Cobalt-copper bimetallic catalyst and preparation method and application thereof

Abstract

The invention relates to the technical field of ORR catalyst preparation, in particular to a cobalt-copper bimetallic catalyst and a preparation method and application thereof. The invention provides a preparation method of a cobalt-copper bimetallic catalyst, which comprises the following steps: dispersing 1, 2, 4-triazole in methanol under a heating condition, then adding a cobalt salt solution and a copper salt solution, and stirring for reaction to obtain the cobalt-copper bimetallic catalyst. The cobalt-copper bimetallic catalyst is a high-performance and stable pyrolysis-free ORR / OER electrocatalyst; when the material is used as a cathode catalyst material of high-efficiency ZABs, high-quality ZABs can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of ORR catalyst preparation, and particularly relates to a cobalt-copper bimetallic catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] As one of the most representative energy devices, rechargeable zinc-air batteries (ZABs) have attracted wide attention due to their high energy density, high safety, environmental friendliness, low cost, etc. However, the redox reactions occurring on the air cathode, such as the oxygen evolution reaction (OER) during charging and the oxygen reduction reaction (ORR) during discharging, have slow reaction kinetics, which limits the large-scale development of ZABs. Pt-based materials and Ru / Ir-based oxide catalysts are currently the most efficient electrocatalysts. However, due to their scarcity, poor durability, and high cost, their development is also restricted. Therefore, developing OER / ORR electrocatalysts with high cost performance and good stability is of great significance for promoting the large-scale development of ZABs.

[0003] Compared with single metals, the electronic synergy effect of bimetals can effectively reduce the reaction energy barrier and improve the catalytic activity. Among the transition metals commonly used in non-precious metal electrocatalysts, 3d transition metals represented by cobalt, nickel, iron, and manganese have attracted much attention due to their excellent redox ability, large reserves, and low cost. Among them, Co-based catalysts have attracted attention due to their rich valence states, high OER activity, high chemical stability, and abundant cobalt resources. By introducing Cu ions, the surface charge redistribution of the catalytic center synergistically overcomes the deficiency of inherent activity and further enriches the active sites. Existing theoretical calculations have shown that among non-precious metals, Cu-based catalysts have special ORR activity because they are near Pt at the top of the volcano plot. The binding between Cu and oxygen molecules is beneficial to adjusting the electronic configuration and reducing the reaction energy barrier of the Co-Nx center, thereby reducing the overpotential of redox. The team of Yuqiao Wang (Li L, Jiang D, Cai S, et al. N-Doped Carbon-Supported CoCu-Layered Double Hydroxide Nanosheets as Antibacterial Oxygen Reduction Catalysts for Microbial Fuel Cells[J]. ACS Applied Energy Materials, 2024,7(7):2854-2861.) synthesized N-doped carbon-supported double hydroxide nanosheets (CoCu-LDH@NC) derived from zeolite-based imidazole ZIF frameworks as a bifunctional cathode catalyst. CoCu-LDH loaded on CoO@NC induces the formation of carbon nanotubes CNTs in the NC matrix. By incorporating CoCu-LDH nanosheets, not only the catalytic activity and stability of CoO@NC are maintained, but also the electronic interaction between CoCu-LDH and CoO@NC enhances the catalytic activity of ORR. However, the performance improvement is limited, and further improvement is still needed to obtain higher-quality ZABs. Summary of the Invention

[0004] The present invention provides a cobalt-copper bimetallic catalyst, a preparation method thereof, and an application thereof. The cobalt-copper bimetallic catalyst is a high-performance and stable non-pyrolytic ORR / OER electrocatalyst; when used as a cathode catalyst material for high-performance ZABs, high-quality ZABs can be obtained.

[0005] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a preparation method of a cobalt-copper bimetallic catalyst, including: dispersing 1,2,4-triazole in methanol under heating conditions, and then adding a cobalt salt solution and a copper salt solution, and reacting to obtain the cobalt-copper bimetallic catalyst.

[0006] In the present invention, highly active Co and Cu are selected as the dual-metal centers of the metal catalyst. By combining Co and Cu, an effect of 1 + 1 > 2 is achieved. During the stirring reaction process, a large number of Co-Nx and Cu-Nx active sites are generated, and the triazole skeleton of 1,2,4-triazole is used to fix the active sites, enabling the synthesized cobalt-copper dual-metal catalyst to have high catalytic activity. Among them, Co-Nx can improve the stability of the catalyst, while Cu-Nx can improve the catalytic performance of the catalyst. By combining these two types of active sites, a cobalt-copper dual-metal catalyst with both high catalytic activity and strong stability can be obtained. In addition, compared with a single metal, the current density and constant-current discharge capacity of the catalyst prepared from the dual metal are significantly higher than those of any single metal, proving the effect of 1 + 1 > 2.

[0007] The test results show that the structure of the cobalt-copper dual-metal catalyst is not damaged under high-temperature pyrolysis, ensuring excellent catalytic performance. The ORR / OER potential difference of the cobalt-copper dual-metal catalyst remains at 0.907 V. The zinc-air battery assembled from it has a high peak density, up to 268.35 mW·cm -2 ; and a high specific capacity, up to 759.96 mAh·g -1 , and the charge-discharge voltage platform is stable.

[0008] Preferably, the solvents in the cobalt salt solution and the copper salt solution are both methanol.

[0009] Preferably, the cobalt salt is at least one of cobalt nitrate, cobalt sulfate, cobalt chloride, and cobalt acetate, and the copper salt is at least one of copper nitrate, copper sulfate, and copper chloride.

[0010] Preferably, the cobalt salt is cobalt nitrate and the copper salt is copper nitrate.

[0011] Preferably, the molar ratio between cobalt in the cobalt salt and copper in the copper salt is (9~1):(1~9).

[0012] Preferably, the molar ratio between cobalt in the cobalt salt and copper in the copper salt is (6~4):(4~6).

[0013] Preferably, the heating condition is heating at 55~65 °C.

[0014] Preferably, the conditions for the stirring reaction are: reacting at 55~65 °C for 10~14 h under stirring conditions.

[0015] A cobalt-copper dual-metal catalyst, the cobalt-copper dual-metal catalyst has a hierarchical structure of micropores and mesopores, and the particle size of the cobalt-copper dual-metal catalyst is 50~200 nm.

[0016] Preferably, the specific surface area of the cobalt-copper bimetallic catalyst is 20~25 m 2 ·g -1 .

[0017] A cathode catalytic material for a zinc-air battery, comprising a cobalt-copper bimetallic catalyst.

[0018] A zinc-air battery uses the cathode catalytic material for a zinc-air battery to prepare a cathode.

[0019] Therefore, the present invention has the following beneficial effects: (1) The cobalt-copper bimetallic catalyst provided by the present invention has high catalytic activity and strong stability, and is a high-performance and stable non-pyrolytic ORR / OER electrocatalyst; when applied as a cathode catalyst material for high-efficiency ZABs, high-quality ZABs can be obtained.

[0020] (2) The present invention selects a specific nitrogen-containing ligand (1,2,4-triazole) as the framework material for fixing Co-Nx and Cu-Nx active sites, which can retain more active sites, and finally obtain a catalytic material with a larger ORR half-wave potential and a larger ZAB power density. Description of the Drawings

[0021] Figure 1 It is an SEM image, where a is Co-MTF, b is Cu-MTF, c is CoCu-BTF, and d is the elemental mapping distribution diagram of CoCu-BTF; Figure 2 It is a structural characterization diagram, where a is an XRD diagram and b is an N2 adsorption-desorption isotherm; Figure 3 It is an XPS diagram, where a is the full-spectrum diagram, b is the high-resolution XPS spectrum of N 1s, c is the high-resolution XPS spectrum of Co 2p, and d is the high-resolution XPS spectrum of Cu 2p; Figure 4 It is an electrochemical performance diagram, where a is the CV diagram in 0.1 M KOH saturated with O2, b is the LSV diagram of ORR, and c is the LSV diagram of OER; Figure 5 It is an electrochemical performance diagram, where a is the LSV potential difference diagram and b is the half-wave potential bar chart; Figure 6 It is an electrochemical performance diagram, where a is the Tafel diagram and b is the number of transferred electrons n and the H2O2 yield diagram; Figure 7 It is the electrochemical performance diagram of Co6Cu4-BTF, where a is the LSV diagram at different rotation speeds and b is the K-L diagram; Figure 8Electrochemical performance diagram of Co6Cu4-BTF, where a is the LSV before and after 5000 cycles, and b is the methanol resistance test; Figure 9 It is the ORR LSV curve of Comparative Example 5; Figure 10 It is the OER LSV curve of Comparative Example 5; Figure 11 It is the discharge polarization curve and power density curve of the ZAB prepared corresponding to Comparative Example 3; Figure 12 It is the ORR LSV curve of Comparative Example 6; Figure 13 It is the OER LSV curve of Comparative Example 6; Figure 14 It is the discharge polarization curve and power density curve of the ZAB prepared corresponding to Comparative Example 4; Figure 15 It is the performance test diagram of the zinc-air battery, where a is the diagram of the ZAB based on CoCu-BTF lighting the blue LED screen, b is the discharge polarization curve and power density curve of the ZAB based on CoCu-BTF and Pt / C+RuO2, c is the constant current discharge capacity curve at 5.026 mA·cm -2 under, d is the discharge curve of the ZAB based on CoCu-BTF and Pt / C+RuO2 at different current densities, and e is the long cycle stability test; Figure 16 It is Figure 15 The enlarged diagram of the long cycle stability test of Co6Cu4-BTF in e; Figure 17 It is Figure 15 The enlarged diagram of the long cycle stability test of Pt / C+RuO2 in e; Figure 18 It is the reaction mechanism diagram. Specific embodiments

[0022] The present invention will be further described below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following descriptions are usually only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0023] The raw materials in this part are as follows: Co(NO3)2·6H2O, Cu(NO3)2·xH2O, methanol, 1,2,4-triazole, benzimidazole, and benzotriazole were purchased from Aladdin Reagent Co., Ltd., with an analytical purity level; the Pt / C catalyst (20%) was purchased from Suzhou Sinero Technology Co., Ltd.; Nafion D520 (5%) was purchased from DuPont (China) Holding Co., Ltd.; RuO2 was purchased from Suzhou Shengnuoke Technology Co., Ltd.

[0024]

Example

[0025] It should be considered that the Co(NO3)2·6H2O and Cu(NO3)2·xH2O selected in this example are only one implementation scheme of the present invention. Other cobalt sulfates and cobalt chlorides similar to Co(NO3)2·6H2O can achieve similar effects to this example, and copper sulfates and copper chlorides similar to Cu(NO3)2·xH2O can achieve similar effects to this example. Multiple combinations of the above-mentioned cobalt salts or multiple combinations of copper salts can achieve similar effects to this example. The above schemes can all be regarded as the disclosed schemes of the present invention.

[0026] Example 2 This example is basically the same as Example 1, the difference is that: the dosage of Co(NO3)2·6H2O is 0.00125 mol, and the dosage of Cu(NO3)2·xH2O is 0.01125 mol, to obtain the product powder Co1Cu9-BTF.

[0027] Example 3 This example is basically the same as Example 1, the difference is that: the dosage of Co(NO3)2·6H2O is 0.0025 mol, and the dosage of Cu(NO3)2·xH2O is 0.01 mol, to obtain the product powder Co2Cu8-BTF.

[0028] Example 4 This example is basically the same as Example 1, except that: the dosage of Co(NO3)2·6H2O is 0.00375 mol, and the dosage of Cu(NO3)2·xH2O is 0.00875 mol, obtaining the product powder Co3Cu7-BTF.

[0029] Example 5 This example is basically the same as Example 1, except that: the dosage of Co(NO3)2·6H2O is 0.005 mol, and the dosage of Cu(NO3)2·xH2O is 0.0075 mol, obtaining the product powder Co4Cu6-BTF.

[0030] Example 6 This example is basically the same as Example 1, except that: the dosage of Co(NO3)2·6H2O is 0.0075 mol, and the dosage of Cu(NO3)2·xH2O is 0.005 mol, obtaining the product powder Co6Cu4-BTF.

[0031] Example 7 This example is basically the same as Example 1, except that: the dosage of Co(NO3)2·6H2O is 0.00875 mol, and the dosage of Cu(NO3)2·xH2O is 0.00375 mol, obtaining the product powder Co7Cu3-BTF.

[0032] Example 8 This example is basically the same as Example 1, except that: the dosage of Co(NO3)2·6H2O is 0.01 mol, and the dosage of Cu(NO3)2·xH2O is 0.0025 mol, obtaining the product powder Co8Cu2-BTF.

[0033] Example 9 This example is basically the same as Example 1, except that: the dosage of Co(NO3)2·6H2O is 0.01125 mol, and the dosage of Cu(NO3)2·xH2O is 0.00125 mol, obtaining the product powder Co9Cu1-BTF.

[0034] Comparative Example 1 This comparative example is basically the same as Example 1, except that: the addition of Co(NO3)2·6H2O is cancelled, obtaining the product powder Cu-MTF.

[0035] Comparative Example 2 This comparative example is basically the same as Example 1, except that: the addition of Cu(NO3)2·xH2O is cancelled, obtaining the product powder Co-MTF.

[0036] Comparative Example 3 This comparative example is basically the same as Example 5, except that 1,2,4-triazole is replaced with an equimolar amount of benzimidazole.

[0037] Comparative Example 4 This comparative example is basically the same as Example 5, except that 1,2,4-triazole is replaced with an equimolar amount of benzotriazole.

[0038] Comparative Example 5 This comparative example is basically the same as Example 6, except that 1,2,4-triazole is replaced with an equimolar amount of benzimidazole.

[0039] Comparative Example 6 This comparative example is basically the same as Example 6, except that 1,2,4-triazole is replaced with an equimolar amount of benzotriazole.

[0040]

Performance Test

[0041] The crystal structures of the electrocatalysts were characterized by X-ray diffraction (XRD), and the results are as Figure 2 shown in a of. It can be observed that CoCu-BTF has similar diffraction peaks with Co-MTF and Cu-MTF at 13.6°, 16.8°, 25.8° and 34.3° respectively, indicating that CoCu-BTF has the same planes as Co-MTF and Cu-MTF, further confirming the successful composite of CoCu-BTF.

[0042] Furthermore, the specific surface areas of the three MTFs were tested by N2 adsorption / desorption isotherms. As Figure 2 shown in b of, the adsorption / desorption isotherms of the three catalysts are all typical type-IV isotherms, indicating that the sample materials have a particle packing structure dominated by mesopores and are embedded with abundant micropores and mesopores. Among them, Co-MTF has the largest specific surface area, which is 38.0524 m 2 ·g -1 ; followed by CoCu-BTF, which is 22.4623 m 2·g -1 ; The specific surface area of Cu-MTF is the smallest, which is 9.4222 m 2 ·g -1 . The pore size distribution curve shows that Co-MTF, Cu-MTF and CoCu-BTF have abundant micropores and mesopores. These porous structures can provide abundant active sites to promote the diffusion of O2 and further improve the catalytic mass transfer efficiency.

[0043] X-ray photoelectron spectroscopy (XPS) analysis reveals the chemical composition and state of Co-MTF, Cu-MTF and CoCu-BTF. As can be seen from Figure 3 a, Co-MTF is mainly composed of Co, C, N and O elements, Cu-MTF is mainly composed of Cu, C, N and O elements, and CoCu-BTF is mainly composed of Co, Cu, C, N and O elements. The single-metal catalysts only show their respective metal peaks, while CoCu-BTF shows both Co and Cu peaks at the same time, further corroborating the successful composite of CoCu-BTF. Figure 3 b in 3- is the high-resolution XPS spectrum of N 1s. It can be seen that the spectra of the three catalysts are all split into four kinds of N, namely Metal-N, pyrrole N, -NH2 and NO 3- . Among them, pyrrole N and -NH2 are brought by the triazole structure. Pyrrole N has been proven to have good catalytic performance for oxygen reduction, and NO Figure 3 in Figure 3 d shows that the Co 2p spectrum can be decomposed into Co 2p 3 / 2 and Co 2p 1 / 2 . Among them, the peaks at 779.45 eV and 779.35 eV belong to Co, and the peaks at 779.75 eV and 780.85 eV belong to Co 2+ . Compared with Co-MTF, the Co 2p of CoCu-MTF shifts to a higher binding energy, indicating that CoCu-BTF is in an electron-deficient state. Generally, the Co-N x interaction is considered to be the active site promoting ORR. Comparing the relative contents of Co-N x in Co-MTF and CoCu-BTF shows that the introduction of Cu can effectively regulate the proportion of the Co-N x active center. From the spectrum of Cu 2p, it can be seen that there are two forms of Cu in the material + and Cu 2+ , Cu 2+is considered to be the active site for ORR and OER. The characteristic peaks of Cu-MTF at 934 eV and 953.8 eV correspond to Cu 2+ of Cu 2p 3 / 2 and Cu 2p 1 / 2 orbitals. The shoulder peaks at 931.7 eV and 951.5 eV confirm the presence of Cu + . For CoCu-BTF, the Cu 2+ of Cu 2p 3 / 2 and Cu 2p 1 / 2 orbitals are located at 933.65 eV and 953.55 eV respectively. The corresponding shoulder peaks of Cu + are located at 931.7 eV and 951.35 eV respectively. Compared with Cu-MTF, the Cu 2p spectrum shifts to lower binding energy, indicating that Cu-MTF is in an electron-rich state.

[0044] 2. Electrochemical Tests The test method in this part is as follows: It is carried out on a CHI760E electrochemical workstation. The oxygen-saturated 0.1 M potassium hydroxide solution is used as the electrolyte. The three-electrode setup: the counter electrode is a platinum (Pt) electrode, the working electrode is a glassy carbon electrode (GCE) coated with catalyst ink, and the reference electrode is a saturated calomel electrode (SCE). Weigh 5 mg of the sample powder and 5 mg of Ketjenblack C KB powder into a 1.5 mL sample tube, add 200 μL of deionized water, 750 μL of ethanol and 50 μL of 5% perfluorosulfonic acid (Nafion) mixed solution. Ultrasonically process the sample tube for 30 min to obtain a uniformly dispersed catalyst ink, and the catalyst concentration is 5 mg·mL -1 .

[0045] The cyclic voltammetry (CV) and linear sweep voltammetry (LSV) are used to detect the oxygen reduction performance of the catalyst. Under the condition of oxygen-saturated electrolyte, scan and activate at least 20 cycles at a scan rate of 100 mV·s -1 in the voltage range of 0 to 1.2 V vs. RHE until the scan curves basically coincide. Then use the rotating disk electrode device, adjust the rotation speed to 1600 rpm, and test the oxygen reduction polarization curve (ORR polarization curve) of the catalyst at a scan rate of 5 mV·s -1 in the voltage range of 0 to 1.2 V vs. RHE.

[0046] Oxygen evolution reaction (OER) polarization curve test information: Similarly, under the condition of oxygen-saturated electrolyte, first activate the electrode, and then at 100 mV·s -1The scanning speed is at least 20 cycles in the voltage range of 1 to 1.8 V vs. RHE, and then using a rotating disk electrode device, the rotation speed is adjusted to 1600 rpm, with a scanning speed of 5 mV·s -1 The oxygen evolution polarization curve (OER polarization curve) of the catalyst is tested in the voltage range of 1 to 1.8 V vs. RHE.

[0047] Repeat the potential cycle until a stable linear sweep voltammogram is obtained. Using a platinum ring electrode with the ring voltage set to 1.5 V (vs RHE), generate ORR polarization curves under the same test conditions, and these curves can be used to calculate the electron transfer number and hydrogen peroxide yield using equations (1) and (2).

[0048] (1) (2) In the above formula, n is the electron transfer number, number; HO 2 - is the peroxide yield, %; I d is the current of the glassy carbon disk, A; I r is the current of the platinum ring, A; N is the current collection efficiency of the RRDE platinum ring (N = 0.37).

[0049] The electrocatalytic stability evaluation adopts the constant current (IT) method for the oxygen reduction reaction. In an oxygen-saturated 0.1 M potassium hydroxide solution, a constant voltage of 0.8 V (vs RHE) is applied to the glassy carbon electrode loaded with the catalyst. Cyclic voltammogram curves with 5000 cycles and a scanning rate of 50 mV·s -1 are used to induce catalyst aging.

[0050] Methanol tolerance test: In an oxygen-saturated 0.1 M potassium hydroxide solution, first activate the electrode, and then through the constant current (IT) method, apply a constant voltage of 0.8 V (vs RHE), with a test time of 2000 s. At 800 s, quickly inject 1 M methanol solution into the electrolyte.

[0051] ① Influence of Co / Cu doping amount on CoCu-BTF series catalysts The oxygen reduction activity of CoCu-BTF series catalysts was tested. First, the oxygen reduction activity of CoCu-BTF series catalysts was measured by cyclic voltammetry (CV), and from Figure 4As can be seen from a in [reference], in a saturated 0.1 M potassium hydroxide solution filled with oxygen, it can be seen that the ORR activity of the CoCu-BTF series catalysts increases with the increase in the amount of Cu used. In addition, the oxygen reduction polarization curve LSV of the CoCu-BTF series catalysts at 1600 rpm in a saturated 0.1 M potassium hydroxide solution filled with oxygen was also measured by RDE; the results are as Figure 4 shown in b in [reference]: All the CoCu-BTF series catalysts have good ORR performance, and the half-wave potential (E 1 / 2 ) is above 0.7 V. The OER performance has an important impact on the charging performance of the battery. Figure 4 c in [reference] is the OER polarization LSV curve of the CoCu-BTF series catalysts. It can be seen that the overpotentials (η) of the CoCu-BTF series catalysts are similar. Among them, the Co8Cu2-BTF catalyst and the Co5Cu5-BTF catalyst have the best performance, and the overpotentials are 0.415 V and 0.433 V respectively. The Co7Cu3-BTF catalyst, the Co3Cu7-BTF catalyst, and the Cu-MTF catalyst all require an applied voltage of 1.673 V when the OER reaches 10 mA·cm -2 , but the limiting current of the Co7Cu3-BTF catalyst with a ratio of 7:3 is much higher than that of other catalysts.

[0052] To evaluate the activity performance of electrocatalysts, the potential difference between the voltage value required when the OER reaches 10 mA·cm -2 and the lower half-wave potential of the ORR can be used as an evaluation index. From the polarization curve in Figure 5 a in [reference], the E 1 / 2 of the ORR of the Co6Cu4-BTF catalyst and the voltage difference required when the OER reaches 10 mA·cm -2 is the smallest, only 0.907 V. From the half-wave potential histogram in Figure 5 b in [reference], it can be seen that with the increase in the molar amount of Cu, the ORR performance of the CoCu-BTF series catalysts is improved to a certain extent. This improvement may be due to the electronic modulation of the Co-N x catalytic center and the synergistic catalytic effect of Cu-N x , as well as the electronic interaction between organic frameworks, which accelerates the electron transfer efficiency during the ORR process. With the addition of Cu, the Co-N x active center rises, and the Co-N x interaction is considered to be the active site promoting the ORR.

[0053] From the perspective of reaction kinetics, as shown in Figure 6 a in [reference], the tafel slope of the Cu-BTF catalyst is the smallest, which is 68 mV·dec-1 , while the Co-MTF catalyst has the largest Tafel slope of 112 mV·dec -1 . The Tafel slopes of the CoCu-BTF series catalysts are between the two, similar to the half-wave potential rule. The Co6Cu4-BTF catalyst has a lower Tafel slope, indicating fast oxygen reduction reaction kinetics. The catalysts were further tested using RRDE. The results show that at 0.5 - 0.8 V, the number of transferred electrons n of the CoCu-BTF catalysts is between 3.85 and 3.94, as shown in b of Figure 6 . At the same time, the hydrogen peroxide H2O2 yield is less than 20%, further indicating that the reaction is a 4-electron (4e - ) oxygen reduction reaction. The number of transferred electrons n and the hydrogen peroxide H2O2 yield of the Co-MTF catalyst are similar to those of the CoCu-BTF catalyst, while the number of transferred electrons of the Cu-MTF catalyst is between 3.4 and 3.7, and the hydrogen peroxide H2O2 yield is higher than 20%.

[0054] Subsequently, to understand the ORR kinetics of the CoCu-BTF catalyst, the oxygen reduction polarization curves of the Co6Cu4-BTF catalyst were measured in the rotational speed range of 400 - 2025 rpm, as shown in a of Figure 7 . It can be seen that its limiting diffusion current density increases with the increase of rotational speed. According to the Kouteckey-Levich (K-L) equation, as shown in b of Figure 8 , showing good linearity and parallelism, the average number of transferred electrons (n) was calculated to be 3.12, indicating that the oxygen reduction reaction catalyzed by the Co6Cu4-BTF catalyst belongs to first-order reaction kinetics, and further corroborating the 4e - transfer pathway.

[0055] In addition to catalytic activity, the evaluation index of electrocatalysts is stability. Therefore, the stability of the CoCu-BTF series catalysts was also evaluated in this section. As shown in a of Figure 8 , it can be seen that the Co-MTF series catalysts have the best stability. After 5000 cycles, the half-wave potential only decreased by 0.002 V, while the stability of the Cu-MTF catalyst decreased by 0.032 V. This is also reflected in the CoCu-BTF series catalysts. As the Co ratio increases, the stability of the CoCu-BTF series catalysts increases accordingly. This rule is opposite to the performance. In terms of performance, Cu-N x dominates, while in terms of stability, Co-N x is more dominant.

[0056] At the same time, the catalysts were also tested for methanol tolerance, as shown in Figure 8As shown in b of [reference], when compared with the commercially available Pt / C+RuO2 catalyst, it can be seen that when 1 M methanol was added at 800 s, the current density of the CoCu-BTF catalyst did not change significantly, while the current density of the commercially available Pt / C+RuO2 catalyst decreased significantly, indicating that the CoCu-BTF catalyst still had good catalytic activity and excellent anti-methanol performance after the addition of methanol.

[0057] ② Influence of different ligands Figures 9 - 10 The electrochemical performance of the Co6Cu4-BTF catalyst prepared with benzimidazole as the ligand, its ORR half-wave potential ( Figure 9 ), and the voltage ( -2 ) required to reach 10 mA·cm Figure 10 for OER showed a significant decline compared to the ORR half-wave potential of the Co6Cu4-BTF catalyst prepared with 1,2,4-triazole as the ligand. The comparison of the electrochemical performance of Co6Cu4-BTF prepared with three different ligands is shown in Table 1 below. It can be observed that there are differences in the electrochemical performance of the catalysts prepared with nitrogen-containing ligands with similar structures, which may be due to the different formation and distribution of Co-Nx and Cu-Nx active sites in the synthesized catalysts caused by different ligands.

[0058] Table 1 Comparison of the performance of catalysts prepared with different ligands

[0059] 3. Zinc-air battery tests As Figure 15 shown in a of [reference], Co-MTF, Cu-MTF, Co4Cu6-BTF, the catalysts obtained in Comparative Example 3, and the catalysts obtained in Comparative Example 4 were assembled into a zinc-air battery (ZAB) to verify the actual application ability of the catalysts, and a zinc-air battery assembled with a commercial Pt / C+RuO2 mixture was selected for comparison. The self-assembled zinc-air battery used a zinc sheet as the negative electrode, carbon paper loaded with Co-MTF, Cu-MTF, Co4Cu6-BTF, the catalysts of Comparative Example 3 and Comparative Example 4 as the air electrode, and a mixed solution of 6 M KOH and 0.2 M Zn(OAc)2 as the electrolyte.

[0060] Figure 15 As shown in b of [reference], the polarization discharge curves of the ZABs assembled with Co-MTF, Cu-MTF, and Co4Cu6-BTF catalysts and Pt / C+RuO2 can be seen. When the Co / Cu ratio was 4:6, the maximum power density of the ZABs assembled with the CoCu-BTF catalyst was 268.35 mW·cm -2 , which was better than that of the ZABs assembled with Pt / C+RuO2 (214.65 mW·cm -2)。 Figure 11 and Figure 14 are the polarization discharge curves of ZABs under different ligands. The maximum power densities of ZABs prepared with three different ligands are compared in Table 2. It can be clearly seen that there are significant differences in the maximum power densities of ZABs under different ligands, which is consistent with the above electrochemical results, further proving that ligand selection has an important impact on the performance of the catalyst.

[0061] Table 2 Performance comparison table of ZABs prepared with different ligands

[0062] Under the constant current discharge condition of 5.026 mA·cm -2 , based on the mass loss of zinc, the specific capacity of ZABs is calculated. The results are shown as c in Figure 15 . Compared with the ZABs assembled with Pt / C+RuO2 (636.76 mAh·g -1 ), the Co6Cu4-BTF has a larger specific capacity of 759.96 mAh·g -1 .

[0063] Figure 15 d in Figure 15 shows the performance of ZABs under constant current discharge at different current densities. Under the round-trip current density, ZABs can exhibit a voltage similar to that before, indicating its good rate performance. -2 In e in Figure 15 , the cycle stability of ZABs is evaluated by constant current charge-discharge tests. Based on Co6Cu4-BTF, in the 290 h charge-discharge cycle measurement at 2.501 mA·cm -2 , the voltage efficiency of ZABs only decreases by 0.5%, indicating that CoCu-BTF has potential application value in zinc-air batteries.

Claims

1. A method for preparing a cobalt-copper bimetallic catalyst, characterized in that: include: Under heating conditions, 1,2,4-triazole is dispersed in methanol, and then a cobalt salt solution and a copper salt solution are added to react to obtain a cobalt-copper bimetallic catalyst; The molar ratio between the cobalt in the cobalt salt and the copper in the copper salt is (9-1): (1-9); The heating conditions are: heating at 55-65°C; The reaction conditions are: stirring at 55-65°C for 10-14 h.

2. The preparation method according to claim 1, characterized in that The solvent in the cobalt salt solution and the copper salt solution is methanol.

3. The preparation method according to claim 1, characterized in that: The cobalt salt is at least one of cobalt nitrate, cobalt sulfate and cobalt chloride, and the copper salt is at least one of copper nitrate, copper sulfate and copper chloride.

4. The cobalt-copper bimetallic catalyst prepared by the preparation method according to any one of claims 1 to 3, characterized in that: The cobalt-copper bimetallic catalyst has a hierarchical structure of micropores and mesopores, and the particle size of the cobalt-copper bimetallic catalyst is 50-200 nm.

5. The cobalt-copper bimetallic catalyst according to claim 4, characterized in that The specific surface area of ​​the cobalt-copper bimetallic catalyst is 20-25 m 2 ·g -1 .

6. A cathode catalytic material for a zinc-air battery, characterized in that: Comprising the cobalt-copper bimetallic catalyst as described in claim 4 or 5.

7. A zinc-air battery, characterized in that: The cathode is prepared by using the cathode catalytic material for zinc-air battery as claimed in claim 6.

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