Preparation of transition metal hydroxides doped with heteroatoms and surface adsorbed sulfate

Abstract

The application discloses a preparation method and application of a transition metal hydroxide doped with heteroatoms and adsorbing sulfate on a surface. The transition metal hydroxide is prepared by dispersing a sulfur source, a copper source and a cobalt source in an organic solvent, using a wet chemical method to prepare a double-metal sulfide precursor, then preparing a three-electrode system, and performing oxidation potential treatment. The transition metal hydroxide prepared by the method has good catalytic performance in an oxygen evolution reaction and excellent stability, and can be used in the field of electrocatalytic water splitting.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation, specifically relating to a method for treating a bimetallic sulfide precursor with oxidation potential to transform it into a transition metal hydroxide doped with heteroatoms and adsorbing sulfate ions on its surface, and the application of the resulting transition metal hydroxide in the field of electrocatalytic water splitting. Background Technology

[0002] The widespread application of renewable energy (solar, wind, etc.) has promoted the development of new energy research technologies. Among them, hydrogen energy, due to its advantages such as being pollution-free, having a high calorific value, and being widely available, has become an ideal alternative to traditional energy. Electrocatalytic water splitting is a clean, pollution-free, renewable, and high-temperature-free method for hydrogen production, and is a major means of future hydrogen production. Electrolysis of water to produce hydrogen involves two half-reactions: hydrogen evolution reaction at the cathode and oxygen evolution reaction at the anode. The oxygen evolution reaction, requiring a high overpotential, is the rate-determining step in the overall water electrolysis process. Currently, the most efficient catalysts for water electrolysis to produce hydrogen are noble metal-based catalysts, such as Pt and RuO2 / IrO2. Their high cost and scarcity hinder the commercial application of water electrolysis technology. Therefore, the development of inexpensive and efficient water electrolysis catalysts has received increasing attention.

[0003] Transition metal hydroxides have attracted researchers' attention due to their high abundance and unique electronic configuration, exhibiting excellent electrochemical performance in water electrolysis. However, the inherent poor conductivity and limited active sites of hydroxides hinder further improvement of their catalytic performance. This invention obtains heteroatom-doped transition metal hydroxides with sulfate adsorbed on their surface by treating transition metal sulfides with oxidation potential. These hydroxides exhibit excellent catalytic performance and high catalytic stability in 1 M KOH electrolyte, showing strong application prospects in the field of electrocatalytic water splitting. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a transition metal hydroxide doped with heteroatoms and with sulfate adsorbed on its surface, so as to improve the problem of low catalytic efficiency of existing transition metal hydroxides in the oxygen evolution reaction.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a heteroatom-doped transition metal hydroxide with surface-adsorbed sulfate ions involves using a sulfur source, a copper source, and a cobalt source as raw materials to prepare a bimetallic sulfide precursor via a wet chemical method; then, the obtained bimetallic sulfide precursor is prepared into a three-electrode system and subjected to oxidation potential treatment to obtain the transition metal hydroxide; the method specifically includes the following steps:

[0007] 1) Disperse sulfur source, copper source and cobalt source in organic solvent, and then react at 240-300℃ for 1 hour under nitrogen atmosphere to obtain bimetallic sulfide precursor material;

[0008] 2) The obtained bimetallic sulfide precursor was added to a mixed solution of naphthol and anhydrous ethanol (1:3, v / v), and ultrasonically dispersed to form a slurry. Then, it was further dispersed at a concentration of 1 mg·cm⁻¹. -2 The amount of sulfide is coated on carbon paper as the working electrode. A three-electrode system is formed by using an Hg / HgO electrode as the reference electrode and a Pt sheet electrode as the counter electrode. Then, through oxidation potential treatment, the sulfide is transformed in situ into the heteroatom-doped transition metal hydroxide with sulfate adsorbed on the surface.

[0009] Furthermore, the amounts of sulfur source, copper source, and cobalt source used in step 1) are converted according to the molar ratio of sulfur to metallic copper and cobalt as 4:1:(0.1-1).

[0010] The sulfur source is any one of N,N-di-n-dibutyldithiocarbamate, iron diethyldithiocarbamate, and nickel dibutyldithiocarbamate.

[0011] The copper source is copper N,N-di-n-dibutyldithiocarbamate;

[0012] The cobalt source is cobalt acetylacetonate.

[0013] Further, the organic solvent in step 1) is a mixture of oleylamine and oleic acid in a volume ratio of 2:1.

[0014] Furthermore, the oxidation potential treatment specifically involves performing 20-200 cyclic voltammetric tests within a voltage range of -2 V to 2 V, or performing 20-200 linear scan voltammetric tests within a voltage range of 0 V to 2 V.

[0015] The resulting transition metal hydroxide can be used for electrocatalytic water splitting to produce hydrogen. Its application method involves using the obtained SO4-containing... 2- A battery system for electrocatalytic water splitting is constructed using a Cu-doped Co(OH)2 electrode as the working electrode, an Hg / HgO electrode as the reference electrode, a platinum electrode as the counter electrode, and a 1M KOH solution as the electrolyte.

[0016] Compared with ordinary transition metal hydroxides, the transition metal hydroxides obtained in this invention have the following advantages:

[0017] (1) Hydroxides transformed from sulfides in situ have a thin and loose layered structure, which generates a large number of oxygen vacancies and provides more active sites;

[0018] (2) The doping of copper and other heterometallic atoms gives the resulting hydroxide a bimetallic synergistic effect, which can promote electron transport and increase the conductivity of the hydroxide.

[0019] (3) The sulfate ions formed by the oxidation of sulfur in the sulfide are adsorbed on the surface of the hydroxide, which increases the hydrophilicity of the material and makes it easier for the material to come into contact with the electrolyte, thereby improving the electron transport efficiency. Attached Figure Description

[0020] Figure 1 The CuCo2S4 precursor and SO4 prepared for the example 2- XRD pattern of @Cu doped Co(OH)2.

[0021] Figure 2 TEM images (a), high-resolution TEM image (b), and SO4 of the CuCo2S4 precursor prepared for the examples are shown. 2- TEM image (c), high-resolution TEM image (d), and EDS spectrum (eh) of Cu dopedCo(OH)2.

[0022] Figure 3 The graph shows the redox reaction performance of the CuCo2S4 precursor prepared in the example under the oxidation potential.

[0023] Figure 4 SO4 prepared for the example 2- LSV curves (a, c) and Tafel slopes (b, d) of the Cu doped Co(OH)2 catalyst.

[0024] Figure 5 SO4 prepared for the example 2- Figure showing the stability test results of the @Cu doped Co(OH)2 catalyst.

[0025] Figure 6 SO4 prepared for comparative purposes 2- LSV curves of the Cu-doped Fe(OH)3 catalyst material. Detailed Implementation

[0026] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto. Example

[0027] A catalyst material (denoted as SO4) that undergoes oxidation potential treatment to transform CuCo2S4 into copper-doped cobalt hydroxide and adsorbs sulfate ions on its surface. 2-The preparation method of @Cu doped Co(OH)2 includes the following steps:

[0028] 1) Take 1 mmol of N,N-di-n-dibutyldithiocarbamate, 1 mmol of cobalt acetylacetonate, 50 mL of oleylamine, and 25 mL of oleic acid, place them in a 250 mL three-necked flask, connect a Schlenk line, heat to 100 °C under a nitrogen atmosphere, degas, then heat to 260 °C, react for 1 hour, cool to room temperature, add a mixture of acetone and isopropanol (1:1, v / v), centrifuge, and resuspend the product in toluene by sonication. Repeat centrifugation / resuspending three times to wash the sample. Then place the sample in a vacuum oven and dry for 8 hours to obtain bimetallic sulfide CuCo2S4.

[0029] 2) Take 50 mg of CuCo2S4 and sonicate it in a mixture of 750 μL anhydrous ethanol and 250 μL naphthol (5 wt%). Take 20 μL and drop it onto a 1×1 cm solution. 2 A carbon paper electrode was used as the working electrode, an Hg / HgO electrode as the reference electrode, and a Pt sheet electrode as the counter electrode. A three-electrode system was used for cyclic voltammetry, with a processing range of -0.5 V to 1.8 V (VS RHE), and a scan rate of 0.1 V s. -1 Scanning 20 cycles yields SO4. 2- @Cu doped Co(OH)2 catalyst material.

[0030] Figure 1 The obtained CuCo2S4 precursor and SO4 2- X-ray diffraction pattern of Cu doped Co(OH)2 Figure 1 As can be seen, the peak energy of the prepared CuCo2S4 precursor corresponds well with that of the standard card (PDF#42-1450), proving the successful preparation of the CuCo2S4 bimetallic sulfide. After oxidation potential treatment, SO42- 2- The peak of @Cu doped Co(OH)2 showed a significant change, corresponding to the peak of the standard card (PDF#74-1057), and also contained a weak peak corresponding to (PDF#13-0420), proving that the sulfide has transformed into the hydroxide.

[0031] Figure 2 TEM image (a), high-resolution TEM image (b), and SO4 of the prepared CuCo2S4. 2-TEM image (c), high-resolution TEM image (d), and EDS spectrum (eh) of Cu doped Co(OH)2. As can be seen from the images, CuCo2S4 is in the form of nanoparticles with a lattice spacing of 0.28 nm, corresponding to the CuCo2S4 (113) crystal plane (b). SO4... 2- The morphology of @Cu doped Co(OH)2 changed significantly, becoming a thin and loose layered structure (c), with its lattice spacing corresponding to the (001) crystal plane of Co(OH)2 (d), and the four elements Cu, Co, O and S were evenly distributed on it (eh).

[0032] Figure 3 The graph shows the redox reaction performance of the prepared CuCo2S4 under the oxidation potential. It can be clearly seen from the graph that there are two oxidation peaks during the scanning process, corresponding to approximately 0.62 V S. 2- Oxidized to SO3 2- and SO3 at around 1.02 V 2- Converted to SO4 2- S 2- The leaching promotes the electrochemical reconstruction of CuCo2S4 into metal (oxide) hydroxides in alkaline electrolyte.

[0033] Prepared SO4 2- Electrochemical performance tests were conducted on the Cu-doped Co(OH)₂ catalyst material using a CHI660E electrochemical workstation. (The text then abruptly shifts to a seemingly unrelated topic: SO₄²⁻.) 2- The Cu-doped Co(OH)₂ electrode was used as the working electrode, the Hg / HgO electrode as the reference electrode, and the platinum sheet electrode as the counter electrode. The electrolyte was a 1 M KOH solution. Using E... RHE =E Hg / HgO The formula +0.059pH+0.098 converts the voltage data into the reversible hydrogen electrode potential (VS.RHE).

[0034] Figure 4 SO4 prepared 2- The LSV curves (a, c) and Tafel slopes (b, d) of the Cu-doped Co(OH)₂ catalyst compared with those of commercially available Pt / C and RuO₂ catalysts are shown in the figure. As can be seen from the figure, the obtained catalyst material requires overpotentials of 121 mV and 272 mV, respectively, to achieve 10 and 100 mA cm⁻¹ in HER. -2 The current density is slightly higher than that of commercial Pt / C (η 10 = 55 mV, η 100 =132 mV), while in the OER, 10 and 100 mA·cm⁻¹ are achieved. -2The overpotentials required for the current density are 211 and 272 mV, respectively, which are superior to those of commercial RuO2 catalysts (η). 10 = 280 mV, η 100 = 389 mV); and its Tafel slope in HER is 51 mV dec. -1 Approaching commercial Pt / C (44 mV dec) -1 In the OER, the Tafel slope is 62 mV dec. -1 The Tafel slope of commercial RuO2 is lower than that of commercial RuO2 (69 mV dec). -1 This demonstrates that it has good HER performance and excellent OER performance.

[0035] Figure 5 SO4 was tested 2- The stability of the Cu-doped Co(OH)₂ catalyst was shown. Results indicated that at 269 mA cm⁻¹... -2 The catalyst can operate stably for more than 20 hours under high current density, demonstrating its excellent stability.

[0036] Comparative Example

[0037] A catalyst material (denoted as SO4) that undergoes oxidation potential treatment to transform CuFeS2 into copper-doped ferric hydroxide and adsorbs sulfate ions on its surface. 2- The preparation method of Cu doped Fe(OH)3 includes the following steps:

[0038] 1) Take 1 mmol of copper dibutyldithiocarbamate, 1 mmol of iron acetylacetone, 50 mL of oleylamine, and 25 mL of oleic acid, place them in a 250 mL three-necked flask, connect a Schlenk line, heat to 100 °C under a nitrogen atmosphere, degas, then heat to 260 °C, react for 1 hour, cool to room temperature, add a mixture of acetone and isopropanol (1:1, v / v), centrifuge, and resuspend the product in toluene by sonication. Repeat centrifugation / resuspending three times to wash the sample. Place the sample in a vacuum oven and dry for 8 hours to obtain bimetallic sulfide CuFeS2.

[0039] 2) Take 50 mg of CuFeS2 and sonicate it in a mixture of 750 μL anhydrous ethanol and 250 μL naphthol (5 wt%). Take 20 μL of this mixture and drop it onto a 1×1 cm solution. 2 A carbon paper electrode was used as the working electrode, an Hg / HgO electrode as the reference electrode, and a Pt sheet electrode as the counter electrode. A three-electrode system was used for cyclic voltammetry, with a processing range of -0.5 V to 1.8 V (VS RHE), and a scan rate of 0.1 V s. -1Scanning 20 cycles yields SO4. 2- @Cu doped Fe(OH)3 catalyst material.

[0040] Figure 6 SO4 prepared 2- The LSV curves of the Cu-doped Fe(OH)3 catalyst are shown in the figure. As can be seen from the figure, the obtained catalyst material exhibits good performance at 10 and 100 mA·cm⁻¹. -2 The overpotentials required for the current density are 321 and 433 mV, respectively.

[0041] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a transition metal hydroxide doped with heteroatoms and with sulfate adsorbed on its surface, characterized in that, Includes the following steps: 1) Using sulfur, copper, and cobalt sources as raw materials, a bimetallic sulfide precursor CuCo2S4 was prepared by a wet chemical method; 2) The obtained bimetallic sulfide precursor was prepared into a three-electrode system. By treating with oxidation potential, the sulfide was transformed in situ into a transition metal hydroxide SO4 doped with heteroatoms and adsorbed with sulfate ions on its surface. 2- @Cu doped Co(OH)2; Step 2) The oxidation potential treatment specifically involves performing 20-200 cyclic voltammetric tests within a voltage range of -2 V to 2 V, or 20-200 linear scan voltammetric tests within a voltage range of 0 V to 2 V.

2. The method for preparing transition metal hydroxides according to claim 1, characterized in that: Step 1) Specifically, sulfur source, copper source and cobalt source are dispersed in an organic solvent, and then reacted at 240-300℃ for 1 hour under a nitrogen atmosphere to obtain the bimetallic sulfide precursor material.

3. The method for preparing transition metal hydroxides according to claim 2, characterized in that: The amounts of sulfur, copper, and cobalt sources used are calculated based on the molar ratio of sulfur to metallic copper and cobalt as 4:1:(0.1-1).

4. The method for preparing transition metal hydroxides according to claim 2 or 3, characterized in that: The sulfur source is any one of N,N-di-n-dibutyldithiocarbamate, iron diethyldithiocarbamate, and nickel dibutyldithiocarbamate. The copper source is copper N,N-di-n-dibutyldithiocarbamate; The cobalt source is cobalt acetylacetonate.

5. The method for preparing transition metal hydroxides according to claim 2, characterized in that: The organic solvent is a mixture of oleylamine and oleic acid in a volume ratio of 2:

1.

6. The method for preparing transition metal hydroxides according to claim 1, characterized in that: Step 2) The preparation of the three-electrode system involves adding the bimetallic sulfide precursor to a mixed solution of naphthol and anhydrous ethanol, ultrasonically dispersing it to form a slurry, and then coating it onto carbon paper as the working electrode. At the same time, an Hg / HgO electrode is used as the reference electrode and a Pt sheet electrode is used as the counter electrode.

7. The method for preparing transition metal hydroxides according to claim 6, characterized in that: The volume ratio of naphthol to anhydrous ethanol in the mixed solution is 1:3; the coating amount of the slurry on the carbon paper is 1 mg·cm⁻¹. -2 .

8. The application of a heteroatom-doped transition metal hydroxide with surface-adsorbed sulfate ions prepared by the method of claim 1 in an electrocatalytic water splitting reaction.

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