Copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst and preparation method and application thereof

Abstract

The invention discloses a copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst and a preparation method and application thereof.The preparation method includes the steps that lanthanum-based perovskite oxide LaCu (1-x) CoxO3 is prepared through a sol-gel method, and x is equal to 0.1-0.5; laCu1-xCoxO3 is placed in hydrogen and argon mixed gas for reduction treatment, and the copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst is obtained and used for preparing ammonia through electro-catalysis nitrate radical reduction. According to the preparation method, an in-situ dissolution strategy is adopted, a copper-cobalt alloy / lanthanum hydroxide strong interface coupled heterostructure is constructed, CuCo alloy nanoparticles provide high conductivity and rich active sites and form a heterostructure with La (OH) 3, the d-band center of the active sites is optimized through interaction of strong electrons, NO3 <-> adsorption and reaction intermediate stability are promoted, and the stability of the reaction intermediate is improved. The excellent electro-catalytic performance is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and particularly relates to a copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst, a preparation method thereof, and an application thereof in electrocatalytic reduction of nitrate ions. Background Art

[0002] Ammonia (NH3), as an important chemical raw material, has been widely used in the agricultural and industrial fields. At the same time, due to its high energy density (4.3 kWh kg -1 ) and hydrogen storage capacity (17.6 wt%), it is regarded as a promising next-generation carbon-free energy carrier. Currently, industrial ammonia synthesis mainly relies on the Haber-Bosch process, that is, N2 and H2 are converted into NH3 by an iron-based catalyst under high temperature and high pressure. However, this process has high energy consumption and is accompanied by a large amount of CO2 greenhouse gas emissions, which is contrary to the sustainable development goal. Therefore, the development of sustainable and efficient ammonia synthesis methods has attracted much attention.

[0003] In recent years, research has focused on using pollution-free electrons as reducing agents to electrochemically synthesize ammonia under mild conditions. This method has the advantages of high efficiency, simple operation, and zero carbon emissions, and is expected to replace the traditional Haber process. Among them, the electrocatalytic nitrate reduction reaction (NO3RR) has become an attractive ammonia synthesis route due to its low N=O bond dissociation energy (204 kJ mol -1 ) and high nitrate solubility. At the same time, the excessive accumulation of nitrates in agricultural and industrial wastewater has caused serious ecological and environmental problems, and even threatened public health. Therefore, the electrochemical conversion of nitrate into NH3 can not only achieve efficient ammonia synthesis but also simultaneously repair environmental pollution, with dual benefits. However, the NO3RR process involves a complex multi-electron / proton transfer path, and the active hydrogen (*H) generated by water dissociation is required to gradually deoxygenate / hydrogenate to generate NH3, and its reaction potential overlaps with the hydrogen evolution reaction (HER), resulting in competitive HER and significantly reducing the overall conversion efficiency. In addition, actual nitrate-containing wastewater is mostly neutral, and there is an urgent need to develop electrocatalysts that can efficiently and selectively catalyze the conversion of nitrate into NH3 under neutral pH conditions. Summary of the Invention

[0004] The present invention aims to address the shortcomings of the existing technology and provides a copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst, a preparation method thereof, and an application thereof in electrocatalytic reduction of nitrate ions. By adopting an in-situ dissolution strategy, a heterostructure with strong interfacial coupling of copper-cobalt alloy / lanthanum hydroxide is constructed, which can effectively regulate the electronic structure of catalytic active sites, optimize the adsorption strength of reaction intermediates during the electrocatalytic process, and has excellent electrocatalytic performance.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0006] A preparation method of a copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst, comprising the following steps:

[0007] (1) Prepare lanthanum-based perovskite oxide LaCu 1-x Co x O3, where x = 0.1 - 0.5;

[0008] (2) Place LaCu 1-x Co x O3 in a hydrogen-argon mixed gas for reduction treatment to obtain a copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst.

[0009] Preferably, in step (1), x = 0.3.

[0010] Preferably, in step (1), the specific process of the sol-gel method is as follows: dissolve soluble lanthanum salt, copper salt and cobalt salt in deionized water, stir until fully mixed to obtain a mixed solution; then add a complexing agent to the mixed solution, stir and evaporate the water until a gel is formed; dry the gel to form a dry gel; perform two-stage calcination on the dry gel to obtain LaCu 1-x Co x O3.

[0011] Preferably, the soluble lanthanum salt, copper salt and cobalt salt are selected from one or more of their respective nitrates, acetates, chlorides and their hydrates.

[0012] Preferably, the complexing agent is selected from one or more of citric acid, ethylene glycol, ethylenediaminetetraacetic acid, ascorbic acid, glucose and polyvinylpyrrolidone.

[0013] Preferably, the specific process of the two-stage calcination is as follows: first calcine at 400 - 600 °C for 4 - 6 h, then raise the temperature to 800 - 1000 °C and continue to calcine for 4 - 6 h.

[0014] Preferably, in step (2), the volume ratio of hydrogen to argon in the hydrogen-argon mixed gas is 1:9.

[0015] Preferably, in step (2), the temperature of the reduction treatment is 400 - 600 °C and the time is 2 - 5 h.

[0016] The present invention also provides a copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst prepared by the above preparation method.

[0017] The present invention also provides an application of the above copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst, which is used for electrocatalytic reduction of nitrate to ammonia.

[0018] The beneficial effects of the present invention:

[0019] The present invention adopts an in-situ dissolution strategy to construct a heterostructure with strong interfacial coupling of copper-cobalt alloy / lanthanum hydroxide, where CuCo alloy nanoparticles provide high conductivity and abundant active sites, and form a heterostructure with La(OH)3. The strong electronic interaction optimizes the d-band center of the active sites, promotes the adsorption of NO3 - and the stabilization of reaction intermediates, and has excellent electrocatalytic performance. For example, the ammonia production rate of R-LaCu 0.7 Co 0.3 O3 after 1 hour of testing by chronoamperometry at a constant potential of -0.8 V under neutral conditions is 8.55 mg h -1 mgcat -1 , corresponding to a Faraday efficiency of 78.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD patterns of the catalyst before and after pyrolytic reduction in Comparative Example 1.

[0021] Figure 2 XRD pattern of the catalyst R-LaCoO3 prepared in Comparative Example 2.

[0022] Figure 3 XRD patterns of the catalyst before and after pyrolytic reduction when x = 0.3 in Example 1.

[0023] Figure 4 TEM image of the catalyst R-LaCu 0.7 Co 0.3 O3 prepared in Example 1.

[0024] Figure 5 LSV curves of the catalyst R-LaCu 0.7 Co 0.3 O3 in 0.5 M K2SO4 electrolyte with / without 0.1 M KNO3.

[0025] Figure 6 Ammonia production rate and Faraday efficiency graphs of the catalyst before and after pyrolytic reduction when x = 0.3 in Example 1 after 1 hour of testing by chronoamperometry at a constant potential of -0.8 V under neutral conditions.

[0026] Figure 7 Ammonia production rate and Faraday efficiency graphs of the catalysts prepared in Example 1 and Comparative Examples 1-2 after 1 hour of testing by chronoamperometry at a constant potential of -0.8 V under neutral conditions. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention and its beneficial technical effects will be described in detail below in conjunction with the drawings and specific embodiments. However, the specific embodiments of the present invention are not limited thereto.

[0028] All electrochemical tests were performed on a Bio-Logic VSP electrochemical workstation. In an H-type electrolytic cell, a three-electrode system was used to test the electrocatalytic performance of the material for nitrate reduction to ammonia. The reference electrode was a saturated calomel electrode (Hg / Hg2Cl2), the counter electrode was a graphite carbon rod, and the working electrode was a carbon paper coated with the catalyst, with a catalyst loading of 0.8 mg cm -2 . The H-type electrolytic cell used a DuPont Nafion 1117 proton exchange membrane to physically separate the cathode chamber and the anode chamber. Among them, the cathode electrolyte was a 0.5 M K2SO4 solution containing 0.1 M KNO3, and the anode electrolyte was a 0.5 M K2SO4 solution. Ammonia (NH4 + ) and nitrite (NO2 - ) were quantitatively analyzed by chronoamperometry. After the reaction at a constant potential, the absorbance of the electrolyte after the reaction was measured by ultraviolet-visible absorption spectroscopy after adding a color reagent.

[0029] Comparative Example 1

[0030] 10 mmol of lanthanum nitrate and 5 mmol of copper nitrate were dissolved in 80 mL of deionized water, and stirred thoroughly to completely dissolve to obtain a transparent and clear solution. 22.5 mmol of citric acid was added to the solution, and 1.7 ml of ethylene glycol was added dropwise. Then, the excess water was evaporated in a water bath at 80 °C until a transparent gel was formed. The obtained gel was dried in an electrothermal blast drying oven at 180 °C for 5 hours to form a fluffy dry gel. The obtained dry gel was thoroughly ground and then placed in a tubular furnace and pre-calcined in an air atmosphere at 400 °C for 4 hours to remove the organic matter in the precursor, and then the temperature was continuously raised to 950 °C and calcined for 5 hours to obtain a copper-based perovskite oxide with the chemical formula La2CuO4. The obtained perovskite oxide was thoroughly ground and then subjected to a high-temperature treatment at 500 °C for 5 hours in a hydrogen-argon mixed gas to obtain a Cu / La(OH)3 electrocatalyst.

[0031] As Figure 1 shown, the structure of the catalyst before hydrogen reduction in the spectrum was the layered perovskite La2CuO4, which was consistent with the standard PDF card. After reduction, for the catalyst R-La2CuO4, the collapse of its perovskite structure was observed, and the main structure was transformed into La(OH)3. At the same time, the presence of a Cu diffraction peak was also found, indicating that the Cu-loaded La(OH)3 electrocatalyst was successfully synthesized.

[0032] As Figure 7 shown, the ammonia production rate of R-La2CuO4 (representing the product after reduction treatment of La2CuO4 in a hydrogen-argon mixed gas) was 3.0 mg h -1 mg cat -1, corresponding to a Faraday efficiency of 53.4%.

[0033] Comparative Example 2

[0034] Dissolve 5 mmol of lanthanum nitrate and 5 mmol of cobalt nitrate in 60 mL of deionized water, stir well to completely dissolve to obtain a transparent and clear solution, add 15 mmol of citric acid to the solution, dropwise add 1.7 ml of ethylene glycol, and then evaporate the excess water in a water bath at 80 °C until a transparent gel is formed. Dry the obtained gel in an electrothermal blast drying oven at 180 °C for 5 hours to form a fluffy dry gel. After thoroughly grinding the obtained dry gel, place it in a tubular furnace and pre-calcine it at 500 °C for 4 hours in an air atmosphere to remove the organic matter in the precursor, and then continue to heat up to 950 °C and calcine for 5 hours to obtain a cobalt-based perovskite oxide with the chemical formula LaCoO3. After thoroughly grinding the obtained perovskite oxide, perform a high-temperature treatment at 500 °C for 5 hours in a hydrogen-argon mixed gas to obtain a Co / LaCoO3 electrocatalyst.

[0035] As Figure 2 shown, the presence of diffraction peaks of metallic Co and LaCoO3 was observed, indicating that the synthesized electrocatalyst is Co / LaCoO3, and metallic Co is loaded on the surface of LaCoO3.

[0036] As Figure 7 shown, the ammonia production rate of R-LaCoO3 (representing the product after reduction treatment of LaCoO3 in a hydrogen-argon mixed gas) is 4.0 mg h -1 mg cat -1 , corresponding to a Faraday efficiency of 79.1%.

[0037] Example 1

[0038] Dissolve 5 mmol of lanthanum nitrate, a total of 5 mmol of copper nitrate and cobalt nitrate, where the molar ratios of copper nitrate to cobalt nitrate are 9:1, 7:3, and 5:5 respectively, in 60 mL of deionized water, stir well to completely dissolve to obtain a transparent and clear solution, add 15 mmol of citric acid to the solution, dropwise add 1.7 ml of ethylene glycol, and then evaporate the excess water in a water bath at 80 °C until a transparent gel is formed. Dry the obtained gel in an electrothermal blast drying oven at 180 °C for 5 hours to form a fluffy dry gel. After thoroughly grinding the obtained dry gel, place it in a tubular furnace and pre-calcine it at 400 °C for 4 hours in an air atmosphere to remove the organic matter in the precursor, and then continue to heat up to 950 °C and calcine for 5 hours to obtain a doped perovskite oxide with the chemical formula LaCu 1-x Co xO3, with x = 0.1, 0.3, and 0.5. The obtained perovskite oxide was thoroughly ground and then heat-treated at 500 °C for 5 hours in a hydrogen-argon mixed gas to obtain the CuCo alloy / La(OH)3 electrocatalyst.

[0039] As Figure 3 shown, the phases of the catalyst before the pyrolysis of LaCu 0.7 Co 0.3 O3 were the coexistence of two perovskites, La2CuO4 and LaCoO3. After reduction, the main phase was La(OH)3, and there were characteristic peaks of the CuCo alloy, indicating that the reduced catalyst formed a CuCo alloy / La(OH)3 heterostructure.

[0040] As Figure 4 shown, in the high-resolution TEM image of LaCu 0.7 Co 0.3 O3, lattice fringes corresponding to La(OH)3 and the CuCo alloy could be clearly observed, indicating that LaCu 1-x Co x O3 perovskite oxide transformed into a CuCo alloy / La(OH)3 heterostructure after hydrogen reduction.

[0041] As Figure 5 shown, compared with the LSV tested in the electrolyte without NO3 - , in the electrolyte added with NO3 - , its current density increased significantly, indicating that R-LaCu 0.7 Co 0.3 O3 has good electrochemical nitrate reduction performance.

[0042] As Figure 6 shown, the Faraday efficiency changed little before and after pyrolysis reduction. It was 78.8% for R-LaCu 0.7 Co 0.3 O3 and 78.6% for LaCu 0.7 Co<{ 0.3 O3; however, the ammonia production rate of the reduced R-LaCu 0.7 Co 0.3 O3 (8.55 mg h -1 mg cat -1 ) was 2.4 times that of the pre-reduced LaCu 0.7 Co 0.3 O3 (3.61 mg h -1 mg cat -1 ).

[0043] As Figure 7 shown, R-LaCu 0.5Co 0.5 O3 (represents the product after reduction treatment of LaCu 0.5 Co 0.5 O3 in a hydrogen-argon mixture) has an ammonia production rate of 5.28 mg h -1 mg cat -1 , corresponding to a Faraday efficiency of 74.6%; R-LaCu 0.7 Co 0.3 O3 (represents the product after reduction treatment of LaCu 0.7 Co 0.3 O3 in a hydrogen-argon mixture) has an ammonia production rate of 8.55 mg h -1 mg cat -1 , corresponding to a Faraday efficiency of 78.8%; R-LaCu 0.9 Co 0.1 O3 (represents the product after reduction treatment of LaCu 0.9 Co 0.1 O3 in a hydrogen-argon mixture) has an ammonia production rate of 5.53 mg h -1 mg cat -1 , corresponding to a Faraday efficiency of 69.8%.

Claims

1. A preparation method of a copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst, characterized in that, It includes the following steps: (1) The lanthanum-based perovskite oxide LaCu 1-x Co x O3 was prepared by the sol-gel method, where x = 0.1 - 0.5; (2) Reduce LaCu 1-x Co x O3 in a hydrogen-argon mixture to obtain a copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), x = 0.

3.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the specific process of the sol-gel method is as follows: Dissolve soluble lanthanum salt, copper salt and cobalt salt in deionized water, stir until fully mixed to obtain a mixed solution; then add a complexing agent to the mixed solution, stir and evaporate the water until a gel is formed; dry the gel to form a xerogel; perform two-stage calcination on the xerogel to obtain LaCu 1-x Co x O3.

4. The preparation method according to claim 3, wherein The soluble lanthanum salt, copper salt and cobalt salt are selected from one or more of their respective nitrates, acetates, chlorides and their hydrates.

5. The preparation method according to claim 3, wherein, The complexing agent is selected from one or more of citric acid, ethylene glycol, ethylenediaminetetraacetic acid, ascorbic acid, glucose and polyvinylpyrrolidone.

6. The preparation method according to claim 3, characterized in that, The specific process of the two-stage calcination is as follows: first calcine at 400-600 °C for 4-6 h, then raise the temperature to 800-1000 °C and continue to calcine for 4-6 h.

7. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the reduction treatment is 300-600 °C and the time is 2-5 h.

8. The preparation method according to claim 1, characterized in that, In step (2), the volume ratio of hydrogen to argon in the hydrogen-argon mixed gas is 1:

9.

9. A copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst prepared by the preparation method according to any one of claims 1-8.

10. Use of the copper-cobalt alloy / lanthanum hydroxide heterojunction catalyst according to claim 9, characterized in that, It is used for electrocatalytic reduction of nitrate to ammonia.

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