High-entropy nano phosphide electrocatalyst as well as preparation method and application thereof

Abstract

The invention provides a high-entropy nano phosphide electrocatalyst as well as a preparation method and application thereof. The catalyst contains six elements of iron, cobalt, nickel, molybdenum, tungsten and phosphorus, and the microstructure of the catalyst is spherical nanoparticles with the average particle size of 20-60 nm. The invention also discloses a preparation method of the electrocatalyst, the high-entropy nano phosphide electrocatalyst synthesized by the method is high in efficiency and excellent in stability when being used for electrocatalytic oxygen evolution reaction, and the performance of the high-entropy nano phosphide electrocatalyst is superior to that of a reported high-entropy alloy catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of water electrolysis, and in particular relates to a high-entropy nano-phosphide electrocatalyst and a preparation method and application thereof. Background Art

[0002] The electrochemical water splitting reaction, driven by electricity, is the most promising hydrogen production technology due to its high efficiency, green nature, and sustainability. The water electrolysis reaction consists of two half-reactions: the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). The anodic oxygen evolution reaction, involving a four-electron transfer process, has a high overpotential, resulting in slow kinetics, which in turn affects the overall electrolysis efficiency. Therefore, it is imperative to find low-cost materials that can effectively reduce the OER overpotential and improve water splitting efficiency.

[0003] Traditional binary or ternary alloys have poor OER catalyst activity due to fewer active sites, and their large miscible gap makes them poorly corroded, hindering their further application. High entropy alloy (HEA) materials have natural advantages in constructing multi-component catalysts due to their flexible composition and stable structure. At the same time, the various elements in high entropy alloy materials can not only produce rich synergistic effects, but also adjust the composition of elements to improve the corrosion resistance of the catalyst and enhance the conductivity of the catalyst, which has attracted considerable interest in catalyzing water electrolysis. Although high entropy alloys can reduce costs by reducing the content of precious metals, their performance is still limited by the proportion of precious metals, especially in some key catalytic reactions, such as hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The activity and stability of precious metals are still key factors. Therefore, the development of low-cost, highly active and continuously stable high entropy alloy catalysts is of great significance for efficient hydrogen production by water electrolysis. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-entropy nano-phosphide electrocatalyst.

[0005] The present invention also aims to provide a method for preparing a high-entropy nano-phosphide electrocatalyst.

[0006] The present invention also aims to provide an application of a high-entropy nano-phosphide electrocatalyst.

[0007] A high-entropy nano-phosphide electrocatalyst comprises six elements: iron, cobalt, nickel, molybdenum, tungsten and phosphorus.

[0008] Preferably, the molar ratio of iron, cobalt, nickel, molybdenum, tungsten and phosphorus is 1:1:3:2:1:2.5.

[0009] Preferably, the metals in the high-entropy nanophosphide electrocatalyst are all in an amorphous state.

[0010] Preferably, the high entropy nano-phosphide electrocatalyst has a microscopic morphology of spherical nanoparticles with an average particle size of 20-60 nm.

[0011] A method for preparing a high-entropy nano-phosphide electrocatalyst comprises the following steps:

[0012] S1. Dissolve the iron, cobalt, and nickel metal salt precursors in deionized water to form a clear solution, then rapidly add molybdate, tungstate, and sodium phosphate under ultrasonic conditions and continue ultrasonication for 5-20 minutes;

[0013] S2. After ultrasonication, stirring was continued for 4-12h. After the solution was fully reacted, the resulting suspension was centrifuged 8-15 times, and the centrifuged product was washed with anhydrous ethanol;

[0014] S3. The washed product was placed in a vacuum drying oven and dried at 80-120°C for 12-24h to obtain a high-entropy nanophosphide electrocatalyst;

[0015] S4. Prepare the obtained catalyst into an ink solution, drop-coat it on carbon paper, and place it in an 80°C oven to dry. After drying, use cyclic voltammetry scanning to reconstruct the catalyst.

[0016] Preferably, the iron, cobalt and nickel metal salt precursors in step S1 are cobalt nitrate hexahydrate, iron nitrate nonahydrate and nickel nitrate hexahydrate, and the molybdate and tungstate are sodium molybdate dihydrate and sodium tungstate dihydrate.

[0017] Preferably, it is characterized in that the amount of sodium phosphate added in step S1 is 0.05-0.15 mol.

[0018] Preferably, the ink solution in step S4 is a mixture of ethanol, ultrapure water, Nafion and a high-entropy nano-phosphide electrocatalyst.

[0019] Preferably, the reconstruction method in step S4 is: using the prepared catalyst as the working electrode, the platinum mesh as the counter electrode, and the Hg / HgO electrode as the reference electrode, cyclic voltammetry reconstruction is performed in 1 M KOH electrolyte at 30° C., with a scanning range of 1.124-1.724 V vs RHE.

[0020] Application of a high-entropy nanophosphide electrocatalyst in oxygen evolution reaction.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention synthesizes high-entropy nanophosphide electrocatalysts via a one-step coprecipitation method, which is simple and easy to implement under mild conditions. Rapid coprecipitation overcomes the thermodynamic solubility limitations of multiple elements, forming a highly disordered amorphous structure. By doping with an appropriate amount of phosphorus, the catalyst's specific surface area and active site density are increased while also avoiding elemental segregation and achieving uniform distribution of components.

[0023] (2) The present invention uses Mo and W as passivation elements of the high-entropy nanocatalyst, utilizing the synergistic effect between them. During the electrolysis process, they act as electron donors, inhibit the excessive oxidation corrosion of the active metal, and provide excellent stability for the catalyst.

[0024] (3) The present invention achieves control over the particle size of high-entropy nanocatalysts by introducing phosphorus atoms, reducing the aggregation tendency of nanoparticles and increasing the exposure rate of highly active sites. The high electronegativity of phosphorus atoms triggers a significant electron redistribution effect, attracting electrons from active metal elements, making the metal sites moderately positive, thereby enabling the active metal to combine with oxygen-containing intermediates (such as *OH, *OOH) to form highly active sites M-OOH, significantly improving the activity of the catalyst. At the same time, P acts as a sacrificial agent, protecting the active metal while also enhancing the electron storage capacity of the metal Mo.

[0025] FeCoNiMoWP prepared by the present invention 0.1 When the high entropy nano-phosphide electrocatalyst is applied to the electrolysis of water and oxygen evolution reaction, the high entropy nano-phosphide electrocatalyst of the present invention is used as the working electrode, the platinum mesh is used as the counter electrode, and the Hg / HgO electrode is used as the reference electrode. The electrolysis of water and oxygen evolution reaction is carried out in 1M KOH electrolyte at 30°C. -2 The current density of FeCoNiMoWP shows an ultra-low overpotential of 75.4mV. 0.1 At 100mA cm -2 After 1350 hours of continuous operation at high current density, the activity decay is negligible, and its stability far exceeds that of traditional transition metal oxide catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 This is a scanning electron microscope image of a high-entropy nanophosphide electrocatalyst;

[0028] Figure 2 is the SEM particle size distribution histogram of high entropy nanophosphide material;

[0029] Figure 3This is a transmission electron microscopy image of a high-entropy nanophosphide electrocatalyst;

[0030] Figure 4 is the X-ray diffraction pattern of high entropy nanophosphide electrocatalyst;

[0031] Figure 5 This is the in-situ Raman spectrum of high entropy nanophosphide electrocatalyst;

[0032] Figure 6 Figure 2 shows the oxygen evolution performance of high-entropy nanophosphide electrocatalysts, including (a) polarization curve, (b) electrochemical impedance spectroscopy, and (c) Tafel curve.

[0033] Figure 7 This is a test curve of oxygen evolution stability of high entropy nanophosphide electrocatalyst. DETAILED DESCRIPTION

[0034] The following specific descriptions are exemplary and are intended to provide further explanation of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solutions of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements shall fall within the scope of protection of the present invention.

[0035] Unless otherwise specified, the test methods used in the following experimental examples are conventional methods.

[0036] Example 1: FeCoNiMoWP 0.1 Synthesis of:

[0037] 0.01mol of ferric nitrate nine hydrate, 0.01mol of cobalt nitrate hexahydrate, and 0.03mol of nickel nitrate hexahydrate were dissolved in 150mL of deionized water to form a clear solution. Then, 0.02mol of sodium molybdate dihydrate, 0.01mol of sodium tungstate dihydrate, and 0.1mol of sodium phosphate were quickly added under ultrasonic conditions with a power of 100W. The ultrasonic treatment was continued for 5min and then stirred for 4h. After the solution was fully reacted, the obtained suspension was centrifuged 8 times with anhydrous ethanol. Finally, the washed product was placed in a vacuum drying oven and dried at 80℃ for 12h to obtain the high entropy nanophosphide electrocatalyst FeCoNiMoWP. 0.1 , SEM (field emission scanning electron microscopy) characterization was performed, and it was determined that the high-microscopic morphology was spherical nanoparticles with an average particle size of 27.1nm; TEM (field emission transmission electron microscopy) and XRD (X-ray diffractometer) analysis determined that it was amorphous; ICP characterization was performed, and the ratio of iron, cobalt, nickel, molybdenum, tungsten, and phosphorus elements was determined to be 1:1.5:3:0.5:1.5:2.5; in situ Raman characterization was performed, and it was determined that M-OOH active species were generated.

[0038] Example 2: FeCoNiMoWP 0.05 Synthesis of:

[0039] The specific implementation conditions are similar to those in Example 1, but the amount of sodium phosphate added is 0.05 mol, and the high entropy nano-phosphide electrocatalyst FeCoNiMoWP is obtained. 0.05 . XRD analysis confirmed that it was amorphous.

[0040] Example 3: FeCoNiMoWP 0.15 Synthesis of:

[0041] The specific implementation conditions are similar to those in Example 1, except that the amount of sodium phosphate added is 0.15 mol. XRD analysis shows that the product is in an amorphous state.

[0042] Example 4: FeCoNiMoWP 0.2 Synthesis of:

[0043] The specific implementation conditions are similar to those in Example 1, except that the amount of sodium phosphate added is 0.2 mol. XRD analysis shows that the product is in an amorphous state.

[0044] Example 5: Synthesis of FeCoNiMoW

[0045] The specific implementation conditions are similar to those in Example 1, but sodium phosphate is not added. XRD analysis shows that the product is in an amorphous state.

[0046] Example 6: Electrolysis of water and oxygen evolution reaction activity test

[0047] The high entropy nano-phosphide electrocatalysts obtained in Examples 1, 2, 3, 4, and 5 were used as working electrodes, platinum mesh as counter electrode, and Hg / HgO electrode as reference electrode, respectively. The electrode materials were reconstructed by cyclic voltammetry (CV) at 30°C under alkaline conditions: the scanning range was 1.124-1.724 V vs RHE, and the scanning time was 50 mVs -1 The activity was evaluated by linear sweep voltammetry (LSV) in the scanning range of 1.094–2.004 V vs RHE at 5 mV s -1 The activity was evaluated at a scan rate of 100 kHz to 0.01 Hz. Electrochemical impedance spectroscopy (EIS) was obtained at a potential of 0.56 V vs. Hg / HgO in the frequency range of 100 kHz to 0.01 Hz.

[0048] Example 7: Stability test of oxygen evolution reaction in electrolyzed water

[0049] The high entropy nano-phosphide electrocatalyst obtained in Example 1 was used as the working electrode, the platinum mesh was used as the counter electrode, and the Hg / HgO electrode was used as the reference electrode. -2 The stability of the current density was tested using chronopotentiometry.

[0050] Attachment Figure 1 This is a scanning electron microscope image of the high entropy nanophosphide material prepared in Example 1 of the present invention. It can be seen that the catalyst is uniformly distributed, small in size, and rich in porous spherical particles.

[0051] Attachment Figure 2 This is the SEM particle size distribution histogram of the high entropy nano-phosphide material prepared in Example 1 of the present invention. 0.1 The particle size of the catalyst is small, only 27.1 nm.

[0052] Attachment Figure 3 These are transmission electron micrographs of the high-entropy nanophosphide materials prepared in Example 1 of the present invention. The catalyst particle sizes are 100 nm and 10 nm, respectively.

[0053] Attachment Figure 4 The X-ray diffraction patterns of the high-entropy nanophosphide materials prepared in Examples 1, 2, 3, 4, and 5 of the present invention are shown. No obvious diffraction peaks are found in the XRD patterns, demonstrating that all five catalysts with different P element addition contents (involving six elements: Fe, Co, Ni, Mo, W, and P) exist primarily in an amorphous form or are dispersed as highly dispersed ultrafine nanoparticles.

[0054] Attachment Figure 5 This is the in-situ Raman spectrum of the high entropy nano-phosphide material prepared in Example 1 of the present invention. -1 There is no obvious peak of the catalyst except the carbon paper peak at . 0.1 The characteristic peak of M-OOH quickly appeared at a low voltage of 1.2V.

[0055] Attachment Figure 6 Oxygen evolution performance of the high-entropy nano-phosphide materials prepared in Example 1 and Examples 2, 3, 4, and 5 of the present invention: (a) polarization curve, (b) electrochemical impedance spectroscopy, and (c) Tafel curve. Figure 6 (a), FeCoNiMoWP 0.1 showed the highest OER activity at 10 mA cm -2 It shows an ultra-low overpotential of 75.4mV, which is better than other samples, FeCoNiMoWP (95.0mV) and FeCoNiMoWP 0.05(77.1mV), FeCoNiMoWP 0.15 (76.8mV), FeCoNiMoWP 0.2 (80.3 mV), which indicates that the addition of an appropriate amount of P improves the OER activity of the catalyst. Figure 6 (b) The electrochemical impedance spectroscopy (EIS) of the catalysts FeCoNiMoWP0 (1.92Ω), FeCoNiMoWP 0.05 (1.70Ω), FeCoNiMoWP 0.15 (1.84Ω) and FeCoNiMoWP 0.2 (1.62Ω) compared to FeCoNiMoWP 0.1 The charge transfer resistance (1.58Ω) is the lowest, which indicates that it has the fastest electron transfer rate. Figure 6 (c), FeCoNiMoWP 0.1 The Tafel slope is the smallest, which is 31.95mV dec -1 , much lower than FeCoNiMoWP (71.09mV dec -1 ) and FeCoNiMoWP 0.05 (35.46mV dec -1 ), FeCoNiMoWP 0.15 (32.74mV dec -1 ), FeCoNiMoWP 0.2 (36.53mV dec -1 ), which proves that it has fast OER kinetics. Combined with the physical characterization results, it can be found that FeCoNiMoWP 0.1 The enhanced activity of the catalyst can be attributed to the smallest particle size, which is conducive to exposing more surface active sites; the introduction of P accelerates the generation of highly active M-OOH species during the activation and self-reconstruction process of the catalyst and introduces abundant active sites and oxygen vacancies.

[0056] Attachment Figure 7 This is the oxygen evolution stability test curve of the high entropy nano-phosphide material prepared in Example 1 of the present invention. -2 The FeCoNiMoWP was studied by constant current test under the current density 0.1 Long-term electrochemical stability of FeCoNiMoWP 0.1 At 100mA cm -2 The electrolysis was sustained and stable for 1350 hours at high current density, maintaining excellent activity. This is attributed to the high-valent elements Mo and W acting as sacrificial agents to protect the high activity of active metal sites, thus enabling the reaction to be sustained and stable.

[0057] The above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A high entropy nanophosphide electrocatalyst, characterized in that: The high-entropy nano-phosphide electrocatalyst includes six elements: iron, cobalt, nickel, molybdenum, tungsten and phosphorus.

2. A high entropy nano-phosphide electrocatalyst according to claim 1, characterized in that The molar ratio of iron, cobalt, nickel, molybdenum, tungsten and phosphorus is 1:1:3:2:1:2.

5.

3. The high entropy nano-phosphide electrocatalyst according to claim 1, characterized in that: The metals in the high-entropy nano-phosphide electrocatalyst are all in an amorphous state.

4. The high entropy nano-phosphide electrocatalyst according to claim 1, characterized in that: The high entropy nano-phosphide electrocatalyst has a microscopic morphology of spherical nano-particles with an average particle size of 20-60 nm.

5. A method for preparing the high entropy nano-phosphide electrocatalyst according to claim 1, characterized in that: The following steps are involved: S1. Dissolve the iron, cobalt, and nickel metal salt precursors in deionized water to form a clear solution, then rapidly add molybdate, tungstate, and sodium phosphate under ultrasonic conditions and continue ultrasonication for 5-20 minutes; S2. After ultrasonication, stirring was continued for 4-12h. After the solution was fully reacted, the resulting suspension was centrifuged 8-15 times, and the centrifuged product was washed with anhydrous ethanol; S3. The washed product was placed in a vacuum drying oven and dried at 80-120°C for 12-24h to obtain a high-entropy nanophosphide electrocatalyst; S4. Prepare the obtained catalyst into an ink solution, drop-coat it on carbon paper, and place it in an 80°C oven to dry. After drying, use cyclic voltammetry scanning to reconstruct the catalyst.

6. The method for preparing a high entropy nano-phosphide electrocatalyst according to claim 5, characterized in that: In step S1, the iron, cobalt and nickel metal salt precursors are cobalt nitrate hexahydrate, iron nitrate nonahydrate and nickel nitrate hexahydrate, and the molybdate and tungstate are sodium molybdate dihydrate and sodium tungstate dihydrate.

7. The method for preparing a high entropy nano-phosphide electrocatalyst according to claim 5, characterized in that: The amount of sodium phosphate added in step S1 is 0.05-0.15 mol.

8. The method for preparing a high entropy nano-phosphide electrocatalyst according to claim 5, characterized in that: The ink solution in step S4 is a mixture of ethanol, ultrapure water, Nafion and a high-entropy nano-phosphide electrocatalyst.

9. The method for preparing a high entropy nano-phosphide electrocatalyst according to claim 5, characterized in that: The reconstruction method in step S4 is as follows: using the prepared catalyst as the working electrode, the platinum mesh as the counter electrode, and the Hg / HgO electrode as the reference electrode, cyclic voltammetry reconstruction is performed in a 1 M KOH electrolyte at 30° C. with a scan range of 1.124-1.724 V vs RHE.

10. Use of the high-entropy nano-phosphide electrocatalyst according to claim 1 in oxygen evolution reaction.

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