Heterojunction catalyst and preparation method and application thereof

Abstract

The invention relates to the technical field of chemical catalysis, and discloses a heterojunction catalyst as well as a preparation method and application thereof, and the catalyst comprises the following raw materials in parts by weight: 5-10 parts of palladium nanoparticles; 45 to 55 parts of graphene nano particles; 10 to 14 parts of tungsten phosphide nano particles; 25 to 35 parts of manganese-cobalt spinel oxide; 20 to 25 parts of a nitrogen-doped carbon nano tube; 10 to 14 parts of disodium ethylene diamine tetraacetate; 5-8 parts of sodium dodecyl benzene sulfonate; 5-9 parts of hydrazine hydrate; in the preparation process, by constructing a heterojunction structure of palladium and graphene, the catalyst achieves the beneficial effect of enhancing the hydrogen adsorption and activation capacity of the fuel cell anode, and due to the heterojunction formed by the palladium nanoparticles and the graphene, the palladium nanoparticles are well dispersed, the hydrogen adsorption and activation capacity of the fuel cell anode is improved, and the hydrogen adsorption and activation capacity of the fuel cell anode is improved. The electron coupling effect of the heterojunction can improve the catalytic oxidation capacity of palladium to hydrogen, so that the fuel cell can efficiently operate at a lower temperature, stable electric energy is output, and finally, the fuel cell can effectively operate at the lower temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical catalysis, and in particular to a heterojunction catalyst and a preparation method and application thereof. Background Art

[0002] With the continuous growth of energy demand and increasing awareness of environmental protection, fuel cells, as efficient and clean energy conversion devices, have attracted widespread attention. In fuel cells, the hydrogen oxidation reaction (HOR) at the anode and the oxygen reduction reaction (ORR) at the cathode are key electrochemical processes. However, while traditional platinum-carbon (Pt / C) catalysts have high catalytic activity, they are expensive, have poor stability, and are susceptible to poisoning by impurities such as carbon monoxide, limiting their large-scale application.

[0003] At the anode of the fuel cell, hydrogen needs to be oxidized to release electrons. This process requires an efficient catalyst to accelerate the adsorption and activation of hydrogen. Palladium (Pd), as a precious metal catalyst, has good hydrogen catalytic oxidation ability, but it is prone to agglomeration in practical applications, resulting in a reduction in active sites and a decrease in catalyst performance. To overcome this problem, researchers have tried to form a heterojunction between palladium and graphene. Graphene has a large specific surface area and excellent conductivity, which can effectively disperse palladium nanoparticles. At the same time, the electronic coupling between the two can further enhance the catalytic oxidation ability of palladium for hydrogen, thereby enabling the fuel cell to operate efficiently at lower temperatures and output stable electrical energy.

[0004] At the cathode of the fuel cell, the oxygen reduction reaction (ORR) is another key factor in the performance of the fuel cell. Traditional platinum-carbon catalysts show high activity in ORR, but they are expensive and have poor resistance to poisoning. In recent years, researchers have been committed to developing low-cost, high-performance alternative catalysts. The heterojunction constructed by manganese cobalt (MnCo) spinel oxide and nitrogen-doped carbon material has gradually become a research hotspot because of its low cost, strong resistance to poisoning and good oxygen reduction catalytic performance. This heterojunction can efficiently catalyze the reduction of oxygen to water at the cathode, maintain the continuous power supply of the fuel cell, and provide new possibilities for the commercial application of fuel cells.

[0005] However, research on heterojunction catalysts that can simultaneously optimize the performance of both the anode and cathode in fuel cells remains limited. Therefore, developing a heterojunction catalyst that can efficiently catalyze both hydrogen oxidation and oxygen reduction reactions and realizing its application in fuel cells through a rational preparation method is of great scientific significance and practical value. Summary of the Invention

[0006] (1) Technical problems solved

[0007] In response to the shortcomings of the existing technology, the present invention provides a heterojunction catalyst and its preparation method and application, which have the advantages of high catalytic performance, low cost, high stability and good anti-poisoning ability, and solve the problems of high cost, poor stability and weak anti-poisoning ability of traditional platinum-carbon catalysts.

[0008] (2) Technical solution

[0009] To achieve the above-mentioned object, the present invention provides the following technical solution: a heterojunction catalyst, wherein the raw materials of the catalyst and their proportions are: 5-10 parts of palladium nanoparticles; 45-55 parts of graphene nanoparticles; 10-14 parts of tungsten phosphide nanoparticles; 25-35 parts of manganese cobalt spinel oxide; 20-25 parts of nitrogen-doped carbon nanotubes; 10-14 parts of disodium ethylenediaminetetraacetic acid; 5-8 parts of sodium dodecylbenzenesulfonate; 5-9 parts of hydrazine hydrate; and 5-10 ml of ammonia water.

[0010] Preferably, the raw materials of the catalyst and their proportions are: 7 parts of palladium nanoparticles; 50 parts of graphene nanoparticles; 13 parts of tungsten phosphide nanoparticles; 30 parts of manganese cobalt spinel oxide; 22 parts of nitrogen-doped carbon nanotubes; 11 parts of disodium ethylenediaminetetraacetic acid; 6 parts of sodium dodecylbenzenesulfonate; 7 parts of hydrazine hydrate; and 8 ml of ammonia water.

[0011] Preferably, the particle size of the palladium nanoparticles is between 1-10 nm, and the sheet diameter of the graphene nanoparticles is between 1-2 μm.

[0012] Preferably, the crystal structure of the manganese-cobalt spinel oxide is spinel-type AB2O4, Mn 2+ Occupies tetrahedral site A, Co 3+ Occupying the octahedral site B, it is prepared from a manganese source and a cobalt source, and its chemical reaction formula is:

[0013] xMn+2yCo+O2→MnCo2O4

[0014] In the reaction formula, x and y represent the molar ratio of the manganese source and the cobalt source respectively. The manganese source and the cobalt source are prepared at a high temperature of 750-800° C. and oxygen is added at the same time to generate manganese-cobalt spinel oxide.

[0015] The preparation method of the heterojunction catalyst is prepared according to the raw materials of the heterojunction catalyst and their weight parts, and includes the following preparation steps:

[0016] Step 1: Prepare raw materials: prepare palladium nanoparticles, graphene nanoparticles, tungsten phosphide nanoparticles, manganese cobalt spinel oxide, nitrogen-doped carbon nanotubes, disodium ethylenediaminetetraacetic acid, sodium dodecylbenzenesulfonate, hydrazine hydrate and ammonia water in a formula ratio;

[0017] Step 2: Preparation of a palladium-graphene composite structure: adding graphene nanoparticles and palladium nanoparticles to deionized water in sequence for dispersion, adding disodium ethylenediaminetetraacetic acid and stirring evenly to form a complex;

[0018] Step 3: Pretreatment of tungsten phosphide nanoparticles: Take tungsten phosphide nanoparticles and sodium dodecylbenzenesulfonate in a formula ratio, add them into deionized water and perform ultrasonic dispersion;

[0019] Step 4: preparing a mixed system: preparing a mixed system of manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes;

[0020] Step 5: Catalyst overall compounding process: Compounding the components obtained from steps 2 to 4 with the remaining raw materials;

[0021] Step 6, catalyst post-treatment: After the reaction is completed, the mixed solution is centrifuged for 20-30 minutes, the separated precipitate is washed alternately with deionized water 5-6 times, and the washed precipitate is dried in an oven at 75-80° C. for 10-15 hours to obtain a heterojunction catalyst.

[0022] Preferably, the palladium-graphene composite structure preparation process in step 2 is:

[0023] S2.1. Add graphene nanoparticles to 299-301 mL of deionized water and disperse them by ultrasonication for 80-90 min.

[0024] S2.2. Add palladium nanoparticles to the graphene dispersion and continue ultrasonic dispersion for 55-60 minutes;

[0025] S2.3. Disodium ethylenediaminetetraacetate is added to the mixed solution and stirred for 25-30 minutes. Disodium ethylenediaminetetraacetate reacts chemically with palladium ions to form a complex to obtain a palladium-graphene mixed solution. The chemical reaction formula is:

[0026] Pd 2+ +EDTA 2- →[Pd(EDTA)] 2-

[0027] In the reaction formula, disodium ethylenediaminetetraacetate acts as a complexing agent to form a stable complex with palladium ions.

[0028] Preferably, in step 3, the tungsten phosphide nanoparticles are pretreated by adding tungsten phosphide nanoparticles and sodium dodecylbenzenesulfonate in a formula ratio to 99.5-100.5 mL of deionized water, and ultrasonically dispersing for 30-45 minutes to obtain a dispersion containing tungsten phosphide nanoparticles.

[0029] Preferably, in the preparation process of the mixed system in step 4, manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes are added to 195-205 mL of deionized water, and ultrasonically dispersed for 70-75 minutes to form a uniform manganese cobalt spinel oxide-nitrogen-doped carbon nanotube mixed suspension.

[0030] Preferably, the catalyst overall compounding process in step 5 is:

[0031] S5.1. Add the palladium-graphene mixture treated with disodium ethylenediaminetetraacetic acid dropwise to the dispersion containing tungsten phosphide nanoparticles, and stir for 55-65 minutes to obtain a mixture;

[0032] S5.2. Add 2-5 ml of aqueous ammonia dropwise to the mixture in S5.1 to adjust the pH of the solution to 9-10.

[0033] S5.3. Add the mixed suspension of manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes dropwise and continue stirring for 115-120 minutes to allow the components to fully contact and initially combine.

[0034] S5.4. Add hydrazine hydrate in the formula ratio dropwise and carry out reduction reaction at a temperature of 65-70°C for 3.5-4h.

[0035] Application of heterojunction catalyst: The heterojunction catalyst obtained according to the above preparation method is used to maintain continuous power supply of fuel cells.

[0036] Compared with the prior art, the present invention provides a heterojunction catalyst and its preparation method and application, which have the following beneficial effects:

[0037] 1. The present invention achieves the beneficial effect of enhancing the hydrogen adsorption and activation capabilities of the fuel cell anode by constructing a heterojunction structure of palladium and graphene. The heterojunction formed by palladium nanoparticles and graphene allows the palladium nanoparticles to be well dispersed. The electronic coupling effect of the heterojunction can enhance the catalytic oxidation ability of palladium for hydrogen, thereby enabling the fuel cell to operate efficiently at a lower temperature and output stable electrical energy, ultimately achieving effective operation of the fuel cell at a lower temperature.

[0038] 2. The present invention achieves the beneficial effects of low-cost and high-efficiency catalysis of oxygen reduction reaction and good anti-poisoning ability through the heterojunction constructed by manganese cobalt spinel oxide and nitrogen-doped carbon material. Among them, the combination of manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes can not only continuously and efficiently catalyze the reduction of oxygen to water to maintain continuous power supply of the fuel cell, but also has lower cost and stronger anti-poisoning ability than traditional platinum carbon catalysts, thereby effectively maintaining stable power supply of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1The figure is a flow chart for the preparation of the catalyst of the present invention. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] See also Figure 1 , heterojunction catalyst, the raw materials of the catalyst and their proportions (including parts by mass and parts by volume) are: 5-10 parts of palladium nanoparticles; 45-55 parts of graphene nanoparticles; 10-14 parts of tungsten phosphide nanoparticles; 25-35 parts of manganese cobalt spinel oxide (MnCo2O4); 20-25 parts of nitrogen-doped carbon nanotubes (N-CNT); 10-14 parts of disodium ethylenediaminetetraacetic acid; 5-8 parts of sodium dodecylbenzenesulfonate; 5-9 parts of hydrazine hydrate; 5-10 ml of ammonia water.

[0042] Specifically, the particle size of the palladium nanoparticles is between 1-10 nm, and the sheet diameter of the graphene nanoparticles is between 1-2 μm.

[0043] Specifically, the crystal structure of manganese cobalt spinel oxide is spinel type AB2O4, Mn 2+ Occupies tetrahedral site A, Co 3+ Occupying the octahedral site B, it is prepared from a manganese source and a cobalt source, and its chemical reaction formula is:

[0044] xMn+2yCo+O2→MnCo2O4

[0045] In the reaction formula, x and y represent the molar ratio of the manganese source and the cobalt source respectively. The manganese source and the cobalt source are prepared at a high temperature of 750-800° C. and oxygen is added at the same time to generate manganese-cobalt spinel oxide.

[0046] Specifically, the preparation method of the heterojunction catalyst is prepared according to the above-mentioned raw materials of the heterojunction catalyst and their weight parts, and includes the following preparation steps:

[0047] Step 1: Prepare raw materials: prepare palladium nanoparticles, graphene nanoparticles, tungsten phosphide nanoparticles, manganese cobalt spinel oxide, nitrogen-doped carbon nanotubes, disodium ethylenediaminetetraacetic acid, sodium dodecylbenzenesulfonate, hydrazine hydrate and ammonia water in a formula ratio;

[0048] Step 2: Preparation of a palladium-graphene composite structure: adding graphene nanoparticles and palladium nanoparticles to deionized water in sequence for dispersion, adding disodium ethylenediaminetetraacetic acid and stirring evenly to form a complex;

[0049] The advantages are: by constructing a heterojunction structure of palladium and graphene, the beneficial effect of enhancing the hydrogen adsorption and activation ability of the fuel cell anode is achieved. Among them, the heterojunction formed by palladium nanoparticles and graphene makes the palladium nanoparticles well dispersed, and the electronic coupling effect of the heterojunction can improve the catalytic oxidation ability of palladium to hydrogen, so that the fuel cell can operate efficiently at a lower temperature and output stable electrical energy, ultimately realizing the effective operation of the fuel cell at a lower temperature.

[0050] Step 3: Pretreatment of tungsten phosphide nanoparticles: Take tungsten phosphide nanoparticles and sodium dodecylbenzenesulfonate in a formula ratio, add them into deionized water and perform ultrasonic dispersion;

[0051] Step 4: preparing a mixed system: preparing a mixed system of manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes;

[0052] The advantages are: the heterojunction constructed by manganese cobalt spinel oxide and nitrogen-doped carbon material achieves the beneficial effects of low-cost and high-efficiency catalysis of oxygen reduction reaction and good anti-poisoning ability. Among them, the combination of manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes can not only continuously and efficiently catalyze the reduction of oxygen to water to maintain continuous power supply of the fuel cell, but also has lower cost and stronger anti-poisoning ability than traditional platinum carbon catalysts, thereby effectively maintaining stable power supply of the fuel cell.

[0053] Step 5: Catalyst overall compounding process: Compounding the components obtained from steps 2 to 4 with the remaining raw materials;

[0054] Step 6: Catalyst post-treatment: After the reaction is completed, the mixed solution is centrifuged for 20-30 minutes, and the separated precipitate is washed alternately with deionized water 5-6 times to remove impurities and unreacted raw materials. The washed precipitate is dried in an oven at 75-80°C for 10-15 hours to obtain the final heterojunction catalyst.

[0055] Specifically, the preparation process of the palladium-graphene composite structure in step 2 is as follows:

[0056] S2.1. Add graphene nanoparticles to 299-301 mL of deionized water and ultrasonically disperse them for 80-90 min to fully disperse the graphene in the water.

[0057] S2.2, adding palladium nanoparticles to the graphene dispersion and continuing ultrasonic dispersion for 55-60 minutes to promote the adhesion of palladium nanoparticles to the graphene surface;

[0058] S2.3. Disodium ethylenediaminetetraacetate is added to the mixed solution and stirred for 25-30 minutes. Disodium ethylenediaminetetraacetate reacts chemically with palladium ions to form a complex to obtain a palladium-graphene mixed solution. The chemical reaction formula is:

[0059] Pd 2+ +EDTA 2- →[Pd(EDTA)] 2-

[0060] In the reaction formula, disodium ethylenediaminetetraacetic acid (EDTA-2Na) acts as a chelating agent to form a stable complex with palladium ions. This complexation not only helps to evenly distribute palladium ions in the solution, but also enhances the binding force between palladium and graphene, further stabilizing the distribution of palladium on graphene.

[0061] Specifically, in step 3, the tungsten phosphide nanoparticles are pretreated by taking tungsten phosphide nanoparticles and sodium dodecylbenzenesulfonate in a formula ratio, adding them to 99.5-100.5 mL of deionized water, and ultrasonically dispersing them for 30-45 minutes to obtain a dispersion containing tungsten phosphide nanoparticles, wherein sodium dodecylbenzenesulfonate is used as a dispersant to ensure that the tungsten phosphide nanoparticles are evenly dispersed and prevent agglomeration.

[0062] Specifically, in step 4, the preparation process of the mixed system is as follows: manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes are added to 195-205 mL of deionized water, and ultrasonically dispersed for 70-75 minutes to form a uniform manganese cobalt spinel oxide-nitrogen-doped carbon nanotube mixed suspension.

[0063] Specifically, the overall catalyst compounding process in step 5 is:

[0064] S5.1. Add the palladium-graphene mixture treated with disodium ethylenediaminetetraacetic acid dropwise to the dispersion containing tungsten phosphide nanoparticles, stir for 55-65 minutes, and obtain a mixture, which is thoroughly mixed with the palladium-graphene and tungsten phosphide.

[0065] S5.2. Add 2-5 ml of aqueous ammonia dropwise to the mixture in S5.1 to adjust the pH of the solution to 9-10. Ammonia promotes the hydrolysis and precipitation of metal ions.

[0066] S5.3. Add the mixed suspension of manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes dropwise and continue stirring for 115-120 minutes to allow the components to fully contact and initially combine.

[0067] S5.4. Add hydrazine hydrate in the formula ratio dropwise and carry out reduction reaction at a temperature of 65-70°C for 3.5-4h. Hydrazine hydrate acts as a reducing agent to enhance the chemical bonding between the components and adjust the electronic structure of the catalyst.

[0068] Specifically, the heterojunction catalyst is used to maintain continuous power supply of a fuel cell.

[0069] Example 1

[0070] Heterojunction catalyst, the raw materials of the catalyst and their proportions are: 7 parts of palladium nanoparticles; 50 parts of graphene nanoparticles; 13 parts of tungsten phosphide nanoparticles; 30 parts of manganese cobalt spinel oxide; 22 parts of nitrogen-doped carbon nanotubes; 11 parts of disodium ethylenediaminetetraacetic acid; 6 parts of sodium dodecylbenzenesulfonate; 7 parts of hydrazine hydrate; and 8 ml of ammonia water.

[0071] Preparation method: The preparation is carried out according to the method of steps 1 to 6 above, that is, first preparing the raw materials, and then carrying out the preparation of the palladium-graphene composite structure, pretreatment of tungsten phosphide nanoparticles, preparation of the mixed system, overall catalyst composite process and catalyst post-treatment.

[0072] Application effect: At the anode of the fuel cell, the adsorption and activation process of hydrogen is enhanced. The heterojunction formed by palladium and graphene makes the palladium nanoparticles well dispersed. The electronic coupling effect improves the catalytic oxidation ability of palladium to hydrogen. The fuel cell can operate efficiently at a lower temperature and output stable electrical energy. In the oxygen reduction reaction at the cathode, the heterojunction constructed by manganese cobalt spinel oxide and nitrogen-doped carbon material has low cost and good anti-poisoning ability, and can sustainably and efficiently catalyze the reduction of oxygen to water, maintaining continuous power supply of the fuel cell.

[0073] Example 2

[0074] Heterojunction catalyst, the raw materials of the catalyst and their proportions are: 10 parts of palladium nanoparticles; 45 parts of graphene nanoparticles; 10 parts of tungsten phosphide nanoparticles; 35 parts of manganese cobalt spinel oxide; 25 parts of nitrogen-doped carbon nanotubes; 14 parts of disodium ethylenediaminetetraacetic acid; 8 parts of sodium dodecylbenzenesulfonate; 9 parts of hydrazine hydrate; and 10 ml of ammonia water.

[0075] Preparation method: same as the preparation steps in Example 1.

[0076] Application effect: In fuel cells, the anode hydrogen oxidation efficiency is high, and it can achieve efficient operation at lower temperatures and output stable electrical energy; in the oxygen reduction reaction at the cathode, the heterojunction of manganese cobalt spinel oxide and nitrogen-doped carbon material exhibits good anti-poisoning ability, continuously and efficiently catalyzes oxygen reduction, maintains stable power supply of the fuel cell, and the cost is lower than traditional platinum carbon catalysts.

[0077] Example 3

[0078] Heterojunction catalyst, catalyst raw materials and proportions: 5 parts of palladium nanoparticles; 55 parts of graphene nanoparticles; 14 parts of tungsten phosphide nanoparticles; 25 parts of manganese cobalt spinel oxide; 20 parts of nitrogen-doped carbon nanotubes; 10 parts of disodium ethylenediaminetetraacetic acid; 5 parts of sodium dodecylbenzenesulfonate; 5 parts of hydrazine hydrate; 5 ml of ammonia water.

[0079] Preparation method: same as the preparation steps in Example 1.

[0080] Application effect: At the anode of the fuel cell, the adsorption and activation effects of hydrogen are good. The heterojunction structure of palladium and graphene helps to improve the catalytic oxidation ability of hydrogen, and realize the effective operation of the fuel cell at a lower temperature; at the cathode, the heterojunction constructed by manganese cobalt spinel oxide and nitrogen-doped carbon material can effectively catalyze the oxygen reduction reaction, with low cost and strong anti-poisoning ability, which can maintain the continuous power supply of the fuel cell.

[0081] Comparative Example 1

[0082] Catalyst raw materials and ratio: A traditional platinum-carbon (Pt / C) catalyst is used, and the platinum (Pt) loading is a conventional ratio of 20 wt% Pt / C (ie, platinum accounts for 20% of the total mass of the catalyst, and the rest is carbon support).

[0083] Preparation method: The platinum-carbon catalyst is prepared by the impregnation reduction method, in which a platinum salt solution is impregnated on a carbon support, and then reduced with a reducing agent to obtain a supported platinum-carbon catalyst.

[0084] Application effect: At the anode of the fuel cell, the catalytic oxidation activity of hydrogen is high, but the activity decreases at lower temperatures, and platinum is prone to agglomeration, resulting in a decrease in catalyst stability; in the oxygen reduction reaction at the cathode, the platinum-carbon catalyst is easily poisoned by impurities such as carbon monoxide, and has poor anti-poisoning ability. A higher platinum loading is required to maintain catalytic activity, which is costly and makes it difficult to maintain the power supply of the fuel cell continuously and efficiently.

[0085] Comparative Example 2

[0086] Catalyst raw materials and proportions: 7 parts of palladium nanoparticles; 50 parts of graphene nanoparticles; but no tungsten phosphide nanoparticles, manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes are added; 11 parts of disodium ethylenediaminetetraacetic acid; 6 parts of sodium dodecylbenzenesulfonate; 7 parts of hydrazine hydrate; 8 ml of ammonia water.

[0087] Preparation method: Prepare according to the method of step 1, step 2 and step 6 of the present invention, that is, prepare the palladium-graphene composite structure after preparing the raw materials, and then perform catalyst post-treatment.

[0088] Application effect: In the anode of the fuel cell, the structure formed by palladium and graphene has a certain effect on the adsorption and activation of hydrogen. However, due to the lack of manganese cobalt spinel oxide and nitrogen-doped carbon nanotube components, it cannot effectively catalyze the oxygen reduction reaction at the cathode, resulting in a decline in the overall performance of the fuel cell, inability to provide continuous and stable power supply, and weak performance in anti-poisoning ability.

[0089] Comparative Example 3

[0090] Catalyst raw materials and proportions: 30 parts of manganese cobalt spinel oxide; 22 parts of nitrogen-doped carbon nanotubes; but no palladium nanoparticles, graphene nanoparticles and tungsten phosphide nanoparticles are added; 11 parts of disodium ethylenediaminetetraacetic acid; 6 parts of sodium dodecylbenzenesulfonate; 7 parts of hydrazine hydrate; 8 ml of ammonia water.

[0091] Preparation method: Prepare according to the method of step 1, step 4 and step 6 of the present invention, that is, prepare the mixed system after preparing the raw materials, and then perform catalyst post-treatment.

[0092] Application effect: At the cathode of the fuel cell, the system constructed by manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes has catalytic ability for oxygen reduction reaction. However, due to the lack of efficient catalytic oxidation of hydrogen by palladium and graphene at the anode, the overall performance of the fuel cell is limited, and it cannot operate efficiently at lower temperatures. The output power is unstable, and the overall cost advantage is not obvious (due to the lack of the cost reduction effect brought by the palladium-graphene system at the anode).

[0093] Summary: By integrating multiple nanomaterials to construct a heterojunction catalyst system in the present invention, the beneficial effects of optimizing the overall performance of the fuel cell and reducing the overall cost are achieved. Compared with traditional platinum-carbon catalysts, the catalyst of the present invention exhibits excellent catalytic performance at both the anode and cathode, and is outstanding in anti-poisoning ability. It can operate efficiently at lower temperatures and output stable electrical energy, while avoiding the problems of easy agglomeration, poor stability and high cost of platinum catalysts. For example, in Examples 1, 2 and 3, the overall performance of the fuel cell is better than that of the traditional platinum-carbon catalyst in Comparative Example 1, and the cost is lower.

[0094] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A heterojunction catalyst, characterized in that: The raw materials of the catalyst and their proportions are: 5-10 parts of palladium nanoparticles; 45-55 parts of graphene nanoparticles; 10-14 parts of tungsten phosphide nanoparticles; 25-35 parts of manganese cobalt spinel oxide; 20-25 parts of nitrogen-doped carbon nanotubes; 10-14 parts of disodium ethylenediaminetetraacetate; 5-8 parts of sodium dodecylbenzenesulfonate; 5-9 parts of hydrazine hydrate; and 5-10 ml of ammonia water.

2. The heterojunction catalyst according to claim 1, wherein: The raw materials of the catalyst and their proportions are: 7 parts of palladium nanoparticles; 50 parts of graphene nanoparticles; 13 parts of tungsten phosphide nanoparticles; 30 parts of manganese cobalt spinel oxide; 22 parts of nitrogen-doped carbon nanotubes; 11 parts of disodium ethylenediaminetetraacetate; 6 parts of sodium dodecylbenzenesulfonate; 7 parts of hydrazine hydrate; and 8 ml of ammonia water.

3. The heterojunction catalyst according to claim 1, wherein: The particle size of the palladium nanoparticles is between 1-10 nm, and the sheet diameter of the graphene nanoparticles is between 1-2 μm.

4. The heterojunction catalyst according to claim 1, wherein: The crystal structure of the manganese-cobalt spinel oxide is spinel-type AB2O4, Mn 2+ Occupies tetrahedral site A, Co 3+ Occupying the octahedral site B, it is prepared from a manganese source and a cobalt source, and its chemical reaction formula is: xMn+2yCo+O2→MnCo2O4 In the reaction formula, x and y represent the molar ratio of the manganese source and the cobalt source respectively. The manganese source and the cobalt source are prepared at a high temperature of 750-800° C. and oxygen is added at the same time to generate manganese-cobalt spinel oxide.

5. A method for preparing a heterojunction catalyst, characterized in that: The raw materials of the heterojunction catalyst according to claim 1 and their mass parts are prepared, comprising the following preparation steps: Step 1: Prepare raw materials: prepare palladium nanoparticles, graphene nanoparticles, tungsten phosphide nanoparticles, manganese cobalt spinel oxide, nitrogen-doped carbon nanotubes, disodium ethylenediaminetetraacetic acid, sodium dodecylbenzenesulfonate, hydrazine hydrate and ammonia water in a formula ratio; Step 2: Preparation of a palladium-graphene composite structure: adding graphene nanoparticles and palladium nanoparticles to deionized water in sequence for dispersion, adding disodium ethylenediaminetetraacetic acid and stirring evenly to form a complex; Step 3: Pretreatment of tungsten phosphide nanoparticles: Take tungsten phosphide nanoparticles and sodium dodecylbenzenesulfonate in a formula ratio, add them into deionized water and perform ultrasonic dispersion; Step 4: preparing a mixed system: preparing a mixed system of manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes; Step 5: Catalyst overall compounding process: Compounding the components obtained from steps 2 to 4 with the remaining raw materials; Step 6, catalyst post-treatment: After the reaction is completed, the mixed solution is centrifuged for 20-30 minutes, the separated precipitate is washed alternately with deionized water 5-6 times, and the washed precipitate is dried in an oven at 75-80° C. for 10-15 hours to obtain a heterojunction catalyst.

6. The method for preparing a heterojunction catalyst according to claim 5, wherein: Preparation process of palladium-graphene composite structure in step 2: S2.

1. Add graphene nanoparticles to 299-301 mL of deionized water and disperse them by ultrasonication for 80-90 min. S2.

2. Add palladium nanoparticles to the graphene dispersion and continue ultrasonic dispersion for 55-60 minutes; S2.

3. Disodium ethylenediaminetetraacetate is added to the mixed solution and stirred for 25-30 minutes. Disodium ethylenediaminetetraacetate reacts chemically with palladium ions to form a complex to obtain a palladium-graphene mixed solution. The chemical reaction formula is: Pd 2+ +EDTA 2- →[Pd(EDTA)] 2- In the reaction formula, disodium ethylenediaminetetraacetate acts as a complexing agent to form a stable complex with palladium ions.

7. The method for preparing a heterojunction catalyst according to claim 5, characterized in that: In the step 3, the tungsten phosphide nanoparticles are pretreated by adding tungsten phosphide nanoparticles and sodium dodecylbenzenesulfonate in a formula ratio into 99.5-100.5 mL of deionized water and ultrasonically dispersing the mixture for 30-45 minutes to obtain a dispersion containing tungsten phosphide nanoparticles.

8. The method for preparing a heterojunction catalyst according to claim 5, wherein: The preparation process of the mixed system in step 4 is as follows: adding manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes into 195-205 mL of deionized water, and ultrasonically dispersing them for 70-75 minutes to form a uniform manganese cobalt spinel oxide-nitrogen-doped carbon nanotube mixed suspension.

9. The method for preparing a heterojunction catalyst according to claim 5, wherein: The overall composite process of the catalyst in step 5: S5.

1. Add the palladium-graphene mixture treated with disodium ethylenediaminetetraacetic acid dropwise to the dispersion containing tungsten phosphide nanoparticles, and stir for 55-65 minutes to obtain a mixture; S5.

2. Add 2-5 ml of aqueous ammonia dropwise to the mixture in S5.1 to adjust the pH of the solution to 9-10. S5.

3. Add the mixed suspension of manganese cobalt spinel oxide and nitrogen-doped carbon nanotubes dropwise and continue stirring for 115-120 minutes to allow the components to fully contact and initially combine. S5.

4. Add hydrazine hydrate in the formula ratio dropwise and carry out reduction reaction at a temperature of 65-70°C for 3.5-4h.

10. Application of heterojunction catalyst, characterized in that, The heterojunction catalyst obtained by the preparation method according to claim 5 is used to maintain continuous power supply of a fuel cell.

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