A method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea

Abstract

The present invention provides a method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea, which comprises the following steps: S1, placing nickel foam in an HCl solution, and ultrasonically treating for 5-15min, purifying the nickel foam after ultrasonic treatment, and then placing it in a vacuum drying oven for drying; S2, pouring a dilute hydrochloric acid solution into a polytetrafluoroethylene autoclave, adding a Cu salt to the solution, adding a magnetic stirring, and when the solution is completely mixed, stopping stirring, taking out the magnetic, placing the dried nickel foam in a polytetrafluoroethylene autoclave, immersing the nickel foam completely in the solution, sealing the polytetrafluoroethylene autoclave, moving the polytetrafluoroethylene autoclave into a blast oven, and washing and drying to obtain a NiCu-OH / nickel foam electrode. The present invention grows NiCu bimetallic nanosheets in situ on a substrate, relying on the excellent electronic regulation ability and CO poisoning resistance of the Cu element, to solve the problems of low activity and poor durability that are prone to occur in traditional electrode materials for electrolysis of urea.

Description

Technical Field

[0001] The invention belongs to the technical field of urea hydrogen production and energy storage, and in particular relates to a method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolyzing urea. Background Art

[0002] Environmental pollution and energy crisis have hindered the development of modern society and are major challenges faced by all mankind. Therefore, the development of advanced clean energy production technology is the key to achieving sustainable development. Hydrogen fuel is considered to be a new energy carrier with great development space because of its high energy density and zero carbon emissions. In this context, water electrolysis for hydrogen production came into being and is generally considered to be an efficient, low-cost and sustainable green hydrogen production technology. The hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode are two important electrochemical processes in the water electrolysis system. However, OER has a theoretical thermodynamic potential higher than 1.23V because the reaction is controlled by multiple complex and slow proton coupling and electron transfer processes. Therefore, finding an anode reaction that can replace OER is the key to achieving energy-saving hydrogen production. In recent years, urea electrolysis technology has gradually come into people's attention. The theoretical working voltage of urea oxidation reaction (UOR) is only 0.37V, which makes urea electrolysis for hydrogen production have the advantage of low energy consumption compared with water electrolysis. In addition, urea electrolysis technology can also treat urea molecules in wastewater and achieve environmental purification while producing hydrogen. Although UOR has a low starting potential, its six-electron transfer process leads to a large overpotential. It can be seen that the preparation of highly active catalyst electrodes is an important part of realizing efficient urea electrolysis engineering.

[0003] Some precious metal materials have been proven to be the most advanced catalysts today, but their high cost and scarce content limit their actual industrial production. Some transition metal elements, represented by Ni, are considered as substitutes for precious metal elements due to their unique electronic configuration and high crustal content. In addition, some recent studies have confirmed that Ni 3+ is the real active site in the UOR process. 2+ Oxidized to Ni 3+ The high oxidation energy barrier required severely slows down the kinetics of the catalysis. In addition, carbon oxides, as one of the main products of UOR, cause many catalysts to be deactivated by CO poisoning during continuous operation, shortening the service life of the electrode. Summary of the invention

[0004] The present invention provides a method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea. The preparation process is a simple "one-pot method". Cu ions are introduced during the acid etching process of nickel foam, thereby in-situ growing Ni-Cu bimetallic hydroxide nanosheets on the surface of the substrate. The high conductivity of the Cu element and its regulating effect on the external electronic structure of Ni accelerate the electron transfer process of the material, thereby reducing the Ni 2+ The oxidation potential of Cu is 2.34V. In addition, the Cu element has a strong resistance to CO poisoning. The introduction of Cu improves the long-term working stability of the electrode, thereby solving the problems of low activity and poor durability that are prone to occur in traditional electrode materials used for electrolysis of urea.

[0005] In order to achieve the above object, the present invention provides a method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea, which comprises the following steps:

[0006] S1, placing the nickel foam in an HCl solution and ultrasonically treating it for 5-15 minutes, purifying the nickel foam after the ultrasonic treatment, and then drying it in a vacuum drying oven;

[0007] S2. Pour the dilute hydrochloric acid solution into a polytetrafluoroethylene autoclave, add Cu salt into the solution, add a magnetic stirrer, and when the solution is completely mixed, stop stirring, take out the magnetic stirrer, place the dried nickel foam in the polytetrafluoroethylene autoclave, immerse the nickel foam in the solution, seal the polytetrafluoroethylene autoclave, move the polytetrafluoroethylene autoclave into a blast oven, react at 80-150°C, and obtain a NiCu-OH / nickel foam electrode after washing and drying.

[0008] As a further description of the above technical solution:

[0009] The concentration of the HCl solution in step S1 is 3M; the post-ultrasonic purification treatment requires placing the nickel foam in ultrapure water for 15 minutes and then placing it in anhydrous ethanol for 10 minutes.

[0010] As a further description of the above technical solution:

[0011] The Cu salt added in step S2 is Cu(NO 3 ) 2 6H 2 O. The Cu salt added was Cu(NO 3 ) 2 6H 2 O. It is worth noting that Cu 2+ With the characteristic of easy reduction, Cu in the system 2+After contacting with nickel, a substitution reaction occurs and Cu cubes are formed on the surface of nickel foam. The size of Cu cubes can reach several microns, providing more space for the growth of nanosheets.

[0012] As a further description of the above technical solution:

[0013] The stirring time in step S2 is 5 min.

[0014] As a further description of the above technical solution:

[0015] The concentration of the dilute hydrochloric acid solution in step S2 is 1.2×10 -3 M, so that the initial pH of the reaction system is stable between 2.8-3.2. In this pH range, elemental Ni is reacted with H + Etching to generate Ni 2+ Similarly, Cu 2+ The replacement reaction can also provide Ni 2+ . When [Ni 2+ ]·[OH - ]≥Ksp, Ni 2+ A hydrolysis reaction will occur to generate Ni(OH) 2 Nanosheets Since the reaction is in an acidic environment, Ni(OH) 2 The thickness of the nanosheet is limited, forming an ultra-thin three-dimensional interconnected nanosheet structure. 2+ The same process will occur, and finally with Ni 2+ Together, double hydroxide nanosheets were generated on the surface of nickel foam and Cu cubes.

[0016] As a further description of the above technical solution:

[0017] Preferably, the reaction temperature in step S2 is 100°C.

[0018] As a further description of the above technical solution:

[0019] The reaction time in step S2 is 10-30 hours.

[0020] As a further description of the above technical solution:

[0021] Preferably, the reaction time is 20 hours.

[0022] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0023] (1) NiCu bimetallic nanosheets were in situ grown on the substrate using the acid etching method. The excellent electron regulation ability of the Cu element accelerated the electron transfer process on the material surface.

[0024] (2) The anti-CO poisoning characteristics of the Cu element are utilized to improve the long-term working ability of the catalyst.

[0025] (3) Micrometer-sized Cu cubes were constructed on the surface of nickel foam, which provided a larger growth space for catalytically active nanosheets and thus increased the density of nanosheets on the substrate.

[0026] (4) The electrode preparation in the present invention adopts a "one-pot method", which has a simple process, is easy to scale up production, and involves very few reaction raw materials, thereby greatly reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 The present invention is a flow chart of a method for preparing a nickel-based high-density nanosheet electrode for electrolyzing urea.

[0029] Figure 2 This is the SEM image of the NiCu-OH / nickel foam involved in Example 1.

[0030] Figure 3 Ni(OH) 2 / SEM image of nickel foam electrode.

[0031] Figure 4 The linear voltammetry (LSV) test curves of different electrode materials applied to the hydrogen evolution process and urea oxidation process in Comparative Example 1 are shown.

[0032] Figure 5 Nyquist curves of different electrodes involved in Comparative Example 1.

[0033] Figure 6 The chronopotentiometry curves of the different electrodes involved in Comparative Example 1 are shown in FIG.

[0034] Figure 7 This is the SEM image of the electrode materials with different Cu doping amounts involved in Comparative Example 2.

[0035] Figure 8The LSV test curves of the electrode materials with different Cu doping amounts involved in Comparative Example 2 applied to the hydrogen evolution process and the urea oxidation process. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention will be described in detail below.

[0037] The present invention provides a method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolyzing urea, comprising the following steps:

[0038] S1, placing the nickel foam in an HCl solution and ultrasonically treating it for 5-15 minutes, purifying the nickel foam after the ultrasonic treatment, and then drying it in a vacuum drying oven;

[0039] S2. Pour the dilute hydrochloric acid solution into a polytetrafluoroethylene autoclave, add Cu salt into the solution, add a magnetic stirrer, and when the solution is completely mixed, stop stirring, take out the magnetic stirrer, place the dried nickel foam in the polytetrafluoroethylene autoclave, immerse the nickel foam in the solution, seal the polytetrafluoroethylene autoclave, move the polytetrafluoroethylene autoclave into a blast oven, react at 80-150°C, and obtain a NiCu-OH / nickel foam electrode after washing and drying.

[0040] The concentration of the HCl solution in step S1 is 3M; the post-ultrasonic purification treatment requires placing the nickel foam in ultrapure water for 15 minutes and then placing it in anhydrous ethanol for 10 minutes.

[0041] The Cu salt added in step S2 is Cu(NO 3 ) 2 6H 2 O. The Cu salt added was Cu(NO 3 ) 2 6H 2 O. It is worth noting that Cu 2+ With the characteristic of easy reduction, Cu in the system 2+ After contacting with nickel, a substitution reaction occurs and Cu cubes are formed on the surface of nickel foam. The size of Cu cubes can reach several microns, providing more space for the growth of nanosheets.

[0042] The stirring time in step S2 is 5 min.

[0043] The concentration of the dilute hydrochloric acid solution in step S2 is 1.2×10 -3 M, so that the initial pH of the reaction system is stable between 2.8-3.2. In this pH range, elemental Ni is reacted with H + Etching to generate Ni 2+ Similarly, Cu 2+The replacement reaction can also provide Ni 2+ . When [Ni 2+ ]·[OH - ]≥Ksp, Ni 2+ A hydrolysis reaction will occur to generate Ni(OH) 2 Nanosheets Since the reaction is in an acidic environment, Ni(OH) 2 The thickness of the nanosheet is limited, forming an ultra-thin three-dimensional interconnected nanosheet structure. 2+ The same process will occur, and finally with Ni 2+ Together, double hydroxide nanosheets were generated on the surface of nickel foam and Cu cubes.

[0044] Preferably, the reaction temperature in step S2 is 100°C.

[0045] The reaction time in step S2 is 10-30 hours. Preferably, the reaction time is 20 hours.

[0046] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0047] (1) NiCu bimetallic nanosheets were in situ grown on the substrate using the acid etching method. The excellent electron regulation ability of the Cu element accelerated the electron transfer process on the material surface.

[0048] (2) The anti-CO poisoning characteristics of the Cu element are utilized to improve the long-term working ability of the catalyst.

[0049] (3) Micrometer-sized Cu cubes were constructed on the surface of nickel foam, which provided a larger growth space for catalytically active nanosheets and thus increased the density of nanosheets on the substrate.

[0050] (4) The electrode preparation in the present invention adopts a "one-pot method", which has a simple process, is easy to scale up production, and involves very few reaction raw materials, thereby greatly reducing the production cost.

[0051] Example 1

[0052] A method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea provided in Example 1 comprises the following steps:

[0053] Pretreatment of nickel foam substrate:

[0054] Place a 2×3 cm commercial nickel foam in a 3M HCl solution and ultrasonically treat it for 10 min. Place the ultrasonically treated nickel foam in ultrapure water and ultrasonically treat it for 15 min. Finally, place the nickel foam in anhydrous ethanol and continue ultrasonically treating it for 10 min. Place the pretreated nickel foam in a 60°C vacuum blower drying oven and dry it for 2 hours.

[0055] Preparation of NiCu bimetallic nanosheet electrode (NiCu-OH / nickel foam):

[0056] 20mL 1.2×10 -3 M dilute hydrochloric acid solution was poured into a 100 mL polytetrafluoroethylene autoclave, and 0.3 mmol Cu(NO 3 ) 2 6H 2 O, add a magnetic bar and stir for 5 minutes. When the solution is completely mixed, stop the stirring device and remove the magnetic bar. Place the dried nickel foam in the reactor, immerse it completely in the solution, and seal the reactor. Move the polytetrafluoroethylene high-pressure reactor into a blast oven and react at 100°C for 20 hours. After the reaction is completed, cool the reactor naturally to room temperature and take out the internal materials. Finally, rinse the material repeatedly with ultrapure water and dry it in a 60°C vacuum blast drying oven for 2 hours to obtain a NiCu-OH / nickel foam electrode.

[0057] Figure 2 This is the SEM image of NiCu-OH / nickel foam. It can be seen from the figure that the surface of the nickel foam substrate is loaded with cubes with a side length of several microns. In fact, it is composed of Cu 2+ The reduced Cu single substance NiCu double hydroxide nanosheets grow on the surface of nickel foam and Cu cubes in a three-dimensional interconnected manner, and the nanosheets can be loaded on the planes of all directions of the Cu cubes, and the thickness of the nanosheets is maintained at 10nm-20nm.

[0058] Comparative Example 1:

[0059] Pretreatment of nickel foam substrate:

[0060] Place a 2×3 cm commercial nickel foam in a 3M HCl solution and ultrasonically treat it for 10 min. Place the ultrasonically treated nickel foam in ultrapure water and ultrasonically treat it for 15 min. Finally, place the nickel foam in anhydrous ethanol and continue ultrasonically treating it for 10 min. Place the pretreated nickel foam in a 60°C vacuum blower drying oven and dry it for 2 hours.

[0061] Ni(OH) 2 Preparation of Nanosheet Electrodes (Ni(OH) 2 / Nickel Foam):

[0062] 20mL 3.6×10-3 Pour the dilute hydrochloric acid solution into a 100mL polytetrafluoroethylene autoclave, and place the dried nickel foam in the autoclave so that it is completely immersed in the solution, and seal the autoclave. Move the polytetrafluoroethylene autoclave into a blast oven and react at 100°C for 20 hours. After the reaction is completed, cool the autoclave naturally to room temperature and take out the internal materials. Finally, rinse the material repeatedly with ultrapure water and dry it in a 60°C vacuum blast oven for 2 hours to obtain Ni(OH) 2 / Nickel foam electrode.

[0063] Due to Cu 2+ Ksp compared to Ni 2+ The size of the catalyst has been reduced by dozens of orders of magnitude, making it easier for the hydrolysis process to occur and produce H + Therefore, when removing Cu from the reaction system 2+ After that, in order to maintain a consistent pH atmosphere, the concentration of the dilute hydrochloric acid solution needs to be appropriately increased.

[0064] Since the NiCu-OH / nickel foam electrode contains single substance Cu, it appears purple-red, while the Ni(OH)2 / nickel foam electrode has only Ni(OH) 2 Nanosheets, their actual color is dark gray.

[0065] Figure 3 For Ni(OH) 2 SEM image of nickel foam. As can be seen from the figure, a large number of nanosheets are loaded on the surface of nickel foam. The thickness of the nanosheets and their three-dimensional interconnected structure are consistent with those of NiCu-OH / nickel foam electrode. The difference is that due to the lack of Cu 2+ , there is no cubic structure on the surface of the material, and the nanosheets grow flat on the same plane.

[0066] Figure 4 The LSV performance comparison of each electrode in comparative example 1 for hydrogen evolution process and urea oxidation process. NiCu-OH / nickel foam electrode has better performance and higher hydrogen production efficiency. The main reason is that Cu adjusts the electronic structure of Ni and increases the conductivity of the material, thereby significantly accelerating the charge transfer process on the electrode surface, making Ni 2+ Easier to convert to Ni 3+ In addition, since the nickel foam surface has Cu cubes and nanosheets with active substances can grow on all planes of the cubes, the electrode has a higher density of nanosheet structures and thus carries more catalytic sites.

[0067] Figure 5: The Nyquist curves of each electrode in Comparative Example 1. Among them, the test curve of NiCu-OH / nickel foam has the smallest radius, indicating that the charge transfer resistance of the material is small, confirming that it has a faster electron transfer process.

[0068] Figure 6 The chronopotentiometry curves of the electrodes in Comparative Example 1 are used to evaluate the long-term working ability of the electrodes. -2 At the current density of , the test curve of NiCu-OH / nickel foam fluctuated within 48 hours, but its potential remained at a relatively stable level. 2 The driving potential of the NiCu-OH / nickel foam electrode increases with the extension of working time. Moreover, this phenomenon does not occur in the HER process, but only in the UOR process. It can be considered that the carbon oxides adsorbed on the electrode surface reduce the activity of the electrode. This also confirms that the excellent stability of NiCu-OH / nickel foam is related to the introduction of Cu.

[0069] Comparative Example 2:

[0070] Pretreatment of nickel foam substrate:

[0071] Place a 2×3 cm commercial nickel foam in a 3M HCl solution and ultrasonically treat it for 10 min. Place the ultrasonically treated nickel foam in ultrapure water and ultrasonically treat it for 15 min. Finally, place the nickel foam in anhydrous ethanol and continue ultrasonically treating it for 10 min. Place the pretreated nickel foam in a 60°C vacuum blower drying oven and dry it for 2 hours.

[0072] Preparation of NiCu bimetallic high-density nanosheet electrodes with different Cu loadings (Ni(OH) 2 / Nickel Foam):

[0073] 20mL 3.6×10 -3 M dilute hydrochloric acid solution was poured into a 100 mL polytetrafluoroethylene autoclave, and 0.1 mmol and 0.5 mmol Cu(NO 3 ) 2 6H 2 O, add a magnetic bar and stir for 5 minutes. When the solution is completely mixed, stop the stirring device and remove the magnetic bar. Place the dried nickel foam in the reactor, immerse it completely in the solution, and seal the reactor. Move the polytetrafluoroethylene high-pressure reactor into a blast oven and react at 100°C for 20 hours. After the reaction is completed, cool the reactor naturally to room temperature and take out the internal materials. Finally, rinse the material repeatedly with ultrapure water and dry it in a 60°C vacuum blast drying oven for 2 hours to obtain NiCu-OH / nickel foam electrodes with different Cu loadings.

[0074] Figure 7 The SEM images of NiCu-OH / nickel foam electrodes with different Cu loadings involved in Comparative Example 2. 3 ) 2 6H 2 When the addition amount of O is 0.1 mmol, there is no obvious Cu cube on the surface of nickel foam, and its basic morphology is similar to that of Ni(OH) 2 / foam nickel. When Cu(NO 3 ) 2 6H 2 When the amount of O added was increased to 0.5 mmol, the surface of nickel foam was covered with a thick layer of Cu element, and no nanosheets were generated.

[0075] Figure 8 The LSV performance of NiCu-OH / nickel foam electrodes with different Cu loadings for hydrogen evolution and urea oxidation is compared. 3 ) 2 6H 2 O is the optimal addition amount. Under this condition, the electrode prepared has the best hydrogen evolution and urea oxidation performance. 3 ) 2 6H 2 O addition, the Cu doping amount is low, so its regulation effect on Ni is not obvious; and due to the absence of Cu cubes, the nanosheets can only grow on the plane, making their growth density low and the catalytic active substances of the electrode insufficient. 3 ) 2 6H 2 For the electrode prepared with less O addition, the thick Cu single layer on the surface hinders the formation of nanosheets.

[0076] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea, It is characterized in that The following steps are involved: S1, placing the nickel foam in an HCl solution and ultrasonically treating it for 5-15 minutes, purifying the nickel foam after the ultrasonic treatment, and then drying it in a vacuum drying oven; S2. Pour 20 mL of dilute hydrochloric acid solution into a polytetrafluoroethylene autoclave, and add 0.3 mmol of Cu salt to the solution. Add a magnetic stirrer. When the solution is completely mixed, stop stirring, take out the magnetic stirrer, place the dried nickel foam in the polytetrafluoroethylene autoclave, immerse the nickel foam in the solution, seal the polytetrafluoroethylene autoclave, move the polytetrafluoroethylene autoclave into a blast oven, react at 80-150°C, and obtain a NiCu-OH / nickel foam electrode after washing and drying.

2. The method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea according to claim 1, It is characterized in that The concentration of the HCl solution in step S1 is 3M; the post-ultrasonic purification treatment requires placing the nickel foam in ultrapure water for 15 minutes and then placing it in anhydrous ethanol for 10 minutes.

3. The method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea according to claim 1, It is characterized in that The Cu salt added in step S2 is Cu(NO 3 ) 2 6H 2 O.

4. The method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea according to claim 1, It is characterized in that The stirring time in step S2 is 5 min.

5. The method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea according to claim 1, It is characterized in that The concentration of the dilute hydrochloric acid solution in step S2 is 1.2×10 -3 M, so that the initial pH of the reaction system is stabilized between 2.8-3.

2.

6. The method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea according to claim 1, It is characterized in that The reaction temperature in step S2 is 100°C.

7. The method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea according to claim 1, It is characterized in that The reaction time in step S2 is 10-30 hours.

8. The method for preparing a nickel-copper bimetallic array nanosheet electrode for electrolysis of urea according to claim 7, It is characterized in that The reaction time is 20 hours.

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