Preparation method and application of sulfate-modified nitrogen-doped cobaltosic oxide bifunctional catalyst

Abstract

The application discloses a preparation method and application of a sulfate-modified nitrogen-doped cobalt tetraoxide bifunctional catalyst. A mixed solution of cobalt chloride hexahydrate, D(+) -glucosamine hydrochloride and 4'4-dihydroxy diphenyl sulfone is subjected to a solvothermal reaction to form a nitrogen and sulfur-containing cobalt precursor, and after drying, the cobalt precursor is subjected to low-temperature oxidation treatment in air to obtain sulfate-modified nitrogen-doped cobalt tetraoxide nanosheets. The catalyst has not only a hierarchical pore structure providing a high mass transfer rate, but also cobalt active sites adjusted by oxygen vacancy defects generated by nitrogen doping, doped nitrogen and surface sulfate groups, so that the catalyst exhibits excellent oxygen reduction and oxygen evolution reaction bifunctional catalytic performance and can be used as a catalyst in a rechargeable zinc-air battery.

Description

Technical Field

[0001] This invention relates to the field of bifunctional oxygen electrocatalyst preparation technology, belonging to the field of energy storage, and particularly to a method for preparing a sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst and its application. Background Technology

[0002] The intermittent nature of renewable energy generation has further driven the development of rechargeable energy storage devices. To date, lithium-ion batteries are considered the most mature rechargeable battery technology and have achieved widespread commercialization. However, lithium-ion batteries suffer from high cost, less than ideal energy density, and potential toxicity. In comparison, zinc-air batteries use zinc, a more abundant, lower-cost, and more environmentally friendly metal than lithium, at the anode, and the oxygen required for the cathode reaction can be obtained from the air, achieving a capacity of 1218 Wh / kg. -1 With its higher theoretical power density, it can serve as an alternative energy storage device to lithium-ion batteries.

[0003] In zinc-air batteries, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) occur at the air electrode during charging and discharging, respectively. Both ORR and OER are slow four-electron kinetic processes, which limit the conversion efficiency and lifespan of zinc-air batteries.

[0004] Currently, platinum-based catalysts are considered the optimal ORR catalysts, but surface oxidation at high potentials leads to poor OER performance. Ruthenium / iridium-based materials, on the other hand, exhibit optimal OER catalytic performance, but their ORR performance is relatively poor. Furthermore, given the high price and scarcity of precious metals, and considering the complexity and high cost of their fabrication, using two different precious metal catalysts on a single working electrode is not economically efficient, necessitating the development of alternative catalysts. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing a sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst and its application. The aim is to prepare a low-cost bifunctional catalyst with both high ORR and OER performance. Specifically, the catalyst is a nitrogen-doped cobalt tetroxide nanosheet material with a sulfate-modified surface. The cobalt atoms within the octahedral cobalt tetroxide provide adsorption active sites for ORR and OER. Nitrogen doping and the resulting oxygen vacancies can regulate the occupied and empty d-orbitals of the cobalt sites, while the sulfate groups adsorbed on the surface can optimize the adsorption and desorption of oxygen-containing intermediates during the reaction, thereby enhancing the ORR and OER catalytic performance of cobalt tetroxide.

[0006] To address the problems in the existing technology, the technical solution adopted by this invention is as follows: A method for preparing a sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst, comprising the following steps, using a solvothermal reaction combined with low-temperature oxidation: (1) Cobalt chloride hexahydrate (CoCl2·6H2O) was dissolved in ethanol and sonicated to obtain a cobalt chloride ethanol solution with a concentration of 65~105 mM. 1-3 mL of concentrated ammonia was added dropwise to the solution and stirred at room temperature for 5 min. D(+)-glucosamine hydrochloride and 4',4-dihydroxydiphenyl sulfone were then added and sonicated and stirred to obtain a uniformly dispersed mixed solution. The mixed solution was then transferred to a reaction vessel for a solvothermal reaction for 2-4 h. After the reaction was completed, the precipitate was obtained by centrifugation, washed with ethanol, and dried under vacuum to obtain a sulfur atom modified nitrogen-containing cobalt precursor. Cobalt chloride rapidly forms cobalt hydroxide (Co(OH)2) under the action of concentrated ammonia. D(+)-glucosamine hydrochloride and 4',4-dihydroxydiphenyl sulfone react with Co(OH)2 in a solvothermal reaction to generate a sulfur-modified nitrogen-containing cobalt precursor.

[0007] (2) The sulfur-modified nitrogen-containing cobalt precursor obtained in the first step is ground and the ground powder is oxidized in air to obtain a sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst.

[0008] In the oxidation process described above, the nitrogen-containing cobalt precursor modified with sulfur atoms is transformed into cobalt tetroxide nanosheets, while the nitrogen in the precursor is simultaneously doped into the cobalt tetroxide crystal structure, forming a large number of oxygen vacancies. Meanwhile, the sulfur atoms on the precursor surface are oxidized into sulfate groups during the low-temperature oxidation process. Furthermore, a large number of micropores and mesopores are formed during the transformation of the precursor into cobalt tetroxide.

[0009] As an improvement, the concentration of D(+)-glucosamine hydrochloride in the mixed solution in step (1) is 50-90 mM, and the concentration of 4',4-dihydroxydiphenyl sulfone is 20-50 mM.

[0010] As an improvement, the temperature of the solvothermal reaction in step (1) is 120-150 °C.

[0011] As an improvement, the oxidation temperature in step (2) is 250-450 °C, and the heating rate is 2 °C / min. -1 The oxidation time is 3 to 5 hours.

[0012] The above-mentioned sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst is used as a catalyst in zinc-air batteries.

[0013] Beneficial effects: Compared with existing technologies, the present invention provides a method for preparing a sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst and its application, which has the following advantages: 1. The sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst obtained by the method of this invention has an ultrathin porous nanosheet morphology, which not only exposes more surface active sites, but also improves the mass transport rate of the catalyst through its porous structure; the nitrogen doped into the lattice and the corresponding abundant oxygen vacancies can modulate the octahedral cobalt sites (3d 6 , ) in e g The occupied and empty orbitals enhance the electron transfer rate in the ORR and OER processes. Simultaneously, the sulfate groups modified on the surface of cobalt tetroxide nanosheets can regulate the adsorption and desorption strengths of *OO, *OOH, *O, and *OH intermediates during ORR and OER, reducing the reaction energy barrier and overall overpotential, thus enhancing the catalytic performance of ORR and OER. Specifically, the sulfate-modified nitrogen-doped cobalt tetroxide catalyst prepared in this invention exhibits a high ORR half-wave potential and a 10 mA cm⁻¹... -2 The minimum difference between the OER potentials at the current density is only 0.62 V, and the peak discharge power density of the zinc-air battery assembled with the catalyst as the air electrode reaches a maximum of 248 mW / cm². -2 .

[0014] 2. This method has a simple process, low energy consumption, is green and pollution-free, and the raw materials are readily available. The prepared products have good consistency and can be used as a highly efficient bifunctional oxygen electrocatalyst for ORR and OER, with the potential to replace noble metal-based catalysts. Attached Figure Description

[0015] Figure 1 X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1; Figure 2 Transmission electron microscopy (TEM) image of the catalyst prepared in Example 1; Figure 3 The nitrogen adsorption-desorption curves and pore size distribution of the catalyst prepared in Example 1; Figure 4 High-resolution X-ray photoelectron spectroscopy (XPS) spectra of N 1s and S 2p for the catalyst prepared in Example 1; Figure 5 Electron paramagnetic resonance (EPR) spectra of the catalyst prepared in Example 1; Figure 6 ORR-OER polarization curves of the catalysts prepared in Examples 1, 2 and 3; Figure 7 The discharge power density curve of an aqueous zinc-air battery for the catalyst prepared in Example 1. Detailed Implementation

[0016] The ORR and OER testing methods in the embodiments of the invention are as follows: The prepared sulfate-modified nitrogen-doped cobalt tetroxide catalyst was formulated into a 2 mg / mL solution. -1 A membrane solution was prepared by dropping the membrane solution onto carbon cloth to form the working electrode. An Ag / AgCl electrode and a carbon rod were used as the reference and counter electrodes, respectively. The electrode was measured at 10 mV s⁻¹. -1 The ORR-OER polarization curve (LSV) was recorded by scanning rate, and the test was performed in an oxygen-saturated 0.1 M KOH solution.

[0017] The zinc-air battery test in the embodiments of the invention was carried out using a self-assembled battery device. The zinc-air battery used a polished zinc sheet as the anode, a carbon cloth loaded with a nitrogen-doped cobalt tetroxide catalyst modified with sulfate as the air electrode, and a mixed solution of 6 M KOH and 0.2 M Zn(Ac)2 as the electrolyte.

[0018] Example 1 First, CoCl₂·6H₂O was ultrasonically dissolved in ethanol at room temperature to form an 83 mM cobalt chloride solution. Then, 1 mL of concentrated ammonia was added dropwise, and the solution was stirred at room temperature for 5 min. Next, D(+)-glucosamine hydrochloride and 4',4-dihydroxydiphenyl sulfone were added to the solution, bringing their concentrations to 67 mM and 33 mM, respectively. The mixture was ultrasonically stirred at room temperature to form a uniformly dispersed solution. The solution was then transferred to a 100 mL reactor and solvothermal reacted at 150 °C for 2 h. The resulting precipitate was washed with ethanol and vacuum dried to obtain a sulfur-modified nitrogen-containing cobalt precursor powder. This powder was then ground and air-dried at 2 °C for 1 min. -1 The temperature was increased to 350 °C and oxidized for 4 h. After cooling, a nitrogen-doped porous cobalt tetroxide bifunctional catalyst modified with sulfate was obtained.

[0019] The prepared sulfate-modified nitrogen-doped porous cobalt tetroxide bifunctional catalyst was characterized, and the XRD pattern is shown below. Figure 1 As shown, the catalyst consists of pure Co3O4 crystals; the microstructure of the catalyst was characterized by TEM, such as... Figure 2 (a) and Figure 2 As shown in (b), the prepared Co3O4 catalyst has an ultrathin nanosheet morphology, which is beneficial for exposing more active sites.

[0020] The nitrogen adsorption-desorption curves of the catalyst were tested and the pore size distribution was calculated, as follows: Figure 3 As shown, the catalyst has abundant micropores and mesopores, with micropores having a diameter of ~1.2 nm and mesopores having a diameter of 2~6 nm, which is beneficial for supporting abundant active sites and improving the mass transfer rate of the catalyst.

[0021] Figure 4 The high-resolution XPS spectrum of the catalyst is shown. Figure 4 The N 1s spectrum of a shows that the catalyst contains Co-N bonds, indicating that N has been successfully doped into the Co3O4 crystal structure. Figure 4 The S 2p spectrum of b shows that the Co3O4 surface is modified with sulfate groups.

[0022] The EPR spectrum of the catalyst was tested, such as... Figure 5 As shown in the figure, the prepared Co3O4 contains oxygen vacancies, which is beneficial for further regulating the electronic structure of cobalt active sites. The above characterization results prove that the prepared catalyst is a sulfate-modified nitrogen-doped cobalt tetroxide porous nanosheet.

[0023] The ORR-OER polarization curves of the catalyst were tested, and the results are as follows: Figure 6 As shown, the ORR half-wave potential and 10 mA cm⁻¹ of the catalyst are... -2 The difference between the OER potentials at the current density is only 0.62 V, which is significantly smaller than the 0.66 V value of the Pt / C + RuO2 catalyst, demonstrating excellent bifunctional oxygen electrocatalytic performance.

[0024] The performance of the catalyst in an aqueous zinc-air battery was tested, and the discharge power density curve of the battery is shown below. Figure 7 As shown, the peak discharge power density of the catalyst reached 248 mW cm⁻¹. -2 This is far higher than the 160 mW cm⁻¹ of the Pt / C + RuO₂ catalyst. -2 This demonstrates the potential of the catalyst for use in zinc-air batteries.

[0025] Example 2 First, CoCl₂·6H₂O was ultrasonically dissolved in ethanol at room temperature to form an 83 mM cobalt chloride solution. Then, 1 mL of concentrated ammonia was added dropwise to the solution, and the mixture was stirred at room temperature for 5 min. Next, D(+)-glucosamine hydrochloride and 4',4-dihydroxydiphenyl sulfone were added to the solution, bringing their concentrations to 67 mM and 33 mM, respectively. The mixture was ultrasonically stirred at room temperature to form a uniformly dispersed solution. The solution was then transferred to a 100 mL reactor and solvothermal reacted at 150 °C for 2 h. The resulting precipitate was washed with ethanol and vacuum dried to obtain a sulfur-modified nitrogen-containing cobalt precursor powder. This powder was then ground and air-dried at 2 °C for 1 min. -1 The catalyst was oxidized at a rate of 250 °C for 4 h, and then cooled to obtain the target catalyst.

[0026] The ORR-OER polarization curves of the prepared catalyst are as follows: Figure 6As shown, the ORR half-wave potential of the catalyst and 10 mA cm⁻¹ -2 The difference between the OER potentials at the current density is 0.75 V.

[0027] Example 3 First, CoCl₂·6H₂O was ultrasonically dissolved in ethanol at room temperature to form a cobalt chloride solution with a concentration of 83 mM. Then, 1 mL of concentrated ammonia was added dropwise to the solution, and the mixture was stirred at room temperature for 5 min. Next, D(+)-glucosamine hydrochloride and 4',4-dihydroxydiphenyl sulfone were added to the solution, bringing their concentrations to 67 mM and 33 mM, respectively. The mixture was ultrasonically stirred at room temperature to form a uniformly dispersed solution. The solution was then transferred to a 100 mL reactor and solvothermal reacted at 150 °C for 2 h. The resulting precipitate was washed with ethanol and vacuum dried to obtain a sulfur-modified nitrogen-containing cobalt precursor powder. This powder was then ground and air-dried at 2 °C for 1 min. -1 The catalyst was oxidized at a rate of 450 °C for 4 h, and after cooling, a nitrogen-doped porous cobalt tetroxide bifunctional catalyst modified with sulfate was obtained.

[0028] The ORR-OER polarization curves of the prepared catalyst are as follows: Figure 6 As shown, the ORR half-wave potential of the catalyst and 10 mA cm⁻¹ -2 The difference between the OER potentials at the current density is 0.68 V, which is close to the 0.66 V value of the Pt / C + RuO2 catalyst.

Claims

1. A method for preparing a sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst, characterized in that, Includes the following steps: (1) Dissolve cobalt chloride hexahydrate in ethanol and sonicate to obtain a cobalt chloride ethanol solution with a concentration of 65~105 mM. Add 1~3 mL of concentrated ammonia to the solution and stir at room temperature for 5 min. Then add D(+)-glucosamine hydrochloride and 4',4 dihydroxydiphenyl sulfone. Continue to sonicate and stir to obtain a uniformly dispersed mixed solution. Then transfer the mixed solution to a reaction vessel and carry out a solvothermal reaction for 2~4 h. After the reaction is completed, centrifuge to obtain the precipitate, wash the precipitate with ethanol, and vacuum dry to obtain a sulfur atom modified nitrogen-containing cobalt precursor. (2) The sulfur-modified nitrogen-containing cobalt precursor obtained in step (1) is ground, and the ground powder is air-dried at 2 °C for min. -1 The temperature was increased to 250 ~ 450 ℃, and the oxidation was carried out at low temperature for 3 ~ 5 h to obtain a sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst.

2. The method for preparing the sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst according to claim 1, characterized in that, The concentration of D(+)-glucosamine hydrochloride in the mixed solution in step (1) is 50 ~ 90 mM, and the concentration of 4',4-dihydroxydiphenyl sulfone is 20 ~ 50 mM.

3. The method for preparing the sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst according to claim 1, characterized in that, The temperature of the solvothermal reaction in step (1) is 120 ~ 150 ℃.

4. The application of the sulfate-modified nitrogen-doped cobalt tetroxide bifunctional catalyst obtained by the method of claim 1 as a catalyst in zinc-air batteries.

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