Oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide, and preparation method and application thereof
By preparing oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide, the problem of insufficient catalytic activity of NiMoO4-based catalysts in direct methanol fuel cells was solved, and a highly active and long-term stable anode catalyst was achieved, which is suitable for direct methanol fuel cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHONGYUAN ENGINEERING COLLEGE
- Filing Date
- 2026-06-11
- Publication Date
- 2026-07-31
AI Technical Summary
Existing NiMoO4-based catalysts suffer from problems such as insufficient catalytic active sites, poor conductivity, nanoparticle aggregation, and electrode surface passivation in the methanol oxidation reaction at the anode of direct methanol fuel cells, leading to rapid decay of catalytic activity and making it difficult to meet the requirements for long-term use.
Oxygen-rich nitrogen-doped nickel-cobalt-molybdenum oxide (N-NiCoMoO) was prepared using a one-step hydrothermal combined annealing process. By constructing pyridine nitrogen, pyrrole nitrogen, and metal-nitrogen coordination bonds through nitrogen doping and oxygen vacancy construction, the electronic structure was synergistically regulated, the adsorption/desorption balance of methanol and reaction intermediates was optimized, and the charge transport efficiency was improved.
It significantly improves the catalytic activity and stability of the catalyst, maintains the current density at 83.6%, lowers the rate-determining energy barrier, has low material cost, and is suitable for large-scale preparation and industrial application.
Smart Images
Figure CN122494682A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of energy conversion and electrocatalytic materials technology, and particularly relates to an anode methanol oxidation electrocatalyst for use in direct methanol fuel cells. Background Technology
[0002] With the escalating global energy crisis and increasingly severe ecological and environmental problems, the development of efficient and green energy conversion and storage technologies has become a key research direction in the energy field. Methanol fuel cells (DMFCs) can directly convert the chemical energy in liquid methanol into electrical energy through electrochemical reactions. They possess outstanding advantages such as high energy density, convenient fuel storage and transportation, wide availability of raw materials, and safe use, and have great application potential in portable electronic devices, small mobile power supplies, and other fields. DMFCs are mainly composed of an anode, cathode, and electrolyte membrane, with the electrode catalyst layer being the core component determining the battery's output performance. Currently, the core bottleneck restricting the large-scale commercial application of direct methanol fuel cells lies in the slow reaction kinetics of the methanol oxidation reaction (MOR) at the anode. Existing commercial precious metal catalysts suffer from drawbacks such as high preparation costs, scarce raw materials, and susceptibility to poisoning and deactivation by reaction intermediates, severely limiting the actual performance and promotional value of the batteries. Therefore, the development of low-cost, high-catalytic-activity, and long-cycle-stability non-precious metal-based methanol oxidation anode catalysts is of significant practical importance for promoting the industrialization of DMFCs.
[0003] Transition metal oxides are preferred alternatives to noble metal catalysts due to their readily available raw materials, strong structural stability, and excellent resistance to poisoning. Among them, nickel-molybdenum oxide (NiMoO4) possesses abundant redox active sites, highly tunable electronic structure, and outstanding potential for electrochemical applications. The nickel component can efficiently drive the methanol dehydrogenation activation process and is the core active site for the methanol oxidation reaction, while the molybdenum component can effectively regulate the interfacial electron distribution, optimize the adsorption behavior of reaction intermediates, and improve the overall conductivity and framework stability of the material. The synergistic effect of the two can effectively reduce the electrochemical reaction energy barrier and accelerate the interfacial charge transport efficiency. However, NiMoO4 alone still has significant performance shortcomings. On the one hand, the intrinsic conductivity of the material is poor, and the catalytic active sites are not fully exposed. On the other hand, during long-term electrocatalytic reactions, nanoparticle aggregation and electrode surface passivation are prone to occur, resulting in rapid decay of catalytic activity and a cycle life that cannot meet the requirements of practical applications.
[0004] Although NiMoO4-based functional materials have been extensively studied, their reaction mechanism in DMFC anode methanol oxidation catalytic systems remains poorly understood. Furthermore, research on strategies employing multi-metal synergistic modification combined with nitrogen doping to construct oxygen-rich vacancy defects, thereby simultaneously enhancing the catalytic activity and stability of NiMoO4-based materials for MOR, is still relatively scarce. Given the limitations of existing technologies, developing a modified nickel-molybdenum-based oxide anode catalyst that is simple to process, operates under mild conditions, can be prepared on a large scale, and possesses both high activity and high stability, has become a pressing technical challenge in this field. Summary of the Invention
[0005] To address the technical problems of insufficient active sites, poor intrinsic conductivity, and slow reaction kinetics in existing single NiMoO4 catalysts, and the difficulty of simultaneously improving catalytic activity and stability with existing modification strategies, this invention proposes an oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide, its preparation method, and its application.
[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:
[0007] A method for preparing oxygen-rich nitrogen-doped nickel-cobalt-molybdenum oxide (N-NiCoMoO) includes the following steps:
[0008] (1) Weigh out nickel salt, cobalt salt and molybdenum salt according to the proportion, add them to deionized water, and stir magnetically until completely dissolved and mixed evenly to obtain a mixed salt solution; transfer the mixed salt solution into a high-pressure reactor lined with polytetrafluoroethylene, then put in foamed nickel that has been pretreated by acid washing and degreasing, seal the reactor and place it in an oven, and carry out a hydrothermal reaction at 140-150 ℃ for 6-8 h; after the reaction is completed, cool naturally to room temperature, wash the product with deionized water and anhydrous ethanol alternately 3-5 times to remove surface impurities, and then dry it in a vacuum oven at 60 ℃ for 6 h to obtain nickel cobalt molybdenum oxide precursor.
[0009] (2) Place the nickel cobalt molybdenum oxide precursor prepared in step (1) at the downwind port of the ceramic boat, weigh a certain amount of nitrogen source and place it at the upwind port of the same ceramic boat, and transfer the ceramic boat to a high-temperature tube furnace; continuously introduce nitrogen or argon into the tube furnace as a protective atmosphere, raise the temperature to 400-500 ℃ at a heating rate of 3-5 ℃ / min, and hold at this temperature for 2-4 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide (N-NiCoMoO).
[0010] In step (1) above, the molar ratio of nickel salt, cobalt salt, and molybdenum salt is 1:1:(2-3), and the molar ratio is 1 for every 6 cm³. 2 The foamed nickel requires 0.5 mmol of nickel salt.
[0011] Furthermore, the nickel salt is at least one of nickel nitrate, nickel sulfate, and nickel chloride; the cobalt salt is at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride; and the molybdenum salt is sodium molybdate or ammonium molybdate.
[0012] Furthermore, the specific steps of the above-mentioned pickling and degreasing pretreatment are as follows: the foamed nickel is placed in 0.5-1 M hydrochloric acid, anhydrous ethanol and deionized water in sequence, and ultrasonically cleaned for 10-20 min respectively to remove the surface oxide layer and oil stains, and then dried for later use.
[0013] Furthermore, in step (2) above, every 6 cm 2 Nickel foam requires 0.3-1.3 g of nitrogen source.
[0014] Furthermore, in step (2) above, the nitrogen source is melamine or dicyandiamine.
[0015] Oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide was prepared using the above-described preparation method.
[0016] The above-mentioned oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxides are used in the methanol oxidation reaction at the anode of direct methanol fuel cells. Specifically, N-NiCoMoO is used as an anode catalyst in the MOR reaction at the anode of alkaline DMFCs.
[0017] The beneficial effects of this invention are:
[0018] (1) The N-NiCoMoO material of the present invention adopts a one-step hydrothermal combined annealing process, which can simultaneously realize nitrogen doping and oxygen vacancy construction. Nitrogen doping can form active nitrogen species such as pyridine nitrogen, pyrrole nitrogen and metal-nitrogen coordination bonds. The oxygen vacancy ratio of N-NiCoMoO is as high as 35.8%, which is significantly higher than the 18.8% of the undoped sample NiCoMoO. The oxygen vacancy, heterostructure and active nitrogen species form a synergistic effect, effectively regulate the electronic structure, optimize the adsorption / desorption balance of methanol and reaction intermediates, reduce the rate-determining energy barrier of the reaction, improve charge transport efficiency, and effectively alleviate the phenomenon of catalyst poisoning and deactivation.
[0019] (2) This invention further enhances the catalytic activity of N-NiCoMoO materials by introducing cobalt to construct a Ni-Mo-Co multi-component synergistic active center. Electrochemical test results show that in a 1 M KOH + 0.5 M CH3OH electrolyte system, the catalyst reaches 10 mA cm⁻¹. -2 The required potential for current density is only 1.310 V (vs. RHE), and the current density retention rate is 83.6% after continuous operation at a constant potential of 1.524 V (vs. RHE) for 12 h, demonstrating both excellent catalytic activity and long-term stability.
[0020] (3) The N-NiCoMoO material prepared by the present invention does not use precious metal raw materials throughout the process. The raw material cost is low, the preparation process is simple, the process repeatability is good, and it is easy to prepare on a large scale and promote industrial application. Attached Figure Description
[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0022] Figure 1 The X-ray diffraction (XRD) patterns of the materials obtained in Example 1 and Comparative Examples 1-3 are shown.
[0023] Figure 2 The images are scanning electron microscope (SEM) images of the materials obtained in Example 1 and Comparative Examples 1-2; wherein, (a) nickel cobalt molybdenum oxide precursor; (b) N-NiCoMoO; (c) N-NiMoO; (d) N-CoMoO.
[0024] Figure 3 The image shows a SEM image of the NiCoMoO material obtained in Comparative Example 3.
[0025] Figure 4 The image shows a transmission electron microscope (TEM) image of the material obtained in Example 1.
[0026] Figure 5 The X-ray photoelectron spectroscopy (XPS) spectra of the materials obtained in Example 1 and Comparative Example 3 are shown in detail; where (a) is the O 1s spectrum and (b) is the N 1s spectrum of N-NiCoMoO.
[0027] Figure 6 Comparison of MOR performance of the materials obtained in Examples 1-3 in 1 M KOH + 0.5 M CH3OH: (a) Scan rate of 50 mV s -1 (a) Cyclic voltammetry (CV) curves at a scanning speed of 5 mV / s; (b) Scanning speed of 5 mV / s -1 (c) Linear sweep voltammetry (LSV) curve; (d) Tafel slope curve; (e) Electrochemical impedance spectroscopy (EIS) curve.
[0028] Figure 7 Comparison of MOR performance of the materials obtained in Examples 1 and 4-7 in 1 M KOH + 0.5 M CH3OH: (a) Scan rate of 50 mV s -1 (a) CV curve at a scanning speed of 5 mV / s; (b) CV curve at a scanning speed of 5 mV / s-1 (c) LSV curve; (d) Tafel slope curve; (e) EIS curve.
[0029] Figure 8 Comparison of the catalytic performance of the materials obtained in Example 1 and Comparative Examples 1-3 in 1 M KOH + 0.5 M CH3OH solution: (a) Scan rate of 50 mV s -1 (a) CV curve at a scanning speed of 5 mV / s; (b) CV curve at a scanning speed of 5 mV / s -1 (c) LSV curve; (d) Tafel slope curve; (e) EIS curve.
[0030] Figure 9 The chronoamperometry (it) curves of the materials obtained in Example 1 and Comparative Examples 1-3 at a potential of 1.524 V (vs. RHE) in 1 M KOH + 0.5 M CH3OH solution are shown. Detailed Implementation
[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0032] The foamed nickel used in this invention was purchased from Huaxiong Environmental Protection Metal Materials, and its dimensions are 1.5 mm (thickness) * 300 mm * 1000 mm.
[0033] Example 1
[0034] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0035] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24 • 4H2O was added to 25 mL of deionized water and magnetically stirred until completely dissolved to obtain a mixed salt solution. The mixed salt solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and nickel foam (2 cm × 3 cm) that had been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water was added. After sealing, the reactor was placed in an oven and hydrothermally reacted at 150 °C for 6 h. After the reaction was completed, the reactor was naturally cooled to room temperature, the product was removed, and washed 4 times alternately with deionized water and anhydrous ethanol to remove residual impurities on the surface. Then it was placed in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0036] (2) Place 1.0 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0037] Example 2
[0038] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0039] (1) Mix 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1 mmol (NH4)6Mo7O 24 • Add 4H2O to 25 mL of deionized water and stir magnetically until completely dissolved to obtain a mixed salt solution. Transfer the mixed salt solution into a high-pressure reactor lined with polytetrafluoroethylene, and add nickel foam (2 cm × 3 cm) that has been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water. After sealing, place it in an oven and hydrothermally react at 150 °C for 6 h. After the reaction is completed, allow it to cool naturally to room temperature, remove the product, and wash it 4 times alternately with deionized water and anhydrous ethanol to remove surface impurities. Then place it in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0040] (2) Place 1.0 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0041] Example 3
[0042] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0043] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.5 mmol (NH4)6Mo7O 24• 4H2O was added to 25 mL of deionized water and magnetically stirred until completely dissolved to obtain a mixed salt solution. The mixed salt solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and nickel foam (2 cm × 3 cm) that had been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water was added. After sealing, the reactor was placed in an oven and hydrothermally reacted at 150 °C for 6 h. After the reaction was completed, the reactor was naturally cooled to room temperature, the product was removed, and washed 4 times alternately with deionized water and anhydrous ethanol to remove residual impurities on the surface. Then it was placed in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0044] (2) Place 1.0 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0045] Example 4
[0046] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0047] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24 • 4H2O was added to 25 mL of deionized water and magnetically stirred until completely dissolved to obtain a mixed salt solution. The mixed salt solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and nickel foam (2 cm × 3 cm) that had been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water was added. After sealing, the reactor was placed in an oven and hydrothermally reacted at 150 °C for 6 h. After the reaction was completed, the reactor was naturally cooled to room temperature, the product was removed, and washed 4 times alternately with deionized water and anhydrous ethanol to remove residual impurities on the surface. Then it was placed in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0048] (2) Place 0.3 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0049] Example 5
[0050] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0051] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24 • 4H2O was added to 25 mL of deionized water and magnetically stirred until completely dissolved to obtain a mixed salt solution. The mixed salt solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and nickel foam (2 cm × 3 cm) that had been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water was added. After sealing, the reactor was placed in an oven and hydrothermally reacted at 150 °C for 6 h. After the reaction was completed, the reactor was naturally cooled to room temperature, the product was removed, and washed 4 times alternately with deionized water and anhydrous ethanol to remove residual impurities on the surface. Then it was placed in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0052] (2) Place 0.4 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0053] Example 6
[0054] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0055] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24 • 4H2O was added to 25 mL of deionized water and magnetically stirred until completely dissolved to obtain a mixed salt solution. The mixed salt solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and nickel foam (2 cm × 3 cm) that had been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water was added. After sealing, the reactor was placed in an oven and hydrothermally reacted at 150 °C for 6 h. After the reaction was completed, the reactor was naturally cooled to room temperature, the product was removed, and washed 4 times alternately with deionized water and anhydrous ethanol to remove residual impurities on the surface. Then it was placed in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0056] (2) Place 0.8 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0057] Example 7
[0058] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0059] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24 • 4H2O was added to 25 mL of deionized water and magnetically stirred until completely dissolved to obtain a mixed salt solution. The mixed salt solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and nickel foam (2 cm × 3 cm) that had been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water was added. After sealing, the reactor was placed in an oven and hydrothermally reacted at 150 °C for 6 h. After the reaction was completed, the reactor was naturally cooled to room temperature, the product was removed, and washed 4 times alternately with deionized water and anhydrous ethanol to remove residual impurities on the surface. Then it was placed in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0060] (2) Place 1.3 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0061] Example 8
[0062] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0063] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24• Add 4H2O to 25 mL of deionized water and stir magnetically until completely dissolved to obtain a mixed salt solution. Transfer the mixed salt solution into a high-pressure reactor lined with polytetrafluoroethylene, and add nickel foam (2 cm × 3 cm) that has been ultrasonically cleaned for 15 min in sequence with 1 M hydrochloric acid, ethanol and deionized water. After sealing, place the reactor in an oven and hydrothermally react at 140 °C for 8 h. After the reaction is completed, allow it to cool naturally to room temperature, remove the product, and wash it 5 times alternately with deionized water and anhydrous ethanol to remove surface impurities. Then place it in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0064] (2) Place 1 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 400 ℃ at a heating rate of 3 ℃ / min and hold for 4 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0065] Example 9
[0066] The preparation method of oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide in this embodiment includes the following steps:
[0067] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24 • 4H2O was added to 25 mL of deionized water and magnetically stirred until completely dissolved to obtain a mixed salt solution. The mixed salt solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and nickel foam (2 cm × 3 cm) that had been ultrasonically cleaned for 15 min in sequence with 0.75 M hydrochloric acid, ethanol and deionized water was added. The reactor was sealed and placed in an oven for hydrothermal reaction at 145 °C for 7 h. After the reaction was completed, the reactor was naturally cooled to room temperature, the product was removed, and washed three times alternately with deionized water and anhydrous ethanol to remove surface impurities. Then it was placed in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0068] (2) Place 1 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 450 ℃ at a heating rate of 4 ℃ / min and hold for 3 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiCoMoO.
[0069] Comparative Example 1
[0070] The preparation method of a cobalt-free oxygen-rich nitrogen-doped nickel-molybdenum oxide according to this comparative example includes the following specific steps:
[0071] (1) Mix 0.5 mmol NiSO4·6H2O and 1.25 mmol (NH4)6Mo7O 24 • Add 4H2O to 25 mL of deionized water and stir magnetically until completely dissolved to obtain a mixed salt solution. Transfer the mixed salt solution into a high-pressure reactor lined with polytetrafluoroethylene, and add nickel foam (2 cm × 3 cm) that has been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water. After sealing, place it in an oven and hydrothermally react at 150 °C for 6 h. After the reaction is completed, allow it to cool naturally to room temperature, remove the product, and wash it 4 times alternately with deionized water and anhydrous ethanol to remove surface impurities. Then place it in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0072] (2) Place 1.0 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-NiMoO.
[0073] Comparative Example 2
[0074] The preparation method of a nickel-free oxygen-rich nitrogen-doped cobalt-molybdenum oxide according to this comparative example includes the following specific steps:
[0075] (1) Mix 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24 • Add 4H2O to 25 mL of deionized water and stir magnetically until completely dissolved to obtain a mixed salt solution. Transfer the mixed salt solution into a high-pressure reactor lined with polytetrafluoroethylene, and add nickel foam (2 cm × 3 cm) that has been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water. After sealing, place it in an oven and hydrothermally react at 150 °C for 6 h. After the reaction is completed, allow it to cool naturally to room temperature, remove the product, and wash it 4 times alternately with deionized water and anhydrous ethanol to remove surface impurities. Then place it in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0076] (2) Place 1 g of melamine at the upper air vent of the ceramic boat, and place the nickel cobalt molybdenum oxide precursor obtained in step (1) at the lower air vent of the same ceramic boat; then transfer the ceramic boat to a high-temperature tube furnace, continuously introduce argon gas as a protective atmosphere, raise the temperature to 500 ℃ at a heating rate of 5 ℃ / min and hold for 2 h; after calcination, cool naturally to room temperature to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, denoted as N-CoMoO.
[0077] Comparative Example 3
[0078] The specific steps of the method for preparing undoped nitrogen nickel-cobalt-molybdenum oxide in this comparative example are as follows:
[0079] (1) Add 0.5 mmol NiSO4·6H2O, 0.5 mmol Co(NO3)2·6H2O and 1.25 mmol (NH4)6Mo7O 24 • 4H2O was added to 25 mL of deionized water and magnetically stirred until completely dissolved to obtain a mixed salt solution. The mixed salt solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene, and nickel foam (2 cm × 3 cm) that had been ultrasonically cleaned for 15 min in sequence with 0.5 M hydrochloric acid, ethanol and deionized water was added. After sealing, the reactor was placed in an oven and hydrothermally reacted at 150 °C for 6 h. After the reaction was completed, the reactor was naturally cooled to room temperature, the product was removed, and washed 4 times alternately with deionized water and anhydrous ethanol to remove residual impurities on the surface. Then it was placed in a vacuum oven at 60 °C for 6 h to obtain the nickel cobalt molybdenum oxide precursor.
[0080] (2) The nickel cobalt molybdenum oxide precursor obtained in step (1) is placed in a ceramic boat and transferred to a high-temperature tube furnace. Argon gas is continuously introduced as a protective atmosphere, and the temperature is raised to 500 ℃ at a rate of 5 ℃ / min and held for 2 h. After calcination, it is naturally cooled to room temperature to obtain oxygen-rich nitrogen-doped nickel cobalt molybdenum oxide, denoted as NiCoMoO.
[0081] Implementation Results Example
[0082] The crystal structure, morphology, and catalytic methanol oxidation performance of the materials prepared in the examples and comparative examples were tested, and the specific results are as follows:
[0083] (1) Characterization and analysis of catalyst phase, morphology and structure
[0084] Figure 1The X-ray diffraction (XRD) patterns of the materials obtained in Example 1 and Comparative Examples 1-3 are shown. The main diffraction peaks of all samples highly coincide with the characteristic peaks of the nickel foam substrate (PDF#04-0850). The diffraction peaks appearing at 2θ = 26.3°, 36.8°, and 53.1° correspond to the (220), (400), and (332) crystal planes of NiMoO4 (PDF#45-0142), respectively; while the diffraction peaks at 2θ = 26.3° and 53.5° correspond to the (002) and (-531) crystal planes of CoMoO4 (PDF#21-0868). The XRD pattern of Example 1 (N-NiCoMoO) simultaneously contains characteristic diffraction peaks of both NiMoO4 and CoMoO4 phases, confirming the successful construction of the NiMoO4 / CoMoO4 heterojunction structure. Comparing the comparative examples, it can be seen that Comparative Example 1 (N-NiMoO) only shows the characteristic peaks of NiMoO4, with no diffraction signal of CoMoO4 phase, further indicating that the introduction of cobalt is the key to the formation of heterojunction, and can also construct Ni-Mo-Co multi-component synergistic active centers to enhance catalytic performance. The diffraction peak positions of Comparative Example 3 (NiCoMoO) are basically consistent with those of Example 1, indicating that the nitrogen doping process did not significantly change the crystal phase structure of the material.
[0085] Figure 2 SEM images of the nickel-cobalt-molybdenum oxide precursor, Example 1 (N-NiCoMoO), and Comparative Examples 1-2 (N-NiMoO, N-CoMoO). Precursor ( Figure 2 a) N-NiCoMoO ( Figure 2 b) and N-NiMoO ( Figure 2 c) all exhibit typical two-dimensional sheet-like structures, while N-CoMoO ( Figure 2 d) transforms into dense particle aggregates, indicating that the lack of cobalt will cause the lamellar structure to be unable to be maintained; Figure 3 The SEM image of Comparative Example 3 (NiCoMoO) shows that it completely transforms into a one-dimensional rod-like morphology. This confirms that without the addition of melamine, the precursor, lacking gas-phase protection and nitrogen doping modification, is prone to crystal plane reconstruction and lamellar agglomeration during high-temperature annealing, ultimately forming a more thermodynamically stable one-dimensional structure. In contrast, the NH3 / N2 gas-phase buffer layer generated by melamine decomposition, along with nitrogen doping, effectively suppresses high-temperature thermal shock and Oswald ripening, reduces the surface energy of high-energy crystal planes, and synergistically maintains the two-dimensional lamellar framework. The introduction of cobalt is key to achieving a stable lamellar morphology.
[0086] TEM images of the N-NiCoMoO material obtained in Example 1 are as follows: Figure 4 As shown. Figure 4Image a is a low-magnification TEM image, showing that the N-NiCoMoO material has a loose and porous microstructure formed by the stacking of fine nanosheets / nanoparticles. This structure can provide a large specific surface area, fully expose the catalytic active sites, and provide sufficient channels for electrolyte penetration and ion diffusion, which is beneficial to improving the kinetic performance of methanol oxidation reaction. Figure 4 b is a high-resolution HRTEM image, in which the lattice stripes with interplanar spacing of 0.292 nm and 0.332 nm correspond to the (400) and (220) crystal planes of NiMoO4, respectively; the lattice stripes with interplanar spacing of 0.334 nm correspond to the (002) crystal plane of CoMoO4, confirming that NiMoO4 and CoMoO4 phases exist simultaneously in the N-NiCoMoO catalyst, and the heterojunction structure is successfully constructed. Figure 4 c is the selected area electron diffraction (SAED) pattern of N-NiCoMoO. The pattern shows clear polycrystalline ring diffraction spots, which can be attributed to the (400), (220), and (66-1) crystal planes of NiMoO4 and the (002) and (-531) crystal planes of CoMoO4, respectively. This pattern is consistent with the interplanar spacing measured by HRTEM, further verifying the coexistence of the two-phase molybdate, which is consistent with the XRD phase analysis results.
[0087] The XPS fine spectra of Example 1 and Comparative Example 3 were analyzed, and the results are as follows: Figure 5 As shown. Figure 5 a is the high-resolution O 1s spectrum. The fine O 1s spectra of both samples can be fitted with three characteristic peaks, corresponding to lattice oxygen (O₂) and O₂. lat 530.6 eV), oxygen vacancy defect oxygen (V o 531.7 eV) and surface-adsorbed oxygen (O abs (532.9 eV). Quantitative analysis results showed that the oxygen vacancy characteristic peak area ratio in Comparative Example 3 (NiCoMoO) was 18.8%, while that in Example 1 (N-NiCoMoO) increased to 35.8%. Compared with Comparative Example 3, the oxygen vacancy characteristic peak area ratio in Example 1 was significantly increased, indicating that the oxygen vacancy defect concentration in the catalyst increased significantly after treatment with the nitrogen-doped high-temperature annealing process of this invention, confirming that N-NiCoMoO successfully constructed an oxygen-rich vacancy structure. The introduction of oxygen vacancies can effectively regulate the electronic structure of the catalyst surface, optimize the adsorption behavior of methanol molecules and reaction intermediates, reduce the reaction energy barrier, and thus significantly improve the activity and stability of the catalyst in methanol oxidation reaction. Figure 5b shows the N 1s high-resolution spectrum of Example 1 (N-NiCoMoO), which can be fitted to graphitic N, pyrrolic N, pyridinic N, metal-nitrogen coordination bonds (MN), and Mo 3p satellite peaks, indicating that nitrogen was successfully doped into the N-NiCoMoO material lattice, forming multiple active nitrogen species. Among them, pyridinic N, pyrrolic N, and metal-nitrogen coordination bonds can directly serve as highly active catalytic sites, accelerating the adsorption and activation of methanol molecules, and synergistically optimizing the catalytic MOR performance with oxygen vacancies.
[0088] (2) Comparative analysis of MOR catalytic performance
[0089] The materials obtained in Examples 1-7 and Comparative Examples 1-3 were used as electrode materials to test the electrocatalytic oxidation performance of methanol. The specific testing method was as follows: a three-electrode test system was assembled using the obtained materials as the working electrode, a platinum sheet as the counter electrode, and an Hg / HgO electrode as the reference electrode. CV, LSV, EIS, and it were tested. The electrolyte was a 1 M KOH + 0.5 M CH3OH solution. All test potentials were calibrated to the reversible hydrogen electrode (RHE) scale using the Nernst equation: E(RHE) = E(Hg / HgO) + 0.059 × pH + 0.098.
[0090] The MOR performance of the N-NiCoMoO catalysts obtained in Examples 1-3 is compared with that of... Figure 6 As shown. Figure 6 a is 50 mV s -1 The CV curves for Examples 1-3 show peak current densities of 335.5, 297.2, and 269.6 mA / cm² at 1.724 V (vs. RHE), respectively. -2 . Figure 6 b is 5 mV s -1 LSV curves at [time unspecified] (without iR compensation). In Examples 1-3, the materials catalyzed a MOR of 10 mA / cm². -2 The required potentials for the current densities are 1.344, 1.350, and 1.356 V (vs. RHE). Figure 6 c represents the Tafel curves for Examples 1-3. The Tafel slope of Example 1 is significantly smaller than that of the other examples, indicating the fastest reaction kinetics. Figure 6 d represents the EIS curves for Examples 1-3. The fitting results show that the charge transfer resistance (R) of Examples 1-3 is... ctThe interfacial charge transfer resistance values were 1.50 Ω, 1.72 Ω, and 1.62 Ω, respectively, with Example 1 exhibiting the lowest resistance. Based on the above results, the N-NiCoMoO catalyst prepared with a nickel salt, cobalt salt, and molybdenum salt molar ratio of 1:1:2.5 demonstrates significant advantages in catalytic activity, reaction kinetics, and charge transport performance, making it the preferred embodiment of this invention.
[0091] The MOR performance of the N-NiCoMoO catalysts obtained in Examples 1 and 4-7 is compared with that of... Figure 7 As shown. Figure 7 a is 50 mV s -1 The CV curve at 1.724 V (vs. RHE) shows the peak current density (335.5 mA cm⁻¹) in Example 1 (melamine dosage 1.0 g). -2 The dosage was significantly higher than that of other samples. Figure 7 b is 5 mV s -1 The LSV curves at the specified time (without iR compensation) show that appropriately increasing the amount of melamine can reduce the reaction potential and increase the current density, while the catalytic performance of MOR decreases significantly after the amount exceeds 1.0 g. Figure 7 c represents the Tafel curves for Examples 1 and 4-7. It can be observed that the Tafel slope for Example 1 is significantly smaller than that for the other examples, indicating the fastest reaction kinetics. Figure 7 d represents the EIS curves for Examples 1 and 4-7. The fitting results show that the R-value of Example 1 is... ct The N-NiCoMoO catalyst prepared with 1.0 g of melamine exhibits the lowest Ω value (1.50 Ω) and the lowest interfacial charge transport resistance. Overall, the results indicate that the N-NiCoMoO catalyst prepared with 1.0 g of melamine demonstrates the best catalytic performance for methanol oxidation.
[0092] The MOR performance of the N-NiCoMoO, N-NiMoO, N-CoMoO and NiCoMoO catalysts obtained in Example 1 and Comparative Examples 1-3 is compared. Figure 8 , Figure 9 As shown. Figure 8 a is 50 mV s -1 The CV curves at 1.724 V (vs. RHE) show that N-NiCoMoO achieves a peak current density of 335.5 mA cm⁻¹. -2 It is significantly higher than that of N-NiMoO (282.8 mA cm⁻¹). -2 ), N-CoMoO (268.4 mAcm) -2 ) and NiCoMoO (245.13 mA cm -2 ). Figure 8 b is 5 mV s -1The LSV curve at that time (iR compensation 90%). N-NiCoMoO reaches 10 mA cm⁻¹. -2 The current density requires the lowest potential, only 1.310 (vs. RHE). Figure 8 The Tafel slope of N-NiCoMoO in c is significantly smaller than that of the other comparative examples, indicating the fastest reaction kinetics. Figure 8 The EIS curve fitting results show that N-NiCoMoO has the smallest R0. ct With a value of 1.50 Ω, the interfacial charge transfer resistance is smaller, and the electron transport rate is faster. Figure 9 The it curve is shown at a potential of 1.524 V (vs. RHE). It can be seen that the current density retention rate of N-NiCoMoO after 12 h of continuous operation is 83.6%, which is significantly better than other comparative examples, demonstrating excellent catalytic stability.
[0093] In summary, the N-NiCoMoO catalyst exhibits comprehensive advantages in terms of activity, kinetics, charge transport, and stability.
[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide, characterized in that, The steps are as follows: (1) Dissolve nickel salt, cobalt salt and molybdenum salt in deionized water to obtain a mixed salt solution; immerse the foamed nickel that has been pretreated by acid washing and degreasing into the mixed salt solution for hydrothermal reaction, and after the reaction is completed, cool it naturally, wash it with deionized water and dry it to obtain nickel cobalt molybdenum oxide precursor; (2) The nickel cobalt molybdenum oxide precursor and nitrogen source obtained in step (1) are placed in a tube furnace and calcined under a protective atmosphere to obtain oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide.
2. The method of claim 1, wherein the oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide is prepared by the steps of: The molar ratio of the nickel salt, cobalt salt and molybdenum salt is 1 : 1 : (2-3), 0.5 mmol of nickel salt is needed for 6 cm 2 of foamed nickel. 3. The method of claim 2, wherein the oxygen-rich vacancy nitrogen-doped nickel cobalt molybdenum oxide is prepared by the following steps: The nickel salt is at least one of nickel nitrate, nickel sulfate, and nickel chloride; the cobalt salt is at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride; and the molybdenum salt is sodium molybdate or ammonium molybdate. 4. The method for preparing oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide according to any one of claims 1-3, characterized in that, The hydrothermal reaction is carried out at a temperature of 140-150 °C for 6-8 h.
5. The method for preparing oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide according to claim 4, characterized in that, In step (2), 0.3-1.3 g of nitrogen source is required per 6 cm 2 of foamed nickel.
6. The method for preparing oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide according to claim 5, characterized in that, The nitrogen source is melamine or dicyandiamine.
7. The method for preparing oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide according to claim 6, characterized in that, The calcination treatment is carried out at a temperature of 400-500 ℃ for 2-4 h, with a heating rate of 3-5 ℃ / min.
8. The method for preparing oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide according to claim 7, characterized in that, The protective atmosphere is nitrogen or argon.
9. Oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide prepared by the preparation method according to any one of claims 1-3 or 5-8.
10. The application of the oxygen-rich vacancy nitrogen-doped nickel-cobalt-molybdenum oxide according to claim 9 in the methanol oxidation reaction at the anode of a direct methanol fuel cell.