Cu-OCTA-coated NF catalyst and preparation method and application thereof

Abstract

The invention provides a Cu-OCTA-coated NF catalyst as well as a preparation method and application thereof, belongs to the technical field of electro-catalysis and clean energy, and is used for solving the technical problems of poor structural controllability, insufficient stability and limited catalytic activity of a copper-based catalyst in a urea oxidation reaction. The preparation method of the Cu-OCTA-coated NF catalyst comprises the following steps: (1) soaking foamed nickel in an acid solution, and then taking out and drying for later use; (2) dissolving copper salt to prepare a precursor solution; and (3) dipping the foamed nickel obtained in the step (1) into a precursor solution, and carrying out replacement reaction. The method is easy and convenient to operate and mild in condition, the obtained material has high dispersity and an exposed high-activity crystal face, meanwhile, strong interface coupling is formed between metal Cu and substrate nickel, and the charge transfer rate and the reaction stability are remarkably improved. When being used for urea oxidation reaction, the composite material shows excellent electro-catalytic performance, has a good application prospect, and is suitable for the fields of green hydrogen energy preparation, urine-containing wastewater treatment and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysis and clean energy, and particularly relates to an electrocatalyst for urea oxidation reaction. BACKGROUND

[0002] With the increasing depletion of fossil energy and the increasingly serious environmental pollution problems, developing clean, efficient and renewable energy conversion and utilization technology has become a research hotspot in the field of energy and environment. Among various energy conversion pathways, urea oxidation reaction (UOR) has attracted widespread attention due to its important application prospects in direct urea fuel cells, electrochemical water splitting and urea-containing wastewater treatment. Compared with the traditional oxygen evolution reaction (OER), UOR has a lower thermodynamic potential of 0.37 V (vs. RHE), which significantly reduces the energy consumption of the overall reaction system, theoretically saving about 70% of energy, and is an important way to realize low-energy electrochemical energy conversion. However, urea oxidation reaction involves multi-step electron transfer and complex intermediate adsorption / desorption processes, which is slow in kinetics and seriously restricts its development in practical applications. Therefore, developing efficient, stable and low-cost UOR electrocatalysts has become a key problem in this field.

[0003] At present, although noble metal (such as Pt, Ru, etc.) catalysts exhibit excellent catalytic performance in UOR, their high cost and resource scarcity limit their large-scale application. In recent years, researchers have gradually shifted their focus to transition metal-based catalytic materials, especially nickel-based systems, which exhibit good activity and stability in UOR. However, compared with copper, which is abundant in resources, low in price and has excellent electrocatalytic potential, developing copper-based electrocatalysts for UOR has important theoretical significance and application value.

[0004] Previous studies have shown that copper can exhibit good urea oxidation catalytic activity under alkaline conditions, especially when it is constructed into a nanostructure, which can significantly increase the specific surface area, expose more active sites, and regulate its electronic structure, thereby further improving its electrocatalytic performance. Through strategies such as morphology control, crystal face selection, oxidation state adjustment and construction of multi-level structure, the activity and stability of copper-based catalysts in the UOR process have been improved to some extent. However, the existing preparation methods of copper-based nanostructure catalysts in the prior art generally have the problems of complex process, poor controllability, difficulty in structure control, insufficient catalytic efficiency, etc., which are difficult to meet the practical application requirements of high-performance UOR catalysts. SUMMARY

[0005] In view of the technical problems of poor controllability of copper-based catalyst structure, insufficient stability and limited catalytic activity in urea oxidation reaction, the application provides a Cu-OCTA@NF catalyst and a preparation method and application thereof, a copper-based electrocatalytic system is constructed to utilize the reversible valence state conversion characteristics (Cu 0 / Cu + / Cu 2+ ) of the copper-based electrocatalytic system, so as to accelerate electron transfer, reduce reaction energy barrier and enhance the tolerance to intermediate products, thereby improving the stability and service life of the catalyst. The prepared Cu-OCTA@NF catalyst exhibits excellent electrocatalytic performance when used in urea oxidation reaction under alkaline conditions.

[0006] In order to achieve the above-mentioned purposes, the technical scheme of the application is as follows:

[0007] A preparation method of a Cu-OCTA@NF catalyst, comprising the following steps:

[0008] (1) soaking the foamed nickel in an acidic solution, and then taking it out for drying;

[0009] (2) dissolving and configuring a precursor solution of copper salt;

[0010] (3) impregnating the foamed nickel obtained in step (1) into the precursor solution to perform displacement reaction, to obtain the Cu-OCTA@NF catalyst.

[0011] The acidic solution is any one or two or more of hydrochloric acid, sulfuric acid, citric acid or oxalic acid.

[0012] The concentration of the acidic solution is 1-6 mol / L.

[0013] The soaking treatment time is 10-30 min, and the temperature is room temperature.

[0014] The drying time is 3-6 h, and the temperature is 25-60 DEG C.

[0015] The copper salt is at least one or two or more of copper chloride, copper sulfate and copper nitrate.

[0016] The concentration of the copper salt in the precursor solution is 0.01-0.04 mol / L.

[0017] The displacement reaction temperature is 60-100 DEG C, and the time is 1-6 h.

[0018] The application has the following beneficial effects:

[0019] 1. The preparation of Cu-OCTA@NF and its application as an electrocatalyst for urea oxidation reaction, using three-dimensional porous nickel foam as a substrate, by soaking in the precursor solution and further combining with a chemical displacement method, a highly dispersed Cu octahedral structure is prepared in situ on the surface of three-dimensional porous nanostructured nickel foam (NF), which has excellent dispersity, regular octahedral crystal form, can effectively avoid agglomeration, and is beneficial to exposing more high-activity crystal faces; the nickel foam itself serves as a three-dimensional conductive skeleton, further improving the overall conductivity.

[0020] 2. The preparation of Cu-OCTA@NF and its application as an electrocatalyst for urea oxidation reaction, by forming a strong interface coupling effect between copper and nickel foam, the rapid transfer ability of electrons is enhanced, thereby improving the catalytic activity of the catalyst, and the catalyst exhibits excellent UOR activity when performing urea electrolysis reaction under industrial current density conditions, wherein Cu-OCTA@NF only requires an overpotential of 1.40 V at a current density of 10 mA·cm -2 , which is significantly better than commercial IrO2 catalyst, showing its application potential in efficient urea electrolysis.

[0021] 3. The preparation of Cu-OCTA@NF and its application as an electrocatalyst for urea oxidation reaction, the synthesis method of the catalyst is simple, the raw materials are easy to obtain, the cost is low, and the process conditions are mild, without the use of expensive reagents or complex equipment, with good operability and repeatability, easy to scale up. The catalyst can be widely used in urea-assisted water electrolysis for hydrogen production, urea-containing industrial wastewater treatment, and energy recovery, and has good industrial application potential and promotion value. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0023] Figure 1 SEM image of Cu-OCTA@NF catalyst prepared in Example 1.

[0024] Figure 2 SEM image of Cu-NS@NF-1 catalyst prepared in Comparative Example 1.

[0025] Figure 3 SEM image of Cu-NS@NF-2 catalyst prepared in Comparative Example 2.

[0026] Figure 4 XRD pattern of Cu-OCTA@NF catalyst prepared for Example 1.

[0027] Figure 5 Electrochemical performance graph (LSV) of catalyst for urea oxidation reaction with Cu-NS@NF.

[0028] Figure 6 Electrochemical performance graph (LSV) of catalyst for urea oxidation reaction with commercial catalyst IrO2, substrate NF. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0030] Example 1

[0031] A Cu-OCTA@NF catalyst, the preparation method comprising the following steps:

[0032] Step S1: 0.171 g of copper chloride dihydrate was added to 50 mL of deionized water and stirred for 10 min to dissolve to obtain a precursor solution;

[0033] Step S2: Foam nickel (2 cm x 3 cm, purity greater than 99.99%) was soaked in 10 mL of 6 mol / L hydrochloric acid for 15 min, and then placed in a 30°C vacuum air drying oven for drying for 6 h.

[0034] Step S3: The pickled foam nickel was soaked in the precursor solution for replacement, the reaction temperature was 80°C, the soaking time was 4 h, and the Cu-OCTA@NF catalyst was obtained after taking out and drying.

[0035] Figure 1 SEM image of Cu-OCTA@NF prepared for Example 1, showing that the foam nickel substrate surface is uniformly loaded with octahedral microstructures with a side length of several microns and regular morphology. The octahedron is composed of Cu 2+ The reduced metal copper, which exhibits excellent crystal face exposure, helps to form a strong interface coupling effect between copper and foam nickel, thereby significantly improving the electron transport efficiency and overall conductivity.

[0036] Figure 4The X-ray diffraction (XRD) pattern of the Cu-OCTA@NF catalyst, the Cu-OCTA@NF catalyst has obvious diffraction peaks at 2theta = 43.3°, 50.4° and 74.1°, respectively corresponding to the (111), (200) and (220) crystal faces of the metal copper (Cu) phase, which is consistent with the standard PDF card (No. 96-431-3208), indicating that the prepared material has a well-crystallized metal copper structure. Combined with the precursor design and morphology characterization results, the metal copper is distributed in the form of an octahedral structure (Cu octahedron) on the surface of the nickel foam (Ni foam) substrate. The above results show that the formation of copper octahedral crystals in the Cu-OCTA@NF catalyst endows it with good crystal structure and stable phase composition.

[0037] Comparative Example 1

[0038] A Cu-NS@NF-1 catalyst, the preparation method comprising the following steps:

[0039] Step S1: 0.428 g of copper chloride dihydrate was added to 50 mL of deionized water and stirred for 10 min to dissolve to obtain a precursor solution;

[0040] Step S2: The nickel foam (2 cm x 3 cm, purity greater than 99.99%) was immersed in 10 mL of hydrochloric acid with a concentration of 6 mol / L for 15 min, and then placed in a 30°C vacuum air drying oven for drying for 6 h.

[0041] Step S3: The acid-washed nickel foam was immersed in the precursor solution for replacement, the reaction temperature was 80°C, the immersion time was 1 h, and the Cu-NS@NF-1 catalyst was obtained after drying.

[0042] Figure 2 The SEM image of Cu-NS@NF-1 shows that the nickel foam substrate surface is partially loaded with nanosheet structures with a side length of several microns.

[0043] Comparative Example 2

[0044] A Cu-NS@NF-2 catalyst, the preparation method comprising the following steps:

[0045] Step S1: 0.855 g of copper chloride dihydrate was added to 50 mL of deionized water and stirred for 10 min to dissolve to obtain a precursor solution;

[0046] Step S2: The nickel foam (2 cm x 3 cm, purity greater than 99.99%) was immersed in 10 mL of hydrochloric acid with a concentration of 6 mol / L for 15 min, and then placed in a 30°C vacuum air drying oven for drying for 6 h.

[0047] Step S3: The acid-washed nickel foam is immersed in the precursor solution for replacement, the reaction temperature is 80℃, the immersion time is 1h, and the Cu-NS-2@NF catalyst is obtained after taking out and drying.

[0048] Figure 3 The SEM image of Cu-NS@NF-2 shows that the foam nickel substrate surface is uniformly loaded with a nanosheet microstructure with a side length of several microns and cross-linking. Figures 1-3 It can be seen that with the increase of copper salt concentration, the structure of Cu gradually changes from octahedron to nanosheet.

[0049] Application Example

[0050] The performance of the Cu-OCTA@NF catalyst prepared in Example 1, the Cu-NS@NF-2 prepared in Comparative Example 2, and the foam nickel (NF) catalyst in the urea oxidation reaction (UOR) was determined by selecting a three-electrode system. A 1.0M KOH solution containing 0.5M urea was used as the electrolyte, Cu-OCTA@NF, IrO2, and NF were used as the working electrode, a platinum mesh was used as the counter electrode, and Hg / HgO was used as the reference electrode. The electrolyte was purged with high-purity argon before testing to remove dissolved oxygen and avoid oxygen interference. During the test, linear sweep voltammetry (LSV) with a scan rate of 5mV / s was used to evaluate the electrochemical performance. The results are shown in Figure 5 and Table 1, Figure 5 is the electrochemical performance diagram (LSV) of the urea oxidation reaction.

[0051] Table 1 Required UOR potential of catalyst at 10mA cm -2 and 50mA cm -2 current density

[0052]

[0053] As shown in Figure 5 , 6 and Table 1, at a current density of 10mA cm -2 , the required potential of the catalyst of Example 1 is 1.40V, which is significantly lower than that of IrO2(1.55V) and NF(1.77V), indicating that Example 1 can drive a higher current density at a lower potential and has more excellent electrocatalytic activity. At a current density of 50mA cm -2At the same time, the potential required by Example 1 is only 1.49 V, which is significantly lower than 1.62 V of IrO2, showing lower overpotential requirement and better electrocatalytic kinetics; in contrast, NF cannot obtain effective potential at this current density, indicating that it cannot operate continuously under high load conditions, and its catalytic performance is much lower than that of Example 1. Most importantly, the potential required by the octahedral microstructure Cu-OCTA@NF is better than that of the nanosheet microstructure Cu-NS@NF-2, and it can exhibit more excellent performance in the urea oxidation reaction, which may be due to the fact that the octahedron belongs to the polyhedral microstructure, and its surface is composed of multiple triangular or rhombic crystal planes. Compared with two-dimensional nanosheets (the sheet structure of Cu-NS@NF-2), the specific surface area of the same mass is larger, and the defect sites such as edges and corners of the crystal plane junction are more dense. These edge and corner sites usually have higher surface energy and are key active centers for the adsorption and activation (such as N-H bond breaking and C-N bond restructuring) of urea molecules in UOR, so they can provide more active sites that can participate in the reaction, directly improving the reaction rate. Furthermore, in Cu-OCTA@NF, the contact mode of the octahedral Cu with the substrate NF (foamed nickel) may be "multi-point anchoring" (compared with "face contact" of nanosheets), which is more likely to induce electron transfer from NF to Cu (or vice versa), adjusting the valence state and d-band center position of Cu. When the d-band center is close to the Fermi level, it is more conducive to the adsorption of N and O atoms in the urea molecule (forming a coordination bond with the d orbit of Cu), accelerating the generation and conversion of reaction intermediates.

[0054] Example 2

[0055] A Cu-OCTA@NF catalyst, the preparation method comprising the following steps:

[0056] Step S1: 0.085 g of copper chloride dihydrate is added to 50 mL of deionized water and stirred for 10 min to dissolve to obtain a precursor solution;

[0057] Step S2: The foamed nickel (2 cm x 3 cm, purity greater than 99.99%) is soaked in 10 mL of 6 mol / L hydrochloric acid for 15 min, and then placed in a 30°C vacuum drying oven for drying for 6 h.

[0058] Step S3: The pickled foamed nickel is soaked in the precursor solution for replacement, the reaction temperature is 60°C, the soaking time is 6 h, and the Cu-OCTA@NF catalyst is obtained after drying. The SEM shows that the foamed nickel substrate surface is uniformly loaded with octahedral microstructures with a side length of several microns and regular morphology.

[0059] Example 3

[0060] A Cu-OCTA@NF catalyst, the preparation method comprising the following steps:

[0061] Step S1: 0.34 g of copper chloride dihydrate was added to 50 mL of deionized water and stirred for 10 min to dissolve to obtain a precursor solution;

[0062] Step S2: The foamed nickel (2 cm x 3 cm, purity greater than 99.99%) was soaked in 10 mL of hydrochloric acid with a concentration of 6 mol / L for 15 min, and then placed in a 30°C vacuum air drying oven for drying for 6 h.

[0063] Step S3: The pickled foamed nickel was soaked in the precursor solution for replacement, the reaction temperature was 100°C, the soaking time was 1 h, and the Cu-OCTA@NF catalyst was obtained after drying. The SEM showed that the foamed nickel substrate surface was uniformly loaded with octahedral microstructures with a side length of several microns and regular morphology.

[0064] Example 4

[0065] A Cu-OCTA@NF catalyst, the preparation method comprising the following steps:

[0066] Step S1: 0.25 g of copper sulfate pentahydrate was added to 50 mL of deionized water and stirred for 10 min to dissolve to obtain a precursor solution;

[0067] Step S2: The foamed nickel (2 cm x 3 cm, purity greater than 99.99%) was soaked in 10 mL of sulfuric acid with a concentration of 6 mol / L for 15 min, and then placed in a 25°C vacuum air drying oven for drying for 6 h.

[0068] Step S3: The pickled foamed nickel was soaked in the precursor solution for replacement, the reaction temperature was 80°C, the soaking time was 4 h, and the Cu-OCTA@NF catalyst was obtained after drying. The SEM showed that the foamed nickel substrate surface was uniformly loaded with octahedral microstructures with a side length of several microns and regular morphology.

[0069] Example 5

[0070] A Cu-OCTA@NF catalyst, the preparation method comprising the following steps:

[0071] Step S1: 0.25 g of copper sulfate pentahydrate was added to 50 mL of deionized water and stirred for 10 min to dissolve to obtain a precursor solution;

[0072] Step S2: The foamed nickel (2 cm x 3 cm, purity greater than 99.99%) was soaked in 10 mL of sulfuric acid with a concentration of 1 mol / L for 15 min, and then placed in a 60°C vacuum air drying oven for drying for 2 h.

[0073] Step S3: the acid-washed nickel foam is immersed in the precursor solution for replacement, the reaction temperature is 70 DEG C, the immersion time is 3h, and the Cu-OCTA@NF catalyst is obtained after taking out and drying. It can be seen from SEM that the foam nickel substrate surface is uniformly loaded with octahedral microstructure with a side length of several microns and regular morphology.

[0074] Example 6

[0075] A Cu-OCTA@NF catalyst, the preparation method comprising the following steps:

[0076] Step S1: 0.24g of copper nitrate trihydrate is added to 50mL of deionized water and stirred for 10min to dissolve to obtain a precursor solution;

[0077] Step S2: the nickel foam (2cm*3cm, purity greater than 99.99%) is immersed in 10mL of 1mol / L citric acid for 15min, and then dried in a 30 DEG C vacuum air drying oven for 6h.

[0078] Step S3: the acid-washed nickel foam is immersed in the precursor solution for replacement, the reaction temperature is 80 DEG C, the immersion time is 4h, and the Cu-OCTA@NF catalyst is obtained after taking out and drying. It can be seen from SEM that the foam nickel substrate surface is uniformly loaded with octahedral microstructure with a side length of several microns and regular morphology.

[0079] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a Cu-OCTA@NF catalyst, characterized in that, The method comprises the following steps: (1) soaking the nickel foam in an acid solution, and then drying for standby; (2) dissolving a copper salt to prepare a precursor solution; (3) immersing the nickel foam obtained in step (1) in the precursor solution for displacement reaction to obtain a Cu-OCTA@NF catalyst.

2. The process for the preparation of Cu-OCTA@NF catalyst as claimed in claim 1, wherein, The acid solution is any one or more of hydrochloric acid, sulfuric acid, citric acid and oxalic acid.

3. The process for the preparation of Cu-OCTA@NF catalyst as claimed in claim 2, wherein, The concentration of the acid solution is 1-6 mol / L.

4. The process for the preparation of Cu-OCTA@NF catalyst as claimed in claim 3, wherein, The soaking time is 10-30 min, and the temperature is room temperature.

5. The process for the preparation of Cu-OCTA@NF catalyst as claimed in claim 4, wherein, The drying time is 2-6 h, and the temperature is 25-60℃.

6. The process for the preparation of Cu-OCTA@NF catalyst according to any one of claims 1-5, characterized by, The copper salt is at least one of copper chloride, copper sulfate and copper nitrate.

7. The process for the preparation of Cu-OCTA@NF catalyst as claimed in claim 6, wherein, The concentration of the copper salt in the precursor solution is 0.01-0.04 mol / L.

8. The process for the preparation of Cu-OCTA@NF catalyst as claimed in claim 7, wherein, The temperature for the displacement reaction is 60-100℃, and the time is 1-6 h.

9. The Cu-OCTA@NF catalyst prepared by the method of any one of claims 1-8.

10. The application of the Cu-OCTA@NF catalyst of claim 9 in urea oxidation reaction.

Images