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

Abstract

The invention discloses a two-phase six-element high-entropy oxide water electrolysis catalyst and a preparation method thereof.The preparation method comprises the steps that metal salt and a solvent are mixed, ultrasonic treatment is conducted till the metal salt is completely dissolved, drying is conducted, precursor powder is obtained, and the metal salt is a mixture of ferric salt, nickel salt, molybdenum salt, ruthenium salt, tungsten salt and aluminum salt; the precursor powder is subjected to pyrolysis, cooling, washing and drying, the two-phase six-element high-entropy oxide electrolyzed water catalyst is obtained, and pyrolysis comprises the steps that pyrolysis is conducted for 2-4 h at the temperature of 200-400 DEG C in the air atmosphere, and then pyrolysis is conducted for 2-4 h at the temperature of 400-700 DEG C in the inert gas atmosphere. According to the two-phase six-element high-entropy oxide water electrolysis catalyst prepared through the preparation method, a heterogeneous interface and crystal defects of a two-phase structure can serve as active sites of water electrolysis oxygen evolution reaction, electron transfer is improved, the performance and stability of the catalyst are effectively enhanced, and the two-phase six-element high-entropy oxide water electrolysis catalyst has remarkable oxygen evolution performance and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of water electrolysis, and specifically relates to a two-phase hexavalent high-entropy oxide water electrolysis catalyst and a preparation method thereof. Background Art

[0002] With the development of society, the excessive use of fossil fuels has led to an intensified energy crisis, and there is an urgent need to seek renewable and environmentally friendly energy as an alternative. Hydrogen energy is not only an environmentally friendly energy that reduces greenhouse gas emissions and solves sustainability issues, but is also a storage fuel that is widely used in the automotive industry, chemical industry and other industries. The process of hydrogen production by electrolysis of water has simple technical equipment, stable and reliable process flow, and the hydrogen produced has no by-products and is extremely pure. It has technical advantages in terms of environmental benefits and energy efficiency, and has become an important way to solve the current energy crisis.

[0003] In general, the water electrolysis reaction consists of two half reactions: the anode oxygen evolution reaction (OER) and the cathode hydrogen evolution reaction (HER). However, there is still a huge room for improvement in the actual water electrolysis process. Due to the four-electron transfer, the oxygen evolution reaction has a slow reaction rate and a high overpotential, which reduces the reaction efficiency of water electrolysis. At present, industrial-grade OER electrocatalysts are highly dependent on precious metal catalysts, but precious metal-based catalysts have disadvantages such as high cost, small crustal reserves, and poor stability.

[0004] As a new type of high entropy material with stable geometric structure and unique electronic properties, high entropy oxides (HEOs) have attracted extensive research in the field of water electrolysis. High entropy oxides are composed of five or more metal elements, with the atomic fraction of each element ranging from 5% to 35%. They have attracted attention in many fields due to their various properties, such as high configurational entropy, lattice distortion, slow diffusion and cocktail effect. However, the widespread use of high entropy oxides still faces many basic problems. The preparation method of high entropy oxide catalysts mainly requires high temperature or high energy to create an extreme synthesis environment. The preparation process is complicated or the preparation conditions are harsh. Therefore, a relatively low-energy operating condition is required to prepare high-performance high entropy oxide catalysts. Summary of the invention

[0005] In view of the deficiencies in the prior art, the object of the present invention is to provide a method for preparing a two-phase hexavalent high entropy oxide water electrolysis catalyst.

[0006] Another object of the present invention is to provide a two-phase hexavalent high entropy oxide water electrolysis catalyst obtained by the above preparation method.

[0007] Another object of the present invention is to provide an application of the above-mentioned two-phase hexavalent high entropy oxide water electrolysis catalyst in the oxygen evolution reaction of water electrolysis.

[0008] The purpose of the present invention is achieved through the following technical solutions.

[0009] A method for preparing a two-phase hexavalent high entropy oxide water electrolysis catalyst comprises the following steps:

[0010] S1, mixing a metal salt and a solvent, ultrasonicating until the metal salt is completely and evenly dispersed, and drying to obtain a precursor powder, wherein the metal salt is a mixture of an iron salt, a nickel salt, a molybdenum salt, a ruthenium salt, a tungsten salt and an aluminum salt;

[0011] In S1, the ultrasonication time is 1 to 2 hours.

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

[0013] In S1, the ratio of the amount of the metal elements in the metal salt to the volume of the solvent is (2.3-3.4):2, the unit of the amount of the metal elements is mmol, and the unit of the volume is mL.

[0014] In S1, the ratio of iron in iron salt, nickel in nickel salt, molybdenum in molybdenum salt, ruthenium in ruthenium salt, tungsten in tungsten salt and aluminum in aluminum salt is 0.6:0.6:0.6:(0.2-0.6):(0.1-0.6):

[0015] (0.2~0.4).

[0016] In the above technical scheme, calculated by the amount of substance, the ratio of iron in iron salt, nickel in nickel salt, molybdenum in molybdenum salt, ruthenium in ruthenium salt, tungsten in tungsten salt and aluminum in aluminum salt is preferably 0.6:0.6:0.6:0.6:0.6:(0.3~0.4).

[0017] S2, pyrolyzing the precursor powder, cooling, washing, and drying to obtain a two-phase hexavalent high entropy oxide water electrolysis catalyst, wherein the pyrolysis is: firstly keeping the temperature at 200-400° C. for 2-4 hours in an air atmosphere, and then keeping the temperature at 400-700° C. for 2-4 hours in an inert gas atmosphere.

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

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

[0020] In the above technical scheme, the electrode prepared by the two-phase hexavalent high entropy oxide water electrolysis catalyst is 200mAcm -2 At current density, the overpotential is 299mV.

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

[0022] The two-phase six-element high entropy oxide water electrolysis catalyst of the present invention is prepared by a simple ion exchange thermal decomposition synthesis method. The two-phase six-element high entropy oxide water electrolysis catalyst has a two-phase structure of a monoclinic phase and an orthorhombic phase. The synthesis process does not involve complex equipment, consumes less energy, and has a short experimental cycle. The two-phase six-element high entropy oxide water electrolysis catalyst is prepared under relatively mild conditions, reducing the complexity and cost of preparing high entropy oxides. The heterogeneous interface and crystal defects of the two-phase structure in the two-phase six-element high entropy oxide water electrolysis catalyst prepared by the preparation method of the present invention can be used as active sites for the oxygen evolution reaction of electrolysis of water, thereby improving electron transfer, effectively enhancing the performance and stability of the catalyst, and having significant oxygen evolution performance and stability. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0024] Figure 2 This is a SEM image of the catalyst prepared in Example 1;

[0025] Figure 3 This is a TEM image of the catalyst prepared in Example 1;

[0026] Figure 4 This is a TEM image of the catalyst prepared in Example 2;

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

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

[0029] Figure 7 The linear sweep voltammetry curves of Examples 5 to 8 are shown in FIG. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0031] NiCl2·6H2O (Tianjin Fuchen Chemical Reagent Co., Ltd., AR), FeCl3·6H2O (Tianjin Komio Chemical Reagent Co., Ltd., GR), RuCl3 (Tianjin Xiensi Biochemical Technology Co., Ltd., metal-based, 99.5%), WCl6 (Shanghai Dibai Biotechnology Co., Ltd., AR99.5%), Al(NO3)3·9H2O (Shanghai Aladdin Biochemical Technology Co., Ltd., AR99.0%), MoO2 (Shanghai Leyan Biopharmaceutical Technology Co., Ltd., 99.0%), CH3OH (Tianjin Fuchen Chemical Reagent Co., Ltd., AR), KOH (Tianjin Komio Chemical Reagent Co., Ltd.).

[0032] In the following embodiments, 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 to 3

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

[0035] S1, mixing a metal salt and a solvent, ultrasonically treating the mixture at an ultrasonic frequency of 40 KHz for 1 h until the metal salt is completely and evenly dispersed, so as to perform a simple ion exchange reaction, and freeze-drying the mixture at -50°C for 6 h to obtain a precursor powder, wherein the metal salt is X, the ratio of each metal element in the metal salt is Y in terms of molar fraction, the solvent is anhydrous ethanol, the ratio of the molar fraction of (all) metal elements in the metal salt to the volume fraction of the solvent is Z, the unit of the molar fraction is mmol, and the unit of the volume fraction is mL;

[0036] S2, placing the precursor powder in a tube furnace for pyrolysis, cooling to room temperature, washing twice with deionized water, then washing once with anhydrous ethanol, and drying in a -50°C freeze drying oven for 8 h to obtain a catalyst (the catalysts prepared in Example 1 and Example 3 are two-phase hexavalent high entropy oxide water electrolysis catalysts), wherein the pyrolysis is: first, keeping warm at 250°C in an air atmosphere (heating to 250°C at a heating rate of 5°C / min) for 2 h, and then keeping warm at 500°C in an Ar atmosphere (from 250°C to 500°C at a heating rate of 5°C / min) 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 hexavalent high entropy oxide water electrolysis catalyst comprises: 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 rotation speed of 500 r / min for 10 min to obtain a precursor powder, placing the precursor powder in a tube furnace, heating the precursor powder to 250°C at a rate of 5°C / min in an air atmosphere and maintaining the temperature at 250°C for 2 h, then heating the precursor powder to 500°C at a rate of 5°C / min in an Ar atmosphere and maintaining the temperature at 500°C for 2 h, cooling the precursor powder, washing the precursor powder twice with deionized water, then washing the precursor powder once with anhydrous ethanol, and drying the precursor powder in a freeze drying oven at -50°C for 8 h to obtain a two-phase hexavalent high entropy oxide water electrolysis catalyst.

[0042] Embodiments 5 to 8

[0043] Three-electrode system: including a working electrode, a counter electrode and a reference electrode, wherein the counter electrode is a platinum wire electrode, and the reference electrode is an Ag / AgCl electrode. The method for preparing the working electrode is: 5 mg of catalyst, 1 mg of carbon black, 990 μl of anhydrous ethanol and 10 μl of 5% Nafion solution are mixed, and ultrasonicated at an ultrasonic frequency of 40 KHz for 1 hour in an ultrasonic machine to obtain a catalyst ink with good dispersion, 4 μl of the catalyst ink is dropped on a glassy carbon electrode with a diameter of 3 mm, and dried at room temperature for 2 hours to obtain a working electrode. The catalyst is one of Examples 1 to 4 (the working electrodes of Examples 5 to 8 are obtained in sequence from the catalysts of Examples 1 to 4).

[0044] LSV oxygen evolution test: In the Chenhua workstation CHI760e, the LSV oxygen evolution test was performed using an activated three-electrode system: First, in the Chenhua workstation CHI760e, the three-electrode system was activated in an 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 50mV / s, and the cycle is 60 times), and the activated three-electrode system was subjected to an LSV oxygen evolution test in the electrolyte. The parameters of the LSV oxygen evolution test are: scanning rate 2mV / s, scanning voltage 1.22-1.82 (vs RHE). Obtained from the LSV oxygen evolution test Figure 7 Linear sweep voltammetry curve of Figure 7 From the LSV curve, we can see that the current density is 10 mA cm -2When the overpotential of the working electrode of Example 6 (the catalyst of Example 2) is 260 mV, the overpotential of the working electrode of Example 7 (the catalyst of Example 3) is 204 mV, and the overpotential of the working electrode of Example 8 (the catalyst of Example 4) is 229 mV. The overpotential of the working electrode of Example 5 (the catalyst of Example 1) is 206 mV, and at 200 mA cm -2 At the current density, the overpotential is 299 mV, which is less than that of Examples 6 to 8. The catalyst prepared in Example 1 has excellent oxygen evolution performance. This shows that the catalyst prepared in Example 1 achieves low-energy electrolysis of water and oxygen evolution reaction.

[0045] Stability test (steady-state durability test): The activated three-electrode system of Examples 5-6 and RuO2 (purchased from Bid Pharmaceuticals, purity 98%) as a catalyst to prepare a working electrode (the method for preparing a working electrode using RuO2 as a catalyst is the same as the method for preparing a working electrode using the catalyst of Example 1) were placed in an electrolyte and subjected to a stability test using a constant potential method, with an initial current density of 10 mA cm -2 . Obtained from stability test Figure 6 Stability diagram of . Figure 6 As shown, the working electrode ( Figure 6 "Example 1" in 10mA / cm 2 The initial current density can maintain stable operation for 100 h, and the current density does not drop significantly. In contrast, the working electrode prepared by the catalyst of Example 2 ( Figure 6 The current density was 10 mA / cm2 at 0 h, and the 2 After 44 hours of operation, the current density dropped to 7 mA / cm 2 ), demonstrating that the catalyst of Example 1 has remarkable long-term stability.

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

[0047] Figure 2 This is the SEM image of the catalyst prepared in Example 1.

[0048] Figure 3 This is the TEM image of the catalyst prepared in Example 1. Figure 4The TEM image of the catalyst prepared in Example 2. The high-resolution projection scanning electron microscopy image (HRTEM) of the catalyst prepared in Example 1 shows that the catalyst has a large number of randomly distributed lattice fringes, indicating the presence of grain boundaries in the catalyst prepared in Example 1, and shows that the lattice spacings of 0.2295nm and 0.3166nm correspond to the Fe2WO6(200) and NiMoO4(-301) crystal planes, respectively, which is consistent with the XRD information. The high-resolution projection scanning electron microscopy image (HRTEM) of the catalyst prepared in Example 2 shows that the lattice fringes with lattice spacings of 0.2487nm and 0.3166nm correspond to the Fe2WO6(002) and NiMoO4(-301) crystal planes, respectively, which is consistent with the XRD information.

[0049] Figure 5 This is the TEM mapping image of the catalyst prepared in Example 1. Figure 5 It is proved that the metal elements Fe, Mo, Ni, Ru, Al, W, and O in the catalyst prepared in Example 1 are uniformly distributed in the catalyst without obvious element aggregation or segregation.

[0050] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A method for preparing a two-phase hexavalent high entropy oxide water electrolysis catalyst, characterized in that: The following steps are involved: S1, mixing a metal salt and a solvent, ultrasonicating until the metal salt is completely and evenly dispersed, and drying to obtain a precursor powder, wherein the metal salt is a mixture of an iron salt, a nickel salt, a molybdenum salt, a ruthenium salt, a tungsten salt and an aluminum salt; S2, pyrolyzing the precursor powder, cooling, washing, and drying to obtain a two-phase hexavalent high entropy oxide water electrolysis catalyst, wherein the pyrolysis is: firstly keeping the temperature at 200-400° C. for 2-4 hours in an air atmosphere, and then keeping the temperature at 400-700° C. for 2-4 hours in an inert gas atmosphere.

2. The preparation method according to claim 1, characterized in that: In S1, the ratio of iron in iron salt, nickel in nickel salt, molybdenum in molybdenum salt, ruthenium in ruthenium salt, tungsten in tungsten salt and aluminum in aluminum salt is 0.6:0.6:0.6:(0.2~0.6):(0.1~0.6):(0.2~0.4) based on the amount of substance.

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

4. The preparation method according to claim 3, characterized in that: In S1, the solvent is one or a mixture of water, anhydrous ethanol and methanol.

5. A two-phase hexavalent high entropy oxide water electrolysis catalyst obtained by the preparation method according to any one of claims 1 to 4.

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

7. The use according to claim 6, characterized in that: Electrodes prepared from two-phase hexavalent high entropy oxide catalysts for water electrolysis at 200 mA cm -2 At current density, the overpotential is 299mV.

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