Preparation method and application of in-situ grown nickel ferrite nanoarray catalyst

Abstract

The present invention discloses a preparation method for in-situ growth of nickel ferrite nanoarray catalyst on nickel foam by a hydrothermal method, and uses the catalyst for electrocatalytic ammonia production. Nickel ferrite, as the most abundant and cheapest spinel, has good electrical conductivity and electrochemical stability and can be used in the field of electrocatalysis. Currently, nano-scale nickel ferrite can be synthesized by co-precipitation, emulsion, pyrolysis, solvent thermal and hydrothermal methods. Among them, solvent thermal and hydrothermal methods are widely used to synthesize catalysts because of their simplicity and large-scale synthesis. The present invention grows nickel ferrite nanoarrays in situ on a nickel foam substrate by a simple hydrothermal method, and directly uses the array as a cathode for electrocatalytic nitrogen synthesis of ammonia, avoiding the experimental error of ammonia synthesis that may be caused by the addition of nitrogen-containing chemical reagents such as urea, and achieves good results.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterial synthesis and electrocatalysis, and specifically relates to a synthesis method of a nickel ferrite nanoarray catalyst and its application in electrocatalytic ammonia production. Background Art

[0002] With the continuous development and advancement of modern science and technology, nanomaterials have become increasingly well-known. Nanomaterials refer to materials with at least one dimension in the nanometer range (1-100nm) or composed of nanomaterials as basic units. These materials primarily include nanoparticles (aggregates of particles 1-100nm), nanosolids (agglomerates of nanoparticles), and nanoassemblies (artificially assembled nanostructured material systems). These materials are widely used in various fields, including mechanical manufacturing, electronics and information technology, chemical and pharmaceutical industries, aerospace, and environmental protection. In the field of electrocatalysis, researchers often prepare nanoscale catalysts to achieve high reaction efficiency.

[0003] Nickel foam (NF), a transition metal-based material with excellent electrical conductivity and electrochemical stability, is widely used in battery electrodes, catalysts, and filters. Furthermore, the excellent dispersibility and high-temperature resistance afforded by the porous structure of nickel foam make it suitable for use as a substrate for catalyst loading via hydrothermal or solvothermal methods. This in-situ loading of the catalyst onto the nickel foam surface not only ensures uniform distribution and excellent conductivity, but also avoids the problems of traditional powdered catalysts that require adhesive dripping onto the electrode, which can cause detachment and reactant contamination.

[0004] Nickel ferrite (NiFe2O4), one of the most abundant and inexpensive spinels on Earth, is a typical soft ferrite material with excellent electrical conductivity and electrochemical properties, meeting the requirements for efficient electrocatalytic catalysts. Currently, nanoscale NiFe2O4 can be synthesized via coprecipitation, emulsion, pyrolysis, solvothermal, and hydrothermal methods. Solvothermal and hydrothermal methods are widely used for synthesizing electrocatalytic catalysts due to their simplicity and large-scale production. However, there have been no reports on the in situ synthesis of nanosized NiFe2O4 on nickel foam using the hydrothermal method, simply by adding iron salts.

[0005] Transition metal elements, particularly iron-nickel-based catalysts, are widely used in electrocatalysis, such as water electrolysis, electrocatalytic ammonia production, and electrocatalytic lignin synthesis, with satisfactory results. While iron-nickel oxides have been reported for electrocatalytic ammonia synthesis, the use of in-situ nickel ferrite nanoarrays supported on nickel foam (NiFe2O4 / NF) for ammonia synthesis has not been reported. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for synthesizing an in situ grown nickel ferrite nanoarray catalyst and its application in electrocatalytic ammonia production. Specifically, nickel foam is used as a nickel source and substrate, and nickel ferrite nanoarrays are in situ loaded on the nickel foam by a hydrothermal method. The nickel foam is directly used as a catalyst for electrocatalytic nitrogen to ammonia production, and good results have been achieved.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A method for synthesizing a nickel ferrite nanoarray catalyst and its application mainly include the following two steps: ① placing nickel foam and an iron-containing aqueous solution in a reactor and in situ loading the nickel ferrite nanoarray onto the nickel foam through a hydrothermal method; ② rinsing and drying the product, and directly using the obtained nickel foam loaded with the nickel ferrite nanoarray in situ as a cathode for electrocatalytic nitrogen production into ammonia.

[0009] The specific preparation method of the catalyst is:

[0010] First, the nickel foam is ultrasonically cleaned with acetone and 2-6 mol / L hydrochloric acid solution for 10-30 minutes to remove organic matter and oxides on the surface, and then cleaned with deionized water and ethanol, and vacuum dried for use; a piece of dried nickel foam is placed obliquely in a polytetrafluoroethylene liner, an iron-containing solution is poured into it, and the liner is sealed in a reactor; the reactor is placed in an electric blast drying oven, the temperature is set at 160°C to 320°C, and the reaction is carried out for 10-20 hours.

[0011] The iron-containing aqueous solution of the present invention is an aqueous solution of ferric nitrate.

[0012] The nickel foam processing method of the present invention is used to control the molar amount of added (Fe(NO3)3·6H2O) and reaction temperature and other parameters, which is conducive to obtaining an ultrathin nanosheet array with a diameter of 2 microns.

[0013] In step ①, the amount of iron salt added is 1.0 to 1.5 mmol;

[0014] Preferably, in step ①, the iron-containing aqueous solution is prepared by weighing 1.0 mmol of iron salt and dissolving it in 15 mL of deionized water to a final concentration of 0.033 mmol / L;

[0015] In step ①, the hydrothermal reaction temperature is 160° C. to 320° C.;

[0016] Preferably, in step ①, a nickel foam with a thickness of 1.0 mm and a 0.033 mmol / L ferric nitrate aqueous solution are placed in a reactor, the reaction temperature is 200° C., and the reaction is carried out for 10 hours, and the nickel ferrite nanoarray is in situ loaded onto the surface of the nickel foam by a hydrothermal method.

[0017] The cleaning in step ② refers to rinsing with deionized water 3 times;

[0018] Drying in step ② refers to drying in an electric blast drying oven at 80°C for 4 hours;

[0019] The nickel ferrite nano-array catalyst provided by the present invention is an ultra-thin nano-sheet array with a diameter of about 2 microns.

[0020] The present invention provides an application of a nickel ferrite nano-array catalyst for electrocatalytic reduction of nitrogen to produce ammonia.

[0021] The specific method of using the nickel ferrite nanoarray catalyst provided by the present invention for electrocatalytic reduction of nitrogen to produce ammonia is as follows:

[0022] The NiFe2O4 / NF prepared above was directly used as the cathode for cathode electrocatalytic nitrogen production of ammonia. By applying different potentials, the ammonia production and Faraday efficiency were calculated.

[0023] This invention directly uses NiFe2O4 / NF as electrodes for electrocatalytic nitrogen reduction to ammonia production, significantly improving the selectivity and rate of ammonia production. The nickel ferrite nanoarray catalyst provided by this invention features a simple and low-cost synthesis method, resulting in stable, uniformly sized nanosheets that significantly promote ammonia production.

[0024] Compared with the prior art, the present invention has the following advantages and effects:

[0025] 1. The preparation process of the green synthetic nickel ferrite nanosheets of the present invention does not require any additional chemical reagents other than the base nickel foam and iron salt, nor does it require expensive equipment. The operation is simple, easy, economical and environmentally friendly.

[0026] 2. The nickel ferrite nanoparticle array catalyst produced by this invention exhibits stable performance, uniform size, good conductivity, and electrochemical stability. Its application in electrocatalytic nitrogen-to-ammonia production significantly improves ammonia production rate and Faradaic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the X-ray diffraction (XRD) pattern of the nickel ferrite nanoarray catalyst prepared in Example 1 of the present invention;

[0028] Figure 2 This is an X-ray energy spectrum (EDS) diagram of the nickel ferrite nanoarray catalyst prepared in Example 1 of the present invention;

[0029] Figure 3 This is a scanning electron microscope (SEM) image of the nickel ferrite nanoarray catalyst prepared in Example 1 of the present invention;

[0030] Figure 4 This is a transmission electron microscope (TEM) image of the nickel ferrite nanoarray catalyst prepared in Example 1 of the present invention;

[0031] Figure 5 This is a Raman spectrum of the nickel ferrite nanoarray catalyst prepared in Example 1 of the present invention;

[0032] Figure 6 This is a scanning electron microscope (SEM) image of the nickel ferrite nanoarray catalyst prepared in Example 2 of the present invention;

[0033] Figure 7 This is a scanning electron microscope (SEM) image of the nickel ferrite nanoarray catalyst prepared in Example 3 of the present invention;

[0034] Figure 8 This is a scanning electron microscope (SEM) image of the nickel ferrite nanoarray catalyst prepared in Example 4 of the present invention;

[0035] Figure 9 This is a scanning electron microscope (SEM) image of the nickel ferrite nanoarray catalyst prepared in Example 5 of the present invention;

[0036] Figure 10 This is an efficiency diagram of the nickel ferrite nanosheet array catalyst prepared in Example 6 of the present invention for electrocatalytic ammonia production. DETAILED DESCRIPTION

[0037] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the following detailed description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0038] Example 1

[0039] The preparation of an in-situ grown nickel ferrite nanoarray catalyst comprises the following steps:

[0040] ① First, the foam nickel substrate was ultrasonically cleaned with acetone and 6 mol / L hydrochloric acid solution for 30 minutes to remove organic matter and oxides on the surface, then washed with deionized water and ethanol, and dried under vacuum at 60°C for later use; ② 0.5 mmol of ferric nitrate hexahydrate (Fe(NO3)3·6H2O) was dissolved in 15 ml of deionized water; ③ A piece of dried foam nickel was placed obliquely in a 20 ml polytetrafluoroethylene liner, the solution prepared in step ② was poured into it, and the liner was sealed in a reactor; ④ The reactor was placed in an electric forced air drying oven, set the temperature to 200°C, and the reaction was carried out for 10 hours; ⑤ The product was rinsed and dried to obtain NiFe2O4 / NF.

[0041] Characterization of the nickel ferrite nanoarray catalyst prepared above:

[0042] The prepared nickel ferrite nanoarray catalyst was characterized, and the XRD patterns were as follows: Figure 1 As shown, the diffraction peaks are sharp, indicating that the sample has a good inverse spinel structure. The diffraction peaks at 18.4°, 30.3°, 35.7°, 37.3°, 43.4°, 47.5°, 53.8°, 57.4°, 62.9°, and 74.6° correspond to the (111), (220), (311), (222), (400), (331), (422), (511), (440), and (533) crystal planes of NiFe2O4, respectively, which are completely consistent with the standard card JCPDS NO.10-0325, and there are no other diffraction peaks, indicating that relatively pure nano nickel ferrite is obtained. In addition, the diffraction peaks at 45.2°, 52.6°, and 76.5° correspond to the (111), (200), and (220) crystal planes of the substrate nickel foam, which is consistent with the standard card JCPDS NO.87-0712. Figure 2 The EDS graph confirmed that the synthesized material contained only three elements: Ni, Fe, and O, and the atomic ratio of the elements was approximately 1:2:4, which is consistent with the chemical formula of NiFe2O4. Figure 3 This is an SEM image of nano-nickel ferrite, which reveals that nickel ferrite nanosheets are evenly loaded on the surface of nickel foam. From the surface morphology, it presents a nanosheet structure. The average diameter of the nanosheet is about 500nm and the thickness is about 10nm. The nanosheets intersect with each other to form the final nanoarray. Figure 4 The TEM image further reveals the flaky structure of nano-NiFe2O4. Figure 5 The Raman spectrum shows that the peak shape of nickel ferrite nanoarrays loaded onto the surface of nickel foam as an electrode remains consistent before and after electrocatalytic ammonia production, proving the stability of its structure.

[0043] Example 2

[0044] The preparation of an in-situ grown nickel ferrite nanoarray catalyst comprises the following steps:

[0045] ① First, the foam nickel substrate was ultrasonically cleaned with acetone and 6 mol / L hydrochloric acid solution for 30 minutes to remove organic matter and oxides on the surface, then washed with deionized water and ethanol, and dried under vacuum at 60°C for later use; ② 1.0 mmol of ferric nitrate hexahydrate (Fe(NO3)3·6H2O) was dissolved in 15 ml of deionized water; ③ A piece of dried foam nickel was placed obliquely in a 20 ml polytetrafluoroethylene liner, the solution prepared in step ② was poured into it, and the liner was sealed in a reactor; ④ The reactor was placed in an electric forced air drying oven, set the temperature to 200°C, and the reaction was carried out for 10 hours; ⑤ The product was rinsed and dried to obtain NiFe2O4 / NF.

[0046] Characterization of the nickel ferrite nanoarray catalyst prepared above:

[0047] The prepared nickel ferrite nanoarray catalyst was characterized, and the SEM images were as follows: Figure 6 As shown, the size and morphology are basically the same as those in Example 1, proving that the amount of added iron salt has nothing to do with the morphology of the formed nickel ferrite nanoarray catalyst.

[0048] Example 3

[0049] The preparation of an in-situ grown nickel ferrite nanoarray catalyst comprises the following steps:

[0050] ① The nickel foam substrate was ultrasonically cleaned with acetone and 6 mol / L hydrochloric acid solution for 30 min to remove organic matter and oxides on the surface, then washed with deionized water and ethanol, and dried under vacuum at 60°C for later use; ② 1.0 mmol of ferric nitrate hexahydrate (Fe(NO3)3·6H2O) was dissolved in 15 ml of deionized water; ③ A piece of dried nickel foam was placed obliquely in a 20 ml polytetrafluoroethylene liner, the solution prepared in step ② was poured into it, and the liner was sealed in a reactor; ④ The reactor was placed in an electric forced air drying oven, set the temperature to 160°C, and the reaction was carried out for 10 h; ⑤ The product was rinsed and dried to obtain NiFe2O4 / NF.

[0051] Characterization of the nickel ferrite nanoarray catalyst prepared above:

[0052] The prepared nickel ferrite nanoarray catalyst was characterized, and the SEM images were as follows: Figure 7 As shown in FIG, when reacted at 160°C for 10 h, the NiFe2O4 formed is also in the form of flakes, but its diameter is about 5 μm and it is piled up together, which reduces the electrochemical active area.

[0053] Example 4

[0054] The preparation of an in-situ grown nickel ferrite nanoarray catalyst comprises the following steps:

[0055] ① First, the foam nickel substrate was ultrasonically cleaned with acetone and 6 mol / L hydrochloric acid solution for 30 minutes to remove organic matter and oxides on the surface, then washed with deionized water and ethanol, and dried under vacuum at 60°C for later use; ② 1.0 mmol of ferric nitrate hexahydrate (Fe(NO3)3·6H2O) was dissolved in 15 ml of deionized water; ③ A piece of dried foam nickel was placed obliquely in a 20 ml polytetrafluoroethylene liner, the solution prepared in step ② was poured into it, and the liner was sealed in a reactor; ④ The reactor was placed in an electric forced air drying oven, set the temperature to 180°C, and the reaction was carried out for 10 hours; ⑤ The product was rinsed and dried to obtain NiFe2O4 / NF.

[0056] Characterization of the nickel ferrite nanoarray catalyst prepared above:

[0057] The prepared nickel ferrite nanoarray catalyst was characterized, and the SEM images were as follows: Figure 8 As shown in Figure 3, when the temperature is changed to 180°C, a cross-nanoarray structure appears, but the distribution is uneven.

[0058] Example 5

[0059] The preparation of an in-situ grown nickel ferrite nanoarray catalyst comprises the following steps:

[0060] ① First, the foam nickel substrate was ultrasonically cleaned with acetone and 6 mol / L hydrochloric acid solution for 30 minutes to remove organic matter and oxides on the surface, then washed with deionized water and ethanol, and dried under vacuum at 60°C for later use; ② 1.0 mmol of ferric nitrate hexahydrate (Fe(NO3)3·6H2O) was dissolved in 15 ml of deionized water; ③ A piece of dried foam nickel was placed obliquely in a 20 ml polytetrafluoroethylene liner, the solution prepared in step ② was poured into it, and the liner was sealed in a reactor; ④ The reactor was placed in an electric forced air drying oven, set the temperature to 220°C, and the reaction was carried out for 10 hours; ⑤ The product was rinsed and dried to obtain NiFe2O4 / NF.

[0061] Characterization of the nickel ferrite nanoarray catalyst prepared above:

[0062] The prepared nickel ferrite nanoarray catalyst was characterized, and the SEM images were as follows: Figure 9 As shown in FIG. 2 , when the temperature is changed to 220° C., the morphology is basically consistent with that of Example 1 and Example 2, indicating that the temperature reaching above 200° C. has little effect on the morphology.

[0063] Example 6

[0064] The NiFe2O4 / NF prepared in Example 1 was used as a cathode for electrocatalytic nitrogen production into ammonia.

[0065] The specific application method is: 1×3cm 2 The nickel foam loaded with NiFe2O4 was cut into 1×1.5cm 2 , directly used as the working electrode, a saturated calomel electrode (SCE) as the reference electrode, and a platinum sheet as the counter electrode. The electrolytic cell was a typical three-electrode electrolytic cell, the electrochemical workstation was a Chenhua CH I 760E, and the electrolyte was a mixture of 15 mL of isopropanol and 15 mL of 0.1 mol / L phosphate buffer. During the electrolysis process, high-purity nitrogen with a purity of 99.999% was continuously introduced, and electrolysis was performed for 2 hours by applying different potentials.

[0066] After electrolysis, samples were taken to test ammonia production using the indophenol blue method;

[0067] Plot the ammonia production and Faraday efficiency at different potentials. Figure 10 This reflects the selectivity for nitrogen reduction at different potentials. When the applied potential is -0.65 V (vs. SCE), the maximum ammonia production and maximum Faradaic efficiency are achieved.

Claims

1. An application of an in-situ grown nickel ferrite nanoarray catalyst in electrocatalytic nitrogen production of ammonia, characterized in that: The in-situ grown nickel ferrite nanoarray catalyst is a nanoarray of ultrathin nickel ferrite nanosheets intersecting each other and uniformly grown on the surface of nickel foam. The preparation method of the in-situ grown nickel ferrite nanoarray catalyst includes the following steps: ① The nickel foam substrate was ultrasonically cleaned with acetone and 2-6 mol / L hydrochloric acid solution for 10-30 min respectively to remove organic matter and oxides on the surface, and then rinsed with deionized water and ethanol, and vacuum dried for later use; ② Dissolve an appropriate amount of iron salt - ferric nitrate hexahydrate in deionized water to a final concentration of 0.033mmol / L; ③ Place a dry nickel foam substrate at an angle in a polytetrafluoroethylene liner, pour the solution prepared in step ② into it, and seal the polytetrafluoroethylene liner in the reactor; ④ Place the assembled reactor in an electric blast drying oven, set the temperature to 200°C, and react for 10 hours; ⑤ After the reaction is completed, cool and dry naturally. After the temperature of the reactor drops to room temperature, remove the lining, rinse the residual material on the surface of the foam nickel substrate with deionized water, and dry it.

2. The use according to claim 1, characterized in that The thickness of the nickel foam substrate is 0.5 mm to 5 mm.

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