Preparation method and application of al-doped cuo nanosheet flower electrocatalyst

Abstract

This invention discloses a method for preparing and applying an Al-doped CuO nanoflower electrocatalyst, belonging to the technical field of electrocatalytic ammonia synthesis catalyst preparation. The method involves in-situ growth of aluminum into copper oxide, while simultaneously altering the morphology of the copper oxide through Joule heating to create nanoflower-like structures. Specifically, copper hydroxide is first prepared, and then aluminum is loaded onto the surface of the copper hydroxide using an aluminum salt as a precursor. The Al-doped CuO nanoflower catalyst material is then prepared using a Joule heating device. This invention significantly improves the electrocatalytic performance of the catalyst by doping CuO with aluminum and simultaneously modifying its morphology. The electrocatalyst prepared by this invention exhibits excellent performance in 0.1 mol / L NO3. ‑ In alkaline solution, it exhibits optimal performance at -0.635 V vs. RHE, achieving a Faraday efficiency of 95.7% and approximately 60 mg h⁻¹. ‑1 cm ‑2 The ammonia yield is high. The electrocatalyst prepared in this invention is simple, convenient, and inexpensive, and the resulting material exhibits excellent electrocatalytic performance in the reduction of nitrates to ammonia.

Description

Technical Field

[0001] This invention relates to the field of high-efficiency electrocatalytic reduction catalyst synthesis technology, and in particular to a method for preparing and applying an Al-doped CuO nanoflower electrocatalyst. Background Technology

[0002] Ammonia (NH3) is considered a promising energy carrier and is expected to play a crucial role in future energy solutions. Simultaneously, NH3 is an essential raw material for the synthesis of important agricultural fertilizers, chemical compounds, and other nitrogen-rich products. Currently, ammonia synthesis worldwide primarily relies on the Harber-Bosch process, but this process still faces several challenges: it requires harsh conditions (high temperatures of 350–550°C and high pressures of 150–350 atm (1 atm = 10⁵ Pa)) to drive the reaction of nitrogen (N₂) and hydrogen (H₂). Furthermore, the Harber-Bosch process consumes large amounts of fossil fuels and emits significant amounts of greenhouse gases, with a nitrogen recovery rate of only about 50%. This not only results in substantial energy waste but also leads to serious environmental problems.

[0003] Electrocatalytic synthesis of NH3 has become a research hotspot as a promising alternative. Electrocatalytic NO3 synthesis... - The NO3RR reduction reaction can synthesize NH3 using electrical energy under environmental conditions. It can generate high-value-added NH3 products while solving the problem of pollutants in wastewater, thus achieving a green nitrogen cycle. Therefore, the research on NO3RR catalysts is a hot topic.

[0004] It is generally believed that the initial NO3 - Reduced to NO2 - The NO3RR reaction is a major obstacle in most metal catalyst systems. Furthermore, competitive hydrogen evolution also occurs simultaneously with the nitrate reduction process. Therefore, to develop electrocatalytic nitrate reduction to ammonia technology, a catalytic electrode with high selectivity and high stability is urgently needed to generate ammonia. Summary of the Invention

[0005] To address the technical problems mentioned in the background section, this invention provides a method for preparing Al-doped CuO nanosheet electrocatalysts, thereby improving the selectivity and stability of ammonia electrocatalysis.

[0006] This invention is achieved using the following technical solution: a method for preparing Al-doped CuO nanosheet electrocatalyst, comprising the following steps:

[0007] Step 1: Ultrasonically clean the foamed copper in hydrochloric acid, ethanol, and water respectively, and finally dry it in a vacuum drying oven for later use.

[0008] Step 2: Immerse the cleaned foamed copper in a mixed solution of sodium hydroxide and ammonium persulfate to react and obtain copper hydroxide;

[0009] Step 3: Immerse the copper hydroxide prepared in Step 2 in an aluminum salt solution, and after a period of time, remove it and let it air dry.

[0010] Step 4: Place the dried material on a graphite plate and heat it using a Joule heating device to obtain the Al-doped CuO nanoparticle catalyst.

[0011] Specifically, in step 1, the concentration of the dilute hydrochloric acid solution is 1-2 mol / L. -1 The ultrasonic treatment time is 15-20 min. The preferred hydrochloric acid concentration is 1 mol / L. -1 .

[0012] Specifically, in step 2, the concentration of the mixed solution of sodium hydroxide and ammonium persulfate is 1 mol / L. -1 Sodium hydroxide and 0.1 mol L -1 Ammonium persulfate. The copper foam is soaked in a mixed solution of sodium hydroxide and ammonium persulfate for 15-30 minutes. Preferably, the copper foam is soaked for 20 minutes.

[0013] Specifically, the aluminum salt in step 3 is one of aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum oxide. Preferably, the aluminum salt is aluminum nitrate. The concentration of the aluminum salt solution is 0.5 mM, and the copper hydroxide soaking time is 10-30 min; preferably, the soaking time is 20 min.

[0014] Specifically, in step 4, the Joule heating temperature is 700-900℃, the voltage is set to 20 V, the current is set to 200-250 A, and the duration is 3-8 s. Preferably, the Joule heating temperature is 800℃, the voltage is set to 20 V, the current is set to 250 A, and the duration is 5 s.

[0015] One object of the present invention is to prepare an Al-doped CuO nanoflower catalyst, which is prepared by the above-described method.

[0016] Another objective of this invention is the application of a catalyst: the catalyst is used in the electrocatalytic reduction of nitrate to ammonia, and the electrocatalytic reduction of nitrate to ammonia is carried out at room temperature and pressure.

[0017] The obtained Al-doped CuO nanoflower electrocatalyst achieves ampere-level current densities when used for the electrocatalytic reduction of nitrate to ammonia, while also exhibiting excellent Faradaic efficiency and ammonia yield. Furthermore, the preparation method of this Al-doped CuO nanoflower electrocatalyst is simple and low-cost. The use of Joule heating not only modifies the microstructure of CuO but also accelerates the material preparation time, significantly saving time and costs. Simultaneously, Al doping alters its internal electronic structure, greatly improving the technical effect of nitrate to ammonia production. This invention has the following superior effects: An Al-doped CuO nanoflower electrocatalyst and its preparation method, firstly, copper foam is cut and immersed in a mixed solution of sodium hydroxide and ammonium persulfate. During this process, the copper on the copper foam is oxidized to copper hydroxide. Then, the copper hydroxide is immersed in an aluminum salt solution. Finally, the material is placed on a graphite plate and heated using a Joule heating device to obtain the Al-doped CuO nanoflower electrocatalyst material.

[0018] The obtained Al-doped CuO nanosheet electrocatalyst material achieved ampere-level current densities when used for the electrocatalytic reduction of nitrate to ammonia, while also exhibiting excellent Faradaic efficiency and ammonia yield. At -0.635 V vs. RHE, it achieved a Faradaic efficiency of 95.7% and a yield of approximately 60 mg h⁻¹. -1 cm -2 ammonia yield.

[0019] The preparation method of this nanoflower electrocatalyst material is low-cost and short-time, and it is expected to have good application prospects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 This is the XRD pattern of the Al-doped CuO nanoflower electrocatalyst material prepared in Example 2.

[0022] Figure 2 This is a SEM image of the Al-doped CuO nanoflower electrocatalyst material prepared in Example 2.

[0023] Figure 3 This is a TEM image of the Al-doped CuO nanosheet electrocatalyst material prepared in Example 2.

[0024] Figure 4 This is the XPS image of the Al-doped CuO nanosheet electrocatalyst material prepared in Example 2.

[0025] Figure 5 This is a comparison chart of the LSV of the Al-CuO material prepared in Example 2 and the CuO material prepared in Comparative Example 1.

[0026] Figure 6 The graph shows the Faraday efficiency and ammonia yield of the Al-doped CuO nanosheet electrocatalyst material prepared in Example 2. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention discloses a method for preparing Al-doped CuO nanosheet electrocatalysts and their applications.

[0029] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0030] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0031] Example 1

[0032] (1) Take 41.67 mL of concentrated hydrochloric acid and add deionized water to 500 mL to obtain 1 M hydrochloric acid.

[0033] (2) Cut 2*3 cm of copper foam, and ultrasonically clean it for 15 min in 1 M hydrochloric acid, ethanol and deionized water respectively. Finally, dry it in a vacuum drying oven at 60 ℃ for later use.

[0034] (3) Weigh 20 g of sodium hydroxide, add the sodium hydroxide to an appropriate amount of deionized water, and after the sodium hydroxide is completely dissolved, transfer the solution to a 500 mL volumetric flask and dilute the solution to the 500 mL mark with deionized water to obtain a 1 M sodium hydroxide solution.

[0035] (4) Weigh 0.4564 g of ammonium persulfate, add 20 mL of 1 M sodium hydroxide solution, and dissolve by sonication. After dissolution, soak the cleaned copper foam in the solution for 20 min to obtain blue copper hydroxide.

[0036] (5) Clean the generated copper hydroxide: repeatedly wash with deionized water. Prepare 20 mL of 0.5 mM aluminum nitrate solution, immerse the cleaned copper hydroxide in the aluminum nitrate solution for 10 min, and then allow the material to air dry naturally.

[0037] (6) Place the dried material on a graphite plate and set the Joule heating program: voltage 20 V, current 250 A, duration 5 s, and temperature 800 ℃. After Joule heating, Al-doped CuO nanosheet material can be obtained.

[0038] Example 2

[0039] (1) Take 41.67 mL of concentrated hydrochloric acid and add a certain amount of deionized water to 500 mL to obtain 1 M hydrochloric acid.

[0040] (2) Cut 2*3 cm of copper foam, and ultrasonically clean it for 15 min in 1 M hydrochloric acid, ethanol and deionized water respectively. Finally, dry it in a vacuum drying oven at 60 ℃ for later use.

[0041] (3) Weigh 20 g of sodium hydroxide, add the sodium hydroxide to an appropriate amount of deionized water, and after the sodium hydroxide is completely dissolved, transfer the solution to a 500 mL volumetric flask and dilute the solution to the 500 mL mark with deionized water to obtain a 1 M sodium hydroxide solution.

[0042] (4) Weigh 0.4564 g of ammonium persulfate, add 20 mL of 1 M sodium hydroxide solution, and dissolve by sonication. After dissolution, soak the cleaned copper foam in the solution for 20 min to obtain blue copper hydroxide.

[0043] (5) Clean the generated copper hydroxide: repeatedly wash with deionized water. Prepare 20 mL of 0.5 mM aluminum nitrate solution, immerse the cleaned copper hydroxide in the aluminum nitrate solution for 20 min, and then allow the material to air dry naturally.

[0044] (6) Place the dried material on a graphite plate and set the Joule heating program: voltage 20 V, current 250 A, duration 5 s, and temperature 800 ℃. After Joule heating, Al-doped CuO nanosheet material can be obtained.

[0045] Example 3

[0046] (1) Take 41.67 mL of concentrated hydrochloric acid and add a certain amount of deionized water to 500 mL to obtain 1 M hydrochloric acid.

[0047] (2) Cut 2*3 cm of copper foam, and ultrasonically clean it for 15 min in 1 M hydrochloric acid, ethanol and deionized water respectively. Finally, dry it in a vacuum drying oven at 60 ℃ for later use.

[0048] (3) Weigh 20 g of sodium hydroxide, add the sodium hydroxide to an appropriate amount of deionized water, and after the sodium hydroxide is completely dissolved, transfer the solution to a 500 mL volumetric flask and dilute the solution to the 500 mL mark with deionized water to obtain a 1 M sodium hydroxide solution.

[0049] (4) Weigh 0.4564 g of ammonium persulfate, add 20 mL of 1 M sodium hydroxide solution, and dissolve by sonication. After dissolution, soak the cleaned copper foam in the solution for 20 min to obtain blue copper hydroxide.

[0050] (5) Clean the generated copper hydroxide: repeatedly wash with deionized water. Prepare 20 mL of 0.5 mM aluminum nitrate solution, immerse the cleaned copper hydroxide in the aluminum nitrate solution for 30 min, and then allow the material to air dry naturally.

[0051] (6) Place the dried material on a graphite plate and set the Joule heating program: voltage 20 V, current 250 A, duration 5 s, and temperature 800 ℃. After Joule heating, Al-doped CuO nanosheet material can be obtained.

[0052] Example 4

[0053] (1) Take 41.67 mL of concentrated hydrochloric acid and add a certain amount of deionized water to 500 mL to obtain 1 M hydrochloric acid.

[0054] (2) Cut 2*3 cm of copper foam, and ultrasonically clean it for 15 min in 1 M hydrochloric acid, ethanol and deionized water respectively. Finally, dry it in a vacuum drying oven at 60 ℃ for later use.

[0055] (3) Weigh 20 g of sodium hydroxide, add the sodium hydroxide to an appropriate amount of deionized water, and after the sodium hydroxide is completely dissolved, transfer the solution to a 500 mL volumetric flask and dilute the solution to the 500 mL mark with deionized water to obtain a 1 M sodium hydroxide solution.

[0056] (4) Weigh 0.4564 g of ammonium persulfate, add 20 mL of 1 M sodium hydroxide solution, and dissolve by sonication. After dissolution, soak the cleaned copper foam in the solution for 20 min to obtain blue copper hydroxide.

[0057] (5) Clean the generated copper hydroxide: repeatedly wash with deionized water. Prepare 20 mL of 0.5 mM aluminum nitrate solution, immerse the cleaned copper hydroxide in the aluminum nitrate solution for 20 min, and then allow the material to air dry naturally.

[0058] (6) Place the dried material on a graphite plate and set the Joule heating program: voltage 20 V, current 200 A, duration 5 s, and temperature 700 ℃. After Joule heating, Al-doped CuO nanosheet material can be obtained.

[0059] Example 5

[0060] (1) Take 41.67 mL of concentrated hydrochloric acid and add a certain amount of deionized water to 500 mL to obtain 1 M hydrochloric acid.

[0061] (2) Cut 2*3 cm of copper foam, and ultrasonically clean it for 15 min in 1 M hydrochloric acid, ethanol and deionized water respectively. Finally, dry it in a vacuum drying oven at 60 ℃ for later use.

[0062] (3) Weigh 20 g of sodium hydroxide, add the sodium hydroxide to an appropriate amount of deionized water, and after the sodium hydroxide is completely dissolved, transfer the solution to a 500 mL volumetric flask and dilute the solution to the 500 mL mark with deionized water to obtain a 1 M sodium hydroxide solution.

[0063] (4) Weigh 0.4564 g of ammonium persulfate, add 20 mL of 1 M sodium hydroxide solution, and dissolve by sonication. After dissolution, soak the cleaned copper foam in the solution for 20 min to obtain blue copper hydroxide.

[0064] (5) Clean the generated copper hydroxide: repeatedly wash with deionized water. Prepare 20 mL of 0.5 mM aluminum nitrate solution, immerse the cleaned copper hydroxide in the aluminum nitrate solution for 20 min, and then allow the material to air dry naturally.

[0065] (6) Place the dried material on a graphite plate and set the Joule heating program: voltage 20 V, current 250 A, duration 5 s, and temperature 900 ℃. After Joule heating, Al-doped CuO nanosheet material can be obtained.

[0066] Comparative Example 1

[0067] (1) Take 41.67 mL of concentrated hydrochloric acid and add a certain amount of deionized water to 500 mL to obtain 1 M hydrochloric acid.

[0068] (2) Cut 2*3 cm of copper foam, and ultrasonically clean it for 15 min in 1 M hydrochloric acid, ethanol and deionized water respectively. Finally, dry it in a vacuum drying oven at 60 ℃ for later use.

[0069] (3) Weigh 20 g of sodium hydroxide, add the sodium hydroxide to an appropriate amount of deionized water, and after the sodium hydroxide is completely dissolved, transfer the solution to a 500 mL volumetric flask and dilute the solution to the 500 mL mark with deionized water to obtain a 1 M sodium hydroxide solution.

[0070] (4) Weigh 0.4564 g of ammonium persulfate, add 20 mL of 1 M sodium hydroxide solution, and dissolve by sonication. After dissolution, soak the cleaned copper foam in the solution for 20 min to obtain blue copper hydroxide.

[0071] (5) Clean the generated copper hydroxide: repeatedly wash with deionized water. Then dry it in a vacuum drying oven at 60°C for later use.

[0072] (6) Place the dried material on a graphite plate and set the Joule heating program: voltage 20 V, current 250 A, duration 5 s, and temperature 800 ℃. CuO nanofiber material can be obtained after Joule heating.

[0073] Characterization test

[0074] 1. Main materials and methods

[0075] Al-doped CuO nanosheet electrocatalyst material prepared in Example 2 (see Example 2) Figure 1 As the test sample, it was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The experimental results are as follows: Figure 1 , Figure 2 As shown.

[0076] The Al-doped CuO nanosheet electrocatalyst material prepared in Example 2 is shown in the figure. Figure 1 As shown. Among them. Figure 1 For XRD images, Figure 2 For SEM images, Figure 3 This is a TEM image. Figure 1 This indicates that the catalyst prepared in Example 2 is mainly copper oxide and copper, and the copper peak is mainly attributed to copper foam. Figure 2 and Figure 3 The catalyst can be seen to have the morphology of nano-flake-like nanoparticles. Figure 4 This is an XPS image from Example 2. Wherein, Figure 4 (a) shows the Cu 2P orbital diagram. Figure 4(b) shows the Al 2P orbital plot. The XPS plot of the Cu 2P orbital shows that the main component of Cu is divalent. Divalent copper exhibits a set of satellite characteristic peaks at 942 eV. Meanwhile, the Cu 2p orbital plot of copper oxide... 3 / 2 The peak has shifted, and its peak width is greater than that of cuprous oxide peak, but it can also be seen from the figure that a small amount of monovalent copper still exists in Cu.

[0077] Measurement of electrochemical performance

[0078] 1. Main materials and methods

[0079] Al-doped CuO nanosheet flower electrocatalyst prepared in Example 2 (see Example 2) Figure 1 The reaction was carried out in an H-type electrolytic cell. 30 mL of 1M NaOH solution was added to the anode, and 30 mL of a mixed solution of NaOH and NaNO3 (1 mol / L NaOH and 0.1 mol / L NaNO3) was added to the cathode. NaNO3 served as the nitrogen source, and the two electrodes were separated by a Nafion proton exchange membrane. The working electrode was the prepared catalyst, the reference electrode was a mercury / mercury oxide electrode, and the counter electrode was a platinum sheet electrode.

[0080] (1) Current density test

[0081] Using the Al-doped CuO nanoparticle catalyst and CuO catalyst prepared in Example 2 and Comparative 1, respectively, as working electrodes, linear sweep voltammetry (LSV) was used for testing. The scan range was 0.2 to -1 V (relative to the standard hydrogen electrode), and the scan rate was 10 mV / s. The experimental results are as follows: Figure 5 As shown. Figure 5 The figure shows a comparison curve of Al-CuO and CuO lsv. It can be seen from the figure that the Al-doped CuO nanosheet electrocatalyst prepared in Example 2 has a significantly improved current density compared with the undoped CuO catalyst, indicating that the catalyst prepared by Al doping has better electrochemical performance and the current density has reached the ampere level.

[0082] (2) Faraday efficiency and yield test of electrocatalytic nitrate reduction reaction

[0083] Using the Al-doped CuO nanosheet electrocatalyst prepared in Example 2 as the working electrode, the yield was determined by potentiostatic method. The working potential was set to -1.2 V, -1.3 V, -1.4 V, -1.5 V, and -1.6 V (relative to the mercury / mercury oxide reference electrode), and the current was continuously applied for 0.5 h. After the reaction was completed, the electrolyte was collected, and the concentration of ammonia was quantitatively analyzed using a UV-Vis spectrophotometer. The ammonia yield and the Faradaic efficiency of nitrate were calculated using the following formulas:

[0084] FE(NH3) = n × F × C(NH4 + ) × V / (M × Q) × 100%

[0085] Where F refers to: Faraday constant (96485 C mol) -1 M is the molecular weight of NH3 (17 g mol). -1 Q is the amount of electricity (C) passing through the electrode; n is the number of electrons consumed in the conversion of nitrate to ammonia, with a value of 8;

[0086] r(NH3) = C(NH4 + ) × V / (t × S cat )

[0087] Where r(NH3) is used to represent the ammonia yield (μg h) -1 cm -2 ); t represents the reaction time (h); S cat Represents the catalyst loading (cm²) -2 ); C(NH4) + The concentration of ammonia in the reaction products (μg / mL) -1 V refers to the volume of the cathode electrolyte (30 mL). Experimental results are as follows: Figure 6 As shown.

[0088] Figure 6 The figures show the Faradaic efficiency and ammonia yield of the Al-doped CuO nanosheet electrocatalyst. Experimental results indicate that at 0.1 mol / L NO3... - In alkaline solution, it exhibits optimal performance at -0.635 V vs. RHE, achieving a Faraday efficiency of 95.7% and approximately 60 mg h⁻¹. -1 cm -2 ammonia yield.

[0089]

[0090] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept, should be covered within the scope of protection of the present invention. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, and substitutions and selections of auxiliary components, etc., all fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing an Al-doped CuO nanosheet electrocatalyst, characterized in that, Includes the following steps: (1) Clean the foamed copper; (2) The obtained cleaned foamed copper was soaked in a mixed solution of sodium hydroxide and ammonium persulfate to react and obtain copper hydroxide. After rinsing with deionized water, it was placed in a vacuum oven to dry for later use. (3) Immerse the obtained copper hydroxide in an aluminum salt solution and allow it to air dry after immersion; (4) Place the dried material on a graphite plate and heat it using a Joule heating program to obtain Al-doped CuO nanoparticle catalyst; In step (2), the concentration of sodium hydroxide in the mixed solution of sodium hydroxide and ammonium persulfate is 1 mol / L. -1 The concentration of the ammonium persulfate is 0.1 mol / L. -1 ; In step (2), the soaking time of the copper foam in the mixed solution of sodium hydroxide and ammonium persulfate is 15-30 min; The concentration of the aluminum salt solution is 0.4-0.6 mM, and the soaking time is 10-30 min; The Joule thermal program is set to a voltage of 200 V, a current of 200 A-250 A, a duration of 3-8 s, and a temperature of 700℃-900℃.

2. The method for preparing an Al-doped CuO nanosheet electrocatalyst according to claim 1, characterized in that: The process of cleaning the foamed copper in step (1) is as follows: the foamed copper is ultrasonically cleaned by immersing it in dilute hydrochloric acid solution, ethanol, and deionized water respectively; the concentration of the dilute hydrochloric acid solution is 1-2 mol / L. -1 The ultrasound time is 15-20 minutes.

3. The method for preparing an Al-doped CuO nanosheet electrocatalyst according to claim 1, characterized in that: The aluminum salt solution is an aluminum nitrate, aluminum sulfate, or aluminum chloride solution.

4. An Al-doped CuO nanoflower electrocatalyst, characterized in that: The electrocatalyst is prepared using any one of the preparation methods described in claims 1-3.

5. The application of the Al-doped CuO nanosheet electrocatalyst according to claim 4, characterized in that: The electrocatalyst is used for the electrocatalytic reduction of nitrate to synthesize ammonia.

Images