Preparation method of NiFe-PBA electrocatalyst based on flame etching

Abstract

The invention discloses a preparation method of a NiFe-PBA electrocatalyst based on flame etching, NiFe-PBA can be prepared from nickel chloride hexahydrate, potassium ferricyanide and sodium citrate at room temperature, then flame etching post-treatment is performed through a spray gun, and the prepared electrocatalyst is expected to replace an Ir-based catalyst and a Ru-based catalyst to be used for an OER reaction. Oxygen vacancies are introduced through flame etching, so that the electron mobility is increased, the conductivity is improved, and the electrocatalytic activity is effectively improved. The synthesis method provided by the invention has the characteristics of simple process, low energy consumption, mild conditions and the like, has a wide application prospect in the field of electro-catalysis, and is suitable for large-scale production and application.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a method for preparing a NiFe-PBA electrocatalyst based on flame etching. Background Art

[0002] As energy crisis and environmental problems continue to intensify, the development of clean and sustainable energy to replace traditional fossil fuels continues to attract worldwide attention. Hydrogen has the advantages of high energy density, renewability, and storability, and is considered to be one of the ideal clean energy carriers. Among various hydrogen production technologies, electrochemical water splitting technology has become a hot topic as an efficient and promising method. Among the two half reactions of water electrolysis (i.e., hydrogen evolution reaction at the cathode and oxygen evolution reaction at the anode), the oxygen evolution reaction (OER) is a relatively complex four-electron transfer process with slow reaction kinetics and high theoretical potential (1.23 V vs. RHE), resulting in a large driving overpotential, which means that the catalyst must accelerate the reaction. Iridium-based catalysts and ruthenium-based catalysts have high activity for OER and can effectively reduce the reaction overpotential, but their high prices hinder their industrial application, thus requiring low-cost and high-yield electrocatalyst alternatives. Therefore, the development of low-cost and high-activity electrolytic catalysts is the main direction to overcome at present. After a long period of exploration and research, abundant transition metals such as Fe, Co, Ni, Cu, and Mo have entered the field of vision of researchers. These metals have good redox properties, and their properties can be improved and enhanced through chemical modification. Therefore, transition metals with variable valence states have aroused considerable interest in water electrolysis.

[0003] Prussian blue analogs (PBAs) are metal-organic framework compounds (MOFs) generated by the reaction of metal ions with transition metal cyanides. First of all, PBAs not only have nanoporous open skeleton structures and large specific surface areas, but also have the advantages of low cost and simple preparation. Secondly, PBAs have adjustable metal active centers and uniform catalytic centers, so they have broad application prospects in electrocatalytic water decomposition. In addition, due to the unique structural characteristics of PBAs, the electrocatalysts derived from them have large specific surface areas and uniform active centers, so PBAs are often used as precursors of electrocatalysts. However, the coordination of metal sites with cyanide groups leads to poor conductivity of PBAs, which results in poor catalytic activity of PBAs. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of high cost, limited reserves and disadvantageous commercial application of existing precious metal catalysts, and provide a method for preparing NiFe-PBA electrocatalyst based on flame etching. The flame-etched PBA electrocatalyst prepared by the present invention greatly increases its electron mobility and conductivity by introducing oxygen vacancies, thereby effectively improving the electrocatalytic activity. Moreover, the synthesis method provided by the present invention has the characteristics of simple process, low energy consumption, mild conditions, etc., and is suitable for large-scale production and application.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing a NiFe-PBA electrocatalyst based on flame etching comprises the following steps: Step (1), preparation of NiFe-PBA: Dissolving potassium ferrocyanide in pure water to obtain a potassium ferrocyanide solution; dissolving nickel chloride hexahydrate in pure water, adding sodium citrate under stirring, and adding the potassium ferrocyanide solution after stirring evenly to fully mix to obtain a mixed solution; placing the cleaned graphite sheet in the mixed solution, reacting in an oven, taking out and washing with pure water, and drying to obtain NiFe-PBA loaded on the graphite sheet; Step (2), flame etching NiFe-PBA: The NiFe-PBA obtained in step (1) is placed in a butane flame and treated with the flame core of the butane flame for 20-40 seconds to obtain a flame-etched NiFe-PBA.

[0006] Preferably, in step (1), the mass volume ratio of the nickel chloride hexahydrate, sodium citrate and pure water is 0.1-0.12 g: 0.19-0.21 g: 15 mL.

[0007] Preferably, in step (1), the mass volume ratio of potassium ferrocyanide to pure water is 0.09-0.1 g:15 mL; and the volume ratio of potassium ferrocyanide solution to nickel chloride mixed solution is 1:1.

[0008] Preferably, in step (1), the graphite sheet has a size of 1×4 cm and is washed with ethanol and pure water.

[0009] Preferably, in step (1), the solutions are mixed and then magnetically stirred for 5-10 minutes.

[0010] Preferably, in step (1), the temperature of drying the washed graphite sheet is 50°C-60°C.

[0011] Preferably, in step (1), the reaction time in the oven is 24-26 hours.

[0012] Preferably, in step (2), the butane flame core is used for treatment for 30 seconds.

[0013] Therefore, the present invention has the following beneficial effects: The method of the present invention provides a new flame etching method, which does not require continuous high-temperature calcination, and only requires a short treatment under a butane flame to prepare a flame-etched NiFe-PBA electrocatalyst with an increased oxygen vacancy content, thereby increasing electron mobility and improving conductivity. In addition, due to the high temperature during the reaction, the catalyst surface is partially pyrolyzed, so that the active sites are fully exposed, thereby greatly improving the oxygen evolution reaction performance. Moreover, the synthesis method provided by the present invention has the characteristics of simple process, low energy consumption, low price, safety and effectiveness, and is suitable for large-scale industrial production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is an XRD pattern of NiFe-PBA prepared by step (1) in Example 1 of the present invention and Example 1; Figure 2 are SEM images of different NiFe-PBAs prepared by the embodiments of the present invention, wherein (a) is the unetched NiFe-PBA prepared in step (1) of embodiment 1, (b) is the flame-etched NiFe-PBA prepared in embodiment 1, (c) is the flame-etched NiFe-PBA prepared in embodiment 2, and (d) is the flame-etched NiFe-PBA prepared in embodiment 3; Figure 3 This is a SEM image of NiFe-PBA prepared by Example 4 of the present invention after flame core etching for 20s; Figure 4 This is a SEM image of NiFe-PBA produced by Example 5 of the present invention after flame core etching for 40s; Figure 5 The Nyquist plot of NiFe-PBA obtained in step (1) of Example 1 of the present invention and Examples 1, 2 and 3 measured in 1M KOH; Figure 6 It is an overpotential diagram of NiFe-PBA obtained in step (1) of Example 1 of the present invention and Examples 1, 4 and 5 measured in 1M KOH. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with the accompanying drawings and specific implementation cases. It should be understood that these embodiments are only used to illustrate the present invention but not to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0016] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0017] There is no particular limitation on the purity of all raw materials in the present invention, and analytical reagent (AR) is preferably used in the present invention.

[0018] The equipment used in the present invention is not particularly limited, and can be a flask, beaker or reactor commonly used in the art, as well as other devices that can meet the technical solution of the present invention.

[0019] In order to further illustrate the present invention, the flame-etched NiFe-PBA electrocatalyst and the synthesis method thereof provided by the present invention are described in detail below in conjunction with the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0020] Embodiment 1: (1) Preparation of NiFe-PBA: Dissolve 0.107g nickel chloride hexahydrate and 0.099g potassium ferrocyanide in 15mL pure water and stir. Add 0.198g sodium citrate to the nickel chloride solution under stirring. After stirring evenly, add the potassium ferrocyanide solution to the nickel chloride solution and stir again for 10min. Put the cleaned 1x4cm graphite sheet and the above 30ml mixed solution into a sample bottle, react at 60℃ for 24h, take out and wash with pure water, dry in an oven at 60℃ to obtain NiFe-PBA loaded on the graphite sheet.

[0021] (2) Preparation of flame-etched NiFe-PBA: The obtained NiFe-PBA was treated with a butane flame (1970°C) of a spray gun for 30 seconds to obtain a flame-etched NiFe-PBA.

[0022] The NiFe-PBA prepared in this example and the flame-etched NiFe-PBA were subjected to XRD (X-ray Diffraction) tests, and the results are as follows: Figure 1 As shown. Figure 1 It can be seen that there is not much change in the structure of the NiFe-PBA electrocatalyst before and after flame etching. The characteristic peak intensity corresponding to NiFe-PBA after flame etching is reduced because oxygen vacancies are successfully generated.

[0023] Embodiment 2: (1) Preparation of NiFe-PBA: Dissolve 0.107g nickel chloride hexahydrate and 0.099g potassium ferrocyanide in 15mL pure water and stir. Add 0.198g sodium citrate to the nickel chloride solution under stirring. After stirring evenly, add the potassium ferrocyanide solution to the nickel chloride solution and stir again for 10min. Put the cleaned 1x4cm graphite sheet and the above 30ml mixed solution into a sample bottle, react at 60℃ for 24h, take out and wash with pure water, and dry at 60℃ to obtain NiFe-PBA loaded on the graphite sheet.

[0024] (2) Preparation of flame-etched NiFe-PBA: The obtained NiFe-PBA was treated with a butane flame (1300°C) of a spray gun for 30s to obtain a flame-etched NiFe-PBA.

[0025] Embodiment 3: (1) Preparation of NiFe-PBA: Dissolve 0.107g nickel chloride hexahydrate and 0.099g potassium ferrocyanide in 15mL pure water respectively and stir. Add 0.198g sodium citrate to the nickel chloride solution under stirring. After stirring evenly, add the potassium ferrocyanide solution to the nickel chloride solution and stir again for 10min. Put the cleaned 1x4cm graphite sheet and the above 30ml mixed solution into a sample bottle, react at 60℃ for 24h, take out and wash with pure water, and dry at 60℃ to obtain NiFe-PBA loaded on the graphite sheet.

[0026] (2) Preparation of flame-etched NiFe-PBA: The obtained NiFe-PBA was treated with a butane flame core (1000° C.) of a spray gun for 30 seconds to obtain a flame-etched NiFe-PBA.

[0027] Embodiment 4: (1) Preparation of NiFe-PBA: Dissolve 0.107g nickel chloride hexahydrate and 0.099g potassium ferrocyanide in 15mL pure water respectively and stir. Add 0.198g sodium citrate to the nickel chloride solution under stirring. After stirring evenly, add the potassium ferrocyanide solution to the nickel chloride solution and stir for 10min. Put the cleaned 1x4cm graphite sheet and the above 30ml mixed solution into a sample bottle, react at 60℃ for 24h, take out and wash with pure water, and dry at 60℃ to obtain NiFe-PBA loaded on the graphite sheet.

[0028] (2) Preparation of flame-etched NiFe-PBA: The obtained NiFe-PBA was treated with a butane flame core of a spray gun for 20 seconds to obtain a flame-etched NiFe-PBA.

[0029] Embodiment 5: (1) Preparation of NiFe-PBA: Dissolve 0.107g nickel chloride hexahydrate and 0.099g potassium ferrocyanide in 15mL pure water respectively and stir. Add 0.198g sodium citrate to the nickel chloride solution under stirring. After stirring evenly, add the potassium ferrocyanide solution to the nickel chloride solution and stir again for 10min. Put the cleaned 1x4cm graphite sheet and the above 30ml mixed solution into a sample bottle, react at 60℃ for 24h, take out and wash with pure water, and dry at 60℃ to obtain NiFe-PBA loaded on the graphite sheet.

[0030] (2) Preparation of flame-etched NiFe-PBA: The obtained NiFe-PBA was treated with a butane flame core of a spray gun for 40 seconds to obtain a flame-etched NiFe-PBA.

[0031] The NiFe-PBA prepared in step (1) of Example 1 and the flame-etched NiFe-PBA prepared in Examples 1-5 were subjected to SEM (scanning electron microscope) test to observe their morphologies. The results are as follows: Figure 2 and Figure 3 shown by Figure 2 It can be seen that the NiFe-PBA catalysts prepared by step (1) in Example 1 and Example 3 of the present invention are mostly block-shaped and uniform in size. The NiFe-PBA catalysts prepared in Example 1 and Example 2 are distorted in morphology due to high-temperature pyrolysis caused by the high flame temperature of the treatment.

[0032] Depend on Figure 3 and Figure 4 It can be seen that the flame-etched NiFe-PBA prepared by Example 4 and Example 5 of the present invention has a block-like morphology and is uniform in size.

[0033] The OER performance of the NiFe-PBA prepared in step (1) of Example 1 and the flame-etched NiFe-PBA prepared in Examples 1-5 was tested. The results are as follows: Figure 5 and Figure 6 shown by Figure 5 and Figure 6 It can be seen that among the catalysts prepared by step (1) in Example 1 and Examples 1-5 of the present invention, the NiFe-PBA obtained by flame core etching for 30 seconds has the smallest transfer resistance and the lowest overpotential, indicating that the catalyst under this condition requires the smallest additional energy for the reaction and has the best catalytic performance.

Claims

1. A method for preparing NiFe-PBA electrocatalyst based on flame etching, characterized in that: The preparation method comprises the following steps: Step (1), preparation of NiFe-PBA: Potassium ferrocyanide is dissolved in pure water to obtain a potassium ferrocyanide solution; nickel chloride hexahydrate is dissolved in pure water, sodium citrate is added under stirring conditions to obtain a nickel chloride solution, and then the potassium ferrocyanide solution is added and fully mixed to obtain a mixed solution; the cleaned graphite sheet is placed in the mixed solution, reacted in an oven, taken out and washed with pure water, and dried to obtain NiFe-PBA loaded on the graphite sheet; Step (2), flame etching NiFe-PBA: The NiFe-PBA obtained in step (1) is placed in a butane flame and treated with the flame core of the butane flame for 20-40 seconds to obtain a flame-etched NiFe-PBA.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass volume ratio of the nickel chloride hexahydrate, sodium citrate and pure water is 0.1-0.12 g: 0.19-0.21 g: 15 mL.

3. The preparation method according to claim 2, characterized in that: In step (1), the mass volume ratio of potassium ferrocyanide to pure water is 0.09-0.1 g:15 mL.

4. The preparation method according to claim 3, characterized in that: In step (1), the volume ratio of the potassium ferrocyanide solution to the nickel chloride solution is 1:1-1.

5.

5. The preparation method according to claim 1, characterized in that: In step (1), the graphite sheet is cleaned with ethanol and pure water.

6. The preparation method according to claim 1, characterized in that: In step (1), the solutions are mixed and then magnetically stirred for 5-10 minutes.

7. The preparation method according to claim 1, characterized in that: In step (1), the drying temperature of the washed graphite sheet is 50°C-60°C.

8. The preparation method according to claim 1, characterized in that: In step (1), the reaction time in the oven is 24-26 hours.

9. The preparation method according to claim 1, characterized in that: In step (2), the butane flame core is used for treatment for 30 seconds.

Images