PtCoRu / carbon nanotube electrocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of new energy materials, in particular to a PtCoRu / carbon nanotube electrocatalyst and a preparation method and application thereof. Cobalt waste liquid generated after ZIF-67 is prepared, a platinum source and ruthenium trichloride are jointly impregnated on a commercial carbon nano tube, heat treatment is conducted under the inert atmosphere to obtain the PtCoRu / carbon nano tube electrocatalyst, the PtCoRu / carbon nano tube electrocatalyst is a nitrogen-doped PtCoRu / CNT composite material, and efficient electrocatalytic oxidation of methanol and ethanol in an acid medium is achieved. According to the method, the cobalt waste liquid generated after ZIF-67 is prepared is used as a raw material for preparing the multi-element noble metal catalyst, so that the problem of insufficient activity of the synthesized multi-element noble metal-based composite material is avoided while the economic cost generated by treating the cobalt waste liquid is avoided, and meanwhile, the problems of use of an organic solution and the cost of subsequent treatment are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and specifically to a PtCoRu / carbon nanotube electrocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Methanol and ethanol fuel cells are a kind of renewable energy, which have attracted extensive research interest. Developing highly efficient and stable electrocatalysts is an important problem in the field of fuel cells. Noble metal (Pt, Pd)-based catalysts have attracted much attention due to their good activity. However, single-component noble metal materials still face the problem of easy poisoning. It has been found that preparing multi-component noble metal-based composite materials can effectively improve the catalytic activity and stability, such as PtRu and PtNi composite materials. However, the existing technologies for synthesizing multi-component noble metal-based composite materials have complex synthesis steps, the use of organic solvents is likely to produce waste liquid, and the preparation costs of PtRu and PtNi composite materials are high and the activity is insufficient.

[0003] In addition, during the synthesis of metal-organic framework structures, a large amount of waste liquid containing metal ions and organic ligands is often generated. For example, when recovering solids from the zeolitic imidazolate framework material (ZIF-67) prepared from cobalt ions and 2-methylimidazole, waste liquid containing cobalt ions and 2-methylimidazole is usually generated, and its treatment and discharge are likely to cause secondary pollution and energy consumption. Summary of the Invention

[0004] In view of the above deficiencies of the prior art, in order to avoid treating the waste liquid generated during the synthesis of metal-organic framework materials, reduce the preparation cost, and prepare a highly active multi-component noble metal-based electrocatalyst, the present invention provides a PtCoRu / carbon nanotube electrocatalyst, a preparation method thereof, and an application thereof. The present invention co-impregnates the cobalt waste liquid generated after preparing ZIF-67, a platinum source, and ruthenium trichloride on commercial carbon nanotubes, and heat-treats them under an inert atmosphere to obtain a PtCoRu / carbon nanotube electrocatalyst. The PtCoRu / carbon nanotube electrocatalyst is a nitrogen-doped PtCoRu / CNT composite material, realizing the efficient electrocatalytic oxidation of methanol and ethanol in acidic media. The present invention uses the cobalt waste liquid generated after preparing ZIF-67 as a raw material for preparing multi-component noble metal catalysts, avoiding the economic cost of treating cobalt waste liquid, avoiding the problem of insufficient activity of the synthesized multi-component noble metal-based composite materials, and at the same time solving the problems of the use of organic solutions and subsequent treatment costs.

[0005] Based on the above problems, the present invention is achieved by the following technical solutions:

[0006] A preparation method of a PtCoRu / carbon nanotube electrocatalyst, comprising the following steps:

[0007] The cobalt waste liquid, carbon nanotubes, platinum source and RuCl3·xH2O generated after preparing ZIF-67 are mixed together in ethanol, stirred and evaporated to dryness to obtain a precursor.

[0008] The precursor is ground to disperse the carbon nanotubes and prevent the carbon nanotubes from agglomerating, and then calcined under an inert atmosphere to obtain the PtCoRu / carbon nanotube electrocatalyst.

[0009] Preferably, the platinum source is selected from chloroplatinic acid, potassium chloroplatinate or sodium chloroplatinate.

[0010] Preferably, ZIF-67 is prepared from a soluble cobalt salt and 2-methylimidazole, and the molar ratio of the soluble cobalt salt to 2-methylimidazole is 1:5-8.

[0011] Preferably, the molar ratio of the cobalt substance amount, platinum source substance amount and RuCl3·xH2O substance amount in the cobalt waste liquid is 1:0.1-0.15:0.02-0.025. Pt is used as the main catalytically active component for the oxidation reaction, and Co and Ru are used as anti-poisoning components in the PtCoRu / carbon nanotube electrocatalyst, and the usage amounts are reduced in turn according to the cost.

[0012] Preferably, the mass ratio of RuCl3·xH2O to carbon nanotubes is 3:15-25. If the amount of carbon nanotubes used is too large, the proportion of the active component PtCoRu nanoparticles will be low and the catalytic performance will be poor; if the amount of carbon nanotubes used is too small, the content of the active component PtCoRu nanoparticles will be high, the preparation cost will increase, and the PtCoRu nanoparticles cannot be effectively dispersed and are prone to agglomeration.

[0013] Preferably, the calcination conditions are: calcination at 600 °C for 2 h-4 h.

[0014] The present invention also protects the PtCoRu / carbon nanotube electrocatalyst prepared by the above preparation method.

[0015] Preferably, in the PtCoRu / carbon nanotube electrocatalyst, the PtCoRu nanoparticles are dispersed on the carbon nanotubes.

[0016] Preferably, the particle size of the PtCoRu nanoparticles is 3.5 nm-5 nm.

[0017] The present invention also protects the application of the PtCoRu / carbon nanotube electrocatalyst in the preparation of fuel cells, and the fuel cells are selected from methanol fuel cells or ethanol fuel cells.

[0018] Preferably, the media of the methanol fuel cell or ethanol fuel cell are both acidic media.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. The present invention is based on cobalt-containing waste liquid generated after synthesizing ZIF-67. Through the impregnation method, Pt, Co, and Ru ions supported on carbon nanotubes are first prepared, and then high-dispersion and nano-sized PtCoRu / carbon nanotube electrocatalysts are further prepared by pyrolysis, and efficient electrocatalytic oxidation of methanol and ethanol molecules is realized in acidic media.

[0021] 2. The present invention utilizes the ZIF-67 waste liquid to provide cobalt ions and nitrogen elements. While realizing waste utilization and avoiding the energy consumption caused by waste liquid treatment, the prepared PtCoRu / carbon nanotube electrocatalyst contains nitrogen doping, and the nitrogen doping improves the conductivity of the carbon nanotubes.

[0022] 3. The present invention prepares high-dispersion and nano-sized ternary PtCoRu / carbon nanotube electrocatalysts by adopting impregnation and pyrolysis means. The high dispersion and nano size can expose more active sites, greatly improving the atomic utilization rate and catalytic activity.

[0023] 4. The PtCoRu / carbon nanotube electrocatalyst of the present invention realizes efficient oxidation of methanol and ethanol in acidic media, and the current density is greater than 1000 mA·mg Pt –1 . Moreover, using the PtCoRu / carbon nanotube electrocatalyst as the electrode, the current densities generated in a solution containing 0.5 mol / L sulfuric acid and 1 mol / L methanol / ethanol are 1052 mA·mg Pt –1 and 1392 mA·mg Pt –1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of the synthesis of the PtCoRu / carbon nanotube electrocatalyst of the present invention.

[0025] Figure 2 is the powder diffraction pattern of the PtCoRu / carbon nanotube electrocatalyst of Example 1.

[0026] Figure 3 is the electron microscope image and element distribution map of the PtCoRu / carbon nanotube electrocatalyst of Example 1; among them, (A) is the transmission electron microscope image; (B) is the high-resolution electron microscope image; (C) is the high-angle annular dark-field scanning transmission electron microscope image; (D) is the Pt element distribution map; (E) is the Ru element distribution map; (F) is the Co element distribution map.

[0027] Figure 4 In, (A) is the 4f electron energy spectrum of Pt; (B) is the 2p electron energy spectrum of Co; (C) is the 3p electron energy spectrum of Ru.

[0028] Figure 5 Among them, (A) is the cyclic voltammetry curve of PtCoRu / CNT of Example 1 and commercial JM-Pt / C in methanol solution; (B) is the cyclic voltammetry curve of PtCoRu / CNT of Example 1 and commercial JM-Pt / C in ethanol solution.

[0029] Figure 6 Among them, (A) is the chronoamperometry curve of PtCoRu / CNT of Example 1 and commercial JM-Pt / C in 0.5 mol / L sulfuric acid and 10.5 mol / L ethanol solution; (B) is the cyclic voltammetry curve of PtCoRu / CNT of Example 1 before and after chronoamperometry test. Detailed implementation manners

[0030] The following will describe the detailed implementation manners of the present invention in detail, but it should be understood that the protection scope of the present invention is not limited by the detailed implementation manners. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0031] Considering the problems existing in the prior art of multi-component noble metal-based composite materials, such as complex synthesis steps, easy generation of waste liquid in the use of organic solvents, and high preparation costs of PtRu and PtNi composite materials, resulting in insufficient activity; in terms of the synthesis steps, the method of the present invention adopts impregnation and pyrolysis means, and the synthesis steps are simple; in terms of the use of organic solvents, the organic solvent used in the present invention is ethanol, and separation can be achieved by heating and stirring without generating waste liquid; in terms of cost, the present invention uses the cobalt waste liquid generated after preparing ZIF-67 as a raw material, which provides a nitrogen source and a cobalt source while effectively reducing the preparation cost.

[0032] Considering the problems that the treatment and discharge of a large amount of waste liquid containing metal ions and organic ligands in the prior art are prone to cause secondary pollution and energy consumption, the present invention uses the cobalt waste liquid generated after preparing ZIF-67 as a raw material. The cobalt waste liquid contains soluble cobalt salt and 2-methylimidazole. The PtCoRu / carbon nanotube electrocatalyst is jointly prepared by using the cobalt waste liquid, carbon nanotubes, a platinum source and RuCl3·xH2O. At this time, in the obtained PtCoRu / carbon nanotube electrocatalyst, the soluble cobalt salt provides a cobalt source, and 2-methylimidazole provides a nitrogen source, so that the obtained PtCoRu / carbon nanotube electrocatalyst is a nitrogen-doped PtCoRu / CNT composite material, solving the problem of the discharge of cobalt waste liquid generated after preparing ZIF-67.

[0033] The following uses examples to study the technical solutions of the present invention, and the specific research methods and results are as follows:

[0034] Example 1

[0035] A preparation method of PtCoRu / carbon nanotube electrocatalyst comprises the following steps:

[0036] S1. Add 1.45 g of cobalt nitrate hexahydrate and 3.2 g of 2-methylimidazole into 40 mL of methanol, stir for 10 min, stand for 24 h, and centrifuge to obtain cobalt waste liquid;

[0037] S2. Mix 0.1 mL of cobalt waste liquid, 0.02 g of carbon nanotubes, 13 mg of H2PtCl6·6H2O and 3 mg of RuCl3·xH2O in 20 mL of ethanol, and stir at 90 °C until no solvent remains to obtain a precursor;

[0038] S3. Grind the precursor and calcine it in an argon atmosphere at 600 °C for 2 h to obtain the PtCoRu / carbon nanotube electrocatalyst.

[0039] Example 2

[0040] A preparation method of PtCoRu / carbon nanotube electrocatalyst comprises the following steps:

[0041] S1. Add 1.45 g of cobalt nitrate hexahydrate and 2.7 g of 2-methylimidazole into 40 mL of methanol, stir for 10 min, stand for 24 h, and centrifuge to obtain cobalt waste liquid;

[0042] S2. Mix 0.1 mL of cobalt waste liquid, 0.015 g of carbon nanotubes, 15 mg of H2PtCl6·6H2O and 3 mg of RuCl3·xH2O in 20 mL of ethanol, and stir at 90 °C until no solvent remains to obtain a precursor;

[0043] S3. Grind the precursor and calcine it in an argon atmosphere at 600 °C for 3 h to obtain the PtCoRu / carbon nanotube electrocatalyst.

[0044] Example 3

[0045] A preparation method of PtCoRu / carbon nanotube electrocatalyst comprises the following steps:

[0046] S1. Add 1.45 g of cobalt nitrate hexahydrate and 4.3 g of 2-methylimidazole into 40 mL of methanol, stir for 10 min, stand for 24 h, and centrifuge to obtain cobalt waste liquid;

[0047] S2. Mix 0.1 mL of cobalt waste liquid, 0.025 g of carbon nanotubes, 19 mg of H2PtCl6·6H2O, and 3 mg of RuCl3·xH2O in 20 mL of ethanol, and stir at 90 °C until the solvent is completely removed to obtain a precursor;

[0048] S3. After grinding the precursor, calcine it at 600 °C for 4 h in an argon atmosphere to obtain the PtCoRu / carbon nanotube electrocatalyst.

[0049] Highly active PtCoRu / carbon nanotube electrocatalysts were prepared in Examples 1 to 3 of the present invention. The synthesis schematic diagram is as Figure 1 shown. Taking the PtCoRu / carbon nanotube electrocatalyst of Example 1 as an example for research, the specific research methods and results are as follows:

[0050] Figure 2 The powder diffraction pattern confirmed the formation of the PtCoRu alloy and the PtCoRu / carbon nanotube electrocatalyst. The diffraction peak at about 25° was for the carbon nanotubes. The crystal planes (111), (200), and (220) matched the Pt (JCPDS No. 04-0802) spectrum. In addition, atomic absorption spectroscopy proved that in the PtCoRu / carbon nanotube electrocatalyst, the metal element contents were Pt 18.8 wt.%, Co 9.6 wt.%, and Ru 1.9 wt.%, respectively.

[0051] Figure 3 In, the transmission electron microscopy and high-resolution electron microscopy images of the PtCoRu / carbon nanotube electrocatalyst proved that the PtCoRu nanoparticles were highly dispersed on the carbon nanotubes, and the size of the PtCoRu nanoparticles was about 3.5 nm.

[0052] Figure 4 In, the Pt 4f electron energy spectrum of the PtCoRu / carbon nanotube electrocatalyst showed that the binding energies of its Pt 4f5 / 2 and Pt 4f7 / 2 were 72.10 eV and 75.44 eV, respectively, corresponding to Pt(0). The absorption peaks at 72.23 eV and 77.83 eV might be due to a small amount of Pt oxide on the surface. The broad peak of the Co 2p electron binding energy at 780.5 eV proved the existence of Co(0). In addition, the electron energy spectrum showed that the binding energies of Ru 3p were 462.5 eV and 484.2 eV, proving that the valence state of Ru was also 0. Similar to Pt, the weak peaks at 467.5 eV and 485.9 eV might be due to a small amount of oxide on the surface.

[0053] Weigh 4 mg of the PtCoRu / carbon nanotube electrocatalyst of Example 1, disperse it into a mixed solution containing 0.98 mL of N,N-dimethylformamide and 0.02 mL of Nafion. After ultrasonic treatment for 1 h, use a pipette to measure 10 μL of the mixed liquid, drop it on a glassy carbon electrode with a diameter of 5 mm, and let it dry naturally for later use. In a 0.5 mol / L sulfuric acid solution, using the glassy carbon electrode as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode, a three-electrode system is formed. Set the voltage range from -0.2 V to 1.0 V, and use cyclic voltammetry to obtain a CV curve at a scan rate of 50 mV / s. Then, respectively, in a solution containing 0.5 mol / L sulfuric acid and 1 mol / L methanol solution and a solution containing 0.5 mol / L sulfuric acid and 1 mol / L ethanol solution, a stable current density curve is obtained at a scan rate of 50 mV, as Figure 5 shown. The current densities of the PtCoRu / carbon nanotube electrocatalyst in the methanol solution( Figure 5 A) and ethanol solution( Figure 5 B) are 1052 mA·mg Pt –1 and 1392 mA·mg Pt –1 , respectively, both more than 5 times higher than that of commercial JM-Pt / C.

[0054] To prove the stability of the PtCoRu / carbon nanotube electrocatalyst, first, using chronoamperometry, set the voltage to 0.62 V, and analyze the PtCoRu / carbon nanotube electrocatalyst and commercial JM-Pt / C in a solution containing 0.5 mol / L sulfuric acid and 1 mol / L ethanol solution, as Figure 6 shown in Figure (A). After 1 h, the current density of the PtCoRu / carbon nanotube electrocatalyst decreased from 632 mA·mg Pt –1 to 179 mA·mg Pt –1 , with a decrease of 71.6%. Under the same conditions, the decrease of commercial JM-Pt / C was 86.5%. In addition, as Figure 6 (B) the cyclic voltammetry curve shows, before and after the chronoamperometry test, the electrocatalytic oxidation of ethanol by the PtCoRu / carbon nanotube electrocatalyst basically did not decrease, further proving that the PtCoRu / carbon nanotube electrocatalyst has excellent stability.

[0055] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations. The above-described embodiments are merely preferred embodiments given to fully illustrate the present invention, and the scope of protection is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the scope of protection of the present invention, and the scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for preparing a PtCoRu / carbon nanotube electrocatalyst, characterized in that: The steps include: The cobalt waste liquid generated after the preparation of ZIF-67, carbon nanotubes, platinum source and RuCl3·xH2O are mixed in ethanol, and the solvent is separated to obtain a precursor; The precursor was ground to disperse the carbon nanotubes and then calcined under an inert atmosphere to obtain the PtCoRu / carbon nanotube electrocatalyst.

2. The method for preparing the PtCoRu / carbon nanotube electrocatalyst according to claim 1, characterized in that: The platinum source is selected from chloroplatinic acid, potassium chloroplatinate or sodium chloroplatinate.

3. The method for preparing the PtCoRu / carbon nanotube electrocatalyst according to claim 1, characterized in that: ZIF-67 is prepared from soluble cobalt salt and 2-methylimidazole, and the molar ratio of the soluble cobalt salt to the 2-methylimidazole is 1:5-8.

4. The method for preparing the PtCoRu / carbon nanotube electrocatalyst according to claim 3, characterized in that: The ratio of the amount of cobalt substance, the amount of platinum source substance and the amount of RuCl3·xH2O substance in the cobalt waste liquid is 1:0.1-0.15:0.02-0.

025.

5. The method for preparing the PtCoRu / carbon nanotube electrocatalyst according to claim 1, characterized in that: The mass ratio of RuCl3·xH2O to carbon nanotubes is 3:15-25.

6. The method for preparing the PtCoRu / carbon nanotube electrocatalyst according to claim 1, characterized in that: The calcination conditions are: calcination at 600°C for 2h to 4h.

7. A PtCoRu / carbon nanotube electrocatalyst, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

8. The PtCoRu / carbon nanotube electrocatalyst according to claim 7, characterized in that: In the PtCoRu / carbon nanotube electrocatalyst, PtCoRu nanoparticles are dispersed on carbon nanotubes.

9. Use of the PtCoRu / carbon nanotube electrocatalyst according to claim 7 in preparing a fuel cell, wherein the fuel cell is selected from a methanol fuel cell or an ethanol fuel cell.

10. The use according to claim 9, characterized in that: The medium of methanol fuel cell or ethanol fuel cell is acidic medium.

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