阅读说明：本技术 一种掺氮石墨烯-碳纳米管复合催化剂及其制备方法 (Nitrogen-doped graphene-carbon nanotube composite catalyst and preparation method thereof ) 是由 贾力 杨裔晟 张宝春 朱秀清 于 2021-10-12 设计创作，主要内容包括：本申请涉及催化剂领域,具体公开了一种掺氮石墨烯-碳纳米管复合催化剂及其制备方法。一种掺氮石墨烯-碳纳米管复合催化剂,所述催化剂包括碳载体以及负载在所述碳载体上的贵金属；所述碳载体由掺氮还原氧化石墨烯和掺氮碳纳米管构成；其制备方法为将掺氮还原氧化石墨烯与贵金属前驱体溶液混合,使贵金属沉积在掺氮还原氧化石墨烯上,得到载贵金属掺氮还原氧化石墨烯；将掺氮碳纳米管与载贵金属掺氮还原氧化石墨烯通过原位化学还原法结合,得到掺氮石墨烯-碳纳米管复合催化剂。本申请的掺氮石墨烯-碳纳米管复合催化剂可用于燃料电池,其具有催化活性高、稳定性高的优点；另外,本申请的制备方法具有方法简单、产量大、适宜批量化生产的优点。(The application relates to the field of catalysts, and particularly discloses a nitrogen-doped graphene-carbon nanotube composite catalyst and a preparation method thereof. A nitrogen-doped graphene-carbon nanotube composite catalyst comprises a carbon carrier and a noble metal loaded on the carbon carrier; the carbon carrier is composed of nitrogen-doped reduced graphene oxide and nitrogen-doped carbon nanotubes; mixing the nitrogen-doped reduced graphene oxide with a noble metal precursor solution, and depositing noble metal on the nitrogen-doped reduced graphene oxide to obtain noble metal-loaded nitrogen-doped reduced graphene oxide; and combining the nitrogen-doped carbon nanotube with the noble metal-loaded nitrogen-doped reduced graphene oxide by an in-situ chemical reduction method to obtain the nitrogen-doped graphene-carbon nanotube composite catalyst. The nitrogen-doped graphene-carbon nanotube composite catalyst can be used for fuel cells and has the advantages of high catalytic activity and high stability; in addition, the preparation method has the advantages of simplicity, high yield and suitability for batch production.)

1. The nitrogen-doped graphene-carbon nanotube composite catalyst is characterized by comprising a carbon carrier and a noble metal loaded on the carbon carrier;

the carbon carrier is composed of nitrogen-doped reduced graphene oxide and nitrogen-doped carbon nanotubes.

2. The preparation method of the nitrogen-doped graphene-carbon nanotube composite catalyst of claim 1, which is characterized by comprising the following steps:

s1, mixing the nitrogen-doped reduced graphene oxide with the noble metal precursor solution to deposit noble metal on the nitrogen-doped reduced graphene oxide to obtain noble metal-loaded nitrogen-doped reduced graphene oxide;

s2, mixing 5-15 parts by weight of nitrogen-doped carbon nano tube with 85-95 parts by weight of noble metal-loaded nitrogen-doped reduced graphene oxide, dispersing the mixture in water, adding a reducing agent, reacting at the temperature of 75-80 ℃ for 6-8 hours to obtain a reduced product, and filtering and drying the reduced product to obtain the nitrogen-doped graphene-carbon nano tube composite catalyst.

3. The method for preparing the nitrogen-doped graphene-carbon nanotube composite catalyst according to claim 2, wherein the step S1 comprises the following steps: uniformly mixing the nitrogen-doped reduced graphene oxide and the noble metal precursor solution, adjusting the pH value to 9-11, adding a sodium borohydride solution, stirring at room temperature for 8-16h, filtering, washing and drying to obtain the noble metal-loaded nitrogen-doped reduced graphene oxide.

4. The method for preparing the nitrogen-doped graphene-carbon nanotube composite catalyst according to claim 2, wherein the nitrogen-doped reduced graphene oxide is prepared by the following method:

dispersing graphene oxide in a hydrochloric acid solution to obtain a suspension; putting the suspension in an ice bath, dripping aniline into the suspension, stirring for 10-20min, adding ammonium persulfate, continuously stirring for 5-7h in the ice bath, and then filtering, washing and drying to obtain PANI-GO; and roasting the PANI-GO in a protective gas to obtain the nitrogen-doped reduced graphene oxide.

5. The method for preparing the nitrogen-doped graphene-carbon nanotube composite catalyst as claimed in claim 4, wherein the calcination temperature is 850-950 ℃ and the calcination time is 1-2 h.

6. The method for preparing the nitrogen-doped graphene-carbon nanotube composite catalyst according to claim 4, wherein the graphene oxide is prepared by the following method:

adding natural graphite powder, phosphorus pentoxide and potassium persulfate into concentrated sulfuric acid, and stirring for 4-5h at the temperature of 75-85 ℃ to obtain a mixed solution; cooling the mixed solution to room temperature, adding deionized water for dilution, then standing the mixed solution, removing supernatant, and filtering, washing and drying the precipitate to obtain pre-oxidized graphite powder;

secondly, carrying out oxidation reaction on the pre-oxidized graphite powder under the action of concentrated sulfuric acid and potassium permanganate, and then respectively carrying out reduction, acid washing, water washing and drying on the oxide by using hydrogen peroxide to obtain the graphene oxide.

7. The method for preparing the nitrogen-doped graphene-carbon nanotube composite catalyst according to claim 2, wherein the nitrogen-doped carbon nanotube is prepared by the following method:

cleaning and drying the growth substrate for later use;

dissolving ferrocene in xylene to prepare a carbon source precursor solution;

putting the growth substrate into a reaction furnace, sealing the reaction furnace, introducing protective gas into the reaction furnace to exhaust air, and heating the reaction furnace;

when the temperature in the reaction furnace reaches 500 ℃, introducing protective gas with the flow rate of 300-; then heating to 600-700 ℃, injecting a carbon source precursor solution at the speed of 0.1-0.3mL/min for 30-40 min; then stopping introducing the mixture and continuously maintaining the mixture at the temperature of 600-700 ℃ for 20-30 min;

stopping introducing the reducing gas, and cooling the reaction furnace to room temperature in the protective gas atmosphere to obtain the nitrogen-doped carbon nanotube.

8. The method for preparing the nitrogen-doped graphene-carbon nanotube composite catalyst according to claim 2, wherein the reducing agent is one or more of hydrazine hydrate, ammonia water, dimethylhydrazine and sodium borohydride.

Technical Field

The application relates to the field of catalysts, in particular to a nitrogen-doped graphene-carbon nanotube composite catalyst and a preparation method thereof.

Background

The metal catalyst is a catalyst taking metal as a main active component, and mainly comprises transition elements such as noble metal, iron, cobalt, nickel and the like; the supported catalyst can be classified into an unsupported metal catalyst and a supported catalyst according to whether an active component of the catalyst is supported on a carrier or not, wherein the supported catalyst is a catalyst in which a metal component is supported on a carrier, and metal particles can be better dispersed by utilizing the large specific surface area of the catalyst carrier, so that the catalytic efficiency of the metal can be improved, and therefore, the supported catalyst is widely applied to the fields of fuel cells, petrochemical industry and the like.

At present, a common catalyst carrier is a carbon black material, wherein vulcan xc-72 has better electrical conductivity and larger specific surface area, and is one of the most studied electrocatalyst carriers, but a catalyst using the vulcan xc-72 as the carrier generally has the problems of poor stability, insufficient catalytic activity and the like. Therefore, in recent years, many novel carbon materials, such as carbon nanotubes, porous carbon, hollow carbon spheres, graphene, and the like, have been successively used as catalyst supports for fuel cells. The materials have the advantages of large specific surface area, good conductivity and high catalytic efficiency, and can overcome the defect of low catalytic activity of the carbon black carrier.

The carbon nano tube is a one-dimensional quantum material with a special structure, and has excellent mechanical, electrical and chemical properties; and the graphene is a two-dimensional carbon material with excellent optical, electrical and mechanical properties. Carbon nanotubes and graphene have similar properties but different structures, and in order to combine the advantages of the two, they are combined to form a three-dimensional network structure. However, when the graphene-carbon nanotube composite carrier is used as a carrier of the noble metal, the noble metal particles are loaded on the carrier only through physical adsorption and deposition, and the phenomenon that the noble metal catalyst falls off easily occurs in the catalytic process, so that the stability of the catalyst is affected.

Disclosure of Invention

In order to improve the stability of the catalyst, the application provides a nitrogen-doped graphene-carbon nanotube composite catalyst and a preparation method thereof.

In a first aspect, the present application provides a nitrogen-doped graphene-carbon nanotube composite catalyst, which adopts the following technical scheme: a nitrogen-doped graphene-carbon nanotube composite catalyst comprises a carbon carrier and a noble metal loaded on the carbon carrier;

the carbon carrier is composed of nitrogen-doped reduced graphene oxide and nitrogen-doped carbon nanotubes.

By adopting the technical scheme, granular graphene is connected through the linear carbon nano tubes to construct a similar three-dimensional net structure, a three-dimensional communicated heat conduction and electric conduction channel is provided, the specific surface area of the carbon carrier can be improved, and the carbon carrier has better catalytic activity. But traditional composite carrier and noble metal particle are connected only through physical adsorption, lead to noble metal particle to drop from composite carrier easily in catalytic process, and this application is through carrying out nitrogen doping to graphite alkene and carbon nanotube, can be with nitrogen atom doping on graphite alkene and carbon nanotube to can provide more active sites for follow-up load noble metal particle, not only can improve the bonding strength of noble metal particle and composite carrier, but also can improve its dispersion homogeneity and the load capacity on composite carrier, thereby greatly improved the stability and the electro-catalytic activity of catalyst, improved the life of catalyst.

In a second aspect, the present application provides a method for preparing a nitrogen-doped graphene-carbon nanotube composite catalyst, which adopts the following technical scheme:

a preparation method of a nitrogen-doped graphene-carbon nanotube composite catalyst comprises the following steps:

s1, mixing the nitrogen-doped reduced graphene oxide with the noble metal precursor solution to deposit noble metal on the nitrogen-doped reduced graphene oxide to obtain noble metal-loaded nitrogen-doped reduced graphene oxide;

s2, mixing 5-15 parts by weight of nitrogen-doped carbon nano tube with 85-95 parts by weight of noble metal-loaded nitrogen-doped reduced graphene oxide, dispersing the mixture in water, adding a reducing agent, reacting at the temperature of 75-80 ℃ for 6-8h to obtain a reduced product, and filtering and drying the reduced product to obtain the nitrogen-doped graphene-carbon nano tube composite catalyst.

By adopting the technical scheme, the traditional preparation of the graphene-carbon nanotube composite carrier has the problems of complex process flow, higher production cost and low yield, and is not beneficial to industrial production; according to the method, nitrogen-doped graphene and carbon nanotubes are respectively used as raw materials, and the advantages of simple preparation method, high preparation speed and high yield of an in-situ chemical reduction method are utilized, so that the batch production of the composite catalyst can be realized; meanwhile, the carbon nano tube and the graphene are respectively subjected to nitrogen doping treatment before combination, so that the defects of a large number of impurity groups and poor product quality of the carrier prepared by the traditional in-situ chemical reduction method can be overcome.

In addition, the graphene and the carbon nano tube which are subjected to nitrogen doping treatment are used as carriers, before the nitrogen-doped reduced graphene oxide is combined with the nitrogen-doped carbon nano tube, the surface of the nitrogen-doped reduced graphene oxide is firstly loaded with noble metal particles, and the bonding force between the noble metal and the reduced graphene oxide can be improved by utilizing active sites generated by nitrogen doping; and then combining the nitrogen-doped reduced graphene oxide loaded with the noble metal with the nitrogen-doped carbon nanotube, which is beneficial to improving the uniformity of the dispersion of the nitrogen-doped reduced graphene oxide and the nitrogen-doped carbon nanotube, so that the composite carrier has better stability.

Preferably, the S1 includes the following steps: uniformly mixing the nitrogen-doped reduced graphene oxide and the noble metal precursor solution, adjusting the pH value to 9-11, adding a sodium borohydride solution, stirring at room temperature for 8-16h, filtering, washing and drying to obtain the noble metal-loaded nitrogen-doped reduced graphene oxide.

The impregnation liquid phase reduction method is a method for loading noble metal with simple process, but has the defects that the prepared catalyst has poor dispersity of noble metal and is easy to cause agglomeration of the noble metal. By adopting the technical scheme, the nitrogen-doped reduced graphene oxide is used as a carrier, an impregnation liquid phase reduction method is adopted, sodium borohydride is used for reducing noble metal salt into noble metal crystals to be adsorbed on a carbon carrier, the nitrogen-doped reduced graphene oxide and the noble metal particles are connected in a chemical bonding mode, so that the bonding strength of the nitrogen-doped reduced graphene oxide and the noble metal crystals is higher, and the dispersion uniformity of the noble metal can be improved and the agglomeration phenomenon of the noble metal can be reduced after the graphene is subjected to nitrogen doping treatment.

Preferably, the nitrogen-doped reduced graphene oxide is prepared by the following method:

dispersing graphene oxide in a hydrochloric acid solution to obtain a suspension; putting the suspension in an ice bath, dripping aniline into the suspension, stirring for 10-20min, adding ammonium persulfate, continuously stirring for 5-7h in the ice bath, and then filtering, washing and drying to obtain PANI-GO; and roasting the PANI-GO in a protective gas to obtain the nitrogen-doped reduced graphene oxide.

By adopting the technical scheme, under the action of ammonium persulfate, aniline is adopted to modify graphene oxide to form polyaniline-graphene oxide, and then nitrogen-doped reduced graphene oxide is formed in a high-temperature roasting mode, so that the method is simple and easy to implement; by forming a plurality of nitrogen-containing sites on the graphene, stronger chemical bonding can be formed during subsequent noble metal loading treatment, so that the bonding strength of the carrier and the noble metal particles is improved.

Preferably, the roasting temperature is 850-950 ℃, and the roasting time is 1-2 h.

By adopting the technical scheme, the roasting temperature is 850-950 ℃, more micropores can be formed on the surface of the graphene so as to increase the specific surface area of the graphene, noble metal particles can be more uniformly deposited on the surface of the graphene when noble metal is subsequently loaded, the uniformity of the loaded noble metal is improved, and the loaded noble metal particles have smaller particle size and are not easy to grow and agglomerate due to the larger specific surface area and micropore volume of the high-temperature roasted graphene, so that the loaded noble metal particles have better catalytic activity.

Preferably, the graphene oxide is prepared by the following method:

adding natural graphite powder, phosphorus pentoxide and potassium persulfate into concentrated sulfuric acid, and stirring for 4-5h at the temperature of 75-85 ℃ to obtain a mixed solution; cooling the mixed solution to room temperature, adding deionized water for dilution, then standing the mixed solution, removing supernatant, and filtering, washing and drying the precipitate to obtain pre-oxidized graphite powder;

secondly, carrying out oxidation reaction on the pre-oxidized graphite powder under the action of concentrated sulfuric acid and potassium permanganate, and then respectively carrying out reduction, acid washing, water washing and drying on the oxide by using hydrogen peroxide to obtain the graphene oxide.

By adopting the technical scheme, after the graphite powder is subjected to the pre-oxidation treatment in the step I, the interlayer spacing of the graphite can be increased, the oxidation stripping in the subsequent step II is easier to perform, and the purity and the oxidation efficiency of the graphene can be improved.

Preferably, the nitrogen-doped carbon nanotube is prepared by the following method:

cleaning and drying the growth substrate for later use;

dissolving ferrocene in xylene to prepare a carbon source precursor solution;

putting the growth substrate into a reaction furnace, sealing the reaction furnace, introducing protective gas into the reaction furnace to exhaust air, and heating the reaction furnace;

when the temperature in the reaction furnace reaches 500 ℃, introducing protective gas with the flow rate of 300-; then heating to 600-700 ℃, injecting a carbon source precursor solution at the speed of 0.1-0.3mL/min for 30-40 min; then stopping introducing the mixture and continuously maintaining the mixture at the temperature of 600-700 ℃ for 20-30 min;

stopping introducing the reducing gas, and cooling the reaction furnace to room temperature in the protective gas atmosphere to obtain the nitrogen-doped carbon nanotube.

By adopting the technical scheme, nitrogen atoms are doped into the carbon nano tube by adopting a chemical vapor deposition method, so that more reaction sites are added on the surface of the carbon nano tube, and the combination of the carbon nano tube and the nitrogen-doped reduced graphene oxide carrying noble metal is facilitated. By adopting the method, the preparation method is simple, easy to realize and suitable for batch production.

In addition, the roasting temperature is selected from 600-700 ℃, compared with the roasting temperature of 900 ℃, although the specific surface area of the carbon nano tube is reduced, the nitrogen content of the carbon nano tube is favorably increased, so that the carbon nano tube contains more nitrogen-containing sites; because the nitrogen-doped reduced graphene oxide and the nitrogen-doped carbon nanotube are combined to be used as the carbon carrier, the advantages of the nitrogen-doped reduced graphene oxide and the nitrogen-doped carbon nanotube can be fully utilized through the treatment; noble metal is loaded by the graphene with high specific surface area, the particle size of noble metal particles can be reduced as much as possible, the uniformity of the noble metal particles on the surface of the graphene is improved, and the nitrogen-doped carbon nanotubes can easily connect the noble metal-loaded reduced graphene oxide particles after the carbon nanotubes with high nitrogen content are mixed with the graphene so as to construct a similar three-dimensional reticular structure. The catalyst prepared by the method has the advantages of high cycle stability and high electrochemical activity.

Preferably, the reducing agent is one or more of hydrazine hydrate, ammonia water, dimethylhydrazine and sodium borohydride.

By adopting the technical scheme, the reducing agent adopts hydrazine hydrate, ammonia water, dimethylhydrazine and sodium borohydride to carry out in-situ chemical reduction reaction, and the raw material source is wide and the production efficiency is high.

In summary, the present application has the following beneficial effects:

1. because the application adopts the nitrogen-doped carbon nano tube and the nitrogen-doped reduced graphene oxide to construct a similar three-dimensional network structure, the catalytic activity of the catalyst can be improved; and because the carbon nano tube and the reduced graphene oxide are respectively subjected to nitrogen doping treatment before combination, the combination strength between the carrier and the noble metal can be improved, so that the stability and the electrocatalytic activity of the catalyst are greatly improved, and the service life of the catalyst is prolonged.

2. Before the nitrogen-doped carbon nanotube and the nitrogen-doped reduced graphene oxide are combined, the nitrogen-doped reduced graphene oxide is loaded with the noble metal, so that the bonding strength between the carrier and the noble metal can be improved, the two carbon materials can be combined more easily, the preparation process is simpler, and the method is suitable for batch production.

3. The roasting temperature for preparing the nitrogen-doped reduced graphene oxide is 850-950 ℃, so that the catalyst has better catalytic activity; the roasting temperature for preparing the nitrogen-doped carbon nano tube is 600-700 ℃, so that the heating temperature can be reduced, the nitrogen-doped carbon nano tube can easily connect the noble metal-loaded reduced graphene oxide particles, and the catalyst has higher stability.

Detailed Description

The present application will be described in further detail with reference to examples.

Examples

The starting materials used in the examples are all commercially available. The noble metal can be one of platinum, iridium, rhodium and ruthenium, platinum is selected in the following embodiments, and chloroplatinic acid is selected as the corresponding noble metal precursor.

As shown in tables 1 and 2, examples 1 to 13 differ mainly in the amount of raw materials and the process parameters.

The following description will be made of example 1.

The preparation method of the nitrogen-doped graphene-carbon nanotube composite catalyst provided in embodiment 1 is as follows:

s1, preparing graphene oxide:

s1-1: adding 30g of natural graphite powder, 50g of phosphorus pentoxide and 50g of potassium persulfate into 240mL of 98% concentrated sulfuric acid, and stirring at 80 ℃ for 4.5 hours to obtain a mixed solution; then cooling the mixed solution to room temperature, adding deionized water to dilute the mixed solution to 500mL, sealing and standing for 12 h; then discarding the supernatant, filtering the precipitate with a microporous filter membrane with the aperture of 0.2 mu m, and then cleaning the filtered precipitate with deionized water to remove redundant acid on the surface of the precipitate to obtain a black solid; placing the black solid in a fume hood, and air-drying for 12h to obtain pre-oxidized graphite powder;

s1-2: adding pre-oxidized graphite powder into 1200mL of concentrated sulfuric acid with the volume fraction of 98% at the temperature of 0 ℃, maintaining the system at 0 ℃, and then slowly adding 150g of potassium permanganate while stirring; then the temperature is raised to 35 ℃ at the speed of 2 ℃/min, and the reaction is carried out for 10 hours under the temperature of 35 ℃ with heat preservation and stirring. After the reaction is finished, adding 2500mL of deionized water (the temperature of the system needs to be kept below 50 ℃ in the process of adding water), and stirring at room temperature for 1h after the water is added; adding 7500mL of deionized water, adding 200mL of 30% (V/V) aqueous solution of hydrogen peroxide, stirring at room temperature for 1h, standing for 12h for layering, and removing supernatant to obtain residue; then sequentially washing the residues with 1L, 10% (V/V) hydrochloric acid and 10L deionized water respectively, and drying at 80 ℃ for 12h to obtain graphite oxide.

S2, preparation of nitrogen-doped reduced graphene oxide:

weighing 0.2g of graphene oxide, placing the graphene oxide in 50mL of 0.5mol/L hydrochloric acid, and performing ultrasonic dispersion treatment for 1 hour to obtain a suspension; putting the suspension into an ice bath, dripping 250 mu L of aniline, stirring for 15min, slowly adding 1.5mL of 1.5mol/L ammonium persulfate, and continuously stirring for 6h under the ice bath; then filtering, collecting the precipitate, washing the precipitate with deionized water, and vacuum-drying at 90 ℃ for 3h to obtain PANI-GO (polyaniline-graphene oxide); place PANI-GO at N₂And roasting for 1h at 850 ℃ in the atmosphere to obtain the nitrogen-doped reduced graphene oxide (N-rGO).

S3, preparation of the platinum-loaded nitrogen-doped reduced graphene oxide:

adding N-rGO into deionized water, and performing ultrasonic dispersion for 30min to obtain an N-rGO solution with the concentration of 0.5 mg/mL; adding 4mL of a 0.295mol/L chloroplatinic acid aqueous solution into 100mL of N-rGO solution, ultrasonically dispersing uniformly, adjusting the pH of the system to 10 by using ammonia water, slowly adding 10mL of a 3mg/mL sodium borohydride solution, magnetically stirring at room temperature for 12 hours, and carrying out reduced pressure suction filtration to obtain a filter cake; and dispersing the filter cake in water, placing the filter cake in a freeze dryer, and freeze-drying the filter cake at the temperature of 50 ℃ below zero for 48 hours until the water is completely removed to obtain the platinum-loaded nitrogen-doped reduced graphene oxide.

S4, preparation of the nitrogen-doped carbon nanotube:

s4-1: taking a quartz glass sheet as a growth substrate, respectively ultrasonically cleaning the quartz glass sheet for 20min by using absolute ethyl alcohol and deionized water, and naturally airing the quartz glass sheet at room temperature for later use; dissolving ferrocene in xylene, and carrying out ultrasonic oscillation for 30min to fully dissolve the ferrocene to prepare a carbon source precursor solution with the concentration of 20 mg/mL;

s4-2: flatly placing the dried quartz glass sheet on a porcelain boat, feeding the porcelain boat into the center of a tube furnace, sealing the tube furnace, and introducing argon (Ar); then starting a tubular furnace temperature control system, heating to 500 ℃ at a heating rate of 10 ℃/min, and starting a preheating system;

s4-3: introducing protective gas Ar with the flow rate of 360sccm and reducing gas H with the flow rate of 120sccm into the reaction furnace₂The two gases were used as a mixed gas. Then, the temperature in the reaction furnace is raised to 600 ℃, the prepared carbon source precursor solution is injected into the tubular furnace through a peristaltic pump at the flow rate of 0.1mL/min, so that the carbon source precursor solution is sublimated under the heating of a preheating temperature control system and is brought into a reaction zone in the middle of the tubular furnace by the mixed gas;

s4-4: stopping introducing the carbon source precursor solution after the carbon source precursor solution is continuously introduced for 40min, and continuously maintaining the carbon source precursor solution at the temperature of 600 ℃ for 20 min; then stopping the introduction of H₂And cooling the whole system to room temperature in Ar atmosphere to obtain the nitrogen-doped carbon nanotube.

S5, preparing the platinum-loaded nitrogen-doped reduced graphene oxide-nitrogen-doped carbon nanotube:

mixing the nitrogen-doped carbon nanotube and the platinum-loaded nitrogen-doped reduced graphene oxide, dispersing the mixture in water, adding a reducing agent hydrazine hydrate, reacting for 6 hours at the temperature of 80 ℃ to obtain a reduction product, filtering the reduction product, and drying the reduction product at the temperature of 80 ℃ for 12 hours to obtain the platinum-loaded nitrogen-doped reduced graphene oxide-nitrogen-doped carbon nanotube composite catalyst.

TABLE 1 raw material usage amount of catalysts of examples 1-3 (unit: g)

Table 2 table of parameter settings in the preparation of catalysts of examples 1, 4-13

Comparative example

Comparative example 1: comparative example 1 is platinum-loaded nitrogen-doped reduced graphene oxide, which was prepared from S1 to S3 of example 1.

Comparative example 2: the comparative example is different from example 1 in that the amount of the nitrogen-doped carbon nanotube is 20g and the amount of the platinum-loaded nitrogen-doped reduced graphene oxide is 80 g.

Performance test

The performance of the catalysts of examples and comparative examples was tested as follows, and the test results are shown in Table 3.

And (3) adopting a three-electrode reaction device to perform cyclic voltammetry on the catalyst. Wherein the glassy carbon electrode is used as a working electrode, the diameter of the glassy carbon electrode is 4mm, and the glassy carbon electrode is respectively polished by 2000# metallographic abrasive paper and 0.05 mu m aluminum oxide powder before use, washed by deionized water and absolute ethyl alcohol respectively, and dried for later use.

Adding 50 mu L of 5 wt% Nafion into 2mL of absolute ethanol, and uniformly stirring to obtain a Nafion ethanol solution; 0.01g of catalyst is added into Nafion ethanol solution, and ultrasonic dispersion is carried out to obtain suspension. And (3) coating 10 mu L of suspension on the surface of the treated glassy carbon electrode, and then placing the glassy carbon electrode at the temperature of 80 ℃ for vacuum drying for 12 h.

In the three-electrode reaction device, a saturated calomel electrode is used as a reference electrode, a platinum wire is used as an auxiliary electrode, 1mol/L sulfuric acid solution is used as electrolyte, a cyclic voltammetry test is carried out on a CHI604 electrochemical workstation, the scanning voltage range is-0.2-1.0V, the scanning speed is 50mV/s, and a cyclic voltammetry curve is recorded. In the cyclic voltammogram, the sizes of the hydrogen desorption peak current and the area can reflect the electrochemical activity area of the catalyst, and the larger the electrochemical activity area is, the higher the oxygen reduction catalytic activity of the catalyst is. The durability test is that the catalyst is subjected to 10000 times of cyclic voltammetry cycles under oxygen saturation, the proportion of the electrochemical active area after the cyclic voltammetry cycles to the initial electrochemical active area is calculated and recorded as the electrochemical active area retention rate, and the higher the electrochemical active area retention rate is, the higher the stability of the catalyst is.

Table 3 electrochemical performance test table of catalysts of examples and comparative examples

According to table 2, it can be seen from the combination of example 1 and comparative example 1 that the electrochemical active area and the retention rate of the electrochemical active area of the catalyst of example 1 are significantly higher than those of comparative example 1, which shows that compared with a single carrier, the nitrogen-doped reduced graphene oxide-nitrogen-doped carbon nanotube adopted in the present application is a composite carrier, and the higher specific surface area of the composite carrier enables the size of the supported platinum particles to be smaller and the distribution to be more uniform, so that the catalyst has better catalytic activity. Compared with a single carrier, the nitrogen-doped reduced graphene oxide-nitrogen-doped carbon nanotube composite carrier has higher binding force with platinum particles, the platinum particles are not easy to fall off from the composite carrier after multiple electrochemical cycles, the catalytic activity of the catalyst is high, and better catalytic stability is presented.

It can be seen from the combination of examples 1 to 3 and comparative example 2 that when the ratio of the nitrogen-doped carbon nanotube to the platinum-loaded nitrogen-doped reduced graphene oxide is changed, the electrochemical active area and the retention rate of the catalyst are changed, when the dosage ratio of the nitrogen-doped carbon nanotube to the platinum-loaded nitrogen-doped reduced graphene oxide is 5-15:85-95, the catalyst has a better chemical active area and electrochemical active area retention rate, and particularly when the dosage ratio of the nitrogen-doped carbon nanotube to the platinum-loaded nitrogen-doped reduced graphene oxide is 1:9, better catalytic activity and stability can be obtained.

Combining the parameters of the electrochemical active areas of the embodiments 1 and 4 to 8, it can be seen that, when the nitrogen-doped reduced graphene oxide is prepared, the electrochemical activity of the catalyst tends to increase first and then decrease with the gradual increase of the roasting temperature; the reason is that the specific surface area of the graphene can be increased by increasing the calcination temperature within a certain range, so that the dispersion uniformity of the platinum particles is increased to increase the catalytic activity of the catalyst, but when the calcination temperature is too high, the agglomeration and size increase of the platinum particles are increased, and the catalytic activity is reduced. As can be seen from the parameters of the retention rates of the electrochemical activity areas of examples 1, 4 to 8, the retention rate of the electrochemical activity of the catalyst gradually decreases with the gradual increase of the calcination temperature; this is because as the calcination temperature increases, the nitrogen content on the surface of the graphene decreases, resulting in a decrease in the bonding strength between the graphene and the platinum particles, and thus a decrease in the stability of the catalyst. When the calcination temperature is 900 ℃, the catalyst can obtain better catalytic activity and stability.

Combining example 1 and examples 9-13, it can be seen that the electrochemical active area and retention rate of the electrochemical active area of the catalyst show a trend of increasing and then decreasing with the gradual increase of the calcination temperature; this is because the specific surface area of the carbon nanotube increases with the gradual increase of the calcination temperature, but the nitrogen content on the surface of the carbon nanotube decreases, and the increased specific surface area can improve the stability of the combination of the nitrogen-doped carbon nanotube and the nitrogen-doped graphene, but the decrease of the nitrogen content can reduce the strength of the combination of the nitrogen-doped carbon nanotube and the nitrogen-doped graphene, and also can affect the stability of the catalyst. When the calcination temperature is 650 ℃, the catalyst can obtain better catalytic activity and stability.

The present embodiment is only for explaining the present application, and it is not limited to the present application, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present application.