Flexible cobalt molybdate / zirconium oxide nanofiber membrane and preparation method thereof
By introducing semi-gel zirconium sol into cobalt molybdate nanofiber solution and employing rapid gel solidification and calcination-liquid nitrogen quenching techniques, flexible cobalt molybdate/zirconia nanofiber membranes were prepared, solving the problems of brittleness and poor deformability, and realizing the industrial production of high-performance fibers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANTONG UNIV
- Filing Date
- 2025-12-29
- Publication Date
- 2026-04-21
AI Technical Summary
Existing cobalt molybdate nanofiber membranes are brittle and have poor deformability, and the introduction of polymers in traditional preparation methods leads to fiber brittleness and poor mechanical properties.
Semi-gel zirconium sol was introduced into molybdenum and cobalt salt solutions. Ammonia fumigation was used for rapid gelation and solidification, followed by rapid calcination and liquid nitrogen quenching. This avoided damage to the fiber structure during high-temperature calcination and resulted in the formation of fine microcrystalline and amorphous/low-order grain boundary structures.
A cobalt molybdate/zirconia nanofiber membrane with excellent flexibility and deformability was obtained, solving the problem of brittle fracture. Moreover, the preparation method is simple, low-cost, and easy to industrialize.
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Figure CN121896793A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of ceramic nanofiber material preparation technology, specifically relating to a method for preparing a flexible cobalt molybdate / zirconia nanofiber membrane. Background Technology
[0002] Cobalt molybdate, as a transition metal oxide, possesses excellent properties such as stable crystal structure, strong redox ability, and good conductivity, making it promising for applications in energy and environmental protection fields such as electrocatalysis, photocatalysis, high-temperature insulation, lithium-ion batteries, and supercapacitors. Currently, most prepared cobalt molybdate materials are in particulate form, primarily loaded onto substrate surfaces via spraying or adhesive bonding. However, the large amount of adhesive covering the particle surface significantly reduces the specific surface area and ion transport rate, severely impacting its catalytic activity. Cobalt molybdate fiber materials offer advantages such as a large aspect ratio, good continuity, and high aggregate structural stability, effectively improving the utilization rate of active sites and catalytic activity. Among numerous fiber material preparation methods, electrospinning, with its simple manufacturing equipment, wide range of spinnable raw materials, and good fiber structure tunability, has become one of the main approaches for preparing nanofiber materials. Currently, over 50 types of inorganic oxide nanofiber membranes have been prepared using electrospinning technology, exhibiting excellent application performance. However, the common problems of high brittleness and poor mechanical properties in existing inorganic fibers still significantly limit their practical applications.
[0003] Electrochimica Acta 196 (2016) 125-130 reported the preparation of cobalt molybdate nanofibers and cobalt molybdate / graphene composite nanofibers using electrospinning. These methods involve the addition of polymers during the preparation of cobalt molybdate nanofibers, resulting in a low ceramic component content in the precursor fiber membrane and consequently, extremely low inorganic fiber yield. Furthermore, excessive organic matter in the precursor fibers leads to severe volume shrinkage during calcination, resulting in a hard, brittle inorganic fiber membrane with poor mechanical properties. Journal of Colloid and Interface Science 553 (2019) 320-327 reported the in-situ formation of cobalt molybdate nanoparticles in porous carbon nanofibers using electrospinning and annealing processes. However, the large amount of polymer in the precursor fibers carbonizes and decomposes during annealing, leading to structural instability and numerous defects in the porous carbon nanofibers, making the fibers brittle and difficult to obtain flexible cobalt molybdate nanofibers. Summary of the Invention
[0004] The purpose of this invention is to provide a flexible cobalt molybdate / zirconia nanofiber membrane and its preparation method, which solves the problems of easy brittleness and poor deformability of existing cobalt molybdate nanofiber membranes.
[0005] This invention significantly improves the spinnability of the spinning solution by introducing semi-gel zirconium sol into molybdenum and cobalt salt solutions. Simultaneously, because no polymer is introduced into the precursor solution, the intact skeletal structure of the single fiber is prevented from being destroyed by the decomposition of a large number of organic components during calcination, ultimately resulting in a flexible cobalt molybdate / zirconia nanofiber membrane. First, the semi-gel zirconium sol is added to a mixed solution of molybdenum and cobalt salts. The incomplete network molecular chain structure in the semi-gel zirconium sol effectively improves the viscoelasticity of the mixed solution. In the subsequent electrospinning process, ammonia fumigation is used in the spinning region, causing the spinning jet tip to locally and rapidly gel and solidify after entering the spinning region from the spinneret. The locally solidified jet continues to fly forward and undergoes sufficient stretching, thereby forming the precursor fiber. Finally, the precursor fiber membrane is directly placed into a muffle furnace heated to a set temperature for calcination. Unlike the slow heating process in conventional ceramic fiber calcination, this effectively avoids the slow growth of grains during the heating process. Furthermore, after holding the membrane in the muffle furnace for a period of time, it is directly removed and rapidly quenched in liquid nitrogen. This significantly inhibits the fusion growth of grains during natural cooling, resulting in the formation of numerous fine microcrystals within the fibers. This yields a cobalt molybdate / zirconia nanofiber membrane with excellent flexibility and deformability. This invention solves the problems of brittleness and poor deformability in existing cobalt molybdate nanofiber membranes. Moreover, the preparation method of this invention is simple, low-cost, and easy to industrialize.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a flexible cobalt molybdate / zirconia nanofiber membrane, comprising the following steps: Step 1): Add the molybdenum salt and cobalt salt to the corresponding solvent and stir for 10-30 minutes until they are completely dissolved; Step 2): Add one or more zirconium salts to a solvent containing an appropriate amount of ligand, adjust the pH of the solution to 2.5~6.5, control the hydrolysis and condensation rate of the zirconium salts, and obtain a semi-gel zirconium sol. Step 3): Mix the semi-gel zirconium sol obtained in Step 2) with the solution in Step 1), and continue stirring for 30-180 min to make it uniformly mixed, so as to prepare a spinnable precursor solution; Step 4): Electrospin the precursor spinning solution from Step 3), and use ammonia water fumigation in the spinning area to promote the rapid gelation and solidification of the spinning jet into fibers, thereby preparing the precursor fiber membrane. Step 5): The precursor fiber membrane obtained in Step 4) is directly placed into a muffle furnace heated to a set temperature for calcination. After a period of time, it is directly taken out and rapidly cooled in liquid nitrogen to finally obtain a flexible cobalt molybdate / zirconia nanofiber membrane.
[0007] Preferably, in step 1), the molybdenum salt is any one or more of ammonium molybdate, molybdenum pentachloride, molybdenum acetylacetonate, and phosphomolybdic acid hydrate; the cobalt salt is any one or more of cobalt acetate, cobalt acetylacetonate, cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, and cobalt chloride hexahydrate; the solvent is one or more of water, methanol, ethanol, ethylene glycol, propanol, acetone, N,N-dimethylformamide, and N,N-dimethylacetamide; the molar ratio of molybdenum salt to cobalt salt is 1:1; and the ratio of molybdenum salt, cobalt salt, and solvent is 10g:25~100mL.
[0008] Preferably, in step 2), the zirconium salt is any one or more of zirconium acetate, zirconium n-propoxide, zirconium n-butoxide, zirconium acetylacetone, basic zirconium carbonate, zirconium nitrate pentahydrate, and zirconium oxychloride octahydrate; the ligand is any one or more of ethylenediaminetetraacetic acid, acetylacetone, acetic acid, citric acid, tartaric acid, and diethanolamine; the ratio of zirconium salt to solvent is 5g:5~50mL; and the molar ratio of zirconium salt to ligand is 1:1~1:10.
[0009] Preferably, in step 3), the molar ratio of zirconium salt to molybdenum salt is 1:100 to 10:100; and the dynamic viscosity of the precursor solution is 1 to 20 Pa·s.
[0010] Preferably, in step 4), the ambient temperature for electrospinning is 38~55℃ and the relative humidity is 30~70%; the process parameters for electrospinning are: voltage 10~60kV, distance between the receiving device and the spinneret 10~50cm, and injection speed 0.1~10mL / h; the saturated vapor pressure of ammonia in the sealed chamber is 5~80kPa.
[0011] Preferably, in step 5), the maximum calcination temperature of the muffle furnace is 700~1400℃, and the temperature is maintained at the maximum temperature for 10~180min; the quenching time in liquid nitrogen is 10~60s.
[0012] Secondly, the present invention provides a flexible cobalt molybdate / zirconia nanofiber membrane, characterized in that the molar ratio of zirconium oxide to cobalt molybdate in the flexible cobalt molybdate / zirconia nanofiber is 1:100~10:100, the average fiber diameter is 30~1000nm, the average grain size inside the fiber is 5~60nm, the flexibility of the fiber membrane is 20~100mN, and the fiber membrane does not break after being repeatedly bent and folded 10,000 times.
[0013] The principle of this invention is as follows: In the spinning solution preparation stage, this invention introduces semi-gel zirconium sol into the molybdenum and cobalt salt solutions. The incomplete network molecular chain structure and hanging hydroxyl groups in the semi-gel zirconium sol effectively improve the viscoelasticity and entanglement density of the molybdenum and cobalt salt mixed solution, thereby giving the precursor solution excellent spinnability. This invention avoids the addition of large amounts of polymers to improve the spinnability of the precursor solution in traditional methods, fundamentally eliminating the risk of single-fiber skeleton structure collapse due to the violent decomposition and escape of a large number of organic components during subsequent high-temperature calcination, thus laying the foundation for obtaining an inorganic fiber network with a complete structure and good mechanical properties. In the fiber forming stage, this invention uses an ammonia steam fumigation environment in the electrospinning area. When the spinning jet is ejected from the spinneret, the jet is affected by the ammonia steam, and the zirconium sol components on the jet surface undergo a rapid condensation reaction from the surface to the interior, resulting in local instantaneous gel solidification at the jet tip. Under the stretching force of an electric field, the uncured portion of the spinning jet is continuously and uniformly stretched and refined, while solvent evaporation and gelation reactions are fully carried out, thus producing a uniform and continuous precursor fiber. Subsequently, in the calcination stage, this invention employs a calcination method different from traditional ceramic materials, namely rapid calcination-liquid nitrogen quenching. The precursor fiber membrane is directly placed into a muffle furnace preheated to the target temperature for rapid calcination, which greatly limits the premature growth and coarsening of crystal nuclei in the low-temperature region. After high-temperature holding, the fiber membrane is quickly removed and immediately immersed in liquid nitrogen for rapid quenching. This rapid cooling process instantly "freezes" the microcrystalline structure and grain boundary state at high temperature, inhibiting the fusion and growth of grains through the Oswald ripening mechanism during natural slow cooling. Ultimately, a unique composite microstructure composed of high-density fine microcrystals and a large number of amorphous / low-order grain boundary regions is formed inside the fiber. This "fine-grained, weak-interface" structure allows stress to be effectively dissipated through flexible grain boundaries during fiber deformation, resulting in excellent flexibility and deformability on a macroscopic scale.
[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a flexible cobalt molybdate / zirconia nanofiber membrane and its preparation method, which effectively solves the problems of easy brittleness and poor deformability of existing cobalt molybdate nanofiber membranes. Moreover, the preparation method is simple, low-cost and easy to industrialize.
[0015] (2) A flexible cobalt molybdate / zirconia nanofiber membrane of the present invention has excellent flexibility and deformability. Attached Figure Description
[0016] Figure 1 The image shows the fiber morphology of the flexible cobalt molybdate / zirconia nanofiber membrane prepared in this invention. Figure 2 The fiber morphology of the fiber membrane prepared by the traditional method is shown in the image. Detailed Implementation
[0017] To more clearly present the purpose, technical solution, and significant beneficial effects of this application, a detailed description of the application is now provided through embodiments. It should be clarified that the embodiments described in this specification are for illustrative purposes only and do not constitute a limitation on the scope of this application.
[0018] For the sake of brevity, only a portion of the numerical ranges are explicitly disclosed in this application. In reality, any lower limit can be combined with any upper limit to form a new range that is not explicitly stated; similarly, any lower limit or any upper limit can be combined to generate ranges that are not explicitly mentioned. Furthermore, even if not explicitly stated in the text, every specific value between the endpoints of a range is included within that range. These values can serve as lower or upper limits, combined with other values, to construct numerical intervals that are not explicitly stated.
[0019] It should be emphasized that the above content of this application is not intended to cover all disclosed implementation methods. The following content will illustrate exemplary implementation methods in more detail through specific examples. Throughout this application, a series of embodiments are used for illustration in many places, and these embodiments can be combined in various ways according to actual needs. Each example is only a typical example and is not a complete enumeration of all possible situations. The following embodiments further illustrate the disclosure of this application in detail and are only illustrative examples. The reagents used in the embodiments can all be obtained by commercial purchase or conventional synthesis methods, and the instruments used are all commercially available.
[0020] Example 1 A method for preparing a flexible cobalt molybdate / zirconia nanofiber membrane includes the following steps: Step 1): Add ammonium molybdate and cobalt acetate to N,N-dimethylformamide and stir for 30 minutes until completely dissolved; Step 2): Add zirconium oxychloride octahydrate to a mixed solution containing water and acetylacetone, adjust the pH of the solution to 3.5, control the hydrolysis and condensation rate of the zirconium salt, and obtain a semi-gel zirconium sol. The ratio of zirconium oxychloride octahydrate to water is 5 g: 20 mL, and the molar ratio of zirconium oxychloride octahydrate to the ligand acetylacetone is 1:8.
[0021] Step 3): Mix the semi-gel zirconium sol obtained in Step 2) with the solution in Step 1), and continue stirring for 120 min to ensure uniform mixing, thus preparing a spinnable precursor solution. The molar ratio of zirconium oxychloride octahydrate to ammonium molybdate is 5:100; the dynamic viscosity of the precursor solution is 15 Pa·s. Step 4): The precursor spinning solution from Step 3) is electrospun, and ammonia water is used to fumigate the spinning area to promote rapid gelation and solidification of the spinning jet into fibers, thus preparing a precursor fiber membrane. The electrospinning environment temperature is 50℃, the relative humidity is 60%, the voltage is 30kV, the distance between the receiving device and the spinneret is 20cm, and the infusion rate is 1mL / h; the saturated vapor pressure of ammonia water in the sealed chamber is 60kPa.
[0022] Step 5): The precursor fiber membrane obtained in Step 4) is directly placed into a muffle furnace heated to the set temperature for calcination. After a period of time, it is directly removed and rapidly cooled in liquid nitrogen to finally obtain a flexible cobalt molybdate / zirconia nanofiber membrane. The maximum calcination temperature of the muffle furnace is 1000℃, and it is held at the maximum temperature for 30 minutes; the quenching time in liquid nitrogen is 60 seconds.
[0023] The cobalt molybdate / zirconia nanofibers prepared above have an average diameter of 360 nm, an average grain size of 25 nm, a fiber membrane flexibility of 80 mN, and do not break after 10,000 repeated bending and folding. The fiber morphology is as follows. Figure 1 As shown.
[0024] Example 2 A method for preparing a flexible cobalt molybdate / zirconia nanofiber membrane includes the following steps: Step 1): Add ammonium molybdate and cobalt chloride hexahydrate to water and stir for 30 minutes until completely dissolved; Step 2): Add zirconium propoxide to a mixed solution containing propanol and acetic acid, adjust the pH of the solution to 5, and control the hydrolysis and condensation rate of the zirconium salt to obtain a semi-gel zirconium sol. The ratio of zirconium propoxide to propanol is 5 g: 30 mL, and the molar ratio of zirconium propoxide to acetic acid is 1:6.
[0025] Step 3): Mix the semi-gel zirconium sol obtained in Step 2) with the solution in Step 1), and continue stirring for 90 min to ensure uniform mixing, thus preparing a spinnable precursor solution. The molar ratio of zirconium propoxide to ammonium molybdate is 5:100; the dynamic viscosity of the precursor solution is 12 Pa·s.
[0026] Step 4): The precursor spinning solution from Step 3) is electrospun, and ammonia water is used to fumigate the spinning area to promote rapid gelation and solidification of the spinning jet into fibers, thus preparing the precursor fiber membrane. The electrospinning environment temperature is 55℃, the relative humidity is 65%, the voltage is 28kV, the distance between the receiving device and the spinneret is 25cm, and the injection rate is 2mL / h; the saturated vapor pressure of ammonia water in the sealed chamber is 55kPa.
[0027] Step 5): The precursor fiber membrane obtained in Step 4) is directly placed into a muffle furnace heated to a set temperature for calcination. After a period of time, it is directly removed and rapidly cooled in liquid nitrogen to finally obtain a flexible cobalt molybdate / zirconia nanofiber membrane. The maximum calcination temperature of the muffle furnace is 1100℃, and it is held at the maximum temperature for 10 minutes; the quenching time in liquid nitrogen is 30 seconds.
[0028] The cobalt molybdate / zirconia nanofibers prepared above have an average diameter of 320 nm, an average grain size of 23 nm, a fiber membrane flexibility of 50 mN, and do not break after 10,000 repeated bending and folding.
[0029] Example 3 A method for preparing a flexible cobalt molybdate / zirconia nanofiber membrane includes the following steps: Step 1): Add molybdenum acetylacetonate and cobalt acetylacetonate to a mixed solution of ethanol and N,N-dimethylformamide and stir for 30 minutes until completely dissolved; Step 2): Add basic zirconium carbonate to a mixed solution containing ethanol and acetic acid, adjust the pH of the solution to 4.5, control the hydrolysis and condensation rate of the zirconium salt, and obtain a semi-gel zirconium sol. The ratio of basic zirconium carbonate to solvent ethanol is 5 g: 40 mL, and the molar ratio of basic zirconium carbonate to ligand acetic acid is 1:6.
[0030] Step 3): Mix the semi-gel zirconium sol obtained in Step 2) with the solution in Step 1), and continue stirring for 150 min to ensure uniform mixing, thus preparing a spinnable precursor solution. The molar ratio of basic zirconium carbonate to molybdenum acetylacetonate is 10:100; the dynamic viscosity of the precursor solution is 16 Pa·s.
[0031] Step 4): The precursor spinning solution from Step 3) is electrospun, and ammonia water is used to fumigate the spinning area to promote rapid gelation and solidification of the spinning jet into fibers, thus preparing the precursor fiber membrane. The electrospinning environment temperature is 60℃, the relative humidity is 55%, the voltage is 25kV, the distance between the receiving device and the spinneret is 28cm, and the infusion rate is 3mL / h; the saturated vapor pressure of ammonia water in the sealed chamber is 52kPa.
[0032] Step 5): The precursor fiber membrane obtained in Step 4) is directly placed into a muffle furnace heated to the set temperature for calcination. After a period of time, it is directly removed and rapidly cooled in liquid nitrogen to finally obtain a flexible cobalt molybdate / zirconia nanofiber membrane. The maximum calcination temperature of the muffle furnace is 900℃, which is maintained at the maximum temperature for 20 minutes; the quenching time in liquid nitrogen is 40 seconds.
[0033] The cobalt molybdate / zirconia nanofibers prepared above have an average diameter of 360 nm, an average grain size of 25 nm, a fiber membrane flexibility of 45 mN, and do not break after 10,000 repeated bending and folding.
[0034] Comparative Example 1 Flexible cobalt molybdate nanofiber membranes were prepared according to the method in Example 1, except that semi-gel zirconium sol was not added to the mixed solution of molybdenum and cobalt salts. When the prepared solution was electrospun, a spray pattern was observed at the needle tip, and no fibers were received. This indicates that without the introduction of semi-gel zirconium sol, the mixed solution lacks spinnability, which does not meet the requirements for the materials developed in this invention.
[0035] Comparative Example 2 Flexible cobalt molybdate nanofiber membranes were prepared according to the method in Example 1, except that a semi-gel zirconium sol was not added to the mixed solution of molybdenum and cobalt salts. Instead, a polymer (e.g., polyvinylpyrrolidone) was added according to a conventional preparation method. Electrospinning of the prepared solution yielded fibers at the needle tip, indicating that the introduction of polyvinylpyrrolidone indeed enhances the spinnability of the mixed solution. However, after calcination of the precursor fibers, it was observed that the fiber grain size was very large and the fibers were very brittle. Figure 2 This does not meet the requirements for the materials developed in this invention.
[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.
Claims
1. A method for preparing a flexible cobalt molybdate / zirconia nanofiber membrane, characterized in that, Includes the following steps: Step 1): Add the molybdenum salt and cobalt salt to the corresponding solvent and stir for 10-30 minutes until they are completely dissolved; Step 2): Add one or more zirconium salts to a solvent containing an appropriate amount of ligand, adjust the pH of the solution to 2.5~6.5, control the hydrolysis and condensation rate of the zirconium salts, and obtain a semi-gel zirconium sol. Step 3): Mix the semi-gel zirconium sol obtained in Step 2) with the solution in Step 1), and continue stirring for 30-180 min to make it uniformly mixed, so as to prepare a spinnable precursor solution; Step 4): Electrospin the precursor spinning solution from Step 3), and use ammonia water fumigation in the spinning area to promote the rapid gelation and solidification of the spinning jet into fibers, thereby preparing the precursor fiber membrane. Step 5): The precursor fiber membrane obtained in Step 4) is directly placed into a muffle furnace heated to a set temperature for calcination. After a period of time, it is directly taken out and rapidly cooled in liquid nitrogen to finally obtain a flexible cobalt molybdate / zirconia nanofiber membrane.
2. The method for preparing the flexible cobalt molybdate / zirconia nanofiber membrane according to claim 1, characterized in that, In step 1), the molybdenum salt is any one or more of ammonium molybdate, molybdenum pentachloride, molybdenum acetylacetonate, and phosphomolybdic acid hydrate; the cobalt salt is any one or more of cobalt acetate, cobalt acetylacetonate, cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, and cobalt chloride hexahydrate; the solvent is one or more of water, methanol, ethanol, ethylene glycol, propanol, acetone, N,N-dimethylformamide, and N,N-dimethylacetamide; the molar ratio of molybdenum salt to cobalt salt is 1:1; and the ratio of molybdenum salt, cobalt salt, and solvent is 10g:25~100mL.
3. The method for preparing the flexible cobalt molybdate / zirconia nanofiber membrane according to claim 1, characterized in that, In step 2), the zirconium salt is any one or more of zirconium acetate, zirconium n-propoxide, zirconium n-butoxide, zirconium acetylacetone, basic zirconium carbonate, zirconium nitrate pentahydrate, and zirconium oxychloride octahydrate; the ligand is any one or more of ethylenediaminetetraacetic acid, acetylacetone, acetic acid, citric acid, tartaric acid, and diethanolamine; the ratio of zirconium salt to solvent is 5g:5~50mL; and the molar ratio of zirconium salt to ligand is 1:1~1:
10.
4. The method for preparing the flexible cobalt molybdate / zirconia nanofiber membrane according to claim 1, characterized in that, In step 3), the molar ratio of zirconium salt to molybdenum salt is 1:100 to 10:100; the dynamic viscosity of the precursor solution is 1 to 20 Pa·s.
5. The method for preparing the flexible cobalt molybdate / zirconia nanofiber membrane according to claim 1, characterized in that, In step 4), the ambient temperature for electrospinning is 38~55℃ and the relative humidity is 30~70%; the process parameters for electrospinning are: voltage 10~60kV, distance between the receiving device and the spinneret 10~50cm, and injection speed 0.1~10mL / h; the saturated vapor pressure of ammonia in the sealed box is 5~80kPa.
6. The method for preparing the flexible cobalt molybdate / zirconia nanofiber membrane according to claim 1, characterized in that, In step 5), the maximum calcination temperature of the muffle furnace is 700~1400℃, and it is maintained at the maximum temperature for 10~180min; the quenching time in liquid nitrogen is 10~60s.
7. The flexible cobalt molybdate / zirconia nanofiber membrane prepared by the method according to any one of claims 1-6, characterized in that, The flexible cobalt molybdate / zirconia nanofibers have a molar ratio of zirconium oxide to cobalt molybdate of 1:100 to 10:100, an average fiber diameter of 30 to 1000 nm, an average internal grain size of 5 to 60 nm, a fiber membrane flexibility of 20 to 100 mN, and the fiber membrane does not break after 10,000 repeated bending and folding.