A molybdenum-doped and nickel-defect-rich nickel ferrite electrocatalyst, and a preparation method and application thereof

Abstract

This invention discloses a molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects, its preparation method, and its applications, belonging to the fields of electrocatalysis and new energy materials. The preparation method includes the following steps: dissolving a nickel source and an iron source in a mixed solvent composed of deionized water and glycerol, and stirring to obtain a transparent solution; adding a molybdenum source to the obtained solution and stirring continuously; adding KOH solution dropwise to the above mixed solution and stirring to form a colloidal precursor solution; transferring the precursor solution to a reaction vessel for hydrothermal reaction; after the reaction is completed, collecting the precipitate and washing, drying, and grinding it to obtain the catalyst. This invention utilizes glycerol-induced nickel vacancies to increase the number of active sites and improve conductivity, while the introduction of molybdenum atoms regulates the electron cloud density of Fe and Ni sites, optimizing their d-band centers. This catalyst exhibits extremely strong durability in continuous constant current testing, overcoming the disadvantage of traditional defect-type materials being prone to structural collapse.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis and new energy materials, specifically relating to a molybdenum-doped nickel ferrite electrocatalyst modified by a synergistic cation defect and atom doping strategy, its preparation method and application. Background Technology

[0002] With the increasing severity of the global energy crisis and environmental pollution, the development of efficient and clean renewable energy conversion technologies has become a focus of scientific research. Electrolysis of water to produce hydrogen is an effective means of obtaining high-purity hydrogen, but its efficiency is mainly limited by the oxygen evolution reaction (OER) at the anode. Because the OER involves a complex four-electron transfer process, its kinetics are extremely slow, requiring a high overpotential to overcome the energy barrier. Currently, although noble metal oxides (such as RuO2 and IrO2) exhibit excellent OER activity, their scarcity, high price, and poor long-term stability in alkaline electrolytes greatly limit their large-scale industrial application.

[0003] Spinel-type oxides (AB₂O₄, such as NiFe₂O₄) are considered among the most promising non-noble metal OER catalysts due to their high intrinsic activity, low cost, and environmental friendliness. However, pristine nickel ferrite still faces challenges such as insufficient exposure of active sites, poor electronic conductivity, and mismatch in adsorption energy for reaction intermediates. Existing modification methods mostly focus on defect engineering or elemental doping, making it difficult to simultaneously balance the catalyst's conductivity and intermediate adsorption kinetics. Therefore, how to achieve efficient heteroatomation while inducing lattice defects through a simple strategy, and elucidate its synergistic enhancement mechanism, is a key challenge and focus in the development of high-performance OER catalysts. Summary of the Invention

[0004] The main objective of this invention is to provide a molybdenum-doped nickel ferrite (denoted as Mo-NFO-VNi) electrocatalyst rich in nickel defects, its preparation method, and its application. This catalyst achieves efficient control of the electronic structure of NiFe2O4 by introducing glycerol as a vacancy inducer in a hydrothermal system and simultaneously introducing high-valence molybdenum (Mo) atoms, which significantly improves its oxygen evolution performance in an alkaline environment.

[0005] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows: A method for preparing a molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects includes the following steps: (1) Dissolve the nickel source and the iron source in a molar ratio of (1-4):(2-8) in a mixed solvent composed of deionized water and glycerol, and stir to obtain a transparent solution; (2) Add a molybdenum source to the solution obtained in step (1) and stir continuously; (3) Add KOH solution dropwise to the above mixed solution and stir to form a colloidal precursor solution; (4) The precursor solution is transferred to the reactor for hydrothermal reaction. After the reaction is completed, the precipitate is collected, washed, dried and ground to obtain a molybdenum-doped nickel ferrite (Mo-NFO-VNi) catalyst rich in nickel defects.

[0006] The nickel source is nickel nitrate hexahydrate, the iron source is ferric nitrate nonahydrate, and the molybdenum source is molybdenum pentachloride; preferably, the nickel source and the iron source are in a molar ratio of 1:2.

[0007] In step (1), the volume ratio of deionized water to glycerol is 1-2:1; preferably, the volume ratio of deionized water to glycerol is 1:1.

[0008] In step (3), the concentration of the KOH solution is 3 mol / L, and its volume is equal to the total volume of the mixed solvent in step (1).

[0009] In step (4), the hydrothermal reaction temperature is 150-170℃ and the reaction time is preferably 8-12 hours; preferably, the hydrothermal reaction temperature is preferably 160℃ and the reaction time is preferably 10 hours.

[0010] A molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects, prepared by the above method, has a spinel structure and a high concentration of nickel vacancies in the lattice, with molybdenum atoms occupying some lattice sites.

[0011] The above-mentioned molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects is used in the alkaline oxygen evolution reaction of water electrolysis.

[0012] In this invention, a mixed solution of deionized water and glycerol is used as the reaction solvent during the synthesis process, fully utilizing the principle of polyol-assisted hydrothermal synthesis. By introducing glycerol as a vacancy inducer, the abundant hydroxyl groups in its molecule are utilized to react with metal cations (Ni... 2+ Fe 3+ The strong chelation effect disrupts the conventional growth kinetics of the spinel lattice, successfully inducing a high concentration of cation defects (i.e., nickel vacancies, VNi) in the intrinsic structure of nickel ferrite (NiFe2O4). Simultaneously, by adding molybdenum pentachloride dropwise to the reaction system, high-valence molybdenum atoms effectively occupy lattice sites in the nickel ferrite. Under this synergistic regulation, the high-temperature, high-pressure hydrothermal environment promotes sufficient diffusion and lattice recombination between components, ultimately yielding a novel spinel-based electrocatalyst with synergistic cation defects and molybdenum doping.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention uses nickel ferrite, a non-noble metal that has shown great potential in the oxygen evolution reaction (OER), as the research matrix. Through a "dual-drive" strategy of defect engineering and heteroatom doping, its electronic structure was deeply optimized at the atomic scale. On the one hand, the introduction of nickel vacancies effectively disrupted the surface charge balance, greatly increasing the active site exposure density and enhancing the charge transfer rate. On the other hand, the doped molybdenum atoms induced a significant "electronic buffering mechanism," which, by dynamically adjusting the d-band centers of Ni and Fe sites during the reaction cycle, balanced the adsorption energy of reaction intermediates (OH*, O, and OOH) on the catalyst surface, thus breaking through the limitations of traditional scaling relationships. This synergistic effect not only solves the problem of poor intrinsic conductivity of traditional spinel oxides but also significantly improves the chemical stability of the material under strongly alkaline environments, enabling it to maintain excellent structural integrity even under long-term high-current operation. Attached Figure Description

[0014] Figure 1 This is a comparison of the LSV polarization curves of the samples obtained in Example 1 and Example 2 tested in 1 M KOH.

[0015] Figure 2 The Mo-NFO-VNi sample obtained in Example 1 was tested at 10 mA cm⁻¹. -2 Long-term timing potential test curve under current density.

[0016] Figure 3 The Raman spectrum of the sample obtained in Example 1 is obtained by analyzing the intensity changes and shifts of the A1g and Eg vibrational peaks.

[0017] Figure 4 The image shows the XRD diffraction pattern of the sample obtained in Example 1.

[0018] Figure 5 The scanning electron microscope (SEM) shows the micro-nano morphology of the Mo-NFO-VNi obtained in Example 1. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. 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. Example 1

[0020] This embodiment provides a method for preparing a molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects, specifically including the following steps: (1) Weigh 0.8 mmol nickel nitrate hexahydrate and 1.6 mmol ferric nitrate nonahydrate and dissolve them in a mixture of 12 mL deionized water and 12 mL glycerol.

[0021] (2) Weigh 5 mg of molybdenum pentachloride (MoCl5) into the solution and stir until completely dissolved. At this point, Mo atoms in the solution coordinate with Ni / Fe atoms.

[0022] (3) Add 24 mL of 3 M KOH solution dropwise to form a dark brown suspension.

[0023] (4) The precursor solution was placed in a reactor at 160 °C for 10 hours.

[0024] (5) The obtained powder was loaded onto carbon paper for electrochemical testing. In 1 M KOH solution, the sample reached 10 mA cm⁻¹. -2 The required overpotential is only 298 mV. Its charge transfer resistance Rct drops to 18.82 Ω, indicating a significant enhancement in conductivity. Stability testing lasted for 60 hours, during which the potential remained stable, and XRD structural analysis showed no significant change in the crystal phase after the reaction.

[0025] Comparative Example

[0026] This comparative example provides a method for preparing a nickel ferrite electrocatalyst rich in nickel defects, specifically including the following steps: (1) Weigh 0.8 mmol nickel nitrate hexahydrate and 1.6 mmol ferric nitrate nonahydrate, dissolve them in a mixed solvent of 12 mL deionized water and 12 mL glycerol, and stir continuously for 15 minutes until a transparent and uniform light green solution is formed. The introduction of glycerol is intended to interfere with the regular arrangement of metal cations through its steric hindrance effect and chelation effect, laying the foundation for the subsequent formation of vacancies.

[0027] (2) In this comparative example, molybdenum pentachloride (MoCl5) is not added, and the remaining components are the same as in step (1) to investigate the effect of a single cation defect on the intrinsic properties of nickel ferrite in the absence of heteroatom doping.

[0028] (3) While stirring vigorously, add 24 mL of 3 M KOH solution dropwise to the above solution. As the alkali solution is added, the solution color gradually deepens and turns into a dark brown suspension colloid. Continue stirring for 30 minutes to ensure that the nickel and iron precursors are fully precipitated and uniformly mixed.

[0029] (4) The obtained precursor suspension was transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and heat-treated at 160 °C for 10 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The precipitate was collected, washed by centrifugation, and dried under vacuum to obtain a black powder.

[0030] (5) The obtained NFO-VNi powder was loaded onto carbon paper for electrochemical testing.

[0031] In 1 M KOH electrolyte, the sample reached 10 mA cm⁻¹. -2 The overpotential required for the current density was significantly higher than that in Example 1, approximately 330-345 mV. Although the charge transfer resistance (Rct) decreased to some extent compared to the original NFO due to the introduction of nickel vacancies, the improvement in catalytic activity was limited due to the lack of the "electron buffering mechanism" regulation by molybdenum atoms. Furthermore, the potential fluctuations were more pronounced in long-term stability tests than in Example 1, demonstrating the necessity of the synergistic strategy in improving both activity and stability.

[0032] Figure 1 The polarization curves of the Mo-NFO-VNi catalyst obtained in Example 1 and the NFO-VNi catalyst obtained in Example 2 in 1 MKOH are shown; the values ​​are expressed at 10 mA cm⁻¹. -2 Using current density as a reference, subtracting the theoretical potential of the oxygen evolution reaction (1.23 V) from the obtained potential value yields its overpotential. Figure 1 It can be seen that Mo-NFO-VNi only requires an overpotential of 298 mV to reach 10 mA cm⁻¹. -2 With a current density (η10 = 298 mV), its catalytic activity is not only far superior to that of the single-defect type NFO-VNi, but also shows the potential to outperform conventional noble metal catalysts.

[0033] Figure 2 The figure shows the chronopotential curve of the catalyst obtained in Example 1 in 1 M KOH. The results show that Mo-NFO-VNi at 10 mA cm⁻¹ -2 After operating continuously for 60 hours at a current density, the voltage fluctuation was extremely small, with a retention rate approaching 100%, demonstrating that the material possesses excellent structural stability and chemical durability in a strongly alkaline oxygen evolution environment. The beneficial effects of this invention are: Figure 3 The Raman spectrum of the catalyst obtained in Example 1 shows that the relative intensity of the Eg peak in Mo-NFO-VNi is significantly reduced by comparing the intensity of the Alg and Eg vibration peaks. This indicates that the original lattice symmetry is broken due to the generation of nickel defects and the heterogeneous doping of molybdenum atoms, which induces severe lattice distortion. Such high unsaturation in the structure usually indicates the exposure of more active sites.

[0034] Figure 4The X-ray diffraction pattern of the molybdenum-doped nickel ferrite (Mo-NFO-VNi) with nickel defects obtained in Example 1 of this invention is shown to demonstrate the spinel structure of the samples and the lattice micro-distortion caused by the introduction of defects. It can be seen that all samples exhibit characteristic diffraction peaks consistent with standard spinel structure nickel ferrite at specific angles, and no other impurity peaks were found, proving that the introduction of molybdenum atoms did not change the crystal structure of NFO. Figure 5 The transmission electron microscope (SEM) image of Mo-NFO-VNi obtained in Example 1 shows that the catalyst exhibits a uniform nanoparticle morphology and clear lattice fringes, which intuitively demonstrates the successful modulation of material structure at the atomic scale by defect engineering.

[0035] (1) This invention adopts a "two-pronged" strategy, which utilizes glycerol-induced nickel vacancies (VNi) to increase the number of active sites and improve conductivity; at the same time, the introduction of molybdenum atoms regulates the electron cloud density of Fe and Ni sites and optimizes their d-band centers.

[0036] (2) Experimental and theoretical analysis shows that Mo doping can act as an “electron pool” to absorb or release charges at different reaction stages, balancing the adsorption energy of intermediates OH*, O*, and OOH* at the metal sites, thereby reducing the reaction energy barrier of the rate-determining step.

[0037] (3) In a 1 M KOH electrolyte, the Mo-NFO-VNi catalyst prepared in this invention reaches 10 mA cm⁻¹. -2 The overpotential at current density is only 298 mV, and the Tafel slope is significantly reduced, exhibiting an extremely fast dynamic response.

[0038] (4) The catalyst exhibits extremely strong durability in continuous operation constant current test, with almost no activity decay after running for more than 60 hours, overcoming the disadvantage of traditional defective materials being prone to structural collapse.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects, characterized in that... Includes the following steps: (1) Dissolve the nickel source and the iron source in a molar ratio of (1-4):(2-8) in a mixed solvent composed of deionized water and glycerol, and stir to obtain a transparent solution; (2) Add a molybdenum source to the solution obtained in step (1) and stir continuously; (3) Add KOH solution dropwise to the above mixed solution and stir to form a colloidal precursor solution; (4) The precursor solution is transferred to the reactor for hydrothermal reaction. After the reaction is completed, the precipitate is collected, washed, dried and ground to obtain a molybdenum-doped nickel ferrite (Mo-NFO-VNi) catalyst rich in nickel defects.

2. The method for preparing a molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects according to claim 1, characterized in that: The nickel source is nickel nitrate hexahydrate, the iron source is ferric nitrate nonahydrate, and the molybdenum source is molybdenum pentachloride.

3. The method for preparing a molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects according to claim 1, characterized in that: In step (1), the volume ratio of deionized water to glycerol is 1-2:

1.

4. The method for preparing a molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects according to claim 1, characterized in that: In step (3), the concentration of the KOH solution is 3 mol / L, and its volume is equal to the total volume of the mixed solvent in step (1).

5. The method for preparing a molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects according to claim 1, characterized in that: In step (4), the hydrothermal reaction temperature is 150-170℃, and the reaction time is preferably 8-12 hours.

6. A molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects, prepared by any one of claims 1-5, characterized in that: The catalyst has a spinel structure with a high concentration of nickel vacancies in the lattice, and molybdenum atoms occupy some lattice sites.

7. The application of the molybdenum-doped nickel ferrite electrocatalyst rich in nickel defects as described in claim 6 in the alkaline oxygen evolution reaction of water electrolysis.

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