A NiFe-LDH-based catalyst, its preparation method and application

Abstract

This invention discloses a NiFe-LDH-based catalyst, its preparation method, and its application. The preparation method of the catalyst includes the following steps: dissolving nickel chloride hexahydrate and urea in deionized water; then adding a mixed aqueous solution containing potassium hydroxide and sodium chloride to the above solution; stirring thoroughly; adding an aqueous solution of ferric nitrate nonahydrate dropwise; continuing to add sodium molybdate dihydrate; continuing to stir to form a homogeneous mixture; further adding hydrogen peroxide solution; transferring the solution to a reaction vessel; and carrying out a hydrothermal reaction at 120°C to obtain Ov-NiFe-LDH-MoO4. This invention utilizes H2O2 pre-oxidation to selectively etch the (003) basal plane of NiFe-LDH, creating oxygen vacancies and nanoporous structures, significantly increasing the exposure ratio of the (012) edge crystal planes; MoO4 2‑ Through Ni 2+ Fe 3+ The formation of strong coordination bonds effectively suppresses the reconstruction of the (012) crystal plane, while electrostatic repulsion resists Cl. ‑ Adsorption and corrosion work synergistically to simultaneously enhance both activity and stability.

Description

Technical Field

[0001] This invention belongs to the field of novel energy conversion materials technology, specifically relating to a NiFe-LDH-based catalyst, its preparation method and application, which is particularly suitable for electrolytic hydrogen production technology in alkaline seawater environments. Background Technology

[0002] The dual challenges of global freshwater scarcity and surging demand for green hydrogen energy have driven the development of direct seawater electrolysis for hydrogen production technology. Seawater accounts for 96.5% of the Earth's total water resources, and using seawater as a feedstock for hydrogen electrolysis can effectively resolve the "hydrogen-water" resource conflict. However, the high concentration of chloride ions (Cl-) in seawater... - This can lead to severe corrosion of the electrocatalyst, causing deactivation of active sites, collapse of the catalyst structure, and the generation of harmful byproducts such as hypochlorite, and even toxic chlorine gas, which seriously restricts the practical application of seawater electrolysis for hydrogen production.

[0003] The oxygen evolution reaction (OER) is a key half-reaction in the water electrolysis process. Its kinetics are slow, requiring highly efficient catalysts to lower the reaction energy barrier. Nickel-iron layered double hydroxides (NiFe-LDH) have become highly promising OER catalysts under alkaline conditions due to their tunable crystal structure, high specific surface area, and unique electronic structure. Studies have confirmed that the (012) crystal facet of NiFe-LDH can directly expose unsaturated Ni / Fe active sites, and its intrinsic activity is 3-5 times that of the (003) basal facet. However, the (012) crystal facet exhibits thermodynamic instability, easily undergoing metal ion dissolution and crystal phase reconstruction under high OER potential conditions, resulting in poor long-term catalyst stability.

[0004] Existing improvement strategies include elemental doping, heterostructure construction, and surface coating, but noble metal doping is costly and difficult to scale up; traditional anion intercalation methods can regulate interlayer interactions to some extent, but their effect on improving the stability of the (012) crystal plane is limited, and the catalyst's resistance to Cl at high current densities is also limited. - Insufficient corrosion resistance. Furthermore, NiFe-LDH nanosheets tend to aggregate and stack, resulting in insufficient exposure of edge active sites, further limiting their catalytic performance.

[0005] Therefore, it is necessary to develop a method that can simultaneously achieve high activity (012) crystal plane stabilization and Cl resistance. - The preparation method of NiFe-LDH-based catalyst with full exposure of corrosion and active sites is of great significance for promoting the industrialization of seawater electrolysis hydrogen production technology. Summary of the Invention

[0006] This invention aims to solve the problems of easy reconfiguration of the (012) crystal facet and resistance to Cl in existing NiFe-LDH catalysts during the electrolysis of brine OER process. -To address the issues of weak corrosion resistance and insufficient exposure of active sites, a MoO4-based solution is provided. 2- The catalyst (Ov-NiFe-LDH-MoO4) obtained by intercalation coupling with H2O2 pre-oxidation to enrich the NiFe-LDH edge structure exhibits excellent OER activity, long-term stability, and resistance to Cl. - Its corrosion resistance makes it highly effective for electrolytic hydrogen production in alkaline freshwater and simulated seawater.

[0007] A method for preparing a NiFe-LDH-based catalyst includes the following steps: dissolving nickel chloride hexahydrate and urea in deionized water; then adding a mixed aqueous solution containing potassium hydroxide and sodium chloride to the above solution; stirring thoroughly; adding an aqueous solution of ferric nitrate nonahydrate dropwise; continuing to add sodium molybdate dihydrate; continuing to stir to form a homogeneous mixture; further adding hydrogen peroxide solution; transferring the solution to a reaction vessel; and carrying out a hydrothermal reaction at 120°C to obtain Ov-NiFe-LDH-MoO4.

[0008] Preferably, the molar ratio of nickel chloride hexahydrate, urea, ferric nitrate nonahydrate, and sodium molybdate dihydrate is 2.25:10:0.75:0.1.

[0009] Preferably, the mass fraction of hydrogen peroxide is 28-32%;

[0010] The concentration of potassium hydroxide in the mixed aqueous solution of potassium hydroxide and sodium chloride is 0.425 M, and the concentration of sodium chloride is 0.5 M.

[0011] Preferably, the molar volume ratio of nickel chloride hexahydrate to deionized water, mixed aqueous solution, aqueous solution of ferric nitrate nonahydrate, and hydrogen peroxide solution is 2.25 mmol: 20 mL: 10 mL: 10 mL: 160 μL.

[0012] The amount of hydrogen peroxide added in this invention can precisely control the oxygen vacancy concentration and the pore structure of the nanosheets, avoiding excessive etching that could lead to the loss of active components.

[0013] Preferably, the hydrothermal reaction time is 8 hours.

[0014] Preferably, after the hydrothermal reaction is completed, the product is naturally cooled to room temperature, centrifuged at 6000 rpm for 5 minutes to collect the product, and washed three times alternately with deionized water and ethanol. Finally, the obtained sample is vacuum dried at 60℃ for 12 hours to obtain pure Ov-NiFe-LDH-MoO4.

[0015] This invention also protects the NiFe-LDH-based catalyst prepared by the above method and its application in the oxygen evolution reaction of water electrolysis.

[0016] Preferably, it is used in a 1 M KOH alkaline freshwater system or a 1 M KOH + 0.5 M NaCl simulated seawater system.

[0017] The beneficial effects of this invention are: 1. The synergistic modification strategy has significant advantages: H2O2 pre-oxidation can selectively etch the (003) basal plane of NiFe-LDH, creating oxygen vacancies and nanoporous structures, significantly increasing the exposure ratio of the (012) edge crystal plane. {003} is the interlayer stacking plane of LDH, with a large interlayer spacing (0.88~0.94 nm) along this crystal plane, and the interlayer anions (CO3²) are abundant. - / NO3 - Water molecules and H2O2 molecules can enter without hindrance, while the atoms on the {110} / {010} sides are densely packed, making it difficult for H2O2 to penetrate and contact. The {003} crystal plane has a large number of coordinated unsaturated metal sites (Ni²) at the layer edges / interlayer interfaces. + / Co² + / Fe³ + These sites, including oxygen vacancies, can efficiently adsorb and activate H2O2, triggering a Fenton-like reaction to generate... Strong oxidizing free radicals such as OH enable precise local etching; while the dense side surface is saturated with metal ions, resulting in extremely weak activation ability of H2O2.

[0018] MoO4 2- Through Ni 2+ Fe 3+ The formation of strong coordination bonds effectively suppresses the reconstruction of the (012) crystal plane, while electrostatic repulsion resists Cl. - Adsorption and corrosion work synergistically to simultaneously enhance both activity and stability.

[0019] 2. In a 1 M KOH system, 100 mA cm -2 The overpotential at the current density is only 234 mV; in a simulated seawater system of 1 M KOH + 0.5 M NaCl, the overpotential at 1000 mA is... cm -2 The overpotential at current density is as low as 357 mV, which is superior to commercial RuO2 and most reported non-noble metal catalysts.

[0020] 3. No significant potential decay was observed after continuous operation in simulated seawater for 32 hours. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 Scanning images of NiFe-LDH (a), NiFe-LDH-MoO4 (b), Ov-NiFe-LDH-MoO4 (c), and Ov-NiFe-LDH (d) prepared in Examples 1 and Comparative Examples 1-3.

[0023] Figure 2 X-ray powder diffraction pattern (a), Raman spectrum (b), infrared spectrum (c) and EPR test (d) of NiFe-LDH, NiFe-LDH-MoO4, OvNiFe-LDH-MoO4 and Ov-NiFe-LDH prepared in Examples 1 and Comparative Examples 1-3.

[0024] Figure 3 The LSV curves (a) of NiFe-LDH, NiFe-LDH-MoO4, Ov-NiFe-LDH-MoO4, Ov-NiFe-LDH, commercial RuO2 and NF (nickel foam) prepared for Example 1 and Comparative Examples 1-3 in alkaline water, and the step current curve (b) of Ov-NiFe-LDH-MoO4.

[0025] Figure 4 The lsv curves (a) of NiFe-LDH, NiFe-LDH-MoO4, Ov-NiFe-LDH-MoO4, Ov-NiFe-LDH, commercial RuO2 and NF (nickel foam) prepared for Examples 1 and Comparative Examples 1-3 in brine, and the step current curve (b) of Ov-NiFe-LDH-MoO4.

[0026] Figure 5 LSV curves (a) of NiFe-LDH, NiFe-LDH-MoO4, Ov-NiFe-LDH-MoO4, Ov-NiFe-LDH, commercial RuO2 and NF (nickel foam) prepared for Examples 1 and Comparative Examples 1-3 in brine and stability test of Ov-NiFe-LDH-MoO4 (b).

[0027] Figure 6 The lsv curves of Ov-NiFe-LDH-MoO4 prepared in Example 1 and Comparative Examples 4-7 in brine; Figure 7The Ov-NiFe-LDH-MoO4, Ov-NiFe-LDH, and Ov-NiFe-LDH-PMo prepared in Examples 1, 2, and 8 respectively 12 LSV curve in saline solution. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: The preparation method of Ov-NiFe-LDH-MoO4 catalyst includes the following steps: 2.25 mmol of nickel chloride hexahydrate (NiCl2) Dissolve 10 mmol of 6H2O and urea in 20 mL of deionized water, stir well, then add 10 mL of a mixed aqueous solution containing 0.425 mol / L potassium hydroxide (KOH) and 0.5 mol / L sodium chloride (NaCl), and continue stirring for 10 min. Then, add dropwise 10 mL of 0.75 mmol of ferric nitrate nonahydrate (Fe(NO3)3)2. An aqueous solution of sodium molybdate dihydrate (Na₂MoO₄) was prepared, and 0.1 mmol of sodium molybdate dihydrate (Na₂MoO₄) was added to the mixture. Add 2H₂O), continue stirring for 30 min to form a homogeneous mixture. Add 160 μL of 30% (w / w) hydrogen peroxide (H₂O₂) solution to the mixture, stir for 10 min, and then transfer to a reaction vessel. Transfer the mixture to a 100 mL PTFE-lined stainless steel reaction vessel, maintain the temperature at 120 °C for 8 h, allow it to cool naturally to room temperature, centrifuge at 6000 rpm for 5 min to collect the product, wash three times alternately with deionized water and ethanol, and vacuum dry at 60 °C for 12 h to obtain oxygen vacancies and MoO₄⁻. 2- Synergistic modification of Ov-NiFe-LDH-MoO4 catalyst.

[0030] Comparative Example 1 The steps are basically the same as in Example 1, except that Na2MoO4 and H2O2 were not added during the synthesis process to obtain the NiFe-LDH electrocatalyst.

[0031] Comparative Example 2 The steps are basically the same as in Example 1, except that Na2MoO4 was not added during the synthesis process, resulting in Ov-NiFe-LDH electrocatalyst.

[0032] Comparative Example 3 The steps are basically the same as in Example 1, except that H2O2 was not added during the synthesis process to obtain the NiFe-LDH-MoO4 electrocatalyst.

[0033] Comparative Example 4 Add 80 μL of a 30% hydrogen peroxide (H2O2) solution, and the rest is the same as in Example 1.

[0034] Comparative Example 5 Add 240 μL of a 30% hydrogen peroxide (H2O2) solution, and the rest is the same as in Example 1.

[0035] Comparative Example 6 Add 0.05 mmol of sodium molybdate dihydrate (Na2MoO4) (2H2O), the rest is the same as in Example 1.

[0036] Comparative Example 7 Add 0.15 mmol of sodium molybdate dihydrate (Na2MoO4) (2H2O), the rest is the same as in Example 1.

[0037] Comparative Example 8 Add 0.1 mmol of phosphotungstic acid, and the rest is the same as in Example 1.

[0038] Scanning electron microscope (SEM) images of NiFe-LDH, NiFe-LDH-MoO4, Ov-NiFe-LDH-MoO4, and Ov-NiFe-LDH obtained in Example 1 and Comparative Examples 1-3 are shown below. Figure 1 As shown. By Figure 1 It can be seen that: MoO4 2- The addition of H2O2 does not change the lamellar structure of LDH. The addition of hydrogen peroxide leads to smaller LDH lamellars, more exposed (012) crystal planes, and improved intrinsic activity of LDH.

[0039] X-ray powder diffraction, Raman spectroscopy, infrared spectroscopy, and EPR of NiFe-LDH, NiFe-LDH-MoO4, Ov-NiFe-LDH-MoO4, and Ov-NiFe-LDH obtained in Examples 1 and Comparative Examples 1-3 are shown below. Figure 2 As shown. By Figure 2 It can be seen that: MoO4- was successfully synthesized. 2- Intercalation and oxygen-deficient Ov-NiFe-LDH-MoO4.

[0040] The OER electrocatalytic performance of NiFe-LDH, NiFe-LDH-MoO4, Ov-NiFe-LDH-MoO4, and Ov-NiFe-LDH obtained in Examples 1 and Comparative Examples 1-3 with commercial RuO2 and NF (nickel foam) in alkaline water is as follows: Figure 3As shown. Nickel foam (NF) was purchased from Shenzhen Kejing Technology Co., Ltd. Commercial RuO2 was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Figure 3 It can be seen that: in Ov-NiFe-LDH-MoO4 at 1M KOH at 100mA cm -2 The overpotential at the current density was 234 mV, exhibiting superior catalytic performance compared to RuO2. After 24 hours of electrolysis in alkaline water, the overpotential at 10 mA cm⁻¹ was [value missing]. -2 It remains at 1.49V even at current density.

[0041] All electrochemical tests were performed on a CHI 760E electrochemical workstation equipped with a three-electrode setup. A carbon rod and a saturated Hg / HgO electrode (1.0 M potassium hydroxide filler) were used as the counter and reference electrodes, respectively. Linear sweep voltammetry (LSV) was performed at 5.0 mV s⁻¹. 1 The scan rate was measured and 95% iR compensation was used. The electrode preparation process was as follows: 50 mg of catalyst, 10 mg of acetylene black, and 250 µL of 5 wt.% Nafion solution were dispersed in 3020 µL of ethanol and 1730 µL of water, and ultrasonically treated for 2 hours to form a uniform ink. The prepared ink was sprayed onto NF (5 cm × 5 cm). Electrochemical performance tests were conducted in alkaline water (1.0 M KOH) and simulated seawater (1.0 M KOH and 0.5 M NaCl).

[0042] The OER electrocatalytic performance of NiFe-LDH, NiFe-LDH-MoO4, Ov-NiFe-LDH-MoO4, and Ov-NiFe-LDH obtained in Examples 1 and Comparative Examples 1-3, compared with commercial RuO2 and NF (nickel foam), in brine is as follows: Figure 4 As shown.

[0043] Depend on Figure 4 It can be seen that: in Ov-NiFe-LDH-MoO4 at 1MKOH, 1000mA cm -2 With an overpotential of 357mV, the performance remained stable after 32 hours of continuous operation, demonstrating superior catalytic performance compared to RuO2.

[0044] The LSV test curves and stability tests of the two-electrode systems obtained from Examples 1 and Comparative Examples 1-3 (NiFe-LDH, NiFe-LDH-MoO4, Ov-NiFe-LDH-MoO4, Ov-NiFe-LDH and commercial RuO2 and NF (nickel foam)) are as follows: Figure 5As shown. Two-electrode system (both sprayed onto nickel foam surface), anode Ov-NiFe-LDH-MoO4, cathode using Pt / C (commercial), catalyst loading of 1 mg for both anode and cathode. . cm -2 .

[0045] Depend on Figure 5 It can be seen that Ov-NiFe-LDH-MoO4 exhibits better OER electrocatalytic performance. Figure 5 b shows that at 200mAcm -2 The Ov-NiFe-LDH-MoO4 was stable for 100 hours at a current density, indicating that Ov-NiFe-LDH-MoO4 has excellent OER catalytic performance and has certain application prospects.

[0046] Depend on Figure 6 It can be seen that the Ov-NiFe-LDH-MoO4 prepared in Example 1 has better OER electrocatalytic performance.

[0047] Depend on Figure 7 It can be seen that after replacing molybdate with phosphotungsten ion for intercalation, the OER electrocatalytic performance of the catalyst decreased after the phosphotungsten ion combined with hydrogen peroxide.

[0048] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0049] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a NiFe-LDH-based catalyst, characterized in that, Includes the following steps: Nickel chloride hexahydrate and urea were dissolved in deionized water. Then, a mixed aqueous solution containing potassium hydroxide and sodium chloride was added to the above solution. After stirring thoroughly, an aqueous solution of ferric nitrate nonahydrate was added dropwise, followed by the addition of sodium molybdate dihydrate. The mixture was stirred to form a homogeneous mixture, and then hydrogen peroxide solution was added. The solution was transferred to a reaction vessel and subjected to a hydrothermal reaction at 120°C to obtain Ov-NiFe-LDH-MoO4.

2. The method for preparing a NiFe-LDH-based catalyst according to claim 1, characterized in that, The molar ratio of nickel chloride hexahydrate, urea, ferric nitrate nonahydrate, and sodium molybdate dihydrate is 2.25:10:0.75:0.

1.

3. The method for preparing a NiFe-LDH-based catalyst according to claim 1 or 2, characterized in that, The mass fraction of hydrogen peroxide is 28-32%; The concentration of potassium hydroxide in the mixed aqueous solution of potassium hydroxide and sodium chloride is 0.425 M, and the concentration of sodium chloride is 0.5 M.

4. The method for preparing a NiFe-LDH-based catalyst according to claim 3, characterized in that, The molar volume ratio of nickel chloride hexahydrate to deionized water, mixed aqueous solution, ferric nitrate nonahydrate aqueous solution, and hydrogen peroxide solution was 2.25 mmol: 20 mL: 10 mL: 10 mL: 160 μL.

5. The method for preparing a NiFe-LDH-based catalyst according to claim 1, characterized in that, The hydrothermal reaction time is 8 hours.

6. The method for preparing a NiFe-LDH-based catalyst according to claim 1, characterized in that, After the hydrothermal reaction was completed, the product was naturally cooled to room temperature, centrifuged at 6000 rpm for 5 minutes to collect the product, and washed three times alternately with deionized water and ethanol. Finally, the obtained sample was vacuum dried at 60℃ for 12 hours to obtain pure Ov-NiFe-LDH-MoO4.

7. The NiFe-LDH-based catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the NiFe-LDH-based catalyst according to claim 7 in the oxygen evolution reaction of water electrolysis.

9. The application according to claim 8, characterized in that, Applications in 1 M KOH alkaline freshwater systems or 1 M KOH + 0.5 M NaCl simulated seawater systems.

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