A direct methanol fuel cell bifunctional catalyst and a preparation method thereof

Abstract

The application provides a direct methanol fuel cell bifunctional catalyst, which takes carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array as a conductive substrate, and platinum-nickel alloy nanochain is wound on the high-conductivity tungsten carbide substrate. A preparation method of the direct methanol fuel cell bifunctional catalyst comprises the following steps: (1) preparing carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array; (2) performing surface treatment through PECVD; (3) synthesizing Pt-Ni alloy polyhedral nanochain through hydrothermal reaction; (4) loading the Pt-Ni alloy polyhedral nanochain on the carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array through self-adsorption; (5) annealing after calcination in air, nitrogen and argon-hydrogen gas in sequence; (6) performing second PECVD treatment, and the direct methanol fuel cell bifunctional catalyst is obtained. The prepared product has the characteristics of high conductivity, high specific surface area and good electrochemical performance. The LSV curve of MOR catalytic performance shows that the current density is obviously improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of direct methanol fuel cell catalysts, and particularly relates to a direct methanol fuel cell bifunctional catalyst and a preparation method thereof. BACKGROUND

[0002] With the rapid advancement of population growth and industrialization, especially the rapid consumption of non-renewable resources such as coal and oil after the industrial revolution, data shows that global energy demand has grown significantly in the last century, and is expected to grow by nearly 48% in the next 20 years to meet the needs of sustainable industrialization and human population. Direct methanol fuel cells (DMFC) gradually come into people's vision due to their high energy density, low working temperature and good portability, and have become one of the most promising electrochemical energy conversion devices, which are applied in the fields of automobiles, aerospace, trucks and other portable energy fields. However, the slow kinetics of anode methanol oxidation reaction (MOR) and cathode oxygen reduction reaction (ORR) seriously hinders the commercial application of DMFC, and in addition, the "mixed potential" caused by methanol permeation reduces the open-circuit voltage and efficiency of the battery, and the actual power output of DMFC is lower than the theoretical value.

[0003] At present, noble metal catalysts, especially platinum-based catalysts, are the most commonly used materials for ORR and MOR, but due to the high cost, scarcity and CO poisoning problems of platinum itself, the development of high-efficiency direct methanol fuel cell bifunctional catalysts is the key. SUMMARY

[0004] In order to solve the above technical problems, the application provides a direct methanol fuel cell bifunctional catalyst and a preparation method thereof, which has the characteristics of high conductivity, high specific surface area and good electrochemical performance.

[0005] The first aspect of the application provides a direct methanol fuel cell bifunctional catalyst, which uses carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array as a conductive substrate, and platinum-nickel alloy nanometer chain is wound on the high-conductivity tungsten carbide substrate.

[0006] The second aspect of the application provides a preparation method of a direct methanol fuel cell bifunctional catalyst, which comprises the following steps:

[0007] (1) preparing carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array;

[0008] (2) performing surface treatment on the carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array by PECVD;

[0009] (3) hydrothermally synthesizing Pt-Ni alloy polyhedral nanometer chain;

[0010] (4) The Pt-Ni alloy polyhedral nanochain synthesized in step 3 is loaded on the carbon cloth with nitrogen-doped tungsten carbide nanometer array treated in step 2 by self-adsorption to obtain a platinum-nickel alloy polyhedral nanochain@tungsten carbide composite material;

[0011] (5) The platinum-nickel alloy polyhedral nanochain@tungsten carbide composite material obtained in step 4 is annealed after being calcined in air, nitrogen and argon-hydrogen in sequence to obtain a carbon cloth with nitrogen-doped tungsten carbide nanometer array loaded with a Pt-Ni alloy polyhedral nanochain catalyst on the surface;

[0012] (6) A second PECVD treatment is performed to obtain an Ar / NH3 plasma modified nitrogen-doped tungsten carbide array surface loaded Pt-Ni alloy polyhedral nanochain catalyst, which is a direct methanol fuel cell bifunctional catalyst.

[0013] Further, the treatment temperature of the second PECVD treatment in step 6 is 100-300℃.

[0014] Further, step 6 comprises: cooling the carbon cloth with nitrogen-doped tungsten carbide nanometer array loaded with a Pt-Ni alloy polyhedral nanochain catalyst on the surface obtained in step 5 and then performing a second PECVD treatment, the gas atmosphere is argon-ammonia, the gas flow is 30 Pa, the plasma discharge radio frequency power source power is 75 W, the treatment time is 60 min, and the treatment temperature is 200℃. After cooling, an Ar / NH3 plasma modified nitrogen-doped tungsten carbide array surface loaded Pt-Ni alloy polyhedral nanochain catalyst is obtained, which is denoted as P-PtNi@P-N-WC@CC.

[0015] Further, step 1 comprises: dissolving tungstic acid powder in hydrogen peroxide, heating at 90-100℃ for 2.5-3.5h, then adding HCl and Na2SO4, dissolving, then placing the carbon cloth in it and heating at 170-180℃ for 11-13h to obtain a WO3 nanometer array, then adding melamine and heating at 800-900℃ under argon for 2.5-3.5h to obtain a nitrogen-doped tungsten carbide array.

[0016] Further, step 2 comprises: performing normal temperature plasma enhanced chemical vapor deposition on the substrate under Ar / NH3 atmosphere, the gas flow is 18-22 Pa, the plasma discharge radio frequency power source power is 95-105 W, and the treatment time is 50-70 min.

[0017] Further, step 3 comprises: mixing a platinum source, a nickel source, cetyltrimethylammonium chloride, glucose and oleylamine, ultrasonic treating the mixture at room temperature to form a uniformly distributed mixed solution, then heating from room temperature to 170-190 DEG C and keeping at the temperature for 11-13 h to complete the reaction, naturally cooling the product to room temperature, collecting the product by centrifugation and washing with ethanol, thereby obtaining the Pt-Ni alloy polyhedral nanochain.

[0018] Preferably, the platinum source is platinum acetylacetone, the nickel source is nickel acetylacetone, and the mass ratio of platinum acetylacetone to nickel acetylacetone is 2:1.

[0019] Further, step 4 comprises: placing the nitrogen-doped tungsten carbide array surface treated in step 2 into cyclohexane and magnetically stirring, ultrasonic dispersing the Pt-Ni alloy polyhedral nanochain prepared in step 3 in another portion of cyclohexane, then mixing the two solutions, and magnetically stirring and dispersing and adsorbing for 12 h, thereby obtaining the platinum-nickel alloy polyhedral nanochain@tungsten carbide composite material.

[0020] Further, step 5 comprises: raising the platinum-nickel alloy polyhedral nanochain@tungsten carbide composite material obtained in step 4 from room temperature to 180 DEG C in 20 min in air, keeping warm for 1 h, passing in nitrogen, keeping warm for 2 h, then raising the temperature to 400 DEG C at a rate of 7-8 DEG C / min in an argon-hydrogen atmosphere, keeping warm for 4 h, thereby obtaining the Pt-Ni alloy polyhedral nanochain catalyst loaded on the surface of the nitrogen-doped tungsten carbide nanometer array loaded carbon cloth, denoted as PtNi@P-N-WC@CC.

[0021] The present application has the following beneficial effects:

[0022] 1. The nitrogen-doped tungsten carbide nanometer array grows in a belt structure on the carbon cloth, has a high specific surface area, and excellent acid and alkali resistance, and can be used as an excellent carrier. After plasma treatment, more active sites are exposed on the surface, which is more conducive to the subsequent loading of noble metals.

[0023] 2. The loaded Pt-Ni alloy polyhedral nanochain retains the structural advantages of nanometer polyhedron and nanowire, effectively reduces the size effect, and the nanowire has abundant atomic interfaces and a Pt-rich surface, which can significantly increase the number of active centers.

[0024] 3. After loading the Pt-Ni alloy polyhedral nanochain on the surface of the nitrogen-doped tungsten carbide nanometer array loaded carbon cloth, a second PECVD treatment is performed to further increase the number of active centers and improve the MOR performance.

[0025] 4, Pt doping in nickel can improve the ability to resist CO poisoning, while tungsten carbide is considered to have complete immunity to CO, and the combination of the two further improves the ability to resist CO poisoning. Due to the high surface area of nitrogen-doped tungsten carbide, the metal atom utilization efficiency is improved, so it shows excellent MOR and ORR performance and is used as a direct methanol fuel cell bifunctional catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Micro-morphology (scale 3 μm) of N-WC@CC prepared for Example 1 under a scanning electron microscope (SEM);

[0027] Figure 2 Linear sweep voltammetry test graph (LSV) of oxygen reduction reaction (ORR) for Example 1, 2, 3 and Comparative Example 1, 2;

[0028] Figure 3 Linear sweep voltammetry test graph (LSV) of methanol oxidation reaction (MOR) for Example 1, 2, 3 and Comparative Example 1, 2;

[0029] 1, PtNi@P-NWC@CC, 2, P-PtNi@P-N-WC@CC-25, 3, P-PtNi@P-N-WC@CC-100, 4, P-PtNi@P-N-WC@CC-200, 5, P-PtNI@P-N-WC@CC-300. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and beneficial technical effects of the present application clearer, the beneficial effects of the direct methanol fuel cell bifunctional catalyst and the preparation method thereof of the present application will be described in detail below in combination with specific embodiments. The embodiments in the present specification are only for explaining the present application, not limiting the present application, and the parameters, proportions, etc. of the embodiments are selected according to the actual situation and have no substantial influence on the results.

[0031] The Ar / NH3 plasma modified nitrogen-doped tungsten carbide array surface loaded Pt-Ni alloy polyhedral nanochain catalyst of the present application takes the carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array as a conductive substrate, and the platinum-nickel alloy nanochain is wound on the high-conductivity tungsten carbide substrate.

[0032] The specific preparation method includes the following steps:

[0033] (I) Preparation of carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array;

[0034] (II) Surface treatment of the carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array by PECVD to increase surface defects and improve substrate hydrophilicity;

[0035] (iii) Hydrothermal synthesis of Pt-Ni alloyed polyhedral nanochains;

[0036] (iv) Loading of the synthesized Pt-Ni alloyed polyhedral nanochains on nitrogen-doped tungsten carbide nanorarray on carbon cloth by self-adsorption;

[0037] (v) Annealing after calcination in air, nitrogen and argon-hydrogen successively to remove surfactant to obtain Pt-Ni alloyed polyhedral nanochain catalyst loaded on the surface of nitrogen-doped tungsten carbide nanorarray on carbon cloth.

[0038] (vi) Second PECVD treatment to obtain final sample of Ar / NH3 plasma modified Pt-Ni alloyed polyhedral nanochain catalyst loaded on the surface of nitrogen-doped tungsten carbide nanorarray. The actual preparation process of the four exemplary samples is taken as a reference, and the corresponding bifunctional catalytic performance is detected to evaluate its performance as a direct methanol fuel cell bifunctional catalyst.

[0039] Example 1:

[0040] A method for preparing a direct methanol fuel cell bifunctional catalyst, specifically comprising the following steps:

[0041] (i) Preparation of nitrogen-doped tungsten carbide nanorarray (N-WC@CC) using tungstic acid (H2WO4), hydrogen peroxide (H2O2) and carbon cloth (CC) as raw materials: WO3 nanorarray was prepared on CC by hydrothermal method. Under magnetic stirring, tungstic acid powder (1.25 g) was dissolved in 40 ml of 12 wt% hydrogen peroxide by heating the hydrogen peroxide solution at 95°C for 3 h. Then 230 μl of HCl and 0.4 g of Na2SO4 were added, and after dissolution, the reaction kettle was placed and 2.5*2.5 cm carbon cloth was placed in it and heated at 180°C for 12 h to obtain WO3 nanorarray. Then 1.5 g of melamine was added and heated at 850°C for 3 h under argon to obtain nitrogen-doped tungsten carbide nanorarray, denoted as N-WC@CC.

[0042] (ii) Surface treatment of nitrogen-doped tungsten carbide nanorarray: The substrate was subjected to room temperature plasma enhanced chemical vapor deposition under Ar / NH3(7%) atmosphere, with gas flow reaching 20 Pa, plasma discharge radio frequency power being 100 W, and duration being 60 min, denoted as P-N-WC@CC.

[0043] (iii) Preparation of Pt-Ni alloy polyhedral nanochain: 0.075 mmol of Pt(acac)2, 0.0375 mmol of Ni(acac)2, 0.15 mmol of cetyltrimethylammonium chloride (CTAC), 0.75 mmol of glucose and 33 mL of oleylamine (Oam) were added into a beaker. The mixture was ultrasonically treated at room temperature for about 1.5 h to form a uniformly distributed mixed solution. Then the mixed solution was transferred into a reaction kettle, and heated from room temperature to 180 °C and kept at this temperature for 12 h to complete the reaction. After that, the product was naturally cooled to room temperature. The product was collected by centrifugation and washed with ethanol, and then dispersed in 15 mL of cyclohexane. The synthesized product is denoted as Pt-Ni PNC.

[0044] (iv) Preparation of Pt-Ni alloy polyhedral nanochain@tungsten carbide composite material: The plasma-treated nitrogen-doped tungsten carbide array was placed in 15 mL of cyclohexane and magnetically stirred for 15 min, while the prepared Pt-Ni alloy polyhedral nanochain was ultrasonically dispersed in another 15 mL of cyclohexane for 15 min. Then the two solutions were mixed and magnetically stirred for 12 h.

[0045] (v) Calcination and annealing of Pt-Ni alloy polyhedral nanochain@tungsten carbide composite material: A common quartz tube furnace was used, and the dried Pt-Ni alloy polyhedral nanochain@tungsten carbide composite material was placed at the bottom of the ceramic boat. The temperature was raised from room temperature to calcination temperature one, which was 180 °C, in 20 min under air, and then the temperature was kept at calcination temperature one for 1 h. Then nitrogen was introduced into the tube furnace at calcination temperature one, and the temperature was kept for 2 h. The temperature was raised from calcination temperature one to calcination temperature two at a rate of 7-8 °C / min, and the calcination temperature two was 400 °C. The temperature was kept at calcination temperature two for 4 h under an argon-hydrogen atmosphere. The product is denoted as PtNi@P-N-WC@CC.

[0046] (vi) Second plasma treatment: The cooled PtNi@P-N-WC@CC was placed at the bottom of the ceramic boat by PECVD. The gas flow reached 30 Pa under an argon-ammonia atmosphere, the plasma discharge radio frequency power was 75 W, and the treatment temperature was 100 °C for 60 min. The final sample was obtained after cooling, and is denoted as P-PtNi@P-N-WC@CC-100.

[0047] The morphology of the N-WC@CC sample obtained in Example 1 was analyzed by scanning electron microscopy (SEM), and the results are shown in FIG. 1. Figure 1 The sample is a belt-shaped nanometer array uniformly grown on the carbon cloth.

[0048] Evaluation of bifunctional catalytic performance:

[0049] The electrocatalytic performance of the prepared sample was carried out by an electrochemical workstation (CHI760E) in a three-electrode device.

[0050] Preparation of working electrode for MOR and ORR performance test: Before using rotating disk electrode (RDE), the glassy carbon electrode (GCE, d = 4.5 mm) was polished to mirror surface with Al2O3 powder polishing cloth, then washed with distilled water, and dried at room temperature for use. The catalyst with a diameter of 4.5 mm was pasted on the surface of GC electrode with Nafion solution (5 wt.%), and dried at room temperature as the working electrode. Electrochemical performance test: During the test, a standard three-electrode electrochemical test system was used, in which the counter electrode was a Pt sheet electrode, the reference electrode was a saturated calomel electrode (SCE), and the working electrode was prepared as described above. For MOR test: the test solution was 0.5M H2SO4+1M CH3OH solution; for ORR test: the test solution was 0.5M H2SO4. All potentials were calculated by referring to the reversible hydrogen electrode (RHE) through the Nernst equation: E(RHE) = E(Hg / Hg2Cl2) + 0.2415 + 0.059pH. Before linear sweep voltammetry (LSV) test, the working electrode was activated by cyclic voltammetry (CV) at a scan rate of 10mVs -1 -1 for 50 cycles. All electrochemical tests were carried out at room temperature.

[0051] The LSV curve of ORR of the PtNi@P-N-WC@CC-100 sample in 0.5M H2SO4 solution saturated with O2 at a rotation speed of 1600rpm was tested by rotating disk electrode (RDE), and the results are shown in Figure 2 .

[0052] The LSV curve of MOR of the PtNi@P-N-WC@CC-100 sample in 0.5M H2SO4+1M CH3OH solution was tested by rotating disk electrode (RDE), and the results are shown in Figure 3 .

[0053] Example 2:

[0054] A preparation method of a direct methanol fuel cell bifunctional catalyst, specifically comprising the following steps:

[0055] (i) Preparation of nitrogen-doped tungsten carbide array (N-WC@CC) using tungstic acid (H2WO4), hydrogen peroxide (H2O2) and carbon cloth (CC) as raw materials: WO3nanometer array was prepared on CC by hydrothermal method. Under magnetic stirring, tungstic acid powder (1.25 g) was dissolved in 40 ml of 12wt% hydrogen peroxide by heating the hydrogen peroxide solution at 95°C for 3h. Then 230μl of HCl, 0.4g of Na2SO4 was added and dissolved, then put into the reaction kettle and 2.5*2.5cm carbon cloth was placed in it, heated at 180°C for 12h to obtain WO3nanometer array. Then 1.5g of melamine was added, heated at 850°C for 3h under argon to obtain nitrogen-doped tungsten carbide array, denoted as N-WC@CC.

[0056] (ii) Surface treatment of nitrogen-doped tungsten carbide array: The substrate was treated by plasma enhanced chemical vapor deposition at room temperature under Ar / NH3(7%) atmosphere, the gas flow reached 20Pa, the plasma discharge radio frequency power was 100W, and the duration was 60min, denoted as P-N-WC@CC.

[0057] (iii) Preparation of Pt-Ni alloy polyhedral nanochain: 0.075mmol of Pt(acac)2, 0.0375mmol of Ni(acac)2, 0.15mmol of cetyltrimethylammonium chloride (CTAC), 0.75mmol of glucose and 33mL of oleylamine (Oam) were added to a beaker. The mixture was ultrasonically treated at room temperature for about 1.5h to form a uniformly distributed mixed solution. Then the mixed solution was transferred to a reaction kettle, and heated from room temperature to 180°C and kept at this temperature for 12h to complete the reaction. After that, the product was naturally cooled to room temperature. The product was collected by centrifugation and washed with ethanol, then dispersed in 15mL of cyclohexane. The synthesized product is denoted as Pt-Ni PNC.

[0058] (iv) Preparation of platinum-nickel alloy polyhedral nanochain@tungsten carbide composite: The plasma treated nitrogen-doped tungsten carbide array was put into 15mL of cyclohexane, and magnetically stirred for 15min, while the prepared Pt-Ni alloy polyhedral nanochain was ultrasonically dispersed in another 15mL of cyclohexane for 15min, then the above two solutions were mixed, and magnetically stirred for 12h.

[0059] (five) annealing after calcination of the platinum-nickel alloy polyhedral nanochain@ tungsten carbide composite material: using a common quartz tube furnace, the dried platinum-nickel alloy polyhedral nanochain@ tungsten carbide composite material is placed at the bottom of the ceramic boat, and the temperature is raised from room temperature to calcination temperature one under air within 20 min, the calcination temperature one is 180℃, and the temperature is kept for 1 h, then nitrogen is introduced into the tube furnace under the calcination temperature one, and the temperature is kept for 2 h; the temperature rising rate from the calcination temperature one to the calcination temperature two is 7-8℃ / min, the calcination temperature two is 400℃, the temperature is kept for 4 h, and the atmosphere is argon-hydrogen gas. The product is denoted as PtNi@P-N-WC@CC.

[0060] (six) secondary plasma treatment: by PECVD, the PtNi@P-N-WC@CC after cooling is placed at the bottom of the ceramic boat, under argon-ammonia atmosphere, the gas flow reaches 30 Pa, the plasma discharge radio frequency power source power is 75 W, and the treatment temperature is 200 degrees Celsius, and the treatment time is 60 min. After cooling, the final sample is obtained, denoted as P-PtNi@P-N-WC@CC-200.

[0061] Evaluation of bifunctional catalytic performance:

[0062] The LSV curve of the ORR of the PtNi@P-N-WC@CC-200 sample in 0.5M H2SO4 solution saturated with O2 was tested by rotating disc electrode (RDE) at a rotating speed of 1600 rpm, and the results are shown in Figure 2 .

[0063] The LSV curve of the MOR of the PtNi@P-N-WC@CC-200 sample in 0.5M H2SO4+1M CH3OH solution was tested by rotating disc electrode (RDE), and the results are shown in Figure 3 .

[0064] Example 3:

[0065] A preparation method of a direct methanol fuel cell bifunctional catalyst, specifically comprising the following steps:

[0066] (i) Preparation of nitrogen-doped tungsten carbide array (N-WC@CC) using tungstic acid (H2WO4), hydrogen peroxide (H2O2) and carbon cloth (CC) as raw materials: WO3nanometer array was prepared on CC by hydrothermal method. Under magnetic stirring, tungstic acid powder (1.25 g) was dissolved in 40 ml of 12wt% hydrogen peroxide by heating the hydrogen peroxide solution at 95°C for 3h. Then 230μl of HCl, 0.4g of Na2SO4 was added and dissolved, then put into the reaction kettle and 2.5*2.5cm carbon cloth was placed in it, heated at 180°C for 12h to obtain WO3nanometer array. Then 1.5g of melamine was added, heated at 850°C for 3h under argon to obtain nitrogen-doped tungsten carbide array, denoted as N-WC@CC.

[0067] (ii) Surface treatment of nitrogen-doped tungsten carbide array: The substrate was treated by plasma enhanced chemical vapor deposition at room temperature under Ar / NH3(7%) atmosphere, the gas flow reached 20Pa, the plasma discharge radio frequency power was 100W, and the duration was 60min, denoted as P-N-WC@CC.

[0068] (iii) Preparation of Pt-Ni alloy polyhedral nanochain: 0.075mmol of Pt(acac)2, 0.0375mmol of Ni(acac)2, 0.15mmol of cetyltrimethylammonium chloride (CTAC), 0.75mmol of glucose and 33mL of oleylamine (Oam) were added to a beaker. The mixture was ultrasonically treated at room temperature for about 1.5h to form a uniformly distributed mixed solution. Then the mixed solution was transferred to a reaction kettle, and heated from room temperature to 180°C and kept at this temperature for 12h to complete the reaction. After that, the product was naturally cooled to room temperature. The product was collected by centrifugation and washed with ethanol, then dispersed in 15mL of cyclohexane. The synthesized product is denoted as Pt-Ni PNC.

[0069] (iv) Preparation of platinum-nickel alloy polyhedral nanochain@tungsten carbide composite: The plasma treated nitrogen-doped tungsten carbide array was put into 15mL of cyclohexane, and magnetically stirred for 15min, while the prepared Pt-Ni alloy polyhedral nanochain was ultrasonically dispersed in another 15mL of cyclohexane for 15min, then the above two solutions were mixed, and magnetically stirred for 12h.

[0070] (five) annealing after calcination of the platinum-nickel alloy polyhedral oligomeric nanochain@tungsten carbide composite material: using a common quartz tube furnace, the dried platinum-nickel alloy polyhedral oligomeric nanochain@tungsten carbide composite material is placed at the bottom of the ceramic boat, and the temperature is raised from room temperature to calcination temperature one under air within 20 min, the calcination temperature one is 180℃, and the temperature is kept for 1 h, then nitrogen is introduced into the tube furnace under the calcination temperature one, and the temperature is kept for 2 h; the temperature is raised from the calcination temperature one to the calcination temperature two at a rate of 7-8℃ / min, the calcination temperature two is 400℃, and the temperature is kept for 4 h, and the atmosphere is argon-hydrogen gas. The product is denoted as PtNi@P-N-WC@CC.

[0071] (six) secondary plasma treatment: by PECVD, the PtNi@P-N-WC@CC after cooling is placed at the bottom of the ceramic boat, under argon-ammonia atmosphere, the gas flow reaches 30 Pa, the plasma discharge radio frequency power source power is 75 W, and the treatment temperature is 300 degrees Celsius, and the treatment time is 60 min. After cooling, the final sample is obtained, denoted as P-PtNi@P-N-WC@CC-300.

[0072] Evaluation of bifunctional catalytic performance:

[0073] The LSV curve of the ORR of the PtNi@P-N-WC@CC-300 sample in 0.5M H2SO4 solution saturated with O2 was tested by rotating disc electrode (RDE) at a rotating speed of 1600 rpm, and the results are shown in Figure 2 .

[0074] The LSV curve of the MOR of the PtNi@P-N-WC@CC-300 sample in 0.5M H2SO4+1M CH3OH solution was tested by rotating disc electrode (RDE), and the results are shown in Figure 3 .

[0075] Comparative example 1

[0076] A preparation method of a direct methanol fuel cell bifunctional catalyst, specifically comprising the following steps:

[0077] (i) Preparation of nitrogen-doped tungsten carbide array (N-WC@CC) using tungstic acid (H2WO4), hydrogen peroxide (H2O2) and carbon cloth (CC) as raw materials: WO3nanometer array was prepared on CC by hydrothermal method. Under magnetic stirring, tungstic acid powder (1.25 g) was dissolved in 40 ml of 12wt% hydrogen peroxide by heating the hydrogen peroxide solution at 95°C for 3h. Then 230μl of HCl, 0.4g of Na2SO4 was added and dissolved, then put into the reaction kettle and 2.5*2.5cm carbon cloth was placed in it, heated at 180°C for 12h to obtain WO3nanometer array. Then 1.5g of melamine was added, heated at 850°C for 3h under argon to obtain nitrogen-doped tungsten carbide array, denoted as N-WC@CC.

[0078] (ii) Surface treatment of nitrogen-doped tungsten carbide array: The substrate was treated by room temperature plasma enhanced chemical vapor deposition under Ar / NH3(7%) atmosphere, the gas flow reached 20Pa, the plasma discharge radio frequency power was 100W, and the duration was 60min, denoted as P-N-WC@CC.

[0079] (iii) Preparation of Pt-Ni alloy polyhedral nanochain: 0.075mmol of Pt(acac)2, 0.0375mmol of Ni(acac)2, 0.15mmol of cetyltrimethylammonium chloride (CTAC), 0.75mmol of glucose and 33mL of oleylamine (Oam) were added to a beaker. The mixture was ultrasonically treated at room temperature for about 1.5h to form a uniformly distributed mixed solution. Then the mixed solution was transferred to a reaction kettle, and heated from room temperature to 180°C and kept at this temperature for 12h to complete the reaction. After that, the product was naturally cooled to room temperature. The product was collected by centrifugation and washed with ethanol, then dispersed in 15mL of cyclohexane. The synthesized product is denoted as Pt-Ni PNC.

[0080] (iv) Preparation of platinum-nickel alloy polyhedral nanochain@tungsten carbide composite: The plasma treated nitrogen-doped tungsten carbide array was put into 15mL of cyclohexane, and magnetically stirred for 15min, while the prepared Pt-Ni alloy polyhedral nanochain was ultrasonically dispersed in another 15mL of cyclohexane for 15min, then the above two solutions were mixed, and magnetically stirred for 12h.

[0081] (five) calcination and annealing of the platinum-nickel alloy polyhedral nanochain@ tungsten carbide composite material: using a common quartz tube furnace, the dried platinum-nickel alloy polyhedral nanochain@ tungsten carbide composite material is placed at the bottom of the pottery boat, and the temperature is raised from room temperature to calcination temperature one under air within 20 min, the calcination temperature one is 180℃, and the temperature is kept for 1 h, then nitrogen is introduced into the tube furnace under the calcination temperature one, and the temperature is kept for 2 h; the temperature rising rate from the calcination temperature one to the calcination temperature two is 7-8℃ / min, the calcination temperature two is 400℃, the temperature is kept for 4 h, and the atmosphere is argon-hydrogen. The product is denoted as PtNi@P-N-WC@CC.

[0082] Evaluation of bifunctional catalytic performance:

[0083] The LSV curve of the ORR of the PtNi@P-N-WC@CC sample in 0.5M H2SO4 solution saturated with O2 was tested by rotating disc electrode (RDE) at a rotating speed of 1600 rpm, and the results are shown in Figure 2

[0084] The LSV curve of the MOR of the PtNi@P-N-WC@CC sample in 0.5M H2SO4+1M CH3OH solution was tested by rotating disc electrode (RDE), and the results are shown in Figure 3

[0085] Comparative example 2

[0086] A preparation method of a direct methanol fuel cell bifunctional catalyst, specifically comprising the following steps:

[0087] (one) preparation of nitrogen-doped tungsten carbide array (N-WC@CC) using tungstic acid (H2WO4), hydrogen peroxide (H2O2) and carbon cloth (CC) as raw materials: WO3 nanometer array is prepared on CC by hydrothermal method. Under magnetic stirring, tungstic acid powder (1.25g) is dissolved in 40ml of 12wt% hydrogen peroxide by heating the hydrogen peroxide solution at 95℃ for 3h. Then 230μl of HCl and 0.4g of Na2SO4 are added, and after dissolution, the reaction kettle is placed and 2.5*2.5cm carbon cloth is placed therein, and after heating at 180℃ for 12h, WO3 nanometer array is obtained. Then 1.5g of melamine is added, heated at 850℃ for 3h under argon to obtain nitrogen-doped tungsten carbide array, denoted as N-WC@CC.

[0088] (two) surface treatment of nitrogen-doped tungsten carbide array: the substrate is treated by plasma enhanced chemical vapor deposition at room temperature under Ar / NH3(7%) atmosphere, the gas flow reaches 20Pa, the plasma discharge radio frequency power is 100W, and the treatment lasts for 60min, denoted as P-N-WC@CC.

[0089] ​​(iii) Preparation of Pt-Ni alloy polyhedral nanochain: 0.075 mmol of Pt(acac)2, 0.0375 mmol of Ni(acac)2, 0.15 mmol of cetyltrimethylammonium chloride (CTAC), 0.75 mmol of glucose and 33 mL of oleylamine (Oam) were added into a beaker. The mixture was ultrasonically treated at room temperature for about 1.5 h to form a uniformly distributed mixed solution. Then the mixed solution was transferred into a reaction kettle, and heated from room temperature to 180 °C and kept at this temperature for 12 h to complete the reaction. After that, the product was naturally cooled to room temperature. The product was collected by centrifugation and washed with ethanol, and then dispersed in 15 mL of cyclohexane. The synthesized product is denoted as Pt-Ni PNC.

[0090] (iv) Preparation of Pt-Ni alloy polyhedral nanochain@tungsten carbide composite material: The plasma treated nitrogen-doped tungsten carbide array was placed in 15 mL of cyclohexane and magnetically stirred for 15 min, while the prepared Pt-Ni alloy polyhedral nanochain was ultrasonically dispersed in another 15 mL of cyclohexane for 15 min. Then the two solutions were mixed and magnetically stirred for 12 h.

[0091] (v) Calcination and annealing of Pt-Ni alloy polyhedral nanochain@tungsten carbide composite material: A common quartz tube furnace was used, and the dried Pt-Ni alloy polyhedral nanochain@tungsten carbide composite material was placed at the bottom of the ceramic boat. The temperature was raised from room temperature to calcination temperature one, which was 180 °C, in 20 min under air, and then the temperature was kept at calcination temperature one for 1 h. Then nitrogen was introduced into the tube furnace at calcination temperature one, and the temperature was kept for 2 h. The temperature was raised from calcination temperature one to calcination temperature two at a rate of 7-8 °C / min, and calcination temperature two was 400 °C. The temperature was kept at calcination temperature two for 4 h under an argon-hydrogen atmosphere. The product is denoted as PtNi@P-N-WC@CC.

[0092] (vi) Secondary plasma treatment: The cooled PtNi@P-N-WC@CC was placed at the bottom of the ceramic boat by PECVD. The gas flow reached 30 Pa under an argon-ammonia atmosphere, and the plasma discharge radio frequency power was 75 W for 60 min at a treatment temperature of 25 °C. The final sample was obtained after cooling and is denoted as P-PtNi@P-N-WC@CC-25.

[0093] Evaluation of bifunctional catalytic performance:

[0094] The LSV curve of the ORR of the PtNi@P-N-WC@CC-25 sample was tested by rotating disc electrode (RDE) at a rotation speed of 1600 rpm in 0.5 M H2SO4 solution saturated with O2, and the results are shown in Figure 2

[0095] ​The LSV curves of the PtNi@P-N-WC@CC-25 sample were tested by using a rotating disc electrode (RDE) in 0.5M H2SO4+1M CH3OH solution MOR, and the results are shown in Figure 3 .

[0096] As shown in Figure 2 , the product obtained in Example 1 is P-PtNi@P-N-WC@CC-100. The product obtained in Example 2 is P-PtNi@P-N-WC@CC-200. The product obtained in Comparative Example 1 is PtNi@P-N-WC@CC. The product obtained in Comparative Example 2 is P-PtNi@P-N-WC@CC-25. The product obtained in Example 3 is P-PtNi@P-N-WC@CC-300.

[0097] The LSV curves of the MOR catalytic activity under the same conditions as the ORR test are shown in Figure 3 . Under the same test conditions, the current density of the product prepared by the preparation process described in Example 1 and Example 2 is obviously higher than that of Comparative Example 1, Comparative Example 2 and Comparative Example 3. Among them, P-PtNi@P-N-WC@CC-200 shows the highest current density. Therefore, the optimal selection of the treatment temperature of the second plasma treatment in step 6 is 200°C.

[0098] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a direct methanol fuel cell bifunctional catalyst, characterized by: Comprising the following steps: (1) Dissolve tungstic acid powder in hydrogen peroxide, heat at 90-100 ℃ for 2.5-3.5 h, then add HCl and Na2SO4, dissolve, then place carbon cloth into it and heat at 170-180 ℃ for 11-13 h to obtain WO3 nanometer array, then add melamine, heat at 800-900 ℃ under argon for 2.5-3.5 h for carbonization to obtain nitrogen-doped tungsten carbide array, and prepare carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array; (2) Perform surface treatment on the carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array by PECVD; (3) Mix a platinum source, a nickel source, cetyltrimethylammonium chloride, glucose and oleylamine, ultrasonically treat the mixture at room temperature to form a uniformly distributed mixed solution, then heat from room temperature to 170-190 ℃ and keep at the temperature for 11-13 h to complete the reaction, and naturally cool the product to room temperature, collect the product by centrifugation and wash with ethanol to obtain Pt-Ni alloy polyhedral nanochains; (4) Load the Pt-Ni alloy polyhedral nanochains synthesized in step 3 on the carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array treated in step 2 by self-adsorption to obtain platinum-nickel alloy polyhedral nanochain@tungsten carbide composite material; (5) Raise the platinum-nickel alloy polyhedral nanochain@tungsten carbide composite material obtained in step 4 from room temperature to 180 ℃ in air within 20 min, and keep at the temperature for 1 h; Pass in nitrogen, keep at the temperature for 2 h, then raise the temperature to 400 ℃ at a rate of 7-8 ℃ / min in an argon-hydrogen atmosphere, and keep at the temperature for 4 h to obtain a Pt-Ni alloy polyhedral nanochain catalyst loaded on the surface of the carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array, denoted as PtNi@P-N-WC@CC; (6) Perform second PECVD treatment on the Pt-Ni alloy polyhedral nanochain catalyst loaded on the surface of the carbon cloth loaded with nitrogen-doped tungsten carbide nanometer array obtained in step 5 after cooling, the atmosphere is argon-ammonia, the gas flow rate is 30 Pa, the plasma discharge radio frequency power is 75 W, the treatment time is 60 min, and the treatment temperature is 200 ℃, and the Ar / NH3 plasma modified nitrogen-doped tungsten carbide array surface loaded Pt-Ni alloy polyhedral nanochain catalyst obtained after cooling is denoted as P-PtNi@P-N-WC@CC.

2. The method for preparing a direct methanol fuel cell bifunctional catalyst according to claim 1, characterized by, Step 2 comprises: performing normal temperature plasma enhanced chemical vapor deposition on the substrate in an Ar / NH3 atmosphere, the gas flow rate is 18-22 Pa, the plasma discharge radio frequency power is 95-105 W, and the treatment time is 50-70 min.

3. The method for preparing the bifunctional catalyst for direct methanol fuel cells according to claim 1, characterized in that, The platinum source is platinum acetylacetonate, the nickel source is nickel acetylacetonate, and the molar ratio of platinum acetylacetonate to nickel acetylacetonate is 2:

1.

4. The method for preparing the bifunctional catalyst for direct methanol fuel cells according to claim 1, characterized in that, Step 4 comprises: placing the nitrogen-doped tungsten carbide array treated in step 2 into cyclohexane, magnetically stirring, ultrasonically dispersing the Pt-Ni alloy polyhedral nanochains prepared in step 3 in another portion of cyclohexane, then mixing the two solutions, and magnetically stirring and dispersing and adsorbing for 12 h to obtain platinum-nickel alloy polyhedral nanochain@tungsten carbide composite material.

5. A direct methanol fuel cell bifunctional catalyst characterized by, obtained by any one of claims 1 to 4.

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