Palladium-nickel cobalt oxide composite material, preparation method and application of palladium-nickel cobalt oxide composite material in ammonia production through electro-catalysis nitrate reduction

Abstract

The invention provides a palladium-nickel cobalt oxide composite material, a preparation method and application of electrocatalytic nitrate reduction to ammonia production, and the preparation method comprises the following preparation steps: S1, nickel cobalt oxide: carbon cloth is placed in an electrolyte containing nickel ions and cobalt ions, electrodeposition is carried out, nickel cobalt hydroxide is formed on the carbon cloth, and the nickel cobalt oxide is obtained; calcining the nickel-cobalt hydroxide to obtain a nickel-cobalt oxide; and S2, preparing the palladium-nickel cobalt oxide composite material: putting the nickel cobalt oxide into an electrolyte containing palladium ions, and carrying out electro-deposition to prepare the palladium-nickel cobalt oxide composite material. In the NCO-Pd composite electro-catalytic material provided by the invention, NCO and Pd form a heterogeneous composite structure, the properties of an NCO electro-catalytic material and a Pd material are integrated, and the NCO-Pd composite electro-catalytic material has high selectivity, high Faraday efficiency and stable performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrocatalytic materials, and relates to a palladium-nickel cobalt oxide composite material and a preparation method thereof, and application of the palladium-nickel cobalt oxide composite material in electrocatalytic reduction of nitrate to ammonia. BACKGROUND

[0002] Ammonia (NH3) as a hydrogen energy carrier has high energy density and safe transportation and storage characteristics, and has broad application prospects in future energy development. At the same time, ammonia is one of the most important raw materials for synthesizing agricultural fertilizers, chemical products and medical products, and plays an indispensable role in industrial production. However, compared with the traditional Haber-Bosch ammonia production method, the electrocatalytic ammonia production technology is green and has more potential in industrial continuous production. Among them, the electrocatalytic reduction of nitrate to ammonia can produce ammonia by electrochemical reduction of nitrate (NO3 - ) in water, and can also achieve simultaneous wastewater denitrification treatment, which is of great significance to solve environmental pollution problems. Since the electrocatalytic reduction of nitrate involves multiple electron and proton transfer processes, the reaction energy barrier is high, the rate is slow, and the generation of competitive hydrogen evolution reaction and by-products significantly reduces the selectivity of ammonia production, making it difficult to improve the ammonia yield. Therefore, how to develop a high-performance electrocatalytic material to improve the faradic efficiency and ammonia yield of electrocatalytic reduction of nitrate has become a technical challenge that needs to be overcome.

[0003] Existing research shows that the synergistic effect of electronic effect and geometric effect generated by metal alloying can optimize the performance of electrocatalytic reduction of nitrate to ammonia. For example, the patent document with the application number 202210374043.0 discloses a double-metal layered hydroxide LDH electrode material catalyst, which can improve the activity of ammonia synthesis and has long-term stability by loading NiCo double-metal hydroxide nanosheets on Cu nanowire arrays; the patent document with the application number 202211294519.6 discloses a Cu / MTiO2 electrocatalyst (M is any one of Fe, Ni, Co, Pt, Ru or Ir), in which the Cu / M heterophase interface is anchored on the TiO2 surface, and the high activity of the Cu / M heterophase interface greatly improves the efficiency of electrochemical nitrate conversion to ammonia. However, the preparation of the above electrode material catalysts needs to rely on specific three-dimensional nanowire arrays or nanorod carriers, which increases the difficulty of preparation and limits the application of the catalyst. Therefore, how to provide an electrode material catalyst that can improve the faradic efficiency and ammonia yield of electrocatalytic reduction of nitrate to ammonia while avoiding the dependence on specific nanowire or nanorod carriers has become a technical problem that needs to be solved. SUMMARY

[0004] The purpose of this invention is to provide a palladium-nickel cobalt oxide composite material and its preparation method, as well as its application in electrocatalytic nitrate reduction to ammonia production. This improves the Faraday efficiency and ammonia yield of electrocatalytic nitrate reduction to ammonia production while avoiding dependence on specific nanowire or nanorod supports, simplifying the process, and enhancing the flexibility and versatility of catalyst preparation.

[0005] In a first aspect, the present invention provides a method for preparing a palladium-nickel cobalt oxide composite material, comprising the following preparation steps: S1. Preparation of nickel cobalt oxide: Carbon is arranged in an electrolyte containing nickel and cobalt ions, and electrodeposition is performed to form nickel cobalt hydroxide on the carbon cloth. The nickel cobalt hydroxide is then calcined to obtain nickel cobalt oxide. S2. Preparation of palladium-nickel cobalt oxide composite material: The nickel cobalt oxide is placed in an electrolyte containing palladium ions and electrodeposited to prepare the palladium-nickel cobalt oxide composite material.

[0006] Optionally, in step S1, electrodeposition is performed using a three-electrode system with constant voltage. The carbon cloth is the working electrode, the silver / silver chloride electrode is the reference electrode, and the platinum sheet is the counter electrode. The electrodeposition voltage is -0.91 to -1.51 V vs. Ag / AgCl, and the electrodeposition time is 15 to 25 min.

[0007] Optionally, in step S1, the atomic ratio of nickel ions to cobalt ions in the electrolyte is (2.5~0.5):(0.5~2.5).

[0008] Optionally, in step S1, the atomic ratio of nickel ions to cobalt ions in the electrolyte is 1:(1.5~2.5).

[0009] Optionally, in step S1, the nickel-cobalt hydroxide is calcined at a temperature of 250–350°C for a time of 0.5–4 hours.

[0010] Optionally, in step S1, the microstructure of the prepared nickel-cobalt oxide comprises closely arranged bent sheet-like nanoparticles, the average particle size of the bent sheet-like nanoparticles being 150 nm to 300 nm, and the average sheet diameter being 10 to 30 nm; in step S2, the microstructure of the prepared palladium-nickel-cobalt-oxide composite material comprises clustered nanoparticles, the average particle size of the clustered nanoparticles being 310 nm to 420 nm.

[0011] Optionally, in step S2, the concentration of palladium ions in the electrolyte is 1–6 mmol / L, an alkaline solution is added to the electrolyte to adjust the pH value to 10–12, the electrodeposition voltage is -0.91–-1.51 V vs Ag / AgCl, and the electrodeposition time is 10–25 min.

[0012] Optionally, in step S2, the Pd content in the prepared palladium-nickel cobalt oxide composite material is 8%–19 at, the Ni content is 13%–32 at, the Co content is 20–31 at, and the balance is O.

[0013] Secondly, the present invention provides a palladium-nickel cobalt oxide composite material, which is obtained by the aforementioned method for preparing palladium-nickel cobalt oxide composite materials.

[0014] Thirdly, the present invention provides an application of the aforementioned palladium-nickel cobalt oxide composite material in the electrocatalytic reduction of nitrate to ammonia, wherein the palladium-nickel cobalt oxide composite material is placed in an electrolyte containing nitrate to perform electrocatalytic reduction of nitrate to ammonia.

[0015] In summary, the present invention has at least one of the following beneficial effects: 1. This application provides a palladium-nickel cobalt oxygen composite material, which provides high activity through surface energy regulation and palladium / nickel / cobalt multimetal interface, reduces the catalyst's dependence on three-dimensional nanocarriers, achieves high activity and stability on ordinary two-dimensional planar supports, and enhances the catalyst's preparation flexibility and wide application range.

[0016] 2. This application provides a palladium-nickel cobalt oxide composite material. The nickel cobalt oxide intermediate interface, with its specific microstructure deposited on a planar support, provides a large number of key active sites. Surface oxygen vacancies become active centers for adsorbing and activating nitrates, interacting strongly with palladium and optimizing the electronic structure. Furthermore, palladium nanoparticles can promote efficient generation and supply of active hydrogen, providing sufficient active hydrogen for the hydrogenation step. After catalytic NO bond cleavage, it hydrogenates the intermediate, while simultaneously suppressing hydrogen evolution side reactions and improving NH3 selectivity. The synergistic effect of palladium and nickel cobalt oxide is reflected in the strong electronic interaction, which optimizes the adsorption intensity of reactants / intermediates on the catalyst surface. The "adsorption activation" of nickel cobalt oxide and the "hydrogenation" function of palladium are tightly coupled, achieving efficient tandem catalysis. Moreover, the interaction between the composite materials enhances palladium anchorage, improving the long-term stability of the composite material as a catalyst.

[0017] 3. This application provides a method for preparing palladium-nickel cobalt oxide composite material, which utilizes electrodeposition to form nickel cobalt hydroxide on a common two-dimensional planar carrier, and further electrodeposits palladium on the nickel cobalt oxide formed after calcination. The preparation method of this invention is simple, green and environmentally friendly, and easy to control. The resulting palladium-nickel cobalt oxide composite electrode material exhibits excellent electrocatalytic performance and can achieve efficient electrocatalytic reduction of nitrate to ammonia. Attached Figure Description

[0018] Figure 1The images are scanning electron microscope (SEM) images of nickel oxide, nickel cobalt oxide, or cobalt oxide prepared with nickel-cobalt molar ratios of 1:0 (a) in Example 1, 2:1 (b) in Example 2, 1:1 (c) in Example 3, 1:2 (d) in Example 4, and 0:1 (e) in Example 5.

[0019] Figure 2 These are scanning electron microscope (SEM) images of composite materials after palladium deposition on nickel oxide, nickel cobalt oxide, or cobalt oxide: (a) Example 1; (b) Example 2; (c) Example 3; (d) Example 4; (e) Example 5; (f) Example 6.

[0020] Figure 3 This is a transmission electron microscope (TEM) image of the palladium-nickel cobalt oxide composite material in Example 4.

[0021] Figure 4 This is an EDS mapping diagram of the palladium-nickel cobalt oxide composite material in Example 4.

[0022] Figure 5 This is the XRD pattern of the palladium-nickel cobalt oxide composite material in Example 4. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer and more explicit, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] Alloyed electrode catalysts in related technologies all rely on specific three-dimensional nanowire arrays or nanorod supports, increasing the difficulty of preparation and limiting the application of the catalysts. To overcome the limitations imposed by three-dimensional supports, the applicant creatively proposed a method for preparing a palladium-nickel cobalt oxide composite material. This method involves two-step electrodeposition on a common two-dimensional carbon cloth substrate, simplifying the preparation process while forming an alloyed composite electrode catalyst material with specific elemental composition, phase structure, microstructure, and phase interface structure. This maximizes the synergistic effect of palladium and nickel cobalt oxide, improving the Faradaic efficiency and ammonia yield of the electrocatalytic nitrate reduction to ammonia production. This invention is based on this research.

[0025] In some embodiments of the present invention, a method for preparing a palladium-nickel cobalt oxide composite material is provided, comprising the following preparation steps: S1. Preparation of nickel cobalt oxide: Carbon is arranged in an electrolyte containing nickel and cobalt ions, and electrodeposition is performed to form nickel cobalt hydroxide on the carbon cloth. The nickel cobalt hydroxide is then calcined to obtain nickel cobalt oxide. S2. Preparation of palladium-nickel cobalt oxide composite material: The nickel cobalt oxide is placed in an electrolyte containing palladium ions and electrodeposited to prepare the palladium-nickel cobalt oxide composite material.

[0026] In some embodiments of the present invention, in step S1, electrodeposition is performed using a three-electrode system constant voltage method, with carbon cloth as the working electrode, silver / silver chloride electrode as the reference electrode, and platinum sheet as the counter electrode. The electrodeposition voltage is -0.91 to -1.51 V vs. Ag / AgCl, preferably -1.21 to -1.41 V vs. Ag / AgCl; the electrodeposition time is 15 to 25 min.

[0027] In some embodiments of the present invention, in step S1, the concentration ratio of nickel ions to cobalt ions in the electrolyte is 0.04~0.02 mol / L: 0.02~0.04 mol / L, preferably 0.03~0.02 mol / L: 0.03~0.04 mol / L; more preferably 0.02 mol / L: 0.03~0.04 mol / L, and even more preferably 0.02 mol / L: 0.04 mol / L.

[0028] In some embodiments of the present invention, in step S1, the atomic ratio of nickel ions to cobalt ions in the electrolyte is (2.5~0.5):(0.5~2.5), preferably 1:(1~2.5), more preferably 1:(1.5~2.5), and even more preferably 1:1.8~2.2.

[0029] In some embodiments of the present invention, in step S1, the nickel-cobalt hydroxide is calcined at a temperature of 250–350°C for a time of 0.5–4 hours, preferably 1.5–2.5 hours; preferably, the nickel-cobalt oxide obtained by calcination is of the NiCo2O4 type, and the atomic ratio of Ni, Co and O is either stoichiometric or non-stoichiometric.

[0030] In some embodiments of the present invention, in step S1, the microstructure of the prepared nickel-cobalt oxide comprises spherical, clustered, or bent-sheet nanoparticles, preferably closely arranged bent-sheet nanoparticles, wherein the average particle size of the bent-sheet nanoparticles is 150 nm to 300 nm, preferably 180 to 240 nm, and the average sheet diameter is 10 to 30 nm; in step S2, the microstructure of the prepared palladium-nickel-cobalt oxide composite material comprises spherical or clustered nanoparticles, preferably clustered nanoparticles, wherein the average particle size of the clustered nanoparticles is 310 nm to 420 nm, preferably 310 nm to 350 nm; preferably, the clustered nanoparticles are dispersed on the closely arranged bent-sheet nanoparticles; preferably, the clustered nanoparticles are uniformly dispersed; more preferably, the palladium and nickel-cobalt oxide interfaces are tightly bonded to form a heterogeneous composite structure.

[0031] In some embodiments of the present invention, in step S2, the concentration of palladium ions in the electrolyte is 1-6 mmol / L, preferably 3-5 mmol / L; an alkaline solution is added to the electrolyte, preferably KOH aqueous solution, the pH value is adjusted to 10-12, the electrodeposition voltage is -0.91--1.51V vs Ag / AgCl, preferably -0.91--1.21V vs Ag / AgCl, more preferably -0.91--1.11V vs Ag / AgCl, and the electrodeposition time is 10-25 min, preferably 10-20 min.

[0032] In some embodiments of the present invention, in step S2, the Pd content in the prepared palladium-nickel cobalt oxide composite material is 8%–19 at, the Ni content is 13%–32 at, the Co content is 20–31 at, and the balance is 0; preferably, the Pd content is 9%–19 at, the Ni content is 13%–28 at, the Co content is 20–31 at, and the balance is 0; more preferably, the Pd content is 10%–19 at, the Ni content is 13%–19 at, the Co content is 30–31 at, and the balance is 0; even more preferably, the Pd content is 10%–11 at, the Ni content is 18%–19 at, the Co content is 30–31 at, and the balance is 0.

[0033] In some embodiments of the present invention, a palladium-nickel cobalt oxide composite material and its application in electrocatalytic nitrate reduction to ammonia are provided, wherein the palladium-nickel cobalt oxide composite material is placed in an electrolyte containing nitrate to perform electrocatalytic nitrate reduction to ammonia.

[0034] The following detailed description is provided in conjunction with the embodiments. Unless otherwise specified, the raw materials of this invention are all commercially available.

[0035] Example 1 This embodiment provides a method for preparing palladium-nickel oxide composite materials, and the specific preparation steps are as follows: S1. Preparation of nickel oxide: Carbon cloth (WOS1011, Suzhou Shengernuo Technology Co., Ltd., 1cm) is used to prepare nickel oxide. 2The nickel oxide was placed in an electrolyte containing nickel ions and electrodeposited using a three-electrode system with constant voltage. Carbon cloth was used as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. The electrolyte was prepared by completely dissolving 0.873 g of nickel nitrate hexahydrate (chemical formula Ni(NO3)2·6H2O, analytical grade) in 50 mL of deionized water. The molar concentration of nickel ions in the electrolyte was 0.057 mol / L. Electrodeposition was performed for 20 min at a voltage of -1.31 V vs Ag / AgCl, forming Ni(OH)2 on the carbon cloth. After the electrodeposition was completed, the carbon cloth was rinsed with deionized water and ethanol, and then dried. Finally, it was calcined to obtain nickel oxide (NiO type) in an air atmosphere at a temperature of 300 °C for 2 h.

[0036] The microstructure of the nickel oxide prepared in Example 1 was tested using scanning electron microscopy (SEM), and the test results are as follows: Figure 1 As shown, from Figure 1 As can be seen in (a), the microstructure of the nickel oxide prepared in Example 1 includes a large number of closely packed spherical nanoparticles. The nanoparticles were tested and statistically analyzed using Nano Measurer software. The average particle size of 70 nanoparticles was calculated to be 170 nm.

[0037] S2. Preparation of palladium-nickel oxide composite material: The carbon cloth and the nickel oxide deposited on it were placed in an electrolyte containing palladium ions, and electrodeposition was performed using a three-electrode system constant voltage method. The carbon cloth and the nickel oxide deposited on it were used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the platinum sheet was used as the counter electrode. The electrolyte was prepared by dissolving 0.0284 g of palladium chloride (PdCl2) in 40 mL of deionized water, with a palladium ion concentration of 4 mmol / L. The electrolyte was stirred for five minutes, and then 40 μL of KOH aqueous solution (concentration of 1 mol / L) was added. The stirring was continued for 15 minutes to adjust the pH value of the electrolyte to 11. Then, electrodeposition was performed at a voltage of -1.01 V vsAg / AgCl for 15 minutes. After the electrodeposition was completed, the mixture was rinsed with deionized water and ethanol, and then dried to obtain the palladium-nickel oxide (NiO-Pd) composite material.

[0038] The microstructure of the NiO-Pd composite material prepared in step S2 of Example 1 was tested using scanning electron microscopy (SEM). The test results are as follows: Figure 2 As shown, from Figure 2 As can be seen in (a), the microstructure of the NiO-Pd composite material prepared in Example 1 includes a large number of closely arranged spherical nanoparticles. The nanoparticles were tested and statistically analyzed using Nano Measurer software. The average particle size of 70 nanoparticles was calculated to be 200 nm.

[0039] The elemental composition of the NiO-Pd composite material prepared in Example 1 was characterized by EDS. The Pd content was 7.82%, the Ni content was 42.35%, and the O content was 49.83% in atomic percentage.

[0040] The palladium-nickel oxide composite material prepared in Example 1 was used as a composite electrocatalytic material to test its electrocatalytic performance in nitrate reduction to ammonia production. An H-type electrolytic cell and a three-electrode system were used, with 0.1 mol / L Na₂SO₄ solution as the electrolyte. Electrolytes were injected into both the cathode and anode chambers, with an additional 0.015 mol / L KNO₃ solution added to the cathode chamber. A composite electrocatalytic material was used as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The chronoamperometry (CA) method was used for testing, with electrocatalytic testing conducted at a constant voltage of -1.41 V vs. Ag / AgCl for 3600 s. The ammonia yield was calculated using the indophenol blue method, with the formula: Yield (NH₃) = (ΔC / (AgCl)) / (AgCl). NH3 ×V) / (t×S), ΔC NH3 Let V be the mass concentration of ammonia produced, V be the volume of the cathode electrolyte, t be the electrocatalytic time, and S be the geometric working area. The Faraday efficiency is given by the formula: FE NH3 (%)=(n×F×C NH3 (×V / Q)×100%, where n is the amount of ammonia, F is the Faraday constant (96485 C / mol), Q is the total charge in the electrolytic cell, and V is the volume of the cathode electrolyte. NH3 This represents the mass concentration of ammonia produced. Specific test results are shown in Table 1.

[0041] Example 2 This embodiment provides a method for preparing palladium-nickel cobalt oxide composite materials, and the specific preparation steps are as follows: S1. Preparation of nickel oxide: Carbon cloth (WOS1011, Suzhou Shengernuo Technology Co., Ltd., 1cm) is used to prepare nickel oxide. 2Electrodeposition was performed using a three-electrode system with a constant voltage method, with carbon cloth as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum sheet as the counter electrode, in an electrolyte containing nickel and cobalt ions. The electrolyte was prepared by completely dissolving 0.582 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O, analytical grade) and 0.291 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O, analytical grade) in 50 mL of deionized water. The molar concentration of nickel ions in the electrolyte was 0.04 mol / L, the molar concentration of cobalt ions was 0.02 mol / L, and the atomic ratio of Ni to Co was 2:1. The electrode was prepared at -1.31 V vs. Nickel-cobalt hydroxide (NiCo(OH)2 type) was formed on carbon cloth by electrodeposition of Ag / AgCl under voltage for 20 min. After the electrodeposition, the nickel-cobalt hydroxide was washed with deionized water and ethanol respectively and dried. Then, it was calcined to obtain nickel-cobalt oxide (NiCo2O4 type). The calcination was carried out in an air atmosphere at a temperature of 300℃ for 2 h.

[0042] The microstructure of the nickel-cobalt oxide prepared in Example 2 was tested using the same method as in Example 1, and the test results are as follows: Figure 1 As shown, from Figure 1 As can be seen in (b), the microstructure of the nickel-cobalt oxide prepared in Example 2 includes a large number of relatively dispersed clustered nanoparticles, and the average particle size of the nanoparticles is 200 nm.

[0043] S2. Preparation of palladium-nickel cobalt oxide composite material: The carbon cloth and the nickel cobalt oxide deposited on it were placed in an electrolyte containing palladium ions, and electrodeposition was performed using a three-electrode system constant voltage method. The carbon cloth and the nickel cobalt oxide deposited on it were used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the platinum sheet was used as the counter electrode. The electrolyte was prepared by dissolving 0.0284 g of palladium chloride (PdCl2) in 40 mL of deionized water, with a palladium ion concentration of 4 mmol / L. The electrolyte was stirred for five minutes, and then 40 μL of KOH aqueous solution (concentration of 1 mol / L) was added. The stirring was continued for 15 minutes to adjust the pH value of the electrolyte to 11. Then, electrodeposition was performed at a voltage of -1.01 V vs Ag / AgCl for 15 minutes. After the electrodeposition was completed, the mixture was rinsed with deionized water and ethanol, and then dried to obtain the palladium-nickel cobalt oxide composite material (NCO-Pd).

[0044] The microstructure of the NCO-Pd composite material prepared in step S2 of Example 2 was tested using the same test method as in Example 1. The test results are as follows: Figure 2 As shown, from Figure 2 As can be seen from (b), the microstructure of the NCO-Pd composite material prepared in Example 2 includes a large number of clustered nanoparticles, and the average particle size of the nanoparticles is 210 nm.

[0045] The elemental composition of the NCO-Pd composite material prepared in Example 2 was tested using the same testing method as in Example 1. The Pd content was found to be 8.36%, the Ni content to be 31.26%, the Co content to be 20.13%, and the O content to be 40.25%.

[0046] The electrocatalytic performance of the NCO-Pd composite material prepared in Example 2 for ammonia production by nitrate reduction was tested using the same test method as in Example 1. The specific test results are shown in Table 1.

[0047] Example 3 The difference between Example 3 and Example 2 is that in step S1, the electrolyte is prepared by completely dissolving 0.4365g of nickel nitrate hexahydrate (chemical formula Ni(NO3)2·6H2O, analytical grade) and 0.4365g of cobalt nitrate hexahydrate (chemical formula Co(NO3)2·6H2O, analytical grade) in 50mL of deionized water. The molar concentration of nickel ions in the electrolyte is 0.03mol / L, the molar concentration of cobalt ions is 0.03mol / L, and the atomic ratio of Ni to Co is 1:1. The remaining preparation steps are the same as in Example 2, and the NCO-Pd composite electrocatalytic material is prepared.

[0048] The microstructure of the NCO prepared in step S1 of Example 3 was tested using the same method as in Example 1. The test results are as follows: Figure 1 As shown in (c), from Figure 1 As can be seen in (c), the microstructure of NCO includes the formation of large, coarse aggregates through significant aggregation.

[0049] The microstructure of the NCO-Pd prepared in step S2 of Example 3 was tested using the same method as in Example 1. The test results are as follows: Figure 2 As shown in (c), from Figure 2 As can be seen in (c), the microstructure of NCO-Pd consists of relatively dispersed clusters.

[0050] The elemental composition of the NCO-Pd composite material prepared in Example 3 was tested using the same testing method as in Example 1. The Pd content was found to be 9.29%, Ni content to be 27.09%, Co content to be 28.14%, and O content to be 35.48%.

[0051] The electrocatalytic performance of the NCO-Pd composite material prepared in Example 3 for ammonia production by nitrate reduction was tested using the same test method as in Example 1. The specific test results are shown in Table 1.

[0052] Example 4 The difference between Example 4 and Example 2 is that in step S1, the electrolyte is prepared by completely dissolving 0.291g of nickel nitrate hexahydrate (chemical formula Ni(NO3)2·6H2O, analytical grade) and 0.582g of cobalt nitrate hexahydrate (chemical formula Co(NO3)2·6H2O, analytical grade) in 50mL of deionized water. The molar concentration of nickel ions in the electrolyte is 0.02mol / L, the molar concentration of cobalt ions is 0.04mol / L, and the atomic ratio of Ni to Co is 1:2. The remaining preparation steps are the same as in Example 2, and the NCO-Pd composite electrocatalytic material is prepared.

[0053] The microstructure of the NCO prepared in step S1 of Example 4 was tested using the same method as in Example 1. The test results are as follows: Figure 1 As shown in (d), from Figure 1 As can be seen in (d), the microstructure of NCO consists of a large number of tightly packed, bent lamellar nanoparticles. The average particle size of the nanoparticles is 220 nm and the average lamellar thickness is 20 nm.

[0054] The microstructure of the NCO-Pd prepared in step S2 of Example 4 was tested using the same method as in Example 1. The test results are as follows: Figure 2 As shown in (d), from Figure 2 As can be seen in (d), the microstructure of NCO-Pd includes relatively dispersed clusters with an average particle size of 320 nm, and the clusters are uniformly dispersed on tightly packed, folded, layered nanoparticles.

[0055] The elemental composition of the NCO-Pd composite material prepared in Example 4 was tested using the same testing method as in Example 1. The Pd content was found to be 10.72%, the Ni content to be 18.44%, the Co content to be 30.26%, and the O content to be 40.58%.

[0056] The electrocatalytic performance of the NCO-Pd composite material prepared in Example 4 for ammonia production by nitrate reduction was tested using the same test method as in Example 1. The specific test results are shown in Table 1.

[0057] The microstructure of the NCO-Pd composite material prepared in Example 4 was tested using TEM, and the test results are as follows: Figure 3 As shown, analysis Figure 3 The test results show that NCO and Pd are tightly bonded at the interface, forming a heterogeneous composite structure.

[0058] The elemental distribution of the NCO-Pd composite material prepared in Example 4 was tested using EDS, and the test results are as follows: Figure 4 As shown, analysis Figure 4The test results show that Ni, O, Co and Pd elements in NCO-Pd composite material exhibit uniform and dispersed distribution characteristics, and Pd shows no obvious segregation or separation phenomenon, achieving uniform distribution of each component.

[0059] The phase structure composition of the NCO-Pd composite material prepared in Example 4 was tested using X-ray diffraction (XRD). The test results are as follows: Figure 5 As shown, the NCO-Pd composite material prepared in Example 4 has a phase composition including NiCo2O4 and Pd, and the detected C peak indicates a carbon cloth substrate. The material exhibits a strong broadening peak at 2θ≈20°, and weak and diffuse diffraction peaks in the 30°-70° range, without sharp characteristic crystalline phase peaks. The overall trend of the sample's diffraction peaks corresponds to the characteristic peak positions of the NiCo2O4 type phase (73-1702) and the Pd type phase (46-1043), with no significant shift.

[0060] Example 5 This embodiment provides a method for preparing palladium-cobalt oxide composite materials, and the specific preparation steps are as follows: S1. Preparation of cobalt oxide: Carbon cloth (WOS1011, Suzhou Shengernuo Technology Co., Ltd., 1cm) was used. 2 The sample was placed in an electrolyte containing cobalt ions and electrodeposited using a three-electrode system with constant voltage. Carbon cloth was used as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. The electrolyte was prepared by completely dissolving 0.873 g of cobalt nitrate hexahydrate (chemical formula Co(NO3)2·6H2O, analytical grade) in 50 mL of deionized water. The molar concentration of cobalt ions in the electrolyte was 0.0576 mol / L. Electrodeposition was performed at a voltage of -1.31 V vs Ag / AgCl for 20 min, forming Co(OH)2 on the carbon cloth. After the electrodeposition was completed, the sample was rinsed with deionized water and ethanol, dried, and then calcined to obtain cobalt oxide (molecular formula Co3O4). The calcination was carried out in an air atmosphere at a temperature of 300 °C for 2 h.

[0061] The microstructure of the cobalt oxide prepared in Example 5 was tested using the same testing method as in Example 1, and the test results are as follows: Figure 1 As shown, from Figure 1 As can be seen in (e), the microstructure of the cobalt oxide prepared in Example 1 includes a large number of lamellar nanoparticles. The average particle size of the nanoparticles is 200 nm and the average sheet size is 20 nm.

[0062] S2. Preparation of Palladium-Cobalt-Oxide Composite Electrode Material: The carbon cloth and the cobalt oxide deposited on it were placed in an electrolyte containing palladium ions, and electrodeposition was performed using a three-electrode system constant voltage method. The carbon cloth and the cobalt oxide deposited on it served as the working electrode, the Ag / AgCl electrode served as the reference electrode, and the platinum sheet served as the counter electrode. The electrolyte was prepared by dissolving 0.0284 g of palladium chloride (PdCl2) in 40 mL of deionized water, with a palladium ion concentration of 4 mmol / L. The electrolyte was stirred for five minutes, and then 40 μL of KOH aqueous solution (concentration of 1 mol / L) was added. The stirring was continued for 15 minutes to adjust the pH value of the electrolyte to 11. Electrodeposition was then performed at a voltage of -1.01 V vs Ag / AgCl for 15 minutes. After the electrodeposition was completed, the material was rinsed with deionized water and ethanol, and then dried to obtain the Co3O4-Pd composite material.

[0063] The microstructure of the Co3O4-Pd composite material prepared in step S2 of Example 5 was tested using the same test method as in Example 1. The test results are as follows: Figure 2 As shown, from Figure 2 As can be seen from (e), the microstructure of the Co3O4-Pd composite material prepared in Example 1 includes a large number of lamellar nanoparticles. The average particle size of the nanoparticles is 210 nm and the average sheet size is 25 nm.

[0064] The elemental composition of the Co3O4-Pd composite material prepared in Example 5 was tested using the same method as in Example 1. The Pd content was found to be 6.33%, the Co content to be 43.05%, and the O content to be 50.62%.

[0065] Example 6 The difference between Example 6 and Example 4 is that in step S2, electrodeposition is performed at a voltage of -1.41V vs Ag / AgCl, while the remaining preparation steps are the same as in Example 4, and NCO-Pd composite electrocatalytic material is prepared.

[0066] The microstructure of the NCO-Pd prepared in step S2 of Example 6 was tested using the same testing method as in Example 1. The test results are as follows: Figure 2 As shown in (f), from Figure 2 Figure 2 As can be seen from (f), the microstructure of NCO-Pd consists of relatively tightly packed clusters, and the average particle size of the clusters is 400 nm.

[0067] The elemental composition of the NCO-Pd composite material prepared in Example 6 was tested using the same method as in Example 1. The Pd content was found to be 18.92%, the Ni content to be 13.44%, the Co content to be 30.06%, and the O content to be 37.58%.

[0068] Table 1. Test performance of composite materials for electrocatalytic nitrate reduction to ammonia production in Examples 1-6 As shown in Table 1, Examples 1-5 investigated the effect of the Ni / Co atomic ratio on the electrocatalytic reduction of nitrate to ammonia by the composite catalyst. In Example 1, the electrodeposition solution in step S1 contained only nickel ions, and the resulting nickel hydroxide, after calcination, formed nano-nickel oxide particles. The palladium deposited in step S2 adsorbed on the surface of the nickel oxide particles to form NiO-Pd remained as nanoparticles with relatively smooth surfaces. The smooth surface of NiO-Pd particles lacked strong adsorption sites for nitrate ions, and the Ni sites competed for space during the intermediate reaction, easily leading to hydrogen evolution reaction and resulting in low ammonia production rate and Faraday efficiency. In Examples 2 and 3, as the Ni in the electrodeposition solution in step S1 increased... The increase in the / Co atomic ratio leads to the formation of nickel-cobalt hydroxide, which, upon calcination, forms nano-nickel-cobalt oxygen particles. The Ni-Co alloying effect provides a large number of surface oxygen vacancies, which become active centers for adsorbing and activating nitrates. These vacancies interact strongly with palladium, forming a heterostructure and optimizing the electronic structure. The palladium nanoparticles can promote the efficient generation and supply of active hydrogen, providing sufficient active hydrogen for the hydrogenation step. After catalytic NO bond cleavage, they hydrogenate the intermediate, while simultaneously suppressing hydrogen evolution side reactions, improving NH3 selectivity, and increasing ammonia yield and Faraday efficiency. In Example 4, the atomic ratio of cobalt in the electrolyte was further increased in step S1, resulting in a tightly stacked, bent, sheet-like structure of nickel-cobalt oxide. The needle-like Pd particles deposited by electrodeposition in step S2 tended to agglomerate into clusters with multiple surface protrusions, significantly increasing the activation area of ​​Pd, increasing the supply of active hydrogen, and further suppressing side reactions. Simultaneously, the Pd clusters were uniformly dispersed at the NCO interface, and the exposed nickel-cobalt oxide in the dispersion gaps enhanced the adsorption and activation of nitrate ions. The synergistic effect of both further improved the ammonia yield and Faraday efficiency. In Example 5, the electrolyte in step S1 contained only Co ions, failing to form an alloying effect with Ni. Furthermore, the Pd electrodeposited in step S2 formed a sheet-like structure on the surface of the sheet-like nickel oxide particles, resulting in a much lower activation effect than in Example 4. Consequently, the ammonia yield and Faraday efficiency of Example 5 were significantly lower than those of Example 4.

[0069] Examples 4 and 6 investigated the effect of palladium deposition voltage on the catalyst’s nitrate reduction performance. In step S2, as the deposition voltage increased, the lamellar Pd deposited in step S2 agglomerated to form clusters. Compared to Example 4, the clusters in Example 6 grew larger and their dispersion at the NCO interface decreased, which reduced the synergy between Pd and NCO, resulting in a decrease in both ammonia yield and Faraday efficiency.

[0070] The above embodiments are only a part of the examples and are not listed one by one. They are not intended to limit the present invention. Researchers in the art can make further developments based on these embodiments, and all such developments should be within the protection scope of the present invention.

Claims

1. A method for preparing a palladium-nickel cobalt oxide composite material, characterized in that, The preparation steps include the following: S1. Preparation of nickel cobalt oxide: Carbon is arranged in an electrolyte containing nickel and cobalt ions, and electrodeposition is performed to form nickel cobalt hydroxide on the carbon cloth. The nickel cobalt hydroxide is then calcined to obtain nickel cobalt oxide. S2. Preparation of palladium-nickel cobalt oxide composite material: The nickel cobalt oxide is placed in an electrolyte containing palladium ions and electrodeposited to prepare the palladium-nickel cobalt oxide composite material.

2. The method for preparing the palladium-nickel cobalt oxide composite material according to claim 1, characterized in that, In step S1, electrodeposition is performed using a three-electrode constant voltage method, with carbon cloth as the working electrode, silver / silver chloride electrode as the reference electrode, and platinum sheet as the counter electrode. The electrodeposition voltage is -0.91 to -1.51 V vs. Ag / AgCl, and the electrodeposition time is 15 to 25 min.

3. The method for preparing the palladium-nickel cobalt oxide composite material according to claim 1, characterized in that, In step S1, the atomic ratio of nickel ions to cobalt ions in the electrolyte is (2.5~0.5):(0.5~2.5).

4. The method for preparing the palladium-nickel cobalt oxide composite material according to claim 3, characterized in that, In step S1, the atomic ratio of nickel ions to cobalt ions in the electrolyte is 1:(1.5~2.5).

5. The method for preparing the palladium-nickel cobalt oxide composite material according to claim 1, characterized in that, In step S1, the nickel-cobalt hydroxide is calcined at a temperature of 250–350°C for 0.5–4 hours.

6. The method for preparing the palladium-nickel cobalt oxide composite material according to claim 1, characterized in that, In step S1, the microstructure of the prepared nickel-cobalt oxide comprises closely packed, bent, sheet-like nanoparticles, the average particle size of which is 150 nm to 300 nm and the average sheet diameter is 10 to 30 nm; in step S2, the microstructure of the prepared palladium-nickel-cobalt oxide composite material comprises clustered nanoparticles, the average particle size of which is 310 nm to 420 nm.

7. The method for preparing the palladium-nickel cobalt oxide composite material according to claim 1, characterized in that, In step S2, the concentration of palladium ions in the electrolyte is 1-6 mmol / L. An alkaline solution is added to the electrolyte to adjust the pH value to 10-12. The electrodeposition voltage is -0.91 to -1.51 V vs Ag / AgCl, and the electrodeposition time is 10-25 min.

8. The method for preparing the palladium-nickel cobalt oxide composite material according to claim 1, characterized in that, In step S2, the prepared palladium-nickel cobalt oxide composite material has a Pd content of 8% to 19 at, a Ni content of 13% to 32 at, a Co content of 20 to 31 at, and the balance is O.

9. A palladium-nickel cobalt oxide composite material, obtained by the preparation method of the palladium-nickel cobalt oxide composite material according to any one of claims 1 to 8.

10. An application of the palladium-nickel cobalt oxide composite material of claim 9 in the electrocatalytic reduction of nitrate to ammonia, wherein the palladium-nickel cobalt oxide composite material is placed in an electrolyte containing nitrate to perform electrocatalytic reduction of nitrate to ammonia.

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