Preparation method and application of nickel hydroxide / cobalt iron alloy nanosheet electrocatalyst

Abstract

This invention provides a method for preparing nickel hydroxide / cobalt-iron alloy nanosheet electrocatalysts and their applications. The method involves dissolving FeSO4·7H2O, CoSO4·7H2O, NH4H2PO4, and Na3(C6H5O7)·2H2O in deionized water to form a mixed solution; using nickel foam as the working electrode and the mixed solution as the electrochemical deposition solution for constant current cathode deposition for a certain period; then washing the obtained sample with deionized water and drying it to obtain the cobalt-iron alloy electrocatalyst; placing the obtained cobalt-iron alloy electrocatalyst in a nickel nitrate solution to allow it to spontaneously and uniformly corrode in the solution for a certain period; after corrosion, washing and drying the sample to obtain the nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst. The morphology, catalytic activity, and oxygen evolution stability of the prepared catalyst are all significantly improved. The nickel nitrate corrosion method proposed in this invention has advantages such as low cost, low energy consumption, and ease of large-scale production. Furthermore, this method is versatile in preparing excellent transition metal OER catalysts and shows great promise for industrial application in the field of water electrolysis for hydrogen production.

Description

Technical Field

[0001] This invention belongs to the field of energy conversion technology, specifically relating to a method for preparing a nickel hydroxide / cobalt iron alloy nanosheet electrocatalyst and its application. Background Technology

[0002] With the depletion of fossil fuels and the increasing severity of environmental pollution, the world today faces the dual challenges of energy transition and environmental solutions. Hydrogen, as an energy carrier, possesses advantages such as high energy density, cleanliness, and wide applicability, and is considered the most promising alternative to fossil fuels. Currently, among numerous hydrogen production technologies, water electrolysis powered by renewable energy sources such as solar and wind power is highly favored due to its simplicity, efficiency, and ease of industrial application. Water electrolysis for hydrogen production involves two half-reactions: the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. However, the OER, involving the coupling transfer of four electrons and protons, has a high energy barrier and slow kinetics, becoming a bottleneck for efficient water electrolysis and severely limiting its efficiency.

[0003] Developing cost-effective, high-performance electrocatalysts capable of long-term stable operation under harsh conditions to lower the energy barrier in the OER process and improve reaction kinetics remains crucial for enhancing the energy conversion efficiency of industrial water electrolysis for hydrogen production. However, platinum group metal electrocatalysts (such as IrO2 and RuO2) with excellent electrocatalytic activity are severely hampered by their scarcity in the Earth's crust, high cost, and susceptibility to deactivation in alkaline media, hindering their industrial application in water electrolysis for hydrogen production. Therefore, developing inexpensive, highly active, and stable non-precious metal electrocatalysts to lower the OER energy barrier, improve reaction kinetics, and ultimately increase the energy conversion efficiency of water electrolysis for hydrogen production remains a formidable challenge.

[0004] To address these issues, researchers have developed numerous non-noble metal electrocatalysts, including alloys, oxides, hydroxides, hydroxyl oxides, phosphides, sulfides, nitrides, carbides, and metal-organic frameworks (MOFs). Among these electrocatalysts, alloys, particularly cobalt-iron alloys, exhibit excellent electrical conductivity and rapid charge transport during electrocatalysis, making them excellent OER catalysts. However, cobalt-iron alloys have inherent limitations; they tend to agglomerate, reducing their overall surface energy. This agglomeration is detrimental to the OER process, as it reduces the number of surface catalytic active sites, hindering OER formation. Furthermore, agglomerates impede charge and mass transport and rapid oxygen bubble diffusion during OER, resulting in slow OER kinetics. In addition, traditional synthesis methods for cobalt-iron alloy catalysts (such as co-precipitation, sol-gel, chemical vapor deposition, and hydrothermal synthesis) are complex, costly, and unsuitable for large-scale production. These factors cannot be ignored when preparing cobalt-iron alloy OER catalysts. Only by fully considering these factors and solving these problems can the industrial production and application of cobalt-iron alloy water electrolysis hydrogen production catalysts be realized. Generally speaking, constructing ultrathin nanosheet electrocatalysts can significantly shorten the charge / mass transport path and reduce transport resistance in the OER process, while accelerating the diffusion rate of oxygen bubbles, thereby accelerating the OER reaction kinetics. However, choosing a simple method to synthesize cobalt-iron alloy catalysts, especially developing effective strategies to control their morphology (such as constructing nanosheets) to prevent agglomeration, increase surface area, increase the number of OER active sites, and enhance structural stability, remains a major challenge for achieving long-term, high-efficiency OER performance at industrial-grade current densities.

[0005] To address the limitations of existing cobalt-iron alloy catalysts, such as easy agglomeration, low catalytic activity, poor stability, complex preparation processes, high costs, and difficulty in large-scale production, this invention proposes a simple, cost-effective, and easily scalable method of improving the morphology of cobalt-iron alloy catalysts through nickel nitrate corrosion, thereby enhancing their electrocatalytic activity and stability. The prepared catalyst exhibits negligible performance degradation after long-term OER testing at industrial-grade flux densities. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing nickel hydroxide / cobalt-iron alloy nanosheet electrocatalysts, employing a nickel nitrate etching method to improve the morphology, catalytic activity, and stability of the cobalt-iron alloy electrocatalyst. The method involves in-situ growth of cobalt-iron alloy onto the surface of nickel foam via electrochemical deposition, followed by electrochemical etching of the cobalt-iron alloy in a nickel nitrate solution of a specific concentration and temperature. This method leverages the inherent characteristic that cobalt-iron alloy is prone to electrochemical corrosion in humid environments, and that iron is even more susceptible to corrosion. This harmful electrochemical corrosion behavior is transformed into an effective strategy for catalyst preparation, successfully producing nickel hydroxide / cobalt-iron alloy nanosheet electrocatalysts. The uniform corrosion of iron on the cobalt-iron alloy surface provides the necessary environment for the uniform growth of nickel hydroxide, while the in-situ grown nickel hydroxide layer acts as a protective film, effectively preventing further iron corrosion. This interaction significantly enhances the mechanical strength of the nickel hydroxide / cobalt-iron alloy nanosheet electrocatalysts, thereby endowing the catalyst with excellent stability under harsh conditions.

[0007] On the other hand, during the corrosion process, the formation of nanosheets not only significantly shortens the charge and mass transport paths during OER, but also reduces the resistance during transport. These structural optimizations work together to enable the catalyst to exhibit more rapid reaction kinetics, thus significantly improving its OER catalytic activity and stability. The nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst was directly used as the working electrode for the OER reaction, and OER performance tests were conducted in an alkaline medium. The results showed that, compared with the cobalt-iron alloy catalyst, this catalyst not only exhibited superior OER activity, but also showed better OER performance at 1200 mA·cm⁻¹. -2 It exhibits excellent stability at current densities, with virtually no performance degradation after 120 hours of stability testing. Furthermore, the nickel nitrate etching method proposed in this invention was used to modify metal-organic frameworks (MOFs), metal sulfides, and metal phosphides electrocatalysts, resulting in significantly improved morphology, catalytic activity, and stability of the prepared catalysts. Compared to traditional OER catalyst preparation methods, the nickel nitrate etching method proposed in this invention offers advantages such as low cost, low energy consumption, ease of large-scale production, and wide applicability. Moreover, this method is versatile in preparing excellent transition metal OER catalysts, demonstrating great promise for industrial application in the field of water electrolysis for hydrogen production.

[0008] Another objective of this invention is to provide an application of nickel hydroxide / cobalt iron alloy nanocatalysts in the field of electrocatalysis.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0010] The preparation method of the nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst of the present invention includes the following steps:

[0011] S1, FeSO4·7H2O, CoSO4·7H2O, NH4H2PO4 and Na3(C6H5O7)·2H2O are dissolved in deionized water to form a mixed solution;

[0012] S2, using the cleaned and dried nickel foam as the working electrode, and using the solution in step S1 as the electrochemical deposition solution, constant current cathode deposition is performed for a certain time; then the obtained sample is washed with deionized water and dried to obtain the cobalt-iron alloy electrocatalyst.

[0013] S3. The cobalt-iron alloy electrocatalyst obtained in step S2 is placed in a nickel nitrate solution of a certain concentration and temperature. Taking advantage of the characteristic that iron is prone to electrochemical corrosion, it is spontaneously and uniformly corroded in the solution. After a certain corrosion time, the sample is washed and dried to obtain nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst.

[0014] In step S1 of this invention, the number of moles of FeSO4·7H2O is 1.0-4.0 mmol, the number of moles of CoSO4·7H2O is 0.2-2.5 mmol, the number of moles of NH4H2PO4 is 1.0-5.0 mmol, the number of moles of Na3(C6H5O7)·2H2O is 1.0-3.0 mmol, and the volume of deionized water is 50 mL.

[0015] The electrochemical deposition time described in this invention is 600-3600 s.

[0016] Preferably, the electrochemical deposition time of the present invention is 1800s.

[0017] The constant current cathode deposition current density described in this invention is -60 mA / cm². 2 .

[0018] The concentration of the nickel nitrate solution described in this invention is 0.02-0.12 mol / L.

[0019] Preferably, the concentration of the nickel nitrate solution of the present invention is 0.10 mol / L.

[0020] The cobalt-iron alloy electrocatalyst described in this invention has a corrosion time of 6-48 hours in nickel nitrate solution.

[0021] Preferably, the corrosion time of the cobalt-iron alloy electrocatalyst of the present invention in nickel nitrate solution is 12 hours.

[0022] The cobalt-iron alloy electrocatalyst described in this invention has a corrosion temperature of 25-55℃ in nickel nitrate solution.

[0023] Preferably, the corrosion temperature of the cobalt-iron alloy electrocatalyst of the present invention in nickel nitrate solution is 45°C.

[0024] The application of the nickel hydroxide / cobalt iron alloy nanosheet electrocatalyst prepared by the method of the present invention in the field of electrocatalysis.

[0025] The nickel nitrate etching method used in the preparation method of the present invention can also be used in the modification of metal-organic frameworks (MOFs), metal sulfides and metal phosphides electrocatalysts.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The electrocatalyst prepared by this invention exhibits an interlocking 3D porous nanosheet structure, which not only facilitates sufficient contact with the electrolyte solution but also reduces charge / mass transport resistance during the OER reaction, accelerating oxygen bubble diffusion and thus accelerating OER reaction kinetics. Furthermore, the interlocking nanosheet structure provides the catalyst with a stable structure.

[0028] 2. In the preparation method of the present invention, the uniform corrosion of iron on the surface of cobalt-iron alloy provides the necessary site for the uniform growth of nickel hydroxide, while the in-situ grown nickel hydroxide layer acts as a protective film, effectively preventing further corrosion of iron. This interaction greatly enhances the mechanical strength of the nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst, thereby endowing the catalyst with excellent stability under harsh conditions.

[0029] 3. In the corrosion process, the formation of nanosheets in this invention not only significantly shortens the charge and mass transport paths during OER, but also reduces the resistance during transport. These structural optimizations work together to make the catalyst exhibit more rapid reaction kinetics, thereby significantly improving catalytic activity and stability (see Table 1). The nickel hydroxide / cobalt-iron alloy electrocatalyst prepared in Example 2 exhibits excellent OER activity and stability, requiring only 193 mV overpotential to provide 10 mA cm⁻¹. -2 The current density and the overpotential of 313mV can provide 1200mA cm⁻¹. -2 After 120 hours of stability testing, the industrial-grade current density decreased by only 32 mA cm⁻¹. -2 However, a single cobalt-iron alloy electrocatalyst requires an overpotential as high as 274 mV to provide 10 mA cm⁻¹. -2 A current density of 445mV and an overpotential of 445mV are required to provide 1200mA cm⁻¹. -2 The catalyst achieved an industrial-grade current density, and its stability showed a significant decline within 20 hours. These results clearly demonstrate that the nickel hydroxide / cobalt-iron alloy electrocatalyst prepared in this invention possesses excellent OER activity and stability, and has great potential for industrial application.

[0030] 4. In the OER performance of the electrocatalysts prepared in Example 2 and Comparative Examples 1 to 3 of the present invention, the nickel hydroxide / cobalt-iron alloy electrocatalyst prepared in Example 2 (10 mA cm⁻¹) showed the best performance. -2 Overpotential: 193mV, Tafel slope: 13.9mVdec -1 Charge transfer resistance: 0.26Ω) Comparison Example 1 (10mA cm -2 Overpotential: 274mV, Tafel slope: 37.1mVdec -1 Charge transfer resistance: 1.42Ω), Comparative Example 2 (10mA cm -2 Overpotential: 213mV, Tafel slope: 25.9mVdec -1 Charge transfer resistance: 0.39Ω) and Comparative Example 3 (10mA cm) -2 Overpotential: 261mV, Tafel slope: 37.9mVdec -1 The electrocatalyst prepared with a charge transfer resistance of 0.78 Ω exhibited lower overpotential, Tafel slope, and charge transfer resistance. Furthermore, the OER performance of the electrocatalyst decreased when one of the metal elements nickel, cobalt, or iron was lacking, indicating a significant synergistic effect of nickel, cobalt, and iron in improving the OER performance of the electrocatalyst.

[0031] 5. The nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst prepared by the method of this invention was directly used as the working electrode for the OER reaction. OER performance was tested in an alkaline medium. The results showed that, compared with the cobalt-iron alloy catalyst, this catalyst not only exhibited superior OER activity, but also showed excellent OER performance at 1200 mA·cm⁻¹. -2 It exhibits excellent stability at current density, and its performance shows virtually no degradation after 120 hours of stability testing.

[0032] 6. The nickel nitrate etching method proposed in this invention can also be used to modify metal-organic frameworks (MOFs), metal sulfides, and metal phosphides electrocatalysts, resulting in significantly improved morphology, catalytic activity, and stability of the prepared catalysts. Compared with traditional OER catalyst preparation methods, the nickel nitrate etching method proposed in this invention has advantages such as low cost, low energy consumption, ease of large-scale production, and wide application range. Moreover, this method is versatile in preparing excellent transition metal OER catalysts and shows great promise for industrial application in the field of water electrolysis for hydrogen production. Attached Figure Description

[0033] Figure 1 Flowchart of the preparation process of nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst;

[0034] Figure 2 SEM image of the nickel hydroxide / cobalt-iron alloy nanosheets prepared in Example 2;

[0035] Figure 3 SEM image of the cobalt-iron alloy prepared in Comparative Example 1;

[0036] Figure 4 SEM image of iron / nickel foam corroded by nickel nitrate solution prepared in Comparative Example 2;

[0037] Figure 5 SEM image of cobalt / nickel foam etched by nickel nitrate solution prepared in Comparative Example 3;

[0038] Figure 6 OER polarization curves of the nickel hydroxide / cobalt iron alloy nanosheet electrocatalysts prepared in Examples 1 to 5;

[0039] Figure 7 Overpotential diagrams of the nickel hydroxide / cobalt-iron alloy nanosheet electrocatalysts prepared in Examples 1 to 5, required to drive the OER reaction at different current densities;

[0040] Figure 8 The nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst prepared in Example 2 and the cobalt-iron alloy prepared in Comparative Example 1 were tested at 1200 mA·cm⁻¹. -2 The OER reaction stability test curve under current density;

[0041] Figure 9 OER reaction polarization curves of the electrocatalysts prepared in Example 2 and Comparative Examples 1 to 3;

[0042] Figure 10 Electrochemical impedance spectroscopy (OER) spectra of the electrocatalysts prepared in Example 2 and Comparative Examples 1 to 3;

[0043] Figure 11 Nickel nitrate etching improves the morphology of FeOOH-MOF, promoting OER reaction activity and stability. Figures: a) SEM image of FeOOH-MOF; b) SEM image of FeOOH-MOF after nickel nitrate etching; c) OER reaction polarization curve of the electrocatalyst; d) SEM image of FeOOH-MOF and FeOOH-MOF after nickel nitrate etching at 710 mA·cm⁻¹. -2 OER reaction stability test curves at current density;

[0044] Figure 12 Nickel nitrate corrosion method improves Fe 1-x The morphology of S promotes the activity and stability of OER reaction. (Figure a) Fe1-x SEM image of S; b) Fe after nickel nitrate corrosion. 1-x SEM image of S; c) Polarization curve of OER reaction of electrocatalyst; d) Fe 1-x S at 1200 mA·cm -2 OER reaction stability test curves at current density and Fe after nickel nitrate corrosion 1-x S at 1300 mA·cm -2 OER reaction stability test curves at current density;

[0045] Figure 13 Nickel nitrate etching improves the morphology of FeP4 and promotes OER reaction activity and stability. Figures: a) SEM image of FeP4; b) SEM image of FeP4 after nickel nitrate etching; c) OER reaction polarization curve of the electrocatalyst; d) FeP4 and FeP4 after nickel nitrate etching at 1258 mA·cm⁻¹. -2 OER reaction stability test curves at current density. Detailed Implementation

[0046] The following embodiments, comparative examples, and extended application examples will further illustrate the present invention, but the content of the present invention is not limited to these embodiments, comparative examples, and extended application examples.

[0047] Example 1

[0048] Step 1: Cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed with hydrochloric acid, deionized water and 95% ethanol for 5 minutes to remove oxides and impurities from the surface, and then dried at 60°C for later use.

[0049] Step 2: Dissolve 1.0 mmol FeSO4·7H2O, 0.2 mmol CoSO4·7H2O, 1.0 mmol NH4H2PO4 and 1.0 mmol Na3(C6H5O7)·2H2O in 50 mL of deionized water at room temperature and stir until homogeneous.

[0050] Step 3: Immerse the cleaned and dried nickel foam, which serves as the working electrode, into the above solution. The effective geometric area of ​​the working electrode is 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 Deposited at a constant current density for 600 s; the obtained sample was taken out, washed with deionized water and dried at 60 °C to obtain a cobalt-iron alloy.

[0051] Step 4: Place the cobalt-iron alloy in 0.02 mol·L⁻¹ -1 The nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst was obtained by corrosion reaction in nickel nitrate solution at 25°C for 6 hours, followed by washing with deionized water and drying at 60°C.

[0052] The preparation flow chart of the nickel hydroxide / cobalt iron alloy nanosheet electrocatalyst is as follows: Figure 1 As shown.

[0053] Example 2

[0054] Step 1: Cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed with hydrochloric acid, deionized water and 95% ethanol for 5 minutes to remove oxides and impurities from the surface, and then dried at 60°C for later use.

[0055] Step 2: Dissolve 3.5 mmol FeSO4·7H2O, 1.0 mmol CoSO4·7H2O, 4.5 mmol NH4H2PO4 and 2.5 mmol Na3(C6H5O7)·2H2O in 50 mL of deionized water at room temperature and stir until homogeneous.

[0056] Step 3: Immerse the cleaned and dried nickel foam, which serves as the working electrode, into the above solution. The effective geometric area of ​​the working electrode is 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 The sample was deposited at a constant current density for 1800 s; the obtained sample was taken out, washed with deionized water and dried at 60 °C to obtain a cobalt-iron alloy.

[0057] Step 4: Place the cobalt-iron alloy in 0.10 mol·L⁻¹ -1 The nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst was obtained by corrosion reaction in nickel nitrate solution at 45°C for 12 hours, followed by washing with deionized water and drying at 60°C.

[0058] Example 3

[0059] Step 1: Cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed with hydrochloric acid, deionized water and 95% ethanol for 5 minutes to remove oxides and impurities from the surface, and then dried at 60°C for later use.

[0060] Step 2: Dissolve 2.0 mmol FeSO4·7H2O, 0.4 mmol CoSO4·7H2O, 2.0 mmol NH4H2PO4 and 2.0 mmol Na3(C6H5O7)·2H2O in 50 mL of deionized water at room temperature and stir until homogeneous.

[0061] Step 3: Immerse the cleaned and dried nickel foam, which serves as the working electrode, into the above solution. The effective geometric area of ​​the working electrode is 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 Deposited at a constant current density for 2400 s; the obtained sample was taken out, washed with deionized water and dried at 60 °C to obtain a cobalt-iron alloy.

[0062] Step 4: Place the cobalt-iron alloy in 0.05 mol·L⁻¹ -1 The nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst was obtained by corrosion reaction in nickel nitrate solution at 35°C for 24 hours, followed by washing with deionized water and drying at 60°C.

[0063] Example 4

[0064] Step 1: Cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed with hydrochloric acid, deionized water and 95% ethanol for 5 minutes to remove oxides and impurities from the surface, and then dried at 60°C for later use.

[0065] Step 2: Dissolve 4.0 mmol FeSO4·7H2O, 1.5 mmol CoSO4·7H2O, 5.0 mmol NH4H2PO4 and 3.0 mmol Na3(C6H5O7)·2H2O in 50 mL of deionized water at room temperature and stir until homogeneous.

[0066] Step 3: Immerse the cleaned and dried nickel foam, which serves as the working electrode, into the above solution. The effective geometric area of ​​the working electrode is 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 Deposited at a constant current density for 3600 s; the obtained sample was taken out, washed with deionized water and dried at 60 °C to obtain a cobalt-iron alloy.

[0067] Step 4: Place the cobalt-iron alloy in 0.02 mol·L⁻¹ -1 The nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst was obtained by corrosion reaction in nickel nitrate solution at 55°C for 48 hours, followed by washing with deionized water and drying at 60°C.

[0068] Example 5

[0069] Step 1: Cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed with hydrochloric acid, deionized water and 95% ethanol for 5 minutes to remove oxides and impurities from the surface, and then dried at 60°C for later use.

[0070] Step 2: Dissolve 2.5 mmol FeSO4·7H2O, 2.5 mmol CoSO4·7H2O, 2.5 mmol NH4H2PO4 and 2.5 mmol Na3(C6H5O7)·2H2O in 50 ml of deionized water at room temperature and stir until homogeneous.

[0071] Step 3: Immerse the cleaned and dried nickel foam, which serves as the working electrode, into the above solution. The effective geometric area of ​​the working electrode is 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 The sample was deposited at a constant current density for 1800 s; the obtained sample was taken out, washed with deionized water and dried at 60 °C to obtain a cobalt-iron alloy.

[0072] Step 4: Place the cobalt-iron alloy in 0.12 mol·L⁻¹ -1 The nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst was obtained by corrosion reaction in nickel nitrate solution at 25°C for 36 hours, followed by washing with deionized water and drying at 60°C.

[0073] For the above embodiments 1-5, due to the standard potential of the iron electrode pair (Fe 2+ / Fe: -0.447V) is less than the standard potential of the cobalt electrode pair (Co 2+ / Co:-0.280V), in cobalt-iron alloys, iron is more prone to electrochemical corrosion.

[0074] Nickel nitrate solution is neutral to slightly acidic (pH = 6-7). Nitrate ions readily undergo reduction at the cathode during electrochemical corrosion, while iron undergoes oxidation at the anode. The electrochemical corrosion process follows these principles:

[0075] Anode: Fe(s) = Fe 2+ (aq)+2e -

[0076] Cathode: H2O(l) + NO3 - (aq)+2e - =2OH - (aq)+NO2- (aq)

[0077] Overall reaction: Fe(s) + NO3 - (aq) + H₂O(l) = Fe 2+ (aq) + 2OH - +NO2 - (aq).

[0078] Due to Ksp Ni(OH)2 / Ksp Fe(OH)2 =40.0, at this point, the order in which Fe(OH)2 and Ni(OH)2 precipitates form is no longer determined by the magnitude of the Ksp of the precipitate, but by the concentration of the metal cations. Because Ni 2+ The concentration is relatively high (0.02-0.12 mol·L⁻¹). -1 Therefore, Ni(OH)2 precipitate is preferentially formed, and the principle is as follows:

[0079] Ni 2+ (aq) + 2OH - (aq)=Ni(OH)2(s).

[0080] Uniform corrosion of iron and in-situ growth of nickel hydroxide form a nanosheet structure. The formation of nanosheets effectively increases the contact area between the electrocatalyst and the electrolyte, thereby improving the utilization rate of the catalyst's active sites. On the other hand, the ultrathin nanosheets facilitate rapid charge / mass transport and rapid bubble diffusion during the electrocatalytic process, thus giving the catalyst excellent OER performance.

[0081] Comparative Example 1

[0082] Step 1: Cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed with hydrochloric acid, deionized water and 95% ethanol for 5 minutes to remove oxides and impurities from the surface, and then dried at 60°C for later use.

[0083] Step 2: Dissolve 3.5 mmol FeSO4·7H2O, 1.0 mmol CoSO4·7H2O, 4.5 mmol NH4H2PO4 and 2.5 mmol Na3(C6H5O7)·2H2O in 50 mL of deionized water at room temperature and stir until homogeneous.

[0084] Step 3: Immerse the cleaned and dried nickel foam, which serves as the working electrode, into the above solution. The effective geometric area of ​​the working electrode is 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm-2 The sample was deposited at a constant current density for 1800 s; the resulting sample was taken out, washed with deionized water and dried at 60 °C to obtain a cobalt-iron alloy.

[0085] Comparative Example 2

[0086] Step 1: Cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed with hydrochloric acid, deionized water and 95% ethanol for 5 minutes to remove oxides and impurities from the surface, and then dried at 60°C for later use.

[0087] Step 2: Dissolve 3.5 mmol FeSO4·7H2O, 4.5 mmol NH4H2PO4 and 2.5 mmol Na3(C6H5O7)·2H2O in 50 mL of deionized water at room temperature and stir until homogeneous;

[0088] Step 3: Immerse the cleaned and dried nickel foam, which serves as the working electrode, into the above solution. The effective geometric area of ​​the working electrode is 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 The sample was deposited at a constant current density for 1800 s; the obtained sample was taken out, washed with deionized water and dried at 60 °C to obtain iron / nickel foam.

[0089] Step 4: Place the iron / nickel foam in 0.10 mol·L⁻¹ -1 The iron / nickel foam electrocatalyst was subjected to a corrosion reaction in a nickel nitrate solution at 45°C for 12 hours. After removal, it was washed with deionized water and dried at 60°C to obtain the nickel nitrate solution-corroded iron / nickel foam electrocatalyst.

[0090] Comparative Example 3

[0091] Step 1: Cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed with hydrochloric acid, deionized water and 95% ethanol for 5 minutes to remove oxides and impurities from the surface, and then dried at 60°C for later use.

[0092] Step 2: Dissolve 1.0 mmol CoSO4·7H2O, 4.5 mmol NH4H2PO4 and 2.5 mmol Na3(C6H5O7)·2H2O in 50 mL of deionized water at room temperature and stir until homogeneous;

[0093] Step 3: Immerse the cleaned and dried nickel foam, which serves as the working electrode, into the above solution. The effective geometric area of ​​the working electrode is 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 The sample was deposited at a constant current density for 1800 s; the resulting sample was removed, washed with deionized water, and dried at 60 °C to obtain cobalt / nickel foam.

[0094] Step 4: Place the cobalt / nickel foam in 0.10 mol·L⁻¹ -1 The cobalt / nickel foam electrocatalyst was subjected to a 12-hour corrosion reaction in a nickel nitrate solution at 45°C. After removal, it was washed with deionized water and dried at 60°C to obtain a cobalt / nickel foam electrocatalyst corroded by nickel nitrate solution.

[0095] Extended Application Example 1

[0096] Step 1: Synthesize FeOOH-MOF via a solvothermal method; first, cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed for 5 min with hydrochloric acid, deionized water, and 95% ethanol to remove oxides and impurities from its surface. It was then dried at 60 °C for later use. Next, 0.375 mmol FeCl2·4H2O and 0.2 mmol terephthalic acid were dissolved in 10 mL N,N-dimethylformamide, 1 mL ethanol, and 1 mL deionized water. After stirring until completely dissolved, the solution was transferred to a 20 mL polytetrafluoroethylene-lined reactor. The cleaned nickel foam was then placed in the reactor containing the solution and reacted at 120 °C for 3 h. Finally, the resulting product was washed three times alternately with ethanol and deionized water and dried at 60 °C for 8 h to obtain FeOOH-MOF.

[0097] Step 2: Place FeOOH-MOF in 0.10 mol·L⁻¹ -1 The FeOOH-MOF electrocatalyst was obtained by corrosion in nickel nitrate solution at room temperature for 12 hours, followed by washing with deionized water and drying at 60°C.

[0098] Extended Application Example 2

[0099] Step 1: Synthesize Fe by electrodeposition 1-x S; First, cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1The nickel foam was ultrasonically washed for 5 min with hydrochloric acid, deionized water, and 95% ethanol to remove oxides and impurities from its surface, and then dried at 60°C for later use. Next, 3.5 mmol FeSO4·7H2O, 2.5 mmol Na3(C6H5O7)·2H2O, 4.5 mmol NH4H2PO4, and 2.5 mmol Na2S·9H2O were dissolved in 50.0 mL of deionized water to prepare the electrodeposition solution. Immediately afterwards, the cleaned and dried nickel foam was used as the working electrode and immersed in the above solution. The effective geometric area of ​​the working electrode was 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 Deposition was performed at a constant current density for 1800 s; the resulting sample was removed, washed with deionized water, and dried at 60 °C to obtain Fe. 1-x S.

[0100] Step 2: Add Fe 1-x S was placed in 0.10 mol·L⁻¹ -1 The Fe was subjected to a nickel nitrate solution corrosion reaction at room temperature for 12 hours. After removal, it was washed with deionized water and dried at 60°C to obtain Fe after nickel nitrate corrosion. 1-x S electrocatalyst.

[0101] Extended Application Example 3

[0102] Step 1: Synthesize FeP4 by electrodeposition; first, cut the nickel foam into 1×2cm pieces. 2 The effective geometric area is 1 cm². 2 , respectively with 1.0 mol·L -1 The nickel foam was ultrasonically washed for 5 min with hydrochloric acid, deionized water, and 95% ethanol to remove oxides and impurities from its surface, and then dried at 60°C for later use. Next, 3.5 mmol FeSO4·7H2O and 9.5 mmol NaH2PO2·H2O were dissolved in 50.0 mL of deionized water to prepare the electrodeposition solution. Immediately afterwards, the cleaned and dried nickel foam was used as the working electrode and immersed in the above solution. The effective geometric area of ​​the working electrode was 1 cm². 2 Silver / silver chloride and platinum sheets were used as reference and counter electrodes, respectively; at -60 mA·cm -2 The sample was deposited at a constant current density for 240 s; the obtained sample was taken out, washed with deionized water and dried at 60 °C to obtain FeP4.

[0103] Step 2: Place FeP4 in 0.10 mol·L⁻¹ -1 The FeP4 electrocatalyst was subjected to a 12-hour corrosion reaction in a nickel nitrate solution at room temperature. After removal, it was washed with deionized water and dried at 60°C to obtain the nickel nitrate-corroded FeP4 electrocatalyst.

[0104] SEM image of the electrocatalyst prepared in Example 2 ( Figure 2 As can be seen, the catalyst exhibits an interwoven 3D porous nanosheet structure. This structure not only facilitates sufficient contact with the electrolyte solution but also reduces the charge / mass transport resistance during the OER reaction, accelerating the diffusion of oxygen bubbles and thus accelerating the OER reaction kinetics. Furthermore, the interwoven nanosheet structure gives the catalyst a stable structure. However, from Comparative Example 1 (… Figure 3 Comparative Example 2 Figure 4 ) and Comparative Example 3 ( Figure 5 The SEM images of the prepared catalyst show that it basically lacks interwoven nanosheet structures. Such catalysts often suffer from limitations such as unsatisfactory catalytic activity and structural instability. The SEM results demonstrate that only when nickel, cobalt, and iron are present simultaneously can the morphology and structure of the catalyst be significantly improved.

[0105] Experimental Example 1: Electrochemical OER Property Test

[0106] The electrocatalysts prepared by the methods of Examples 1 to 5, Comparative Examples 1 to 3, and Extended Application Examples 1 to 3 were directly used as working electrodes for electrochemical OER reactions. Graphite rods and calibrated mercury / mercury oxide were used as counter electrodes and reference electrodes, respectively, and their electrochemical properties were tested on the Shanghai Chenhua Electrochemical Workstation.

[0107] Result: From Figure 6 , Figure 7 , Figure 8 As can be seen from Table 1, the nickel hydroxide / cobalt-iron alloy electrocatalyst prepared in Examples 1 to 5 of the present invention, especially Example 2, exhibits excellent OER activity and stability, providing 10 mA cm⁻¹ with only an overpotential of 193 mV. -2 The current density and the overpotential of 313mV can provide 1200mA cm⁻¹. -2 After 120 hours of stability testing, the industrial-grade current density decreased by only 32 mA cm⁻¹. -2 However, a single cobalt-iron alloy electrocatalyst requires an overpotential as high as 274 mV to provide 10 mA cm⁻¹. -2 A current density of 445mV and an overpotential of 445mV are required to provide 1200mA cm⁻¹. -2 The catalyst achieved an industrial-grade current density, and its stability showed a significant decline within 20 hours. These results clearly demonstrate that the nickel hydroxide / cobalt-iron alloy electrocatalyst prepared in this invention possesses excellent OER activity and stability, and has great potential for industrial application.

[0108] Table 1

[0109]

[0110] from Figure 9 , Figure 10 As can be seen from Table 2, among the electrocatalysts prepared in Example 2 and Comparative Examples 1 to 3 of this invention, the nickel hydroxide / cobalt-iron alloy electrocatalyst prepared in Example 2 (10 mA cm⁻¹) exhibits the best OER performance. -2 Overpotential: 193mV, Tafel slope: 13.9mV dec -1 Charge transfer resistance: 0.26Ω) Comparison Example 1 (10mA cm -2 Overpotential: 274mV, Tafel slope: 37.1mV dec -1 Charge transfer resistance: 1.42Ω), Comparative Example 2 (10mA cm -2 Overpotential: 213mV, Tafel slope: 25.9mV dec -1 Charge transfer resistance: 0.39Ω) and Comparative Example 3 (10mA cm) -2 Overpotential: 261mV, Tafel slope: 37.9mV dec -1 The electrocatalyst prepared with a charge transfer resistance of 0.78 Ω exhibited lower overpotential, Tafel slope, and charge transfer resistance. Furthermore, the OER performance of the electrocatalyst decreased when one of the metal elements nickel, cobalt, or iron was lacking, indicating a significant synergistic effect of nickel, cobalt, and iron in improving the OER performance of the electrocatalyst.

[0111] Table 2

[0112]

[0113]

[0114] from Figure 11 It can be seen that the morphology and structure of the FeOOH-MOF catalyst are significantly improved after nickel nitrate etching; and the FeOOH-MOF after nickel nitrate etching has the lowest OER onset potential and overpotential. Furthermore, compared with FeOOH-MOF, FeOOH-MOF after nickel nitrate etching exhibits excellent OER stability at 710 mA cm⁻¹. -2 After operating at the specified current density for 120 hours, no significant performance degradation was observed. This result indicates that the nickel nitrate etching method can significantly improve the morphology and structure of FeOOH-MOF, thereby enhancing the OER reaction activity and stability of the catalyst.

[0115] from Figure 12 It can be seen that after nickel nitrate corrosion, Fe 1-x The morphology and structure of the S catalyst were significantly improved; and the Fe catalyst after nickel nitrate corrosion was further enhanced. 1-x S has the lowest OER onset potential and overpotential. Additionally, Fe after nickel nitrate etching... 1-x S exhibits excellent OER stability at 1300 mA cm⁻¹ -2 After operating at a current density for 120 hours, there was no significant performance degradation, while Fe... 1-x S at 1200mA cm -2 The stability at the specified current density decreased significantly within 20 hours. This result indicates that the nickel nitrate etching method can significantly improve the stability of Fe. 1-x The morphology and structure of S can improve the OER reaction activity and stability of the catalyst.

[0116] from Figure 13 It can be seen that the morphology and structure of the FeP4 catalyst are significantly improved after nickel nitrate etching; and the FeP4 etched with nickel nitrate exhibits the lowest OER onset potential and overpotential. Furthermore, the FeP4 etched with nickel nitrate demonstrates excellent OER stability at 1258 mA cm⁻¹. -2 After operating at a current density of [value] for 120 hours, there was no significant performance degradation, while at 1258 mA cm [value]... -2 The stability of FeP4 under high current density showed a significant decline within 20 h. This result indicates that nickel nitrate etching can significantly improve the morphology and structure of FeP4, thereby enhancing the OER reaction activity and stability of the catalyst.

[0117] The above descriptions are merely several embodiments, comparative examples, and extended application examples of the present invention, and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with preferred embodiments, comparative examples, and extended application examples, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the disclosed structure and technical content to create equivalent embodiments without departing from the scope of the present invention. However, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention's technical solution shall still fall within the scope of the present invention's technical solution.

Claims

1. A method for preparing a nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst, characterized in that, Includes the following steps: S1, FeSO4·7H2O, CoSO4·7H2O, NH4H2PO4 and Na3(C6H5O7)·2H2O are dissolved in deionized water to form a mixed solution; The amount of FeSO4·7H2O is 1.0-4.0 mmol, the amount of CoSO4·7H2O is 0.2-2.5 mmol, the amount of NH4H2PO4 is 1.0-5.0 mmol, the amount of Na3(C6H5O7)·2H2O is 1.0-3.0 mmol, and the volume of deionized water is 50 mL. S2, Using the cleaned and dried nickel foam as the working electrode, and the solution from step S1 as the electrochemical deposition solution, at a current density of -60 mA / cm². 2 Constant current cathode deposition was performed for 600-3600 s; then the obtained sample was washed with deionized water and dried to obtain a cobalt-iron alloy electrocatalyst. S3. The cobalt-iron alloy electrocatalyst obtained in step S2 is placed in a 0.02-0.12 mol / L nickel nitrate solution. Taking advantage of the characteristic that iron is prone to electrochemical corrosion, it is spontaneously and uniformly corroded in the nickel nitrate solution at 25-55 ℃. After corrosion for 6-48 h, the sample is washed and dried to obtain nickel hydroxide / cobalt-iron alloy nanosheet electrocatalyst.

2. The preparation method according to claim 1, characterized in that, The electrochemical deposition time in step S2 is 1800 s.

3. The preparation method according to claim 1, characterized in that, The concentration of the nickel nitrate solution in step S3 is 0.10 mol / L.

4. The preparation method according to claim 1, characterized in that, The cobalt-iron alloy electrocatalyst described in step S3 is subjected to corrosion in nickel nitrate solution for 12 hours at a corrosion temperature of 45 °C.

5. The application of the nickel hydroxide / cobalt iron alloy nanosheet electrocatalyst prepared by the method described in claim 1 in the field of electrocatalysis.

6. The application of the nickel hydroxide / cobalt iron alloy nanosheet electrocatalyst as described in claim 5 in the modification of metal-organic frameworks (MOFs), metal sulfides and metal phosphides electrocatalysts.

Images