Preparation method for constructing Co-N-C catalytic material by adjusting Co electronic characteristics and application of Co-N-C catalytic material

Abstract

The invention belongs to the field of electrochemical energy storage, and relates to an efficient electrocatalyst for enhancing the performance of zinc air batteries (ZABs), in particular to a preparation method and application of a Co-N-C catalytic material constructed by adjusting the electronic characteristics of Co. According to the preparation method provided by the invention, sp hybrid nitrogen (sp-N) is introduced into a Co-N-C matrix, and an electronic structure of an electrocatalytic active site is regulated and controlled to accelerate reaction kinetics and improve conductivity, so that oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are remarkably enhanced. The catalyst shows efficient activity and excellent cycling stability, so that the catalyst shows excellent performance and stability in application of advanced zinc air batteries, and important technical support is provided for constructing an efficient and lasting electro-catalysis system.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical energy storage, relates to a high-efficiency electrocatalyst for enhancing the performance of zinc-air batteries (ZABs), and specifically relates to a preparation method and application of a Co-NC catalytic material constructed by adjusting the electronic properties of Co. Background Art

[0002] As an efficient energy storage and conversion system, ZABs have the potential for wide application in clean energy conversion and storage. However, their application is restricted by the resistance difference between the cathode and the anode and the complex electron transfer process of the oxygen reaction, which leads to a high overpotential. Therefore, the development of low-cost and efficient bifunctional catalysts has become the key to solving the bottleneck of ZABs application.

[0003] Co-NC is considered to be a highly active and stable catalytic material for zinc-air batteries. However, since the Co active unit is difficult to precisely control and often leads to severe aggregation, the ORR performance has the following disadvantages: (1) Irreversible aggregation greatly reduces the surface active sites, thereby limiting the activity; (2) The catalyst prepared by crude pyrolysis has a low specific surface area and poor pore structure, which hinders the reactants from entering the active center; (3) The weak manipulation of the distribution of active centers reduces the reproducibility of the catalyst. Therefore, the development of a Co-NC catalytic material with a high specific surface area, rich pore structure, and the ability to adjust the electronic properties of Co has become an urgent problem to be solved. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a preparation method for constructing Co-NC catalytic materials by regulating the electronic properties of Co. The method adopts the strategy of regulating the electronic structure through sp-N doping to significantly improve the performance of Co-N-GDY electrocatalyst in electrocatalytic ORR. In the proposed structure, the Co-N active site optimizes the local electron density of cobalt atoms through the combined action of sp-N and hydroxyl ligands, thereby increasing the adsorption energy of oxygen adsorption intermediates at the active site and accelerating the reaction kinetics. The electrocatalyst exhibits an excellent half-wave potential (0.85 V) during the electrocatalytic ORR process, and only requires an overpotential of 324 mV to reach 10 mA cm during the electrocatalytic OER process. -2 The current density of 2.5 Å / min further verifies its practical application potential in ZABs. In addition, the introduction of sp-N avoids structural defects and ensures high conductivity and stability, thus showing good electrochemical durability in long-term cycle tests. The preparation method is simple to operate and solves the problems of high cost and low reserves of noble metal catalysts in the prior art.

[0005] The present invention also provides the use of the Co-NC catalytic material in electrocatalytic oxygen reduction, oxygen evolution reaction, and ZABs.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: The present invention provides a method for preparing a Co-NC catalytic material by adjusting the electronic properties of Co, comprising the following steps: (1) adding graphyne to a PVP solution, stirring for 20-30 min, filtering and drying, and then heat-treating the graphyne to obtain modified graphyne; (2) Place modified graphyne and cobalt chloride at both ends of a container in a specific ratio, seal it, and introduce nitrogen for a certain period of time; (3) Turn off the nitrogen, introduce ammonia, perform segmented calcination, and collect the prepared powder after cooling to obtain Co-NC catalytic material.

[0007] Preferably, in step (1), the mass concentration of the PVP solution is 12-15%; and the stirring time is 20-30 min.

[0008] Preferably, in step (1), the heat treatment is carried out under vacuum conditions at 200-300° C. for 2-3 hours.

[0009] Preferably, in step (2), the mass ratio of graphyne to cobalt chloride is 10:1; the vessel is a corundum boat; the cobalt chloride is placed upstream of the corundum boat; and the time for introducing nitrogen is 20 min.

[0010] Preferably, in step (3), the conditions for the staged calcination are: in an ammonia atmosphere, firstly heating to 300°C at a heating rate of 5°C / min and keeping at that temperature for 1 hour; then heating to 800°C at a heating rate of 5°C / min and keeping at that temperature for 2-4 hours.

[0011] The present invention also provides a Co-NC catalytic material prepared by the above preparation method.

[0012] The present invention also provides application of the Co-NC catalytic material in the field of electrocatalysis.

[0013] The preparation method provided by the present invention accelerates the reaction kinetics and improves the conductivity by introducing sp hybridized nitrogen (sp-N) into the Co-NC matrix and regulating the electronic structure of the electrocatalytic active site, thereby significantly enhancing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The catalyst exhibits high activity and excellent cycle stability, which enables it to show excellent performance and stability in the application of advanced zinc-air batteries, providing important technical support for the construction of efficient and durable electrocatalytic systems.

[0014] The Co-NC catalytic material prepared by the present invention improves the adsorption energy of oxygen adsorption intermediates on the active site and accelerates the reaction kinetics due to the synergistic effect of sp-N and hydroxyl ligands on the electronic structure of cobalt atoms, thereby enhancing the ORR activity. In addition, the introduction of sp-N does not produce defects, thereby improving the performance of the catalyst without affecting the conductivity. The resulting enhancement of reaction kinetics and ORR activity is crucial to the improvement of ZABs performance, which is mainly reflected in the increase of battery power density and the stability of long-term operation. Therefore, the sp-N anchored cobalt-based electrocatalyst not only performs well in laboratory tests, but also shows great potential in practical applications. This achievement is of great significance to promoting the practical application and development of ZABs.

[0015] The beneficial effects of the present invention are: (1) The preparation method of the present invention is a cobalt-based electrocatalyst designed by sp-N doping strategy, which has significant electrocatalytic ORR and OER performance. This method adjusts the electronic structure of the active site by introducing sp-N, thereby optimizing the adsorption energy of oxygen adsorption intermediates and effectively accelerating the reaction kinetics. In addition, the coupling of sp-N doping and cobalt can reduce the local electron density, further improve the conductivity and electrochemical stability, and enable it to show excellent cycle stability and energy density in ZABs. Compared with commercial Pt / C+IrO 2 The catalyst exhibits a higher half-wave potential and a smaller overpotential, indicating its great application potential in energy storage as an efficient and stable non-precious metal catalyst.

[0016] (2) This type of Co-NC structure has a significant interfacial synergistic effect, which can adjust the local charge distribution, accelerate the electron transfer rate in the electrochemical reaction, and optimize the active sites in the redox process. In addition, this structure helps to alleviate the corrosion or degradation problems under high voltage and strong alkaline conditions, providing an important theoretical and experimental basis for the design of efficient and stable ZABs electrocatalysts. This study provides strong support and innovative ideas for the future design of low-cost, high-performance catalysts for electrochemical technologies such as ZABs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 ORR performance (a) and Tafel slope (b) graphs of Examples 1-3; Figure 2 OER performance (a) and Tafel slope (b) graphs of Examples 1-3; Figure 3 Example 1, Comparative Example 1, Comparative Example 2 and Commercial IrO 2 OER performance (a), Tafel slope (b), Example 1 and commercial IrO 2Stability curve comparison chart (c); Figure 4 Raman spectra of Example 1, Comparative Example 1 and Comparative Example 2; Figure 5 . Performance of zinc-air batteries (ZABs): a) Based on Example 1 and Pt / C+IrO 2 b) Open circuit voltage curves of ZABs at 100 mA cm -2 The total discharge capacity under . DETAILED DESCRIPTION

[0018] The exemplary embodiments disclosed in the present invention will be described in more detail below with reference to the accompanying drawings. These embodiments are intended to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art. Although the exemplary embodiments disclosed in the present invention are shown in the accompanying drawings, it should be understood that the present invention should not be limited by the embodiments described herein.

[0019] Example 1 (1) Adding graphyne to a 12 wt% PVP solution, stirring for 30 min, filtering and drying, heating the graphyne to 250 °C under vacuum conditions, and keeping the temperature for 2 h to obtain modified graphyne; (2) Weigh 20 mg of modified graphyne and 2.0 g of cobalt chloride and place them at both ends of a covered corundum boat, ensuring that the cobalt chloride is located at the upstream air inlet. After sealing the tube furnace, introduce nitrogen for 20 minutes to remove the air; (3) After nitrogen is introduced in step (2), the nitrogen is turned off and ammonia is introduced. In the ammonia atmosphere, the temperature is increased to 300°C at a heating rate of 5°C / min and kept at this temperature for 1 hour; then the temperature is increased to 800°C at a heating rate of 5°C / min and kept at this temperature for 3 hours. After natural cooling, the Co-N-GDY-3 sample is obtained.

[0020] Example 2 Steps (1) and (2) are the same as in Example 1; (3) After nitrogen is introduced in step (2), the nitrogen is turned off and ammonia is introduced. In the ammonia atmosphere, the temperature is increased to 300°C at a heating rate of 5°C / min and kept at this temperature for 1 hour; then the temperature is increased to 800°C at a heating rate of 5°C / min and kept at this temperature for 2 hours. After natural cooling, the Co-N-GDY-2 sample is obtained.

[0021] Example 3 Steps (1) and (2) are the same as in Example 1; (3) After nitrogen is introduced in step (2), the nitrogen is turned off and ammonia is introduced. In the ammonia atmosphere, the temperature is increased to 300°C at a heating rate of 5°C / min and kept at this temperature for 1 hour; then the temperature is increased to 800°C at a heating rate of 5°C / min and kept at this temperature for 4 hours. After natural cooling, the Co-N-GDY-4 sample is obtained.

[0022] Comparative Example 1 (1) Weigh 20 mg of graphyne and 2.0 g of cobalt chloride and place them at both ends of a covered corundum boat, making sure that the cobalt chloride is located at the upstream air inlet. After sealing the tube furnace, introduce nitrogen for 20 minutes to remove the air.

[0023] (2) After nitrogen is introduced in step (1), the nitrogen is turned off and ammonia is introduced. In the ammonia atmosphere, the sample is heated to 800°C at a rate of 5°C / min and maintained at this temperature for 3 hours. After natural cooling, a Co-NC sample is obtained.

[0024] Comparative Example 2 (1) Weigh 20 mg of carbon nanotubes and 2.0 g of cobalt chloride and place them at both ends of a covered corundum boat, making sure that the cobalt chloride is located at the upstream air inlet. After sealing the tube furnace, introduce nitrogen for 20 minutes to remove the air.

[0025] (2) After nitrogen is introduced in step (1), the nitrogen is turned off and ammonia is introduced. In the ammonia atmosphere, the sample is heated to 800°C at a rate of 5°C / min and maintained at this temperature for 3 hours. After natural cooling, a Co-N-CNT sample is obtained.

[0026] Effect Example The ORR and OER electrocatalytic performances of Examples 1, 2, and 3 and Comparative Examples 1 and 2 were tested by a three-electrode test system in 0.1 M KOH and 1 M KOH electrolyte solutions, respectively, using a Chenhua CHI760E electrochemical workstation.

[0027] (A) Linear scanning polarization curves of ORR of Examples 1-3 under 0.1 M KOH ( Figure 1 a) and Tafel slope curve ( Figure 1 b) It can be seen that Example 1 exhibits a higher half-wave potential, starting potential, limiting diffusion current density and a smaller Tafel slope, indicating that the electrochemical reaction kinetics of the electrocatalytic material deposited for 3 hours is faster, which means that the catalyst can reach the required current density at a lower overpotential, and also shows that the reaction rate can get a good response in different electrode potential ranges. In addition, the graphical results show that the rate-controlling step of the electrochemical reaction may be the rapid reaction of the electrochemical intermediate, indicating that the catalyst has good electrolyte transfer ability and intermediate stability. In summary, the deposition time has a significant effect on the catalytic performance of the material.

[0028] (ii) Linear scanning polarization curves of OER under 1 M KOH of Examples 1-3 ( Figure 2 a) It can be seen that Example 1 exhibits an overpotential of 324 mV at a current density of 10 mA cm⁻², which is significantly lower than that of Example 2 and Example 3. The Tafel slope ( Figure 2 b) It can be seen that Example 1 exhibits the most favorable Tafel slope of 86.5 mV dec -1 , which is lower than 94.2 mV dec in Example 2 -1 and 118.5 mV dec in Example 3 -1 . It shows that Example 1 exhibits excellent reaction kinetics in the OER process.

[0029] (III) Through Example 1, Comparative Examples 1, 2 and commercial IrO 2 Comparison of linear scan polarization curves of OER under 1 M KOH ( Figure 3 a) It can be seen that Example 1 can reach 10 mA cm at a lower overpotential. -2 At a current density of , it is significantly lower than that of Comparative Examples 1, 2 and commercial IrO 2 .pass Figure 3 b It can be seen that Example 1 exhibits the most favorable Tafel slope of 86.5 mV dec -1 , which is lower than 94.2 mV dec of Comparative Example 1 -1 and 185.2 mV dec of Comparative Example 2 -1 This finding indicates that the regulation of Co electrons by sp-N in Example 1 significantly improves its electrocatalytic OER performance. Moreover, after a cycle stability test (potential 1.55 V), it was found that the current density of Example 1 fluctuated very little within 50,000 seconds, showing a significant improvement over the commercial IrO 2 Better stability.

[0030] (IV) The intensity ratio of the D band and the G band in the Raman spectrum (I D / I G ) is often used as an indicator for evaluating the graphitization degree and disorder of carbon materials. By comparing the Raman spectra of Example 1, Comparative Example 1 and Comparative Example 2 ( Figure 4 ) It can be seen that the I of Example 1 D / I G The value is 1.20, which is significantly lower than 1.92 of Comparative Example 2 and 2.63 of Comparative Example 1. This indicates that Example 1 has a higher degree of graphitization and fewer defects, ultimately enhancing the electrochemical catalytic performance by improving stability and conductivity.

[0031] (V) In order to investigate the performance of zinc-air batteries, we used zinc foil as the anode, Example 1 or Pt / C+IrO 2 As the air cathode, a Zn-air battery was assembled in 6 M KOH electrolyte and its performance was tested. Figure 5 It can be seen that the ZABs assembled in Example 1 exhibit an open circuit voltage of about 1.54 V, which exceeds that of Pt / C+IrO 2 (1.46 V), which is close to the theoretical maximum value of ZABs, 1.65 V. In addition, Figure 5 b shows the -2 At a constant current density, the specific capacity of the ZABs using Example 1 is 660 mAh g -1 , exceeding the commercial Pt / C+IrO 2 642 mAhg of base battery -1 .

Claims

1. A method for preparing Co-NC catalytic materials by adjusting the electronic properties of Co, characterized in that: The following steps are involved: (1) adding graphyne to a PVP solution, stirring for 20-30 min, filtering and drying, and then heat-treating the graphyne to obtain modified graphyne; (2) Place modified graphyne and cobalt chloride at both ends of a container in a specific ratio, seal it, and introduce nitrogen for a certain period of time; (3) Turn off the nitrogen, introduce ammonia, perform segmented calcination, and collect the prepared powder after cooling to obtain Co-NC catalytic material.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass concentration of the PVP solution is 12-15%; and the stirring time is 20-30 minutes.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the heat treatment is carried out under vacuum conditions at 200-300°C for 2-3 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step (2), the mass ratio of graphyne to cobalt chloride is 10:1; the vessel is a corundum boat; the cobalt chloride is placed upstream of the corundum boat; and the time for introducing nitrogen is 20 min.

5. The method according to any one of claims 1 to 4, characterized in that: In step (3), the conditions for the staged calcination are: in an ammonia atmosphere, firstly, heating to 300°C at a heating rate of 5°C / min and keeping at that temperature for 1 hour; then, heating to 800°C at a heating rate of 5°C / min and keeping at that temperature for 2-4 hours.

6. A Co-NC catalytic material prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the Co-NC catalytic material according to claim 6 in the field of electrocatalysis.

Images