CN115110113B - Rod-shaped Co 2 C-MoN composite material and preparation method and application thereof - Google Patents

Abstract

The invention provides a bar-shaped Co ₂ C-MoN composite material, and a preparation method and application thereof. The preparation method of the rod-shaped composite material comprises the steps of placing foam nickel in a mixed solution for hydrothermal reaction to prepare a cobalt molybdate precursor material; and then, high-temperature calcination is carried out by a high-temperature calcination method to obtain the composite material. The composite material prepared by the method has excellent catalytic performance on urea oxidation reaction of an anode and hydrogen evolution reaction of a cathode in alkaline solution containing urea; on this basis, a double-electrode electrolytic cell system was constructed. At a current density of 50 mA.cm ^‑2 When the voltage required for the overall urea aqueous solution decomposition was 1.507V, the voltage required for the overall urea aqueous solution decomposition was 171mV lower than that required for the overall urea aqueous solution decomposition. In addition, the prepared catalyst not only can catalyze hydrogen production with high efficiency, but also can treat urea in wastewater effectively. Therefore, it would be a very promising green electrocatalyst.

Description

A kind of rod-shaped Co2C-MoN composite material and its preparation method and application

Technical field

The invention relates to the technical field of composite materials, and in particular to a rod-shaped Co ₂ C-MoN composite material and its preparation method and application.

Background technique

In order to develop clean new energy, countries around the world are developing new alternative energy sources such as nuclear energy, solar energy, wind energy and hydrogen energy according to local conditions, among which hydrogen energy has attracted much attention. The first thing that needs to be solved in the development and utilization of hydrogen energy is the problem of cheap and large-scale hydrogen production. Methods for preparing hydrogen include: hydrogen production by water electrolysis, hydrogen production by fossil energy, and hydrogen production by biomass. Among them, hydrogen produced by electrolysis of water has higher purity and has been widely used in industry. Electrolysis of water includes hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Theoretically, water electrolysis can be carried out with a voltage exceeding 1.229V. However, in actual electrolysis, due to the existence of overpotential in the hydrogen and oxygen generation reaction, especially the complex multi-electron steps in OER, water decomposition requires a higher voltage. Therefore, the urea oxidation reaction (UOR) with a lower oxidation potential is used to replace OER, thereby reducing the overpotential during the reaction. In order to further reduce the reaction overpotential, a suitable electrocatalyst still needs to be developed. At present, the noble metals Pt/C and _IrO have been proven to have excellent catalytic effects for HER and OER respectively. However, their high cost and low storage capacity become huge obstacles to large-scale application production.

In recent years, various non-noble metal catalysts, such as transition metal oxides, have been studied, which have the following advantages: abundant reserves, low price, easy preparation, and environmental friendliness. Transition metal elements such as Mn, Fe, Co, Ni, etc. have multiple valence states and can form oxides with various crystal structures. They have a good catalytic effect on the oxygen evolution reaction, but have poor catalytic effect on the hydrogen evolution reaction.

Based on the shortcomings of current non-noble metal catalysts, it is necessary to improve this.

Contents of the invention

In view of this, the present invention proposes a rod-shaped Co ₂ C-MoN composite material and its preparation method and application to solve or partially solve the problem of excessive energy consumption in the existing technology.

In a first aspect, the invention provides a method for preparing rod-shaped Co ₂ C-MoN composite materials, which includes the following steps: adding cobalt salt to water to obtain a first solution; adding molybdate to water to obtain a second solution; The first solution and the second solution are mixed to obtain a mixed solution; the nickel foam is placed in the mixed solution and reacted at 150-170°C for 4-8 hours to obtain a precursor material; the precursor material and dicyandiamide are placed in a tubular In the furnace, under the protection of inert gas, the temperature is raised to 500-700°C and maintained for 1-3 hours to obtain the Co ₂ C-MoN composite material.

In a second aspect, the present invention also provides a rod-shaped Co ₂ C-MoN composite material, which is prepared by the preparation method.

In a third aspect, the present invention also provides an application of the rod-shaped Co ₂ C-MoN composite material as a catalyst.

The preparation method and catalytic performance of a rod-shaped Co ₂ C-MoN composite material of the present invention have the following beneficial effects compared with the existing technology:

The preparation method of the rod-shaped Co ₂ C-MoN composite material of the present invention is to prepare the cobalt molybdate precursor material by placing nickel foam in a mixed solution for a hydrothermal reaction; and then using a high-temperature calcination method to prepare the cobalt molybdate precursor material. The bulk material and dicyandiamide are placed in a tube furnace and calcined at high temperature to obtain the Co ₂ C-MoN composite material. The Co ₂ C-MoN composite material prepared by this application has excellent catalytic performance for the urea oxidation reaction of the anode and the hydrogen evolution reaction of the cathode in an alkaline solution containing urea; further, it is prepared at a calcination temperature of 600°C The obtained target product (Co ₂ C/MoN-600/NF) has optimal catalytic performance for both the urea oxidation reaction at the anode and the hydrogen evolution reaction at the cathode in an alkaline solution containing urea. On this basis, a two-electrode electrolyzer system (Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF) was constructed. When the current density is 50mA·cm ^-2 , the voltage required for overall urea water decomposition is 1.507V (vs RHE), which is 171mV lower than the voltage required for overall water decomposition. In addition, the prepared catalyst can not only efficiently catalyze hydrogen production, but also effectively treat urea in wastewater. Therefore, it will be a promising green electrocatalyst.

Description of drawings

In order to more clearly explain the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is an X-ray diffraction pattern of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 of the present invention;

Figure 2 is the X-ray photoelectron spectrum of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 of the present invention;

Figure 3 is a scanning electron microscope (SEM) image of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 of the present invention under different magnification conditions;

Figure 4 is a transmission electron microscope (TEM) image of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 of the present invention under different magnification conditions;

Figure 5 is a comparison chart of the LSV curves of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 of the present invention in three electrolytes;

Figure 6 shows the precursor materials (CoMoO ₆ ·0.9H ₂ O/NF), Co ₂ C/MoN-600/NF, bare nickel foam (NF), and Pt/C/NF prepared in Example 1 of the present invention respectively. Comparison of LSV curves of HER in 1M KOH electrolyte;

Figure 7 is a comparison chart of the LSV curves of HER in 1M KOH electrolyte for the Co ₂ C/MoN composite materials prepared in Examples 1 to 5 of the present invention;

Figure 8 shows the precursor materials (CoMoO ₆ ·0.9H ₂ O/NF), Co ₂ C/MoN-600/NF, bare nickel foam (NF), and Pt/C/NF prepared in Example 1 of the present invention respectively. The corresponding Tafel curve in electrolytic HER;

Figure 9 is a Tafel curve corresponding to the Co ₂ C/MoN composite materials prepared in Examples 1 to 5 of the present invention in electrolytic HER respectively;

Figure 10 is the LSV curve of HER at different scan rates in the Co ₂ C/MoN-600/NF material prepared in Example 1 of the present invention in 1M KOH electrolyte;

Figure 11 is a multi-step voltage step curve diagram of Co ₂ C/MoN-600/NF prepared in Example 1 of the present invention as a catalyst;

Figure 12 is an ampere-time curve (it) diagram of Co ₂ C/MoN-600/NF prepared in Example 1 of the present invention after electrolysis in 1M KOH electrolyte for 25 hours at a voltage of -176mV;

Figure 13 shows the Co ₂ C/MoN-600/NF prepared in Example 1 of the present invention, respectively, in 1M KOH (oxygen evolution reaction (OER)), 0.5M urea, 1M KOH and 0.5M urea (urea oxidation reaction (UOR)). )) LSV curve comparison chart in solution;

Figure 14 shows the precursor materials (CoMoO ₆ ·0.9H ₂ O/NF), Co ₂ C/MoN-600/NF, bare nickel foam (NF) and IrO ₂ /NF prepared in Example 1 of the present invention respectively. Comparison of LSV curves of UOR in 1M KOH electrolyte containing 0.5M urea;

Figure 15 is a comparison chart of the UOR LSV curves of the Co ₂ C/MoN composite materials prepared in Examples 1 to 5 of the present invention in 1MKOH electrolyte containing 0.5M urea;

Figure 16 shows the precursor materials (CoMoO ₆ ·0.9H ₂ O/NF), Co ₂ C/MoN-600/NF, bare nickel foam (NF) and IrO ₂ /NF prepared in Example 1 of the present invention respectively. Tafel curve corresponding to UOR in urea electrolysis;

Figure 17 is a Tafel curve diagram corresponding to the UOR of the Co ₂ C/MoN composite materials prepared in Examples 1 to 5 of the present invention in urea electrolysis;

Figure 18 is the LSV curve of UOR of Co ₂ C/MoN-600/NF in a 1M KOH solution containing 0.5M urea at different scan speeds in Example 1 of the present invention;

Figure 19 is a multi-step voltage step curve of the Co ₂ C/MoN-600/NF catalyst in an electrolyte solution containing 0.5M urea and 1M KOH;

Figure 20 shows the LSV comparison curve of Co ₂ C/MoN-600/NF in 1M KOH electrolyte containing 0.5M urea before and after 3000 cycles of cyclic voltammetry scanning;

Figure 21 shows the relative electrochemical active surface areas of the precursor materials (CoMoO ₆ ·0.9H ₂ O/NF), Co ₂ C/MoN-600/NF, and bare nickel foam (NF) prepared in Example 1 of the present invention. Electric double layer capacitance value;

Figure 22 is the electric double layer capacitance value of the relative electrochemically active surface area of the Co ₂ C/MoN composite material prepared in Examples 1 to 5 of the present invention;

Figure 23 shows the precursor materials (CoMoO ₆ ·0.9H ₂ O/NF), Co ₂ C/MoN-600/NF and bare nickel foam (NF) prepared in Example 1 of the present invention respectively in the solution containing 0.5M urea. Electrochemical impedance spectroscopy (EIS) comparison chart in 1M KOH solution;

Figure 24 is a comparison chart of the electrochemical impedance spectroscopy (EIS) of the Co ₂ C/MoN composite materials prepared in Examples 1 to 5 of the present invention in 1 M KOH solution containing 0.5 M urea;

Figure 25 is a schematic structural diagram of a dual-electrode system using Co ₂ C/MoN-600/NF in Example 1 as the anode and cathode respectively;

Figure 26 is a comparison diagram of the polarization curves of Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF in a 1M KOH solution containing 0.5M urea and a 1M KOH solution without urea;

Figure 27 shows CoMoO ₆ ·0.9H ₂ O/NF‖CoMoO ₆ ·0.9H ₂ O/NF, Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF, Pt/C/NF‖IrO Comparison of polarization curves of ₂ /NF in 1M KOH solution containing 0.5M urea;

Figure 28 is an ampere-time curve (it) diagram of Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF electrolyzing urea at a battery voltage of 1.5V.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

The embodiments of this application provide a method for preparing rod-shaped Co ₂ C-MoN composite materials, which includes the following steps:

S1. Add cobalt salt to water to obtain the first solution;

S2. Add molybdate to water to obtain a second solution;

S3. Mix the first solution and the second solution to obtain a mixed solution;

S4. Place the nickel foam in the mixed solution and react at 150-170°C for 4-8 hours to obtain the precursor material;

S5. Place the precursor material and dicyandiamide in a tube furnace respectively, and under the protection of inert gas, raise the temperature to 500-700°C and maintain it for 1-3 hours to obtain the Co ₂ C-MoN composite material.

The preparation method of the rod-shaped Co ₂ C-MoN composite material of the present application is to prepare the cobalt molybdate precursor material by placing nickel foam in a mixed solution for a hydrothermal reaction; and then using a high-temperature calcination method to prepare the cobalt molybdate precursor material. The material and dicyandiamide are placed in a tube furnace and calcined at high temperature to obtain the Co ₂ C-MoN composite material. The Co ₂ C-MoN composite material prepared by this application has excellent catalytic performance for the urea oxidation reaction of the anode and the hydrogen evolution reaction of the cathode in an alkaline solution containing urea; further, it is prepared at a calcination temperature of 600°C The obtained target product (Co ₂ C/MoN-600/NF) has optimal catalytic performance for both the urea oxidation reaction at the anode and the hydrogen evolution reaction at the cathode in an alkaline solution containing urea. On this basis, a two-electrode electrolyzer system (Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF) was constructed. When the current density is 50mA·cm ^-2 , the voltage required for overall urea water decomposition is 1.507V (vs RHE), which is 171mV lower than the voltage required for overall water decomposition. In addition, the prepared catalyst can not only efficiently catalyze hydrogen production, but also effectively treat urea in wastewater. Therefore, it will be a promising green electrocatalyst.

In some embodiments, the cobalt salt includes at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride.

In some embodiments, the molybdate includes at least one of ammonium molybdate, sodium molybdate, potassium molybdate, and ammonium heptamolybdate.

In some embodiments, in the step of adding cobalt salt to water, the molar volume ratio of cobalt salt to water is (0.5-2) mmol: (15-25) mL;

And/or, in the step of adding molybdate to water, the molar volume ratio of molybdate to water is (0.1~0.2) mmol: (5~15) mL;

And/or, the molar mass ratio of the cobalt salt and dicyandiamide is (0.5-2) mmol: (0.3-0.7) g.

In some embodiments, the precursor material and dicyandiamide are placed in a tube furnace respectively, and under the protection of inert gas, the temperature is raised to 500-700°C at a rate of 3-7°C/min and maintained for 1-3 hours, that is, Obtain Co ₂ C-MoN composite material.

Specifically, the inert gas can be a rare gas or nitrogen; put the precursor material and dicyandiamide into two porcelain boats respectively and then place them in a tube furnace for calcination. After natural cooling, the Co ₂ C-MoN composite material is obtained.

In some embodiments, before placing the foamed nickel in the mixed solution, the foamed nickel is also subjected to ultrasonic cleaning using hydrochloric acid, acetone, ultrapure water and ethanol in sequence.

In some embodiments, the nickel foam is placed in a mixed solution, reacted at 150-170°C for 4-8 hours, washed, and then dried at 40-80°C to obtain the precursor material.

Based on the same inventive concept, the embodiment of the present application also provides a rod-shaped Co ₂ C-MoN composite material, which is prepared using the above preparation method.

Based on the same inventive concept, the embodiments of the present application also provide an application of the above-mentioned rod-shaped Co ₂ C-MoN composite material as a catalyst.

Specifically, the rod-shaped Co ₂ C-MoN composite material of the present application can be used as a catalyst to efficiently catalyze hydrogen production, and can also effectively catalyze the decomposition of urea in wastewater.

The preparation method of the rod-shaped Co ₂ C-MoN composite material of the present application is further described below with specific examples. This section further explains the content of the present invention in conjunction with specific examples, but should not be understood as a limitation of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

Example 1

The embodiments of this application provide a method for preparing rod-shaped Co ₂ C-MoN composite materials, which includes the following steps:

S1. Use dilute hydrochloric acid solution (mass concentration: 5%), acetone, ultrapure water and ethanol in sequence to ultrasonically clean the cut nickel foam (4×2cm ² , that is, the length is 4cm and the width is 2cm), and vacuum dry for backup. use;

S2. Dissolve 1 mmol of cobalt nitrate in 20 mL of deionized water, and disperse evenly by ultrasonic to obtain the first solution;

S3. Dissolve 0.15 mmol of ammonium heptamolybdate in 10 mL of deionized water, and disperse evenly by ultrasonic to obtain a second solution;

S3. Add the second solution to the first solution, stir for 30 minutes to mix evenly, and obtain a mixed solution;

S4. Place the mixed solution into a 50mL polytetrafluoroethylene-lined reaction kettle, then add the nickel foam in step S1, and react at 160°C for 6 hours. After the reaction is completed, wash with water and absolute ethanol, and then incubate at 60°C. The precursor material is obtained by vacuum drying;

S5. Put the precursor material and 0.5g of dicyandiamide in step S4 into two porcelain boats respectively, then place them in a tube furnace, and under nitrogen protection, raise the temperature to 600°C at a heating rate of 5°C/min. , calcined for 2 hours and cooled naturally, the target product Co ₂ C-MoN composite material (denoted as Co ₂ C/MoN-600/NF) was finally obtained.

Example 2

The preparation method of the rod-shaped Co ₂ C-MoN composite material provided in the examples of this application is the same as that of Example 1. The difference is that in step S5, it is calcined at 500°C for 2 hours. The other process parameters are the same as those of Example 1. The prepared Co ₂ C-MoN composite material is denoted as Co ₂ C/MoN-500/NF.

Example 3

The preparation method of the rod-shaped Co ₂ C-MoN composite material provided in the examples of this application is the same as that of Example 1. The difference is that in step S5, it is calcined at 550°C for 2 hours. The other process parameters are the same as those of Example 1. The prepared Co ₂ C-MoN composite material is denoted as Co ₂ C/MoN-550/NF.

Example 4

The preparation method of the rod-shaped Co ₂ C-MoN composite material provided in the examples of this application is the same as that of Example 1. The difference is that in step S5, it is calcined at 650°C for 2 hours. The other process parameters are the same as those of Example 1. The prepared Co ₂ C-MoN composite material is denoted as Co ₂ C/MoN-650/NF.

Example 5

The preparation method of the rod-shaped Co ₂ C-MoN composite material provided in the examples of this application is the same as that of Example 1. The difference is that in step S5, it is calcined at 700°C for 2 hours. The other process parameters are the same as those of Example 1. The prepared Co ₂ C-MoN composite material is denoted as Co ₂ C/MoN-700/NF.

Performance Testing

Figure 1 is the X-ray diffraction (XRD) pattern of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1. In Figure 1, the XRD patterns of Ni, Co ₂ C, and MoN are located below the Co ₂ C/MoN-600/NF material pattern.

As can be seen from Figure 1, Co ₂ C/MoN-600/NF was successfully synthesized.

Figure 2 is the X-ray photoelectron spectrum (XPS) of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1, wherein: in Figure 2, (a) the high-resolution split peak spectrum of Co 2p Figure; (b) high-resolution peak split spectrum of Mo 3d; (c) high-resolution peak split spectrum of N1s; (d) high-resolution peak split spectrum of C 1s; it can be seen that Co ₂ C Exists at the same time as MoN.

Figure 3 is a scanning electron microscope (SEM) image of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 under different magnification conditions. As can be seen from Figure 3, the as-prepared material exhibits a rod-like structure.

Figure 4 is a transmission electron microscope (TEM) picture of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 under different magnification conditions; Figure 4(b) is an enlarged view of the dotted box in (a).

As can be seen from Figure 4, the surface of the rod-shaped structure of the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 has nanoparticles with a diameter of approximately 50 nm.

Figure 5 shows a three-electrode system using the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 as the working electrode, the Hg/HgO electrode as the reference electrode, the carbon rod as the counter electrode, and 5 mV Comparison of LSV curves of the hydrogen evolution reaction (HER) in electrolyte solutions of 1M KOH solution, 0.5M urea (i.e. urea), 1M KOH and 0.5M urea at a scan rate of /s.

As can be seen from Figure 5, the two polarization curves in 1M KOH, 1M KOH and 0.5M urea electrolytes basically overlap, indicating that urea has little effect on HER performance.

Figure 6 shows the precursor material (CoMoO ₆ ·0.9H ₂ O/NF) prepared in step S4 of Example 1 and the Co ₂ C/MoN-600/NF prepared in Example 1 in a three-electrode system. , bare nickel foam (NF), Pt/C/NF (composed of 5.0 mg of Pt/C (20wt%) powder purchased from McLean Company, 200 μL of isopropyl alcohol, 32 μL of naphthol and 768 μL of deionized water, mixed evenly, and then 200 μL of the mixture was dropped onto nickel foam (0.5cm × 0.5cm) as the working electrode, the Hg/HgO electrode was used as the reference electrode, the carbon rod was used as the counter electrode, and electrolysis was carried out in 1M KOH at a scanning rate of 5mV/s. Comparison of LSV curves of HER in liquid.

Figure 7 is a comparison chart of the LSV curves of the HER of the Co ₂ C/MoN composite materials prepared in Examples 1 to 5 in 1M KOH electrolyte.

As can be seen from Figures 6 to 7, the HER performance of the Co ₂ C/MoN-600/NF material prepared in Example 1 is closest to that of Pt/C/NF.

Figure 8 shows the precursor material (CoMoO ₆ ·0.9H ₂ O/NF) prepared in step S4 of Example 1 and Co ₂ C/MoN-600/NF prepared in Example 1 in a three-electrode system. , bare nickel foam (NF), Pt/C/NF as the working electrode, Hg/HgO electrode as the reference electrode, carbon rod as the counter electrode, and the corresponding Tafel curve in the electrolysis HER at a scan rate of 5mV/s.

Figure 9 shows the corresponding Tafel curves of the Co ₂ C/MoN composite materials prepared in Examples 1 to 5 in electrolytic HER.

It can be seen from Figures 8 to 9 that the Tafel slope of Co ₂ C/MoN-600/NF prepared in Example 1 is closest to that of Pt/C/NF, indicating its excellent catalytic kinetics.

Figure 10 shows a three-electrode system using the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 as the working electrode, the Hg/HgO electrode as the reference electrode, and the carbon rod as the counter electrode. At 1M LSV curves of HER at different scan rates in KOH electrolyte; it can be seen that the scan rate and current have a good linear relationship, indicating that Co ₂ C/MoN-600/NF has higher charge and quality during the catalytic process transmission efficiency.

Figure 11 is a multi-step process in a three-electrode system using the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 as the working electrode, the Hg/HgO electrode as the reference electrode, and the carbon rod as the counter electrode. Voltage step curve comparison chart; it can be seen that the current responds quickly and remains stable as the voltage increases, indicating that Co ₂ C/MoN-600/NF has good mass transfer performance.

Figure 12 shows a three-electrode system using the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 as the working electrode, the Hg/HgO electrode as the reference electrode, and the carbon rod as the counter electrode at 5 mV/ s scan rate in a 1M KOH solution environment at -176mV voltage after 25h electrolysis ampere-time curve (it) diagram; it can be seen that Co ₂ C/MoN-600/NF has good long-term electrochemical stability .

Figure 13 shows a three-electrode system using the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 as the working electrode, the Hg/HgO electrode as the reference electrode, the carbon rod as the counter electrode, and 5 mV /s scan rate comparison chart of LSV curves in 1MKOH (oxygen evolution reaction (OER)), 0.5M urea, 1M KOH and 0.5M urea (urea oxidation reaction (UOR)) solutions.

As can be seen from Figure 13, the voltage required by UOR is much lower than that of OER.

Figure 14 shows the precursor material (CoMoO ₆ ·0.9H ₂ O/NF) prepared in step S4 of Example 1 and Co ₂ C/MoN-600/NF prepared in Example 1 in a three-electrode system. , bare nickel foam (NF), IrO ₂ /NF (composed of 5.0 mg IrO ₂ (20wt%) powder purchased from McLean Company, 200 μL isopropyl alcohol, 32 μL naphthol and 768 μL deionized water). After mixing evenly, take 200 μL of the mixture. Added dropwise to nickel foam (0.5cm×0.5cm)) as the working electrode, Hg/HgO electrode as the reference electrode, carbon rod as the counter electrode, and a scanning rate of 5mV/s in each electrode containing 0.5M Comparison of LSV curves of UOR in 1M KOH electrolyte of urea.

Figure 15 shows a three-electrode system using the Co ₂ C/MoN composite material prepared in Examples 1 to 5 as the working electrode, the Hg/HgO electrode as the reference electrode, and the carbon rod as the counter electrode. Scan rate comparison of LSV curves of UOR in 1M KOH electrolyte containing 0.5M urea.

It can be seen from Figures 14 to 15 that the Co ₂ C/MoN-600/NF prepared in Example 1 has the best UOR catalytic effect.

Figure 16 shows the precursor material (CoMoO ₆ ·0.9H ₂ O/NF) prepared in step S4 of Example 1 and Co ₂ C/MoN-600/NF prepared in Example 1 in a three-electrode system. , bare nickel foam (NF), IrO ₂ /NF as the working electrode, Hg/HgO electrode as the reference electrode, carbon rod as the counter electrode, and the Tafel curve corresponding to UOR in urea electrolysis at a scan rate of 5mV/s.

Figure 17 shows a three-electrode system using the Co ₂ C/MoN composite material prepared in Examples 1 to 5 as the working electrode, the Hg/HgO electrode as the reference electrode, the carbon rod as the counter electrode, and 5mV/ The scan rate of s is the Tafel curve corresponding to UOR in urea electrolysis.

It can be seen from Figures 16 to 17 that Co ₂ C/MoN-600/NF in Example 1 has fast charge transfer kinetics and good catalytic performance.

Figure 18 shows a three-electrode system using the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 as the working electrode, the Hg/HgO electrode as the reference electrode, and the carbon rod as the counter electrode. LSV plot of UOR in 0.5M urea in 1M KOH solution at different scan speeds.

As can be seen from Figure 18, Co ₂ C/MoN-600/NF has higher charge and mass transfer efficiency.

Figure 19 shows a three-electrode system using the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 as the working electrode, the Hg/HgO electrode as the reference electrode, the carbon rod as the counter electrode, and 5 mV Multi-step voltage step curve in an electrolyte containing 0.5M urea in 1M KOH at a scan rate of /s. As can be seen from Figure 19, Co ₂ C/MoN-600/NF has good electrical conductivity and mass transfer performance.

Figure 20 shows a three-electrode system using the rod-shaped Co ₂ C/MoN-600/NF material prepared in Example 1 as the working electrode, the Hg/HgO electrode as the reference electrode, the carbon rod as the counter electrode, and 5mV /s scan rate in the environment of 1M KOH solution containing 0.5M urea. LSV comparison curve before and after 3000 cycles of cyclic voltammetric scanning; as can be seen from Figure 20, Co ₂ C/MoN-600/NF has better electrochemical properties. Chemical stability.

Figure 21 shows the precursor material (CoMoO ₆ ·0.9H ₂ O/NF) prepared in step S4 of Example 1, Co ₂ C/MoN-600/NF prepared in Example 1, and bare nickel foam (NF) The electric double layer capacitance value relative to the electrochemically active surface area.

Figure 22 shows the electric double layer capacitance value relative to the electrochemically active surface area of the Co ₂ C/MoN composite material prepared in Examples 1 to 5.

As can be seen from Figures 21 to 22, Co ₂ C/MoN-600/NFF has the largest electric double layer capacitance (C _dl ) value, indicating that the catalyst has the largest electrochemical active area.

Figure 23 shows the precursor material (CoMoO ₆ ·0.9H ₂ O/NF) prepared in step S4 of Example 1 and the Co ₂ C/MoN-600/NF prepared in Example 1 in a three-electrode system. , bare nickel foam (NF) as the working electrode, Hg/HgO electrode as the reference electrode, carbon rod as the counter electrode, electrochemical impedance spectroscopy in 1MKOH solution containing 0.5M urea at a scanning rate of 5mV/s. (EIS) comparison chart.

Figure 24 shows a three-electrode system using the Co ₂ C/MoN composite material prepared in Examples 1 to 5 as the working electrode, the Hg/HgO electrode as the reference electrode, the carbon rod as the counter electrode, and 5mV/ The scan rate of s is compared with the electrochemical impedance spectroscopy (EIS) in 1M KOH solution containing 0.5M urea.

As can be seen from Figures 23 to 24, Co ₂ C/MoN-600/NF has the smallest resistance, which means a faster electron transfer rate.

Figure 25 shows a dual-electrode system (Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF) in which Co ₂ C/MoN-600/NF in Example 1 is used as the anode and cathode respectively. Schematic.

Figure 26 is a comparison diagram of the polarization curves of Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF in a 1M KOH solution containing 0.5M urea and a 1M KOH solution without urea; the results show that , when reaching the same current density, the two-electrode system containing urea requires a much smaller cell voltage than the system without urea.

According to the above method, the precursor material CoMoO ₆ ·0.9H ₂ O/NF prepared in Example 1 was used as anode and cathode respectively to form a dual-electrode system CoMoO ₆ ·0.9H ₂ O/NF‖CoMoO ₆ ·0.9H ₂ O/NF; Pt/C/NF and IrO ₂ /NF are used as anode and cathode respectively to form a two-electrode system Pt/C/NF‖IrO ₂ /NF.

Figure 27 shows CoMoO ₆ ·0.9H ₂ O/NF‖CoMoO ₆ ·0.9H ₂ O/NF, Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF, Pt/C/NF‖IrO Comparison of polarization curves of ₂ /NF in 1M KOH solution containing 0.5M urea; as can be seen from Figure 27, the two-electrode system containing urea requires the lowest voltage, indicating its good catalytic performance.

Figure 28 is an ampere-time curve (it) diagram of Co ₂ C/MoN-600/NF‖Co ₂ C/MoN-600/NF (inset) electrolysis of urea at a battery voltage of 1.5V; from Figure 28 It can be seen that it has good stability.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (9)

1. A method for preparing rod-shaped Co ₂ C-MoN composite material, which is characterized by comprising the following steps: Add cobalt salt to water to obtain a first solution; Add molybdate to water to obtain a second solution; Mix the first solution and the second solution to obtain a mixed solution; Place the nickel foam in the mixed solution and react at 150-170°C for 4-8 hours to obtain the precursor material; The precursor material and dicyandiamide are placed in a tube furnace respectively, and under the protection of inert gas, the temperature is raised to 500-700°C and maintained for 1-3 hours to obtain the Co ₂ C-MoN composite material. 2. The preparation method of rod-shaped Co ₂ C-MoN composite material according to claim 1, wherein the cobalt salt includes at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride. 3. The preparation method of rod-shaped Co ₂ C-MoN composite material according to claim 1, characterized in that the molybdate includes at least one of sodium molybdate, potassium molybdate, and ammonium heptamolybdate. 4. The preparation method of rod-shaped Co ₂ C-MoN composite material as claimed in claim 1, characterized in that, in the step of adding cobalt salt to water, the molar volume ratio of cobalt salt and water is (0.5~2) mmol: (15～25)mL; And/or, in the step of adding molybdate to water, the molar volume ratio of molybdate to water is (0.1~0.2) mmol: (5~15) mL; And/or, the molar mass ratio of the cobalt salt and dicyandiamide is (0.5-2) mmol: (0.3-0.7) g. 5. The preparation method of rod-shaped Co ₂ C-MoN composite material as claimed in claim 1, characterized in that the precursor material and dicyandiamide are placed in a tube furnace respectively, under the protection of inert gas, at 3 Raise the temperature to 500-700°C at a rate of ~7°C/min and keep it for 1-3 hours to obtain Co ₂ C-MoN composite material. 6. The preparation method of rod-shaped Co ₂ C-MoN composite material according to claim 1, characterized in that, before placing the foamed nickel in the mixed solution, it also includes sequentially using hydrochloric acid, acetone, water and ethanol to process the foamed nickel. Ultrasonic cleaning. 7. The preparation method of rod-shaped Co ₂ C-MoN composite material as claimed in claim 1, characterized in that foamed nickel is placed in a mixed solution, reacted at 150-170°C for 4-8 hours, washed, and then at 40 The precursor material is obtained by drying at ~80°C. 8. A rod-shaped Co ₂ C-MoN composite material, characterized in that it is prepared by the preparation method as described in any one of claims 1 to 7. 9. Application of the rod-shaped Co ₂ C-MoN composite material as claimed in claim 8 as a catalyst.