A preparation method of a bifunctional alkaline electrolytic water manganese-doped nickel sulfide / porous nickel foam electrode

Abstract

The application belongs to the field of materials, and discloses a preparation method of a bifunctional alkaline water electrolysis manganese-doped nickel sulfide / porous nickel foam electrode. The application is prepared by two-step electrodeposition, first activates the nickel foam substrate, and then electrodeposits nickel sulfide on the activated porous nickel foam substrate and dopes manganese. The manganese-doped nickel sulfide nanostructure grown on the porous nickel foam builds an electrode that can be used for bifunctional water electrolysis. The porous structure of the electrode can effectively accelerate the mass transfer process and promote the rapid escape of the bubbles generated by the reaction under high current density. In addition, the doping of manganese optimizes the electronic structure of the nickel sulfide, and the nickel sulfide has the characteristics of enhanced conductivity, increased electrochemical active area, fully exposed active sites, and optimized intermediate adsorption. The preparation method provides an effective strategy for the preparation of high-performance electrodes in actual water electrolysis.

Description

TECHNICAL FIELD

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

[0002] Under the background of the global active search for clean and sustainable energy forms, hydrogen energy has become an ideal energy carrier due to its zero emissions, high energy density, easy storage and transportation, and other significant advantages. At present, the problem of climate change is becoming increasingly serious, air quality is deteriorating, and the over-reliance of human society on oil resources makes it an urgent task for the world to find clean and sustainable energy forms.

[0003] The application scope of hydrogen is extremely wide, covering fuel cell vehicles, industrial gases, energy storage and other fields. There are various methods for preparing hydrogen, among which water electrolysis is particularly advantageous. In this process, the only by-products are water and oxygen, which do not pollute the environment at all, and thus highly meet the concept of sustainable development. Therefore, water electrolysis has been developing vigorously. The basic principle of water electrolysis technology is to use electric current to decompose water molecules into hydrogen and oxygen. In this reaction process, the current intensity directly determines the hydrogen production. Therefore, using large current water decomposition has become a key path to improve the efficiency of hydrogen production. Compared with the traditional small current electrolysis method, large current water decomposition has significant advantages. It not only can greatly improve the hydrogen production rate, but also can meet the demand for large-scale hydrogen production in industrial production, and is one of the core technologies for realizing the industrialization of hydrogen energy.

[0004] The key to breaking through the development bottleneck of water electrolysis technology is to develop advanced catalytic materials that can withstand high current density. At present, platinum, palladium, rhodium, ruthenium and iridium, etc. noble metals are still the most effective catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, they are expensive and scarce in reserves, which seriously limits their widespread application in practice.

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

[0006] The water dissociation rate of electrocatalysts and the binding strength of intermediates fundamentally depend on their surface electronic structure, which further affects the adsorption and desorption behavior. Therefore, the regulation of surface electronic structure is an effective method to accelerate the catalytic kinetics. By regulating the size and structure of the catalyst, its mechanical and chemical stability can be enhanced. For example, patent CN119372705A uses doping to synthesize a carbon-doped non-noble metal high-entropy alloy hydrogen evolution catalytic electrode; patent CN119372697A prepares a protonated layered iridium oxide H-IrO-2 nanosheet structure, in which the iridium oxide nanosheet is layered, the interlayer can accommodate protons, and there are metal iridium vacancy defects in the in-plane of the layered structure; patent CN119392285A prepares a cross-array electrocatalyst, which directly corrodes the nickel mesh to form a nanosheet array structure supported by each other. For 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 poor, the catalyst is easy to fall off under high current conditions. Moreover, the use of adhesives also introduces an undesirable active interface resistance, which not only shields active sites, but also affects the catalytic efficiency and stability. For example, the material prepared in patent CN119194487A is suitable for acidic oxygen evolution reaction process under large current density, but the material is in powder form, needs to use adhesives, and has the problems of high price and poor stability. Therefore, self-supporting electrodes grown in situ on the substrate have unique advantages, which can maintain the integrity and stability of the electrode structure only by relying on the inherent properties of the active material itself.

[0007] Therefore, the application discloses a preparation method of a bifunctional alkaline water electrolysis manganese-doped nickel sulfide / porous nickel foam electrode. The material is prepared by means of a two-step electrodeposition method. In the first step, the porous nickel substrate is subjected to activation treatment, so that the activated porous nickel foam electrode is obtained. Then, the manganese-doped nickel sulfide material is directly deposited on the activated porous nickel substrate by using the electrodeposition method again. The process has the characteristics of high efficiency and rapidity, and the reaction condition is mild, and the process can be carried out at room temperature. The electrode prepared by using the process has the catalyst closely connected with the substrate, which creates a smooth channel for the transfer of electrons and ions, and the large electrochemical active area makes the catalytic sites exposed as much as possible, so that the electrode has high conductivity and high catalytic activity. SUMMARY

[0008] The application provides a preparation method of a bifunctional alkaline water electrolysis manganese-doped nickel sulfide / porous nickel foam electrode.

[0009] The technical scheme of the application is as follows:

[0010] The application provides a preparation method of a bifunctional alkaline water electrolysis manganese-doped nickel sulfide / porous nickel foam electrode.

[0011] 1) cleaning of the porous nickel: the porous nickel is cut, and is ultrasonically cleaned in anhydrous ethanol, a hydrochloric acid solution and deionized water respectively, so that the treated porous nickel is obtained and dried for later use;

[0012] 2) activation treatment of the porous nickel: the porous nickel obtained in the step 1) is placed as a working electrode in an electrolyte 1, and is electrodeposited by using a two-electrode system and a constant current I-T method; after the electrodeposition is completed, the working electrode is taken out, and is repeatedly cleaned with deionized water and anhydrous ethanol and dried for later use, so that the activated porous nickel is obtained;

[0013] 3) deposition process of the nickel sulfide: the activated porous nickel obtained in the step 2) is placed as a working electrode in an electrolyte 2, and is electrodeposited by using a three-electrode system and a constant potential E-T method; after the electrodeposition is completed, the electrode is taken out, and is repeatedly cleaned with deionized water and anhydrous ethanol and dried, so that the manganese-doped nickel sulfide / porous nickel foam electrode is obtained. The bifunctional manganese-doped nickel sulfide / porous nickel foam electrode is suitable for an alkaline water electrolysis process.

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

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

[0016] Further, 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 two-electrode system is operated by constant current I-T method for electrodeposition as follows:

[0018] Clean nickel foam is used as the working electrode, and a graphite rod is used as the counter electrode; when electrodeposition is performed by constant current method, a deposition current density of -1.0 to -2.5 A cm -2 is provided for 300 s to 1500 s.

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

[0020] Further, 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] Further, the concentration of the manganese salt and the nickel salt is 1.0 M in total, the concentration of the nickel salt is 0.2 to 0.8 M, and the concentration of thiourea is 0.5 to 1.5 M;

[0022] In step 3), the three-electrode system is operated by constant voltage E-T method for electrodeposition as follows:

[0023] Activated nickel foam is used as the working electrode, a graphite rod is used as the counter electrode, and Ag / AgCl is used as the reference electrode; when electrodeposition is performed by constant potential method, a deposition potential of -1.4 to -1.8 V is provided for 5 min to 30 min.

[0024] Advantages of the present application:

[0025] 1) The present application has a simple manufacturing process, is convenient and fast, and can be prepared in large quantities. The material uses non-noble metals and has low cost.

[0026] 2) The present application uses a self-supporting electrode, and the active material is directly grown 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 the two electrodes are composed of the same material, which can alleviate the cross-contamination problem. A high-activity, stable and economical bifunctional electrocatalyst is developed to drive HER and OER to achieve efficient overall water splitting (OWS).

[0028] 4) The manganese-doped nickel sulfide / porous nickel foam electrode obtained has high activity and significant HER and OER catalytic activity under high current density. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The preparation flowchart of the present application is shown in the figure.

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

[0031] Figure 3 Figure 3 is a transmission electron microscope (TEM) image of the manganese-doped nickel sulfide / porous nickel foam electrode of Example 1 of the present application, wherein (a) is a TEM image of the observed micro-whole, and (b) is a crystal lattice fringe image of the micro-zoning at a high magnification.

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

[0033] Figure 5 Figure 5 is a linear sweep voltammetry (LSV) image of the hydrogen evolution and oxygen evolution reactions of the manganese-doped nickel sulfide / porous nickel foam electrode of Example 1 of the present application and Comparative Examples 1 and 2 under test conditions of 25°C and 1M KOH, wherein (a) is an LSV image of Example 1 and Comparative Examples 1 and 2 in the oxygen evolution reaction, and (b) is an LSV image of Example 1 and Comparative Examples 1 and 2 in the hydrogen evolution reaction. DETAILED DESCRIPTION

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

[0035] Example 1

[0036] The method for preparing the manganese-doped nickel sulfide / porous nickel foam electrode specifically comprises the following steps:

[0037] Step 1, cut the nickel foam into 1.5 cm x 1 cm, and ultrasonically clean it in anhydrous ethanol, 6M hydrochloric acid solution and deionized water for 20 min, respectively, to obtain the treated nickel foam which is placed in a 60°C vacuum tube drying oven for drying.

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

[0039] Step 3: In the three-electrode system, a constant potential deposition method was used in electrolyte 2. A graphite electrode and an Ag / AgCl electrode were selected as the counter electrode and reference electrode, respectively. The activated nickel foam from step 2 was used as the working electrode. The applied potential was set to -1.6V, and the electrodeposition time was 15 min. Electrolyte 2 was a mixed aqueous solution of 0.5M manganese sulfate tetrahydrate, 0.5M nickel sulfate hexahydrate, and 1.0M thiourea. The electrodeposited nickel foam was repeatedly washed three times with deionized water and anhydrous ethanol, and then dried in a 60℃ vacuum tube drying oven for later use.

[0040] At 25℃, 1 mol L -1 The tests were conducted in KOH solution, using the dried nickel foam from step 3 as the working electrode, a graphite rod as the counter electrode, and Hg / HgO as the reference electrode. Linear scan voltammetry tests for HER and OER were performed at a scan rate of 5 mV / s.

[0041] SEM images clearly show a smooth structure on the nickel foam before electrodeposition. Figure 2 a) After electrodeposition, a large number of particles grow on the surface of the nickel foam, and these particles have a porous structure. Figure 2 b). Figure 3 The transmission electron microscopy (TEM) images also revealed obvious lattice fringes of manganese-doped nickel sulfide, confirming the successful preparation of the material. The manganese-doped nickel sulfide / porous nickel foam electrode catalytic material prepared in Example 1 exhibited excellent catalytic activity for OER, HER, and overall water splitting at high current densities. Figure 4 and Figure 5 ): OER: η 500 =300mV, η 1000 =350mV and HER: η 500 =239mV, η 1000 =295mV has a low overpotential and exhibits good electrochemical activity.

[0042] Note: η 500 This indicates a current density of ±500 mA / cm². -2 The corresponding overpotential, η 1000 This indicates a current density of ±1000 mA cm⁻¹ -2 The corresponding overpotential, the same below.

[0043] Example 2

[0044] The difference between this embodiment and Embodiment 1 is that the electrodeposition time in step 3 is 5 minutes, while the other conditions are the same as in Embodiment 1.

[0045] Example 3

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

[0047] Example 4

[0048] This example and Example 1 differ in that the electrodeposition time of step 2 is 1200 s, and the rest of the conditions are the same as in Example 1.

[0049] Example 5

[0050] This example and Example 1 differ in that the deposition current density in step 2 is set to -2.0 Acm -2 , and the rest of the conditions are the same as in Example 1.

[0051] Example 6

[0052] This example and Example 1 differ in that the concentration of thiourea in electrolyte 2 of step 3 is 1.5 M, and the rest of the conditions are the same as in Example 1.

[0053] The deposition time of manganese-doped nickel sulfide in Example 2 is shorter, the loading is less, and the growth on the substrate is not uniform enough, thus leading to poorer 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, by adjusting the proportion of manganese elements doped into nickel sulfide, it can be found that when the manganese doping amount is too high, it will inhibit the electrocatalytic reaction activity, leading to an increase in overpotential Figure 4 a, b): 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 and Example 1 differ in that step 2 is not performed, i.e., the activated treatment of the nickel foam substrate is not performed, and the cleaned nickel foam is used as the working electrode for direct electrochemical deposition.

[0056] Comparative Example 2

[0057] This comparative example and Example 1 differ in that electrolyte 2 only contains 1.0 M nickel sulfate hexahydrate and 1.0 M thiourea, and the rest of the conditions are the same as in Example 1.

[0058] The performance of the catalytic material prepared in Comparative Example 1 is as shown in Table 1 Figure 5 a, b: in OER: η = 393 mV, η = 470 mV and in HER: η = 404 mV, η = 510 mV. 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 conventional method, the porous nickel foam electrode substrate of Example 1 is beneficial to the gas diffusion and mass transfer at high current density, and provides a larger electrochemical active area.

[0059] The performance of the catalytic material prepared in Comparative Example 2 is as shown in Table 2 Figure 5 a, b: in OER: η = 393 mV, η = 470 mV and in HER: η = 404 mV, η = 510 mV. 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 optimized electronic structure of the nickel sulfide due to the manganese doping, which increases the exposure of active sites and promotes the adsorption of reaction intermediates. Therefore, the optimized manganese-doped nickel sulfide / porous nickel foam electrode has higher activity and durability in HER and OER.

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

Claims

1. A method for preparing a bifunctional alkaline water electrolysis manganese-doped nickel sulfide / porous nickel foam electrode, characterized in that, The steps are as follows: 1) Cleaning of nickel foam: Cut the nickel foam into pieces and ultrasonically clean it in anhydrous ethanol, hydrochloric acid solution and deionized water respectively to obtain the treated nickel foam. Dry it for later use. 2) Activation treatment of nickel foam: The nickel foam obtained in step 1) is placed in electrolyte 1 as the working electrode. A two-electrode system is used to perform electrodeposition by constant current IT method. After completion, the working electrode is removed, and then repeatedly washed with deionized water and anhydrous ethanol and dried for later use to obtain activated nickel foam. The electrolyte 1 is an aqueous solution of nickel salt and ammonium salt; 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 2.0 M. The specific operation of electrodeposition using the constant current IT method in the two-electrode system is as follows: Clean nickel foam was used as the working electrode, and a graphite rod as the counter electrode; when using the constant current electrodeposition method, a current of -1.0 to -2.5 A cm⁻¹ was provided. -2 The deposition current density lasted for 300 s to 1500 s. 3) Nickel sulfide deposition process: The activated nickel foam from step 2) is placed in electrolyte 2 as the working electrode. A three-electrode system is used to perform electrodeposition using the constant potential ET method. After deposition, the electrode is removed and repeatedly cleaned with deionized water and anhydrous ethanol and dried to obtain manganese-doped nickel sulfide / porous nickel foam electrode. The electrolyte 2 is an aqueous solution of manganese salt, nickel salt and thiourea; 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 nickel salt is 1.0 M, the concentration of the nickel salt is 0.2~0.8 M, and the concentration of thiourea is 0.5~1.5 M.

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

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