CN113460993B - A zinc-nitrogen modified double-carbon catalytic material, its preparation method and its application in zinc-air batteries - Google Patents

Abstract

The invention discloses a zinc-nitrogen modified dual-carbon catalytic material, a preparation method thereof and application thereof in a zinc-air battery. Synthesizing a metal framework ZIF-8 by using dimethyl imidazole and zinc salt as raw materials, carrying out first heat treatment on the metal framework ZIF-8 in a protective atmosphere to obtain a zinc-modified porous carbon material, ball-milling and mixing the zinc-modified porous carbon material, a saccharide compound and a nitrogen source compound, and carrying out second heat treatment in the protective atmosphere to obtain a zinc-nitrogen-modified dual-carbon catalytic material; the catalytic material has zinc-nitrogen double modification, is rich in defects and porous structures, has good conductivity and a 3D network structure, and is applied to a zinc-air battery to obtain high power density and specific capacity; the preparation method of the catalytic material has low cost and simple steps, and is beneficial to industrial production.

Description

A kind of zinc-nitrogen modified double carbon catalytic material and its preparation method and application in zinc-air battery

technical field

The invention relates to a zinc-air battery electrode material, in particular to a zinc-nitrogen modified double-carbon catalytic material, a preparation method thereof and the application of the zinc-nitrogen modified double-carbon catalytic material in a zinc-air battery, belonging to zinc-air batteries The technical field of battery catalytic materials.

Background technique

Rechargeable zinc-air batteries have received increasing attention due to their high theoretical energy density, low cost, environmental friendliness, and high safety. Zinc-air batteries are driven by the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharge and charge, respectively. However, the sluggish kinetics of ORR and OER on air cathodes greatly limit the commercial application of Zn-air batteries.

Precious metal catalysts (such as platinum, ruthenium, iridium, etc.) are considered to be effective electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), however, the scarcity of precious metal catalysts, high cost, poor stability, and poor methanol resistance are serious obstacles. Large-scale application of zinc-air batteries. Based on the advantages of abundant resources, diverse structures, and environmental friendliness of carbon-based materials, they have gradually attracted widespread attention as catalysts for zinc-air batteries. In particular, doping carbon materials with non-metals and metals can change the electron distribution around carbon atoms and improve materials. The electrical conductivity can greatly improve the electrochemical performance and stability of carbon materials. At present, there have been some studies on the modification of carbon materials with heteroatoms. In the Chinese patent (CN112397733A), the carbon source is dissolved in an organic solvent, and organic cobalt salt is added. In the second step, the carbon source is also dissolved in the organic solvent, and inorganic iron is added. The iron-cobalt-supported nitrogen-doped carbon material is obtained by electrospinning, but the synthesis process is relatively complicated and the cost is high. Chinese patent (CN111554945A) metal salt and nitrogen source (dopamine, urea) are stirred and distributed uniformly in the aqueous solution to further volatilize water, and the mixing process of this method is relatively complicated. In Chinese patent (CN111889114A), a carbon-coated nano-CoFe alloy catalyst with a shell-core structure constructed by hydrogen reduction technology, the Co and Fe elements obtained by this method are highly dispersed in the bimetallic organic framework of the porous structure, which avoids the formation of nano-CoFe alloys. Agglomeration is conducive to the full exposure of electrochemically active sites, however, the process adopts hydrogen reduction, which has a high risk factor.

SUMMARY OF THE INVENTION

In view of the defects existing in the prior art, the first object of the present invention is to provide a double-carbon structure containing zinc atoms and heteroatom nitrogen double modification, developed pores, a three-dimensional carbon skeleton inside and a carbon shell outside, and Defect-rich zinc-nitrogen modified two-carbon catalytic materials.

The second object of the present invention is to provide a method for modifying a two-carbon catalytic material with zinc and nitrogen, which has simple steps and low cost, and can control the doping amount of heteroatoms by adjusting the ratio of raw materials, and at the same time, by adjusting the heat treatment conditions Controlling and adjusting the degree of graphitization of the double-carbon structure, and using zinc-coordinated metal as a raw material, can realize atomic doping of zinc metal element, so that the distribution of active sites is more uniform, which has obvious advantages over the existing technology.

The third object of the present invention is to provide the application of the zinc-nitrogen modified double-carbon catalytic material in the zinc-air battery, and the zinc-nitrogen modified double-carbon catalytic material is applied to the cathode of the zinc-air battery, and the obtained zinc-air battery exhibits excellent performance electrochemical properties, such as high power density and specific capacity.

In order to achieve the above technical purpose, the present invention provides a preparation method of a zinc-nitrogen modified double-carbon catalytic material, the method comprising the following steps:

1) Synthesize metal framework ZIF-8 with dimethylimidazole and zinc salt as raw materials;

2) The metal frame ZIF-8 is subjected to the first heat treatment under a protective atmosphere to obtain a zinc-modified porous carbon material;

3) After mixing the zinc-modified porous carbon material with sugar compounds and nitrogen source compounds by ball milling, the second heat treatment is performed under a protective atmosphere to obtain a zinc-nitrogen modified double-carbon catalytic material.

The technical scheme of the present invention firstly uses dimethylimidazole and zinc salt as raw materials to obtain a metal framework ZIF-8 with regular morphology and pores and the coordination and complexation of metal zinc in the form of a single metal ion. Three-dimensional zinc-modified porous carbon materials with regular morphology, and zinc is highly dispersed and doped in the three-dimensional porous carbon materials in the form of metal zinc atoms, so that the active site distribution is more uniform; The material is nitrogen-doped and constructed with a double-carbon structure, and the surface of the carbon skeleton of the zinc-modified porous carbon material is coated with a layer of uniform, defect-rich carbon coating with high catalytic activity using sugar compounds and nitrogen source compounds. layer, while introducing nitrogen source to form zinc-nitrogen co-doping, which helps the whole zinc-nitrogen modified double-carbon catalytic material to exhibit higher ORR activity.

As a preferred solution, dimethylimidazole and zinc salt are dissolved in an alcohol solvent and reacted at a temperature of 20-40° C. for 8-16 h to obtain a metal framework ZIF-8. Under the optimal reaction conditions, a metal frame ZIF-8 with a uniform particle size and a particle size in the range of 200-300 nm and a regular dodecahedron morphology can be obtained. The metal frame ZIF-8 with this morphology is the most useful. As a raw material for zinc-nitrogen modified two-carbon catalytic materials. If the reaction temperature is not within the preferred range, the morphology of the obtained metal framework ZIF-8 is irregular spherical, and the size uniformity is poor. In addition, the type of zinc salt will also affect the morphology of the metal framework ZIF-8. The preferred zinc salt in the present invention is zinc nitrate, and the alcohol solvent used is methanol, ethanol and the like.

As a preferred solution, the molar ratio of dimethylimidazole and zinc salt is (0.5-1):1.

As a preferred solution, the conditions of the first heat treatment are: in an argon atmosphere, the temperature is raised to 700-1000°C at a heating rate of 3-5°C/min, and kept for 1-4 hours. Under the optimal heat treatment conditions, the high-temperature carbonization and partial graphitization of the metal framework ZIF-8 can be achieved to form a three-dimensional zinc-modified porous carbon material with regular morphology. Three-dimensional zinc-modified porous carbon materials in the framework. If the temperature condition of the heat treatment is too low, the carbonization will not be complete, and if the temperature is too high, the yield will be reduced.

As a preferred solution, the mass ratio of the zinc-modified porous carbon material to the carbohydrate compound and the nitrogen source compound is 1:(0.01-0.1):(0.5-1). Sugar compounds and nitrogen source compounds mainly form a uniform nitrogen-doped carbon coating layer on the surface of the carbon skeleton of the three-dimensional zinc-modified porous carbon material, so the ratio control of the three is more important. In the selected ratio range, the nitrogen source compound mainly controls the doping amount of nitrogen. As the nitrogen source compound increases from low to high, the nitrogen doping amount shows an increasing trend, but when the proportion of the nitrogen source compound increases to a certain amount, the nitrogen doping amount increases. Not much has changed. Sugar compounds are mainly used as carbon sources. If the ratio is too low, the carbon material will be unevenly coated on the surface of the carbon skeleton of the three-dimensional zinc-modified porous carbon material. The porous structure of the carbon material is blocked.

As a preferred solution, the carbohydrate compound is at least one of sucrose and fructose. The selected small-molecule carbohydrates are rich in polar groups, which can fully cover the surface of ZIF-8, form a 3D interconnected porous network structure, and can effectively protect the volatilization of zinc atoms.

As a preferred solution, the nitrogen source compound is at least one of cyanamide, dimethyl cyanamide and dibenzyl cyanamide.

As a preferred solution, the conditions of the second heat treatment are as follows: in an argon atmosphere, the temperature is first heated to 400-650°C at a heating rate of 3-5°C/min, maintained for 2-6 hours, and then heated to 3-5°C at a temperature of 3-5°C. /min heating rate to 900 ~ 1000 ℃, holding time 2 ~ 6h. The second heat treatment needs to be carried out in stages. The first stage of heating is carried out at a lower temperature. The main purpose is to achieve preliminary carbonization of sugar compounds, cover ZIF-8 and form a 3D interconnected network structure, and help reduce further The loss of Zn at high temperature, and the heating in the second stage makes part of the carbon in the double carbon structure graphitized to improve the electrical conductivity of the material. If the heat treatment temperature is too high, the metal zinc will volatilize, resulting in a decrease in the amount of zinc modification and a decrease in activity.

As a preferred solution, the conditions of the ball milling are as follows: the rotational speed is 200-240 r/min, and the time is 0.5-1.5 h.

In the technical scheme of the present invention, after the second heat treatment process, the heat treatment product undergoes conventional washing and drying treatment to obtain a zinc-nitrogen modified double-carbon catalytic material. Washing process, it is best to wash to neutral. The drying temperature used in the drying treatment is 50-80°C, and the time is 10-12h.

The present invention also provides a zinc-nitrogen modified double-carbon catalytic material obtained by the preparation method. The zinc-nitrogen modified double-carbon catalytic material has a 3D interconnected porous network structure, and the connection points of the network structure are irregular spherical structures. It can be seen from the morphology that the irregular spherical structures have a shell-core structure. The inner layer increases the degree of graphitized carbon due to the number of carbonizations, and the outer layer due to the volatilization of zinc atoms and the formation of a large number of active sites with nitrogen and carbon lead to the majority of defective carbons. This double carbon layer structure can significantly improve the ORR capability. Air electrodes of air batteries have high power density and specific capacity.

The invention also provides an application of a zinc-nitrogen modified double-carbon catalytic material, which is used as a cathode catalytic material for a zinc-air battery.

Relative to the prior art, the beneficial technical effects brought about by the technical solution of the present invention;

(1) The zinc-nitrogen modified double-carbon catalytic material of the present invention has the characteristics of developed pore structure, good electrical conductivity, and many active sites. As a negative electrode catalytic material for zinc-air batteries, it can significantly increase the onset potential and accelerate the kinetics. The reaction process improves ORR capacity.

(2) The zinc-nitrogen modified double-carbon catalytic material of the present invention has a double-carbon structure, which provides a carbon skeleton structure with ZIF-8 pyrolytic carbon, which is conducive to the formation of a 3D network double-carbon structure, and the degree of graphitization of ZIF-8 pyrolytic carbon Higher, endowed the composite with good electrical conductivity, while sugar compounds mainly modified the surface of the carbon skeleton structure, providing a defect-rich, highly active carbon modification layer, endowed with higher ORR catalytic activity.

(3) The zinc-nitrogen modified double-carbon catalytic material of the present invention uses ZIF-8 as a zinc source, the zinc is uniformly distributed in an ionic state, and the in-situ reduction and coordination zinc ions form atomic-level doping, so that the active site distribution is more uniform, It is more helpful to improve the catalytic activity.

(4) In the zinc-nitrogen modified two-carbon catalytic material of the present invention, the zinc-nitrogen doping amount can be effectively adjusted by adjusting the ratio, and the control of the reactive site can be controllably realized.

(5) The present invention uses carbohydrate compounds as carbon sources, which have wide sources and low prices, and can be well covered on the precursors during the process of heat treatment and converted into carbon materials to form a 3D interconnected network structure.

(6) The zinc-nitrogen modified double-carbon catalytic material prepared by the present invention is used as an air cathode catalytic material of a zinc-air battery, and the prepared zinc-air battery exhibits high power density and specific capacity.

Description of drawings

[Fig. 1] is a SEM image of the zinc-nitrogen modified double-carbon catalytic material prepared in Example 3 of the present invention.

[FIG. 2] is the XPS diagram of the zinc-nitrogen modified double-carbon catalytic material prepared in Example 3 of the present invention.

Detailed ways

The content of the present invention will be further described below in conjunction with the embodiments, without limiting the protection scope of the present invention.

Example 1

Zinc nitrate hexahydrate (1.0g) and dimethylimidazole (0.7g) were dissolved in 50mL of methanol respectively, the dissolved dimethylimidazole was poured into zinc nitrate hexahydrate, and after stirring for 5 minutes, there was a white suspension appeared, moved to 30°C for 12 h, centrifuged and washed to obtain ZIF-8. The prepared ZIF-8 was placed in a quartz boat, placed in a tube furnace, filled with argon gas, heated to 900 °C at a heating rate of 5 °C min ^-1 , kept at 900 °C for 2 hours, and finally cooled naturally. At room temperature, a black solid powder was obtained; the powder (1g) was mixed with cyanamide (0.7g) and sucrose (0.05g), and the ball milling speed was 240r min ^-1 , and the ball milling time was 0.5h. The mixed sample was placed in a quartz The boat was placed in a tube furnace, argon gas was introduced, the temperature was raised to 500°C at a heating rate of 5°C min ^-1 for annealing, and the temperature was kept at 500°C for 5 hours, and then the temperature was raised to 1000 at a heating rate of 5°C min ^-1 . annealed at 1000°C for 5h, and finally cooled to room temperature naturally, washed with deionized water until neutral, and finally dried at 100°C for 12h to obtain a zinc-nitrogen modified double-carbon catalytic material.

The obtained zinc-nitrogen modified double-carbon material catalyst is used as an air cathode to assemble a zinc-air battery. The electrolyte is 6mol L ^{- 1} KOH, and its maximum power density can reach 286.3mW cm ^-2 .

Example 2

Zinc nitrate hexahydrate (1.0g) and dimethylimidazole (0.5g) were dissolved in 50mL of methanol respectively, the dissolved dimethylimidazole was poured into zinc nitrate hexahydrate, and after stirring for 5 minutes, there was a white suspension appeared, moved to 40°C for 12 h, centrifuged and washed to obtain ZIF-8. The prepared ZIF-8 was placed in a quartz boat, placed in a tube furnace, filled with argon gas, heated to 700 °C at a heating rate of 3 °C min ^-1 , kept at 700 °C for 1 h, and finally cooled naturally. At room temperature, a black solid powder was obtained; the powder (1g) was mixed with dibenzylcyanamide (0.5g) and fructose (0.03g), and the ball milling speed was 220r min ^-1 , and the ball milling time was 1h. In a quartz boat, placed in a tube furnace, heated to 400°C at a heating rate of 3°C min ^-1 for annealing, kept at 400°C for 5 hours, and then heated to 950°C at a heating rate of 3°C min ^-1 for annealing , and kept at 950 °C for 5 h, and finally cooled to room temperature naturally, washed with deionized water until neutral, and finally dried at 100 °C for 12 h to obtain a zinc-nitrogen modified double-carbon catalytic material.

The obtained zinc-nitrogen modified double-carbon material catalyst is used as an air cathode to assemble a zinc-air battery. The electrolyte is 6mol L ^{- 1} KOH, and its maximum power density can reach 277.5mW cm ^-2 .

Example 3

Zinc nitrate hexahydrate (1.0g) and dimethylimidazole (0.9g) were dissolved in 50mL of methanol respectively, the dissolved dimethylimidazole was poured into zinc nitrate hexahydrate, and after stirring for 5 minutes, there was a white suspension appeared, moved to 20°C for 12 h, centrifuged and washed to obtain ZIF-8. The prepared ZIF-8 was placed in a quartz boat, placed in a tube furnace, filled with argon gas, heated to 800 °C at a heating rate of 4 °C min ^-1 , kept at 800 °C for 3 hours, and finally cooled naturally. Upon reaching room temperature, a black solid powder was obtained; this powder (1 g) was mixed with dimethylcyanamide. (1g) and glucose (0.08g), the ball milling mixing speed was 220r min ^-1 , the ball milling time was 1h, the mixed sample was placed in a quartz boat, placed in a tube furnace, and the heating rate was 4 ℃ min ^-1 Heat up to 650°C for annealing, keep at 650°C for 3h, then heat up to 900°C at a heating rate of 4°C min ^-1 for annealing, keep at 900°C for 2h, and finally cool to room temperature naturally, wash with deionized water to Neutral, and finally dried at 100 °C for 12 h to obtain a zinc-nitrogen modified double-carbon catalytic material. It can be seen from the SEM in Figure 1 that the zinc-nitrogen modified double-carbon catalytic material has a 3D interconnected porous network structure. It can be seen from the XPS in Figure 2 that zinc and nitrogen elements are co-modified. It can be seen from charging and discharging that the zinc-nitrogen modified double-carbon catalytic material has a 3D interconnected porous network structure. The material is used as the air electrode of the zinc-air battery, and it has excellent cycle life.

The obtained zinc-nitrogen modified double-carbon material catalyst was used as an air cathode to assemble a zinc-air battery. The electrolyte was 6mol L ^{- 1} KOH, and the maximum power density was up to 326.1mW cm ^-2 , and the constant current discharge lasted for 1500min.

Comparative Example 1

Zinc nitrate hexahydrate (1.0g) and dimethylimidazole (0.9g) were dissolved in 50mL of methanol respectively, the dissolved dimethylimidazole was poured into zinc nitrate hexahydrate, and after stirring for 5 minutes, there was a white suspension appeared, moved to 20°C for 12 h, centrifuged and washed to obtain ZIF-8. The prepared ZIF-8 was placed in a quartz boat, placed in a tube furnace, filled with argon gas, heated to 800 °C at a heating rate of 4 °C min ^-1 , kept at 800 °C for 3 hours, and finally cooled naturally. When the temperature reaches room temperature, a black solid powder is obtained; the powder (1 g) is directly placed in a quartz boat, placed in a tube furnace, heated to 650°C at a heating rate of 4°C min ^-1 for annealing, and kept at 650°C for 3 hours. , then the temperature was raised to 900°C at a heating rate of 4°C min ^-1 for annealing, and kept at 900°C for 2 hours, and finally cooled to room temperature naturally, washed with deionized water until neutral, and finally dried at 100°C for 12 hours to obtain the control Zinc-modified carbon catalytic materials.

In the control experiment, since no sugar compounds and nitrogen source compounds were added, a zinc-modified carbon catalytic material was obtained. It was also used as an air cathode to assemble a zinc-air battery. The electrolyte was 6mol L ^-1 KOH, and the maximum power density was tested. Up to 256.7mW cm ^-2 , the constant current discharge can last for 300min.

Claims (8)

1. a preparation method of zinc-nitrogen modified double-carbon catalytic material, is characterized in that: comprise the following steps: 1) Synthesize metal framework ZIF-8 with dimethylimidazole and zinc salt as raw materials; 2) The metal frame ZIF-8 is subjected to the first heat treatment under a protective atmosphere to obtain a zinc-modified porous carbon material; 3) After mixing the zinc-modified porous carbon material with sugar compounds and nitrogen source compounds by ball milling, a second heat treatment is performed under a protective atmosphere to obtain a zinc-nitrogen modified double-carbon catalytic material; the zinc-modified porous carbon material and the sugar compound are obtained The mass ratio of the nitrogen source compound is 1:(0.01-0.1):(0.5-1); the nitrogen source compound is at least one of cyanamide, dimethyl cyanamide and dibenzyl cyanamide. 2. The preparation method of a zinc-nitrogen modified double-carbon catalytic material according to claim 1, wherein the dimethylimidazole and the zinc salt are dissolved in an alcohol solvent, and reacted at a temperature of 20 to 40 ° C for 8 to 16 hours, get the metal frame ZIF-8. 3 . The method for preparing a zinc-nitrogen modified double-carbon catalytic material according to claim 2 , wherein the molar ratio of dimethylimidazole and zinc salt is (0.5～1):1. 4 . 4 . The method for preparing a zinc-nitrogen modified double-carbon catalytic material according to claim 1 , wherein the condition for the first heat treatment is: in an argon atmosphere, the temperature is increased at a temperature of 3 to 5° C./min. 5 . The rate of heating was raised to 700-1000°C, and the temperature was kept for 1-4h. 5 . The method for preparing a zinc-nitrogen modified two-carbon catalytic material according to claim 1 , wherein the carbohydrate compound is at least one of sucrose and fructose. 6 . 6 . The method for preparing a zinc-nitrogen modified double-carbon catalytic material according to claim 1 , wherein the conditions for the second heat treatment are: under an argon atmosphere, firstly at a temperature of 3 to 5° C./min. 7 . The heating rate is increased to 400-650 °C, and the temperature is maintained for 2-6 h, and then the temperature is increased to 900-1000 °C at a heating rate of 3-5 °C/min, and the holding time is 2-6 h. 7 . A zinc-nitrogen modified double-carbon catalytic material, characterized in that: it is obtained by the preparation method according to any one of claims 1 to 6 . 8. The application of a zinc-nitrogen modified double-carbon catalytic material according to claim 7, characterized in that it is used as a cathode catalytic material for a zinc-air battery.

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