An evaluation method for regulating stability of diatomic catalytic structure by metal cluster

Abstract

The application belongs to the technical field of electrocatalytic material structure screening and design, and discloses an evaluation method for regulating stability of diatomic catalytic structure by using metal clusters. The method firstly constructs a diatomic catalyst PtTMN6, TM is a transition metal atom, and anchors a Pt4 tetrahedral cluster above the diatomic atom; then, by means of ab initio molecular dynamics simulation, the stability mechanism of the Pt4 cluster to the diatomic atom under high-temperature vacuum environment, hydrogen reduction atmosphere and normal-temperature aqueous solution environment is explored in sequence, so as to screen the most stable catalytic material configuration; the above different systems can exhibit different degrees of stability at high temperature, and the intrinsic factor analysis of the above stability modes by using COHP, differential charge density and Bader charge shows that the PtNi system structure stability is the best. The application firstly introduces the inevitable metal cluster in the experimental preparation into the stability evaluation framework, and solves the problem that the microstructure of the calculation model is disconnected with the actual configuration.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic material structure screening and design technology, and provides an evaluation method for regulating the stability of diatomic catalytic structures using metal clusters. Background Technology

[0002] As the global energy structure accelerates its transformation towards a green and sustainable direction, the development of efficient and stable electrocatalysts has become a core issue driving the development of clean energy technologies such as hydrogen fuel cells and water electrolysis. In recent years, atomically dispersed metal-nitrogen-carbon materials, especially carbon diatomic catalysts, have shown great potential in the field of energy catalysis due to their well-defined active sites and tunable electronic structures, serving as a bridge between homogeneous and heterogeneous catalysis. Currently, theoretical research in this field heavily relies on the idealized, isolated M1M2N6 model, based on which excellent catalytic performance has been predicted. However, experimental preparation methods, such as wet chemical methods and high-temperature pyrolysis processes, inevitably introduce metal nanoclusters due to differences in precursor reduction kinetics, resulting in actual catalysts being heterogeneous systems where diatomic, single-atom, and cluster-based substances coexist. This gap between "ideal" and "reality" has left a key scientific question unresolved for a long time: what role do these metal clusters, which are inevitably present in the preparation process and are close to the active sites, play in real catalytic environments? Although recent experimental work suggests that Pt particles may stabilize FeN4 sites, the universality mechanism and atomic-scale picture remain unclear.

[0003] Therefore, systematically studying the influence of metal clusters on the stability of diatomic catalysts is not only a core challenge that must be faced in moving from theory to application, but it may also reveal a novel "cluster-diatom" synergistic stabilization mechanism, which has key scientific significance and application value for guiding the rational design of highly stable catalysts. To answer this question, this study adopts a multi-scale computational simulation strategy of "from simple to complex, layer by layer in-depth". First, under vacuum and high-temperature conditions, through systematic AIMD simulations, the influence of Pt4 clusters on the thermal stability of PtTMN6 structures with different metal pairings (Pt-TM, TM=Mn, Fe, Co, Ni, Cu, Zn) is investigated, aiming to discover universal interaction laws and behavioral patterns. Then, the research is extended to a more complex environment that closely resembles the real catalytic process, successively examining the effects of hydrogen-rich reducing atmosphere and room-temperature aqueous solution environment on the above interactions, and finally constructing a theoretical framework that can predict the stability of diatomic catalysts under different operating conditions. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problem in existing studies on the stability of diatomic catalysts that ignore the unavoidable proximity effect of metal clusters during experimental preparation, leading to a disconnect between theoretical calculation models and the actual microstructure of catalysts, and making it impossible to accurately predict the structural stability under real operating conditions.

[0005] To achieve the above objectives, the present invention employs the following technical means:

[0006] This invention provides a method for evaluating the stability of diatomic catalytic structures by utilizing metal clusters, comprising the following steps:

[0007] Step 1: Using nitrogen-doped carbon material as a carrier, we first construct an isolated PtTMN6 diatomic model and a Pt4@PtTMN6 model loaded with Pt4 tetrahedral clusters; where TM represents transition metal atoms of Mn, Fe, Co, Ni, Cu, and Zn.

[0008] Step 1.1: Using materials simulation and molecular modeling software, construct a 6×6 supercell monolayer graphene with a periodic vacuum layer thickness ≥15 Å to avoid periodic mirror interactions.

[0009] Step 1.2: Remove two adjacent C atoms from a C6 ring to expose four C vacancies. Replace the four C vacancies with N atoms. Add a Pt atom at the geometric center of these four N atoms. Then, select one N atom and the adjacent bonded C atom and remove them, exposing three C vacancies. Replace the three C vacancies with N atoms. Finally, add a TM atom next to the Pt atom and bond the TM atom to the N atom to establish the PtTMN6 model.

[0010] Step 1.3: Place the Pt4 tetrahedral clusters above the PtTM diatomic sites at a vertical distance of approximately 1.5-3 Å, so that the metal clusters and diatomic sites form chemical bonds, thus establishing the Pt4@PtTMN6 catalyst model.

[0011] Step 2: Based on the first-principles calculation (DFT) method of density functional theory, the geometric structure of the constructed Pt4@PtTMN6 model is optimized to obtain the ground-state stable structure with the lowest energy.

[0012] Step 2.1: The core calculation parameters for geometric structure optimization are as follows: PBE functional is used, plane wave cutoff energy is 450 eV, K-point sampling is a 1×1×1 Γ point, and electronic step self-consistent convergence threshold is 10. -5 The ion step force converges to 0.02 eV / Å.

[0013] Step 3: Using the ab initio molecular dynamics (AIMD) method, molecular dynamics simulations were performed on the optimized Pt4@PtTMN6 catalyst model in vacuum high-temperature environment, hydrogen-rich reducing atmosphere and room temperature aqueous solution environment to obtain atomic trajectories under different environmental conditions for simulation duration.

[0014] Step 3.1: The simulation conditions for the vacuum high-temperature environment are NVT canonical ensemble, Nose-Hoover heat bath temperature control at 900K, time step of 1 fs, total simulation time of 10 ps, ​​and K-point sampling as Γ point of 1×1×1.

[0015] Step 3.2: The simulation conditions for the hydrogen-rich reducing atmosphere environment are as follows: H2 molecules are added to the vacuum layer of the Pt4@PtTMN6 model to construct a hydrogen-containing system, NVT canonical ensemble, Nose-Hoover thermostat temperature control at 900 K, time step 1 fs, total simulation time 10 ps, ​​and K-point sampling is a 1×1×1 Γ point.

[0016] Step 3.3: The simulation conditions for the ambient temperature aqueous solution environment are as follows: the Pt4@PtTMN6 model is filled with dominant water molecules to construct a hydration system, NVT canonical ensemble is used, Nose-Hoover heat bath temperature is controlled at 298 K, time step is 1 fs, total simulation time is 10 ps, ​​and K point is sampled as Γ point of 1×1×1.

[0017] Step 4: Visualize the simulated trajectory using VMD software, perform statistical analysis on the diatomic Pt-TM bond lengths, obtain the bond length distribution, mean and fluctuation characteristics, and quantitatively characterize the structural stability of different systems.

[0018] Step 5: Based on the structural evolution and bond length analysis results of the vacuum high-temperature system, define three intrinsic stability behavior modes of metal clusters and diatomic sites: TM atom precipitation mode, cooperative stability mode, and Pt atom precipitation mode; combined with electronic structure analysis, clarify the intrinsic factors for these three behavior modes.

[0019] Step 5.1: To understand the intrinsic factors of the diatomic system in a vacuum environment under three behavioral modes, differential charge density analysis, Bader charge analysis, and COHP analysis were performed. The charge transfer between the Pt4 cluster and the diatoms and the interaction strength between TM-N, TM-Pt, and TM-Pt4 clusters were quantitatively evaluated, revealing the influence of transition metal species on the cooperative stability of cluster-diatoms. Based on this, three intrinsic stability behavior modes of cluster-diatomic interactions were defined.

[0020] Step 6: Compare the bond length evolution and electronic structure response under different environmental conditions, construct a stability evaluation model that includes bond length stability threshold and environmental regulation parameters, and output the stability level of each PtTM system and the results of the optimal catalyst screening.

[0021] Because the present invention employs the above-mentioned technical means, it has the following beneficial effects:

[0022] 1. For the first time, unavoidable metal clusters in experimental preparation were introduced as core variables into the theoretical evaluation model, and the effects of different environmental media on catalyst stability were systematically investigated, solving the problem of the disconnect between the ideal model and the actual situation.

[0023] 2. By comparing the structural evolution under three environments—vacuum, hydrogen-rich, and room-temperature aqueous solution—this study elucidates for the first time the dynamic law by which the stability of a catalyst is jointly shaped by its atomic configuration and its chemical environment, providing a fundamental theoretical framework for understanding the structural evolution of real heterogeneous catalytic materials. Attached Figure Description

[0024] Figure 1 Schematic diagrams of PtTMN6 and Pt4@PtTMN6 structures.

[0025] Figure 2 The diagram shows the bond length distribution of diatomic PtTM under vacuum at 900 K and three behavioral modes.

[0026] Figure 3 The diagram shows the electronic structure analysis of the three behavioral modes under vacuum at 900K.

[0027] Figure 4 The structure of H2-Pt4@PtTMN6 and the distribution of diatomic PtTM bond lengths are shown.

[0028] Figure 5 The structure of H2O-Pt4-PtTMN6 and the distribution of diatomic PtTM bond lengths are shown. Detailed Implementation

[0029] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, any modifications or equivalent substitutions made to the present invention should be covered within the scope of the claims of the present invention.

[0030] The purpose of this invention is to address the technical problems of existing diatomic catalyst stability studies neglecting cluster proximity effects and failing to accurately predict structural stability in practical applications. This invention provides a closed-loop research method for regulating the structural stability of diatomic catalysts using metal clusters, comprehensively covering macroscopic behavior and microscopic mechanisms, and offering universal applicability. This method employs a progressive design of "first clarifying intrinsic vacuum behavior, then revealing multi-environment regulation mechanisms," combined with AIMD kinetic simulations and related electronic structure calculations. For the first time, it defines three intrinsic stability behavior modes of cluster-diatomic sites under vacuum conditions, revealing the intrinsic reasons for different stability modes at the electronic structure level. Subsequently, it reveals universal stabilization regulation mechanisms under real-world operating conditions, constructing a complete theoretical framework for predicting the stability of diatomic catalysts under different operating conditions. This provides a standardized research paradigm and theoretical support for the rational design of highly stable atomically dispersed catalysts.

[0031] Furthermore, to better illustrate the present invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art will understand that the present invention can be implemented without these specific details. The following example illustrates the application of the method, including the following steps:

[0032] Step 1: Using materials simulation and molecular modeling software, a PtTMN6 diatomic center model (TM = Mn, Fe, Co, Ni, Cu, Zn) was constructed using nitrogen-doped graphene as a carrier. Approximately 2 Å above this diatomic site, a Pt4 tetrahedral cluster was placed to construct a Pt4@PtTMN6 composite model with unit cell parameters a = 14.73 Å, b = 12.82 Å, c = 15 Å.

[0033] Step 2: Optimize the geometry of the above model to obtain the ground-state stable structure with the lowest energy, eliminating atomic overlap and internal stress in the initial structure; the plane wave cutoff energy is 450 eV, the K point is selected as the Γ point of 1×1×1, and the convergence criteria for electronic self-consistent iteration and ion relaxation are set to convergence to energy of 10 eV. -5 The eV and atomic force converge to 0.02 eV / Å.

[0034] Step 3: AIMD simulation calculations were performed using multi-scale material simulation software. A PBE functional was used, with a cutoff energy set to 450 eV. K-point sampling employed a 1×1×1 Γ-point. AIMD simulations were conducted within the NVT ensemble, using a Nose-Hoover thermostat for temperature control at 900 K, a time step of 1 fs, and a total simulation duration of 10 ps. The simulation trajectory was visualized using VMD software, and the Pt-TM bond lengths were statistically analyzed to obtain average values, thereby quantitatively characterizing the intrinsic structural stability of different systems. Based on the visualization results and bond length analysis data, three types of intrinsic stability behavior patterns were defined according to the standards established in this invention, clarifying the intrinsic interaction rules between clusters and diatomic sites.

[0035] like Figure 2 Three types of intrinsically stable behavioral patterns were defined:

[0036] Mode I (TM atom precipitation): Represented by the Pt-Mn system. During the simulation, Mn atoms detach from the N3 coordination ring and are captured by Pt4 clusters to form Pt4Mn alloy clusters; bond length statistics are as follows... Figure 2 The results show that the average bond length of the Pt-Mn bond is about 2.90 Å, and breakage events with bond lengths exceeding 4.0 Å occur frequently in the simulation.

[0037] Mode II (Cooperative Stability): Represented by the Pt-Ni and Pt-Co systems. During the simulation, the diatomic structure and Pt4 cluster remained intact, with no atomic migration; the average bond length of the Pt-Ni bond stabilized at approximately 2.46 Å, and the average bond length of the Pt-Co bond stabilized at approximately 2.55 Å, with minimal bond length fluctuations and no significant stretching events, indicating that the Pt4 cluster exerted a cooperative stabilizing effect on these two systems.

[0038] Mode III (Pt atom precipitation): Represented by Pt-Cu, Pt-Fe, and Pt-Zn systems. During the simulation, Pt atoms detach from the diatomic sites and merge into Pt4 clusters to form Pt5 clusters. The average bond length of the Pt-TM bond exceeds 2.65 Å.

[0039] Step 4: To understand the intrinsic factors of the diatomic system in the vacuum environment under three behavioral modes, differential charge density, Bader charge and COHP analysis were performed to quantitatively assess the charge transfer between the Pt4 cluster and the diatomic system and the interaction strength between TM-N, TM-Pt and TM-Pt4 clusters, revealing the decisive influence of transition metal type on the cooperative stability of diatomic-cluster systems.

[0040] like Figure 3 Define the bond and strength index K = -ICOHP, and calculate ΔK = (K TM-N +K TM-Pt1 )-K TM-PtclusterA larger ΔK value indicates a stronger anchoring effect of the diatomic sites on TM and Pt compared to the pulling effect of the cluster, resulting in a stronger Pt-TM diatomic bond. Differential charge and Bader charge analysis show charge transfer between the Pt4 cluster and the diatomic sites. In the Mode II cooperative stabilization system, the ΔK value is larger than that in Modes I and III, and Bader charge analysis shows no significant charge transfer between the Pt4 cluster and the diatomic sites (the transfer amount is only 0.01 |e|), indicating good electronic structure matching and no obvious driving force for atomic migration, ultimately leading to a cooperative stabilization effect.

[0041] Step 5: Fill the six optimized Pt4@PtTMN6 periodic vacuum layers from Step 2 with 14 H2 molecules to construct six independent hydrogen-rich reducing atmosphere simulation systems. Perform 10 ps AIMD simulations on the six optimized hydrogen-rich atmosphere systems under NVT ensemble conditions at 900 K, recording atomic trajectories and energy data. Figure 4 The fluctuation range of Pt-TM bond lengths in all systems was significantly narrowed, and breakage events with bond lengths exceeding 4.0 Å observed in a vacuum environment almost disappeared. The Pt-Mn (Mode I), Pt-Cu (Mode III), and Pt-Zn (Mode III) systems, which were originally intrinsically unstable in a vacuum, saw their average Pt-TM bond lengths shorten to 2.57 Å, 2.48 Å, and 2.71 Å, respectively, demonstrating significantly improved bonding stability with no atomic precipitation or structural collapse. Under a hydrogen-rich reducing atmosphere, H2 molecules dissociate and adsorb at metal sites, enhancing Pt-TM bond strength through chemical passivation, inhibiting metal atom migration, and stabilizing the diatomic sites.

[0042] Step 6: Fill the six optimized Pt4@PtTMN6 periodic vacuum layers from Step 2 with a certain number of dominant water molecules to construct six independent room-temperature aqueous solution environment simulation systems. Perform AIMD simulations (10 ps) on the six pre-optimized aqueous solution systems under NVT ensemble conditions at 298 K, recording atomic trajectories. Figure 5 In a room-temperature aqueous solution environment, the Pt-TM bond dynamics of all systems tend to stabilize, with more convergent average bond lengths and significantly smaller fluctuation amplitudes compared to the vacuum environment. Even in the intrinsically unstable Pt-Mn system under vacuum, the Pt-Mn bond length fluctuates within a narrow range of approximately 2.55 Å, and instability is greatly suppressed. No atomic precipitation or structural instability occurs in any system. In a room-temperature aqueous solution environment, the thermodynamic kinetic energy of the system is significantly reduced, and water molecules form a tight hydrated shell at the diatomic and cluster interfaces through a hydrogen bond network. This lower operating temperature, combined with the steric hindrance and solvation shielding effect of the hydrated shell, works synergistically to increase the diffusion barrier of atoms, achieving overall system stability.

[0043] The research method described in this invention, through progressive model construction, multi-environment simulation, and analysis from macroscopic to microscopic dimensions, first clarifies three intrinsic stability behavior modes of metal clusters and diatomic sites under vacuum and high-temperature conditions. Combined with the analysis of three types of electronic structures—Bader charge, differential charge density, and COHP—it reveals the intrinsic reasons for different modes from the root. Then, it systematically reveals the universal stabilization regulation mechanism under hydrogen-rich reducing atmosphere and room-temperature aqueous solution environments, and establishes a complete theoretical framework that can predict the stability of diatomic catalysts under different operating conditions.

[0044] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for evaluating the stability of diatomic catalytic structures by utilizing metal clusters, characterized in that, Includes the following steps: Step 1: Using nitrogen-doped carbon material as a carrier, we first construct an isolated PtTMN6 diatomic model and a Pt4@PtTMN6 model loaded with Pt4 tetrahedral clusters; where TM represents a transition metal atom. Step 2: Based on the first-principles calculation method of density functional theory, the geometric structure of the constructed Pt4@PtTMN6 model is optimized to obtain the ground-state stable structure with the lowest energy. Step 3: Using ab initio molecular dynamics, molecular dynamics simulations were performed on the optimized Pt4@PtTMN6 catalyst model in vacuum high-temperature environment, hydrogen-rich reducing atmosphere and room temperature aqueous solution environment to obtain atomic trajectories under different environmental conditions for simulation duration. Step 4: Visualize the simulated atomic trajectories and perform bond length statistical analysis to obtain the distribution characteristics, mean characteristics, and fluctuation characteristics of the bond lengths between diatomic atoms, and quantitatively characterize the structural stability of different systems; Step 5: Based on the structural evolution and bond length analysis results under vacuum and high temperature environment, the charge transfer between Pt4 clusters and diatomic sites and the bonding strength of TM-N, TM-Pt, and TM-Pt4 are quantified by differential charge density, Bader charge and crystal orbital Hamiltonian population COHP analysis. Based on this, three intrinsic stability behavior modes of cluster-diatomic interaction are defined. Step 6: Compare the bond length evolution and electronic structure response under different environmental conditions, construct a stability evaluation model that includes bond length stability threshold and environmental regulation parameters, and output the stability level of each PtTM system and the results of the optimal catalyst screening.

2. The method according to claim 1, characterized in that, The TM is any one of the transition metal atoms selected from Mn, Fe, Co, Ni, Cu, and Zn.

3. The method for evaluating the stability of diatomic catalytic structures using metal clusters according to claim 1, characterized in that: Step 1.1: Using materials simulation and molecular modeling software, construct a 6×6 supercell monolayer graphene with a periodic vacuum layer thickness ≥15 Å. Step 1.2: Remove two adjacent C atoms from a C6 ring to expose four C vacancies. Replace the four C vacancies with N atoms. Add a Pt atom at the geometric center of these four N atoms. Then, select one N atom and the adjacent bonded C atom and remove them, exposing three C vacancies. Replace the three C vacancies with N atoms. Finally, add a TM atom next to the Pt atom and bond the TM atom with the N atom to establish the PtTMN6 model. Step 1.3: Place the Pt4 tetrahedral clusters above the PtTM diatomic sites at a vertical distance of approximately 1.5-3 Å, so that the metal clusters and diatomic sites form chemical bonds, thus establishing the Pt4@PtTMN6 catalyst model.

4. The method for evaluating the stability of diatomic catalytic structures using metal clusters according to claim 1, characterized in that, In step 2, the core computational parameters for geometric structure optimization are: using a PBE functional, a plane wave cutoff energy of 450 eV, K-point sampling as a 1×1×1 Γ-point, and an electronic step self-consistent convergence threshold of 1×10⁻⁶. -5 The ion step force converges to 0.02 eV / Å.

5. The method for evaluating the stability of diatomic catalytic structures using metal clusters according to claim 1, characterized in that, Step 3 includes the following steps: Step 3.1: Perform molecular dynamics simulation on the optimized Pt4@PtTMN6 catalyst model under vacuum and high temperature. The simulation conditions are as follows: NVT canonical ensemble, Nose-Hoover thermostat temperature control at 900 K, time step of 1 fs, total simulation time of 10 ps, ​​and K-point sampling as Γ point of 1×1×1. Step 3.2: Molecular dynamics simulation of the optimized Pt4@PtTMN6 catalyst model under a hydrogen-rich reducing atmosphere was performed. The simulation conditions were as follows: H2 molecules were added to the vacuum layer of the Pt4@PtTMN6 model to construct a hydrogen-containing system, NVT canonical ensemble was used, Nose-Hoover thermostat was used to control the temperature at 900 K, the time step was 1 fs, the total simulation time was 10 ps, ​​and the K point was sampled as a 1×1×1 Γ point. Step 3.3: Perform molecular dynamics simulations on the optimized Pt4@PtTMN6 catalyst model under ambient temperature aqueous solution conditions. The simulation conditions are as follows: fill the vacuum layer of the Pt4@PtTMN6 model with dominant water molecules to construct a hydration system, use NVT canonical ensemble, control the temperature in a Nose-Hoover thermostat at 298 K, set the time step to 1 fs, and the total simulation time to 10 ps. The K-point is sampled as a 1×1×1 Γ-point.

6. The method for evaluating the stability of diatomic catalytic structures using metal clusters according to claim 1, characterized in that, In step 4, the simulated trajectory is visualized using molecular dynamics analysis software. The distribution and average value of the diatomic Pt-TM bond length during the simulation time are tracked and statistically analyzed, serving as a quantitative criterion for structural stability.

7. The method for evaluating the stability of diatomic catalytic structures using metal clusters according to claim 1, characterized in that, In step 5, the interaction modes between the Pt4 cluster and the diatomic PtTM under the vacuum environment are divided into three categories: TM atom precipitation mode, cooperative stabilization mode, and Pt atom precipitation mode. To understand the intrinsic factors of the diatomic system in a vacuum environment under three behavioral modes, differential charge density analysis, Bader charge analysis, and COHP analysis were performed to quantitatively assess the charge transfer between the Pt4 cluster and the diatomic system, as well as the interaction strength between TM-N, TM-Pt, and TM-Pt4 clusters, revealing the decisive influence of transition metal species on the cooperative stability of the diatomic-cluster system.

8. The method for evaluating the stability of diatomic catalytic structures using metal clusters according to claim 1, characterized in that, In step 6: Under hydrogen-rich reducing atmosphere conditions, H2 molecules dissociate and adsorb at metal sites, enhancing the Pt-TM bonding strength through chemical passivation effect, inhibiting metal atom migration, and stabilizing the diatomic sites. Under normal temperature aqueous solution conditions, water molecules form a tight hydration shell at the interface between diatoms and clusters through hydrogen bonds. The decrease in operating temperature, the steric hindrance of the hydration shell, and the solvation shielding effect work synergistically to increase the diffusion barrier of atoms and achieve synergistic stability of the entire system.

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