Method for preparing yolk shell structure high-entropy phosphide FeCoNiCrMn-P catalyst by using low-temperature phosphating method

Abstract

The invention relates to the technical field of crossing of material chemistry and water electrolysis oxygen evolution, in particular to a method for preparing a yolk shell structure high-entropy phosphide FeCoNiCrMn-P catalyst through a low-temperature phosphating method. The method comprises the following steps: dissolving a plurality of nitrates in isopropanol and a glycerin solvent to react to obtain high-entropy glycerate; carrying out hydrothermal reaction on the reacted high-entropy glycerate to generate a high-entropy hydroxide; the high-entropy hydroxide and a phosphorus source are subjected to a low-temperature phosphating reaction to generate the high-entropy phosphide catalyst. According to the invention, the reactant FeCoNiCrMn-P with a graded egg yolk shell structure not only exposes more active sites and provides abundant mass transfer channels, but also provides a uniform environment for heterogeneous catalysis, so that OER is promoted. In addition, the shell layer can also play a role of a protective layer, prevents the active components from deforming and dissolving in the catalytic process, and enhances the stability of the active components. When the current density is 10 mA cm <-2 >, the FeCoNiCrMn-P2 has the best OER performance, and the overpotential of the FeCoNiCrMn-P2 is 329 mV, so that the FeCoNiCrMn-P2 has high practical application value.

Description

Technical Field

[0001] The invention relates to the cross-technical field of material chemistry and electrolytic water oxygen evolution, and in particular to a method for preparing a yolk-shell structure high-entropy phosphide FeCoNiCrMn-P catalyst by using a low-temperature phosphating method. Background Art

[0002] In order to reduce dependence on fossil fuels and alleviate the environmental problems caused by fossil fuel consumption, the development of renewable clean energy is urgent. Electrolytic water splitting is an efficient and environmentally friendly way to produce green and clean hydrogen energy, and is considered a potential alternative to traditional fossil fuels. In an operating electrolytic water tank, the cathode (negative electrode) generates H2 through the hydrogen evolution reaction (HER), and the anode (positive electrode) generates O2 through the oxygen evolution reaction (OER). However, due to the slow reaction kinetics caused by the electron transport mechanism, OER has been considered to be the bottleneck of the water splitting system. At present, precious metal Ru and Ir-based compounds (oxides) have been widely studied due to their excellent OER activity. However, their high price, small reserves and instability in alkaline media limit their application in industrial practice. Therefore, the development of economical and efficient transition metal electrocatalysts has become the key to achieving electrolytic water splitting.

[0003] High entropy materials, composed of five or more metal elements, have broad prospects in the field of energy and electrocatalysts. Due to the unique high entropy effect, lattice distortion, hysteresis diffusion effect and cocktail effect, high entropy materials have the advantages of multiple active centers, adjustable electronic structure and good stability, and can be used as electrocatalysts for water electrolysis. Therefore, high entropy catalysts have been widely explored in the past few years. Studies have found that a large number of high entropy materials, such as oxides, sulfides, alloys, phosphides and selenides, can be used as OER catalysts and show excellent OER performance under alkaline conditions. Among them, phosphides have good conductivity and activity and have attracted widespread attention. However, due to the differences in elements, the complexity of components and the harshness of experimental conditions, the synthesis of high entropy phosphides is challenging. In addition, the synthesis of yolk-shell structured high entropy phosphides with large specific surface area and fast material transport is challenging and has not yet been explored. Summary of the invention

[0004] In view of the problems existing in the background technology, a method for preparing a yolk-shell structure high-entropy phosphide FeCoNiCrMn-P catalyst by a low-temperature phosphating method is proposed. The method has simple operation and low synthesis cost. The prepared high-entropy phosphide has uniform size, high controllability, and can be prepared on a large scale.

[0005] The present invention provides a method for preparing a yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by a low-temperature phosphating method, comprising the following steps:

[0006] S1, dissolving various nitrates in isopropanol and reacting with glycerol solvent to obtain high entropy glycerate;

[0007] S2, generating high entropy hydroxide through a hydrothermal reaction of the reacted high entropy glycerate;

[0008] S3, high entropy hydroxide and phosphorus source generate high entropy phosphide catalyst through low temperature phosphating reaction.

[0009] Preferably, the nitrates described in S1 include Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Cr(NO3)3·9H2O and Mn(NO3)2·4H2O, and their concentrations are all 0.05-0.25 mmol; the amount of isopropanol is 50-60 mL, and the amount of glycerol is 5-15 mL; the solvent thermal reaction temperature is 100°C-200°C; and the solvent thermal reaction time is 8-12 h.

[0010] Preferably, the mass of the high entropy glycerate described in S2 is 30-70 mg; the volume of the deionized water is 10-30 mL; the hydrothermal reaction temperature is 120° C.-160° C.; and the hydrothermal reaction temperature is 3-6 h.

[0011] Preferably, the high entropy hydroxide described in S3 is 15-40 mg; the phosphorus source is NaH2PO2·H2O and the mass ratio of high entropy hydroxide to phosphorus source is 1:(10-20); the phosphating reaction temperature is 300°C-500°C, the phosphating reaction heating rate is 1-5°C / min; the phosphating insulation time is 1-5h.

[0012] Compared with the prior art, the present invention has the following beneficial technical effects: the method for preparing the phosphide catalyst in the present invention is simple to operate and has low synthesis cost; the prepared high entropy phosphide is uniform in size, highly controllable, and can be prepared on a large scale; the synergistic effect of multiple elements can not only promote the redistribution of electrons between multiple metals, but also regulate the adsorption and desorption capabilities of reaction intermediates. The obtained hierarchical spherical yolk-shell structure is not only conducive to the reactants exposing more active sites and providing abundant mass transfer channels, but also provides a uniform environment for the catalytic reaction, thereby promoting OER. In addition, the shell layer can also act as a protective layer to prevent the active components from deforming and dissolving during the catalytic process and enhance their stability. Therefore, the FeCoNiCrMn-P prepared by the method of the present invention also has excellent application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the SEM image of FeCoNiCrMn-P2 in Example 2.

[0014] Figure 2 This is the TEM image of FeCoNiCrMn-P2 in Example 2.

[0015] Figure 3 This is the XRD spectrum of FeCoNiCrMn-P2 in Example 2.

[0016] Figure 4 It is the OER-LSV curve of the high entropy phosphide FeCoNiCrMn-P in Examples 1-4.

[0017] Figure 5 2 and 3. The OER-LSV curves of different phosphides in Example 2 and Examples 5-7. DETAILED DESCRIPTION

[0018] Example 1

[0019] The present invention proposes a method for preparing a yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by low-temperature phosphating method, the steps of which are as follows:

[0020] Step A: Dissolve equimolar Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Cr(NO3)3·9H2O and Mn(NO3)2·4H2O (0.20 mmol each) in 57 mL of isopropanol, stir vigorously for 15 min, then add 9 mL of glycerol, stir for 45 min and ultrasonicate for 30 min to form a uniform light brown suspension. Then, transfer the above suspension to a 100 mL Teflon-lined autoclave and heat at 180 ° C for 10 h. After cooling to room temperature, the product obtained by centrifugation is named FeCoNiCrMn-G;

[0021] Step B: 50 mg of high entropy glycerate (FeCoNiCrMn-G) powder was dispersed in 25 mL of water, ultrasonicated for 15 min, and then the mixed product was transferred to a 50 mL Teflon-lined autoclave and kept at 150 ° C for 5 h. After natural cooling, the precipitate was collected by centrifugation and washed with ethanol several times, and the obtained powder was dried in a vacuum oven at 60 ° C for 12 h. The final sample was named E-FeCoNiCrMn;

[0022] Step C: 20 mg of high entropy hydroxide powder (E-FeCoNiCrMn) and 100 mg of NaH2PO2·H2O were placed in the ceramic, and NaH2PO2·H2O was placed upstream of the tube furnace. Then, under the atmosphere of N2 gas, the temperature was raised to 350°C at a heating rate of 2°C / min and maintained at this temperature for 2 hours. The obtained high entropy phosphide catalyst was recorded as FeCoNiCrMn-P1.

[0023] Example 2

[0024] The present invention proposes a method for preparing a yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by low-temperature phosphating method, the steps of which are as follows:

[0025] Step A: same as step A in Example 1;

[0026] Step B: same as step B in Example 1;

[0027] Step C: The same as step C in Example 1, except that the added NaH2PO2·H2O is 200 mg, and the high entropy phosphide obtained is named FeCoNiCrMn-P2;

[0028] Example 3

[0029] The present invention proposes a method for preparing a yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by low-temperature phosphating method, the steps of which are as follows:

[0030] Step A: same as step A in Example 1;

[0031] Step B: same as step B in Example 1;

[0032] Step C: The same as step C in Example 1, except that 300 mg of NaH2PO2·H2O was added, and the high entropy phosphide obtained was named FeCoNiCrMn-P3;

[0033] Example 4

[0034] The present invention proposes a method for preparing a yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by low-temperature phosphating method, the steps of which are as follows:

[0035] Step A: same as step A in Example 1;

[0036] Step B: same as step B in Example 1;

[0037] Step C: The same as step C in Example 1, except that 400 mg of NaH2PO2·H2O was added, and the high entropy phosphide obtained was named FeCoNiCrMn-P4.

[0038] Figure 1 This is a microscopic characterization of the high entropy phosphide in Example 2. Combined with the pictures, it can be seen that FeCoNiCrMn-P2 presents a yolk-shell structure composed of smaller nanosheets, and these nanosheets are connected to each other, increasing the exposure of active sites.

[0039] Figure 2This is the TEM image of the high entropy phosphide in Example 2. Combined with the picture, it can be seen that there is a gap between the core and shell of FeCoNiCrMn-P2, indicating that a spherical yolk-shell structure is formed, which is consistent with the SEM image.

[0040] Figure 3 This is the XRD spectrum of Example 2. Combined with the picture, it can be seen that the diffraction peaks of FeCoNiCrMn-P2 at 2θ=31.6°, 36.3°, 48.1° and 56.8° correspond to the (011), (111), (211) and (013) crystal planes of CoP (ICDD 89-2598), respectively.

[0041] Example 5

[0042] The present invention proposes a method for preparing a phosphide catalyst FeCo-P by a low-temperature phosphating method, the steps of which are as follows:

[0043] Step A: Dissolve equimolar Fe(NO3)3·9H2O and Co(NO3)2·6H2O (0.20 mmol each) in 57 mL of isopropanol, stir vigorously for 15 min, then add 9 mL of glycerol, stir for 45 min and ultrasonicate for 30 min to form a uniform light brown suspension. Then, transfer the above suspension to a 100 mL Teflon-lined autoclave and heat at 180 ° C for 10 h. After cooling to room temperature, the product obtained by centrifugation is named FeCo-G;

[0044] Step B: 50 mg of glycerate (FeCo-G) powder was dispersed in 25 mL of water, ultrasonicated for 15 min, and then the mixed product was transferred to a 50 mL Teflon-lined autoclave and kept at 150 ° C for 5 h. After natural cooling, the precipitate was collected by centrifugation and washed with ethanol several times, and the obtained powder was dried in a vacuum oven at 60 ° C for 12 h. The final sample was named E-FeCo;

[0045] Step C: 20 mg of hydroxide powder (E-FeCo) and 200 mg of NaH2PO2·H2O were placed in the ceramic, and NaH2PO2·H2O was placed upstream of the tube furnace. Then, under the atmosphere of N2 gas, the temperature was raised to 350°C at a heating rate of 2°C / min and maintained at this temperature for 2 hours. The obtained phosphide catalyst was recorded as FeCo-P.

[0046] Example 6

[0047] The present invention proposes a method for preparing a phosphide catalyst FeCoNi-P by a low-temperature phosphating method, the steps of which are as follows:

[0048] Step A: The same as step A in Example 5; the difference is that Ni(NO3)2·6H2O is added to Fe(NO3)3·9H2O and Co(NO3)2·6H2O, and the final product is named FeCoNi-G;

[0049] Step B: The same as step B in Example 5, except that the added glycerate is FeCoNi-G, and the final product is named E-FeCoNi;

[0050] Step C: The same as step C in Example 5, except that the added hydroxide is E-FeCoNi, and the final product is named FeCoNi-P;

[0051] Example 7

[0052] The present invention proposes a method for preparing a phosphide catalyst FeCoNiCr-P by a low-temperature phosphating method, the steps of which are as follows:

[0053] Step A: The same as step A in Example 5; except that Ni(NO3)2·6H2O and Cr(NO3)3·9H2O are added to Fe(NO3)3·9H2O and Co(NO3)2·6H2O, and the final product is named FeCoNiCr-G;

[0054] Step B: The same as step B in Example 5, except that the added glycerate is FeCoNiCr-G, and the final product is named E-FeCoNiCr;

[0055] Step C: The same as step C in Example 5; except that the added hydroxide is E-FeCoNiCr, and the final product is named FeCoNiCr-P.

[0056] Application Examples

[0057] In this example, the three-electrode system on the Autolab PG302N electrochemical workstation was used to perform electrochemical test characterization on the phosphide catalysts prepared in Examples 1-7. The steps specifically include:

[0058] Step A: 4 mg of electrocatalyst was dispersed into 1000 μL of a mixed solution (600 μL of ultrapure water, 350 μL of ethanol and 50 μL of Nafion) and ultrasonicated for half an hour to obtain a 4 mg / L catalyst ink;

[0059] Step B: Use a pipette to drop 10 μL of ink onto a 3 mm diameter glassy carbon electrode (glassy carbon area: 0.0706 cm 2 , loading: 0.56 mg cm -2 ), and dried at room temperature;

[0060] Step C: Graphite rod was used as counter electrode, saturated calomel (SCE) as reference electrode, and the prepared phosphide as working electrode. Before all electrochemical tests, cyclic voltammetry (CV) was used at 100 mV s -1 The catalyst was activated under 40 °C. Linear sweep voltammetry (LSV) was used for linear polarization with a scan rate of 5 mV s -1 , and all LSV curves are 90% iR corrected. Electrochemical impedance spectroscopy (EIS) was performed in the frequency range of 0.1-100 kHz with an amplitude of 5 mV.

[0061] The catalytic performance of the high entropy phosphide prepared in Examples 1-4 for oxygen evolution is shown in Figure 4 It can be seen that at a current density of 10 mA cm -2 When , the overpotential of FeCoNiCrMn-P2 is 329mV.

[0062] The catalytic performance of oxygen evolution of the phosphides prepared in Examples 5-7 is shown in Figure 5 As the amount of metal elements increases, the OER performance of the phosphide gradually increases. -2 The OER performance is the best under the overpotential of 329 mV.

[0063] In summary, the spherical yolk-shell structure of the FeCoNiCrMn-P of the present invention not only facilitates the reactants to expose more active sites and provide abundant mass transfer channels, but also provides a uniform environment for heterogeneous catalysis, thereby promoting OER. In summary, the prepared FeCoNiCrMn-P has excellent application value.

[0064] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto, and various changes can be made within the knowledge scope of technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A method for preparing a yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by low temperature phosphating method, characterized in that: The following steps are involved: S1, dissolving various nitrates in isopropanol and reacting with glycerol solvent to obtain high entropy glycerate; S2, generating high entropy hydroxide by hydrothermal reaction of the high entropy glycerate after the reaction; S3, high entropy hydroxide and phosphorus source generate high entropy phosphide catalyst through low temperature phosphating reaction.

2. The method for preparing the yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by low temperature phosphating method according to claim 1, characterized in that: The nitrates described in S1 include Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Cr(NO3)3·9H2O and Mn(NO3)2·4H2O, and their concentrations are all 0.05-0.25 mmol; the amount of isopropanol is 50-60 mL, and the amount of glycerol is 5-15 mL; the solvent thermal reaction temperature is 100°C-200°C; and the solvent thermal reaction time is 8-12 h.

3. The method for preparing the yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by low temperature phosphating method according to claim 1, characterized in that: The mass of the high entropy glycerate described in S2 is 30-70 mg; the volume of the deionized water is 10-30 mL; the hydrothermal reaction temperature is 120°C-160°C; and the hydrothermal reaction temperature is 3-6h.

4. The method for preparing the yolk-shell structure high entropy phosphide FeCoNiCrMn-P catalyst by low temperature phosphating method according to claim 1, characterized in that: The high entropy hydroxide described in S3 is 15-40 mg; the phosphorus source is NaH2PO2·H2O and the mass ratio of high entropy hydroxide to phosphorus source is 1:(10-20); the phosphating reaction temperature is 300°C-500°C, the phosphating reaction heating rate is 1-5°C / min; the phosphating insulation time is 1-5h.

5. A yolk-shell structure high entropy phosphide catalyst prepared by the method as claimed in claim 1.

6. The use of a yolk-shell structure high entropy phosphide catalyst as claimed in claim 5, characterized in that: The catalyst is suitable for the anode oxygen evolution reaction in alkaline water electrolysis.

7. The use of a yolk-shell structure high entropy phosphide catalyst according to claim 6, characterized in that: The application steps are as follows: disperse the electrocatalyst in a mixed solution of ultrapure water, ethanol and Nafion to obtain catalyst ink; drop the catalyst ink onto a glassy carbon electrode; use a graphite rod as a counter electrode, saturated calomel as a reference electrode, and the prepared phosphide as a working electrode to carry out oxygen evolution reaction.

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