A directional water-draining catalyst layer structure with hydrophobic / hydrophilic composite structure and a cathode electrode

Abstract

The utility model discloses a kind of directional drainage catalytic layer structure and cathode electrode with hydrophobic / hydrophilic composite structure, including first sublayer and second sublayer are sequentially laminated, first sublayer is the dense structure of catalyst composition, second sublayer is the loose structure of hydrophilic agent composition, conical pore channel structure is arranged and is extended from the top of second sublayer towards first sublayer, and along the thickness direction of second sublayer is penetrated and extended to first sublayer, its diameter gradually decreases along the thickness direction and its inner wall is modified as strong hydrophobic, the projection shape of conical pore channel structure on the top surface of second sublayer is dendritic network structure, water produced in the catalysis of catalyst in first sublayer is sucked by hydrophilic agent of second sublayer along conical pore channel structure, and is gradually collected and discharged along the channel path formed by dendritic network structure, this structure can decouple and cooperatively optimize the complex material transport network inside catalytic layer.

Description

Technical Field

[0001] This utility model relates to the field of proton exchange membrane fuel cells, and in particular to a directional drainage catalyst layer structure and cathode electrode with a hydrophobic / hydrophilic composite structure. Background Technology

[0002] In electrochemical devices such as proton exchange membrane fuel cells (PEMFCs), the catalyst layer (CL) is the core site where electrochemical reactions occur, and its microstructure directly determines the device's performance, cost, and durability. The function of the catalyst layer is to construct an efficient system for supplying reactants (gases such as O2, liquids such as H2O, and protons such as H+) to reactants. + ) and electrons (e - The platform through which all three phases participate in the reaction is called the "three-phase interface".

[0003] In existing technologies, catalyst layers are often produced by uniformly coating a slurry composed of catalysts, polymer ionomers, and conductive supports. This results in a homogeneous structure with uniform porosity and wettability. This type of structure presents an inherent contradiction: on the one hand, to reduce charge transfer impedance and ohmic impedance, a relatively dense structure is needed to ensure a continuous transport network for protons and electrons; on the other hand, to reduce concentration polarization and ensure that reactants can quickly reach the reaction sites and products can be discharged promptly, a loose structure with high porosity is required to construct low-resistance mass transport channels. For example... Figure 1 As shown, the catalyst, ionomers, and pores within a traditional catalyst layer are randomly and uniformly distributed without functional partitioning. This "one-size-fits-all" homogeneous structure leads to a performance contradiction between proton / electron conduction and gas / liquid transport.

[0004] This single homogeneous structure cannot synergistically optimize the aforementioned mutually restrictive requirements, causing the mass transfer process to become the main performance bottleneck under high current density (i.e., high power output) conditions. Specifically, the liquid water generated by the electrochemical reaction in the cathode catalyst layer cannot be discharged in time, accumulating in large quantities on the catalyst surface and in the pores, causing a severe "flooding" phenomenon. This not only clogs the pores and hinders the supply of oxygen, but also covers the catalytic active sites, ultimately leading to a precipitous drop in the battery output voltage, severely limiting the peak power density and operational stability of the device. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a directional drainage catalyst layer structure and cathode electrode with a hydrophobic / hydrophilic composite structure.

[0006] To achieve the above objectives, the technical solution of this utility model is as follows:

[0007] A directional drainage catalytic layer structure with a hydrophobic / hydrophilic composite structure includes a first sublayer and a second sublayer stacked sequentially. The first sublayer is a dense structure composed of a catalyst, and the second sublayer is a loose structure composed of a hydrophilic agent. A conical channel structure extends from the top of the second sublayer toward the first sublayer. The conical channel structure penetrates and extends into the first sublayer along the thickness direction of the second sublayer. The depth of the conical channel structure in the first sublayer is one-half to two-thirds of the thickness of the first sublayer. The diameter of the conical channel structure gradually decreases along the thickness direction, and its inner wall is modified to be strongly hydrophobic. The projection shape of the conical channel structure on the top surface of the second sublayer is a dendritic network structure. Water generated in the first sublayer under the catalysis of the catalyst is absorbed by the hydrophilic agent of the second sublayer along the conical channel structure and gradually collected and discharged along the channel path formed by the dendritic network structure.

[0008] Preferably, the network structure includes a dendritic network structure, a linear array structure, or a cross-grid structure.

[0009] Preferably, the dendritic network structure includes a trunk, branches, and apexes with decreasing widths in sequence. One end of the trunk is connected to the branches and apexes in sequence, and the other end of the trunk is a water outlet. The channel path is from the apex to the branches to the trunk in sequence.

[0010] Preferably, the surface at one end of the main trunk is higher than the surface at the other end of the main trunk, and its slope ranges from 2% to 5%, the distance between two adjacent tips is 10 to 20 μm, and the bifurcation angle between two adjacent tips is 30° to 75°.

[0011] Preferably, the diameter of the tapered channel structure at the top and bottom of the second sublayer ranges from 5 to 8 μm and 1 to 2 μm, respectively.

[0012] Preferably, the thickness of the first sublayer is in the range of 5~8μm, and the thickness of the second sublayer is in the range of 5~10μm.

[0013] Preferably, the porosity of the first sublayer ranges from 20% to 40%, and the porosity of the second sublayer ranges from 50% to 80%.

[0014] Preferably, the catalyst is the catalyst used in the process of reduction reaction at the cathode to produce water, and the hydrophilic agent includes Nafion®.

[0015] Preferably, the first and second sublayers are prepared by 3D printing or electrospinning.

[0016] A cathode electrode comprising any one of the above-mentioned directional drainage catalytic layer structures with a hydrophobic / hydrophilic composite structure, the cathode electrode comprising a proton exchange membrane, a directional drainage catalytic layer structure and a gas diffusion layer stacked sequentially, wherein a first sublayer of the directional drainage catalytic layer structure is connected to the proton exchange membrane, a second sublayer is connected to the gas diffusion layer, and water discharged from the directional drainage catalytic layer structure flows toward the gas diffusion layer.

[0017] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0018] (1) The directional drainage catalyst layer structure with hydrophobic / hydrophilic composite structure proposed in this invention first constructs a functionally decoupled bilayer structure in the thickness direction, decomposing the catalyst layer into two functionally distinct regions: First sublayer (electrochemical reaction functional layer): This first sublayer is adjacent to the proton exchange membrane, and its design goal is to maximize the density of the three-phase interface and optimize charge transport. By adopting a high ionomer / carbon support ratio (I / C) and a dense microstructure, an efficient proton-electron synergistic conduction network is constructed, thereby minimizing the activation overpotential. Second sublayer (multiphase mass transfer functional layer): This second sublayer is oriented towards the gas diffusion layer, and its design goal is to minimize the mass transport resistance. By adopting a low I / C ratio, a high-porosity macroporous matrix is ​​constructed, providing a low-resistance channel for macroscopic transport of the gas / liquid two phases, effectively reducing the coupling resistance of each transport process, comprehensively optimizing the mass transport kinetics within the catalyst layer, and ensuring the continuous unobstructed flow of the reaction gas diffusion channel through an active and efficient drainage mechanism, thereby maximally suppressing concentration polarization and fundamentally eliminating the "flooding" problem.

[0019] (2) The directional drainage catalytic layer structure with hydrophobic / hydrophilic composite structure proposed in this invention introduces a deterministic, non-random macroscopic transport network—a dendritic network structure—inside the second sublayer. This dendritic network structure imitates the optimal transport system in nature that follows Murray's law (such as leaf veins), and adopts a fractal geometric structure to ensure maximum coverage of the entire two-dimensional plane and the most efficient fluid collection with the lowest flow resistance pressure drop. The dendritic network forms a conical channel structure in the thickness direction, which is designed as a Laval nozzle-like structure with a narrow inlet and a wide outlet. It utilizes the principle of microfluidic dynamics: the strong capillary effect of the narrow inlet enhances the ability to capture liquid water, while the gradually increasing channel cross-sectional area along the flow direction significantly reduces the flow resistance, realizing the accelerated discharge of product water. It can achieve maximum coverage of the entire reaction area and the fastest liquid collection and discharge with the lowest energy dissipation (flow resistance pressure drop). Its drainage efficiency and response speed are far superior to simple linear or grid-arranged structures.

[0020] (3) The directional drainage catalytic layer structure with a hydrophobic / hydrophilic composite structure proposed in this invention constructs a strong wettability gradient field inside the catalytic layer structure through selective surface modification. The porous matrix of the second sublayer is designed to be hydrophilic, which enables it to actively "absorb" and conduct the liquid water generated in the reaction zone of the first sublayer to its own interior through capillary wicking. The inner wall of the conical channel structure is modified to be strongly hydrophobic to achieve spontaneous water management based on the Laplace pressure gradient, generating an intrinsic driving force to actively drive water away from the reaction zone to the discharge channel. Compared with passive drainage relying solely on physical structure, this represents a qualitative leap in water management efficiency and reliability. By solving the mass transfer bottleneck, the cathode electrode can maintain a high reaction rate and stable output voltage under high load conditions, thereby significantly improving the peak power density and operational stability of the electrochemical device. Attached Figure Description

[0021] Figure 1 A schematic diagram of a cathode electrode using a conventional homogeneous catalyst structure;

[0022] Figure 2 This is a cross-sectional schematic diagram of a cathode electrode comprising a directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure, according to Embodiment 1 of this application.

[0023] Figure 3 This is a cross-sectional schematic diagram of the directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to Embodiment 1 of this application;

[0024] Figure 4 This is a top view schematic diagram of the directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to Embodiment 1 of this application;

[0025] Reference numerals: 1. Directional drainage catalyst layer structure; 11. First sublayer; 12. Second sublayer; 13. Conical pore structure; 2. Gas diffusion layer; 3. Proton exchange membrane. Detailed Implementation

[0026] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. The accompanying drawings are merely illustrative to facilitate understanding of the present invention, and their specific proportions can be adjusted according to design requirements. The vertical relationships of relative elements and the definitions of front / back in the graphics described herein should be understood by those skilled in the art to refer to the relative positions of the components; therefore, they can all be flipped to present the same component, and all of this should fall within the scope disclosed in this specification.

[0027] Example 1

[0028] refer to Figure 2-4This application proposes a directional drainage catalytic layer structure 1 with a hydrophobic / hydrophilic composite structure, comprising a first sublayer 11 and a second sublayer 12 stacked sequentially. The first sublayer 11 is a dense structure composed of a catalyst, with a porosity ranging from 20% to 40%. This dense structure is used for electrochemical reactions. The catalyst is used in the reduction reaction at the cathode to produce water, thus accelerating water generation under the action of the catalyst. The second sublayer 12 is a loose structure composed of a hydrophilic agent, with a porosity ranging from 50% to 80%. This loose structure is used for mass transport, i.e., transporting water from the first sublayer 11 out. Therefore, it embodies the core design concept of functional zoning and gradient porosity. (Reference) Figure 3 A conical pore structure 13 extends from the top of the second sub-layer 12 toward the first sub-layer 11. This conical pore structure 13 penetrates the second sub-layer 12 along its thickness direction and extends into the first sub-layer 11. The diameter of the conical pore structure 13 gradually decreases along its thickness direction, and its inner wall is modified to be highly hydrophobic. This can be achieved through a surface modification process. When liquid water is transported from the hydrophilic second sub-layer 12 to the interface of the highly hydrophobic conical pore structure 13, a strong Laplace pressure gradient pointing inwards towards the interior of the conical pore structure 13 is generated due to the significant surface energy difference between the two sides. This pressure gradient acts as an intrinsic driving force, actively "injecting" liquid water from the high-flow-resistance hydrophilic microporous network into the low-flow-resistance hydrophobic macroscopic conical pore structure 13. The conical channel structure 13 extends to a depth of one-half to two-thirds of the thickness of the first sub-layer 11. It is important to note that the conical channel structures 13 in the first sub-layer 11 and the second sub-layer 12 have a one-to-one correspondence. In the thickness direction, the conical channel structure 13 provides directional drainage microchannels from the first sub-layer 11 to the second sub-layer 12. The projected shape of the conical channel structure 13 on the top surface of the second sub-layer 12 is a network structure. In embodiments of this application, this network structure can be a dendritic network structure. Water generated in the first sub-layer 11 under the catalysis of the catalyst is absorbed by the hydrophilic agent of the second sub-layer 12 along the conical channel structure 13 and gradually collected and discharged along the channel path formed by the dendritic network structure. (Reference) Figure 4 From a top-down view, the conical channel structure 13 exists in a dendritic network structure along the length of the second sub-layer 12, providing a channel path for the water flow to converge in the conical channel structure 13 for step-by-step convergence.

[0029] In a specific embodiment, the dendritic network structure includes a trunk, branches, and tips whose widths decrease sequentially. One end of the trunk is connected to a branch and a tip, and the other end of the trunk is the outlet. The channel path is sequentially from the tip to the branch to the trunk. In one example, the spacing between two adjacent tips is 10-20 μm, and the bifurcation angle between two adjacent tips is 30°-75°. Water is absorbed through the widely distributed tips and gradually collected along the branches and trunk. The surface at one end of the trunk is higher than the surface at the other end, and its slope ranges from 2% to 5%. Therefore, the water flows along the slope towards the outlet, where it converges into the gas diffusion layer 2.

[0030] In a specific embodiment, the diameters of the conical channel structure 13 at the top and bottom of the second sub-layer 12 range from 5 to 8 μm and 1 to 2 μm, respectively. Therefore, the conical channel structure 13 has a narrow inlet and a wide outlet in the second sub-layer 12, with a narrow inlet diameter (1 to 2 μm) and a wide outlet diameter (5 to 8 μm). This unique "Laval-like nozzle" structure is the core of achieving efficient, active drainage. The thickness of the first sub-layer 11 ranges from 5 to 8 μm, and the thickness of the second sub-layer 12 ranges from 5 to 10 μm. The hydrophilic agent includes Nafion®. The first sub-layer 11 and the second sub-layer 12 are prepared by 3D printing or electrospinning, both of which can be used to obtain the structures of the first sub-layer 11 and the second sub-layer 12 involved in the embodiments of this application. Nafion® has extremely strong hydrophilicity and can be used to prepare the desired structure of the second sub-layer 12 using processes such as 3D printing or electrospinning.

[0031] The working principle of the directional drainage catalyst layer structure 1 with a hydrophobic / hydrophilic composite structure proposed in the embodiments of this application is as follows:

[0032] Under high current density, water generated in the first sublayer 11 is "drawn out" by the hydrophilic Nafion® dendritic network in the second sublayer 12, much like a capillary. The biomimetic dendritic network design of the second sublayer 12 ensures that water generated at any location within the first sublayer 11 can reach the nearest terminal channel within a very short distance. Thanks to the narrow inlet and hydrophobic inner wall of the terminal channel, liquid water is efficiently "drawn" into the terminal channel. Subsequently, the water flow converges step by step along the path of "terminal → branch → main channel". As the channels widen at each stage, the flow resistance (pressure drop) decreases sharply, and the water is finally discharged at high speed from the main channel to the gas diffusion layer 2.

[0033] Specifically, the liquid water generated in the first sublayer 11 is first captured and conducted by the capillary force of the hydrophilic agent in the second sublayer 12. When the liquid water is transported in the second sublayer 12 to the inner wall of the highly hydrophobic conical channel structure 13, a strong Laplace pressure gradient pointing towards the interior of the conical channel structure 13 is generated due to the huge surface energy difference on both sides. This pressure gradient acts as an intrinsic driving force, actively "injecting" the liquid water from the high-flow-resistance hydrophilic microporous network into the low-flow-resistance hydrophobic macroscopic conical channel structure 13. Once inside the conical channel structure 13, the water is rapidly collected in the low-resistance, hydrodynamically optimized biomimetic dendritic network and discharged to the gas diffusion layer 2.

[0034] Correspondingly, refer to Figure 2 The embodiments of this application also propose a cathode electrode comprising the aforementioned directional drainage catalyst layer structure 1 with a hydrophobic / hydrophilic composite structure. The cathode electrode includes a proton exchange membrane 3, the directional drainage catalyst layer structure 1, and a gas diffusion layer 2 stacked sequentially. A first sublayer 11 of the directional drainage catalyst layer structure 1 is connected to the proton exchange membrane 3, and a second sublayer 12 is connected to the gas diffusion layer 2. Water discharged from the directional drainage catalyst layer structure 1 flows towards the gas diffusion layer 2. The proton exchange membrane 3, the directional drainage catalyst layer structure 1, and the gas diffusion layer 2 form a "sandwich" multilayer structure, with the upper and lower sides respectively held by two electrode plates. In one example, the thickness of the directional drainage catalyst layer structure 1 is 10-20 μm, the thickness of the gas diffusion layer 2 is 180-300 μm, and the thickness of the proton exchange membrane 3 is 80-120 μm.

[0035] Example 2

[0036] The network structure in Embodiment 2 of this application can be simplified to a linear array structure or a cross-grid structure, depending on the manufacturing cost and specific application requirements. Furthermore, the catalyst layer structure can be prepared using an integrated molding process to form an integral structure with a continuously varying porosity gradient and containing directional channels.

[0037] The above embodiments are only used to further illustrate the technical solution of this utility model, but this utility model is not limited to the embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this utility model shall fall within the protection scope of the technical solution of this utility model.

Claims

1. A directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure, characterized in that, The system comprises a first sublayer and a second sublayer stacked sequentially. The first sublayer is a dense structure composed of a catalyst, and the second sublayer is a loose structure composed of a hydrophilic agent. A conical channel structure extends from the top of the second sublayer toward the first sublayer. The conical channel structure penetrates and extends into the first sublayer along the thickness direction of the second sublayer. The depth of the conical channel structure in the first sublayer is one-half to two-thirds of the thickness of the first sublayer. The diameter of the conical channel structure gradually decreases along the thickness direction, and its inner wall is modified to be strongly hydrophobic. The projection shape of the conical channel structure on the top surface of the second sublayer is a network structure. Water generated in the first sublayer under the catalysis of the catalyst is absorbed by the hydrophilic agent of the second sublayer along the conical channel structure and gradually collected and discharged along the channel path formed by the network structure.

2. The directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to claim 1, characterized in that, The network structure includes a dendritic network structure, a linear array structure, or a cross-grid structure.

3. The directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to claim 2, characterized in that, The dendritic network structure includes a trunk, branches, and apexes with decreasing widths. One end of the trunk is connected to the branches and apexes in sequence, and the other end of the trunk is the water outlet. The channel path is from the apex to the branches to the trunk in sequence.

4. The directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to claim 3, characterized in that, The surface at one end of the main trunk is higher than the surface at the other end of the main trunk, and its slope ranges from 2% to 5%. The distance between two adjacent tips is 10 to 20 μm, and the bifurcation angle between two adjacent tips is 30° to 75°.

5. The directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to claim 1, characterized in that, The diameter range of the tapered channel structure at the top and bottom of the second sublayer is 5~8μm and 1~2μm, respectively.

6. The directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to claim 1, characterized in that, The thickness of the first sublayer ranges from 5 to 8 μm, and the thickness of the second sublayer ranges from 5 to 10 μm.

7. The directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to claim 1, characterized in that, The porosity of the first sublayer ranges from 20% to 40%, and the porosity of the second sublayer ranges from 50% to 80%.

8. The directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to claim 1, characterized in that, The catalyst is the catalyst used in the process of reduction reaction at the cathode to produce water, and the hydrophilic agent includes Nafion®.

9. The directional drainage catalyst layer structure with a hydrophobic / hydrophilic composite structure according to claim 1, characterized in that, The first and second sublayers are prepared by 3D printing or electrospinning.

10. A cathode electrode comprising a directional drainage catalyst layer structure having a hydrophobic / hydrophilic composite structure as described in any one of claims 1-9, characterized in that, The cathode electrode comprises a proton exchange membrane, a directional drainage catalytic layer structure, and a gas diffusion layer stacked sequentially. The first sublayer of the directional drainage catalytic layer structure is connected to the proton exchange membrane, and the second sublayer is connected to the gas diffusion layer. The water discharged from the directional drainage catalytic layer structure flows to the gas diffusion layer.

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