A ruthenium-based bifunctional fuel cell catalyst, its preparation method and application

Abstract

A ruthenium-based bifunctional fuel cell catalyst, its preparation method and application. The present invention belongs to the field of electrochemistry. The present invention solves the problems of different cathode and anode catalysts in existing fuel cells and the scarcity of bifunctional catalysts. Using glucose as the carbon source, NH4Cl as the N source, and nano-MgO as the template, a porous nitrogen-containing carbon nanosphere encapsulating MgO is obtained by high-temperature pyrolysis reaction under an inert atmosphere, and then the MgO template is removed by pickling to obtain a porous spherical shell-shaped nitrogen-containing carbon nanomaterial. The ruthenium-based bifunctional fuel cell catalyst prepared by the present invention is ruthenium loaded on a nitrogen-containing spherical shell-shaped porous nanocarbon material, having the dual functions of hydrogen oxidation and oxygen reduction. After the ruthenium-based bifunctional fuel cell catalyst is assembled as the cathode and anode catalysts into a hydrogen-oxygen fuel cell, its actual discharge performance is about 70% of that of the platinum-based catalyst, which can effectively replace the platinum catalyst, reduce the cost of fuel cells, and is beneficial to the popularization and use of industrialization.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and particularly relates to a ruthenium-based bifunctional fuel cell catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] A fuel cell is an important electrochemical device that converts the chemical energy of a fuel into electrical energy through an electrochemical reaction, and is one of the key technologies for promoting sustainable economic development. Different from traditional thermal cycle systems, fuel cells are not restricted by the Carnot cycle and have a high energy conversion efficiency. In the prior art, fuel cell catalysts are usually platinum-based catalysts. However, to achieve large-scale production and commercialization of fuel cells, the high price of platinum must be considered. In recent decades, people have been committed to developing high-performance and stable electrocatalysts to replace or reduce the amount of platinum-based catalysts used in oxygen reduction and hydrogen oxidation in proton exchange membrane fuel cells. Ruthenium, as a precious metal with properties similar to those of platinum, is much cheaper than platinum, and its price is only about 10% of that of platinum. A multifunctional catalyst is a substance that can catalyze multiple reaction functions simultaneously. Such substances generally have multiple catalytic active centers, and under their action, multiple different types of catalytic reactions can be completed in one reaction process. Compared with the research on bifunctional catalysis in hydrogen evolution and oxygen evolution, the bifunctional catalysis of ruthenium in hydrogen oxidation and oxygen reduction is rarely reported. Therefore, developing a ruthenium-based bifunctional fuel cell catalyst with high cost performance is of great significance for the practical application of fuel cells. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems of different cathode and anode catalysts in fuel cells and the scarcity of bifunctional catalysts in the prior art. The present invention provides a ruthenium-based bifunctional fuel cell catalyst, a preparation method thereof, and an application thereof.

[0004] The technical solution of the present invention is as follows:

[0005] One of the purposes of the present invention is to provide a preparation method of a ruthenium-based bifunctional fuel cell catalyst, and the method:

[0006] S1: Dissolve glucose hydrate in deionized water, ultrasonicate, add NH4Cl, and continue the reaction to obtain a transparent viscous solution;

[0007] S2: Add nano-MgO to the transparent viscous solution of S1. After the reaction is completed, dry and calcine to obtain a porous nitrogen-containing carbon nanosphere wrapped with MgO;

[0008] S3: Grind the porous nitrogen-containing carbon nanosphere wrapped with MgO in S2, add H2SO4, and perform acid washing under hydrothermal conditions to remove MgO, wash, filter, and dry to obtain a nitrogen-containing spherical shell-shaped porous nanocarbon material;

[0009] S4: Disperse the nitrogen-containing spherical porous nanocarbon material described in S3 in deionized water and ethanol, and perform ultrasonic oscillation to obtain a mixed solution;

[0010] S5: Adjust the pH of the mixed solution in S4 to be alkaline, add RuCl3 solution, perform hydrothermal reaction, wash, filter, dry, and calcine to obtain a ruthenium-based bifunctional fuel cell catalyst.

[0011] Further limit that in S1, the mass ratio of glucose hydrate to deionized water is 1:1 - 1.5, and the mass ratio of glucose hydrate to NH4Cl is 1 - 2:1.

[0012] Further limit that the mass ratio of the nano-MgO in S2 to the glucose hydrate in S1 is 2 - 3:1.

[0013] Further limit that the calcination condition in S2 is that under the condition of passing Ar, the heating rate is 5 °C / min -1 , heat up to 800 - 900 °C, and the calcination time is 1 - 2 h.

[0014] Further limit that the concentration of H2SO4 in S3 is 1 mol / L.

[0015] Further limit that the hydrothermal reaction temperature in S3 is 80 - 85 °C, and the time is 10 - 12 h.

[0016] Further limit that in S4, the concentration of the nitrogen-containing spherical porous nanocarbon material is 0.4 - 1 wt%, and the concentration of ethanol is 15 - 20 wt%.

[0017] Further limit that the pH value in S5 is 8 - 9, the concentration of RuCl3 solution is 1 wt%, the hydrothermal reaction temperature is 120 - 130 °C, the time is 10 - 12 h, and the calcination condition is that under the condition of passing H2, the heating rate is 5 °C / min -1 , heat up to 300 - 500 °C, the calcination time is 1 - 2 h, and the Ru loading is 0.4 - 1 wt%.

[0018] The second object of the present invention is to provide a ruthenium-based bifunctional fuel cell catalyst, and the ruthenium-based bifunctional fuel cell catalyst is prepared by the above preparation method.

[0019] The third object of the present invention is to provide an application of the above ruthenium-based bifunctional fuel cell catalyst in a fuel cell.

[0020] Compared with the prior art, the specific advantages of the present invention are as follows:

[0021] (1) The ruthenium-based bifunctional fuel cell catalyst provided by the present invention has a large specific surface area and a rich pore structure, which is beneficial to the actual mass transfer and application of fuel cells. This catalyst exhibits excellent electrocatalytic activity and stability for oxygen reduction reaction and hydrogen oxidation reaction in acidic media. After being assembled into a hydrogen-oxygen fuel cell, the actual discharge performance of the ruthenium-based bifunctional fuel cell catalyst prepared by the present invention can reach 70% of that of the platinum-based catalyst, and the price of ruthenium is only about 10% of that of platinum, so ruthenium can be used to replace platinum to reduce the cost of fuel cells.

[0022] (2) The ruthenium-based bifunctional fuel cell catalyst prepared by the present invention can be used as the catalyst for the cathode and anode of fuel cells, and has the dual characteristics of oxygen reduction and hydrogen oxidation. Moreover, the preparation method of the present invention is simple and easy to operate, which is beneficial to industrial production.

[0023] (3) The present invention first uses the method of glucose-coated hard-template nano-MgO to prepare a nitrogen-containing spherical porous nano-carbon material. Using NH4Cl as a nitrogen source and precursor, taking advantage of its easy volatility at high temperatures, a large number of pore structures are generated in the carbon material, and at the same time, the N-doping content of the material can be increased. Ruthenium is attached to the nitrogen-containing spherical porous nano-carbon material by hydrothermal and high-temperature reduction reactions, thus forming a ruthenium-based bifunctional fuel cell catalyst with multiple active sites. Through the combined action of N, C of the nitrogen-containing spherical porous nano-carbon material and the loaded ruthenium, it can be used as the catalyst for the cathode and anode of fuel cells. Brief Description of the Drawings

[0024] Figure 1 X-ray single crystal diffraction patterns of MgO@p-CNS, @p-CNS / N, @Ru / NC·H2O and Ru / NC in Example 1;

[0025] Figure 2 In (a) is the SEM morphology diagram of MgO@p-CNS in Example 1, Figure 2 In (b) is the SEM morphology diagram of @p-CNS / N in Example 1, Figure 2 In (c) is the SEM morphology diagram of @Ru / NC·H2O in Example 1, Figure 2 In (d) is the SEM morphology diagram of Ru / NC in Example 1;

[0026] Figure 3 In (a) and Figure 3 In (b) is the aberration-corrected scanning electron microscopy morphology diagram of Ru / NC in Example 1, Figure 3 In (c) is the Ru element distribution diagram of Ru / NC in Example 1, Figure 3 In (d) is the C element distribution diagram of Ru / NC in Example 1, Figure 3 In (e) is the N element distribution diagram of Ru / NC in Example 1, Figure 3In (f) is the O element distribution map of Ru / NC in Example 1;

[0027] Figure 4 In (a) is the XPS map of the overall elements of Ru / NC in Example 1, Figure 4 In (b) is the N element valence state distribution map of Ru / NC in Example 1, Figure 4 In (c) is the Ru element valence state distribution map of Ru / NC in Example 1;

[0028] Figure 5 In (a) is the BET specific surface area map of Ru / NC in Example 1 and Ru / C in Comparative Example 1, Figure 5 In (b) is the pore size distribution map of Ru / NC in Example 1 and Ru / C in Comparative Example 1;

[0029] Figure 6 In (a) is the ORR voltammogram of Ru / NC in Example 1 and Pt / C in Comparative Example 1 in acidic medium, Figure 6 In (b) is the polarization curve of Ru / NC in Example 1 and Pt / C in Comparative Example 1 in acidic medium;

[0030] Figure 7 is the HOR polarization curve of Ru / NC in Example 1 and Pt / C in Comparative Example 1 in acidic medium;

[0031] Figure 8 is the steady-state test polarization curve of the hydrogen-oxygen fuel cell prepared in Example 1. Detailed implementation manners

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, and those skilled in the art can obtain them through commercial channels without special instructions.

[0034] Example 1:

[0035] Preparation of nitrogen-containing spherical porous nanocarbon material:

[0036] Dissolve 1 g of C6H 12O6·H2O was dissolved in 1 mL of deionized water and ultrasonically shaken evenly. 0.5 g of NH4Cl was added and the reaction continued to obtain a transparent viscous solution. 2 g of nano-MgO was added and shaken for 0.5 h, then placed in a vacuum drying oven at 90 °C and dried for 10 h. Then it was placed in a tubular furnace and heated to 850 °C at a heating rate of 5 °C min -1 to obtain the product denoted as MgO@p-CNS;

[0037] After taking 3.5 g of MgO@p-CNS and thoroughly grinding it in a mortar, 100 mL of 1 mol / L H2SO4 solution was added, and it was stirred in a water bath at 85 °C for 12 h to remove nano-MgO. After the pickling, it was first rinsed 3 times with deionized water, then rinsed 2 times with absolute ethanol, and finally placed in a vacuum oven at 60 °C and dried for 8 h to obtain a nitrogen-containing spherical porous nanocarbon material, and this product was denoted as @p-CNS / N.

[0038] Preparation of ruthenium-based bifunctional fuel cell catalyst:

[0039] 0.5 g of @p-CNS / N was dispersed in 100 mL of deionized water and 20 mL of ethanol, ultrasonically shaken, the pH was adjusted to 9 with ammonia water, 2.5 mL of 1% RuCl3 solution by mass was added, and hydrothermal reaction was carried out at 130 °C for 10 h. It was diluted with 100 mL of deionized water and ultrasonically dispersed for 30 min and then filtered. It was first rinsed 3 times with deionized water, then rinsed 2 times with absolute ethanol, and finally placed in a vacuum oven at 60 °C and dried for 8 h. The obtained product was denoted as @Ru / NC·H2O;

[0040] Weighed 0.2 g of @Ru / NC·H2O in a porcelain boat, placed it in a tubular furnace, and heated it to 500 °C at a heating rate of 5 °C min -1 and held for 1 h under H2 to obtain a ruthenium-based bifunctional fuel cell catalyst, denoted as Ru / NC.

[0041] Preparation of ruthenium-based bifunctional fuel cell:

[0042] Took 6 mg of Ru / NC, 50 μL of 5% perfluorosulfonic acid-based polymer solution (Nafion solution) and 0.95 mL of ethanol solution to prepare an electrochemical test ink solution (ink solution), and ultrasonically dispersed it for 2 h. Selected a glassy carbon electrode head with a diameter of 5 mm, and dropped 20 μL of the ink solution (ink solution) on the glassy carbon electrode head and air-dried it naturally to make a test electrode. At this time, the catalyst loading of the electrode head was 0.6 mg cm -2 for subsequent testing.

[0043] Comparative Example 1:

[0044] Preparation of Ru / C:

[0045] The difference between Comparative Example 1 and Example 1 is that NH4Cl is not added in the step of preparing the nitrogen-containing spherical porous nanocarbon material, and other steps are the same as those in Example 1.

[0046] Comparative Example 2:

[0047] Prepare a commercial Pt / C electrode:

[0048] Weigh 5 mg of 20% commercial Pt / C, add 50 μL of 5% perfluorosulfonic acid-based polymer solution (Nafion solution) and 0.95 mL of isopropanol, and ultrasonically disperse for 1 h to obtain a mixed solution. Take 4 μL of the mixed solution and drop it onto a 5 mm glassy carbon electrode, and let it dry naturally. At this time, the Pt / C electrode loading is 20 μg (Pt) cm -2 。

[0049] Figure 1 are the X-ray single crystal diffraction patterns of MgO@p-CNS, @p-CNS / N, @Ru / NC·H2O, and Ru / NC in Example 1. From Figure 1 it can be seen that the MgO template was successfully removed in this experiment, and the Ru / NC catalyst was successfully prepared.

[0050] Figure 2 In (a) is the SEM morphology of MgO@p-CNS in Example 1, Figure 2 In (b) is the SEM morphology of @p-CNS / N in Example 1, Figure 2 In (c) is the SEM morphology of @Ru / NC·H2O in Example 1, Figure 2 In (d) is the SEM morphology of Ru / NC in Example 1. From Figure 2 it can be seen that the Ru / NC catalyst prepared in this experiment has a spherical shell structure with a higher specific surface area, which is beneficial to the actual mass transfer and application of fuel cells.

[0051] Figure 3 In (a) and Figure 3 In (b) are the aberration-corrected scanning electron microscopy morphologies of Ru / NC in Example 1, Figure 3 In (c) is the elemental distribution map of Ru / NC in Example 1. From Figure 3 In (a) and Figure 3 In (b) it can be seen that single-atom ruthenium is uniformly distributed on the spherical shell-shaped nanocarbon material. From Figure 3 In (c), Figure 3 In (d), Figure 3 In (e) and Figure 3 In (f) it can be seen that ruthenium, nitrogen, and oxygen elements are uniformly distributed on the spherical shell-shaped nanocarbon material.

[0052] Figure 4Figure (a) is the XPS spectrum of the overall Ru / NC elements in Example 1, Figure 4 Figure (b) is the valence state distribution diagram of N element in Ru / NC in Example 1, Figure 4 Figure (c) is the valence state distribution diagram of Ru element in Ru / NC in Example 1. From Figure 4 Figure (b), it can be seen that the catalyst contains pyridine nitrogen, pyrrole nitrogen and graphitic nitrogen, Figure 4 and from Figure (c), it can be seen that the valence states of ruthenium element are mainly 0 valence and +2 valence, indicating that there are different ruthenium-based active sites in the catalyst.

[0053] Figure 5 Figure (a) is the BET specific surface area diagram of Ru / NC in Example 1 and Ru / C in Comparative Example 1, Figure 5 Figure (b) is the pore size distribution diagram of Ru / NC in Example 1 and Ru / C in Comparative Example 1. From Figure 5 it can be seen that after adding NH4Cl as a precursor and introducing N into the catalyst, a catalyst with a larger specific surface area and a more abundant pore structure can be obtained.

[0054] Figures 1 - 5 All physical characterizations have proved that the present invention has successfully prepared a spherical shell-shaped nano nitrogen-containing catalyst Ru / NC, and Ru / NC has a large specific surface area and a rich pore structure, which are all beneficial to the actual mass transfer and application of fuel cells.

[0055] Figure 6 Figure (a) is the ORR voltammogram of Ru / NC in Example 1 and Pt / C in Comparative Example 1 in acidic medium, Figure 6 Figure (b) is the polarization curve of Ru / NC in Example 1 and Pt / C in Comparative Example 1 in acidic medium. The CV test characterization was carried out using a Shanghai Chenhua CHI730e electrochemical workstation. Under the test conditions of 0.1 mol / L HClO4 in acidic medium, after continuously introducing O2 for 0.5 h to saturate it, the rotation speed of the LSV polarization curve was 1600 rpm and the scan rate was 10 mV s -1 . From Figure 6 it can be seen that in acidic medium, the half-wave potential of Ru / NC in Example 1 is only 61 mV less than that of Pt / C in Comparative Example 2, showing good electrocatalytic activity.

[0056] Figure 7 is the HOR polarization curve of Ru / NC in Example 1 and Pt / C in Comparative Example 2 in acidic medium. The LSV test characterization was carried out using a Shanghai Chenhua CHI730e electrochemical workstation. Under the test conditions of 0.1 mol / L HClO4 in acidic medium, after continuously introducing H2 for 0.5 h to saturate it, the rotation speed of the LSV polarization curve was 2500 rpm and the scan rate was 10 mV s -1 . From Figure 7It can be seen that in an acidic medium, the polarization curve of Ru / NC in Example 1 is similar to that of Pt / C in Comparative Example 2, and the half-wave potential only differs by 61 mV, proving that the catalytic performances are similar.

[0057] Figure 8 This is the polarization curve of the steady-state test of the hydrogen-oxygen fuel cell prepared in Example 1. Ru / NC of Example 1 was used as the cathode and anode catalysts in the PEMFC system, and then its actual application effect was evaluated. The preparation methods of the anode and cathode electrodes of the battery are as follows: Weigh 30 mg and 3 mg of Ru / NC, and add them to 600 mg of 5 wt% perfluorosulfonic acid polymer solution (Nafion solution) and 600 mg of isopropyl alcohol solution respectively, and ultrasonically disperse for 2 h to form a uniform slurry. Use a scraper to coat the catalyst on the pre-prepared microporous layer, and finally weigh to prepare a cathode electrode with a loading of 4.0 mg cm -2 and an anode electrode with a loading of 0.4 mg cm -2 . Similarly, a Pt / C anode electrode was prepared, and the loading of Pt was controlled at 0.4 mg cm -2 . The prepared cathode electrode and anode electrode were hot-pressed at 130 °C under a pressure of 30 kgf for 120 s to form a sandwich-structured MEA. It was installed in a hydrogen-oxygen fuel cell mold for battery performance testing, and the polarization curve is as shown in Figure 8 . As can be seen from Figure 8 , the maximum output power of Ru / NC in Example 1 on the H2-O2 battery can reach 618 mW cm -2 , which is about 71% of that of Pt / C, showing very good battery performance. Therefore, the Ru / NC prepared in this experiment can replace Pt / C as the anode and cathode catalysts of fuel cells.

[0058] As mentioned above, the above are only the preferred specific embodiments of the present invention. These specific embodiments are all different implementation manners based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of a ruthenium-based bifunctional fuel cell catalyst, characterized in that, The method: S1: Dissolve the glucose hydrate in deionized water, ultrasonicate, add NH4Cl, and continue the reaction to obtain a transparent viscous solution; S2: Add nano-MgO to the transparent viscous solution of S1. After the reaction is completed, dry and calcine to obtain porous nitrogen-containing carbon nanospheres coated with MgO; S3: Grind the porous nitrogen-containing carbon nanospheres coated with MgO in S2, add H2SO4, and perform acid washing under hydrothermal conditions to remove MgO. Wash, filter, and dry to obtain a nitrogen-containing spherical shell-like porous nanocarbon material; S4: Disperse the nitrogen-containing spherical shell-like porous nanocarbon material described in S3 in deionized water and ethanol, and ultrasonically oscillate to obtain a mixed solution; S5: Adjust the pH of the mixed solution in S4 to be alkaline, add RuCl3 solution, carry out hydrothermal reaction, wash, filter, dry, and calcine under the condition of passing H2, with a heating rate of 5 °C min -1 , heat up to 300 - 500 °C, the calcination time is 1 - 2 h, and the Ru loading is 0.4 - 1 wt%, to obtain a ruthenium-based bifunctional fuel cell catalyst.

2. The method according to claim 1, wherein In S1, the mass ratio of the glucose hydrate to the deionized water is 1:1 - 1.5, and the mass ratio of the glucose hydrate to NH4Cl is 1 - 2:

1.

3. The method according to claim 1, characterized in that In S2, the mass ratio of the nano-MgO to the glucose hydrate in S1 is 2 - 3:

1.

4. The method according to claim 1, wherein The calcination conditions of S2 are as follows: under the condition of Ar flow, the heating rate is 5 °C / min -1 , heat up to 800 - 900 °C, and the calcination time is 1 - 2 h.

5. The method according to claim 1, wherein The concentration of H2SO4 in S3 is 1 mol / L.

6. The method according to claim 1, characterized in that The hydrothermal reaction temperature in S3 is 80 - 85 °C, and the time is 10 - 12 h.

7. The method according to claim 1, characterized in that, In S4, the concentration of the nitrogen-containing spherical shell-like porous nanocarbon material is 0.4 - 1 wt%, and the concentration of ethanol is 15 - 20 wt%.

8. The method according to claim 1, characterized in that, The pH value in S5 is 8 - 9, the concentration of the RuCl3 solution is 1 wt%, the hydrothermal reaction temperature is 120 - 130 °C, and the time is 10 - 12 h.

9. A ruthenium-based bifunctional fuel cell catalyst, characterized in that, The ruthenium-based bifunctional fuel cell catalyst is prepared by the preparation method according to any one of claims 1 - 8.

10. The application of the ruthenium-based bifunctional fuel cell catalyst according to claim 9 in a fuel cell.

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