A self-supporting co (oh) 2 / cuo x Nanowire array electrode, method of making and use in electrocatalytic reduction of nitrate to ammonia

Abstract

A self-supporting Co(OH)2 / CuO x Nanowire array electrodes, their preparation method, and their application in the electrocatalytic reduction of nitrate to ammonia. The key feature is that 1x1cm nanowire array electrodes are prepared by electro-oxidation. 2 Copper foam was placed in NaOH solution, and Cu(OH)₂ nanowires were grown on the surface of the copper foam by applying an anodic current; then the Cu(OH)₂ nanowires obtained in step (1) were placed in a muffle furnace and calcined in air to obtain CuO. x Nanowires were immersed in anhydrous ethanol and cooled; then CuO was added. x Co(OH)₂ / CuO was obtained by pulse electrodeposition of nanowires in a cobalt source aqueous solution. x Electrode. The Co(OH)₂ / CuO developed by the method of this invention. x The electrode preparation method involves using CuO. x Co(OH)₂ can be obtained by pulse electrodeposition on nanowires, with NO₃ at an alkaline cathode. ‑ The RR reaction exhibits an ampere-level current density, reaching 1.5 A·cm⁻¹ at -0.5 V vs. RHE. ‑2 At the given current density, the Faraday efficiency reached 94.2%, and the ammonia yield reached 4.53 mmol·h⁻¹. ‑1 ·cm ‑2 In CuO x Introducing a cobalt source into the nanowire significantly enhances the hydrogenation reduction capability of the electrode, greatly increasing the ability to convert nitrate ions into ammonia. This provides a new approach for replacing traditional high-energy-consuming chemical technologies and designing electrocatalytic ammonia production.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic materials technology, specifically a self-supporting Co(OH)2 / CuO material. x Nanowire array electrodes, their preparation methods, and their application in electrocatalytic nitrate reduction to ammonia. Background Technology

[0002] The Haber-Bosch process is currently the main method for industrial ammonia synthesis. It requires high temperature (400-500℃) and high pressure (10-30 MPa) conditions, resulting in huge energy consumption and significant CO2 emissions. With the development of renewable energy and advancements in electrocatalysis technology, electrocatalytic nitrate reduction (NO3) is gaining momentum. - (RR) ammonia synthesis is considered a green alternative route for ammonia synthesis that can be carried out under mild conditions. This process not only utilizes renewable electricity to convert nitrate pollutants in wastewater into high-value-added ammonia, turning waste into treasure, but also avoids the high energy consumption and high carbon emissions of the traditional Haber-Bosch process, which is of great significance for achieving the "dual carbon" goal and the sustainable development of the nitrogen cycle.

[0003] Currently, while noble metal-based catalysts (such as Pt, Pd, and Ru) exhibit high catalytic activity for nitrate reduction, their high cost and resource scarcity severely restrict their large-scale application. Copper-based catalysts have attracted widespread attention due to their good nitrate reduction activity and relatively low price; however, single copper-based catalysts face the problem of insufficient active hydrogen (*H) supply, leading to limited hydrogenation steps for reaction intermediates (such as nitrite and NO), easily causing byproduct accumulation, and reducing ammonia selectivity and yield. Studies have shown that introducing a second component with water dissociation-promoting capabilities (such as hydroxides of Co, Fe, and Ni) can effectively enhance active hydrogen generation, thereby accelerating the hydrogenation process of intermediates. Furthermore, by constructing heterogeneous interfaces, the electronic structure of the catalyst can be tuned, optimizing the adsorption energy of reactants and intermediates on the catalyst surface, reducing the reaction energy barrier, and further improving catalytic activity and selectivity. Therefore, designing the interfacial and electronic structures of copper-based catalysts is a key strategy for improving the performance of electrocatalytic nitrate reduction to ammonia.

[0004] Based on this, the present invention provides a Co(OH)2 / CuO xA nanowire array electrocatalyst and its preparation method were developed. This catalyst was prepared via a three-step method of electro-oxidation-calcination-pulse electrodeposition. A CuO / Cu2O composite phase with a unique nanowire array structure was grown in situ on a copper substrate, and Co(OH)2 was uniformly loaded via pulse electrodeposition to form a catalytic electrode with abundant heterogeneous interfaces. The introduction of Co(OH)2 promoted the dissociation of H2O, continuously providing active hydrogen (*H) to the active sites of CuO / Cu2O. Simultaneously, the pulse electrodeposition process achieved uniform dispersion of Co(OH)2 on the nanowire surface, significantly increasing the number of active sites at the three-phase interface. This resulted in a substantial increase in the current density and ammonia yield of nitrate reduction to ammonia, while exhibiting excellent stability. The successful development of this electrocatalytic nitrate reduction to ammonia method provides a new approach and solution for efficient, stable, and low-cost green ammonia synthesis technology. Summary of the Invention

[0005] The purpose of this invention is to provide a self-supporting Co(OH)2 / CuO x Nanowire array electrodes, their preparation method, and their application in the electrocatalytic reduction of nitrate to ammonia were described. A three-step method of electro-oxidation-calcination-pulse electrodeposition was used to prepare a self-supporting nanowire array catalytic electrode with abundant heterostructures. The preparation method is simple, low-cost, and exhibits high catalytic activity.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A self-supporting Co(OH)2 / CuO x Nanowire array electrodes, their preparation method, and their application in the electrocatalytic reduction of nitrate to ammonia. The preparation method is as follows:

[0008] (1) Preparation of Cu(OH)2 nanowires: cut into 1x1cm pieces 2 Copper foam was ultrasonicated in anhydrous ethanol for 10 min, then ultrasonicated in deionized water for 10 min, repeated 3 times. Subsequently, it was placed in 50 mL of 1 M NaOH solution and subjected to an A·cm⁻¹ pressure. -2 Cu(OH)2 nanowires were obtained by applying an anodic current for 10 min.

[0009] (2) CuO x Preparation of nanowires: The Cu(OH)₂ obtained in step (1) was placed in the middle of a muffle furnace and calcined at 350°C for 3 min in an air atmosphere. It was then rapidly immersed in anhydrous ethanol to cool, and after cooling, CuO was obtained. x Nanowires;

[0010] (3) Co(OH)2 / CuO x Preparation of nanowires: The CuO obtained in step (2) xNanowires were placed in a 0.1 M Co(NO3)2·6H2O aqueous solution with a volume of 50 mL. The voltage for pulse electrodeposition was -1 V vs. Ag / AgCl. on The time is 2 seconds, t off The time is 10 s, and 150 cycles are performed to obtain Co(OH)2 / CuO. x electrode.

[0011] Co(OH)2 / CuO prepared by the above method x The catalyst inherits CuO x The nanowire structure, with Co(OH)2 attached to CuO x On the surface of the nanowire structure, a self-supporting nanowire array catalytic electrode with abundant heterostructure interfaces was obtained. Co(OH)₂ / CuO x Nanowire electrodes can be used as alkaline cathodes for NO3. - The electrocatalyst for the RR reaction is NO3 at an alkaline cathode. - The RR reaction exhibits an ampere-level current density, reaching 1.5 A·cm⁻¹ at -0.5 V vs. RHE. -2 At the given current density, the Faraday efficiency reached 94.2%, and the ammonia yield reached 4.53 mmol·h⁻¹. -1 ·cm -2 Compared with the prior art, the beneficial effects of the present invention are:

[0012] 1. The Co(OH)2 / CuO prepared by this invention x The nanowire electrode catalyst maintains CuO throughout the three-step preparation process of electro-oxidation-calcination-pulse electrodeposition. x The nanowire structure, with pulsed electrodeposition loaded Co(OH)2 attached to CuO x By utilizing the nanowire structure surface, a self-supporting nanowire array catalytic electrode with abundant heterostructure interfaces was obtained.

[0013] 2. The Co(OH)2 / CuO prepared by this invention x In the nanowire electrode catalyst, Co(OH)2 gradually adheres to CuO during the electro-oxidation-calcination-pulse electrodeposition process. x Co(OH)2 / CuO is formed on the surface of the nanowires. x The heterojunction, where the hetero interface between CuO and Cu2O in the composite phase facilitates the modulation of the electronic structure of active sites, while the ordered arrangement of the nanowire array provides a large specific surface area and abundant reactive sites; furthermore, Co(OH)2 is uniformly attached to CuO. x On the surface of the nanowires, a Co(OH)₂ / CuO structure with abundant heterogeneous interfaces is formed. xMultilayer composite structure. This unique nanowire array structure allows the active material to be directly exposed to the electrolyte, effectively increasing the solid-liquid contact area. The open gaps between the nanowires are beneficial for reactants (NO3). - The rapid diffusion and transport of the product shortens the ion transport path; at the same time, the strong interfacial synergistic effect between Co(OH)2 and CuO / Cu2O significantly promotes interfacial charge transfer, greatly improving the reaction rate of electrocatalytic nitrate reduction to ammonia.

[0014] 3. The Co(OH)2 / CuO developed by the method of this invention x A method for fabricating nanowire array electrodes was developed, involving in-situ growth of self-supporting catalytic electrodes on a copper substrate via a three-step process of electro-oxidation, calcination, and pulsed electrodeposition. These electrodes exhibited excellent catalytic activity in the electrocatalytic reduction of nitrate to ammonia, achieving a current density as high as 1.5 A·cm⁻¹ at -0.5 V vs. RHE potential. -2 The Faraday efficiency reached 94.2%, and the ammonia yield reached 4.53 mmol·h⁻¹. -1 ·cm -2 It exhibits good stability and durability. Attached Figure Description

[0015] Figure 1 Scanning electron microscope images of the catalysts prepared in Examples 1-2:

[0016] (a) Co(OH)2 / CuO x (b) CuO x

[0017] Figure 2 The XRD patterns of the samples synthesized in Examples 1-2 are shown below.

[0018] Figure 3 The Co(OH)2 / CuO prepared in Examples 1-2 x with CuO x Catalyst performance comparison chart:

[0019] (a) NO3 - LSV plot of RR, (b) Co(OH)2 / CuO x FE diagrams for each potential, (c) NO3 - RR's FE and yield diagram Detailed Implementation

[0020] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0021] Example 1

[0022] A self-supporting Co(OH)2 / CuO x The nanowire array electrode and its fabrication method are carried out according to the following steps:

[0023] (1) Preparation of Cu(OH)2 nanowires: cut into 1x1cm pieces 2 Copper foam was ultrasonicated in anhydrous ethanol for 10 min, then ultrasonicated in deionized water for 10 min, repeated three times. Subsequently, 10 g of NaOH was dissolved in 250 mL of deionized water to obtain a 1 M NaOH solution. The copper foam was then placed in 50 mL of the 1 M NaOH solution and subjected to an application rate of 20 mA·cm⁻¹. -2 The anodic current was applied for 10 minutes without stirring (to prevent the nanowires from collapsing) to obtain Cu(OH)2 nanowires;

[0024] (2) CuO x Preparation of nanowires: The Cu(OH)₂ obtained in step (1) was placed in the middle of a muffle furnace and calcined at 350°C for 3 min in an air atmosphere. It was then rapidly immersed in anhydrous ethanol to cool, and after cooling, CuO was obtained. x Nanowires;

[0025] (3) Co(OH)2 / CuO x Preparation of nanowires: The CuO obtained in step (2) x Nanowires were placed in a 0.1 M Co(NO3)2·6H2O aqueous solution with a volume of 50 mL. The voltage for pulse electrodeposition was -1 V vs. Ag / AgCl. on The time is 2 seconds, t off The time is 10 s, and 150 cycles are performed to obtain Co(OH)2 / CuO. x Nanowires.

[0026] Example 2

[0027] A comparative catalyst CuO x The specific steps for preparing nanowires are as follows:

[0028] (1) Preparation of Cu(OH)2 nanowires: cut into 1x1cm pieces 2 Copper foam was ultrasonicated in anhydrous ethanol for 10 min, then ultrasonicated in deionized water for 10 min, repeated three times. Subsequently, 10 g of NaOH was dissolved in 250 mL of deionized water to obtain a 1 M NaOH solution, which was then placed in 50 mL of the 1 M NaOH solution and subjected to an application rate of 20 mA·cm⁻¹. -2The anodic current was applied for 10 minutes without stirring (to prevent the nanowires from collapsing) to obtain Cu(OH)2 nanowires;

[0029] (2) CuO x Preparation of nanowires: The Cu(OH)₂ obtained in step (1) was placed in the middle of a muffle furnace and calcined at 350°C for 3 min in an air atmosphere. It was then rapidly immersed in anhydrous ethanol to cool, and after cooling, CuO was obtained. x Nanowires;

[0030] Relevant performance tests:

[0031] This section only tests samples provided in some of the embodiments; other samples also have the same or similar physicochemical properties.

[0032] (1) NO3 - RR test conditions

[0033] Three-electrode system: The working electrode is 0.5 x 0.5 cm. 2 Co(OH)2 / CuO x Nanowires or contrast sample CuO x Nanowires, clamped with platinum electrode clips, with an Hg / HgO electrode as the reference electrode, 1 x 1 cm 2 The platinum sheet is used as the counter electrode. The electrolyte in the cathode cell is 30 mL of 1 M KOH + 0.1 M KNO3 solution, and the electrolyte in the anode cell is 30 mL of 1 M KOH solution.

[0034] (2) NO3 - RR's LSV test

[0035] Under normal temperature and pressure conditions, the electrolyte was passed through an Ar gas flow for 30 min to remove other gases from the solution. Cyclic voltammetry was first performed for 30 cycles to activate the catalyst, followed by LSV testing at a scan rate of 10 mV / s.

[0036] (3) NO3 - RR cycle performance test:

[0037] Under normal temperature and pressure conditions, an Ar gas flow was introduced for 30 min to remove other gases from the solution. Cyclic voltammetry was first performed for 30 cycles to activate the catalyst, followed by electrolysis reactions at various potentials for 2 h each. The potential with the best performance was selected for cyclic stability testing.

[0038] (4) Product identification methods

[0039] Ammonia nitrogen (NH4) +Determination of ammonia nitrogen content: Nessler's reagent was used as the colorimetric reagent. First, a certain amount of electrolyte was taken from the electrolytic cell and diluted to 50 mL (to keep it within the detection linear range). Then, 1 mL of potassium sodium tartrate solution (ρ=500 g / L) was added, mixed thoroughly, and then 1 mL of Nessler's reagent was added dropwise. After standing for 20 min, the absorbance value was recorded at a wavelength of 420 nm. A concentration-absorbance standard curve was plotted using a series of standard ammonium chloride solutions for quantification.

[0040] Nitrite (NO2) - The determination of nitrite was performed using a mixed solution of p-aminobenzenesulfonamide (4 g), N-(1-naphthyl)ethylenediamine dihydrochloride (0.2 g), ultrapure water (50 mL), and phosphoric acid (10 mL, ρ = 1.70 g / mL) as the colorimetric reagent. A certain amount of electrolyte was taken from the electrolytic cell and diluted to 50 mL (to ensure it was within the detection linear range). Then, 1 mL of the colorimetric reagent was added to the 50 mL solution, mixed well, and allowed to stand for 20 min. The absorbance value was recorded at 540 nm. A concentration-absorbance standard curve was plotted using a series of standard sodium nitrite solutions for quantification.

[0041] Figure 1 The morphology of the catalysts prepared in Examples 1-2 was analyzed. Figure 1 (a) is Co(OH)2 / CuO x Scanning electron microscope (SEM) images of nanowire materials. Figure 1 (b) is CuO x SEM image of the nanowire precursor. Figure 1 (b) shows the CuO generated after electro-oxidation-calcination treatment. x It exhibits a clear and orderly one-dimensional nanowire array morphology. The nanowires have smooth surfaces, uniform sizes, and are uniformly grown on the copper substrate, forming a self-supporting open array structure, which is beneficial for electrolyte wetting and rapid ion diffusion. In contrast, Figure 1 (a) After Co(OH)₂ was introduced via pulse electrodeposition, the surface of the nanowires became slightly rough, confirming that Co(OH)₂ was successfully and uniformly loaded onto CuO. x The surface of the nanowires. Simultaneously, abundant open gaps and macroporous structures are maintained between the nanowires, which is beneficial for reactants (NO3). - Efficient transport of CuO and its products. x The unique core-shell structure, with nanowires as the core and Co(OH)2 as the shell, not only provides a large specific surface area and abundant active sites, but also facilitates the interaction between Co(OH)2 and CuO. x The interfacial synergistic effect promotes interfacial charge transfer, providing a favorable structural basis for the efficient electrocatalytic reduction of nitrate to ammonia.

[0042] Figure 2 CuO x Nanowires and Co(OH)2 / CuO x X-ray diffraction (XRD) pattern of nanowire material. The image shows strong diffraction peaks belonging to the copper substrate at 2θ≈43.3°, 50.4°, and 74.1° for the CuOx sample. Furthermore, diffraction peaks consistent with CuO (PDF#00-045-0937) appear at ~35.5°, 38.7°, 48.7°, and 53.5°, while characteristic peaks corresponding to Cu2O (PDF#04-003-6433) are present at ~36.4°, 42.3°, and 61.4°, indicating the formation of a CuO / Cu2O composite phase after short-term calcination at 350℃. After the introduction of Co(OH)₂, the composite material exhibited a characteristic diffraction peak at ~11.5° attributed to the loaded Co(OH)₂ (PDF#00-46-0605), and weak diffraction signals of the loaded Co(OH)₂ were also observed at ~38.9°, confirming the successful loading of Co(OH)₂. It is noteworthy that the introduction of Co(OH)₂ did not alter the CuO composition. x The original phase structure of the CuO / Cu2O composite phase was preserved, and due to the low loading, the Co(OH)2 diffraction peak intensity was weak, indicating that it was highly dispersed on the nanowire surface. XRD results showed that this method successfully prepared nanowire catalytic materials with CuO / Cu2O composite phase as the main body and Co(OH)2 loaded on the surface, and the introduction of Co(OH)2 did not change the CuO / Cu2O composite phase. x The phase structure.

[0043] Figure 3 The electrocatalytic reduction of nitrate (NO3) by the catalyst was systematically evaluated. - RR) performance. (By...) Figure 3 As shown in the LSV curve of (a), in an electrolyte containing nitrate, the Co(OH)2 / CuO ratio is... x The electrodes exhibit far superior performance compared to pure CuO. x The electrode exhibits catalytic activity with a current density as high as approximately 1.5 A·cm⁻¹ at -0.5 V vs. RHE. -2 The weak response in the blank electrolyte confirms that this large current is specific to NO3. - RR process. Figure 3 (b) indicates that Co(OH)2 / CuO x It maintains extremely high selectivity over a wide operating potential range, and its ammonia production faradaic efficiency (FE) is... NH3 The concentration of nitrite (NO2) reached a peak of nearly 94.2% near -0.5 V vs. RHE. - Byproducts are effectively suppressed. For example... Figure 3(c) shows a direct comparison, at the optimal potential, Co(OH)2 / CuO x ammonia yield (4.53 mmol·h) -1 ·cm -2 ) and FE NH3 (94.2%) all achieved the desired effect on pure CuO. x A significant leap in performance, and NO2 - The accumulation was almost zero. This fully demonstrates that the introduction of Co(OH)2 significantly enhanced the active hydrogen supply at the interface, accelerated the hydrogenation kinetics of the intermediate, and thus achieved efficient and highly selective ammonia conversion.

Claims

1. A self-supporting Co(OH)2 / CuO x Nanowire array electrode, method of making the same, and use thereof in electrocatalytic reduction of nitrate to ammonia. (1) 1x1 cm foam copper was oxidized to Cu(OH)2nanowires by electro-oxidation method by placing the foam copper in NaOH solution and applying an anodic current; 2 to oxidize the foam copper to Cu(OH)2nanowires; (2) High temperature air atmosphere calcination: Cu(OH)2nanowires obtained from the reaction of step (1) were placed in a muffle furnace and calcined in air to obtain CuO x nanowires; (3) Take the CuO obtained in step (2) x Co(OH)₂ / CuO was obtained by pulse electrodeposition in an aqueous cobalt source solution using the pulse electrodeposition method. x electrode.

2. A self-supporting Co(OH)2 / CuO according to claim 1 x Nanowire array electrodes, their preparation methods, and their application in electrocatalytic nitrate reduction to ammonia production, characterized in that... In step (1), the NaOH solution is 50 mL of 1 M NaOH aqueous solution.

3. A self-supporting Co(OH)₂ / CuO according to claim 1 x Nanowire array electrodes, their preparation methods, and their application in electrocatalytic nitrate reduction to ammonia production, characterized in that... In step (2), the temperature of air calcination is 350℃ and the time is 3 minutes.

4. A self-supporting Co(OH)₂ / CuO according to claim 1 x Nanowire array electrodes, their preparation methods, and their application in electrocatalytic nitrate reduction to ammonia production, characterized in that... In step (3), the voltage for pulse electrodeposition is -1 V vs. Ag / AgCl, t on The time is 2 seconds, t off The time is 10 seconds, and 150 cycles are performed.

5. A self-supporting Co(OH)2 / CuO according to claim 1 x Nanowire array electrodes, their preparation methods, and their application in electrocatalytic nitrate reduction to ammonia production, characterized in that... In step (3), the cobalt source is a 0.1 M aqueous solution of Co(NO3)2·6H2O with a volume of 50 mL.

6. A self-supporting Co(OH)₂ / CuO prepared by the method described in claims 1-5 x Nanowire array electrodes, characterized in that: The electrode has a nanowire structure, and due to the pulse electrodeposition loading of Co(OH)2, a Co(OH)2 / CuO formation is formed on its surface. x Heterogeneous junction structure.

7. The self-supporting Co(OH)2 / CuO according to claim 6 x Nanowire array electrodes, characterized in that The specific application method is as follows: Combine Co(OH)2 / CuO x The working electrode is made of nanowire array electrode, which realizes the electrocatalytic conversion of nitrate to ammonia under alkaline conditions.

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