A rod-shaped cobalt-manganese-molybdate electrode catalyst, a preparation method and application thereof

Abstract

This invention relates to a rod-shaped cobalt-manganese molybdate electrode catalyst, its preparation method, and its application. The preparation method includes the following steps: (S1) Cobalt salt, manganese salt, and an organic ligand are dissolved in water at a molar ratio of 1:(0.9~1.1):(1~2) and undergo a coordination reaction to obtain solution A; the molar amounts of cobalt salt and manganese salt are calculated as Co and Mn, respectively; the organic ligand is 2-phosphonobutane-1,2,4-tricarboxylic acid and / or aminotrimethylenephosphonic acid; (S2) Alkali metal molybdate is dissolved in water to obtain solution B; solution B is added to solution A for a co-precipitation reaction to obtain a precursor powder; (S3) The precursor powder is calcined under an oxygen-containing atmosphere to obtain the rod-shaped cobalt-manganese molybdate electrode catalyst. This invention simultaneously introduces cobalt and manganese into the molybdate system and pre-complexes Co using an organic ligand. 2+ and Mn 2+ Finally, a rod-shaped cobalt manganese molybdate electrode catalyst with uniform atomic-scale distribution was prepared, which exhibited excellent ORR / OER bifunctional catalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, specifically relating to a rod-shaped cobalt manganese molybdate electrode catalyst, its preparation method, and its application. Background Technology

[0002] With the urgent need for a global energy structure transition towards green and low-carbon practices, the development of high-energy-density and high-efficiency energy storage and conversion technologies is crucial. Lithium-air batteries (LABs) are open-cell conversion batteries that use oxygen from the air as the positive electrode active material. They store and convert energy based on the generation and decomposition of Li₂O₂. Because air is sourced externally, their theoretical energy density (approximately 3500 Wh / kg) is higher; therefore, lithium-air batteries are considered a highly promising next-generation energy storage system. However, the commercialization of lithium-air batteries is limited by the slow oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics on the positive electrode side, resulting in high charge / discharge overpotentials, low energy conversion efficiency, and exacerbated corrosion of the positive electrode material and decomposition of the electrolyte, thus severely shortening the battery's cycle life. Therefore, developing efficient and stable bifunctional (ORR / OER) positive electrode catalysts is key to overcoming the technological bottlenecks of lithium-air batteries.

[0003] Transition metal oxides (TMOs) and their derivatives have become a research hotspot for replacing noble metal catalysts (such as platinum and ruthenium) due to their advantages of low cost, abundant reserves, and tunable structure. Among them, transition metal molybdates show promising applications in electrocatalysis due to their simple synthesis and stable structure. However, traditional single-metal molybdate catalysts have a single catalytic active site, making it difficult to simultaneously and efficiently promote the two distinct reaction processes, ORR and OER. This leads to an imbalance in the generation and decomposition kinetics of discharge products (such as Li2O2) on the positive electrode side during battery operation, exacerbating a series of side reactions such as electrode passivation, electrolyte decomposition, and positive electrode structural decay, severely limiting the cycle life and actual performance of the battery.

[0004] To overcome the aforementioned shortcomings, researchers have attempted to develop polymetallic molybdate catalysts to leverage the synergistic effect between different metals to enhance the bifunctional catalytic activity of ORR / OER. However, in the conventional co-precipitation method for preparing polymetallic molybdates, the different precipitation rates of different metal ions easily lead to uneven product composition, making it difficult to achieve uniform composition distribution at the atomic scale, and resulting in numerous morphological defects, thus limiting the improvement in catalytic activity and stability. CN117568849A discloses a rod-shaped high-entropy metal molybdate catalyst, its preparation method, and its applications. This invention utilizes MoO3 as a precursor to prepare the target catalyst through a one-step hydrothermal reaction. The active components of the prepared high-entropy metal molybdate catalyst include molybdates of four transition metals (any four of Ni, Co, Fe, Cu, Zn, and Mn), which possess good conductivity and excellent physicochemical stability. As an electrocatalyst, it exhibits excellent oxygen evolution reaction catalytic activity and can effectively replace noble metal catalysts such as RuO2 and IrO2. However, in this invention, multiple metal ions undergo a one-step hydrothermal reaction in a hydrothermal system, making it difficult to ensure a truly uniform distribution at the atomic scale. Furthermore, the resulting catalyst only involves the oxygen evolution reaction (OER) activity and does not involve the catalytic performance of the oxygen reduction reaction (ORR).

[0005] Therefore, there is an urgent need to develop a novel molybdate catalyst that can overcome the defects of traditional coprecipitation methods, achieve uniform metal distribution at the atomic level, and possess highly efficient ORR / OER bifunctional catalytic capabilities and excellent stability, so as to significantly improve the overall electrochemical performance of lithium-air batteries. Summary of the Invention

[0006] To address the problems of uneven component distribution, uncontrollable morphology, and poor ORR / OER bifunctional catalytic activity and insufficient stability in the preparation of polymetallic molybdate catalysts by existing coprecipitation methods, this invention provides a rod-shaped cobalt-manganese molybdate electrode catalyst with uniform composition, regular morphology, and excellent ORR / OER bifunctional catalytic performance, as well as its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a rod-shaped cobalt manganese molybdate electrode catalyst includes the following steps:

[0009] (S1) Cobalt salt, manganese salt and organic ligand are dissolved together in water at a molar ratio of 1:(0.9~1.1):(1~2) and a coordination reaction is carried out under stirring to form solution A; the molar amount of cobalt salt is calculated as Co and the molar amount of manganese salt is calculated as Mn; the organic ligand is 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) and / or aminotrimethylenephosphonic acid (ATMP).

[0010] (S2) Dissolve alkali metal molybdate in water to form solution B; add solution B to solution A and carry out a coprecipitation reaction under stirring; after the reaction is completed, separate, wash and dry to obtain precursor powder;

[0011] (S3) The precursor powder was calcined in an oxygen-containing atmosphere to obtain a rod-shaped cobalt manganese molybdate electrode catalyst.

[0012] In traditional coprecipitation methods, metal ions (such as Co) 2+ Mn 2+ In solution, they are independent and free, but when MoO4 is added... 2- At this time, due to the different precipitation kinetic rates of different metal ions, the composition of the precursor formed by co-precipitation becomes uneven, resulting in low catalytic activity of metal molybdates. In a first aspect, the present invention introduces multidentate organic ligands (PBTCA, ATMP) in step (S1), which can react with Co... 2+ Mn 2+ Simultaneously, a stable, soluble metal-organic complex is formed, achieving atomic-scale pre-assembly and homogenization of Co and Mn. This fundamentally solves the problem of compositional inhomogeneity caused by the independent existence of metal ions in traditional coprecipitation, laying the foundation for obtaining a final product with atomic-scale homogeneity. Secondly, in step (S2), the dropwise addition of the alkali metal molybdate solution gradually increases the pH of the system, weakening the interaction between the organic ligand and Co. 2+ Mn 2+ Coordination strength, making Co 2+ Mn 2+ Slow and controlled release effectively avoids the effects of Co. 2+ Mn 2+ The component segregation caused by the difference in precipitation rate ensured that the two metal ions reacted synchronously and uniformly with MoO4. 2- Coprecipitation provides kinetic assurance for the formation of a uniform solid solution at the atomic scale. Simultaneously, during the coprecipitation reaction, the initially formed cobalt manganese molybdate crystal nuclei are bonded with incompletely detached organic ligand molecules. The inherent spatial configuration of these ligand molecules induces preferential crystal growth along a one-dimensional direction, ultimately yielding a one-dimensional rod-shaped cobalt manganese molybdate with high specific surface area and favorable mass transfer. In other words, the organic ligands (PBTCA, ATMP) act as precipitation kinetic controllers and morphology-guided soft templates. Thirdly, due to the difference in electronegativity between cobalt and manganese and their coexistence in the crystal lattice, multiple valence states (Co...) can stably coexist under the aforementioned preparation conditions. 3+ / Co 2+ With Mn 3+ / Mn 2+This constitutes a dynamic redox pair. This characteristic, combined with the aforementioned atomically uniformly distributed components and one-dimensional rod-like morphology, significantly promotes charge transfer efficiency and structural stability during the catalytic process, ultimately achieving excellent and stable ORR / OER bifunctional catalytic performance.

[0013] Preferably, in step (S1), the molar ratio of cobalt salt, manganese salt, and organic ligand is 1:(0.9~1.1):(1.5~2), more preferably 1:(0.95~1.05):(1.5~2), and even more preferably 1:(0.98~1.02):(1.5~2), such as 1:1:1.5~2. Controlling the molar ratio of these three components in this invention is crucial to ensuring uniform bimetallic complexation and subsequent effective precipitation. First, controlling the molar ratio of Co to Mn within the range of 1:0.9~1.1 is beneficial for forming a uniform cobalt manganese molybdate solid solution and a mixed valence pair (Co) with matching quantities and potentials. 3+ / Co 2+ With Mn 3+ / Mn 2+ This allows for the synergistic catalytic effect of bimetals. Secondly, the amount of organic ligand used also needs to be balanced. If the amount is too low, the complexation will be insufficient, and the bimetals cannot be pre-homogenized at the molecular scale; however, the amount should not be too high, otherwise the cost will increase.

[0014] Further, in step (S1), the cobalt salt is selected from at least one of cobalt chloride (CoCl2), cobalt sulfate (CoSO4), cobalt nitrate (Co(NO3)2), and their hydrates; the manganese salt is selected from at least one of manganese chloride (MnCl2), manganese nitrate (Mn(NO3)2), manganese sulfate (MnSO4), and their hydrates; and the total concentration of Co ions and Mn ions in solution A is 0.2~0.4 mol / L.

[0015] Further, in step (S1), the conditions for the coordination reaction are: pH 2.0~5.0, reaction at 20~40℃ for 0.5~2h.

[0016] Furthermore, in step (S2), the ratio of solution A to solution B satisfies the molar ratio of (Co+Mn):Mo of 1:1.05~1.2.

[0017] Further, in step (S2), the alkali metal molybdate is selected from at least one of sodium molybdate, potassium molybdate, or their hydrates; the MoO4 in solution B 2- The concentration is 0.1~0.3 mol / L.

[0018] Further, in step (S2), the temperature of the coprecipitation reaction is 30-50℃, preferably 40-50℃; the time of the coprecipitation reaction is 4-6 hours; the separation is centrifugal separation; the washing is 2-4 times with deionized water; and the drying is 60-80℃ for 6-12 hours. Solution A is acidic, and during the dropwise addition of the alkaline molybdate solution, the pH of the system gradually increases, and MoO4... 2- It undergoes slow ligand exchange and coprecipitation reactions with metal-organic complexes.

[0019] Further, in (S3), the calcination temperature is 400~600℃, and the calcination time is 3~5h; the oxygen-containing atmosphere is air and / or oxygen. The purpose of calcination in an oxygen-containing atmosphere is to drive the atoms to rearrange themselves through high temperature and at the same time remove residual organic ligands, forming a final product with a regular crystal structure and high catalytic activity.

[0020] Secondly, the present invention also provides a rod-shaped cobalt manganese molybdate electrode catalyst prepared by the aforementioned preparation method. The catalyst has a one-dimensional rod-shaped structure with a rod diameter of 100~200 nm and a length of 0.5~5 μm.

[0021] Thirdly, the present invention also provides the application of the rod-shaped cobalt manganese molybdate electrode catalyst as a positive electrode catalyst in lithium-air batteries.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention utilizes multidentate organic ligands (PBTCA, ATMP) to pre-complex Co 2+ and Mn 2+ Simultaneously forming stable soluble complexes, the pre-assembly and uniform distribution of the two metal ions are achieved, which changes the problem of uneven composition caused by independent reaction of metal ions in the traditional co-precipitation method. It ensures the uniformity of the precursor composition from the source and ensures atomic-level uniform doping of the bimetal in the molybdate lattice, laying the foundation for the formation of stable and synergistic active sites.

[0024] 2. The organic ligands act as both precipitation kinetic controllers and morphology-guided soft templates during co-precipitation, guiding the product to preferentially grow along a one-dimensional direction, thus successfully preparing a one-dimensional rod-shaped cobalt manganese molybdate electrode catalyst with high specific surface area and good mass transfer.

[0025] 3. This invention introduces both cobalt and manganese into the molybdate system, forming a stable mixed valence pair (Co and Mn) between the uniformly distributed Co and Mn. 3+ / Co 2+ With Mn 3+ / Mn 2+The intrinsic activity of the catalyst is significantly improved through the synergistic effect of its atomically uniform composition and one-dimensional rod-shaped morphology. When applied to the cathode of lithium-air batteries, it exhibits excellent ORR / OER bifunctional catalytic activity, lower charge / discharge overpotential, higher discharge specific capacity, and ultra-long cycle life. Attached Figure Description

[0026] Figure 1 The image shows the SEM image and elemental distribution mapping of the CoMnMoO4 electrode catalyst prepared in Example 1.

[0027] Figure 2 The image shows the SEM image and elemental distribution mapping of the CoMnMoO4 electrode catalyst prepared in Comparative Example 1.

[0028] Figure 3 The image shows the XRD pattern of the CoMnMoO4 electrode catalyst prepared in Example 1.

[0029] Figure 4 The image shows the XPS spectrum of the CoMnMoO4 electrode catalyst prepared in Example 1.

[0030] Figure 5 The images show SEM images of the positive electrode of a lithium-air battery assembled using CoMnMoO4 prepared in Example 1 as the positive electrode catalyst after full-capacity discharge and charging at a current density of 500 mA / g. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0033] Example 1

[0034] (S1) 10 mmol of cobalt chloride hexahydrate (CoCl2·6H2O), 10 mmol of manganese chloride tetrahydrate (MnCl2·4H2O) and 15 mmol of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) were dissolved in 150 mL of pure water, the pH was adjusted to 4.0, and the coordination reaction was carried out at 200 rpm and 30 °C for 1.5 h to form a transparent solution A;

[0035] (S2) Dissolve 21 mmol of sodium molybdate dihydrate (Na2MoO4·2H2O) in 150 mL of pure water to form solution B; under stirring at 200 rpm, add solution B dropwise to solution A (the addition is controlled to be completed in 1 h). After the addition is completed, continue stirring and carry out a co-precipitation reaction at 45 °C for 5 h, and a precipitate is formed; after the reaction is completed, the product is separated by centrifugation, washed 3 times with deionized water until the supernatant is clear, the solid is collected, and dried in a vacuum oven at 60 °C for 12 h to obtain the precursor powder;

[0036] (S3) The precursor powder was placed in a muffle furnace and calcined at 450°C for 4 hours at a rate of 5°C / min in air atmosphere. After natural cooling, rod-shaped cobalt manganese molybdate (CoMnMoO4) electrode catalyst was obtained.

[0037] Example 2

[0038] The rest is the same as in Example 1, except that in step (S1), the amount of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) is 10 mmol.

[0039] Example 3

[0040] The rest is the same as in Example 1, except that in step (S1), the amount of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) is 12 mmol.

[0041] Example 4

[0042] The rest is the same as in Example 1, except that in step (S1), the amount of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) is 18 mmol.

[0043] Example 5

[0044] The rest is the same as in Example 1, except that in step (S1), the amount of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) is 20 mmol.

[0045] Example 6

[0046] The rest is the same as in Example 1, except that in step (S1), aminotrimethylenephosphonic acid (ATMP) is used in equimolar substitution for 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA); and the amount of manganese chloride tetrahydrate is 9 mmol.

[0047] Example 7

[0048] The rest is the same as in Example 1, except that: in step (S1), the amount of manganese chloride tetrahydrate is 111 mmol; in step (S2), the amount of sodium molybdate dihydrate is 22.5 mmol, and the coprecipitation reaction conditions are: coprecipitation reaction at 35°C for 6 h.

[0049] Comparative Example 1

[0050] The rest is the same as in Example 1, except that in step (S1), aminotrimethylenephosphonic acid was not used for coordination reaction; instead, a coprecipitation reaction was carried out directly. Specifically:

[0051] (S1) Dissolve 10 mmol of cobalt chloride hexahydrate (CoCl2·6H2O) and 10 mmol of manganese chloride tetrahydrate (MnCl2·4H2O) together in 100 mL of pure water to form a transparent solution A;

[0052] (S2) Same as Example 1;

[0053] (S3) Same as Example 1.

[0054] Comparative Example 2

[0055] The rest is the same as in Example 1, except that in step (S1), the amount of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) is 5 mmol.

[0056] Comparative Example 3

[0057] The rest is the same as in Example 1, except that the amount of manganese chloride tetrahydrate used in step (S1) is 20 mmol, that is, the molar ratio of Co to Mn is not close to 1:1.

[0058] Application examples

[0059] The electrode catalysts prepared in the above examples and comparative examples were applied to the positive electrode of a lithium-air battery and assembled into a lithium-air battery. The specific steps are as follows: the prepared electrode catalyst, conductive agent Super P and binder polyvinylidene fluoride were mixed at a mass ratio of 7:2:1, and then ultrasonically dispersed in N-methylpyrrolidone (NMP) to form a uniform slurry; the slurry was coated on carbon paper, dried at 80°C for 24 hours, and cut into electrode sheets with a diameter of 14 mm, i.e., positive electrode sheets; in an argon glove box, a lithium metal sheet was used as the negative electrode, a glass fiber membrane was used as the separator, and a 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) / dimethyl sulfoxide (DMSO) solution was used as the electrolyte. These were assembled with the above-cut positive electrode sheets into a button cell, i.e., a coin cell lithium-air battery.

[0060] Testing and Analysis

[0061] I. Structural Characterization

[0062] SEM analysis: The SEM image and elemental distribution mapping of the CoMnMoO4 electrode catalyst prepared in Example 1 are shown below. Figure 1 ,in Figure 1 (a) is a SEM image. Figure 1 (b) is the element distribution mapping diagram. From Figure 1 As clearly observed in (a), CoMnMoO4 exhibits a one-dimensional nanorod structure with no obvious particle aggregation or irregular morphology. Furthermore, the stacked nanorods create voids, forming unobstructed mass transfer channels that facilitate electrolyte wetting and the rapid transport of oxygen and lithium ions. Further statistical analysis shows that the nanorods have a diameter of approximately 150–200 nm and a length of 0.5–5 μm. Figure 1 As can be visually observed in the mapping diagram of (b), the four elements Co, Mn, Mo, and O are distributed continuously and uniformly throughout the entire nanorod crystal structure, with no local enrichment or aggregation of any element. The distribution areas of each element completely overlap and are highly consistent with the morphological contour of the nanorod. This result proves from the elemental distribution level that Co... 2+ With Mn 2+ It has been successfully and uniformly distributed in the molybdate lattice. SEM images of the CoMnMoO4 electrode catalysts prepared in the remaining examples are shown below. Figure 1 Similarly, CoMnMoO4 exhibits a one-dimensional nanorod structure with a diameter of approximately 100–200 nm and a length of 0.5–5 μm.

[0063] SEM images and elemental mapping diagrams of the CoMnMoO4 electrode catalyst prepared in Comparative Example 1 (without organic ligands) are shown below. Figure 2 As shown, from Figure 2 As can be seen in (a), CoMnMoO4 is not a uniform nanorod shape, but exhibits particle aggregation or irregular morphology; Figure 2 In the mapping diagram of (b), it can be visually observed that the distribution areas of Co and Mn do not completely overlap. The CoMnMoO4 electrode catalyst prepared in Comparative Example 2 (with insufficient organic ligand) also exhibits similar structural inhomogeneity. Figure 1 and Figure 2 The comparison demonstrates that the pre-complexation of an appropriate amount of organic ligands plays a decisive role in achieving the atomic-level uniform distribution of Co and Mn and the one-dimensional rod-like structure.

[0064] XRD analysis: The XRD pattern of the CoMnMoO4 electrode catalyst prepared in Example 1 is shown below. Figure 3As shown in the spectrum, the overall characteristic peak positions of CoMnMoO4 are consistent with the standard characteristic peak trends of single-metal molybdates CoMoO4 (standard card number: JCPDS 00-021-0868) and MnMoO4 (standard card number: JCPDS 00-027-1280), indicating that the simultaneous introduction of Co and Mn did not disrupt the basic crystal structure framework of molybdates, and the catalyst still maintains the typical phase characteristics of the molybdate system. Further analysis of the characteristic peak details shows that the XRD characteristic peaks of CoMnMoO4 do not simultaneously exhibit the (002) crystal plane diffraction peak unique to CoMoO4 and the (220) crystal plane diffraction peak unique to MnMoO4. Instead, they present only a set of continuous and single diffraction peaks with sharp peaks and no impurity interference, indicating that CoMnMoO4 has high crystallinity and extremely low impurity content. This result directly proves that Co... 2+ With Mn 2+ The CoMnMoO4 has been successfully incorporated into the molybdate lattice and uniformly doped. The prepared CoMnMoO4 is not a physical mixture of CoMoO4 and MnMoO4, but rather a CoMnMoO4 solid solution. The XRD patterns of the CoMnMoO4 electrode catalysts prepared in the other examples are shown below. Figure 3 similar.

[0065] XPS analysis: The XPS spectrum of the CoMnMoO4 electrode catalyst prepared in Example 1 is shown below. Figure 4 As shown. Figure 4 The full spectrum of (a) reveals the characteristic peaks of the four elements Co, Mn, Mo and O in the CoMnMoO4 material (corresponding binding energies are: Co 2p≈780eV, Mn 2p≈640eV, Mo 3d≈232eV, O 1s≈530eV). Figure 4 In (b), the high-resolution spectrum of Mo 3d clearly shows a pair of characteristic double peaks located at 235.2 eV and 232.1 eV, corresponding to Mo 6+ 3D 3 / 2 and 3D 5 / 2 The electron orbitals indicate that Mo in this catalyst exists only as Mo. 6+ The form exists without valence state shift, and bimetallic doping does not change the chemical environment stability of Mo in the molybdate lattice. Figure 4 In (c), the O 1s spectrum can be well fitted to the lattice oxygen (O) at 530.3 eV. L ) and hydroxyl groups of surface-adsorbed water at 532.3 eV (O w ). Figure 4 After peak fitting, the fine Co 2p spectrum in (d) can be used to identify Co. 2+ With Co 3+ The characteristic peaks were calculated, and the peak area ratio of the two peaks was 30.4:29.4. Figure 4 The fine spectrum of Mn 2p in (e), Mn 2+ With Mn 3+ The characteristic peaks were also clearly distinguishable, with a peak area ratio of 58.8:52.0. These results indicate that both Co and Mn elements exist in molybdates in a mixed valence state, with both divalent and trivalent oxidation states. This may be due to the difference in electronegativity between Co (electronegativity 1.88) and Mn (electronegativity 1.55), leading to localized non-uniform charge distribution within the molybdate crystal after bimetallic doping. To maintain lattice charge balance, some Mn... 2+ Oxidized to Mn 3+ To balance the charge, and thus form Co 3+ / Co 2+ and Mn 3+ / Mn 2+ The dynamic redox pair. This dynamic reduction pair can synergistically promote charge transport in both ORR and OER processes, thereby synergistically improving charge transport efficiency and providing a key electronic structure basis for enhancing the performance of bifunctional catalysis. The XPS spectra of the CoMnMoO4 electrode catalysts prepared in the other examples are compared with... Figure 4 similar.

[0066] II. Electrochemical Performance

[0067] In lithium-air batteries, the discharge process corresponds to the oxygen reduction reaction (ORR), and its discharge voltage plateau height mainly depends on the ORR catalytic activity of the cathode catalyst. The charging process corresponds to the oxygen evolution reaction (OER), and its charging voltage plateau height mainly depends on the OER catalytic activity of the cathode catalyst. Therefore, the charge-discharge performance of the battery directly reflects the ORR / OER bifunctional activity of the cathode catalyst. Specifically, a higher median discharge voltage (closer to 2.96V) indicates a lower discharge overpotential, signifying better ORR catalytic activity; a lower median charging voltage indicates a lower charging overpotential, signifying better OER catalytic activity. In other words, a lower charge-discharge overpotential (median charging voltage - median discharging voltage) indicates higher ORR / OER bifunctional activity.

[0068] To systematically evaluate the performance of the electrode catalysts prepared in the examples and comparative examples in lithium-air batteries, the rate performance, deep discharge performance, and long-cycle performance of the coin-type lithium-air batteries assembled in the application examples were tested under a high-purity oxygen atmosphere (99.99% oxygen purity). Specific conditions are as follows:

[0069] Rate performance testing: The test current densities were set sequentially to 100 mA / g, 200 mA / g, 500 mA / g, 1000 mA / g, and 100 mA / g, with a capacity limit of 500 mAh / g. Test results showed that the lithium-air batteries assembled using the electrode catalysts prepared in the examples as positive electrode catalysts exhibited low charge / discharge overpotentials (median charging voltage - median discharging voltage) at different rates. Table 1 shows the median initial discharge voltage, median initial charging voltage, and charge / discharge overpotentials of the lithium-air batteries assembled using the electrode catalysts prepared in each example and comparative example as positive electrode catalysts at a current density of 500 mAh / g.

[0070] Deep discharge performance test: The current density was set at 500 mA / g, the discharge capacity was not limited, and the voltage range was 2.0~4.5V. The maximum discharge capacity of the battery was tested. The discharge specific capacity of lithium-air batteries assembled with the electrode catalysts prepared in each example and comparative example as positive electrode catalysts at a current density of 500 mAh / g is shown in Table 1.

[0071] Long-cycle performance test: The current density was set at 500 mA / g, the capacity was limited to 500 mAh / g, and the voltage range was 2.0~4.8V. In this invention, "stable cycling" is defined as a cycling process that simultaneously meets the following two conditions: (1) the charging and discharging processes are completed within the above voltage window; (2) the increase in overpotential between the charging and discharging cycles and the fifth cycle is less than 0.1 V. The test results show that the lithium-air batteries assembled using the electrode catalyst prepared in the examples as the positive electrode catalyst all achieved more than 500 stable cycles. The number of stable cycles for the other examples and comparative examples is shown in Table 1.

[0072] To further investigate the reasons for the battery's excellent cycle stability, the morphology of the positive electrode after cycling was analyzed (e.g., Figure 5 ),like Figure 5 As shown in (a), the Li2O2 generated after discharge exhibits a micron-scale nanosheet structure (nanosheet thickness approximately 50-100 nm, lateral size approximately 1-3 μm), and does not show the common coarse aggregate particle morphology. Figure 5 As shown in (b), after full charging, the Li2O2 product was completely removed, and the electrode regained its porous structure. This phenomenon indicates that the CoMnMoO4 catalyst can effectively promote the reversible formation and decomposition of Li2O2, avoiding electrode pore blockage and catalyst active site failure caused by Li2O2 residue. This excellent cycle stability test corroborates each other, jointly demonstrating that the catalyst has highly efficient bifunctional catalytic ability and excellent structural stability in actual battery operation.

[0073] Table 1 Electrochemical performance test

[0074] .

[0075] As shown in Table 1, the lithium-air batteries assembled using the catalysts prepared in the embodiments of the present invention as positive electrode catalysts exhibit higher median voltage at the first discharge and lower median voltage at the first charge, thus their charge-discharge overload is significantly lower than that of the comparative example. The higher discharge voltage directly reflects the excellent ORR activity of the catalyst, while the lower charge voltage directly reflects its excellent OER activity, jointly demonstrating its superior bifunctional catalytic performance. Furthermore, the lithium-air batteries assembled using the catalysts prepared in the embodiments of the present invention also exhibit high specific capacity and good cycle stability, especially the preferred examples 1, 4, and 5.

[0076] As described above, the electrode catalyst prepared in Comparative Example 1 (without organic ligands) exhibits irregular morphology and uneven distribution of Co and Mn. These structural defects lead to high charge-discharge overpotentials and poor cycle stability in the assembled lithium-air battery. The lithium-air battery prepared with the electrode catalyst prepared in Comparative Example 2 (with insufficient organic ligands) also shows high charge-discharge overpotentials and poor cycle stability. The performance of Comparative Example 3 is significantly degraded. Based on the XRD analysis results of Example 1, this is likely due to an imbalance in the ratio of Co and Mn metals, making it difficult to form a uniform cobalt manganese molybdate solid solution, resulting in Co... 3+ / Co 2+ With Mn 3 + / Mn 2+ The dynamic redox synergy between them is disrupted, thus affecting its bifunctional catalytic activity.

Claims

1. A method for producing a rod-shaped cobalt-manganese-molybdate electrode catalyst, characterized by, Includes the following steps: (S1) Cobalt salt, manganese salt and organic ligand are dissolved together in water at a molar ratio of 1:(0.9~1.1):(1~2), and a coordination reaction is carried out under stirring to form solution A; the molar amount of cobalt salt is calculated as Co, and the molar amount of manganese salt is calculated as Mn; the organic ligand is 2-phosphonobutane-1,2,4-tricarboxylic acid and / or aminotrimethylenephosphonic acid; (S2) Dissolve alkali metal molybdate in water to form solution B; add solution B to solution A and carry out a coprecipitation reaction under stirring; after the reaction is completed, separate, wash and dry to obtain precursor powder; the ratio of solution A to solution B satisfies the molar ratio of (Co+Mn):Mo of 1:1.05~1.2; (S3) The precursor powder was calcined in an oxygen-containing atmosphere to obtain a rod-shaped cobalt manganese molybdate electrode catalyst.

2. The production method according to claim 1, characterized by, In step (S1), the molar ratio of cobalt salt, manganese salt and organic ligand is 1:(0.9~1.1):(1.5~2).

3. The preparation method according to claim 1, characterized in that, In step (S1), the molar ratio of cobalt salt, manganese salt and organic ligand is 1:(0.95~1.05):(1.5~2).

4. The preparation method according to claim 1, characterized in that, In step (S1), the cobalt salt is selected from at least one of cobalt chloride, cobalt sulfate, cobalt nitrate and their hydrates; the manganese salt is selected from at least one of manganese chloride, manganese nitrate, manganese sulfate and their hydrates; and the total concentration of Co ions and Mn ions in solution A is 0.2~0.4 mol / L.

5. The preparation method according to claim 1, characterized in that, In step (S1), the conditions for the coordination reaction are: pH 2.0~5.0, reaction at 20~40℃ for 0.5~2h.

6. The preparation method according to claim 1, characterized in that, In step (S2), the alkali metal molybdate is selected from at least one of sodium molybdate, potassium molybdate, or a hydrate thereof; the MoO4 2- concentration of solution B is 0.1-0.3 mol / L.

7. The preparation method according to claim 1, characterized in that, In step (S2), the temperature of the coprecipitation reaction is 30~50℃; the time of the coprecipitation reaction is 4~6h; the separation is centrifugal separation; the washing is washing with deionized water 2~4 times; and the drying is drying at 60~80℃ for 6~12h.

8. The preparation method according to claim 1, characterized in that, In step (S3), the calcination temperature is 400~600℃ and the calcination time is 3~5h; the oxygen-containing atmosphere is air and / or oxygen.

9. A rod-shaped cobalt manganese molybdate electrode catalyst prepared by the method according to any one of claims 1-8, characterized in that, The catalyst has a one-dimensional rod-shaped structure with a diameter of 100~200nm and a length of 0.5~5μm.

10. The application of the rod-shaped cobalt manganese molybdate electrode catalyst prepared by the preparation method according to any one of claims 1-8 as a positive electrode catalyst in lithium-air batteries.

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