Preparation method and application of a self-supporting ni-based catalyst

Abstract

The application relates to the technical field of electrocatalysis, and discloses a preparation method of a self-supporting Ni-based catalyst, which comprises the following steps: immersing a foamed copper into an electrodeposition solution, performing electrodeposition under a constant current density, washing with clean water after taking out, drying, and obtaining the self-supporting Ni-based catalyst; the electrodeposition solution comprises a nickel source, a tungsten source, a citrate, boric acid and sodium chloride. The Ni-W amorphous catalyst is directly grown on the foamed copper substrate through a one-step constant current electrodeposition method, a self-supporting structure is formed, no binder is needed, the active substance is firmly combined with the substrate, is not easy to fall off, and has good stability. By introducing disordered W doping into the Ni, the electrocatalytic nitrate reduction performance of the catalyst is significantly improved: the overpotential is obviously reduced, the current density is significantly increased, and the ammonia production Faraday efficiency is as high as 94% at-0.3 V.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, and in particular to a method for preparing a self-supporting Ni-based catalyst and its application. Background Technology

[0002] Ammonia (NH3) plays a vital role in agriculture and the chemical industry, and also shows great promise as a next-generation hydrogen-rich fuel. Currently, ammonia is mainly synthesized through the Haber-Bosch process, which is energy-intensive (accounting for approximately 1-2% of global energy consumption) and emits large amounts of carbon dioxide (approximately 1.3%). Electrocatalytic nitrate reduction (NO3⁻RR) can convert nitrate ions in wastewater into high-value-added ammonia under mild conditions, turning waste into treasure, and has therefore attracted widespread attention.

[0003] Transition metals (such as Fe, Co, Ni, and Cu) are commonly used catalysts for nitrate reduction. Among them, Ni-based materials are relatively inexpensive and possess certain catalytic activity. However, existing Ni-based catalysts still have many drawbacks: incomplete nitrate reduction, intense competition for hydrogen evolution reaction, low current density, and susceptibility to catalyst poisoning and deactivation. For example, patent CN119824474A discloses a perylene-based composite material with Ni supported on carbon cloth, but its ammonia production Faradaic efficiency at -1.2 V (vs. RHE) is only 31.49%, indicating a high overpotential. Patent CN116334670A reports Ni nanoparticles rich in crystal defects; although the Faradaic efficiency can reach over 90%, it requires a high-concentration nitrate electrolyte of 1 mol / L, far exceeding the nitrate concentration in actual wastewater (typically 0.01~0.1 mol / L), thus lacking practical application potential.

[0004] Therefore, developing a Ni-based catalyst that can produce ammonia efficiently, with low overpotential and high current density at low nitrate concentrations is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] To address the technical problems mentioned in the background section, this invention provides a method for preparing a self-supporting Ni-based catalyst and its application.

[0006] The present invention is achieved by the following technical solution: One of the objectives of the present invention is to propose a method for preparing a self-supporting Ni-based catalyst, comprising the following steps: immersing copper foam in an electrodeposition solution, performing electrodeposition at a constant current density, rinsing with water after removal, and drying to obtain a self-supporting Ni-based catalyst; the electrodeposition solution contains a nickel source, a tungsten source, citrate, boric acid, and sodium chloride.

[0007] Furthermore, in the electrodeposition solution: the nickel source is nickel sulfate hexahydrate with a concentration of 0.02 mol / L-0.06 mol / L; the tungsten source is sodium tungstate dihydrate with a concentration greater than 0 mol / L and less than or equal to 0.1 mol / L; the citrate is trisodium citrate dihydrate with a concentration of 0.05 mol / L-0.3 mol / L; the boric acid concentration is 0.5 mol / L-1 mol / L; the sodium chloride concentration is 0.05 mol / L-0.4 mol / L; and the pH value of the electrodeposition solution is 6-7.

[0008] Furthermore, the constant current density is 10 mA / cm²-100 mA / cm², and the electrodeposition time is 1 min-10 min; The copper foam was pretreated before being immersed in the electrodeposition solution: the copper foam was cut to 2 cm × 4 cm, soaked in 1 mol / L hydrochloric acid solution for 10 minutes, and then sonicated in acetone for 10 minutes. After being removed, it was rinsed with ethanol and dried.

[0009] Furthermore, the electrodeposition is performed at 25 degrees Celsius.

[0010] Furthermore, when the foamed copper is immersed in the electrodeposition solution, the immersion area is 0.5 cm × 0.5 cm.

[0011] The second objective of this invention is to provide a self-supporting Ni-based catalyst obtained by the above preparation method.

[0012] Furthermore, the catalyst has an amorphous structure and contains Ni and W elements.

[0013] The third objective of this invention is to apply a self-supporting Ni-based catalyst in the electrocatalytic reduction of nitrate to ammonia, comprising the following steps: fabricating the self-supporting Ni-based catalyst into a working electrode; using a platinum sheet electrode as the counter electrode, and selecting an Hg / HgO electrode or an Ag / AgCl electrode as the reference electrode according to the pH value of the electrolyte to form a three-electrode system; and placing the working electrode in an electrolyte containing nitrate to carry out the electrocatalytic reduction reaction.

[0014] Furthermore, when the electrolyte pH=7, the reference electrode is Ag / AgCl; when the electrolyte pH=14, the reference electrode is Hg / HgO.

[0015] Furthermore, the electrolyte contains potassium nitrate, potassium hydroxide, or potassium sulfate, and argon gas is pre-purged into the electrolyte for 30 minutes; wherein the concentration of potassium nitrate is 0.01 mol / L-0.1 mol / L, the concentration of potassium sulfate is 0.5 mol / L, and the concentration of potassium hydroxide is 1 mol / L.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention directly grows Ni-W amorphous catalyst on a copper foam substrate using a one-step constant current electrodeposition method, forming a self-supporting structure. No binder is required, the active material is firmly bonded to the substrate, it is not easy to fall off, and it has good stability.

[0017] This invention significantly improves the electrocatalytic nitrate reduction performance of the catalyst by introducing disordered W doping into Ni: the overpotential is significantly reduced, the current density is significantly increased (reaching 1 A / cm² at -0.8 V vs. Hg / HgO), and the ammonia production Faraday efficiency is as high as 94% at -0.3 V.

[0018] The catalyst of this invention maintains excellent activity over a wide nitrate concentration range (0.01-0.1 mol / L) and a wide pH range (7-14), and its Faraday efficiency still exceeds 80% even at a low concentration of 0.01 mol / L, making it suitable for practical wastewater treatment.

[0019] The raw materials used in this invention (nickel sulfate, sodium tungstate, trisodium citrate, boric acid, sodium chloride, etc.) are inexpensive and readily available. The preparation process is carried out at room temperature and pressure, requiring no complex equipment, and is simple to operate with good reproducibility, thus having broad prospects for industrial application. Attached Figure Description

[0020] Figure 1 The image shows a scanning electron microscope (SEM) image of the self-supporting Ni-based catalyst prepared in Example 1 of this invention, including magnified images at different magnifications, showing that the material maintains the network structure of copper foam, indicating uniform electrodeposition.

[0021] Figure 2 The X-ray diffraction (XRD) patterns of foamed copper, W-doped Ni-based catalyst, and undoped Ni-based catalyst in this invention show that all three materials only have characteristic peaks of the copper substrate and no crystalline peaks of Ni or W, indicating that Ni and W exist in amorphous form.

[0022] Figure 3 The images show the X-ray photoelectron spectroscopy (XPS) spectra of the undoped Ni-based catalyst and the W-doped Ni-based catalyst in this invention. The left image shows the Ni 2p peak, and the right image shows the W 4f peak after W doping, confirming that W... 0 and W 6 The successful incorporation of ⁺.

[0023] Figure 4 The image shows a comparison of the linear voltammetric scan (LSV) curves of the W-doped Ni-based catalyst and the undoped Ni-based catalyst in 0.1 mol / L potassium nitrate (pH=14). It shows that the overpotential decreases and the current density increases significantly after doping with W.

[0024] Figure 5The graph shows a comparison of the Faraday efficiency of ammonia production between the W-doped Ni-based catalyst and the undoped Ni-based catalyst at different potentials. It shows that the Faraday efficiency is significantly improved after doping with W, reaching 94% at -0.3 V.

[0025] Figure 6 The LSV curves and ammonia production Faraday efficiency graphs of the W-doped Ni-based catalyst in 0.05 mol / L potassium nitrate (pH=7) and at different potentials are shown, indicating that the Faraday efficiency still exceeds 85%.

[0026] Figure 7 The LSV curves and ammonia production Faraday efficiency graphs of the W-doped Ni-based catalyst in 0.01 mol / L potassium nitrate (pH=7) and at different potentials are shown, indicating that the Faraday efficiency still exceeds 80%.

[0027] Figure 8 The graph shows the long-term stability of the W-doped Ni-based catalyst for the electrocatalytic reduction of potassium nitrate to ammonia in this invention. It shows that it still has a long stability of up to 25 hours and the ammonia production Faraday efficiency is still over 90% at industrial current density. Detailed Implementation

[0028] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0029] In the following embodiments, the pretreatment method for copper foam is uniformly as follows: Cut the copper foam to 2 cm × 4 cm, immerse it in a 1 mol / L hydrochloric acid solution for 10 minutes, then sonicate it in acetone for 10 minutes. After removal, rinse with plenty of ethanol and dry for later use. This pretreatment step is applicable to all preparation embodiments to ensure the cleanliness of the substrate surface and the adhesion of subsequent electrodeposition.

[0030] It is worth mentioning that the self-supporting Ni-based catalyst of the present invention is prepared by a one-step constant current electrodeposition method. The electrodeposition solution contains nickel sulfate hexahydrate, sodium tungstate dihydrate (optional), trisodium citrate dihydrate, boric acid, and sodium chloride. The pH of the electrodeposition solution is adjusted to 6-7, and the electrodeposition temperature is 25 degrees Celsius. Furthermore, during the deposition process, only a 0.5 cm × 0.5 cm area of ​​copper foam is immersed in the electrodeposition solution, and deposition is carried out at a constant current density of 10-100 mA / cm² for 1-10 minutes. After removal, it is rinsed with plenty of deionized water and dried to obtain the self-supporting catalyst. The above parameter ranges are for illustrative purposes only; specific values ​​can be found in the various embodiments.

[0031] Example 1:

[0032] This embodiment describes a method for preparing a self-supporting Ni-based catalyst, comprising the following steps: The pretreated copper foam was cut into 0.5 cm × 1 cm pieces, and each 0.5 cm × 0.5 cm piece was immersed in an electrodeposition solution for electrodeposition. The electrodeposition solution contained the following components: 0.06 mol / L nickel sulfate hexahydrate, 0.1 mol / L sodium tungstate dihydrate, 0.3 mol / L trisodium citrate dihydrate, 1 mol / L boric acid, and 0.15 mol / L sodium chloride. The pH of the electrodeposition solution was 6-7.

[0033] Electrodeposition was performed in a constant current mode with a current density of 100 mA / cm², a deposition time of 10 minutes, and a temperature maintained at 25 degrees Celsius.

[0034] After electrodeposition, the working electrode was rinsed with a large amount of deionized water and dried to obtain a self-supporting Ni-W catalyst.

[0035] Example 2:

[0036] The difference between this embodiment and Example 1 lies in the concentration of sodium tungstate dihydrate in the electrodeposition solution. Specifically, the pretreated copper foam is cut into 0.5 cm × 1 cm pieces, and each 0.5 cm × 0.5 cm piece is immersed in the electrodeposition solution. The composition of the electrodeposition solution is as follows: 0.06 mol / L nickel sulfate hexahydrate, 0.08 mol / L sodium tungstate dihydrate, 0.3 mol / L trisodium citrate dihydrate, 1 mol / L boric acid, 0.15 mol / L sodium chloride, and the pH value is 6-7.

[0037] Electrodeposition was performed in constant current mode at a current density of 100 mA / cm², for a deposition time of 10 minutes, at a temperature of 25 degrees Celsius. After electrodeposition, the working electrode was rinsed thoroughly with deionized water and then dried.

[0038] Example 3:

[0039] The difference between this embodiment and Example 1 is that the concentration of sodium tungstate dihydrate in the electrodeposition solution is lower. Specifically, the pretreated copper foam is cut into 0.5 cm × 1 cm pieces, and each 0.5 cm × 0.5 cm piece is immersed in the electrodeposition solution. The composition of the electrodeposition solution is: 0.06 mol / L nickel sulfate hexahydrate, 0.04 mol / L sodium tungstate dihydrate, 0.3 mol / L trisodium citrate dihydrate, 1 mol / L boric acid, 0.15 mol / L sodium chloride, and the pH value is 6-7.

[0040] Electrodeposition was performed in constant current mode at a current density of 100 mA / cm², for a deposition time of 10 minutes, at a temperature of 25 degrees Celsius. After electrodeposition, the working electrode was rinsed thoroughly with water and then dried.

[0041] Example 4:

[0042] This example is a comparative sample without tungsten doping. Specifically, the pretreated copper foam was cut into 0.5 cm × 1 cm pieces, and each 0.5 cm × 0.5 cm piece was immersed in the electrodeposition solution. The composition of the electrodeposition solution was: 0.06 mol / L nickel sulfate hexahydrate, 0.3 mol / L trisodium citrate dihydrate, 1 mol / L boric acid, and 0.15 mol / L sodium chloride (without sodium tungstate dihydrate), with a pH of 6-7.

[0043] Electrodeposition was performed in a constant current mode with a current density of 100 mA / cm², a deposition time of 10 minutes, and a temperature of 25 degrees Celsius. After electrodeposition, the working electrode was rinsed with a large amount of deionized water and dried to obtain an undoped W-based self-supporting Ni-based catalyst.

[0044] It should be noted that in Examples 1-4 above, the concentrations of each component in the electrodeposition solution can be adjusted within the following ranges according to actual needs: nickel sulfate hexahydrate 0.02-0.06 mol / L, sodium tungstate dihydrate 0-0.1 mol / L, trisodium citrate dihydrate 0.05-0.3 mol / L, boric acid 0.5-1 mol / L, sodium chloride 0.05-0.4 mol / L, the constant current density can be selected within the range of 10-100 mA / cm², and the deposition time can be selected within the range of 1-10 min. The above examples are merely illustrative examples of the present invention and are not intended to limit it.

[0045] Example 5:

[0046] Catalytic performance testing and characterization methods In this embodiment, the self-supporting Ni-based catalysts prepared in Examples 1-4 above were used for performance testing of electrocatalytic nitrate reduction to ammonia.

[0047] First, the electrode was prepared and the testing system was set up: the prepared electrode was clamped with electrode clamps to serve as the working electrode. Testing was conducted in a three-electrode system, with a platinum sheet (1 cm × 1 cm) as the counter electrode. The selection of the reference electrode was determined based on the electrolyte pH: when pH=7, an Ag / AgCl electrode was used as the reference electrode; when pH=14, a Hg / HgO electrode was used. Furthermore, argon gas was pre-purged into the electrolyte for 30 minutes before testing to remove dissolved oxygen. The electrolyte composition was as follows: potassium nitrate concentration of 0.01-0.1 mol / L, with 0.5 mol / L potassium sulfate or 1 mol / L potassium hydroxide added to adjust the ionic strength and pH value.

[0048] The testing methods included linear voltammetry (LSV) and chronoamperometry (it): the LSV test was performed at a scan rate of 50 mV / s to study the electrocatalytic activity of the catalyst; the it test was performed at different potentials (-0.2 V, -0.3 V, -0.4 V, -0.5 V, -0.6 V, -0.7 V) to evaluate the ammonia production Faraday efficiency.

[0049] Ammonia concentration was determined using the indophenol blue colorimetric method: 1 mL of the tested electrolyte was diluted 20 times. Then, 2 mL of the diluted electrolyte was added sequentially to 2 mL of solution A, 1 mL of solution B, and 0.2 mL of solution C. The mixture was allowed to develop color in the dark for 1 hour. After color development, the absorbance at 655 nm was measured using a UV spectrophotometer. The ammonia concentration in the electrolyte was calculated based on the absorbance and the standard curve. The preparation methods for colorimetric solutions A, B, and C are as follows: Solution A: Add 8 g sodium hydroxide, 10 g sodium citrate, and 10 g salicylic acid to 200 mL of water.

[0050] Solution B: Dilute 50 mL of sodium hypochlorite to 100 mL.

[0051] Solution C: 0.2 g sodium nitrosoferricyanide dissolved in 20 mL of water.

[0052] Results Analysis See Figure 1 The self-supporting Ni-based catalyst was characterized by scanning electron microscopy. The magnified images showed that the material exhibited a network structure consistent with the foamed copper substrate, indicating that the material was uniformly deposited on the foamed substrate during the electrodeposition process.

[0053] See Figure 2 XRD patterns ( Figure 2 The results show that the three materials—foamed copper, W-doped Ni-based catalyst, and undoped Ni-based catalyst—all exhibited the same XRD peaks as the standard card (PDF#85-1326), without the characteristic peaks of Ni and W-related species. This indicates that the Ni and W species after electrodeposition exist in an amorphous form. It is worth noting that the addition of W can stabilize the amorphous state of the material, which is beneficial for the synthesis of amorphous materials.

[0054] See Figure 3 X-ray photoelectron spectroscopy was performed on the undoped catalyst and the W-doped catalyst. Figure 3 (Left and right), the Ni 2p peak appeared in both catalysts. 0 The peaks of Ni²⁺ were observed, and W was detected in the W-doped catalyst. 0 W 6 The above results all indicate the successful incorporation of W.

[0055] The performance test results are as follows: See Figure 4 LSV (scan rate 50 mV / s) tests were performed in a 0.1 mol / L potassium nitrate electrolyte at pH 14, using the W-doped Ni-based catalyst and the undoped Ni-based catalyst prepared above as working electrodes, respectively. Figure 4 As shown, compared with the undoped Ni-based catalyst, the overpotential of the reaction is significantly reduced after W doping, and the current density is significantly increased, reaching 1 A / cm² at -0.8 V. These results indicate that W doping effectively improves catalytic performance and enables high current density catalytic reactions at low potentials.

[0056] See Figure 5 Using the W-doped self-supported Ni-based catalyst and the undoped Ni-based catalyst prepared above as working electrodes, chronoamperometry was performed at different potentials (-0.2 V to -0.7 V) to calculate the ammonia production Faraday efficiency. Figure 5 As shown, compared with the undoped Ni-based catalyst, the Faraday efficiency of the W-doped catalyst was significantly improved within the test potential range. The Faraday efficiency of ammonia production reached 94% at -0.3 V, indicating that W doping can significantly improve the Faraday efficiency of ammonia production in the catalyst.

[0057] See Figure 6 The electrolyte was changed to a 0.05 mol / L potassium nitrate solution with pH=7, and LSV and it were tested. Figure 6 As shown on the left (LSV curve) and right (Faraday efficiency), when the nitrate concentration in the electrolyte is reduced to 0.05 mol / L, the ammonia production Faraday efficiency can still reach over 85%.

[0058] See Figure 7 When the nitrate concentration in the electrolyte is further reduced to 0.01 mol / L (pH=7), as... Figure 7 As shown on the left (LSV curve) and right (Faraday efficiency), the ammonia production Faradaic efficiency can reach over 80%. This indicates that this catalyst can achieve efficient ammonia production at relatively low concentrations (0.01-0.05 mol / L), and has the potential to treat practical wastewater.

[0059] See Figure 8 The electrolyte was a 0.1 mol / L potassium nitrate solution, and the stability of the catalyst was tested. Figure 8 As shown, the self-supported Ni-based catalyst maintained a 90% ammonia production Faradaic efficiency and a current density of 800 mA / cm² within 25 hours, exhibiting excellent catalytic activity and stability.

[0060] In summary, this invention successfully prepared a self-supporting Ni-based material through one-step electrodeposition. The W doping strategy can increase water dissociation, enhance nitrate adsorption, and improve the catalytic activity of the catalyst. Furthermore, the synthesized material is inexpensive and readily available, the synthesis method is feasible, and the catalyst can achieve a high current density of 1 A / cm² under alkaline conditions. It also exhibits excellent ammonia production performance over a wide range of nitrate concentrations and pH values ​​(7-14), showing promising prospects for industrial applications.

[0061] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a self-supporting Ni-based catalyst, characterized in that, Includes the following steps: Copper foam was immersed in an electrodeposition solution and electrodeposited at a constant current density. After removal, it was rinsed with water and dried to obtain a self-supporting Ni-based catalyst. The electrodeposition solution contained a nickel source, a tungsten source, citrate, boric acid, and sodium chloride.

2. The preparation method according to claim 1, characterized in that, The electrodeposition solution contains: nickel source as nickel sulfate hexahydrate with a concentration of 0.02 mol / L-0.06 mol / L; tungsten source as sodium tungstate dihydrate with a concentration greater than 0 mol / L and less than or equal to 0.1 mol / L; citrate as trisodium citrate dihydrate with a concentration of 0.05 mol / L-0.3 mol / L; boric acid with a concentration of 0.5 mol / L-1 mol / L; sodium chloride with a concentration of 0.05 mol / L-0.4 mol / L; and a pH of 6-7.

3. The preparation method according to claim 1, characterized in that, The constant current density is 10 mA / cm²-100 mA / cm², and the electrodeposition time is 1 min-10 min. The copper foam was pretreated before being immersed in the electrodeposition solution: the copper foam was cut to 2 cm × 4 cm, soaked in 1 mol / L hydrochloric acid solution for 10 minutes, and then sonicated in acetone for 10 minutes. After being removed, it was rinsed with ethanol and dried.

4. The preparation method according to claim 1, characterized in that, The electrodeposition was performed at 25 degrees Celsius.

5. The preparation method according to claim 1, characterized in that, When the copper foam is immersed in the electrodeposition solution, the immersion area is 0.5 cm × 0.5 cm.

6. A self-supporting Ni-based catalyst obtained by the preparation method according to any one of claims 1-5.

7. The self-supporting Ni-based catalyst according to claim 6, characterized in that, The catalyst has an amorphous structure and contains Ni and W elements.

8. The application of the self-supporting Ni-based catalyst according to claim 6 or 7 in the electrocatalytic reduction of nitrate to ammonia, characterized in that, Includes the following steps: The self-supporting Ni-based catalyst was used to form the working electrode; A three-electrode system was formed by using a platinum sheet electrode as the counter electrode and selecting either an Hg / HgO electrode or an Ag / AgCl electrode as the reference electrode based on the pH value of the electrolyte. The working electrode was placed in an electrolyte containing nitrate to carry out an electrocatalytic reduction reaction.

9. The application according to claim 8, characterized in that, When the electrolyte pH=7, the reference electrode is Ag / AgCl; when the electrolyte pH=14, the reference electrode is Hg / HgO.

10. The application according to claim 8, characterized in that, The electrolyte contains potassium nitrate, potassium hydroxide, or potassium sulfate, and argon gas is pre-purified into the electrolyte for 30 minutes; wherein the concentration of potassium nitrate is 0.01 mol / L-0.1 mol / L, the concentration of potassium sulfate is 0.5 mol / L, and the concentration of potassium hydroxide is 1 mol / L.

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