042] In the example shown in FIG. 3, the bipolar plate 314 has a plurality of ridges 322 and a plurality of channels 324. The outer surface of the cathode gas diffusion layer 208 has a region in contact with the ridge 322 of the bipolar plate 314. Further, the outer surface of the cathode gas diffusion layer 208 also has a region that is not in contact with the bipolar plate 314, i.e., an area corresponding to the channel 324 of the bipolar plate 314. The ridge 322 of the bipolar plate 314 is in contact with the cathode gas diffusion layer 208 and serves to support the membrane electrode 300 as well as deriving electrons. Air as a reactant may enter the cathode gas diffusion layer 208 from the channel 324 of the bipolar plate 314 and be transmitted to the cathode catalyst layer 204. At the cathode catalyst layer 204, oxygen in the air may react with the positive ions to produce water. To enable the electrons to be derived by the bipolar plate 314, the hydrophobic layer 312 may be disposed in a region where the cathode gas diffusion layer 208 corresponds to the channel 324 of the bipolar plate 314. In this way, the hydrophobic layer 312 can slow moisture loss, retaining moisture inside the membrane electrode 300 without affecting the electrons being derived through the ridge 322 of the bipolar plate 314. As shown in FIG. 3, the hydrophobic layer 312 may cover only a portion of the region of the cathode gas diffusion layer 208 corresponding to the channel 324 of the bipolar plate 314. In this way, air as a reactant is able to enter the cathode catalyst layer 204 of the membrane electrode 300 to react with the positive ions to generate water.

[0043] In some embodiments, the bipolar plate has a frame portion for conducting electricity and a window for ventilation, the region in which the cathode gas diffusion layer is in contact with the bipolar plate is a region in which the outer surface of the cathode gas diffusion layer is in contact with the frame portion of the bipolar plate, and the region in which the cathode gas diffusion layer is not in contact with the bipolar plate is a region in which the outer surface of the cathode gas diffusion layer corresponds to the window of the bipolar plate.

[0044] FIGS. 4A to 4B show a schematic view of an example fuel cell membrane electrode 400 having a hydrophobic layer where the bipolar plate has a window, consistent with some embodiments of the present disclosure. As shown in FIG. 4A, the membrane electrode 400 includes a proton exchange membrane 202, a cathode catalyst layer 204, an anode catalyst layer 206, a cathode gas diffusion layer 208, an anode gas diffusion layer 210, and a hydrophobic layer 412, wherein the cathode catalyst layer 204 is disposed on the cathodic side of the proton exchange membrane 202, the cathode gas diffusion layer 208 is disposed on the outer side of the cathode catalyst layer 204, and the hydrophobic layer 412 is disposed on the outer surface of the cathode gas diffusion layer 208.

[0045] In the example shown in FIG. 4A, the bipolar plate 414 has a frame portion 422 and a plurality of windows 424. The outer surface of the cathode gas diffusion layer 208 has a region in contact with the frame portion 422 of the bipolar plate 414. Further, the outer surface of the cathode gas diffusion layer 208 also has a region that is not in contact with the bipolar plate 414, i.e. , a region corresponding to the window 424. The frame portion 422 of the bipolar plate 414 is in contact with the cathode gas diffusion layer 208 and serves to support the membrane electrode 400 as well as to derive electrons. Air as a reactant may enter the cathode gas diffusion layer 208 from the window 424 of the bipolar plate 414 and be transmitted to the cathode catalyst layer 204. At the cathode catalyst layer 204, oxygen in the air may react with the positive ions to produce water. To enable the electrons to be derived by the bipolar plate 414, the hydrophobic layer 412 may be disposed in a region where the cathode gas diffusion layer 208 corresponds to the window 424 of the bipolar plate 414 without covering the region where the cathode gas diffusion layer 208 is in contact with the frame portion 422 of the bipolar plate 414.

[0046] FIG. 4B shows a top view of the hydrophobic layer 412 disposed in the window 424 of the bipolar plate 414. It should be noted that although the window 424 is shown as rectangular in FIG. 4B, the present disclosure is not intended to limit the shape and size of the window 424. Rather, the window 424 may be any shape, such as square, circular, and irregular shape, as well as any size. As shown in FIG. 4B, the hydrophobic layer 412 may cover only a portion of the window 424 of the bipolar plate 414. In this way, air as a reactant may at least enter the membrane electrode 400 passing through the region of the window 424 that does not cover the hydrophobic layer 412. In this way, the hydrophobic layer 412 is able to slow moisture loss, retaining moisture inside the membrane electrode 400 without affecting the electrons being derived through the frame portion 422 of the bipolar plate 414. In some embodiments, the hydrophobic layer has a porous structure. In some embodiments, the pore size of the hydrophobic layer is greater than the first predetermined pore size threshold and less than the second predetermined pore size threshold. In some embodiments, the hydrophobic layer having the porous structure may completely cover a region where the cathode gas diffusion layer is not in contact with the bipolar plate.

[0047] FIG. 5 shows a schematic view of an example fuel cell membrane electrode 500 having a porous hydrophobic layer, consistent with some embodiments of the present disclosure. As shown in FIG. 5, the membrane electrode 500 includes a proton exchange membrane 202, a cathode catalyst layer 204, an anode catalyst layer 206, a cathode gas diffusion layer 208, an anode gas diffusion layer 210, and a hydrophobic layer 512, wherein the cathode catalyst layer 204 is disposed on the cathodic side of the proton exchange membrane 202, the cathode gas diffusion layer 208 is disposed on the outer side of the cathode catalyst layer, and the hydrophobic layer 512 is disposed on the outer side of the cathode gas diffusion layer 208.

[0048] As shown in FIG. 5, the hydrophobic layer 512 includes a porous structure in addition to being constructed from a hydrophobic material thereby having hydrophobic properties. The hydrophobic layer 512 may be made of a waterproof, breathable material, such as expanded polytetrafluorethylene (e-PTFE). As shown in FIG. 5, the bipolar plate 214 is in close contact with the cathode gas diffusion layer 208 for supporting the membrane electrode 500. The outer surface of the cathode gas diffusion layer 208 has regions 216-1 , 216-2, and 216-3 (collectively referred to as region 216) in contact with the bipolar plate 214. Further, the outer surface of the cathode gas diffusion layer 208 also has regions 218-1 , 218-2, and 218-3 (collectively referred to as region 218) that are not in contact with the bipolar plate 214. The region 216 in which the bipolar plate 214 is in contact with the cathode gas diffusion layer 208, in addition to supporting the membrane electrode 200, may also export electrons to an external circuit to form a current. To enable the electrons to be derived by the bipolar plate 214, the hydrophobic layer 512 may be provided to bypass or avoid the region 216 in which the bipolar plate 214 contacts the cathode gas diffusion layer 208 (i.e., no hydrophobic layer 512 is provided within the region 216 of the cathode gas diffusion layer 208 surface). In this way, the electrons may be conductive to the bipolar plate 214 via the region 216 without being influenced by the hydrophobic layer 512.

[0049] As shown in FIG. 5, the hydrophobic layer 512 having the hydrophobic properties and porous structure may completely (almost completely or substantially) cover the region 218 where the cathode gas diffusion layer 208 is not in contact with the bipolar plate 214. Because the hydrophobic layer 512 is made of a hydrophobic material, the hydrophobic layer 512 may reduce moisture loss due to air blowing, thereby enabling water generated at the cathode to be retained inside the membrane electrode 200. Further, since the hydrophobic layer 512 completely covers the region 218 that causes moisture loss, it is possible to improve the water retention effect. In addition, as the hydrophobic layer 512 has a porous structure, air as a reactant may enter the membrane electrode 500 through the holes in the hydrophobic layer 512 to participate in the chemical reaction. In order for moisture to remain within the membrane electrode 500, the pore size of the hydrophobic layer 512 may be less than a predetermined pore size threshold. Meanwhile, in order for air to enter the membrane electrode 500 through the hydrophobic layer 512, the pore size of the hydrophobic layer 512 may be greater than another predetermined pore size threshold. The pore size of the hydrophobic layer 512 may be adjusted between these two predetermined pore size thresholds to balance the air flow into the membrane electrode 500 and moisture loss.

[0050] In this way, the hydrophobic layer 512 is capable of hindering the loss of moisture in the membrane electrode 500, the electrons being derived through the region 216 where the cathode gas diffusion layer 208 is in contact with the bipolar plate 214, while air as a reactant is able to enter the membrane electrode 500 through the holes of the hydrophobic layer 512, thereby preserving moisture in the membrane electrode 500 and improving the performance and lifespan of the fuel cell. In addition, the hydrophobic layer 512 is capable of completely covering the region 218 in which the cathode gas diffusion layer 208 is not in contact with the bipolar plate 214, thereby further improving water retention and fuel cell performance.

[0051] FIG. 6 shows a schematic view of an example fuel cell membrane electrode 600 having a porous hydrophobic layer where a bipolar plate has a channel, consistent with some embodiments of the present disclosure. As shown in FIG. 6, the membrane electrode 600 includes a proton exchange membrane 202, a cathode catalyst layer 204, an anode catalyst layer 206, a cathode gas diffusion layer 208, an anode gas diffusion layer 210, and a hydrophobic layer 612, wherein the cathode catalyst layer 204 is disposed on the cathodic side of the proton exchange membrane 202, the cathode gas diffusion layer 208 is disposed on the outer side of the cathode catalyst layer 204, and the hydrophobic layer 612 is disposed on the outer surface of the cathode gas diffusion layer 208.

[0052] In the example shown in FIG. 6, the bipolar plate 314 has a plurality of ridges 322 and a plurality of channels 324. The outer surface of the cathode gas diffusion layer 208 has a region in contact with the ridge 322 of the bipolar plate 314. Further, the outer surface of the cathode gas diffusion layer 208 also has a region that is not in contact with the bipolar plate 314, i.e. , a region corresponding to the channel 324 of the bipolar plate 314. The ridge 322 of the bipolar plate 314 is in contact with the cathode gas diffusion layer 208 and serves to support the membrane electrode 600 as well as to derive electrons. Air as a reactant may enter the cathode gas diffusion layer 208 from the channel 324 of the bipolar plate 314 and through the holes of the hydrophobic layer 612 and be transmitted to the cathode catalyst layer 204. At the cathode catalyst layer 204, oxygen in the air may react with the positive ions to produce water. To enable the electrons to be derived by the bipolar plate 314, the hydrophobic layer 612 may be disposed in a region where the cathode gas diffusion layer 208 corresponds to the channel 324 of the bipolar plate 314. In this way, the hydrophobic layer 312 is able to slow moisture loss, retaining moisture inside the membrane electrode 600 without affecting the electrons being derived through the ridge 322 of the bipolar plate 314.

[0053] As shown in FIG. 6, the hydrophobic layer 612 may completely cover the region where the cathode gas diffusion layer 208 corresponds to the channel 324 of the bipolar plate 314. In this way, the air as a reactant can participate in the chemical reaction by entering the membrane electrode 600 through the holes of the hydrophobic layer 612. Further, since the outer surface of the cathode gas diffusion layer 208 is completely covered by the hydrophobic layer 612 and the ridge 322 of the bipolar plate 314, the resulting water can be retained to the maximum extent inside the membrane electrode 600 to reduce moisture loss. FIGS. 7A to 7B show a schematic view of an example fuel cell membrane electrode 600 having a porous hydrophobic layer where the bipolar plate has a window, consistent with some embodiments of the present disclosure. As shown in FIG. 4A, the membrane electrode 700 includes a proton exchange membrane 202, a cathode catalyst layer 204, an anode catalyst layer 206, a cathode gas diffusion layer 208, an anode gas diffusion layer 210, and a hydrophobic layer 712, wherein the cathode catalyst layer 204 is disposed on the cathodic side of the proton exchange membrane 202, the cathode gas diffusion layer 208 is disposed on the outer side of the cathode catalyst layer 204, and the hydrophobic layer 712 is disposed on the outer surface of the cathode gas diffusion layer 208.

[0054] In the example shown in FIG. 7A, the bipolar plate 414 has a frame portion 422 and a plurality of windows 424. The outer surface of the cathode gas diffusion layer 208 has a region in contact with the frame portion 422 of the bipolar plate 414. Further, the outer surface of the cathode gas diffusion layer 208 also has a region that is not in contact with the bipolar plate 414, i.e. , a region corresponding to the window 424. The frame portion 422 of the bipolar plate 414 is in contact with the cathode gas diffusion layer 208 and serves to support the membrane electrode 400 as well as to derive electrons. Air as a reactant may enter the cathode gas diffusion layer 208 from the window 424 of the bipolar plate 414 and through the holes of the hydrophobic layer 712 and be transmitted to the cathode catalyst layer 204. At the cathode catalyst layer 204, oxygen in the air may react with the positive ions to produce water. To enable the electrons to be derived by the bipolar plate 414, the hydrophobic layer 412 may be disposed in a region where the cathode gas diffusion layer 208 corresponds to the window 424 of the bipolar plate 414 without covering the region where the cathode gas diffusion layer 208 is in contact with the frame portion 422 of the bipolar plate 414.

[0055] FIG. 7B shows a top view of the hydrophobic layer 712 disposed in the window 424 of the bipolar plate 414. It is to be noted that although the window 424 is shown as rectangular in FIG. 7B, the present disclosure is not intended to limit the shape and size of the window 424; rather, the window 424 may be any shape, such as square, circular, and irregular shape, as well as any size. As shown in FIG. 7B, the hydrophobic layer 712 may completely cover the window 424 of the bipolar plate 414. In this way, air as a reactant can enter the membrane electrode 400 through the holes of the hydrophobic layer 712. Further, since the outer surface of the cathode gas diffusion layer 208 is completely covered by the hydrophobic layer 712 and the frame portion 422 of the bipolar plate 414, the resulting water can be retained to the maximum extent inside the membrane electrode 700 to reduce moisture loss.

[0056] As described above, in some embodiments, the pore size of the hydrophobic layer may be greater than the first predetermined pore size threshold and less than the second predetermined pore size threshold. If the pore size of the hydrophobic layer is too large, moisture may be more easily lost to the outside of the membrane electrode through the pore. If the pore size of the hydrophobic layer is too small, the air as a reactant cannot smoothly enter the membrane electrode to participate in the chemical reaction. In some embodiments, the pore size of the hydrophobic layer may be determined based on a breakthrough pressure that causes a water drop to pass through the hydrophobic layer, a surface tension of water, and a contact angle of water on the hydrophobic material.

[0057] FIG. 8 shows a schematic diagram of an example process 800 for determining the pore size of a porous hydrophobic layer, consistent with some embodiments of the present disclosure. As shown in FIG. 8, the process 800 can determine a breakthrough pressure 802 that causes a water drop to pass through the hydrophobic layer, a surface tension 804 of water, and a contact angle 806 of water on the hydrophobic material. The process 800 may then determine a pore size 808 of the hydrophobic layer based on the breakthrough pressure 802, the surface tension 804, and the contact angle 806. As the holes of the hydrophobic layer are not uniform, the pore size 808 may be considered an average pore size. The larger the pore size 808 of the hydrophobic layer, the smaller the breakthrough pressure 802 to cause the water drop to pass through the hydrophobic layer. Moreover, the greater the contact angle 806 of water on the hydrophobic material, the greater the hydrophobicity of the hydrophobic layer, and the greater the allowable pore size 808 of the hydrophobic layer. Thus, the contact angle 806 may be determined by selecting the hydrophobic material. Further, the surface tension 804 of the water may be determined by determining the operating environment of the membrane electrode. The process 800 may then determine an acceptable range for the breakthrough pressure 802 based on the desired water retention effect, thereby enabling a determination of a range of suitable pore sizes 808 based on the breakthrough pressure 802, the surface tension 804, and the contact angle 806. In this way, the pore size suitable for the hydrophobic layer can be accurately calculated so that the hydrophobic layer can have the water retention function while allowing air to enter the membrane electrode through the pore size to participate in the chemical reaction.

[0058] In some embodiments, the thickness of the hydrophobic layer may be determined based on a desired gas mass transfer flux, a surface area of the hydrophobic layer, a gas diffusion rate, and a concentration gradient. FIG. 9 shows a schematic diagram of an example process 900 for determining a thickness of a porous hydrophobic layer, consistent with some embodiments of the present disclosure. As shown in FIG. 9, the process 900 can determine a desired gas mass transfer flux 902, a surface area 904 of the hydrophobic layer, a gas diffusion rate 906, and a concentration gradient 908. The process 900 may then determine a thickness 910 of the hydrophobic layer based on the mass transfer flux 902, the surface area 904, the gas diffusion rate 906, and the concentration gradient 908. The relationship between the mass transfer flux 902 and the surface area of the mass transfer (i.e. , the surface area 904 of the hydrophobic layer) can be understood by the rate of mass transfer on a unit area. The rate of mass transfer is the mass transfer flux on a unit area, which is directly proportional to the surface area 904. Thus, if the surface area 904 is increased, the mass transfer rate per unit area will also increase, resulting in an increase in the mass transfer flux 902. When the pore size is smaller, the effective area in the surface area 904 that can transfer mass is small, which will directly reduce the mass transfer flux 902. In addition, the mass transfer flux 902 is also associated with the gas diffusion rate 906 of the mass transfer, the concentration gradient 908 of the mass transfer, and the mass transfer distance (i.e., the thickness 910 of the hydrophobic layer). When the thickness 910 of the hydrophobic layer is large, the concentration gradient 908 is small, and therefore the mass transfer flux 902 is also reduced. Accordingly, after determining the mass transfer flux 902 of the air, the surface area 904, the gas diffusion rate 906, and the concentration gradient 908 of the hydrophobic layer required for the membrane electrode, the process 900 can determine the thickness 910 of the hydrophobic layer. In this way, the thickness suitable for the hydrophobic layer can be accurately calculated so that air can smoothly enter the membrane electrode through the pore size of the hydrophobic layer to participate in the chemical reaction.

[0059] Embodiments of the present disclosure also provide a fuel cell system comprising a fuel cell membrane electrode. The fuel cell membrane electrode includes a proton exchange membrane. The fuel cell membrane electrode also includes a cathode catalyst layer disposed on the cathodic side of the proton exchange membrane. The fuel cell membrane electrode also includes a cathode gas diffusion layer disposed on an outer side of the cathode catalyst layer, the outer surface of the cathode gas diffusion layer having a first region in contact with the bipolar plate and a second region not in contact with the bipolar plate. Further, the fuel cell membrane electrode further comprises a hydrophobic layer disposed on an outer side of the cathode gas diffusion layer, wherein the hydrophobic layer has hydrophobic properties and the hydrophobic layer covers at least a portion of the region in the second region.

[0060] Embodiments of the present disclosure also provide an electrical device, which may include, for example, a vehicle, an aircraft, etc. The electrical device includes a fuel cell system that includes a fuel cell membrane electrode. The fuel cell membrane electrode includes a proton exchange membrane. The fuel cell membrane electrode also includes a cathode catalyst layer disposed on the cathodic side of the proton exchange membrane. The fuel cell membrane electrode also includes a cathode gas diffusion layer disposed on an outer side of the cathode catalyst layer, the outer surface of the cathode gas diffusion layer having a first region in contact with the bipolar plate and a second region not in contact with the bipolar plate. Further, the fuel cell membrane electrode further comprises a hydrophobic layer disposed on an outer side of the cathode gas diffusion layer, wherein the hydrophobic layer has hydrophobic properties and the hydrophobic layer covers at least a portion of the region in the second region.

[0061] Utilizing a fuel cell system or an electrical device of the present disclosure, at least one of a number of advantages that can be achieved by a method or process as described above may be achieved. For example, it is possible to retain moisture in the membrane electrodes, improve the performance and lifespan of fuel cells, and also provide cost savings.

[0062] In the description of the examples of the present disclosure, the term “comprise” and other similar expressions should be understood as open-ended inclusion, that is, “comprising but not limited to”. The term “based on” should be understood as “at least partially based on”. The term “one example” or “this example” should be understood as “at least one example”. The terms “first”, “second”, etc. may refer to and represent different or the same object. Other explicit and implicit definitions may be included below. Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and operations described above are merely exemplary forms of implementing the claims.

Claims

CLAIMS1. A fuel cell membrane electrode (200, 300, 400, 500, 600, 700), comprising: a proton exchange membrane (202); a cathode catalyst layer (204) disposed on a cathodic side of the proton exchange membrane (202); a cathode gas diffusion layer (208) disposed on an outer side of the cathode catalyst layer (204), an outer surface of the cathode gas diffusion layer (208) having a first region in contact with a bipolar plate (214, 314, 414) and a second region not in contact with the bipolar plate (214, 314, 414); and a hydrophobic layer (212, 312, 412, 512, 612, 712) disposed on an outer side of the cathode gas diffusion layer (208), wherein the hydrophobic layer (212, 312, 412, 512, 612, 712) has hydrophobic properties and the hydrophobic layer (212, 312, 412, 512, 612, 712) covers at least a portion of a region in the second region.

2. The fuel cell membrane electrode according to Claim 1 , wherein the bipolar plate has a ridge (322) for conducting electricity and a channel (324) for transmitting gas, the first region being an area in which the outer surface of the cathode gas diffusion layer (208) is in contact with the ridge (322) of the bipolar plate, and the second region being an area in which the outer surface of the cathode gas diffusion layer (208) corresponds to the channel (324) of the bipolar plate.

3. The fuel cell membrane electrode according to Claim 1 , wherein the bipolar plate has a frame portion (414) for conducting electricity and a window (424) for ventilation, the first region being an area where the outer surface of the cathode gas diffusion layer (208) is in contact with the frame portion (414) of the bipolar plate, and the second region being an area where the outer surface of the cathode gas diffusion layer (208) corresponds to the window (424) of the bipolar plate.

4. The fuel cell membrane electrode according to Claim 1 , wherein the hydrophobic layer comprises a hydrophobic material, and the ratio of the hydrophobic material in thehydrophobic layer is greater than a predetermined proportional threshold.

5. The fuel cell membrane electrode according to Claim 1 , wherein the hydrophobic layer is disposed to avoid the first region where the outer surface of the cathode gas diffusion layer (208) is in contact with the bipolar plate (214, 314, 414).

6. The fuel cell membrane electrode according to Claim 1 , wherein the hydrophobic layer has a porous structure.

7. The fuel cell membrane electrode according to Claim 6, wherein a pore size of the hydrophobic layer is greater than a first predetermined pore size threshold and is less than a second predetermined pore size threshold, wherein the first predetermined pore size threshold is less than the second predetermined pore size threshold.

8. The fuel cell membrane electrode according to Claim 7, wherein the hydrophobic layer completely covers the second region in which the outer surface of the cathode gas diffusion layer (208) is not in contact with the bipolar plate (214, 314, 414).

9. The fuel cell membrane electrode according to Claim 7, wherein the pore size of the hydrophobic layer is determined based on a breakthrough pressure making water drop pass through the hydrophobic layer, a surface tension of water, and a contact angle of water on a hydrophobic material.

10. The fuel cell membrane electrode according to Claim 9, wherein the hydrophobic layer has a thickness determined based on a desired gas mass transfer flux, a surface area of the hydrophobic layer, a gas diffusion rate, and a concentration gradient.11 . The fuel cell membrane electrode according to Claim 6, wherein the hydrophobic layer comprises expanded polytetrafluorethylene.

12. The fuel cell membrane electrode according to Claim 1 , wherein the fuel cellmembrane electrode is a membrane electrode of an air-cooled fuel cell.

13. A fuel cell system comprising the fuel cell membrane electrode (200, 300, 400, 500, 600, 700) according to Claims 1 to 12.

14. An electrical device comprising a fuel cell system comprising the fuel cell membrane electrode (200, 300, 400, 500, 600, 700) according to Claims 1 to 12.

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