A non-precious metal-based self-supporting electrode, its preparation method, and its application in high-efficiency water electrolysis.

Abstract

This invention relates to a non-precious metal-based self-supporting electrode, its preparation method, and its application in high-efficiency water electrolysis. The self-supporting electrode comprises a non-precious metal substrate layer, and a transition layer and a catalytic active layer sequentially disposed on the surface of the non-precious metal substrate layer. The transition layer comprises NiFe nanoparticles; the catalytic active layer comprises CoFeLDH, which is arranged in a cactus-like structure as a nanoneedle array. A heterojunction interface exists between the transition layer containing NiFe nanoparticles and the catalytic active layer containing CoFeLDH. This invention exhibits a low oxygen evolution overpotential, high charge density, and excellent stability under operating conditions. Constructing a transition layer between the catalytic active layer and the nickel foam substrate optimizes the interfacial contact between the catalytic active layer and the substrate, contributing to a more uniform stress distribution and better interfacial adhesion, enhancing charge transfer and mass transfer, thereby achieving electrode interfacial stability.

Description

Technical Field

[0001] This invention relates to the field of hydrogen production technology through water electrolysis, and in particular to a non-precious metal-based self-supporting electrode, its preparation method, and its application in high-efficiency water electrolysis. Background Technology

[0002] Excellent renewable resources such as solar, wind, and hydropower, due to their volatility and intermittency, are insufficient to meet our ever-growing energy demands, necessitating solutions to their storage and conversion problems. Among these, hydrogen energy, with its ultra-high energy density, sustainability, and zero carbon emissions, is considered a green energy source that can be vigorously developed under a carbon-neutral environment. Currently, the bottleneck restricting hydrogen energy development lies in the difficulty and high cost of hydrogen production technology. Reducing the cost of hydrogen production to the level of coal and natural gas could potentially solve the global energy crisis. Existing water electrolysis hydrogen production technologies include four main routes: alkaline (ALK) water electrolysis, proton exchange membrane (PEM) water electrolysis, solid oxide electrolysis (SOEC) water electrolysis, and anion exchange membrane (AEM) water electrolysis. Compared to other electrolyzer technologies, ALK has a maximum single-cell capacity of 1500 standard cubic meters and a longer service life and lower annual maintenance costs compared to PEM. Therefore, investment cost and service life determine that ALK is the most suitable for large-scale water electrolysis hydrogen production applications.

[0003] However, the practical application of ALK water electrolysis for hydrogen production remains challenged by slow reaction kinetics and poor long-term performance at high current densities. Compared to the hydrogen evolution reaction (HER) occurring at the cathode, the oxygen evolution reaction (OER) occurring at the anode involves a four-electron transfer process, which is much slower and is the rate-determining step of the water electrolysis reaction. Therefore, to realize the commercialization of ALK water electrolysis for hydrogen production, it is necessary to design and develop highly efficient catalysts to lower the OER reaction energy barrier. However, the high cost and scarcity of currently available commercially available precious metal catalysts severely hinder their large-scale application in ALK water electrolysis for hydrogen production. Summary of the Invention

[0004] To address the above technical problems, this invention provides a non-precious metal-based self-supporting electrode, its preparation method, and its application in high-efficiency water electrolysis. The self-supporting alkaline water electrolysis electrode obtained by this invention exhibits a low oxygen evolution overpotential, high dielectric constant, and excellent stability under operating conditions. The preparation method is simple, controllable, and low-cost, and the electrode performance is excellent, making it suitable for practical industrial applications.

[0005] The first objective of this invention is to provide a non-precious metal-based self-supporting electrode, comprising a non-precious metal substrate layer, and a transition layer and a catalytic active layer sequentially disposed on the surface of the non-precious metal substrate layer;

[0006] The transition layer comprises NiFe unit cell nanoparticles;

[0007] The catalytic active layer includes CoFe LDH, which is composed of a nanoneedle array and exhibits a cactus-like morphology.

[0008] A heterojunction interface is formed between the transition layer containing NiFe unit cell nanoparticles and the catalytic active layer containing CoFe LDH through intermetallic forces.

[0009] In some embodiments of the present invention, the pore size of the transition layer and the catalytic active layer increases from small to large from the transition layer to the catalytic active layer.

[0010] The non-precious metal substrate layer includes nickel foam, nickel felt, nickel-iron foam, copper foam, or carbon paper.

[0011] In some embodiments of the present invention, the thickness of the transition layer is 0.5-1 μm; the thickness of the catalytic active layer is 10-15 μm.

[0012] The second objective of this invention is to provide a method for preparing the aforementioned non-noble metal-based self-supporting electrode, comprising the following steps:

[0013] A pretreated non-precious metal substrate is provided, as well as a metal seed solution obtained by mixing a nickel salt solution and an iron salt solution;

[0014] A non-noble metal substrate is placed in the metal seed solution, and NiFe unit cell nanoparticles are generated by in-situ etching on the surface of the metal substrate to form a transition layer.

[0015] Cobalt salt, iron salt, initiator, and surfactant are dissolved in a solvent to obtain a pre-solution;

[0016] A metal substrate with a transition layer formed on its surface is subjected to a hydrothermal reaction in a pre-solution to obtain a CoFeLDH nanoneedle array loaded on the NiFe unit cell nanoparticles, forming a catalytic active layer, thus obtaining a non-noble metal-based self-supporting electrode.

[0017] In some embodiments of the present invention, the non-precious metal substrate is degreased and surface oxide layer is removed. The process includes sequentially acid treatment, water washing, and vacuum drying of the non-precious metal substrate. The acid used for acid treatment is hydrochloric acid with a concentration of 4-5 wt%.

[0018] In some embodiments of the present invention, the nickel source in the nickel salt solution is selected from one or more of nickel nitrate hexahydrate, nickel chloride, nickel acetate, or nickel sulfate, and the concentration of the nickel source solution is 0.05 to 0.8 mol / L. Exemplarily, it can be 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, etc., or any range between any two values.

[0019] The iron salt in the iron salt solution is selected from one or more of ferrous sulfate heptahydrate, ferrous chloride, or ferrous nitrate; the concentration of the iron salt solution is 0.05-0.2 mol / L, and for example, it can be 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, etc., or any range between any two values;

[0020] The molar ratio of the nickel salt to the iron source is (1:1) to (4:1). For example, it can be 1:1, 2:1, 3:1, 4:1, or any range between any two values.

[0021] Furthermore, after the NiFe cell nanoparticles are generated on the surface of the non-precious metal substrate, they are rinsed multiple times with deionized water and ethanol and then dried in a vacuum drying oven.

[0022] In some embodiments of the present invention, the in-situ etching conditions are: room temperature 25°C, and a settling time of not less than 2 hours. Further, a settling time of 24 hours is preferred.

[0023] In some embodiments of the present invention, the cobalt salt is selected from one or more of cobalt nitrate hexahydrate, cobalt acetate, or cobalt chloride;

[0024] The iron salt is selected from one or more of ferric nitrate nonahydrate, ferric sulfate, or ferric chloride;

[0025] The inducing agent is selected from one or more of urea, sodium hydroxide, or ammonia solution;

[0026] The surfactant is selected from one or more of ammonium fluoride, disodium ethylenediaminetetraacetate, hexadecyltrimethylammonium bromide, or sodium dodecyl sulfonate.

[0027] In some embodiments of the present invention, the concentration of the iron salt is 0.003-0.015 mol / L, and exemplaryly, it can be 0.003 mol / L, 0.005 mol / L, 0.010 mol / L, 0.015 mol / L, or any range between any two values; the concentration of the cobalt salt is 0.015-0.15 mol / L, and exemplaryly, it can be 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.035 mol / L, 0.040 mol / L, 0.045 mol / L, 0.05 mol / L, 0.055 mol / L, 0.060 mol / L, 0.065 mol / L, 0.070 mol / L, 0.075 mol / L, 0.080 mol / L, 0.085 mol / L, 0.090 mol / L, etc. The concentrations are 0.095 mol / L, 0.10 mol / L, 0.15 mol / L, or any range between any two values; the concentration of the initiator is 0.025-0.25 mol / L, and for example, it can be 0.025 mol / L, 0.030 mol / L, 0.040 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.15 mol / L, 0.20 mol / L, 0.25 mol / L, etc., or any range between any two values; the concentration of the surfactant is 0.05-0.5 mol / L, and for example, it can be 0.05, 0.10, 0.15, 0.2, 0.3, 0.35, 0.4, 0.45, 0.5, etc., or any range between any two values.

[0028] The molar ratio of the iron salt, cobalt salt, initiator and surfactant is (1:1:9:18) to (1:10:9:18).

[0029] In some embodiments of the present invention, the hydrothermal reaction conditions are: hydrothermal reaction temperature of 100-150°C and reaction time of 2-24 hours.

[0030] Furthermore, after the CoFeLDH nanoneedle array is grown, it is rinsed multiple times with deionized water and ethanol and then dried in a vacuum drying oven to obtain the finished electrode.

[0031] A third objective of this invention is to provide a highly efficient water electrolysis device, including the aforementioned non-precious metal-based self-supporting electrode.

[0032] The technical solution of the present invention has the following advantages over the prior art:

[0033] 1. An in-situ etching method is used to generate a NiFe unit cell transition layer. Constructing a transition layer between the catalytic active layer and the nickel foam substrate can optimize the interfacial contact between the catalytic active layer and the substrate, which helps to achieve a more uniform stress distribution and better interfacial adhesion, enhance charge transfer and mass transfer, and thus achieve catalyst interfacial stability.

[0034] 2. A simple hydrothermal synthesis method was used to grow a CoFeLDH catalytic active layer on the NiFe unit cell transition layer. CoFeLDH exhibits a unique cactus-like structure composed of a plate-needle array, which has abundant active sites, greatly increasing the specific surface area of ​​the catalyst and enhancing its mass transfer capacity.

[0035] 3. During water electrolysis, the strong interaction between the NiFe unit cell transition layer and CoFeLDH leads to electron transfer at the interface. The Mott-Schottky heterojunction can also induce special interface effects such as electron coupling and defects, thereby optimizing the adsorption / desorption behavior of the catalyst for various reaction intermediates, increasing the number of reaction sites, and improving electrocatalytic performance.

[0036] 4. CoFeLDH / NiFe-NF exhibits faster reaction kinetics than single-phase NiFe-NF or CoFeLDH-NF, and demonstrates excellent high current density, low overpotential, and superior high current stability in simulated electrolytic cells.

[0037] 5. The pore size gradient transition layer of CoFeLDH / NiFe-NF increases structural stability, and the two-phase heterojunction interface induces the formation of an internal electric field to accelerate the transfer of space charge and stabilize the intermetallic synergistic effect. From the macroscopic structure to the microscopic structure, the OER catalytic activity and high current density durability of ALK water electrolysis are comprehensively optimized, thereby reducing the energy consumption of ALK water electrolysis. This makes it possible for the CoFeLDH / NiFe-NF catalyst to realize the transformation from laboratory to commercial application. Attached Figure Description

[0038] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0039] Figure 1 These are SEM images of comparative examples and embodiments of the present invention; wherein, (a) is comparative example 1, (b) is comparative example 2, and (c) is embodiment 1.

[0040] Figure 2 This is a TEM image of Embodiment 1 of the present invention.

[0041] Figure 3 These are XRD diagrams of the comparative examples and embodiments of the present invention.

[0042] Figure 4 These are (a) specific surface area diagrams and (b) pore size distribution diagrams of the comparative examples and embodiments of the present invention.

[0043] Figure 5 These are XPS high-resolution images of comparative examples and embodiments of the present invention. Among them, (a) is a high-resolution image of the Ni 2p orbital, (b) is a high-resolution image of the Co 2p orbital, and (c) is a high-resolution image of the O 1s orbital.

[0044] Figure 6 These are the (a) LSV curve, (b) Tafel curve, and (c) stability curve of the comparative examples and embodiments of the present invention.

[0045] Figure 7 These are (a) Nyquist plots and (b)-(d) Bode plots of the comparative examples and embodiments of the present invention.

[0046] Figure 8 The figures are (a) current density-voltage relationship curves of the embodiments and comparative examples of the present invention, and (b) running time-voltage relationship curves of Example 3.

[0047] Figure 9 These are SEM images of the comparative examples and embodiments of the present invention after oxygen evolution testing, wherein (a) is comparative example 1, (b) is comparative example 2, and (c) is embodiment 1. Detailed Implementation

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0049] An embodiment of the high-efficiency oxygen evolution non-precious metal-based self-supporting alkaline water electrolysis electrode of the present invention includes nickel foam, on which NiFe cell nanoparticles are grown, and the NiFe cell nanoparticles are covered with a CoFeLDH nanoneedle array. The NiFe cell nanoparticle transition layer is not only tightly bonded to the nickel foam substrate, but also tightly connected to the CoFe LDH catalytic active layer. The NiFe cell nanoparticle transition layer provides good adhesion between the catalyst and the substrate, increasing the structural stability of the catalyst, while the CoFe LDH catalytic active layer provides a large specific surface area for the catalyst, increasing the number of active sites and improving catalyst mass transfer. Furthermore, the heterojunction interface between the NiFe cell nanoparticle transition layer and the CoFe LDH catalytic active layer induces the formation of an internal electric field, accelerating the transfer of space charge, thereby enhancing the intrinsic catalytic activity of the electrode.

[0050] Specifically, the water electrolysis electrode prepared in this application is described in detail with reference to the following comparative examples and embodiments.

[0051] Comparative Example 1:

[0052] This comparative example provides a method for fabricating a Ni-based self-supporting electrode by in-situ etching a NiFe transition layer on nickel foam, including the following steps:

[0053] (1) Cut commercial 0.3mm thick nickel foam into 2cm*2cm pieces, place them in 4wt% hydrochloric acid and sonicate for 30min, then rinse with deionized water until neutral, sonicate with deionized water for 10min, then replace with clean deionized water and sonicate for 20min, and finally sonicate with anhydrous ethanol for 30min. Place them in a vacuum drying oven at 60℃ and dry for 12h for later use.

[0054] (2) Dissolve 20 mmol of Ni(NO3)2·6H2O in 100 mL of isopropanol and sonicate for 30 min to form solution A. Dissolve 3 mmol of FeSO4·7H2O in 33 mL of deionized water and stir for 5 min to form solution B.

[0055] (3) Pour solution B into solution A and mix for 1 min to obtain a mixed solution. Quickly immerse the 2cm*2cm foam nickel that has been pretreated in step (1) into the mixed solution. After standing at room temperature for 24 h, take out the foam nickel and rinse it with deionized water. Then rinse the foam nickel with anhydrous ethanol and put it into a vacuum drying oven. Dry it at 60°C for 12 h to obtain the foam nickel with in-situ etched NiFe transition layer.

[0056] Comparative Example 2:

[0057] This comparative example provides a method for preparing a Ni-based self-supporting electrode of CoFeLDH cactus balls synthesized hydrothermally on nickel foam, including the following steps:

[0058] (1) Cut commercial 0.3mm thick nickel foam into 2cm*2cm pieces, place them in 4wt% hydrochloric acid and sonicate for 30min, then rinse with deionized water until neutral, sonicate with deionized water for 10min, then replace with clean deionized water and sonicate for 20min, and finally sonicate with anhydrous ethanol for 30min. Place them in a vacuum drying oven and dry at 60℃ for 12h for later use.

[0059] (2) Dissolve 1.5 mmol of Co(NO3)2·6H2O, 0.3 mmol of Fe(NO3)3·9H2O, 2.7 mmol of urea and 5.6 mmol of ammonium fluoride in 35 mL of deionized water and stir for 10 min to form a mixed solution.

[0060] (3) Immerse the 2cm*2cm foam nickel that has been pretreated in step (1) into the mixed solution obtained in step (2), transfer the mixed solution to a 50mL polytetrafluoroethylene reactor liner, place it in a forced-air drying oven, react at 120℃ for 10h, and after the temperature drops to room temperature, take out the foam nickel, rinse it with deionized water, rinse the foam nickel with anhydrous ethanol, put it in a vacuum drying oven, dry it at 60℃ for 12h, and obtain foam nickel with CoFeLDH cactus balls grown on the surface.

[0061] Comparative Example 3:

[0062] A piece of Comparative Example 1 was cut into 2cm*2cm pieces and used as the anode. A commercial Raney nickel electrode was selected as the cathode, and a commercial composite diaphragm was selected as the diaphragm. The electrode was assembled in an electrolytic cell fixture. The electrolyte was a 30wt% KOH solution. The voltage of the electrolytic cell fixture was tested at different current densities at 80℃.

[0063] Comparative Example 4

[0064] A piece of Comparative Example 2 was cut into 2cm*2cm pieces and used as the anode. A commercial Raney nickel electrode was selected as the cathode, and a commercial composite diaphragm was selected as the diaphragm. The electrode was assembled in an electrolytic cell fixture. The electrolyte was a 30wt% KOH solution. The voltage of the electrolytic cell fixture was tested at different current densities at 80℃.

[0065] Example 1:

[0066] This embodiment provides a method for fabricating a high-efficiency oxygen-evolving non-noble metal Ni-based self-supporting electrode, as detailed below:

[0067] (1) Cut commercial 0.3mm thick nickel foam into 2cm*2cm pieces, place them in 4wt% hydrochloric acid and sonicate for 30min, then rinse with deionized water until neutral, sonicate with deionized water for 10min, then replace with clean deionized water and sonicate for 20min, and finally sonicate with anhydrous ethanol for 30min. Place them in a vacuum drying oven and dry at 60℃ for 12h for later use.

[0068] (2) Dissolve 20 mmol of Ni(NO3)2·6H2O in 100 mL of isopropanol and sonicate for 30 min to form solution A. Dissolve 3 mmol of FeSO4·7H2O in 33 mL of deionized water and stir for 5 min to form solution B.

[0069] (3) Pour solution B into solution A and mix and stir for 1 min to obtain a mixed solution. Quickly immerse the 2cm*2cm foam nickel that has been pretreated in step (1) into the above mixed solution. After standing at room temperature for 24 h, take out the foam nickel and rinse it with deionized water. Then rinse the foam nickel with anhydrous ethanol and put it into a vacuum drying oven. Dry it at 60℃ for 12 h for later use to obtain the foam nickel with in-situ grown NiFe cell transition layer.

[0070] (4) Dissolve 1.5 mmol of Co(NO3)2·6H2O, 0.3 mmol of Fe(NO3)3·9H2O, 2.7 mmol of urea and 5.6 mmol of ammonium fluoride in 35 mL of deionized water and stir for 10 min to form a mixed solution.

[0071] (5) Immerse the nickel foam with the in-situ grown NiFe cell transition layer obtained in step (3) into the mixed solution obtained in step (4), transfer the mixed solution to a 50 mL polytetrafluoroethylene reactor liner, place it in a forced-air drying oven, react at 120 °C for 10 h, and after the temperature drops to room temperature, take out the nickel foam and rinse it with deionized water, then rinse the nickel foam with anhydrous ethanol, and put it in a vacuum drying oven at 60 °C for 12 h to obtain a high-efficiency oxygen-evolving non-precious metal Ni-based self-supporting electrode.

[0072] Example 2:

[0073] Example 1 was cut into 2cm*2cm pieces and used as the anode. A commercial Raney nickel electrode was selected as the cathode, and a commercial Agfa220 composite diaphragm was selected as the diaphragm. These were assembled in an electrolytic cell fixture. The electrolyte was a 30wt% KOH solution. The voltage of the electrolytic cell fixture was tested at 80°C under different current densities. The experimental results are shown in Table 4. Figure 8 .

[0074] Example 3:

[0075] Two foamed nickel electrodes obtained in Example 1 were cut into 2cm*2cm pieces and used as the anode and cathode, respectively. A commercially available composite separator, Agfa220, was selected as the separator. The electrodes were assembled in an electrolytic cell fixture. The electrolyte was a 30wt% KOH solution, and the electrolysis was carried out at 80°C and 3000 A / m. 2 Long-term stability tests and start-stop experiments were conducted at a current density of [value missing], and the voltage change curve of the fixture over time was recorded. The experimental results are shown in Table 4. Figure 8 .

[0076] To clearly observe the structural morphology of the synthesized electrodes and their formation process, SEM and TEM characterization techniques were used to analyze the morphology of the NiFe-NF electrode with NiFe unit cell nanoparticles grown on nickel foam, the CoFeLDH-NF electrode with CoFeLDH nanoneedle arrays grown on nickel foam, and the final CoFeLDH / NiFe-NF electrode with a transition layer. Figure 1 The images shown in Figures 1 and 2 are SEM images of the Ni-based self-supporting electrodes prepared in Comparative Example 1, Comparative Example 2, and Example 1, respectively. Figure 1 As can be seen in Figure a, in Comparative Example 1, the electrode is formed by the growth of spindle-shaped unit cell particles on nickel foam, creating a uniform and dense nanolayer; as shown in Figure a. Figure 1 As shown in Figure b, in Comparative Example 2, the electrode consists of a nanosheet array grown on nickel foam. The top of the array is composed of fine nanoneedles, which aggregate to form spiky cacti, significantly increasing the electrode's specific surface area. The transformation of the array from nanosheets to nanoneedles facilitates charge transport. Figure 1 Figure c shows the electrode obtained in Example 1. It can be seen that the electrode surface is uniformly covered with spiky cacti, indicating that the regeneration of CoFeLDH on the NiFe nanolayer can be more uniform. Figure 2 The TEM image of Example 1 confirms that the surface-grown spiny cactus CoFeLDH is composed of nanosheets and nanoneedles. The structural characterization of the electrode indicates that the presence of the nano-transition layer increases the bonding force between CoFeLDH and the nickel foam substrate, which is beneficial for further increasing the specific surface area and the exposure of active sites.

[0077] To better understand the evolution of crystal structure during electrode synthesis, XRD characterization was used for further analysis. For example... Figure 3 As shown, the crystallinity of the electrodes in Comparative Example 1, Comparative Example 2, and Example 1 is excellent, perfectly matching the standard card, proving the successful growth of NiFe and CoFeLDH. In Example 1, the peak intensity of NiFe is weakened, which is due to the growth of CoFeLDH partially covering the NiFe signal. From the N2 adsorption-desorption isotherm and pore size distribution diagram, it can be seen that... Figure 4 In Table 1 (ab), the NiFe-NF electrode in Comparative Example 1 has the smallest specific surface area, while the CoFeLDH / NiFe-NF electrode in Example 1 has the largest specific surface area. Specific values ​​can be found in Table 1. The electrode in Example 1 was measured to have the largest specific surface area of ​​24.398 m². 2 g -1 Pore ​​size analysis reveals its mesoporous nature, with a maximum porosity of 0.037 cc g. -1 High specific surface area and large porosity provide abundant active regions between the electrode and electrolyte, which is beneficial for electron migration.

[0078] The electronic structure of a catalyst directly affects the electrochemical reaction; therefore, XPS analysis was used to investigate the surface chemical state of the catalyst. For example... Figure 5 As shown in Figure a, the Ni 2p binding energy position in CoFeLDH / NiFe-NF undergoes a significant positive shift (0.33 eV). This is because the formation of the heterojunction modulates the electronic configuration around Ni, reducing its surrounding electron density. Fitting calculations show that the Ni 2p binding energy in CoFeLDH / NiFe-NF and NiFe-NF... 3+ / Ni 2+ The peak areas were 0.46 and 0.25, respectively (Table 2), indicating that Ni in CoFeLDH / NiFe-NF... 3+ The increased content is due to the decrease in electron density around Ni in some Ni components. 2+ Oxidized into Ni 3 + .like Figure 5 As shown in Figure b, compared with the Co 2p orbitals of CoFeLDH-NF, the Co 2p binding energy of CoFeLDH / NiFe-NF also shows a significant negative shift (0.52 eV), indicating an increase in the electron cloud density around Co 2p. The Co 2p binding energy of CoFeLDH / NiFe-NF and CoFeLDH-NF was calculated using fitting. 3+ / Co 2+ The peak areas were 1.42 and 3.1 (Table 2), respectively, indicating that after the formation of the heterojunction, electrons transferred from NiFe to CoFeLDH, thereby increasing the electron cloud density around Co and leading to a large amount of Co. 3+ Reduced to Co 2+ In Example 1, electrons are transferred from NiFe to CoFeLDH, thereby optimizing the electronic structure of the heterostructure interface and contributing to improved OER activity. Figure 5 The high-resolution spectrum of O1s shown in Figure c can be fitted with three main peaks at 529.75 eV, 531.41 eV, and 532.47 eV, indicating lattice oxygen (O). L ), surface reactive oxygen vacancies (O V ) and surface physically adsorbed oxygen (O C Based on the peak area ratio, it can be determined that O in CoFeLDH / NiFe-NF... L It was 4.31%, O V The oxygen vacancy rate was 69.96%, which is more than that in NiFe-NF (Table 2), and CoFeLDH-NF had the most oxygen vacancies. This indicates that the formation of CoFeLDH can introduce a large number of oxygen vacancies, which is beneficial to the adsorption of OH- on the electrode surface, thereby effectively improving the OER reaction activity.

[0079] For alkaline oxygen evolution (OER) performance testing and impedance (EIS) testing, electrocatalytic oxygen evolution tests were conducted in a standard three-electrode system using 1.0 MkOH as the electrolyte to investigate the influence of the heterojunction interface on OER performance. The working electrode was the electrode prepared in Comparative Examples 1-2 and Example 1, the counter electrode was a graphite rod, and the reference electrode was a Hg / HgO electrode. The electrode was placed in a 1 mol / L KOH electrolyte at room temperature (25°C). Cyclic voltammetry (CV) activation was performed using an Autolab electrochemical workstation. The working electrode was activated at 50 mV s⁻¹ within a voltage range of -1.6 to 0.9 V vs. RHE. -1 The scan rate was cycled 30 times for activation. All linear sweep voltammetry (LSV) tests were performed; to avoid interference from oxidation peaks, the LSV curves for all electrodes were obtained via negative scans, with a test voltage range of 0–1.1 V vs. RHE. EIS was performed from 100 kHz to 0.01 Hz, with an AC potential amplitude of 5 mV. In-situ impedance Bode plots were obtained in the voltage range of 0–0.6 V.

[0080] LSV curve as follows Figure 6 As shown in Figure a, it can be seen that Example 1 achieves the highest current density, requiring only an overpotential of 218mV to reach 100Am. -2 The current density was lower than the overpotential required for Comparative Example 1 (230 mV) and Comparative Example 2 (258 mV) (Table 4). This indicates that the presence of the transition layer greatly improves OER performance, while CoFeLDH can improve OER performance at high current density, and the synergistic effect of the heterojunction interface further enhances OER performance. Besides the overpotential indicating the catalytic performance of the electrode, the Tafel slope is also used to characterize the reaction kinetics during the OER process; a smaller Tafel slope indicates faster reaction kinetics. The Tafel slopes for Example 1, Comparative Example 1, and Comparative Example 2 were 47.7, 61.1, and 80.4 mV, respectively. -1 ( Figure 6 As shown in Figure b), Example 1 exhibits superior electrocatalytic activity, demonstrating that the heterojunction between the NiFe active layer and CoFeLDH significantly enhances the OER reaction kinetics. Electrode stability is crucial in practical applications, particularly at 1000 Am. -2 At the current density, the electrode of Example 1 can be maintained for 250 hours without significant attenuation. Figure 6 (As shown in c). The LSV curves before and after continuous stability testing were also recorded; the final LSV curve showed a slight decrease in the OER region compared to the initial LSV. Figure 6 As shown in the illustration in Figure c, the electrode of Example 1 exhibits excellent stability.

[0081] In electrocatalysis, the electron transfer rate has a significant impact on performance, and electrochemical impedance spectroscopy can be used to further investigate the OER kinetics of different catalysts. For example... Figure 7 The Nyquist plot of a was obtained under conditions of 1.524V (vs. RHE). All points obtained from the test were based on the equivalent circuit diagram ( Figure 7 (As shown in the inset a) can be fitted into three parts, including the electrolyte impedance R s and charge transfer impedance R ct =R ct1 +R ct2 (See Table 3). The charge transfer impedance of Example 1 was the lowest at 0.422 Ω, compared to 0.573 Ω in Comparative Example 1 and 0.713 Ω in Comparative Example 2, indicating rapid electron transfer in all three electrodes. The electrodes exhibit good mass transfer capacity and conductivity, with the fastest transfer observed in CoFeLDH / NiFe-NF. This rapid electron transfer effectively enhances catalytic performance. Since the electrocatalytic oxygen evolution process is typically accompanied by catalyst reconstruction, the speed of reconstruction also affects OER performance. To further investigate the synergistic effect between the NiFe active layer and CoFeLDH on the composite material's performance and the interfacial interaction process, the Bode plots of the synthesized catalysts were analyzed in detail. (See Table 3.) Figure 7 As shown in (b)-(d), Bode plots obtained from in-situ EIS testing of all electrodes reveal two stages of oxygen evolution evolution based on high and low frequencies: First, the electro-oxidation process of the catalyst occurs in the HF region, where surface oxidation reconstruction is completed. The interface corresponding to this stage is the interface between the catalyst and the DDL. After surface reconstruction, the OER process begins, occurring at the LF region interface formed between the reconstructed catalyst and the DDL. Therefore, it can be determined that between 0.924-1.274V, the phase angle of the electrode in Example 1 begins to decrease in the high-frequency region, indicating surface oxidation reconstruction, and no significant current is generated during this stage. When the potential reaches 1.299V, oxidation is complete, and the phase angle shifts from the high-frequency region to the low-frequency region, signifying the start of the OER process, at which point the current begins to increase significantly. Furthermore, as the potential increases, the phase angle in the low-frequency region gradually decreases, indicating the onset of a vigorous OER process. Similarly, the potentials at which surface oxidation reconstruction was completed in Comparative Example 1 and Comparative Example 2 electrodes were 1.374 V and 1.399 V, respectively, indicating a slower oxidation process, which increased the onset potential of OER. Analysis of the results further demonstrates a synergistic effect between the NiFe active layer and CoFeLDH, which can promote electrode surface reconstruction, improve reaction kinetics, and reduce the OER onset potential.

[0082] Regarding the electrolytic cell testing, the CoFeLDH / NiFe-NF composite electrode obtained in Example 1 was cut into 2cm*2cm pieces as the anode, and a commercial Raney nickel electrode was selected as the cathode; a commercial composite diaphragm was selected, and the two were assembled in the electrolytic cell testing device. The electrolyte was a 30wt% KOH solution, and the temperature was 80℃. The voltage of the electrolytic cell device was measured under different current densities. Figure 8 As shown in Figure a, at 3000 A / m 2 At the specified current densities, the assembled electrolytic cell voltages in Examples 2, 3, and 4 were 1.68V, 1.723V, and 1.725V, respectively; at 10000A / m 2 At the specified current densities, the assembled electrolytic cell voltages in Examples 2, 3, and 4 were 1.898V, 1.988V, and 2.028V, respectively. For stability testing, two 2cm*2cm CoFeLDH / NiFe-NF electrodes were used as the cathode and anode, respectively. A commercially available composite diaphragm was selected. The electrodes were assembled in an electrolytic cell testing apparatus. The electrolyte was a 30wt% KOH solution, the temperature was 80℃, and the current was 3000 A / m. 2 The system operated at current density for 176 hours, with a start-stop cycle every 8 hours, and the voltage of the electrolytic cell was recorded. Figure 8 As shown in Figure b, the voltage retention rate of Example 3 reached 90.4% after 175 hours, indicating that the CoFeLDH / NiFe-NF electrode still exhibits good stability under industrial current densities. To investigate the structural stability of the CoFeLDH / NiFe-NF electrode material, the electrode after OER testing was characterized by SEM, as shown below. Figure 9 As shown in (a)-(c), it can be seen that the NiFe active layer on the electrode surface of Comparative Example 1 is significantly detached, the electrode of Comparative Example 2 exhibits some detachment, while the electrode surface of Example 1 shows almost no detachment. This further demonstrates that the growth of CoFeLDH in these examples is beneficial to improving the stability of the electrode structure, and the interaction between the NiFe active layer and CoFeLDH can further enhance electrode stability. In short, the present invention's construction of a transition layer between the catalytic active layer and the nickel foam substrate optimizes the OER performance of water electrolysis, and can significantly improve the structural stability of the electrode under operating conditions, providing a feasible strategy for designing efficient non-precious metal-based self-supporting alkaline water electrolysis electrodes.

[0083] Table 1. BET specific surface area, pore size distribution, and pore volume of electrodes obtained in the comparative examples and embodiments of the present invention.

[0084]

[0085] Table 2 XPS peak area of ​​the comparative examples and embodiments of the present invention

[0086]

[0087]

[0088] Table 3. Resistance values ​​calculated from electrochemical impedance spectroscopy for the comparative examples and embodiments of the present invention (Rs: electrolyte resistance; Rct: charge transfer resistance).

[0089]

[0090] Table 4 Oxygen evolution performance of comparative examples and embodiments of the present invention

[0091]

[0092] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A non-noble metal based self-supporting electrode, characterized in that, The non-noble metal-based substrate layer, the transition layer and the catalytically active layer are sequentially arranged on the surface of the non-noble metal-based substrate layer; The transition layer comprises NiFe unit cell nanoparticles; The catalytically active layer comprises CoFe LDH, the CoFe LDH is composed of a nanoneedle array, and has a cactus ball morphology; The transition layer comprising NiFe unit cell nanoparticles and the catalytically active layer comprising CoFe LDH form a heterojunction interface through intermetallic interaction; The preparation method of the non-noble metal-based self-supporting electrode comprises the following steps: A pretreated non-noble metal substrate is provided, 20 mmol of Ni(NO3)2·6H2O is dissolved in 100 mL of isopropyl alcohol and ultrasonically treated for 30 min to form solution A, 3 mmol of FeSO4·7H2O is stirred and dissolved in 33 mL of deionized water and stirred for 5 min to form solution B; solution B is poured into solution A and mixed and stirred for 1 min to obtain a mixed solution; the mixed solution is used as a metal seed solution; The non-noble metal substrate is placed in the metal seed solution, and NiFe unit cell nanoparticles are generated in situ on the surface of the metal substrate to form a transition layer; A cobalt salt, an iron salt, an inducing agent and ammonium fluoride are dissolved in a solvent to obtain a pre-solution; The metal substrate with the formed transition layer on the surface is subjected to a hydrothermal reaction in the pre-solution to obtain a CoFe LDH nanoneedle array loaded on the NiFe unit cell nanoparticles to form a catalytically active layer, thereby obtaining a non-noble metal-based self-supporting electrode; The non-noble metal substrate is a nickel foam.

2. The non-noble metal based self-supported electrode according to claim 1, wherein, The thickness of the transition layer is 0.5-1 μm, and the thickness of the catalytically active layer is 10-15 μm.

3. The non-noble metal based self-supported electrode according to claim 1, wherein, The in-situ etching conditions are: room temperature 25℃, and a standing time of not less than 2 hours.

4. The non-noble metal based self-supported electrode according to claim 1, wherein, The cobalt salt is selected from one or more of cobalt nitrate hexahydrate, cobalt acetate or cobalt chloride; The iron salt is selected from one or more of iron nitrate nonahydrate, iron sulfate or iron chloride; The inducing agent is selected from one or more of urea, sodium hydroxide or ammonia water.

5. The non-noble metal based self-supported electrode according to claim 1, wherein, The concentration of the iron salt is 0.003-0.015 mol / L, the concentration of the cobalt salt is 0.015-0.15 mol / L, the concentration of the inducing agent is 0.025-0.25 mol / L, and the concentration of ammonium fluoride is 0.05-0.5 mol / L; The molar ratio of the iron salt, the cobalt salt, the inducing agent and ammonium fluoride is (1:1:9:18)~(1:10:9:18).

6. The non-noble metal based self-supported electrode according to claim 1, wherein, The hydrothermal reaction conditions are: a hydrothermal reaction temperature of 100-150℃, and a reaction time of 2~24 h.

7. A device for efficiently electrolyzing water, characterized by The non-noble metal-based self-supporting electrode of any one of claims 1-6.

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