A catalyst of lattice-confined iridium single atom and cluster coupling and a preparation method thereof

Abstract

The application relates to the technical field of catalysts, and particularly discloses a catalyst with lattice-confined iridium single atoms and cluster coupling and a preparation method.The catalyst takes flower-shaped hierarchical molybdenum dioxide with a multi-stage pore structure and an oxygen vacancy structure as a carrier, so that iridium single atoms and iridium clusters coexist and form a coupling active structure.In the preparation, a molybdenum-based organic precursor powder is obtained first, the flower-shaped molybdenum dioxide carrier is formed through heat treatment, then the carrier is mixed and dispersed with an iridium precursor salt, and annealing treatment is carried out in an inert atmosphere to obtain the target catalyst.The catalyst can be used as a cathode catalyst for alkaline electrolytic water hydrogen evolution reaction, is favorable for improving the dispersion degree and structural stability of iridium active species, promoting water molecule activation and hydrogen intermediate conversion, and has good hydrogen evolution activity and operation stability.

Description

Technical Field

[0001] This invention relates to the fields of electrocatalytic functional materials and hydrogen energy conversion technology. More specifically, this invention relates to a catalyst with lattice-confined iridium single atoms and cluster coupling and its preparation method. Background Technology

[0002] Hydrogen possesses the significant advantages of being clean and having zero carbon emissions, making it an ideal alternative energy source to fossil fuels. Green hydrogen can be directly produced by using intermittent electricity from wind and solar power to drive water electrolysis. This cutting-edge technology has enormous potential for large-scale application and can provide crucial support for alleviating the energy crisis and mitigating global warming. Compared to the acidic hydrogen evolution reaction (HER), the alkaline hydrogen evolution reaction has attracted widespread attention due to its milder electrolyte corrosivity and higher system stability. However, the concentration of free hydrogen protons is lower in an alkaline environment, leading to challenges in the water splitting process (H₂O + e⁻). - →H * +OH - The need to overcome additional energy barriers results in catalytic kinetics performance far inferior to that of acidic electrolyte systems. Even commercial platinum-carbon (Pt / C) catalysts exhibit significantly lower intrinsic kinetic activity for the hydrogen evolution reaction in alkaline systems compared to acidic systems. Therefore, developing catalysts with both excellent activity and long-term stability is a crucial bottleneck that urgently needs to be overcome in the study of alkaline hydrogen evolution reactions.

[0003] Iridium (Ir) and platinum (Pt) share similar face-centered cubic (fcc) crystal structures and similar d-band electronic configurations, and both possess intrinsically similar hydrogen adsorption energies, appearing near their peak values ​​in the hydrogen evolution reaction volcano diagram. However, despite their structural and electronic similarities, iridium-based catalysts generally exhibit weaker kinetics under alkaline conditions. In alkaline systems, the water splitting step on the iridium surface exhibits relatively slow kinetics, making it more likely to become the rate-determining step compared to platinum, further widening the activity gap between iridium and platinum in the alkaline hydrogen evolution reaction. Therefore, it is necessary to rationally design and prepare iridium-based electrocatalysts with high intrinsic reaction kinetics.

[0004] Hybrid structures composed of single atoms and clusters can reduce the loading of noble metals while enhancing the intrinsic catalytic performance of active sites, and have become a research hotspot in the field of electrocatalysis. Previous studies have confirmed that the electronic structures of pure single-atom materials or pure cluster materials are relatively simple, with limited tunable ranges for d-band centers. In contrast, electron transfer and band coupling can occur between single atoms and clusters, enabling precise control of d-band centers and accelerating reaction kinetics. Simultaneously, single atoms and clusters require suitable supports to construct confined environments, inhibiting the migration, aggregation, and shedding of active species, thereby maintaining excellent catalytic performance. Molybdenum-based electrocatalysts possess diverse d-orbital configurations and easily tunable electronic structures, making them suitable for preparing high-performance electrocatalysts. Among various molybdenum-based materials, molybdenum dioxide has a surface rich in oxygen vacancies, which can not only effectively anchor single atoms and clusters but also generate strong adsorption and polarization of water molecules, significantly reducing the energy barrier for water dissociation reactions under alkaline conditions. Therefore, developing a catalyst with high-density Ir active sites on a molybdenum dioxide substrate to achieve efficient electrocatalytic hydrogen evolution is of great significance. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of existing technologies, this invention provides a lattice-confined iridium single-atom and cluster coupling catalyst and its preparation method. Using flower-like hierarchical MoO2 as a support, multi-level channels and oxygen vacancies are utilized to anchor Ir single atoms and Ir clusters, constructing a coupled active structure where the two coexist. This improves the dispersibility and stability of Ir active species and enhances water molecule activation and hydrogen intermediate conversion, thereby solving the problems of low atom utilization, easy aggregation, and sluggish alkaline hydrogen evolution kinetics in iridium-based catalysts.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A lattice-confined catalyst coupling iridium single atoms and clusters, the catalyst comprising a flower-like hierarchical MoO2 support and Ir active species supported on the flower-like hierarchical MoO2 support, the Ir active species comprising Ir single atoms and Ir clusters, the Ir single atoms and the Ir clusters coexisting in the flower-like hierarchical MoO2 support.

[0007] As a further embodiment of the present invention, the flower-like hierarchical MoO2 support has a multi-level pore structure and an oxygen vacancy structure, and the Ir single atoms and the Ir clusters are anchored to the flower-like hierarchical MoO2 support.

[0008] A method for preparing a catalyst in which lattice-confined iridium single atoms and clusters are coupled includes the following steps: Step 1: Prepare Mo-based organic precursor powder; Step 2: Heat-treat the Mo-based organic precursor powder to obtain a flower-like MoO2 support; Step 3: Mix and disperse the flower-like MoO2 support with the iridium precursor salt to obtain the iridium-loaded precursor; Step four: The iridium-supported precursor is annealed in an inert atmosphere to obtain a catalyst in which lattice-confined iridium single atoms and clusters are coupled.

[0009] As a further embodiment of the present invention, step one includes mixing, reacting, separating, washing, drying, and grinding to obtain the Mo-based organic precursor powder.

[0010] As a further embodiment of the present invention, the heating rate of the annealing treatment in step four is 2℃ / min, and the holding time is 2h.

[0011] Application of a catalyst in which lattice-confined iridium single atoms and clusters are coupled.

[0012] As a further aspect of the present invention, a catalyst with lattice-confined iridium single atoms and clusters coupled together is used as a cathode catalyst for the alkaline water electrolysis hydrogen evolution reaction.

[0013] Compared with the prior art, the beneficial effects of the present invention, which describes a lattice-confined iridium single-atom and cluster coupling catalyst and its preparation method, are as follows: This invention employs a flower-like hierarchical MoO2 support with a multi-level porous structure and oxygen vacancy structure. Characterization using transmission electron microscopy (TEM), high-resolution TEM, and high-angle annular dark-field scanning TEM revealed that Ir single atoms and Ir clusters are uniformly dispersed and anchored on the flower-like hierarchical MoO2 support, forming a coupling interface between Ir single atoms, Ir clusters, and the support. No significant large-area aggregation was observed, and the original flower-like hierarchical porous crystal structure was not significantly disrupted. Compared to existing catalysts where Ir active species are prone to migration and aggregation, the hierarchical flower-like structure provides more anchoring sites and mass transfer channels, which is beneficial for improving the utilization rate of noble metal atoms and providing a stable structural substrate for constructing the coupled catalytic interface.

[0014] This invention constructs a coupled structure in which Ir single atoms and Ir clusters coexist on the same flower-like hierarchical MoO2 support. Electrochemical testing results show that the catalyst prepared by this invention exhibits rapid alkaline hydrogen evolution reaction kinetics and is beneficial for the activation of interfacial water molecules. Compared with pure single-atom samples and pure cluster samples, the coexistence structure of Ir single atoms and Ir clusters is beneficial for balancing water molecule activation and hydrogen intermediate desorption processes, resulting in a catalyst with better alkaline hydrogen evolution activity and long-term operational stability.

[0015] This invention constructs a coupled structure of Ir single atoms and Ir clusters within a lattice confinement, regulating the interfacial electronic microenvironment, which facilitates the formation of a synergistic catalytic pathway and improves the Volmer step of water splitting and the hydrogen desorption process. Compared with existing iridium-based catalysts, this coupled structure helps alleviate the bottleneck problems of traditional iridium-based catalysts, such as low noble metal utilization, high water dissociation energy barrier, sluggish hydrogen evolution kinetics, high noble metal cost, and easy agglomeration and deactivation over long periods. The resulting catalyst exhibits higher atom utilization, faster reaction kinetics, and better stability. Attached Figure Description

[0016] Figure 1 The MoO2 support and MoO2-Ir in Example 1 SA&Cluster Microstructure diagram of the catalyst.

[0017] Figure 2 The images show the X-ray diffraction patterns of each catalyst sample in Example 1.

[0018] Figure 3 The graph shows the test results of the alkaline hydrogen evolution performance of each catalyst sample in Example 1.

[0019] Figure 4 This is a diagram showing the differential charge density and reaction energy barrier of the hydrogen evolution reaction for different catalytic systems.

[0020] Figure 5 This is a schematic diagram illustrating the construction of a coupled structure of Ir single atoms and Ir clusters confined within a MoO2 lattice.

[0021] Among them, Figure 1 middle, Figure 1 Image a shows a transmission electron microscope image of the flower-like hierarchical MoO2 support. Figure 1 Image b is a high-resolution transmission electron microscope image of the flower-like hierarchical MoO2 support. Figure 1 c represents MoO2-Ir SA&Cluster High-angle annular dark-field scanning transmission electron microscope image of the catalyst. Figure 1 d represents MoO2-Ir SA&Cluster High-angle annular dark-field scanning transmission electron microscope image of the catalyst from another field of view; Figure 3 In the figure, 'a' represents the hydrogen evolution polarization curve of each catalyst sample; Figure 3 In the figure, b represents the Tafel curve of each catalyst sample; Figure 3 In the figure, c represents the conversion frequency curves of each catalyst sample at different overpotentials; Figure 3 In the figure, d represents a comparison of the mass activities of each catalyst sample; Figure 3 e represents MoO2-Ir SA&Cluster Stability test curves of the catalyst after 200 hours of continuous operation; Figure 4 middle, Figure 4 In this context, 'a' represents MoO2-Ir.SA MoO2-Ir Cluster and MoO2-Ir SA&Cluster Differential charge density plot of the system; Figure 4 b represents MoO2 or MoO2-Ir SA MoO2-Ir Cluster and MoO2-Ir SA&Cluster The graph showing the change in free energy of the hydrogen evolution reaction in the system. Detailed Implementation

[0022] The technical solutions of this embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0023] Example 1

[0024] This embodiment provides a lattice-confined catalyst coupling iridium single atoms and clusters. The catalyst comprises a flower-like hierarchical MoO2 support and Ir active species supported on the flower-like hierarchical MoO2 support. The Ir active species include Ir single atoms and Ir clusters, which coexist within the flower-like hierarchical MoO2 support. The flower-like hierarchical MoO2 support has a hierarchical porous structure and oxygen vacancy structure, and the Ir single atoms and Ir clusters are anchored to the flower-like hierarchical MoO2 support.

[0025] Unless otherwise specified, all raw materials and reagents used in this application are commercially available. The raw materials used in the preparation of the examples and their descriptions are as follows:

[0026] The preparation method of the lattice-confined iridium single atom and cluster coupled catalyst includes steps one to four.

[0027] Step 1: Preparation of Mo-based organic precursor powder. Specifically, 1.2 g of ammonium heptamolybdate tetrahydrate was added to a mixed solvent consisting of 40 mL of deionized water and 74 mL of anhydrous ethanol, dispersing the ammonium heptamolybdate tetrahydrate in the mixed solvent; then 2 mL of 28% ammonia solution was added and stirred for 10 min, followed by the addition of 0.8 g of dopamine hydrochloride, and stirring was continued for 30 min. The resulting mixture was then placed on a magnetic stirrer and stirred for another 10 h at room temperature to obtain a brown precursor solution.

[0028] The brown precursor solution was centrifuged and washed, then freeze-dried. The resulting solid was collected and ground thoroughly in a mortar to obtain Mo-based organic precursor powder.

[0029] Step two involves heat-treating the Mo-based organic precursor powder to obtain a flower-like hierarchical MoO2 support. Specifically, the Mo-based organic precursor powder obtained in step one is placed in a tube furnace and heat-treated at 800°C under an argon atmosphere for 2 hours to obtain MoO2 powder in the form of a flower-like black powder.

[0030] The obtained MoO2 powder was washed and purified with 300 mL of deionized water, followed by centrifugation, washing, and freeze-drying to obtain a flower-like hierarchical MoO2 support. The resulting flower-like hierarchical MoO2 support possesses a flower-like hierarchical structure, a multi-level porous structure, and an oxygen vacancy structure, making it suitable for loading Ir active species.

[0031] Step 3: The flower-like graded MoO2 support is mixed and dispersed with the iridium precursor salt to obtain the iridium-loaded precursor. Specifically, 31 mg of the flower-like graded MoO2 support obtained in Step 2 is weighed, and the flower-like graded MoO2 support is mixed with the corresponding mass of iridium acetylacetone. 22 mL of deionized water is added for ultrasonic dispersion to ensure uniform dispersion of the flower-like graded MoO2 support and iridium acetylacetone in the deionized water. The resulting dispersion is then freeze-dried to obtain the iridium-loaded precursor.

[0032] By adjusting the amount of iridium acetylacetone added, specifically to: 0.5% (40 mg MoO2 + 0.4 mg iridium acetylacetone), 0.75% (40 mg MoO2 + 0.6 mg iridium acetylacetone), and 1.0% (40 mg MoO2 + 0.8 mg iridium acetylacetone), MoO2-Ir was prepared respectively. SA Precursor, MoO2-Ir SA&Cluster Precursors and MoO2-Ir Cluster Precursor.

[0033] Step four involves annealing the iridium-supported precursor under an inert atmosphere to obtain a catalyst with lattice-confined iridium single atoms and cluster coupling. Specifically, the iridium-supported precursor obtained in step three is placed in a tube furnace and heated to 520°C at a heating rate of 2°C / min under an argon atmosphere, and held at 520°C for 2 hours to complete the annealing treatment of the iridium-supported precursor, thereby obtaining a MoO2-Ir series alkaline hydrogen evolution electrocatalyst.

[0034] The iridium-supported precursors prepared with different amounts of acetylacetone-iridium in step three were annealed to obtain MoO2-Ir. SA Catalyst, MoO2-Ir SA&Cluster Catalyst and MoO2-IrCluster Catalyst. Among them, MoO2-Ir SA&Cluster The catalyst includes a flower-like hierarchical MoO2 support and Ir active species supported on the flower-like hierarchical MoO2 support. The Ir active species include Ir single atoms and Ir clusters. The Ir single atoms and Ir clusters coexist and are anchored to the flower-like hierarchical MoO2 support, resulting in a lattice-confined iridium single atom and cluster coupling catalyst of this embodiment.

[0035] To characterize the microstructure of the material obtained in this embodiment, transmission electron microscopy and high-resolution transmission electron microscopy were used to observe the flower-like hierarchical MoO2 support obtained in step two. The results are as follows: Figure 1 a and Figure 1 As shown in b; the MoO2-Ir obtained in step four was examined using a high-angle annular dark-field scanning transmission electron microscope. SA&Cluster The catalyst was observed, and the results are as follows: Figure 1 c and Figure 1 As shown in d.

[0036] Depend on Figure 1 It can be seen that the MoO2 support obtained in step two has a flower-like hierarchical structure and forms multi-level channels; the MoO2-Ir obtained in step four SA&Cluster In the catalyst, Ir single atoms and Ir clusters are uniformly anchored within the lattice of the flower-like hierarchical MoO2 support. The Ir active species remain dispersed, without large-area aggregation, and the original flower-like hierarchical porous crystal structure of the MoO2 support is not disrupted. Thus, a structure in which Ir single atoms and Ir clusters coexist on the same flower-like hierarchical MoO2 support is formed, providing a structural basis for constructing the catalytic interface between Ir single atoms, Ir clusters, and the flower-like hierarchical MoO2 support.

[0037] Further X-ray diffraction was used to examine the MoO2 support and MoO2-Ir obtained in this embodiment. SA Catalyst, MoO2-Ir SA&Cluster Catalyst and MoO2-Ir Cluster The catalyst was characterized by its crystal phase, and the resulting X-ray diffraction pattern is shown below. Figure 2 As shown. By Figure 2 It is evident that after introducing Ir single atoms, Ir single atoms and Ir clusters coexisting structures, and Ir clusters, the crystal phase of the flower-like hierarchical MoO2 support remains stable, and no obvious iridium diffraction peaks were observed, indicating that the Ir active species have a high degree of dispersion on the flower-like hierarchical MoO2 support.

[0038] The MoO2 carrier and MoO2-Ir obtained in this embodiment are used. SA Catalyst, MoO2-Ir SA&Cluster Catalyst and MoO2-Ir ClusterThe catalyst was used for the alkaline water electrolysis hydrogen evolution reaction, and its hydrogen evolution performance was tested using a commercially available 20wt% Pt / C catalyst as a control catalyst. The test results are as follows: Figure 3 As shown.

[0039] Depend on Figure 3 The current response results shown in 'a' are and Figure 3 As shown in the Tafel slope results (b), MoO2-Ir SA&Cluster The catalyst exhibits a high current response and a small Tafel slope, indicating the coexistence of Ir single atoms and Ir clusters in MoO2-Ir. SA&Cluster The catalyst exhibits high basic hydrogen evolution catalytic activity and fast reaction kinetics. Figure 3 As can be seen from c in the figure, at different working potentials, MoO2-Ir SA&Cluster The catalysts all maintained a high TOF; Figure 3 From d, we can know that MoO2-Ir SA&Cluster The catalyst achieves maximum mass activity at a potential of 100 mV.

[0040] In a 1 mol / L KOH alkaline electrolyte, MoO2-Ir SA&Cluster Catalyst reaches 100 mA·cm -2 The required overpotential for the current density is 132 mV; at a potential of 100 mV, the MoO2-Ir SA&Cluster The noble metal mass activity of the catalyst reaches 16.4 A·mgIr. -1 Under 25mV conditions, the MoO2-Ir SA&Cluster The catalyst achieved a conversion frequency of 2.47 H₂·s⁻¹. -1 Compared to MoO2-Ir SA Catalyst, MoO2-Ir Cluster Catalysts and commercial 20wt% Pt / C catalysts, the MoO2-Ir SA&Cluster The catalyst exhibits high overall alkaline hydrogen evolution performance.

[0041] like Figure 3 As shown in e, at 10 mA·cm -2 Under current conditions, MoO2-Ir SA&Cluster The catalyst underwent a 200-hour stability test, during which no significant attenuation of catalytic performance was observed, indicating that the lattice-confined iridium single-atom and cluster coupled catalyst prepared in this embodiment has long-term operational stability.

[0042] Figure 4 Demonstrating MoO2-Ir SA MoO2-Ir Cluster and MoO2-Ir SA&ClusterThe differential charge density of the system and MoO2,MoO2-Ir SA MoO2-Ir Cluster and MoO2-Ir SA&Cluster The reaction energy barrier for the complete hydrogen evolution reaction in the model. Figure 4 From the differential charge density results shown in a, we can see that the MoO2-Ir shown in (1) in a SA In the model, the amount of electrons transferred from the Ir single atom to MoO2 is the largest, as shown in (2) of a, MoO2-Ir Cluster In the model, the amount of electrons transferred from the Ir cluster to MoO2 is the smallest, as shown in (3) of a, MoO2-Ir SA&Cluster The charge transfer degree of the model is between that of MoO2-Ir SA Model and MoO2-Ir Cluster Between the models, an interfacial electronic microenvironment is formed, which is between a single-atom system and a cluster system.

[0043] Depend on Figure 4 The calculated reaction free energy shown in b indicates that MoO2-Ir SA&Cluster The energy barrier for the water dissociation step in the alkaline hydrogen evolution reaction in the model is 0.36 eV, which is lower than that of the MoO2 model and the MoO2-Ir model. SA Model and MoO2-Ir Cluster The energy barrier corresponding to the model. The coexistence structure of Ir single atoms and Ir clusters can balance the activation process of water molecules and the desorption process of hydrogen intermediates, thus achieving a balance between the electronic structure of MoO2-Ir. SA&Cluster The kinetics of the alkaline hydrogen evolution reaction of the catalyst are explained.

[0044] The MoO2-Ir obtained in this embodiment SA&Cluster The catalyst can be used as a cathode catalyst in the alkaline water electrolysis hydrogen evolution reaction to catalyze the dissociation of water molecules and the generation of hydrogen in the alkaline electrolyte.

[0045] Furthermore, when further adjustment of catalyst interface defects is required, the catalyst obtained in step four can be placed together with an appropriate amount of melamine in a tube furnace, annealed at 700°C under an argon atmosphere and held for 2 hours to obtain a nitrogen-modified MoO2-Ir catalyst.

[0046] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0047] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A catalyst for lattice-confined coupling of iridium single atoms and clusters, characterized in that, The catalyst comprises a flower-like hierarchical MoO2 support and an iridium single-atom and cluster coupling structure anchored on the flower-like hierarchical MoO2 support; the iridium single-atom and cluster coupling structure comprises Ir single atoms and Ir clusters, the Ir single atoms and Ir clusters being anchored on the flower-like hierarchical MoO2 support; the flower-like hierarchical MoO2 support has a multi-level pore structure and an oxygen vacancy structure.

2. The catalyst for lattice-confined coupling of iridium single atoms and clusters according to claim 1, characterized in that, Catalysts with lattice-confined iridium single atoms and clusters coupled together can serve as cathode catalysts for the alkaline water electrolysis hydrogen evolution reaction.

3. The catalyst for lattice-confined coupling of iridium single atoms and clusters according to claim 1, characterized in that, Catalysts with lattice-confined iridium single-atom and cluster coupling achieve 100 mA·cm⁻¹ -2 The required overpotential for the current density is 132mV.

4. The catalyst for lattice-confined coupling of iridium single atoms and clusters according to claim 3, characterized in that, Simultaneously reaching 16.4 A·mgIr -1 High activity, 2.47H2·s -1 The conversion frequency.

5. The method for preparing a catalyst with lattice-confined iridium single atoms and cluster coupling according to claim 1, characterized in that, Includes the following steps: Step 1: Prepare Mo-based organic precursor powder; Step 2: Heat-treat the Mo-based organic precursor powder to obtain a flower-like MoO2 support; Step 3: Mix and disperse the flower-like MoO2 support with the iridium precursor salt to obtain the iridium-loaded precursor; Step four: The iridium-supported precursor is annealed in an inert atmosphere to obtain a catalyst in which lattice-confined iridium single atoms and clusters are coupled.

6. The method for preparing a catalyst with lattice-confined iridium single atoms and cluster coupling according to claim 5, characterized in that, Step one includes mixing, reacting, separating, washing, drying, and grinding to obtain the Mo-based organic precursor powder.

7. The method for preparing a catalyst with lattice-confined iridium single atoms and cluster coupling according to claim 5, characterized in that, The annealing process in step four involves a heating rate of 2°C / min and a holding time of 2 hours.

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