Method for randomly generating physical structure of catalyst layer of proton exchange membrane fuel cell

Abstract

The invention provides a random generation method for a physical structure of a catalytic layer of a proton exchange membrane fuel cell, which comprises the following steps: firstly, calculating control parameters, and secondly, generating a carbon carrier phase, specifically, S21, generating a new carbon sphere; s22, judging whether the new carbon sphere is a growth nucleus, if not, executing S23, if so, further judging whether the new carbon sphere is overlapped with other carbon spheres, if so, returning to S21, and if not, executing S25; s23, judging whether the new carbon ball coincides with other carbon balls or not, if yes, executing S24, and if not, returning to S21; s24, judging whether the contact ratio of the new carbon ball and other carbon balls is not greater than a predefined allowable maximum contact ratio value among the carbon balls, if so, executing S25, and if not, returning to S21; s25, confirming the generation of the new carbon spheres, and converting all lattice points in the area occupied by the new carbon spheres into carbon carrier phase lattice points; s26, checking whether the volume fraction of the carbon carrier phase at the moment meets the requirement or not, and if not, repeating S21 to S25; and finally generating a platinum particle phase and an electrolyte phase.

Description

Technical Field

[0001] The invention belongs to the field of high-temperature proton exchange membrane fuel cell simulation, and specifically relates to a method for randomly generating the real physical structure of a catalyst layer of a proton exchange membrane fuel cell. Background Art

[0002] The use of numerical simulation methods for the performance prediction of proton exchange membrane fuel cells (PEMFCs) can greatly save time and cost. Mature macroscopic numerical models can simulate the heat and mass transfer processes and electrochemical kinetic phenomena in the battery as a whole, but they are helpless in dealing with the influence of microporous structures (such as the ratio and specific distribution of electrolytes, platinum powder and carbon particles in the catalyst layer, the distribution and connectivity of voids in the microporous layer and diffusion layer, etc.).

[0003] Macroscopic numerical models usually use some empirical formulas or parameters to characterize the relationship between the structural parameters and flow parameters of porous media, such as the gas-liquid phase transition law of water and the relationship between capillary pressure and liquid water volume fraction. On the one hand, there are limitations in the determination of these empirical formulas or reference data. For example, they cannot accurately reflect the influence of the microstructure of porous media. On the other hand, they are restricted by experimental environment / experimental methods and material factors. The acquisition of these empirical formulas or reference data is usually costly and time-consuming, and the accuracy and applicability of the empirical formulas or parameter values ​​are not satisfactory.

[0004] The temperature, pressure, concentration and potential gradients inside porous media will cause related natural convection and diffusion processes and the complex coupling effects between them. In addition, the microscale effect and slip effect at the void scale make the heat and mass transfer characteristics in the micropores very different from those at the macroscale. Therefore, traditional macroscopic numerical models are difficult to reflect the real transmission and electrochemical mechanisms inside the battery.

[0005] Only by simulating based on the real porous media microstructure can we obtain accurate heat and mass transfer mechanisms. Due to the differences in scales between different components within the catalyst layer, it is very important to use appropriate modeling methods to establish partial models. Summary of the invention

[0006] The purpose of the present invention is to provide a method for randomly generating the physical structure of a catalyst layer of a proton exchange membrane fuel cell, which simulates the microstructure of a porous medium, thereby improving the accuracy and applicability of a numerical model of the catalyst layer.

[0007] In order to achieve the above objectives, the present invention provides a random generation algorithm for the physical structure of a catalyst layer of a proton exchange membrane fuel cell, characterized in that it comprises the following steps:

[0008] S1, control parameter calculation, specifically including: calculating the volume fractions (ε C , ε Pt , ε ion ) and platinum loading γ Pt , as a control parameter in the subsequent reconstruction process;

[0009] S2, generating a carbon support phase, specifically comprising:

[0010] S21, a new carbon ball is generated;

[0011] S22, determine whether the new carbon ball is a growth nucleus, if not, execute S23, if yes, further determine whether the new carbon ball overlaps with other carbon balls, if yes, return to S21, if no, execute S25;

[0012] S23, determine whether the new carbon ball overlaps with other carbon balls, if so, execute S24, if not, return to S21;

[0013] S24, determining whether the overlap between the new carbon ball and other carbon balls is not greater than the maximum overlap allowed between carbon balls defined in advance, if so, executing S25, if not, returning to S21;

[0014] S25, confirming the generation of the new carbon sphere, and converting all lattice points in the region occupied by the new carbon sphere into carbon support phase lattice points;

[0015] S26, checking whether the volume fraction of the carbon support phase meets the requirement, if so, the generation of the carbon support phase is terminated, if not, repeating S21 to S25;

[0016] S3, the QSGS method was used to generate the platinum particle phase and the electrolyte phase.

[0017] Optionally, the preset statistical parameters include the catalytic layer porosity ε, thickness δ, platinum carbon mass ratio and electrolyte contentθ ion .

[0018] Optionally, the control parameters are calculated according to the following control equations:

[0019]

[0020] γ Pt =ε Pt ρ Pt δ

[0021] In the formula, ρ C represents the carbon carrier density, ρ Pt represents the density of platinum particles, ρ ion represents the electrolyte density.

[0022] Optionally, step S21 generates a new carbon ball, specifically comprising:

[0023] A carbon sphere carrier with a diameter varying in a specified interval is generated at a random position within the specified area as the i-th carbon sphere.

[0024] Optionally, step S22 determines whether the carbon ball is a growth nucleus, specifically including:

[0025] Generate a random number in the interval [0, 1], assume that the initial distribution probability of the carbon carrier phase growth nucleus is P, and determine whether the generated random number is less than P. If so, determine that the new carbon ball generated in step S21 is a new growth nucleus.

[0026] Optionally, in step S24, the degree of overlap between the new carbon ball and other carbon balls is obtained by calculating the volume percentage occupied by other carbon balls in the area occupied by the new carbon ball.

[0027] Optionally, when the QSGS method is used to generate platinum powder in step S3, the growth position of the platinum powder particles is restricted to the lattice points adjacent to the carbon carrier.

[0028] Optionally, when the electrolyte phase is generated by the QSGS method in step S3, the growth position of the electrolyte is restricted to the lattice points adjacent to the carbon support and the platinum particles.

[0029] Compared with the prior art, the present invention has the following advantages: the present invention adopts a four-variable random variable generation algorithm to establish the microstructure of the porous medium of the fuel cell catalyst layer, and can superimpose porous media of multiple different components on the basis of a single-component porous medium, so that the generated catalyst layer components are more realistic, and the porous medium structure is also closer to the actual morphology of the fuel cell catalyst layer, thereby improving the accuracy and reliability of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for the description. Obviously, the drawings described below are an embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work:

[0031] Figure 1 A flowchart of the random generation method provided by the present invention;

[0032] Figure 2 A three-dimensional view of a three-dimensional proton exchange membrane fuel cell catalyst layer generated by the method of the present invention;

[0033] Figure 3 A two-dimensional slice of a three-dimensional proton exchange membrane fuel cell catalyst layer generated by the method of the present invention. DETAILED DESCRIPTION

[0034] The scheme proposed by the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer according to the following description. It should be noted that the accompanying drawings are in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0035] The catalytic layer has a multi-scale structure, which is very difficult to reconstruct. In terms of material composition, the catalytic layer includes three different phases: a porous phase (or gas phase), a mixed electronic phase (carbon carriers and platinum particles), and an electrolyte phase. In terms of the size of the catalytic layer and its constituent materials, the thickness of the catalytic layer is about 5 to 10 microns, the diameter of a single platinum powder particle is 2 to 5 microns, the diameter of the carbon carrier is 10 to 100 microns, and the diameter of the gaps between them and the electrolyte is about 100nm. Taking into account the limitations of computing power, the grid scale and spatial resolution of the catalytic layer calculation domain used in flow simulation cannot be too high. Therefore, the present invention often partially simplifies the specific microstructural features when reconstructing the catalytic layer.

[0036] like Figure 1 As shown, the method for randomly generating the physical structure of the catalyst layer of a proton exchange membrane fuel cell provided by the present invention comprises the following steps:

[0037] S1, control parameter calculation, specifically including: calculating the volume fractions (ε C , ε Pt , ε ion ) and platinum loading γ Pt , as a control parameter in the subsequent reconstruction process.

[0038] The preset statistical parameters include rate ε, thickness δ, platinum-carbon mass ratio and electrolyte contentθ ion (electrolyte and electrode mass ratio), the relationship between them and the control parameters satisfies certain control equations, as follows:

[0039]

[0040] γ Pt =ε Pt ρ Pt δ

[0041] In the formula, ρ C represents the carbon carrier density, ρ Pt represents the density of platinum particles, ρ ion represents the electrolyte density.

[0042] S2, generating a carbon support phase, specifically comprising:

[0043] S21, generating a new carbon sphere; specifically, generating a carbon sphere carrier with a diameter varying in a specified interval at a random position within a specified area as the i-th carbon sphere.

[0044] S22, determine whether the new carbon ball is a growth nucleus, generate a random number in the interval [0, 1], assume that the initial distribution probability of the growth nucleus of the carbon carrier phase is P, determine whether the generated random number is less than P, if so, determine that the new carbon ball generated in step S21 is a new growth nucleus. If it is not a growth nucleus, execute S23. If it is a growth nucleus, the position of the new carbon ball needs to be calibrated at this time. If the new carbon ball has any overlap with the previous i-1 carbon balls, it is necessary to return to S21 and grow again until the generated new carbon ball has no intersection with other carbon balls. If the new carbon ball has no overlap with the previous i-1 carbon balls, execute S25. This process is performed to ensure that the final generated carbon balls are distributed more evenly, rather than clumping together.

[0045] S23, determine whether the new carbon ball overlaps with other carbon balls, if so, execute S24, if not, return to S21;

[0046] S24, determining whether the overlap between the new carbon ball and other carbon balls is not greater than the maximum overlap allowed between carbon balls defined in advance, if so, executing S25, if not, returning to S21;

[0047] S25, confirming the generation of the new carbon sphere, and converting all lattice points in the region occupied by the new carbon sphere into carbon support phase lattice points;

[0048] S26, check whether the volume fraction of the carbon support phase meets the requirement (i.e., whether it satisfies the control parameter ε calculated in step S1) C ), if yes, the generation of the carbon support phase is terminated, if no, S21 to S25 are repeated;

[0049] S3, using the QSGS method to generate platinum particle phase and electrolyte phase (need to meet the control parameter ε calculated in step S1) Pt , ε ion , γ Pt ).

[0050] The growth process of platinum powder particles is basically the same as the steps described in the QSGS method, except that the growth position is limited to the lattice points adjacent to the carbon carrier (to ensure effective contact between the platinum powder and the carbon carrier). The program can impose limiting conditions to ensure that each platinum particle is in contact with at least one carbon carrier lattice point.

[0051] Based on the QSGS method, a non-uniform distribution of electrolyte on the Pt / C surface can be achieved. The growth restriction conditions are similar to those of platinum powder, which limits the growth position of the electrolyte to the lattice points adjacent to the carbon support and platinum particles.

[0052] The QSGS method (four-parameter random growth method) is a method for generating random pore structures of porous media materials. By randomly generating pore structures, the real microstructure of porous media can be simulated to provide more accurate data for engineering analysis. Since the QSGS method is an existing conventional method, the specific process of generating platinum particle phase and electrolyte phase using the QSGS method will not be described in detail.

[0053] Figure 2 and Figure 3 The three-dimensional microscopic model and two-dimensional slice of the fuel cell catalyst layer generated based on the method of the present invention show that the porous medium structure generated by the method of the present invention is relatively close to the actual microscopic morphology of the fuel cell catalyst layer.

[0054] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for randomly generating the physical structure of a catalyst layer of a proton exchange membrane fuel cell, characterized in that: The following steps are involved: S1, control parameter calculation, specifically including: calculating the volume fractions (ε C , ε Pt , ε ion ) and platinum loading γ Pt , as a control parameter in the subsequent reconstruction process; S2, generating a carbon support phase, specifically comprising: S21, a new carbon ball is generated; S22, determine whether the new carbon ball is a growth nucleus, if not, execute S23, if yes, further determine whether the new carbon ball overlaps with other carbon balls, if yes, return to S21, if no, execute S25; S23, determine whether the new carbon ball overlaps with other carbon balls, if so, execute S24, if not, return to S21; S24, determining whether the overlap between the new carbon ball and other carbon balls is not greater than the maximum overlap allowed between carbon balls defined in advance, if so, executing S25, if not, returning to S21; S25, confirming the generation of the new carbon sphere, and converting all lattice points in the region occupied by the new carbon sphere into carbon support phase lattice points; S26, checking whether the volume fraction of the carbon support phase meets the requirement, if so, the generation of the carbon support phase is terminated, if not, repeating S21 to S25; S3, the QSGS method was used to generate the platinum particle phase and the electrolyte phase.

2. The method for randomly generating the physical structure of the catalyst layer of a proton exchange membrane fuel cell according to claim 1, characterized in that: The preset statistical parameters include the catalytic layer porosity ε, thickness δ, platinum carbon mass ratio and electrolyte contentθ ion .

3. The method for randomly generating the physical structure of the catalyst layer of a proton exchange membrane fuel cell according to claim 2, characterized in that: The control parameters are calculated according to the following control equations: c Pt =e Pt r Pt d In the formula, ρ C represents the carbon carrier density, ρ Pt represents the density of platinum particles, ρ ion represents the electrolyte density.

4. The method for randomly generating the physical structure of the catalyst layer of a proton exchange membrane fuel cell according to claim 1, characterized in that: Step S21 generates a new carbon ball, which specifically includes: A carbon sphere carrier with a diameter varying in a specified interval is generated at a random position within the specified area as the i-th carbon sphere.

5. The method for randomly generating the physical structure of the catalyst layer of a proton exchange membrane fuel cell according to claim 1, characterized in that: Step S22 determines whether the carbon ball is a growth nucleus, specifically including: Generate a random number in the interval [0, 1], assume that the initial distribution probability of the carbon carrier phase growth nucleus is P, and determine whether the generated random number is less than P. If so, determine that the new carbon ball generated in step S21 is a new growth nucleus.

6. The method for randomly generating the physical structure of the catalyst layer of a proton exchange membrane fuel cell according to claim 1, characterized in that: In step S24, the overlap between the new carbon ball and other carbon balls is obtained by calculating the volume percentage of other carbon balls in the area occupied by the new carbon ball.

7. The method for randomly generating the physical structure of the catalyst layer of a proton exchange membrane fuel cell according to claim 1, characterized in that: When the QSGS method is used to generate platinum powder in step S3, the growth position of the platinum powder particles is restricted to the lattice points adjacent to the carbon carrier.

8. The method for randomly generating the physical structure of the catalyst layer of a proton exchange membrane fuel cell according to claim 1, characterized in that: When the electrolyte phase is generated by the QSGS method in step S3, the growth position of the electrolyte is restricted to the lattice points adjacent to the carbon support and the platinum support.

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