A method for preparing a cobalt-based composite metal material and its application in electrocatalytic urea oxidation.

Abstract

This invention discloses a method for preparing a cobalt-based composite metal material and its application in electrocatalytic urea oxidation. The method involves a hydrothermal reaction of zinc acetate, cobalt acetate, hexadecyltrimethylammonium bromide, and 2-methylimidazole to obtain a ZnCo-ZIF precursor. The ZnCo-ZIF precursor is then dissolved in methanol with ferrous chloride and stirred for a certain period. After centrifugation, washing, and drying, FeZnCo-OH material is obtained. Finally, FeZnCo-OH material and sodium hypophosphite are placed separately in a tube furnace, nitrogen gas is introduced, and the reaction is heated. After cooling to room temperature, P-Fe2O3 / ZnCo2O4 material is obtained. Based on this, the cobalt-based composite metal material can be applied to electrocatalytic urea oxidation in 1.0 M KOH and 0.33 M urea solutions with a current density of 10 mA cm⁻¹. ‑2 The potential at which it is applied is 1.3353V, and it exhibits excellent catalytic activity for urea oxidation.

Description

Technical Field

[0001] This invention belongs to the fields of transition composite metal materials and electrocatalysis technology, specifically relating to a method for preparing a cobalt-based composite metal material and its application in electrocatalytic urea oxidation. Background Technology

[0002] With the rapid development of human society and the improvement of living standards, the demand for energy is constantly increasing. Currently, global energy consumption is approximately 15 terawatts (TWh), and this figure is projected to increase to 23 TWh by 2030 and reach 30 TWh by 2050. However, the limited reserves of fossil resources and the increasingly serious energy security, environmental pollution, and climate change problems caused by their consumption will severely impact the future of humanity. Therefore, it is imperative to vigorously develop new and renewable energy sources and optimize the existing energy structure. Hydrogen energy, as a clean, efficient, high-calorific-value, and environmentally friendly sustainable secondary energy source, is considered a promising energy carrier for meeting our future fuel needs.

[0003] Among various hydrogen production methods, electrocatalytic hydrogen production is considered a promising technology due to its high efficiency, cleanliness, and high purity. However, traditional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) require high overpotentials, leading to energy consumption. Furthermore, Pt and Ru, noble metals, are often used as highly efficient catalysts in common water electrolysis catalysts, but their high cost and scarcity significantly hinder their large-scale application.

[0004] The superiority of transition metals such as Fe, Co, and Ni, as well as their sulfides, phosphides, nitrides, selenides, or bimetallic heterojunctions and hydroxides in electrocatalytic water splitting and their greater availability compared to precious metals, are attracting increasing attention.

[0005] Based on this, the present invention proposes a method for preparing cobalt-based composite metal materials and their application in electrocatalytic urea oxidation. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and provide a simple preparation method for a cobalt-based composite metal material with high catalytic performance and its application in electrocatalytic urea oxidation. This invention combines the high electrocatalytic efficiency of transition metals with the low potential characteristic of UOR hydrogen production. A cubic interpenetrating polymer (ZIF) precursor is obtained through the hydrothermal reaction of zinc acetate, cobalt acetate, hexadecyltrimethylammonium bromide, and 2-methylimidazole to increase the specific surface area of ​​the catalyst material. Simultaneously, ferrous chloride is added to increase the active sites of the electrocatalytic material, and low-temperature phosphating yields the cobalt-based composite metal material, further enhancing the catalytic activity of the electrocatalytic material in urea oxidation coupled with hydrogen production and effectively reducing the UOR overpotential.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A cobalt-based composite metal material is prepared by the following steps:

[0009] (1) Zinc acetate, cobalt acetate, and hexadecyltrimethylammonium bromide were dissolved in water to obtain solution A, and 2-methylimidazolium was dissolved in water to obtain solution B. Solution A and solution B were mixed and transferred to a hydrothermal reactor for hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and vacuum dried to obtain the ZnCo-ZIF precursor.

[0010] (2) The ZnCo-ZIF precursor and ferrous chloride tetrahydrate were dispersed in methanol and mixed and stirred for a certain time. After centrifugation, washing and vacuum drying, FeZnCo-OH material was obtained.

[0011] (3) Place the FeZnCo-OH material and sodium hypophosphite at both ends of a tubular calcining furnace and calcine them under a nitrogen atmosphere. After cooling to room temperature, wash and vacuum dry to obtain P-Fe2O3 / ZnCo2O4 material.

[0012] Furthermore, the molar ratio of zinc acetate, cobalt acetate, and hexadecyltrimethylammonium bromide used in step (1) is 10:5:3-3.5.

[0013] Furthermore, the molar ratio of 2-methylimidazole to zinc acetate used in step (1) is 30:1.

[0014] Furthermore, the hydrothermal reaction conditions in step (1) are 120℃-140℃ and the reaction time is 8-12h.

[0015] Furthermore, the mass ratio of the ZnCo-ZIF precursor and ferrous chloride tetrahydrate used in step (2) is 1:2.

[0016] Furthermore, the stirring temperature in step (2) is 25°C and the stirring time is 30-90 min.

[0017] Furthermore, the mass ratio of FeZnCo-OH material and sodium hypophosphite used in step (3) is 1:5-10.

[0018] Furthermore, the calcination conditions described in step (3) involve introducing nitrogen gas and heating the temperature to 300-350°C at a rate of 3°C-5°C / min, and holding the temperature for 2-3 hours.

[0019] Application of cobalt-based composite metal materials prepared according to any one of the above preparation methods in electrocatalytic urea oxidation.

[0020] Furthermore, the above application is carried out in the following way: a cobalt-based composite metal material is placed on a glassy carbon electrode as the working electrode, a Hg / HgO electrode as the reference electrode, a graphite rod electrode as the counter electrode, and a 1.0M KOH and 0.33M urea solution as the electrolyte.

[0021] This invention combines the high electrocatalytic efficiency of transition metals with the low potential of UOR hydrogen production. A cubic interpenetrating polymer (ZIF) precursor is obtained through the hydrothermal reaction of zinc acetate, cobalt acetate, hexadecyltrimethylammonium bromide, and 2-methylimidazole to increase the specific surface area of ​​the catalyst material. Simultaneously, ferrous chloride is added to enhance the active sites of the electrocatalytic material, and a cobalt-based composite metal material is obtained through low-temperature phosphating. These improvements further enhance the catalytic activity of the electrocatalytic material in urea oxidation coupled with hydrogen production, effectively reducing the UOR overpotential.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) In terms of type, this invention is the first to propose a cobalt-based composite metal material with a cubic interpenetrating structure;

[0024] (2) In terms of raw materials, iron atom exchange and phosphating were used for the first time to prepare cobalt-based composite metal materials;

[0025] (3) From the perspective of application, the present invention can effectively improve the efficiency of electrocatalytic urea oxidation coupled to hydrogen production and reduce overpotential. Attached Figure Description

[0026] Figure 1 Scanning electron microscope image of the ZnCo-ZIF precursor prepared in Example 1.

[0027] Figure 2 The image shows a scanning electron microscope image of the FeZnCo-OH material prepared in Example 1.

[0028] Figure 3 The image shows a scanning electron microscope image of the P-Fe2O3 / ZnCo2O4 material prepared in Example 1.

[0029] Figure 4 The image shows the X-ray diffraction pattern of the P-Fe2O3 / ZnCo2O4 material prepared in Example 1.

[0030] Figure 5 This is a comparison of the LSV curves of the materials prepared in Example 1 and Comparative Example 1 at UOR.

[0031] Figure 6 LSV curves of the P-Fe2O3 / ZnCo2O4 material prepared in Example 1 at OER and UOR. Detailed Implementation

[0032] A cobalt-based composite metal material is prepared by the following steps:

[0033] (1) Zinc acetate, cobalt acetate, and hexadecyltrimethylammonium bromide were dissolved in water at a molar ratio of 10:5:3-3.5 to obtain solution A, and 30 mmol of 2-methylimidazole was dissolved in water to obtain solution B, wherein the molar ratio of 2-methylimidazole to zinc acetate was 30:1; solution A and solution B were mixed and transferred to a hydrothermal reactor, the reaction temperature was 120℃-140℃, the reaction time was 8-12h, and after cooling to room temperature, the ZnCo-ZIF precursor was obtained by centrifugation, washing, and vacuum drying.

[0034] (2) The ZnCo-ZIF precursor and ferrous chloride were dissolved in methanol at a mass ratio of 1:2 and mixed and stirred at a temperature of 25°C for 30-90 min. Then, the mixture was centrifuged, washed, and vacuum dried to obtain FeZnCo-OH material.

[0035] (3) Place FeZnCo-OH material and sodium hypophosphite at both ends of a tubular calcining furnace at a mass ratio of 1:5-10. Heat the material to 300-350℃ at a heating rate of 3℃-5℃ / min under a nitrogen atmosphere, hold for 2-3 hours, cool to room temperature, wash, and vacuum dry to obtain P-Fe2O3 / ZnCo2O4 material.

[0036] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0037] Example 1

[0038] Preparation of ZnCo-ZIF precursor: 1 mmol zinc acetate (Zn(CH3COO)2•2H2O), 0.5 mmol cobalt acetate (Co(CH3COO)2•4H2O), and 0.33 mmol hexadecyltrimethylammonium bromide (CTAB) were dissolved in 38 ml of deionized water to prepare solution A; 30 mmol 2-methylimidazole was dissolved in 38 ml of deionized water to prepare solution B; solution A was quickly poured into solution B and stirred, then transferred to a Teflon reactor and reacted at 120°C for 12 h. After cooling to room temperature, the solution was washed three times by centrifugation with methanol and ethanol, and then vacuum dried to obtain the purple ZnCo-ZIF precursor.

[0039] Preparation of FeZnCo-OH material: 150 mg ZnCo-ZIF precursor was dissolved in 10 ml methanol and sonicated for 15 min to obtain solution A; 300 mg ferrous chloride (FeCl2·4H2O) was dissolved in 15 ml methanol to obtain solution B. Solution B and solution A were mixed and stirred at 25°C for 60 min. After centrifugation and washing, the mixture was vacuum dried to obtain brownish-yellow FeZnCo-OH material.

[0040] Preparation of P-Fe2O3 / ZnCo2O4 material: 30 mg of FeZnCo-OH material and 300 mg of sodium hypophosphite (NaH2PO2) were placed downstream and upstream of a tubular calcining furnace, respectively. Nitrogen gas was introduced and the temperature was raised to 350°C at a rate of 5°C / min. The temperature was held for 2 hours, cooled to room temperature, washed, and vacuum dried to obtain P-Fe2O3 / ZnCo2O4 material.

[0041] The P-Fe2O3 / ZnCo2O4 composite material obtained in Example 1 was characterized as follows:

[0042] Scanning electron microscopy (SEM): Scanning electron micrographs of ZnCo-ZIF precursor, FeZnCo-OH material, and P-Fe2O3 / ZnCo2O4 material are shown below. Figure 1 , Figure 2 , Figure 3 As shown, the P-Fe2O3 / ZnCo2O4 composite material is a nanomaterial composed of interpenetrating cubic materials, which effectively increases the specific surface area and active sites.

[0043] X-ray diffraction (XRD): The X-ray diffraction pattern of the P-Fe2O3 / ZnCo2O4 material is shown below. Figure 4As shown, the characteristic diffraction peaks of the P-Fe2O3 / ZnCo2O4 material are 18.9°, 31.2°, 33.1°, 35.6°, 36.8°, 44.7°, 49.5°, 54.1°, 59.3°, 62.4°, 64.0°, 65.1°, and 72.3°, respectively, corresponding to the (1 0 4), (1 1 0), (0 2 4), (11 6), (2 1 4), (3 0 0), and (1 1 9) crystal planes of Fe2O3 (PDF#86-0550), and the (1 1 1), (2 2 0), (3 11), (4 0 0), (5 1 1), and (4 4 ) crystal planes of ZnCo2O4 (PDF#23-1390). 0) Crystal plane, indicating that P-Fe2O3 / ZnCo2O4 has been successfully synthesized.

[0044] Comparative Example 1

[0045] Preparation of ZnCo-ZIF precursor: 1 mmol zinc acetate (Zn(CH3COO)2•2H2O), 0.5 mmol cobalt acetate (Co(CH3COO)2•4H2O), and 0.33 mmol hexadecyltrimethylammonium bromide (CTAB) were dissolved in 38 ml of deionized water to prepare solution A; 30 mmol 2-methylimidazole was dissolved in 38 ml of deionized water to prepare solution B; solution A was quickly poured into solution B and stirred, then transferred to a Teflon reactor and reacted at 120°C for 12 h. After cooling to room temperature, the solution was washed three times by centrifugation with methanol and ethanol, and then vacuum dried to obtain the purple ZnCo-ZIF precursor.

[0046] Preparation of FeZnCo-OH material: 150 mg ZnCo-ZIF precursor was dissolved in 10 ml methanol and sonicated for 15 min to obtain solution A; 300 mg ferrous chloride (FeCl2·4H2O) was dissolved in 15 ml methanol to obtain solution B. Solution B and solution A were mixed and stirred at 25°C for 60 min. After centrifugation and washing, the mixture was vacuum dried to obtain brownish-yellow FeZnCo-OH material.

[0047] The prepared ZnCo-ZIF precursor, FeZnCo-OH material, and P-Fe2O3 / ZnCo2O4 material were used as working electrodes, respectively. The reference electrode was a Hg / HgO electrode, and the counter electrode was a graphite rod electrode. The electrolyte was a 1.0M KOH and 0.33M urea solution with a volume of 40 ml. LSV was measured at a scan rate of 10 mV / s. The experimental results are as follows. Figure 5 As shown, phosphating materials can effectively reduce the potential of UOR at a current density of 10 mA cm⁻¹. -2 The potentials of the three materials are 1.3601V, 1.3561V, and 1.3353V, respectively.

[0048] Example 2

[0049] Preparation of ZnCo-ZIF precursor: 1 mmol zinc acetate (Zn(CH3COO)2•2H2O), 1 mmol cobalt acetate (Co(CH3COO)2•4H2O), and 0.33 mmol hexadecyltrimethylammonium bromide (CTAB) were dissolved in 38 ml of deionized water to prepare solution A; 30 mmol 2-methylimidazole was dissolved in 38 ml of deionized water to prepare solution B; solution A was quickly poured into solution B and stirred, then transferred to a Teflon reactor and reacted at 120°C for 12 h. After cooling to room temperature, the solution was washed three times by centrifugation with methanol and ethanol, and then dried under vacuum to obtain the purple ZnCo-ZIF precursor.

[0050] Preparation of FeZnCo-OH material: 150 mg ZnCo-ZIF precursor was dissolved in 10 ml methanol and sonicated for 15 min to obtain solution A; 300 mg ferrous chloride (FeCl2·4H2O) was dissolved in 15 ml methanol to obtain solution B. Solution B and solution A were mixed and stirred at 25°C for 90 min. After centrifugation and washing, the mixture was vacuum dried to obtain brownish-yellow FeZnCo-OH material.

[0051] Preparation of P-Fe2O3 / ZnCo2O4 material: 30 mg of FeZnCo-OH material and 300 mg of sodium hypophosphite (NaH2PO2) were placed downstream and upstream of a tubular calcining furnace, respectively. Nitrogen gas was introduced and the temperature was raised to 350°C at a rate of 5°C / min. The temperature was held for 2 hours, cooled to room temperature, washed, and vacuum dried to obtain P-Fe2O3 / ZnCo2O4 material.

[0052] Application examples

[0053] Application of P-Fe2O3 / ZnCo2O4 composite material in electrocatalytic urea oxidation

[0054] (a) Application Method

[0055] 1) Add 4 mg of P-Fe2O3 / ZnCo2O4 composite material to a mixture of 30 μL Nafion and 2 ml anhydrous ethanol, sonicate for 30 minutes, and then drop 6 μL of the dispersion onto a glassy carbon electrode to obtain the electrode material of P-Fe2O3 / ZnCo2O4 composite material.

[0056] 2) Using an AUTOLAB-302N electrochemical workstation, a three-electrode electrolytic cell was used as the electrolytic cell. The P-Fe2O3 / ZnCo2O4 composite material was used as the working electrode, the reference electrode was an Hg / HgO electrode, the counter electrode was a graphite rod electrode, and the electrolyte was a 1.0M KOH and 0.33M urea solution with a volume of 40ml.

[0057] 3) LSV Test: At a scan rate of 10 mV / s, the OER and UOR of the electrode material were tested in 1.0 M KOH solution and 1.0 M KOH + 0.33 M urea solution, respectively. The electrode potential was referenced to the reversible hydrogen electrode (RHE): E RHE = E (Hg / HgO) +0.0591pH+0.098. The LSV curves of the OER and UOR of the P-Fe2O3 / ZnCo2O4 composite material are shown below. Figure 6 As shown, the P-Fe2O3 / ZnCo2O4 composite material achieved a current density of 10 mA cm⁻¹ during the electrocatalytic oxidation of urea. -2 The potential is 1.3353V, indicating that UOR preferentially occurs over OER. By replacing OER, urea oxidation can occur at a low potential, effectively reducing energy consumption.

[0058] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a cobalt-based composite metal material, characterized in that: Includes the following steps: (1) Zinc acetate, cobalt acetate, and hexadecyltrimethylammonium bromide were dissolved in water to obtain solution A, and 2-methylimidazolium was dissolved in water to obtain solution B. Solution A and solution B were mixed and transferred to a hydrothermal reactor for hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed, and vacuum dried to obtain the ZnCo-ZIF precursor. (2) The ZnCo-ZIF precursor and ferrous chloride tetrahydrate were dispersed in methanol and mixed and stirred for a certain time. After centrifugation, washing and vacuum drying, FeZnCo-OH material was obtained. (3) Place the FeZnCo-OH material and sodium hypophosphite at both ends of a tubular calcining furnace and calcine them under a nitrogen atmosphere. After cooling to room temperature, wash and vacuum dry to obtain P-Fe2O3 / ZnCo2O4 material.

2. The preparation method according to claim 1, characterized in that: The molar ratio of zinc acetate, cobalt acetate and hexadecyltrimethylammonium bromide used in step (1) is 10:5:3-3.

5.

3. The preparation method according to claim 1, characterized in that: The molar ratio of 2-methylimidazole to zinc acetate used in step (1) is 30:

1.

4. The preparation method according to claim 1, characterized in that: The hydrothermal reaction conditions in step (1) are 120℃-140℃ and the reaction time is 8-12h.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the ZnCo-ZIF precursor and ferrous chloride tetrahydrate used in step (2) is 1:

2.

6. The preparation method according to claim 1, characterized in that: The stirring temperature in step (2) is 25°C and the stirring time is 30-90 min.

7. The preparation method according to claim 1, characterized in that: The mass ratio of FeZnCo-OH material and sodium hypophosphite used in step (3) is 1:5-10.

8. The preparation method according to claim 1, characterized in that: The calcination process in step (3) involves heating the temperature to 300-350℃ at a rate of 3℃-5℃ / min and holding it at that temperature for 2 hours.

9. A cobalt-based composite metal material prepared by the preparation method according to any one of claims 1-8.

10. The application of the cobalt-based composite metal material according to claim 9 in the electrocatalytic oxidation of urea, characterized in that, The cobalt-based composite metal material was placed on a glassy carbon electrode as the working electrode, the reference electrode was an Hg / HgO electrode, the counter electrode was a stone rod electrode, and the electrolyte was a 1.0M KOH and 0.33M urea solution.

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