A self-supporting heterostructure electrocatalytic oxygen evolution electrode and a preparation method thereof

Abstract

The application discloses a self-supporting heterostructure electrocatalytic oxygen evolution electrode and a preparation method thereof. A ZIF-67 precursor is in-situ grown on a multi-hole conductive carrier nickel foam, and then the ZIF-67 precursor is continuously annealed at 700 DEG C for two hours to obtain Co-C@NF. A self-supporting NiFe-LDH coated Co-C heterostructure catalytic electrode is prepared by using the high specific surface area of the Co-C@NF and electrodepositing NiFe-LDH on the surface of the Co-C@NF. The electrode not only uses the high specific surface area of the ZIF-67 to firmly anchor the NiFe-LDH on the surface of the Co-C, increases the interlayer spacing of the NiFe-LDH and exposes the high-efficiency active sites of the NiFe-LDH, but also uses the coordination of the three transition metal centers of Ni, Fe and Co to make the electrode reach a current density of 10 mA cm-2 at an ultralow overpotential of 147 mV, so that the electrode has application prospects in an oxygen evolution cell. ‑2 ​

Description

Technical Field

[0001] This invention relates to the field of catalytic electrode materials technology, specifically to a self-supporting heterostructure electrocatalytic oxygen evolution electrode and its preparation method. Background Technology

[0002] Currently, fossil fuels face problems such as oil shortages, environmental pollution, and greenhouse gas emissions. Hydrogen energy, with its environmentally friendly products and abundant reserves, is a promising future energy option. Water electrolysis is a primary method for hydrogen production; however, the oxygen evolution reaction (OER) at the anolyte involves four electrons, resulting in slow reaction kinetics and a high overpotential. IrO2 and RuO2 are highly efficient precious metal catalysts for OER; however, their high cost limits their widespread application. Therefore, there is an urgent need to develop transition metal catalysts, such as Ni, Fe, and Co-based catalysts, to improve the efficiency of hydrogen production through water electrolysis.

[0003] ZIF-67 and NiFe-LDH are two commonly used non-noble metal OER catalysts. ZIF-67 is a cobalt-centered MOF with dimethylimidazolium as a ligand. Its porous structure increases the exposure of active sites, providing a certain catalytic effect. However, its poor intrinsic activity and structural instability limit its use in OER catalysis. In contrast, NiFe-LDH exhibits a significant increase in intrinsic catalytic activity due to the synergistic effect of electrons between Ni and Fe hydroxide. However, the small interlayer spacing of LDH makes it difficult to fully expose active sites. Therefore, this invention aims to develop a catalytic oxygen evolution electrode with the advantages of high exposure of catalytic active sites and effective reduction of overpotential. Summary of the Invention

[0004] The purpose of this invention is to address the current situation where existing OER noble metal catalysts are difficult to widely use, and to provide a transition metal catalytic OER electrode.

[0005] To achieve the above objectives, the present invention provides a method for preparing a self-supporting heterostructure electrocatalytic oxygen evolution electrode, the specific steps of which are as follows:

[0006] S1. The nickel foam is ultrasonically washed sequentially with acetone, dilute hydrochloric acid, anhydrous ethanol and deionized water, and then dried in a vacuum oven at 60°C to obtain pretreated nickel foam.

[0007] S2. Prepare Co(NO3)2·6H2O-methanol solution, 2-methylimidazole-methanol solution, and triethylamine-methanol solution. Immerse the pretreated nickel foam in each of the Co(NO3)2·6H2O-methanol solution, 2-methylimidazole-methanol solution, and triethylamine-methanol solution forty times respectively to obtain nickel foam with ZIF-67 growth. Wash it with methanol several times and dry it in a vacuum drying oven at 60℃ for 8 hours to obtain ZIF-67@NF.

[0008] S3. ZIF-67@NF was heated to 700℃ and held for 2 hours under an inert atmosphere, and Co-C@NF material was obtained by inert high-temperature annealing.

[0009] S4. Prepare a mixed solution of NiSO4 and Fe(NO3)3 with a total concentration of 0.2M as the electrolyte;

[0010] S5. The Co-C@NF electrodeposited NiFe-LDH in the electrolyte. After the reaction was completed, the electrodepositor was washed three times with anhydrous ethanol and deionized water, and then dried in a vacuum drying oven at 60°C for 8 hours to obtain the NiFe-LDH / Co-C@NF electrocatalytic oxygen evolution electrode.

[0011] Preferably, the concentration of dilute hydrochloric acid in the preparation method S1 is 0.1M.

[0012] Preferably, the concentrations of the methanol solution of Co(NO3)2·6H2O, the methanol solution of 2-methylimidazole, and the methanol solution of triethylamine are 0.125M, 0.5M, and 0.125M, respectively.

[0013] Preferably, the inert atmosphere in the above preparation method is an inert gas, preferably high-purity argon.

[0014] Preferably, in the electrolyte prepared in the above method, the molar ratio of NiSO4 to Fe(NO3)3 solute is 1:1.

[0015] Preferably, the electrodeposition reaction in the above preparation method is set to a potential of -1V and a deposition time of 600s.

[0016] The present invention also provides an oxygen evolution electrode prepared by the above preparation method, which can be used in an oxygen evolution battery, including electrode materials for preparing an oxygen evolution battery, etc. The electrode material has the advantages of high exposure of catalytic active sites and effective reduction of overpotential.

[0017] The present invention has the following advantages:

[0018] The electrode material preparation process provided by this invention is simple, mild, and low-cost, using inexpensive raw materials. Both preparation steps are performed at room temperature, resulting in short preparation time and high efficiency. The catalytically active material is grown in situ in porous nickel foam, avoiding the use of adhesives and saving costs. Furthermore, in-situ growth further prevents catalyst deactivation due to film detachment.

[0019] This invention utilizes the porous structure of ZIF-67 as a precursor to increase the interlayer spacing of NiFe-LDH, forming a nanoflower heterostructure catalyst. This exposes more active sites while enhancing the catalytic activity through the synergistic effect of the two structures. Attached Figure Description

[0020] Figure 1 This is a SEM structure diagram of Co-C@NF in this invention.

[0021] Figure 2 This is a SEM image of the NiFe-LDH grown on nickel foam in this invention.

[0022] Figure 3 This is a SEM image of the electrode material NiFe-LDH / Co-C@NF provided in this invention.

[0023] Figure 4 The XRD results are for NiFe-LDH / Co-C@NF in this invention.

[0024] Figure 5 This is a comparison diagram of the double-layer capacitance of three different materials used in this invention.

[0025] Figure 6 This is a comparison of the oxygen evolution performance of the NiFe-LDH / Co-C@NF electrode material provided in this invention.

[0026] Figure 7 This is a comparison of the Tafel slopes of the three different materials in this invention with NF and RuO2@NF.

[0027] Figure 8 The NiFe-LDH / Co-C@NF electrode material provided by this invention operates at 100 mA cm⁻¹ -2 Long-term durability test under constant high current density. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Note: Unless otherwise specified, the experimental methods in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0030] Example 1

[0031] This embodiment provides a method for preparing a self-supporting heterostructure electrocatalytic oxygen evolution electrode NiFe-LDH / Co-C@NF, as detailed below:

[0032] S1. The nickel foam (NF) (1cm*5cm) was ultrasonically cleaned sequentially with acetone, 0.1M HCl, ethanol and water, respectively, for 15 minutes each time. The cleaned nickel foam was then dried in a vacuum drying oven at 60℃.

[0033] S2. Prepare a 0.125M Co(NO3)2·6H2O-methanol solution, a 0.5M 2-methylimidazole-methanol solution, and a 0.125M triethylamine-methanol solution. Immerse the nickel foam in each of the three solutions forty times in the order of Co(NO3)2·6H2O-methanol solution, 2-methylimidazole-methanol solution, and triethylamine-methanol solution. Wash the nickel foam coated with ZIF-67 several times with methanol and dry it in a vacuum drying oven at 60℃ for 8 hours to obtain ZIF-67@NF.

[0034] S3. Carbonization: After placing the sample obtained in S2 in a corundum ceramic boat, it is placed in a tube furnace filled with an inert gas (such as high-purity argon) and heated to 700℃ for 2 hours. Co-C@NF material is obtained by inert high-temperature annealing.

[0035] S4. Prepare a mixed solution of NiSO4 and Fe(NO3)3 with a total concentration of 0.2M as an electrolyte, wherein the molar ratio of the two solutes in the electrolyte is 1:1;

[0036] S5. The Co-C@NF material prepared in S3 was subjected to NiFe-LDH electrodeposition reaction in an electrolyte with a potential set to -1V and a deposition time of 600s. After the reaction was completed, the material was washed three times with anhydrous ethanol and deionized water respectively, and then dried in a vacuum drying oven at 60℃ for 8h to obtain the NiFe-LDH / Co-C@NF electrocatalytic oxygen evolution electrode.

[0037] Characterization of Electrode Materials in Experiment Example 1

[0038] 1. The SEM images of the samples Co-C@NF, NiFe-LDH@NF, and NiFe-LDH / Co-C@NF from Example 1 were obtained by electron microscopy and are shown below. Figure 1 , Figure 2 , Figure 3 As shown. Figure 1 Here is a SEM image of the sample Co-C@NF; Figure 2 The image shows the SEM structure of NiFe-LDH grown on nickel foam. It can be seen that NiFe-LDH grows on nickel foam in a flat, layered structure with small interlayer spacing and tight stacking. Figure 3 The image shows the SEM structure of NiFe-LDH / Co-C@NF. The NiFe-LDH grown on Co-C@NF material exhibits a nano-flower-like layer structure encapsulating spherical structures. Compared to the structure grown on nickel foam, the NiFe-LDH grown on Co-C@NF material possesses a larger interlayer spacing and specific surface area, fully exposing the catalytic active sites.

[0039] 2. XRD patterns of NiFe-LDH / Co-C@NF materials were determined, and the results are as follows: Figure 4 As shown in the figure. The horizontal axis represents the diffraction angle (2θ), and the vertical axis represents the diffraction intensity. The figure shows that due to the limited growth freedom on the nickel foam, some positions were blocked by the nickel foam skeleton, resulting in the absence of the (003) crystal phase. The (006), (012), (015), (018), and (0015) crystal phases at 23.28°, 34.56°, 39.01°, 46.43°, and 60.28° are respectively the corresponding to the (006), (012), (015), (018), and (0015) crystal phases, indicating that NiFe-LDH was successfully grown on Co-C@NF.

[0040] 3. The double-layer capacitance of three different materials (Co-C@NF, NiFe-LDH@NF, and NiFe-LDH / Co-C@NF) was compared, and the comparison results are as follows: Figure 5 As shown, the horizontal axis represents the scan rate, and the vertical axis represents the change in current density (Δj). The larger the slope, the higher the double-layer capacitance (C). dl The larger the value, the larger the corresponding electrochemical active area (ECSA). Figure 5 The results show that the ECSA of NiFe-LDH grown on nickel foam is very small, but the ECSA is greatly increased by growing on the Co-C surface, which indirectly shows that Co-C is beneficial for NiFe-LDH to increase the interlayer spacing and expose active sites.

[0041] 4. The performance of electrode materials in oxygen evolution was measured and compared.

[0042] (1) Linear cyclic voltammetry (LSV) results of NiFe-LDH / Co-C@NF electrode material, comparative NiFe-LDH@NF electrode material, comparative Co-C@NF electrode material, RuO2@NF electrode material and pretreated NF are as follows: Figure 6 As shown, the horizontal axis represents the potential (E) relative to the reversible hydrogen electrode (RHE), and the vertical axis represents the current density. It can be seen that the NiFe-LDH / Co-C@NF electrode material exhibits the best electrochemical performance at a current density of 10 mA cm⁻¹. -2 At that time, the overpotential was only 147mV.

[0043] (2) Tafel slope determination results of NiFe-LDH / Co-C@NF electrode material, comparative NiFe-LDH@NF electrode material, comparative Co-C@NF electrode material, RuO2@NF electrode material and pretreated NF are as follows: Figure 7 As shown in the figure, the horizontal axis represents the logarithm of the current density (Logj), and the vertical axis represents the potential (E) relative to the RHE. The lower the Tafel slope, the faster the kinetic OER reaction rate. It can be seen that the NiFe-LDH / Co-C@NF electrode material provided by this invention has a faster OER reaction rate.

[0044] 5. By testing the NiFe-LDH / Co-C@NF electrode material provided by the invention at 100 mA cm⁻¹ -2 Long-term durability under constant high current density was tested, and the results are as follows: Figure 8 As shown in the figure, the horizontal axis represents time, and the vertical axis represents the potential (E) relative to the RHE. It can be seen that the material provided by this invention remains stable after 100 hours without significant performance degradation, demonstrating the excellent stability of this catalyst.

[0045] In summary, this invention provides a self-supporting heterostructure electrocatalytic oxygen evolution electrode NiFe-LDH / Co-C@NF and its preparation method. By impregnating a nickel foam layer with ZIF-67 grown in situ, the high specific surface area of ​​ZIF-67 provides growth sites for NiFe-LDH, increasing the interlayer spacing of NiFe-LDH and exposing active sites. Furthermore, the two materials form a heterostructure, utilizing their synergistic effect to improve catalytic activity and effectively reduce overpotential. The NiFe-LDH / Co-C@NF provided by this invention has potential application value in electrode materials for oxygen evolution batteries.

[0046] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a self-supporting heterostructure electrocatalytic oxygen evolution electrode, characterized in that, The specific steps are as follows: S1. The nickel foam was ultrasonically washed sequentially with acetone, 0.1 M dilute hydrochloric acid, anhydrous ethanol and deionized water for 15 min, and then dried in a vacuum oven at 60℃ to obtain pretreated nickel foam. S2. Prepare Co(NO3)2·6H2O-methanol solution, 0.5M 2-methylimidazole-methanol solution, and 0.125M triethylamine-methanol solution with concentrations of 0.125M, respectively. Immerse the pretreated nickel foam in each of the Co(NO3)2·6H2O-methanol solution, 2-methylimidazole-methanol solution, and triethylamine-methanol solution forty times in sequence to obtain nickel foam with ZIF-67 growth. Then wash it several times with methanol and dry it in a vacuum drying oven at 60℃ for 8 h to obtain ZIF-67@NF. S3. The ZIF-67@NF was heated to 700℃ and held for 2 h in a high-purity argon atmosphere, and then Co-C@NF material was obtained by inert high-temperature annealing; S4. Prepare a mixed solution with a total concentration of 0.2 M and a solute molar ratio of NiSO4 to Fe(NO3)3 of 1:1 as the electrolyte; S5. Co-C@NF was subjected to NiFe-LDH electrodeposition reaction in the electrolyte. The potential was set to -1 V and the deposition time was 600 s. After the reaction was completed, the electrodeposition electrode was washed three times with anhydrous ethanol and deionized water, respectively, and then dried in a vacuum drying oven at 60℃ for 8 h to obtain NiFe-LDH / Co-C@NF electrocatalytic oxygen evolution electrode.

2. The oxygen evolution electrode prepared by the preparation method according to claim 1.

3. The application of the oxygen evolution electrode as described in claim 2 in the electrolysis of water to produce hydrogen.

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