Self-supporting heterostructure electrocatalytic oxygen evolution electrode and preparation method thereof

Abstract

The invention discloses a self-supporting heterostructure electrocatalytic oxygen evolution electrode and a preparation method thereof. The method comprises the following steps: growing a ZIF-67 precursor on a porous conductive carrier foamed nickel in situ, and continuously annealing at 700 DEG C for two hours to obtain Co-C-coated NF; the high specific surface area of Co-C-coated NF is utilized, NiFe-LDH is electrically deposited on the surface of the Co-C-coated NF, and the self-supporting NiFe-LDH coated Co-C heterostructure catalytic electrode is prepared. According to the electrode, NiFe-LDH is firmly anchored on the surface of Co-C by utilizing the characteristic of high specific surface area of ZIF-67, the interlayer spacing of NiFe-LDH is increased, the efficient active sites of NiFe-LDH are exposed, and the electrode can reach the current density of 10mA cm <-2 > under the ultralow overpotential of 147mV by utilizing the coordination effect of three transition metal centers of Ni, Fe and Co, so that the electrode has an application prospect in oxygen evolution batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic electrode materials, and in particular to a self-supporting heterogeneous structure electrocatalytic oxygen evolution electrode and a preparation method thereof. Background Art

[0002] At present, fossil energy has problems such as oil shortage, environmental pollution and greenhouse gas emissions. Hydrogen energy products are environmentally friendly and have abundant reserves, making it one of the favorable choices for future energy. Water electrolysis is a major way to produce hydrogen, but since the anode oxygen evolution reaction (OER) is a four-electron transfer process, the reaction kinetics are slow and there is a high overpotential. IrO 2 and RuO 2 It is an efficient noble metal catalyst for OER. However, noble metal materials are difficult to be widely used due to their high prices. Therefore, it is urgent to develop transition metal catalysts, such as Ni, Fe, and Co-based catalysts, to improve the efficiency of hydrogen production by water electrolysis.

[0003] ZIF-67 and NiFe-LDH are two commonly used non-precious metal OER catalysts; ZIF-67 is a MOF structure with cobalt as the metal center and dimethylimidazole as the ligand. Its porous structure increases the exposure of active sites and provides a certain catalytic effect. However, its poor intrinsic activity and unstable structure limit its use in OER catalysis. NiFe-LDH is just the opposite of ZIF-67. The electronic synergy between Ni and Fe hydroxide greatly improves its intrinsic catalytic activity, but LDH is difficult to fully expose active sites due to the small interlayer spacing. Based on this, the present invention intends 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 the present invention is to provide a transition metal catalyzed OER electrode in view of the fact that existing OER noble metal catalysts are difficult to be widely used.

[0005] In order to achieve the above object, the present invention provides a method for preparing a self-supporting heterostructure electrocatalytic oxygen evolution electrode, the specific steps are as follows:

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

[0007] S2. Configuration Co(NO 3 ) 2 6H 2 The pretreated nickel foam was sequentially exposed to Co(NO 3 ) 2 6H2 O-methanol solution, 2-methylimidazole-methanol solution, and triethylamine-methanol solution were immersed forty times respectively to obtain nickel foam covered with ZIF-67, which was washed with methanol several times and dried in a vacuum drying oven at 60°C for 8 hours to obtain ZIF-67@NF;

[0008] S3. The ZIF-67@NF was heated to 700 °C in an inert atmosphere for 2 h, and the Co-C@NF material was obtained by inert high temperature annealing.

[0009] S4. Prepare NiSO with a total concentration of 0.2M 4 and Fe(NO 3 ) 3 A mixed solution of is used as an electrolyte;

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

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

[0012] Preferably, the above-mentioned Co(NO 3 ) 2 6H 2 The concentrations of the methanol solution of O, the methanol solution of 2-methylimidazole, and the methanol solution of triethylamine are 0.125 M, 0.5 M, and 0.125 M, respectively.

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

[0014] Preferably, the electrolyte in the above preparation method, wherein NiSO 4 and Fe(NO 3 ) 3 The solute molar ratio is 1:1.

[0015] Preferably, in the electrodeposition reaction in the above preparation method, the potential is set to -1V and the deposition time is 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, and comprises an electrode material for preparing an oxygen evolution battery, etc. The electrode material has the advantages of high exposure of catalytic active sites and can effectively reduce overpotential.

[0017] The present invention has the following advantages:

[0018] The electrode material preparation production process provided by the present invention is simple, the conditions are mild, the cost is low, the raw materials are cheap, and the two steps of preparation are synthesized at room temperature, the preparation time is short, and the preparation efficiency is high. The catalytically active material is grown in situ on the porous nickel foam, avoiding the use of adhesives, saving costs, and the in-situ growth further avoids the situation where the film layer falls off and causes the catalyst to be deactivated.

[0019] The present invention utilizes the porous structure of ZIF-67 as a precursor, increases the interlayer spacing of NiFe-LDH, forms a nanoflower heterostructure catalyst, exposes more active sites, and utilizes the synergistic effect of the two structures to enhance its catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0023] Figure 4 This is the XRD result of NiFe-LDH / Co-C@NF in the present invention.

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

[0025] Figure 6 The results are a comparison of the oxygen evolution performance of the NiFe-LDH / Co-C@NF electrode material provided in the present invention.

[0026] Figure 7 The three different materials in the present invention are NF, RuO 2 @NF's Tafel slope comparison chart.

[0027] Figure 8 The NiFe-LDH / Co-C@NF electrode material provided by the present invention has a high conductivity at 100 mA cm -2 Long-term durability testing at constant high current density. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0030] Example 1

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

[0032] S1. Ultrasonic cleaning of nickel foam (NF) (1cm*5cm) was performed with acetone, 0.1M HCl, ethanol and water respectively, with each cleaning lasting 15min. The cleaned nickel foam was placed in a vacuum drying oven at 60℃ for drying;

[0033] S2., prepare Co(NO 3 ) 2 6H 2 O-methanol solution, 0.5M 2-methylimidazole-methanol solution, 0.125M triethylamine-methanol solution, and the nickel foam was prepared according to Co(NO 3 ) 2 6H 2 The nickel foam covered with ZIF-67 was washed with methanol for several times and dried in a vacuum oven at 60°C for 8 h to obtain ZIF-67@NF.

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

[0035] S4. Prepare NiSO with a total concentration of 0.2M 4 and Fe(NO 3 ) 3 A mixed solution of is used 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 the potential set to -1 V and the deposition time being 600 s. After the reaction, it was washed three times with anhydrous ethanol and deionized water respectively and dried in a vacuum drying oven at 60 °C for 8 h to obtain a NiFe-LDH / Co-C@NF electrocatalytic oxygen evolution electrode.

[0037] Experimental Example 1 Characterization of electrode materials

[0038] 1. The samples Co-C@NF, NiFe-LDH@NF and NiFe-LDH / Co-C@NF in Example 1 were observed by electron microscope, and their SEM structures were shown in Figure 1 , Figure 2 , Figure 3 shown. Figure 1 The SEM structure of the sample Co-C@NF; Figure 2 This is the SEM structure of NiFe-LDH grown on nickel foam. It can be seen that NiFe-LDH grows on nickel foam as a flat layered structure with small interlayer spacing and close stacking. Figure 3 This is the SEM structure of NiFe-LDH / Co-C@NF. The NiFe-LDH grown on the Co-C@NF material is a nano-flower sheet structure wrapped around a spherical structure. Compared with the structure grown on nickel foam, the NiFe-LDH grown on the Co-C@NF material has a larger interlayer spacing and specific surface area, fully exposing the catalytic active sites.

[0039] 2. XRD spectrum of NiFe-LDH / Co-C@NF material was measured, and the results are as follows Figure 4 As shown. The horizontal axis represents the diffraction angle (2θ), and the vertical axis represents the diffraction intensity (Intensity). The figure shows that due to the unfree growth on nickel foam, some positions are blocked by the nickel foam skeleton, resulting in the absence of the (003) crystal phase. 23.28°, 34.56°, 39.01°, 46.43°, 60.28°, etc. correspond to the (006), (012), (015), (018), (0015) and other crystal phases, respectively, indicating that NiFe-LDH has been successfully grown on Co-C@NF.

[0040] 3. The double-layer capacitance of three different materials (Co-C@NF, NiFe-LDH@NF, NiFe-LDH / Co-C@NF) is compared. The comparison results are as follows: Figure 5 As shown, the horizontal axis represents the scan rate (Scan rate), and the vertical axis represents the current density change (Δj). Among them, the larger the slope, the higher the double layer capacitance (C dl ) is larger, the corresponding electrochemically active area (ECSA) is larger. Figure 5 This indicates 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 indicates that Co-C is beneficial for NiFe-LDH to increase the interlayer spacing and expose active sites.

[0041] 4. Measure and compare the oxygen evolution performance of electrode materials.

[0042] (1) NiFe-LDH / Co-C@NF electrode material, comparison of NiFe-LDH@NF electrode material, comparison of Co-C@NF electrode material, RuO 2 The linear cyclic voltammetry (LSV) results of the NF electrode materials and pretreated NF are shown in Figure 6 As shown in the figure, the horizontal axis is the potential (E) relative to the reversible hydrogen electrode (RHE), and the vertical axis represents the current density (Current density). It can be seen that the NiFe-LDH / Co-C@NF electrode material has the best electrochemical performance. When the current density is 10mA cm -2 When , the overpotential is only 147mV.

[0043] (2) NiFe-LDH / Co-C@NF electrode material, comparison of NiFe-LDH@NF electrode material, comparison of Co-C@NF electrode material, RuO 2 @NF electrode material and pretreated NF Tafel slope measurement results are shown in Figure 7 As shown. The abscissa represents the logarithm of the current density (Logj), and the ordinate represents the potential relative to RHE (E). 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 the present invention has a faster OER reaction rate.

[0044] 5. The NiFe-LDH / Co-C@NF electrode material provided by the invention was subjected to a 100 mA cm -2 The long-term durability under constant high current density was tested, and the results are as follows Figure 8 As shown. The horizontal axis is time (Time), and the vertical axis is the potential (E) relative to RHE. It can be seen that the material provided by the present invention is still in a stable state after 100 hours and the performance does not decrease significantly, indicating that the catalyst has excellent stability.

[0045] In summary, the present invention provides a self-supporting heterostructure electrocatalytic oxygen evolution electrode NiFe-LDH / Co-C@NF and a preparation method thereof, wherein ZIF-67 is grown in situ by immersion in the upper layer of nickel foam, and the high specific surface area of ​​ZIF-67 is utilized to provide growth sites for NiFe-LDH, increase the interlayer spacing of NiFe-LDH, expose active sites, and the two materials form a heterostructure, and the synergistic effect thereof is utilized to improve the catalytic activity and effectively reduce the overpotential. The NiFe-LDH / Co-C@NF provided by the present invention has potential application value in electrode materials of oxygen evolution batteries.

[0046] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited 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 sequentially ultrasonically washed with acetone, dilute hydrochloric acid, anhydrous ethanol and deionized water, and dried in a vacuum oven at 60°C to obtain a pretreated nickel foam; S2. Prepare Co(NO3)2·6H2O-methanol solution, 2-methylimidazole-methanol solution, and triethylamine-methanol solution, and immerse the pretreated nickel foam in the Co(NO3)2·6H2O-methanol solution, 2-methylimidazole-methanol solution, and triethylamine-methanol solution forty times, respectively, to obtain a nickel foam covered with ZIF-67, and then wash it with methanol for several times, and place it in a vacuum drying oven at 60°C for 8 hours to obtain ZIF-67@NF; S3. The ZIF-67@NF is heated to 700° C. in an inert atmosphere for 2 h to obtain a Co-C@NF material by inert high temperature annealing; S4. A mixed solution of NiSO4 and Fe(NO3)3 with a total concentration of 0.2M is configured as an electrolyte; S5. The Co-C@NF is subjected to an electrodeposition reaction of NiFe-LDH in the electrolyte. After the reaction, it is washed three times with anhydrous ethanol and deionized water respectively, and dried in a vacuum drying oven at 60°C for 8 hours to obtain a NiFe-LDH / Co-C@NF electrocatalytic oxygen evolution electrode.

2. The preparation method according to claim 1, characterized in that: The concentration of the dilute hydrochloric acid in S1 is 0.1M.

3. The preparation method according to claim 1, characterized in that: In the S2, the concentrations of Co(NO3)2·6H2O-methanol solution, 2-methylimidazole-methanol solution, and triethylamine-methanol solution are 0.125M, 0.5M, and 0.125M, respectively.

4. The preparation method according to claim 1, characterized in that: The inert atmosphere is an inert gas.

5. The preparation method according to claim 4, characterized in that: The inert gas is preferably high-purity argon.

6. The preparation method according to claim 1, characterized in that: The solute molar ratio of NiSO4 and Fe(NO3)3 in the electrolyte is 1:

1.

7. The preparation method according to claim 1, characterized in that: The potential of the electrodeposition reaction is set to -1V and the deposition time is 600s.

8. An oxygen evolution electrode prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the oxygen evolution electrode as claimed in claim 8 in an oxygen evolution battery.

10. The use according to claim 9, characterized in that: The application includes preparing electrode materials for oxygen evolution batteries.

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