A method for modeling and molecular simulation of nanoparticle composite proton exchange membranes
By constructing a nanoparticle composite proton exchange membrane model and combining it with molecular dynamics simulations, the problem of the inability to deeply understand the swelling phenomenon in existing technologies has been solved, enabling the reproduction of the swelling process and analysis of the proton conduction mechanism at the molecular scale.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2024-03-07
- Publication Date
- 2026-05-19
AI Technical Summary
Existing experimental simulations cannot deeply explore the swelling phenomenon and performance improvement mechanism of nanoparticle composite proton exchange membranes, and there is a lack of suitable molecular simulation models and strategies.
A model of a nanoparticle composite proton exchange membrane was constructed, and the diffusion process of solvent in the composite membrane was simulated using molecular dynamics. The degree of swelling was determined by the vacuum layer density difference, and the swelling process was accelerated by combining molecular dynamics. The solvent distribution and dynamic characteristics of each phase region were analyzed.
The swelling phenomenon observed in the experiment was reproduced, the solvent adsorption mechanism of the nanoparticle composite membrane was explained, and a theoretical basis was provided for understanding the proton conduction mechanism and screening high-performance composite membranes.
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Figure CN118098387B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of molecular simulation and water electrolysis for hydrogen production, specifically to a method for modeling and molecular simulation of a nanoparticle composite proton exchange membrane. Background Technology
[0002] With the goal of achieving carbon peak and carbon neutrality, clean hydrogen energy production and application technologies are beginning to take center stage in energy-efficient and low-carbon applications. Proton exchange membrane (PEM) water electrolysis and PEM fuel cell technologies are hailed as the most promising clean energy technologies, capable of addressing energy supply and demand imbalances and environmental pollution. The PEM is an indispensable component, responsible for conducting protons, isolating electrons, and separating gases. Currently, commercially available Nafion fluorosulfonic acid polymer membranes, with their high proton conductivity, chemical stability, and excellent durability, are frequently used as PEMs. However, their high cost, rapid performance degradation at low humidity, and fluorine pollution problems hinder their practical application. Therefore, in recent years, researchers have increasingly developed non-fluorosulfonic acid polymer membranes (including sulfonated polyethersulfone, sulfonated polysulfone, sulfonated polyetherketone, sulfonated polyimide, etc.) as alternatives to perfluorosulfonic acid polymer membranes.
[0003] To expand applications and improve performance, various experimental methods and strategies have been employed to enhance the overall performance of PEM (polyethylene terephthalate). Among these, doping PEM polymer substrates with inorganic water-absorbing fillers has attracted attention due to its ability to significantly improve the water retention and proton conductivity of polymer membranes. In particular, the addition of nanoparticles (NPs), which effectively restrict gas diffusion and promote proton migration, is particularly noteworthy. These NPs are typically porous materials with particle diameters on the nanometer scale, possessing high specific surface area, highly tunable pore structure, and diverse functional group modifications. In recent years, researchers have doped PEM polymers to prepare corresponding composite membranes, finding that the addition of NPs enhances their swelling and proton conductivity. Many possible explanations and hypotheses have been proposed regarding this swelling phenomenon and performance improvement, but a consensus has not yet been reached. A deeper understanding of the underlying causes of this swelling phenomenon and performance improvement is a prerequisite for designing and fabricating high-performance NP@PEM composite membranes.
[0004] In summary, the existing research techniques have the following problems: current experimental simulations cannot explore the swelling phenomenon and performance improvement mechanism of NP@PEM composite films at the microscopic level through current testing techniques, and there is no suitable model in molecular simulation to describe the composite film composed of NP microstructure and PEM polymer structure. It is also urgent to design a suitable molecular simulation strategy to realize the swelling process of NP@PEM composite films in solvents. Summary of the Invention
[0005] The purpose of this invention is to provide a modeling and molecular simulation method for nanoparticle composite proton exchange membranes. By using this modeling and swelling method to construct and simulate NP@PEM composite membranes, the swelling phenomenon of experimentally prepared composite membranes can be reproduced, and the microscopic mechanism of composite membrane swelling can be established for analysis.
[0006] To achieve the above objectives, the technical solution of the present invention is as follows:
[0007] The purpose of this invention is to provide a modeling and molecular simulation method for nanoparticle composite proton exchange membranes, which includes the following steps:
[0008] Based on the chemical composition and structure of nanoparticles, an NP microstructure model was constructed; based on the monomer structure and degree of polymerization of proton exchange membranes, a PEM polymer structure model was constructed.
[0009] Using the length and width of the cross-section of the NP microstructure model as the length and width of the simulation box, the PEM polymer structure model, the NP microstructure model, and the PEM polymer structure model are sequentially placed inside the simulation box along the height direction of the simulation box. The PEM polymer structure model, the NP microstructure model, and the PEM polymer structure model form a "sandwich" structure, and vacuum layers are provided on both sides of the simulation box. The length of the simulation box is greater than the length of the PEM polymer structure model and the NP microstructure model, forming an NP@PEM composite membrane structure.
[0010] Solvent is added into the vacuum layer until the solvent density reaches saturation, forming an NP@PEM solution structure model. Solvent molecules are diffused into the NP@PEM composite membrane structure using molecular dynamics methods to swell the NP@PEM solution structure model. The degree of swelling of the NP@PEM composite membrane model is obtained by measuring the change in solvent density in the vacuum layer. The swelling performance of NP@PEM is obtained by equilibrium simulation.
[0011] Furthermore, the degree of swelling of the NP@PEM composite membrane model is judged by comparing the error range between the solvent density difference in the vacuum layer and the set upper limit of the density difference (0-10%). If the calculated density difference is higher than the set upper limit, it indicates that solvent molecules in the vacuum layer are continuously entering the NP@PEM composite membrane, meaning the composite membrane is not fully swollen. In this case, sufficient solvent molecules are added to the vacuum layer, and the NP@PEM composite membrane structure is reconstructed and the swelling of the NP@PEM composite membrane is simulated again. The formula for calculating the solvent density difference in the vacuum layer is as follows:
[0012]
[0013] In the formula: DD is the density difference; ρ bulk，initial and ρ bulk，finalThese are the densities of the solvent in the vacuum layer before and after the annealing process, respectively, in g / cm³. 3 .
[0014] Furthermore, during the swelling process of the NP@PEM solution structure model, molecular dynamics methods were used to allow solvent molecules to freely diffuse into the NP@PEM composite membrane structure. Then, based on an annealing simulation process, the NP@PEM composite membrane structure underwent structural relaxation in the NVT ensemble. The timing for ending the cyclic annealing process was determined based on the degree of swelling in the NP@PEM composite model. Increasing the temperature further increased the molecular migration rate, accelerating molecular diffusion within the composite membrane and thus accelerating the swelling process. The ensemble equilibrium simulation under the NVT ensemble yielded the NP@PEM swollen structure, and the physical quantities in the system were statistically analyzed. These physical quantities included the number of molecules, mass density, and mean square displacement.
[0015] Furthermore, based on the density distribution of each component in the NP@PEM composite membrane structure in the vacuum layer, and according to the NP@PEM swelling structure being divided into different bulk phases, by statistically analyzing the physical quantities in each bulk phase, the distribution and dynamic characteristics of solvent molecules in each bulk phase within the NP@PEM swelling structure are calculated, thereby determining the swelling phenomenon and performance of the NP@PEM composite membrane. Each bulk phase includes the solvent phase, the PEM phase, and the NP phase.
[0016] Furthermore, the simulation box has vacuum layers on both sides, and the length of the vacuum layers is greater than the cutoff radius used to calculate molecular interactions in molecular simulations.
[0017] Furthermore, the specific method for constructing a PEM polymer structure model includes the following steps:
[0018] Based on the monomer structure and degree of polymerization of PEM, a single-chain structure of PEM is established. Then, molecular dynamics methods are used to compress two or more PEM single chains in the length and width directions until the size of the compressed structure in the length and width planes matches the truncated section of the microstructure of NP, thus constructing a PEM polymer structure model.
[0019] Furthermore, the specific method for constructing the NP microstructure model includes the following steps:
[0020] Based on the given chemical composition and structure of NP, the corresponding nanocrystal structure is constructed. The crystal structure of NP is truncated along the crystal plane that dominates crystal growth, and the normal direction of the truncated plane is parallel to the height direction of the simulation box. Then, the unsaturated atoms of the truncated plane are filled with corresponding atoms or groups to construct a microstructure model of NP.
[0021] Furthermore, the nanoparticles include, but are not limited to, one of MOFs, COFs, zeolites, porous carbon materials, metal particles, two-dimensional graphene, and two-dimensional boron carbide.
[0022] Furthermore, the proton exchange membrane may be of the following types, including but not limited to one of perfluorosulfonic acid polymers and non-fluorosulfonic acid polymers. The perfluorosulfonic acid polymers may include, but are not limited to, Nafion or DOW perfluorosulfonic acid polymers, and the non-fluorosulfonic acid polymers may include, but are not limited to, one of sulfonated polyethersulfone, sulfonated polysulfone, sulfonated polyether ketone, or sulfonated polyimide.
[0023] Furthermore, the solvent includes, but is not limited to, water, salt solution, or organic solvent.
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] This invention provides a modeling and molecular simulation method for nanoparticle composite proton exchange membranes (NP@PEM). By constructing an NP@PEM composite membrane model and combining it with a proposed swelling simulation strategy, the swelling physical process in the NP@PEM composite membrane structure can be maximized at the molecular scale, reproducing the swelling phenomenon obtained from experimental testing and explaining the mechanism of solvent adsorption and swelling of the NP@PEM composite membrane. The technical solution provided by this invention is beneficial for clarifying the adsorption and swelling mechanism of NP@PEM composite membranes in solvents, thereby laying a theoretical foundation and providing technical support for studying the proton transport mechanism of NP@PEM composite membranes and screening high-performance NP@PEM composite membranes. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of the modeling and molecular simulation process for the gas nanoparticle composite proton exchange membrane of the present invention.
[0027] Figure 2 The structure diagram of the UiO-66@Nafion composite membrane provided in Embodiment 1 of the present invention;
[0028] Figure 3 This is a diagram showing the density distribution and phase region division of each component in the UiO-66@Nafion composite membrane model provided in Embodiment 1 of the present invention;
[0029] Figure 4 This is a diagram showing the number of water molecules in each phase region of the Nafion and UiO-66@Nafion composite membrane provided in Embodiment 1 of the present invention.
[0030] Figure 5 The mean square displacement diagram of each phase region of the UiO-66@Nafion composite membrane provided in Embodiment 1 of the present invention. Detailed Implementation
[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.
[0033] This invention provides a method for modeling and molecular simulation of nanoparticle composite proton exchange membranes, the flowchart of which is shown below. Figure 1 As shown, the method includes the following steps:
[0034] Based on the chemical composition and structure of nanoparticles, an NP microstructure model is constructed; in this invention, the nanoparticles include, but are not limited to, one of MOFs, COFs, zeolites, porous carbon materials, metal particles, two-dimensional graphene, and two-dimensional boron carbide.
[0035] Based on the monomer structure and degree of polymerization of the proton exchange membrane, a PEM polymer structure model is constructed. In this invention, the proton exchange membrane includes, but is not limited to, one of perfluorosulfonic acid polymers and non-fluorosulfonic acid polymers. Perfluorosulfonic acid polymers include, but are not limited to, Nafion or DOW perfluorosulfonic acid polymers, and non-fluorosulfonic acid polymers include, but are not limited to, sulfonated polyethersulfone, sulfonated polysulfone, sulfonated polyether ketone, or sulfonated polyimide.
[0036] Using the length and width of the cross-section of the NP microstructure model as the length and width of the simulation box, and based on the initial simulation box size of the NP@PEM composite membrane, the PEM polymer structure model, the NP microstructure model, and the PEM polymer structure model are sequentially placed inside the simulation box along the height direction of the simulation box. The PEM polymer structure model, the NP microstructure model, and the PEM polymer structure model form a "sandwich" structure, and vacuum layers are provided on both sides of the simulation box. The length of the simulation box is greater than the length of the PEM polymer structure model and the NP microstructure model, thus forming the NP@PEM composite membrane structure.
[0037] A solvent is added to the vacuum layer until the solvent density reaches saturation, forming an NP@PEM solution structure model. Molecular dynamics methods are used to diffuse solvent molecules into the NP@PEM composite membrane structure, causing the NP@PEM solution structure model to swell. The degree of swelling of the NP@PEM composite membrane model is obtained by measuring the change in solvent density in the vacuum layer. Equilibrium simulations are then performed to obtain the swelling performance of the NP@PEM. In this invention, the solvent includes, but is not limited to, water, salt solutions, or organic solvents. Salt solutions include inorganic acids and inorganic salts; organic solvents include organic acids and alcohols. The purpose of the solvent is to allow free diffusion into the NP@PEM composite membrane structure; therefore, the type of solvent is not limited. The concentration of the salt solution is calculated based on the pH of the electrolyte, generally within the pH range of 0-7.
[0038] This invention, by constructing an NP@PEM composite membrane model and combining it with a proposed composite membrane swelling simulation, can maximize the reproduction of the NP@PEM composite membrane swelling process in a solvent at the molecular scale, reproduce the experimentally measured water absorption and swelling phenomenon of the NP@PEM composite membrane, and analyze the microscopic mechanism of water distribution during this process. The technical solution provided by this invention is beneficial for understanding the excellent water adsorption performance of the NP@PEM composite membrane during the swelling process from a microscopic perspective, thereby providing technical support for a deeper understanding of the proton conduction mechanism in composite proton exchange membranes.
[0039] The molecular dynamics (MD) simulation employed in this invention, based on Newton's laws of motion, simulates the microscopic processes of a system's evolution over time and statistically calculates the system's equilibrium parameters and transport properties. Molecular dynamics can simulate the conformation of microscopic particles to reveal the properties of macroscopic matter, thus bridging the gap between microscopic and macroscopic research. Using molecular simulation methods, an Np@PEM composite membrane model can be constructed, and the swelling process of the composite membrane in a solvent can be reproduced based on the actual particle interactions and motion states within the system, thereby statistically calculating the distribution and dynamic properties of solvent molecules.
[0040] In a specific embodiment, the error range between the solvent density difference in the vacuum layer and a set upper limit for the density difference is 0-10%. In this invention, the error range can be any value between 0-10%, such as 0, 1%, 2%, 3%, 5%, 8%, or 10%, but is not limited to the listed values. Other unlisted values within the above range are also applicable and will not be elaborated upon here. The degree of swelling of the NP@PEM composite film model is determined by comparing the error range. If the calculated density difference is higher than the set upper limit for the density difference, it indicates that solvent molecules in the vacuum layer are continuously entering the NP@PEM composite film, meaning the composite film swelling is incomplete. In this case, sufficient solvent molecules are added to the vacuum layer, and the NP@PEM composite film structure is reconstructed and the swelling of the NP@PEM composite film is simulated again. The formula for calculating the solvent density difference in the vacuum layer is as follows:
[0041]
[0042] In the formula: DD is the density difference; ρ bulk，initial and ρ bulk，final These are the densities of the solvent in the vacuum layer before and after the annealing process, respectively, in g / cm³. 3 .
[0043] In one specific embodiment, during the swelling process of the NP@PEM solution structure model, molecular dynamics (MD) is used to allow solvent molecules to freely diffuse into the NP@PEM composite membrane structure. Then, based on an annealing simulation process, the NP@PEM composite membrane structure undergoes structural relaxation in the NVT ensemble (molecular dynamics ensemble). The timing for ending the cyclic annealing process is determined based on the degree of swelling of the NP@PEM composite model. Increasing the temperature increases the molecular migration rate to accelerate molecular diffusion within the composite membrane, thereby accelerating the swelling process of the NP@PEM composite membrane. A system equilibrium simulation is performed under the NVT ensemble to obtain the NP@PEM swollen structure, and various physical quantities in the ensemble are statistically analyzed. These physical quantities include the number of molecules, mass density, and mean square displacement. In this invention, the above physical quantities are calculated by statistically analyzing the atomic distribution in the height direction and the atomic migration distance using trajectory files obtained from molecular dynamics.
[0044] The specific scheme for equilibrium simulation is to conduct MD simulation for a sufficient time (e.g., 10 ns) at a selected temperature (e.g., room temperature). During this stage, since the system reaches equilibrium and is stable, the statistical physical quantities are also stable and reliable. Therefore, the distribution and dynamic characteristics of solvent molecules in each bulk phase within the NP@PEM swelling structure can be obtained more accurately through the statistical physical quantities.
[0045] In one specific embodiment, based on the density distribution of each component in the vacuum layer, the NP@PEM swelling structure is divided into different bulk phases. The distribution and dynamic characteristics of solvent molecules in each bulk phase within the NP@PEM swelling structure are calculated, including the number of solvent molecules in each phase and the mean square displacement. The swelling phenomenon and performance of the NP@PEM composite membrane are determined. Each bulk phase includes a solvent phase, a PEM phase, and an NP phase. The mechanism for improving the water absorption performance of the composite membrane is analyzed. Specifically, based on the density distribution, different phase regions of the NP@PEM composite membrane structure model after swelling are divided, and the static distribution and dynamic characteristics of solvent molecules in each phase region are calculated to analyze the swelling phenomenon and performance of the NP@PEM composite membrane.
[0046] In one specific embodiment, vacuum layers are provided on both sides of the simulation box, and the length of the vacuum layers is greater than the cutoff radius used to calculate molecular interactions in the molecular simulation. The purpose is to avoid the influence of inter-molecular interactions between adjacent unit cells due to periodicity.
[0047] In a specific embodiment, the method for constructing a PEM polymer structure model includes the following steps:
[0048] Based on the monomer structure and degree of polymerization of PEM, a single-chain structure of PEM is established. Then, molecular dynamics methods are used to compress two or more PEM single chains in both length and width directions until the dimensions of the compressed structure in the length and width planes are adapted to the truncation plane of the NP microstructure, thus constructing a PEM polymer structure model. This method allows for the simple and rapid acquisition of polymers with consistent degrees of polymerization from monomer structures, and the polymers can be adapted to the truncation plane of the NP microstructure, facilitating subsequent composite of the NP and PEM models. In this invention, the process parameters for molecular simulation mainly include temperature, pressure, and cutoff radius. These parameters can be set as needed, with the temperature range being 20-90℃, the pressure range being 1-1000 bar, and the cutoff radius range being 0.5-2 nm. The compression process parameter is mainly pressure, ranging from 10-1000 bar.
[0049] In a specific embodiment, the method for constructing the NP microstructure model includes the following steps:
[0050] Based on the given chemical composition and structure of polymeric substances (NPs), a corresponding nanocrystal structure is constructed. The NP crystal structure is truncated along the crystal plane dominated by crystal growth, with the normal direction of the truncated plane parallel to the z-direction. The unsaturated atoms on the truncated plane are then filled with corresponding atoms or groups, ultimately forming a microstructure model of the NP. This allows for the truncation of unbounded crystal structures and the construction of corresponding surface models, enabling composite modeling with polymers.
[0051] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.
[0052] Example 1
[0053] A modeling and molecular simulation method for nanoparticle composite proton exchange membranes, the flowchart of which is shown below. Figure 1 As shown, the method includes the following steps:
[0054] S1. Constructing the NP microstructure model and the PEM polymer structure model
[0055] To construct a microstructure model of UiO-66, firstly, based on the unit cell structure of UiO-66, the surface formation of each crystal plane of UiO-66 was calculated using the Bravais-Friedel-Donnay-Harker (BFDH) method to obtain the crystal plane that dominates crystal growth. Then, the crystal structure of UiO-66 was truncated along this crystal plane, with the normal direction of the truncated plane parallel to the z-direction (the height direction of the simulated box). The truncated plane was a square of 2.07 nm × 2.07 nm, and the unsaturated metal clusters of the truncated plane were supplemented with methyl and carboxyl groups. The length in the z-direction was 3.74 nm, finally forming the NP microstructure model.
[0056] A Nafion polymer structural model was constructed. Based on the monomer structure of Nafion and the degree of polymerization of 10, a PEM single-chain structure was established. Then, the MD method was used to compress two Nafion single chains in the x and y directions with a pressure of 1000 bar until the size of the xy plane was reduced to a square of 2.07 nm × 2.07 nm, which is consistent with the cross-section of the microstructure of UiO-66. The length in the z direction was 5.00 nm, and the PEM polymer model was finally formed.
[0057] S2. Constructing the NP@PEM composite membrane structure
[0058] First, the initial simulation box dimensions for the UiO-66@Nafion composite film were determined. The dimensions in the x (length) and y (width) directions of the simulation box corresponded to the cross-sectional size of the NP microstructure, set to 2.07 nm × 2.07 nm, and the z-direction dimension was set to 20 nm. Then, the Nafion polymer structure and the UiO-66 microstructure were arranged in a "sandwich" order of Nafion + UiO-66 + Nafion, with each structure tightly packed along the z-direction in the middle of the simulation box, leaving sufficient vacuum layers on both sides. This ultimately formed the UiO-66@Nafion composite film structure, as shown below. Figure 2 As shown;
[0059] S3, Simulated NP@PEM Composite Membrane Swelling
[0060] First, sufficient water molecules are added to the two vacuum layers in the UiO-66@Nafion composite model structure until the water density of the vacuum layer reaches saturation, thus forming the UiO-66@Nafion solution structure model.
[0061] Secondly, the diffusion of water molecules into the UiO-66@Nafion composite membrane structure was achieved using the MD method. Based on a rigorous annealing simulation process, as shown in Table 1, the UiO-66@Nafion composite membrane structure was subjected to structural relaxation in the NVT ensemble, and the swelling process of the UiO-66@Nafion composite membrane was accelerated.
[0062] Finally, the water density difference in the vacuum layer was calculated using the following formula and compared with the set upper limit of density difference (5%) to determine the degree of swelling. The water density difference in the vacuum layer can indirectly reflect the degree to which water molecules enter the UiO-66@Nafion composite membrane, i.e., the degree of swelling of the composite membrane. If the calculated density difference is higher than 5%, it indicates that water molecules in the vacuum layer are continuously entering the UiO-66@Nafion composite membrane, i.e., the composite membrane is not completely swollen. In this case, sufficient water molecules are added to the vacuum layer, and steps two and three are repeated. The system equilibrium simulation is performed under the NVT ensemble to obtain the swollen structure of UiO-66@Nafion, and the physical quantities in the system are statistically analyzed for subsequent analysis.
[0063]
[0064] In the formula: DD is the density difference, ρbulk, initial, and final are the densities of the solvent in the vacuum layer before and after the annealing process, respectively, in g / cm³. 3 .
[0065] In the above NVT ensemble simulation, the microstructure of UiO-66 is kept fixed at all times, while the Nafion polymer structure is constrained by the MD and can deform freely in the simulation system.
[0066] Table 1. Annealing Simulation Process of UiO-66@Nafion Composite Film
[0067] step Series Temperature (K) Simulated time points (ps) 1 NVT 700 0 2 NVT 700 3000 3 NVT 300 7000 4 NVT 300 10000
[0068] S4. Analyze the swelling phenomenon of the MOF@PEM composite membrane model.
[0069] like Figure 3 As shown, based on the density distribution of water, Nafion, and UiO-66 along the z-axis, the UiO-66@Nafion swollen structure obtained in S3 is divided into three phase regions: solvent phase, PEM phase, and NP phase. The number of water molecules distributed in the PEM and NP phase regions is calculated, as shown below. Figure 4As shown, the number of water molecules in the PEM phase of the UiO-66@Nafion structure is slightly smaller than that in the Nafion monolayer. However, after adding water molecules from the NP phase, the number of water molecules in the composite membrane is higher than that in the monolayer, indicating that water molecules enter the NP phase via the PEM phase. The presence of the NP phase is beneficial to increasing the water absorption capacity of the composite membrane. The mean square displacement of water molecules in the PEM and NP phase regions is calculated, as shown below. Figure 5 As shown, the slope of the curve for the PEM phase is lower than that for the NP phase, indicating that the self-diffusion rate of water molecules in the PEM phase is lower than that in the NP phase.
[0070] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.
[0071] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A method for modeling and molecular simulation of nanoparticle composite proton exchange membranes, characterized in that, The method includes the following steps: Based on the chemical composition and structure of nanoparticles, an NP microstructure model was constructed; based on the monomer structure and degree of polymerization of proton exchange membranes, a PEM polymer structure model was constructed. Using the length and width of the NP microstructure model's cross-section as the length and width of the simulation box, the PEM polymer structure model, the NP microstructure model, and the PEM polymer structure model are sequentially placed inside the simulation box along the height direction of the simulation box, and vacuum layers are provided on both sides of the simulation box to form an NP@PEM composite membrane structure. Solvent is added into the vacuum layer until the solvent density reaches saturation, forming an NP@PEM solution structure model. Solvent molecules are diffused into the NP@PEM composite membrane structure using molecular dynamics methods to swell the NP@PEM solution structure model. The degree of swelling of the NP@PEM composite membrane model is obtained by measuring the change in solvent density in the vacuum layer. The swelling performance of NP@PEM is obtained by equilibrium simulation.
2. The modeling and molecular simulation method for nanoparticle composite proton exchange membranes according to claim 1, characterized in that, The degree of swelling of the NP@PEM composite film model is determined by comparing the error range between the solvent density difference in the vacuum layer and the set upper limit of the density difference. The formula for calculating the solvent density difference in the vacuum layer is as follows: In the formula: DD is the density difference; ρ bulk，initial and ρ bulk，final These are the densities of the solvent in the vacuum layer before and after the annealing process, respectively, in g / cm³. 3 .
3. The modeling and molecular simulation method for nanoparticle composite proton exchange membranes according to claim 2, characterized in that, During the swelling process of the NP@PEM solution structure model, the solvent molecules are allowed to diffuse freely into the NP@PEM composite membrane structure using molecular dynamics. Then, based on the annealing simulation process, the NP@PEM composite membrane structure is subjected to structural relaxation in the NVT ensemble. The timing of ending the cyclic annealing process is determined according to the degree of swelling of the NP@PEM composite model. The NP@PEM swollen structure is obtained by equilibrium simulation in the NVT ensemble, and the physical quantities in the ensemble are obtained, including the number of molecules, mass density, and mean square displacement.
4. The modeling and molecular simulation method for nanoparticle composite proton exchange membranes according to claim 3, characterized in that, Based on the density distribution of each component in the vacuum layer of the NP@PEM composite membrane structure, the NP@PEM swelling structure is divided into different bulk phases. By statistically analyzing the physical quantities in each bulk phase, the distribution and dynamic characteristics of solvent molecules in the NP@PEM swelling structure are calculated, and the swelling phenomenon and performance of the NP@PEM composite membrane are determined. Each bulk phase includes the solvent phase, PEM phase, and NP phase.
5. The modeling and molecular simulation method for nanoparticle composite proton exchange membranes according to claim 1, characterized in that, The simulation box has vacuum layers on both sides, and the length of the vacuum layers is greater than the cutoff radius used to calculate molecular interactions in molecular simulations.
6. The modeling and molecular simulation method for nanoparticle composite proton exchange membranes according to claim 1, characterized in that, The specific method for constructing a PEM polymer structure model includes the following steps: Based on the monomer structure and degree of polymerization of PEM, a single-chain structure of PEM is established. Then, molecular dynamics methods are used to compress two or more PEM single chains in the length and width directions of the simulation box until the size of the compressed structure in the length and width plane of the simulation box matches the cross-section of the microstructure of NP, thus constructing a PEM polymer structure model.
7. The modeling and molecular simulation method for nanoparticle composite proton exchange membranes according to claim 1, characterized in that, The specific method for constructing the NP microstructure model includes the following steps: Based on the given chemical composition and structure of NP, the corresponding nanocrystal structure is constructed. The crystal structure of NP is truncated along the crystal plane that dominates crystal growth, and the normal direction of the truncated plane is parallel to the height direction of the simulation box. Then, the unsaturated atoms of the truncated plane are filled with corresponding atoms or groups to construct a microstructure model of NP.
8. The method for modeling and molecular simulation of nanoparticle composite proton exchange membranes according to claim 1, characterized in that, The nanoparticles are one of MOFs, COFs, zeolites, porous carbon materials, metal particles, two-dimensional graphene, and two-dimensional boron carbide.
9. The modeling and molecular simulation method for nanoparticle composite proton exchange membranes according to claim 1, characterized in that, The proton exchange membrane is one of perfluorosulfonic acid polymers or non-fluorosulfonic acid polymers.
10. The method for modeling and molecular simulation of nanoparticle composite proton exchange membranes according to claim 1, characterized in that, The solvent is one of water, salt solution or organic solvent.