Alkaline electrolytic cell anode oxygen evolution reaction catalyst Co4S3 and preparation method thereof

Abstract

The invention discloses a Co4S3 oxygen evolution reaction catalyst and a preparation method thereof, solves the problem of slow anode oxygen evolution reaction kinetics in the existing alkaline electrolyzed water research, and selects zeolite imidazate framework materials (ZIFs) with ordered structure, high specific surface area and adjustable pores to prepare the catalyst with low cost and excellent performance. According to the method, firstly, a ZIFs-cube is prepared to serve as a substrate, a precursor is finally formed through the etching effect of sodium sulfide, finally, the nanocube Co4S3 catalyst is obtained through further heating reaction through a tubular furnace, the overpotential of the catalyst is as low as 156 mV under the current density of 10 mA cm <-2 >, and 89% of initial current can still be kept after continuous reaction is conducted for 72 h.

Description

Technical Field

[0001] The invention relates to a method for preparing a catalyst material for oxygen evolution reaction at an alkaline water electrolysis anode. Background Art

[0002] Energy is usually the foundation and driving force of scientific and technological progress. However, about 65% of the world's energy demand currently comes from fossil energy. As energy consumption continues to rise, greenhouse gas emissions are increasing year by year. At present, carbon dioxide emissions mainly come from the use of fossil energy and manufacturing production activities. Among them, coal, as a key energy source to promote industrialization and urbanization, accounts for 75% of the total carbon emissions. Excessive greenhouse gas emissions have caused many serious problems such as climate warming and environmental degradation, posing a serious threat to the global ecological balance. Therefore, exploring clean and sustainable energy to replace traditional fossil fuels is regarded as one of the effective ways to cope with climate change and energy shortages, which requires the efficient conversion of renewable energy into a stable power supply. Hydrogen energy is recognized as a highly promising clean energy because of its high energy density and zero pollution, and its calorific value is 3-4 times higher than that of hydrocarbon fuels such as coke and gasoline. At present, a large number of researchers have been conducting research on electrochemical water splitting systems, including the anode oxygen evolution reaction (OER) in alkaline water electrolysis. However, due to the high reaction barrier and slow kinetic process, it is difficult to improve the activity of the overall water electrolysis cell, which seriously restricts the industrial application of water electrolysis technology. Therefore, the development of efficient electrocatalysts that can drive OER reactions at low potentials has become a top priority.

[0003] When exploring efficient OER electrocatalytic materials, many factors are usually considered comprehensively, such as high conductivity, large specific surface area, intrinsic activity of the catalyst itself, optimized configuration of active sites, excellent charge transfer ability, efficient active material transfer and porous structure. Among many emerging research directions, metal organic frameworks (MOFs) stand out as a very promising candidate for constructing functional and new carbon materials. MOFs materials usually have a large specific surface area and pore volume, can accurately control the type, quantity and location of metals, and are easy to introduce other heteroatoms to achieve composites with metals or metal compounds. With these unique advantages, the directional design and precise construction of materials can be achieved. MOFs materials can act as catalysts independently or as catalyst carriers. Their porous structure is extremely beneficial to the diffusion and adsorption process of substrate molecules, which can significantly improve the overall efficiency of the reaction and provide a more efficient catalytic platform for related chemical reactions. Among them, zeolite imidazolate framework (ZIF) is a subclass of MOFs materials. It is composed of nitrogen atoms bonded to imidazolate rings to encapsulate metal ions such as cobalt (Co), iron (Fe), zinc (Zn), and copper (Cu), and has unique structural characteristics. At the same time, it exhibits porous characteristics and has a zeolite topological structure, combining the advantages of zeolites and traditional metal organic frameworks. The present invention uses cobalt-based ZIFs (ZIF-67) as a precursor, and finally forms a precursor through the etching of sodium sulfide, and then further heats the reaction through a tubular furnace to optimize the intrinsic activity of the active sites, thereby improving the OER catalytic performance. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of low electrocatalytic performance and high cost of precious metal catalysts in the oxygen evolution reaction at the anode of alkaline water electrolysis in the prior art, and to provide a method for preparing Co4S3, a catalyst suitable for oxygen evolution reaction.

[0005] A Co4S3 oxygen evolution reaction catalyst material is a composite material prepared from a cobalt source and a sulfur source, wherein the composite material is a cobalt sulfide composite material with a particle size of about 500 nm; the mass ratio of the cobalt source to the sulfur source is 1:(2-3).

[0006] A preparation method of a Co4S3 oxygen evolution reaction catalyst material is specifically carried out in the following steps: 1) 0.23 g of cobalt-based ZIFs (ZIF-67) is uniformly dispersed in a mixed solution of 200 mL of ethanol and deionized water, and ultrasonicated for 0.5 h to obtain solution A; 2) 0.4 g of sodium sulfide is uniformly dispersed in 80 mL of ethanol to obtain solution B; 3) the solution A obtained in step 1) is placed in a three-necked flask, reacted in an oil bath at 110°C for 0.5 h, and then the solution B obtained in step 2) is added, and the reaction is continued in an oil bath at 110°C for 2 h, followed by centrifugation, washing with ethanol, and drying to obtain a solid sample; 4) the solid sample obtained in step 3) is placed in a porcelain boat, and reacted in a nitrogen atmosphere tubular furnace at 350°C for 2 h to obtain the final product Co4S3.

[0007] The preparation of the cobalt-based ZIFs (ZIF-67) required in the above step 1) is carried out according to the following steps: first, 0.584 g of cobalt nitrate hexahydrate is uniformly dispersed in 20 mL of deionized water containing 10 mg of CTAB to obtain solution C, and then 9.08 g of 2-methylimidazole is dissolved in 140 mL of deionized water to obtain solution D. Solutions C and D are mixed and stirred for 0.5 h, washed with ethanol, collected by centrifugation, and dried for 24 h to obtain ZIF-67.

[0008] In the above step 1), the ratio of ethanol to deionized water in the 200 mL mixed solution of ethanol and deionized water is 4:1.

[0009] The present invention has the following beneficial effects:

[0010] 1. The Co4S3 alkaline water electrolysis oxygen evolution reaction catalyst material prepared by the present invention uses ZIF-67 as a precursor to prepare the catalyst during the preparation process, maximizes the advantage of its controllable morphology, and regulates the reaction conditions through a series of methods to prepare a hollow nanocube-shaped polyhedron morphology, thereby increasing the specific surface area of ​​the catalyst and facilitating the exposure of more active sites.

[0011] 2. The Co4S3 alkaline water electrolysis oxygen evolution reaction catalyst material prepared by the present invention has an OER overpotential of only 156 mV after a series of performance tests, and can still maintain 89% of the initial current after a 72 h stability test, showing high catalytic performance and stability, and has excellent OER performance.

[0012] 3. After the sulfur atom is introduced into the Co4S3 alkaline water electrolysis oxygen evolution reaction catalyst material prepared by the present invention, it can be obtained through a simple pyrolysis step. The operation is simple, and the types of chemicals used are few, which effectively reduces the preparation cost and provides a theoretical basis for large-scale application production. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 SEM images of the uncarbonized intermediate sample (ab) and the carbonized final sample (cd) of the Co4S3 oxygen evolution reaction catalyst material prepared in Example 2;

[0014] Figure 2 XRD pattern of the Co4S3 oxygen evolution reaction catalyst material prepared in Example 2;

[0015] Figure 3 LSV diagrams of Co4S3 oxygen evolution reaction catalyst materials and RuO2 prepared in Examples 1, 2, and 3;

[0016] Figure 4 The Tafel diagram of the Co4S3 oxygen evolution reaction catalyst material and RuO2 prepared in Examples 1, 2 and 3;

[0017] Figure 5 EIS graphs of Co4S3 oxygen evolution reaction catalyst materials and RuO2 prepared in Examples 1, 2 and 3;

[0018] Figure 6 This is a stability test diagram of the Co4S3 oxygen evolution reaction catalyst material and RuO2 prepared in Example 2. DETAILED DESCRIPTION

[0019] Example 1

[0020] A preparation method of a Co4S3 oxygen evolution reaction catalyst material is specifically carried out in the following steps: 1) First, 0.584 g of cobalt nitrate hexahydrate is uniformly dispersed in 20 mL of deionized water containing 10 mg of CTAB to obtain solution C, and then 9.08 g of 2-methylimidazole is dissolved in 140 mL of deionized water to obtain solution D, and solutions C and D are mixed and stirred for 0.5 h, washed with ethanol, collected by centrifugation, and dried for 24 h to obtain ZIF-67. 2) 0.23 g of ZIF-67 obtained in step 1) is uniformly dispersed in 200 mL (160 mL of ethanol, 40 mL of deionized water) mixed solution, ultrasonicated for 0.5 h to obtain solution A; 3) 0.4 g of sodium sulfide is uniformly dispersed in 80 mL of ethanol to obtain solution B; 4) Solution A obtained in step 2) is placed in a three-necked flask, reacted in an oil bath at 110 ° C for 0.5 h, and then solution B obtained in step 3) is added, and the reaction is continued in an oil bath at 110 ° C for 2 h later, the mixture was collected by centrifugation, washed with ethanol and dried to obtain a solid sample; 5) the solid sample obtained in step 4) was placed in a porcelain boat, and reacted in a nitrogen atmosphere tube furnace at 300 °C for 2 h to obtain the final product Co4S3.

[0021] Example 2

[0022] Specifically, the following steps are followed: Steps 1), 2), 3), and 4) are the same as those in Example 1, except that in step 5), the solid sample obtained in step 4) is placed in a porcelain boat and reacted in a nitrogen atmosphere tubular furnace at 350°C for 2 h to obtain the final product Co4S3.

[0023] Example 3

[0024] Specifically, the following steps are followed: Steps 1), 2), 3), and 4) are the same as those in Example 1, except that in step 5), the solid sample obtained in step 4) is placed in a porcelain boat and reacted in a nitrogen atmosphere tubular furnace at 400°C for 2 h to obtain the final product Co4S3.

[0025] The catalyst obtained in the above manner was subjected to OER electrochemical testing using an electrochemical workstation (CHI760E, Shanghai Chenhua Instrument Co., Ltd.) to verify its catalytic performance. The tests used 1 M KOH (alkaline) as the electrolyte solution, a Hg / HgO electrode as the reference electrode, and a graphite rod as the counter electrode.

[0026] Preparation of electrochemical working electrode: The nickel foam was first pretreated by soaking it in acetone for 24 h, and then rinsed with ethanol and water for multiple times to remove surface organic impurities before use. Then 5 mg Co4S3, 1 mg carbon black and 30 μL Nafion (5 wt%) were evenly dispersed in 40 μL mixed solution (deionized water: ethanol = 1:1), and ultrasonicated for 0.5 h to obtain a uniform sample ink. The sample ink was evenly applied on a 1 cm*1 cm nickel foam and dried to make a working electrode.

[0027] The catalytic materials of specific embodiments 1 to 3 and their corresponding characterization and performance analysis:

[0028] Figure 1 (ab) are SEM images of the intermediate sample that was etched but not carbonized during the preparation of the Co4S3 oxygen evolution reaction catalyst material prepared in Example 2. In the image, precursor particles of about 500 nm in size can be seen, and irregular protrusions of the surface nanosheet structure can be observed, while the cubic structure is still effectively maintained; Figure 1 (cd) are SEM images of the final sample of the Co4S3 oxygen evolution reaction catalyst material prepared in Example 2 after carbonization. It can be seen from the figure that the morphology of the sample has changed dramatically. After carbonization, the nanosheet-like irregular protrusions on the surface of the precursor are transformed into "hill"-like irregular protrusions with unclear protrusions, and an obvious hollow cubic structure of about 500 nm in size is still visible.

[0029] Figure 2This is the XRD pattern of the Co4S3 oxygen evolution reaction catalyst material prepared in Example 2. As can be seen from the figure, the XRD peak of the Co4S3 catalyst prepared in Example 2 is consistent with the standard card of Co4S3 (PDF#02-1338), proving the successful synthesis of the catalyst.

[0030] Figure 3 LSV diagrams of Co4S3 oxygen evolution reaction catalyst materials and RuO2 prepared in Examples 1, 2, and 3. It can be seen from the figure that Example 2 can reach 10 mA cm with an overpotential of only 156 mV. -2 The current density is lower than that of Examples 1, 3 and RuO2 (216 mV, 223 mV, 391 mV), the catalytic activity is higher, and higher OER activity can be obtained.

[0031] Figure 4 The Tafel diagrams of the Co4S3 oxygen evolution reaction catalyst materials and RuO2 prepared in Examples 1, 2, and 3 show that the Tafel values ​​of Examples 1, 2, and 3 and RuO2 are 163 mV dec, respectively. -1 、139 mV dec -1 、168 mV dec -1 、223 mV dec -1 , which is consistent with the LSV test results.

[0032] Figure 5 The EIS diagram of the Co4S3 oxygen evolution reaction catalyst material and RuO2 prepared in Examples 1, 2, and 3 shows that the R CT The value (4 Ω) is much lower than that of Example 1 (27.4 Ω), Example 3 (18 Ω) and RuO2 (79.2 Ω), indicating that Example 2 has a higher charge transfer efficiency.

[0033] Figure 6 The stability test diagram of the Co4S3 oxygen evolution reaction catalyst material and RuO2 prepared in Example 2 is shown in Figure 1. -2 The data obtained from continuous measurement for 72 h show that 89% of the initial current can still be maintained after 72 h, confirming the excellent OER performance.

Claims

1. A method for preparing an oxygen evolution reaction catalyst, characterized in that The preparation of the oxygen evolution reaction catalyst is achieved by the following steps: 1) 0.23 g of cobalt-based ZIFs (ZIF-67) was uniformly dispersed in a mixed solution of 200 mL of ethanol and deionized water, and ultrasonicated for 0.5 h to obtain solution A; 2) 0.4 g of sodium sulfide was uniformly dispersed in 80 mL of ethanol to obtain solution B; 3) Solution A obtained in step 1) was placed in a three-necked flask, reacted in an oil bath at 110°C for a period of time, and then solution B obtained in step 2) was added, and the reaction was continued in an oil bath at 110°C for 2 h, then centrifuged and collected, washed with ethanol and dried to obtain a solid sample; 4) The solid sample obtained in step 3) was placed in a porcelain boat, and reacted in a nitrogen atmosphere tubular furnace at a certain temperature for 2 h to obtain the final product Co4S3.

2. The method for preparing an oxygen evolution reaction catalyst according to claim 1, characterized in that In step 1), the volume of the mixed solution of ethanol and deionized water is such that the ratio of ethanol to deionized water is 4:

1.

3. The method for preparing an oxygen evolution reaction catalyst according to claim 1, characterized in that In step 3), after reacting in an oil bath at 110° C. for 0.5 h, solution B obtained in step 1) was added.

4. The method for preparing an oxygen evolution reaction catalyst according to claim 1, characterized in that In step 4), the reaction was carried out in a nitrogen atmosphere tube furnace at 350° C. for 2 h.

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