Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst as well as preparation method and application thereof

Abstract

The invention provides a Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst as well as a preparation method and application thereof, and belongs to the technical field of preparation of electrocatalytic materials. According to the preparation method disclosed by the invention, Ce modification is carried out on the CuO nanowires, so that the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst with a large number of oxygen vacancies is obtained; by doping Ce, more oxygen vacancies appear in the catalyst, and an electronic structure is optimized, so that adsorption of an intermediate is promoted; the catalyst is beneficial to activation and dissociation of interface water, can promote generation of active hydrogen and hydrogenation of reaction intermediates, has good application in the field of electro-catalysis nitrate reduction, and has good practicability.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalytic material preparation, and specifically relates to a Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst and a preparation method and application thereof. Background Art

[0002] Ammonia is an important raw material for industrial and agricultural production. It is also considered a clean energy carrier. Therefore, there is an urgent need to develop a sustainable ammonia production process that can achieve large-scale production. However, the current industrial production of ammonia is still mainly based on the Haber-Bosch process, which has disadvantages such as high energy consumption and harsh process conditions. In addition, it produces a large amount of carbon dioxide during the production process, which exacerbates environmental problems. The electrochemical method for producing ammonia has attracted extensive research due to its low cost, energy saving and high efficiency. However, the electrocatalytic nitrogen reduction method for ammonia production is limited by the stable N≡N bond and the low solubility of nitrogen in water, and it is accompanied by severe competition from the hydrogen evolution reaction during the reduction process. Therefore, there is an urgent need to use a new alternative nitrogen source to solve the above problems so as to achieve high electrochemical activity and selective production of ammonia.

[0003] Nitrates have the following advantages as a nitrogen source instead of nitrogen gas: (1) The N=O bond in nitrates (204 kJ mol -1 ) is much lower than the N≡N bond in nitrogen (941KJ mol -1 ) bond energy, greatly reducing the reaction energy barrier; (2) Nitrate (880gL -1 ) is more soluble in water than nitrogen (0.02 g L -1 ) has high solubility in water, avoiding complex gas-liquid-solid interface interactions; (3) The excessive use and discharge of nitrates in industry and agriculture pose a serious threat to the ecosystem. Using nitrates as a nitrogen source to synthesize ammonia can contribute to the important issue of eliminating nitrate pollution. However, the electrocatalytic nitrate reduction reaction to produce ammonia (NO 3 - +6H 2 O+8e - →NH 3 +9OH - ) is a slow eight-electron transfer process and involves many byproducts, such as NO 2 - , NO, NH 2 OH, NH 2 This is a huge challenge for the design of catalysts.

[0004] Precious metals such as palladium, rhodium, ruthenium, gold, and platinum have been used for electrocatalytic nitrate reduction to produce ammonia, but their scarcity and high prices have greatly limited large-scale industrial production. Copper-based materials, as one of the most effective and inexpensive metal catalysts, can convert nitrate to ammonia with high conversion efficiency under ambient conditions, and have therefore been widely studied. Copper tends to transfer d electrons to the lowest unoccupied molecular orbital (π* orbital) of the nitrate ion, and its unique electronic structure can enhance the adsorption of nitrogen-containing intermediates during the reduction of nitrate to ammonia, making the entire process of nitrate reduction to ammonia continuous. However, the insufficient activation ability of copper for interfacial water limits the generation of active hydrogen, thereby inhibiting the nitrate hydrogenation process, which seriously hinders the ammonia production process and is difficult to apply to the electrocatalytic nitrate reduction reaction.

[0005] Therefore, it is necessary to design and develop an electrocatalytic nitrate catalyst that can facilitate the activation and dissociation of interfacial water, promote the generation of active hydrogen and the hydrogenation of reaction intermediates. Summary of the invention

[0006] In view of some deficiencies in the prior art, the present invention provides a Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst and a preparation method and application thereof; the present invention modifies CuO nanowires with Ce to obtain a Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst with a large number of oxygen vacancies; the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst is in the structure of nanoflowers and nanowires, and the nanoflowers are composed of Cu in the gaps between CuO nanowires. 2+ CuO nanosheets are formed and then piled up during the annealing process, and the modified Ce replaces part of the Cu sites on the nanowire and nanoflower structures; the present invention causes more oxygen vacancies to appear in the catalyst and optimizes the electronic structure by doping Ce, thereby promoting the adsorption of intermediates; the catalyst of the present invention is beneficial to the activation and dissociation of interfacial water, and can promote the generation of active hydrogen and the hydrogenation of reaction intermediates, and has good application in the field of electrocatalytic nitrate reduction and has good practicality.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical means:

[0008] The present invention first provides a Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst, wherein Ce is doped on the surface of CuO nanowires; the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst is in the structure of nanoflowers and nanowires, wherein the nanoflowers are composed of Cu in the gaps between the CuO nanowires. 2+ CuO nanosheets are formed during the annealing process and then piled up, and the modified Ce replaces some Cu sites on the nanowire and nanoflower structures.

[0009] The present invention also provides a method for preparing the above Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst, the preparation method comprising:

[0010] (1) Pre-treating the copper foam to remove the oxide layer and impurities on the surface, then immersing the treated copper foam in a mixed solution of ammonium persulfate and sodium hydroxide and letting it stand for a period of time, washing and drying after the standing period to obtain in-situ grown blue Cu(OH) 2 Nanowires;

[0011] (2) Blue Cu(OH) 2 The nanowires are immersed in an aqueous solution of cerium nitrate hexahydrate for a period of time, and then calcined at a certain temperature. After the calcination, a Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst is obtained.

[0012] Preferably, in the mixed solution of ammonium persulfate and sodium hydroxide in step (1), the concentration of ammonium persulfate is 0.125 mol / L, and the concentration of sodium hydroxide is 2.5 mol / L.

[0013] Preferably, in step (1), the standing condition is: standing at room temperature for 10 to 30 minutes.

[0014] Preferably, in step (1), the drying condition is: the drying temperature does not exceed 60°C.

[0015] Preferably, in step (2), the concentration of the aqueous solution of cerium nitrate hexahydrate is 1 to 20 mmol / L.

[0016] Preferably, in step (2), the immersion time is 0.5 to 1.5 hours.

[0017] Preferably, in step (2), the calcination conditions are: a heating rate of 5°C / min, a heating temperature of 100-300°C, and a calcination time of 1 hour.

[0018] The present invention also provides the use of the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst in electrocatalytic reduction of nitrate.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst of the present invention is doped with Ce on the surface of the CuO nanowire; the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst is in the structure of nanoflowers and nanowires, and the nanoflower is composed of Cu in the gaps of the CuO nanowires. 2+During the annealing process, CuO nanosheets are formed and then piled up, and the modified Ce replaces some Cu sites on the nanowire and nanoflower structures. This structure can produce more reaction sites, which is conducive to the adsorption of nitrates and their intermediates and improves the catalytic performance.

[0021] The introduction of cerium in the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst prepared by the present invention makes more oxygen vacancies appear in the catalyst and optimizes the electronic structure of copper, thereby promoting the adsorption of intermediates. In addition, the introduction of cerium enhances the activation and dissociation of interfacial water, produces more active hydrogen, improves the problem of insufficient activation ability of CuO for interfacial water, and thus promotes the hydrogenation of nitrogen-containing intermediates to produce ammonia during nitrate reduction. 10 / CuO at a potential of -0.4 V vs. RHE, the ammonia yield reached 4.04 mmol cm -2 h -1 The ammonia yield of CuO was increased by 1.2 mmol cm -2 h -1 , and its Faraday efficiency reached 97.2% at this potential. After several cycles and long-term tests, its synthetic ammonia yield and its corresponding potential current density remained almost unchanged, indicating that the catalyst has good stability. 3 - Battery, at 38mA cm -2 The peak power density reached 14.5 mW cm -2 , and at 40mAcm -2 The Faradaic efficiency of ammonia reaches 98.4%, exceeding many reported catalysts.

[0022] The preparation method of the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst of the present invention is simple and low in cost, and has good application in the field of electrocatalytic nitrate reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 For Ce 10 / Schematic diagram of the synthesis of CuO nanoflower-nanowire heterogeneous materials.

[0024] Figure 2 CuO nanowires (a) and Ce 10 / CuO nanoflower-nanowire heterogeneous materials (b, c).

[0025] Figure 3 For Ce 10 / CuO nanoflower-nanowire heterogeneous material mapping element diagram; a in the figure is Ce 10a is the SEM image of the Cu / CuO nanoflower-nanowire heterogeneous material, b is the mapping image of the Cu element, c is the mapping image of the O element, and d is the mapping image of the Ce element.

[0026] Figure 4 For Ce 10 HRTEM image of / CuO nanoflower-nanowire heterogeneous material.

[0027] Figure 5 For Ce 10 XRD pattern of / CuO nanoflower-nanowire heterogeneous material.

[0028] Figure 6 For Ce 10 XPS full spectrum comparison of CuO nanoflower-nanowire heterogeneous materials and CuO nanowires (a), high-resolution XPS comparison of Cu (b), O (c), and Ce 10 High-resolution XPS spectrum of Ce element in CuO nanoflower-nanowire heterogeneous materials (d).

[0029] Figure 7 For Ce 10 LSV comparison of CuO nanoflower-nanowire heterogeneous materials and CuO nanowires.

[0030] Figure 8 For Ce 10 Ammonia yield and Faradaic efficiency of CuO nanoflower-nanowire heterogeneous materials (a) and CuO nanowires (b) at different potentials.

[0031] Fig. 9 For Ce 10 / CuO nanoflower-nanowire heterogeneous material ammonia yield and Faraday efficiency cycle diagram at the same potential.

[0032] Fig.10 For Ce 10 The in situ infrared spectra of CuO nanoflower-nanowire heterogeneous material (a) and CuO nanowire (b) are located at 3110-3690 cm -1 Part of Ce at different potentials 10 / CuO and the ratio of the OH dangling bond resonance peak (danglingO-H) of CuO catalyst (c) and Ce 10 tetra-H / CuO 2 O, tri-H 2 Schematic diagram of the wavelength shift of O and dangling OH as the potential changes (d).

[0033] Fig.11 For Ce 10In situ IR spectra of CuO / CuO nanoflower-nanowire heterogeneous material (a) and CuO nanowires (b).

[0034] Fig.12 For Ce 10 / Mechanism diagram of the electrocatalytic reduction of nitrate to ammonia by CuO nanoflower-nanowire heterogeneous materials.

[0035] Fig.13 Zn-NO 3 - Battery schematic (a) and using two Zn-NO 3 - Photo of a battery powering a red LED (b).

[0036] Fig.14 Zn-NO 3 - The discharge curve of the battery and the corresponding power density curve.

[0037] Fig.15 For Ce 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst as cathode for Zn-NO 3 - Ammonia production and Faradaic efficiency of the cell. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0039] Example 1: Ce 1 Preparation of CuO nanoflower-nanowire heterogeneous electrocatalysts

[0040] This embodiment is based on Figure 1 The process shown in the figure is to prepare Ce / CuO nanoflower-nanowire heterogeneous electrocatalysts. The preparation principle is to in situ grow Cu(OH) on the smooth copper foam surface by oxidation etching. 2 Nanowires, and then the Cu on the catalyst surface under the action of concentration gradient 2+ and OH - diffuse outward and remain in the gaps between nanowires. 3+ Due to the concentration difference, Cu in the nanowire gaps also diffuses to the nanowire surface. 2+ and OH - During the subsequent annealing process, Cu(OH) 2 Nanosheets are stacked into nanoflowers. 3+ diffused into the nanowire gaps and nanowire surfaces, and successfully doped Cu(OH) 2Nanowires and Cu(OH) 2 On nanoflowers.

[0041] The specific preparation steps are as follows:

[0042] (1) cleaning the copper foam in 3 mol / L hydrochloric acid solution, ethanol and deionized water respectively with 100W ultrasonic cleaning for 10 min to obtain the cleaned copper foam for later use;

[0043] 2.5 mmol of ammonium persulfate was added to 20 mL of a 2.5 mol / L sodium hydroxide solution, and ultrasonicated to form a uniform mixed solution of ammonium persulfate and sodium hydroxide for later use.

[0044] The cleaned copper foam was immersed in a mixed solution of ammonium persulfate and sodium hydroxide and allowed to stand for 10 minutes. After standing, it was rinsed with deionized water and ethanol respectively, and then dried to obtain blue Cu(OH) 2 Nanowires.

[0045] (2) Blue Cu(OH) 2 The nanowires were immersed in a 1 mmol / L cerium nitrate hexahydrate aqueous solution for 0.5 hours and then calcined at 100 °C for 1 hour. After calcination, Ce / CuO nanoflower-nanowire heterogeneous electrocatalysts were obtained, denoted as Ce 1 / CuO nanoflower-nanowire heterogeneous electrocatalyst.

[0046] Example 2: Ce 20 Preparation of CuO nanoflower-nanowire heterogeneous electrocatalysts

[0047] (1) cleaning the copper foam in 3 mol / L hydrochloric acid solution, ethanol and deionized water respectively with 100W ultrasonic cleaning for 10 min to obtain the cleaned copper foam for later use;

[0048] 2.5 mmol of ammonium persulfate was added to 20 mL of a 2.5 mol / L sodium hydroxide solution, and ultrasonicated to form a uniform mixed solution of ammonium persulfate and sodium hydroxide for later use.

[0049] The cleaned copper foam was immersed in a mixed solution of ammonium persulfate and sodium hydroxide and allowed to stand for 30 minutes. After standing, it was rinsed with deionized water and ethanol respectively, and then dried to obtain blue Cu(OH) 2 Nanowires.

[0050] (2) Blue Cu(OH) 2 The nanowires were immersed in a 20 mmol / L cerium nitrate hexahydrate aqueous solution for 1.5 hours and then calcined at 300 °C for 1 hour. After calcination, Ce / CuO nanoflower-nanowire heterogeneous electrocatalysts were obtained, denoted as Ce 20 / CuO nanoflower-nanowire heterogeneous electrocatalyst.

[0051] Example 3: Ce 10 Preparation of CuO nanoflower-nanowire heterogeneous electrocatalysts

[0052] (1) cleaning the copper foam in 3 mol / L hydrochloric acid solution, ethanol and deionized water respectively with 100W ultrasonic cleaning for 10 min to obtain the cleaned copper foam for later use;

[0053] 2.5 mmol of ammonium persulfate was added to 20 mL of a 2.5 mol / L sodium hydroxide solution, and ultrasonicated to form a uniform mixed solution of ammonium persulfate and sodium hydroxide for later use.

[0054] The cleaned copper foam was immersed in a mixed solution of ammonium persulfate and sodium hydroxide and allowed to stand for 20 minutes. After standing, it was rinsed with deionized water and ethanol respectively, and then dried to obtain blue Cu(OH) 2 Nanowires.

[0055] (2) Blue Cu(OH) 2 The nanowires were immersed in a 10 mmol / L cerium nitrate hexahydrate aqueous solution for 1 hour, and then calcined at 200°C for 1 hour. After the calcination, the Ce 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst.

[0056] The blue Cu(OH) 2 The nanowires were directly calcined at 200°C for 1 hour to obtain CuO nanowires, which were used as a comparison.

[0057] Figure 2 a is the SEM image of CuO nanowires. Figure 2 bc is Ce 10 SEM image of CuO nanoflower-nanowire heterogeneous material. It can be seen from the figure that after cerium doping, the morphology changes from a single nanowire to a nanoflower structure formed by a large number of nanosheets evenly distributed on the surface of the nanowire. This structure can produce more reaction sites, which is conducive to the adsorption of nitrates and their intermediates and improves the catalytic performance. Figure 3 For Ce 10 / Mapping element diagram of CuO nanoflower-nanowire heterogeneous materials. It can be seen from the figure that the three elements Cu, O and Ce exist, which further confirms the successful synthesis of the material.

[0058] Figure 4 For Ce 10 HRTEM image of CuO nanoflower-nanowire heterogeneous material. It can be seen from the figure that the characteristic crystal plane spacing of 0.250nm is attributed to the (1 1 -1) crystal plane of CuO.

[0059] Figure 5 The XRD spectrum shows that Ce 10 The three strongest diffraction peaks attributable to the foamed copper were observed at 43.61°, 50.67°, and 74.29° for Ce / CuO, while the characteristic diffraction peaks corresponding to the (-1 1 1) and (1 1 1) crystal planes of CuO appeared at 35.60° and 38.83°. 10 Only the diffraction peaks of CuO and Cu were observed in / CuO, indicating that Ce ions were likely to replace Cu ions relative to the CuO precursor, but the low doping amount during the synthesis resulted in no obvious shift in the peaks.

[0060] Figure 6 a is Ce 10 The XPS spectra of CuO nanoflower-nanowire heterogeneous materials and CuO nanowires confirm that Ce 10 / CuO Ce element was successfully doped into CuO. Figure 6 b shows Ce 10 High-resolution Cu 2p spectra of CuO nanoflower-nanowire heterogeneous materials and CuO nanowires. After doping with Ce, the position of the Cu 2p-related characteristic peaks shifts to lower binding energy. Cu may become an electron acceptor, and the accumulated charge may lead to an increase in the charge density of Cu. Figure 6 c shows Ce 10 High-resolution O1s spectra of CuO / CuO nanoflower-nanowire heterogeneous materials and CuO nanowires, indicating that the proportion of oxygen vacancies increases after Ce doping. Figure 6 Shows Ce 10 Ce was introduced on the surface of CuO 3+ and Ce 4+ A mixture of Ce 3+ The presence of ions as defect indicators promotes the generation of oxygen vacancies.

[0061] Embodiment 4:

[0062] In this example, CuO nanowires were used as a control to investigate the Ce prepared in Example 3. 10 The electrocatalytic performance, electrocatalytic nitrate reduction performance and stability of the CuO nanoflower-nanowire heterogeneous electrocatalyst are specifically investigated as follows:

[0063] (1) Ce 10 Investigation of electrocatalytic performance of CuO nanoflower-nanowire heterogeneous electrocatalysts:

[0064] Take 1cm*2cm of Ce respectively 10 / CuO nanoflower-nanowire heterogeneous materials and CuO nanowires were used as working electrodes, the reference electrode was Hg / HgO electrode, and the counter electrode was a platinum sheet electrode. An H-type electrolytic cell was used with 0.1 M KNO 3 +1M KOH solution as cathode electrolyte, 1M KOH solution as anode electrolyte, separated by Nafion117 proton exchange membrane. Linear sweep voltammetry was used with a scan rate of 20mV / s to test the current density of the working electrode. The test results are shown in Figure 7 shown.

[0065] It can be seen from the figure that the current density of Ce-doped CuO is higher at the same potential, indicating that the Ce 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst has better conductive properties.

[0066] (2) Ce 10 Investigation of the electrocatalytic nitrate reduction performance of CuO nanoflower-nanowire heterogeneous electrocatalysts:

[0067] In this step, the reaction system and working electrode described in step (1) are used for electrochemical testing. The test is performed at 0, -0.1, -0.2, -0.3, -0.4, and -0.5 V vs. RHE potentials, and then the cathode chamber solution is collected and tested for ammonia concentration using Nessler's reagent. Then, the synthetic ammonia yield and Faraday efficiency are calculated. The results are as follows: Figure 8 shown.

[0068] As can be seen from the figure, Ce 10 The / CuO nanoflower-nanowire heterogeneous electrocatalyst has significantly increased ammonia yield and Faradaic efficiency, indicating that Ce doping is beneficial to the synthesis of ammonia by nitrate reduction.

[0069] (3) Ce 10 Investigation on the stability of CuO nanoflower-nanowire heterogeneous electrocatalysts:

[0070] In this step, the reaction system and working electrode described in step (1) were used for electrochemical testing. Seven cycles were performed at -0.3 V vs. RHE. The test results were as follows: Fig. 9 shown.

[0071] As can be seen from the figure, Ce 10 The yield and Faraday efficiency of the CuO nanoflower-nanowire heterogeneous electrocatalyst remained almost unchanged during the seven cycle tests, indicating that the Ce 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst has excellent stability. In summary, the introduction of cerium promotes the nitrate reduction process. 10 / CuO at a potential of -0.4 V vs. RHE, the ammonia yield reached 4.04 mmol cm -2 h -1 The ammonia yield of CuO was increased by 1.2 mmol cm -2 h -1 , and its Faraday efficiency reached 97.2% at this potential. After several cycles and long-term tests, its synthetic ammonia yield and its corresponding potential current density remained almost unchanged, indicating that the catalyst has good stability.

[0072] Embodiment 5:

[0073] In this example, in-situ infrared characterization was used to investigate the 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst electrocatalyst electrocatalyst nitrate reduction mechanism and reaction pathway, the method is as follows:

[0074] The measurements were performed in a two-chamber photoelectrochemical cell consisting of three electrodes, including Ce as the working electrode. 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst, platinum wire as counter electrode and standard silver / silver chloride electrode as reference electrode. All in situ infrared spectra were obtained using a Fourier transform infrared spectrophotometer (FT-IR, Nicolet iS50, Thermo Fischer Scientific.) equipped with a mercury cadmium telluride (MCT) detector. In the test, the working electrode was initially activated by performing CV cycles in the potential range of 0 to -0.8V vs.RHE at a scan rate of 0.05V / S until it stabilized. The spectrum at open circuit voltage was then collected as the background. Next, the cathode potential fluctuated from 0 to -0.8Vvs.RHE, and each potential lasted for 2 minutes to collect the spectrum. The test results are shown in Fig.10 shown.

[0075] As can be seen from the figure, Ce 10 / CuO nanoflower-nanowire heterogeneous materials and CuO nanowires as electrocatalysts are located at 3110-3690 cm -1 The spectral bands in the range correspond to the OH stretching mode of water molecules. As the applied voltage changes, the proportions and positions of the three water peaks change accordingly ( Fig.10 a and Fig.10 b); Ce doping is beneficial to the activation of interfacial water, promoting the generation of active hydrogen and the hydrogenation of nitrogen-containing intermediates ( Fig.10 c); Ce 10 The dangling OH of the CuO nanoflower-nanowire heterocatalyst exhibits a steeper Stark slope (-49.7 cm -1 / V), which indicates that free water is more sensitive to changes in the applied electric field. 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst free water is more easily dissociated to form active hydrogen, which is beneficial to the ammonia synthesis process ( Fig.10 d).

[0076] Combination Fig.11 and 12 It can be seen that the reaction path of electrocatalytic nitrate is: *NO 3 →*NO 2 →*NO→*NH 2 OH→*NH→*NH 2 →NH 3 , and Ce doping accelerates the consumption of nitrate and the production of ammonia.

[0077] Embodiment 6:

[0078] like Fig.13 As shown, this embodiment uses Ce 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst as cathode and polished Zn plate as anode to assemble Zn-NO 3 - Battery; the Zn-NO 3 - The battery is an H-type battery, which contains a cathode electrolyte (0.1M KOH + 0.1M KNO 3 ) and anolyte (6 M KOH), which were separated by a Nafion 117 membrane.

[0079] In order to evaluate the performance of the battery, the power density, Zn-NO 3 - The discharge curve of the battery is as follows Fig.14 As shown in the figure, the Zn-NO 3 - Battery at 38mAcm -2 The peak power density is 14.5 mW cm -2 .

[0080] Take the electrolyte after discharge test at different potentials for product testing. The test results are as follows: Fig.15 As shown in the figure, it can be seen that with the increase of current density, Zn-NO 3 - The ammonia yield and Faradaic efficiency of the battery gradually increased. -2 The yield reached 0.18 mmol cm -2 h -1 , and the Faradaic efficiency reaches 98.4%, exceeding many existing catalysts.

[0081] In summary, the present invention modifies CuO nanowires to obtain Ce with a large number of oxygen vacancies. 10 / CuO nanoflower-nanowire heterogeneous electrocatalyst; the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst is a nanoflower and nanowire structure, and the nanoflower is composed of Cu in the gap of CuO nanowire. 2+ CuO nanosheets are formed during the annealing process and then piled up, and the modified Ce replaces part of the Cu sites on the nanowire and nanoflower structures; the present invention makes more oxygen vacancies appear in the catalyst by doping Ce and optimizes the electronic structure, thereby promoting the adsorption of intermediates; the catalyst of the present invention is conducive to the activation and dissociation of interfacial water, which can promote the generation of active hydrogen and the hydrogenation of reaction intermediates, and the Ce 10 The preparation method of CuO nanoflower-nanowire heterogeneous electrocatalyst is simple and low-cost, and it has great application in the field of electrocatalytic nitrate reduction and has good practicality.

[0082] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst, characterized in that: The Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst is doped with Ce on the surface of the CuO nanowire; the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst is in the structure of nanoflowers and nanowires, and the nanoflower is composed of Cu in the gaps of the CuO nanowires. 2+ CuO nanosheets are formed during the annealing process and then piled up, and the modified Ce replaces some Cu sites on the nanowire and nanoflower structures.

2. The method for preparing the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst according to claim 1, characterized in that: The preparation method comprises: (1) pre-treating the copper foam to remove the oxide layer and impurities on the surface, then immersing the treated copper foam in a mixed solution of ammonium persulfate and sodium hydroxide and letting it stand for a period of time, washing and drying after the standing period to obtain in-situ grown blue Cu(OH)2 nanowires; (2) The blue Cu(OH)2 nanowires are immersed in an aqueous solution of cerium nitrate hexahydrate for a period of time, and then calcined at a certain temperature. After the calcination, Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst is obtained.

3. The method for preparing the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst according to claim 2, characterized in that: In the mixed solution of ammonium persulfate and sodium hydroxide in step (1), the concentration of ammonium persulfate is 0.125 mol / L, and the concentration of sodium hydroxide is 2.5 mol / L.

4. The method for preparing the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst according to claim 2, characterized in that: In step (1), the standing condition is: standing at room temperature for 10 to 30 minutes.

5. The method for preparing the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst according to claim 2, characterized in that: In step (1), the drying condition is: the drying temperature does not exceed 60°C.

6. The method for preparing the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst according to claim 2, characterized in that: In step (2), the concentration of the aqueous solution of cerium nitrate hexahydrate is 1 to 20 mmol / L.

7. The method for preparing the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst according to claim 2, characterized in that: In step (2), the immersion time is 0.5 to 1.5 hours.

8. The method for preparing the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst according to claim 2, characterized in that: In step (2), the calcination conditions are: heating rate of 5°C / min, heating temperature of 100-300°C, and calcination time of 1 hour.

9. Use of the Ce / CuO nanoflower-nanowire heterogeneous electrocatalyst according to claim 1 in electrocatalytic reduction of nitrate.

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