Preparation method and application of feather-shaped NiFe-PBA

Abstract

The invention discloses a method for preparing a feather-shaped Prussian blue-based material NiFe-PBA by adopting a hydrothermal method. According to the method, a hydrothermal method is used, a sodium nitroprusside (Na3Fe [(CN) 5NO]) solution is used as a solvent, and then clean foamed nickel is added. Reacting for 4 hours at the high temperature of 160 DEG C; the feather-shaped NiFe-PBA catalyst with different sizes is prepared by regulating and controlling the concentration of a sodium nitroprusside solution in an experiment, and the catalyst has excellent urea oxidation reaction performance (UOR). In an experiment, the synthesized feather-shaped NiFe-PBA-X (X = 0.005, 0.01, 0.05, 0.1, mol dm <-3 >) catalyst is synthesized and then is washed with water and ethanol respectively, finally, the catalyst is dried in a drying oven at 40 DEG C for 6 hours, and the catalyst is taken out and used for a performance test of electro-oxidation urea.

Description

Technical Field

[0001] The present invention belongs to the field of nanomaterials, and more specifically, relates to a preparation method of feather-like nickel-iron Prussian blue NiFe-PBA and its use for electro-oxidation of urea. Background Art

[0002] In recent years, renewable hydrogen energy, as a clean energy source, has received increasing attention. Renewable hydrogen energy can be produced in various ways and, as a renewable energy source, helps to alleviate the energy shortage problem. Hydrogen is an ideal alternative to fossil energy and can be produced by electrochemically decomposing water. This technology is an attractive advanced technology for developing storable green fuels. Therefore, there is an urgent need for electrocatalysts that are efficient, energy-saving, multifunctional, and durable for hydrogen energy production. By adding small organic molecules (hydrazine hydrate, urea, amine, glucose, etc.) with low activation barriers to electrocatalytic water decomposition and replacing it with the oxidation reaction of small molecules, not only can the anodic reaction of electrocatalytic water decomposition be optimized, but also the cell voltage for hydrogen production by electrolyzing water can be reduced. The common urea oxidation reaction is one of such anodic reactions. Using UOR with a theoretical potential of only 0.37 V (vs. RHE) instead of OER with a theoretical potential of 1.23 V (vs. RHE) is an effective method to reduce the required potential and total energy cost. Among the UOR catalysts studied, Ni-based materials such as nickel-containing Prussian blue analogues NiFe-PBA have unique advantages.

[0003] There are various methods for synthesizing nickel-containing Prussian blue analogue NiFe-PBA powder, but there are multiple difficulties in preparing high-performance NiFe-PBA grown in situ on a foam substrate. First, the synthetic methods for in situ growth are relatively few, and the in situ growth conditions are relatively harsh. Second, the control of synthesis conditions. The synthesis of NiFe-PBA usually needs to be carried out at a specific temperature and time to ensure the purity and crystallinity of the product. Too high a temperature or too long a reaction time may lead to side reactions or product decomposition. Third, in terms of controlling the crystallinity and morphology of the product, different NiFe-PBA morphologies can be prepared currently, such as nanocubes and nanowires. The morphology of the product (such as nanoparticles, nanosheets, etc.) has a significant impact on its application performance. How to control the synthesis conditions to obtain an ideal morphology is a challenge. Fourth, the stability and durability of the product. NiFe-PBA may undergo oxidation or decomposition in air or aqueous solution, affecting its long-term stability. In electrochemical applications, the durability of NiFe-PBA is a key issue, and how to improve its stability is a research difficulty. Summary of the Invention

[0004] The object of the present invention is to synthesize NiFe-PBA with different loadings. The oxidant used is sodium nitroprusside (Na 3 Fe[(CN)5 NO]), the reducing agent is elemental nickel derived from copper foam. The solvent is deionized water and no additional surfactant is required. This liquid-phase synthesis is carried out in a reaction kettle, with a simple procedure and low cost, having practical applicability. The present invention is achieved through the following technical solutions:

[0005] A preparation method of feather-like NiFe-PBA is as follows:

[0006] S1: Dissolve a certain amount of sodium nitroprusside (Na 3 Fe[(CN) 5 NO]) in 60 mL of deionized water by ultrasonic treatment to obtain solution A. Then stir solution A at room temperature for 30 min and transfer it to a reaction kettle.

[0007] S2: Ultrasonically wash a 1 cm * 1 cm nickel foam with hydrochloric acid, ethanol, acetone, and water for 5 min each to obtain a nickel foam B with a clean surface and no dirt.

[0008] S3: Transfer nickel foam B into solution A in the reaction kettle and react at 160 °C for 4 h. In the high-temperature reaction kettle, the nickel foam substrate reacts fully with sodium nitroprusside, and then the obtained NiFe-PNA is in-situ grown on the nickel foam substrate. After the reaction, the nickel foam B loaded with the sample is washed repeatedly with deionized water and ethanol and dried in an oven at 40 °C for 6 h to recover a feather-like NiFe-PBA.

[0009] Further, in step S1, the mass of sodium nitroprusside (Na 3 Fe[(CN) 5 NO]) is 89 mg, 179 mg, 894 mg, or 1788 mg.

[0010] Further, sodium nitroprusside (Na 3 Fe[(CN) 5 NO]) in step S1 is both an oxidizing agent and a complexing agent.

[0011] Further, the exposed nickel foam B in step S2 is both a reducing agent and a carrier for in-situ growth of the electrode material.

[0012] An application of the feather-like NiFe-PBA, where the feather-like NiFe-PBA is used for performance testing of urea electrooxidation.

[0013] Compared with the prior art, the present application has the following effects:

[0014] There are various preparation methods for the laboratory preparation of nickel-iron Prussian blue analogues (NiFe-PBA), such as hydrothermal method, solvothermal method, electrodeposition method, chemical precipitation method, template method, etc. In this application, the hydrothermal method is used to synthesize NiFe-PBA / NF. Under hydrothermal conditions, first, the ideal morphology, i.e., feather-like NiFe-PBA, can be obtained; second, because the synthesis conditions of NiFe-PBA in-situ grown on nickel foam are harsh, and in-situ growth cannot occur below 100 °C; third, the NiFe-PBA / NF synthesized by the hydrothermal method has the advantages of high product crystallinity, controllable morphology, and high purity. In this experiment, by controlling the reaction concentration, the size and loading amount of the feather-like Prussian blue are affected. A low concentration of sodium nitroprusside usually results in smaller feather-like Prussian blue, while a high concentration of sodium nitroprusside will yield relatively larger feather-like Prussian blue. In this application, the mass of sodium nitroprusside (Na 3 Fe[(CN) 5 NO]) is selected as 89 mg, 179 mg, 894 mg, or 1788 mg, and the obtained concentration of sodium nitroprusside is moderate. The concentration of the sodium nitroprusside solution is 0.2 - 6 mmol. The performance of the samples synthesized by adding more than 6 mmol of sodium nitroprusside will not improve, and NiFe-PBA with this morphology cannot be synthesized with less than 0.2 mmol of sodium nitroprusside. This method has a certain degree of flexibility and controllability for the preparation of feather-like NiFe-PBA with different sizes and good dispersion. Brief Description of the Drawings

[0015] Figure 1 It is a scanning electron microscope (SEM) image of the feather-like NiFe-PBA electrode material with a length of about 6.89 μm prepared by the present invention.

[0016] Figure 2 It is a scanning electron microscope (SEM) image of the feather-like NiFe-PBA electrode material with a length of about 8.18 μm prepared by the present invention.

[0017] Figure 3 It is a scanning electron microscope (SEM) image of the feather-like NiFe-PBA electrode material with a length of about 8.42 μm prepared by the present invention.

[0018] Figure 4 It is a scanning electron microscope (SEM) image of the feather-like NiFe-PBA electrode material with a length of about 8.23 nm prepared by the present invention.

[0019] Figure 5 It is an X-ray diffraction photograph (XRD) of the feather-like NiFe-PBA electrode materials prepared in Examples 1 - 4.

[0020] Figure 6Linear sweep voltammetry (LSV) curves of urea electrooxidation of the feather-shaped NiFe-PBA electrode materials prepared in Examples 1-4.

[0021] Figure 7 Linear sweep voltammetry curves of urea electrooxidation of the feather-like NiFe-PBA electrode material prepared in Examples 1-4 at 10 mA cm – 2 , 100mA cm – 2 and 500mA cm – 2 Corresponding bar graph of potential values.

[0022] Figure 8 This is the Tafel slope diagram of the feather-like NiFe-PBA electrode material prepared in Examples 1-4.

[0023] Figure 9 This is the impedance spectroscopy (EIS) of the feather-shaped NiFe-PBA electrode material prepared in Examples 1-4. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with the accompanying drawings. The reagents, methods and equipment used in the experiments are all conventional reagents, methods and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0025] Example 1

[0026] S1: 89 mg (0.005 mol dm -3 ) of sodium nitroprusside (Na 3 Fe[(CN) 5 NO]) was ultrasonically dissolved in 60 mL of deionized water to obtain solution A, which was then stirred at room temperature for 30 min and transferred into a reactor.

[0027] S2: 1 cm*1 cm nickel foam was ultrasonically washed with hydrochloric acid, ethanol, acetone, and water for 5 min respectively to obtain a clean nickel foam B with no dirt on the surface.

[0028] S3: The nickel foam B is transferred into the solution A in the reactor and reacted at 160°C for 4 hours. The nickel foam substrate in the high-temperature reactor fully reacts with sodium nitroprusside, and then the NiFe-PNA obtained by the reaction is in situ grown on the nickel foam substrate. After the reaction, the nickel foam B loaded with the sample is washed with deionized water and ethanol for multiple times, and dried in an oven at 40°C for 6 hours to recover a feather-like NiFe-PBA.

[0029] Example 2

[0030] S1: Dissolve 179 mg (0.01 mol dm -3 ) of sodium nitroprusside (Na 3 Fe[(CN) 5 NO]) in 60 mL of deionized water by ultrasonic treatment to obtain solution A. Then stir solution A at room temperature for 30 min and transfer it to a reaction kettle.

[0031] S2: Ultrasonically wash a 1 cm × 1 cm nickel foam with hydrochloric acid, ethanol, acetone, and water for 5 min each to obtain a nickel foam B with a clean surface without dirt.

[0032] S3: Transfer nickel foam B into solution A in the reaction kettle and react at 160 °C for 4 h. In the high-temperature reaction kettle, the nickel foam substrate reacts fully with sodium nitroprusside, and then the obtained NiFe-PNA is in-situ grown on the nickel foam substrate. After the reaction, the nickel foam B loaded with the sample is washed repeatedly with deionized water and ethanol and dried in an oven at 40 °C for 6 h to recover a feather-like NiFe-PBA.

[0033] Example 3

[0034] S1: Dissolve 894 mg (0.05 mol dm -3 ) of sodium nitroprusside (Na 3 Fe[(CN) 5 NO]) in 60 mL of deionized water by ultrasonic treatment to obtain solution A. Then stir solution A at room temperature for 30 min and transfer it to a reaction kettle.

[0035] S2: Ultrasonically wash a 1 cm × 1 cm nickel foam with hydrochloric acid, ethanol, acetone, and water for 5 min each to obtain a nickel foam B with a clean surface without dirt.

[0036] S3: Transfer nickel foam B into solution A in the reaction kettle and react at 160 °C for 4 h. In the high-temperature reaction kettle, the nickel foam substrate reacts fully with sodium nitroprusside, and then the obtained NiFe-PNA is in-situ grown on the nickel foam substrate. After the reaction, the nickel foam B loaded with the sample is washed repeatedly with deionized water and ethanol and dried in an oven at 40 °C for 6 h to recover a feather-like NiFe-PBA.

[0037] Example 4

[0038] S1: Dissolve 1788 mg (0.1 mol dm -3 ) of sodium nitroprusside (Na 3 Fe[(CN) 5 NO]) in 60 mL of deionized water by ultrasonic treatment to obtain solution A. Then stir solution A at room temperature for 30 min and transfer it to a reaction kettle.

[0039] S2: The 1 cm * 1 cm nickel foam was ultrasonically washed with hydrochloric acid, ethanol, acetone, and water for 5 min respectively to obtain nickel foam B with a clean surface and no dirt.

[0040] S3: Transfer the nickel foam B into solution A in the reaction kettle and react at 160 °C for 4 h. In the high-temperature reaction kettle, the nickel foam substrate reacts fully with sodium nitroprusside, and then the obtained NiFe-PNA is in-situ grown on the nickel foam substrate. After the reaction, the nickel foam B loaded with the sample is washed repeatedly with deionized water and ethanol and dried in an oven at 40 °C for 6 h to recover a feather-like NiFe-PBA.

[0041] Taking the products prepared in Examples 1–4 as the research objects, the present invention uses scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques to characterize the phase structure of the nanomaterials, as described below:

[0042] (1) Morphology characterization

[0043] The structure of the prepared feather-like NiFe-PBA was detected using an S-4800 type SEM instrument, and the results are shown in Figure 1 –4. As can be seen from Figure 1 –4, the morphology of this material is a feather-like structure, and the length is 6.5–8.5 μm.

[0044] (2) Structure characterization

[0045] The structure of the prepared nanomaterials was characterized using a Bruker D8 Advance type XRD, and the results are shown in Figure 5 . As can be seen from the figure, the corresponding molecular formula of the prepared feather-like NiFe-PBA is Ni[Fe(CN) 5 NO], and the corresponding card for this material is JCPDS No. 01-0239, indicating that the NiFe-PBA material was successfully prepared.

[0046] (3) Linear sweep voltammetry (LSV) test

[0047] Using the NiFe-PBA loaded on the prepared nickel foam as the working electrode material, the saturated calomel electrode as the reference electrode, and the carbon rod as the counter electrode, the urea oxidation performance of NiFe-PBA was tested in a three-electrode system. The electrolyte was 1.0 mol dm - 3 KOH + 0.5 mol dm -3 urea. In the three-electrode system, linear sweep voltammetry (LSV) transient photocurrent testing was used to evaluate this electrode material, and the results are shown in Figure 6As shown, the performance tests indicate that the feathery NiFe-PBA exhibits excellent urea electrooxidation performance, with the required potentials at low and high current densities being 1.27 V (vs. 10 mA cm – 2 ) and 1.30 V (vs. 500 mA cm – 2 ), respectively.

[0048] (4) Tafel slope test

[0049] Taking the feathery NiFe-PBA prepared in Examples 1–4 as the research object, it can be known from the corresponding Tafel values that this material has a relatively fast chemical reaction rate.

[0050] (5) AC impedance test

[0051] Taking the feathery NiFe-PBA prepared in Examples 1–4 as the research object, the material loaded on nickel foam is directly used as the working electrode material for urea electrooxidation catalysis. The EIS test still adopts a three-electrode system. Electrochemical impedance spectroscopy is used to further evaluate the ion transport and charge transfer impedance of the prepared active electrode material NiFe-PBA / NF. The NiFe-PBA-0.05 / NF sample has the lowest charge transfer impedance, demonstrating the good charge mass transfer rate of this material.

Claims

1. A method for preparing feather-like NiFe-PBA, characterized in that: The specific steps are as follows: S1: a certain amount of sodium nitroprusside was ultrasonically dissolved in 60 mL of deionized water to obtain solution A, and then solution A was stirred at room temperature for 30 min and then transferred into a reactor; S2: 1 cm*1 cm nickel foam was ultrasonically washed with hydrochloric acid, ethanol, acetone, and water for 5 min respectively to obtain a nickel foam B with no dirt on the surface and a clean surface; S3: The nickel foam B is transferred into the solution A in the reactor and reacted at 160°C for 4 hours. In the high-temperature reactor, the nickel foam substrate fully reacts with sodium nitroprusside, and then the NiFe-PNA obtained by the reaction is in situ grown on the nickel foam substrate. After the reaction, the nickel foam B loaded with the sample is washed with deionized water and ethanol for multiple times, and dried in an oven at 40°C for 6 hours to recover a feather-like NiFe-PBA.

2. An application of a feather-like NiFe-PBA, characterized in that: The feathery NiFe-PBA was used for performance testing of urea electro-oxidation.

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