An iron single-atom catalyst and its preparation method and application

Abstract

The present invention discloses an iron single-atom catalyst and its preparation method and application, belonging to the field of catalyst preparation technology. The present invention combines gelation, non-solvent to phase separation process and amidoximation reaction to prepare porous amidoximated polyacrylonitrile from polyacrylonitrile powder, and then obtains porous amidoximated polyacrylonitrile chelated with iron ions and zinc ions by immersion in a metal salt solution, and finally performs a high-temperature pyrolysis process to convert the porous metal chelate precursor into a porous iron single-atom catalyst. The prepared catalyst has a high specific surface area and a rich three-dimensional continuous hierarchical porous structure, contains a rich number of Fe-N2O2 catalytic active sites, and can efficiently catalyze the cathode oxygen reduction reaction in fuel cells and metal-air batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to an iron single-atom catalyst and a preparation method and application thereof. Background Art

[0002] Fuel cells and metal-air batteries are a type of clean energy technology that can efficiently convert chemical energy into electrical energy. They show great application potential in many fields such as transportation power supply, stationary power generation systems, and portable power devices. In the working principle of fuel cells and metal-air batteries, an oxidation reaction of the fuel or metal occurs at the anode, and an oxygen reduction reaction (ORR) occurs at the cathode. Compared with the anode reaction, the kinetics of the cathode ORR are slow, and a catalyst is usually required to accelerate the reaction kinetics. For a long time, platinum-based catalysts have dominated due to their high ORR catalytic performance. However, platinum is a precious metal, and its high cost and resource scarcity have become the main bottlenecks restricting the large-scale commercialization of these technologies. Therefore, there is an urgent need to develop non-precious metal ORR catalysts with high catalytic activity.

[0003] Currently, many studies focus on the preparation of iron single-atom catalysts by pyrolysis of metal-organic frameworks (MOFs). Although MOFs offer significant advantages in the preparation of single-atom catalysts, this technical approach is also accompanied by a series of challenges. The primary challenge is the thermal stability of MOFs during high-temperature pyrolysis, which may lead to the destruction of the material structure and the collapse of the pore structure, thereby negatively affecting the performance of the catalyst. Secondly, single-atom catalysts derived from MOFs typically have a smaller pore size, which may increase mass transfer resistance and limit the efficiency of the catalytic reaction. In addition, the synthesis process of MOFs is not only technically demanding but also expensive, which may become an obstacle to its application on an industrial scale. Another key issue is that the loading of monodispersed iron in the iron single-atom catalyst obtained by pyrolysis of MOFs is typically low (generally less than 1 wt.%), which limits the number of iron single-atom active sites in the catalyst, thereby affecting the overall performance of the catalyst. Therefore, developing iron single-atom catalysts with hierarchical porous structures with high specific surface area, increasing the iron loading while maintaining high dispersion of iron species, and achieving low-cost large-scale production is one of the key challenges in realizing commercially valuable iron single-atom catalysts. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an iron single-atom catalyst and a preparation method and application thereof, so as to solve the technical problem of poor catalyst activity and stability.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for preparing an iron single-atom catalyst, comprising the following steps:

[0006] S1, dissolving polyacrylonitrile in an organic solvent to obtain a uniform polyacrylonitrile organic solution, and then allowing the polyacrylonitrile organic solution to stand for 2-24 hours. As the solution temperature decreases and the organic solvent partially evaporates, the polyacrylonitrile organic solution gradually gels to form a polyacrylonitrile organogel;

[0007] S2. placing the polyacrylonitrile organogel in a hydroxylamine aqueous solution and soaking it at 3-5° C. for 2-72 hours, then placing it in a metal salt solution and soaking it at room temperature for another 6-72 hours, finally rinsing and drying to obtain an intermediate;

[0008] Because polyacrylonitrile is poorly soluble in water, polyacrylonitrile organogel undergoes non-solvent-induced phase separation in water, forming a polymer-rich phase and a solvent-rich phase. This separation of polyacrylonitrile from the organic solvent results in the formation of a porous polyacrylonitrile. Simultaneously, a nucleophilic addition reaction occurs between polyacrylonitrile and hydroxylamine, converting the cyano groups into amidoxime groups, thereby generating porous amidoximated polyacrylonitrile (APAN). Porous amidoximated polyacrylonitrile contains abundant amidoxime groups, which have excellent chelating properties for many metal ions, providing abundant anchoring sites for the introduction of iron and zinc ions.

[0009] Immersing APAN in a mixed metal salt solution containing iron and zinc ions achieves efficient chemical adsorption of both metal ions. Both iron and zinc ions form chelates with the amidoxime groups in the porous amidoxime-modified polyacrylonitrile, containing FeN2O2 and ZnN2O2 coordination structures. The Zn-N2O2 coordination structure primarily dilutes the Fe-N2O2 coordination structure, preventing the aggregation of iron species during pyrolysis. Furthermore, zinc, due to its low boiling point, completely evaporates during subsequent pyrolysis, ensuring the conversion of the Fe-N2O2 coordination structure into isolated Fe-N2O2 single-atom active sites. Compared to simple physical mixing, the amidoxime metal chelate formation ensures uniform distribution of iron and zinc ions in the precursor, while also forming well-defined Fe-N2O2 and Zn-N2O2 coordination structures, providing an ideal precursor for the preparation of single-atom catalysts with Fe-N2O2 sites.

[0010] S3. The intermediate is placed in a protective atmosphere and heat treated at 200-300°C for 1-3 hours to stabilize the pore structure, and then heated to 600-1200°C and pyrolyzed for 2-8 hours to obtain an iron single-atom catalyst containing FeN2O2 sites.

[0011] On the basis of the above technical solution, the present invention can also be improved as follows:

[0012] Furthermore, the organic solvent is N,N-dimethylformamide or disulfide.

[0013] Furthermore, the concentration of the polyacrylonitrile organic solution is 50-500 g / L.

[0014] Furthermore, the concentration of the hydroxylamine aqueous solution is 0.02-2 mol / L.

[0015] Furthermore, the metal salt solution is a mixed solution of iron salt and zinc salt, wherein the total concentration of metal ions is 0.02-2 mol / L, and the molar ratio of iron ion concentration to total metal ion concentration is 0.001-0.5:1.

[0016] Furthermore, the iron salt is iron nitrate, iron chloride or iron sulfate, and the zinc salt is zinc nitrate, zinc chloride or zinc sulfate.

[0017] Furthermore, the drying temperature is 40-80° C. and the drying time is 1-4 h.

[0018] Furthermore, the protective atmosphere is made of nitrogen, argon or helium.

[0019] Furthermore, the pyrolysis is divided into two stages, specifically: first pyrolysis at 950-1200°C for 1-4 hours, and then pyrolysis at 600-1200°C for 1-4 hours.

[0020] During the pyrolysis process, the aggregation tendency of iron species is suppressed by the introduction of zinc species, effectively avoiding the aggregation of iron species and thus promoting the formation of single-atom sites. When the first pyrolysis is carried out at temperatures above 950°C, the Fe-N2O2 coordination structure is transformed into Fe-N2O2 single-atom active sites, and the Zn-N2O2 coordination structure undergoes a carbothermal reduction reaction to elemental zinc, which is then completely evaporated at high temperature. The secondary pyrolysis can increase the specific surface area of ​​the material, thereby increasing the number of Fe-N2O2 single-atom sites in the catalyst and enhancing the catalyst's activity.

[0021] The invention also discloses an iron single-atom catalyst prepared by the preparation method.

[0022] The invention also discloses the application of the iron single-atom catalyst in the preparation of battery electrodes.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention prepares an iron single-atom catalyst containing FeN2O2 sites by thermally decomposing porous amidoximated polyacrylonitrile chelated with iron ions and zinc ions. The catalyst has a high specific surface area and a rich three-dimensional continuous hierarchical porous structure, contains a large number of Fe-N2O2 catalytic active sites, and can efficiently catalyze the cathode reaction ORR in fuel cells and metal-air batteries. The single-atom catalyst prepared by the method of the present invention was tested, and the iron loading was measured by inductively coupled plasma mass spectrometry to be up to

[0025] The content of the catalyst was 1.5wt.%. The rotating disk electrode test found that its half-wave potential could reach 0.92V and 0.79V in alkaline and acidic electrolytes respectively, and it still maintained high activity after undergoing accelerated stress testing, so it has high catalytic activity and stability.

[0026] 2. The raw materials used in the present invention are economical, the process steps are simple, and it is suitable for large-scale production and has high industrial application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Fe3NOC-900, Fe3NOC, NOC-900 and Fe 100 Scanning electron microscope image of NOC-900;

[0028] Figure 2 Fe3NOC-900, Fe3NOC, NOC-900 and Fe 100 Transmission electron microscope image of NOC-900;

[0029] Figure 3 X-ray near-edge absorption structure (XANES) spectra of Fe3NOC-900 and Fe3NOC;

[0030] Figure 4 Extended edge absorption structure (EXAFS) spectra of Fe3NOC-900 and Fe3NOC;

[0031] Figure 5 Nitrogen isothermal adsorption-desorption curves of Fe3NOC-900 and Fe3NOC;

[0032] Figure 6 Fe3NOC-900, Fe3NOC, NOC-900 and Fe 100 ORR polarization curve of NOC-900 in alkaline electrolyte;

[0033] Figure 7 Fe3NOC-900, Fe3NOC, NOC-900 and Fe 100 ORR polarization curve of NOC-900 in acidic electrolyte;

[0034] Figure 8 ORR polarization curves of Fe3NOC-900 before and after stability test in alkaline electrolyte;

[0035] Figure 9 Figure 2 shows the ORR polarization curve of Fe3NOC-900 before and after stability test in acidic electrolyte. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. In the examples, where specific conditions are not specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. It is obvious to those skilled in the art that various modifications are within the spirit and scope of the present invention as defined and determined by the appended claims, and all inventions and creations utilizing the present invention are protected.

[0037] Example 1

[0038] A method for preparing an iron single-atom catalyst comprises the following steps:

[0039] S1. Dissolve 0.5 g of polyacrylonitrile (PAN) in 2.5 mL of N,N-dimethylformamide (DMF) to obtain a polyacrylonitrile organic solution. Pour the polyacrylonitrile organic solution into a container with a size of 60 × 20 × 2 mm. 3 The polyacrylonitrile organogel was obtained by placing the polyacrylonitrile in a rectangular polytetrafluoroethylene mold and allowing it to stand at room temperature for 2 hours.

[0040] S2. The polyacrylonitrile organogel was placed in a 0.02 mol / L hydroxylamine aqueous solution and soaked at 3°C ​​for 72 h to generate porous amidoximated polyacrylonitrile (APAN). The APAN was then placed in a mixed aqueous solution of 6 mmol / L ferric chloride and 194 mmol / L zinc chloride and soaked for another 6 h at room temperature. Finally, the APAN was rinsed with deionized water and dried in an oven at 40°C for 4 h to obtain the intermediate (Fe3Zn 97 -APAN);

[0041] S3. The intermediate is placed in an argon-filled atmosphere and heat treated at 200°C for 3 hours. The temperature is then raised to 950°C for a first pyrolysis for 4 hours. The temperature is then adjusted to 600°C and pyrolyzed for a second time for 1 hour to obtain an iron single-atom catalyst containing FeN2O2 sites (Fe3NOC-600).

[0042] Example 2

[0043] A method for preparing an iron single-atom catalyst comprises the following steps:

[0044] S1, 0.5g polyacrylonitrile (PAN) was dissolved in 2.5mL disulfide sulfoxide (DMSO) to obtain a polyacrylonitrile organic solution, and then the polyacrylonitrile organic solution was poured into a container with a size of 60×20×2mm. 3 The polyacrylonitrile organogel was obtained by placing the polyacrylonitrile organogel in a rectangular polytetrafluoroethylene mold and allowing it to stand at room temperature for 24 hours.

[0045] S2. The polyacrylonitrile organogel was placed in a 2 mol / L hydroxylamine aqueous solution and soaked at 5 ° C for 2 h to generate porous amidoximated polyacrylonitrile (APAN). The APAN was then placed in a mixed aqueous solution of 6 mmol / L ferric sulfate and 194 mmol / L zinc sulfate and soaked at room temperature for 48 h. Finally, it was rinsed with deionized water and dried in an oven at 80 ° C for 1 h to obtain the intermediate (Fe3Zn 97 -APAN);

[0046] S3. The intermediate is placed in a helium-filled atmosphere and heat treated at 300°C for 2 hours. The temperature is then raised to 1200°C for a primary pyrolysis for 2.5 hours. The temperature is then adjusted to 1200°C and a secondary pyrolysis is performed for 4 hours to obtain an iron single-atom catalyst containing FeN2O2 sites (Fe3NOC-1200).

[0047] Example 3

[0048] A method for preparing an iron single-atom catalyst comprises the following steps:

[0049] S1. Dissolve 0.5 g of polyacrylonitrile (PAN) in 2.5 mL of N,N-dimethylformamide (DMF) to obtain a polyacrylonitrile organic solution. Pour the polyacrylonitrile organic solution into a container with a size of 60 × 20 × 2 mm. 3 The polyacrylonitrile organogel was obtained by placing the polyacrylonitrile in a rectangular polytetrafluoroethylene mold and allowing it to stand at room temperature for 3 hours.

[0050] S2. The polyacrylonitrile organogel was placed in a 0.2 mol / L hydroxylamine aqueous solution and soaked at 4°C for 72 h to generate porous amidoximated polyacrylonitrile (APAN). The APAN was then placed in a mixed aqueous solution of 6 mmol / L ferric nitrate and 194 mmol / L zinc nitrate and soaked at room temperature for 48 h. Finally, the APAN was rinsed with deionized water and dried in an oven at 60°C for 2.5 h to obtain the intermediate (Fe3Zn 97 -APAN);

[0051] S3. The intermediate was placed in a nitrogen-filled atmosphere and heat treated at 270°C for 1 hour. The temperature was then raised to 1000°C for a primary pyrolysis of 2.5 hours. The temperature was then adjusted to 900°C for a secondary pyrolysis of 2.5 hours to obtain an iron single-atom catalyst containing FeN2O2 sites (Fe3NOC-900).

[0052] Comparative Example 1

[0053] The difference between this comparative example and Example 3 is that the secondary pyrolysis treatment in step S3 is omitted, and the remaining implementation conditions are the same as those in Example 3 to obtain a Fe3NOC catalyst.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 3 is that the metal salt solution in step S2 is replaced by a mixed solution of 6 mmol / L ferric nitrate and 194 mmol / L zinc nitrate with a zinc nitrate solution with a concentration of 200 mmol / L, and the other implementation conditions are the same as those in Example 3, to obtain an Fe-free nitrogen / oxygen co-doped carbon catalyst (NOC-900).

[0056] Comparative Example 3

[0057] The difference between this comparative example and Example 3 is that the metal salt solution in step S2 is replaced by a mixed solution of 6 mmol / L ferric nitrate and 194 mmol / L zinc nitrate with a 200 mmol / L ferric nitrate solution, and the other implementation conditions are the same as those in Example 3 to obtain a nitrogen / oxygen co-doped carbon catalyst (Fe) containing Fe particles. 100 NOC-900).

[0058] The samples used in the following experiments were the ORR catalysts prepared in Example 3 and Comparative Examples 1-3.

[0059] Experimental Example 1 Structural Characterization

[0060] Example 3 (Fe3NOC-900), Comparative Example 1 (Fe3NOC), Comparative Example 2 (NOC-900) and Comparative Example 3 (Fe 100 The scanning electron microscopy (SEM) of the catalyst prepared by NOC-900 is as follows Figure 1 As shown. It can be seen that Fe3NOC-900, Fe3NOC-900, NOC-900 and Fe 100 NOC-900 all present a similar three-dimensional continuous open pore structure with a pore size of 100-300 nm, which belongs to the macroscopic macropore category, indicating that porous APAN is a favorable precursor for the preparation of porous carbon-based materials.

[0061] Fe3NOC-900, Fe3NOC, NOC-900 and Fe 100Transmission electron microscopy (TEM) of NOC-900 Figure 2 As shown in the figure, it can be seen that Fe3NOC, Fe3NOC-900 and NOC-900 without Fe all present a lamellar structure, and no metal particles are observed. 100 The presence of a large number of metal particles in NOC-900 indicates that the appropriate introduction of Zn in the precursor can effectively prevent the aggregation of Fe species to form particles during pyrolysis, thereby ensuring that Fe exists in a highly dispersed single atomic form.

[0062] The X-ray near-edge absorption structure (XANES) spectra of Fe3NOC-900 and Fe3NOC are shown in Figure 2. Figure 3 As shown in the figure, compared with the reference samples (iron foil, chlorinated iron phthalocyanine), the Fe oxidation state in Fe3NOC-900 and Fe3NOC is similar to that of chlorinated iron phthalocyanine, both close to +3. This result indicates that Fe3NOC-900 and Fe3NOC do not contain iron particles because the oxidation state of elemental iron in iron foil is 0. The extended edge absorption structure (EXAFS) spectra of Fe3NOC-900 and Fe3NOC are shown in the figure. Figure 4 As shown in the figure, Fe3NOC-900 and Fe3NOC have no peak at the Fe-Fe distance, only Peaks are present within a distance of 100 nm, indicating that the sample contains only Fe-N / O coordination structures, meaning that all Fe species are distributed as single atoms. These phenomena indicate that secondary pyrolysis does not cause aggregation of Fe species. In summary, the method of the present invention can successfully prepare Fe single-atom catalysts.

[0063] The nitrogen isothermal adsorption and desorption curves of Fe3NOC-900 and Fe3NOC are as follows: Figure 5 Fe3NOC-900 and Fe3NOC showed typical IV type adsorption-desorption curves with an obvious hysteresis loop in the P / P0 range of 0.42-0.95, indicating that both have microporous / mesoporous structures, but the BET specific surface area of ​​Fe3NOC is 236m 2 / g, and the BET specific surface area of ​​Fe3NOC-900 is 483m 2 Although Fe3NOC-900 and Fe3NOC have similar Fe single-atom sites, secondary pyrolysis can increase the specific surface area of ​​the material, indicating that the present invention can successfully prepare a hierarchical Fe single-atom catalyst with a large specific surface area and rich macropores, micropores, and mesopores.

[0064] The Fe3NOC-900 prepared in Example 3 was tested by inductively coupled plasma mass spectrometry, and the iron loading in the catalyst was finally measured to be 1.5 wt.%.

[0065] Experimental Example 2 Electrochemical Performance Test

[0066] Weigh 10 mg of catalyst samples (Fe3NOC-900, Fe3NOC, NOC-900 and Fe 100 NOC-900) was fully dispersed with a mixed solution of 950 μL water and 50 μL Nafion (5 wt%), and then 12 μL of the suspension was dropped onto a glassy carbon electrode (electrode area 0.196 cm 2 ) on the electrode surface. After the electrode surface was completely dry, ORR polarization curves were collected in O2-saturated 0.1M KOH or HClO4 solutions using a rotating disk test technique. The electrode rotation speed was 1600 rpm, the potential range was 0.05-1.1 V vs RHE, and the scan rate was 10 mV / s. The catalyst stability was tested using accelerated stress tests (ASTs). Cyclic voltammetry scans were performed on the electrode in 0.1M KOH or HClO4 solutions at a scan rate of 100 mV / s over a potential range of 0.6-1.0 V vs RHE for 10,000 cycles.

[0067] Fe3NOC-900, Fe3NOC, NOC-900 and Fe 100 The ORR polarization curve of NOC-900 is shown in Figure 6 and Figure 7 As shown. It can be seen that in alkaline electrolyte (0.1M KOH), Fe containing Fe particles 100 The ORR catalytic performance of NOC-900 is better than that of NOC-900 without Fe, but lower than that of Fe single-atom catalysts Fe3NOC and Fe3NOC-900, among which the half-wave potential of Fe3NOC-900 reaches 0.92 V. In acidic electrolyte (0.1 M HClO4), NOC-900 without Fe has almost no ORR activity, while Fe containing Fe particles has a 100 NOC-900 exhibits poor ORR catalytic performance, while the Fe single-atom catalysts Fe3NOC and Fe3NOC-900 exhibit higher activity, with Fe3NOC-900 reaching a half-wave potential of 0.79 V. However, Fe3NOC-900 exhibits superior catalytic activity to Fe3NOC in both alkaline and acidic electrolytes, demonstrating that secondary pyrolysis can enhance the activity of Fe single-atom catalysts. This demonstrates that the Fe single-atom catalysts prepared by the present invention exhibit high activity in both alkaline and acidic environments.

[0068] The ORR polarization curves of Fe3NOC-900 before and after stability tests in acidic and alkaline environments are shown in Figure 2. Figure 8 and Figure 9As shown in the figure, the half-wave potential of Fe3NOC-900 decreased by 20 mV after ASTs in an alkaline electrolyte (0.1 M KOH); and the half-wave potential of Fe3NOC-900 decreased by 16 mV after ASTs in an acidic electrolyte (0.1 M HClO4). These results demonstrate that the Fe single-atom catalyst prepared in this invention exhibits high stability in both alkaline and acidic electrolytes.

[0069] In summary, the present invention utilizes porous amidoxime polyacrylonitrile to simultaneously chelate iron ions and zinc ions as pyrolysis precursors, which can effectively avoid the aggregation of iron species during the pyrolysis process, thereby preparing an Fe single-atom catalyst with a rich hierarchical porous structure and a large specific surface area. The prepared Fe single-atom catalyst has high activity and stability in catalyzing ORR.

Claims

1. A method for preparing an iron single-atom cathode catalyst for use in a fuel cell or a metal-air battery, characterized in that: The following steps are involved: S1, dissolving polyacrylonitrile in an organic solvent, and then standing for 2-24 hours to obtain a polyacrylonitrile organogel; S2. placing the polyacrylonitrile organogel in a hydroxylamine aqueous solution, soaking it at 3-5° C. for 2-72 hours, then placing it in a metal salt solution, soaking it at room temperature for 6-72 hours, and finally rinsing and drying it to obtain an intermediate; the metal salt solution is a mixed solution of iron salt and zinc salt; S3. The intermediate is placed in a protective atmosphere, heat treated at 200-300° C. for 1-3 hours, and then heated to 600-1200° C. for pyrolysis for 2-8 hours to obtain an iron single-atom catalyst.

2. The method for preparing an iron single-atom cathode catalyst for a fuel cell or a metal-air battery according to claim 1, wherein: The organic solvent is N,N-dimethylformamide or disulfide.

3. The method for preparing an iron single-atom cathode catalyst for a fuel cell or a metal-air battery according to claim 1, wherein: The concentration of the hydroxylamine aqueous solution is 0.02-2 mol / L.

4. The method for preparing an iron single-atom cathode catalyst for a fuel cell or a metal-air battery according to claim 1, wherein: The total concentration of metal ions in the metal salt solution is 0.02-2 mol / L, and the molar ratio of iron ion concentration to total metal ion concentration is 0.001-0.5:

1.

5. The method for preparing an iron single-atom cathode catalyst for a fuel cell or a metal-air battery according to claim 4, wherein: The iron salt is ferric nitrate, ferric chloride or ferric sulfate, and the zinc salt is zinc nitrate, zinc chloride or zinc sulfate.

6. The method for preparing an iron single-atom cathode catalyst for a fuel cell or a metal-air battery according to claim 1, wherein: The drying temperature is 40-80° C. and the drying time is 1-4 hours.

7. The method for preparing an iron single-atom cathode catalyst for a fuel cell or a metal-air battery according to claim 1, wherein: The protective atmosphere is made of nitrogen, argon or helium.

8. The method for preparing an iron single-atom cathode catalyst for a fuel cell or a metal-air battery according to claim 1, wherein: The pyrolysis is divided into two stages, specifically: first pyrolysis at 950-1200° C. for 1-4 hours, and then pyrolysis at 600-1200° C. for 1-4 hours.

9. An iron single-atom cathode catalyst for use in a fuel cell or a metal-air battery, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. Use of the iron single-atom cathode catalyst for fuel cells or metal-air batteries according to claim 9 in the preparation of battery electrodes.

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