Preparation method of manganese-doped nickel sulfide / porous foamed nickel electrode for bifunctional alkaline electrolytic water

Abstract

The invention belongs to the field of materials, and discloses a preparation method of a manganese-doped nickel sulfide / porous foamed nickel electrode for bifunctional alkaline electrolytic water. Through a two-step electro-deposition mode, firstly, a foamed nickel substrate is activated, and then nickel sulfide is electro-deposited on the activated porous foamed nickel substrate and manganese is doped. According to the invention, the manganese-doped nickel sulfide nanostructure grown on the porous foamed nickel constructs an electrode for bifunctional water electrolysis, and the porous structure of the electrode can effectively accelerate the mass transfer process under high current density, and at the same time promotes bubbles generated by reaction to escape quickly. In addition, nickel sulfide is doped with manganese, so that the electronic structure is optimized, and the nickel sulfide has the characteristics of enhanced conductivity, increased electrochemical active area, fully exposed active sites, optimized intermediate adsorption and the like. The preparation method provides an effective strategy for preparation of high-performance electrodes in actual water electrolysis.

Description

Technical Field

[0001] The present invention belongs to the field of materials and relates to a preparation method of a manganese-doped nickel sulfide / porous nickel foam electrode for bifunctional alkaline water electrolysis. Background Art

[0002] In the context of the global active search for clean and sustainable energy forms, hydrogen energy has become an ideal energy carrier attracting much attention due to its significant advantages such as zero emissions, high energy density, easy storage and transportation. Currently, with the increasingly serious problem of climate change and the continuous deterioration of air quality, the over-reliance of human society on oil resources makes the search for clean and sustainable energy forms an urgent task globally.

[0003] The application scope of hydrogen is extremely wide, covering multiple fields such as fuel cell vehicles, industrial gases, and energy storage. There are various methods for hydrogen production. Among them, hydrogen production by electrolyzing water, especially the process of high-current water decomposition, has extremely prominent advantages. In this process, the by-products are only water and oxygen, without causing any pollution to the environment, which highly conforms to the concept of sustainable development, so it has developed vigorously. The basic principle of the water electrolysis decomposition technology is to disassemble water molecules into hydrogen and oxygen by means of an electric current. In this reaction process, the current intensity plays a direct decisive role in the hydrogen production. Therefore, adopting high-current water decomposition is the key path to improve the hydrogen production efficiency. Compared with the traditional small-current electrolysis method, high-current water decomposition has significant advantages. It can not only greatly improve the hydrogen production rate, but also properly meet the demand for large-scale hydrogen in industrial production, and is one of the core key technologies for realizing the industrialization of hydrogen energy.

[0004] The core of breaking through the development bottleneck of water electrolysis technology lies in the research and development of advanced catalytic materials that can withstand high current density. At present, noble metals such as platinum, palladium, rhodium, ruthenium, and iridium are still the most effective catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). However, their high prices and scarce reserves seriously limit their wide application in practice.

[0005] Meanwhile, due to the extremely slow kinetics of both HER and OER, in practical applications, different electrocatalysts are usually used for the cathode and anode. However, catalysts with different functions require different precursors, equipment, and procedures for synthesis, electrode assembly, and device manufacturing, resulting in an increase in the overall cost. Moreover, considering the harsh conditions during the water electrolysis process, such as extreme pH, high potential, and long-term use, the structural reorganization of electrocatalysts (such as metal leaching) is almost inevitable, which will trigger serious cross-contamination problems between the two different electrodes. If the electrocatalysts for HER and OER can use the same material, then this cross-contamination problem is expected to be alleviated. Therefore, the strategy of developing bifunctional electrocatalysts with high activity, high stability, and economic efficiency, which can drive both HER and OER simultaneously to achieve efficient overall water splitting (OWS), has attracted extensive attention.

[0006] Fundamentally speaking, the hydrolysis rate of electrocatalysts and the binding strength of intermediates depend on their surface electronic structure, which further affects the adsorption and desorption behaviors. Therefore, regulating the surface electronic structure is an effective method to accelerate catalytic kinetics. By regulating the size and structure of the catalyst, its mechanical stability and chemical stability can be enhanced. For example, Patent CN119372705A synthesized a carbon-doped non-precious metal high-entropy alloy hydrogen evolution catalytic electrode by doping; Patent CN119372697A prepared a protonated layered iridium oxide H-IrO-2 nanosheet structure, in which the iridium oxide nanosheets are layered, the interlayer can accommodate protons, and there are metal iridium vacancy defects in the plane of the layered structure; Patent CN119392285A prepared a cross-array electrocatalyst, which directly corrodes the nickel mesh to form an intercrossed and supported nanosheet array structure. In the application of powder electrodes, adhesives are often used to connect the catalyst to the substrate. However, if the adhesion of the adhesive is poor or the corrosion resistance is low, the catalyst is extremely likely to fall off under high-current conditions. Moreover, the use of adhesives will also introduce an undesirable active interface resistance, which will not only shield the active sites but also affect the catalytic efficiency and stability. For example, the material prepared in Patent CN119194487A is suitable for the acidic oxygen evolution reaction process under high current density, but this material is in powder form, requires the use of adhesives, and has problems such as high price and poor stability. Therefore, self-supported electrodes grown in situ on the substrate have unique advantages, and they can maintain the integrity and stability of the electrode structure only relying on the inherent characteristics of the active material itself.

[0007] Therefore, the present invention discloses a preparation method of a bifunctional alkaline electrolyzed water manganese-doped nickel sulfide / porous nickel foam electrode. This material is prepared by a two-step electrodeposition method. In the first step, the nickel foam substrate is activated to obtain the activated porous nickel foam electrode. Immediately afterwards, on the activated nickel foam substrate, the manganese-doped nickel sulfide material is directly deposited by electrodeposition again. This process is efficient, rapid, and has mild reaction conditions, which can be carried out at room temperature. The electrode prepared by this process has the catalyst tightly connected to the matrix, which creates a smooth channel for the transfer of electrons and ions. At the same time, the large electrochemically active area exposes the catalytic sites as much as possible, resulting in high electrical conductivity and high catalytic activity. Summary of the Invention

[0008] The present invention provides a preparation method for a bifunctional alkaline electrolyzed water manganese-doped nickel sulfide / porous nickel foam electrode.

[0009] The technical solution of the present invention:

[0010] A preparation method for a bifunctional alkaline electrolyzed water manganese-doped nickel sulfide / porous nickel foam electrode comprises the following steps:

[0011] 1) Cleaning of nickel foam: Cut the nickel foam and ultrasonically clean it in absolute ethanol, hydrochloric acid solution, and deionized water respectively to obtain the treated nickel foam, and dry it for later use;

[0012] 2) Activation treatment of nickel foam: Use the nickel foam obtained in step 1) as the working electrode and place it in electrolyte 1. Adopt a two-electrode system and perform electrodeposition by the constant current I-T method. After completion, take out the working electrode, and then repeatedly wash it with deionized water and absolute ethanol and dry it for later use to obtain the activated nickel foam;

[0013] 3) Deposition process of nickel sulfide: Use the activated nickel foam in step 2) as the working electrode and place it in electrolyte 2. Adopt a three-electrode system and perform electrodeposition treatment by the constant potential E-T method. After deposition, take out the electrode, and then repeatedly wash it with deionized water and absolute ethanol and dry it to obtain the manganese-doped nickel sulfide / porous nickel foam electrode. This bifunctional manganese-doped nickel sulfide / porous nickel foam electrode is applicable to the alkaline electrolyzed water process.

[0014] In step 2), electrolyte 1 is an aqueous solution of nickel salt and ammonium salt;

[0015] Furthermore, the nickel salt is nickel chloride hexahydrate, nickel nitrate hexahydrate, or nickel sulfate hexahydrate; the ammonium salt is ammonium fluoride or ammonium chloride;

[0016] Furthermore, the molar ratio of the nickel salt to the ammonium salt is 1:6 - 1:30, and the concentration of the nickel salt is 1.0 - 2.0 M;

[0017] In step 2), the specific operation of electro-deposition of the two-electrode system by the constant current I-T method is as follows:

[0018] Use clean nickel foam as the working electrode and a graphite rod as the counter electrode; when using the constant current method for electro-deposition, provide a deposition current density of -1.0 to -2.5 A cm -2 for a duration of 300 s to 1500 s.

[0019] In step 3), the electrolyte 2 is an aqueous solution of manganese salt, nickel salt and thiourea;

[0020] Furthermore, the manganese salt is manganese sulfate tetrahydrate or manganese chloride tetrahydrate; the nickel salt is nickel chloride hexahydrate, nickel nitrate hexahydrate or nickel sulfate hexahydrate;

[0021] Furthermore, the total concentration of the manganese salt and the nickel salt is 1.0 M, the concentration of the nickel salt is 0.2 to 0.8 M, and the thiourea concentration is 0.5 to 1.5 M;

[0022] In step 3), the specific operation of electro-deposition of the three-electrode system by the constant voltage E-T method is as follows:

[0023] Use the activated nickel foam as the working electrode, a graphite rod as the counter electrode, and Ag / AgCl as the reference electrode; when using the constant potential method for electro-deposition, provide a deposition potential of -1.4 to -1.8 V for a duration of 5 min to 30 min.

[0024] Advantages of the present invention:

[0025] 1) The manufacturing process of the present invention is simple, convenient and fast, easy to prepare in large quantities, and the material uses non-precious metals, with low cost.

[0026] 2) The present invention uses a self-supporting electrode, and the active material grows directly on the conductive framework, avoiding the blockage of active sites caused by the use of a binder, reducing the interfacial impedance between the active material and the conductive framework, and effectively preventing the active material from falling off the substrate under high current density conditions.

[0027] 3) The electrocatalysts of both electrodes are composed of the same material, which can alleviate the problem of cross-contamination. Develop highly active, stable and cost-effective bifunctional electrocatalysts to drive HER and OER to achieve efficient overall water splitting (OWS).

[0028] 4) Obtain a manganese-doped nickel sulfide / porous nickel foam electrode with high activity, which has significant HER and OER catalytic activities at high current densities. Description of the Drawings

[0029] Figure 1 It is a preparation flow chart of the present invention.

[0030] Figure 2 Scanning electron microscope (SEM) images of the materials, where (a) is the SEM image of pure nickel foam; (b) is the SEM image of the manganese-doped nickel sulfide / porous nickel foam electrode.

[0031] Figure 3 Transmission electron microscope (TEM) image of the manganese-doped nickel sulfide / porous nickel foam electrode of Example 1 of the present invention, where (a) is the TEM image of the observed overall microstructure, and (b) is the lattice fringe image of the microscopic partition at a high magnification.

[0032] Figure 4 Linear sweep voltammetry (LSV) graphs of hydrogen evolution and oxygen evolution reactions of the manganese-doped nickel sulfide / porous nickel foam electrode of Example 1 and Examples 2 and 3 under the test conditions of 25 °C and 1 M KOH, where (a) is the LSV graph of Examples 1, 2, and 3 in the oxygen evolution reaction, and (b) is the LSV graph of Examples 1, 2, and 3 in the hydrogen evolution reaction.

[0033] Figure 5 Linear sweep voltammograms of hydrogen evolution and oxygen evolution reactions of the manganese-doped nickel sulfide / porous nickel foam electrode of Example 1 and Comparative Examples 1 and 2 under the test conditions of 25 °C and 1 M KOH, where (a) is the LSV graph of Example 1 and Comparative Examples 1 and 2 in the oxygen evolution reaction, and (b) is the LSV graph of Example 1 and Comparative Examples 1 and 2 in the hydrogen evolution reaction. Detailed implementation manners

[0034] The technical solutions of the present invention will be further described below in conjunction with the drawings and technical solutions.

[0035] Example 1

[0036] Preparation method of the manganese-doped nickel sulfide / porous nickel foam electrode, specifically including the following steps:

[0037] Step 1: Cut the nickel foam into 1.5 cm × 1 cm, ultrasonically clean it in absolute ethanol, 6 M hydrochloric acid solution, and deionized water for 20 min respectively, and place the treated nickel foam in a 60 °C vacuum tube drying oven for drying and standby;

[0038] Step 2: In a two-electrode system, in electrolyte 1, use the constant current deposition method, use a graphite rod electrode as the counter electrode and nickel foam as the working electrode, and set the cathode current density to -1.0 A cm -2 , and the duration is 600 s; Electrolyte 1 is an aqueous solution of 0.1 M nickel chloride hexahydrate and 2.0 M ammonium fluoride. The electrodeposited nickel foam is repeatedly washed 3 times with deionized water and absolute ethanol, and placed in a 60 °C vacuum tube drying oven for drying and standby.

[0039] Step 3: In a three-electrode system, in electrolyte 2, the potentiostatic deposition method is adopted. The graphite electrode and Ag / AgCl electrode are selected as the counter electrode and reference electrode respectively, and the nickel foam activated in Step 2 is used as the working electrode. The applied potential is set to -1.6 V, and the electrodeposition time is 15 min. Electrolyte 2 is a mixed aqueous solution of 0.5 M manganese sulfate tetrahydrate, 0.5 M nickel sulfate hexahydrate and 1.0 M thiourea. The electrodeposited nickel foam is repeatedly washed 3 times with deionized water and absolute ethanol, and then placed in a vacuum drying oven at 60 °C for drying for later use;

[0040] The test is carried out in 1 mol L -1 KOH solution at 25 °C. The finally dried nickel foam in Step 3 is used as the working electrode, the graphite rod is used as the counter electrode, and Hg / HgO is used as the reference electrode. Under the condition of a scanning rate of 5 mV / s, linear sweep voltammetry tests of HER and OER are carried out.

[0041] It can be clearly observed from the SEM image that the surface of the nickel foam before electrodeposition is a smooth structure ( Figure 2 a), and after electrodeposition, a large number of particles grow on the surface of the nickel foam, and it is a porous structure ( Figure 2 b). Figure 3 The lattice fringes of manganese-doped nickel sulfide can also be clearly seen in the transmission electron microscope image, which proves that the material has been successfully prepared. The manganese-doped nickel sulfide / porous nickel foam electrode catalytic material prepared in Example 1 has excellent catalytic activity for OER, HER and overall water splitting at high current densities ( Figure 4 and Figure 5 ): In OER: η 500 = 300 mV, η 1000 = 350 mV and in HER: η 500 = 239 mV, η 1000 = 295 mV have lower overpotentials, showing good electrochemical activity.

[0042] Note: η 500 represents the overpotential corresponding to a current density of ±500 mA cm -2 , η 1000 represents the overpotential corresponding to a current density of ±1000 mA cm -2 , and the same applies hereinafter.

[0043] Example 2

[0044] The difference between this example and Example 1 is that the electrodeposition time in Step 3 is 5 min, and the other conditions are the same as those in Example 1.

[0045] Example 3

[0046] Example 3 is different from Example 1 in that in electrolyte 2 of step 3, manganese sulfate tetrahydrate is 0.75 M, nickel sulfate hexahydrate is 0.25 M, and thiourea is 1.0 M, and the remaining conditions are the same as those in Example 1.

[0047] Example 4

[0048] This example is different from Example 1 in that the electrodeposition time in step 2 is 1200 s, and the remaining conditions are the same as those in Example 1.

[0049] Example 5

[0050] This example is different from Example 1 in that the deposition current density is set to -2.0 A / cm² in step 2 -2 , and the remaining conditions are the same as those in Example 1.

[0051] Example 6

[0052] This example is different from Example 1 in that thiourea is 1.5 M in electrolyte 2 of step 3, and the remaining conditions are the same as those in Example 1.

[0053] In Example 2, the deposition time of manganese-doped nickel sulfide is short, the loading amount is small, and the growth on the substrate is not uniform enough, resulting in poor catalytic performance ( Figure 4 a, b), OER: η 500 = 352 mV, η 1000 = 411 mV and in HER: η 500 = 295 mV, η 1000 = 393 mV. In Example 3, it can be found by adjusting the proportion of manganese element doped into nickel sulfide that when the manganese doping amount is too high, it will instead inhibit the electrocatalytic reaction activity, resulting in an increase in overpotential ( Figure 4 a, b): in OER: η 500 = 411 mV, η 1000 = 499 mV and in HER: η 500 = 388 mV, η 1000 = 463 mV.

[0054] Comparative Example 1

[0055] This comparative example is different from Example 1 in that step 2 is not carried out, that is, the nickel foam substrate is not activated, and the cleaned nickel foam is used as the working electrode for direct electrochemical deposition.

[0056] Comparative Example 2

[0057] This comparative example is different from Example 1 in that electrolyte 2 only contains 1.0 M nickel sulfate hexahydrate and 1.0 M thiourea, and the remaining conditions are the same as those in Example 1.

[0058] The performance of the catalytic material prepared in Comparative Example 1 is as follows Figure 5 shown in a and b: In OER: η 500 = 369 mV, η 1000 = 416 mV and in HER: η 500 = 368 mV, η 1000 = 443 mV. Compared with Comparative Example 1 prepared by the traditional method, the nickel foam electrode substrate in Example 1 has a porous structure, which is beneficial to gas diffusion and mass transfer at high current densities and provides a larger electrochemically active area.

[0059] The performance of the catalytic material prepared in Comparative Example 2 is as follows Figure 5 shown in a and b. In OER: η 500 = 393 mV, η 1000 = 470 mV and in HER: η 500 = 404 mV, η 1000 = 510 mV. Compared with Comparative Example 2, the manganese-doped nickel sulfide / porous nickel foam electrode catalytic material prepared in Example 1 has an optimized electronic structure of nickel sulfide due to manganese doping, increasing the exposure of active sites and promoting the adsorption of reaction intermediates. Therefore, the optimized manganese-doped nickel sulfide / porous nickel foam electrode has high activity and durability in both HER and OER.

[0060] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made by using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A method for preparing a bifunctional manganese-doped nickel sulfide / porous nickel foam electrode for alkaline water electrolysis, characterized in that: Here are the steps: 1) Cleaning of nickel foam: cutting the nickel foam, and ultrasonically cleaning it in anhydrous ethanol, hydrochloric acid solution and deionized water respectively to obtain the treated nickel foam, and drying it for later use; 2) Activation treatment of nickel foam: the nickel foam obtained in step 1) is placed in electrolyte 1 as a working electrode, and a two-electrode system is used to perform electrodeposition by a constant current IT method. After completion, the working electrode is taken out, and then repeatedly washed with deionized water and anhydrous ethanol and dried for standby use to obtain an activated nickel foam; 3) Deposition process of nickel sulfide: The nickel foam activated in step 2) is placed in electrolyte 2 as a working electrode, and a three-electrode system is used to perform electrodeposition by constant potential ET method. After the deposition is completed, the electrode is taken out, and then repeatedly washed with deionized water and anhydrous ethanol and dried to obtain a manganese-doped nickel sulfide / porous nickel foam electrode.

2. The preparation method according to claim 1, characterized in that: In step 2), the electrolyte 1 is an aqueous solution of nickel salt and ammonium salt.

3. The preparation method according to claim 2, characterized in that: In step 2), the nickel salt is nickel chloride hexahydrate, nickel nitrate hexahydrate or nickel sulfate hexahydrate; the ammonium salt is ammonium fluoride or ammonium chloride; the molar ratio of the nickel salt to the ammonium salt is 1:6 to 1:30, and the concentration of the nickel salt is 1.0 to 2.0M.

4. The preparation method according to claim 1, characterized in that: In step 2), the specific operation of the two-electrode system for electrodeposition by constant current IT method is as follows: Clean nickel foam is used as the working electrode and graphite rod is used as the counter electrode. When using constant current electrodeposition, -1.0~-2.5Acm -2 The deposition current density is 300s~1500s.

5. The preparation method according to claim 1, characterized in that: In step 3), the electrolyte 2 is an aqueous solution of manganese salt, nickel salt and thiourea.

6. The preparation method according to claim 5, characterized in that: In step 3), the manganese salt is manganese sulfate tetrahydrate or manganese chloride tetrahydrate; the nickel salt is nickel chloride hexahydrate, nickel nitrate hexahydrate or nickel sulfate hexahydrate; the total concentration of the manganese salt and the nickel salt is 1.0M, the concentration of the nickel salt is 0.2-0.8M, and the concentration of thiourea is 0.5-1.5M.

7. The preparation method according to claim 1, characterized in that: In step 3), the specific operation of the three-electrode system for electrodeposition by constant voltage ET method is as follows: The activated nickel foam is used as the working electrode, the graphite rod is used as the counter electrode, and the Ag / AgCl is used as the reference electrode. When the constant potential method is used for electrodeposition, a deposition potential of -1.4 to -1.8 V is provided, and the duration is 5 minutes to 30 minutes.

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