Cobalt single-atom electrocatalyst with distorted octahedral coordination, its preparation method and application

Abstract

The present invention discloses a cobalt single-atom electrocatalyst with distorted octahedral coordination, its preparation method and application, belonging to the technical field of electrocatalytic chemistry. Using cobalt nitrate (Co(NO3)2) as the cobalt source, hydrogen fluoride as the fluorine source, and ammonia (NH3) as the nitrogen source, a cobalt single-atom electrocatalyst with distorted octahedral coordination was synthesized by a hydrothermal method and a chemical vapor deposition method (CVD). During the hydrothermal process, cobalt ions form negatively charged groups with fluoride ions and are embedded in the defect sites of graphene oxide, and then a unique distorted octahedral coordination structure is formed under high-temperature nitridation. This catalyst has excellent four-electron oxygen reduction electrocatalytic performance, with high catalytic activity, strong selectivity, stable performance, and the coordination environment of the active sites can be regulated.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical catalysis, and in particular relates to a distorted octahedral coordinated cobalt single atom electrocatalyst and a preparation method and application thereof. Background Art

[0002] Zinc-air batteries (ZABs) have a high theoretical energy density (1086 W h kg -1 ), ultra-long service life and green environmental protection, it has attracted widespread attention as a clean and sustainable energy device. However, the cathode oxygen reduction reaction (ORR) kinetics in ZABs is very slow, and expensive platinum is required as a catalyst to promote the reaction, which greatly increases the manufacturing cost and limits the large-scale application of ZABs. Therefore, it is particularly urgent to explore non-precious metal catalysts with excellent activity and durability to replace platinum catalysts. In recent years, single-atom catalysts (SACs) coordinated by metal-nitrogen-carbon (MNC, M=Fe, Co, Cu, Mn, Ni, etc.) have shown great potential due to their maximum atomic utilization and unique coordination environment. Among them, Fe-NC and Co-NC catalysts have always been the focus of attention. Although Fe-NC has high ORR performance, the active sites of the catalyst will be affected by the Fenton reaction (Fe 2+ +H 2 O 2 ) is destroyed, thus accelerating the detachment and agglomeration of the catalyst, which is detrimental to the long-term ORR activity and stability. 2 O 2 ) has a weak reactivity and does not participate in the Fenton reaction, and has become the most promising candidate catalyst to replace platinum catalysts. Therefore, designing efficient and highly selective cobalt single-atom catalysts has become an important and challenging task.

[0003] Adjusting the coordination structure of the active site is one of the most effective strategies to further optimize the ORR performance. Studies have shown that electrocatalysts with high coordination structures have appropriate adsorption strength and high selectivity for ORR intermediates, especially in the case of four-electron (4e - ) is considered to be the active site of ORR due to its unique electronic and geometric structure. However, the precise regulation of high-coordination structures faces great challenges because metal atoms easily form unstable low-coordination compounds during heat treatment. In addition, in traditional methods, non-metallic heteroatoms (F, S, P, B, etc.) tend to coordinate with carbon atoms rather than metal atoms, making the regulation of axial ligands difficult. Therefore, it is an urgent problem to select a simple and effective method to prepare transition metal single-atom catalysts with adjustable coordination environment of active sites. Summary of the Invention

[0004] In order to overcome the disadvantages of the above-mentioned prior art, the purpose of the present invention is to provide a cobalt single-atom electrocatalyst with distorted octahedral coordination, its preparation method and application, so as to solve the technical problem that the existing preparation methods are difficult to precisely control the coordination structure of metal atoms at the atomic level.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions to be realized:

[0006] The present invention discloses a preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination, including the following steps:

[0007] S1: Mix a cobalt source, a fluorine source and a graphene oxide suspension to obtain a precursor solution; perform a hydrothermal reaction on the precursor solution to obtain a reaction product;

[0008] S2: Dry the reaction product to obtain a columnar product; perform a high-temperature nitridation reaction on the columnar product by chemical vapor deposition to obtain a cobalt single-atom electrocatalyst with distorted octahedral coordination.

[0009] Further, in S1, the preparation method of the graphene oxide suspension is: disperse graphene oxide in deionized water and perform ultrasonic treatment for 4 - 8 h to obtain a graphene oxide suspension.

[0010] Further, the concentration of the graphene oxide suspension is 1 - 5 mg / mL.

[0011] Further, in S1, the cobalt source is cobalt nitrate hexahydrate; the fluorine source is hydrogen fluoride;

[0012] The percentage of cobalt metal in cobalt nitrate hexahydrate in the mass of graphene oxide in the graphene oxide suspension is 1 - 10%.

[0013] Further, the addition amount of hydrogen fluoride is such that the percentage of fluorine in hydrogen fluoride in the mass of graphene oxide in the graphene oxide suspension is 0 - 6%.

[0014] Further, in S1, the temperature of the hydrothermal reaction is 150 - 200 °C, and the time of the hydrothermal reaction is 10 - 20 h; mix cobalt nitrate hexahydrate, hydrogen fluoride and the graphene oxide suspension and perform ultrasonic treatment for 1 - 4 h to obtain a precursor solution.

[0015] Further, in S2, the drying treatment is freeze-drying treatment; the time of the freeze-drying treatment is 2 - 12 h.

[0016] Further, in S2, the process parameters of the high-temperature nitridation reaction by chemical vapor deposition are: in Ar and NH3 Perform a heating reaction under a mixed atmosphere, with the temperature ranging from 600 to 1000 °C, the reaction time being 1 to 3 h, the gas flow rate of Ar being 100 ± 50 sccm, and NH 3 The gas flow rate of is 50 ± 50 sccm.

[0017] The present invention also discloses a cobalt single-atom electrocatalyst with a distorted octahedral coordination prepared by the above preparation method.

[0018] The present invention also discloses the application of the above cobalt single-atom electrocatalyst with a distorted octahedral coordination. The cobalt single-atom electrocatalyst with a distorted octahedral coordination is used as a catalyst for the four-electron oxygen reduction reaction to generate water.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention discloses a preparation method of a cobalt single-atom electrocatalyst with a distorted octahedral coordination. Using graphene as a carrier, during the hydrothermal process, cobalt ions in the cobalt source and fluoride ions in the fluorine source form a negatively charged group and are embedded in the defect sites of graphene oxide. Subsequently, the coordination environment of the active sites is regulated by chemical vapor deposition (CVD) to synthesize a catalyst with a unique distorted octahedral coordination structure; during the preparation process, due to the rich defects in graphene oxide, a large number of anchoring sites are provided for the uniform dispersion of cobalt atoms, inhibiting the formation of low-activity metal clusters and particles, and forming a stable and well-dispersed high-coordination single-atom catalyst; moreover, during the hydrothermal process, cobalt metal ions and fluoride ions combine to form a precursor with a high-coordination configuration. Subsequently, during the high-temperature nitridation process, some fluorine elements are replaced by nitrogen elements to form a single-atom configuration with a distorted octahedral coordination; the synthesis process of the present invention is simple, the preparation cycle is short, and the precursor is cheap and easily available, having good application prospects; through the hydrothermal method and chemical vapor deposition (CVD), the geometric configuration and coordination environment of the single atoms are regulated, and a cobalt single-atom electrocatalyst with a distorted octahedral coordination is synthesized.

[0021] The present invention also discloses a cobalt single-atom electrocatalyst with a distorted octahedral coordination prepared by the above method, which has excellent oxygen reduction electrochemistry performance, and the coordination environment of the active sites can be regulated. It has high activity, strong selectivity, and stable performance, superior to commercial Pt / C and most other reported electrocatalysts.

[0022] The present invention also discloses the application of the cobalt single-atom electrocatalyst with a distorted octahedral coordination as a catalyst for the four-electron oxygen reduction reaction to generate water. As the cathode catalyst of a zinc-air battery, this catalyst exhibits excellent power density and cycle stability, having broad application prospects. Brief Description of the Drawings

[0023] Figure 1 XRD pattern of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1;

[0024] Figure 2 Raman spectrum of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1;

[0025] Figure 3 Infrared spectrum of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1;

[0026] Figure 4 XRD pattern of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 4;

[0027] Figure 5 Raman spectrum of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 5;

[0028] Figure 6 Infrared spectrum of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 5;

[0029] Figure 7 TEM image of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1;

[0030] where: a - 200 nm; b - 100 nm;

[0031] Figure 8 Schematic diagram of the elemental content of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1;

[0032] Figure 9 XPS fine structure peak deconvolution of N 1s and Co 2p of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1 and Example 5;

[0033] where: a - N 1s; b - Co 2p;

[0034] Figure 10 Performance schematic diagram of the 4e – ORR of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1 on the RDE device;

[0035] where: a - polarization curve; b - corresponding Koutecky-Levich (K-L) plot;

[0036] Figure 11 4e of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1 of the present invention under the RRDE device – ORR performance graph;

[0037] Wherein: a - Tafel slope graph; b - stability curve;

[0038] Figure 12 It is the discharge polarization curve and power density graph of the cobalt single - atom electrocatalyst with distorted octahedral coordination prepared in Example 1 under a zinc - air battery device. Detailed implementation manners

[0039] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art regarding the present invention. In case of conflicts, the definitions in this specification shall prevail.

[0040] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall in no way limit the scope of the present invention, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0041] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub - ranges and individual numerical values within the range (including integers and fractions).

[0042] In this article, unless otherwise specified, terms such as "comprising", "including", "containing", "having", or similar expressions cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0043] In this article, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as falling within the scope described in this specification.

[0044] The following further elaborates the present invention in combination with specific examples. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0045] Conventional instruments and equipment in the art are used in the following examples. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples. Unless otherwise specified, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0046] Graphene oxide in the following examples was prepared by the improved Hummers method. The specific preparation process is as follows: Under an ice-water bath at 0 °C, 3.0 g of graphite powder was dispersed in a mixed solution with a volume ratio of 9:1 of concentrated H 2 SO 4 / H 3 PO 4 (360:40 mL), and 18 g of KMnO 4 was slowly added while continuously mechanically stirring to oxidize the graphite powder and slowly release heat. Subsequently, the water bath temperature was raised to 50 °C and the reaction was maintained for 12 h; after the solution was cooled to room temperature, it was poured into 400 mL of pre-prepared crushed ice cubes, continuously stirred until completely dissolved, and then an appropriate amount of H 2 O 2 (30%) was slowly added to remove the excess KMnO 4 in the solution until the solution showed a bright yellow color; subsequently, through centrifugal separation, it was repeatedly washed with a 30% hydrochloric acid solution by mass concentration, deionized water, and ether, and vacuum dried for more than 24 h to obtain graphene oxide.

[0047] Example 1

[0048] A preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination includes the following steps:

[0049] S1: Disperse 0.16 g of graphene oxide in 80 mL of deionized water and ultrasonicate for 6 h to obtain a graphene oxide suspension;

[0050] Accurately transfer 6 mL of cobalt nitrate hexahydrate and 30 μL of hydrogen fluoride into the obtained graphene oxide suspension. The mass percentages of cobalt and fluorine in the graphene oxide are 6% and 2.0% respectively, and ultrasonicate for 2 h to obtain a uniformly dispersed precursor solution;

[0051] Transfer the precursor solution to a hydrothermal autoclave and carry out a hydrothermal reaction. The temperature of the hydrothermal reaction is 180 °C and the time of the hydrothermal reaction is 12 h. After the reaction ends, a reaction product is obtained;

[0052] S2: Place the obtained reaction product in a freeze dryer for vacuum freeze-drying treatment for 12 h to obtain a black columnar product; place the black columnar product at the center of a tubular furnace and carry out a high-temperature nitridation reaction by chemical vapor deposition. The process parameters of the chemical vapor deposition method are as follows: the furnace temperature is 800 °C, the reaction time is 2 h, and the gas flow rates are Ar: 100 sccm and NH 3 : 50 sccm to obtain a cobalt single-atom electrocatalyst (CoFNC-2.0) with distorted octahedral coordination.

[0053] Example 2

[0054] A preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination includes the following steps:

[0055] S1: Disperse 0.16 g of graphene oxide in 80 mL of deionized water and ultrasonicate for 6 h to obtain a graphene oxide suspension;

[0056] Accurately pipette 6 mL of cobalt nitrate hexahydrate and 50 μL of hydrogen fluoride into the obtained graphene oxide suspension. The mass percentages of cobalt and fluorine in the graphene oxide are 6% and 3.3% respectively, and ultrasonicate for 2 h to obtain a uniformly dispersed precursor solution;

[0057] Transfer the precursor solution to a hydrothermal autoclave for hydrothermal reaction. The temperature of the hydrothermal reaction is 180 °C, and the time of the hydrothermal reaction is 12 h. After the reaction, a reaction product is obtained;

[0058] S2: Place the obtained reaction product in a freeze dryer for vacuum freeze-drying treatment for 12 h to obtain a black columnar product; place the black columnar product at the center of a tubular furnace and carry out a high-temperature nitridation reaction by chemical vapor deposition. The process parameters of the chemical vapor deposition method are as follows: the furnace temperature is 800 °C, the reaction time is 2 h, and the gas flow rates are Ar: 100 sccm and NH 3 : 50 sccm to obtain a cobalt single-atom electrocatalyst (CoFNC-3.3) with distorted octahedral coordination.

[0059] Example 3

[0060] A preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination includes the following steps:

[0061] S1: Disperse 0.16 g of graphene oxide in 80 mL of deionized water and ultrasonicate for 6 h to obtain a graphene oxide suspension;

[0062] Accurately pipette 6 mL of cobalt nitrate hexahydrate and 75 μL of hydrogen fluoride into the obtained graphene oxide suspension. The mass percentages of cobalt and fluorine in the graphene oxide are 6% and 5.0% respectively. Ultrasonic for 2 h to obtain a uniformly dispersed precursor solution;

[0063] Transfer the precursor solution to a hydrothermal reactor for hydrothermal reaction. The temperature of the hydrothermal reaction is 180 °C and the time is 12 h. After the reaction, the reaction product is obtained;

[0064] S2: Place the obtained reaction product in a freeze dryer for vacuum freeze-drying treatment for 12 h to obtain a black columnar product; Place the black columnar product in the center of a tubular furnace and carry out high-temperature nitridation reaction by chemical vapor deposition. The process parameters of the chemical vapor deposition method are: furnace temperature 800 °C, reaction time 2 h, gas flow rate Ar: 100 sccm, NH 3 : 50 sccm to obtain a cobalt single-atom electrocatalyst with distorted octahedral coordination (CoFNC-5.0).

[0065] Example 4

[0066] A preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination includes the following steps:

[0067] S1: Disperse 0.16 g of graphene oxide in 80 mL of deionized water and ultrasonic for 6 h to obtain a graphene oxide suspension;

[0068] Accurately pipette 6 mL of cobalt nitrate hexahydrate and 50 μL of hydrogen fluoride into the obtained graphene oxide suspension. The mass percentages of cobalt and fluorine in the graphene oxide are 6% and 3.3% respectively. Ultrasonic for 2 h to obtain a uniformly dispersed precursor solution;

[0069] Transfer the precursor solution to a hydrothermal reactor for hydrothermal reaction. The temperature of the hydrothermal reaction is 180 °C and the time is 12 h. After the reaction, the reaction product is obtained;

[0070] S2: Place the obtained reaction product in a freeze dryer for vacuum freeze-drying treatment for 12 h to obtain a black columnar product; Place the black columnar product in the center of a tubular furnace and carry out high-temperature nitridation reaction by chemical vapor deposition. The process parameters of the chemical vapor deposition method are: furnace temperature 800 °C, reaction time 2 h, gas flow rate Ar: 100 sccm, NH 3 : 50 sccm to obtain a cobalt single-atom electrocatalyst with distorted octahedral coordination (CoFNC-3.3).

[0071] Example 5

[0072] A preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination includes the following steps:

[0073] S1: Disperse 0.16 g of graphene oxide in 80 mL of deionized water and ultrasonicate for 6 h to obtain a graphene oxide suspension;

[0074] Accurately pipette 6 mL of cobalt nitrate hexahydrate into the obtained graphene oxide suspension. The mass percentages of cobalt and fluorine in the graphene oxide are 6% and 0% respectively. Ultrasonicate for 2 h to obtain a uniformly dispersed precursor solution;

[0075] Transfer the precursor solution to a hydrothermal autoclave and conduct a hydrothermal reaction. The temperature of the hydrothermal reaction is 180 °C and the time of the hydrothermal reaction is 12 h. After the reaction, a reaction product is obtained;

[0076] S2: Place the obtained reaction product in a freeze dryer for vacuum freeze-drying treatment for 12 h to obtain a black columnar product; Place the black columnar product in the center of a tube furnace and conduct a high-temperature nitridation reaction by chemical vapor deposition. The process parameters of the chemical vapor deposition method are: the furnace temperature is 800 °C, the reaction time is 2 h, and the gas flow rates are Ar: 100 sccm, NH 3 : 50 sccm to obtain a cobalt single-atom electrocatalyst (CoFNC) with distorted octahedral coordination.

[0077] Example 6

[0078] A preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination includes the following steps:

[0079] S1: Disperse 0.06 g of graphene oxide in 80 mL of deionized water and ultrasonicate for 4 h to obtain a graphene oxide suspension;

[0080] Accurately pipette 1 mL of cobalt nitrate hexahydrate and 80 μL of hydrogen fluoride into the obtained graphene oxide suspension. The mass percentages of cobalt and fluorine in the graphene oxide are 1% and 6.0% respectively. Ultrasonicate for 1 h to obtain a uniformly dispersed precursor solution;

[0081] Transfer the precursor solution to a hydrothermal autoclave and conduct a hydrothermal reaction. The temperature of the hydrothermal reaction is 150 °C and the time of the hydrothermal reaction is 10 h. After the reaction, a reaction product is obtained;

[0082] S2: Place the obtained reaction product in a freeze dryer for vacuum freeze-drying treatment for 2 h to obtain a black columnar product; place the black columnar product at the center of a tubular furnace and carry out a high-temperature nitridation reaction by chemical vapor deposition. The process parameters of the chemical vapor deposition method are as follows: the furnace temperature is 600 °C, the reaction time is 3 h, and the gas flow rate is Ar: 100 sccm, NH 3 : 50 sccm to obtain a cobalt single-atom electrocatalyst (CoFNC-6.0) with distorted octahedral coordination.

[0083] Example 7

[0084] A preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination, comprising the following steps:

[0085] S1: Disperse 0.5 g of graphene oxide in 100 mL of deionized water and ultrasonicate for 8 h to obtain a graphene oxide suspension;

[0086] Accurately pipette 10 mL of cobalt nitrate hexahydrate and 80 μL of hydrogen fluoride into the obtained graphene oxide suspension. The mass percentages of cobalt and fluorine in the graphene oxide mass are 10% and 6.0% respectively, and ultrasonicate for 4 h to obtain a uniformly dispersed precursor solution;

[0087] Transfer the precursor solution to a hydrothermal autoclave for hydrothermal reaction. The temperature of the hydrothermal reaction is 150 °C, and the time of the hydrothermal reaction is 10 h. After the reaction, a reaction product is obtained;

[0088] S2: Place the obtained reaction product in a freeze dryer for vacuum freeze-drying treatment for 8 h to obtain a black columnar product; place the black columnar product at the center of a tubular furnace and carry out a high-temperature nitridation reaction by chemical vapor deposition. The process parameters of the chemical vapor deposition method are as follows: the furnace temperature is 1000 °C, the reaction time is 1 h, and the gas flow rate is Ar: 100 sccm, NH 3 : 50 sccm to obtain a cobalt single-atom electrocatalyst (CoFNC-6.0) with distorted octahedral coordination.

[0089] Application Example 1

[0090] Using a cobalt single-atom electrocatalyst with distorted octahedral coordination as a catalyst in the reaction of generating water through the oxygen reduction reaction with a four-electron pathway by electrocatalysis: Electrochemical tests were carried out using a Pine Rotating Disk Electrode (RDE) and a Rotating Ring-Disk Electrode (RRDE; electrode model: AFE6R2) and a zinc-air battery (ZABs) in the United States, respectively. Among them, the rotation speed of the RDE was set between 225 and 2025 rpm; 2 mg of the catalyst was ultrasonically mixed with a mixture of 200 μL of ethanol, 200 μL of water, and 40 μL of 5% Nafion solution for 20 min, and 5 μL of the catalyst ink was drop-coated onto the disk electrode (the disk area of the RDE: 0.196 cm 2 or the disk area of the RRDE: 0.2376 cm 2 , and the platinum ring area was 0.2356 cm 2 ). After natural drying for at least 24 h, the test was carried out; the areal mass loading of the electrocatalyst was 0.12 mg cm -2 (RDE) or 0.10 mg cm -2 (RRDE); in an O 2 -saturated 0.1 M KOH electrolyte solution, a platinum wire was used as the counter electrode, an Ag / AgCl (saturated potassium chloride) electrode was used as the reference electrode, and an RDE or RRDE coated with a cobalt single-atom electrocatalyst with distorted octahedral coordination was used as the working electrode to form a three-electrode system; before the experiment, in a nitrogen-saturated or oxygen-saturated 0.10 M KOH aqueous solution, the electrode was activated by cyclic voltammetry (CV) with a scanning rate of 100 mV s -1 for 30 min; linear sweep voltammetry (LSV) was tested in an oxygen-saturated electrolyte of 0.2 - 1.1 V at different rotation speeds (225 - 1600 rpm) with a scanning rate of 5 mV s -1 . The zinc-air battery was assembled and tested in a self-made battery; 10 mg of the catalyst and 10 mg of carbon black were dispersed into a mixed solution of 100 μL of isopropanol, 100 μL of 5% Nafion, 50 μL of polytetrafluoroethylene (PTFE), and 1.9 mL of water, and after ultrasonic treatment for 4 h, a catalyst dispersion was obtained. Then, the obtained catalyst dispersion was dropped onto a 3.5×6 cm hydrophobic carbon paper as the cathode electrode, and the loading amount of the catalyst was 1.0 mg cm -2 (coating size: 1.5×1.5 cm). A 3.5×6 cm zinc plate with a thickness of 0.5 mm was polished, ultrasonically cleaned with alcohol and acetone for 20 min in sequence, and after the zinc plate was dried, it was used as the anode electrode, and a 6 M KOH aqueous solution containing 0.2 M ZnCl 2 was used as the electrolyte.

[0091] The cobalt single-atom electrocatalyst with distorted octahedral coordination can efficiently catalyze the generation of water from oxygen, with a half-wave potential of 0.91 V, and has good stability while maintaining low H 2 O 2 Faraday efficiency and productivity, demonstrating good 4e - ORR performance.

[0092] Figure 1 The XRD pattern of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1 is shown. There are only two diffraction peaks at around 25° and 44° in the figure, which belong to the (002) and (101) planes of graphite carbon, respectively. At the same time, no obvious diffraction peaks of metallic elements and their compounds are observed, indicating that cobalt is grafted onto the graphene framework in the form of single atoms or clusters.

[0093] Figure 2 The Raman spectrum of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1 is shown. The appearance of the D peak (1348 cm -1 ) is caused by disordered carbon atoms, and the appearance of the G peak is caused by the in-plane vibration of sp 2 carbon atoms; as can be seen from the figure, the D peak representing carbon atom defects is the strongest, indicating that the prepared graphene is defect-enriched; the intensity ratio of the D peak to the G peak (I D / I G ) is 1.14.

[0094] Figure 3 The infrared spectrum of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1 is shown. As can be seen from the figure, the cobalt single-atom electrocatalyst with distorted octahedral coordination has rich oxygen functional groups, and the vibration of metal cations at the octahedral position (~600 cm -1 ) also indicates that the catalyst has an octahedral coordination structure.

[0095] Figure 4 The XRD pattern of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 4 is shown, showing the diffraction of the (002) and (100) crystal planes of graphene. At the same time, obvious diffraction peaks of cobalt metal are also observed, confirming that nitrogen elements can fix Co atoms on the graphene surface.

[0096] Figure 5 The Raman spectrum of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 5 is shown. The D peak representing carbon atom defects is the strongest, indicating that the prepared graphene is defect-enriched. The intensity ratio of the D peak to the G peak (I D / I G ) is 1.12.

[0097] Figure 6The infrared spectrum of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 5 is shown, which also indicates that the catalyst has abundant oxygen-containing functional groups, but no peaks belonging to metal cations in the octahedral position appear.

[0098] As Figure 7 a and Figure 7 b shown, they are the low-magnification and high-magnification TEM images of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1, respectively, indicating that the prepared cobalt single-atom electrocatalyst with distorted octahedral coordination presents a curly appearance and a layered structure, with abundant wrinkles and corrugations. This morphology is beneficial for exposing more active sites and promoting the electrochemical reactions on the surface.

[0099] Figure 8 It is a schematic diagram of the element content of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1, where Co: 0.6, F: 0.2, C: 88, N: 3.9, O: 7.3, indicating that cobalt and nitrogen elements are successfully doped into graphene.

[0100] As Figure 9 a and Figure 9 b shown, they are the XPS fine structure deconvolution of N1s and Co 2p of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1, respectively. Among them Figure 9 a, the characteristic peaks near 398.0, 399.2, 400.3, and 401.3 eV can be seen and are attributed to pyridine nitrogen, Co-N, pyrrole nitrogen, and graphitic nitrogen respectively; among them, pyridine nitrogen and Co-N components are beneficial for the – ORR reaction to proceed. After doping with F element, the content of Co-N component in the catalyst increases significantly, indicating that F atoms around cobalt ions are replaced by N atoms during the nitridation process and a Co-N structure is formed; Figure 9 b is the Co 2p fine spectrum. The characteristic XPS peak of Co 2+ is located at 780.3 - 781.2 eV. After doping with F element, the characteristic peak of Co in the catalyst 2+ shifts 0.8 eV towards the lower binding energy direction, which may be due to the formation of more Co-N structures and Co 2+ obtaining electrons from N atoms.

[0101] As Figure 10 shown, it is the performance of the cobalt single-atom electrocatalyst with distorted octahedral coordination prepared in Example 1 in the 4e – ORR on the RDE device. Among them Figure 10 a and Figure 10 b are the polarization curve and the corresponding Koutecky-Levich (K-L) diagram in 0.1 KOH electrolyte respectively, where the catalyst has a high half-wave potential (E 1 / 2, 0.91 V), the limiting current density (J D , 5.6 mA cm -2 ), and the kinetic current density (J K At 0.85 V, 16 mA cm -2 ); Moreover, the number of electron transfers (n) was calculated from the K-L plot, and the n value of the catalyst was 4.00, indicating an ideal 4-electron transfer path.

[0102] As Figure 11 shown, it is the performance of the distorted octahedral coordinated cobalt single-atom electrocatalyst prepared in Example 1 for 4e – ORR on the RDE device, where Figure 11 a and Figure 11 b are the Tafel slope plot and stability curve in 0.1 KOH electrolyte respectively. The Tafel slope of the catalyst is 76 mV dec -1 , indicating that the catalyst has superior kinetics, and the catalyst can maintain high stability during continuous operation for up to 9 hours without obvious attenuation of the current density. The above performance indices all indicate that the cobalt single-atom electrocatalyst with distorted octahedral coordination has excellent 4e - ORR activity and stability.

[0103] As Figure 12 shown, it is the discharge polarization curve and power density map of the distorted octahedral coordinated cobalt single-atom electrocatalyst prepared in Example 1 in the zinc-air battery device. Using the above catalyst as the cathode catalyst of the zinc-air battery, a peak power density of 246 mW cm -2 can be provided, proving that the catalyst has the prospect of practical application while taking into account excellent catalytic activity and stable performance.

[0104] The above content is only to illustrate the technical idea of the present invention and cannot limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination, characterized in that, it includes the following steps: S1: Mix a cobalt source, a fluorine source and a graphene oxide suspension to obtain a precursor solution; Perform a hydrothermal reaction on the precursor solution to obtain a reaction product; S2: Dry the reaction product to obtain a columnar product; Perform a high-temperature nitridation reaction on the columnar product by chemical vapor deposition to obtain a cobalt single-atom electrocatalyst with distorted octahedral coordination; In S1, the cobalt source is cobalt nitrate hexahydrate; the fluorine source is hydrogen fluoride; The percentage of cobalt metal in cobalt nitrate hexahydrate in the mass of graphene oxide in the graphene oxide suspension is 1-10%; the temperature of the hydrothermal reaction is 150-200 °C, and the time of the hydrothermal reaction is 10-20 h; Mix cobalt nitrate hexahydrate, hydrogen fluoride and the graphene oxide suspension and perform ultrasonic treatment for 1-4 h to obtain a precursor solution; In S2, the process parameters for the high-temperature nitridation reaction by chemical vapor deposition are as follows: heating reaction is carried out under a mixed atmosphere of Ar and NH 3 , the temperature is 600 - 1000 °C, the reaction time is 1 - 3 h, the gas flow rate of Ar is 100 ± 50 sccm, and NH 3 's gas flow rate is 50 ± 50 sccm.

2. The preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination according to claim 1, characterized in that, In S1, the preparation method of the graphene oxide suspension is: Disperse graphene oxide in deionized water and perform ultrasonic treatment for 4-8 h to obtain a graphene oxide suspension.

3. The preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination according to claim 2, characterized in that, The concentration of the graphene oxide suspension is 1-5 mg / mL.

4. The preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination according to claim 1, characterized in that, The addition amount of hydrogen fluoride is such that the percentage of fluorine in hydrogen fluoride in the mass of graphene oxide in the graphene oxide suspension is 2%-6%.

5. The preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination according to claim 1, characterized in that, In S2, the drying treatment is freeze-drying treatment; the time of the freeze-drying treatment is 2-12 h.

6. A cobalt single-atom electrocatalyst with distorted octahedral coordination, characterized in that, The cobalt single-atom electrocatalyst with distorted octahedral coordination is prepared by using the preparation method of a cobalt single-atom electrocatalyst with distorted octahedral coordination described in any one of claims 1-5.

7. The application of the cobalt single-atom electrocatalyst with distorted octahedral coordination described in claim 6, characterized in that, The cobalt single-atom electrocatalyst with distorted octahedral coordination is used as a catalyst for the four-electron oxygen reduction reaction to generate water.

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