A layered oxygen evolution catalyst, its preparation method and its application

Abstract

This invention belongs to the field of electrocatalysis and new energy materials technology, and relates to a layered oxygen evolution catalyst, its preparation method, and its application. The layered oxygen evolution catalyst is supported on the surface of a conductive substrate and includes: a bottom protective layer, which is bonded to the surface of the conductive substrate and is a dense layer containing iron and sulfur; and an upper catalytic array, which is disposed on the side of the bottom protective layer opposite to the conductive substrate and is a discrete nanoarray structure containing nickel. This invention solves the technical problems of existing surface core-shell coating and homogeneous anion intercalation methods, such as the difficulty in simultaneously achieving mass transfer and protection, the susceptibility of the outer structure to instability, and insufficient resistance to chlorine corrosion at the bottom interface.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis and new energy materials technology, and relates to a stratified oxygen evolution catalyst, its preparation method and its application. Background Technology

[0002] In water electrolysis hydrogen production technology driven by renewable energy sources such as wind and solar power, directly utilizing abundant natural seawater to replace freshwater resources for electrolysis is considered an ideal development path for achieving large-scale, low-cost green hydrogen production. However, the oxygen evolution reaction at the anode involves a relatively slow four-electron-proton coupling transfer process, which is the core bottleneck limiting the energy conversion efficiency of the electrolysis system. Even more challenging is the fact that natural seawater contains high concentrations of highly destructive free chloride ions, posing a severe engineering challenge to the anode catalyst under the strong anodic polarization potential driving high current density.

[0003] On the one hand, chloride ions readily undergo competitive chlorine evolution reactions, which not only generate toxic chlorine gas or hypochlorite, severely reducing the Faraday efficiency of the oxygen evolution reaction, but also cause corrosion and damage to the electrolytic cell equipment and the surrounding environment. On the other hand, free chloride ions can penetrate the surface of traditional electrocatalysts, reaching the bottom and triggering severe oxidation and dissolution of the conductive metal substrate. Under conditions of strong anodic polarization and high current, this corrosion spreads rapidly, eventually leading to the complete dissolution and physical collapse of the metal electrode framework. With the failure of the underlying metal substrate support, the attached surface catalyst material also completely disintegrates, causing the complete failure of the electrolytic cell anode.

[0004] To address the aforementioned interfacial corrosion problem, existing technologies mainly include the following two protection approaches. The first approach involves constructing a core-shell structure, such as introducing a carbon layer or other insulating layer on the outer surface of the catalyst, to prevent chloride ions from contacting the internal active components or conductive substrate. However, this type of external protection method still has significant limitations under high-current anodic oxygen evolution conditions. First, if the outer layer uses carbon-based materials, electrochemical oxidation may occur at higher anodic polarization potentials, thus affecting the long-term stability of the protective layer. Second, there is usually a trade-off between the density of the outer layer structure and its mass transfer performance; an overly dense shell may hinder reactant transport and interfacial charge transfer, while an overly loose or porous structure is unlikely to effectively suppress the continuous penetration of chloride ions. Third, at high current densities, a large number of oxygen bubbles are continuously generated on the anode surface. If the outer layer structure does not facilitate the timely desorption of these bubbles, it may induce localized mass transfer restriction and additional mechanical stress, thereby reducing structural stability.

[0005] The second type involves introducing sulfate, carbonate, or other anions into the catalyst through anion intercalation or specific adsorption to form a protective layer, thereby improving the material's corrosion resistance. However, this type of homogeneous control method also has certain limitations. On the one hand, to accommodate the large intercalated anions, the catalyst lattice often expands to varying degrees, potentially leading to additional lattice strain and affecting structural stability under long-term strong electric fields or high current operation. On the other hand, these anions are usually distributed throughout the entire catalyst bulk phase, making it difficult to form a local barrier with sufficient protective strength at the critical interface between the catalyst layer and the metal substrate. Therefore, when chloride ions penetrate along catalyst layer defects or pores to the bottom interface, they may still cause substrate corrosion and catalyst layer stripping.

[0006] Therefore, existing methods of surface coating and homogeneous intercalation cannot simultaneously achieve optimal surface catalytic activity, mass transfer and exhaust performance, and chlorine corrosion resistance at the bottom interface. Based on this, there is an urgent need to develop a new structural design that spatially distinguishes between surface catalytic function and bottom interface protection function, allowing different structural units to respectively undertake efficient oxygen evolution, rapid exhaust, and chlorine corrosion resistance, thereby improving the long-term operational stability of the anode under high-current natural seawater electrolysis conditions. Summary of the Invention

[0007] The purpose of this invention is to provide a layered oxygen evolution catalyst to solve the technical problems existing in the current surface core-shell coating and homogeneous anion intercalation methods, such as the difficulty in balancing mass transfer and protection, the easy instability of the outer layer structure, and the insufficient resistance to chlorine corrosion at the bottom interface.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] A stratified oxygen evolution catalyst is disclosed, wherein the catalyst is supported on the surface of a conductive substrate. The conductive substrate is preferably nickel foam, and the nickel foam has a three-dimensional porous framework. The stratified oxygen evolution catalyst includes a bottom protective layer and an upper catalytic array. The bottom protective layer is bonded to the surface of the conductive substrate and is a dense layer containing iron and sulfur, preferably in the form of sulfate ions. The bottom protective layer coats the surface of the three-dimensional porous framework. By setting the bottom protective layer, this invention can form a tightly adhering polyanionic chloride-resistant barrier between the conductive substrate and the upper catalytic array. The dense layer physically blocks free chloride ions, while the sulfate ions further inhibit the deep penetration of chloride ions through strong electrostatic repulsion, thereby effectively preventing pitting corrosion and oxidative dissolution of the conductive substrate and significantly improving the structural stability of the catalyst-substrate interface.

[0010] The upper catalytic array is disposed on the side of the bottom protective layer opposite to the conductive substrate. The upper catalytic array is a discrete nanoarray structure and contains nickel. The discrete nanoarray structure includes sheet-like or columnar structures extending outward from the surface of the bottom protective layer. By setting the upper catalytic array as a discrete nanoarray structure, on the one hand, the effective electrochemical active area of ​​the catalyst is significantly increased, exposing more surface active sites; on the other hand, the discrete nanoarray structure exhibits excellent superhydrophobic properties in the electrolyte, which can effectively reduce the adhesion force of bubbles on the catalyst surface and promote the rapid desorption of a large number of oxygen bubbles generated under high current oxygen evolution conditions. This avoids local mass transfer limitation and additional mechanical stress caused by bubble coverage, ensuring sufficient contact between the electrolyte and the catalytic active sites.

[0011] Furthermore, the stratified oxygen evolution catalyst also contains a third metal element, which is selected from at least one of cobalt, manganese, and chromium. By introducing the third metal element, the electronic structure and local coordination environment of the catalytic active center can be effectively controlled, and the adsorption and desorption energy barriers of the reaction intermediates can be optimized, thereby further enhancing the oxygen evolution activity of the catalyst.

[0012] A method for preparing the above-mentioned stratified oxygen evolution catalyst, the method comprising the following steps:

[0013] (1) Dissolve the first metal salt, the second metal salt and the morphology guiding agent in a solvent to obtain a mixed electrodeposition solution; wherein the first metal salt is a nickel salt, the second metal salt is an iron salt and the morphology guiding agent is thiourea;

[0014] (2) Using a conductive substrate as the working electrode, cathodic electrodeposition is performed in the mixed electrodeposition solution to obtain a pre-assembled electrode;

[0015] (3) The pre-assembled electrode is placed in an alkaline electrolyte and electrochemically activated by applying a constant anodic current density to obtain the stratified oxygen evolution catalyst.

[0016] In step (1), the molar concentration of the first metal salt in the mixed electrodeposition solution is 10-40 mM, the molar concentration of the second metal salt is 5-20 mM, and the molar concentration of the thiourea is 0.3-0.8 M. Preferably, the molar ratio of the first metal salt to the second metal salt is 2:1; more preferably, the molar concentration of the first metal salt is 18 mM, the molar concentration of the second metal salt is 9 mM, and the molar concentration of the thiourea is 0.5 M. By controlling the molar ratio and concentration of nickel and iron salts, it is possible to ensure that the subsequently formed upper catalytic array has a suitable nickel-iron ratio, thereby obtaining high catalytic activity; at the same time, the introduction of thiourea not only provides a sulfur source for the bottom protective layer, but also acts as a morphology guide to guide the formation of discrete nanoarray precursors.

[0017] Furthermore, the mixed electrodeposition solution in step (1) may optionally contain a third metal salt, which is selected from at least one of cobalt, manganese, and chromium salts, and the molar concentration of the third metal salt is 5-20 mM. By introducing a third metal element through co-deposition, the catalyst composition can be flexibly controlled.

[0018] In step (2), the conductive substrate is selected from one of nickel foam, titanium mesh, and stainless steel mesh. The cathodic electrodeposition is performed using a constant potential method, with a deposition potential of -0.8 V to -1.2 V, a deposition temperature of 20 to 35 °C, and a total coulombic deposition of -8 C to -12 C. Preferably, the deposition potential is -1.0 V, and the total coulombic deposition is -10 C. During the cathodic electrodeposition process, nickel and iron ions are reduced and deposited on the surface of the conductive substrate, while thiourea is adsorbed or decomposed at the interface, resulting in the co-deposition of low-valence sulfur species with iron and nickel precursors and their enrichment at the interface of the conductive substrate. At the same time, the guiding effect of thiourea promotes the formation of a discrete array-like precursor structure on the outside.

[0019] In step (3), the alkaline electrolyte is a 0.5-2.0 M aqueous solution of potassium hydroxide or sodium hydroxide. The electrochemical activation conditions include an anolyte current density of 50-200 mA cm⁻¹. -2 The temperature is 20~30 °C, and the activation time is 0.5~36 h. Preferably, the anolyte current density is 100 mA cm⁻¹. -2 The activation time was 12 h. Under strong anodic polarization, the low-valent sulfur species enriched at the interface underwent irreversible electrochemical oxidation, evolving in situ into a dense polyanion protective layer rich in high-valent sulfate, i.e., the bottom protective layer; at the same time, the external nickel-iron-based precursor underwent adaptive oxidative reconstruction, transforming into a discrete nanoarray of hydroxyl oxides open to the electrolyte, i.e., the upper catalytic array.

[0020] An application of a stratified oxygen evolution catalyst in hydrogen production by seawater electrolysis or by electrolysis of electrolytes containing chloride ions. Because the stratified oxygen evolution catalyst possesses high catalytic activity, excellent bubble desorption capability, and resistance to chloride corrosion in the bottom layer, it is particularly suitable for high-current direct electrolysis hydrogen production systems in natural alkaline seawater or electrolytes containing high concentrations of chloride ions.

[0021] The layered oxygen evolution catalyst of this invention forms a layered structure through in-situ electrochemical interface reconstruction. The upper layer is used for efficient oxygen evolution reaction and to promote bubble desorption, while the lower layer inhibits chloride ion penetration into the metal substrate and enhances interfacial corrosion resistance, thereby improving the long-term operational stability of the anode during high-current seawater electrolysis. Compared with existing technologies, the advantages of this invention are:

[0022] 1. This invention constructs a layered structure with a separate surface catalytic exhaust layer and a bottom layer of chloride-resistant protective layer, which can spatially distinguish different functional areas. The upper layer facilitates the oxygen evolution reaction and bubble desorption, while the bottom layer helps to inhibit chloride ion penetration into the metal substrate, thus balancing catalytic activity, mass transfer performance, and interfacial corrosion resistance.

[0023] 2. This invention forms a dense polyanionic protective layer in situ in the interface region near the conductive metal substrate. The sulfate ions in this protective layer can strongly electrostatically repel and block chloride ion intrusion, and the dense layer itself provides physical barriers, significantly slowing down pitting corrosion and oxidative dissolution of the metal substrate, thereby improving the structural stability of the catalyst layer-substrate interface and reducing the risk of electrode peeling failure.

[0024] 3. The upper catalytic structure of this invention is a discrete nanoarray morphology open to the electrolyte, exhibiting lower mass transfer resistance and better bubble release capability. Compared with the outer surface-covered protective structure, this configuration is more conducive to exposing catalytic active sites, promoting interfacial charge transfer, and effectively mitigating the problems of bubble coverage and localized mass transfer restriction under high current conditions.

[0025] 4. The preparation method of this invention employs a one-step cathodic electrodeposition combined with constant-current anodic electrochemical activation under alkaline conditions. The process is simple, highly controllable, and suitable for nickel-iron-based catalytic systems. Furthermore, transition metals such as cobalt, manganese, and chromium can be introduced for component regulation, demonstrating good material scalability. The resulting layered catalyst can maintain long-term stable operation under high current density conditions during natural alkaline seawater electrolysis, exhibiting excellent potential for industrial application. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope top view of the oxygen evolution catalyst of Example 1;

[0027] Figure 2 This is a cross-sectional scanning electron microscope image of the oxygen evolution catalyst of Example 1;

[0028] Figure 3 This is the cross-sectional energy dispersive spectroscopy (EDS) elemental distribution diagram of the stratified oxygen evolution catalyst of Example 1;

[0029] Figure 4 This is a linear sweep voltammetric curve of the oxygen evolution catalyst of Example 1 in a simulated alkaline seawater electrolyte;

[0030] Figure 5 This is a constant current stability test diagram of the stratified oxygen evolution catalyst of Example 1 in a simulated alkaline seawater electrolyte. Detailed Implementation

[0031] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0032] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0033] Unless otherwise specified, the reagents used in the following examples can be purchased from a regular biochemical reagent store.

[0034] Nickel foam, thickness: 1 mm, Suzhou Shengernuo Technology Co., Ltd.

[0035] Acetone, CH3COCH3, AR, ≥99.5%, Huzhou Shuanglin Chemical Technology Co., Ltd.

[0036] Hydrochloric acid solution, HCl, AR, 36%–38%, Sinopharm Chemical Reagent Co., Ltd.; Anhydrous ethanol, CH3CH2OH, GR, ≥99.8%, Sinopharm Chemical Reagent Co., Ltd.; Nickel nitrate, Ni(NO3)2·6H2O, AR, ≥98%, Sinopharm Chemical Reagent Co., Ltd.; Ferric nitrate, Fe(NO3)3·9H2O, AR, ≥98.5%, Sinopharm Chemical Reagent Co., Ltd.; Thiourea, CH4N2S, LR, 99%, Shanghai Maclean Biochemical Technology Co., Ltd.; Potassium hydroxide, KOH, LR, 95%, Shanghai Maclean Biochemical Technology Co., Ltd.; Chromium nitrate, Cr(NO3)3·9H2O, AR, ≥99%, Sinopharm Chemical Reagent Co., Ltd.; Cobalt nitrate, Co(NO3)2·6H2O, AR, ≥98.5%, Sinopharm Chemical Reagent Co., Ltd.

[0037] Example 1

[0038] A layered oxygen evolution catalyst and its preparation method are described below:

[0039] (1) Conductive substrate pretreatment: 1 cm × 1 cm foam nickel was immersed in acetone, 3.0 M hydrochloric acid solution, deionized water and anhydrous ethanol in sequence, and ultrasonically cleaned for 3 min each to remove surface oil and oxide layer. Then it was placed in a vacuum chamber to dry to obtain the pretreated foam nickel conductive substrate.

[0040] (2) Preparation of mixed electrodeposition solution: In a glass electrolytic cell, nickel nitrate, ferric nitrate, and thiourea are dissolved in deionized water and brought to a final volume of 150 mL. The solution is then magnetically stirred until homogeneous to obtain the mixed electrodeposition solution. In the mixed electrodeposition solution, the molar concentration of nickel nitrate as the first metal salt is 18 mM, the molar concentration of ferric nitrate as the second metal salt is 9 mM, and the molar concentration of thiourea as the morphology guiding agent is 0.5 M.

[0041] (3) Cathodic electrodeposition: A three-electrode system was constructed, with the pretreated nickel foam from step (1) as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. After connecting the three-electrode system to the electrochemical workstation, cathodic electrodeposition was performed using the constant potential method. The system temperature was controlled at a constant 25 °C, and a constant potential of -1.0 V relative to the saturated calomel electrode was applied to precisely control the total coulombic amount of the deposition to -10 C. During this co-deposition process, nickel ions and iron ions underwent electrochemical reduction deposition on the conductive substrate surface. Thiourea molecules and their electrochemical decomposition products underwent specific adsorption and enrichment at the solid-liquid interface. This not only served as a sulfur source to introduce low-valent sulfur precursors into the deposition layer, but also played a key morphological guiding role in the growth of nickel-iron deposits, promoting the formation of array-like precursors with discrete characteristics in the external region, while the interface region was enriched with iron and sulfur species. After deposition, the electrode was removed, and the surface residual electrolyte was slowly rinsed with deionized water to obtain a pre-assembled electrode loaded with discrete array precursors.

[0042] (4) Anodic electrochemical activation: The pre-assembled electrode was transferred to an electrolytic cell containing a 1.0 M potassium hydroxide aqueous solution. Using the pre-assembled electrode as the working electrode, the temperature of the alkaline electrolyte was kept constant at 25 °C. An electrochemical workstation was used to apply 100 mA cm⁻¹ of electrolyte. -2Electrochemical in-situ activation was performed at a constant anodic current density for 12 h. During this strong anodic polarization, the electrode interface underwent reconstruction: on the one hand, the low-valent sulfur precursor enriched at the conductive substrate interface underwent irreversible electrochemical oxidation under strong oxidation potential, transforming in-situ into a dense polyanion layer rich in high-valent sulfate ions. This polyanion layer, together with iron, forms a tightly bonded bottom protective layer. On the other hand, the external nickel-iron-based precursor, far from the interface, underwent hydrolysis, oxidation, and adaptive morphology evolution, rearranging its crystal structure and transforming into a discrete nanoarray structure of hydroxyl oxides fully open to the electrolyte, i.e., the upper catalytic array. After activation, the electrode was removed, thoroughly washed with deionized water, and vacuum dried to obtain the layered oxygen evolution catalyst.

[0043] Example 2

[0044] A layered oxygen evolution catalyst and its preparation method differ from Example 1 mainly in that the molar concentrations of nickel and iron salts and the electrochemical activation process parameters are adjusted. The specific steps are as follows:

[0045] (1) Conductive substrate pretreatment: 1 cm × 1 cm foam nickel was immersed in acetone, 3.0 M hydrochloric acid solution, deionized water and anhydrous ethanol in sequence, and ultrasonically cleaned for 3 min each to remove surface oil and oxide layer. Then it was placed in a vacuum box to dry for later use.

[0046] (2) Preparation of mixed electrodeposition solution: In a glass electrolytic cell, nickel nitrate, ferric nitrate and thiourea are dissolved in deionized water and brought to a final volume of 150 mL. The solution is then magnetically stirred until homogeneous. The molar concentration of nickel nitrate is 27 mM, the molar concentration of ferric nitrate is 18 mM, and the molar concentration of thiourea is 0.5 M.

[0047] (3) Cathodic electrodeposition: A three-electrode system was constructed, with pretreated nickel foam as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The three-electrode system was connected to an electrochemical workstation, and cathodic electrodeposition was performed using a potentiostatic method. The system temperature was controlled at a constant 30 °C, and a constant potential of -1.0 V relative to the saturated calomel electrode was applied, controlling the total coulombic deposition to be -10 C. After deposition, the electrode was removed and slowly rinsed with deionized water to obtain a pre-assembled electrode loaded with a discrete array precursor.

[0048] (4) Anodic electrochemical activation: The pre-assembled electrode was transferred to an electrolytic cell containing a 1.0 M potassium hydroxide aqueous solution. The temperature of the alkaline electrolyte was kept constant at 25 °C, and a 200 mA cm⁻¹ anode was applied. -2Electrochemical in-situ activation was performed at a constant anodic current density for 20 h. Under this high current density activation condition, the low-valent sulfur precursor at the interface underwent rapid oxidative reconstruction, forming a denser sulfate-enriched anion-based protective layer in situ. Simultaneously, the external nickel-iron components experienced intense oxidation and lattice rearrangement, forming a discrete nanosheet array structure with high roughness. After activation, the catalyst was removed, washed with deionized water, and vacuum dried to obtain the stratified oxygen evolution catalyst.

[0049] Example 3

[0050] A layered oxygen evolution catalyst and its preparation method differ from Example 1 mainly in that a third metal element, chromium, is introduced to further optimize the electronic structure of the catalytic active center. The specific steps are as follows:

[0051] (1) Conductive substrate pretreatment: 1 cm × 1 cm foam nickel was immersed in acetone, 3.0 M hydrochloric acid solution, deionized water and anhydrous ethanol in sequence, and ultrasonically cleaned for 3 min each to remove surface oil and oxide layer. Then it was placed in a vacuum box to dry for later use.

[0052] (2) Preparation of mixed electrodeposition solution: In a glass electrolytic cell, nickel nitrate, ferric nitrate, chromium nitrate and thiourea are dissolved in deionized water and brought to a final volume of 150 mL. The solution is then magnetically stirred until homogeneous. The molar concentrations of nickel nitrate, ferric nitrate, chromium nitrate (as the third metal salt), and thiourea are 18 mM, 9 mM, 9 mM, and 0.5 M respectively.

[0053] (3) Cathodic electrodeposition: A three-electrode system was constructed, using pretreated nickel foam as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. This three-electrode system was connected to an electrochemical workstation, and cathodic electrodeposition was performed using a potentiostatic method. The system temperature was controlled at a constant 25 °C, and a constant potential of -1.0 V relative to the saturated calomel electrode was applied, controlling the total coulombic deposition to be -10 C. The introduction of chromium ions led to the formation of a nickel-iron-chromium ternary composite hydroxide precursor in the deposition precursor. The guiding effect of thiourea ensured that the composite precursor remained uniformly loaded on the conductive substrate surface in a discrete array. After deposition, the electrode was removed and slowly rinsed with deionized water to obtain a pre-assembled electrode.

[0054] (4) Anodic electrochemical activation: The pre-assembled electrode was transferred to an electrolytic cell containing a 1.0 M potassium hydroxide aqueous solution. The temperature of the alkaline electrolyte was kept constant at 25 °C, and a 100 mA cm⁻¹ anode was applied. -2Electrochemical in-situ activation was performed using a constant anolyte current density for 24 hours. During activation, chromium entered the lattice of the upper catalytic array, effectively regulating the electron cloud density and metal-oxygen bond covalentity of the nickel active center, and optimizing the adsorption energy barrier of the reaction intermediate. Simultaneously, the sulfur precursor at the interface was oxidized in-situ to sulfate and formed a bottom protective layer with iron. After activation, the catalyst was removed, washed with deionized water, and vacuum dried to obtain a chromium-containing layered oxygen evolution catalyst.

[0055] Example 4

[0056] A layered oxygen evolution catalyst and its preparation method differ from Example 1 mainly in that cobalt and chromium, two third metal elements, are introduced simultaneously, and the electrodeposition temperature and activation time are appropriately adjusted. The specific steps are as follows:

[0057] (1) Conductive substrate pretreatment: 1 cm × 1 cm foam nickel was immersed in acetone, 3.0 M hydrochloric acid solution, deionized water and anhydrous ethanol in sequence, and ultrasonically cleaned for 3 min each to remove surface oil and oxide layer. Then it was placed in a vacuum box to dry for later use.

[0058] (2) Preparation of mixed electrodeposition solution: In a glass electrolytic cell, nickel nitrate, ferric nitrate, cobalt nitrate, chromium nitrate, and thiourea are dissolved in deionized water and brought to a final volume of 150 mL. The solution is then magnetically stirred until homogeneous. The molar concentrations of nickel nitrate, ferric nitrate, cobalt nitrate, chromium nitrate, and thiourea are 27 mM, 13.5 mM, 9 mM, 9 mM, and 0.5 M, respectively.

[0059] (3) Cathodic electrodeposition: A three-electrode system was constructed, using pretreated nickel foam as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. This three-electrode system was connected to an electrochemical workstation, and cathodic electrodeposition was performed using a potentiostatic method. The system temperature was controlled at a constant 35 °C, and a constant potential of -1.0 V relative to the saturated calomel electrode was applied, controlling the total coulombic deposition to -10 C. A higher deposition temperature facilitates the co-reduction and uniform doping of various metal ions, and under these conditions, thiourea guides the formation of a more developed discrete array precursor structure. After deposition, the electrode was removed and slowly rinsed with deionized water to obtain a pre-assembled electrode.

[0060] (4) Anodic electrochemical activation: The pre-assembled electrode was transferred to an electrolytic cell containing a 1.0 M potassium hydroxide aqueous solution. The temperature of the alkaline electrolyte was kept constant at 25 °C, and a 50 mA cm⁻¹ anode was applied. -2Electrochemical in-situ activation was performed at a constant anolyte current density for 36 hours. Under these relatively long and mild activation conditions, cobalt and chromium fully entered the lattice sites of the upper nickel-iron-based catalytic array, significantly optimizing the adsorption and desorption balance of oxygen intermediates through synergistic electronic effects; a highly crystalline, dense iron-sulfur protective layer slowly and thoroughly formed at the interface. After activation, the catalyst was removed, washed with deionized water, and vacuum dried to obtain a cobalt- and chromium-containing stratified oxygen evolution catalyst.

[0061] Comparative Example 1 NiFe-LDH

[0062] A conventional method for preparing a nickel-iron layered double hydroxide oxygen evolution catalyst by electrodeposition differs from Example 1 mainly in that: no thiourea morphology directing agent is added to the mixed electrodeposition solution, thus preventing the formation of the underlying protective layer and the discrete nanoarray upper structure described in this invention. The specific steps are as follows:

[0063] (1) Conductive substrate pretreatment: 1 cm × 1 cm foam nickel was immersed in acetone, 3.0 M hydrochloric acid solution, deionized water and anhydrous ethanol in sequence, and ultrasonically cleaned for 3 min each to remove surface oil and oxide layer. Then it was placed in a vacuum box to dry for later use.

[0064] (2) Preparation of mixed electrodeposition solution: In a glass electrolytic cell, only nickel nitrate and ferric nitrate are added, dissolved in deionized water, and the volume is adjusted to 150 mL. The solution is then magnetically stirred until homogeneous. The molar concentration of nickel nitrate is 18 mM, and the molar concentration of ferric nitrate is 9 mM. There are no surface guiding agents or sulfur sources in this system.

[0065] (3) Cathodic electrodeposition: A three-electrode system was constructed, using pretreated nickel foam as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. This three-electrode system was connected to an electrochemical workstation, and cathodic electrodeposition was performed using a potentiostatic method. The system temperature was controlled at a constant 25 °C, and a constant potential of -1.0 V relative to the saturated calomel electrode was applied, controlling the total coulombic deposition to -10 C. Due to the lack of morphology guidance and interface regulation by thiourea, a dense, continuous thin film precursor loaded on the nickel foam surface was obtained after deposition, rather than a discrete array structure. The electrodes were then removed and slowly rinsed with deionized water.

[0066] (4) Anodic electrochemical activation: The above electrode was transferred to an electrolytic cell containing a 1.0 M potassium hydroxide aqueous solution, and the temperature of the alkaline electrolyte was kept constant at 25 °C. A 100 mA cm⁻¹ solution was applied. -2Electrochemical in-situ activation was performed at a constant anolyte current density for 12 h. Since no sulfur precursor participated in the interface reconstruction, only a homogeneous nickel-iron layered double hydroxide catalyst layer was obtained after activation; the spatially layered configuration of a dense, sulfate-rich bottom protective layer and a discrete nanoarray upper catalyst layer was not formed. After activation, the catalyst was removed, washed with deionized water, and vacuum dried to obtain a conventional electrodeposited nickel-iron layered double hydroxide oxygen evolution catalyst.

[0067] Performance testing

[0068] The microstructure characterization and electrochemical performance tests of the layered oxygen evolution catalysts prepared in Examples 1 to 4 and the conventional nickel-iron layered double hydroxide catalyst prepared in Comparative Example 1 were carried out in a simulated alkaline seawater electrolyte of 1.0 M potassium hydroxide + 0.5 M sodium chloride.

[0069] like Figure 1 As shown, the layered oxygen evolution catalyst prepared in Example 1 achieved uniform coverage on the surface of the nickel foam conductive substrate, without obvious agglomeration or exposed substrate areas, indicating that the one-step electrodeposition process has excellent structural uniformity and load strength.

[0070] like Figure 2 As shown in the cross-sectional scanning electron microscope image, it can be clearly observed that the catalyst exhibits a significant heterogeneous layered configuration in the vertical space, consisting of an upper array and a bottom dense layer, completely abandoning the traditional homogeneous structure or surface dense coating structure.

[0071] like Figure 3 As shown, the cross-sectional energy dispersive spectroscopy elemental distribution map reveals a high degree of regional selectivity in the spatial distribution of each element: nickel is mainly enriched in the upper discrete nanoarray region, dominating the efficient oxygen evolution catalysis process; while the crucial sulfur element does not undergo homogeneous doping in the overall catalyst, but specifically co-enriches with iron at the interface between the catalyst and the foamed nickel conductive substrate. This phenomenon fully demonstrates that during the strong anodic polarization activation process, the sulfur-containing precursor introduced by thiourea undergoes deep irreversible electrochemical oxidation at the solid-liquid interface, evolving in situ into a dense polyanion protective layer rich in high-valence sulfate ions. This bottom barrier utilizes the electrostatic repulsion of high-valence anions to effectively block free chloride ions attempting to penetrate; simultaneously, the physical barrier effect of the dense layer further cuts off the path for chloride ions to contact the metal substrate.

[0072] Figure 4The electrochemical oxidation process curve of the layered oxygen evolution catalyst prepared in Example 1 in a 1.0 M potassium hydroxide + 0.5 M sodium chloride electrolyte, measured by linear sweep voltammetry, is shown. Compared with the conventional nickel-iron layered double hydroxide catalyst of the comparative example, the oxygen evolution reaction activity of Example 1 is significantly better, and the anodic overpotential required at the same current density is significantly reduced, indicating that this layered structure has excellent electrocatalytic activity in a simulated alkaline seawater electrolyte.

[0073] Figure 5 The results of the long-term stability test in Example 1, measured by the galvanostatic method in the same electrolyte, show that the current density used in the test was 1 A cm⁻¹. -2 The results show that this stratified oxygen evolution catalyst can be applied at 1 A cm⁻¹. -2 It has been operating stably for more than 1600 hours under high current density conditions, demonstrating its excellent long-term operational stability in alkaline electrolytes containing chloride ions; while conventional nickel-iron layered double hydroxide catalysts lack an underlying chloride-resistant protective layer, and chloride ions will cause corrosion of the metal substrate after penetrating the catalyst layer, eventually leading to the complete stripping and failure of the catalyst structure.

[0074] Table 1 shows the results of the layered oxygen evolution catalysts prepared in the various embodiments of the present invention and Comparative Example 1 (conventional electrodeposited NiFe-LDH catalyst) at different current densities (200 mA cm⁻¹) in a simulated alkaline seawater electrolyte of 1 M KOH + 0.5 M NaCl. -2 and 500mA cm -2 Comparison of overpotential parameters of the electrochemical oxygen evolution reaction.

[0075] Table 1. Comparison of electrocatalytic performance of each embodiment and comparative example in simulated alkaline seawater electrolyte.

[0076]

[0077] As shown in Table 1, at 200 mA cm -2 At a current density of 500 mA cm⁻¹, the oxygen evolution overpotential of Example 1 was 253 mV, which was 30 mV lower than the 283 mV of the comparative example; at 500 mA cm⁻¹ -2 In Example 1, the overpotential was 262 mV, which was 61 mV lower than the 323 mV of the comparative example. As the current density increased, the difference in overpotential between the present invention and Comparative Example 1 significantly widened, indicating that the layered structure exhibits more prominent kinetic advantages under high current conditions. The overpotentials of Examples 2 to 4 were also significantly lower than those of the comparative example, demonstrating that the preparation method described in this invention has a wide process window and can maintain excellent electrocatalytic activity under different parameter and component controls.

[0078] In this invention, the upper discrete nanoarray possesses a large specific surface area and superhydrophobic properties, effectively reducing bubble adhesion and promoting rapid degassing and mass transfer under high current density, thereby significantly reducing overpotential. The bottom dense protective layer, rich in iron and sulfur, blocks the penetration path of chloride ions into the metal substrate through the synergistic effect of electrostatic repulsion of high-valence sulfate ions and physical density, fundamentally avoiding electrode failure caused by substrate corrosion. Examples 3 and 4 further introduce chromium or cobalt, or other third metal elements, and by regulating the electronic structure of the active center, further optimize the catalytic activity while maintaining the protective capability of the bottom layer, demonstrating that this layered structure has good component scalability.

[0079] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A layered oxygen evolution catalyst characterized in that, The stratified oxygen evolution catalyst is supported on the surface of a conductive substrate, and the stratified oxygen evolution catalyst comprises: A bottom protective layer is bonded to the surface of the conductive substrate. The bottom protective layer is a dense layer and contains iron and sulfur elements. The upper catalytic array is disposed on the side of the bottom protective layer away from the conductive substrate. The upper catalytic array is a discrete nanoarray structure and contains nickel.

2. The layered oxygen evolution catalyst of claim 1, wherein, The sulfur element in the bottom protective layer exists in the form of sulfate; the upper catalytic array includes a sheet-like structure or a columnar structure extending outward from the surface of the bottom protective layer.

3. The layered oxygen evolution catalyst of claim 1, wherein, The conductive substrate is nickel foam and has a three-dimensional porous skeleton; the bottom protective layer covers the surface of the three-dimensional porous skeleton.

4. The layered oxygen evolution catalyst of any one of claims 1 to 3, wherein, The stratified oxygen evolution catalyst further comprises a third metal element selected from at least one of cobalt, manganese, and chromium.

5. The method of making a layered oxygen evolution catalyst of claim 1, wherein, The method includes the following steps: (1) Dissolve the first metal salt, the second metal salt and the morphology guiding agent in a solvent to obtain a mixed electrodeposition solution; wherein the first metal salt is a nickel salt, the second metal salt is an iron salt and the morphology guiding agent is thiourea; (2) Using a conductive substrate as the working electrode, cathodic electrodeposition is performed in the mixed electrodeposition solution to obtain a pre-assembled electrode; (3) The pre-assembled electrode is placed in an alkaline electrolyte and electrochemically activated by applying a constant anodic current density to obtain the stratified oxygen evolution catalyst.

6. The method according to claim 5, characterized in that, In step (1), the molar concentration of the first metal salt in the mixed electrodeposition solution is 10-40 mM, the molar concentration of the second metal salt is 5-20 mM, and the molar concentration of the thiourea is 0.3-0.8 M.

7. The method according to claim 5, characterized in that, In step (1), the mixed electrodeposition solution further comprises a third metal salt, which is selected from at least one of cobalt salt, manganese salt and chromium salt; the molar concentration of the third metal salt is 5 to 20 mM.

8. The method according to claim 5, characterized in that, In step (2), the conductive substrate is selected from one of nickel foam, titanium mesh and stainless steel mesh; the cathode electrodeposition adopts the constant potential method, the deposition potential is -0.8 V to -1.2 V, the deposition temperature is 20 to 35 ℃, and the total coulombic amount of the deposition is -8 C to -12 C.

9. The method according to claim 5, characterized in that, In step (3), the alkaline electrolyte is a 0.5-2.0 M aqueous solution of potassium hydroxide or sodium hydroxide; the electrochemical activation conditions include an anode current density of 50-200 mA cm -2 , a temperature of 20-30 °C, and an activation time of 0.5-36 h.

10. The application of a layered oxygen evolution catalyst as described in claim 1 or a layered oxygen evolution catalyst prepared by the method as described in claim 5 in hydrogen production by seawater electrolysis or hydrogen production by chloride ion-containing electrolyte electrolysis.

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