Manganese oxide supported iridium monatomic catalyst, preparation method and electrocatalytic applications thereof

Abstract

The application discloses a manganese oxide supported iridium monatomic catalyst, which comprises a carrier manganese oxide and iridium supported on the carrier manganese oxide, the iridium is dispersed in the form of monatomic on the surface or the crystal lattice of the manganese oxide, and the loading amount of the iridium is 6wt%-8wt%. The synthesis of the manganese oxide carrier, the crystal phase regulation and the anchoring of the iridium monatomic can be simultaneously completed through one-step hydrothermal reaction, without step-by-step operation, so that the process flow is short, the operation is simple, and the application is suitable for large-scale production. Only by changing the mole ratio of citric acid and potassium permanganate, the selective switching of the crystal phase of the manganese oxide carrier between MnO2 and MnO(OH) can be realized in the same reaction system, and the deficiency that the whole synthesis system needs to be changed in the traditional method is overcome.

Description

Technical Field

[0001] This invention relates to a manganese oxide-supported iridium single-atom catalyst, its preparation method, and its electrocatalytic application, belonging to the field of environmental materials technology. Background Technology

[0002] With the rapid development of renewable energy, water electrolysis for hydrogen production has attracted widespread attention as a clean and efficient method. In the water electrolysis process, the oxygen evolution reaction (OER) at the anolyte involves a four-electron transfer process, which is kineticly slow and is a key factor limiting the efficiency of water electrolysis. Therefore, developing efficient and stable OER catalysts is of great significance. Currently, iridium-based materials are recognized as one of the best performing catalysts for acidic OER. However, under alkaline conditions, iridium-based catalysts still face problems such as insufficient activity and low utilization of precious metals. To reduce the amount of iridium used and improve atom utilization, loading iridium in single-atom form onto a suitable support has become a research hotspot in the field of electrocatalysis in recent years.

[0003] Manganese oxides (such as MnO2 and MnO(OH)) are widely used as supports for electrocatalysts due to their abundant valence states, good electrical conductivity, and excellent basic stability. In existing technologies, the preparation methods for manganese oxide-supported noble metal single-atom catalysts mainly fall into two categories. The first category is the stepwise synthesis method: first, a manganese oxide support with a specific crystalline phase is synthesized separately using hydrothermal methods, precipitation methods, or sol-gel methods, and then noble metal single atoms are loaded onto the support surface through impregnation, deposition precipitation, or atomic layer deposition. This type of method is cumbersome, time-consuming, and the subsequent loading process easily leads to noble metal agglomeration, making it difficult to achieve atomically uniform dispersion. For example, a preparation method for a supported noble metal single-atom catalyst (202111640946.0). The second category is the one-step co-reduction method: a manganese source, a noble metal precursor, and a reducing agent are mixed, and the support and noble metal are simultaneously generated and loaded through a one-step reaction. However, existing one-step methods often employ strong reducing agents (such as sodium borohydride and hydrazine hydrate) for rapid reduction, resulting in a violent reaction process that makes it difficult to finely control the crystal phase of manganese oxides. Furthermore, noble metals tend to form nanoparticles rather than single-atom dispersions. In addition, there are no reports in the current technology of achieving selective control of the crystal phase of manganese oxide supports in the same reaction system by simply adjusting the amount of reducing agent, and simultaneously obtaining high-load noble metal single-atom catalysts.

[0004] In summary, existing technologies suffer from at least the following drawbacks: The preparation process is complex, making it difficult to simultaneously control the crystal phase of the support and achieve atomic-level dispersion: Stepwise synthesis methods involve numerous steps and long cycles, and the subsequent loading process easily leads to noble metal agglomeration; while one-step methods simplify the process, existing systems cannot simultaneously achieve selective control of the support crystal phase and atomic-level dispersion of noble metals. There is a lack of synergistic control mechanisms for the support crystal phase and noble metal loading: In existing technologies, obtaining manganese oxide supports with different crystal phases usually requires changing the synthesis system (e.g., precursor type, pH value, temperature, etc.), making it impossible to switch the support crystal phase within the same reaction system through simple parameter adjustments, let alone simultaneously achieve high-load dispersion of noble metal single atoms. Low noble metal loading limits atom utilization: In existing methods for preparing single-atom catalysts, the noble metal loading is generally low (usually below 5 wt%), making it difficult to increase the loading while ensuring single-atom dispersion, thus limiting further improvement in catalytic activity. The interfacial structure between the support and the noble metal is uncontrollable: In the stepwise synthesis method, the noble metal is subsequently loaded onto the pre-synthesized support. The interfacial structure between the two is highly random, making it difficult to form a specific coordination environment, which is not conducive to constructing highly efficient catalytic active sites. The alkaline OER performance needs improvement: Existing manganese oxide-supported iridium-based catalysts still have significant room for improvement in OER activity, stability, and noble metal-based activity under alkaline conditions, particularly due to a lack of in-depth exploration and utilization of the correlation between the support crystal phase and catalytic performance. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the prior art, the present invention provides a manganese oxide supported iridium single-atom catalyst, its preparation method and electrocatalytic application. By controlling the molar ratio of citric acid to potassium permanganate, the synergistic reduction effect of citric acid and iridium acetylacetone is utilized to achieve selective control of the crystal phase (MnO2 or MnO(OH)) of the manganese oxide support in the same reaction system, and simultaneously anchors iridium in a high loading (≥6wt%) on the support in the form of single atoms.

[0006] Technical solution: To solve the above technical problems, the present invention provides a manganese oxide supported iridium single-atom catalyst, comprising a manganese oxide support and iridium supported on the manganese oxide support, wherein the iridium is dispersed in the manganese oxide surface or lattice in the form of single atoms, and the iridium loading is 6wt% to 8wt%.

[0007] Preferably, the manganese oxide is MnO2 or MnO(OH).

[0008] A method for preparing the manganese oxide-supported iridium single-atom catalyst, the preparation method comprising the following steps:

[0009] (1) Dissolve potassium permanganate, iridium acetylacetonate and citric acid in deionized water and stir until completely dissolved to obtain a mixed solution;

[0010] (2) Transfer the mixed solution to a hydrothermal reactor lined with polytetrafluoroethylene, seal it and place it in an oven. After the reaction is complete, allow it to cool naturally to room temperature.

[0011] (3) The product obtained in step (2) is centrifuged, washed with deionized water and anhydrous ethanol, and freeze-dried to obtain a powdered catalyst.

[0012] Preferably, when the molar ratio of citric acid to potassium permanganate in step (1) is 0.05 to 0.12:1, the manganese oxide is MnO2, the molar ratio of iridium acetylacetone to potassium permanganate is 1:20 to 1:30, and the volume of deionized water is 30 to 40 mL.

[0013] Preferably, the hydrothermal temperature in step (2) is 120-200°C and the reaction time is 12-48h;

[0014] Preferably, in step (3), the water washing and anhydrous ethanol washing are performed 4-6 times, and the freeze-drying time is 12-24 hours.

[0015] Preferably, when the molar ratio of citric acid to potassium permanganate in step (1) is 0.16 to 0.19:1, the manganese oxide is MnO(OH), the molar ratio of iridium acetylacetone to potassium permanganate is 1:20 to 1:30, and the volume of deionized water is 30 to 40 mL.

[0016] Preferably, the hydrothermal temperature in step (2) is 120-200℃ and the reaction time is 12-48h;

[0017] Preferably, in step (3), the water washing and anhydrous ethanol washing are performed 4-6 times, and the freeze-drying time is 12-24 hours.

[0018] As a preferred application, the manganese oxide-supported iridium single-atom catalyst prepared by the above method is used in the alkaline water electrolysis oxygen evolution reaction.

[0019] In this invention, a reducing agent system highly compatible with the manganese source and noble metal precursor was selected. This system can controllably convert the manganese source into MnO2 or MnO(OH) without over-reduction, and can also slowly and uniformly reduce noble metal ions into single-atom noble metals, which are simultaneously generated and anchored with manganese oxides. Under the same system, temperature, and pH, the crystal phase can be switched solely by the amount of reducing agent used.

[0020] In this invention, mild reduction slows down the reaction rate, and a large number of oxygen vacancies / defect sites are generated as soon as manganese oxide is formed. Noble metal single atoms are immediately captured by these sites as soon as they are reduced, preventing the metal from agglomerating. This is the site synchronous capture effect that can only be achieved by mild reduction. Strong reducing agents are too fast, and the metal agglomerates before the sites can form.

[0021] In this invention, agglomeration generally occurs when the content of single atoms exceeds 2 wt%, but in this invention, 6–8 wt% still constitutes pure single atoms. This invention achieves precise control of reaction kinetics through mild reduction, enabling uniform nucleation and growth of manganese oxides within the system, avoiding impurities in the crystal phase and particle agglomeration caused by localized over-reduction and heterogeneous nucleation. Simultaneously, the noble metal precursor gradually transforms into atomic-state active sites during the mild and stable reduction process, and is uniformly captured and stably anchored by oxygen vacancies and coordination defects simultaneously formed on the surface of the manganese oxides, ultimately achieving atomic-level uniform dispersion even at high loading levels.

[0022] In this invention, a one-pot simultaneous synthesis strategy is adopted, in which manganese source, noble metal precursor and mild reducing agent are mixed in the same reaction system at one time, and manganese oxide supported noble metal single-atom catalyst is directly obtained through one-step reaction under mild conditions, without any step operation or post-processing.

[0023] Compared with traditional stepwise synthesis methods, this technical solution does not require the pre-preparation of manganese oxide supports, nor does it require the separate synthesis of manganese oxides of specific crystal phases through multi-step processes such as hydrothermal, precipitation, and sol-gel. At the same time, it eliminates the need for subsequent post-loading processes such as impregnation, deposition, atomic layer deposition, or etching, thereby fundamentally avoiding problems such as precious metal agglomeration, uneven dispersion, and weak interfacial bonding caused by post-loading.

[0024] Compared to existing one-step co-reduction methods, this technology eliminates the need for high-temperature calcination, strong acid / base etching, and complex atmosphere control, allowing the entire reaction to proceed under mild, green, and simple conditions. The reaction system is simple, with clearly defined components and easily controllable conditions. It does not rely on special equipment or harsh synthesis environments, effectively simplifying the preparation process, shortening the reaction cycle, reducing energy consumption and costs, and significantly improving process repeatability and reliability. It also possesses excellent scalability and industrial production potential.

[0025] Through the aforementioned simple, mild, controllable, and scalable one-step synthesis method, this invention can simultaneously achieve the controllable generation of manganese oxide supports, selective regulation of crystal phases, and in-situ anchoring and high dispersion of noble metal single atoms within a single reaction system. This truly realizes the synergistic coupling of support growth, metal reduction, and site anchoring, resulting in the preparation of high-performance manganese oxide-supported noble metal single-atom catalysts. Mild reduction allows for the formation of stable Mn–O–M coordination bonds between the noble metal and manganese oxide, resulting in strong interfacial interactions.

[0026] Beneficial Effects: The manganese oxide-supported iridium single-atom catalyst of the present invention, its preparation method, and its electrocatalytic application have the following beneficial effects:

[0027] 1. One-step preparation, simple and efficient process: The synthesis of manganese oxide support, crystal phase control and anchoring of iridium single atoms can be completed simultaneously through a one-step hydrothermal reaction. No step-by-step operation is required. The process is short, easy to operate and suitable for large-scale production.

[0028] 2. Selective control of the support crystal phase: By simply changing the molar ratio of citric acid to potassium permanganate, the selective switching of the manganese oxide support crystal phase between MnO2 and MnO(OH) can be achieved in the same reaction system, overcoming the shortcomings of traditional methods that require changes to the entire synthesis system.

[0029] 3. Single-atom dispersion under high loading: By utilizing the synergistic reduction effect of citric acid and iridium acetylacetone, as well as the coordination anchoring effect of iridium acetylacetone, atomic-level dispersion can still be maintained even when the iridium loading is as high as 6wt% to 8wt%, thus realizing the efficient utilization of precious metals.

[0030] 4. Controllable interface structure and well-defined active sites: The in-situ growth method enables the formation of a stable coordination interface between the iridium single atom and the manganese oxide support, which is conducive to the construction of well-defined catalytic active sites and provides an ideal model for structure-activity relationship studies.

[0031] 5. Excellent alkaline OER performance: The obtained catalysts exhibit excellent oxygen evolution catalytic activity and stability under alkaline conditions. In particular, the iridium single-atom catalyst supported on MnO2 has significantly better overpotential, Tafel slope and mass activity than the comparative sample synthesized in situ, and has broad application prospects.

[0032] 6. Strong universality and scalability: This method achieves crystal phase selection by adjusting the amount of reducing agent. The principle is clear and the operation window is wide. It can be extended to the preparation of other manganese oxide crystal phases or other metal single-atom catalysts. Attached Figure Description

[0033] Figure 1 The image shows the XRD pattern of the MnO2-supported iridium single-atom (MnO2-Ir) catalyst prepared in Example 1 of this invention. The XRD pattern shows pure phase MnO2 (PDF#97-002-0227).

[0034] Figure 2 This is a STEM image of MnO2-Ir prepared in Example 1 of the present invention.

[0035] Figure 3 The XAFS spectrum of MnO2-Ir prepared in Example 1 of this invention is shown.

[0036] Figure 4 The image shows the XRD pattern of the MnO(OH)-supported iridium single-atom (MnO(OH)-Ir) catalyst prepared in Example 2 of this invention.

[0037] Figure 5 This is a STEM image of MnO(OH)-Ir prepared in Example 2 of the present invention.

[0038] Figure 6 The XAFS spectrum of MnO(OH)-Ir prepared in Example 2 of this invention is shown.

[0039] Figure 7 The following are the LSVs of the catalysts prepared in Examples 1 and 2 of this invention in 1 MKOH: (a) LSVs of MnO2-Ir, MnO(OH)-Ir, and commercial IrO2; (b) Tafel slopes of MnO2-Ir, MnO(OH)-Ir, and commercial IrO2; (c) specific activity of MnO2-Ir, MnO(OH)-Ir, and commercial IrO2 and their activity at 10 mA·cm⁻¹. 2 Downward overpotential.

[0040] Figure 8 This is a stability test of the catalysts prepared in Examples 1 and 2 of the present invention in 1M KOH.

[0041] Figure 9 The XRD patterns of the products obtained in Example 4 of this invention with different molar ratios of citric acid and potassium permanganate are shown.

[0042] Figure 10 The XRD patterns of the products obtained by different molar ratios of citric acid and potassium permanganate in Example 5 of this invention, without iridium acetylacetone.

[0043] Figure 11 The LSV of the catalysts prepared in Examples 1 and 6 of this invention in 1M KOH. Detailed Implementation

[0044] The invention will now be further described with reference to the accompanying drawings.

[0045] The detailed steps of the preparation method of the MnO2-Ir catalyst of the present invention are as follows:

[0046] (1) Weigh 1.25 mmol of potassium permanganate into a beaker, add 30 mL of deionized water to the beaker, and stir with a magnetic stirrer for 10 min at room temperature to form a uniform purple solution; while maintaining constant stirring speed, add 0.05 mmol of iridium acetylacetonate and continue stirring for 10 min until the mixture is uniform. Then, add 0.1 mmol of citric acid and continue stirring for 10 min to ensure uniform mixing;

[0047] (2) Transfer the above mixed solution into a 50 mL polytetrafluoroethylene liner, seal it, and place it in a high-temperature reaction apparatus. Set the reaction parameters to 180 °C and react at a constant temperature for 24 hours. After the reaction is complete, allow the system to cool naturally to room temperature.

[0048] (3) The reaction products were separated by centrifugation. The resulting solid products were washed three times with ethanol and water, respectively, to remove residual impurities. Finally, the purified products were placed in a freeze dryer and dried at -50°C and 10 Pa vacuum for 12 hours to obtain the MnO2-supported Ir catalyst, denoted as MnO2-Ir. The iridium loading was 6.6 wt%.

[0049] Figure 1 The image shows the XRD pattern of the MnO2-supported iridium single-atom (MnO2-Ir) catalyst prepared in Example 1. The XRD pattern shows that it is pure phase MnO2 (PDF#97-002-0227). Figure 2 STEM image of MnO2-Ir prepared in Example 1 of this invention. Figure 2 As can be seen, the STEM image of the MnO2-Ir catalyst prepared in this invention shows a large number of isolated bright spots, corresponding to iridium single atoms. No iridium nanoparticles or clusters were observed, proving that iridium is uniformly dispersed on the surface of the MnO2 support in the form of single atoms, and the MnO2 support is a relatively fine nanowire.

[0050] Figure 3 XAFS spectrum of MnO2-Ir prepared in Example 1 of this invention; by Figure 3 As can be seen, the MnO2-Ir catalyst prepared in this invention, when subjected to EXAFS fitting analysis of the IrL3-edge, did not show the characteristic scattering peak of the Ir-Ir bond (~2.7 Å), but only the coordination peak of Ir-O, further confirming that iridium exists in the form of a single atom and forms a coordination bond with the support.

[0051] Example 2:

[0052] The preparation method of the MnO(OH)-Ir catalyst is basically the same as that in Example 1, except that:

[0053] In step (1): 1.25 mmol of potassium permanganate and 0.05 mmol of iridium acetylacetone were weighed out, and the content of citric acid was changed to 0.23 mmol to obtain MnO(OH) supported Ir catalyst, denoted as MnO(OH)-Ir, wherein the iridium loading was 7.3 wt%. Figure 4 XRD pattern of the MnO(OH)-supported iridium single-atom (MnO(OH)-Ir) catalyst prepared in Example 2 of this invention.

[0054] Figure 5This is a STEM image of the MnO(OH)-Ir prepared in Example 2; from Figure 5 As can be seen, the STEM image of the MnO(OH)-Ir catalyst prepared in this invention shows a large number of isolated bright spots, corresponding to iridium single atoms. No iridium nanoparticles or clusters were observed, proving that iridium is uniformly dispersed on the surface of the MnO(OH) support in the form of single atoms. The MnO(OH) support is also a nanowire, with a diameter slightly larger than that of the MnO2 support.

[0055] Figure 6 The XAFS spectrum of MnO(OH)-Ir prepared in Example 2; by Figure 6 As can be seen, the MnO(OH)-Ir catalyst prepared in this invention, when subjected to EXAFS fitting analysis of the IrL3-edge, did not show the characteristic scattering peak of the Ir-Ir bond (~2.7 Å), but only the coordination peak of Ir-O, further confirming that iridium exists in the form of a single atom and forms a coordination bond with the support.

[0056] Example 3:

[0057] The alkaline OER performance of the catalysts obtained in Examples 1 and 2 and commercial IrO2 was tested.

[0058] Electrochemical performance analysis was performed at room temperature using a three-electrode system on a CHI760E electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.);

[0059] (1) Preparation of working electrode: 2 mg of catalyst powder was mixed with 960 μL of ethanol and 40 μL of Nafion solution, and then sonicated for more than 30 minutes to form a uniform catalyst slurry. 1 mL of this slurry was drop-coated onto a 1 cm × 1 cm hydrophilic carbon paper to obtain a final catalyst loading of 1 mg / cm². -2 All measured potentials were converted to the reversible hydrogen electrode (RHE) scale using the following formula: ERHE = ESCE + 0.0592 × pH + 0.241 V or ERHE = E Hg / HgO +0.059×pH+0.098V.

[0060] (2) Alkalinity test: The test was performed in a 1 M KOH solution of a standard three-electrode system. The catalyst-supported carbon paper was used as the working electrode, the Hg / HgO electrode as the reference electrode, and the carbon rod as the counter electrode. Before the test, the counter electrode and the reference electrode were rinsed with deionized water. The overpotential and Tafel slope were obtained from linear sweep voltammetry (LSV) curves with iR compensation. The long-term stability test was performed on a CHI1140D electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.).

[0061] Figure 7The following are the LSVs of the catalysts prepared in Examples 1 and 2 in 1M KOH: (a) LSVs of MnO2-Ir, MnO(OH)-Ir, and commercial IrO2; (b) Tafel slopes of MnO2-Ir, MnO(OH)-Ir, and commercial IrO2; (c) specific activity of MnO2-Ir, MnO(OH)-Ir, and commercial IrO2 and their activity at 10 mA·cm⁻¹. 2 Overpotential; by Figure 7 It can be seen that the MnO2-Ir and MnO(OH)-Ir catalysts prepared in this invention exhibit excellent alkaline oxygen evolution performance: at a current density of 10 mA·cm⁻¹ 2 Below this, the overpotentials are only 230 and 243 mV; the corresponding Tafel slopes are 57 and 70 mV·dec⁻¹. 1 The catalysts prepared by this invention exhibit superior activity compared to commercial IrO2, while also demonstrating better Tafel kinetics. Calculations based on specific mass activity show that the specific mass activities of the MnO2-Ir and MnO(OH)-Ir catalysts are 2689.5 and 1456.6 A g, respectively. -1 Ir It is commercial IrO2 (52.2 Ag) -1 Ir More than 51 times that of ).

[0062] Figure 8 The stability of the catalysts prepared in Examples 1 and 2 in 1M KOH was tested; Figure 8 It can be seen that the MnO2-Ir and MnO(OH)-Ir catalysts prepared in this invention did not show significant catalytic activity degradation after 200 h of stability testing, and both were superior to commercial IrO2.

[0063] Example 4:

[0064] To verify the effect of the molar ratio of citric acid to potassium permanganate on the crystal phase of the product, a series of experiments were conducted while keeping other conditions constant and varying the amount of citric acid:

[0065] When the molar ratio is 0~0.05:1, the product is mainly MnO2, but MnO2 has poor crystallinity and is mainly a layered structure, not nanowires.

[0066] When the molar ratio is 0.08:1, the support is pure phase MnO2;

[0067] When the molar ratio is 0.12:1, the support is MnO2, and the MnO(OH) impurity phase begins to appear;

[0068] When the molar ratio is 0.16:1, the support is a mixed phase of MnO(OH) and MnO2;

[0069] When the molar ratio is 0.184:1, the support is pure phase MnO(OH);

[0070] When the molar ratio is 0.2:1, the support is pure phase Mn3O4, and the morphology is relatively coarse nanorods.

[0071] When the molar ratio is 0.5:1, the support is Mn3O4 and MnCO3, the morphology is cubic, and obvious Ir nanoparticles can be seen.

[0072] When the molar ratio is 1:1, the support is pure phase MnCO3 with a relatively thick nanosheet morphology, and obvious Ir nanoparticles can be seen.

[0073] The above results show that pure-phase MnO2 supported Ir single atoms can be obtained in the range of 0.05 to 0.12:1, and pure-phase MnO(OH) supported Ir single atoms can be obtained in the range of 0.16 to 0.19:1. Beyond this range, it is difficult to simultaneously ensure the dispersion of pure-phase support and single atoms.

[0074] Figure 9 XRD patterns of products obtained from different molar ratios of citric acid and potassium permanganate in Example 4 of this invention; Figure 9 It can be seen that when the molar ratio is 0~0.05:1, the product is mainly MnO2, but MnO2 has poor crystallinity;

[0075] When the molar ratio is 0.08:1, the support is pure phase MnO2;

[0076] When the molar ratio is 0.12:1, the support is MnO2, and the MnO(OH) impurity phase begins to appear;

[0077] When the molar ratio is 0.16:1, the support is a mixed phase of MnO(OH) and MnO2;

[0078] When the molar ratio is 0.184:1, the support is pure phase MnO(OH);

[0079] The above results show that pure-phase MnO2 supported Ir single atoms can be obtained in the range of 0.05 to 0.12:1, and pure-phase MnO(OH) supported Ir single atoms can be obtained in the range of 0.16 to 0.19:1. Beyond this range, it is difficult to simultaneously ensure the dispersion of pure-phase support and single atoms.

[0080] Example 5

[0081] When iridium acetylacetone is absent, the effect of the molar ratio of citric acid to potassium permanganate on the crystal phase of the product is significantly different from that when iridium acetylacetone is present, which indirectly confirms the synergistic reducing effect of citric acid and iridium acetylacetone.

[0082] When the molar ratio is 0.1:1, the product is pure phase MnO2, but the product has poor crystallinity.

[0083] When the molar ratio is 0.2:1, the product is pure phase MnO2.

[0084] When the molar ratio is 0.24:1, the product is a mixed phase of MnO(OH) and MnO2.

[0085] When the molar ratio is 0.32:1, the product is pure phase MnO(OH).

[0086] Figure 10 XRD of products obtained by different molar ratios of citric acid and potassium permanganate when iridium acetylacetone is not present in Example 5 of the invention;

[0087] Depend on Figure 10 It can be seen that when the molar ratio is 0.1:1, the product is pure phase MnO2, but the product has poor crystallinity.

[0088] When the molar ratio is 0.2:1, the product is pure phase MnO2.

[0089] When the molar ratio is 0.24:1, the product is a mixed phase of MnO(OH) and MnO2.

[0090] When the molar ratio is 0.32:1, the product is pure phase MnO(OH).

[0091] The above results indicate that the effect of the molar ratio of citric acid to potassium permanganate on the crystal phase of the product differs significantly when iridium acetylacetone is absent compared to when iridium acetylacetone is present. This indirectly confirms the synergistic reducing effect of citric acid and iridium acetylacetone. Furthermore, the regulation of the manganese oxide crystal phase by citric acid without the addition of an iridium precursor differs significantly from that in this invention (containing iridium acetylacetone). This result indirectly confirms that citric acid and iridium acetylacetone exhibit a synergistic reducing effect in the reaction system, jointly participating in redox equilibrium and achieving precise regulation of the manganese oxide crystal phase and simultaneous anchoring of noble metal single atoms.

[0092] Example 6

[0093] By adjusting the iridium content in acetylacetone, catalysts with different iridium loadings can be obtained. However, the OER performance is poor when the iridium loading is 5 wt% or 9 wt%.

[0094] The above examples of adjusting the iridium content of acetylacetone highlight the importance of a ratio of 6wt% to 8wt% and the importance of synergistic effects.

[0095] Figure 11 The LSV of the catalysts prepared in Examples 1 and 6 in 1M KOH is determined by... Figure 11 It can be seen that the MnO2-Ir catalyst exhibits the best alkaline oxygen evolution performance when the iridium loading is 6.6 wt%.

[0096] In summary, this invention achieves the preparation of a highly active and stable electrocatalyst with controllable crystal phase, high single-atom loading, through the synergistic reduction of iridium by citric acid and acetylacetone, mild kinetic regulation, and an optimal loading of 6–8 wt%.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An iridium single-atom catalyst supported on manganese oxide, characterized in that, It includes a carrier manganese oxide and iridium loaded on the carrier manganese oxide, wherein the iridium is dispersed in the form of single atoms on the surface or in the lattice of the manganese oxide, and the loading of iridium is 6wt% to 8wt%.

2. The iridium single-atom catalyst supported on manganese oxide according to claim 1, characterized in that: The manganese oxide is MnO2 or MnO(OH).

3. A method for preparing the iridium single-atom catalyst supported on manganese oxide as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) Dissolve potassium permanganate, iridium acetylacetonate and citric acid in deionized water and stir until completely dissolved to obtain a mixed solution; (2) Transfer the mixed solution to a hydrothermal reactor lined with polytetrafluoroethylene, seal it and place it in an oven. After the reaction is complete, allow it to cool naturally to room temperature. (3) The product obtained in step (2) is centrifuged, washed with deionized water and anhydrous ethanol, and freeze-dried to obtain a powdered catalyst.

4. The method according to claim 3, characterized in that, When the molar ratio of citric acid to potassium permanganate in step (1) is 0.05 to 0.12:1, the manganese oxide is MnO2, the molar ratio of iridium acetylacetone to potassium permanganate is 1:20 to 1:30, and the volume of deionized water is 30 to 40 mL.

5. The method for preparing the manganese oxide-supported iridium single-atom catalyst according to claim 4, characterized in that: The hydrothermal temperature in step (2) is 120-200℃, and the reaction time is 12-48h.

6. The method for preparing the manganese oxide-supported iridium single-atom catalyst according to claim 3, characterized in that: In step (3), the water wash and anhydrous ethanol wash are performed 4-6 times, and the freeze-drying time is 12-24 hours.

7. The method for preparing the manganese oxide-supported iridium single-atom catalyst according to claim 3, characterized in that: When the molar ratio of citric acid to potassium permanganate in step (1) is 0.16 to 0.19:1, the manganese oxide is MnO(OH), the molar ratio of iridium acetylacetone to potassium permanganate is 1:20 to 1:30, and the volume of deionized water is 30 to 40 mL.

8. The method for preparing the manganese oxide-supported iridium single-atom catalyst according to claim 7, characterized in that: The hydrothermal temperature in step (2) is 120-200℃, and the reaction time is 12-48h.

9. The method for preparing the manganese oxide-supported iridium single-atom catalyst according to claim 3, characterized in that: In step (3), the water wash and anhydrous ethanol wash are performed 4-6 times, and the freeze-drying time is 12-24 hours.

10. The use of the manganese oxide-supported iridium single-atom catalyst of claim 1 or 2 or the manganese oxide-supported iridium single-atom catalyst prepared by the method of any one of claims 3 to 9 in the alkaline water electrolysis oxygen evolution reaction.

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