A Ag / Cr x -NiFe 1-x OOH / NF catalyst for oxygen evolution by electrolysis of seawater and its preparation and application

Abstract

The present invention relates to an Ag / Cr x ‑NiFe 1‑x OOH / NF electrolysis seawater oxygen evolution catalyst and its preparation method and application, the present invention is to in situ construct Cr on the nickel foam substrate by mixing a solution containing a divalent nickel source, a trivalent iron source, a trivalent chromium source, urea and an alkaline solution. x ‑NiFe 1‑x OOH / NF, and using spontaneous redox reaction to load silver nanoparticles on its surface, a Ag / Cr with excellent chlorine corrosion resistance was obtained. x ‑NiFe 1‑x OOH / NF. By precisely controlling the ratio of Cr to Fe, the present invention achieves a delicate balance between order and disorder in the crystal structure of the material, achieving controllable growth of nanosheets within a thickness range of 25-1 nm and controllable adjustment of the nanosheet morphology. At the same time, Ag nanoparticles and CrO₄²⁻ anion groups generated in situ under high potential synergistically construct a barrier against chloride ion corrosion, forming a "surface Ag-Cl fixed + interlayer CrO4 2‑ -Dual anti-Cl2 with "shielding effect" – Corrosion structure, significantly improving corrosion resistance and catalytic activity, also has high selectivity and high stability, and can be used for electrolysis of alkaline water or seawater for oxygen evolution.

Description

Technical Field

[0001] The present invention belongs to the field of electrolysis of seawater to produce hydrogen catalysts, and specifically relates to an Ag / Cr x -NiFe 1-x OOH / NF catalyst for oxygen evolution by electrolysis of seawater and its preparation and application. Background Art

[0002] Hydrogen, with its high energy density of 141.6 MJ / kg and zero carbon emissions, is considered a core energy carrier for addressing the energy crisis and achieving carbon neutrality. While pure water electrolysis hydrogen production technology offers advantages such as process flexibility and high product purity, the scarcity and uneven distribution of freshwater resources severely constrain the development of green hydrogen. Seawater, which accounts for 96.5% of global water resources and is abundant, is an inexhaustible natural electrolyte raw material. Therefore, seawater electrolysis hydrogen production is considered a key direction for future hydrogen energy development. However, the presence of abundant chloride ions in natural seawater not only triggers the chlorine evolution reaction (CER) at the anode, competing with the oxygen evolution reaction (OER), but also easily corrodes the electrode, significantly reducing the stability of the anode catalyst. In alkaline seawater electrolysis systems, the theoretical potential of the oxygen evolution reaction (OER) is 490 mV lower than that of the chlorine evolution reaction (CER). The development of highly selective anode catalysts can inhibit the competing chloride reaction and reduce chloride ion corrosion on the catalyst. Therefore, it is very necessary to develop electrocatalysts that are efficient, highly active and highly stable under large currents and can directly utilize seawater. Summary of the Invention

[0003] To address the challenges of the prior art, this invention provides a silver-chromium co-doped two-dimensional nanosheet material, its preparation method, and its application in seawater electrolysis for oxygen evolution. By regulating the ratio of Fe to Cr, the size of the nanoflowers, as well as the morphology and thickness of the nanosheets, can be controlled, achieving a delicate balance between order and disorder in the material's crystal structure, enabling controlled growth of the nanosheets within a thickness range of 25-1 nm. By optimizing the catalyst's structure, the catalyst's electron transport capacity is enhanced, while its corrosion resistance is also improved. This achieves synergistic optimization of oxygen evolution reaction (OER) activity and chloride ion corrosion resistance, thus addressing the challenges of the prior art.

[0004] Ag / Cr x -NiFe 1-x The preparation method of the OOH / NF catalyst for electrolyzing seawater oxygen evolution comprises the following steps:

[0005] (1) The nickel foam substrate is placed in a mixed solution containing a divalent nickel source, a trivalent iron source, a trivalent chromium source, urea and an alkaline solution, and reacted at a temperature of 100-150°C for 6-18 hours, and then ultrasonically cleaned and dried to obtain Cr x -NiFe 1-xOOH / NF composite material (chromium gradient doped nickel-iron layered hydroxide heterogeneous nanosheets); preferably, the drying temperature is 50 ° C and the drying time is 10 to 30 minutes;

[0006] (2) Cr x -NiFe 1-x The OOH / NF composite material was immersed in a silver salt solution, taken out, ultrasonically cleaned, and vacuum dried to obtain Ag / Cr x -NiFe 1-x OOH / NF catalyst for oxygen evolution by electrolysis of seawater.

[0007] Furthermore, the divalent nickel source includes nickel nitrate hexahydrate, nickel chloride hexahydrate, nickel sulfate hexahydrate, nickel acetate tetrahydrate, and nickel carbonate; the trivalent iron source includes ferric nitrate nonahydrate, ferric chloride hexahydrate, ferric sulfate, and ferric acetate; the trivalent chromium source includes chromium nitrate nonahydrate, chromium chloride hexahydrate, chromium sulfate, and chromium acetate; the silver salt includes silver nitrate and silver acetate; and the alkaline solution includes one or more of ammonium fluoride, sodium carbonate, sodium hydroxide, and disodium ethylenediaminetetraacetate.

[0008] Furthermore, the solvent of the mixed solution is water or a binary solvent of water and ethylene glycol mixed in a volume ratio of 1:1.

[0009] Furthermore, in step (1), the molar ratio of the trivalent chromium source to the trivalent iron source is 0.67-1.5:1.

[0010] Furthermore, the molar ratio of the divalent nickel source, the trivalent iron source, the trivalent chromium source, urea and ammonium fluoride is 1:0.1~0.9:0.1~0.9:30:8.

[0011] Furthermore, the silver nitrate concentration in step (2) is 10 to 60 mmol / L, and the immersion is carried out in the dark for 10 to 120 minutes. Immersion in the silver nitrate solution is for loading Ag. Electrodeposition has been attempted to load Ag, but it was found that Ag aggregation and uneven distribution were easily caused by electrodeposition.

[0012] Furthermore, the ultrasonic cleaning in step (1) and step (2) is performed using deionized water and ethanol at 25-40° C. for 10-30 minutes, respectively.

[0013] Furthermore, the vacuum drying temperature in step (1) and step (2) is 50-60°C, and the drying time is 10-30 minutes.

[0014] The Ag / Cr prepared by the above preparation method x -NiFe 1-x OOH / NF catalyst for oxygen evolution by electrolysis of seawater.

[0015] The above Ag / Cr x -NiFe 1-x The application of OOH / NF electrolysis seawater oxygen evolution catalyst is used for electrolysis of alkaline water or seawater to evolve oxygen.

[0016] The present invention constructs a self-supporting Ag / Cr with defect sites through a simple hydrothermal method / solvothermal method and a simple immersion spontaneous redox method. x -NiFe 1-x OOH / NF ultra-thin layered two-dimensional materials can effectively increase the surface area of ​​the catalyst and expose more active sites; Ag / Cr x -NiFe 1-x Electronic coupling forms between the OOH / NF support, accelerating charge transfer. This invention modifies the microstructure by regulating the metal composition ratio, including optimizing parameters such as nanosheet thickness, roughness, and specific surface area. This results in a highly selective and stable seawater electrolysis catalyst. The prepared catalyst exhibits excellent selectivity in seawater electrolysis, effectively suppresses chlorine evolution, and achieves an oxygen evolution Faradaic efficiency close to 100%.

[0017] In order to enhance the corrosion resistance of the catalyst, the present invention introduces Ag and Cr elements through a two-step method to form a synergistic effect on the catalyst surface. Chromium oxyhydroxide reduces Cl at the active site by selective adsorption. - The silver nanoparticles regulate the surface charge distribution through electronic effects. The Ag nanoparticles and the CrO4²⁻ anion groups generated in situ at high potentials synergistically build a barrier against chloride ion corrosion. This electrode structure design provides an innovative solution for catalysts for direct electrolysis of seawater to produce oxygen. In alkaline seawater, the electrode has a conductivity of 1000 mA·cm -2 It can operate stably for more than 1000 hours at high current density. Especially when the Cl - Under harsh conditions with a concentration three times higher, the catalyst can react stably for more than 120 hours.

[0018] The present invention successfully prepares a new material with unique structural characteristics by precisely controlling the molar ratio of Cr to Fe. This material breaks the limitations of traditional layered double hydroxides (LDHs) and is at the critical point between LDHs and amorphous materials. It is a new composite material that combines the characteristics of both. Specifically, its internal structure retains the partially ordered layered characteristics of LDHs while introducing the disorder of amorphous materials. This special structure gives the material unique properties. From a crystallographic point of view, the crystal structure of this material has incomplete long-range order, the regularity of the interlayer arrangement is reduced, and the atomic distribution within the layer also shows a certain degree of disorder. From the perspective of materials science, this new material at the critical point between LDH and amorphous has a unique internal atomic arrangement.

[0019] The present invention achieves unique interatomic interactions through fine-tuning the Cr:Fe ratio, which modifies the material's electronic and band structures, thereby optimizing its physicochemical properties. The Ni and O peaks of the Cr-doped sample shift toward higher binding energies compared to the undoped sample, indicating that the unique interactions between Ni, Cr, and O atoms alter the material's electronic structure, enhance the metal-oxygen bond energy, and optimize overall performance. Furthermore, at low Cr doping levels, the nanosheets grown on the nickel foam substrate exhibit two-dimensional planar ductility, orderly interlayer stacking, and stable spacing, facilitating electron transport. At higher Cr doping levels, the nanosheets exhibit curling behavior and disordered interlayer stacking, resulting in nanoflower clusters coating the nickel foam substrate, replacing the vertically oriented nanosheet growth pattern. As the Cr content continues to increase, the flower-like clusters exhibit tunable size. When separated from the NF substrate, by adjusting the Fe:Cr ratio, self-assembled nanoflower structures can be grown, with sizes precisely controlled between 100 nm and 10 μm.

[0020] The present invention loads Ag onto the catalyst surface through a simple immersion process. This unique surface modification allows Ag to exist in a highly dispersed state, reducing the severe crystal structure distortion caused by disordered doping of Ag ions in the LDH lattice. This significantly enhances the material's corrosion resistance. Furthermore, Ag and Cl⁻ form an in-situ AgCl passivation layer, which forms a dense passivation layer with chromium anion clusters, effectively reducing the Cl⁻ concentration near the active sites.

[0021] Compared with the existing technology, the present invention achieves a delicate balance between order and disorder in the crystal structure of the material by precisely controlling the ratio of Cr and Fe under the support condition of nickel foam (NF) substrate. It realizes the controllable growth of nanosheets in the range of 25-1nm and the controllable adjustment of nanosheet morphology. The modification of Ag also improves the electron transfer rate of the catalyst and reduces the problem of poor conductivity of hydroxide. Ag nanoparticles are modified on Cr by chemical bonds. x -NiFe 1-x OOH / NF surface, forming "surface Ag-Cl fixed + interlayer CrO4 2- -Dual anti-Cl2 with "shielding effect" – Corrosion structure. Ag / Cr of the present invention x -NiFe 1- x The OOH / NF oxygen evolution electrode has excellent performance, with a current density of 1000 mA·cm at an overpotential of 300 mV. -2 Above 100%, the oxygen evolution efficiency is close to 100%; in 1 M KOH with a Cl⁻ concentration three times that of seawater (1.5 M NaCl), 1000 mA cm -Stable operation for >120 hours; in 1M KOH+0.5M NaCl electrolyte, 1000 mA cm - After 1000 hours of continuous operation at high current, the morphology remained unchanged. Furthermore, it maintained stable operation for over 300 hours in real seawater with 1M KOH, effectively resisting interference from impurity ions and exhibiting no scaling or poisoning. As an oxidation electrode in alkaline brine and seawater, it exhibited excellent corrosion resistance and industrial-grade current density stability, demonstrating potential application in the development of transition metal OER catalysts for oxygen evolution from seawater electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The Cr prepared in Examples 1 to 7 of the present invention x -NiFe 1-x XRD pattern of OOH / NF composite material (left) and enlarged view of the peak range corresponding to the (003) crystal plane in the XRD pattern (right);

[0023] Figure 2 Cr prepared in Examples 3 to 7 of the present invention x -NiFe 1-x Scanning electron microscope images of OOH / NF composite materials; A~E are Cr 0.1 -NiFe 0.9 OOH、Cr 0.2 -NiFe 0.8 OOH、Cr 0.5 -NiFe 0.5 OOH、Cr 0.8 -NiFe 0.2 OOH、Cr 0.9 -NiFe 0.1 Scanning electron microscope images of OOH; a~e are Cr 0.1 -NiFe 0.9 OOH / NF、Cr 0.2 -NiFe 0.8 OOH / NF、Cr 0.5 -NiFe 0.5 OOH / NF、Cr 0.8 -NiFe 0.2 OOH / NF、Cr 0.9 -NiFe 0.1 SEM images of OOH / NF;

[0024] Figure 3 Scanning electron micrographs of NiCrOOH / NF prepared in Example 1 of the present invention (left) and NiFeOOH / NF prepared in Example 2 (right);

[0025] Figure 4 The Ag / Cr prepared in Example 9 of the present invention 0.5 -NiFe 0.5 EDS of OOH;

[0026] Figure 5 The LSV curves of the OER of the oxygen evolution electrodes prepared from the composite materials of Examples 1, 2, 5, 8, and 9 of the present invention are shown;

[0027] Figure 6 Polarization curves of composite materials prepared in Examples 1, 2, 5, 8, and 9 of the present invention;

[0028] Figure 7 EIS graphs of the composite materials prepared in Examples 5, 9, and 10 of the present invention;

[0029] Figure 8 The composite materials prepared in Examples 3, 5, and 9 of the present invention were subjected to 1.5 M NaCl + 1 M KOH electrolyte at 1000 mA cm -2 Scanning electron microscope image after 120 hours of reaction at a current density of ;

[0030] Figure 9 Scanning electron microscope images of the composite materials prepared in Examples 5 (left) and 10 (right) of the present invention. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] Cut the nickel foam into pieces 3 cm long, 2 cm wide, and 1.5 mm thick. Ultrasonic wash the foam with 3 mol / L hydrochloric acid, deionized water, and ethanol, sequentially, for approximately 30 minutes. Place the cleaned nickel foam in a vacuum drying oven at 50°C and dry for 30 minutes.

[0034] Prepare 0.01 mol·L -1 Nickel nitrate hexahydrate, 0.01 mol·L -1 Chromium nitrate nonahydrate, 0.3 mol·L -1 Urea, 0.08 mol·L -1 Add the washed nickel foam to 50 ml of the mixed solution. Hydrothermally react at 120°C for 12 hours. After cooling to room temperature, ultrasonically clean the foam with deionized water and then ethanol for approximately 30 minutes. Dry the foam in a 50°C vacuum oven to obtain NiCrOOH / NF.

[0035] Example 2

[0036] Cut the nickel foam into pieces 3 cm long, 2 cm wide, and 1.5 mm thick. Ultrasonic wash the foam with 3 mol / L hydrochloric acid, deionized water, and ethanol, sequentially, for approximately 30 minutes. Place the cleaned nickel foam in a vacuum drying oven at 50°C and dry for 30 minutes.

[0037] Prepare 0.01 mol·L -1 Nickel nitrate hexahydrate, 0.01 mol·L -1 Ferric nitrate nonahydrate, 0.3 mol·L -1 Urea, 0.08 mol·L -1 Add the washed nickel foam to 50 ml of the mixed solution. Hydrothermally react at 120°C for 12 hours. After the reaction is complete and cooled to room temperature, ultrasonically clean the foam with deionized water and ethanol for approximately 30 minutes, followed by drying in a 50°C vacuum oven to obtain NiFeOOH / NF.

[0038] Example 3

[0039] Cut the nickel foam into pieces 3 cm long, 2 cm wide, and 1.5 mm thick. Ultrasonic wash the foam with 3 mol / L hydrochloric acid, deionized water, and ethanol, sequentially, for approximately 30 minutes. Place the cleaned nickel foam in a vacuum drying oven at 50°C and dry for 30 minutes.

[0040] Prepare 0.01 mol·L -1 Nickel nitrate hexahydrate, 0.009 mol·L -1 Ferric nitrate nonahydrate, 0.001 mol·L -1 Chromium nitrate nonahydrate, 0.3 mol·L -1 Urea, 0.08 mol·L -1 Take more than 50 ml of the mixed solution and add the washed nickel foam into it. Use hydrothermal method to react at 120 ℃ for 12 hours. After the reaction is completed and cooled to room temperature, use deionized water and ethanol, wash it with ultrasonic for about 30 minutes in sequence, and then dry it in a vacuum drying oven at 50 ℃ to obtain Cr 0.1 -NiFe 0.9 OOH / NF.

[0041] Example 4

[0042] Cut the nickel foam into pieces 3 cm long, 2 cm wide, and 1.5 mm thick. Ultrasonic wash the foam with 3 mol / L hydrochloric acid, deionized water, and ethanol, sequentially, for approximately 30 minutes. Place the cleaned nickel foam in a vacuum drying oven at 50°C and dry for 30 minutes.

[0043] Prepare 0.01 mol·L -1 Nickel nitrate hexahydrate, 0.008 mol·L -1 Ferric nitrate nonahydrate, 0.002 mol·L -1 Chromium nitrate nonahydrate, 0.3 mol·L -1 Urea, 0.08 mol·L -1 Take more than 50 ml of the mixed solution and add the washed nickel foam into it. Use hydrothermal method to react at 120 ℃ for 12 hours. After the reaction is completed and cooled to room temperature, use deionized water and ethanol, wash it with ultrasonic for about 30 minutes in sequence, and then dry it in a vacuum drying oven at 50 ℃ to obtain Cr 0.2 -NiFe 0.8 OOH / NF.

[0044] Example 5

[0045] Cut the nickel foam into pieces 3 cm long, 2 cm wide, and 1.5 mm thick. Ultrasonic clean the foam with 3 mol / L hydrochloric acid, deionized water, and ethanol, sequentially, for approximately 30 minutes. Place the cleaned nickel foam in a vacuum drying oven at 50°C and dry for 30 minutes.

[0046] Prepare 0.01 mol·L -1 Nickel nitrate hexahydrate, 0.005 mol·L -1 Ferric nitrate nonahydrate, 0.005 mol·L -1 Chromium nitrate nonahydrate, 0.3 mol·L -1 Urea, 0.08 mol·L -1 Take more than 50 ml of the mixed solution and add the washed nickel foam into it. Use hydrothermal method to react at 120 ℃ for 12 hours. After the reaction is completed and cooled to room temperature, use deionized water and ethanol, wash it with ultrasonic for about 30 minutes in sequence, and then dry it in a vacuum drying oven at 50 ℃ to obtain Cr 0.5 -NiFe 0.5 OOH / NF.

[0047] Example 6

[0048] Cut the nickel foam into pieces 3 cm long, 2 cm wide, and 1.5 mm thick. Ultrasonic wash the foam with 3 mol / L hydrochloric acid, deionized water, and ethanol, sequentially, for approximately 30 minutes. Place the cleaned nickel foam in a vacuum drying oven at 50°C and dry for 30 minutes.

[0049] Prepare 0.01 mol·L -1 Nickel nitrate hexahydrate, 0.002 mol·L -1Ferric nitrate nonahydrate, 0.008 mol·L -1 Chromium nitrate nonahydrate, 0.3 mol·L -1 Urea, 0.08 mol·L -1 Take more than 50 ml of the mixed solution and add the washed nickel foam into it. Use hydrothermal method to react at 120 ℃ for 12 hours. After the reaction is completed and cooled to room temperature, use deionized water and ethanol, wash it with ultrasonic for about 30 minutes in sequence, and then dry it in a vacuum drying oven at 50 ℃ to obtain Cr 0.8 -NiFe 0.1 OOH / NF.

[0050] Example 7

[0051] Cut the nickel foam into pieces 3 cm long, 2 cm wide, and 1.5 mm thick. Ultrasonic wash the foam with 3 mol / L hydrochloric acid, deionized water, and ethanol, sequentially, for approximately 30 minutes. Place the cleaned nickel foam in a vacuum drying oven at 50°C and dry for 30 minutes.

[0052] Prepare 0.01 mol·L -1 Nickel nitrate hexahydrate, 0.001 mol·L -1 Ferric nitrate nonahydrate, 0.009 mol·L -1 Chromium nitrate nonahydrate, 0.3 mol·L -1 Urea, 0.08 mol·L -1 Take more than 50ml of the mixed solution and add the washed nickel foam into it. Use hydrothermal method to react at 120℃ for 12h. After the reaction is completed and cooled to room temperature, use deionized water and ethanol, wash it with ultrasonic for about 30 minutes in sequence, and then dry it in a vacuum drying oven at 50℃ to obtain Cr 0.9 -NiFe 0.1 OOH / NF.

[0053] Example 8

[0054] A 0.04 mol / L silver nitrate solution was prepared, and the NiFeOOH / NF prepared in Example 2 was immersed in the silver nitrate solution for 60 minutes. The Ag / NiFeOOH / NF was then taken out and ultrasonically cleaned with deionized water and ethanol for 10 minutes respectively, and dried to obtain the Ag / NiFeOOH / NF.

[0055] Example 9

[0056] Prepare 0.04 mol / L silver nitrate solution and add the Cr 0.5 -NiFe 0.5The OOH / NF was immersed in silver nitrate solution for 60 minutes, taken out and ultrasonically washed with deionized water and ethanol for 10 minutes respectively, and dried to obtain the Ag / Cr 0.5 -NiFe 0.5 OOH / NF.

[0057] Example 10

[0058] Cut the nickel foam into pieces 3 cm long, 2 cm wide, and 1.5 mm thick. Ultrasonic wash the foam with 3 mol / L hydrochloric acid, deionized water, and ethanol, sequentially, for approximately 30 minutes. Place the cleaned nickel foam in a vacuum drying oven at 50°C and dry for 30 minutes.

[0059] Deionized water and ethylene glycol were mixed in a volume ratio of 1:1 to form a binary solvent system, and 0.01 mol·L -1 Nickel nitrate hexahydrate, 0.005 mol·L -1 ferric nitrate nonahydrate, 0.005 mol·L -1 Chromium nitrate nonahydrate, 0.3 mol·L -1 Urea, 0.08 mol·L -1 Take more than 50 ml of the mixed solution and add the washed nickel foam into it. Use the solvent thermal method to react at 120℃ for 12 hours. After the reaction is completed and cooled to room temperature, use deionized water and ethanol, wash it with ultrasonic for about 30 minutes in sequence, and then dry it in a vacuum drying oven at 50℃ to obtain Cr 0.5 -NiFe 0.5 OOH / NF (solvothermal method).

[0060] Prepare 0.04 mol / L silver nitrate solution and add Cr 0.5 -NiFe 0.5 OOH / NF (solvothermal method) was immersed in silver nitrate solution for 60 minutes, taken out and ultrasonically washed with deionized water and ethanol for 10 minutes respectively, and dried to obtain the Ag / Cr 0.5 -NiFe 0.5 OOH / NF (solvothermal method).

[0061] Performance testing

[0062] from Figure 1 It can be seen that the present invention successfully prepared Cr x -NiFe 1-x OOH / NF, due to the low content of Ag, does not show any diffraction peaks related to Ag nanoparticles in XRD. Table 1 lists the Cr x -NiFe 1-xThe half-peak width of the (003) crystal plane of OOH / NF in different catalysts. In typical layered double hydroxide (LDH) materials, the low-angle region usually presents a characteristic layered diffraction peak, while amorphous materials mainly show a broad diffuse scattering peak. A narrow half-peak width indicates that the layered structure is relatively complete and ordered, while a wider half-peak width means that there is a certain degree of disorder or defects. Figure 1 As can be seen from Table 1, the diffraction peak half-maximum width of the (003) crystal plane of typical NiFeOOH (NiFe-LDH) is narrow; 0.5 -NiFe 0.5 The half-peak width of OOH is twice that of NiFeOOH, but narrower than that of NiCrOOH with fiber structure, and is between the two. It should be pointed out that NiCrOOH is not a typical LDH. Figure 3 It can be observed that it has a fibrous structure. x -NiFe 1-x The 2θ angle of OOH shifted, indicating that the interlayer spacing changed, further confirming that the introduction of amorphous material reduced the regularity of the interlayer arrangement.

[0063] Table 1 Half-peak width data of (003) crystal plane of different catalysts

[0064]

[0065] from Figure 2 As shown in Table 2, by synergistically controlling the Fe and Cr metal doping ratios, precise construction and morphological evolution of catalyst nanostructures can be achieved on the surface of nickel-based foam substrates. When the Cr:Fe ratio is less than 1, a vertically oriented two-dimensional nanosheet structure is obtained, characterized by two-dimensional planar ductility, sharp edges, orderly interlayer stacking, and stable spacing. As the Cr:Fe ratio increases above 1, the nanosheets undergo significant structural distortion, and the material growth mode undergoes a fundamental shift, with the surface being completely covered by a three-dimensional hierarchical nanoflower structure (flower diameter 100 nm-250 nm). As the Cr content continues to increase, the flower-like clusters exhibit tunable size.

[0066] As shown in Table 2, when the Cr doping concentration x = 0.1, a large number of radial nanoflowers grow, with the largest nanoflower diameter reaching 10 μm. With increasing Cr doping, the size of the nanoflowers decreases significantly, and the nanosheets become transparent, with both thickness and size decreasing. When the Cr:Fe ratio is less than 1, a vertically oriented two-dimensional nanosheet structure is obtained. These nanosheets exhibit two-dimensional planar ductility, sharp edges, and orderly interlayer stacking with stable spacing, which facilitates electron transport. This regular array structure optimizes mass transfer channels and enhances electron transport. As the Cr:Fe ratio increases above 1, the nanosheets undergo significant structural distortion, exhibiting a three-dimensional curled configuration. This morphological feature facilitates the exposure of more active sites. When the Cr:Fe ratio exceeds 4:1, the morphology undergoes significant distortion, with the surface completely covered by a three-dimensional hierarchical nanoflower structure (flower diameters ranging from 100 nm to 250 nm), replacing the vertically oriented nanosheet growth pattern. The nanosheets exhibit a pronounced curling phenomenon. Due to their small size, SEM images are less clear, and their conductivity is also reduced. As the Cr doping level increases, the NF is covered with tiny nanoflowers, replacing the vertically oriented nanosheet growth pattern. The nanoflowers are very small, and the nanosheets that make up the nanoflower shape are thin and curled. Especially when the Cr:Fe ratio reaches 9:1, the nanoflowers become smaller, denser, and more uniform. By adjusting the Fe:Cr ratio when separated from the NF substrate, self-assembled nanoflower structures can be grown, with sizes precisely controlled between 100nm and 10μm.

[0067] Table 2 Comparison of nanoflower size and nanosheet thickness

[0068]

[0069] The present invention found through comparison of results and performance that when the atomic ratio of Cr to Fe (Cr / (Cr+Fe)) is in the range of 0.4-0.6, the catalyst exhibits significantly improved comprehensive performance in alkaline electrolyte.

[0070] from Figure 3 SEM shows that, unlike Cr x -NiFe 1-x The morphology of OOH / NF and NiCrOOH is a fiber structure, while the NiFeOOH material presents a nanosheet morphology with sharp edges and regular arrangement.

[0071] from Figure 4 It can be seen from EDS that Ag nanoparticles are successfully modified onto the surface of nanosheets, and Cr, Fe, Ni, and Ag elements are evenly distributed.

[0072] Depend on Figure 5From the linear voltammetry (LSV) curve, it can be seen that after Ag modification, the Ag / Cr x -NiFe 1-x The OER performance of OOH / NF is improved.

[0073] Depend on Figure 6 It can be seen from the polarization curve that Ag / Cr 0.5 -NiFe 0.5 OOH / NF has the best corrosion resistance.

[0074] Depend on Figure 7 The electrochemical impedance spectroscopy shows that Ag / Cr 0.5 -NiFe 0.5 OOH / NF has a smaller charge transfer resistance, reflecting the Ag / Cr 0.5 -NiFe 0.5 OOH / NF has better electrical conductivity, thus promoting rapid electron transfer on the catalyst. 0.5 -NiFe 0.5 The OOH / NF catalyst exhibits superior conductive properties and its resistance is significantly reduced.

[0075] Depend on Figure 8 It can be seen from the SEM that under the condition of high concentration of chloride ions (1.5 M NaCl + 1 M KOH), 1000 mA cm -2 At a high current density, Ag / Cr 0.5 -NiFe 0.5 The structure of OOH / NF has not changed significantly, and it has excellent resistance to chloride ion corrosion. -2 Under industrial current density, 1 mol L - 1 KOH + 0.5 mol L -1 After 100 hours of testing in NaCl electrolyte, the surface of the unmodified NiFe-LDH catalyst peeled off on a large scale, the nanosheets became curled, and the nickel foam substrate was exposed. However, the peeling area of ​​Ag / NiFe-LDH was less obvious, but the Cl⁻ concentration increased to 1.5 mol L -1 When Cr 0.5 -NiFe 0.5 OOH still maintained the intact structure of nanosheets after running for 100 hours under the same conditions, and at 1.5 mol L -1 It can run stably in Cl⁻ environment for more than 120 hours, but there is still a phenomenon of partial catalyst shedding on its surface. 0.5 -NiFe 0.5OOH composite catalyst at 1.5 mol L -1 After running for 120 hours under Cl⁻ conditions, the nickel foam skeleton remained intact. Mechanism studies have shown that in a low chloride ion concentration environment, silver (Ag) interacts with chloride ions to form AgCl colloids, reducing the chloride ion concentration around the catalyst through an electrostatic repulsion mechanism. However, when the chloride ion concentration is too high, the AgCl colloid formed by Ag is difficult to resist the erosion of high concentration chloride ions, resulting in the collapse of the electrode structure. The addition of chromium (Cr) provides an effective solution to this problem, which can form CrO4 in situ. 2- This CrO4 2- The generation of CrO4 on the surface effectively reduces the chloride ion concentration at the active site, thereby significantly enhancing the stability of the electrode. This fully demonstrates the "surface Ag-Cl fixed + interlayer CrO4 2- The synergistic effect of the unique structure of "shielding effect" realizes the efficient regulation of chloride ions and ensures the stability and catalytic performance of the electrode under different chloride ion concentration conditions.

[0076] Depend on Figure 9 SEM images show that localized accumulation of nanosheets occurs in some areas of the surface of the catalyst prepared by the hydrothermal method, resulting in poor surface uniformity. In contrast, the catalyst prepared by the solvothermal method exhibits a more uniform surface morphology, with more orderly distribution and growth of nanosheets, without obvious accumulation or unevenness. This difference demonstrates that the solvothermal method has significant advantages in controlling the growth and distribution of nanosheets, helping to form a more uniform catalyst surface structure and thus optimize catalytic performance.

[0077] Ag / Cr of the present invention x -NiFe 1-x OOH / NF electrolysis of seawater oxygen evolution catalyst in alkaline brine, 1000 mA·cm -2 It can operate stably for more than 1000 hours at high current density. In particular, under harsh conditions with a chloride ion concentration three times higher than that of seawater, the catalyst can react stably for more than 100 hours. As an oxidation electrode for alkaline salt water and alkaline seawater, it exhibits excellent corrosion resistance and industrial-grade current density stability, and has potential application value in the development of transition metal OER catalysts for electrolysis of seawater for oxygen evolution.

[0078] Depend on Figure 9SEM images show that compared to nanosheets prepared by conventional hydrothermal methods, the nanosheets prepared using the solvothermal method in Example 10 exhibit irregular morphology and reduced size. This unique nanostructure enables more uniform growth on the nickel foam, significantly improving the surface smoothness of the nickel foam. More importantly, the catalyst prepared using the solvothermal method in Example 10 exhibits superior electrical conductivity, with significantly reduced resistance.

[0079] The present invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement made under the spirit and principle of the present invention shall be deemed to be within the protection scope of the present invention.

Claims

1. Ag / Cr x -NiFe 1-x The preparation method of OOH / NF electrolysis seawater oxygen evolution catalyst is characterized by: The following steps are involved: (1) The nickel foam substrate is placed in a mixed solution containing a divalent nickel source, a trivalent iron source, a trivalent chromium source, urea and an alkaline solution, and reacted in a reactor at 120°C for 6 to 18 hours, then ultrasonically cleaned and vacuum dried to obtain Cr x -NiFe 1-x OOH / NF composites; (2) Cr x -NiFe 1-x The OOH / NF composite material was immersed in a silver salt solution, taken out, ultrasonically cleaned, and vacuum dried to obtain Ag / Cr x -NiFe 1-x OOH / NF electrolysis catalyst for oxygen evolution from seawater; The molar ratio of the divalent nickel source, the trivalent iron source, the trivalent chromium source, the urea and the ammonium fluoride is 1:0.1~0.9:0.1~0.9:30:8; the solvent of the mixed solution is water or a binary solvent of water and ethylene glycol mixed in a volume ratio of 1:

1.

2. The preparation method according to claim 1, characterized in that The divalent nickel source includes nickel nitrate hexahydrate, nickel chloride hexahydrate, nickel sulfate hexahydrate, nickel acetate tetrahydrate, and nickel carbonate; the trivalent iron source includes ferric nitrate nonahydrate, ferric chloride hexahydrate, ferric sulfate, and ferric acetate; the trivalent chromium source includes chromium nitrate nonahydrate, chromium chloride hexahydrate, chromium sulfate, and chromium acetate; the silver salt includes silver nitrate and silver acetate; and the alkaline solution includes one or more of ammonium fluoride, sodium carbonate, sodium hydroxide, and disodium ethylenediaminetetraacetate.

3. The preparation method according to claim 1, characterized in that The silver salt concentration in step (2) is 10 to 60 mmol / L, and the soaking is carried out in the dark for 10 to 120 minutes.

4. The preparation method according to claim 1, characterized in that The ultrasonic cleaning in step (1) and step (2) is performed by using deionized water and ethanol at 25-40°C for 10-30 minutes respectively.

5. The preparation method according to claim 1, characterized in that In step (1) and step (2), the vacuum drying temperature is 50-60°C, and the drying time is 10-30 minutes.

6. The Ag / Cr prepared according to any one of claims 1 to 5 x -NiFe 1-x OOH / NF catalyst for oxygen evolution by electrolysis of seawater.

7. Ag / Cr according to claim 6 x -NiFe 1-x The application of OOH / NF electrolysis seawater oxygen evolution catalyst is characterized by: Used for electrolysis of alkaline water or seawater to release oxygen.

Images