A double-shell FeNi-O aerogel and its preparation method and application

Abstract

The present invention provides a double-shell FeNi-O aerogel, its preparation method, and application. The preparation steps of the FeNi-O aerogel are as follows: using a metal salt solution as a precursor and sodium borohydride as a reducing agent, FeNi hydrogel is prepared by a sol-gel method, which is then placed under normal temperature and pressure for auto-oxidation in air, and finally freeze-dried to obtain the FeNi-O aerogel. The method of the present invention is simple, green, and low-cost. The FeNi-O aerogel synthesized by this method has a double-shell hollow structure and exhibits excellent OER activity and good catalytic stability in alkaline electrolytes, achieving a refractive index of 50 mA cm with an overpotential of only 280 mV. ‑1 The current density is high and the catalytic stability is good (>50h). In addition, the present invention does not require high-temperature calcination and long-term hydrothermal treatment, and has the advantages of a simple and controllable preparation process, low cost, and good product performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and in particular relates to a double-shell FeNi-O aerogel and a preparation method and application thereof. Background Art

[0002] Faced with increasingly serious environmental pollution and energy crisis, it is urgent to find alternative clean energy. Electrochemical water decomposition to produce hydrogen is an effective way to develop green energy and alleviate the energy crisis. Compared with the hydrogen evolution reaction (HER) at the cathode, the oxygen evolution reaction (OER) at the anode during water electrolysis has slow kinetics, which greatly reduces the reaction rate and energy conversion efficiency, and is the key to restricting the development of the electrolysis water hydrogen production industry. The use of catalysts is an effective means to improve electrolysis efficiency. At present, precious metal-based catalysts such as IrO2 and RuO2 have high catalytic activity, but due to the scarcity of resources and high costs, their large-scale application in this field is limited. Therefore, it is crucial to develop green, highly active, abundant and cheap OER electrocatalysts.

[0003] In recent years, iron-nickel-based materials have attracted considerable attention due to their excellent catalytic activity and stability in alkaline electrolytes. However, iron-nickel oxides are typically prepared using methods such as calcination, hydrothermal methods, and laser ablation. These complex, costly, and polluting synthesis methods severely restrict their practical applications. Furthermore, some FeNi oxide catalysts exhibit significant agglomeration, resulting in a small specific surface area and a small number of active sites, resulting in a high initial overpotential, poor electrocatalytic activity, and poor durability. Therefore, further structural control is needed to avoid agglomeration and increase the density of exposed active sites.

[0004] Aerogels, due to their large specific surface area, high porosity and good electrical conductivity, show great application prospects in the field of electrocatalysis. By combining the excellent catalytic activity of iron-nickel oxide with the unique structure of aerogels, high-performance catalytic materials can be obtained. In addition, the hollow structure has large pores, which can reduce the ion transfer resistance and ion diffusion distance, and improve the mobility and diffusion of electrolytes, making it widely concerned. Currently, the preparation of complex hollow structures mostly uses the template method. However, this method is usually cumbersome and costly, and during the template removal process, the structure is prone to collapse, resulting in reduced aerogel quality. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a double-shell FeNi-O aerogel and its preparation method and application, so as to solve the technical problems of complex preparation process and low energy conversion efficiency of existing catalysts.

[0006] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for preparing a double-shell FeNi-O aerogel, comprising the following steps:

[0007] S1: Adding a metal salt solution to a reducing agent to react at room temperature, followed by aging for 3-4 days to prepare a FeNi hydrogel;

[0008] S2: The FeNi hydrogel was placed in air for oxidation for 28-32 hours, and then freeze-dried to obtain FeNi-O aerogel.

[0009] The beneficial effect of the above-mentioned further technical solution adopted by the present invention is that compared with FeNi hydrogel, FeNi-O aerogel forms more double-shell hollow structures. During the self-oxidation process, the transformation of the nanoparticles from the core-shell to the double-shell hollow structure is mainly due to the Kirkendall effect. Since Fe is more easily oxidized than Ni during the self-oxidation process, the internal Fe near the Ni shell will be preferentially oxidized to form an iron oxide shell, which will hinder the oxidation of Fe inside the core. Further reactions will continue through the interfacial diffusion of atoms. The outward diffusion rate of Fe is greater than the inward diffusion rate of oxygen, resulting in the appearance of Kirkendall voids inside, and ultimately forming a double-shell hollow structure.

[0010] On the basis of the above technical solution, the present invention can also be improved as follows:

[0011] Furthermore, during the aging process in step S1, the deionized water is replaced every 12 hours.

[0012] Furthermore, the solutes in the metal salt solution include anhydrous ferric chloride and NiCl2·6H2O, and the molar ratio of anhydrous ferric chloride to NiCl2·6H2O is 2-3:1; the reducing agent is a NaBH4 solution with a concentration of 0.1-1 mol / L.

[0013] Furthermore, the molar ratio of anhydrous ferric chloride to NiCl2·6H2O is 2:1; and the concentration of the NaBH4 solution is 0.1 mol / L.

[0014] Furthermore, the volume ratio of the metal salt solution to the NaBH4 solution is 1:3.

[0015] Furthermore, the reaction time in step S1 is 8-10 h.

[0016] Furthermore, the freezing temperature is -20 to -15°C, and the freezing time is 4 to 6 hours; the drying temperature is -50 to -45°C, and the drying time is 24 to 28 hours.

[0017] Furthermore, the freezing temperature is -20°C, and the freezing time is 5 hours; the drying temperature is -45°C, and the drying time is 26 hours.

[0018] The invention also discloses a FeNi-O aerogel prepared by a preparation method of the FeNi-O aerogel.

[0019] The invention also discloses the application of FeNi-O aerogel in oxygen evolution reaction by water electrolysis.

[0020] The present invention has the following beneficial effects:

[0021] (1) Compared with FeNi hydrogel, FeNi-O aerogel forms more double-shell hollow structures. The hollow structure has larger pores, which can reduce the ion transfer resistance and ion diffusion distance, improve the mobility and diffusion of the electrolyte, and strong electronic interaction occurs at the interface of the double shell, which can accelerate the electron transfer rate. These make the FeNi-O aerogel prepared by the present invention have excellent OER activity and stability, and have good application prospects in the field of electrocatalysis;

[0022] (2) The present invention converts FeNi hydrogel into FeNi-O aerogel by self-oxidation, without the need for long-term hydrothermal and high-temperature calcination, and the entire preparation process is carried out in air at room temperature and pressure, with simple process and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The XRD patterns of Example 1 and Comparative Examples 1-3 are shown;

[0024] Figure 2 Field emission scanning electron microscope images of Example 1 and Comparative Example 1;

[0025] Figure 3 Transmission electron microscope images of Example 1 and Comparative Example 1;

[0026] Figure 4 is the nitrogen physical adsorption isotherm of Example 1 and Comparative Example 1;

[0027] Figure 5 is the pore size distribution curve of Example 1 and Comparative Example 1;

[0028] Figure 6 The linear sweep voltammetry curves of Example 1 and Comparative Examples 1-3 are shown;

[0029] Figure 7 The Tafel diagrams of Example 1 and Comparative Examples 1-3 are shown;

[0030] Figure 8 Nyquist plots of Example 1 and Comparative Examples 1-3;

[0031] Figure 9 This is the stability (it) curve of Example 1. DETAILED DESCRIPTION

[0032] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0033] Example 1:

[0034] A method for preparing a double-shell FeNi-O aerogel comprises the following steps:

[0035] S1: Anhydrous ferric chloride and NiCl2·6H2O were dissolved in water at a molar ratio of 2:1 at room temperature to obtain a metal salt solution. The metal salt solution was then added to a 0.1 mol / L NaBH4 solution. After reacting for 8 hours, a black precipitate was produced. The solution was then aged for 3 days, and deionized water was replaced every 12 hours during the aging process to remove residual impurities, thereby preparing FeNi hydrogel. The volume ratio of the metal salt solution to the NaBH4 solution was 1:3.

[0036] S2: FeNi hydrogel was oxidized in air for 28 h, then frozen at -20 °C for 5 h, and then dried at -45 °C for 26 h to prepare FeNi-O aerogel.

[0037] Example 2:

[0038] A method for preparing a double-shell FeNi-O aerogel comprises the following steps:

[0039] S1: Anhydrous ferric chloride and NiCl2·6H2O were dissolved in water at a molar ratio of 3:1 at room temperature to obtain a metal salt solution. The metal salt solution was then added to a 1 mol / L NaBH4 solution. A black precipitate was produced after 10 hours of reaction. The solution was then aged for 4 days, with deionized water replaced every 12 hours during the aging process to remove residual impurities, to produce FeNi hydrogel. The volume ratio of the metal salt solution to the NaBH4 solution was 1:3.

[0040] S2: FeNi hydrogel was oxidized in air for 32 h, then frozen at -15 °C for 4 h, and then dried at -50 °C for 28 h to prepare FeNi-O aerogel.

[0041] Example 3:

[0042] A method for preparing a double-shell FeNi-O aerogel comprises the following steps:

[0043] S1: Anhydrous ferric chloride and NiCl2·6H2O were dissolved in water at a molar ratio of 2:1 at room temperature to obtain a metal salt solution. The metal salt solution was then added to a 0.5 mol / L NaBH4 solution. A black precipitate was produced after 9 hours of reaction. The solution was then aged for 3.5 days, with deionized water replaced every 12 hours during the aging process to remove residual impurities, to produce FeNi hydrogel. The volume ratio of the metal salt solution to the NaBH4 solution was 1:3.

[0044] S2: FeNi hydrogel was oxidized in air for 30 h, then frozen at -17 °C for 6 h, and then dried at -47 °C for 24 h to prepare FeNi-O aerogel.

[0045] Comparative Example 1:

[0046] A method for preparing FeNi aerogel comprises the following steps:

[0047] S1: Anhydrous ferric chloride and NiCl2·6H2O were dissolved in water at a molar ratio of 2:1 at room temperature to obtain a metal salt solution. The metal salt solution was then added to a 0.1 mol / L NaBH4 solution. After reacting for 8 hours, a black precipitate was produced. The solution was then aged for 3 days, and deionized water was replaced every 12 hours during the aging process to remove residual impurities, thereby preparing FeNi hydrogel. The volume ratio of the metal salt solution to the NaBH4 solution was 1:3.

[0048] S2: The FeNi hydrogel was frozen at -20 °C for 5 h and then dried at -45 °C for 26 h to prepare the FeNi aerogel.

[0049] Comparative Example 2:

[0050] A method for preparing Fe-O aerogel comprises the following steps:

[0051] S1: Anhydrous ferric chloride was dissolved in water at room temperature to obtain a metal salt solution, which was then added to a 0.1 mol / L NaBH4 solution for 8 h, followed by aging for 3 d. During the aging process, deionized water was replaced every 12 h to remove residual impurities, thereby preparing an Fe hydrogel. The volume ratio of the metal salt solution to the NaBH4 solution was 1:3.

[0052] S2: Fe hydrogel was oxidized in air for 28 h, then frozen at -20 °C for 5 h, and then dried at -45 °C for 26 h to prepare Fe-O aerogel.

[0053] Comparative Example 3:

[0054] A method for preparing a Ni-O aerogel comprises the following steps:

[0055] S1: NiCl2·6H2O was dissolved in water at room temperature to obtain a metal salt solution. The metal salt solution was then added to a 0.1 mol / L NaBH4 solution for 8 h, followed by aging for 3 d. During the aging process, deionized water was replaced every 12 h to remove residual impurities, thereby preparing a Ni hydrogel. The volume ratio of the metal salt solution to the NaBH4 solution was 1:3.

[0056] S2: Ni hydrogel was oxidized in air for 28 h, then frozen at -20 °C for 5 h, and then dried at -45 °C for 26 h to prepare Ni-O aerogel.

[0057] Experimental example:

[0058] The aerogels prepared in Example 1 and Comparative Examples 1-3 were used as working electrodes, and Ag / AgCl and graphite rods were used as reference electrodes and counter electrodes, respectively. Electrochemical performance tests were performed using a standard three-electrode system in an alkaline electrolyte.

[0059] Result analysis:

[0060] Figure 1 The XRD patterns of Example 1 and Comparative Examples 1-3 show that compared with FeNi aerogel, the peak intensity corresponding to Fe2O3 in FeNi-O aerogel increases, and the characteristic peaks of Fe and Ni are significantly weakened or even disappear. This may be due to the formation of iron and nickel oxides. A new characteristic peak of α-Ni(OH)2 appears at 11.3° in FeNi-O aerogel, indicating that the number of active sites available for nickel oxidation increases. However, no peaks attributable to NiO are observed in the figure. X The obvious characteristic peaks are attributed to the formation of an amorphous structure during the auto-oxidation process. In addition, small characteristic peaks corresponding to Fe3O4 appear at 30°, 35.4°, 56.8°, and 62.5°. The Fe-O aerogel shows characteristic peaks of Fe2O3, Fe3O4, FeOOH, and Fe. The Ni-O aerogel shows typical broad diffraction peaks without any sharp diffraction peaks, indicating that an amorphous structure is formed during the process.

[0061] Figure 2 The scanning electron microscope images of Example 1 and Comparative Example 1 show that both FeNi aerogel and FeNi-O aerogel exhibit nanoparticles ( Figure 2 a) and two-dimensional nanosheets ( Figure 2 b) Two forms, granular nanoparticles aggregate into chains. FeNi-O aerogel presents a three-dimensional porous network structure ( Figure 2 c), the 2D nanosheet and nanoparticle morphologies can still be observed ( Figure 2 d).

[0062] Figure 3is a transmission electron microscope image of Example 1 and Comparative Example 1, FeNi aerogel ( Figure 3 a) and FeNi-O aerogel ( Figure 3 b) All of them present three morphologies: core-shell nanoparticles, hollow nanoparticles and two-dimensional nanosheets ( Figure 3 Compared with FeNi aerogels, FeNi-O aerogels contain more amorphous double-shell hollow structures. The hollow structures have larger pores, which can reduce ion transfer resistance and ion diffusion distance, improve electrolyte mobility and diffusion, and effectively alleviate the volume expansion problem caused by ion circulation and shuttle, thereby improving electrochemical stability. Strong electronic interactions occur at the double-shell interface, which can accelerate electron transfer rate. The amorphous structure has more unsaturated active sites and defects, which leads to faster oxygen evolution kinetics.

[0063] Figure 4 is the nitrogen physical adsorption isotherm of Example 1 and Comparative Example 1, Figure 5 is the pore size distribution curve. The specific surface areas of FeNi and FeNi-O aerogels are 45.02 cm 2 g -1 and 74.276cm 2 g -1 , and the average pore size is 0.082cm 3 g -1 and 0.1888cm 3 g -1 Compared with FeNi, FeNi-O aerogel has a larger BET surface area and pores, which is due to the fact that FeNi-O aerogel has more double-shell hollow nanoparticles, which not only increases the contact area of ​​the electrode-electrolyte interface but also provides sufficient active sites for the reaction.

[0064] Figure 6 The linear sweep voltammetric curves of Example 1 and Comparative Examples 1-3 are shown. The FeNi-O aerogel is -1 The OER overpotential at a current density of 280 mV is significantly better than that of FeNi (370 mV), Ni-O (450 mV) and Fe-O (620 mV).

[0065] Figure 7 The Tafel plots of Example 1 and Comparative Examples 1-3 show that the Tafel slope of the FeNi-O aerogel is 32.5 mV dec. -1 , less than FeNi(66.1mV dec -1 )、Ni-O(129.8mV dec -1 ) and Fe-O (118.5mV dec-1 ), the smaller the Tafel slope, the faster the reaction kinetics.

[0066] Figure 8 The Nyquist plots of Example 1 and Comparative Examples 1-3 are shown. The charge transfer ability of the catalyst is evaluated by the Nyquist plot. Compared with FeNi, Fe-O and Ni-O aerogels, FeNi-O aerogel shows a small semicircle, indicating that it has the smallest charge transfer resistance (Rct) and faster charge transfer ability.

[0067] Figure 9 This is the stability test diagram of Example 1. The FeNi-O aerogel is tested at 50 mA cm -1 The stability test was carried out for 50 h at a current density of 1.5 GHz, and the results showed only slight degradation, which indicates that the FeNi-O aerogel has excellent long-term durability.

[0068] The above results show that the FeNi-O aerogel prepared in the present invention has excellent OER performance.

[0069] 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 in the scope of protection of the present invention.

Claims

1. A method for preparing a double-shell FeNi-O aerogel, characterized in that: The following steps are involved: S1: adding a metal salt solution to a reducing agent at room temperature for reaction for 8-10 hours, and then aging for 3-4 days to prepare a FeNi hydrogel; the solute in the metal salt solution includes anhydrous ferric chloride and NiCl2·6H2O, and the molar ratio of the anhydrous ferric chloride to NiCl2·6H2O is 2-3:1; the reducing agent is a NaBH4 solution with a concentration of 0.1-1 mol / L; and the volume ratio of the metal salt solution to the NaBH4 solution is 1:3; S2: The FeNi hydrogel is placed in air for oxidation for 28-32 hours, and then freeze-dried to obtain FeNi-O aerogel; the freezing temperature is -20~-15°C, and the freezing time is 4-6 hours; the drying temperature is -50~-45°C, and the drying time is 24-28 hours.

2. The method for preparing FeNi-O aerogel according to claim 1, wherein: During the aging process in step S1, the deionized water is replaced every 12 hours.

3. The method for preparing FeNi-O aerogel according to claim 1, wherein: The molar ratio of the anhydrous ferric chloride to NiCl2·6H2O is 2:1; the concentration of the NaBH4 solution is 0.1 mol / L.

4. The method for preparing FeNi-O aerogel according to claim 1, wherein: The freezing temperature is -20°C, and the freezing time is 5 hours; the drying temperature is -45°C, and the drying time is 26 hours.

5. FeNi-O aerogel prepared by the method for preparing FeNi-O aerogel according to any one of claims 1 to 4.

6. Use of the FeNi-O aerogel according to claim 5 in oxygen evolution reaction by water electrolysis.

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