Metal alloy nanoparticle-loaded porous carbon fiber membrane electrode for lithium oxygen / air battery and preparation method of metal alloy nanoparticle-loaded porous carbon fiber membrane electrode

Abstract

The invention discloses a metal alloy nanoparticle-loaded porous carbon fiber membrane electrode for a lithium oxygen / air battery and a preparation method of the porous carbon fiber membrane electrode. The preparation method comprises the following steps: dissolving a carbon-making agent in water, adding a pore-forming agent and a cross-linking agent, uniformly mixing to obtain spinning solution slurry, and carrying out electrostatic spinning and two-step sintering to form the porous carbon fiber membrane electrode; and dropwise adding the mixed metal salt solution onto the porous carbon fiber membrane electrode, and carrying out carbon thermal shock to obtain the porous carbon fiber membrane electrode loaded with the metal alloy nanoparticles. The electrode which contains abundant micropores, mesopores and macropores and is loaded with the alloy nanoparticles is constructed, three-phase interfaces and catalytic active sites required by charging and discharging can be effectively increased, the catalytic reaction activity and the discharging capacity of the electrode are increased, the charging and discharging overpotential is reduced, and therefore side reactions are reduced, and the electrode with the structure is used.

Description

Technical Field

[0001] This invention belongs to the field of lithium-oxygen / air battery technology, specifically relating to a porous carbon fiber thin film electrode for lithium-oxygen / air batteries loaded with metal alloy nanoparticles and its preparation method. Background Technology

[0002] The lithium-oxygen / air battery is a type of metal fuel cell with an extremely high theoretical energy density. It operates using metallic lithium as the negative electrode and oxygen, which is ubiquitous in the air, as the positive electrode. Due to its theoretical energy density, comparable to gasoline, it holds immense potential in the fields of electric vehicles and energy storage.

[0003] To achieve better catalytic activity and performance in lithium-oxygen / air batteries, existing research focuses on electrode structure design and highly catalytically active electrode materials. In electrode structure design, reducing particle size increases the length of the three-phase interface (ionic conductor, electronic conductor, and reactant gas); increasing the electrode's specific surface area and pore volume provides more growth space for discharge products. However, due to the battery's large overpotential, the materials are unstable during charge and discharge, necessitating the use of highly catalytically active electrode materials.

[0004] Rare-earth-containing high-entropy alloys possess abundant active sites and tunable electronic structures, exhibiting excellent catalytic activity. Therefore, finding a suitable method to synthesize porous electrode materials containing rare-earth-containing high-entropy alloys is of great significance. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of the invention, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a porous carbon fiber thin film electrode loaded with metal alloy nanoparticles for lithium-oxygen / air batteries.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, The carbon-forming agent is dissolved in water, and a pore-forming agent and a crosslinking agent are added. After mixing evenly, a spinning solution slurry is obtained. Electrospinning is performed on the spinning solution slurry to obtain spun fiber films; The spun fiber film is sintered in two steps to form a porous carbon fiber film electrode. A mixed metal salt solution was prepared by using a metal precursor and a solvent; A mixed metal salt solution is dropped onto a porous carbon fiber thin film electrode, and then subjected to a carbothermal shock at 1600~2800℃ for 50~500 ms by Joule heating to obtain a porous carbon fiber thin film electrode for lithium-oxygen / air batteries loaded with metal alloy nanoparticles.

[0009] In a preferred embodiment of the preparation method described in this invention, the carbon-forming agent comprises one or more of the following: polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyethersulfone (PES), polyurethane (PU), polylactic acid (PLA), polystyrene (PS), polyimide (PI), polyetherimide (PEI), poly(p-phenylene isophthalamide) (PMIA), collagen, silk fibroin, hyaluronic acid, chitosan, and chitin; the pore-forming agent comprises one or more of the following: polymer microspheres and inorganic non-metallic elemental particles; and the crosslinking agent comprises one or more of the following: polyacids, polyols, and organic compounds containing unsaturated double bonds.

[0010] In a preferred embodiment of the preparation method described in this invention, the mass ratio of the carbonizing agent to the pore-forming agent is 1:2~4, and the amount of crosslinking agent added relative to the total mass of the carbonizing agent and the pore-forming agent is 0.02~0.04wt%.

[0011] In a preferred embodiment of the preparation method described in this invention, the mixed metal salt solution is prepared by using a metal precursor and a solvent, wherein the metal precursor includes rare earth metal salts, transition metal salts, and inorganic metal acids; and the concentration of each metal ion in the mixed metal salt solution is 0.01~0.1 mol·L⁻¹. -1 .

[0012] In a preferred embodiment of the preparation method described in this invention, the mixed metal salt solution is dropped onto the porous carbon fiber thin film electrode, wherein the amount of the mixed metal salt solution added is 10~100 μL·cm. -2 .

[0013] In a preferred embodiment of the preparation method described in this invention, the spinning solution slurry is electrospinned, wherein the electrospinning voltage is 10~40 kV and the electrospinning solution flow rate is 0.3~5 mL·h. -1 The receiving distance for electrospinning is 15~30 cm, the ambient temperature for electrospinning is 20~30℃, and the ambient humidity for electrospinning is 25~40 RH.

[0014] In a preferred embodiment of the preparation method described in this invention, the spun fiber film is subjected to a two-step sintering process, wherein the two-step sintering includes pre-oxidation sintering and carbonization sintering; the pre-oxidation sintering temperature is 220~280℃, the pre-oxidation sintering time is 2~4 h, and the pre-oxidation sintering atmosphere is air; the carbonization sintering temperature is 600~1200℃, the carbonization sintering time is 1.5~4 h, and the carbonization sintering atmosphere is one or more of argon, nitrogen, and carbon dioxide.

[0015] In a preferred embodiment of the preparation method described in this invention, graphite plates are used to provide tensile force during both sintering steps.

[0016] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a porous carbon fiber thin film electrode for lithium-oxygen / air batteries using loaded metal alloy nanoparticles.

[0017] As a preferred embodiment of the porous carbon fiber thin film electrode for lithium-oxygen / air batteries loaded with metal alloy nanoparticles according to the present invention, the electrode is a porous structure electrode, the porous structure including microporous structure, mesoporous structure and macroporous structure, the pore size of the microporous structure is 0~3 nm, the pore size of the mesoporous structure is 3~50 nm, and the pore size of the macroporous structure is >50 nm.

[0018] Beneficial effects of this invention: (1) This invention addresses the technical problems of uneven and unreasonable pore size distribution and weak catalyst adjustability in the cathode of lithium-oxygen / air batteries in the prior art. It designs a novel preparation method for alloy catalyst cathodes for lithium-oxygen / air batteries, innovatively using Joule heating to subject the precursor material to carbothermal shock, thereby obtaining high-entropy alloy nanoparticles loaded on porous carbon nanofibers. This electrode structure can effectively expand the area of ​​the three-phase interface between the electrode, electrolyte, and discharge products. Simultaneously, the uniformly distributed alloy catalyst can reduce the charge-discharge overpotential of the battery, thereby improving battery performance. Furthermore, batteries using this structure have self-supporting characteristics and do not require the use of binders.

[0019] (2) The electrode prepared by the method of the present invention not only has abundant pore size, but also has alloy catalyst particles uniformly loaded on the electrode surface, which can reduce overpotential and improve discharge capacity and battery reversibility. In addition, the preparation method provided by the present invention has simple synthesis steps and is suitable for large-scale production, promotion and application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a SEM image of the porous carbon fiber thin film electrode prepared in Example 1 of the present invention.

[0022] Figure 2 The image shows the XRD pattern of the porous carbon fiber thin film electrode prepared in Example 1 of this invention.

[0023] Figure 3 This is a pore size distribution diagram of the porous carbon fiber thin film electrode prepared in Example 1 of the present invention.

[0024] Figure 4 This is a density of states distribution diagram of the RuPtFeCoCe high-entropy alloy catalyst prepared in Example 1 of this invention supported on porous carbon fibers.

[0025] Figure 5 This is the density of states distribution diagram of the rare earth-free high-entropy alloy catalyst RuPtFeCoNi prepared in Comparative Example 3 of this invention.

[0026] Figure 6 This is a SEM image of the porous carbon fiber thin film electrode prepared in Comparative Example 4 of this invention.

[0027] Figure 7 This is a SEM image of the porous carbon fiber thin film electrode prepared in Comparative Example 5 of the present invention.

[0028] Figure 8 This is a SEM image of the porous carbon fiber thin film electrode prepared in Comparative Example 6 of this invention.

[0029] Figure 9 This is a SEM image of the porous carbon fiber thin film electrode prepared in Comparative Example 7 of the present invention.

[0030] Figure 10 The image shows the XRD pattern of the porous carbon fiber thin film electrode prepared in Comparative Example 8 of this invention. Detailed Implementation

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0032] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0034] In this invention, the polyvinyl alcohol (PVA) is designated as PVA1788 (viscosity 25.0-30.0 mPa·s) and manufactured by Aladdin; the polytetrafluoroethylene (PTFE) is a 60wt% concentrated dispersion and manufactured by Aladdin; and the boric acid (BA) is of ultrapure grade and manufactured by Aladdin.

[0035] Example 1 This embodiment provides a method for preparing porous carbon fiber thin film electrodes loaded with metal alloy nanoparticles for lithium-oxygen / air batteries, specifically as follows: (1) Dissolve 1.2 g of polyvinyl alcohol (PVA) powder (carbon-forming agent) in 7.8 g of water, add 8 g of 60 wt% polytetrafluoroethylene (PTFE) emulsion (pore-forming agent) and 24 μL of 5 wt% boric acid (BA) solution (crosslinking agent), and mix evenly to obtain a spinning solution slurry. The mass ratio of PVA to PTFE is 1:4, and the amount of BA added relative to the total mass of PVA and PTFE is 0.02 wt%. (2) Set the voltage to 22 kV, the spinning distance to 18 cm, and the spinning solution flow rate to 1 mL / h. -1 The ambient temperature was 25℃ and the ambient humidity was 40 RH%. The spinning solution slurry obtained in step (1) was electrospun for 4 h to obtain a spun fiber film. (3) Cut the spun fiber film obtained in step (2) into 5*5 cm sheets and press it with a 5 mm thick graphite plate for two-step sintering. First, pre-oxidize and sinter in a muffle furnace at 230°C in air for 3 hours, and then transfer it to a tube furnace at 900°C in argon for 2 hours to form a porous carbon fiber film electrode. (4) A mixed metal salt solution was prepared by using cerium chloride, ruthenium chloride, chloroplatinic acid, ferric chloride, and cobalt chloride as metal precursors and ethanol as solvent, wherein the concentration of each metal ion in the mixed metal salt solution was 0.01 mol·L⁻¹. -1 ; (5) Dissolve the mixed metal salt solution obtained in step (4) at 30 μL·cm-2 The amount is uniformly added to the porous carbon fiber thin film electrode prepared in step (3), and then subjected to carbon thermal shock at 2000℃ for 100 ms by Joule heating to obtain the porous carbon fiber thin film electrode loaded with metal alloy nanoparticles for lithium-oxygen / air batteries.

[0036] The surface morphology, XRD diffraction pattern, and pore size distribution of the porous carbon fiber thin film electrode prepared in Example 1 were tested, and the results are as follows: Figures 1-3 As shown.

[0037] Figure 1 The surface morphology of the porous carbon fiber thin film electrode is shown. Figure 2 The XRD diffraction pattern of the porous carbon fiber thin film electrode is shown. Figure 3 This is a pore size distribution diagram of the porous carbon fiber thin film electrode in Example 1, combined with... Figures 1-3 As can be seen, the example successfully prepared a porous structure with nanoscale. The processed electrode surface has a large number of channels distributed in the range of micropores, mesopores and macropores. Alloy nanoparticles are uniformly loaded on the porous fibers. This porous structure can effectively increase the three-phase interface area of ​​the battery reaction, catalyze the reaction, reduce the overpotential, and improve the discharge capacity and battery reversibility.

[0038] Example 2 The difference between this embodiment and embodiment 1 is that cerium chloride in step (4) is replaced with lanthanum chloride, while the rest of the preparation methods are the same as in embodiment 1, thus obtaining the porous carbon fiber thin film electrode of this embodiment.

[0039] Example 3 The difference between this embodiment and embodiment 1 is that cerium chloride in step (4) is replaced with praseodymium chloride, while the rest of the preparation methods are the same as in embodiment 1, thus obtaining the porous carbon fiber thin film electrode of this embodiment.

[0040] Example 4 The difference between this embodiment and embodiment 1 is that in step (4), cerium chloride is replaced with neodymium chloride, and the rest of the preparation methods are the same as in embodiment 1, so as to obtain the porous carbon fiber thin film electrode of this embodiment.

[0041] Comparative Example 1 The difference between this comparative example and Example 1 is that steps (4) and (5) are not performed, while the rest of the preparation methods are the same as in Example 1, resulting in the porous carbon fiber thin film electrode of this comparative example.

[0042] Comparative Example 2 The difference between this comparative example and Example 1 is that cerium chloride, ferric chloride, and cobalt chloride are not added in step (4), while the rest of the preparation methods are the same as in Example 1, resulting in the porous carbon fiber thin film electrode of this comparative example.

[0043] Comparative Example 3 The difference between this comparative example and Example 1 is that in step (4), cerium chloride is replaced with nickel chloride, while the rest of the preparation methods are the same as in Example 1, thus obtaining the porous carbon fiber thin film electrode of this comparative example.

[0044] The lithium-oxygen battery performance of the porous carbon fiber thin film electrodes prepared in Examples 1-4 and Comparative Examples 1-3 was tested under the overpotential test condition of 100 mA g. -1 The battery cycle test conditions are 500 mA g. -1 1000 mAh g -1 The test results are shown in Table 1.

[0045] Table 1. Effect of metal precursors on the performance of lithium-oxygen batteries

[0046] As can be seen from Examples 1 to 4 in Table 1, only by using rare earth metal elements loaded on porous carbon fiber films as the positive electrode for lithium-oxygen batteries can the overpotential be reduced and the number of cycles significantly increased. Comparing Example 1 and Comparative Example 3 in Table 1, it can be seen that the overpotential of the lithium-oxygen battery without the introduction of rare earth high-entropy alloy is increased by 1 times compared with the positive electrode containing rare earth high-entropy alloy, and the number of battery cycles is reduced by about 70%.

[0047] Further testing of the density of states distribution images of the catalysts prepared in Example 1 and Comparative Example 3 yielded the following results: Figures 4-5 As shown. Among them, Figure 4 This is an image showing the density of states distribution of the RuPtFeCoCe high-entropy alloy catalyst supported on porous carbon fibers, prepared in Example 1 of this invention. Figure 5 This is a density of states distribution image of the rare-earth-free high-entropy alloy catalyst RuPtFeCoNi prepared in Comparative Example 3 of this invention. (Comparison) Figure 4 and Figure 5 It is evident that the introduction of rare earth elements restructures the electronic distribution of each element in the alloy, resulting in an overall decrease in the d-band center. This can further regulate the catalyst's ability to bind reaction intermediates and optimize catalytic performance. Therefore, thanks to the regulation of the density of states of each element in the alloy and the optimization of the d-band center by the introduction of rare earth elements, the overpotential of the battery using a rare earth high-entropy alloy is reduced and the cycle life is significantly increased compared to a cathode without a rare earth high-entropy alloy.

[0048] Comparative Example 4 The difference between this comparative example and Example 1 is that the carbon thermal shock temperature in step (5) is adjusted to 800°C, while the rest of the preparation methods are the same as in Example 1, thus obtaining the porous carbon fiber thin film electrode of this comparative example.

[0049] Comparative Example 5 The difference between this comparative example and Example 1 is that the carbon thermal shock time in step (5) is adjusted to 10 ms, while the rest of the preparation methods are the same as in Example 1, thus obtaining the porous carbon fiber thin film electrode of this comparative example.

[0050] Comparative Example 6 The difference between this comparative example and Example 1 is that the amount of the mixed metal salt solution added in step (5) is adjusted to 200 mL·cm⁻¹. -2 The remaining preparation methods are the same as in Example 1, resulting in the porous carbon fiber thin film electrode of this comparative example.

[0051] SEM images of the porous carbon fiber thin film electrodes prepared in Comparative Examples 4-6 are shown below. Figures 6-8 As shown. According to Figure 1 and Figure 6 It is evident that a carbon thermal shock temperature as low as 800℃ is insufficient to completely decompose and reduce the metal precursor. (Comparison) Figure 1 and Figure 7 It was found that even with a relatively short carbon thermal shock time, it was difficult to completely decompose and reduce the metal precursor. And combined with... Figure 1 and Figure 8 It can be seen that excessive metal precursor loading reduces the electrical and thermal conductivity of the material, making it difficult to decompose and reduce after carbon thermal shock.

[0052] Comparative Example 7 The difference between this comparative example and Example 1 is that the amount of PTFE solution used in step (1) is adjusted to 2 g, the mass ratio of PVA to PTFE is 1:1, the amount of BA added relative to the total mass of PVA and PTFE is 0.05 wt%, and the rest of the preparation methods are the same as in Example 1, so as to obtain the porous carbon fiber thin film electrode of this comparative example.

[0053] The SEM images of the porous carbon fiber thin film electrode prepared in Comparative Example 7 are shown below. Figure 9 As shown. Comparison Figure 1 and Figure 9 It can be seen that adding less pore-forming agent reduces the number of pores in the synthesized porous carbon nanofibers, thus reducing the oxygen and electrolyte channels when used as the positive electrode of a lithium-air battery, and decreasing the space for the reaction products to be contained.

[0054] Comparative Example 8 The difference between this comparative example and Example 1 is that ruthenium chloride and chloroplatinic acid are not added in step (4), while the rest of the preparation methods are the same as in Example 1, and the porous carbon fiber thin film electrode of this comparative example is obtained.

[0055] The XRD pattern of the porous carbon fiber thin film electrode prepared in Comparative Example 8 is shown in the figure. Figure 10 As shown. From Figure 10 As can be seen, due to the reduction of metal elements, only cerium chloride, ferric chloride, and cobalt chloride remain. The weak entropy effect results in low solubility of rare earth elements, making it difficult for rare earth Ce to form an alloy with Fe and Co. The alloy is difficult to form a phase and exhibits very weak metal alloy XRD diffraction peaks.

[0056] In summary, this invention accelerates electrode reactions and improves battery performance by synthesizing rare-earth-containing high-entropy catalysts supported on porous carbon nanofibers. It addresses the problems of uneven and unreasonable pore size distribution and weak catalyst adjustability in existing lithium-oxygen / air battery cathodes. The invention innovatively uses Joule heating to subject the precursor material to carbothermic shock, thereby obtaining high-entropy alloy nanoparticles supported on porous carbon nanofibers. By comprehensively controlling the ratio of pore-forming agent to carbon-forming agent, the amount and type of metal precursor, and the Joule heating process parameters, the resulting electrode not only possesses abundant pores but also exhibits uniformly loaded alloy catalyst particles on the porous carbon fiber surface. This reduces the overpotential of the lithium-oxygen battery and significantly improves the discharge capacity and battery reversibility.

[0057] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a porous carbon fiber thin film electrode loaded with metal alloy nanoparticles for lithium-oxygen / air batteries, characterized in that: include, The carbon-forming agent is dissolved in water, and a pore-forming agent and a crosslinking agent are added. After mixing evenly, a spinning solution slurry is obtained. Electrospinning is performed on the spinning solution slurry to obtain spun fiber films; The spun fiber film is sintered in two steps to form a porous carbon fiber film electrode. A mixed metal salt solution was prepared by using a metal precursor and a solvent; A mixed metal salt solution is dropped onto a porous carbon fiber thin film electrode, and then subjected to a carbothermal shock at 1600~2800℃ for 50~500 ms by Joule heating to obtain a porous carbon fiber thin film electrode for lithium-oxygen / air batteries loaded with metal alloy nanoparticles.

2. The preparation method according to claim 1, characterized in that: The carbon-forming agent includes one or more of the following: polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyethersulfone (PES), polyurethane (PU), polylactic acid (PLA), polystyrene (PS), polyimide (PI), polyetherimide (PEI), poly(p-phenylene isophthalamide) (PMIA), collagen, silk fibroin, hyaluronic acid, chitosan, and chitin; the pore-forming agent includes one or more of the following: polymer microspheres and inorganic non-metallic elemental particles; the crosslinking agent includes one or more of the following: polybasic acids, polyols, and organic compounds containing unsaturated double bonds.

3. The preparation method according to claim 2, characterized in that: The mass ratio of the carbonizing agent to the pore-forming agent is 1:2~4, and the amount of crosslinking agent added relative to the total mass of the carbonizing agent and the pore-forming agent is 0.02~0.04wt%.

4. The preparation method according to claim 1, characterized in that: The method involves preparing a mixed metal salt solution using a metal precursor and a solvent. The metal precursor includes rare earth metal salts, transition metal salts, and inorganic metal acids. The concentration of each metal ion in the mixed metal salt solution is 0.01–0.1 mol·L⁻¹. -1 .

5. The preparation method according to claim 1, characterized in that: The mixed metal salt solution is dropwise added to the porous carbon fiber thin film electrode, wherein the amount of mixed metal salt solution added is 10~100 μL·cm. -2 .

6. The preparation method according to claim 1, characterized in that: The spinning solution slurry is electrospinned, wherein the electrospinning voltage is 10~40 kV and the electrospinning solution flow rate is 0.3~5 mL·h. -1 The receiving distance for electrospinning is 15~30 cm, the ambient temperature for electrospinning is 20~30℃, and the ambient humidity for electrospinning is 25~40 RH.

7. The preparation method according to claim 1, characterized in that: The process involves a two-step sintering of the spun fiber film, comprising pre-oxidation sintering and carbonization sintering. The pre-oxidation sintering temperature is 220-280℃, the pre-oxidation sintering time is 2-4 h, and the pre-oxidation sintering atmosphere is air. The carbonization sintering temperature is 600-1200℃, the carbonization sintering time is 1.5-4 h, and the carbonization sintering atmosphere is one or more of argon, nitrogen, and carbon dioxide.

8. The preparation method according to claim 7, characterized in that: In both sintering processes, graphite plates are used to provide stretching force.

9. A porous carbon fiber thin film electrode for lithium-oxygen / air batteries prepared by the preparation method according to any one of claims 1 to 8.

10. The porous carbon fiber thin film electrode for lithium-oxygen / air batteries with loaded metal alloy nanoparticles as described in claim 9, characterized in that: The electrode is a porous structure electrode, which includes microporous structure, mesoporous structure and macroporous structure. The pore size of the microporous structure is 0~3 nm, the pore size of the mesoporous structure is 3~50 nm, and the pore size of the macroporous structure is >50 nm.

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