Preparation method of anion exchange membrane electrolyzer catalytic electrode, product and application thereof

Abstract

The application discloses a preparation method of a catalytic electrode of an anion exchange membrane electrolytic cell, a product and application thereof, and relates to the technical field of catalytic electrodes, in particular to a preparation method of a catalytic electrode of an anion exchange membrane electrolytic cell, a product and application thereof. On one hand, the non-noble metal material is used to reduce the cost, the method is simple and easy to operate; on the other hand, the catalyst is in-situ grown on the base material to avoid the use of ionomers, simplify the process, and the self-supporting catalytic electrode has more excellent durability. In addition, the nano-taper-nano-needle multi-level microstructure formed provides a larger active area for the electrode material, also makes the material more hydrophilic and less gas, and promotes the mass transfer in the reaction process. The multi-metal components introduced into the material also adjust the electronic structure of the material, which is beneficial to the improvement of the catalytic performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalytic electrode preparation, and particularly relates to a preparation method of a catalytic electrode of an anion exchange membrane electrolyzer, a product thereof and application. BACKGROUND

[0002] Anion exchange membrane water electrolysis (AEMWE) as a new water electrolysis technology can operate in a weak alkali solution or pure water environment, and its electrolyzer uses inexpensive structural components, so that the cost can be greatly reduced, and it has broad application prospects. However, the four-electron transfer process in the anode oxygen evolution reaction (OER) leads to slow intrinsic reaction kinetics, which requires a high overpotential, limiting the wide application of AEMWE. Therefore, it is necessary to design efficient catalysts to overcome the reaction energy barrier and catalyze the reaction to proceed quickly and efficiently.

[0003] Traditional noble metal-based catalysts (such as Pt / C and Ir / C electrocatalysts) exhibit excellent OER performance in alkaline media, but high cost, scarcity and poor stability are important factors limiting their large-scale commercial application. Therefore, researchers have tried many non-noble metal-based materials as OER catalysts for AEMWE, but there are always problems of low activity and poor durability, which are difficult to meet the actual application requirements.

[0004] Many existing powder-type catalysts usually need alkaline ionomers to adhere to the substrate material, and the adhesion between the catalyst coated by the ionomer and the gas / liquid diffusion layer is weak. During the reaction process, the catalyst is easy to fall off, which leads to a decrease in durability, and limits the transfer of electrons, resulting in poor conductivity and limited catalytic effect of the catalyst.

[0005] Therefore, how to prepare an efficient, stable and low-cost electrocatalyst is a technical problem to be solved. SUMMARY

[0006] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments.

[0007] As one aspect of the present application, the present application provides a preparation method of a catalytic electrode of an anion exchange membrane electrolyzer, which comprises,

[0008] (1) preparing an electrolyte: dispersing nickel salt, boric acid and ammonium salt in water to obtain an electrolyte;

[0009] (2) the product is obtained by placing the three electrodes into the electrolyte for electrochemical deposition, washing and drying the product, to obtain Ni / NF;

[0010] (3) the product is obtained by dispersing iron salt and cobalt salt in water, adding Ni / NF for soaking, heating reaction, washing and drying.

[0011] As a preferred scheme of the preparation method of the catalytic electrode of the anion exchange membrane electrolyzer, in step (1), the nickel salt comprises nickel chloride, the ammonium salt comprises ammonium chloride, and the molar ratio of the nickel salt, boric acid and ammonium salt is 1:1-1.5:1-2.

[0012] As a preferred scheme of the preparation method of the catalytic electrode of the anion exchange membrane electrolyzer, in step (1), the concentration of boric acid is 1-1.5M; the molar ratio of the nickel salt, boric acid and ammonium salt is 0.025:0.03mol:0.043; and the dispersion in water includes ultrasonic dispersion, heating to 55-60℃, and adjusting pH=4.

[0013] As a preferred scheme of the preparation method of the catalytic electrode of the anion exchange membrane electrolyzer, in step (2), the electrochemical deposition is carried out at a constant current of 20mA cm -2 for 8-10min.

[0014] As a preferred scheme of the preparation method of the catalytic electrode of the anion exchange membrane electrolyzer, in step (3), the iron salt is ferric chloride, and the cobalt salt is cobalt nitrate; and the molar ratio of the iron salt and cobalt salt is 1-1.5:1.

[0015] As a preferred scheme of the preparation method of the catalytic electrode of the anion exchange membrane electrolyzer, in step (3), the molar ratio of the iron salt and cobalt salt is 0.27:0.22; and the concentration of the iron salt is 18-20mM.

[0016] As a preferred scheme of the preparation method of the catalytic electrode of the anion exchange membrane electrolyzer, in step (3), the soaking time is 1-1.5h; and the heating reaction is carried out at 120℃ for 12-14h.

[0017] As a preferred scheme of the preparation method of the catalytic electrode of the anion exchange membrane electrolyzer, in step (2), the foam nickel is pretreated by immersing the foam nickel in a hydrochloric acid solution to remove surface oxidized impurities, then rinsing with ethanol and deionized water, and drying.

[0018] The application has the beneficial effects that the application develops a self-supporting anode catalytic electrode with nano-cone-nano-needle multi-level microstructure for anion exchange membrane electrolysis of water. First, using foam nickel as a base material, using iron, cobalt and nickel non-noble metals as raw materials, the catalyst is grown in situ on the base material by electrodeposition and hydrothermal synthesis. On the one hand, the use of non-noble metal materials reduces the cost, the method is simple and easy to operate; on the other hand, the in-situ growth of the catalyst on the base material avoids the use of ionomers, simplifies the process, and the self-supporting catalytic electrode has more excellent durability. In addition, the nano-cone-nano-needle multi-level microstructure formed provides a larger active area for the electrode material, also makes the material more hydrophilic and less gas, and promotes the mass transfer in the reaction process. The introduction of multi-metal components into the material also adjusts the electronic structure of the material, which is beneficial to the improvement of the catalytic performance. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed to be used in the embodiment description will be briefly introduced as follows:

[0020] Figure 1 SEM images of electrode materials before and after growing catalyst on foam nickel substrate.

[0021] Figure 2 XRD images of Ni-CoFe2O4 / NF catalytic electrode and comparative samples NiFe2O4 / NF, NiCi2O4 / NF.

[0022] Figure 3 XPS total spectrum and Fe 2p, Co 2p, Ni 2p sub-spectrum of Ni-CoFe2O4 / NF catalytic electrode and comparative samples NiFe2O4 / NF, NiCi2O4 / NF, Ni / NF, Ni Foam.

[0023] Figure 4 Water contact angle comparison chart of Ni-CoFe2O4 / NF catalytic electrode and Ni / NF and Ni Foam.

[0024] Figure 5 Performance and morphology comparison chart of Ni / NF electrode materials synthesized by different electrodeposition times.

[0025] Figure 6 Performance and morphology comparison chart of Ni / NF electrode materials synthesized at different current densities.

[0026] Figure 7 Performance and morphology comparison chart of Ni-CoFe2O4 / NF synthesized by hydrothermal synthesis at different temperatures.

[0027] Figure 8Performance and morphology comparison chart of Ni-CoFe2O4 / NF hydrothermally synthesized for different reaction times.

[0028] Figure 9 OER performance comparison chart of Ni-CoFe2O4 / NF catalytic electrode and comparative samples NiFe2O4 / NF, NiCo2O4 / NF, Ni / NF, Ni Foam in three-electrode system, including linear sweep voltammetry curve, Tafel slope, Cdl curve and electrochemical impedance chart.

[0029] Figure 10 Stability test curve of Ni-CoFe2O4 / NF catalytic electrode in three-electrode system under constant current density of 100 mA cm-2 and 500 mA cm-2, respectively. -2 -2 Stability test curve of Ni-CoFe2O4 / NF catalytic electrode in three-electrode system under constant current density of 100 mA cm-2 and 500 mA cm-2, respectively.

[0030] Figure 11 Performance comparison of anion exchange membrane electrolyzer assembled by taking Ni-CoFe2O4 / NF catalytic electrode and commercial catalyst RuO2 / NF as anode and Pt / C catalyst as cathode, including polarization curve and electrochemical impedance chart.

[0031] Figure 12 Stability test of anion exchange membrane electrolyzer assembled by taking Ni-CoFe2O4 / NF catalytic electrode as anode and Pt / C catalyst as cathode. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below.

[0033] Example 1:

[0034] Preparation steps of nickel-cobalt-iron three-metal self-supporting electrode (Ni-CoFe2O4 / NF) based on nickel foam substrate: foam nickel with size of 2 cm×3 cm, thickness of 1 mm, porosity of 95%, PPI of 110, surface density of 280 g m-2 and area density of 280 g m-2 was used as substrate. -2 -1 ​​The nickel foam was sonicated in HCl solution for 30 min to remove surface oxidized impurities, followed by alternating rinsing with ethanol and deionized water. Once the nickel foam reached neutral pH, it was transferred to a 60℃ vacuum drying oven for later use. In a beaker, 0.025 mol NiCl₂·6H₂O, 0.03 mol H₃₈O₃, and 0.043 mol NH₄Cl were added sequentially, followed by 30 mL H₂O. The mixture was sonicated for 30 min to ensure uniform dispersion. The sonicated solution was preheated in a 60℃ water bath until it became a completely transparent blue-green solution. NaOH was then added to adjust the pH to 4. The nickel foam pretreated with HCl was cut into 1 cm × 2 cm pieces. These pieces were clamped with electrode clips to serve as the working electrode; an Ag / AgCl electrode was used as the reference electrode; and a Pt sheet electrode was used as the counter electrode. The three electrodes were placed in the prepared electrolyte solution and subjected to an induction heating at 20 mA cm⁻¹. -2 Electrochemical deposition was performed under a constant current for 8 min. The deposited sample was rinsed with ethanol and deionized water, and then dried in an oven at 60°C for 30 min. The surface of the nickel foam turned black, and the sample was designated Ni / NF. 0.27 mmol FeCl3·6H2O, 0.22 mmol Co(NO3)2·4H2O, and 15 mL H2O were added sequentially to a beaker and sonicated in a water bath for 30 min. The homogenized solution was transferred to a 50 mL hydrothermal reactor, and the prepared 0.98 mmol Ni / NF was added and allowed to stand for 1 h. The hydrothermal reactor was then placed in a forced-air oven and reacted at 120°C for 12 h. The reacted sample was removed, and its surface was thoroughly cleaned with ethanol and deionized water. The cleaned sample was then dried in a vacuum oven at 90°C for 4 h to obtain the sample: Ni-CoFe2O4 / NF.

[0035] Example 2:

[0036] Preparation steps of nickel-cobalt-iron trimetallic self-supported electrode for AEM electrolytic cell membrane electrode: 1cm × 1cm nickel foam is placed in 3mol / L... -1The foam nickel was pretreated with HC1 solution for 30 min under ultrasonic to remove the surface oxidized impurities, and then washed with ethanol and deionized water alternately. After the foam nickel was washed to neutral, it was transferred to a 60°C vacuum drying oven for drying. 5 μL of Nafion solution (Nafion 117), 4 mg of Pt / C catalyst (40%) were added to 995 μL of ethanol solution as a slurry; the slurry was ultrasonically dispersed for 20 min in an ice bath to make the slurry uniformly dispersed. The slurry was taken by a pipette in 100 times (10 μL each time) and drop-coated on the HC1 pretreated foam nickel, and dried under an infrared lamp as the cathode material of the membrane electrode. The Ni-CoFe2O4 / NF synthesized in Example 1 was cut into a size of 1 cm x 1 cm and used as the anode material of the membrane electrode. The Sustainion X37-50 membrane was cut into a size of 2 cm x 2 cm and placed in 1 mol L -1 The membrane electrode was activated in KOH solution for 48 h as an anion exchange membrane in the membrane electrode. The membrane electrode was assembled by PTFE gaskets placed on the graphite bipolar plate, and a torque of 5 N·m was applied to the four corners of the clamp to keep the force uniform.

[0037] Comparative Example 1:

[0038] Preparation steps of the foam nickel pretreated with HC1: A foam nickel with a size of 2 cm x 3 cm was placed in 3 mol L -1 The foam nickel was pretreated with HC1 solution for 30 min under ultrasonic to remove the surface oxidized impurities, and then washed with ethanol and deionized water alternately. After the foam nickel was washed to neutral, it was transferred to a 60°C vacuum drying oven for drying. 5 μL of Nafion solution (Nafion 117), 4 mg of Pt / C catalyst (40%) were added to 995 μL of ethanol solution as a slurry; the slurry was ultrasonically dispersed for 20 min in an ice bath to make the slurry uniformly dispersed. The slurry was taken by a pipette in 100 times (10 μL each time) and drop-coated on the HC1 pretreated foam nickel, and dried under an infrared lamp as the cathode material of the membrane electrode. The Ni-CoFe2O4 / NF synthesized in Example 1 was cut into a size of 1 cm x 1 cm and used as the anode material of the membrane electrode. The Sustainion X37-50 membrane was cut into a size of 2 cm x 2 cm and placed in 1 mol L

[0039] Comparative Example 2:

[0040] Preparation steps of electrochemical deposition of nickel metal on the foam nickel: 0.025 mol of NiCl2·6H2O, 0.03 mol of H3BO3, and 0.043 mol of NH4Cl were sequentially added to a beaker, and then 30 mL of H2O was added and ultrasonically dispersed for 30 min. The ultrasonically dispersed solution was placed in a 60°C water bath for preheating, and then NaOH was added to adjust the pH to 4. The foam nickel pretreated with HC1 was cut into a size of 1 cm x 2 cm, and an electrode holder was used to hold the foam nickel as a working electrode; an Ag / AgCl electrode was used as a reference electrode; and a Pt sheet electrode was used as a counter electrode. The three electrodes were placed in the prepared electrolyte and electrochemically deposited for 8 min under a constant current of 20 mA cm -2 The sample obtained after deposition was washed with ethanol and deionized water, and then placed in an oven for drying at 60°C for 30 min. The surface of the foam nickel turned black, and the sample was recorded as Ni / NF.

[0041] Comparative Example 3:

[0042] Preparation steps of the sample obtained by reducing the synthesis time of Ni / NF: The electrolyte was prepared according to the steps in Comparative Example 2. The three electrodes were placed in the prepared electrolyte and electrochemically deposited at a constant current of 20 mA cm -2 for 4 min (the remaining steps were the same as Comparative Example 2). The sample obtained after deposition was rinsed clean with ethanol and deionized water, placed in an oven at 60 °C and dried for 30 min, the surface of the nickel foam turned black, and the sample was recorded as Ni / NF-1.

[0043] Comparative Example 4:

[0044] Preparation steps of the sample obtained by increasing the synthesis time of Ni / NF: The electrolyte was prepared according to the steps in Comparative Example 2. The three electrodes were placed in the prepared electrolyte and electrochemically deposited at a constant current of 20 mA cm -2 for 16 min (the remaining steps were the same as Comparative Example 2). The sample obtained after deposition was rinsed clean with ethanol and deionized water, placed in an oven at 60 °C and dried for 30 min, the surface of the nickel foam turned black, and the sample was recorded as Ni / NF-2.

[0045] Comparative Example 5:

[0046] Preparation steps of the sample obtained by reducing the current density of Ni / NF synthesis: The electrolyte was prepared according to the steps in Comparative Example 2. The three electrodes were placed in the prepared electrolyte and electrochemically deposited at a constant current of 10 mA cm -2 for 8 min (the remaining steps were the same as Comparative Example 2). The sample obtained after deposition was rinsed clean with ethanol and deionized water, placed in an oven at 60 °C and dried for 30 min, the surface of the nickel foam turned black, and the sample was recorded as Ni / NF-3.

[0047] Comparative Example 6:

[0048] Preparation steps of the sample obtained by increasing the current density of Ni / NF synthesis: The electrolyte was prepared according to the steps in Comparative Example 2. The three electrodes were placed in the prepared electrolyte and electrochemically deposited at a constant current of 40 mA cm -2 for 8 min (the remaining steps were the same as Comparative Example 2). The sample obtained after deposition was rinsed clean with ethanol and deionized water, placed in an oven at 60 °C and dried for 30 min, the surface of the nickel foam turned black, and the sample was recorded as Ni / NF-4.

[0049] Comparative Example 7:

[0050] Preparation procedure of the sample obtained by reducing the hydrothermal synthesis temperature of Ni-CoFe2O4 / NF: The solution was prepared according to the procedure of Example 1. The uniformly dispersed solution was transferred into a 50 mL hydrothermal reactor, and then the Ni / NF was put into the reactor and soaked for 1 h. The hydrothermal reactor was placed into a blast oven and reacted at 100 °C for 12 h (the remaining steps were the same as Example 1). The sample after reaction was taken out, and its surface was thoroughly cleaned with ethanol and deionized water. The cleaned sample was placed into a vacuum oven and dried at 90 °C for 4 h to obtain the sample: Ni-CoFe2O4 / NF-1.

[0051] Comparative Example 8:

[0052] Preparation procedure of the sample obtained by increasing the hydrothermal synthesis temperature of Ni-CoFe2O4 / NF: The solution was prepared according to the procedure of Example 1. The uniformly dispersed solution was transferred into a 50 mL hydrothermal reactor, and then the Ni / NF was put into the reactor and soaked for 1 h. The hydrothermal reactor was placed into a blast oven and reacted at 160 °C for 12 h (the remaining steps were the same as Example 1). The sample after reaction was taken out, and its surface was thoroughly cleaned with ethanol and deionized water. The cleaned sample was placed into a vacuum oven and dried at 90 °C for 4 h to obtain the sample: Ni-CoFe2O4 / NF-2.

[0053] Comparative Example 9:

[0054] Preparation procedure of the sample obtained by reducing the hydrothermal synthesis time of Ni-CoFe2O4 / NF: The solution was prepared according to the procedure of Example 1. The uniformly dispersed solution was transferred into a 50 mL hydrothermal reactor, and then the Ni / NF was put into the reactor and soaked for 1 h. The hydrothermal reactor was placed into a blast oven and reacted at 160 °C for 10 h (the remaining steps were the same as Example 1). The sample after reaction was taken out, and its surface was thoroughly cleaned with ethanol and deionized water. The cleaned sample was placed into a vacuum oven and dried at 90 °C for 4 h to obtain the sample: Ni-CoFe2O4 / NF-3.

[0055] Comparative Example 10:

[0056] Preparation procedure of the sample obtained by increasing the hydrothermal synthesis time of Ni-CoFe2O4 / NF: The solution was prepared according to the procedure of Example 1. The uniformly dispersed solution was transferred into a 50 mL hydrothermal reactor, and then the Ni / NF was put into the reactor and soaked for 1 h. The hydrothermal reactor was placed into a blast oven and reacted at 120 °C for 16 h (the remaining steps were the same as Example 1). The sample after reaction was taken out, and its surface was thoroughly cleaned with ethanol and deionized water. The cleaned sample was placed into a vacuum oven and dried at 90 °C for 4 h to obtain the sample: Ni-CoFe2O4 / NF-4.

[0057] Comparative Example 11:

[0058] Preparation steps of nickel cobalt bimetallic catalytic electrode material: 0.22 mmol Co(N03)2-4H20 and 15 mL H20 were added into a beaker and ultrasonic in water bath for 30 min. The uniformly dispersed solution was transferred to a 50 mL hydrothermal kettle, and then the Ni / NF was put into the kettle and soaked for 1 h. The hydrothermal kettle was placed in a blast oven and reacted at 120 °C for 12 h. The sample after reaction was taken out, and its surface was thoroughly cleaned with ethanol and deionized water. The cleaned sample was placed in a vacuum oven and dried at 90 °C for 4 h to obtain a sample, which was recorded as: NiC12O4 / NF.

[0059] Comparative example 12:

[0060] Preparation steps of nickel iron bimetallic catalytic electrode material: 0.27 mmol FeCl3-6H20 and 15 mL H20 were added into a beaker and ultrasonic in water bath for 30 min. The uniformly dispersed solution was transferred to a 50 mL hydrothermal kettle, and then the Ni / NF was put into the kettle and soaked for 1 h. The hydrothermal kettle was placed in a blast oven and reacted at 120 °C for 12 h. The sample after reaction was taken out, and its surface was thoroughly cleaned with ethanol and deionized water. The cleaned sample was placed in a vacuum oven and dried at 90 °C for 4 h to obtain a sample, which was recorded as: NiFe2O4 / NF.

[0061] Comparative example 13:

[0062] Preparation steps of commercial Ru02catalyst as anode for AEM electrolyzer membrane electrode: 1 cm x 1 cm size of nickel foam was immersed in 3 mol L -1The foam nickel was pre-treated with HCl solution for 30 min under ultrasonication to remove the surface-oxidized impurities, and then washed with ethanol and deionized water alternately. After the foam nickel was washed to neutral, it was transferred to a vacuum drying oven at 60 °C for drying. 5 μL of Nafion solution (Nafion 117), 4 mg of Pt / C catalyst (40%) were added to 995 μL of ethanol solution as a slurry; the slurry was ultrasonicated in an ice bath (40 kHz) for 20 min to disperse the slurry uniformly. The slurry was dropped onto the HCl pre-treated foam nickel using a pipette in 100 times (10 μL each time) and dried under an infrared lamp as the cathode material of the membrane electrode. The same size of foam nickel was pre-treated with HCl according to the above method and reserved. 5 μL of Nafion solution (Nafion 117), 4 mg of RuO2 catalyst (>95 wt%) were added to 995 μL of ethanol solution as a slurry; the slurry was ultrasonicated in an ice bath (40 kHz) for 20 min to disperse the slurry uniformly. The slurry was dropped onto the HCl pre-treated foam nickel using a pipette in 100 times (10 μL each time) and dried under an infrared lamp as the anode material of the membrane electrode. The Sustainion X37-50 membrane was cut into a size of 2 cm x 2 cm and placed in 1 mol L -1 The Sustainion X37-50 membrane was activated in KOH solution for 48 h as the anion exchange membrane in the membrane electrode. The membrane electrode was assembled by placing it on the graphite bipolar plate through a PTFE gasket, and a torque of 5 N·m was applied to the four corners of the clamp to keep the force uniform.

[0063] Material characterization: Figure 1 SEM images of the electrode material before and after the reaction (a) Comparative Example 1 (b) Comparative Example 2 (c) Example 1.

[0064] The foam nickel as a substrate material had a relatively smooth and flat surface before the reaction, as shown in Figure 1 a. After electrochemical deposition, a large number of conical structures were formed on the surface of the foam nickel, denoted as Ni / NF, as shown in Figure 1 b. Such structures have a small radius of curvature, which is conducive to the hydrophilicity and air repellency of the material and promotes mass transfer; compared with the foam nickel, Ni / NF has a larger active area. By further hydrothermal reaction of Ni / NF, a sample with a nano-cone-nanopin multi-level structure was synthesized, denoted as Ni-CoFe2O4 / NF, as shown in Figure 1 c. The structure has a smaller radius of curvature than Ni / NF, providing more active sites for the OER reaction and being more conducive to the removal of bubbles.

[0065] Figure 2 XRD test of the electrode material (a) Example 1 and Comparative Example 2 (b) Comparative Example 11 (c) Comparative Example 12.

[0066] To explore the structure and composition of the prepared electrode material, we carried out the corresponding XRD test, in Figure 2 a, the XRD pattern of Example 1 at 35.4°, 56.9° and 62.5° corresponds to the (311), (511) and (440) planes of CoFe2O4(PDF#22-1086) respectively. The XRD pattern of Comparative Example 2 at 44.5°, 51.8° and 76.3° corresponds to the (111), (200) and (220) planes of Ni(PDF#04-0850) respectively, and there are also corresponding peaks in the XRD pattern of Example 1, so it can be determined that the sample of Example 1 is composed of Ni-CoFe2O4. The XRD patterns of Comparative Examples 11 and 12 correspond well to the NiCo2O4(PDF#02-1074) and NiFe2O4(PDF#54-0964) PDF cards respectively, see Figure 2 b and Figure 2 c, it can be determined that the samples of Comparative Examples 11 and 12 are composed of NiCo2O4 and NiFe2O4.

[0067] Figure 3 For XPS test comparison of Example 1 and Comparative Examples 2, 11, 12 (a) total spectrum (b) Fe 2p spectrum (c) Co 2p spectrum (d) Ni 2p spectrum.

[0068] To explore the element composition and valence state of the material, we carried out the corresponding XPS test. First, Figure 3 a, the XPS total spectrum of Example 1 and Comparative Examples 2, 11, 12, from the total spectrum, it can be seen that Ni-CoFe2O4 / NF contains elements such as Ni, Co, Fe, O, etc. To explore the adjustment of each element to the electronic structure, we tested the spectrum of each element, according to the displacement of the element peak in the spectrum to judge the role of the incorporation of different elements to the adjustment of the electronic structure of the material. By deconvolution of the Fe 2p spectrum of Ni-CoFe2O4 / NF and NiFe2O4 / NF, see Figure 3 b, it can be seen that the Fe 2p spectrum is fitted into a pair of identifiable peaks: the iron 2P3 / 2 peak at 713.6 eV and the Fe 2P1 / 2 peak at 725.4 eV. The 2P 3 / 2 peak at 713.2 eV and the Fe2P 1 / 2 peak at 724.8 eV were deconvoluted, which clearly revealed the existence of Fe 3+ on the surface of the electrode. After adding Co element, the material Fe 3+characteristic peak to the low binding energy direction, the electron is transferred from Co to Fe, indicating the electron-rich structure of Fe, and the electron-rich structure of Fe site enhances the OER activity. Further peak processing of the Co 2p spectrum of Ni-CoFe2O4 / NF and NiCo2O4 / NF is shown in Figure 3 c. It can be seen that the Co 2p XPS spectrum can be deconvoluted into Co 3+ and Co 2+ two peaks. As can be clearly seen from the figure, compared with NiCo2O4 / NF, the Co 2p3 / 2 in Ni-CoFe2O4 / NF is positively shifted. Further confirms the electron transfer from Co to Fe. Finally, the Ni 2p spectrum of Ni-CoFe2O4 / NF and Ni / NF is peak processed, as shown in Figure 3 d. Although Ni-CoFe2O4 / NF has similar Ni 2+ (854.8eV) and Ni 3+ (855.4eV) chemical states as Ni / NF, due to the synergistic induction of Co and Fe, the Ni 3+ peak of Ni-CoFe2O4 / NF has a negative shift of 0.2eV compared with Ni / NF, which proves that the electron is also transferred to Ni. The incorporation of Co and Fe adjusts the electronic structure of the substrate Ni, promoting the electron transfer of the material.

[0069] Figure 4 The water contact angle test of Example 1 and Comparative Examples 1 and 2 is shown in (a) Comparative Example 1 (b) Comparative Example 2 (c) Example 1 before water contact (d) Example 1 after 1s of water contact.

[0070] To explore the relationship between the structure of the material and the hydrophobicity, we tested the water contact angle of the electrode material. First, the water contact angle of the nickel foam was tested, as shown in Figure 4 a. The water contact angle of the nickel foam is 106°, indicating that the nickel foam without any catalytic material grown thereon is a hydrophobic structure. The water contact angle of the material Ni / NF obtained by electrochemical deposition on the nickel foam was tested, as shown in Figure 4 b. The water contact angle is 39°. Combined with the SEM test results, it is shown that the conical structure electrochemically deposited on the nickel foam changes the hydrophobicity of the material, and the material exhibits hydrophilic properties. The water contact angle test of Ni-CoFe2O4 / NF obtained by further hydrothermal reaction on Ni / NF found that the water droplet was absorbed by the material at the moment of contact with the material, as shown in Figure 4 c, d. Combined with the SEM test results, it is shown that the nano-needle structure further grown on the nano-cone structure of Ni / NF has a smaller radius of curvature and is a more hydrophilic and air-repellent structure. The electrode material is converted into a super-hydrophilic material after having a nano-cone-nano-needle multi-level structure.

[0071] Figure 5 To compare the performance and morphology of Ni / NF synthesized at different electrodeposition times, (a) performance image, (b) SEM morphology of comparative example 2, (c) SEM morphology of comparative example 3, and (d) SEM morphology of comparative example 4.

[0072] To investigate the effect of electrodeposition time on the performance of synthesized Ni / NF electrode materials, we conducted experiments at a fixed current density (20 mA cm⁻¹). -2 Linear sweep voltammetry (LSV) curves were performed on electrode materials prepared at different reaction times under different conditions. The LSV curves of the electrode materials were measured at 1 mol L... -1 The test was conducted in KOH solution, using the synthesized electrode material as the working electrode, a platinum sheet electrode as the counter electrode, and an Hg / HgO electrode as the reference electrode. The voltage was set to 0–1 V (compared to the reversible hydrogen electrode (RHE)). Overpotential is a key parameter in the LSV curve for judging the OER performance of the electrode material; it is the difference between the potential required for the reaction to reach a specific current density and the theoretical potential. The theoretical voltage for the water electrolysis reaction is 1.23 V (vs. RHE), therefore η = E RHE -1.23V, E RHE This represents the actual required electrode potential. Generally, the overpotential of the catalyst at the same current density is compared on the LSV curve; a smaller overpotential value indicates better catalytic performance. Figure 5 As can be seen from a, at a current density of 20 mA / cm² -2 The electrode material obtained with a deposition time of 8 min exhibited the lowest overpotential and the best OER performance. To investigate the reason for the different OER performance of samples obtained at different deposition times, we performed SEM characterization on the samples. At a deposition time of 4 min, the sample surface showed only linear structures, as shown in the image. Figure 5 c. Failed to form a cone-shaped structure with optimal OER performance, see Figure 5 b. Further extending the electrodeposition time leads to cross-linking on the material surface, thereby disrupting the material's conical structure, see... Figure 5 d. The appearance of this cross-linked structure may be the reason for the decline in the performance of the electrode material.

[0073] Figure 6 To compare the performance and morphology of Ni / NF synthesized by electrodeposition under different current densities: (a) Performance image; (b) SEM morphology of Comparative Example 2; (c) SEM morphology of Comparative Example 5; (d) SEM morphology of Comparative Example 6.

[0074] To investigate the effect of the current density used in the electrodeposition reaction on the performance of the synthesized Ni / NF electrode material, we performed LSV curve tests on the electrode materials prepared at the optimal electrodeposition time (8 min) and different current densities. (At 20 mA cm⁻¹) -2 The synthesized Ni / NF still exhibits the best OER performance, see Figure 6 a. When the current density used for electrodeposition of the electrode material is reduced, the synthesized samples exhibit only a small number of conical structures, with the majority being "stone-like" structures with large radii of curvature. (See...) Figure 6 c. This structure is detrimental to the mass transfer process of the catalytic electrode, which may be the reason for the degradation of the electrode material performance. Furthermore, when the current density used for electrodeposition is increased, severe cross-linking occurs on the material surface, destroying the original conical structure. (See...) Figure 6 d, which leads to a decrease in the performance of the catalytic electrode.

[0075] Figure 7 To compare the performance and morphology of Ni-CoFe2O4 / NF synthesized hydrothermally at different temperatures: (a) Performance diagram; (b) SEM morphology of Example 1; (c) SEM morphology of Comparative Example 7; (d) SEM morphology of Comparative Example 8.

[0076] To investigate the effect of hydrothermal reaction temperature on the performance of synthesized Ni-CoFe2O4 / NF electrode materials, we performed LSV curve tests on the synthesized materials under different temperature conditions with the same reaction time (12 h). Figure 7 In section a, the Ni-CoFe2O4 / NF synthesized at 120℃ exhibited the lowest overpotential, i.e., the best OER performance. To investigate the reason for this performance difference, we also performed SEM tests on several comparative examples to study the relationship between their structure and performance. When the material was synthesized at 100℃, compared with the sample synthesized at 120℃, see [see section a]. Figure 7 b. The sparse distribution of nanoneedles on the surface may lead to a reduction in reactive sites, see [reference needed]. Figure 7 c. Increasing the reaction temperature disrupts the original conical structure, see... Figure 7 d, also caused a loss of active area, which in turn reduced the OER performance of the electrode material.

[0077] Figure 8 Comparison of the performance and morphology of Ni-CoFe2O4 / NF synthesized by hydrothermal synthesis after different reaction times: (a) Performance diagram; (b) SEM morphology of Example 1; (c) SEM morphology of Comparative Example 9; (d) SEM morphology of Comparative Example 10.

[0078] To explore the effect of hydrothermal reaction time on the performance of Ni-CoFe2O4 / NF electrode material, we tested the LSV curves of the materials synthesized under the optimal reaction temperature (120℃) and different reaction times. The results showed that the electrode material synthesized for 12h had the best OER performance. The study on the structure-activity relationship of the catalytic electrode by SEM test found that the material synthesized for 10h had more sparse nanocone and nanoneedle structure than the material synthesized for 12h, see Figure 8 b, c, the reduction of active sites caused the decline of the OER performance of the material. The nanoneedle formed by the electrode material synthesized for 16h was more elongated, which destroyed the original nanocone structure, see Figure 8 d, causing the decline of the material performance.

[0079] Figure 9 To compare the performance of Example 1 and Comparative Examples 1, 2, 11 and 12 in three-electrode test, (a) LSV curve, (b) Tafel slope, (c) Cdl curve and (d) electrochemical impedance diagram.

[0080] To explore the effect of the introduction of multi-metal components on the performance of the electrode material, we tested the LSV curves of the electrode material. In Figure 9 a, the overpotential of Ni-CoFe2O4 / NF was only 244mV at a current density of 100mA cm -2 , which was much lower than that of NiFe2O4 / NF (320mV), NiCo2O4 / NF (410mV) and Ni / NF (425mV) under the same current density, and the overpotential of the nickel foam was as high as 500mV. Therefore, Ni-CoFe2O4 / NF had the best OER catalytic performance. Compared with the nickel foam, the Ni / NF with cone structure significantly reduced the OER overpotential, which indicated that the cone structure played a promoting role in improving the electrochemical active area and mass transfer. Compared with NiCo2O4 / NF, NiFe2O4 / NF had more excellent OER catalytic activity, which indicated that Fe was the main active site. Compared with NiFe2O4 / NF, Ni-CoFe2O4 / NF had lower overpotential, which indicated that Co played a role in adjusting the electronic structure and further improving the OER catalytic activity, and the XPS test results also confirmed this conclusion. Compared with the nickel foam, Ni-CoFe2O4 / NF had significantly reduced overpotential at a current density of 100mA cm -2 , which indicated that the multi-level structure composed of nanocone and nanoneedle also had a promoting effect on OER.

[0081] The Tafel slope of the electrode material is calculated from the corresponding LSV curve, and the Tafel slope is inversely proportional to the charge transfer coefficient. The stronger the charge transfer ability of the catalyst, the smaller the Tafel slope obtained. In Figure 9 b, the sample Ni / NF with long nanotaper electrodeposited on the nickel foam has a smaller Tafel slope (89 mV dec -1 ) than the nickel foam (133 mV dec -1 ), and further hydrothermal synthesis of nanoneedle structure on the Ni / NF sample obtains Ni-CoFe2O4 / NF, NiFe2O4 / NF, NiCi2O4 / NF with smaller Tafel slopes of 30 mV dec -1 , 70 mV dec -1 , 75 mV dec -1 , respectively. This shows that both the nanotaper structure electrodeposited and the nanoneedle structure hydrothermally synthesized have a promoting effect on the OER electrochemical reaction kinetics of the catalyst, and Ni-CoFe2O4 / NF as an electrode material has the smallest Tafel slope, which shows that it has the best electrochemical reaction kinetics, which can be attributed to the incorporation of Co and Fe metal components to adjust the electronic structure of the Ni substrate.

[0082] The electrochemical active area (ECSA) of the electrode material is positively correlated with the double-layer capacitance value (the slope of the Cdl curve). The double-layer capacitance of the catalyst can be obtained by testing the CV curve at different scan rates (20 mV s -1 ~ 100 mV s -1 ) in the non-faradic region and the double-layer current density (i c ). The Cdl slope value of Ni-CoFe2O4 / NF (20.81 mF cm -2 ) is much higher than that of Ni / NF (8.72 mF cm -2 ) and nickel foam (6.96 mF cm -2 ), as shown in Figure 9 c. The Cdl slope of Ni / NF is slightly higher than that of nickel foam, which shows that the cone structure and needle structure synergistically provide a larger electrochemical active area. The larger the active area of the electrode material, the greater the surface density of the active sites, and also represents a higher mass transfer rate and more excellent overall catalytic activity.

[0083] At the same time, in order to further study the OER reaction kinetics of several catalytic electrode materials, their electrochemical impedance spectra were collected at a voltage of 300 mV overpotential, as shown in Figure 9d. Ni-CoFe2O4 / NF has the lowest charge transfer resistance (0.5Ω), lower than NiFe2O4 / NF (0.8Ω), NiCo2O4 / NF (1.5Ω), Ni / NF (2Ω) and nickel foam (2.8Ω), indicating that Ni-CoFe2O4 / NF has faster charge transfer during OER. This can be attributed to the modulation of electronic structure by charge transfer between different elements, and the acceleration of charge transfer by the multilevel structure.

[0084] Figure 10 This is a stability test graph from Example 1. To test the OER stability of Ni-CoFe2O4 / NF, a chronopotentiometric method was used at 1 mol L... -1 In KOH solution, under a fixed current density of 100 mA cm⁻¹ -2 and 500mA cm -2 The Ni-CoFe2O4 / NF catalytic electrode was tested under the following conditions: 100 mA cm⁻¹. -2 The voltage remained constant at 1.7V for 100 hours without decay at a current density of 500mA cm⁻¹. -2 The voltage remained constant at 1.6V for 100 hours without decay under the given current density. Figure 10 This confirms that the Ni-CoFe2O4 / NF self-supporting catalytic electrode has good stability.

[0085] Figure 11 The following are comparison diagrams of the performance of the AEM electrolyzers in Example 2 and Comparative Example 13: (a) polarization curve and (b) electrochemical impedance diagram.

[0086] To explore the commercial application potential of the Ni-CoFe2O4 / NF electrode material, we conducted performance tests on it using an AEM electrolytic cell. The polarization curves of the electrolytic cell were obtained with alkali solution introduced on the anode side at a flow rate of 8 ml / min. -1 The torque is 5 Nm -1 The tests were conducted under experimental conditions at 80℃. We compared the performance of AEM electrolyzers using a commercial Pt / C catalyst as the cathode and Ni-CoFe2O4 / NF electrode material and RuO2 / NF commercial electrode material as the anode, respectively. The polarization curves are shown in [Figure number missing]. Figure 11 a. The electrolyzer using Ni-CoFe2O4 / NF electrode material as the anode exhibits excellent water electrolysis performance, reaching 1000 mA cm⁻¹ at a voltage of 1.76 V. -2 The industrial-grade current density is superior to that of commercial electrode materials RuO2 / NF (reaching 1000 mA cm⁻¹ at 1.85 V). -2electrolysis performance. To further compare the charge transfer resistance of Ni-CoFe2O4 / NF electrode material and RuO2 / NF commercial electrode material as anode, we tested their electrochemical impedance spectroscopy, see Fig. 6. Figure 11 b. Compared with RuO2 / NF (1 Ω), Ni-CoFe2O4 / NF electrode material has smaller charge transfer resistance of 0.6 Ω, indicating that Ni-CoFe2O4 / NF electrode material can also promote charge transfer in AEM electrolyzer, thereby improving the overall water electrolysis performance.

[0087] Figure 12 AEM electrolyzer stability test curve of Example 2. To test the durability of electrode material at high current density, we assembled AEM electrolyzer with Ni-CoFe2O4 / NF electrode material as anode and commercial Pt / C catalyst as cathode for testing, the torque, temperature, liquid flow rate conditions are consistent with the polarization curve test. As shown in Fig. 7, Ni-CoFe2O4 / NF||Pt / C was tested at a high current density of 1 A cm Figure 12 -2 The voltage is stable at 1.9 V, and the test time lasts for 220 h without voltage decay, indicating that Ni-CoFe2O4 / NF electrode material has good durability when running at industrial current density.

[0088] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.​

Claims

1. A method for preparing a catalytic electrode for an anion exchange membrane electrolyzer, characterized in that: include, (1) Preparation of electrolyte: Nickel salt, boric acid and ammonium salt are added to water and dispersed to obtain electrolyte; (2) Using nickel foam as the working electrode, Ag / AgCl electrode as the reference electrode, and Pt sheet electrode as the counter electrode, the three electrodes are placed in the electrolyte for electrochemical deposition. The product is washed and dried to obtain Ni / NF. (3) Disperse iron salt and cobalt salt in water, add Ni / NF to soak, heat to react, wash, and dry to obtain Ni-CoFe2O4 / NF; In step (1), the nickel salt includes nickel chloride, the ammonium salt includes ammonium chloride, and the molar ratio of the nickel salt, boric acid, and ammonium salt is 1:1~1.5:1~2; the concentration of boric acid is 1~1.5M. In step (2), the electrochemical deposition is performed at 20 mA cm⁻¹. -2 Electrochemical deposition under constant current for 8-10 min; In step (3), the molar ratio of the iron salt to the cobalt salt is 1~1.5:1; the heating reaction is carried out at 120 °C for 12~14 h.

2. The method for preparing the catalytic electrode of the anion exchange membrane electrolyzer according to claim 1, characterized in that: In step (1), the molar ratio of nickel salt, boric acid and ammonium salt is 0.025:0.03 mol:0.043; the dispersing in water includes ultrasonic dispersion followed by heating to 55~60℃ and adjusting pH=4.

3. The method for preparing the catalytic electrode of the anion exchange membrane electrolyzer according to claim 1 or 2, characterized in that: In step (3), the iron salt is ferric chloride and the cobalt salt is cobalt nitrate.

4. The method for preparing the catalytic electrode of the anion exchange membrane electrolyzer according to claim 1 or 2, characterized in that: In step (3), the molar ratio of the iron salt to the cobalt salt is 0.27:0.22; the concentration of the iron salt is 18~20mM.

5. The method for preparing the catalytic electrode of the anion exchange membrane electrolyzer according to claim 1 or 2, characterized in that: In step (3), the soaking time is 1 to 1.5 h.

6. The method for preparing the catalytic electrode of the anion exchange membrane electrolyzer according to claim 1 or 2, characterized in that: In step (2), the nickel foam is pretreated by immersing it in hydrochloric acid solution to remove surface oxidized impurities, then rinsing it with ethanol and deionized water, and drying it.

7. The anion exchange membrane electrolyzer catalytic electrode prepared by the preparation method according to claim 1.

8. The application of the anion exchange membrane electrolyzer catalytic electrode prepared by the preparation method according to claim 1 in the preparation of anion exchange membrane electrolyzer membrane electrodes.

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