NiCoFe LDH-h2o2 electrocatalyst based on co valence state regulation and preparation method and application thereof

Abstract

This invention provides a NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation, its preparation method, and its application, relating to the field of electrochemistry. The preparation method of the NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation includes the following steps: S1, ultrasonically immersing nickel foam in isopropanol and hydrochloric acid respectively, followed by washing and drying; S2, immersing a cobalt salt in a mixed H2O2 solution; then adding nickel and iron salts to prepare a solution; S3, immersing the pretreated nickel foam from step S1 in the solution from step S2 to achieve in-situ growth; then adding a mixed alkaline solution, followed by an equal volume and concentration of H2O2 solution as in step S2, mixing thoroughly, and allowing to stand; S4, removing the nickel foam treated in step S3, washing with anhydrous ethanol, and vacuum drying to obtain the NiCoFe LDH-H2O2 material. The NiCoFe LDH-H2O2 electrocatalyst prepared by this invention has structural advantages, high cycling stability, and excellent electrochemical performance; moreover, the method is green and low-carbon, showing good prospects for industrial scale-up.

Description

Technical Field

[0001] This invention relates to the field of electrochemistry, and in particular to a NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy technologies, electrochemical energy conversion and storage systems play a crucial role in the utilization of renewable energy. Among them, zinc-air batteries (ZABs) have attracted widespread attention due to their high energy density and environmental friendliness. However, the core process of these batteries—the oxygen evolution reaction (OER)—is kineticly slow, severely limiting overall efficiency and device lifespan. Therefore, developing efficient, stable, and low-cost OER electrocatalysts is of significant theoretical and engineering value for promoting the large-scale application of clean energy technologies.

[0003] Existing high-performance catalysts mostly rely on noble metals (such as RuO2 and Ir / C), which are expensive and have poor long-term stability. NiCoFe layered double hydroxides (LDHs) are considered one of the ideal candidates to replace noble metal catalysts due to their low cost and excellent performance. However, the Co²⁺ in LDHs... + The electrochemical activity of this material is low. How can it be selectively oxidized to highly active Co under mild conditions? 3+ Maintaining the integrity of the LDH crystal structure while simultaneously addressing this critical issue is crucial in this field. Traditional methods for controlling valence states (such as high-temperature calcination and elemental doping) are often complex and demanding, easily disrupting the original crystal structure of NiCoFe layered double hydroxide (LDH). To address the aforementioned cost, stability, and complex preparation process issues, this invention proposes a preparation process for NiCoFe LDH-H2O2 electrocatalysts based on Co valence state control.

[0004] This invention employs an H2O2 oxidation strategy to control the valence state of metals at room temperature. The process is simple and the conditions are mild. While improving the OER activity, it effectively preserves the layered structure of LDH, providing a new route for the preparation of low-cost, high-performance bifunctional catalysts. Summary of the Invention

[0005] In view of this, the present invention proposes a method for preparing a self-supported oxygen evolution reaction (OER) electrocatalyst by growing NiCoFe layered double hydroxide (LDH) in situ on nickel foam (NF) using a green and mild immersion method, and by using hydrogen peroxide (H2O2) to achieve precise control of the valence state of the transition metal Co.

[0006] The technical solution of this invention is achieved as follows: a method for preparing a NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation, comprising the following steps: S1. Soak the nickel foam in isopropanol and hydrochloric acid by ultrasonication, then wash and dry. S2. Soak the cobalt salt in a mixture of H2O2 solution; then add nickel salt and iron salt to prepare a mixed solution. S3. Immerse the pretreated nickel foam from step S1 in the solution from step S2 to achieve in-situ growth; then add the mixed alkaline solution, and then add an equal volume and concentration of H2O2 solution as in step S2. After mixing evenly, let it stand. S4. Take out the foamed nickel processed in step S3, wash it with anhydrous ethanol, and vacuum dry it to obtain NiCoFe LDH-H2O2 material.

[0007] Furthermore, in step S1, the dimensions of the nickel foam are (2-2.5) × (3.5-4.5) cm. 2 The concentration of the hydrochloric acid is 2.5-3.5 mol / L, and the ultrasonic soaking time in isopropanol and hydrochloric acid is 20-30 min respectively.

[0008] Furthermore, in step S2, the nickel salt is at least one of nickel nitrate, nickel chloride, and nickel sulfate; The cobalt salt is at least one of cobalt nitrate, cobalt chloride, and cobalt sulfate; The iron salt is at least one of ferric nitrate, ferric chloride, and ferric sulfate.

[0009] Furthermore, in step S2, the nickel salt, cobalt salt, and iron salt are in a molar ratio of Ni:Co:Fe = (1.9-2.1):(4.8-5.2):(2.9-3.1); the total metal ion concentration of the mixed solution is 0.2-0.3 mol / L.

[0010] Furthermore, in step S2, the soaking time is 10-20 min; the mass concentration of the H2O2 solution is 25%-35%; and the molar volume ratio of the cobalt salt to the H2O2 solution in step S2 is (0.12-0.13) mol:(10-100) μL.

[0011] Furthermore, in step S3, the soaking time is 12-15 hours; the standing time is 12-15 hours.

[0012] Further, in step S3, the mixed alkaline solution consists of 0.08-0.12 mol / L Na2CO3 and 0.08-0.12 mol / L NaOH; the volume ratio of the mixed alkaline solution in step S3 to the nickel foam in step S1 is 20-30 mL: 7-11.25 cm³. 3 .

[0013] Furthermore, in step S4, the vacuum drying temperature is 65-75℃, and the drying time is 4-6 hours.

[0014] A NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation is prepared by any one of the preparation methods described in this invention.

[0015] The NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation described in this invention is used in the preparation of zinc-air batteries.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for preparing a self-supported oxygen evolution reaction (OER) electrocatalyst by growing NiCoFe layered double hydroxide (LDH) in situ on nickel foam (NF) using a green and mild immersion method and by utilizing hydrogen peroxide (H2O2) to achieve precise control of the valence state of the transition metal Co.

[0017] (1) The NiCoFe LDH-H2O2 electrocatalyst prepared in this invention has structural advantages. Its self-supporting structure does not require a binder, and the nanosheet array is uniformly distributed, providing a direct channel for electrolyte diffusion and increasing the electrochemical active surface area.

[0018] (2) The preparation method of the NiCoFe LDH-H2O2 electrocatalyst of the present invention is green and low-carbon. It adopts a mild soaking method, and the by-products are only water and oxygen. The preparation process does not destroy the LDH structure and has good prospects for industrial scale-up.

[0019] (3) The present invention adopts a two-step H2O2 oxidation strategy: H2O2 is added in stages during the metal salt soaking stage and the alkali precipitation stage to achieve oxidation of Co. 2+ / Co 3+ Precise control of the proportion.

[0020] (4) The present invention utilizes the trimetallic electron synergistic regulation of NiCoFe: the redistribution of electrons between Ni and Fe is induced by the change in the valence state of Co, thereby optimizing the adsorption energy of the intermediate; at 100 mA cm⁻¹ -2 At the current density, the optimized NiCoFe LDH-20 H2O2 overpotential is only 178 mV.

[0021] (5) The high cycle stability self-supporting electrode of the present invention: the catalyst structure that achieves more than 5,000 stable cycles when applied in zinc-air batteries. Attached Figure Description

[0022] Figure 1OER performance graphs of NiCoFe LDH sample of Comparative Example 1, NiCoFe LDH-20 H2O2 sample of Example 1, and NiCoFe LDH-200 H2O2 sample of Example 2 are shown, where the Y-axis represents current density and the X-axis represents voltage.

[0023] Figure 2 Scanning electron microscope (SEM) image of the NiCoFe LDH-20 H2O2 sample of this invention.

[0024] Figure 3 The charge-discharge cycle curve of the zinc-air battery prepared by NiCoFe LDH-20 H2O2 according to the present invention is shown in the figure, where Y (lower axis) is time (hours), the upper axis is the number of cycles, and the X axis is voltage V. Detailed Implementation

[0025] Unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods; Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0026] Example 1 A method for preparing a NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation includes the following steps: S1. Pretreatment of nickel foam: Pretreatment of nickel foam with dimensions of 2.2×4cm... 2 Nickel foam (NF) was ultrasonically soaked in isopropanol and 3 M HCl solutions for 20 min to remove surface impurities and oxide layers, and then washed and dried.

[0027] S2. Initial soaking and valence state pre-regulation: Mix 0.125 mol Co(NO3)2 with 10 μL of 30% wt H2O2 solution and soak for 10 min. Then add nickel nitrate and ferric nitrate in a molar ratio of Ni:Co:Fe = 2:5:3 to prepare a mixed solution with a total metal ion concentration of 0.25 M.

[0028] S3, In-situ Growth and Secondary Oxidation: The pretreated NF was immersed in the solution from step S2 above for 12 h to achieve in-situ growth. Then, 25 mL of mixed alkaline solution (0.1 M Na2CO3 and 0.1 M NaOH) was added, followed by the addition of an equal volume (10 μL) of 30% wt H2O2 solution, and the mixture was allowed to stand for another 12 h.

[0029] S2.4 Post-treatment: NF was removed and washed with anhydrous ethanol, and then vacuum dried at 70 °C for 5 h to obtain NiCoFe LDH-20 H2O2 self-supporting catalyst, i.e., NiCoFe LDH-20 H2O2 controlled by 20 μL H2O2 solution.

[0030] Example 2 A method for preparing a NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation includes the following steps: S1. Pretreatment of nickel foam: Pretreatment of nickel foam with dimensions of 2.2×4cm... 2 Nickel foam (NF) was ultrasonically soaked in isopropanol and 3 M HCl solutions for 20 min to remove surface impurities and oxide layers, and then washed and dried.

[0031] S2. Initial soaking and valence state pre-regulation: Mix 0.125 mol Co(NO3)2 with 100 μL of 30% wt H2O2 and soak for 10 min. Then add nickel nitrate and ferric nitrate in a molar ratio of Ni:Co:Fe = 2:5:3 to prepare a mixed solution with a total metal ion concentration of 0.25 M.

[0032] S3, In-situ Growth and Secondary Oxidation: The pretreated NF was immersed in the solution from step S2 above for 12 h to achieve in-situ growth. Then, 25 mL of mixed alkaline solution (0.1 M Na2CO3 and 0.1 M NaOH) was added, followed by the addition of an equal volume (100 μL) of 30% wt H2O2 solution, and the mixture was allowed to stand for another 12 h.

[0033] S4. Post-treatment: NF was removed and washed with anhydrous ethanol, and then vacuum dried at 70 °C for 5 h to obtain NiCoFe LDH-200 H2O2 self-supporting catalyst, i.e., NiCoFe LDH-200 H2O2 controlled by 200 μL H2O2 solution.

[0034] Comparative Example 1 A method for preparing layered double hydroxides (NiCoFe-LDH) includes the following steps: S1. Pretreatment of nickel foam: Pretreatment of nickel foam with dimensions of 2.2×4cm... 2 Nickel foam (NF) was ultrasonically soaked in isopropanol and 3 M HCl solutions for 20 min to remove surface impurities and oxide layers, and then washed and dried.

[0035] S2. Initial soaking: Add nickel nitrate, cobalt nitrate and iron nitrate in a molar ratio of Ni:Co:Fe = 2:5:3 to prepare a mixed solution with a total metal ion concentration of 0.25 M.

[0036] S3. In-situ growth: The pretreated NF was immersed in the above solution for 12 h to achieve in-situ growth. Then, 25 mL of mixed alkaline solution (0.1 M Na2CO3 and 0.1 M NaOH) was added, mixed thoroughly, and allowed to stand for another 12 h. The 12 h period ensured uniform growth.

[0037] S4. Post-treatment: The in-situ grown NF was removed, washed with anhydrous ethanol, and vacuum dried at 70 °C for 5 h to obtain the NiCoFe LDH self-supporting catalyst, i.e., the layered double hydroxide (NiCoFe-LDH).

[0038] The material performance test results obtained in Examples 1-2 and Comparative Example 1 are as follows: Table 1. OER performance of samples from Examples 1-2 and Comparative Example 1

[0039] like Figure 1 And as shown in Table 1, OER performance optimization: at 100 mA cm⁻¹ -2 At the current density, the optimized NiCoFeLDH-20 H2O2 overpotential is only 178 mV, which is significantly better than the 211 mV of the untreated NiCoFe LDH sample and the 189 mV of the overtreated NiCoFe LDH-200 H2O2; NiCoFe LDH-200 H2O2 is also significantly better than NiCoFe LDH.

[0040] Specifically, Figure 1 The results from the three groups of different materials show that, in order to evaluate the effect of H2O2 on improving OER activity, polarization curve (LSV) tests were performed on a series of catalysts in 1.0 M KOH solution. Figure 1 As shown, the LSV curves clearly reflect the differences in OER performance among the catalysts. NiCoFe LDH-20 H2O2 exhibits the most outstanding OER activity, reaching 100 mAcm⁻¹. 2 At high current densities, its overpotential is only 178 mV, significantly better than untreated NiCoFe LDH (211 mV) and over-oxidized NiCoFe LDH-200 H2O2 (189 mV). Notably, even under high current density operating conditions, this catalyst maintains an extremely low overpotential at 400 mA cm⁻¹. 2 Under high load current, the overpotential only increases to 301 mV. This excellent high-current discharge capability indicates that moderate H2O2 treatment optimizes the activity of the material.

[0041] like Figure 2As shown, the morphology of NiCoFe LDH-20 H2O2 is a layered nanosheet structure, which is a classic LDH morphology, proving that the synthesis was successful.

[0042] Specifically, Figure 2 The growth state of NiCoFe LDH nanosheets treated with H2O2 is clearly demonstrated. As shown in the figure, the NiCoFe LDH-20H2O2 sample treated with 20 μL of H2O2 exhibits a regular and dispersed nanosheet array structure. This vertically grown sheet configuration is a typical feature of LDH structure, growing uniformly in situ on the surface of a three-dimensional NF substrate. This uniform distribution constructs abundant open channels, which not only significantly increases the exposed area of ​​electrochemical active sites but also facilitates the deep penetration of the electrolyte and accelerates the rapid release of oxygen bubbles from the reaction product, thereby greatly improving the interfacial mass transfer efficiency.

[0043] Zinc-air batteries were assembled using the NiCoFe LDH-20 H2O2 sample prepared in Example 1 of this invention, and their performance was tested.

[0044] The assembly steps for zinc-air batteries include: during ZAB assembly, the anode and cathode are sequentially assembled into the battery template and then tightened and sealed with bolts. The battery structure from top to bottom is as follows: anode plate, Zn anode, anode separator, electrolyte flow channel plate, cathode separator, air cathode, and cathode plate. Finally, four long screws are used to evenly tighten the assembly to ensure consistency and good contact. The Zn anode uses a 2 mm thick zinc sheet, which is sanded before testing to remove the surface oxide layer and obtain a more uniform surface condition; the air cathode has a load of 1 mg cm⁻¹. -2 Pt / C NiCoFe LDH-20 H2O2. After battery assembly, the battery was connected to the peristaltic pump tubing and run at a fixed speed for 5 minutes to allow the electrolyte (6 M KOH and 0.2 M (CH3COO)2Zn) to fully wet the electrodes and bring the system to a relatively stable operating state. The peristaltic pump speed was set to n = 20.0 r / min. -1 .

[0045] The air cathode was constructed using NiCoFe LDH-20 H2O2: First, hydrophobic carbon cloth was cut to a size slightly larger than the block catalyst, ensuring that the catalyst retained an edge region of approximately 0.50 cm around the carbon cloth. Then, the catalyst and carbon cloth were stacked and composite fixed under hot-pressing conditions: 120 ℃, 1.50 atm, 5 min. 10 mg of Pt / C was added to a mixed solution of 909 μL anhydrous ethanol and 91 μL 5wt.% Nafion, and sonicated continuously for 1 h until the slurry became a uniform ink-like consistency. 100 μL of the slurry was then added dropwise to obtain the air cathode.

[0046] like Figure 3 As shown, the zinc-air battery performance is as follows: the assembled battery achieved charge-discharge cycle stability exceeding 5000 cycles (approximately 833 hours). Cycle life is a core indicator for evaluating the application prospects of ZABs.

[0047] Specifically, such as Figure 3 As shown, at 10 mA cm 2 Long-term cycling tests were conducted at current density for 10 minutes per cycle (5 minutes each for charge and discharge). Figure 3 As shown, the NiCoFe LDH-20 H2O2-based ZABs achieved over 5000 charge-discharge cycles, with a total operating time of approximately 810 hours. This ultra-long operational durability is attributed to: the electron redistribution induced by H2O2 treatment endowing the material with extremely high OER activity and reducing the oxidation potential during charging; and the ultra-thin nanosheet array grown in situ on a three-dimensional nickel foam framework, which not only provides an ultra-high effective contact area, but its stable interfacial coupling also effectively prevents the physical shedding of active materials during long-term gas evolution, thus ensuring the energy efficiency of the battery under high-current cycling. The NiCoFeLDH-20 H2O2 catalyst exhibits excellent power output and ultra-long cycle life in actual ZABs, demonstrating good practical application value.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation, characterized in that, Includes the following steps: S1. Soak the nickel foam in isopropanol and hydrochloric acid by ultrasonication, then wash and dry. S2. Soak the cobalt salt in a mixture of H2O2 solution; then add nickel salt and iron salt to prepare a mixed solution. S3. Immerse the pretreated nickel foam from step S1 in the solution from step S2 to achieve in-situ growth; then add the mixed alkaline solution, and then add an equal volume and concentration of H2O2 solution as in step S2. After mixing evenly, let it stand. S4. Take out the foamed nickel processed in step S3, wash it with anhydrous ethanol, and vacuum dry it to obtain NiCoFe LDH-H2O2 material.

2. The preparation method of NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation according to claim 1, characterized in that, In step S1, the dimensions of the nickel foam are (2-2.5) × (3.5-4.5) cm. 2 The concentration of the hydrochloric acid is 2.5-3.5 mol / L, and the ultrasonic soaking time in isopropanol and hydrochloric acid is 20-30 min respectively.

3. The preparation method of the NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation according to claim 1, characterized in that, In step S2, the nickel salt is at least one of nickel nitrate, nickel chloride, and nickel sulfate; The cobalt salt is at least one of cobalt nitrate, cobalt chloride, and cobalt sulfate; The iron salt is at least one of ferric nitrate, ferric chloride, and ferric sulfate.

4. The preparation method of the NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation according to claim 1, characterized in that, In step S2, the nickel salt, cobalt salt, and iron salt are mixed in a molar ratio of Ni:Co:Fe = (1.9-2.1):(4.8-5.2):(2.9-3.1); the total metal ion concentration of the mixed solution is 0.2-0.3 mol / L.

5. The preparation method of the NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation according to claim 1 or 4, characterized in that, In step S2, the soaking time is 10-20 min; the mass concentration of the H2O2 solution is 25%-35%; and the molar volume ratio of the cobalt salt to the H2O2 solution in step S2 is (0.12-0.13) mol:(10-100) μL.

6. The preparation method of the NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation according to claim 1, characterized in that, In step S3, the soaking time is 12-15 hours; the standing time is 12-15 hours.

7. The method for preparing the NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation according to claim 1 or 6, characterized in that, In step S3, the mixed alkaline solution consists of 0.08-0.12 mol / L Na2CO3 and 0.08-0.12 mol / L NaOH; the volume ratio of the mixed alkaline solution in step S3 to the nickel foam in step S1 is 20-30 mL: 7-11.25 cm³. 2 .

8. The preparation method of the NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation according to claim 1, characterized in that, In step S4, the vacuum drying temperature is 65-75℃ and the drying time is 4-6 hours.

9. A NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the NiCoFe LDH-H2O2 electrocatalyst based on Co valence state regulation as described in claim 9 in the preparation of zinc-air batteries.

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