Anode catalyst for alkaline direct urea fuel cell and method for preparing the same

Abstract

The present application relates to a kind of anode catalysts for alkaline system direct urea fuel cell, it is with nickel salt, H3BO3 and PVP dispersed in water heating reaction preparation precursor, then under inert atmosphere calcination obtained, by nitrogen-containing carbon material wrapped elemental nickel / nickel oxide / nickel boride nanocrystalline composite material.The present application introduces non-metallic boron and PVP carbon material, after calcination, active substance nickel / nickel oxide / nickel boride replaces traditional noble metal, by forming metal boride and oxide to adjust catalyst electronic structure, improve the catalytic activity and electrode conductivity of catalyst, with it as the anode catalyst for alkaline system direct urea fuel cell, with excellent electrochemical reaction activity.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical catalytic oxidation technology, and relates to fuel cell anode catalysts, particularly to non-precious metal-based carbon material anode catalysts for direct urea fuel cells in alkaline systems and their preparation methods. The catalysts prepared by this invention can be used for the electrochemical catalytic oxidation of urea fuel. Background Technology

[0002] Humans and animals produce a large amount of urine daily, which contains approximately 2-2.5% urea. The industrial production of urea and its use as nitrogen fertilizer in agriculture also generate significant amounts of urea-containing wastewater. Urea can degrade into ammonia (NH3) in ecosystems, causing secondary pollution to the environment.

[0003] Currently, the purification of urea-containing wastewater mainly involves various methods such as thermal hydrolysis, biological decomposition, and chemical oxidation. However, these methods generally suffer from high costs, harsh working conditions, or excessive energy consumption, which greatly hinders their widespread application.

[0004] However, urea is inexpensive, abundant, relatively safe, and easy to store and transport, making it suitable for direct use in fuel cells, replacing the traditional anode in direct urea fuel cells (DUFCs). The electrochemical oxidation of urea not only reduces pollution from urea-containing wastewater but also simultaneously generates hydrogen at the cathode, thus attracting increasing attention from academia and industry.

[0005] Generally, noble metals such as Pt, Pd, and Ru possess excellent catalytic activity and are widely used as anode catalysts in direct fuel cells (DUFCs). However, these noble metal-based catalysts exhibit limited performance in urea oxidation, and their high cost directly hinders the large-scale commercialization of DUFCs. Therefore, there is an urgent need to develop a low-cost, highly active, and stable urea oxidation anode catalyst.

[0006] Among numerous non-precious metal-based catalysts, nickel is abundant in the Earth's crust and inexpensive, making nickel-based catalysts effective anode catalysts for the urea oxidation reaction (UOR). Various UOR catalysts, such as NiMo@ZnO / NF (J. Cao, H. Li, R. Zhu, L. Ma, K. Zhou, Q. Wei, F. Luo, Improved hydrogen generation via a urea-assisted method over 3D hierarchical NiMo-based composite microrodarrays), have been developed. J. Alloy. Compd. 844(2020), 155382.), CuO-Ni(OH)2 nanomeshes(JHYang, M. Chen, X. Xu, S. Jiang, Y. Zhang, Y. Wang, Y. Li, J. Zhang, D. Yang,CuO-Ni(OH)2 nanosheets as effective electro-catalysts for urea oxidation, Appl. Surf. Sci . 560(2021), 150009.), Fe3O4-NiO / NF (M. Han, G. Yan, Prussianblue analogue-derived porous bimetallic oxides Fe3O4-NiO / NF as urea oxidationelectrocatalysis, Chem. Pap (e.g., 74(2020), 4473-4480.) revealed the great potential of nickel-based materials in UOR.

[0007] Nickel-based catalysts typically used in direct fuel cell anodes involve loading nickel onto carbon materials such as graphene, carbon black, and carbon nanotubes to improve the conductivity and dispersibility of the nickel active component. However, the preparation processes and methods of traditional nickel-based catalysts are complex, and the uniform dispersion of the active component nickel is not high, directly affecting its electrochemical reactivity with UOR.

[0008] For example, the NiMo@ZnO / NF, CuO-Ni(OH)2nanomeshes, and Fe3O4-NiO / NF catalysts mentioned in the above literature exhibit high current densities ( j ) is 10mA cm -2 The required potentials for UOR at these times are too high, specifically 1.405V (vs RHE), 1.41V (vs RHE), and 1.44V (vs RHE). Therefore, it is necessary to introduce non-metallic elements to enhance the electronic interactions between transition metal atoms, precisely adjust the electronic structure of the metal active center, and further optimize the surface oxygen adsorption energy, thereby promoting the improvement of the material's catalytic ability and enabling it to have higher UOR electrocatalytic activity. Summary of the Invention

[0009] The purpose of this invention is to provide an alkaline system direct urea fuel cell anode catalyst and its preparation method, which improves the catalytic activity and electrode conductivity by introducing heteroatoms to regulate the electronic structure of the catalyst.

[0010] The alkaline system direct urea fuel cell anode catalyst of the present invention is prepared by dispersing nickel salt, H3BO3 and PVP in water and heating to prepare a precursor, and then calcining the precursor under an inert atmosphere to obtain a nitrogen-containing carbon material-encapsulated elemental nickel / nickel oxide / nickel boride nanocrystalline composite material.

[0011] This invention also provides a specific preparation method for the alkaline system direct urea fuel cell anode catalyst, which involves mixing and dispersing nickel salt, H3BO3 and PVP in deionized water, heating to 180-220°C under continuous stirring to prepare a precursor, and then calcining the precursor obtained in the reaction at 400-600°C under an inert atmosphere to prepare a Ni / NiO / NiB@NC composite catalyst.

[0012] Furthermore, the present invention preferably involves reacting PVP with a mass ratio of 1:3 to 4.5 of soluble nickel salt.

[0013] Furthermore, the H3BO3 added in the reaction is preferably 0.9 to 1.5 times the mass of the soluble nickel salt.

[0014] More specifically, the present invention involves drying the precursor obtained from the reaction and then calcining it at a rate of 2–4 °C / min from room temperature to 400–600 °C to prepare a Ni / NiO / NiB@NC composite catalyst.

[0015] The preferred calcination time is 2 to 5 hours.

[0016] Furthermore, the present invention preferably involves mixing and dispersing nickel salt, H3BO3 and PVP in deionized water, and continuously stirring at 50-80°C for no less than 30 minutes.

[0017] The present invention also provides an anode for a direct urea fuel cell in an alkaline system, which is an anode material coated with the anode catalyst described in the present invention.

[0018] This invention uses PVP as a novel carbon source, and forms a nickel-based metal compound to replace traditional precious metals through a simple heating reaction. After calcination, a nitrogen-containing carbon nanocrystalline composite material encapsulating elemental nickel, nickel oxide / nickel boride is obtained. This composite material is used as an anode catalyst for alkaline direct urea fuel cells and exhibits good electrochemical reactivity.

[0019] The anode catalyst prepared in this invention is dispersed in deionized water and anhydrous ethanol, then directly coated onto the surface of hydrophilic conductive carbon cloth. After drying, it forms the anode for an alkaline direct urea fuel cell. Using it as the working electrode eliminates the need for any binder, avoiding the presence of inactive areas and resulting in better conductivity.

[0020] This invention introduces heteroatoms B and N into the catalyst to regulate its electronic structure, further improving the catalytic activity of the Ni / NiO / NiB@NC composite catalyst. The UOR activity, conductivity, and stability of the composite catalyst were tested using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA). The peak anolyte current density reached 264 mA cm⁻¹ in a mixed electrolyte of 1 M KOH + 0.33 M CO(NH₂)₂ solution at a scan rate of 50 mV / s and a voltage of 1.67 V (vsRHE). -2 At a current density of 10 mA cm -2 The required potential for UOR at that time was 1.37V (vs RHE), which showed a significant catalytic effect on urea, and the current density of the chronoamperometry CA test remained at 222.4mA cm⁻¹ for 12 hours. -2 The retention rate was 84.58%. Attached Figure Description

[0021] Figure 1 The images show the X-ray diffraction patterns of the Ni / NiO / NiB@NC-500 composite catalyst prepared in Example 1 and the comparative examples Ni / NiO@NC-500 and NC-500.

[0022] Figure 2 This is an X-ray diffraction pattern of the precursor prepared in Example 1.

[0023] Figure 3 The CV diagrams are for different catalysts prepared in Example 1 and the comparative example in 1M KOH + 0.33M CO(NH2)2 solution.

[0024] Figure 4 The LSV diagrams are for different catalysts prepared in Example 1 and the comparative example in 1M KOH + 0.33M CO(NH2)2 solution.

[0025] Figure 5 These are EIS diagrams of different catalysts prepared in Example 1 and the comparative example.

[0026] Figure 6 This is a 12-hour chronoamperometry CA test result of the composite catalyst prepared in Example 1. Implementation

[0027] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can better understand and utilize the present invention, and are not intended to limit the scope of protection of the present invention.

[0028] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, which are very clear and distinct in the relevant application areas. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0029] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art. Example

[0030] Example 1

[0031] Weigh out 1.5g (5.16mmol) NiNO3·6H2O and 0.5g PVP ((C6H9NO)). n ), 1.86g (30.08mmol) H3BO3, added to 50mL of deionized water, and stirred rapidly at 60℃ in a magnetic stirrer until dissolved and homogeneous.

[0032] The solution was transferred to a gray dish, placed in an oven, and heated to 200°C for 10 hours to prepare the precursor.

[0033] The yellowish-brown precursor powder obtained from the reaction was taken out and placed in a tube furnace. Under N2 atmosphere, the temperature was increased from room temperature to 500℃ at a rate of 2℃ / min. After holding at this temperature for 2 hours, it was cooled to room temperature under N2 protection.

[0034] The reaction product was removed, ground evenly, and the Ni / NiO / NiB@NC-500 composite catalyst was prepared.

[0035] Comparative Example 1

[0036] Without adding H3BO3, weigh out 1.5g (5.16mmol) NiNO3·6H2O and 0.5g PVP ((C6H9NO)). n Add 50 mL of deionized water and stir rapidly at 60 °C in a magnetic stirrer until dissolved and homogeneous. Transfer to a gray dish, place in an oven, and heat to 200 °C for 10 h to prepare the precursor.

[0037] The precursor was placed in a tubular reactor and heated from room temperature to 500°C at a rate of 2°C / min under N2 atmosphere. After calcination at this temperature for 2 hours, the product was cooled to room temperature under N2 protection. The reaction product was then removed, ground uniformly, and the Ni / NiO@NC-500 composite catalyst was prepared.

[0038] Comparative Example 2

[0039] Without adding PVP, weigh 1.5 g (5.16 mmol) NiNO3·6H2O and 1.86 g (30.08 mmol) H3BO3 and add them to 50 mL of deionized water. Stir rapidly at 60 °C in a magnetic stirrer until dissolved and homogeneous. Transfer to a gray dish, place in an oven, and heat to 200 °C for 10 h to prepare the precursor.

[0040] The precursor was placed in a tubular reactor and heated from room temperature to 500°C at a rate of 2°C / min under N2 atmosphere. After calcination at this temperature for 2 hours, the product was cooled to room temperature under N2 protection. The reaction product was then removed, ground uniformly, and the Ni / NiO / NiB-500 composite catalyst was prepared.

[0041] Comparative Example 3

[0042] Without adding nickel salt and H3BO3, weigh out 0.5g of PVP ((C6H9NO)). n Add 50 mL of deionized water and stir rapidly at 60 °C in a magnetic stirrer until dissolved and homogeneous. Transfer to a gray dish, place in an oven, and heat to 200 °C for 10 h to prepare the precursor.

[0043] The precursor was placed in a tubular reactor and heated from room temperature to 500°C at a rate of 2°C / min under N2 atmosphere. After calcination at this temperature for 2 hours, the product was cooled to room temperature under N2 protection. The reaction product was then removed, ground evenly, and the NC-500 catalyst was prepared.

[0044] Powder X-ray diffraction analysis was used to test the active material and corresponding crystal planes in the catalysts prepared in Example 1, Comparative Examples 1 and 3, and the results were obtained. Figure 1 The diffraction pattern shown.

[0045] The diffraction pattern of the Ni / NiO / NiB@NC-500 composite catalyst was compared with the Joint Committee on Powder Diffraction Standards (JCPDS) card No. 04-0850. The diffraction angles 2θ = 44.5°, 51.9° and 76.3° correspond to three different crystal planes of nickel with face-centered cubic structure: (111), (200) and (220), respectively, proving that one of the active substances in the catalyst is elemental nickel.

[0046] Furthermore, by comparing with the Joint Committee on Powder Diffraction Standards (JCPDS) card No. 44-1159, the diffraction angles 2θ = 37.2°, 43.3° and 62.9° correspond to three different crystal planes of nickel oxide with rhombic structure: (101), (012) and (104). This proves that one of the active substances in the catalyst is nickel oxide.

[0047] Compared with the Joint Committee on Powder Diffraction Standards (JCPDS) card No. 06-0567, the diffraction angles 2θ = 24.2°, 38.9° and 49.4° correspond to the (020), (021) and (040) crystal planes of orthorhombic nickel boride, respectively, proving that nickel boride is one of the active substances in the catalyst.

[0048] In contrast, the diffraction pattern of the Ni / NiO@NC-500 composite catalyst in Comparative Example 1 clearly shows no characteristic peaks of NiB, indicating that no NiB was formed.

[0049] No characteristic peaks were observed in the diffraction pattern of the NC-500 catalyst in Comparative Example 3, indicating that no active material was generated.

[0050] Meanwhile, powder X-ray diffraction measurements were also performed on the precursor before calcination in Example 1, and the results were obtained. Figure 2 The diffraction pattern shown also reveals that no crystal planes appear, indicating that the prepared precursor is amorphous.

[0051] This invention introduces boron atoms and transforms the catalyst from an amorphous state to a crystalline state through high-temperature calcination, forming metal oxides and borides. This strengthens the electronic interactions between transition metal atoms, precisely adjusts the electronic structure of the metal active center, and further optimizes the surface oxygen adsorption energy, thereby improving the catalytic activity and stability of the catalyst.

[0052] Example 2

[0053] Weigh 1.75g ​​(6.02mmol) NiNO3·6H2O, 0.5g PVP ((C6H9NO) n ), 1.72g (27.82mmol) H3BO3, added to 50mL of deionized water, and stirred rapidly at 60℃ in a magnetic stirrer until dissolved and homogeneous.

[0054] The solution was transferred to a gray dish, placed in an oven, and heated to 180°C for 10 hours to prepare the precursor.

[0055] The yellowish-brown precursor powder obtained from the reaction was taken out and placed in a tube furnace. Under N2 atmosphere, the temperature was increased from room temperature to 400℃ at a rate of 2℃ / min. After holding at this temperature for 2 hours, it was cooled to room temperature under N2 protection.

[0056] The reaction product was removed, ground evenly, and the Ni / NiO / NiB@NC-400 composite catalyst was prepared.

[0057] Example 3

[0058] Weigh out 2.0 g (6.88 mmol) NiNO3·6H2O and 0.5 g PVP ((C6H9NO)).n ), 2.00g (32.35mmol) H3BO3, added to 50mL of deionized water, and stirred rapidly at 60℃ in a magnetic stirrer until dissolved and homogeneous.

[0059] The solution was transferred to a gray dish, placed in an oven, and heated to 220°C for 10 hours to prepare the precursor.

[0060] The yellowish-brown precursor powder obtained from the reaction was taken out and placed in a tube furnace. Under N2 atmosphere, the temperature was increased from room temperature to 600℃ at a rate of 2℃ / min. After holding at this temperature for 2 hours, it was cooled to room temperature under N2 protection.

[0061] The reaction product was removed, ground evenly, and the Ni / NiO / NiB@NC-600 composite catalyst was prepared.

[0062] Application Example 1

[0063] Weigh 2 mg of the Ni / NiO / NiB@NC-500 composite catalyst prepared in Example 1, place it in a centrifuge tube, add 20 µL of anhydrous ethanol and 20 µL of deionized water, sonicate for 15 min, pipette 20 µL, and evenly drop it onto the surface of a 0.5 cm × 1.5 cm hydrophilic carbon cloth, and dry it in an oven at 80 °C.

[0064] Using the carbon cloth coated with the Ni / NiO / NiB@NC-500 composite catalyst as the working electrode, a 3cm×4cm stainless steel sheet as the counter electrode, and a saturated calomel electrode as the reference electrode, a three-electrode system was adopted. The electrochemical performance of the Ni / NiO / NiB@NC-500 composite catalyst was characterized by CV, LSV, EIS, and CA.

[0065] The UOR reaction activity was tested using a mixed solution of 1M KOH and 0.33M CO(NH2)2 as the electrolyte solution and a Shanghai Chenhua CHI 660E electrochemical workstation.

[0066] Meanwhile, working electrodes were prepared using the Ni / NiO@NC-500 composite catalyst prepared in Comparative Example 1, the Ni / NiO / NiB-500 composite catalyst prepared in Comparative Example 2, and the precursor in Example 1, and their electrochemical performance was tested.

[0067] CV test results as follows Figure 3 As shown, in a mixed solution of 1M KOH + 0.33M CO(NH2)2, at the same scan rate of 50mV / s and a voltage of 1.67V (vs RHE), the Ni / NiO / NiB@NC-500 composite catalyst exhibits the highest current density, at 264mA cm⁻¹. -2 At a current density of 10 mA cm-2 When the required potential for UOR is 1.37V (vs RHE), it proves that the catalyst has a significant catalytic effect on urea.

[0068] Figure 4 The UOR activity of different catalysts was further compared using LSV at the same current density (10 mA cm⁻¹). -2 Under the given conditions, the driving voltage required for UOR by the Ni / NiO / NiB@NC-500 composite catalyst (1.37V) is lower than that of Ni / NiO / NiB-500 (1.38V), Ni / NiO@NC-500 (1.39V), Precursor (1.4V), and NC-500 (1.61V), indicating that Ni / NiO / NiB@NC-500 has the best activity for UOR among all catalysts.

[0069] also, Figure 5 The conductivity of different catalysts was also compared using EIS. It can be seen that the Ni / NiO / NiB@NC-500 composite catalyst has the lowest charge transfer resistance (Rct), indicating that it has the fastest charge transfer rate in the UOR process. This is attributed to the highly conductive metal borides accelerating the charge transfer between urea and the catalyst surface.

[0070] Furthermore, based on Figure 6 In the same 1M KOH + 0.33M CO(NH2)2 mixed solution, after 12 hours of CA testing, i.e., examining the change trend of current density over time at a voltage of 1.67V (vs RHE), the current density decreased from 264mA cm⁻¹ after 12 hours. -2 Decreased to 222.4 mA cm -2 The current density retention rate was 84.58%, indicating that the Ni / NiO / NiB@NC-500 composite catalyst has good stability.

[0071] In addition, Table 1 below provides a comparison of performance indicators of nickel-based catalysts reported in some literature. Because the preparation methods and processes of traditional nickel-based catalysts are complex, and the uniform dispersion of the active component nickel is not high, it directly affects their electrochemical reaction activity in urea oxidation.

[0072] As can be seen from the data in Table 1, at a current density of 10 mA cm⁻¹ -2In the literature, the required potentials for UOR were 1.405V (vs RHE), 1.41V (vs RHE), and 1.44V (vs RHE), respectively, all greater than the 1.37V (vs RHE) required for the catalyst prepared in this invention, indicating that its urea oxidation activity was not high. To improve the catalyst activity, the catalyst provided in this invention, which combines an active nickel component with a carbon material with good conductivity, can significantly reduce the voltage required at a fixed current, thus improving the catalytic oxidation activity of urea.

[0073]

[0074] [1] J. Cao, H. Li, R. Zhu, L. Ma, K. Zhou, Q. Wei, F. Luo, Improved hydrogen generation via a urea-assisted method over 3D hierarchical NiMo-based composite microrod arrays, J. Alloy. Compd. 844 (2020) 155382.

[0075] [2] J.-H. Yang, M. Chen, X. Xu, S. Jiang, Y. Zhang, Y. Wang, Y. Li,J. Zhang, D. Yang, CuO-Ni(OH)2 nanosheets as effective electro-catalysts forurea oxidation, Appl. Surf. Sci. 560 (2021) 150009.

[0076] [3] M. Han, G. Yan, Prussian blue analogue-derived porous bimetallicoxides Fe3O4–NiO / NF as urea oxidation electrocatalysis, Chem. Pap. 74 (2020)4473-4480.

[0077] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. The anode catalyst for alkaline system direct urea fuel cell is a composite material of elemental nickel / nickel oxide / nickel boride nanocrystals encapsulated by nitrogen-containing carbon material. It is prepared by dispersing nickel salt, H3BO3 and PVP in water and heating to prepare a precursor, and then calcining the precursor under an inert atmosphere.

2. The method for preparing the alkaline system direct urea fuel cell anode catalyst according to claim 1 involves mixing and dispersing nickel salt, H3BO3 and PVP in deionized water, continuously stirring until uniformly dissolved, then heating to 180-220°C to prepare a precursor, and then calcining the precursor obtained in the reaction at 400-600°C under an inert atmosphere to produce a composite material of elemental nickel / nickel oxide / nickel boride nanocrystals encapsulated by nitrogen-containing carbon materials.

3. The method for preparing the anode catalyst for a direct urea fuel cell in an alkaline system according to claim 2, characterized in that: The mass ratio of PVP to nickel salt is 1:3 to 4.

5.

4. The method for preparing the anode catalyst for a direct urea fuel cell in an alkaline system according to claim 2 or 3, characterized in that: The amount of H3BO3 used is 0.9 to 1.5 times the mass of the nickel salt.

5. The method for preparing the anode catalyst for a direct urea fuel cell in an alkaline system according to claim 2, characterized in that: After drying, the obtained precursor was calcined at 400–600 °C from room temperature at a rate of 2–4 °C / min under an inert atmosphere.

6. The method for preparing the anode catalyst for a direct urea fuel cell in an alkaline system according to claim 2 or 5, characterized in that: The calcination time is 2 to 5 hours.

7. The method for preparing the anode catalyst for a direct urea fuel cell in an alkaline system according to claim 2, characterized in that: Nickel salt, H3BO3 and PVP are mixed and dispersed in deionized water and stirred continuously at 50-80°C for no less than 30 minutes.

8. An anode for a direct urea fuel cell in an alkaline system, wherein the anode is coated with the anode catalyst of claim 1.

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