High-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst and preparation method thereof

Abstract

The invention belongs to the technical field of alkaline fuel cells, and discloses a high-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst and a preparation method thereof. The preparation method of the catalyst comprises two main steps: firstly, modifying the surface of carbon black with polydopamine (PDA), then dispersing the active component ruthenium onto the surface of the modified carbon black through the polydopamine (PDA), and carrying out thermal annealing treatment to obtain the catalyst. According to the material preparation method provided by the invention, ruthenium active sites in an electron-deficient state can be constructed on the surface of the carbon substrate, and the sites can weaken excessive adsorption of ruthenium to a reaction intermediate, so that a catalyst is prevented from being inactivated due to passivation in a reaction process. The prepared ruthenium / carbon composite electrocatalyst shows extremely high hydrogen oxidation (HOR) activity and excellent stability under an alkaline condition, and still retains catalytic activity when the overpotential reaches 0.9 V (vs.RHE).

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alkaline fuel cells, and particularly relates to a high-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst and a specific preparation method of the catalyst. BACKGROUND

[0002] In a hydrogen-oxygen fuel cell, the hydrogen oxidation reaction (HOR) is the anode reaction of the cell, and the anode catalyst is one of the key technical points for determining the overall performance of the fuel cell and realizing cost control. At present, the proton exchange membrane fuel cell (PEMFC) which is relatively mature and has been commercialized relies on platinum-based catalysts, and therefore has a high cost, which greatly limits the popularization and application of this type of fuel cell. In contrast, the fuel cell system based on anion exchange membrane (AEMFC) can greatly reduce the dependence on platinum-based catalytic materials due to its operation in alkaline conditions, and has gradually become a research hotspot in this field.

[0003] The alkaline fuel cell system based on anion exchange membrane has a large number of non-noble metal-based catalyst material candidates for the cathode, such as Fe-N-C materials. However, the anode still mainly uses platinum-based materials at present, and therefore in order to further reduce the cost of the alkaline fuel cell, it is urgent to develop new non-platinum anode electrocatalysts. Ruthenium (Ru) is considered as one of the most potential alternative materials due to its lower price than platinum and higher hydrogen oxidation activity in alkaline medium. However, the existing ruthenium-based catalysts have obvious deficiencies when applied to the alkaline hydrogen oxidation reaction: the stable potential window is limited, and when the potential exceeds about 0.1 V (vs. RHE), strong adsorption of hydroxyl (OH*) occurs, which leads to full coverage of the catalyst surface by hydroxyl and deactivation.

[0004] Although the existing improvement methods such as alloying of ruthenium or doping of heteroelements can partially improve the stability of the ruthenium-based hydrogen oxidation electrocatalyst, the preparation process is complex and the cost is high, and such methods often lead to a decrease in the overall conductivity of the catalyst, thereby affecting the overall power output of the fuel cell. Therefore, how to develop a ruthenium-based hydrogen oxidation electrocatalyst with high activity and high stability, and with economic feasibility, is still one of the key technical problems to be solved in this field. SUMMARY

[0005] Invention purposes: The application provides a high-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst and a preparation method thereof. In the synthesis process, polydopamine (PDA) is introduced twice to build electron-deficient ruthenium active sites on the surface of carbon black particles, which greatly improves the adsorption strength of ruthenium to reaction intermediates such as hydroxyl, and finally improves the stability of the ruthenium-based catalyst in the alkaline hydrogen oxidation reaction (HOR). The prepared catalyst, as a high-stability HOR catalytic material, exhibits excellent catalytic performance, and can still maintain the catalytic activity for hydrogen at a overpotential of 0.9 V (vs. RHE).

[0006] Technical solutions: The catalyst of the application uses polydopamine (PDA)-wrapped carbon black as a carrier, then disperses ruthenium nanoparticles on the surface of the modified carbon black using polydopamine (PDA) again, and obtains the catalyst through annealing treatment in an inert gas atmosphere. The catalyst has low raw material cost and excellent stability, and can be used in alkaline fuel cells as a potential material to replace commercial platinum-carbon catalysts.

[0007] The application provides a method for preparing a high-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst, which comprises the following steps:

[0008] (1) A certain amount of carbon black particles is weighed and dispersed in a water / ethanol mixed solution and subjected to magnetic stirring;

[0009] (2) A certain amount of dopamine is weighed and added to the solution in step (1), and stirring is continued;

[0010] (3) Ammonia is added dropwise to the solution in step (2), and the pH value of the solution is continuously measured using a pH meter until the pH of the solution reaches 9-10, and then the solution is subjected to centrifugation, washing and drying treatment after sufficient reaction;

[0011] (4) A certain amount of the modified carbon black particles in step (3) is weighed and dispersed in a water / ethanol mixed solution and subjected to magnetic stirring, and then a certain amount of a ruthenium precursor salt and dopamine powder are added;

[0012] (5) Ammonia is added dropwise to the solution in step (4), and the pH value of the solution is continuously measured using a pH meter until the pH of the solution reaches 8-9, and then the solution is subjected to centrifugation, washing and drying treatment after stirring for a period of time;

[0013] (6) The solid product obtained in step (5) is subjected to annealing treatment in a tube furnace to obtain the high-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst of the application.

[0014] The preparation method of the high-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst has the characteristics that,

[0015] The carbon black particle size in step (1) is 20-200 nm, the mass ratio of carbon black to solvent is 1:(100-200), the volume ratio of water to ethanol in the solvent is 1:1, and the magnetic stirring rate is 500-1000 rpm.

[0016] The mass ratio of the amount of dopamine added to carbon black in step (2) is (2-4):1.

[0017] The mass concentration of ammonia in step (3) is 20%-40%, the reaction time is 8-12 hours, the centrifugal speed is 3000-8000 rpm, the centrifugal time is 3-5 minutes, the washing solvent is deionized water, the drying temperature is 80-100°C, and the drying time is 8-12 hours.

[0018] The mass ratio of the modified carbon black to solvent in step (4) is 1:(600-1000), the volume ratio of water to ethanol in the solvent is 1:1, the magnetic stirring rate is 500-1000 rpm, the ruthenium-containing precursor salt is one or more of ruthenium trichloride, ruthenium trichloride trihydrate or ruthenium nitrosyl nitrate, and the mass ratio among the ruthenium-containing precursor salt, dopamine powder and carbon black is (1-2):(0.25-0.5):1.

[0019] The mass concentration of ammonia in step (5) is 20%-40%, the continuous stirring time is 24-36 hours, the centrifugal speed is 3000-8000 rpm, the centrifugal time is 3-5 minutes, the washing solvent is deionized water, the drying temperature is 80-100°C, and the drying time is 8-12 hours.

[0020] The annealing temperature in step (6) is 300-500°C, the atmosphere is nitrogen or argon, the tube furnace heating rate is 5-10°C / min, and the annealing time is 2-4 hours.

[0021] Advantages: Compared with the prior art, the advantages of the present application are as follows: (1) the method for preparing the ruthenium / carbon composite hydrogen oxidation electrocatalyst provided by the present application is simple to operate, the raw materials of the catalyst are cheap and easy to obtain, and the production can be scaled up; (2) the ruthenium / carbon composite hydrogen oxidation electrocatalyst provided by the present application shows excellent stability, and the stable operating voltage range can reach 0.9 V (vs. RHE) compared with existing catalysts of the same type. Therefore, the present application can promote the development of low-cost alkaline fuel cells. BRIEF DESCRIPTION OF DRAWINGS

[0022] Fig. 1 The scanning electron microscope image of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Example 1;

[0023] Fig. 2 Transmission electron micrograph of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Example 1;

[0024] Fig. 3 Ruthenium 3p XPS spectrum of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Example 1;

[0025] Fig. 4 Scanning electron micrograph of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Comparative Example 1;

[0026] Fig. 5 Transmission electron micrograph of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Comparative Example 1;

[0027] Fig. 6 Ruthenium 3p XPS spectrum of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Comparative Example 1;

[0028] Fig. 7 Hydrogen oxidation performance graph of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Example 1;

[0029] Fig. 8 Hydrogen oxidation performance graph of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Comparative Example 1. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be further described in detail below in combination with examples.

[0031] Example 1

[0032] (1) 50 mg of carbon black powder was weighed and dispersed in 5 mL of a mixed solution of deionized water / 5 mL of ethanol, and a magnetic stirrer was used to stir at a rotation speed of 500 rpm;

[0033] (2) 120 mg of dopamine powder was weighed and added to the solution in step (1) and stirring was continued;

[0034] (3) 30 wt% ammonia water was added dropwise to the solution in step (2), and a pH meter was used to continuously measure the pH value of the solution until the pH value became between 9 and 10. After 12 hours of continuous stirring, centrifugation was performed at a rotation speed of 6000 rpm for 5 minutes, and the modified carbon black particles were collected after being washed with deionized water and centrifuged three times, and then placed in an oven at 80°C for drying for 12 hours;

[0035] (4) 50 mg of the modified carbon black from step (3) was weighed and dispersed in a mixture of 20 mL of deionized water and 20 mL of ethanol, and magnetic stirring was performed, and then 52.3 mg of ruthenium trichloride trihydrate and 25 mg of dopamine powder were added to the solution;

[0036] (5) Ammonia water with a mass concentration of 30 wt% was added dropwise to the mixed solution of step (4), and the pH value of the solution was continuously measured using a pH meter until the pH value became between 8 and 9. After continuous stirring for 24 hours, centrifugation was performed at a speed of 6000 rpm for 5 minutes, and after washing with deionized water and re-centrifugation for three times, the carbon black loaded with the ruthenium active component was collected, and then was placed in an oven at 80°C for drying for 12 hours;

[0037] (6) The carbon black loaded with the ruthenium active component obtained in step (5) was placed in a tube furnace in an argon atmosphere, and was heated to 400°C at a heating rate of 5°C / min and was kept for 2 hours, and then was naturally cooled to room temperature to obtain the ruthenium / carbon composite hydrogen oxidation electrocatalyst of the present example.

[0038] The catalyst obtained in the present example was subjected to physical characterization analysis, and the results are shown in Figs. 1-3 The scanning electron microscope image and the transmission electron microscope image of the sample showed that the ruthenium particles were uniformly distributed in the form of nanometer on the surface of the carbon black particles, and the XPS energy spectrum showed that the binding energy of ruthenium was shifted to high energy, indicating that there was effective charge transfer between ruthenium and the carbon substrate, so that the electronic structure of the ruthenium active site could be effectively adjusted.

[0039] Comparative Example 1

[0040] (1) 50 mg of unmodified carbon black powder was weighed and dispersed in a mixture of 20 mL of deionized water and 20 mL of ethanol, and magnetic stirring was performed, and then 52.3 mg of ruthenium trichloride trihydrate was added to the solution;

[0041] (2) Ammonia water with a mass concentration of 30 wt% was added dropwise to the mixed solution of step (1), and the pH value of the solution was continuously measured using a pH meter until the pH value became between 8 and 9. After continuous stirring for 24 hours, centrifugation was performed at a speed of 6000 rpm for 5 minutes, and after washing with deionized water and re-centrifugation for three times, the carbon black loaded with the ruthenium active component was collected, and then was placed in an oven at 80°C for drying for 12 hours;

[0042] (3) The carbon black loaded with the ruthenium active component obtained in step (2) was placed in a tube furnace in an argon atmosphere, and was heated to 400°C at a heating rate of 5°C / min and was kept for 2 hours, and then was naturally cooled to room temperature to obtain the ruthenium / carbon composite hydrogen oxidation electrocatalyst of the present example.

[0043] The catalyst obtained in the present comparative example was subjected to physical characterization analysis, and the results are shown in Table 1. Figs. 4-6 The scanning electron microscope images and the transmission electron microscope images of the sample indicated that the ruthenium particle size obtained in the present comparative example was comparable to the carbon black substrate and was unevenly distributed, while the degree of shift of the ruthenium binding energy in the XPS energy spectrum analysis was less than that of the catalytic material obtained in Example 1, indicating that the interaction between ruthenium and the substrate material in the catalytic material obtained in the present comparative example was weaker.

[0044] Example 2

[0045] (1) 5 mg of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Example 1 was weighed out, dispersed in 1 mL of an ethanol solution containing 40 μL of a Nafion solution, and ultrasonicated for 30 minutes to form a uniform slurry;

[0046] (2) 10 μL of the catalyst slurry obtained in step (1) was taken up using a pipette, slowly dropped onto a rotating disc electrode with a diameter of 4 mm, and then naturally air-dried to serve as the working electrode;

[0047] (3) The hydrogen oxidation performance of the material was tested in a hydrogen-saturated 0.1 M KOH solution using a rotating disc device and taking a Hg / HgO electrode and a graphite electrode as the reference electrode and the counter electrode, respectively;

[0048] (4) The experimental device was connected to an electrochemical workstation, a linear voltammetry scanning method was used, the scanning rate was 1 mV / s, scanning was performed from -0.05 V to 0.9 V (vs. RHE), and the size of the oxidation current during the scanning process was recorded, and the recorded results were the hydrogen oxidation performance of the catalytic material.

[0049] The test results are shown in Table 2. Fig. 7 In a wide voltage range, the ruthenium / carbon composite hydrogen oxidation electrocatalyst prepared in Example 1 showed excellent stability, and no obvious current drop trend was observed in the entire voltage range, indicating that the material had excellent HOR performance.

[0050] Comparative Example 2

[0051] (1) 5 mg of the ruthenium / carbon composite hydrogen oxidation electrocatalyst obtained in Comparative Example 1 was weighed out, dispersed in 1 mL of an ethanol solution containing 40 μL of a Nafion solution, and ultrasonicated for 30 minutes to form a uniform slurry;

[0052] (2) 10 μL of the catalyst slurry obtained in step (1) was taken up using a pipette, slowly dropped onto a rotating disc electrode with a diameter of 4 mm, and then naturally air-dried to serve as the working electrode;

[0053] (3) using rotating disc device, and using Hg / HgO electrode and graphite electrode as reference electrode and counter electrode respectively, hydrogen oxidation performance test of the material was carried out in 0.1M KOH solution saturated with hydrogen;

[0054] (4) connecting the experimental device to electrochemical workstation, using linear voltammetry scanning method, scanning from-0.05V to 0.9V (vs. RHE) at a scanning rate of 1mV / s, and recording the size of oxidation current in the scanning process, and the recorded results were hydrogen oxidation performance of the catalytic material.

[0055] The test results are shown in Table 1. Fig. 8 The ruthenium / carbon composite hydrogen oxidation electrocatalyst prepared in Comparative Example 1 showed typical ruthenium deactivation characteristics, and when the operating voltage exceeded 0.1V (vs. RHE), the hydrogen oxidation current decreased obviously, which also proved from the side that the preparation method of the high-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst proposed in the application was feasible for improving the stability of ruthenium-based materials in alkaline hydrogen oxidation reaction.

[0056] It should be pointed out that the above examples / comparative examples are not limiting to the application, and any modification, equivalent replacement and improvement within the spirit and principles of the application should be covered within the protection scope of the application.

Claims

1. A highly stable ruthenium / carbon composite hydrogen oxidation electrocatalyst, characterized in that: The catalyst uses carbon black coated with polydopamine (PDA) as a support. Then, the active component ruthenium nanoparticles are dispersed onto the modified carbon black surface again using polydopamine (PDA) and obtained by annealing in an inert gas atmosphere.

2. A method for preparing the highly stable ruthenium / carbon composite hydrogen oxidation electrocatalyst according to claim 1, characterized in that... Includes the following steps: (1) Weigh a certain mass of carbon black particles, disperse them in a water / ethanol mixture and stir magnetically. (2) Weigh a certain amount of dopamine and add it to the solution in step (1), and continue stirring; (3) Add ammonia water dropwise to the solution in step (2) and continuously measure the pH value of the solution with a pH meter until the pH of the solution reaches between 9 and 10. After the reaction is complete, centrifuge, wash and dry the solution. (4) Weigh a certain amount of the modified carbon black particles in step (3) and redisperse them into a water / ethanol mixture and stir them magnetically. Then add a certain amount of ruthenium precursor salt and dopamine powder. (5) Add ammonia water dropwise to the solution in step (4) and continuously measure the pH value of the solution with a pH meter until the pH of the solution reaches between 8 and 9. Then continue stirring for a period of time and then centrifuge, wash and dry. (6) The solid product obtained in step (5) is annealed in a tube furnace to obtain the high-stability ruthenium / carbon composite hydrogen oxidation electrocatalyst of the present invention.

3. The preparation method according to claim 2, characterized in that: In step (1), the carbon black particles have a particle size of 20-200 nm, the mass ratio of carbon black to solvent is 1:(100-200), the volume ratio of water to ethanol in the solvent is 1:1, and the magnetic stirring speed is 500-1000 rpm.

4. The preparation method according to claim 2, characterized in that: In step (2), the mass ratio of the amount of dopamine added to carbon black is (2-4):

1.

5. The preparation method according to claim 2, characterized in that: In step (3), the mass concentration of the ammonia water is 20% to 40%, the reaction time is 8 to 12 hours, the centrifugation speed is 3000 to 8000 rpm, the centrifugation time is 3 to 5 minutes, the solvent used for washing is deionized water, the drying temperature is 80 to 100℃, and the drying time is 8 to 12 hours.

6. The preparation method according to claim 2, characterized in that: In step (4), the mass ratio of the modified carbon black to the solvent is 1:(600-1000), the volume ratio of water to ethanol in the solvent is 1:1, the magnetic stirring speed is 500-1000 rpm, the ruthenium precursor salt is one or more of ruthenium trichloride, ruthenium trichloride trihydrate or ruthenium nitrite, and the mass ratio between the ruthenium precursor salt, dopamine powder and carbon black is (1-2):(0.25-0.5):

1.

7. The preparation method according to claim 2, characterized in that: In step (5), the mass concentration of the ammonia water is 20% to 40%, the stirring time is 24 to 36 hours, the centrifugation speed is 3000 to 8000 rpm, the centrifugation time is 3 to 5 minutes, the solvent used for washing is deionized water, the drying temperature is 80 to 100°C, and the drying time is 8 to 12 hours.

8. The preparation method according to claim 2, characterized in that: In step (6), the annealing temperature is 300-500℃, the atmosphere is nitrogen or argon, the heating rate of the tube furnace is 5-10℃ / min, and the annealing time is 2-4 hours.

9. The highly stable ruthenium / carbon composite hydrogen oxidation electrocatalyst prepared according to claims 2-8 is further characterized in that: It is used in alkaline hydrogen-oxygen fuel cells.

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