Porous transmission layer structure of proton exchange membrane electrolytic cell based on capillary pressure gradient

Abstract

The invention discloses a porous transmission layer structure of a proton exchange membrane electrolytic cell based on capillary pressure gradient, and belongs to the field of hydrogen production by water electrolysis of a proton exchange membrane. The structure comprises a plurality of inverted circular-truncated-cone-shaped pores formed in a titanium substrate; the long bottom edge of each pore is close to the catalyst layer, and the short bottom edge of each pore is close to the flow field; the pore surface is subjected to hydrophilic gasification treatment, and capillary pressure gradient can be generated through radius difference between the upper end and the lower end of the pore. The gas transmission performance of the CPD-PTL is improved under the conditions of high current density and low current density, and the CPD-PTL with high porosity and high flow shows excellent performance in the operation process. In short, compared with a commercial porous transmission layer, the design is efficient, convenient and wide in application range.

Description

Technical Field

[0001] The invention belongs to the field of hydrogen production by electrolysis of water using a proton exchange membrane, and in particular relates to a porous transmission layer structure of a proton exchange membrane electrolyzer based on a capillary pressure gradient. Background Art

[0002] Currently, platinum and iridium oxide are the most commonly used catalysts in proton exchange membrane electrolyzers. Despite this, the cost remains high, which has prompted people to reduce costs by improving energy utilization, especially maximizing current density at low voltage. The membrane electrode assembly, porous transport layer and bipolar plate constitute the proton exchange membrane electrolyzer. The porous transport layer is an intermediate layer between the membrane electrode and the bipolar plate. Its main function is to promote the transport of products and provide electrical connection between the membrane electrode and the bipolar plate. However, when the current density is high, bubbles will quickly generate and block the reaction sites of the catalyst, thereby reducing the utilization of the catalyst and causing unstable battery performance. The optimized design of the porous transport layer can improve the efficiency of proton exchange membrane water electrolysis and reduce costs by effectively managing mass transfer in the gas and liquid phases.

[0003] Porous media made of titanium metal have high conductivity and corrosion resistance under high pressure conditions, so they are often used as porous transport layer materials for proton exchange membrane water electrolysis. In order to obtain the best porous transport layer, scholars have studied porosity, pore size and thickness. However, these macroscopic parameters of the porous transport layer ignore the transport mechanism of two-phase flow, that is, "one throat once" flow, because the gas is limited by the throat size inside the porous medium. To study its mechanism, Arbabi et al. and Lee et al. established a microfluidic platform to study the movement and growth of oxygen bubbles in the porous transport layer. Similarly, Zlobinski et al. used high spatial resolution neutron imaging technology to study the effects of various current densities and pressures on mass transfer losses. The above studies show that the movement of bubbles in the porous transport layer is determined by the structure of the porous medium, rather than by operational factors such as current density and flow rate. In addition, the study also showed that the main factor hindering the movement of bubbles in the porous transport layer is capillary force.

[0004] After exploring the transport mechanism of two-phase flow in the porous transport layer, the researchers hope to optimize the porous transport layer design to enhance the mass transfer of bubbles. Since the vertical movement of bubbles in the proton exchange membrane water electrolysis process is more valuable than the horizontal movement, some papers have tried to create a vertical gradient to reduce the resistance of bubbles. Scholars believe that the porous transport layer design with gradient porosity is superior in flow resistance and ohmic resistance. Lee et al. explored the liquid water transport behavior of the gradient structure through pore network modeling. Compared with the traditional structure, the oxygen saturation is greatly reduced when the porosity of the porous transport layer increases from the catalyst layer-porous transport layer interface to the porous transport layer-flow field interface. When a structure with an opposite porosity gradient is used, oxygen is deposited near the catalyst layer-porous transport layer interface. However, this method of generating a porosity gradient does not guarantee that the gas will flow through the expected path because it lacks consideration of the porous medium structure. Therefore, in order to strengthen the control of the gas flow, scholars proposed a structured porous transport layer design. Lee et al. designed patterned through holes to process pores below the flow field channel. The results showed that the gas saturation at the catalyst layer-porous transport layer interface was reduced by 43.5%. Zhang et al. studied the performance of thin titanium-based porous transport layers with well-tunable pore morphology and demonstrated that porous transport layers with well-tunable pore morphology can enhance battery mass transport compared to titanium felt. Summary of the invention

[0005] In the prior art, commercial porous transport layers do not take into account the correlation between the gas flow path and the capillary pressure. The purpose of the present invention is to overcome the defects in the prior art and provide a proton exchange membrane electrolyzer porous transport layer based on capillary pressure gradient (referred to as capillary pressure driven porous transport layer, capillary-driven porous transport layer, CPD-PTL) structure. This is because studies have found that capillary pressure has a significant effect on the transport of bubbles in porous media than other forces. Therefore, the present invention proposes a pore design of an inverted truncated cone structure, called a capillary pressure driven porous transport layer, which improves gas mass transfer by establishing a capillary pressure gradient to promote the transport of bubbles from the catalytic layer to the flow field. In addition, the factors affecting the capillary pressure gradient are analyzed using the established lattice Boltzmann model. The feasibility of the application of CPD-PTL is verified experimentally, and its role in mass transport and electrochemical reactions is studied through polarization curves.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] The present invention provides a porous transport layer structure of a proton exchange membrane electrolyzer based on capillary pressure gradient, comprising a plurality of inverted truncated cone-shaped pores opened on a titanium substrate; the longitudinal cross-section of the pore is a trapezoid, the long bottom side of which is close to the catalytic layer, and the short bottom side is close to the flow field; the pore surface is treated with gas affinity, and a capillary pressure gradient can be generated through the radius difference between the upper and lower ends of the pore.

[0008] Preferably, the pore diameter on the catalyst layer side of the pore is 300±5 μm, and the pore diameter on the flow field side is 200±5 μm.

[0009] Preferably, the contact angle θ of the pore surface satisfies 60°<θ<90°.

[0010] Preferably, the titanium substrate is formed by stacking a plurality of titanium sheets, and the inverted frustum cone-shaped pores are formed by coaxially opening circular holes of different diameters on each titanium sheet.

[0011] Furthermore, the thickness of each titanium sheet is the same, which is 25 μm.

[0012] Furthermore, the titanium sheet has 10 layers in total.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1) Considering the relationship between the gas flow path and the capillary force, the present invention designs a pore design with an inverted truncated cone structure, called a capillary pressure driven porous transport layer (CPD-PTL), which can effectively utilize the capillary pressure to help bubble separation and improve the efficiency of the proton exchange membrane electrolyzer.

[0015] 2) The present invention establishes a lattice Boltzmann model to explore how a single pore affects the movement of bubbles. After analyzing different factors affecting the pores, such as gas affinity, inclination, and speed, the pore structure that produces the best results (i.e., an inverted truncated cone structure) is selected to drive the bubbles.

[0016] 3) The present invention produces a capillary pressure driven porous transmission layer by stacking titanium sheets with circular holes of different diameters, which greatly reduces the overall production cost and processing technology difficulty of the capillary pressure driven porous transmission layer.

[0017] 4) The present invention verifies the effectiveness of the inverted truncated cone pore network through experimental methods: experiments using commercial platinum and iridium catalysts show that 1.92A / cm 2 of current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the difference between commercial porous transport layer and capillary pressure driven porous transport layer (CPD-PTL).

[0019] Figure 2 Verification results of model boundary conditions and parameters: (a) boundary conditions and geometric parameters of pores in the model; (b) comparison between the model and analytical solution of the relationship between bubble radius and pressure difference; (c) relationship between model parameters and contact angle.

[0020] Figure 3 Cross-sectional diagram of the gas volume fraction within 150 ms in a straight hole, a truncated cone hole, and an inverted truncated cone hole.

[0021] Figure 4 It is a preferred processing method for CPD-PTL. DETAILED DESCRIPTION

[0022] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0023] like Figure 1 As shown, commercial porous transport layers do not take into account the correlation between the gas flow path and the capillary pressure. The present invention aims to improve gas mass transfer by using a structural porous transport layer design to establish a capillary pressure gradient. For the transport of bubbles in porous media, capillary pressure has a significant effect than other forces. Therefore, the present invention proposes a pore design of an inverted truncated cone structure, called a capillary pressure driven porous transport layer (CPD-PTL), which maximizes the use of capillary pressure to promote the transport of bubbles from the catalytic layer to the flow field. And using the established lattice Boltzmann model, the factors affecting the capillary pressure gradient are analyzed. The feasibility of the application of CPD-PTL is verified experimentally, and its role in mass transport and electrochemical reactions is studied through polarization curves.

[0024] Specifically, the present invention provides a capillary pressure gradient-based porous transport layer structure for a proton exchange membrane electrolyzer, wherein the capillary pressure driven porous transport layer (CPD-PTL) mainly comprises a plurality of inverted truncated cone-shaped pores opened on a titanium substrate. The longitudinal cross-section of the pore is a trapezoid, with the long bottom side close to the catalyst layer side and the short bottom side close to the flow field side. The pore surface is treated with gas affinity, and a capillary pressure gradient can be generated by the radius difference between the upper and lower ends of the pore.

[0025] As a preferred embodiment of the present invention, the pore size on the side close to the catalyst layer is 300±5 μm, and the pore size on the side close to the flow field is 200±5 μm.

[0026] As a preferred embodiment of the present invention, the contact angle θ of the pore surface satisfies 60°<θ<90° by performing gas affinity treatment on the pore surface.

[0027] As a preferred embodiment of the present invention, Figure 4 As shown, the titanium matrix is ​​a whole formed by stacking multiple layers of titanium sheets; the inverted truncated cone-shaped pores are formed by coaxially opening circular holes of different diameters on each titanium sheet, and stacking the titanium sheets with circular holes of different diameters from top to bottom in descending order according to the diameter of the circular holes. In actual use, each titanium sheet can be set to the same thickness, preferably 25μm, and a total of 10 layers of titanium sheets are set, that is, the thickness of the titanium matrix is ​​250μm. However, it should be noted that the number of layers of titanium sheets and the thickness of each layer of titanium sheets can be adjusted according to actual conditions. The more layers and the smaller the thickness, the closer the pores can be to the inverted truncated cone type.

[0028] The following is a detailed description of a design method for a porous transport layer structure of a proton exchange membrane electrolyzer based on capillary pressure gradient provided by the present invention and the corresponding effects.

[0029] S1. Design different types of pores: According to the working conditions of the proton exchange membrane electrolyzer, three different pore shapes were designed to verify and analyze the advantages of the capillary pressure-driven porous transport layer in gas transport. The three types of pores are straight pores, truncated cone pores and inverted truncated cone pores. Assuming that the diameter of the bubbles released by the catalytic layer exceeds 200-300μm, the upper and lower diameters of the designed straight pores are 300μm, and the long bottom diameters of the truncated cone pores and inverted truncated cone pores are 300μm and 200μm respectively.

[0030] S2. Numerical simulation based on lattice Boltzmann model. The three-dimensional single relaxation time pseudopotential D3Q19 lattice Boltzmann model and Guo's forcing scheme are used to simulate the bubble transport in the porous transport layer of the proton exchange membrane electrolyzer unit. The model runs in parallel on NVIDIA GeForce RTX 3090GPUs with a computationally unified device architecture; the model parameters are verified using surface tension tests and contact angle tests. It is crucial to determine the appropriate parameters to evaluate the surface tension because the present invention requires the study of how the surface tension affects the behavior of bubbles in the porous transport layer. The model is verified by calculating the pressure difference inside and outside the bubble at equilibrium using the Young-Laplace equation. A 50×50×50 cubic bubble is initialized in a computational domain with a grid number of 100×100×100, and periodic boundary conditions are applied. The surface tension enables it to gradually condense into a sphere until a steady state is reached, and the pressure difference is calculated. The model is evaluated under various surface tensions by changing the value of the parameter G (G represents the strength of the interaction force between different phases). In addition, the static contact angle of the bubble on the solid surface was simulated. The initial conditions are the same as above, except that the mid-rebound boundary conditions are used for the gas-solid and liquid-solid surface tensions on half of the cross-section of the calculation area. The results of this model show a certain linear trend compared with the analytical solution, which is accurate in simulating the movement and surface tension of bubbles. The flow process of gas-liquid two-phases in the porous transport layer is simulated by combining the lattice Boltzmann equation, the Naiver-Stokes equation, the force between the gas-liquid two-phases and the interaction force between the fluid-solid two-phases. In this model, under the same initial conditions, the bubble flow in different pore shapes is compared to verify and analyze the advantages of CPD-PTL in gas transport. The results show that the gas movement is affected by the different shapes of the pores. The speed of the inverted truncated cone pore is greater than that of the straight pore, while the speed of the truncated cone pore is lower than that of the straight pore, which is consistent with the theoretical calculation. The radius difference at both ends of the pore will directly affect the pressure applied to the fluid. In addition, the hydrophilicity of the pore surface is the main determinant of pore performance. Under the same boundary conditions, the transport efficiency of the inverted truncated cone pore with an aerophilic surface is 28.4% higher than that of the aerophobic surface. Therefore, the study believes that the inverted truncated cone pore with an aerophilic surface is the most effective capillary pressure-driven porous transport layer design.

[0031] S3. Produce a capillary pressure-driven porous transport layer by stacking titanium sheets of different diameters. This method is cost-effective and ensures a high diameter-to-height ratio, but it does not significantly reduce the thickness of the PTL (porous transport layer). This embodiment takes a 25 μm thick titanium plate as an example. Holes with diameters of 200 to 300 μm are drilled successively on a 25 μm thick titanium plate, and then the titanium plates are layered to form an inverted truncated cone pore structure. Due to the low cost of machining pores, this method greatly reduces the overall production cost of the capillary pressure-driven porous transport layer. However, this design still has certain limitations. Insufficient stacking of layers will result in a large difference in diameter between layers, thereby reducing the bubble transmission efficiency.

[0032] S4, based on Nafion N117 membrane, Ir as anode catalyst (1mg / cm 2 ), Pt as cathode catalyst (0.5 mg / cm 2 ), the active area is 1cm 2 The membrane electrode (MEA) was used to construct a comprehensive test system for proton exchange membrane water electrolysis. This experiment included three groups, and the porous transport layers used were commercial titanium fiber felt. Self-made straight-pore titanium porous transport layer and CPD-PTL. The thickness of these porous transport layers is 250 μm, while the porosity of commercial titanium fiber felt is 55%. The porosity of straight-pore titanium porous transport layer and CPD-PTL is determined by the number of holes drilled. The experiments were conducted at 1 cm 2 400, 625 and 900 pores were processed in area, with porosities of 20%, 31% and 45%, respectively. Transparent acrylic end plates and hollow serpentine flow field plates were used to observe the internal bubble flow. Linear sweep voltammetry was used to generate the polarization curve of the electrolytic cell. Deionized water was heated to 60°C at normal pressure and then passed into the electrolytic cell at flow rates of 50, 75, and 100 mL / min. At the same time, the voltage was scanned from 1 V to 2 V. At 400 and 1000 mA / cm 2 The electrochemical impedance spectroscopy was measured at 10 frequency points in each order of magnitude in the frequency range from 10kHz to 100MHz. At the same time, a high-speed camera was used to capture the bubble flow inside the flow field. Experiments using commercial platinum and iridium catalysts showed that a current of 1.92A / cm2 could be achieved at 2V. 2 In addition, it can be inferred from the observed bubbles and polarization curves that the inverted truncated cone pore structure design of the present invention enhances bubble separation and reduces bubble coverage, thereby improving the performance and efficiency of the electrolyzer.

[0033] The method for constructing the lattice Boltzmann model in the present invention is described in detail below.

[0034] The present invention uses the three-dimensional single relaxation time pseudopotential D3Q19 lattice Boltzmann model and Guo's forcing scheme to simulate bubble transport in the porous transport layer of a proton exchange membrane electrolyzer unit. The model implements a self-written Python model that runs in parallel on NVIDIA GeForce RTX 3090GPUs with a computationally unified device architecture. The flow process of the gas-liquid two-phase in the porous transport layer is simulated by combining the lattice Boltzmann equation, the Naiver-Stokes equation, the gas-liquid two-phase force and the fluid-solid two-phase interaction force. The following is an in-depth description of the equations, boundary conditions, initial conditions, parameter verification, and unit conversion used in the present invention.

[0035] The lattice Boltzmann equation can be expressed as:

[0036] f k (x+c k Δt,t+Δt)=f k (x,t)+Ω k (x,t)+S k (x,t) (1)

[0037] This shows that in the next step t+Δt, the particle distribution f k (x,t) is subject to collision operator Ω k and the source term S k The influence of the k Move to the point x+c k Δt. The variable k represents the direction of the particle velocity. The mass density ρ and momentum density ρv can be calculated using the moment f k The weighted sum is achieved:

[0038]

[0039]

[0040] The Bhatnagar-Gross-Krook (BGK) operator is used as the collision operator in the Navier-Stokes simulation:

[0041]

[0042] Balanced distribution of particles Given by:

[0043]

[0044] Where: w k is the weighting coefficient, represents the speed of sound. The weight factor and discrete velocity of this model are given by

[0045]

[0046] In order to study the motion of two-phase flow, external forces are introduced into the model. k The forcing term F k Instead:

[0047]

[0048] Guo's coercive plan is:

[0049]

[0050] In the water electrolysis system, there is a multi-component fluid composed of water and gas, which is simulated using the Shan-Chen pseudopotential method. The interaction force between the components is calculated as follows:

[0051]

[0052] in is the fluid component σ and The interaction coefficient, ψ(σ) and represents the components σ and It is worth mentioning that this model uses an individual f k (σ) To describe the distribution of each component, the individual follows equations (1) to (9). In the Shan-Chen pseudopotential model, the velocity in the equilibrium distribution is replaced by the barycentric coordinate velocity:

[0053]

[0054] The pseudopotential is defined as:

[0055] ψ(ρ)=ρ0[1-exp(-ρ / ρ0)] (12)

[0056] Where: ρ0 is the reference density of the unit in the grid cell. The pressure can be determined by the equation of state:

[0057]

[0058] The model simulates not only the interaction between the gas and liquid phases, but also the interaction between the fluid and the solid phase:

[0059]

[0060] Where: G σsis the interaction strength between the fluid component and the solid boundary, and s(x) is an indicator function that takes the values ​​0 and 1 for the fluid and solid lattice, respectively. In summary, Equation (3) generally operates in two steps, with collision being the first step:

[0061]

[0062] The second step is diversion:

[0063] f k (x+c k Δt,t+Δt)=f k * (x,t) (16)

[0064] The specific method of setting the boundary conditions and initial values ​​of the lattice Boltzmann model is described in detail below.

[0065] In this model, three different pore shapes are designed to verify and analyze the advantages of CPD-PTL in gas transport. The three types of pores are straight pores, truncated cone pores, and inverted truncated cone pores. Assuming that the diameter of the bubbles released from the catalyst layer exceeds 200–300 μm, the upper and lower diameters of the straight pores are 300 μm, while the long bottom diameters of the truncated cone and inverted truncated cone are 300 μm and 200 μm respectively. They are subject to the same boundary conditions, such as Figure 2 (a). The following equations will give a comprehensive explanation for each boundary condition.

[0066] At the water inlet, a velocity boundary condition is applied so that water enters the pore at a specific velocity u:

[0067]

[0068] Where: Representation and initial direction The opposite direction of velocity, x b Represents the grid points at the boundary.

[0069] At the interface between the solid phase and the fluid phase, a no-slip velocity boundary condition is applied:

[0070]

[0071] At the fluid outlet, a pressure boundary condition is applied as follows:

[0072]

[0073] Where: u w for:

[0074]

[0075] In order to simulate the bubble dynamics in the pores, the gas phase with a density of 1 is set in the cross section with a height of 100 μm at the bottom of the pore when the model is initialized, as shown in Figure 2 As shown in (a), a liquid phase with density 1 is set in the rest of the pore. The initial velocities of both phases are zero.

[0076] It is crucial to determine the appropriate parameters to evaluate the surface tension, because the present invention requires studying how the surface tension affects the behavior of bubbles in the porous transport layer. Surface tension test and contact angle test are used to verify the model parameters, and the model is verified by calculating the pressure difference inside and outside the bubble under equilibrium state using the Young-Laplace equation:

[0077]

[0078] Where: The radius R is defined as the radius at which the density distribution reaches (ρ g +ρ l ) / 2 radial position, gas pressure p g The liquid pressure p is obtained by averaging the pressure on the 4×4 point grid at the center of the bubble. l is the pressure away from the center. Both pressures can be calculated by equation (13).

[0079] To verify the surface tension of the above model, a 50×50×50 cubic bubble was initialized in a computational domain with a grid size of 100×100×100, and periodic boundary conditions were applied. The surface tension enables it to gradually condense into a sphere. The pressure difference is calculated until a steady state is reached. In the present invention, the model is evaluated under various surface tensions by changing the value of the parameter G. The research results are shown in Figure 2. Figure 2 (b) shows that the surface tension gradually increases with the increase of G value. The results of this model show a certain linear trend compared with the analytical solution, which is accurate in simulating the movement of bubbles and surface tension.

[0080] In addition, the static contact angle of the bubble on the solid surface is simulated. The initial conditions are the same as above, except that the gas-solid and liquid-solid surface tensions use mid-bounce boundary conditions on half of the calculation area. The magnitude of the surface tension is adjusted by changing the parameters. Once the bubble reaches a stable state, the following formula can be used to calculate the contact angle θ of the bubble:

[0081]

[0082] Where: the diameter of the bubble and the solid interface is represented by a, and the height of the bubble from the solid interface is represented by b. In this paper, the gas-solid interface parameter G value is equal to the negative sum of the liquid-solid interface parameter G value. The relationship between the behavior of the gas at different contact angles and the G value can be understood as a linear relationship, such as Figure 2(c) as shown.

[0083] The present invention neglects the density and viscosity ratio between gas and water due to the main effect of capillary forces in the microscopic pores, which outweighs the effects of other viscosity, inertia and gravity. Therefore, the density below the lattice unit is l and relaxation time τ l are all uniform. Time scale C t The derivation of can be done through the length scale C l The value of is:

[0084] C t =C l 2 (τ-0.5)c s 2 / v p (twenty three)

[0085] Pressure scale C p It can be expressed by the dimensionless Euler number (Eu = p / ρu 2 ) and Weber number (We=ρu 2 l / σ) to obtain:

[0086] C p =σ p / (C l σ l ) (twenty four)

[0087] In the present invention, the length scale C l 2 microns, based on the Laplace test lattice unit σ l The surface tension is 0.075 and the pressure scale is C p and time scale C t Calculated as 4.8×10 5 Pa and 7.44×10 -6 s.

[0088] like Figure 3 As shown in Figure 2, the present invention studies the efficiency of three different pore shapes, namely straight pores, truncated cone pores and inverted truncated cone pores, in gas transport. The gas flows vertically along the z-axis, and its movement is affected by the change in pore shape. The results show that the inverted truncated cone pore shows a greater velocity than the straight pore, while the truncated cone pore shows a lower velocity than the straight pore, which is consistent with Eq (25): the radius difference at both ends of the pore directly affects the pressure on the fluid.

[0089] The present invention proposes a novel porous transport layer structure that uses capillary pressure to drive bubbles. The design utilizes a unique pore structure to create a surface tension pressure difference at both ends of the bubble, thereby improving the transport of the bubble. The present invention selects the pore structure that produces the best results (i.e., inverted frustum-shaped pores) to drive the bubble. In addition, the present invention also verifies the effectiveness of the design through experimental methods. Experiments using commercial platinum and iridium catalysts show that 1.92A / cm can be achieved at a voltage of 2V. 2 of current density. From the observed bubbles and polarization curves, it can be inferred that the design enhances bubble separation and reduces bubble coverage, thereby improving the performance and efficiency of the electrolyzer. Finally, the present invention evaluated the CPD-PTL under different operating environments. The results show that CPD-PTL improves gas transmission performance at both high and low current densities, and the high-porosity, high-flow CPD-PTL shows superior performance during operation. In short, compared with commercial porous transport layers, this design is efficient, convenient, and has a wide range of applications.

[0090] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A porous transport layer structure of a proton exchange membrane electrolyzer based on capillary pressure gradient, characterized in that: It includes a plurality of inverted truncated cone-shaped pores opened on a titanium substrate; the longitudinal section of the pore is a trapezoid, with its long bottom side close to the catalytic layer and its short bottom side close to the flow field; the pore surface is treated with gas affinity, and a capillary pressure gradient can be generated through the radius difference between the upper and lower ends of the pore.

2. The porous transport layer structure of a proton exchange membrane electrolyzer based on capillary pressure gradient according to claim 1, characterized in that: The pore diameter on the catalyst layer side is 300±5 μm, and the pore diameter on the flow field side is 200±5 μm.

3. The porous transport layer structure of a proton exchange membrane electrolyzer based on capillary pressure gradient according to claim 1, characterized in that: The contact angle θ of the pore surface satisfies 60°<θ<90°.

4. The porous transport layer structure of a proton exchange membrane electrolyzer based on capillary pressure gradient according to claim 1, characterized in that: The titanium matrix is ​​formed by stacking a plurality of titanium sheets, and the inverted truncated cone-shaped pores are formed by coaxially opening circular holes of different diameters on each titanium sheet.

5. The porous transport layer structure of a proton exchange membrane electrolyzer based on capillary pressure gradient according to claim 4, characterized in that: The thickness of each titanium sheet is the same, which is 25 μm.

6. The porous transport layer structure of a proton exchange membrane electrolyzer based on capillary pressure gradient according to claim 4, characterized in that: The titanium sheet has 10 layers in total.

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