Application of cobalt-nickel-based composite material with nanocone array structure in electro-catalysis nitrate reduction

Abstract

The invention discloses an application of a cobalt-nickel-based composite material with a nanocone array structure in electro-catalysis nitrate reduction. The cobalt-nickel-based composite material comprises a foamed nickel substrate and a nickel-cobalt nanocone array loaded on the foamed nickel substrate, and the nickel-cobalt nanocone array grows on the foamed nickel substrate in situ. When the cobalt-nickel-based composite material with the nanocone array structure is applied to electro-catalysis nitrate reduction, the bimetallic catalyst with the nanocone array structure can accelerate optimization of the nitrate reduction process, strengthen adsorption and reduction of nitrate, improve the selectivity of ammonia production through reaction reduction, inhibit hydrogen evolution side reaction and improve the hydrogen evolution efficiency. Meanwhile, after multiple cycles, the morphology of the catalyst material is not changed, and the catalyst material still has good catalytic activity, so that the catalyst material has long-term use stability.

Description

Technical Field

[0001] The invention relates to application of a cobalt-nickel based composite material with a nano-cone array structure in electrocatalytic nitrate reduction, belonging to the technical field of electrochemistry. Background Art

[0002] Electrochemical nitrate reduction (NITRR) technology has the advantages of being environmentally friendly, flexible in operation, and low in processing cost. Converting nitrate into ammonia (NH3) not only reduces the processing difficulty but also realizes the recycling of nitrogen resources. The process of electrocatalytic nitrate reduction to ammonia involves a multi-electron transfer process of 9 protons and 8 electrons. First, nitrate (NO3 - ) chemically adsorbs on the catalyst surface to form surface-adsorbed nitrate, which then enters the catalyst interface electron transfer channel. Subsequently, NO3 - After a two-step single-electron reduction process, the nitrite intermediate *NO2 is generated - After that, it is further reduced to *NO. The subsequent conversion path of *NO directly determines whether the final product is NH3 or N2. In the electron-dominated pathway, *NO is gradually converted into *NOH, *NHOH and *NH2OH through the continuous proton-coupled electron transfer (PCET) mechanism; while in the hydrogen adsorption pathway, *NO is further reduced to *N, and then gradually combines with surface active hydrogen *H to form *NH and *NH2. Finally, *NH2OH combines with electrons or *NH2 combines with H to generate NH3 and complete desorption. The key to improving the efficiency of nitrate reduction to ammonia (NRA) is to simultaneously reduce the reaction energy barrier and balance the dynamic distribution of active hydrogen (*H): an appropriate amount of *H drives the breaking of NO bonds and the formation of NH bonds, while an excess triggers the hydrogen evolution side reaction (HER). By constructing *H transport and NO x The spatial isolation of adsorption enables directional synergy between the intermediate and *H, breaking through the bottleneck of Faraday efficiency.

[0003] Although precious metal-based materials (such as Pt and Ru) have high catalytic activity, their scarcity and high cost restrict their large-scale application; transition metal catalysts (such as Fe and Ni) are limited by low active site density and insufficient electron transfer efficiency, resulting in low ammonia selectivity and decreased electron utilization caused by competition for the hydrogen evolution side reaction (HER). In recent years, nickel-cobalt bimetallic materials have attracted much attention due to their unique electronic synergistic effect: the high conductivity of nickel combined with the multivalent state characteristics of cobalt can form an active interface with adjustable d-band center, which can theoretically simultaneously optimize nitrate adsorption and hydrogenation kinetics. Common structures of existing nickel-cobalt-based catalysts include hollow sphere structures, two-dimensional layered structures, flower-ball-shaped assembly structures, core-shell structures, etc.; nickel-cobalt-based catalysts with the above structures have problems such as easy structural changes and insufficient adsorption capacity of reaction intermediates during the electrochemical nitrate reduction process, which can lead to low catalytic activity and catalytic stability of the catalyst. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a cobalt-nickel-based composite material with a nanocone array structure for use in electrocatalytic nitrate reduction. When the cobalt-nickel-based composite material with this structure is selected as a catalyst for electrocatalytic nitrate reduction, the catalyst material can effectively reduce the reaction activation energy barrier, and simultaneously enhance the selectivity of the ammonia synthesis pathway (the catalyst can increase the proton hydrogen production capacity, thereby providing more proton hydrogen / active hydrogen for nitrate reduction hydrogenation) and the electron transfer efficiency, thereby greatly improving the Faraday efficiency and ammonia production rate. At the same time, the catalyst material also has good cycle stability and still has good catalytic activity after multiple cycles of use.

[0005] Technical solution: Application of the cobalt-nickel based composite material with a nanocone array structure in the present invention in electrocatalytic nitrate reduction.

[0006] The cobalt-nickel based composite material comprises a nickel foam substrate and a nickel-cobalt nanocone array loaded on the nickel foam substrate, and the nickel-cobalt nanocone array is in-situ grown on the nickel foam substrate.

[0007] The cobalt-nickel based composite material is prepared by the following method, which specifically comprises the following steps:

[0008] (1) preparing an electrodeposition solution: dispersing nickel salt, cobalt salt, boric acid and ammonium chloride in deionized water to obtain an electrodeposition solution;

[0009] (2) The pH of the electrodeposition solution is adjusted to weak acidity; a two-electrode system is used, with nickel foam as the working electrode and Pt as the counter electrode, which are placed in the electrodeposition solution to start the electrodeposition reaction. After the reaction, a nickel-cobalt-based composite material with a nanocone array structure is obtained.

[0010] In step (1), the nickel salt is nickel chloride hexahydrate and the cobalt salt is cobalt chloride hexahydrate.

[0011] In step (1), in the electrodeposition solution, the total molar concentration of the cobalt salt and the nickel salt is 0.8-0.9 mol / L, the concentration of H3BO3 is 0.65-0.7 mol / L, and the concentration of NH4Cl is 1.8-1.9 mol / L.

[0012] The molar ratio of the added cobalt salt to the nickel salt is 1:4-5.

[0013] In step (2), before electrodeposition, the pH of the electrodeposition solution is adjusted to 4 to 4.5.

[0014] In step (2), during the electrodeposition process, the current density is 30-40 mA / cm 2 The deposition time is 10 to 20 minutes, and the deposition temperature is 60 to 70°C.

[0015] The specific application process is as follows: in a three-electrode system with good airtightness, a cobalt-nickel based composite material with a nanocone array structure is used as the working electrode, and the reference electrode is Hg / HgO. The working electrode and the reference electrode are placed in the cathode electrolyte, which is a mixed solution of 1 mol / L KOH and 0.1 mol / L KNO3; the counter electrode is a Pt sheet, which is placed in the anode electrolyte, which is a mixed solution of 1 mol / L KOH and 0.1 mol / L KNO3; the voltage of the reaction process is -0.2 to -0.7 V, and the reaction time is 1 hour.

[0016] The catalyst structure of the present invention can realize the construction of *H transport and NO x Spatial isolation of adsorption: The tip curvature of the nanocone array is very small, and a strong local electric field is generated through the tip enhancement effect. This electric field drives the cations in the electrolyte to be enriched at the cone tip, forming a cationic microenvironment specifically for promoting water dissociation to generate *H, while the side walls or base of the cone are reserved for NOx adsorption, achieving spatial isolation.

[0017] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: when the cobalt-nickel-based composite material with a nanocone array structure is used in the electrocatalytic nitrate reduction, the bimetallic catalyst with a nanocone array structure can accelerate and optimize the nitrate reduction process, strengthen the adsorption and reduction of nitrate, and improve the selectivity of the reduction reaction to produce ammonia (relying on the tip effect to enhance the local electric field to promote the enrichment of cations in the electrolyte to the cone tip, significantly promote the polarization of interfacial water molecules and water dissociation, and efficiently generate *H); at the same time, the nickel-cobalt bimetallic sites on the side walls of the cone enhance the adsorption and activation of nitrate through the electronic synergistic effect. This spatial partitioning structure of cone tip enrichment and sidewall adsorption can achieve physical isolation of H transmission and reactant adsorption, and directionally promote H to adsorbed NO x Continuous hydrogenation of the intermediates overcomes the bottleneck of nitrite desorption and improves the selectivity of the reduction reaction to ammonia production. Meanwhile, the hydrogen evolution side reaction is suppressed, significantly increasing the ammonia yield and Faradaic efficiency. Furthermore, after multiple cycles, the catalyst material's morphology remains unchanged and maintains good catalytic activity, thus ensuring long-term stability. Therefore, when the cobalt-nickel-based composite material with a nanocone array structure is used in electrocatalytic nitrate reduction, the bimetallic catalyst with the nanocone array structure exhibits high activity, high selectivity, and high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope image of the cobalt-nickel based composite material prepared in Example 1;

[0019] Figure 2 This is a scanning electron microscope image of the cobalt-nickel based composite material prepared in Comparative Example 1;

[0020] Figure 3 Graph showing the Faraday efficiency and ammonia yield of the cobalt-nickel based composite material prepared in Example 1 at different cycle numbers;

[0021] Figure 4 1 is a comparison chart of the Faradaic efficiency and ammonia yield of the cobalt-nickel based composite materials prepared in Example 1 and Comparative Example 1 at different test voltages;

[0022] Figure 5 The present invention in situ grows a cobalt-nickel bimetallic nanocone array structure on nickel foam and an SEM image of the catalyst material after the catalyst has undergone 10 cycles. DETAILED DESCRIPTION

[0023] Example 1

[0024] The method for preparing the cobalt-nickel based composite material of the present invention comprises the following steps:

[0025] (1) Cut the nickel foam with a thickness of 1.0 mm into 1×5 cm 2 The surface nickel oxide passivation layer (NiO x ), and then drying the nickel foam under a nitrogen atmosphere;

[0026] (2) 16.8 mmol of nickel chloride hexahydrate (NiCl2·6H2O), 67.2 mmol of cobalt chloride hexahydrate (CoCl2·6H2O), 65 mmol of boric acid (H3BO3) and 186 mmol of ammonium chloride (NH4Cl) were dispersed in 100 mL of deionized water and ultrasonicated for 10 minutes to obtain a uniformly mixed electrochemical deposition electrolyte;

[0027] (3) Before deposition, the pH value of the electrochemical deposition electrolyte was adjusted to 4 using 10 wt % sodium hydroxide and 10 wt % hydrochloric acid, and the electrochemical deposition solution was placed in a constant temperature oil bath at 60° C.;

[0028] (4) A two-electrode system was used, and the nickel foam pretreated in step (1) was used as the working electrode and Pt was used as the counter electrode. The nickel foam was placed in an electrochemical deposition electrolyte at a current density of 30 mA / cm 2 Electrochemical deposition was carried out under conditions of 20 min and 60 °C to obtain a nickel-cobalt based composite material with a nanocone array structure, which was labeled Co-Ni NCA / NF.

[0029] The scanning electron microscope image of the cobalt-nickel based composite material prepared in Example 1 is as follows: Figure 1 As shown, through Figure 1 It can be seen that the nickel-cobalt based composite material prepared in the present invention has a nano-cone array structure.

[0030] Comparative Example 1

[0031] A method for preparing a cobalt-nickel based composite material comprises the following steps:

[0032] (1) Cut the nickel foam with a thickness of 1.0 mm into 1×5 cm 2 The surface nickel oxide passivation layer (NiO x ), and then drying the nickel foam under a nitrogen atmosphere;

[0033] (2) 16.8 mmol of nickel nitrate hexahydrate, 67.2 mmol of cobalt nitrate hexahydrate, 65 mmol of boric acid (H3BO3) and 186 mmol of ammonium chloride (NH4Cl) were dispersed in 100 mL of deionized water and ultrasonicated for 10 minutes to obtain a uniformly mixed electrochemical deposition electrolyte;

[0034] (3) Before deposition, the pH value of the electrochemical deposition electrolyte was adjusted to 4 using 10 wt % sodium hydroxide and 10 wt % hydrochloric acid, and the electrochemical deposition solution was placed in a constant temperature oil bath at 60° C.;

[0035] (4) A two-electrode system was used, and the nickel foam pretreated in step (1) was used as the working electrode and Pt was used as the counter electrode. The nickel foam was placed in an electrochemical deposition electrolyte at a current density of 30 mA / cm 2 Electrochemical deposition was carried out under the conditions of 20 min and 60 °C to obtain a nickel-cobalt based composite material, which was labeled Co-Ni / NF.

[0036] The scanning electron microscope image of the cobalt-nickel based composite material prepared in Comparative Example 1 is as follows: Figure 2 As shown, through Figure 2 It can be seen that the nickel-cobalt based composite material prepared in Comparative Example 1 has a nano-flower-like structure.

[0037] The nickel-cobalt-based composite materials of Example 1 and Comparative Example 1 were used as catalysts in the electrocatalytic reduction of nitrate. The specific application process was as follows: in a three-electrode system with good airtightness, the cobalt-nickel-based composite material was used as the working electrode, the reference electrode was Hg / HgO (saturated KCl electrolyte), the working electrode and the reference electrode were placed in a cathode electrolyte, and the cathode electrolyte was a mixed solution of 1 mol / L KOH and 0.1 mol / L KNO3; the counter electrode was a Pt sheet (1 cm×1 cm), which was placed in an anolyte, and the anolyte was a mixed solution of 1 mol / L KOH and 0.1 mol / L KNO3. The Faraday efficiency and ammonia yield corresponding to the two catalyst materials were measured at different voltages. The results are shown in Tables 1 and Figure 4 shown.

[0038] The yields of possible products and Faradaic efficiency (FE) after electrolysis were calculated by UV-visible spectroscopy. The concentrations of nitrite and NH3 in the diluted catholyte after electrolysis were determined by Grylls method and phenol blue method, respectively.

[0039] Depend on Figure 4 It can be seen that the ammonia yield of the catalyst of Example 1 is much greater than that of the catalyst of Comparative Example 1. At the same time, as the voltage shifts negatively, the ammonia yield of the nickel-cobalt based composite material with nanocone array morphology continues to increase, and at -0.7 V vs. RHE, the yield reaches 76.679 mg / h / cm 2 ; and the Faraday efficiency of nickel-cobalt based composite materials with nanocone array morphology remains above 90%.

[0040] The average values ​​of ammonia yield, ammonia Faraday efficiency and ammonia partial current density corresponding to the catalysts of Example 1 and Comparative Example 1 during the experiment are shown in Table 1:

[0041] Table 1

[0042]

[0043]

[0044] The nickel-cobalt-based composite material of Example 1 is used as a catalyst in the electrocatalytic reduction of nitrate. The specific application process is as follows: in a three-electrode system with good airtightness, the cobalt-nickel-based composite material is used as the working electrode, the reference electrode is Hg / HgO (saturated KCl electrolyte), the working electrode and the reference electrode are placed in the cathode electrolyte, the cathode electrolyte is a mixed solution of 1mol / LKOH and 0.1mol / LKNO3; the counter electrode is a Pt sheet (1cm×1cm), which is placed in the anode electrolyte, the anode electrolyte is a mixed solution of 1mol / L KOH and 0.1mol / L KNO3, the reaction process voltage is -0.5v, and the reaction time is 1h. Multiple cycles are carried out under the above reaction conditions, and the Faraday efficiency and ammonia yield results measured under different cycle numbers are shown as follows: Figure 3 As shown by Figure 3 It can be seen that the nickel-cobalt based composite material of Example 1 maintains a Faraday efficiency of more than 90% after 10 cycles, and the ammonia production rate is 50 mg / h / cm 2 above.

Claims

1. Application of a cobalt-nickel based composite material with a nanocone array structure in electrocatalytic nitrate reduction.

2. The use according to claim 1, characterized in that: The cobalt-nickel based composite material comprises a foam nickel substrate and a nickel-cobalt nanocone array supported on the foam nickel substrate. The nickel-cobalt nanocone array is in-situ grown on the foam nickel substrate.

3. The use according to claim 1, characterized in that: The cobalt-nickel based composite material is prepared by the following method, which specifically comprises the following steps: (1) preparing an electrodeposition solution: dispersing nickel salt, cobalt salt, boric acid and ammonium chloride in deionized water to obtain an electrodeposition solution; (2) The pH of the electrodeposition solution is adjusted to weak acidity; a two-electrode system is used, nickel foam is used as the working electrode, and Pt is used as the counter electrode, which are placed in the electrodeposition solution to start the electrodeposition reaction. After the reaction, a nickel-cobalt-based composite material with a nanocone array structure is obtained.

4. The use according to claim 3, characterized in that: In step (1), the nickel salt is nickel chloride hexahydrate and the cobalt salt is cobalt chloride hexahydrate.

5. The use according to claim 3, characterized in that: In step (1), in the electrodeposition solution, the total molar concentration of the cobalt salt and the nickel salt is 0.8-0.9 mol / L; the concentration of H3BO3 is 0.65-0.7 mol / L; and the concentration of NH4Cl is 1.8-1.9 mol / L.

6. The use according to claim 5, characterized in that: The molar ratio of the cobalt salt to the nickel salt is 1:4-5.

7. The use according to claim 3, characterized in that: In step (2), before electrodeposition, the pH of the electrodeposition solution is adjusted to 4 to 4.

5.

8. The use according to claim 3, characterized in that: In step (2), during the electrodeposition process, the current density is 30-40 mA / cm 2 The deposition time is 10 to 20 minutes, and the deposition temperature is 60 to 70°C.

9. The use according to claim 3, characterized in that: In step (2), the nickel foam is pretreated nickel foam, and the pretreatment process is: washing the nickel foam with hydrochloric acid, acetone and ethanol in sequence to remove nickel oxide on its surface.

10. The use according to claim 1, characterized in that: The specific application process is as follows: in a three-electrode system, a cobalt-nickel-based composite material with a nanocone array structure is used as the working electrode, and the reference electrode is Hg / HgO. The working electrode and the reference electrode are placed in the cathode electrolyte, which is a solution containing nitrate; the counter electrode is a Pt sheet, which is placed in the anode electrolyte, which is a solution containing nitrate; the voltage of the reaction process is -0.2 to -0.7V, and the reaction time is not less than 1h.

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