Silane modified rare earth oxide doped composite proton exchange membrane and preparation method thereof

Abstract

The invention belongs to the technical field of organic and inorganic compounds, and provides a silane modified rare earth oxide doped composite proton exchange membrane and a preparation method thereof. The method comprises the following steps: dropwise adding a cerium oxide solution into a silane coupling agent hydrolysate for reaction; and adding an oxidizing agent into the reaction product to carry out oxidation reaction, mixing the obtained modified cerium oxide, polybenzimidazole and a solvent, and drying. Nano cerium oxide uniformly dispersed by ethanol is added into silane coupling agent hydrolysate, silane groups of a silane coupling agent and hydroxyl groups attached to the surface of cerium oxide generate covalent bonds under a dehydration condensation reaction to complete modification, and a condensation reaction product is oxidized to obtain cerium oxide modified by corresponding functional groups. And the product is doped into a PBI film to form an inorganic-organic composite film, so that the conductivity and the mechanical property of the inorganic-organic composite film can be improved at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of organic-inorganic composite materials, and in particular to a silane-modified rare earth oxide-doped composite proton exchange membrane and a preparation method thereof. Background Art

[0002] The proton membrane is the core component of the fuel cell and plays a key role in the performance of the battery. It not only acts as a barrier but also conducts protons. To date, the most commonly used proton exchange membrane (PEMFC) is still the Nafion® membrane of DuPont, USA, which has the advantages of high proton conductivity and good chemical stability. However, Nafion® membranes still have the following disadvantages: (1) Difficult to manufacture and high cost. The synthesis and sulfonation of perfluorinated substances are very difficult. In addition, hydrolysis and sulfonation during the membrane formation process can easily denature and degrade the polymer, making it difficult to form a membrane and resulting in high cost. (2) High requirements for temperature and water content. The optimal operating temperature of the Nafion® series membrane is 70-90°C. Exceeding this temperature will cause its water content to drop sharply and its conductivity to drop rapidly, which hinders the problem of increasing the electrode reaction rate and overcoming catalyst poisoning by appropriately increasing the operating temperature. (3) Some hydrocarbons, such as methanol, have a high permeability and are not suitable for use as proton exchange membranes for direct methanol fuel cells (DMFCs). The problems with the proton membranes currently in use are still low proton conductivity, short service life, and mechanical properties that need to be improved.

[0003] In order to improve the performance of proton exchange membranes, the following improvement methods can be adopted: (1) Organic / inorganic nanocomposite proton exchange membranes, relying on the small size and large specific surface area of ​​nanoparticles to improve the water retention capacity of the composite membrane, thereby achieving the purpose of expanding the operating temperature range of proton exchange membrane fuel cells; (2) Improving the skeleton material of the proton exchange membrane, targeting the shortcomings of the most commonly used membranes, or improving on the basis of the membrane, or using new skeleton materials; (3) Adjusting the internal structure of the membrane to increase the micropores in it to facilitate membrane formation and solve the problem of catalyst poisoning.

[0004] Cerium is an important rare earth element. In the large family of rare earth elements, cerium is the well-deserved big brother. First, it is because of its high content, accounting for 28% of the total rare earth elements. Second, cerium is the second rare earth element discovered after yttrium. Cerium oxide itself can also be used as a fuel cell electrolyte. It has stable performance and properties. It does not react with organic matter and has acceptable mechanical properties. Modification of it can ensure that the performance is improved while giving the membrane a certain mechanical property improvement and at the same time ensuring the stability of the membrane.

[0005] Therefore, it is of great significance to provide a silane-modified rare earth oxide-doped composite proton exchange membrane and a preparation method thereof. Summary of the invention

[0006] The purpose of the present invention is to provide a silane-modified rare earth oxide-doped composite proton exchange membrane and a preparation method thereof in order to overcome the deficiencies of the prior art.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a silane-modified rare earth oxide-doped composite proton exchange membrane, comprising the following steps:

[0009] 1) dispersing cerium oxide in anhydrous ethanol to obtain a cerium oxide solution; reacting a silane coupling agent, water and anhydrous ethanol to obtain a silane coupling agent hydrolyzate;

[0010] 2) adding the cerium oxide solution dropwise to the silane coupling agent hydrolyzate to react and obtain a reaction product; adding an oxidant to the reaction product to carry out an oxidation reaction and obtain modified cerium oxide;

[0011] 3) The modified cerium oxide, polybenzimidazole and solvent are mixed and dried to obtain a silane-modified rare earth oxide-doped composite proton exchange membrane.

[0012] Preferably, in step 1), the volume ratio of the silane coupling agent, water and anhydrous ethanol is 7-9:16-24:73-83; the silane coupling agent comprises one or more of vinyltrimethoxysilane, (3-mercaptopropyl)trimethoxysilane and 3-aminopropyltriethoxysilane.

[0013] Preferably, the mass of cerium oxide is ≤ 3% of the mass of the silane coupling agent hydrolyzate.

[0014] Preferably, the reaction temperatures in step 1) and step 2) are independently 55-65° C., and the reaction times are independently 1.5-2.5 h.

[0015] Preferably, when the silane coupling agent is vinyltrimethoxysilane, the oxidant is concentrated sulfuric acid and potassium permanganate;

[0016] When the silane coupling agent is (3-mercaptopropyl)trimethoxysilane, the oxidant is hydrogen peroxide;

[0017] When the silane coupling agent is 3-aminopropyltriethoxysilane, the oxidant is hydrogen peroxide.

[0018] Preferably, the specific process of adding concentrated sulfuric acid and potassium permanganate to the reaction product for oxidation reaction is: the reaction product and concentrated sulfuric acid are subjected to a first low-temperature reaction, and then potassium permanganate is added to sequentially conduct a second low-temperature reaction and a high-temperature reaction;

[0019] The temperature of the first low temperature reaction and the second low temperature reaction are independently 10-25°C, and the time is independently 12-17 minutes; the temperature of the high temperature reaction is 75-85°C, and the time is 3.5-4.5 hours.

[0020] Preferably, the mass of the modified cerium oxide in step 3) is 0.2-1.1% of the mass of the polybenzimidazole.

[0021] The invention also provides a composite proton exchange membrane doped with silane-modified rare earth oxide prepared by the preparation method.

[0022] The beneficial effects of the present invention include the following:

[0023] 1) The present invention adds nano cerium oxide uniformly dispersed by ethanol (cerium oxide is dispersed in ethanol and has hydroxyl groups attached to the surface) to the hydrolyzed solution of the silane coupling agent, and the silane group of the silane coupling agent and the hydroxyl groups attached to the surface of the cerium oxide form covalent bonds under the dehydration condensation reaction to complete the modification, and oxidizes the condensation reaction product to oxidize its functional group to the target functional group to obtain cerium oxide modified with the corresponding functional group, and dopes the product into the PBI film to form an inorganic-organic composite film. The method of the present invention is applicable to the modification of various inorganic substances using silane coupling agents.

[0024] 2) In the present invention, the grafting of acidic functional groups can improve proton conductivity, while the doping of inorganic nanoparticles can improve the mechanical properties of the organic membrane. The silane-modified rare earth oxide-doped composite proton exchange membrane prepared by the present invention can simultaneously improve the electrical conductivity and mechanical properties of the inorganic-organic composite proton exchange membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The condensation reaction product CeO in Example 1 2 -C 2 H 3 , modified cerium oxide CeO 2 -COOH and pure CeO 2 XRD pattern of

[0026] Figure 2 is the XPS spectrum of the modified cerium oxide of Example 1, wherein a is the full spectrum, b is the Ce spectrum, c is the O spectrum, and d is the Si spectrum;

[0027] Figure 3 The condensation reaction product CeO in Example 1 2 -C 2 H 3 , modified cerium oxide CeO 2 -COOH and pure CeO 2 FTIR spectrum of

[0028] Figure 4 The cross-sectional views are of the silane-modified cerium oxide-doped composite proton exchange membrane and the pure PBI membrane of Example 1, wherein (A) and (B) are pure PBI membranes, and (C) and (D) are the composite proton exchange membrane of Example 1;

[0029] Figure 5 This is an EDS spectrum of a cross section of a silane-modified cerium oxide-doped composite proton exchange membrane of Example 1, wherein red corresponds to the O element, yellow corresponds to the Ce element, and green corresponds to the C element;

[0030] Figure 6 Impedance diagrams of the silane-modified cerium oxide-doped composite proton exchange membrane and pure PBI membrane at 80° C. and 160° C. of Example 1;

[0031] Figure 7 Graphs showing the proton conductivity of the silane-modified cerium oxide-doped composite proton exchange membranes and pure PBI membranes of Examples 1 and 2;

[0032] Figure 8 80° C. is a power density diagram of the silane-modified cerium oxide-doped composite proton exchange membrane and pure PBI membrane of Example 1;

[0033] Fig. 9 160° C. is a power density diagram of the silane-modified cerium oxide-doped composite proton exchange membrane and pure PBI membrane of Example 1;

[0034] Fig.10 is the amount of acid adsorbed by the silane-modified cerium oxide-doped composite proton exchange membrane and the pure PBI membrane of Example 1 and Example 2;

[0035] Fig.11 It is the volume swelling ratio of the silane-modified cerium oxide-doped composite proton exchange membrane and the pure PBI membrane of Example 1 and Example 2 after absorbing phosphoric acid. DETAILED DESCRIPTION

[0036] The present invention provides a method for preparing a silane-modified rare earth oxide-doped composite proton exchange membrane, comprising the following steps:

[0037] 1) dispersing cerium oxide in anhydrous ethanol to obtain a cerium oxide solution; reacting a silane coupling agent, water and anhydrous ethanol to obtain a silane coupling agent hydrolyzate;

[0038] 2) adding the cerium oxide solution dropwise to the silane coupling agent hydrolyzate to react and obtain a reaction product; adding an oxidant to the reaction product to carry out an oxidation reaction and obtain modified cerium oxide;

[0039] 3) The modified cerium oxide, polybenzimidazole (PBI) and a solvent are mixed and dried to obtain a silane-modified rare earth oxide-doped composite proton exchange membrane.

[0040] In the present invention, the mass volume ratio of cerium oxide and anhydrous ethanol in step 1) is preferably 1g:10-15mL, further preferably 1g:11-14mL, and more preferably 1g:12-13mL; the purpose of dispersing cerium oxide in anhydrous ethanol is to allow hydroxyl groups to attach to the surface of cerium oxide to facilitate subsequent reactions.

[0041] In the present invention, the volume ratio of the silane coupling agent, water and anhydrous ethanol in step 1) is preferably 7-9:16-24:73-83, more preferably 7.5-8.5:18-22:76-80, and more preferably 8:20:78; the silane coupling agent preferably comprises one or more of vinyltrimethoxysilane, (3-mercaptopropyl)trimethoxysilane and 3-aminopropyltriethoxysilane.

[0042] In the present invention, the mass of cerium oxide is preferably ≤3% of the mass of the silane coupling agent hydrolyzate, and more preferably ≤2.5% of the mass of the silane coupling agent hydrolyzate.

[0043] In the present invention, the reaction temperature of step 1) and step 2) is independently preferably 55-65°C, more preferably 57-63°C, more preferably 60°C, and the reaction time is independently preferably 1.5-2.5h, more preferably 1.8-2.2h, more preferably 2h.

[0044] In the present invention, when the silane coupling agent is vinyltrimethoxysilane, the oxidant is concentrated sulfuric acid and potassium permanganate; the volume mass ratio of the concentrated sulfuric acid and potassium permanganate is preferably 28-32 mL: 0.8-1.2 g, and more preferably 30 mL: 1 g;

[0045] When the silane coupling agent is (3-mercaptopropyl)trimethoxysilane, the oxidant is hydrogen peroxide, and the mass concentration of hydrogen peroxide is preferably 28-32%, and more preferably 30%; the mass volume ratio of the reaction product and hydrogen peroxide is preferably 2.5-3.5 g:8-12 mL, and more preferably 2.8-3.2 g:9-11 mL, and more preferably 3 g:10 mL, and the oxidation reaction time is preferably 0.8-1.2 h, and more preferably 1 h;

[0046] When the silane coupling agent is 3-aminopropyltriethoxysilane, the oxidant is hydrogen peroxide; the mass concentration of hydrogen peroxide is preferably 28-32%, and more preferably 30%; the mass volume ratio of the reaction product and hydrogen peroxide is preferably 1.5-2.5g:18-22mL, and more preferably 1.8-2.2g:19-21mL, and more preferably 2g:20mL, and the oxidation reaction time is preferably 3.5-4.5h, and more preferably 4h.

[0047] In the present invention, the specific process of adding concentrated sulfuric acid and potassium permanganate to the reaction product for oxidation reaction is preferably: the reaction product and concentrated sulfuric acid are subjected to a first low-temperature reaction, and then potassium permanganate is added to sequentially conduct a second low-temperature reaction and a high-temperature reaction;

[0048] The temperature of the first low-temperature reaction and the second low-temperature reaction is independently preferably 10-25°C, more preferably 15-20°C, and the time is independently preferably 12-17 min, more preferably 14-16 min, and more preferably 15 min; the temperature of the high-temperature reaction is preferably 75-85°C, more preferably 78-82°C, and more preferably 80°C, and the time of the high-temperature reaction is preferably 3.5-4.5 h, and more preferably 4 h.

[0049] The dripping rate of the cerium oxide solution in step 2) of the present invention is preferably 4-6 mL / min, more preferably 4.5-5.5 mL / min, and more preferably 5 mL / min.

[0050] In the present invention, cerium oxide is dispersed in anhydrous ethanol, a large number of hydroxyl groups are attached to the surface of cerium oxide, and the cerium oxide solution is added dropwise into the coupling agent hydrolyzate using a separatory funnel to cause a condensation reaction. After the reaction is completed, the product is dried, and then an oxidant is added for oxidation to obtain modified cerium oxide, which is dark green or black.

[0051] In the present invention, the use method and mechanism of the silane coupling agent are substantially the same. Different coupling agents are selected according to the type of the grafted functional group. The reaction mechanism has the following general formula.

[0052] The reaction formula of the present invention is:

[0053] ①Silane coupling agent hydrolyzes:

[0054]

[0055] Wherein, R is any functional group, R 1 , R 2 and R 3 is an alkoxy group;

[0056] ② The hydrolyzate of the silane coupling agent and the rare earth oxide solution undergo a condensation reaction to obtain a modified rare earth oxide;

[0057]

[0058] Wherein, R is any functional group, and M is any rare earth oxide particle;

[0059] ③ The modified rare earth oxide is subjected to oxidation treatment to obtain an organic-inorganic composite proton exchange membrane containing derivative functional groups.

[0060] In the present invention, when the silane coupling agent is vinyltrimethoxysilane, acetic acid is preferably used as an auxiliary agent, and hydrolysis is carried out under acidic conditions. The amount of acetic acid added is preferably such that the pH value of the reaction system is 4 to 5; the hydrolysis reaction and condensation reaction are shown below.

[0061] ① Hydrolysis of coupling agent: methoxy group on coupling agent is replaced by hydroxyl group:

[0062]

[0063] ② The hydrolyzate of the silane coupling agent and the cerium oxide solution undergo a condensation reaction to obtain a condensation product:

[0064]

[0065] ③Further oxidation of the vinyl group to obtain carboxyl-modified cerium oxide:

[0066]

[0067] In the present invention, when the silane coupling agent is (3-mercaptopropyl)trimethoxysilane, it can be hydrolyzed in a solution of anhydrous ethanol and water. The hydrolysis reaction and condensation reaction are shown below.

[0068] ①Hydrolysis of coupling agent:

[0069]

[0070] ② The hydrolyzate of the silane coupling agent and the cerium oxide solution undergo a condensation reaction to obtain a condensation product:

[0071]

[0072] ③ Oxidize the mercapto group to a sulfonic acid group to obtain sulfonic acid group-modified cerium oxide:

[0073]

[0074] In the present invention, when the silane coupling agent is 3-aminopropyltriethoxysilane, it can be hydrolyzed in a solution of anhydrous ethanol and water. The hydrolysis reaction and condensation reaction are shown below.

[0075] ①Hydrolysis of coupling agent:

[0076]

[0077] ② The hydrolyzate of the silane coupling agent and the cerium oxide solution undergo a condensation reaction to obtain a condensation product:

[0078]

[0079] ③Oxidation of the amino group to obtain nitro-modified cerium oxide:

[0080]

[0081] In the present invention, the mass of the modified cerium oxide in step 3) is preferably 0.2-1.1% of the mass of the polybenzimidazole, and more preferably 0.2%, 0.5%, 0.8%, or 1.1% of the mass of the polybenzimidazole.

[0082] In the present invention, the mass volume ratio of polybenzimidazole to N,N-dimethylacetamide is preferably 0.3-0.4 g:6-8 mL, more preferably 0.32-0.37 g:6.5-7.5 mL, and more preferably 0.35 g:7 mL.

[0083] In the present invention, the solvent in step 3) is preferably N,N-dimethylacetamide; the mixing is preferably polybenzimidazole dissolved in a solvent and then the modified cerium oxide is added to be uniformly dispersed.

[0084] The invention also provides a composite proton exchange membrane doped with silane-modified rare earth oxide prepared by the preparation method.

[0085] When the silane coupling agent of the present invention is vinyltrimethoxysilane, the silane coupling agent performs surface modification or grafting on the cerium oxide particles, and the reaction mechanism is:

[0086] (1) The coupling agent of the present invention is a silane coupling agent, and its silane group can react with the hydroxyl group (-OH) on the surface of cerium oxide to form a silicon-oxygen-cerium (Si-O-Ce) covalent bond. The vinyl group (-CH 2 =CH 2 ) extends towards the surface or substrate;

[0087] (2) After grafting the vinyl group, the vinyl group is converted into a carboxyl group (-COOH) through an oxidation reaction;

[0088] (3) Connection method between cerium oxide and carboxyl group:

[0089] After oxidation, the hydroxyl groups on the surface of cerium oxide are connected to cerium oxide through the silane groups on the coupling agent. This method is usually divided into the following two types. The first type: covalent bonding. If there is no direct reaction between the hydroxyl groups (-OH) on the surface of cerium oxide or the silane groups on the surface of the coupling agent and the carboxyl groups (-COOH), then the carboxyl groups are connected through covalent bonds with the silane groups (-Si-O-Ce) on the surface of the coupling agent. The silicon atoms of the silane coupling agent form silicon-oxygen-cerium (Si-O-Ce) bonds with the oxygen atoms on the surface of cerium oxide, and the grafted groups can enhance the bonding by interacting with the hydroxyl groups or oxygen vacancies on the surface of cerium oxide. The second type: oxygen vacancy effect on the surface of cerium oxide: If the surface oxygen vacancies (O 2-) participates in the connection reaction, and the oxygen in the carboxyl group can form a coordination or ligand effect with the oxygen vacancy to enhance the connection between cerium oxide and the carboxyl group. Combined with the mechanism of proton conduction, the proton conduction process can rely on oxygen vacancies. The higher the concentration of oxygen vacancies, the greater the help it can provide when it plays the auxiliary role of proton conduction. In the Vehicle mechanism, the proton transfer between water, acid, and polybenzimidazole is divided into three steps: adsorption and binding, carrying and transport, and release and transfer. The grafted -COOH group acts as a proton donor and carrier in this mechanism. As a carrier, it will release protons to other suitable positions in the material, usually in a new negatively charged group or water molecule. This is achieved by transferring protons from the carrier molecule to a new binding position. This process is usually reversible, that is, a carrier can accept and release protons multiple times.

[0090] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0091] In the embodiment, the particle size of cerium oxide is 20 nm.

[0092] Example 1

[0093] 1 g of cerium oxide was dispersed in 12 mL of anhydrous ethanol to obtain a cerium oxide solution; vinyltrimethoxysilane, deionized water, and anhydrous ethanol were mixed in a volume ratio of 8:20:78, acetic acid was added to make the pH value of the mixture 4, and the mixture was reacted at 60° C. for 2 hours to obtain a silane coupling agent hydrolyzate.

[0094] The cerium oxide solution was added dropwise to the silane coupling agent hydrolyzate (the mass of cerium oxide was 2.8% of the mass of the silane coupling agent hydrolyzate) at a rate of 5 mL / min, and the condensation reaction was carried out at 60°C. After the reaction for 2 h, the condensation reaction product (CeO 2 -C 2 H 3 ); concentrated sulfuric acid was added to 2.5 g of the condensation reaction product, and the reaction was carried out at 20° C. for 15 min, followed by the addition of 0.9 g of potassium permanganate, and the reaction was carried out at 20° C. for 15 min and then at 80° C. for 4 h. The volume mass ratio of concentrated sulfuric acid to potassium permanganate was 30 mL:1 g, and the mass concentration of concentrated sulfuric acid was 98%. The product was washed with deionized water and dried to obtain modified cerium oxide (CeO 2 -COOH).

[0095] 0.35 g of polybenzimidazole membrane was dissolved in 7 mL of N,N-dimethylacetamide, and then modified cerium oxide was added (the mass of the modified cerium oxide was 1.1% of the mass of the polybenzimidazole membrane) and dispersed evenly, and then dried at 60° C. under a vacuum condition of 50 Pa to obtain a silane-modified cerium oxide-doped composite proton exchange membrane.

[0096] Example 2

[0097] The masses of the modified cerium oxide were 0%, 0.2%, 0.5%, 0.8% and 1.4% of the mass of the polybenzimidazole film, respectively. Other conditions were the same as those in Example 1.

[0098] Example 3

[0099] 1 g of cerium oxide was dispersed in 10 mL of anhydrous ethanol to obtain a cerium oxide solution; (3-mercaptopropyl)trimethoxysilane, water, and anhydrous ethanol were mixed in a volume ratio of 7.5:18:76, and reacted at 57° C. for 2.5 hours to obtain a silane coupling agent hydrolyzate;

[0100] The cerium oxide solution was added dropwise to the silane coupling agent hydrolyzate (the mass of the cerium oxide was 2.5% of the mass of the silane coupling agent hydrolyzate) at a rate of 4.5 mL / min, and a condensation reaction was carried out at 57°C. After reacting for 2 hours, the mixture was dried to obtain a condensation reaction product. 10 mL of 30% hydrogen peroxide was added to 3 g of the condensation reaction product, and the mixture was reacted at room temperature for 1 hour. The product was washed with deionized water and dried to obtain modified cerium oxide.

[0101] 0.35 g of polybenzimidazole membrane was dissolved in 7 mL of N,N-dimethylacetamide, and then modified cerium oxide was added (the mass of the modified cerium oxide was 0.8% of the mass of the polybenzimidazole membrane) and dispersed evenly, and then dried at 60° C. under a vacuum condition of 50 Pa to obtain a silane-modified cerium oxide-doped composite proton exchange membrane.

[0102] Example 4

[0103] 1 g of cerium oxide was dispersed in 15 mL of anhydrous ethanol to obtain a cerium oxide solution; 3-aminopropyltriethoxysilane, water, and anhydrous ethanol were mixed in a volume ratio of 8.5:22:80, and reacted at 63° C. for 1.5 h to obtain a silane coupling agent hydrolyzate;

[0104] The cerium oxide solution was added dropwise to the silane coupling agent hydrolyzate (the mass of the cerium oxide was 2.7% of the mass of the silane coupling agent hydrolyzate) at a rate of 5.5 mL / min, and a condensation reaction was carried out at 63°C. After the reaction for 1.8 hours, the condensation reaction product was obtained by drying. 20 mL of 30% hydrogen peroxide was added to 2 g of the condensation reaction product, and the reaction was carried out at room temperature for 4 hours. The product was washed with deionized water and dried to obtain modified cerium oxide.

[0105] 0.35 g of polybenzimidazole membrane was dissolved in 7 mL of N,N-dimethylacetamide, and then modified cerium oxide was added (the mass of the modified cerium oxide was 0.5% of the mass of the polybenzimidazole membrane) and dispersed evenly, and then dried at 60° C. under a vacuum condition of 50 Pa to obtain a silane-modified cerium oxide-doped composite proton exchange membrane.

[0106] The condensation reaction product CeO of Example 1 2 -C 2 H 3 , modified cerium oxide CeO 2 -COOH and pure CeO 2 The XRD pattern of Figure 1 As shown. Figure 1 It can be seen that the XRD of cerium oxide powder has not changed before and after modification, indicating that the crystal structure of nano cerium oxide powder has not been damaged during the modification process. Therefore, the modification method of the present invention is a bonding modification, rather than an embedded attachment that damages the crystal structure. Cerium oxide is stable because in its crystal structure, Ce 4+ and O 2- The ions are arranged in an octahedral manner, Ce 4+ is located at the center of the cube, and O 2- The fluorite structure of the face-centered cubic structure provides a stable crystal framework for cerium oxide, which enables it to maintain structural stability at high temperatures. Therefore, the modification without destroying the crystal structure is conducive to improving the performance of the composite film. The method of the present invention is to modify cerium oxide while ensuring the stability of cerium oxide.

[0107] The XPS spectrum of the modified cerium oxide of Example 1 is as follows: Figure 2 As shown, a is the full spectrum, b is the Ce spectrum, c is the O spectrum, and d is the Si spectrum. Figure 2 The peaks at 898.2eV and 916.5eV in the Ce3d spectrum correspond to Ce Ⅳ 3d 5 / 2 With Ce Ⅳ 3d 3 / 2 , the peaks at 882.3eV and 900.8eV correspond to Ce Ⅲ 3d 5 / 2 and Ce Ⅲ 3d 3 / 2 SU1 and SU2 in Figure b are Ce Ⅲ The vibration associated peaks, 903eV and 907eV peaks correspond to Ce Ⅲ 3d 3 / 2 , the peaks at 885eV and 889eV correspond to Ce Ⅲ 3d 5 / 2 , compared with Ce in Ce3d Ⅲ With Ce Ⅳ The peak area of ​​​​the two is approximately equal to 1, which means that Ce ⅢThe content is relatively high, and the sample has a high surface oxygen vacancy; the peaks at 529.4eV and 531.1eV in the O1s spectrum of Figure c correspond to the surface adsorbed oxygen and lattice oxygen, and the peaks at 533.6eV, 532.8eV and 532.1eV are attributed to -COOH, CO / Si-O / OH and C=O groups; Figure d is the Si2p spectrum, and the peak corresponding to the peak at 102eV is the organic Si peak, which corresponds to the silane coupling agent used before, which contains a large amount of Si element, which appears as organic Si in the spectrum. The results in the spectrum correspond to the organic Si in the silane coupling agent, which can be determined that the silicon in the silane coupling agent of the powder sample still exists after oxidation, and the powder is indeed grafted with the carboxyl functional group.

[0108] The condensation reaction product CeO of Example 1 2 -C 2 H 3 , modified cerium oxide CeO 2 -COOH and pure CeO 2 The FTIR spectrum of Figure 3 Vinyl cerium oxide (CeO 2 -C 2 H 3 ) at 1604cm -1 The peak at 1410 cm is the C=C stretching vibration. -1 Si-CH=CH 2 CH 2 The in-plane bending vibration peak of CeO 2 -CH=CH 2 ), after oxidation, this peak changes, indicating that its functional group changes, carboxylated cerium oxide (CeO 2 -COOH) at 1632cm -1 The absorption peak at 1091 cm is C=O in the carboxyl (-COOH) functional group. -1 The characteristic absorption peak at 3500 cm is attributed to the Si-O-Si bond; -1 Nearby, vinyl cerium oxide and carboxylated cerium oxide both present a large absorption peak, but the absorption peak area of ​​carboxylated cerium oxide is larger. The reason is that after oxidation, in addition to the -OH stretching vibration peak, it also contains the characteristic peak of OH stretching vibration in the carboxyl functional group. The absorption peak of carboxylated cerium oxide is 1091cm -1 、960cm -1 and 720cm -1The absorption peak is related to the lattice vibration of cerium oxide, and possible characteristic absorption peaks of COC or CO, indicating that the carboxyl group is chemically adsorbed on the surface of cerium oxide (the carboxyl group is connected to cerium oxide through a covalent bond Si-O-Ce). Therefore, it can be concluded that vinylated cerium oxide is successfully oxidized to carboxylated cerium oxide, and carboxyl-modified cerium oxide is successfully obtained.

[0109] The cross-sectional view of the silane-modified cerium oxide-doped composite proton exchange membrane and the pure PBI membrane of Example 1 is shown in FIG. Figure 4 As shown, (A) and (B) are pure PBI membranes, and (C) and (D) are composite proton exchange membranes of Example 1.

[0110] The cross-sectional EDS spectrum of the silane-modified cerium oxide-doped composite proton exchange membrane of Example 1 is as follows: Figure 5 As shown, red corresponds to the O element, yellow corresponds to the Ce element, and green corresponds to the C element. Figure 5 The distribution of the modified cerium oxide in PBI can be observed, and the three elements Ce, O, and C are evenly distributed in PBI. It can be seen that the modified cerium oxide of the present invention has good compatibility with PBI and can be well dispersed in PBI.

[0111] The mechanical properties of the composite proton exchange membranes of Example 1 and Example 2 at different dosages of modified cerium oxide are shown in Table 1.

[0112] Table 1 Mechanical properties of composite proton exchange membranes with different dosages of modified cerium oxide

[0113]

[0114]

[0115] From the data in Table 1, it can be seen that when the thickness of the specimen (composite proton exchange membrane) is almost unchanged, as the amount of modified cerium oxide doping increases, the maximum tensile strength that the specimen can withstand shows a trend of first increasing and then decreasing, and the cross-sectional elongation continues to decrease; it can be seen that the amount of modified cerium oxide doping in the specimen is negatively correlated with its ductility, and there is a quadratic correlation between the tensile strength and the amount of modified cerium oxide doping. The reason for this result is that inorganic substances usually have higher hardness and rigidity, and adding them to PBI can significantly improve the overall rigidity and hardness of PBI. The presence of inorganic particles can limit the movement of PBI molecular chains, making the material harder and less prone to deformation. In particular, inorganic nanoparticles (such as CeO 2 etc.) have a high elastic modulus and can effectively improve the rigidity of the composite material, which is specifically manifested as an increase in tensile strength. At the same time, inorganic nanoparticles (such as CeO 2) in the polymer matrix reduces the freedom of the molecular chain and reduces its ductility, which is manifested as a decrease in the elongation of the section.

[0116] The impedance diagrams of the silane-modified cerium oxide-doped composite proton exchange membrane and the pure PBI membrane at 80°C and 160°C are shown in FIG. Figure 6 As shown, the proton conductivity of the composite proton exchange membrane doped with silane-modified cerium oxide and the pure PBI membrane of Example 1 and Example 2 is shown in FIG. Figure 7 As shown, the power density diagram of the silane-modified cerium oxide-doped composite proton exchange membrane and the pure PBI membrane of Example 1 at 80°C is shown in Figure 8 As shown, the power density diagram of the silane-modified cerium oxide-doped composite proton exchange membrane and the pure PBI membrane of Example 1 at 160°C is shown in FIG. Fig. 9 shown.

[0117] Depend on Figure 6 It can be seen that after doping with modified cerium oxide, the impedance of the composite membrane is lower than that of the pure PBI membrane at both 80°C and 160°C. Figure 7 It can be seen that when the doping amount of modified cerium oxide is less than 1.1wt%, the proton conductivity continues to rise, but when it reaches 1.4wt%, the proton conductivity shows a cliff-like drop. The reason for this is: when the doping amount is low, the high oxygen vacancy concentration of the modified cerium oxide itself promotes the transfer of protons, and the carboxyl group (-COOH) grafted thereon acts as a proton donor and acceptor, which greatly increases the rate of proton conduction. However, when the doping amount exceeds 1.1wt%, the proton transfer channel may be blocked due to excessive inorganic particles doped in PBI. Even if there are more auxiliary means of proton transfer, the proton cannot smoothly complete the entire transfer process due to the blockage of the proton channel, so the proton conductivity shows a cliff-like drop. Figures 8-9 It can be seen that the power density of the composite membrane is higher than that of the pure PBI membrane at both 80°C and 160°C. The power density of the pure PBI membrane at 80°C is 260mW / cm 2 At the same temperature, the power density of the composite film is close to 300mW / cm 2 At 160°C, the power density of pure PBI membrane is 330mW / cm 2 The composite film reached 364.02mW / cm 2 Therefore, the doping of the modified cerium oxide of the present invention can improve the electrochemical performance (proton conductivity and power density) of the organic-inorganic composite membrane.

[0118] The adsorption amount of acid by the silane-modified cerium oxide-doped composite proton exchange membrane and the pure PBI membrane of Example 1 and Example 2 is as follows: Fig.10 As shown, through Fig.10It can be seen that the acid adsorption capacity of the pure PBI membrane reached 347.73%. With the increase of the amount of inorganic doping, the acid adsorption capacity continued to increase, reaching a peak of 449.86% when the doping amount was 1.1wt%. This is because the doping of inorganic substances provides additional adsorption sites for the adsorption of phosphoric acid, thereby increasing the adsorption amount of phosphoric acid; when the doping amount of inorganic substances continues to increase, the adsorbed phosphoric acid decreases. This is because the internal volume of PBI is limited. When the inorganic doping is too much, the inorganic substances will occupy most of the effective volume inside PBI, and the additional surface area that can be provided by itself will also be reduced due to agglomeration, resulting in fewer exposed phosphoric acid adsorption sites, and the adsorption sites and effective volume left for phosphoric acid are correspondingly reduced, so the adsorption amount of phosphoric acid has decreased.

[0119] The volume swelling ratios of the silane-modified cerium oxide-doped composite proton exchange membranes and the pure PBI membranes after absorbing phosphoric acid are shown in Table 1. Fig.11 As shown in the figure, the swelling rate of the pure PBI membrane is 56.5%. As the amount of inorganic doping increases, the swelling rate of the membrane continues to decrease, which means that the swelling of the membrane has been alleviated. This is because after doping with inorganic substances, the doping of inorganic substances limits the free expansion of PBI. Under acidic conditions, the expansion of PBI depends on the expansion and water absorption of the molecular chain, and the addition of inorganic substances limits the expansion of the molecular chain. The carboxyl groups on the surface of inorganic substances interact with the polar part of the PBI molecular chain, which makes PBI subject to a strong constraint effect. The hydrogen bonds between the carboxyl groups and the PBI molecular chains enhance the interfacial bonding force. The large distribution of cerium oxide increases the structural density inside the composite membrane, making the inside of the membrane denser and less likely to expand.

[0120] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a silane-modified rare earth oxide-doped composite proton exchange membrane, characterized in that: The following steps are included: 1) dispersing cerium oxide in anhydrous ethanol to obtain a cerium oxide solution; reacting a silane coupling agent, water and anhydrous ethanol to obtain a silane coupling agent hydrolyzate; 2) adding the cerium oxide solution dropwise to the silane coupling agent hydrolyzate to react and obtain a reaction product; adding an oxidant to the reaction product to carry out an oxidation reaction and obtain modified cerium oxide; 3) The modified cerium oxide, polybenzimidazole and solvent are mixed and dried to obtain a silane-modified rare earth oxide-doped composite proton exchange membrane.

2. The preparation method according to claim 1, characterized in that: Step 1) The volume ratio of the silane coupling agent, water and anhydrous ethanol is 7-9:16-24:73-83; the silane coupling agent comprises one or more of vinyltrimethoxysilane, (3-mercaptopropyl)trimethoxysilane and 3-aminopropyltriethoxysilane.

3. The preparation method according to claim 1 or 2, characterized in that: The mass of cerium oxide is ≤ 3% of the mass of the silane coupling agent hydrolyzate.

4. The preparation method according to claim 3, characterized in that: The reaction temperatures of step 1) and step 2) are independently 55-65°C, and the reaction time is independently 1.5-2.5h.

5. The preparation method according to claim 3, characterized in that: When the silane coupling agent is vinyltrimethoxysilane, the oxidant is concentrated sulfuric acid and potassium permanganate; When the silane coupling agent is (3-mercaptopropyl)trimethoxysilane, the oxidant is hydrogen peroxide; When the silane coupling agent is 3-aminopropyltriethoxysilane, the oxidant is hydrogen peroxide.

6. The preparation method according to claim 5, characterized in that: The specific process of adding concentrated sulfuric acid and potassium permanganate to the reaction product for oxidation reaction is as follows: the reaction product and concentrated sulfuric acid are subjected to a first low-temperature reaction, and then potassium permanganate is added to sequentially conduct a second low-temperature reaction and a high-temperature reaction; The temperature of the first low temperature reaction and the second low temperature reaction are independently 10-25°C, and the time is independently 12-17 minutes; the temperature of the high temperature reaction is 75-85°C, and the time is 3.5-4.5 hours.

7. The preparation method according to claim 1, characterized in that: Step 3) The mass of the modified cerium oxide is 0.2-1.1% of the mass of the polybenzimidazole.

8. A composite proton exchange membrane doped with silane-modified rare earth oxide prepared by the preparation method according to any one of claims 1 to 7.

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