P / Fe-CN electrolyzed water catalyst and preparation method and application thereof

Abstract

The invention relates to a P / Fe-CN electrolyzed water catalyst and a preparation method and application thereof, and belongs to the technical field of inorganic synthesis and material preparation. The catalyst takes Fe-ZIF-8 as a core, PB (Prussian Blue) grows outside the Fe-ZIF-8, a composite structure is formed through high-temperature phosphating treatment, and the electrocatalytic water decomposition performance is good. The preparation method comprises the following steps: (1) synthesizing Fe-ZIF-8; 2) growing a PB shell; the material has a three-dimensional pore structure, the conductivity and the catalytic activity can be improved, the overpotentials of a hydrogen evolution reaction (HER) and an oxygen evolution reaction (OER) are 276.8 mV and 292.8 mV respectively under the current density of 10 mA cm <-2 >, and the potential is 1.81 V under the current density of 10 mA cm <-2 > when the material is assembled into a full-hydrolysis battery. The preparation method is simple, low in cost and suitable for large-scale production, and has a certain application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic synthesis and material preparation, and particularly relates to a hollow nanostructured electrolytic water decomposition catalyst, a preparation method thereof, and an application thereof, and is particularly suitable for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the electrocatalytic water decomposition reaction. Background Art

[0002] Electrocatalytic water splitting for hydrogen production, as an efficient clean energy production method, has received extensive attention. Electrocatalytic water splitting includes two half-reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In order to achieve efficient electrocatalytic water splitting, it is crucial to develop electrocatalysts with high catalytic activity and stability.

[0003] Zeolitic imidazolate frameworks (ZIFs) are porous crystalline materials constructed from transition metal cations and imidazole-based ligands, and have advantages such as high surface area, good stability, and adjustable pore structure. They show potential application value in many fields, such as gas storage and separation, heterogeneous catalysis, drug delivery, chemical detection, etc. Among them, the application of ZIFs materials as electrocatalysts has received much attention. However, the inherent low conductivity of ZIFs materials hinders the charge transfer within the framework. The single-metal derivatives of ZIFs materials show relatively low electrochemically electrocatalytic water splitting catalytic activity, and the number of active sites in pure ZIF materials is limited. Most of the activity comes from the central metal ions, but these sites are unevenly distributed, making it difficult to effectively improve the catalytic activity. Prussian Blue (PB) is a material with excellent electrochemical properties, and its structure contains a large number of Fe²⁺ and Fe³⁺ active sites, which can serve as the active centers for electrocatalytic reactions. Although the conductivity of pure PB is poor, through phosphating treatment, the Fe element in PB can be converted into FeP, significantly improving its conductivity.

[0004] In the present invention, by combining ZIF-8 with PB and performing high-temperature phosphating treatment, the conductivity and catalytic activity of the material can be improved, thereby obtaining an efficient electrocatalytic water splitting material. Compared with noble metal catalysts (such as Pt / C), the cost of the P / Fe-CN catalyst of the present invention is significantly reduced. Summary of the Invention

[0005] The technical solution of the present invention is as follows:

[0006] A preparation method of a P / Fe-CN catalyst, comprising the following steps:

[0007] Preparation of Fe-ZIF-8: Dissolve 2-methylimidazole, iron acetylacetonate (Fe(acac)3), and zinc nitrate (Zn(NO3)2·6H2O) in methanol, stir and react for 24 hours, and obtain Fe-ZIF-8 after washing and drying.

[0008] Growth of Prussian Blue (PB) shell: Disperse Fe-ZIF-8 in ethanol, add potassium ferricyanide (K3[Fe(CN)6]) solution, stir and react, add glacial acetic acid solution to adjust the pH, and allow PB to grow on the surface of Fe-ZIF-8 to obtain the Fe-ZIF-8@PB composite material.

[0009] High-temperature phosphating treatment: Place Fe-ZIF-8@PB and sodium hypophosphite (NaH2PO2) in porcelain boats respectively, and heat at 600 °C for 2 hours under an argon atmosphere to obtain the P / Fe-CN composite material.

[0010] Application of P / Fe-CN electrocatalytic water splitting catalyst: This material can be used as the cathode and anode catalysts for electrocatalytic water splitting reaction, showing good HER and OER catalytic performances.

[0011] Compared with the prior art, the advantages of the present invention are as follows:

[0012] (1) The electrocatalytic water splitting material prepared by the present invention through growing PB on the outside of ZIF and then performing high-temperature phosphating treatment has a unique composite structure. ZIF-8 provides good structural support as the core, PB enhances the electrochemical activity as the shell, and the high-temperature phosphating treatment further improves the conductivity and stability of the material.

[0013] (2) The preparation method of the present invention is simple and easy to implement, with low cost, and is suitable for large-scale production.

[0014] (3) The material of the present invention shows good catalytic performance in the electrocatalytic water splitting reaction and has a low overpotential. Description of the Drawings

[0015] Figure 1 is the scanning electron microscope image of Fe-ZIF-8@PB.

[0016] Figure 2 is the powder diffraction pattern of Fe-ZIF-8@PB.

[0017] Figure 3 is the thermogravimetric analysis graph of Fe-ZIF-8.

[0018] Figure 4 is the thermogravimetric analysis graph of PB.

[0019] Figure 5 is the powder diffraction pattern of P / Fe-CN.

[0020] Figure 6 is the LSV curve graph of OER of P / Fe-CN sample in 1M KOH.

[0021] Figure 7 Tafel curve of OER for P / Fe-CN sample

[0022] Figure 8 LSV curve of HER for P / Fe-CN sample in 1 M KOH

[0023] Figure 9 Tafel curve of HER for P / Fe-CN sample

[0024] Figure 10 LSV curve of the all-hydrolysis cell assembled with P / Fe-CN sample in 1 M KOH Specific implementation mode

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] The preparation method of the P / Fe-CN material in the embodiment includes the following steps:

[0027] (1) Preparation of Fe-ZIF-8: Take 0.657 g (8 mmol) of 2-methylimidazole and 1.765 g (5 mmol) of Fe(acac)3 and dissolve them in 30 mL of anhydrous methanol, denoted as solution A. Dissolve 0.297 g (1 mmol) of Zn(NO3)2·6H2O in 15 mL of anhydrous methanol, denoted as solution B. Mix solution A and solution B and continuously stir for 24 hours. Wash several times with methanol and dry at 60 °C.

[0028] (2) Preparation of Fe-ZIF-8@PB: Take 25 mg of Fe-ZIF-8 and disperse it in 15 mL of ethanol, add 5 mL of a solution containing 50 mg of K3[Fe(CN)6], add 50 μL of 0.1 M glacial acetic acid solution, and continuously stir the mixed solution at 80 °C for 1 hour.

[0029] (3) Preparation of P / Fe-CN: Take 0.1 g of Fe-ZIF-L-8@PB and 2.0 g of NaPO2H2⋅H2O and place them in two porcelain boats respectively. Place NaH2PO2 upstream of the tubular furnace and Fe-ZIF-L-8@PB downstream of the tubular furnace, and keep at 600 °C for 2 hours under an argon atmosphere with a heating rate of 2 °C / min.

[0030] The following is the basic characterization of the ZIF-8@PB-P material prepared by the preparation method in the embodiment of the present invention.

[0031] Figure 1 Scanning electron micrograph of the prepared Fe-ZIF-8@PB Figure 2is the powder diffraction pattern of Fe-ZIF-8@PB, Figure 5 is the powder diffraction pattern of P / Fe-CN.

[0032] SEM and XRD experiments have demonstrated the successful synthesis of Fe-ZIF-8@PB. As Figure 1 shown, observing the morphology of the material Fe-ZIF-8@PB, the material maintains the shape of the ZIF-8 dodecahedron, with a rough surface and a granular appearance. After partial Fe-ZIF-8@PB is broken, a hollow structure of the material can be observed. Figure 2 is the XRD result of Fe-ZIF-8@PB. The diffraction peaks match well with those of ZIF-8 and PB, proving that the particles on the surface of the material are PB and demonstrating the successful synthesis of Fe-ZIF-8@PB. Through thermogravimetric analysis experiments on Fe-ZIF-8 and PB (the results are as Figure 3 , shown in Figure 4), the pyrolysis temperature of phosphidation is determined to be 600 °C. An XRD experiment is carried out on the pyrolyzed material P / Fe-CN to determine its phase. The results are as Figure 5 shown. Characteristic diffraction peaks appear in the phosphated material at (32.6°), (46.3°), (47.1°), and (48.4°), indicating that the material has undergone successful phosphidation treatment.

[0033] The electrochemical performance of the material P / Fe-CN is evaluated by testing and analyzing it with a Chenhua electrochemical workstation. The specific steps are as follows:

[0034] (1) Weigh 5 mg of the prepared sample, grind it thoroughly, add 30 μL of 5% Nafion and 470 μL of ethanol, treat it with an ultrasonic machine for 30 min, then take 10 μL of the mixed slurry and drop-coat it on a 1 cm * 1 cm nickel foam (NF), and leave it to dry at room temperature for 5 hours.

[0035] (2) Prepare a KOH electrolyte with a concentration of 1.0 mol / L. Take 30 mL of the electrolyte into an electrolytic cell, use the NF coated with P / Fe-CN as the working electrode, and conduct cyclic voltammetry tests in a three-electrode system to activate the sample. The voltage range for the cyclic voltammetry test is 0 to 0.9 V (versus the Hg / HgO electrode), the scanning rate is 0.05 V / s, and the number of cycles is 60. After the cyclic voltammetry test, linear sweep voltammetry is used for testing, with a voltage range of 0 to 0.9 V (versus the Hg / HgO electrode) and a scanning rate of 5 mV / s.

[0036] (3) Take 30 mL of the electrolyte in an electrolytic cell. Using the NF coated with P / Fe-CN as the working electrode, perform cyclic voltammetry tests in a three-electrode system to activate the sample. The voltage range for the cyclic voltammetry test is -0.6 to -0.9 V (versus the Hg / HgO electrode), the scanning rate is 0.05 V / s, and the number of cycles is 60. After the cyclic voltammetry test, perform a linear sweep voltammetry test with a voltage range of -0.9 to -1.2 V (versus the Hg / HgO electrode) and a scanning rate of 5 mV / s.

[0037] (4) Take 30 mL of the electrolyte in an electrolytic cell. Two NFs coated with P / Fe-CN are used as the cathode and anode respectively to perform cyclic voltammetry tests to activate the sample. The voltage range for the cyclic voltammetry test is 0 to 2.1 V (versus the Hg / HgO electrode), the scanning rate is 0.05 mV / s, and the number of cycles is 60. After the cyclic voltammetry test, perform a linear sweep voltammetry test with a voltage range of 1.2 to 2.1 V (versus the Hg / HgO electrode) and a scanning rate of 5 mV / s.

[0038] The OER catalytic performance of the material P / Fe-CN is shown in Figures 6 - 10 , and P / Fe-CN has good catalytic performance. The OER requires an overpotential of 292.8 mV to reach a current density of 10 mA cm -2 , and the Tafel slope is only 50.7 mV / dec -1 , and the overpotential of HER at 10 mA cm -2 is 276.8 mV, and the Tafel slope is 135.7 mV dec -1 . Assemble the material P / Fe-CN into a battery, and the potential at 10 mA cm -2 is 1.81 V.

Claims

1. A P / Fe-CN electrocatalytic water decomposition material, characterized in that: The Prussian Blue (PB) shell was grown from Fe-ZIF-8 and prepared by high-temperature phosphating. SEM images show that the composite material Fe-ZIF-8@PB has a three-dimensional hollow structure, and X-ray powder diffraction experimental results show that Fe-ZIF-@PB has characteristic peaks of both Fe-ZIF-8 and PB. The material after phosphating has the characteristic peak of FeP.

2. A method for preparing a P / Fe-CN material, comprising the following steps: (1) Synthesis of Fe-ZIF-8: 2-Methylimidazole, ferric acetylacetonate and zinc nitrate were mixed in a methanol solution and stirred at room temperature to obtain Fe-ZIF-8. (2) PB shell growth: Fe-ZIF-8 powder was dispersed in ethanol, potassium ferrocyanide solution was added, and after mixing, glacial acetic acid was added to adjust the pH. PB was grown on the surface of Fe-ZIF-8 by co-precipitation method to obtain Fe-ZIF-8@PB composite material. (3) High-temperature phosphating treatment: The Fe-ZIF-8@PB composite material and sodium hypophosphite were placed in two porcelain boats respectively and subjected to high-temperature phosphating treatment under an inert atmosphere to obtain P / Fe-CN material.

3. The preparation method according to claim 2, characterized in that: In the step 2), glacial acetic acid solution is added to adjust the pH value of the solution to between 4 and 5.

4. The temperature of step 3) high temperature phosphating is 550-800°C and the time is 2-3 hours.

Images