Ag / Crx-NiFe1-xOOH / NF electrolysis seawater oxygen evolution catalyst and preparation and application thereof

Abstract

The invention relates to an Ag / Crx-NiFe1-xOOH / NF electrolysis seawater oxygen evolution catalyst and a preparation method and application thereof.The preparation method comprises the steps that a mixed solution containing a bivalent nickel source, a trivalent iron source, a trivalent chromium source, urea and an alkaline solution is subjected to in-situ construction of Crx-NiFe1-xOOH / NF on a foamed nickel substrate, silver nanoparticles are loaded on the surface of the Crx-NiFe1-xOOH / NF through spontaneous oxidation-reduction reaction, and the Ag / Crx-NiFe1-xOOH / NF electrolysis seawater oxygen evolution catalyst is obtained; and the Ag / Crx-NiFe1-xOOH / NF with excellent chlorine corrosion resistance is obtained. By accurately controlling the proportion of Cr to Fe, the crystal structure of the material reaches a subtle balance between order and disorder, and controllable growth of the nanosheet within the thickness range of 25-1 nm and controllable adjustment of the morphology of the nanosheet are achieved. Meanwhile, the Ag nanoparticles and CrOanion groups generated in situ under high potential synergistically construct a chloride ion corrosion resistant barrier, a dual Cl <-> corrosion resistant structure with surface Ag-Cl immobilization and interlayer CrO42 <-> shielding effect is formed, the corrosion resistance and catalytic activity are remarkably improved, and the catalyst also has high selectivity and high stability and can be used for oxygen evolution by electrolyzing alkaline water or seawater.

Description

Technical Field

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

[0002] Due to its high energy density of 141.6 MJ / kg and zero carbon emission characteristics, hydrogen energy is regarded as the core energy carrier to cope with the energy crisis and carbon neutrality goals. Although the technology of producing hydrogen by electrolyzing pure water has the advantages of flexible process and high product purity, the shortage and uneven distribution of fresh water resources seriously limit the development of green hydrogen. Seawater accounts for 96.5% of the global water resources and has rich reserves. It is a natural electrolyte raw material that is inexhaustible, so electrolyzing seawater to produce hydrogen is regarded as one of the important directions for future hydrogen energy development. However, there are a large number of chloride ions in natural seawater, which will not only cause the chlorine evolution reaction (CER) on the anode, competing with the oxygen evolution reaction (OER), but also easily corrode the electrode, greatly reducing the stability of the anode catalyst. In the alkaline seawater electrolysis system, the theoretical potential of the oxygen evolution reaction (OER) is 490 mV lower than that of the chlorine evolution reaction (CER). By developing highly selective anode catalysts, the chlorine competition reaction can be inhibited, and the corrosion of the catalyst by chloride ions can be reduced. Therefore, it is very necessary to develop an efficient electrocatalyst that can directly utilize seawater and has high activity and high stability under high current. Summary of the Invention

[0003] The present invention provides a silver and chromium co-doped two-dimensional nanosheet material, its preparation method and application in oxygen evolution by electrolyzing seawater for the problems existing in the prior art. By regulating the ratio of Fe to Cr, the size of the nanoflowers, the morphology and thickness of the nanosheets can be controllably adjusted, so that the crystal structure of the material reaches a delicate balance between order and disorder, and the thickness of the nanosheets can be controllably grown within the range of 25 - 1 nm. By optimizing the structure of the catalyst, the electron transport ability of the catalyst is improved, and at the same time, the corrosion resistance of the catalyst is also improved, realizing the synergistic optimization of the oxygen evolution reaction (OER) activity and the chloride ion corrosion resistance performance to solve the problems existing in the prior art.

[0004] Ag / Cr x -NiFe 1-x Preparation method of the OOH / NF oxygen evolution catalyst for electrolyzing seawater, comprising the following steps: (1) Place the nickel foam substrate material in a mixed solution containing divalent nickel source, trivalent iron source, trivalent chromium source, urea and alkaline solution, react at a temperature of 100 - 150 °C for 6 - 18 hours, then ultrasonically clean and dry to obtain Cr x -NiFe 1-xOOH / NF composite material (chromium-gradient-doped nickel-iron layered double hydroxide heteronanoplates); preferably, the drying temperature is 50 °C and the drying time is 10 - 30 minutes; (2) Immerse the Cr x -NiFe 1-x OOH / NF composite material in a silver salt solution, take it out, ultrasonically clean and vacuum dry it; obtain the Ag / Cr x -NiFe 1-x OOH / NF electrocatalyst for seawater oxygen evolution. Furthermore, the divalent nickel source includes nickel nitrate hexahydrate, nickel chloride hexahydrate, nickel sulfate hexahydrate, nickel acetate tetrahydrate, nickel carbonate; the trivalent iron source includes iron nitrate nonahydrate, iron chloride hexahydrate, iron sulfate, iron acetate; the trivalent chromium source includes chromium nitrate nonahydrate, chromium chloride hexahydrate, chromium sulfate, chromium acetate; the silver salt includes silver nitrate and silver acetate; the alkaline solution includes one or more of ammonium fluoride, sodium carbonate, sodium hydroxide and disodium ethylenediaminetetraacetate.

[0005] 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.

[0006] Furthermore, in step (1), the molar ratio of the trivalent chromium source to the trivalent iron source is 0.67 - 1.5:1.

[0007] 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.

[0008] Furthermore, in step (2), the concentration of silver nitrate is 10 - 60 mmol / L, and the immersion is carried out for 10 - 120 minutes under dark conditions. Immersion in the silver nitrate solution is for loading Ag. The method of electrodeposition was tried to load Ag, but it was found that electrodeposition was prone to Ag aggregation and uneven distribution.

[0009] Furthermore, in steps (1) and (2), ultrasonic cleaning is carried out with deionized water and ethanol respectively at 25 - 40 °C for 10 - 30 minutes.

[0010] Furthermore, in steps (1) and (2), the vacuum drying temperature is 50 - 60 °C and the drying time is 10 - 30 minutes.

[0011] The Ag / Cr x -NiFe 1-x OOH / NF electrocatalyst for seawater oxygen evolution prepared by the above preparation method.

[0012] The above Ag / Cr x-NiFe 1-x Application of OOH / NF electrolytic seawater oxygen evolution catalyst for electrolyzing alkaline water or seawater for oxygen evolution.

[0013] In the present invention, a self-supporting Ag / Cr with defect sites is constructed by a simple hydrothermal method / solvothermal method and a simple immersion spontaneous redox method. x -NiFe 1-x OOH / NF ultrathin layer two-dimensional material can effectively increase the surface area of the catalyst and expose more active sites; an electron coupling is formed between Ag / Cr x -NiFe 1-x OOH / NF supports, accelerating charge transfer. In the present invention, by regulating the metal composition ratio, the microstructure is changed, including the optimization of parameters such as the thickness, roughness, and specific surface area of the nanosheets. A highly selective and highly stable electrolytic seawater catalyst is prepared, and the prepared catalyst exhibits excellent selectivity in seawater electrolysis, can effectively inhibit the chlorine evolution reaction, and achieve an oxygen evolution Faraday efficiency close to 100%.

[0014] To enhance the corrosion resistance of the catalyst, in the present invention, Ag and Cr elements are introduced by a two-step method to form a synergistic effect on the catalyst surface. Chromium hydroxyoxide reduces the Cl - concentration at the active sites through selective adsorption, and silver nanoparticles regulate the surface charge distribution through the electron effect. The Ag nanoparticles and the CrO4²⁻ anion groups in-situ generated at high potential synergistically construct a chloride ion erosion-resistant barrier. This electrode structure design provides an innovative solution for the catalyst for direct electrolysis of seawater to produce oxygen. This electrode can stably operate for more than 1000 hours at a high current density of 1000 mA·cm -2 in alkaline seawater. Especially under the harsh condition of more than 3 times the Cl - concentration of seawater, this catalyst can stably react for more than 120 hours.

[0015] In the present invention, by precisely regulating the molar ratio of Cr to Fe, a new material with unique structural characteristics is successfully prepared. This material breaks through the limitations of traditional layered double hydroxides (LDHs), is at the critical point between LDHs and amorphous substances, and is a new composite material with the characteristics of both. Specifically, its internal structure retains some ordered layered characteristics of LDHs and introduces the disorder of amorphous substances. This special structure endows the material with unique properties. From the perspective of crystallography, 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, for this new material at the critical point between LDHs and amorphous substances, the internal atomic arrangement is unique.

[0016] The present invention realizes special interactions between atoms through fine adjustment of the Cr:Fe ratio. This interaction changes the electronic structure and band structure of the material, thereby optimizing its physical and chemical properties. The Ni peak and O peak of the sample after Cr doping shift towards higher binding energies compared to the undoped sample, indicating that the special interactions between Ni, Cr, and O atoms change the electronic structure of the material, enhance the bond energy of the metal-oxygen bond, and optimize the overall performance. In addition, at a lower Cr doping amount, the nanosheets grown on the nickel foam substrate have two-dimensional planar ductility, ordered interlayer stacking, and stable spacing, which is beneficial for electron transport; at a higher Cr doping amount, the nanosheets exhibit curling behavior and disordered interlayer stacking, coating the nickel foam substrate with nanoflower clusters, replacing the growth mode of vertically oriented nanosheets. As the Cr content continues to increase, the flower-like clusters exhibit adjustable size characteristics. When detached from the NF substrate, by regulating the ratio of Fe to Cr, self-assembled nanoflower structures can be grown, and their size can be precisely controlled between 100 nm and 10 μm.

[0017] In the present invention, Ag is loaded onto the catalyst surface through simple soaking. This unique surface modification enables Ag to exist in a highly dispersed state, reducing the serious distortion of the crystal structure caused by the disordered doping of Ag ions in the LDH lattice. Thereby, the corrosion resistance of the material is significantly enhanced, and Ag reacts in-situ with Cl⁻ to form an AgCl passivation layer and forms a dense passivation layer with chromium anion groups, effectively reducing the Cl⁻ concentration near the active sites.

[0018] Compared with the prior art, under the support condition of a nickel foam (NF) substrate, by precisely controlling the ratio of Cr to Fe, the crystal structure of the material reaches a delicate balance between order and disorder. The controllable growth of the nanosheet thickness in the range of 25 - 1 nm and the controllable adjustment of the nanosheet morphology are realized. The modification of Ag also improves the electron transfer rate of the catalyst and reduces the problem of poor conductivity of hydroxides. Ag nanoparticles are modified on the surface of Cr x -NiFe 1-x OOH / NF to form a dual anti-Cl 2- corrosion structure of "surface Ag-Cl fixation + interlayer CrO4 – – shielding effect". The oxygen evolution electrode performance of the Ag / Cr x -NiFe 1- x OOH / NF of the present invention is excellent. At an overpotential of 300 mV, the current density reaches 1000 mA·cm -2 or more, and the oxygen evolution efficiency is close to 100%; in 1 M KOH with 3 times the seawater Cl⁻ concentration (1.5 M NaCl), 1000 mA cm -² Stable operation for >120 hours at low current; in an electrolyte of 1M KOH + 0.5M NaCl, 1000 mA cm - ² After continuous operation for 1000 hours at high current, the morphology did not change significantly; it can stably operate for more than 300 hours in real seawater of 1M KOH, effectively resisting the interference of impurity ions, without scaling or poisoning. As an oxidation electrode for alkaline brine 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 seawater electrolysis oxygen evolution. Brief Description of the Drawings

[0019] Figure 1 is the XRD pattern of the Cr x -NiFe 1-x OOH / NF composite materials prepared in Examples 1-7 of the present invention (left) and the enlarged view of the peak range corresponding to the (003) crystal plane in the XRD pattern (right); Figure 2 is the scanning electron microscope image of the Cr x -NiFe 1-x OOH / NF composite materials prepared in Examples 3-7 of the present invention; among them, A~E are respectively 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 OOH scanning electron microscope images; a~e are respectively 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 OOH / NF scanning electron microscope images; Figure 3 is the scanning electron microscope image of NiCrOOH / NF prepared in Example 1 of the present invention (left) and NiFeOOH / NF prepared in Example 2 (right); Figure 4 is Ag / Cr prepared in Example 9 of the present invention 0.5 -NiFe0.5 EDS of OOH; Figure 5 LSV curves of OER of the oxygen evolution electrodes for preparing the composite materials in Examples 1, 2, 5, 8, and 9 of the present invention; Figure 6 Polarization curves of the composite materials prepared in Examples 1, 2, 5, 8, and 9 of the present invention; Figure 7 EIS diagrams of the composite materials prepared in Examples 5, 9, and 10 of the present invention; Figure 8 Scanning electron microscope images after reacting for 120 hours at a current density of 1000 mA cm -2 in the electrolyte of 1.5 M NaCl + 1 M KOH for the composite materials prepared in Examples 3, 5, and 9 of the present invention; Figure 9 Scanning electron microscope images of the composite materials prepared in Example 5 (left) and Example 10 (right) of the present invention. Detailed implementation manners

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] Example 1 Cut the nickel foam into a size of 3 cm in length, 2 cm in width, and 1.5 mm in thickness, and ultrasonically wash it with 3 mol / L hydrochloric acid, deionized water, and ethanol in sequence for about 30 minutes. Put the washed nickel foam into a vacuum drying oven at 50 °C and dry it for 30 minutes.

[0022] Prepare nickel nitrate hexahydrate of 0.01 mol·L -1 , chromium nitrate nonahydrate of 0.01 mol·L -1 , urea of 0.3 mol·L -1 , and ammonium fluoride of 0.08 mol·L -1 . Take more than 50 ml of the mixed solution and add the washed nickel foam into it. React under hydrothermal conditions at 120 °C for 12 h. After the reaction is completed and cooled to room temperature, ultrasonically wash it with deionized water and ethanol in sequence for about 30 minutes and then dry it in a vacuum drying oven at 50 °C to obtain NiCrOOH / NF.

[0023] Example 2 Cut the nickel foam into a size of 3 cm in length, 2 cm in width, and 1.5 mm in thickness, and ultrasonically wash it with 3 mol / L hydrochloric acid, deionized water, and ethanol in sequence for about 30 minutes. Put the washed nickel foam into a vacuum drying oven at 50 °C and dry it for 30 minutes.

[0024] Prepare nickel nitrate hexahydrate at 0.01 mol·L -1 and iron nitrate nonahydrate at 0.01 mol·L -1 , urea at 0.3 mol·L -1 , and ammonium fluoride at 0.08 mol·L -1 . Take more than 50 ml of the mixed solution and add the washed nickel foam to it. React for 12 h under the condition of 120 °C using the hydrothermal method. After the reaction is completed and cooled to room temperature, wash it with deionized water and ethanol in sequence by ultrasonic for about 30 minutes, and then dry it in a vacuum drying oven at 50 °C to obtain NiFeOOH / NF.

[0025] Example 3 Cut the nickel foam into pieces with a length of 3 cm, a width of 2 cm, and a thickness of 1.5 mm, and wash it with 3 mol / L hydrochloric acid, deionized water, and ethanol in sequence by ultrasonic for about 30 minutes. Put the washed nickel foam into a vacuum drying oven at 50 °C and dry it for 30 minutes.

[0026] Prepare nickel nitrate hexahydrate at 0.01 mol·L -1 , iron nitrate nonahydrate at 0.009 mol·L -1 , chromium nitrate nonahydrate at 0.001 mol·L -1 , urea at 0.3 mol·L -1 , and ammonium fluoride at 0.08 mol·L -1 . Take more than 50 ml of the mixed solution and add the washed nickel foam to it. React for 12 h under the condition of 120 °C using the hydrothermal method. After the reaction is completed and cooled to room temperature, wash it with deionized water and ethanol in sequence by ultrasonic for about 30 minutes, and then dry it in a vacuum drying oven at 50 °C to obtain Cr 0.1 -NiFe 0.9 OOH / NF.

[0027] Example 4 Cut the nickel foam into pieces with a length of 3 cm, a width of 2 cm, and a thickness of 1.5 mm, and wash it with 3 mol / L hydrochloric acid, deionized water, and ethanol in sequence by ultrasonic for about 30 minutes. Put the washed nickel foam into a vacuum drying oven at 50 °C and dry it for 30 minutes.

[0028] Prepare nickel nitrate hexahydrate at 0.01 mol·L -1 , iron nitrate nonahydrate at 0.008 mol·L -1 , chromium nitrate nonahydrate at 0.002 mol·L -1 , urea at 0.3 mol·L -1 , and ammonium fluoride at 0.08 mol·L -1Ammonium fluoride. Take more than 50 ml of the mixed solution and add the washed nickel foam into it. React under hydrothermal conditions at 120 °C for 12 h. After the reaction is completed and cooled to room temperature, wash it with deionized water and ethanol in sequence by ultrasonic for about 30 minutes, and then dry it in a vacuum drying oven at 50 °C to obtain Cr 0.2 -NiFe 0.8 OOH / NF.

[0029] Example 5 Cut the nickel foam into pieces with a length of 3 cm, a width of 2 cm, and a thickness of 1.5 mm, and wash it with 3 mol / L hydrochloric acid, deionized water, and ethanol in sequence by ultrasonic for about 30 minutes. Put the washed nickel foam into a vacuum drying oven at 50 °C and dry it for 30 minutes.

[0030] Prepare 0.01 mol·L -1 nickel nitrate hexahydrate, 0.005 mol·L -1 iron(III) nitrate nonahydrate, 0.005 mol·L -1 chromium(III) nitrate nonahydrate, 0.3 mol·L -1 urea, 0.08 mol·L -1 ammonium fluoride. Take more than 50 ml of the mixed solution and add the washed nickel foam into it. React under hydrothermal conditions at 120 °C for 12 h. After the reaction is completed and cooled to room temperature, wash it with deionized water and ethanol in sequence by ultrasonic for about 30 minutes, and then dry it in a vacuum drying oven at 50 °C to obtain Cr 0.5 -NiFe 0.5 OOH / NF.

[0031] Example 6 Cut the nickel foam into pieces with a length of 3 cm, a width of 2 cm, and a thickness of 1.5 mm, and wash it with 3 mol / L hydrochloric acid, deionized water, and ethanol in sequence by ultrasonic for about 30 minutes. Put the washed nickel foam into a vacuum drying oven at 50 °C and dry it for 30 minutes.

[0032] Prepare 0.01 mol·L -1 nickel nitrate hexahydrate, 0.002 mol·L -1 iron(III) nitrate nonahydrate, 0.008 mol·L -1 chromium(III) nitrate nonahydrate, 0.3 mol·L -1 urea, 0.08 mol·L -1Ammonium fluoride. Take more than 50 ml of the mixed solution and add the washed nickel foam into it. React for 12 h under the condition of 120 °C by hydrothermal method. After the reaction is completed and cooled to room temperature, wash it with deionized water and ethanol in sequence by ultrasonic for about 30 minutes, and then dry it in a vacuum drying oven at 50 °C to obtain Cr 0.8 -NiFe 0.1 OOH / NF.

[0033] Example 7 Cut the nickel foam into pieces with a length of 3 cm, a width of 2 cm, and a thickness of 1.5 mm, and wash it with 3 mol / L hydrochloric acid, deionized water, and ethanol in sequence by ultrasonic for about 30 minutes. Put the washed nickel foam into a vacuum drying oven at 50 °C and dry it for 30 minutes.

[0034] Prepare 0.01 mol·L -1 nickel nitrate hexahydrate, 0.001 mol·L -1 iron(III) nitrate nonahydrate, 0.009 mol·L -1 chromium(III) nitrate nonahydrate, 0.3 mol·L -1 urea, 0.08 mol·L -1 ammonium fluoride. Take more than 50 ml of the mixed solution and add the washed nickel foam into it. React for 12 h under the condition of 120 °C by hydrothermal method. After the reaction is completed and cooled to room temperature, wash it with deionized water and ethanol in sequence by ultrasonic for about 30 minutes, and then dry it in a vacuum drying oven at 50 °C to obtain Cr 0.9 -NiFe 0.1 OOH / NF.

[0035] Example 8 Prepare 0.04 mol / L silver nitrate solution, immerse the NiFeOOH / NF prepared in Example 2 into the silver nitrate solution for 60 minutes, take it out and wash it ultrasonically with deionized water and ethanol for 10 minutes respectively, and dry it to obtain the Ag / NiFeOOH / NF.

[0036] Example 9 Prepare 0.04 mol / L silver nitrate solution, immerse the Cr 0.5 -NiFe 0.5 OOH / NF prepared in Example 5 into the silver nitrate solution for 60 minutes, take it out and wash it ultrasonically with deionized water and ethanol for 10 minutes respectively, and dry it to obtain the Ag / Cr 0.5 -NiFe 0.5 OOH / NF.

[0037] Example 10 Cut the nickel foam into pieces with a length of 3 cm, a width of 2 cm, and a thickness of 1.5 mm, and ultrasonically wash them with 3 mol / L hydrochloric acid, deionized water, and ethanol in sequence for about 30 minutes. Put the washed nickel foam into a vacuum drying oven at 50 °C and dry for 30 minutes.

[0038] Mix deionized water and ethylene glycol in a volume ratio of (1:1) to form a binary solvent system, and prepare nickel nitrate hexahydrate at 0.01 mol·L -1 -1, iron(III) nitrate nonahydrate at 0.005 mol·L -1 -1, chromium(III) nitrate nonahydrate at 0.005 mol·L -1 -1, urea at 0.3 mol·L -1 -1, and ammonium fluoride at 0.08 mol·L -1 -1. Take more than 50 ml of the mixed solution and add the washed nickel foam into it. React for 12 h under the condition of 120 °C by solvothermal method. After the reaction is completed and cooled to room temperature, ultrasonically wash it with deionized water and ethanol in sequence for about 30 minutes and then dry it in a vacuum drying oven at 50 °C to obtain Cr 0.5 -NiFe 0.5 OOH / NF (solvothermal method).

[0039] Prepare a silver nitrate solution at 0.04 mol / L, soak the Cr 0.5 -NiFe 0.5 OOH / NF (solvothermal method) in the silver nitrate solution for 60 minutes, take it out and ultrasonically wash it with deionized water and ethanol for 10 minutes respectively, and dry it to obtain the Ag / Cr 0.5 -NiFe 0.5 OOH / NF (solvothermal method).

[0040] Performance testing As can be seen from Figure 1 , the present invention successfully prepared Cr x -NiFe 1-x OOH / NF. Due to the low content of Ag, no diffraction peaks related to Ag nanoparticles are shown in the XRD. Table 1 lists the full-width at half-maximum data of the (003) crystal plane of Cr x -NiFe 1-x OOH / NF in different catalysts. In typical layered double hydroxide (LDH) materials, characteristic layered diffraction peaks usually appear in the low-angle region, while amorphous substances mainly show broad diffuse scattering peaks. A narrower full-width at half-maximum indicates a more complete and ordered layered structure, while a wider one means a certain degree of disorder or defects. From Figure 1As can be seen from Table 1, for typical NiFeOOH (NiFe-LDH), the full width at half maximum (FWHM) of the diffraction peak of its (003) crystal plane is relatively narrow; while for Cr 0.5 -NiFe 0.5 OOH, the FWHM is twice that of NiFeOOH, but narrower than that of NiCrOOH with a fibrous structure, being in between. It should be noted that NiCrOOH is not a typical LDH, and from Figure 3 it can be observed that it exhibits a fibrous structure. In addition, the 2θ angle of Cr x -NiFe 1-x OOH has shifted, indicating a change in the interlayer spacing, further confirming that the introduction of amorphous substances has reduced the regularity of the interlayer arrangement.

[0041] Table 1 Full width at half maximum data of the (003) crystal plane of different catalysts

[0042] From Figure 2 and Table 2, it can be seen that by synergistically regulating the doping ratios of Fe and Cr metals, precise construction and morphological evolution of the catalyst nanostructure can be achieved on the surface of the nickel foam substrate. When the Cr:Fe ratio is less than 1, a two-dimensional nanosheet layer structure with vertical orientation growth can be obtained, which is characterized by the nanosheets having two-dimensional planar ductility, sharp edges and ordered interlayer stacking with a stable spacing. As the Cr:Fe ratio is greater than 1, significant structural distortion occurs in the nanosheet layer, and the material growth mode undergoes an essential transformation, with the surface being completely covered by a three-dimensional hierarchical nanoflower structure (flower diameter 100 nm - 250 nm), and with the continuous increase of the Cr content, the flower-like clusters exhibit adjustable size characteristics.

[0043] As can be seen from Table 2, when the Cr doping amount x = 0.1, a large number of radially-shaped nanoflowers grow, and the maximum diameter of the nanoflowers can reach 10 μm. With the increase of the Cr doping amount, the size of the nanoflowers decreases significantly, and the nanosheets become transparent, and both the thickness and size show a decreasing trend. When the Cr:Fe ratio is less than 1, a two-dimensional nanosheet layer structure with vertical orientation growth can be obtained, which is characterized by the nanosheets having two-dimensional planar ductility, sharp edges, and ordered interlayer stacking with a stable spacing, which is beneficial to electron transport. This regular array structure can optimize the mass transfer channel and improve electron transport. As the Cr:Fe ratio is greater than 1, significant structural distortion occurs in the nanosheet layer, presenting a three-dimensional curled configuration, and this morphological feature is beneficial to exposing more active sites. When Cr:Fe is greater than 4:1, the morphology undergoes significant distortion, and the surface is completely coated with a three-dimensional hierarchical nanoflower structure (flower diameter 100 nm - 250 nm), replacing the vertical-oriented nanosheet growth mode, and obvious curling of the nanosheets occurs. Due to the small size of the nanosheets, the SEM images are not clear enough, and the conductivity of the nanosheets also decreases. With the increase of the Cr doping amount, the NF is covered by small nanoflowers one by one, replacing the vertical-oriented nanosheet growth mode. The size of the nanoflowers is very small, and the nanosheets forming the nanoflower shape are very thin and curled. Especially when the Cr:Fe ratio reaches 9:1, the nanoflowers become smaller, denser, and more uniform. When detaching from the NF substrate, by regulating the ratio of Fe to Cr, a self-assembled nanoflower structure can be grown, and its size can be precisely regulated between 100 nm and 10 μm.

[0044] Table 2 Comparison of nanoflower size and nanosheet thickness

[0045] Through the comparison of the results and performance of the present invention, it is found that when the atomic ratio of Cr to Fe (Cr / (Cr + Fe)) is in the range of 0.4 - 0.6, the catalyst shows significantly improved comprehensive performance in alkaline electrolyte.

[0046] From Figure 3 SEM, it can be seen that different from Cr x -NiFe 1-x OOH / NF, the morphology of NiCrOOH is a fibrous structure. While the NiFeOOH material presents a nanosheet morphology with sharp edges and regular arrangement.

[0047] From Figure 4 EDS, it can be seen that Ag nanoparticles are successfully modified on the surface of the nanosheets, and the elements Cr, Fe, Ni, and Ag are evenly distributed.

[0048] From Figure 5 the linear sweep voltammetry (LSV) curve, it can be seen that after the modification of Ag, Ag / Crx -NiFe 1-x The OER performance of OOH / NF has been improved.

[0049] From Figure 6 the polarization curve, it can be seen that Ag / Cr 0.5 -NiFe 0.5 OOH / NF has the best corrosion resistance.

[0050] From Figure 7 the electrochemical impedance spectroscopy, it can be seen that Ag / Cr 0.5 -NiFe 0.5 OOH / NF has a smaller charge transfer resistance, indicating that Ag / Cr 0.5 -NiFe 0.5 OOH / NF has better electrical conductivity, thus promoting rapid electron transfer on the catalyst. The Ag / Cr 0.5 -NiFe 0.5 OOH / NF catalyst prepared by the solvothermal method in Example 10 exhibits better electrical conductivity, and its resistance is significantly reduced.

[0051] From Figure 8 the SEM, it can be seen that under the condition of high chloride ion concentration (1.5 M NaCl + 1 M KOH), at a large current density of 1000 mA cm -2 after reacting for 120 hours, the structure of Ag / Cr 0.5 -NiFe 0.5 OOH / NF has not changed significantly, and it has excellent resistance to chloride ion corrosion. At an industrial current density of 1000 mA cm -2 after 100 hours of testing in 1 mol L - 1 KOH + 0.5 mol L -1 NaCl electrolyte, the surface of the unmodified NiFe-LDH catalyst has large-area peeling, the nanosheets become curly, and the nickel foam substrate is exposed; while the peeling area of Ag / NiFe-LDH is less obvious, but when the Cl⁻ concentration is increased to 1.5 mol L -1 the electrode collapses within 30 minutes. Cr 0.5 -NiFe 0.5 OOH still maintains the complete structure of the nanosheets after operating for 100 hours under the same conditions, and can stably operate for >120 hours in a 1.5 mol L -1 Cl⁻ environment, but there is still local catalyst shedding on its surface. Ag / Cr 0.5 -NiFe 0.5 OOH composite catalyst in 1.5 mol L -1After running for 120 hours under Cl⁻ conditions, the nickel foam skeleton remained intact. Mechanistic studies have shown that in an environment with low chloride ion concentration, silver (Ag) interacts with chloride ions to form AgCl colloids, reducing the chloride ion concentration around the catalyst through the electrostatic repulsion mechanism. However, when the chloride ion concentration is too high, the AgCl colloids formed by Ag are 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, and it can in-situ form CrO4 2- . The formation of this CrO4 2- effectively reduces the chloride ion concentration at the active sites, thus significantly enhancing the stability of the electrode. This fully demonstrates the synergistic effect of the unique structure of "surface Ag-Cl fixation + interlayer CrO4 2- shielding effect", achieving efficient regulation of chloride ions and ensuring the stability and catalytic performance of the electrode under different chloride ion concentration conditions.

[0052] From Figure 9 the SEM, it can be seen that on the surface of the catalyst prepared by the hydrothermal method, local accumulation of nanosheets appears in some areas, resulting in poor surface uniformity. In contrast, the catalyst prepared by the solvothermal method exhibits a more uniform surface morphology, with the distribution and growth of nanosheets being more orderly and no obvious accumulation or non-uniformity. This difference indicates that the solvothermal method has significant advantages in controlling the growth and distribution of nanosheets, which helps to form a more uniform catalyst surface structure, thereby optimizing the catalytic performance.

[0053] The Ag / Cr x -NiFe 1-x OOH / NF electrolytic seawater oxygen evolution catalyst can stably operate for more than 1000 hours at a high current density of 1000 mA·cm -2 in alkaline brine. Especially under harsh conditions where the chloride ion concentration is three times higher than that of seawater, this catalyst can stably react for more than 100 hours. As an oxidation electrode for alkaline brine 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 electrolytic seawater oxygen evolution. From Figure 9 the SEM, it can be seen that compared with the nanosheets prepared by the traditional hydrothermal method, the nanosheets prepared by the solvothermal method of Example 10 exhibit irregular characteristics in morphology and the size of the nanosheets is reduced. This unique nanostructure makes it grow more uniformly on the nickel foam, thus greatly improving the smoothness of the nickel foam surface. More importantly, the catalyst prepared by the solvothermal method of Example 10 exhibits more superior electrical conductivity, and its resistance is significantly reduced.

[0054] 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 regarded as being within the protection scope of the present invention.

Claims

1. Ag / Cr x -NiFe 1-x Preparation method of OOH / NF electrolytic seawater oxygen evolution catalyst, characterized in that, It includes the following steps: (1) Place the nickel foam substrate material in a mixed solution containing divalent nickel source, trivalent iron source, trivalent chromium source, urea and alkaline solution, react in a reaction kettle at 100 - 150 °C for 6 - 18 hours, then ultrasonically clean and vacuum dry to obtain Cr x -NiFe 1-x OOH / NF composite material; (2) Immerse the Cr x -NiFe 1-x OOH / NF composite material in a silver salt solution, take it out, ultrasonically clean and vacuum dry it; obtain the Ag / Cr x -NiFe 1-x OOH / NF electrocatalyst for seawater oxygen evolution.

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, nickel carbonate; the trivalent iron source includes ferric nitrate nonahydrate, ferric chloride hexahydrate, ferric sulfate, ferric acetate; the trivalent chromium source includes chromium nitrate nonahydrate, chromium chloride hexahydrate, chromium sulfate, chromium acetate; the silver salt includes silver nitrate and silver acetate; 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 solvent of the mixed solution is water or a binary solvent formed by mixing water and ethylene glycol in a volume ratio of 1:

1.

4. The preparation method according to claim 1, wherein, In step (1), the molar ratio of the trivalent chromium source to the trivalent iron source is 0.67 - 1.5:

1.

5. The preparation method according to claim 1, wherein, The molar ratio of the divalent nickel source, trivalent iron source, trivalent chromium source, urea and ammonium fluoride is 1:0.1~0.9:0.1~0.9:30:

8.

6. The preparation method according to claim 1, wherein In step (2), the concentration of the silver salt is 10~60 mmol / L, and the soaking is carried out for 10 - 120 minutes under dark conditions.

7. The preparation method according to claim 1, wherein In steps (1) and (2), ultrasonic cleaning is carried out with deionized water and ethanol respectively at 25~40 °C for 10~30 minutes.

8. The preparation method according to claim 1, wherein In steps (1) and (2), the vacuum drying temperature is 50~60 °C, and the drying time is 10~30 minutes.

9. The Ag / Cr x -NiFe 1-x OOH / NF electrocatalyst for seawater oxygen evolution prepared by the preparation method according to any one of claims 1-8.

10. Application of Ag / Cr x -NiFe 1-x OOH / NF electrolytic seawater oxygen evolution catalyst, characterized in that It is used for electrolyzing alkaline water or oxygen evolution from seawater.

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