A screening method for a curved double-atom phthalocyanine electrocatalyst, the catalyst and application thereof

Abstract

The application discloses a kind of curved surface double-atom phthalocyanine electrocatalyst screening method, catalyst and application, belong to electrocatalytic material design and renewable resource high-value conversion technical field.The application is calculated by density functional theory, constructs M1-M2-Pc model (M1,M2=Co or Fe) with specific curvature (double metal spacing 2.3-2.4Å), the whole path gibbs free energy of CO2 reduction reaction and NO reduction reaction coupling urea is calculated systematically.By comparing the step diagram of Co-Co-Pc, Co-Fe-Pc, Fe-Co-Pc, Fe-Fe-Pc four configurations, it is first found that the curved surface confinement effect makes C-N coupling step from the kinetic bottleneck of plane structure to thermodynamic spontaneous process.The application constructs Fe / Co double-metal phthalocyanine model with specific curvature on atomic scale, and systematically evaluates its catalytic activity, selectivity and reaction mechanism, provides theoretical guidance for the design of high selectivity urea electrocatalyst, gets rid of the dependence on noble metal, reduces experimental trial and error cost.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic material design and high-value conversion of renewable resources, and provides a screening method for curved two-atom phthalocyanine electrocatalysts, the catalyst and its application. Background Technology

[0002] Urea, the world's largest producer of chemical nitrogen fertilizer and an important industrial chemical raw material, has an annual output exceeding 150 million tons. Currently, industrial urea production relies entirely on the Bosch-Meiser process, which requires high temperatures (approximately 180-200°C) and high pressures (approximately 150-200 bar) to react with liquid ammonia and carbon dioxide as feedstocks. More critically, the upstream Haber-Bosch process for ammonia synthesis consumes approximately 2% of global energy supply and contributes about 1.5% of global carbon dioxide emissions. Therefore, developing a green synthetic route that directly converts carbon- and nitrogen-containing small molecules in the environment into urea under mild conditions using renewable electricity is of paramount scientific and industrial value.

[0003] Against this backdrop, electrocatalytic carbon-nitrogen coupling reactions have emerged. This technology aims to simultaneously activate carbon dioxide and nitrogen-containing species (such as NO and NO3) at the cathode through an electrochemical process, using water as a proton source and oxygen acceptor. - The process utilizes nitrogen (N2) to reduce urea and induce CN coupling, ultimately producing urea. This process not only achieves the resource utilization of inert small molecules but also enables distributed, low-carbon urea production. Compared to traditional processes, the electrocatalytic route has the following significant advantages:

[0004] (1) The reaction conditions are mild and can be carried out at room temperature and pressure;

[0005] (2) Driven by renewable electricity, it aligns with the "dual carbon" goal;

[0006] (3) CO2 and NOx in industrial flue gas can be directly utilized to realize the resource utilization of pollutants.

[0007] In recent years, atomically dispersed metal-nitrogen-carbon materials, especially single-atom and diatomic catalysts, have exhibited excellent catalytic performance in CO2 reduction and nitrogen reduction reactions due to their extremely high atomic utilization and unique electronic structures. Metal phthalocyanine molecules with M-N4 coordination structures have become a research hotspot in the field of electrocatalysis due to their well-defined structures and ease of modification. However, current technologies still face the following core bottlenecks:

[0008] First, the constraint of linear scaling. On conventional planar phthalocyanine catalysts, the adsorption energies of key intermediates (such as CO and NH2) are limited by inherent linear scaling relationships, making independent regulation difficult. Specifically, if CO adsorption is enhanced to promote CO2 activation, CO easily poisons the adsorption sites; if CO adsorption is weakened to facilitate desorption, CO2 activation becomes difficult. This seesaw effect makes it difficult for the CO2RR and NORR ends to simultaneously reach their optimal states, resulting in low CN coupling efficiency.

[0009] Second, the competing reactions are intense. In aqueous electrocatalytic systems, the hydrogen evolution reaction (HER) is the most significant competing side reaction between CO2RR and NORR. In planar structures, the adsorption of H* by metal active sites competes with the adsorption of CO2 / NO, especially at negative potentials, where the HER dominates, resulting in extremely low urea Faraday efficiency, typically less than 20%.

[0010] Third, CN coupling kinetics are slow. In a planar rigid phthalocyanine framework, the bimetallic center-to-center distance is fixed at approximately 2.35 Å. When the CO and NH2 intermediates are adsorbed onto the two metal sites respectively, their spatial orientation is restricted to a configuration parallel to the molecular plane. CN coupling requires overcoming significant steric hindrance and energy barriers, becoming the kinetic bottleneck of the entire reaction.

[0011] Fourth, there is a gap between theory and experiment. Current theoretical research is mostly based on idealized planar models, while experimentally prepared phthalocyanine molecules often exhibit varying degrees of bending distortion due to substrate effects or intermolecular stacking. This difference between the "ideal plane" and the "actual curved surface" leads to a systematic deviation between theoretically predicted catalytic performance and experimental results.

[0012] To address the aforementioned issues, recent studies have shown that introducing curvature strain into catalysts can effectively break the symmetry of planar structures and adjust the d-band center position of metal active centers, thereby optimizing the adsorption strength of key reaction intermediates. For example, in carbon nanotube-supported iron-nitrogen-carbon catalysts, curved surfaces can significantly improve the selectivity of NO3RR. However, current research on curved diatomic phthalocyanines in the specific complex tandem reaction of CO2RR and NORR to produce urea remains lacking. In particular, systematic theoretical understanding and high-throughput screening methods are still needed for different metal combinations (Co-Co, Co-Fe, Fe-Co, Fe-Fe) under curved strain regarding the coupling mechanism of the two reaction pathways, the transfer law of the rate-determining step, and the microscopic reaction kinetics.

[0013] Therefore, this invention aims to provide a method for systematic screening using density functional theory, constructing a Fe / Co diatomic phthalocyanine model with a specific curvature, systematically revealing its intrinsic mechanism of catalytic carbon-nitrogen coupling to urea production, and determining the optimal combination and configuration of metal sites based on thermodynamic and electronic structure analysis, providing precise theoretical guidance for the experimental synthesis of high-performance urea electrocatalysts. Summary of the Invention

[0014] The purpose of this invention is to solve the technical problems of high CN coupling energy barrier, low catalytic activity and poor selectivity in the electrocatalytic synthesis of urea from CO2 and NO, caused by the rigid structure and linear scaling relationship of existing planar phthalocyanine catalysts.

[0015] To achieve the above objectives, the present invention adopts the following technical solution:

[0016] This invention provides a method for screening curved diatomic phthalocyanine electrocatalysts, comprising the following steps:

[0017] Step 1: Construct a curvature diatomic phthalocyanine molecular model, wherein the model is M1-M2-Pc, and M1 and M2 are independently selected from Co or Fe. By fixing the Cartesian coordinates of the edge hydrogen atoms, geometric constraints are applied, and the internal C, N, and transition metal atoms are relaxed with full degrees of freedom to simulate the bending stress generated by the confinement of the carbon support or the molecular stacking, so that the model bends and deforms, and the distance between the bimetallic centers M1 and M2 converges to the range of 2.3 Å to 2.4 Å.

[0018] Step 2: Based on the first-principles calculation method of density functional theory, the geometric structure of the constructed surface M1-M2-Pc model is optimized to obtain the ground state stable structure with the lowest energy.

[0019] Step 3: Calculate the adsorption free energy of key intermediates in the CO2 reduction and NO reduction pathways at the optimized curved diatomic sites, and calculate the Gibbs free energy changes for each elementary step. The key intermediates include *CO2, *COOH, and CO in the CO2 reduction pathway, and NO, *NHO, HNOH, and NH in the NO reduction pathway;

[0020] Step 4: Calculate the adsorption free energy of the key CN coupling intermediates CONH and NHCONH, and draw the Gibbs free energy step diagram of the entire reaction path from the initial reactants to the final product urea.

[0021] Step 5: Extract the rate-determining step energy barrier and CN coupling drive based on the Gibbs free energy step diagram, and comprehensively screen out the optimal catalyst configuration;

[0022] Step 6: Perform electronic structure analysis on the selected optimal catalyst configuration, including density of states calculation, differential charge density analysis and Bader charge analysis, to reveal the intrinsic physicochemical mechanism of enhanced catalytic activity.

[0023] In the above scheme, step 1, which involves constructing a diatomic phthalocyanine molecular model with gradient curvature, specifically includes:

[0024] Step 1.1: Construct a planar metallic phthalocyanine framework C with D4h symmetry. 34 H 16 N8 has two transition metal atoms, Co or Fe, embedded in its central cavity, forming four configurations: Co-Co-Pc, Co-Fe-Pc, Fe-Co-Pc, and Fe-Fe-Pc.

[0025] Step 1.2: By fixing the Cartesian coordinates of the 12 edge hydrogen atoms around the phthalocyanine, the four hydrogen atoms close to the inside of the catalyst do not need to be fixed. The C, N, and transition metal M atoms inside are relaxed with full degrees of freedom to simulate the bending stress generated by the confinement of the carbon support or the molecular stacking, thereby shortening the bimetallic spacing and forming a non-planar curved surface structure. This method effectively simulates the bending stress generated by the confinement adsorption of the carbon support or the π-π stacking between molecules, and is in high agreement with the actual experimental conditions.

[0026] Step 1.3: The optimized bimetallic spacing d(M1-M2) converges to 2.35 Å ± 0.05 Å. This distance is significantly smaller than the approximately 2.6 Å in the planar configuration, indicating that curvature induces the convergence of the bimetallic centers. At such a close distance, the d orbitals of the two metal atoms will exhibit significant spatial overlap, providing a structural basis for electronic cooperation effects.

[0027] In the above scheme, the first principle calculation parameters in step 2 are set as follows:

[0028] Using Device Studio software, the electronic exchange correlation functional is performed using the Perdew-Burke-Ernzerhof (GGA-PBE) functional under the generalized gradient approximation.

[0029] The plane wave cutoff energy was set to 520 eV to ensure computational accuracy. Since phthalocyanine molecules are relatively large and located in a sufficiently large vacuum layer (≥15 Å), a 1×1×1 Gamma point sampling method is sufficient to meet the accuracy requirements. The convergence criterion for electronic self-consistent iteration is an energy difference of less than 10 eV. -5 eV; the convergence criterion for ion relaxation is that the force on the atom is less than 0.02 eV / Å;

[0030] To accurately describe the van der Waals interactions between the reaction intermediate and the catalyst surface, the DFT-D3 method was used for Grimme van der Waals correction. Spin polarization calculations were performed on Fe and Co atoms, and initial magnetic moments were set (approximately 4 μB for Fe and 3.5 μB for Co) to distinguish between high-spin and low-spin states and avoid falling into metastable states.

[0031] Furthermore, the overall reaction formula for the electrocatalytic coupling of CO2 and NO to synthesize urea is as follows:

[0032] 2NO + CO2 + 8H + + 8e - → CO(NH2)2 + 2H2O

[0033] This reaction is a coupling of the NORR and CO2RR pathways. Based on DFT calculations, the following key elementary steps are identified:

[0034] NORR branch (right end, path: NO → HNO → NHOH → NH):

[0035] (1) NO adsorption: * + NO(g) → NO

[0036] (2) First protonation: NO + H + + e - → HNO

[0037] (3) Second protonation: HNO + H + + e - → *HNOH

[0038] (4) NO bond breaking and dehydration: *HNOH + H + + e - → *NH + H2O

[0039] CO2RR branch (left end, generates *CO intermediate):

[0040] (5) CO2 adsorption: * + CO2(g) → CO2

[0041] (6) First protonation: CO2 + H + + e - → COOH

[0042] (7) Second protonation and dehydration: COOH + H + + e - → *CO + H2O

[0043] CN coupling branch (middle, generating urea):

[0044] (8) CN coupling: *CO + NH → CONH

[0045] (9) Hydrogenation of CONH: CONH + H + + e - → CONH2

[0046] (10) Hydrogenation of CONH2: *CONH2 + H + + e - → NH2CONH

[0047] (11) Hydrogenation of NH2CONH: *NH2CONH + H + + e - → NH2CONH2 (urea)

[0048] (12) Urea desorption: NH2CONH2→ * + CO(NH2)2(g)

[0049] In the above scheme, the formula for calculating the Gibbs free energy in steps 3 and 4 is as follows:

[0050] For the reaction step *A + H + + e - → *AH:

[0051] ΔG = E_(AH) - E_(A) - 1 / 2·E_H2

[0052] For the reaction step *A + B → *AB (without proton transfer):

[0053] ΔG = E_(AB) - E_(A) - E_(B)

[0054] In the formula, E_(A), E_(AH), and E_(*AB) are the total energy of the system in each adsorption state, respectively; E_(B) is the energy of isolated reactant B.

[0055] In the above scheme, the criteria for comprehensive screening of catalyst performance in step 5 include:

[0056] (1) Energy barrier for determining the velocity step: Take max(ΔG1, ΔG2, ..., ΔG) n ), corresponding to the initial potential;

[0057] (2) CN coupling driving force: calculation steps *CO + *NH → *CONH Gibbs free energy change ΔG_C-N

[0058] The larger the negative value, the more spontaneous the coupling. In planar structures, this step is usually positive or close to zero, constituting a dynamic bottleneck.

[0059] In the above scheme, the screening further includes: when the difference in the velocity step energy barrier between the two configurations is less than a preset threshold, the absolute value of the CN coupling driving force ΔG_C-N is used as a secondary screening criterion.

[0060] Further explanation: The optimal catalyst configurations obtained after screening are Co-Fe-Pc or Co-Co-Pc. ​​Among them, the rate-determining energy barrier of Co-Fe-Pc is +0.363 eV, which is the lowest among the four catalysts, 0.064 eV lower than Co-Co-Pc (+0.427 eV), exceeding the 0.05 eV tie threshold, thus constituting a clear activity advantage. Since a clear winner has been determined on the primary criterion ΔG_RDS, there is no need to use the secondary criterion ΔG_C-N. Although Co-Fe-Pc's -2.334 eV is relatively weak in terms of CN coupling driving force (Co-Co-Pc is -2.923 eV, Fe-Fe-Pc is -3.414 eV), under the curved confinement structure, -2.334 eV itself is already strongly exothermic (ΔG < -2.3 eV), and CN coupling is completely spontaneous with sufficient driving force. Therefore, the relative disadvantage of Co-Fe-Pc in coupling driving force does not affect its decisive advantage in velocity-step energy barrier.

[0061] This invention provides a curved diatomic phthalocyanine catalyst obtained by the method described above. The catalyst has a non-planar curved three-dimensional structure with the molecular formula M1-M2-Pc, wherein M1 and M2 are independently selected from Co or Fe, and the metal center distance between M1 and M2 is 2.35 Å. The metal combination is Co-Co, Fe-Co, Co-Fe, or Fe-Fe.

[0062] The present invention also provides an application of a curved diatomic phthalocyanine catalyst in the electrocatalytic synthesis of urea, wherein the application conditions are as follows: in a CO2-saturated NO gas or nitrate electrolyte, the electrode loaded with the catalyst is used as the working electrode, and a cathode potential of -0.4 V to -1.0 V relative to the reversible hydrogen electrode is applied.

[0063] The screening results based on the above criteria indicate that:

[0064] Firstly, the Co-Fe-Pc configuration exhibits optimal overall catalytic performance. Specifically, the rate-determining energy barrier of Co-Fe-Pc is only +0.363 eV, corresponding to a theoretical onset potential of -0.37 V vs RHE, which is the lowest among the four catalysts. This means that Co-Fe-Pc can initiate the urea synthesis reaction at the lowest overpotential, with the lowest energy consumption. Furthermore, the overall NORR phase operates smoothly. Except for the first protonation step, which requires overcoming a +0.296 eV energy barrier, subsequent steps are either strongly exothermic or have extremely low energy barriers, resulting in smooth overall NORR phase operation and an ample supply of *NH intermediates. At a 2.6 Å surface confinement distance, the CN coupling step of Co-Fe-Pc (*CO + *NH → *CONH) ΔG = -2.334 eV is a strongly exothermic reaction, with spontaneous and rapid coupling, and does not constitute a bottleneck for the overall reaction.

[0065] The Co-Co-Pc configuration is the second-best. Its rate-determining energy barrier is relatively low; the *NO → *NHO step barrier is +0.427 eV, second only to Co-Fe-Pc. The theoretical onset potential is -0.43 V vs RHE. Secondly, the NHO → NHOH step exhibits the strongest driving force, with an exothermic step of -1.180 eV, the highest exothermic among the four catalysts, indicating that the Co-Co site possesses excellent catalytic ability for the second protonation.

[0066] Secondly, by adopting a geometric constraint strategy of "fixed edges and relaxed interior", this invention constructs a curved diatomic phthalocyanine model with the bimetallic spacing precisely controlled at 2.30 Å ± 0.1 Å. This confined distance forces CO and NH to be in extremely close positions, significantly reducing the spatial steric hindrance and entropy loss of coupling. It solves the problem that the CN coupling step constitutes a kinetic bottleneck due to large spatial steric hindrance and high entropy loss, and achieves the effect of transforming the CN coupling step into a thermodynamically spontaneous process in all candidate configurations.

[0067] Thirdly, this invention provides a curved diatomic phthalocyanine catalyst configuration obtained by the above-described method. The catalyst is characterized by having a non-planar, curved three-dimensional structure, with a bimetallic center-to-center distance of 2.30 Å to 2.40 Å, preferably 2.35 Å. This addresses the problem in existing technologies of a lack of clear theoretical understanding of the optimal metal combination in the carbon-nitrogen coupled urea production reaction, achieving the effect of screening Co-Fe-Pc as the optimal catalyst and revealing the asymmetric bimetallic "specialization and synergy" mechanism.

[0068] Fourthly, by establishing a calculation scheme for the total reaction coupling free energy including the NORR pathway (*NO → *NHO → *NHOH → NH) and the CO2RR pathway (CO2 → COOH → CO), this invention solves the problem that existing technologies only study a single half of the reaction in isolation and cannot evaluate the overall matching of tandem catalysis. It achieves the effect of systematically revealing the coupling mechanism of the two reaction pathways and accurately locating the rate-determining step. Attached Figure Description

[0069] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0070] Figure 1 This is a schematic diagram of the planar diatomic phthalocyanine structure constructed in this invention;

[0071] Figure 2 This is a schematic diagram of the curved diatomic phthalocyanine structure constructed in this invention;

[0072] Figure 3 Gibbs free energy step diagrams (full path) for four configurations: Co-Co-Pc, Co-Fe-Pc, Fe-Co-Pc, and Fe-Fe-Pc. Detailed Implementation

[0073] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0074] This invention relates to constructing a Fe / Co bimetallic phthalocyanine model with a specific curvature at the atomic scale through density functional theory calculations, and systematically evaluating its catalytic activity, selectivity and reaction mechanism in the coupled CO2 reduction and NO reduction reaction to produce urea.

[0075] This invention provides a method for screening curved diatomic phthalocyanine electrocatalysts, comprising the following steps:

[0076] Step 1: Construct a curvature diatomic phthalocyanine molecular model, wherein the model is M1-M2-Pc, and M1 and M2 are independently selected from Co or Fe. By fixing the Cartesian coordinates of the edge hydrogen atoms, geometric constraints are applied, and the internal C, N, and transition metal atoms are relaxed with full degrees of freedom to simulate the bending stress generated by the confinement of the carbon support or the molecular stacking, so that the model bends and deforms, and the distance between the bimetallic centers M1 and M2 converges to the range of 2.3 Å to 2.4 Å.

[0077] Step 2: Based on the first-principles calculation method of density functional theory, the geometric structure of the constructed surface M1-M2-Pc model is optimized to obtain the ground state stable structure with the lowest energy.

[0078] Step 3: Calculate the adsorption free energy of key intermediates in the CO2 reduction and NO reduction pathways at the optimized curved diatomic sites, and calculate the Gibbs free energy changes for each elementary step. The key intermediates include *CO2, *COOH, and CO in the CO2 reduction pathway, and NO, *NHO, HNOH, and NH in the NO reduction pathway;

[0079] Step 4: Calculate the adsorption free energy of the key CN coupling intermediates CONH and NHCONH, and draw the Gibbs free energy step diagram of the entire reaction path from the initial reactants to the final product urea.

[0080] Step 5: Extract the rate-determining step energy barrier and CN coupling drive based on the Gibbs free energy step diagram, and comprehensively screen out the optimal catalyst configuration;

[0081] Step 6: Perform electronic structure analysis on the selected optimal catalyst configuration, including density of states calculation, differential charge density analysis and Bader charge analysis, to reveal the intrinsic physicochemical mechanism of enhanced catalytic activity.

[0082] In the above scheme, step 1, which involves constructing a diatomic phthalocyanine molecular model with gradient curvature, specifically includes:

[0083] Step 1.1: Construct a planar metallic phthalocyanine framework C with D4h symmetry. 34 H 16 N8 has two transition metal atoms, Co or Fe, embedded in its central cavity, forming four configurations: Co-Co-Pc, Co-Fe-Pc, Fe-Co-Pc, and Fe-Fe-Pc.

[0084] Step 1.2: By fixing the Cartesian coordinates of the 12 edge hydrogen atoms around the phthalocyanine, the four hydrogen atoms close to the inside of the catalyst do not need to be fixed. The C, N, and transition metal M atoms inside are relaxed with full degrees of freedom to simulate the bending stress generated by the confinement of the carbon support or the molecular stacking, thereby shortening the bimetallic spacing and forming a non-planar curved surface structure. This method effectively simulates the bending stress generated by the confinement adsorption of the carbon support or the π-π stacking between molecules, and is in high agreement with the actual experimental conditions.

[0085] Step 1.3: The optimized bimetallic spacing d(M1-M2) converges to 2.35 Å ± 0.05 Å. This distance is significantly smaller than the approximately 2.6 Å in the planar configuration, indicating that curvature induces the convergence of the bimetallic centers. At such a close distance, the d orbitals of the two metal atoms will exhibit significant spatial overlap, providing a structural basis for electronic cooperation effects.

[0086] In the above scheme, the first principle calculation parameters in step 2 are set as follows:

[0087] Using Device Studio software, the electronic exchange correlation functional is performed using the Perdew-Burke-Ernzerhof (GGA-PBE) functional under the generalized gradient approximation.

[0088] The plane wave cutoff energy was set to 520 eV to ensure computational accuracy. Since phthalocyanine molecules are relatively large and located in a sufficiently large vacuum layer (≥15 Å), a 1×1×1 Gamma point sampling method is sufficient to meet the accuracy requirements. The convergence criterion for electronic self-consistent iteration is an energy difference of less than 10 eV. -5 eV; the convergence criterion for ion relaxation is that the force on the atom is less than 0.02 eV / Å;

[0089] To accurately describe the van der Waals interactions between the reaction intermediate and the catalyst surface, the DFT-D3 method was used for Grimme van der Waals correction. Spin polarization calculations were performed on Fe and Co atoms, and initial magnetic moments were set (approximately 4 μB for Fe and 3.5 μB for Co) to distinguish between high-spin and low-spin states and avoid falling into metastable states.

[0090] Furthermore, the overall reaction formula for the electrocatalytic coupling of CO2 and NO to synthesize urea is as follows:

[0091] 2NO + CO2 + 8H + + 8e - → CO(NH2)2 + 2H2O

[0092] This reaction is a coupling of the NORR and CO2RR pathways. Based on DFT calculations, the following key elementary steps are identified:

[0093] NORR branch (right end, path: NO → HNO → NHOH → NH):

[0094] (1) NO adsorption: * + NO(g) → NO

[0095] (2) First protonation: NO + H + + e - → HNO

[0096] (3) Second protonation: HNO + H + + e - → *HNOH

[0097] (4) NO bond breaking and dehydration: *HNOH + H + + e - → *NH + H2O

[0098] CO2RR branch (left end, generates *CO intermediate):

[0099] (5) CO2 adsorption: * + CO2(g) → CO2

[0100] (6) First protonation: CO2 + H + + e - → COOH

[0101] (7) Second protonation and dehydration: COOH + H + + e - → *CO + H2O

[0102] CN coupling branch (middle, generating urea):

[0103] (8) CN coupling: *CO + NH → CONH

[0104] (9) Hydrogenation of CONH: CONH + H + + e - → CONH2

[0105] (10) Hydrogenation of CONH2: *CONH2 + H + + e - → NH2CONH

[0106] (11) Hydrogenation of NH2CONH: *NH2CONH + H + + e - → NH2CONH2 (urea)

[0107] (12) Urea desorption: NH2CONH2→ * + CO(NH2)2(g)

[0108] In the above scheme, the formula for calculating the Gibbs free energy in steps 3 and 4 is as follows:

[0109] For the reaction step *A + H + + e - → *AH:

[0110] ΔG = E_(AH) - E_(A) - 1 / 2·E_H2

[0111] For the reaction step *A + B → *AB (without proton transfer):

[0112] ΔG = E_(AB) - E_(A) - E_(B)

[0113] In the formula, E_(A), E_(AH), and E_(*AB) are the total energy of the system in each adsorption state, respectively; E_(B) is the energy of isolated reactant B.

[0114] In the above scheme, the criteria for comprehensive screening of catalyst performance in step 5 include:

[0115] (1) Energy barrier for determining the velocity step: Take max(ΔG1, ΔG2, ..., ΔG) n ), corresponding to the initial potential;

[0116] (2) CN coupling driving force: calculation steps *CO + *NH → *CONH Gibbs free energy change ΔG_C-N

[0117] The larger the negative value, the more spontaneous the coupling. In planar structures, this step is usually positive or close to zero, constituting a dynamic bottleneck.

[0118] In the above scheme, the screening further includes: when the difference in the velocity step energy barrier between the two configurations is less than a preset threshold, the absolute value of the CN coupling driving force ΔG_C-N is used as a secondary screening criterion.

[0119] Further explanation: The optimal catalyst configurations obtained after screening are Co-Fe-Pc or Co-Co-Pc. ​​Among them, the rate-determining energy barrier of Co-Fe-Pc is +0.363 eV, which is the lowest among the four catalysts, 0.064 eV lower than Co-Co-Pc (+0.427 eV), exceeding the 0.05 eV tie threshold, thus constituting a clear activity advantage. Since a clear winner has been determined on the primary criterion ΔG_RDS, there is no need to use the secondary criterion ΔG_C-N. Although Co-Fe-Pc's -2.334 eV is relatively weak in terms of CN coupling driving force (Co-Co-Pc is -2.923 eV, Fe-Fe-Pc is -3.414 eV), under the curved confinement structure, -2.334 eV itself is already strongly exothermic (ΔG < -2.3 eV), and CN coupling is completely spontaneous with sufficient driving force. Therefore, the relative disadvantage of Co-Fe-Pc in coupling driving force does not affect its decisive advantage in velocity-step energy barrier.

[0120] This invention provides a curved diatomic phthalocyanine catalyst obtained by the method described above. The catalyst has a non-planar curved three-dimensional structure with the molecular formula M1-M2-Pc, wherein M1 and M2 are independently selected from Co or Fe, and the metal center distance between M1 and M2 is 2.35 Å. The metal combination is Co-Co, Fe-Co, Co-Fe, or Fe-Fe.

[0121] The present invention also provides an application of a curved diatomic phthalocyanine catalyst in the electrocatalytic synthesis of urea, wherein the application conditions are as follows: in a CO2-saturated NO gas or nitrate electrolyte, the electrode loaded with the catalyst is used as the working electrode, and a cathode potential of -0.4 V to -1.0 V relative to the reversible hydrogen electrode is applied.

[0122] Example 1: Construction and structural optimization of a curved two-atom phthalocyanine model

[0123] This embodiment details the construction process and structural optimization results of the curved two-atom phthalocyanine catalyst model.

[0124] 1.1 Initial Construction of the Planar Model

[0125] First, a standard metal phthalocyanine molecular framework was constructed using Materials Studio molecular modeling software. The molecular formula of phthalocyanine is C1. 34 H 16 N 12 It possesses D4h point group symmetry and a central cavity diameter of approximately 2.8 Å. Two transition metal M atoms are embedded in the central cavity to form a diatomic phthalocyanine M1-M2-Pc. This embodiment constructs four configurations: Co-Co-Pc, Co-Fe-Pc, Fe-Co-Pc, and Fe-Fe-Pc. In these configurations, the metal atoms form an M-N4 coordination structure with the four surrounding isoindole nitrogen atoms, and the initial MN bond length is set to 1.8 Å.

[0126] For the planar configuration, unconstrained full-degree-of-freedom structural optimization was performed, and the optimized bimetallic center-to-center distance MM was 2.6 Å, which is consistent with the experimental value reported in the literature.

[0127] 1.2 Construction of curved surface configuration

[0128] To simulate the bending effect induced by carbon support confinement or molecular stacking in real catalytic systems, this embodiment employs a geometric constraint strategy of "edge fixation and internal relaxation." The specific operation is as follows:

[0129] The optimized planar phthalocyanine molecule was selected, and the 12 saturated hydrogen atoms on the molecule's periphery (three H atoms surrounding each benzene ring terminal group) were identified. In the structure optimization input file, the Cartesian coordinates of these 12 H atoms were marked as F (Fixed) using the Selective Dynamics tag, indicating they are fixed. The 34 C atoms, 12 N atoms, 2 H atoms, and 2 transition metal atoms inside the molecule were marked as T (Free), allowing them to move freely under stress.

[0130] This setup simulates the mechanical state of phthalocyanine molecules when anchored to a curved substrate (such as the surface of carbon nanotubes) or compressed by surrounding molecules. With the edges fixed, the internal atoms will displace under the drive of minimizing energy, naturally forming a curved configuration.

[0131] 1.3 Structural Optimization Parameters

[0132] Structural optimization is performed using the Device Studio software package. Specific calculation parameters are as follows:

[0133] Exchange-correlation functional: GGA-PBE

[0134] Plane wave cutoff energy: 520 eV

[0135] K-point sampling: 1×1×1 Gamma point (molecules are placed in a periodic box of 25 Å × 23 Å × 15 Å with a sufficiently large vacuum layer)

[0136] Electronic convergence criterion: 10 -5 eV

[0137] Ion convergence criterion: Atom force < 0.02 eV / Å

[0138] Van der Waals correction: DFT-D3 (Grimme)

[0139] Spin polarization: On, initial magnetic moment MAGMOM = 4.0 for Fe and 3.5 for Co.

[0140] After optimization and convergence, it is evident that by introducing edge-fixed constraints, the MM distance for all surface configurations is significantly reduced to the range of 2.30–2.38 Å, with an average of approximately 2.34 Å. Compared to the planar configuration, this reduction is approximately 10%. This significant geometric distortion provides a direct structural driving force for subsequent electronic structure rearrangement and catalytic performance modulation. The optimized surface configurations are shown below. Figure 2 As shown.

[0141] Example 2: Calculation of the free energy of the entire reaction pathway for urea production using the coupled CO2RR and NORR reaction.

[0142] Based on the surface configuration optimized in Example 1, this embodiment systematically calculates and analyzes the free energy changes of each elementary step in the CO2RR and NORR paths.

[0143] 2.1 Total Reaction Pathway Assumption

[0144] The overall reaction formula for the electrocatalytic coupling of CO2 and NO to synthesize urea is:

[0145] 2NO + CO2 + 8H + + 8e - → CO(NH2)2 + 2H2O

[0146] This reaction is a coupling of the NORR and CO2RR pathways. Based on DFT calculations, the following key elementary steps are identified:

[0147] NORR branch (right end, generates *NH intermediate):

[0148] (1) NO adsorption: * + NO(g) → NO

[0149] (2) First protonation: NO + H + + e - → HNO

[0150] (3) Second protonation: HNO + H + + e - → *HNOH

[0151] (4) NO bond breaking and dehydration: *HNOH + H + + e - → *NH + H2O

[0152] CO2RR branch (left end, generates *CO intermediate):

[0153] (5) CO2 adsorption: * + CO2(g) → CO2

[0154] (6) First protonation: CO2 + H + + e - → COOH

[0155] (7) Second protonation and dehydration: COOH + H + + e - → *CO + H2O

[0156] CN coupling branch (middle, generating urea):

[0157] (8) CN coupling: *CO + NH → CONH

[0158] (9) Hydrogenation of CONH: CONH + H + + e - → CONH2

[0159] (10) Hydrogenation of CONH2: *CONH2 + H + + e - → NH2CONH

[0160] (11) Hydrogenation of NH2CONH: *NH2CONH + H + + e - → NH2CONH2 (urea)

[0161] (12) Urea desorption: NH2CONH2→ * + CO(NH2)2(g)

[0162] 2.2 Adsorption Configuration and Energy Calculation

[0163] On the four optimized surface configurations M1-M2-Pc, the aforementioned intermediates were adsorbed onto Fe or Co sites, respectively. For asymmetric configurations (Co-Fe-Pc and Fe-Co-Pc), two sites were tested, and the lower energy was selected. Structural optimization was performed on each adsorption configuration using the same parameters as in Example 1. After optimization, static self-consistent calculations were performed to obtain the precise energy.

[0164] 2.3 Total Energy Analysis of the System for Each Intermediate

[0165] The rate-determining step for Co-Fe-Pc is the *CO2→*COOH step at the CO2RR end, with an energy barrier of +0.363 eV; the rate-determining step for Co-Co-Pc is the *NO→*NHO step at the NORR end, with an energy barrier of +0.427 eV; the rate-determining step for Fe-Fe-Pc is the *NHOH→*NH step at the NORR end, with an energy barrier of +0.645 eV; and the rate-determining step for Fe-Co-Pc is the *CO2→*COOH step at the CO2RR end, with an energy barrier of +0.767 eV.

[0166] Based on DFT calculations and using rate-determining step energy barrier, CN coupling driving force, and intermediate coverage balance as evaluation criteria, the overall performance of the four catalysts is ranked as follows: Co-Fe-Pc > Co-Co-Pc > Fe-Fe-Pc > Fe-Co-Pc.

[0167] In summary, this invention systematically investigated the catalytic performance of surface-mounted diatomic phthalocyanines (Co-Co-Pc, Co-Fe-Pc, Fe-Co-Pc, Fe-Fe-Pc) with a confinement distance of 2.35 Å in the electrocatalytic coupling of CO2 and NO to synthesize urea using density functional theory. The study shows that surface strain-induced bimetallic convergence transforms the CN coupling step from a kinetic bottleneck of planar structures into a thermodynamically spontaneous process, with the rate-determining step shifting to *CO formation at the CO2RR end or *NO bond breaking at the NORR end. This invention provides theoretical guidance and a screening paradigm for the rational design of high-performance non-noble metal urea electrocatalysts.

Claims

1. A method for screening curved diatomic phthalocyanine electrocatalysts, characterized in that, Includes the following steps: Step 1: Construct a diatomic phthalocyanine molecular model with gradient curvature, wherein the model is M1-M2-Pc, and M1 and M2 are independently selected from Co or Fe. Geometric constraints are applied by fixing the Cartesian coordinates of the edge hydrogen atoms, while the internal carbon, nitrogen and metal atoms are relaxed without constraints with full degrees of freedom. Since the positions of the edge hydrogen atoms are locked, the internal atoms cannot extend outward in the process of tending to the lowest energy. The molecular skeleton is forced to arch in the Z-axis direction perpendicular to the molecular plane. This accumulation of internal stress caused by the fixed boundary conditions eventually leads to the natural contraction of the bimetallic center spacing from 3.4 Å in the plane to about 2.6 Å, thereby forming a three-dimensional catalytic configuration with significant curvature strain effect. Step 2: Based on the first-principles calculation method of density functional theory, the geometric structure of the constructed surface M1-M2-Pc model is optimized to obtain the ground state stable structure with the lowest energy. Step 3: Calculate the adsorption free energy of key intermediates in the CO2 reduction and NO reduction pathways at the optimized curved diatomic sites, and calculate the Gibbs free energy changes for each elementary step. The key intermediates include *CO2, *COOH, and CO in the CO2 reduction pathway, and NO, *NHO, HNOH, and NH in the NO reduction pathway; Step 4: Calculate the adsorption free energy of the key CN coupling intermediates CONH and NHCONH, and draw the Gibbs free energy step diagram of the entire reaction path from the initial reactants to the final product urea. Step 5: Extract the rate-determining step energy barrier, CN coupling driving force, and side reaction competition index based on the Gibbs free energy step diagram, and comprehensively screen out the optimal catalyst configuration; Step 6: Perform electronic structure analysis on the selected optimal catalyst configuration, including density of states calculation, differential charge density analysis and Bader charge analysis, to reveal the intrinsic physicochemical mechanism of enhanced catalytic activity.

2. The method according to claim 1, characterized in that, The construction of the diatomic phthalocyanine molecular model with gradient curvature in step 1 specifically includes: Step 1.1: Construct an M2-Pc structure with D4h symmetry, which consists of four isoindole rings connected by two methyltriamine units, creating a central cavity capable of accommodating two metal atoms. Two transition metal atoms, Co or Fe, are embedded in the central cavity, forming four configurations: Co-Co-Pc, Co-Fe-Pc, Fe-Co-Pc, and Fe-Fe-Pc. Step 1.2: By fixing the Cartesian coordinates of the 12 outermost edge hydrogen atoms of phthalocyanine, the 4 hydrogen atoms close to the inside of the catalyst do not need to be fixed, and the C, N and transition metal atoms inside are relaxed with full degrees of freedom to simulate the bending stress generated by the confinement of carbon support or molecular stacking, thereby shortening the bimetallic spacing and forming a non-planar curved surface structure.

3. The method according to claim 1, characterized in that, In step 2, the first principle calculation parameters are set as follows: Using Device Studio software, the electronic exchange correlation functional adopts GGA-PBE; The plane wave cutoff energy is set to 520 eV; K-point sampling uses 1×1×1 Gamma points; The convergence criterion for electronic self-consistent iteration is an energy difference of less than 10. -5 eV; The convergence criterion for ion relaxation is that the atomic force is less than 0.02 eV / Å; Grimme van der Waals correction was performed using the DFT-D3 method. Spin polarization calculations were performed on Fe and Co atoms, and initial magnetic moments were set.

4. The method according to claim 1, characterized in that, The formula for calculating the Gibbs free energy mentioned in steps 3 and 4 is as follows: For the reaction step *A + H + + e - → *AH: ΔG = E_(AH) - E_(A) - 1 / 2·E_H2 For the reaction step *A + B → *AB: ΔG = E_(AB) - E_(A) - E_(B) In the formula, E_(A), E_(AH), and E_(*AB) are the total energy of the system in each adsorption state, respectively; E_(B) is the energy of isolated reactant B.

5. The method according to claim 1, characterized in that, The criteria for comprehensive screening of catalyst performance in step 5 include: (1) Rate-determining step energy barrier: Take the maximum positive value max(ΔG1, ΔG2, ..., ΔG) of the Gibbs free energy change of each elementary step in the entire reaction path. n The value directly determines the minimum thermodynamic overpotential required for the catalytic reaction; the smaller the value, the higher the catalytic activity and the lower the energy consumption. (2) CN coupling driving force: Calculate the Gibbs free energy change ΔG_C-N of the key coupling step *CO + *NH → *CONH to determine whether the coupling step is thermodynamically spontaneous. The more negative the value, the stronger the coupling driving force, and the more favorable it is for urea formation.

6. The method according to claim 5, characterized in that, The screening also includes: when the difference in the velocity step energy barrier between the two configurations is less than a preset threshold, the absolute value of the CN coupling driving force ΔG_C-N is used as a secondary screening criterion.

7. A curved diatomic phthalocyanine catalyst obtained by screening according to any one of claims 1-6, characterized in that, The catalyst has a non-planar curved three-dimensional structure, and the general structural formula of the catalyst is M1-M2-Pc, wherein M1 and M2 are independently selected from Co or Fe, and the metal center distance between M1 and M2 is 2.35 Å, and the metal combination is Co-Co, Fe-Co, Co-Fe or Fe-Fe.

8. The application of the curved diatomic phthalocyanine catalyst according to claim 7 in the electrocatalytic synthesis of urea, characterized in that, The application conditions are as follows: in a CO2-saturated NO gas or nitrate electrolyte, the electrode loaded with the catalyst is used as the working electrode, and a cathode potential of -0.4 V to -1.0 V relative to the reversible hydrogen electrode is applied.

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