A transition metal-doped OER catalyst, design method and application

Abstract

The present invention provides a transition metal-doped OER catalyst, design method and application, which utilizes the first principle molecular dynamics method to construct a stable structure of a solution layer and a transition metal oxyhydroxide, adds an angular structure on the basis of constructing a boundary structure on a cross section, and creatively creates an OER catalyst with a high active site in a low coordination environment, which can have good OER catalytic performance while being stable in an alkaline environment.

Description

Technical Field

[0001] The present invention relates to the technical field of computational material chemistry, and in particular to a transition metal-doped OER catalyst, a design method and an application thereof. Background Art

[0002] Nowadays, due to the consumption of traditional fossil fuels and the emission of large amounts of greenhouse gases, energy and environmental issues have attracted more and more attention. Due to the advantages of hydrogen's high calorific value and pollution-free combustion, water decomposition to produce hydrogen as a clean alternative energy source provides a new idea to solve this problem. As one of the two half reactions of the water decomposition reaction, the oxygen evolution reaction (OER) will limit the overall efficiency of the water decomposition reaction due to the complex four-electron-proton coupling process. OER catalysts can reduce the reaction energy barrier and improve the OER catalytic performance, so it is very necessary to develop efficient OER catalysts.

[0003] So far, for OER catalysts, iridium oxide and ruthenium oxide are more efficient in acidic systems, but their abundance is too low and their prices are relatively high. In alkaline systems, it is found that transition metal hydroxide oxides can have relatively good stability in alkaline solutions and also have relatively good OER catalytic performance. However, so far, the catalytic mechanism and catalytic active sites are still unclear, which limits the preparation of OER catalysts in alkaline systems. Theoretical prediction has become an important means to study its catalytic mechanism. On the basis of understanding its mechanism, rational catalyst design can be further carried out. Summary of the invention

[0004] The purpose of the present invention is to provide a transition metal-doped OER catalyst, a design method and an application, and to construct a highly active and stable transition metal-doped OER catalyst in an alkaline system using the first principles of computer science.

[0005] Before introducing the core content of this plan, we first explain the professional terms that may be involved in the research methods of this plan:

[0006] Computational Materials Science is an emerging interdisciplinary subject that has developed rapidly in recent years. It aims to use modern high-speed computers to simulate the various physical and chemical properties of materials, deeply understand the various phenomena and characteristics of materials from microscopic to macroscopic scales, and make theoretical predictions on the structure and physical properties of materials, so as to achieve the purpose of designing new materials. Computational Materials Science mainly includes two aspects: on the one hand, computational simulation, that is, starting from experimental data, simulating the actual process by establishing mathematical models and numerical calculations; on the other hand, computer design of materials, that is, directly predicting or designing material structure and performance through theoretical models and calculations. This program uses computer science to study the catalytic mechanism and catalytic active sites of OER catalysts in alkaline environments to design a highly active OER catalyst.

[0007] The first principles method is a calculation method based on the theory of quantum mechanics. It only requires a few known parameters, such as the atomic fine structure constant, electron mass and charge, nuclear mass and charge, Planck constant and the speed of light. Based on the principles of interaction between nuclei and electrons and their basic laws of motion, it can directly solve the Schrödinger equation after multiple approximate processing to obtain (almost) all the ground state properties of the material.

[0008] Molecular dynamics (MD) is a computational method based on the statistical mechanics of classical physics. It analyzes the behavior of molecular motion by solving the potential function of intermolecular interaction and the equation of motion, simulates the dynamic evolution of the system, and gives the relationship between microscopic quantities (such as molecular coordinates and velocity) and macroscopic observable quantities (such as system temperature, pressure, heat capacity, etc.), thereby studying the equilibrium properties and mechanical properties of the composite system. It is an effective research method for studying phenomena such as fluid behavior inside materials and channel transport.

[0009] To achieve the above objectives, the present technical solution provides a method for designing a transition metal-doped OER catalyst, comprising the following steps:

[0010] The coordination structure of the transition metal oxyhydroxide and the ion layer of the alkaline solution is constructed by first principle molecular dynamics, and the coordination structure with low chemical potential energy is extracted, wherein the molecular formula of the transition metal oxyhydroxide is MOOH, and the metal ions and H2O in the alkaline solution respectively form coordination structures with the metal in the transition metal oxyhydroxide;

[0011] The coordination structure is processed by sectioning to construct a boundary structure of metal sites containing an unsaturated coordination environment, and a 0-MO corner structure is constructed on the boundary structure to obtain a modular unit of the catalyst reaction surface. The catalyst reaction surface and the bottom structure of other modular units are isolated by a vacuum layer to obtain a transition metal-doped OER catalyst.

[0012] It is worth noting that the OER catalyst obtained in this scheme is obtained by periodically arranging multiple designed module units, and the catalyst reaction surface of a single module unit and the bottom structure of the adjacent module unit are isolated by a vacuum layer.

[0013] In some embodiments, the transition metal in the horn structure is different from the metal in the transition metal oxyhydroxide.

[0014] In some embodiments, the transition metal can be selected from one or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, Ag, W, Ir, Pt and Au. In some embodiments, the transition metal is preferably Fe, followed by Rh, Cr, Mn and Mo.

[0015] It is worth mentioning that the catalytic mechanism and catalytic active sites of transition metal hydroxides in alkaline solutions are currently unknown. Therefore, this scheme constructs a reaction network based on the adsorption energy of key intermediates. On the basis of electrochemical rate control, it strictly calculates several different thermochemical reaction kinetic energy barriers related to the oxygen-oxygen (OO) bond formation mechanism, and then screens out the transition metal with the best performance.

[0016] In the step of "Using first-principles molecular dynamics to construct the coordination structure of transition metal hydroxide oxide and alkaline solution ion layer, and extracting the coordination structure with low chemical potential energy", the schematic diagram of the coordination structure is as follows Figure 1 As shown, M represents the metal of the transition metal hydroxide oxide, A represents the alkaline ion in the alkaline solution ion layer, H represents hydrogen, and O represents oxygen. This scheme takes A as a potassium ion as an example for explanation. At this time, the molecular formula of the coordination structure is [M3KO6·2H2O].

[0017] The base metal of the transition metal oxyhydroxide can be selected from transition metals such as Mn, Fe, Co, Ni, etc. Figure 1 The coordination structures shown simulate the real reaction conditions of transition metal oxyhydroxides in alkaline solutions.

[0018] In some embodiments, a first-principles molecular dynamics simulation of more than 15 picoseconds to obtain a stable potential energy basis is set as a screening condition, and several relatively stable structures with relatively low chemical potential energy are extracted. First-principles structural optimization calculations are performed on them, and the coordination structure with the most stable energy after optimization is selected for subsequent catalyst design.

[0019] This scheme is different from the planar structure of previous OER catalysts. This scheme innovatively proposes to construct a transition metal hydroxide oxide with a low coordination angle structure, thereby improving its stability while retaining its good OER catalytic performance.

[0020] like Figure 2 The figure shows the schematic diagram of the cross-section processed coordination structure. Figure 2 The upper part of the figure is the constructed boundary structure, and the lower part is the section direction; Figure 3 It is the cut-out boundary structure. Figure 3 The dotted line in the figure is the catalyst surface before the vacuum layer is added; Figure 4 This is a schematic diagram after the corner structure is constructed. Figure 4 The position indicated by the arrow is the transition metal with angular structure.

[0021] Specifically, in the step of "cutting the coordination structure to construct a boundary structure of a metal site containing an unsaturated coordination environment", the coordination structure is cut to expose the boundary structure of a metal site containing an unsaturated coordination environment, wherein the coordination of at least one metal site in the boundary structure is unsaturated.

[0022] In the step of "constructing a corner structure of 0-MO on the boundary structure to obtain a catalyst reaction surface", the corner structure and the unsaturated coordination environment in the boundary structure are coordinated to obtain a catalyst reaction surface. The corner structure has the effect of low coordination environment and low steric hindrance.

[0023] It is worth mentioning that the OER catalyst of this scheme is obtained by analyzing three different OO bond formation mechanisms, among which the OO bond formation mechanism is the water nucleophilic attack mechanism in the solution, the intramolecular adsorbed oxygen free radical OO bond coupling mechanism, and the intramolecular adsorbed oxygen free radical and lattice oxygen reaction mechanism.

[0024] Figure 5 This is a schematic diagram of the boundary structure obtained by isolating the catalyst reaction surface and another cut surface with a vacuum layer. Figure 5 The lower two layers of the structure in each periodic unit are the bottom structure, and the upper two layers are the catalyst reaction surface with added corner structures.

[0025] In a second aspect, the present scheme obtains a transition metal-doped OER catalyst constructed according to the above method.

[0026] Thirdly, the OER catalyst obtained in this scheme can be used to stably and efficiently catalyze the oxygen evolution reaction in the water decomposition reaction.

[0027] Compared with the existing technology, this technical solution utilizes the principle that transition metal oxides still have relatively good stability in alkaline solutions and have good OER catalytic performance. It uses the first-principles molecular dynamics method to construct a stable structure of the solution layer and transition metal hydroxide oxide, and adds an angular structure on the basis of the boundary structure constructed by the cross-section, creatively creating an OER catalyst with high active sites in a low coordination environment.

[0028] In addition, this scheme also proposes the formation mechanism of several key intermediates in the reaction process. By studying the formation mechanism of key intermediates, the key rate-determining steps can be predicted, the accuracy of the prediction can be improved, and the consumption of computing resources and the time cost of computing can be greatly reduced during the calculation process. It can realize the screening of transition metals and then select transition metal-doped OER catalysts with excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of transition metal oxyhydroxide dissolving in alkaline solution.

[0030] Figure 2 It is a schematic diagram of the cutting direction of the cross-section processing coordination structure.

[0031] Figure 3 It is a schematic diagram of the corner structure obtained by cutting.

[0032] Figure 4 It is a schematic diagram of building a corner structure on a corner structure.

[0033] Figure 5 It is a schematic diagram of the vacuum layer separating the catalyst surface and bottom structure.

[0034] Figure 6 This is a principle explanation of the mechanism of water nucleophilic attack.

[0035] Figure 7 This is a principle explanation of the O-O bond coupling mechanism of intramolecular adsorbed oxygen free radicals.

[0036] Figure 8 It is a principle explanation of the reaction mechanism of intramolecularly adsorbed oxygen radicals with lattice oxygen.

[0037] Fig. 9 The OER reaction performance of successfully synthesized NiOOH / NF, Mn-NiOOH / NF, Cr-NiOOH / NF, Mo-NiOOH / NF and Fe-NiOOH / NF in CV curves is compared.

[0038] Fig.10 Schematic diagram of OER test voltage under 35 hours of continuous electrolysis. DETAILED DESCRIPTION

[0039] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0040] This scheme provides a method for preparing a transition metal-doped OER catalyst, which constructs a stable structure of a solution layer and a transition metal oxyhydroxide by first-principles molecular dynamics, adds a corner structure on the basis of constructing an edge structure on a cut surface, and creates a highly active site with a low coordination environment for the first time. In addition, this scheme provides a key intermediate formation mechanism to realize the screening of transition metals to construct an efficient OER catalyst.

[0041] Before introducing how to screen out the preferred transition metal, this proposal first explains the research on the formation mechanism of key intermediates:

[0042] This scheme is to construct a reaction network based on the adsorption energy of key intermediates, strictly calculate several different thermochemical reaction kinetic energy barriers related to the oxygen-oxygen (OO) bond formation mechanism based on electrochemical rate control, and use the thermochemical reaction kinetic energy barriers as screening conditions to screen transition metals.

[0043] In the electrochemical step, the deprotonation of H2O, the deprotonation of OH* and the deprotonation of OOH* are mainly considered; in the thermochemical step, the formation energy barrier of the OO bond and the change of the reaction free energy are mainly considered; and the formation of the OO bond may involve multiple reaction pathways: such as the water nucleophilic attack mechanism (WNA) in the solution, the OO bond coupling mechanism of intramolecular adsorbed oxygen free radicals, and the reaction mechanism of intramolecular adsorbed oxygen free radicals with lattice oxygen, among which Figure 5 This is the process description of the water nucleophilic attack mechanism. Figure 6 This is a process description of the coupling mechanism of the intramolecular adsorption of oxygen free radicals OO bonds. Figure 7 It is a process description of the reaction mechanism of intramolecularly adsorbed oxygen radicals with lattice oxygen.

[0044] Example:

[0045] In this scheme, Ni00H is used as the transition metal hydroxide oxide, KOH is used as the alkaline solution ion layer, and different transition metals are selected to replace the transition metals in the corner structure to prepare the OER catalyst using the above method.

[0046] like Figure 7 As shown in the figure, in the analysis of the O-O bond coupling mechanism of intramolecular adsorbed oxygen free radicals, it was found that there were two electrochemical steps of OH* deprotonation, namely S2 to S3 and S3 to S4 processes, which have the largest overpotential; in the S4 to S5 process, the O-O bond coupling reaction of intramolecular adsorbed oxygen free radicals occurred, thus involving a thermochemical endothermic process and a kinetic reaction energy barrier related to the O-O bond coupling transition state. These three reaction processes are the key reaction steps identified.

[0047] A series of transition metals in the periodic table were selected to replace the M site in the corner structure, and the transition state reaction barriers of their two OH* deprotonation reactions and OO bond coupling processes were accurately calculated, and the data shown in Table 1 were obtained:

[0048] Table 1 Energy barriers of OO bond coupling reactions of different transition metals

[0049]

[0050] Priority is given to analyzing the electrochemical reaction steps of different transition metal components (S2 to S3 and S3 to S4 processes), and then analyzing the OO bond coupling reaction energy barrier under the standard that the electrochemical reaction free energy change is within 2.0eV. The smaller the reaction energy barrier, the better. Specifically, among the many transition metals tried, Cr, Mn, Fe, Mo, Ru, Rh and Ir were screened out from the electrochemical rate-controlling step. The electrochemical reaction free energy changes of these doped transition metals are all less than 2.0eV; among the candidate metals preliminarily screened, further screening of the reaction energy barrier showed that the best catalyst was Fe, followed by Rh, Mo, Mn and Cr. In order to verify the activity of the catalyst designed in this scheme, after actual experimental synthesis, it was found that the addition of a small amount of Fe to NiOOH-based materials can greatly improve their OER reaction activity in alkaline solutions.

[0051] Embodiment 2

[0052] In order to verify that the OER catalyst constructed in this scheme is more stable and has better catalytic performance than ordinary OER catalysts, the applicant conducted the following control experiments:

[0053] The NiOOH predicted by theoretical catalyst design is used as the substrate of transition metal hydroxide oxide, and a small amount of Fe, Cr, Mn or Mo is doped in it, and compared with the undoped NiOOH substrate, and the catalyst with the best catalytic activity is compared to illustrate the feasibility of the theoretical catalyst design framework of this scheme. Rh is not included in the actual synthesis reference due to its high price and low reserves. The specific scheme is as follows:

[0054] 1. Synthesis steps:

[0055] 1.5 mmol (0.436 g) Ni(NO3)2·6H2O, 0.3 mmol (0.121 g) Fe(NO3)3·9H2O, 12 mmol (0.72 g) CO(NH2)2 and 8 mmol (0.296 g) NH4F were dissolved in 30 mL deionized water solution, and then the mixed solution was transferred to a 50 mL reactor, and then the nickel foam (2×2 cm 2 ) was placed in it and reacted at 120°C for 12 hours. After the reaction was completed, the electrode was taken out, rinsed repeatedly with deionized water and ethanol, and dried to obtain a Fe-Ni(OH)2 / NF electrode.

[0056] The Fe-Ni(OH)2 / NF electrode prepared above was placed in a 10 mA cm -2 The Fe-NiOOH / NF electrode can be obtained by electrolysis at a constant current density of 0.5 h.

[0057] The preparation methods of NiOOH / NF, Mn-NiOOH / NF, Cr-NiOOH / NF, and Mo-NiOOH / NF electrodes were similar to those of Fe-NiOOH / NF electrodes. The only difference was that no Fe source was added during the hydrothermal synthesis or Fe(NO3)3·9H2O was replaced by equal amounts of Mn(COOH)2·4H2O (0.0735 g), Cr(NO3)3·9H2O (0.12 g), and (NH4)6Mo7O 24 ·4H2O (0.0726 g) was used instead.

[0058] 2. Electrochemical test:

[0059] The electrochemical tests were all conducted on a CHI 660E electrochemical workstation. At room temperature, the catalyst-modified NF was used as the working electrode, Hg / HgO was used as the reference electrode (0.098V vs. RHE, reversible hydrogen electrode), Pt mesh was used as the counter electrode, and the electrolyte was 1M KOH solution. Unless otherwise specified, all potentials in this chapter were converted to relative reversible hydrogen electrode. The conversion formula is as follows:

[0060] E RHE =E HgO / Hg +0.0592pH+0.098V

[0061] Before the electrochemical test, the working electrode synthesized above was charged at 10 mA cm -2 The electrolysis was carried out at a constant current density of 0.5 h, and then the OER performance was tested. The cyclic voltammetry (CV) curve can directly reflect the OER performance difference between different electrodes. In this test, the CV curve was obtained at 5 mV s -1The stability of the catalyst was mainly tested by constant current test, that is, at 10 mA cm -2 The voltage variation with time was observed at a current density of .

[0062] like Fig. 9 As shown in the figure, the OER reaction performance of successfully synthesized NiOOH / NF, Mn-NiOOH / NF, Cr-NiOOH / NF, Mo-NiOOH / NF and Fe-NiOOH / NF in CV curves is compared. It is obvious that at 10 mA cm -2 The voltages observed at the current density were 1.558V (Mn-NiOOH / NF), 1.530V (Cr-NiOOH / NF), 1.519V (Mo-NiOOH / NF) and 1.474V (Fe-NiOOH / NF). The corresponding overpotentials were 328mV, 300mV, 289mV and 244mV. NiOOH / NF was too inactive to reach 10mA within the tested 1.6V bias range. In summary, the activity of these doped catalysts is Fe>>Mo>Cr>Mn, which is basically consistent with our theoretical predictions. The best catalyst is Fe-NiOOH / NF.

[0063] In addition, to determine the stability of Fe-NiOOH / NF, we conducted a 10 mA cm -2 Long-term electrolysis test at constant current density. Fig.10 As shown in the figure, under 35 hours of continuous electrolysis, the catalyst can maintain a constant OER test voltage, indicating that it has good stability.

[0064] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for designing a transition metal-doped OER catalyst, characterized in that: The following steps are involved: First principles molecular dynamics are used to construct the coordination structure of a transition metal oxyhydroxide and an alkaline solution ion layer, and a coordination structure with low chemical potential energy is extracted, wherein the molecular formula of the transition metal oxyhydroxide is MOOH, and metal ions and H2O in the alkaline solution respectively form coordination structures with the metal in the transition metal oxyhydroxide; the coordination structure is sectioned to construct a boundary structure of a metal site containing an unsaturated coordination environment, a 0-MO corner structure is constructed on the boundary structure to obtain a catalyst reaction surface, and a vacuum layer is used to isolate the catalyst reaction surface and the bottom structure of another periodic structure section thereof to obtain a transition metal-doped OER catalyst.

2. The method for designing a transition metal-doped OER catalyst according to claim 1, characterized in that: The transition metal in the horn structure is different from the metal in the transition metal oxyhydroxide.

3. The design method of the transition metal-doped OER catalyst according to claim 1, characterized in that: The transition metal in the corner structure is selected from one or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, Ag, W, Ir, Pt and Au.

4. The method for designing a transition metal-doped OER catalyst according to claim 3, characterized in that: The transition metals are selected in the order of Fe, Rh, Mo, Mn and Cr.

5. The method for designing a transition metal-doped OER catalyst according to claim 1, characterized in that: The metal of the transition metal oxyhydroxide is selected from one of Mn, Fe, Co and Ni.

6. The method for designing a transition metal-doped OER catalyst according to claim 1, characterized in that: The corner structure is coordinated with the unsaturated coordination environment in the boundary structure to obtain a catalyst reaction surface, and the corner structure has a low coordination environment and low steric hindrance.

7. The method for designing a transition metal-doped OER catalyst according to claim 1, characterized in that: The results are obtained by analyzing three different OO bond formation mechanisms, including the nucleophilic attack mechanism of water in solution, the OO bond coupling mechanism of intramolecular adsorbed oxygen free radicals, and the reaction mechanism of intramolecular adsorbed oxygen free radicals with lattice oxygen.

8. A method for designing a transition metal-doped OER catalyst according to claim 1, characterized in that: The designed OER catalyst is applied to efficiently catalyze the oxygen evolution reaction in the water decomposition reaction.

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