Method for in-situ preparation of nickel-cobalt sulfide catalyst with assistance of hydrogen peroxide

Abstract

The invention discloses a method for in-situ preparation of a nickel-cobalt sulfide catalyst with assistance of hydrogen peroxide. The method comprises the following steps: mixing pretreated foamed nickel, cobaltous sulfate heptahydrate, sodium thiosulfate pentahydrate and hydrogen peroxide, adding the mixture into a hydrothermal kettle for hydrothermal reaction, and washing and drying the reacted foamed nickel to obtain the nickel-cobalt sulfide catalyst for in-situ growth on the surface of the foamed nickel through auxiliary regulation. According to the invention, by adding hydrogen peroxide, the morphology and composition of the catalyst are optimized, a loose microstructure with nanosheets accompanied with nanoflowers and a proper nickel-cobalt ratio are formed, and the catalytic performance of the prepared catalyst in the process of electrooxidizing 5-hydroxymethylfurfural is obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of 5-hydroxymethylfurfural electro-oxidation reaction catalysts and relates to a method for in-situ preparation of a nickel-cobalt sulfide catalyst with the assistance of hydrogen peroxide. Background Art

[0002] Hydrogen (H 2 ) has been considered as a highly potential new energy source to replace traditional energy. It has the advantages of non-toxicity and almost zero greenhouse gas emissions. Renewable energy-driven water electrolysis can produce high-purity H 2 (>99.9%). However, in the process of hydrogen production by water electrolysis, the oxygen evolution reaction (OER) occurring at the anode usually requires a higher overpotential to facilitate the reaction because of the sluggish kinetics of its four-electron oxidation process. In addition, the oxygen generated at the anode is too low in value, and H 2 and O 2 There is also a risk of mixing. Replacing the traditional anode OER by electrooxidation reactions of other substrates is an effective way to solve these problems.

[0003] 5-Hydroxymethylfurfural (HMF), produced by the dehydration of fructose or glucose, is one of the top biomass derivatives. It can be used as a universal platform molecule to manufacture value-added products such as plastics, fine chemicals and liquid fuels. Its theoretical electro-oxidation potential compared to the reversible hydrogen electrode (vs. RHE) is only 0.113V, which is much smaller than the 1.23V vs. RHE of OER, and its oxidation product 2,5-furandicarboxylic acid (FDCA) is an important raw material for the preparation of renewable bio-based plastics, which can replace the petroleum-based monomer terephthalic acid of polyethylene terephthalate (PET). Replacing OER with the electro-oxidation reaction of HMF can produce high value-added products while producing hydrogen at a lower potential, and its products can further reduce dependence on fossil energy.

[0004] At present, there are still many problems to be solved in the research on HMF electro-oxidation. The inevitable OER competition at high potential during the electrolysis process will lead to low charge utilization efficiency (low Faradaic efficiency). In addition, although the electro-oxidation of HMF will be promoted under high pH conditions, HMF will easily degrade into useless humus if it exists in a strong alkaline electrolyte environment for a long time. Therefore, it is particularly important to make HMF quickly converted at low potential in a strong alkaline electrolyte and ensure good conversion rate, yield and Faradaic efficiency.

[0005] Currently, nickel-cobalt metal sulfides have attracted much attention due to their good conductivity and catalytic activity in HMF electrooxidation. However, most prepared nickel-cobalt sulfides still have difficulty in achieving rapid electrolysis of HMF at low potentials. For example, Zhao et al. prepared a precursor by mixing nickel nitrate, cobalt nitrate and 2-methylimidazole, and then hydrothermally sulfided the precursor to obtain nickel-cobalt sulfide. In the end, they only achieved 23 mA cm at a potential of 1.45 V (compared to the reversible hydrogen potential) in an electrolyte of 1 M KOH and 10 mM HMF. -2 The current density is (Zhao ZF, Guo TY, Luo XY, et al. Bimetallic sites and coordination effects: electronic structure engineering of NiCo-based sulfide for 5-hydroxymethyl furfural electrooxidation, Catal. Sci. Technol. 2022, 12: 3817-3825.). Further optimization and adjustment of the preparation method are still needed. Chen et al. added an appropriate amount of hydrogen peroxide to the system of hydrothermal synthesis of nickel sulfide. Hydrogen peroxide, as a strong oxidant, can accelerate the oxidation process of foamed nickel and sodium thiosulfate during the hydrothermal process, accelerate the reaction process, and successfully control the micromorphology of nickel sulfide and prepare a special nickel sulfide material with nanoflowers on nanorods. It shows better performance than general nickel sulfide in the field of supercapacitors (CHEN X, JIANG DM, LI HY, et al. Hydrogen peroxide-induced growth of hierarchical Ni 3 S 2 nanorod / sheet arrays for high performance supercapacitors[J]. Journal of Colloid and Interface Science, 2020,575:168-176). Summary of the invention

[0006] The object of the present invention is to provide a method for in-situ preparation of a nickel-cobalt sulfide catalyst assisted by hydrogen peroxide. The method utilizes hydrogen peroxide to assist in regulating the in-situ growth of a nickel-cobalt sulfide catalyst on the surface of nickel foam, which can efficiently catalyze HMF electrooxidation.

[0007] The technical solution for realizing the purpose of the present invention is as follows:

[0008] A method for preparing a nickel-cobalt sulfide catalyst in situ with the assistance of hydrogen peroxide, wherein the pretreated nickel foam, cobalt sulfate heptahydrate, sodium thiosulfate pentahydrate and hydrogen peroxide are mixed and added to a hydrothermal kettle for hydrothermal reaction, and the nickel foam after the reaction is washed and dried to obtain a nickel-cobalt sulfide catalyst assisted in controlling the in-situ growth on the surface of the nickel foam. The specific steps are as follows:

[0009] Under stirring conditions, 30 wt.% of hydrogen peroxide is added dropwise to a sodium thiosulfate pentahydrate solution, and then quickly mixed with a cobalt sulfate heptahydrate solution. The mixed solution is then mixed with a nickel foam and placed in a hydrothermal kettle for a hydrothermal reaction at 130-140° C. After the reaction is completed, the nickel foam is taken out, washed with water, and dried to obtain a nickel-cobalt sulfide catalyst.

[0010] Preferably, the molar ratio of cobalt sulfate heptahydrate, sodium thiosulfate pentahydrate, and hydrogen peroxide is 0.1-0.4:0.96:0.489-1.408, more preferably 0.3:0.96:0.978.

[0011] Preferably, in the mixed solution, the molar concentration of cobalt sulfate is 0.00238 to 0.00952 mol / L, more preferably 0.00714 mol / L.

[0012] Preferably, the thickness of the nickel foam is 1±0.1 mm, and the ratio of the cut area to the volume of the mixed solution is 0.143±0.1 cm 2 / mL.

[0013] Preferably, the hydrothermal time is more than 2 hours.

[0014] Preferably, the drying temperature is 60±5° C. and the drying time is more than 24 hours.

[0015] The present invention also provides a nickel-cobalt sulfide catalyst prepared by the preparation method.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The synthesis method of the present invention is simple. In addition to being able to regulate the morphology of the catalyst, the added hydrogen peroxide can also regulate the component ratio in the nickel cobalt sulfide catalyst. Compared with the nickel cobalt sulfide prepared without adding hydrogen peroxide, the HMF electro-oxidation catalytic performance is significantly improved, and faster HMF electro-conversion at a lower potential can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 SEM images of the catalysts prepared without and with hydrogen peroxide at 10 μm and 500 nm scales.

[0019] Figure 2This is a graph showing the effect of the amount of hydrogen peroxide added on the proportion of nickel and cobalt elements in the prepared nickel-cobalt sulfide catalyst.

[0020] Figure 3 The effect of adding hydrogen peroxide or not on the binding energy of different valence states of nickel element in the prepared nickel cobalt sulfide catalyst.

[0021] Figure 4 This is a graph showing the effect of the amount of cobalt sulfate heptahydrate added on the catalytic HMF electro-oxidation performance of the prepared nickel cobalt sulfide catalyst.

[0022] Figure 5 This is a graph showing the effect of the amount of hydrogen peroxide added on the electro-oxidation performance of HMF catalyzed by the prepared nickel cobalt sulfide catalyst.

[0023] Figure 6 Figure 3. Changes in the components of the electrolyte during HMF electrooxidation catalyzed by the nickel cobalt sulfide catalyst in situ grown on the surface of nickel foam with the assistance of hydrogen peroxide. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific embodiments and drawings.

[0025] Example 1

[0026] Cut a piece of nickel foam with a thickness of 1mm and an area of ​​2cm×3cm, and ultrasonically wash it with 3MHCl, ethanol and deionized water for 15min respectively, and vacuum dry it at 60℃ for use. Weigh 0.3mmol of cobalt sulfate heptahydrate and dissolve it in 21mL of deionized water to form solution A. Weigh 0.96mmol of sodium thiosulfate pentahydrate and dissolve it in 21mL of deionized water to form solution B. Add 100μL of 30% mass concentration of hydrogen peroxide dropwise to solution B while stirring, then quickly mix it with solution A, and immediately pour it into the hydrothermal kettle containing the treated nickel foam, and keep it warm at a hydrothermal temperature of 130℃ for 2h. After the hydrothermal kettle naturally drops to room temperature, take out the nickel foam, rinse it with deionized water several times, and dry it in a vacuum oven at 60℃ to obtain a nickel-cobalt sulfide catalyst grown in situ on the surface of the nickel foam.

[0027] Comparative Example 1

[0028] This comparative example is substantially the same as Example 1, except that cobalt sulfate heptahydrate is not added.

[0029] Example 2

[0030] This example is substantially the same as Example 1, except that the amount of cobalt sulfate heptahydrate added is 0.1 mmol.

[0031] Example 3

[0032] This example is substantially the same as Example 1, except that the amount of cobalt sulfate heptahydrate added is 0.2 mmol.

[0033] Example 4

[0034] This example is substantially the same as Example 1, except that the amount of cobalt sulfate heptahydrate added is 0.4 mmol.

[0035] Comparative Example 2

[0036] This comparative example is substantially the same as Example 1, except that no hydrogen peroxide is added.

[0037] Example 5

[0038] This embodiment is basically the same as embodiment 1, the only difference being that the amount of hydrogen peroxide added is 50 μL.

[0039] Example 6

[0040] This embodiment is substantially the same as embodiment 1, except that the amount of hydrogen peroxide added is 144 μL.

[0041] Figure 1 The microscopic morphology of Example 1 and Comparative Example 2 is compared, wherein Figure 1 a and 1c are the morphological performances of comparative example 2 (i.e., no hydrogen peroxide was added) at 10 μm and 500 nm scales, Figure 1 b and 1d are the morphological performances of Example 1 (i.e., adding 100 μL of hydrogen peroxide) at 10 μm and 500 nm scales. It can be seen that when 100 μL of hydrogen peroxide is added, the catalyst changes from a simple flat nanosheet to a structure with many protruding nanoflowers on the nanosheet, and the sheet structure is thinner and the agglomeration phenomenon is significantly improved. It can be seen that the surface area of ​​the catalyst has been significantly increased, which can effectively increase the number of active sites on the catalyst surface.

[0042] Figure 2 The figure is the effect of the amount of hydrogen peroxide added on the ratio of nickel and cobalt in the prepared nickel-cobalt sulfide catalyst, and the result is measured by inductively coupled plasma spectroscopy. The nickel-cobalt ratio Ni / Co in the nickel-cobalt sulfide catalyst prepared without adding hydrogen peroxide (Comparative Example 2), adding 50 μL hydrogen peroxide (Example 5) and adding 100 μL hydrogen peroxide (Example 1) is 3.462, 6.706 and 7.074 respectively. It can be seen that with the addition of hydrogen peroxide, the relative content of nickel in the catalyst increases significantly.

[0043] Figure 3 The effect of adding hydrogen peroxide on the X-ray diffraction photoelectron spectroscopy results of nickel in the catalyst was investigated. It was found that Ni in the nickel cobalt sulfide catalyst prepared after adding 100 μL hydrogen peroxide was 2+ and Ni3+ The corresponding peaks all moved toward the high energy field by about 0.55 eV, indicating that the electron cloud density of nickel in the nickel-cobalt sulfide catalyst sample prepared by adding hydrogen peroxide was decreasing, which was more conducive to the formation of high-valent nickel as the active site for HMF electrooxidation. This also shows that the addition of hydrogen peroxide has a significant effect on the electron distribution in the nickel-cobalt sulfide catalyst.

[0044] Figure 4 The linear sweep voltammetry (LSV) curve of nickel cobalt sulfide catalyst prepared with different amounts of cobalt sulfate added. The test conditions are: a three-electrode system consisting of a homemade catalyst as the working electrode, a platinum sheet as the counter electrode, and Hg / HgO as the reference electrode. The electrolyte on the anode side of the electrolytic cell is 1MKOH+10mMHMF, and the electrolyte on the cathode side is 1MKOH, and the middle is separated by a Nafion117 proton exchange membrane. When testing the curve, a stirrer provides 500RPM stirring on the anode side to enhance mass transfer, and the final result is 90% IR compensation. The test was carried out in an H-type electrolytic cell. It can be seen from the figure that as the amount of cobalt sulfate added increases, the starting potential of the LSV curve gradually decreases, while the current density peak increases first and then decreases and reaches the maximum when the amount of cobalt sulfate added is 0.3mmol. Taking all factors into consideration, the nickel cobalt sulfide catalyst prepared by adding 0.3 mmol of cobalt sulfate (Example 1) has the best HMF electrooxidation catalytic performance, which can achieve 200 mA cm at a voltage of 1.38 V (compared to the reversible hydrogen potential). -2 The current density is very high at a relatively low potential.

[0045] Figure 5 The linear sweep voltammetric curves of nickel cobalt sulfide catalysts prepared with different amounts of hydrogen peroxide added. Figure 4 The test conditions are the same. From the figure, we can see that with the addition of hydrogen peroxide, although the starting potential of the curve increases, the current density before the inflection point of OER has increased significantly, which can achieve faster HMF electroconversion in a limited voltage window.

[0046] Figure 6 The nickel cobalt sulfide catalyst (Example 1) grown in situ on the surface of nickel foam assisted by hydrogen peroxide was regulated at 0.5 V vs. E Hg / HgOChanges of each component in the electrolyte during electrolysis under potential for a period of time. The electrolytic cell used for electrolysis is an H-type electrolytic cell separated by a Nafion117 proton exchange membrane in the middle. The anolyte is a mixed solution of 40mL of 1M KOH and 10mM HMF, and the cathode electrolyte is 40mL of 1M KOH solution. The electrolysis time is about 2h. Samples are taken in stages during the electrolysis process. Each time, 90μm of the anolyte is neutralized with 30μm of 3M hydrochloric acid, and then diluted with 880μm of water. The sample was analyzed by high performance liquid chromatography. The chromatographic column was AgilentC18XB, and the mobile phase was 30% methanol plus 70% of 5mM ammonium formate solution. The detection used an ultraviolet wavelength of 265nm and a column temperature of 30°C. From the figure, we can see that the reactant 5-hydroxymethylfurfural (HMF) gradually decreases, and the corresponding product 2,5-furandicarboxylic acid (FDCA) gradually increases, among which 5-formyl-2-furancarboxylic acid (FFCA), 2,5-diformylfuran (DFF) and 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) are all intermediate products. It can be calculated from the data in this figure that it finally achieved a conversion rate of 98.7% and a yield of 97.4%, which is an excellent performance.

Claims

1. A method for in-situ preparation of a nickel-cobalt sulfide catalyst assisted by hydrogen peroxide, characterized in that: The specific steps are as follows: Under stirring conditions, 30 wt.% hydrogen peroxide was added dropwise to a sodium thiosulfate pentahydrate solution, and then quickly mixed with a cobalt sulfate heptahydrate solution. The mixed solution was then mixed with nickel foam and placed in a hydrothermal kettle for a hydrothermal reaction at 130-140°C. After the reaction was completed, the nickel foam was taken out, washed with water, and dried to obtain a nickel-cobalt sulfide catalyst.

2. The method according to claim 1, characterized in that The molar ratio of cobalt sulfate heptahydrate, sodium thiosulfate pentahydrate, and hydrogen peroxide is 0.1~0.4:0.96:0.489~1.

408.

3. The method according to claim 1, characterized in that The molar ratio of cobalt sulfate heptahydrate, sodium thiosulfate pentahydrate, and hydrogen peroxide is 0.3:0.96:0.

978.

4. The method according to claim 1, characterized in that In the mixed solution, the molar concentration of cobalt sulfate is 0.00238~0.00952 mol / L.

5. The method according to claim 1, characterized in that In the mixed solution, the molar concentration of cobalt sulfate is 0.00714 mol / L.

6. The method according to claim 1, characterized in that The thickness of nickel foam is 1 ± 0.1 mm, and the ratio of the cut area to the volume of the mixed solution is 0.143 ± 0.1 cm 2 / mL.

7. The method according to claim 1, characterized in that The hydrothermal time is more than 2 h.

8. The method according to claim 1, characterized in that The drying temperature is 60±5℃ and the drying time is more than 24 hours.

9. A nickel-cobalt sulfide catalyst prepared according to any one of claims 1 to 8.

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