Two-phase six-element high-entropy oxide water electrolysis catalyst and preparation method thereof

Abstract

The application discloses a two-phase six-element high-entropy oxide water electrolysis catalyst and a preparation method thereof. The preparation method comprises the following steps: mixing metal salts and a solvent, ultrasonicating until the metal salts are completely dissolved, drying to obtain a precursor powder, wherein the metal salts are a mixture of iron salts, nickel salts, molybdenum salts, ruthenium salts, tungsten salts and aluminum salts; pyrolyzing the precursor powder, cooling, washing, drying to obtain the two-phase six-element high-entropy oxide water electrolysis catalyst, wherein the pyrolyzing is first pyrolyzed at 200-400 DEG C for 2-4 hours under an air atmosphere, and then pyrolyzed at 400-700 DEG C for 2-4 hours under an inert gas atmosphere. The two-phase six-element high-entropy oxide water electrolysis catalyst prepared by the preparation method has a two-phase structure heterojunction and crystal defects, which can be used as active sites for water electrolysis oxygen evolution reaction, improves electron transfer, effectively enhances the performance and stability of the catalyst, and has significant oxygen evolution performance and stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrolysis of water, and particularly relates to a two-phase six-element high-entropy oxide electrolysis of water catalyst and a preparation method thereof. BACKGROUND

[0002] With the development of society, the overuse of fossil fuels has led to an intensifying energy crisis, and it is urgent to seek renewable and environmentally friendly energy as a replacement. Hydrogen energy is not only an environmentally friendly energy that reduces greenhouse gas emissions and solves sustainability problems, but also a kind of energy storage fuel, which is widely used in the automobile industry, the chemical industry and other industries. The process of electrolysis of water to produce hydrogen has simple technical equipment and stable and reliable process flow, and the produced hydrogen has no by-products and extremely high purity, and has technical superiority in environmental benefits and energy efficiency, which is an important way to solve the current energy crisis.

[0003] Generally speaking, the electrolysis of water reaction is composed of two half-reactions of anode oxygen evolution reaction (OER) and cathode hydrogen evolution reaction (HER). However, there is still a lot of room for improvement in the actual electrolysis of water process. The oxygen evolution reaction has a slow reaction rate and a high overpotential due to four-electron transfer, which reduces the efficiency of the electrolysis of water reaction. At present, the industrial OER electrocatalyst is highly dependent on noble metal catalysts, but noble metal-based catalysts have the disadvantages of high cost, low crustal reserves and poor stability.

[0004] High-entropy oxides (HEOs) as a new type of high-entropy material with stable geometric structure and unique electronic properties have attracted extensive research in the field of electrolysis of water. High-entropy oxides are composed of five or more metal elements, and the atomic fraction of each element is between 5% and 35%. Due to its multiple properties such as high configurational entropy, lattice distortion, slow diffusion and cocktail effect, it has attracted attention in many fields. However, the widespread use of high-entropy oxides still faces many fundamental problems. The preparation method of high-entropy oxide catalysts mainly requires high temperature or high energy to create extreme synthesis environment, and the preparation process is complex or the preparation conditions are harsh. Therefore, it is necessary to develop a relatively low-energy operating condition to prepare high-performance high-entropy oxide catalysts. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of a two-phase six-element high-entropy oxide electrolysis of water catalyst.

[0006] Another purpose of the present application is to provide a two-phase six-element high-entropy oxide electrolysis of water catalyst obtained by the above preparation method.

[0007] Another purpose of the present application is to provide the application of the above two-phase six-element high-entropy oxide electrolysis of water catalyst in the oxygen evolution reaction of electrolysis of water.

[0008] The purpose of the present application is achieved by the following technical solutions.

[0009] A preparation method of a two-phase six-element high-entropy oxide water electrolysis catalyst, comprising the following steps:

[0010] S1, mixing metal salts and a solvent, ultrasonicating until the metal salts are completely and uniformly dispersed, drying to obtain a precursor powder, the metal salts being a mixture of iron salts, nickel salts, molybdenum salts, ruthenium salts, tungsten salts and aluminum salts;

[0011] In S1, the ultrasonicating time is 1-2h.

[0012] In S1, the solvent is a mixture of one or more of water, anhydrous ethanol and methanol.

[0013] In S1, the ratio of the number of moles of (all) metal elements in the metal salts to the volume fraction of the solvent is (2.3-3.4):2, the unit of the number of moles being mmol and the unit of the volume fraction being mL.

[0014] In S1, the ratio of the number of moles of iron elements in the iron salts, nickel elements in the nickel salts, molybdenum elements in the molybdenum salts, ruthenium elements in the ruthenium salts, tungsten elements in the tungsten salts and aluminum elements in the aluminum salts is 0.6:0.6:0.6:(0.2-0.6):(0.1-0.6):(0.2-0.4).

[0015]

[0016] In the above technical solution, the ratio of the number of moles of iron elements in the iron salts, nickel elements in the nickel salts, molybdenum elements in the molybdenum salts, ruthenium elements in the ruthenium salts, tungsten elements in the tungsten salts and aluminum elements in the aluminum salts is preferably 0.6:0.6:0.6:0.6:0.6:(0.3-0.4).

[0017] S2, pyrolyzing the precursor powder, cooling, washing, drying to obtain a two-phase six-element high-entropy oxide water electrolysis catalyst, the pyrolyzing being first heat preservation at 200-400℃ under an air atmosphere for 2-4h, and then heat preservation at 400-700℃ under an inert gas atmosphere for 2-4h.

[0018] The two-phase six-element high-entropy oxide water electrolysis catalyst obtained by the above preparation method.

[0019] The above two-phase six-element high-entropy oxide water electrolysis catalyst is used in an oxygen evolution reaction of water electrolysis.

[0020] In the above technical solution, the electrode prepared from the two-phase six-element high-entropy oxide water electrolysis catalyst has an overpotential of 299mV at a current density of 200mAcm -2 .

[0021] ​Compared with the prior art, the present application has the beneficial effects that:

[0022] The two-phase six-element high-entropy oxide water electrolysis catalyst is prepared by a simple ion exchange pyrolysis synthesis method, has a two-phase structure of monoclinic phase and orthorhombic phase, and is prepared under relatively mild conditions, thereby reducing the complexity and cost of the preparation of the high-entropy oxide. The hetero-interface and crystal defects of the two-phase structure in the two-phase six-element high-entropy oxide water electrolysis catalyst prepared by the method can serve as active sites for the oxygen evolution reaction of water electrolysis, improve the electron transfer, and effectively enhance the performance and stability of the catalyst, thereby having significant oxygen evolution performance and stability. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The XRD pattern of the catalyst prepared in Example 1;

[0024] Figure 2 The SEM pattern of the catalyst prepared in Example 1;

[0025] Figure 3 The TEM pattern of the catalyst prepared in Example 1;

[0026] Figure 4 The TEM pattern of the catalyst prepared in Example 2;

[0027] Figure 5 The TEM mapping pattern of the catalyst prepared in Example 1;

[0028] Figure 6 The stability diagram of Examples 5-6 and RuO2;

[0029] Figure 7 The linear sweep voltammetry curve diagram of Examples 5-8. DETAILED DESCRIPTION

[0030] The technical solutions of the present application are further described below in combination with specific examples.

[0031] NiCl2·6H2O (Tianjin Fukun Chemical Reagent Co., Ltd., AR), FeCl3·6H2O (Tianjin Kemeluo Chemical Reagent Co., Ltd., GR), RuCl3 (Tianjin Xinsisheng Biological Technology Co., Ltd., metal base, 99.5%), WCl6 (Shanghai Dibai Biological Technology Co., Ltd., AR 99.5%), Al(NO3)3·9H2O (Shanghai Aladdin Biochemical Technology Co., Ltd., AR 99.0%), MoO2 (Shanghai Luyan Biological Medicine Technology Co., Ltd., 99.0%), CH3OH (Tianjin Fukun Chemical Reagent Co., Ltd., AR), KOH (Tianjin Kemeluo Chemical Reagent Co., Ltd.).

[0032] In the following examples, the iron salt is FeCl3·6H2O, the nickel salt is NiCl2·6H2O, the molybdenum salt is MoO2, the ruthenium salt is RuCl3, the tungsten salt is WCl6, and the aluminum salt is Al(NO3)3·9H2O.

[0033] Examples 1-3

[0034] A method for preparing a catalyst, comprising the following steps:

[0035] S1, mixing a metal salt and a solvent, ultrasonicating at an ultrasonic frequency of 40 KHz for 1 h to completely and uniformly disperse the metal salt, to carry out a simple ion exchange reaction, freeze-drying at -50℃ for 6 h to obtain a precursor powder, the metal salt being X, the ratio of each metal element in the metal salt being Y, the solvent being anhydrous ethanol, the ratio of the amount of substance of the metal element(s) in the metal salt (all) to the volume fraction of the solvent being Z, the amount of substance being in mmol, and the volume fraction being in mL;

[0036] S2, pyrolyzing the precursor powder in a tube furnace, cooling to room temperature, washing twice with deionized water and once with anhydrous ethanol, and drying in a freeze-drying box at -50℃ for 8 h to obtain a catalyst (the catalysts prepared in Examples 1 and 3 are two-phase six-element high-entropy oxide water electrolysis catalysts), wherein the pyrolysis is: first heat treatment at 250℃ (heat to 250℃ at a heating rate of 5℃ / min) under an air atmosphere for 2 h, and then heat treatment at 500℃ (heat from 250℃ to 500℃ at a heating rate of 5℃ / min) under an Ar atmosphere for 2 h.

[0037] X, Y and Z are shown in Table 1.

[0038] Table 1

[0039]

[0040] Example 4

[0041] A preparation method of a two-phase six-member high-entropy oxide water electrolysis catalyst, comprising: placing 0.6 mmol FeCl3·6H2O, 0.6 mmol NiCl2·6H2O, 0.6 mmol MoO2, 0.6 mmol RuCl3, 0.6 mmol WCl6 and 0.357 mmol Al(NO3)3·9H2O in a mortar, grinding at a speed of 500 r / min for 10 min to obtain a precursor powder, placing the precursor powder in a tube furnace, heating to 250 DEG C at a rate of 5 DEG C / min in an air atmosphere and keeping at 250 DEG C for 2 h, then heating to 500 DEG C at a rate of 5 DEG C / min in an Ar atmosphere and keeping at 500 DEG C for 2 h, cooling, first washing with deionized water for 2 times, then washing with anhydrous ethanol for 1 time, and placing in a freeze-drying box at -50 DEG C for drying for 8 h to obtain the two-phase six-member high-entropy oxide water electrolysis catalyst.

[0042] Examples 5-8

[0043] A three-electrode system includes a working electrode, a counter electrode and a reference electrode, wherein the counter electrode is a platinum wire electrode, the reference electrode is an Ag / AgCl electrode, and the working electrode is prepared by mixing 5 mg of the catalyst, 1 mg of carbon black, 990 microliters of anhydrous ethanol and 10 microliters of a 5% Nafion solution, ultrasonicating in an ultrasonic machine at an ultrasonic frequency of 40 KHz for 1 h to obtain a catalyst ink with good dispersibility, dropping 4 microliters of the catalyst ink on a glassy carbon electrode with a diameter of 3 mm, and drying at room temperature for 2 h to obtain the working electrode, and the catalyst is one of examples 1-4 (the working electrodes of examples 5-8 are obtained in turn from the catalysts of examples 1-4).

[0044] LSV oxygen evolution test: in the CHI760e workstation of Chenhua, the activated three-electrode system is used for LSV oxygen evolution test: first, in the CHI760e workstation of Chenhua, the above-mentioned three-electrode system is activated in the electrolyte (the electrolyte is a mixture of electrolyte and solvent, the electrolyte in the electrolyte is KOH, the concentration of the electrolyte in the electrolyte is 1 mol / L, and the solvent of the electrolyte is deionized water. The activation method is cyclic voltammetry, the scanning voltage is set to 1.22-1.82 (vs RHE), the scanning speed is set to 50 mV / s, and the cycle is 60 times), and the activated three-electrode system is used for LSV oxygen evolution test in the electrolyte, and the parameters of the LSV oxygen evolution test are: scanning rate 2 mV / s, scanning voltage 1.22-1.82 (vs RHE). The linear sweep voltammetry curve of Figure 7 from the LSV curve in Figure 7 It can be seen that the current density is 10 mA cm -2At that time, the overpotential of the working electrode in Example 6 (catalyst of Example 2) was 260 mV, the overpotential of the working electrode in Example 7 (catalyst of Example 3) was 204 mV, and the overpotential of the working electrode in Example 8 (catalyst of Example 4) was 229 mV. The overpotential of the working electrode in Example 5 (catalyst of Example 1) was 206 mV, and at 200 mA cm⁻¹... -2 At the specified current density, its overpotential is 299 mV, which is lower than that of Examples 6-8. The catalyst prepared in Example 1 exhibits excellent oxygen evolution performance. This indicates that the catalyst prepared in Example 1 achieves the low-energy-consumption water electrolysis oxygen evolution reaction.

[0045] Stability testing (steady-state durability testing): The activated three-electrode systems of Examples 5-6 and the working electrode prepared using RuO2 (purchased from Bide Pharmaceuticals, purity 98%) as a catalyst (the method for preparing the working electrode using RuO2 as a catalyst is the same as the method for preparing the working electrode using the catalyst of Example 1) were placed in the electrolyte and the stability was tested using the potentiostatic method, with an initial current density of 10 mA cm⁻¹. -2 Obtained from stability tests Figure 6 The stability plot. (For example...) Figure 6 As shown, the working electrode prepared from the catalyst of Example 1 ( Figure 6 (Example 1) at 10mA / cm 2 It can maintain stable operation for 100 hours at the initial current density, and the current density does not decrease significantly. In contrast, the working electrode prepared from the catalyst in Example 2 ( Figure 6 In Example 2, the current density decreased by 30% over 44 hours (current density was 10 mA / cm² at 0 hours). 2 After 44 hours of operation, the current density dropped to 7 mA / cm². 2 This demonstrates that the catalyst in Example 1 exhibits significant long-term stability.

[0046] Figure 1 The image shows the XRD pattern of the catalyst prepared in Example 1. The catalyst prepared in Example 1 mainly matches the characteristic peaks of the Fe2WO6 (PDF#42-0492) and NiMoO4 (PDF#33-0948) spectra, proving that the catalyst of Example 1 is composed of a monoclinic phase with space group I2 / m and an orthorhombic phase with space group Pmmn.

[0047] Figure 2 The image shows the SEM image of the catalyst prepared in Example 1.

[0048] Figure 3 The image shows a TEM image of the catalyst prepared in Example 1. Figure 4TEM mapping of the catalyst prepared in Example 2 was prepared. The high resolution transmission electron microscopy (HRTEM) of the catalyst prepared in Example 1 showed that there were a large number of randomly distributed lattice fringes, indicating that there were crystal boundaries in the catalyst prepared in Example 1, and the lattice spacing of 0.2295 nm and 0.3166 nm corresponded to the Fe2WO6(200) and NiMoO4(-301) crystal planes, respectively, which was consistent with the XRD information. The high resolution transmission electron microscopy (HRTEM) of the catalyst prepared in Example 2 showed that the lattice spacing of 0.2487 nm and 0.3166 nm corresponded to the Fe2WO6(002) and NiMoO4(-301) crystal planes, respectively, which was consistent with the XRD information.

[0049] Figure 5 TEM mapping of the catalyst prepared in Example 1 was prepared. Figure 5 It was proved that the metal elements Fe, Mo, Ni, Ru, Al, W and O in the catalyst prepared in Example 1 were uniformly distributed in the catalyst, and there was no obvious element aggregation or segregation.

[0050] The above has made an exemplary description of the present application, it should be explained that, without departing from the core of the present application, any simple modification, change or other equivalent replacement which can not cost the creative labor of the person skilled in the art falls into the protection scope of the present application.

Claims

1. A method for preparing a two-phase six-membered high-entropy oxide water electrolysis catalyst, characterized in that, The method comprises the following steps: S1, mixing a metal salt and a solvent, ultrasonicating until the metal salt is completely and uniformly dispersed, drying to obtain a precursor powder, wherein the metal salt is a mixture of iron salt, nickel salt, molybdenum salt, ruthenium salt, tungsten salt and aluminum salt; S2, pyrolyzing the precursor powder, cooling, washing and drying to obtain a two-phase six-element high-entropy oxide water electrolysis catalyst, wherein the pyrolyzing comprises the following steps: first, heat preservation at 200-400 °C for 2-4 h in an air atmosphere, and then heat preservation at 400-700 °C for 2-4 h in an inert gas atmosphere; The two-phase six-element high-entropy oxide water electrolysis catalyst has a two-phase structure of monoclinic phase and orthorhombic phase.

2. The production method according to claim 1, characterized by, In S1, the ratio of iron element in the iron salt, nickel element in the nickel salt, molybdenum element in the molybdenum salt, ruthenium element in the ruthenium salt, tungsten element in the tungsten salt and aluminum element in the aluminum salt is 0.6:0.6:0.6:(0.2-0.6):(0.1-0.6):(0.2-0.4) in terms of the amount of substance.

3. The preparation method according to claim 1, characterized in that, In S1, the ratio of the amount of substance of metal elements in the metal salt to the volume of the solvent is (2.3-3.4):2, wherein the amount of substance is in mmol and the volume is in mL.

4. The production method according to claim 3, characterized by, In S1, the solvent is a mixture of one or more of water, anhydrous ethanol and methanol.

5. The two-phase six-element high-entropy oxide water electrolysis catalyst obtained by the preparation method of any one of claims 1-4.

6. The use of the two-phase six-element high-entropy oxide water electrolysis catalyst of claim 5 in the oxygen evolution reaction of water electrolysis.

7. Use according to claim 6, characterized in that, Electrodes prepared from two-phase, six-membered high-entropy oxide water electrolysis catalysts exhibit a current density of 200 mA cm -2 at a current density of 200 mA cm-2, with an overpotential of 299 mV.

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