Cobalt hydroxide electrode and preparation method and application thereof

Abstract

The invention discloses a cobalt hydroxide electrode, the cobalt hydroxide electrode is cobalt hydroxide loaded by foamed nickel, the cobalt hydroxide is amorphous phase cobalt hydroxide, and the microstructure of the cobalt hydroxide is a nanoneedle. The electrode obtained by the invention has the characteristics of relatively high catalytic activity and relatively strong reaction kinetics. The invention further discloses a preparation method and application of the cobalt hydroxide electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalysis, in particular to a cobalt hydroxide electrode and a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for hydrogen energy, electrocatalytic overall water splitting as an efficient hydrogen production technology has attracted widespread attention, but the core bottleneck of this technology is the lack of a bifunctional electrode with high activity, high stability and low cost. Co(OH)2-based catalysts have adjustable electronic structures and active sites, and are used for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). However, the current Co(OH)2has the problems of slow reaction kinetics and insufficient exposure of active sites; and some electrodes are prone to crystal phase transformation or morphology collapse during long-term electrolysis, resulting in stability decay. SUMMARY

[0003] The purpose of the present application is to provide a cobalt hydroxide electrode and a preparation method thereof.

[0004] A cobalt hydroxide electrode, the cobalt hydroxide electrode is a cobalt hydroxide loaded on a foamed nickel, the cobalt hydroxide is amorphous cobalt hydroxide (Co(OH)2), which can increase the number of its catalytic active sites, and can enhance the adsorption strength of intermediates when used in OER and HER processes, and can dissociate water molecules; the microstructure of the cobalt hydroxide includes nanoneedles, which can increase the number of its catalytic active sites compared with a flaky structure, and the electrolyte can penetrate into the interior of the cobalt hydroxide electrode, thereby increasing the contact area between the electrolyte and the electrode, and thus improving the catalytic activity thereof; in addition, when used in OER and HER processes, the nanoneedles can pierce the hydrogen and oxygen gas bubbles generated in the OER and HER processes, thereby enhancing gas desorption, reducing the degree of blockage of the catalytic active sites, and improving the catalytic activity thereof.

[0005] The length of the nanoneedles is 1.5 ~ 2 μm, the electrolyte can penetrate into the interior of the cobalt hydroxide electrode, thereby increasing the contact area between the electrolyte and the electrode, and thus improving the catalytic activity thereof; the tip diameter of the nanoneedles is about 50 nm, which can increase the probability of piercing the hydrogen and oxygen gas bubbles generated in the OER and HER processes when used in the OER and HER processes, thereby enhancing gas desorption, reducing the degree of blockage of the catalytic active sites, and improving the catalytic activity thereof.

[0006] Optionally, the nanoneedles have pores, which are beneficial to increasing the number of catalytic active sites of the cobalt hydroxide electrode, forming unsaturated coordination cobalt atomic sites, and enhancing the adsorption strength of intermediates when used in OER and HER processes, thereby improving the catalytic activity thereof.

[0007] Optionally, cobalt hydroxide is an amorphous β-phase Co(OH)₂. Hydroxyl groups occupy all eight vertices, with cobalt atoms at the center forming a regular octahedron. Compared to α-phase Co(OH)₂, β-phase Co(OH)₂ lacks heteroatoms and interlayer anions, resulting in a more stable interlayer spacing. Furthermore, cobalt can bond with the hydroxide ions of water molecules, thereby dissociating water molecules into hydroxide and hydrogen ions, leading to faster catalytic rates in OER and HER processes.

[0008] Optionally, the surface of the cobalt hydroxide electrode has fluoride ions, which can regulate the electronic structure of cobalt, increase the d-band width of cobalt, increase the adsorption strength of the cobalt hydroxide surface, and thus enhance its catalytic activity.

[0009] A method for preparing a cobalt hydroxide electrode, the method comprising: Step 1: Wash the nickel foam sequentially with HCl, ethanol and deionized water. Dissolve NH4F, Co(NO3)2·6H2O and CO(NH2)2 in deionized water to obtain a mixed solution. Transfer the mixed solution and the nickel foam to a hydrothermal reactor, seal it and heat it in an oven at 120 °C for 6 hours to obtain the product. After the reaction is complete, wash the product with water and ethanol, and dry the washed product at 60 °C for 4 hours to obtain Co(OH)F / NF.

[0010] Step 2: The Co(OH)F / NF precursor was treated by cathodic cyclic voltammetry (CV) in an electrochemical workstation, with Co(OH)F / NF as the working electrode, Hg / HgO as the reference electrode, and a graphite rod as the counter electrode. Fluorine has an electronegativity of 3.98, greater than oxygen (O), but its radius (1.31 Å) is similar to that of O (1.38 Å). The bond strength of MF is weaker than that of MO, making MF ionic and more easily dissociated in the electrolyte. This creates vacancies in Co(OH)F, which are readily occupied by hydroxide ions in the alkaline solution, thus promoting the formation of β-phase Co(OH)2 during CV scanning. Furthermore, during CV scanning, fluoride ions in the solution partially adsorb onto the surface of Co(OH)2, thereby modulating the electronic structure of Co(OH)2, improving its ability to adsorb and dissociate water, and enhancing the strength of adsorption intermediates, ultimately improving the catalytic activity of HER and OER.

[0011] Optionally, in step 2, the potential range of the cathode cyclic voltammetry scan is -0.9 ~ -1.3 V. vs Under the influence of the cathode potential, the Co ions in Co(OH)F undergo reduction, causing them to precipitate from the crystal lattice and generate vacancies. These vacancies indirectly form coordinate-unsaturated Co sites, enhancing the adsorption of intermediates during HER and OER processes, thereby improving catalytic activity.

[0012] Optionally, in step 2, the scan rate of the cathode cyclic voltammetry is 50 mV / s. -1 The electrolyte substances can be transported to the electrode surface in a timely manner to participate in the reaction, which accelerates the reconstruction reaction of the Co(OH)F surface and helps to achieve deep reconstruction of Co(OH)F.

[0013] Optionally, in step 2, the number of scan cycles for the cathode cyclic voltammetry is 2000~8000. When the number of cycles is less than 2000, Co(OH)F will undergo surface reconstruction, but the interior of the electrode will not be reconstructed, thus failing to achieve deep reconstruction; while when the number of cycles is greater than 8000, Co(OH)F will undergo excessive deep reconstruction, leading to structural collapse and the generation of hydroxyl oxides with low catalytic activity.

[0014] The cobalt hydroxide electrode obtained above is used for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Attached Figure Description

[0015] Figure 1 The XRD patterns are of Co(OH)F / NF-2k CV obtained in Example 1, Co(OH)F / NF-4k CV obtained in Example 2, Co(OH)F / NF-6k CV obtained in Example 3, Co(OH)F / NF-8k CV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1. Figure 2 This is a scanning electron microscope (SEM) image of Co(OH)F / NF obtained in Comparative Example 1; Figure 3 This is a scanning electron microscope (SEM) image of Co(OH)F / NF-6k CV obtained in Example 3; Figure 4 This is a transmission electron microscope (TEM) image of Co(OH)F / NF-6k CV obtained in Example 3; Figure 5 This is the HRTEM image of Co(OH)F / NF-6k CV obtained in Example 3; Figure 6 This is the XPS full spectrum of Co(OH)F / NF-6k CV obtained in Example 3; Figure 7 The linear sweep voltammetry (LSV) curves of the catalytic hydrogen evolution of Co(OH)F / NF-2kCV obtained in Example 1, Co(OH)F / NF-4kCV obtained in Example 2, Co(OH)F / NF-6kCV obtained in Example 3, Co(OH)F / NF-8kCV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1 in 1 MKOH electrolyte are shown. Figure 8 The images show the Tafel diagrams of the catalytic hydrogen evolution of Co(OH)F / NF-2k CV obtained in Example 1, Co(OH)F / NF-4k CV obtained in Example 2, Co(OH)F / NF-6k CV obtained in Example 3, Co(OH)F / NF-8k CV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1 in 1 MKOH electrolyte. Figure 9 The images show the EIS diagrams of the catalytic hydrogen evolution of Co(OH)F / NF-2kCV obtained in Example 1, Co(OH)F / NF-4kCV obtained in Example 2, Co(OH)F / NF-6kCV obtained in Example 3, Co(OH)F / NF-8kCV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1 in 1 MKOH electrolyte. Figure 10 The double-layer capacitance (C) of Co(OH)F / NF-2kCV obtained in Example 1, Co(OH)F / NF-4kCV obtained in Example 2, Co(OH)F / NF-6kCV obtained in Example 3, Co(OH)F / NF-8kCV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1 are shown. dl ) Calculation graph; Figure 11 The LSV curves of Co(OH)F / NF-2kCV obtained in Example 1, Co(OH)F / NF-4kCV obtained in Example 2, Co(OH)F / NF-6kCV obtained in Example 3, Co(OH)F / NF-8kCV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1 for catalytic oxygen evolution in 1.0M KOH solution are shown. Figure 12 The images show the Tafel diagrams of the catalytic oxygen evolution of Co(OH)F / NF-2kCV obtained in Example 1, Co(OH)F / NF-4kCV obtained in Example 2, Co(OH)F / NF-6kCV obtained in Example 3, Co(OH)F / NF-8kCV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1 in 1.0M KOH solution.

[0016] Figure 13 The graphs show the total water splitting performance of Co(OH)F / NF-6k and Pt / C||RuO2 obtained in Example 3. Figure 14 The Co(OH)F / NF-6k CV obtained in Example 3 at 100 mA cm⁻¹ -2 The timing potential curve is shown below. Detailed Implementation

[0017] The present application will be further described below with reference to the accompanying drawings and specific embodiments: To enable those skilled in the art to better understand the technical solutions of this application, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the drawings described below are merely some embodiments of this application, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] A cobalt hydroxide electrode is disclosed, comprising cobalt hydroxide supported on nickel foam. The cobalt hydroxide is an amorphous phase (Co(OH)2), which increases the number of catalytic active sites. When used in OER and HER processes, it enhances the adsorption strength of intermediates and can dissociate water molecules. The microstructure of the cobalt hydroxide includes nanoneedles, which, compared to a sheet-like structure, increases the number of catalytic active sites. The electrolyte can penetrate deeper into the cobalt hydroxide electrode, increasing the contact area between the electrolyte and the electrode, thereby improving its catalytic activity. Furthermore, when used in OER and HER processes, the nanoneedles can puncture hydrogen and oxygen bubbles generated during these processes, thereby enhancing gas desorption, reducing the degree of blockage of catalytic active sites, and improving catalytic activity.

[0019] In one embodiment, the length of the nanoneedles is 1.5 to 2 μm, allowing the electrolyte to penetrate deeper into the cobalt hydroxide electrode, thereby increasing the contact area between the electrolyte and the electrode and enhancing its catalytic activity. The tip diameter of the nanoneedles is about 50 nm. When used in OER and HER processes, the nanoneedles can increase the probability of puncturing the hydrogen and oxygen bubbles generated in the OER and HER processes, thereby enhancing gas desorption, reducing the degree of blockage of catalytic active sites, and improving its catalytic activity.

[0020] In one embodiment, the nanoneedles have pores, which helps to increase the number of catalytic active sites on the cobalt hydroxide electrode and form unsaturated coordinated cobalt atom sites. When used in OER and HER processes, they can enhance the adsorption strength of intermediates, thereby improving their catalytic activity.

[0021] In one embodiment, cobalt hydroxide is an amorphous β-phase Co(OH)₂. Hydroxyl groups occupy the eight vertices, and cobalt atoms are located at the center, forming a regular octahedron. Compared to α-phase Co(OH)₂, β-phase Co(OH)₂ has no heteroatoms, no anions in the interlayer, and the interlayer spacing tends to be stable. Furthermore, cobalt can bond with the hydroxide ions of water molecules, thereby dissociating water molecules into hydroxide ions and hydrogen, resulting in faster catalytic rates when used in OER and HER processes.

[0022] In one embodiment, the surface of the cobalt hydroxide electrode has fluoride ions, which can regulate the electronic structure of cobalt, thereby increasing the d-band width of cobalt and increasing the adsorption strength of the cobalt hydroxide surface, thus enhancing its catalytic activity.

[0023] A method for preparing a cobalt hydroxide electrode, the method comprising: Step 1: Wash the nickel foam sequentially with HCl, ethanol and deionized water. Dissolve NH4F, Co(NO3)2·6H2O and CO(NH2)2 in deionized water to obtain a mixture. Transfer the mixture and nickel foam to a hydrothermal reactor, seal it and heat it in an oven at 120 °C for 6 hours to obtain the product. After the reaction is complete, wash the product with water and ethanol, and dry the washed product at 60 °C for 4 hours to obtain Co(OH)F / NF.

[0024] Step 2: The Co(OH)F / NF precursor was treated by cathodic cyclic voltammetry (CV) in an electrochemical workstation, with Co(OH)F / NF as the working electrode, Hg / HgO as the reference electrode, and a graphite rod as the counter electrode. Fluorine has an electronegativity of 3.98, greater than oxygen (O), but its radius (1.31 Å) is similar to that of O (1.38 Å). The bond strength of MF is weaker than that of MO, making MF ionic and more easily dissociated in the electrolyte. This creates vacancies in Co(OH)F, which are readily occupied by hydroxide ions in the alkaline solution, thus promoting the formation of β-phase Co(OH)2 during CV scanning. Furthermore, during CV scanning, fluoride ions in the solution partially adsorb onto the surface of Co(OH)2, thereby modulating the electronic structure of Co(OH)2, improving its ability to adsorb and dissociate water, and enhancing the strength of adsorption intermediates, ultimately improving the catalytic activity of HER and OER.

[0025] In one embodiment, in step 2, the potential range of the cathode cyclic voltammetry scan is -0.9 ~ -1.3 V. vs Under the influence of the cathode potential, the Co ions in Co(OH)F undergo reduction, causing them to precipitate from the crystal lattice and generate vacancies. These vacancies indirectly form coordinate-unsaturated Co sites, enhancing the adsorption of intermediates during HER and OER processes, thereby improving catalytic activity.

[0026] In one embodiment, in step 2, the scan rate of the cathode cyclic voltammetry is 50 mV / s. -1 The electrolyte substances can be transported to the electrode surface in a timely manner to participate in the reaction, which accelerates the reconstruction reaction of the Co(OH)F surface and helps to achieve deep reconstruction of Co(OH)F.

[0027] In one embodiment, in step 2, the number of scan cycles for the cathode cyclic voltammetry is 2000-8000. When the number of cycles is less than 2000, Co(OH)F undergoes surface reconstruction, but the interior of the electrode does not reconstruct, thus failing to achieve deep reconstruction. When the number of cycles is greater than 8000, Co(OH)F undergoes excessive deep reconstruction, leading to structural collapse and the generation of hydroxyl oxides with low catalytic activity.

[0028] Electrochemical tests were performed using an electrochemical workstation (CHI 760 E) equipped with a three-electrode system. In the three-electrode system, the prepared electrodes, Hg / HgO, graphite plate, and Pt sheet (30 × 30 mm) were used. 2 The electrode (OER) was used as the working electrode, reference electrode, and counter electrode, respectively. The solution being measured was 1.0 M (mol / L) KOH. The time was 50 mV / s. −1 The electrode was subjected to cyclic voltammetry (CV) scans for 80 cycles at scan rates ranging from -0.026 to -0.374 V vs. RHE (HER) and from 1.126 to 1.726 V vs. RHE (OER) to stabilize the electrode surface. The voltammetry was performed at 5 mV / s. −1 The scan rate is used to record the linear scan voltammetry (LSV) curve. The potential is corrected according to the following formula: E RHE = E Hg / HgO + 0.098 + 0.0591 × pH Electrochemical impedance spectroscopy (EIS) was measured at potentials of −1.15 V (HER) and 0.6 V (OER), with interference frequencies ranging from 100 kHz to 0.1 Hz. Non-Radidatic reaction potentials (0.066–0.136 V vs. RHE) were recorded in the range of 20–100 mV s. −1 CV curves at different scan rates were plotted. The relationship between the current difference and the scan rate at 0.101 V (vs. RHE) was plotted; half the slope value represents the double-layer capacitance (Cdl). At 10 mA cm⁻¹... −2 The stability of the HER electrode was evaluated by measuring the chronopotential (CP) curve at 100 mAcm. −2 The CP curve was measured to evaluate the stability of the electrode OER.

[0029] The raw material information involved in the above embodiments is as follows: Example 1 1×3 cm² of NF was ultrasonically washed sequentially in 3 M HCl, ethanol, and deionized water for 10 minutes to remove the surface oxide layer and impurities, and then dried for later use. 9.6 mmol NH₄F, 2.4 mmol Co(NO₃)₂・6H₂O, and 12 mmol CO(NH₂)₂ were dissolved in 30 mL of deionized water and stirred until a homogeneous solution was obtained. The solution and the pretreated NF were transferred together to a 50 mL hydrothermal reactor, sealed, and heated in a 120 °C oven for 6 hours. After the reaction, the NF was removed and washed 6 times alternately with deionized water and ethanol to remove residual salts, and then dried in a 60 °C vacuum drying oven for 4 hours to obtain crystalline Co(OH)F / NF. Using Co(OH)F / NF as the working electrode, Hg / HgO as the reference electrode, and a graphite rod as the counter electrode, a CV scan was performed in a 1.0 M KOH electrolyte. The scan parameters were: potential range -0.9 V ~ -1.3 V (vs). Hg / HgO), scan rate 50 mV s⁻ 1 The scanning circle was 2000 times to obtain an amorphous Co(OH)2 electrode, labeled as Co(OH)F / NF-2k CV.

[0030] Example 2 1×3 cm² of NF was ultrasonically washed sequentially in 3 M HCl, ethanol, and deionized water for 10 minutes to remove the surface oxide layer and impurities, and then dried for later use. 9.6 mmol NH₄F, 2.4 mmol Co(NO₃)₂・6H₂O, and 12 mmol CO(NH₂)₂ were dissolved in 30 mL of deionized water and stirred until a homogeneous solution was obtained. The solution and the pretreated NF were transferred together to a 50 mL hydrothermal reactor, sealed, and heated in a 120 °C oven for 6 hours. After the reaction, the NF was removed and washed 6 times alternately with deionized water and ethanol to remove residual salts, and then dried in a 60 °C vacuum drying oven for 4 hours to obtain crystalline Co(OH)F / NF. Using Co(OH)F / NF as the working electrode, Hg / HgO as the reference electrode, and a graphite rod as the counter electrode, a CV scan was performed in 1.0 M KOH electrolyte. Scan parameters: potential range -0.9 V ~ -1.3 V (vs. Hg / HgO), scan rate 50. mV s⁻¹, 4000 scans, to obtain an amorphous Co(OH)2 electrode, labeled as Co(OH)F / NF-4k CV.

[0031] Example 3 1×3 cm² of NF was ultrasonically washed sequentially in 3 M HCl, ethanol, and deionized water for 10 minutes to remove the surface oxide layer and impurities, and then dried for later use. 9.6 mmol NH₄F, 2.4 mmol Co(NO₃)₂・6H₂O, and 12 mmol CO(NH₂)₂ were dissolved in 30 mL deionized water and stirred until a homogeneous solution was obtained. The solution and the pretreated NF were transferred together to a 50 mL hydrothermal reactor, sealed, and heated in a 120 °C oven for 6 hours. After the reaction, the NF was removed and washed 6 times alternately with deionized water and ethanol to remove residual salts, and then dried in a 60 °C vacuum drying oven for 4 hours to obtain crystalline Co(OH)F / NF. Using Co(OH)F / NF as the working electrode, Hg / HgO as the reference electrode, and a graphite rod as the counter electrode, a CV scan was performed in 1.0 M KOH electrolyte. Scan parameters: potential range -0.9 V ~ -1.3 V (vs. Hg / HgO), scan rate 50. mV s⁻¹, 6000 scans, to obtain an amorphous Co(OH)2 electrode, labeled as Co(OH)F / NF-6k CV.

[0032] Example 4 1×3 cm² of NF was ultrasonically washed sequentially in 3 M HCl, ethanol, and deionized water for 10 minutes to remove the surface oxide layer and impurities, and then dried for later use. 9.6 mmol NH₄F, 2.4 mmol Co(NO₃)₂・6H₂O, and 12 mmol CO(NH₂)₂ were dissolved in 30 mL of deionized water and stirred until a homogeneous solution was obtained. The solution and the pretreated NF were transferred together to a 50 mL hydrothermal reactor, sealed, and heated in a 120 °C oven for 6 hours. After the reaction, the NF was removed and washed 6 times alternately with deionized water and ethanol to remove residual salts, and then dried in a 60 °C vacuum drying oven for 4 hours to obtain crystalline Co(OH)F / NF. Using Co(OH)F / NF as the working electrode, Hg / HgO as the reference electrode, and a graphite rod as the counter electrode, a CV scan was performed in 1.0 M KOH electrolyte. Scan parameters: potential range -0.9 V to 1.3 V (vs. Hg / HgO), scan rate 50 mV. s⁻¹, scanning 8000 times, to obtain an amorphous Co(OH)2 electrode, labeled as Co(OH)F / NF-8k CV.

[0033] Comparative Example 1 1×3 cm² of NF was ultrasonically washed sequentially in 3 M HCl, ethanol, and deionized water for 10 minutes to remove the surface oxide layer and impurities, and then dried for later use. 9.6 mmol NH4F, 2.4 mmol Co(NO3)2・6H2O, and 12 mmol CO(NH2)2 were dissolved in 30 mL of deionized water and stirred until a homogeneous solution was obtained. The solution and the pretreated NF were transferred together to a 50 mL hydrothermal reactor, sealed, and heated in an oven at 120 °C for 6 hours. After the reaction was completed, the NF was removed and washed 6 times alternately with deionized water and ethanol to remove residual salts. Then it was dried in a vacuum drying oven at 60 °C for 4 hours to obtain crystalline Co(OH)F / NF, labeled as Co(OH)F / NF.

[0034] Figure 1 The X-ray diffraction (XRD) patterns of Co(OH)F / NF-2k CV, Co(OH)F / NF-4k CV, Co(OH)F / NF-6k CV, Co(OH)F / NF-8k CV, and Co(OH)F / NF obtained in Examples 1, 2, 3, 4, and Comparative Example 1 of this invention are shown. In addition to the diffraction peak of NF, Co(OH)F / NF also shows diffraction peaks at 20.83°, 32.31°, 33.53°, 35.56°, 38.78°, and 39.91°, corresponding to the (110), (310), (201), (111), (211), and (410) crystal planes of Co(OH)F (JCPDS No. 50-0827). However, in the Co(OH)F / NF-2k CV, besides the NF peak, only the 20° and 32° peaks show raised "bun" shapes, corresponding to the peak positions of β-Co(OH)2. This indicates that Co(OH)F has transformed into amorphous β-Co(OH)2. Furthermore, the intensity of the amorphous peaks increases with the number of scan cycles.

[0035] Figure 2 The image shown is a SEM image of Co(OH)F / NF obtained in Comparative Example 1 of this invention. Figure 2 It can be seen that Co(OH)F exhibits a nanoneedle-like structure, which is densely, uniformly, and vertically covered on the NF surface. The nanoneedles are 1.5 to 2 micrometers in length and grow perpendicular to the nickel foam surface. The formation process of the nanoneedle-like structure mainly involves the decomposition of urea at high temperature to generate NH3 and CO2, and the combination of NH3 and water to form NH4+. 4+ and OH - ions. Simultaneously, NH4F ionizes to produce NH4+. 4+ and F - Then, Co released from Co(NO3)2 2+ With OH - and F -The reaction forms Co(OH)F. Importantly, the addition of urea and NH4F facilitates the formation of nanoneedle-like structures. Urea acts as both a reactant and a capping agent, and can be used to cap anionic polymers and guide Co... 2+ and F - It combines with hydroxyl groups to form Co(OH)F.

[0036] Figure 3 This is a SEM image of the Co(OH)F / NF-6k CV obtained in Example 3. The Co(OH)F / NF-6k CV exhibits a nanoneedle-like structure, indicating that it can still maintain the original nanoneedle morphology of Co(OH)F / NF after 6000 CV scans. The nanoneedle-like structure allows the electrolyte to penetrate more deeply into the cobalt hydroxide electrode, increasing the contact area between the electrolyte and the electrode, thereby enhancing its catalytic activity. The tip diameter of the nanoneedles is 20~100 nm. When used in OER and HER processes, the nanoneedles can increase the probability of puncturing the hydrogen and oxygen bubbles generated in the OER and HER processes, thereby enhancing gas desorption, reducing the degree of blockage of catalytic active sites, and improving its catalytic activity.

[0037] Figure 4 This is a TEM image of the Co(OH)F / NF-6k CV obtained in Example 3. The Co(OH)F / NF-6k CV has a nano-needle-like structure with a length of 1.5~2 μm. The electrolyte can penetrate into the interior of the cobalt hydroxide electrode, which increases the contact area between the electrolyte and the electrode, thereby enhancing its catalytic activity.

[0038] Figure 5 The image shows the HRTEM image of the Co(OH)F / NF-6k CV obtained in Example 3. As can be seen from the image, the surface atoms are in a disordered state, without complete lattice fringes, indicating that the Co(OH)F / NF-6k CV has an amorphous structure, consistent with the XRD results. The nanoneedles of Co(OH)F / NF-6k CV have pores, which is beneficial for increasing the number of catalytic active sites in the cobalt hydroxide electrode and forming unsaturated coordinated cobalt atom sites. When used in OER and HER processes, this can enhance the adsorption strength of intermediates, thereby improving its catalytic activity.

[0039] Figure 6 The image shows the XPS full spectrum of the Co(OH)F / NF-6k CV obtained in Example 3. As can be seen from the image, fluorine (F) elements still exist on the catalyst surface, indicating that some F ions from the solution are re-adsorbed onto the surface of the cobalt hydroxide nanoneedles during the CV scan of Co(OH)F. The fluorine ions on the surface can modulate the electronic structure of cobalt, increasing the d-band width of cobalt and thus increasing the adsorption strength on the cobalt hydroxide surface, thereby enhancing its catalytic activity.

[0040] Figure 7These are linear sweep voltammetry (LSV) curves of Co(OH)F / NF-2kCV obtained in Example 1, Co(OH)F / NF-4kCV obtained in Example 2, Co(OH)F / NF-6kCV obtained in Example 3, Co(OH)F / NF-8kCV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1 in 1M KOH electrolyte. Figure 7 It can be seen that the CV of Co(OH)F / NF-6k is at 10 mAcm −2 The overpotential was 161 mV, lower than that of Co(OH)F / NF (247 mV), Co(OH)F / NF-2kCV (212 mV), Co(OH)F / NF-4kCV (217 mV), and Co(OH)F / NF-8kCV (207 mV). This indicates that the remodeling caused by surface amorphization can enhance the catalytic activity of Co(OH)F.

[0041] from Figure 8 It can be seen that the Tafel slope of Co(OH)F / NF is 158.46 mV dec. −1 The slope of the Co(OH)F / NF-6k CV is the smallest (46.64 mV dec). −1 ), lower than the 93.97 mV dec of Co(OH)F / NF-2k CV. −1 , 63.87mV dec of Co(OH)F / NF-4k CV −1 The CV of Co(OH)F / NF-8k is 57.17 mV dec. −1 Because the Tafel slope of the Volmer step (dissociation of H2O) in alkaline hydrogen evolution is 120 mV dec −1 The Tafel slope of the Heyrovsky reaction (or Tafel reaction) step is 40 mV dec. -1 It is evident that after surface reconstruction of Co(OH)F, the rate-limiting step changed from the Volmer step to the Heyrovsky step, indicating that surface amorphization can significantly enhance the kinetics of the catalytic hydrogen evolution reaction. This is mainly because the amorphous substances generated by surface reconstruction weaken the adsorption strength of OH, thereby accelerating the dissociation of H₂O and improving the HER activity.

[0042] Figure 9 The EIS plots are of the Co(OH)F / NF-2k CV obtained in Example 1, the Co(OH)F / NF-4k CV obtained in Example 2, the Co(OH)F / NF-6k CV obtained in Example 3, the Co(OH)F / NF-8k CV obtained in Example 4, and the Co(OH)F / NF obtained in Comparative Example 1. Figure 9It can be seen that the charge transfer resistance Rct of Co(OH)F / NF-6kCV is 76.27 Ω, which is lower than that of Co(OH)F / NF (159.6 Ω), Co(OH)F / NF-2kCV (79.25 Ω), Co(OH)F / NF-4kCV (78.52 Ω), and Co(OH)F / NF-8kCV (77.25 Ω). The charge transfer resistance of Co(OH)F / NF-6kCV is the smallest among all the studied electrodes, indicating that it has the best charge transfer capability and the ability to improve liquid phase mass transfer.

[0043] from Figure 10 It can be seen from this that the C of Co(OH)F / NF dl It is 1.24 mF cm -2 Co(OH)F / NF-6k CV of C dl Maximum (53.24 mF cm) -2 ), higher than the 35.76 mF cm⁻¹ of Co(OH)F / NF⁻²k⁻¹. -2 48.58mF cm⁻¹ of Co(OH)F / NF-4k CV -2 The CV of Co(OH)F / NF-8k is 45.84 mF cm⁻¹. -2 Because of C dl The relationship is directly proportional to the electrochemical active area (ECSA). This indicates that CV-based amorphous reconstruction of the Co(OH)F surface can increase the electrochemical active area of ​​Co(OH)F, increasing the probability of contact between reactants and catalytic active sites, thereby enhancing catalytic activity.

[0044] Figure 11 The figures show the LSV curves of the following Co(OH)F / NF-2k CV obtained in Example 1, Co(OH)F / NF-4k CV obtained in Example 2, Co(OH)F / NF-6k CV obtained in Example 3, Co(OH)F / NF-8k CV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1, in 1.0 M KOH solution for catalytic oxygen evolution. The figures show that the initial Co(OH)F / NF exhibited poor performance, but its activity improved after CV activation, with Co(OH)F / NF-6k CV showing the best performance. The Co(OH)F / NF-6k CV was measured at 10 mA cm⁻¹. -2The overpotential of Co(OH)F / NF is 280 mV, lower than that of Co(OH)F / NF (350 mV), Co(OH)F / NF-2kCV (330 mV), Co(OH)F / NF-4kCV (290 mV), and Co(OH)F / NF-8kCV (290 mV), exhibiting a similar trend at high current densities. Co(OH)F / NF-6kCV at 100 mA cm⁻¹... -2 The overpotential is 320 mV, which is lower than 480 mV for Co(OH)F / NF, 420 mV for Co(OH)F / NF-2kCV, 350 mV for Co(OH)F / NF-4kCV, and 340 mV for Co(OH)F / NF-8kCV.

[0045] Figure 12 The images show the Tafel plots of the catalytic oxygen evolution reaction (OER) of Co(OH)F / NF-2kCV obtained in Example 1, Co(OH)F / NF-4kCV obtained in Example 2, Co(OH)F / NF-6kCV obtained in Example 3, Co(OH)F / NF-8kCV obtained in Example 4, and Co(OH)F / NF obtained in Comparative Example 1 in 1.0 M KOH solution. The Tafel slope of Co(OH)F / NF-6kCV is 46.84 mV dec. -1 The Tafel slopes of Co(OH)F / NF, Co(OH)F / NF-2k CV, Co(OH)F / NF-4k CV, and Co(OH)F / NF-8k CV are 141.71 mV dec. -1 95.02 mV dec -1 63.94 mV dec -1 and 53.19 mV dec -1 This indicates that the OER kinetics of Co(OH)F are enhanced after surface reconstruction, and the kinetics are optimal when the surface reconstruction is moderate.

[0046] like Figure 13 and Figure 14 As shown, the CV of Co(OH)F / NF-6k at 10, 100, and 300 mA cm⁻¹ −2 The cell voltage required is only 1.7, 2.1, and 2.5 V, lower than that of Pt / C (manufactured by Shanghai Hesen Electric Co., Ltd.) and RuO2 (manufactured by Shanghai Aladdin Biochemical Technology Co., Ltd.), indicating that the Co(OH)F / NF-6k CV bifunctional electrode has good potential in industrial applications. Furthermore, this bifunctional electrolyzer can operate at 100 mA cm⁻¹. −2The Co(OH)F / NF-6k CV bifunctional electrode exhibits good long-term stability under high current density after stable electrolysis for 40 h with no significant cell voltage decay.

[0047] It should be noted that the above embodiments are only used to illustrate this application and are not intended to limit the technical solutions described in this application. Although this specification has described this application in detail with reference to the above embodiments, those skilled in the art should understand that they can still make modifications or equivalent substitutions to this application. All technical solutions and improvements that do not depart from the spirit and scope of this application should be covered within the scope of the claims of this application.

Claims

1. A cobalt hydroxide electrode, characterized in that, The cobalt hydroxide electrode is cobalt hydroxide supported on nickel foam, the cobalt hydroxide is amorphous cobalt hydroxide, and the microstructure of the cobalt hydroxide includes nanoneedles.

2. The cobalt hydroxide electrode according to claim 1, characterized in that, The nanoneedles have pores.

3. The cobalt hydroxide electrode according to claim 1 or 2, characterized in that, The cobalt hydroxide is an amorphous β-phase Co(OH)2.

4. The cobalt hydroxide electrode according to any one of claims 1 to 3, characterized in that, The surface of the cobalt hydroxide electrode has fluoride ions.

5. A method for preparing a cobalt hydroxide electrode, characterized in that, The method for preparing the cobalt hydroxide electrode includes: Step 1: Wash the nickel foam sequentially with HCl, ethanol and deionized water. Dissolve NH4F, Co(NO3)2·6H2O and CO(NH2)2 in deionized water to obtain a mixture. Transfer the mixture and the nickel foam to a hydrothermal reactor, seal it and heat it in an oven at 120 °C for 6 hours to obtain the product. After the reaction is complete, wash the product with water and ethanol, and dry the washed product at 60 °C for 4 hours to obtain Co(OH)F / NF. Step 2: The Co(OH)F / NF is treated by cathodic cyclic voltammetry in an electrochemical workstation, wherein Co(OH)F / NF is the working electrode, Hg / HgO is the reference electrode, and a graphite rod is the counter electrode.

6. The method for preparing the cobalt hydroxide electrode according to claim 5, characterized in that, In step 1, the molar concentration ratio is NH4F:Co(NO3)2·6H2O:CO(NH2)2 = 4:1:

5.

7. The method for preparing the cobalt hydroxide electrode according to claim 5, characterized in that, In step 2, the potential range of the cathode cyclic voltammetry scan is -0.9 V to -1.3 V. vs Hg / HgO.

8. The method for preparing the cobalt hydroxide electrode according to claim 5, characterized in that, In step 2, the scan rate of the cathode cyclic voltammetry is 50 mV / s. -1 .

9. The method for preparing the cobalt hydroxide electrode according to claim 5, characterized in that, In step 2, the number of scan cycles for the cathode cyclic voltammetry is 2000~8000.

10. An application characterized in that, The cobalt hydroxide electrode according to any one of claims 1 to 4 or the cobalt hydroxide electrode prepared according to any one of claims 5 to 9 is applied to an electrocatalytic reaction, wherein the electrocatalytic reaction is a cathode hydrogen evolution reaction or an anode oxygen evolution reaction.

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