Modified graphene nanorolls, method for preparing the same and use thereof

Abstract

The application relates to the technical field of catalysts, in particular to a modified graphene nanocoil as well as a preparation method and application thereof. The preparation method of the modified graphene nanocoil comprises the following steps: sequentially performing liquid nitrogen cooling and microwave treatment on a mixed solution containing a reducing organic solvent, a noble metal source and a graphite-based carbon material to obtain a graphene nanocoil loaded with noble metal nanoparticles; wherein the graphite-based carbon material is selected from one or more of graphite oxide and doped graphite oxide. The above preparation method can effectively avoid the formation of an agglomerated structure of the graphene carrier and improve the catalytic activity of the catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a modified graphene nanoroll and a preparation method and application thereof. BACKGROUND

[0002] Proton exchange membrane fuel cell can convert chemical energy into electrical energy without producing pollutants, and is a very promising new energy technology. Proton exchange membrane fuel cell mainly discharges through oxygen reduction reaction at cathode. The oxygen reduction reaction is a slow kinetic process, which needs a suitable catalyst for catalysis. The noble metal catalyst has good low temperature performance and is considered to be the most effective cathode catalyst, but the noble metal catalyst needs to be loaded on a suitable carrier to realize its catalytic performance. Among them, graphene is considered to be a suitable carrier, and the current research is mostly to load noble metal catalyst on graphene or functionalized graphene sheet directly. The preparation process of the catalyst usually includes heat treatment and drying of graphene or functionalized graphene sheet. However, during the heat treatment or sample drying process, graphene tends to re-stack through strong π-π surface interaction, forming an agglomerated structure. This agglomerated structure is not conducive to the opening of the catalyst active surface, and will hinder the transport of reactive substances, thereby greatly reducing the catalytic effect of the catalyst. SUMMARY

[0003] Therefore, it is necessary to provide a modified graphene nanoroll and a preparation method and application thereof, which can effectively avoid the formation of agglomerated structure of graphene carrier and improve the catalytic activity of the catalyst.

[0004] In a first aspect, the present application provides a preparation method of a modified graphene nanoroll, which comprises the following steps:

[0005] The mixed solution containing a reducing organic solvent, a noble metal source and a graphite-based carbon material is sequentially subjected to liquid nitrogen cooling and microwave treatment to obtain a graphene nanoroll loaded with noble metal nanoparticles; wherein the graphite-based carbon material is selected from one or more of graphite oxide and doped graphite oxide.

[0006] In one embodiment, the noble metal source is selected from one or more of chloroplatinic acid, platinum chloride and palladium chloride.

[0007] In one embodiment, the reducing organic solvent is selected from one or more of ethylene glycol, ethanol, methanol and formic acid.

[0008] In one embodiment, in the mixed solution, the mass of the noble metal source is 0.1 mg to 2 mg relative to 1 mL of the reducing organic solvent.

[0009] In one of the embodiments, the mass ratio of the noble metal source to the graphite-based carbon material is (0.2-2):1.

[0010] In one of the embodiments, the volume ratio of the reducing organic solvent to the liquid nitrogen is 1:(1-5).

[0011] In one of the embodiments, the microwave treatment is performed at a power of 1 kW-5 kW for 5 s-300 s.

[0012] In one of the embodiments, after the microwave treatment, the graphene nanorolls are subjected to a washing and / or drying step.

[0013] The drying is freeze drying, and the freeze drying is performed at a temperature of -10℃- -120℃ for 0.5 h-2 h.

[0014] In the second aspect, the application provides a modified graphene nanoroll prepared by the preparation method as described above.

[0015] In one of the embodiments, the loading amount of the noble metal nanoparticles on the graphene nanorolls is 10wt%-70wt%.

[0016] In the third aspect, the application further provides an application of the modified graphene nanoroll as described above as a catalyst in an electrocatalytic oxidation-reduction reaction.

[0017] In the fourth aspect, the application provides a proton exchange membrane fuel cell comprising a cathode catalyst layer, wherein the cathode catalyst layer comprises the modified graphene nanoroll as described above.

[0018] In the preparation method of the modified graphene nanorolls provided by the application, during the mixing of the noble metal source, the reducing organic solvent and the graphite-based carbon material, the noble metal source is first adsorbed on the graphite-based carbon material. Subsequently, under the action of microwave treatment, the graphite-based carbon material absorbs microwaves and expands in volume, and under the action of microwave radiation, the thermal motion of the hydroxyl groups, carboxyl groups and other groups on the carbon layer of the graphite-based carbon material is induced and excited, thereby instantaneously destroying the van der Waals bonding between the layers of the oxidized graphite, so as to form graphene oxide sheets. Meanwhile, under the action of the temperature difference generated by the liquid nitrogen cooling and the microwave treatment, the graphene oxide sheets shrink, and the surface strain generated thereby serves as a driving force to make the graphene oxide sheets form graphene nanorolls. Moreover, the high temperature generated by the microwave treatment and the reducing effect of the reducing organic solvent together reduce the noble metal source into noble metal nanoparticles, and under the high-temperature environment generated by the microwave, the formed graphene oxide is further reduced into graphene, thereby forming graphene nanorolls loaded with noble metal nanoparticles.

[0019] The graphene nanorolls formed by the method can avoid the problem of easy agglomeration of graphene or functionalized graphene sheets directly as a carrier, improve the chemical stability and specific surface area of graphene, and further increase the active sites of the graphene carrier, improve the loading amount of noble metal nanoparticles with catalytic effect on the graphene carrier, and thus improve the catalytic activity of the modified graphene nanorolls. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the drawings needed to be used in the description of the specific embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 Scanning electron microscope images of catalysts prepared for Examples 1-7;

[0022] Figure 2 ORR catalytic performance curve of catalysts prepared for Example 3 and Comparative Examples 1-4;

[0023] Figure 3 Scanning electron microscope images of catalysts prepared for Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0024] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the related drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0026] An ideal support for noble metal catalysts has several characteristics: high surface area, excellent electronic conductivity, electrochemical stability, and the ability to uniformly support nanoparticles. Graphene has excellent electrical conductivity and specific surface area, but the applicant found through research that when traditional graphene or functionalized graphene sheets are directly used as a support, they are prone to agglomeration, which is not conducive to opening the active surface of the supported noble metal catalyst and making it difficult to play its catalytic role. Therefore, it is necessary to regulate the structure of graphene to avoid the problem of agglomeration of graphene as a catalyst support and improve the catalytic performance of graphene-supported noble metal catalysts.

[0027] The first aspect of the present application provides a method for preparing modified graphene nanorolls, comprising the following steps:

[0028] A mixed solution containing a reducing organic solvent, a noble metal source, and a graphite-based carbon material is subjected to liquid nitrogen cooling and microwave treatment in sequence to obtain graphene nanorolls loaded with noble metal nanoparticles; wherein the graphite-based carbon material is selected from one or more of graphite oxide and doped graphite oxide.

[0029] The above method for preparing modified graphene nanorolls, in the mixing process of the noble metal source, the reducing organic solvent, and the graphite-based carbon material, the noble metal source is first adsorbed on the graphite-based carbon material. Subsequently, under the action of microwave treatment, the graphite-based carbon material expands in volume, and under the action of microwave radiation, the thermal motion of hydroxyl, carboxyl, and other groups on the carbon layer of the graphite-based carbon material can be induced and excited, instantaneously destroying the van der Waals bonding between the layers of graphite oxide, thereby forming graphene oxide sheets. At the same time, under the action of the temperature difference generated by liquid nitrogen cooling and microwave treatment, the graphene oxide sheets shrink, and the surface strain generated thereby serves as a driving force to form graphene oxide nanorolls. Moreover, the high temperature generated by microwave treatment and the reducing effect of the reducing organic solvent together reduce the noble metal source to noble metal nanoparticles. Under the high-temperature environment generated by the microwave, the formed graphene oxide is further reduced to graphene, and thus graphene nanorolls loaded with noble metal nanoparticles are formed.

[0030] By this method, traditional graphene is structurally optimized to form graphene nanorolls, thereby inhibiting the agglomeration of graphene, improving its chemical stability and specific surface area, and thus improving the active sites of the graphene support and increasing the loading of noble metal nanoparticles with catalytic activity on the graphene support, thereby improving the catalytic activity of the modified graphene nanorolls.

[0031] In some embodiments, the mixed solution can be obtained by adding the noble metal source and the graphite-based carbon material to the reducing organic solvent, dissolving the noble metal source in the reducing organic solvent, and dispersing the graphite-based carbon material in the solvent.

[0032] In some embodiments, in order to mix uniformly and to make the noble metal source better adsorbed on the graphitic carbon material, a stirring process can be used for mixing in the process of forming the mixed solution containing the reducing organic solvent, the noble metal source and the graphitic carbon material. The stirring process includes mechanical stirring and / or ultrasonic process. The ultrasonic process has a condition of ultrasonic power of 200-800 W and a time of 30-60 min.

[0033] In some embodiments, the noble metal source can be selected from noble metal sources commonly used in the field of catalysts, such as platinum (Pt) sources and palladium (Pd) sources. Specifically, the noble metal source is selected from one or more of chloroplatinic acid, platinum chloride and palladium chloride.

[0034] As an exemplary illustration, when the noble metal source is a platinum (Pt) source, the nanoparticles loaded on the surface of the graphene nanorolls are Pt nanoparticles; when the noble metal source is a palladium (Pd) source, the nanoparticles loaded on the surface of the graphene nanorolls are Pd nanoparticles.

[0035] In the present application, the graphitic carbon material is selected from one or more of graphite oxide and doped graphite oxide. Graphite oxide, also known as graphite oxide or graphite acid, is usually composed of carbon, hydrogen and oxygen elements. The graphite oxide can be prepared by methods well known in the art or commercially available, and the preparation method can be Hummers method or modified Hummers method.

[0036] The doped graphite oxide can be nitrogen-doped graphite oxide, phosphorus-doped graphite oxide, sulfur-doped graphite oxide, sulfur-nitrogen co-doped graphite oxide, etc. The doped graphite oxide can be obtained by commercial purchase or prepared by methods well known in the art.

[0037] In some embodiments, the reducing organic solvent is selected from one or more of ethylene glycol, ethanol, methanol and formic acid, and is preferably ethylene glycol. The reducing organic solvent can play a reducing role on the noble metal source adsorbed on the graphite oxide in the high-temperature environment generated by the microwave treatment during the microwave treatment, so as to reduce it to noble metal nanoparticles.

[0038] In some embodiments, the mass of the noble metal source in the mixture is 0.1 mg to 2 mg relative to 1 mL of the reducing organic solvent. That is, the concentration of the noble metal source in the reducing organic solvent can be any value between 0.1 mg / mL and 2 mg / mL, for example, 0.2 mg / mL, 0.3 mg / mL, 0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, 0.8 mg / mL, 0.9 mg / mL, 1 mg / mL, 1.2 mg / mL, 1.5 mg / mL, 1.8 mg / mL. Controlling the concentration of the noble metal source within this range can enable the noble metal source to be uniformly adsorbed in the graphite-based carbon material, thereby avoiding agglomeration of the subsequently generated noble metal nanoparticles in the graphene nanorolls.

[0039] In some embodiments, the mass ratio of the noble metal source to the graphite-based carbon material is (0.2 to 2): 1, for example, 0.5:1, 1:1, 1.5:1. Controlling the mass ratio of the noble metal source to the graphite-based carbon material within this range can ensure that the noble metal nanoparticle loading is within a suitable range while avoiding excessive agglomeration of the noble metal nanoparticles.

[0040] In some embodiments, the volume ratio of the reducing organic solvent to liquid nitrogen is 1:(1 to 5), for example, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5. Controlling the volume ratio of the reducing organic solvent to liquid nitrogen within this range can ensure that the reducing organic solvent has a reducing effect on the noble metal source and that the liquid nitrogen has a cooling effect. If the volume of the reducing organic solvent is too small, it can be difficult to reduce the noble metal source. If the volume of the reducing organic solvent is too large, the cooling effect of the liquid nitrogen can not be obvious, thereby making it difficult to form graphene nanorolls.

[0041] In some embodiments, the microwave treatment has a power of 1 kW to 5 kW, for example, 2 kW, 3 kW, 4 kW, and a time of 5 s to 300 s, for example, 10 s, 20 s, 50 s, 80 s, 100 s, 120 s, 140 s, 160 s, 180 s, 200 s, 220 s, 250 s, 280 s. Controlling the microwave treatment parameters within the above ranges can ensure that the noble metal source and the graphite oxide absorb sufficient energy, thereby effectively reducing the noble metal source and the graphene oxide on the surface of the graphite oxide, and also forming a sufficient temperature difference with the liquid nitrogen cooling process to enable the graphene oxide to form nanorolls. On the other hand, it can also avoid carbonization of the graphene nanorolls and a decrease in catalytic activity caused by excessive microwave power or a long treatment time.

[0042] Further, the temperature reached by the microwave treatment can be 600-1000℃.

[0043] In some embodiments, after the microwave treatment, the method further comprises a step of washing and / or drying the graphene nanorolls.

[0044] In some embodiments, the washing method is not limited, and any conventional washing method can be used, for example, the graphene nanorolls can be washed 3-5 times by suction filtration.

[0045] In some embodiments, the drying method can be freeze-drying, and the freeze-drying conditions include a temperature of -10- -120℃ and a time of 0.5-2h.

[0046] According to a specific embodiment, the method for preparing the modified graphene nanorolls comprises:

[0047] S1: adding a noble metal source and a graphite-based carbon material into a reducing organic solvent, and ultrasonically dispersing at 200-800W for 30-60min to obtain a mixed solution;

[0048] S2: rapidly cooling the mixed solution in liquid nitrogen for 2-5s to obtain a solid-liquid mixed component;

[0049] S3: microwave treating the solid-liquid mixed component obtained in step S2;

[0050] S4: washing and drying the product after microwave treatment in step S3.

[0051] The second aspect of the present application provides a modified graphene nanoroll prepared by the above-mentioned method.

[0052] In some embodiments, the loading amount of the noble metal nanoparticles on the graphene nanorolls can be 10-70wt%.

[0053] The third aspect of the present application provides an application of the above-mentioned modified graphene nanorolls as a catalyst in an electrocatalytic oxidation-reduction reaction.

[0054] The modified graphene nanoroll catalyst provided by the present application uses graphene nanorolls as a carrier, which can avoid the problem of agglomeration of traditional graphene carriers, and has higher chemical stability and specific surface area, more active sites, and thus can load more noble metal nanoparticles, and has higher electrocatalytic activity.

[0055] The fourth aspect of the present application provides a proton exchange membrane fuel cell comprising a cathode catalyst layer, wherein the cathode catalyst layer comprises the above-mentioned modified graphene nanorolls.

[0056] The application will be described in further detail below with reference to specific embodiments.

[0057] The graphite oxide is prepared by a known Hummers method; the content of nitrogen atoms in the nitrogen-doped graphite oxide is 0.1 at% to 30 at%, and the content of oxygen atoms is 5 at% to 50 at%.

[0058] Example 1

[0059] 1) Preparation of a reaction solution: 20 mg of chloroplatinic acid and 100 mg of graphite oxide are dispersed in 100 mL of ethylene glycol solution to prepare an ethylene glycol solution of chloroplatinic acid and graphite oxide;

[0060] 2) Liquid nitrogen cooling: the ethylene glycol solution of chloroplatinic acid and graphite oxide prepared in step 1) is poured into 100 mL of liquid nitrogen and cooled for 2 s to obtain a chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component;

[0061] 3) Microwave treatment: the chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component prepared in step 2) is placed in a microwave reactor and subjected to microwave treatment at 5 kW for 2 min to obtain a graphene nanoroll-Pt nanoparticle precursor. Subsequently, the graphene nanoroll-Pt nanoparticle precursor is subjected to suction filtration and washing 5 times, and freeze-drying at -70°C for 1 h to obtain a modified graphene nanoroll, i.e., a graphene nanoroll-Pt catalyst.

[0062] The graphite oxide adsorbing chloroplatinic acid is subjected to liquid nitrogen cooling and microwave treatment in sequence. Under the action of microwave irradiation, the graphite oxide is heated to a high temperature, and volume expansion occurs. Under the action of microwave irradiation, the thermal motion of hydroxyl groups, carboxyl groups and other groups on the carbon layer of the graphite-based carbon material is induced and excited, and the van der Waals bonding between the layers of the graphite oxide is destroyed in an instant, thereby forming graphene oxide sheets. At the same time, under the action of the temperature difference generated by liquid nitrogen cooling and microwave treatment, the graphene oxide sheets shrink, and under the action of surface strain driving force, the graphene oxide sheets curl to form graphene oxide nanorolls. At the same time, the high temperature generated by microwave irradiation and the reduction effect of ethylene glycol together reduce the chloroplatinic acid adsorbed on the surface of the graphite oxide to Pt nanoparticles, and the microwave action also reduces the graphene oxide to graphene, thereby forming a graphene nanoroll catalyst loaded with Pt nanoparticles. The SEM image of the catalyst is shown in FIG. 1. Figure 1

[0063] Example 2

[0064] Example 2 and Example 1 have basically the same preparation method, except that the mass ratio of chloroplatinic acid to graphite oxide is different. The specific steps are as follows:

[0065] ​1) Preparation of reaction solution: 200 mg of chloroplatinic acid and 100 mg of graphite oxide were dispersed in 100 mL of ethylene glycol solution to prepare a chloroplatinic acid and graphite oxide ethylene glycol solution;

[0066] 2) Liquid nitrogen cooling: the chloroplatinic acid and graphite oxide ethylene glycol solution prepared in step 1) was poured into 100 mL of liquid nitrogen and cooled for 2 s to obtain a chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component;

[0067] 3) Microwave treatment: the chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component prepared in step 2) was placed in a microwave reactor and treated with a 5 kW microwave for 2 min to obtain a graphene nanoroll-Pt nanoparticle precursor. Subsequently, the graphene nanoroll-Pt nanoparticle precursor was washed by suction filtration for 5 times and freeze-dried at -70°C for 1 h to obtain a modified graphene nanoroll, i.e. a graphene nanoroll-Pt catalyst. The SEM image of the catalyst is shown in Figure 1 .

[0068] Example 3

[0069] Example 3 is basically the same as the preparation method of Example 1, except that the mass ratio of chloroplatinic acid and graphite oxide, and the specific steps are as follows:

[0070] 1) Preparation of reaction solution: 150 mg of chloroplatinic acid and 100 mg of graphite oxide were dispersed in 100 mL of ethylene glycol solution to prepare a chloroplatinic acid and graphite oxide ethylene glycol solution;

[0071] 2) Liquid nitrogen cooling: the chloroplatinic acid and graphite oxide ethylene glycol solution prepared in step 1) was poured into 100 mL of liquid nitrogen and cooled for 2 s to obtain a chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component;

[0072] 3) Microwave treatment: the chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component prepared in step 2) was placed in a microwave reactor and treated with a 5 kW microwave for 2 min to obtain a graphene nanoroll-Pt nanoparticle precursor. Subsequently, the graphene nanoroll-Pt nanoparticle precursor was washed by suction filtration for 5 times and freeze-dried at -70°C for 1 h to obtain a modified graphene nanoroll, i.e. a graphene nanoroll-Pt catalyst. The SEM image of the catalyst is shown in Figure 1 , and the ORR catalytic performance curve is shown in Figure 2 .

[0073] Example 4

[0074] Example 4 is basically the same as the preparation method of Example 3, except that the volume ratio of ethylene glycol and liquid nitrogen, and the specific steps are as follows:

[0075] 1) Preparation of reaction solution: 150 mg of chloroplatinic acid and 100 mg of graphite oxide were dispersed in 100 mL of ethylene glycol solution to prepare a chloroplatinic acid and graphite oxide ethylene glycol solution;

[0076] 2) Liquid nitrogen cooling: the chloroplatinic acid and graphite oxide ethylene glycol solution prepared in step 1) was poured into 500 mL of liquid nitrogen and cooled for 2 s to obtain a chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component;

[0077] 3) Microwave treatment: the chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component prepared in step 2) was placed in a microwave reactor and treated with a 5 kW microwave for 2 min to obtain a graphene nanoroll-Pt nanoparticle precursor. Subsequently, the graphene nanoroll-Pt nanoparticle precursor was washed by suction filtration for 5 times and freeze-dried at -70°C for 1 h to obtain a modified graphene nanoroll, i.e. a graphene nanoroll-Pt catalyst. The SEM image of the catalyst is shown in FIG. 1. Figure 1

[0078] Example 5

[0079] Example 5 is basically the same as the preparation method of Example 3, except that the parameters of microwave treatment are different. The specific steps are as follows:

[0080] 1) Preparation of reaction solution: 150 mg of chloroplatinic acid and 100 mg of graphite oxide were dispersed in 100 mL of ethylene glycol solution to prepare a chloroplatinic acid and graphite oxide ethylene glycol solution;

[0081] 2) Liquid nitrogen cooling: the chloroplatinic acid and graphite oxide ethylene glycol solution prepared in step 1) was poured into 100 mL of liquid nitrogen and cooled for 2 s to obtain a chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component;

[0082] 3) Microwave treatment: the chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component prepared in step 2) was placed in a microwave reactor and treated with a 2 kW microwave for 2 min to obtain a graphene nanoroll-Pt nanoparticle precursor. Subsequently, the graphene nanoroll-Pt nanoparticle precursor was washed by suction filtration for 5 times and freeze-dried at -70°C for 1 h to obtain a modified graphene nanoroll, i.e. a graphene nanoroll-Pt catalyst. The SEM image of the catalyst is shown in FIG. 2. Figure 1

[0083] Example 6

[0084] Example 6 is basically the same as the preparation method of Example 3, except that the types of noble metal and graphite oxide are different. The specific steps are as follows:

[0085] ​​1) Preparation of reaction solution: 150 mg of palladium chloride and 100 mg of nitrogen-doped graphite oxide were dispersed in 100 mL of ethylene glycol solution to prepare a palladium chloride and nitrogen-doped graphite oxide ethylene glycol solution. The content of nitrogen atoms in the nitrogen-doped graphite oxide was 9 at%, and the content of oxygen atoms was 12 at%;

[0086] 2) Liquid nitrogen cooling: the palladium chloride and nitrogen-doped graphite oxide ethylene glycol solution prepared in step 1) was poured into 100 mL of liquid nitrogen and cooled for 2 s to obtain a palladium chloride-nitrogen-doped graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component;

[0087] 3) Microwave treatment: the palladium chloride-nitrogen-doped graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component prepared in step 2) was placed in a microwave reactor and treated with a 5 kW microwave for 2 min to obtain a graphene nanoroll-palladium nanoparticle precursor. Subsequently, the graphene nanoroll-palladium nanoparticle precursor was washed by suction filtration for 5 times and freeze-dried at -70°C for 1 h to obtain a modified graphene nanoroll, i.e., a graphene nanoroll-palladium catalyst. The SEM image of the catalyst is shown in Figure 1 .

[0088] Example 7

[0089] Example 7 and the preparation method of Example 3 are basically the same, except that ethanol is used instead of ethylene glycol. The specific steps are as follows:

[0090] 1) Preparation of reaction solution: 150 mg of palladium chloride and 100 mg of nitrogen-doped graphite oxide were dispersed in 100 mL of ethylene glycol solution to prepare a palladium chloride and nitrogen-doped graphite oxide ethylene glycol solution. The content of nitrogen atoms in the nitrogen-doped graphite oxide was 9 at%, and the content of oxygen atoms was 12 at%;

[0091] 2) Liquid nitrogen cooling: the palladium chloride and nitrogen-doped graphite oxide ethylene glycol solution prepared in step 1) was poured into 100 mL of liquid nitrogen and cooled for 2 s to obtain a palladium chloride-nitrogen-doped graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component;

[0092] 3) Microwave treatment: the palladium chloride-nitrogen-doped graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component prepared in step 2) was placed in a microwave reactor and treated with a 5 kW microwave for 2 min to obtain a graphene nanoroll-palladium nanoparticle precursor. Subsequently, the graphene nanoroll-palladium nanoparticle precursor was washed by suction filtration for 5 times and freeze-dried at -70°C for 1 h to obtain a modified graphene nanoroll, i.e., a graphene nanoroll-palladium catalyst. The SEM image of the catalyst is shown in Figure 1 .

[0093] Comparative Example 1

[0094] The preparation method of Comparative Example 1 and the preparation method of Example 3 are basically the same, except that no liquid nitrogen cooling treatment is performed. The specific steps are as follows:

[0095] 1) Preparation of reaction solution: 150 mg of chloroplatinic acid and 100 mg of graphite oxide were dispersed in 100 mL of ethylene glycol solution to prepare a chloroplatinic acid and graphite oxide ethylene glycol solution;

[0096] 2) Microwave treatment: the chloroplatinic acid and graphite oxide ethylene glycol solution prepared in step 1) was placed in a microwave reactor and treated with a 5 kW microwave for 2 min to obtain a graphene-Pt nanoparticle precursor. Subsequently, the graphene-Pt nanoparticle precursor was washed by suction filtration for 5 times and freeze-dried at -70°C for 1 h to obtain modified graphene, i.e. graphene-Pt catalyst. The SEM image of the catalyst is shown in Figure 3 , and the ORR catalytic performance curve is shown in Figure 2 . As can be seen from Figure 3 , the graphene prepared in this comparative example did not form nanorolls.

[0097] Comparative Example 2

[0098] The preparation method of Comparative Example 2 is basically the same as that of Example 3, except that the volume ratio of ethylene glycol and liquid nitrogen is different. The specific steps are as follows:

[0099] 1) Preparation of reaction solution: 150 mg of chloroplatinic acid and 100 mg of graphite oxide were dispersed in 100 mL of ethylene glycol solution to prepare a chloroplatinic acid and graphite oxide ethylene glycol solution;

[0100] 2) Liquid nitrogen cooling: the chloroplatinic acid and graphite oxide ethylene glycol solution prepared in step 1) was poured into 80 mL of liquid nitrogen and cooled for 2 s to obtain a chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component;

[0101] 3) Microwave treatment: the chloroplatinic acid-graphite oxide-ethylene glycol-liquid nitrogen solid-liquid mixed component prepared in step 2) was placed in a microwave reactor and treated with a 5 kW microwave for 2 min to obtain a graphene-Pt nanoparticle precursor. Subsequently, the graphene-Pt nanoparticle precursor was washed by suction filtration for 5 times and freeze-dried at -70°C for 1 h to obtain modified graphene, i.e. graphene-Pt catalyst. The SEM image of the catalyst is shown in Figure 3 , and the ORR catalytic performance curve is shown in Figure 2 . As can be seen from Figure 3 , the graphene prepared in this comparative example did not form nanorolls.

[0102] Comparative Example 3

[0103] The preparation method of Comparative Example 3 is basically the same as that of Example 3, except that water is used instead of ethylene glycol. The specific steps are as follows:

[0104] 1) Preparation of reaction solution: 150 mg of chloroplatinic acid and 100 mg of graphite oxide were dispersed in 100 mL of water to prepare an aqueous solution of chloroplatinic acid and graphite oxide;

[0105] 2) Liquid nitrogen cooling: The aqueous solution of chloroplatinic acid and graphite oxide prepared in step 1) was poured into 100 mL of liquid nitrogen to obtain a chloroplatinic acid-graphite oxide-water-liquid nitrogen solid-liquid mixed component;

[0106] 3) Microwave treatment: The chloroplatinic acid-graphite oxide-water-liquid nitrogen solid-liquid mixed component prepared in step 2) was placed in a microwave reactor and subjected to microwave treatment at 5 kW for 2 min to obtain a graphene nanoroll-Pt nanoparticle precursor. Subsequently, the graphene nanoroll-Pt nanoparticle precursor was suction-filtered and washed 5 times, and freeze-dried at -70°C for 1 h to obtain a modified graphene nanoroll, i.e., a graphene nanoroll-Pt catalyst. The ORR catalytic performance curve of the catalyst is shown in Figure 2

[0107] Comparative Example 4

[0108] The preparation method of Comparative Example 4 is basically the same as that of Example 3, except that the graphene nanorolls were first formed, and then Pt nanoparticles were loaded on the surface of the graphene nanorolls. The specific steps are as follows:

[0109] 1) Preparation of graphene nanorolls: 100 mg of graphene oxide was dispersed in 100 mL of water to obtain a graphene oxide dispersion, and then 200 mL of liquid nitrogen was added to the graphene oxide dispersion to obtain a graphene oxide-liquid nitrogen solid-liquid mixed component. The graphene oxide-liquid nitrogen solid-liquid mixed component was freeze-dried to obtain a graphene nanoroll precursor, which was heat-treated at 500°C for 2 h under a nitrogen atmosphere to obtain graphene nanorolls.

[0110] 2) Graphene nanorolls loaded with Pt nanoparticles: The graphene nanorolls obtained in step 1) and 150 mg of chloroplatinic acid were dispersed in 100 mL of ethylene glycol to obtain a graphene nanoroll-chloroplatinic acid-ethylene glycol solution. The graphene nanoroll-chloroplatinic acid-ethylene glycol solution was placed in a microwave reactor and subjected to microwave treatment at 5 kW for 2 min to obtain a graphene nanoroll-Pt nanoparticle precursor. Subsequently, the graphene nanoroll-Pt nanoparticle precursor was suction-filtered and washed 5 times, and freeze-dried at -70°C for 1 h to obtain a modified graphene nanoroll, i.e., a graphene nanoroll-Pt catalyst. The ORR catalytic performance curve of the catalyst is shown in Figure 2

[0111] The raw materials and microwave treatment process parameters in the preparation methods of Examples 1 to 7 and Comparative Examples 1 to 3 are listed in Table 1 below:

[0112] Table 1​​

[0113]

[0114] The specific surface area test and noble metal nanoparticle loading test were performed on the graphene catalyst materials prepared in Examples 1-7 and Comparative Examples 1-4, and the test results are shown in Table 2 below.

[0115] Among them, the specific surface area test national standard is GB.T 19587-2004; the noble metal nanoparticle loading test national standard is GB.T 20042.4-2009.

[0116] Table 2

[0117]

[0118] As can be seen from Table 2 above, compared with Comparative Example 1, the specific surface area of Example 3 is higher, indicating that the temperature difference generated by liquid nitrogen and microwave radiation is conducive to the formation of graphene nanometer roll structure, the specific surface area is increased, and more noble metal nanoparticles can be loaded. Compared with Comparative Example 2, the specific surface area of Comparative Example 2 is lower, indicating that too much volume of reducing organic solvent will result in that the liquid nitrogen cooling effect is not obvious, so that it is difficult to form graphene nanometer roll, the specific surface area is reduced, and the loading amount of noble metal nanoparticles is reduced. Compared with Comparative Example 3, the specific surface area of Example 3 and Comparative Example 3 is equivalent, but the loading amount of Pt nanoparticles in Example 3 is high, indicating that using ethylene glycol as a reducing agent can improve the loading amount of noble metal nanoparticles on graphene nanometer roll. Compared with Comparative Example 4, the specific surface area of Example 3 and Comparative Example 4 is equivalent, but the loading amount of Pt nanoparticles in Comparative Example 4 is much lower than that in Example 3, indicating that by preparing graphene nanometer roll first and then loading Pt nanoparticles, the loaded Pt nanoparticles are less.

[0119] The electrocatalytic oxygen reduction reaction (ORR) performance test was performed on the graphene catalyst materials prepared in Examples 1-7 and Comparative Examples 1-4, and the test results are shown in Table 3.

[0120] Among them, the specific surface area test national standard is GB.T 19587-2004; the noble metal nanoparticle loading test national standard is GB.T 20042.4-2009.

[0121] Table 3

[0122] Group Half-wave potential (mV vs. RHE) Example 1 633 Example 2 638 Example 3 639 Example 4 635 Example 5 635 Example 6 639 Example 7 633 Comparative Example 1 526 Comparative Example 2 528 Comparative Example 3 535 Comparative Example 4 520

[0123] As can be seen from Table 3, the half-wave potential of Example 3 is higher than that of Comparative Example 1, indicating that after the graphene forms nanoroll structures, the catalytic activity of the catalyst can be improved; the half-wave potential of Comparative Example 2 is lower than that of Example 3, indicating that too much volume of the reducing organic solvent results in poor graphene rolling effect, reduced specific surface area, and decreased loading of noble metal nanoparticles, thereby reducing the catalytic activity of the catalyst; the half-wave potential of Example 3 is higher than that of Comparative Example 3, indicating that the loading of Pt nanoparticles is higher, and the catalytic activity of the catalyst is high. The half-wave potential of Comparative Example 4 is lower than that of Example 3, indicating that by preparing graphene nanorolls first and then introducing Pt nanoparticles, the loading of Pt nanoparticles is less, and the catalytic activity of the graphene nanoroll catalyst is reduced.

[0124] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present disclosure.

[0125] The above-described embodiments only express several implementation manners of the present application, and the description is specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims, and the description and drawings can be used to explain the scope of the claims.

Claims

1. A method for preparing a modified graphene nanoroll, characterized by, The method comprises the following steps: The mixed solution containing a reducing organic solvent, a noble metal source and a graphite-based carbon material is subjected to liquid nitrogen cooling and microwave treatment in sequence to obtain graphene nanorolls loaded with noble metal nanoparticles; wherein the graphite-based carbon material is selected from one or more of graphite oxide and doped graphite oxide; The preparation of the mixed solution comprises the following steps: The noble metal source and the graphite-based carbon material are added into the reducing organic solvent for ultrasonic dispersion treatment; The graphite-based carbon material comprises at least one of graphite oxide and doped graphite oxide; In the mixed solution, the mass of the noble metal source is 0.1 mg to 2 mg relative to 1 mL of the reducing organic solvent; The mass ratio of the noble metal source to the graphite-based carbon material is (0.2-2):1; The volume ratio of the reducing organic solvent to the liquid nitrogen is 1:(1-5); The microwave treatment has a power of 1 kW to 5 kW and a time of 5 s to 300 s.

2. The method for preparing modified graphene nanorolls as described in claim 1, characterized in that, The preparation method has at least one of the following characteristics: 1) The noble metal source is selected from one or more of chloroplatinic acid, platinum chloride and palladium chloride; 2) The reducing organic solvent is selected from one or more of ethylene glycol, ethanol, methanol and formic acid.

3. The method for preparing modified graphene nanorolls according to any one of claims 1 to 2, characterized in that, After the microwave treatment, the graphene nanorolls are subjected to washing and / or drying; The drying is freeze-drying, and the freeze-drying has a temperature of -10°C to -120°C and a time of 0.5 h to 2 h.

4. A modified graphene nanoroll prepared by the preparation method of any one of claims 1-3.

5. The modified graphene nanorolls of claim 4, wherein, The loading amount of the noble metal nanoparticles on the graphene nanorolls is 10 wt% to 70 wt%.

6. Use of the modified graphene nanorolls of claim 4 or 5 as catalysts in electrocatalytic oxidation-reduction reactions.

7. A proton exchange membrane fuel cell characterized by A cathode catalyst layer comprising the modified graphene nanorolls of claim 4 or 5.

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