Oxygen electrode, preparation method and application thereof, and zinc-air flow battery

Abstract

The invention relates to an energy storage and battery technology, in particular to an oxygen electrode, a preparation method and application thereof and a zinc-air flow battery. The oxygen electrode comprises a gas diffusion layer and an integrated catalyst layer, wherein the integrated catalyst layer comprises layered foamed nickel and a Co3O4-Fe active material loaded on the layered foamed nickel. When the integrated catalyst layer is used for preparing the oxygen electrode, the performance of the oxygen electrode is improved, the discharge performance and the cycle stability of a flow battery, especially a zinc-air flow battery prepared by adopting the oxygen electrode are remarkably improved, and the flow battery has higher power application capability and has the characteristic of long-term stable use.

Description

Technical Field

[0001] The present invention relates to energy storage and battery technologies, and particularly to an oxygen electrode, a preparation method and application thereof, and a zinc-air flow battery. Background Art

[0002] In the field of energy storage and battery technologies, zinc-air flow batteries have been widely studied and applied. However, there are some problems and deficiencies in the prior art. First of all, the discharge performance of existing zinc-air flow batteries is relatively low, which limits their use in high-power applications. Secondly, the cycle stability of the battery needs to be improved, because with the increase in the number of uses, problems such as the loss of active substances and the deactivation of catalysts will gradually appear.

[0003] In the prior art, the coating method is generally used to coat the active material onto the gas diffusion layer to prepare the electrode. However, the traditional coating method has many disadvantages; on the first hand, the cost of powder coating equipment and raw materials is relatively high, making the cost of the whole preparation process relatively high; and the powder coating preparation speed is slow, and the production efficiency is relatively low. Usually, it is a preparation method suitable for small batches or laboratory scale, and it is difficult to be applied to large-scale industrial production; on the second hand, powder coating involves multiple steps, including powder preparation, coating, drying and sintering, etc. The preparation process is relatively complex and requires high technical requirements and operation skills; and parameters such as coating thickness and uniformity during the powder coating process are affected by various factors. Therefore, it is difficult to ensure the consistency and stability of electrodes in different batches, and even due to some uncontrollable factors during the preparation process, the surface quality of the powder-coated electrode is not good; on the third hand, during the powder coating process, a certain amount of powder waste is often generated, which not only increases the cost but also causes a certain degree of environmental pollution. In addition, some materials may not be suitable for preparing electrodes by powder coating, which limits the range of material selection. Preparing the electrode by integrated preparation can effectively improve the above problems and become a new direction for the preparation of flow battery electrodes. The low discharge performance and poor cycle stability of the zinc-air flow battery existing in the prior art limit the practical application of the battery, and there is an urgent need for further breakthroughs in improving the battery performance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems that the low discharge performance and poor cycle stability of the zinc-air flow battery existing in the prior art limit the practical application of the battery, and to provide an oxygen electrode, a preparation method and application thereof, and a zinc-air flow battery. The oxygen electrode includes an integrated catalytic layer, which significantly improves the discharge performance and cycle stability of the zinc-air flow battery, and meets the requirements of higher power demand and long-term stable use of the flow battery.

[0005] To achieve the above object, a first aspect of the present invention provides an oxygen electrode, which includes a gas diffusion layer and an integrated catalytic layer. The integrated catalytic layer includes layered nickel foam and Co3O4-Fe active material loaded on the layered nickel foam.

[0006] A second aspect of the present invention provides a method for preparing the oxygen electrode of the present invention. The method includes: hot pressing the gas diffusion layer and the integrated catalytic layer to obtain the oxygen electrode; the integrated catalytic layer includes layered nickel foam and Co3O4-Fe active material loaded on the layered nickel foam.

[0007] A third aspect of the present invention provides an application of the oxygen electrode of the present invention as a cathode in a flow battery.

[0008] A fourth aspect of the present invention provides a zinc-air flow battery, which includes an anode, a cathode, a diaphragm separating the anode and the cathode, and an electrolyte; the cathode is the oxygen electrode of the present invention.

[0009] Through the above technical solutions, the present invention prepares the oxygen electrode of the present invention with an integrated catalytic layer, improving the performance of the oxygen electrode. The discharge performance and cycle stability of the flow battery prepared with this oxygen electrode are significantly improved; the flow battery of the present invention has the ability to be applied at higher power and has the characteristics of long-term stable use.

[0010] At the same time, the preparation method of the oxygen electrode of the present invention is simple. Compared with the electrodes prepared by the prior art, it does not require the use of substances such as binders. In addition, the preparation method of the oxygen electrode of the present invention is particularly suitable for the preparation of large-size (for example, 50*30 cm 2 ) oxygen electrodes, and can improve the discharge performance and cycle stability of large-size flow batteries, providing feasibility for the large-scale application of flow batteries. Description of the Drawings

[0011] Figure 1 is a SEM image of the Co3O4-Fe catalyst prepared in Example 1 of the present invention; Figure 1a It is the SEM image of the catalyst at a scale of 100 μm, Figure 1b It is the SEM image of the catalyst at a scale of 1 μm;

[0012] Figure 2 It is the BET curve of the Co3O4-Fe catalyst prepared in Example 1 of the present invention;

[0013] Figure 3 It is the XPS spectrum of the Co3O4-Fe catalyst prepared in Example 1 of the present invention;

[0014] Figure 4 It is the power density diagram of the zinc-air flow battery prepared in Example 1 of the present invention;

[0015] Figure 5 It is a schematic diagram of the voltage comparison of the zinc-air flow battery prepared in Example 1 and Example 2 of the present invention;

[0016] Figure 6 It is the cycle stability diagram of the zinc-air flow battery prepared in Example 1 of the present invention;

[0017] Figure 7 It is the energy efficiency diagram of the zinc-air flow battery prepared in Example 1 of the present invention. Detailed implementation manners

[0018] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0019] In the present invention, the integrated catalytic layer refers to layered nickel foam and Co3O4-Fe active material supported on the layered nickel foam. Among them, the Co3O4-Fe active material forms an integrated catalytic layer by synthesis and loading on the layered nickel foam; rather than loading the Co3O4-Fe active material on the layered nickel foam or on carbon paper by coating or other means.

[0020] In the present invention, the structure of the Co3O4-Fe is a uniform Fe-doped Co3O4 porous layered nanostructure.

[0021] In the first aspect of the present invention, an oxygen electrode is provided. The oxygen electrode includes a gas diffusion layer and an integrated catalytic layer, and the integrated catalytic layer includes layered nickel foam and Co3O4-Fe active material supported on the layered nickel foam. The oxygen electrode of the present invention introduces an expandable integrated catalytic layer to optimize the performance of the oxygen electrode.

[0022] In the present invention, the area of the integrated catalytic layer has a relatively wide optional range. According to a preferred embodiment of the present invention, the area of the integrated catalytic layer is not less than the area of the gas diffusion layer.

[0023] In the present invention, different from the effect that enlarging the electrode size in the prior art may lead to a decrease in the discharge performance and cycle performance of the flow battery, the oxygen electrode of the present invention has a large size (for example, an area of 10-1500 cm 2) can further improve the performance of the flow battery under certain circumstances, and also provides feasibility for the large-scale application of the flow battery. According to a preferred embodiment of the present invention, the area of the integrated catalytic layer is 10 - 1500 cm 2 , for example, 15 cm 2 , 30 cm 2 , 50 cm 2 , 100 cm 2 , 200 cm 2 , 400 cm 2 , 600 cm 2 , 800 cm 2 , 1000 cm 2 , 1200 cm 2 , 1400 cm 2 , or the range composed of any two of the above values.

[0024] In the present invention, the optional range of the integrated catalytic layer is relatively wide. For illustrative purposes only, it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the thickness of the integrated catalytic layer is 7 - 10 mm, for example, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, or the range composed of any two of the above values.

[0025] In the present invention, in the integrated catalytic layer, the loading amount of the Co3O4 - Fe active material on the layered nickel foam has a relatively wide optional range. For illustrative purposes only, it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the loading amount is 3 - 10 mg cm -2 , for example, 4 mg cm -2 , 5 mg cm -2 , 6 mg cm -2 , 7 mg cm -2 , 8 mg cm -2 , 9 mg cm -2 .

[0026] In the present invention, the types of the gas diffusion layer have a relatively wide optional range. For illustrative purposes only, it does not limit the scope of the present invention. In the embodiments of the present invention, commercial carbon paper (Freudenberg carbon paper, model H14CX653) is used as an example to illustrate the advantages of the present invention, but it does not limit the scope of the present invention.

[0027] Currently, the synthesis methods of catalysts commonly used in flow batteries are complex and costly. At the same time, the size of the catalysts is small, which limits the practical application of the batteries. In the present invention, the integrated catalytic layer with the aforementioned characteristics can meet the requirements of the present invention and achieve the purpose of the present invention. There are no special requirements for the preparation method of the integrated catalytic layer. According to a preferred embodiment of the present invention, the preparation method of the integrated catalytic layer of the present invention includes: mixing a solution containing an iron source, a cobalt source, ammonium fluoride, and urea with layered nickel foam, and performing a solvothermal reaction; washing, drying, and calcining.

[0028] The preparation method of the aforementioned integrated catalytic layer of the present invention can prepare a large-sized integrated catalyst. The integrated catalytic layer prepared by this preparation method is used to prepare an oxygen electrode, which can not only further improve the performance of the flow battery, but also provide feasibility for the large-scale application of the flow battery.

[0029] In the present invention, in the solution containing an iron source, a cobalt source, ammonium fluoride, and urea, the concentration range of cobalt element is relatively wide. For illustrative purposes only, but not limiting the scope of the present invention thereby. According to a preferred embodiment of the present invention, the concentration of cobalt element in the solution is 0.1 - 1 mol / L, for example, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 0.9 mol / L, or the range composed of any two of the above values. In the examples of the present invention, the advantage of the present invention is exemplified by 0.1 mol / L of cobalt element, but not limiting the scope of the present invention thereby.

[0030] In the present invention, in the solution containing an iron source, a cobalt source, ammonium fluoride, and urea, the dosage range of the iron source is relatively wide. For illustrative purposes only, but not limiting the scope of the present invention thereby. According to a preferred embodiment of the present invention, the iron source is calculated as iron element, and the cobalt source is calculated as cobalt element. The molar ratio of the cobalt source to the iron source is 1:0.1 - 1, for example, 1:0.2, 1:0.3, 1:0.5, 1:0.7, 1:0.9. In the examples of the present invention, the advantage of the present invention is exemplified by the molar ratio of the cobalt source to the iron source being 1:0.1, but not limiting the scope of the present invention thereby.

[0031] In the present invention, in the solution containing an iron source, a cobalt source, ammonium fluoride, and urea, the dosage range of ammonium fluoride is relatively wide. For illustrative purposes only, but not limiting the scope of the present invention thereby. According to a preferred embodiment of the present invention, the molar ratio of the cobalt source to ammonium fluoride is 1:1 - 2, for example, 1:1.2, 1:1.4, 1:1.5, 1:1.7, 1:1.9. In the examples of the present invention, the advantage of the present invention is exemplified by the molar ratio of the cobalt source to ammonium fluoride being 1:2, but not limiting the scope of the present invention thereby..

[0032] In the present invention, in the solution containing an iron source, a cobalt source, ammonium fluoride and urea, the dosage range of urea can be selected relatively widely. For illustrative purposes only, this does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the molar ratio of the cobalt source to urea is 1:2 - 10, such as 1:3, 1:5, 1:7, 1:9. In the examples of the present invention, the advantage of the present invention is exemplified by a molar ratio of the cobalt source to urea of 1:5, but this does not limit the scope of the present invention..

[0033] In the present invention, as long as the object of the present invention can be achieved, there are no special requirements for the solvothermal reaction conditions. For illustrative purposes only, this does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the solvothermal reaction conditions include: the temperature is 100 - 120 °C, such as 105 °C, 110 °C, 115 °C; the reaction time can be determined according to actual needs, and preferably is 10 - 15 h.

[0034] In the present invention, there are no special requirements for the drying conditions, and conventional drying conditions in the art can be used. For illustrative purposes only, this does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the drying conditions include: the temperature is 50 - 70 °C, such as 55 °C, 60 °C, 65 °C; the drying time can be determined according to actual needs, and preferably is 7 - 10 h. In the examples of the present invention, the advantage of the present invention is exemplified by drying at 50 °C for 10 h, but this does not limit the scope of the present invention.

[0035] In the present invention, there are no special requirements for the calcination conditions, and conventional calcination conditions in the art can be used. For illustrative purposes only, this does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the calcination conditions include: the temperature is 300 - 400 °C, such as 310 °C, 320 °C, 330 °C, 350 °C, 360 °C, 370 °C, 380 °C, 390 °C; the calcination time can be determined according to actual needs, and preferably is 10 - 15 h. In the examples of the present invention, the advantage of the present invention is exemplified by calcination at 350 °C for 10 h, but this does not limit the scope of the present invention.

[0036] In the present invention, the area of the layered nickel foam can be selected within a relatively wide range. For illustrative purposes only, this does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the area of the layered nickel foam is 10 - 1500 cm 2 , such as 15 cm 2 , 30 cm 2 , 50 cm 2 , 100 cm 2 , 200 cm 2 , 400 cm 2 , 600 cm 2 , 800 cm 2, 1000 cm 2 , 1200 cm 2 , 1400 cm 2 , or a range composed of any two of the above values.

[0037] In the present invention, after the solvothermal reaction is completed, the product needs to be washed to remove impurities. The present invention has no particular limitation on the washing. For example, it can be washed with deionized water. Exemplarily, in the examples of the present invention, the product is washed 3 times with deionized water.

[0038] In the present invention, before the washing, the product after the reaction needs to be cooled first. The present invention has no particular limitation on the cooling. Exemplarily, in the examples of the present invention, the product after the reaction is naturally cooled to room temperature.

[0039] In the present invention, the type of the iron source has a relatively wide optional range. By way of demonstration, but not limiting the scope of the present invention thereby, according to a preferred embodiment of the present invention, the iron source is selected from one or more of the soluble salts of iron. More preferably, the iron source is selected from one or more of iron nitrate and iron sulfate.

[0040] In the present invention, the type of the cobalt source has a relatively wide optional range. By way of demonstration, but not limiting the scope of the present invention thereby, according to a preferred embodiment of the present invention, the cobalt source is selected from one or more of the soluble salts of cobalt. More preferably, the cobalt source is selected from one or more of cobalt nitrate and cobalt sulfate.

[0041] In the present invention, the type of the solvent has a relatively wide optional range. By way of demonstration, but not limiting the scope of the present invention thereby, in the examples of the present invention, water is used to illustrate the advantages of the present invention by way of example, but not limiting the scope of the present invention thereby.

[0042] In the present invention, there is no particular limitation on the amount of the solution containing the iron source, cobalt source, ammonium fluoride and urea, as long as it can cover the layered nickel foam.

[0043] In the present invention, before the mixing, the layered nickel foam needs to be pretreated to remove the oxide layer on the surface of the nickel foam. There is no particular limitation on the pretreatment method, and the conventional treatment methods in the art can be used. According to an embodiment of the present invention, the layered nickel foam is acid-treated and washed with an acid cleaning agent.

[0044] In the present invention, the type of the acid cleaning agent has a relatively wide optional range. According to a preferred embodiment of the present invention, the acid cleaning agent is selected from one or more of hydrochloric acid solution and nitric acid; the concentration of the acid cleaning agent is 0.7 - 5 mol / L.

[0045] According to an embodiment of the present invention, the time for the acid treatment is 15 - 30 min.

[0046] In the present invention, the cleaning method is not particularly limited as long as it can clean the surface of the layered nickel foam. According to an embodiment of the present invention, the acid-treated layered nickel foam is cleaned with acetone and distilled water.

[0047] In the present invention, the pretreatment is carried out under ultrasonic conditions. According to an embodiment of the present invention, the ultrasonic conditions are: the ultrasonic frequency is 80 - 100 HZ; the ultrasonic time is 30 - 45 min.

[0048] The second aspect of the present invention provides a method for preparing the oxygen electrode described in the present invention, which includes: hot-pressing a gas diffusion layer and an integrated catalytic layer to obtain an oxygen electrode; the integrated catalytic layer includes layered nickel foam and Co3O4-Fe active material loaded on the layered nickel foam. Through the above technical solution, an expandable integrated catalytic layer is introduced, and the prepared oxygen electrode has more excellent performance. When applied to a flow battery, it can significantly improve the discharge performance and cycle stability of the flow battery.

[0049] In the present invention, the hot-pressing conditions have no special requirements, and conventional hot-pressing conditions in the art can be used. For illustrative purposes only, but not limiting the scope of the present invention thereby. According to a preferred embodiment of the present invention, the hot-pressing conditions include: the temperature is 50 - 100 °C, such as 55 °C, 60 °C, 65 °C, 70 °C, 80 °C, 90 °C; the pressure is 5 - 10 MPa, such as 6 MPa, 7 MPa, 8 MPa, 9 MPa; the hot-pressing time can be determined according to actual needs, preferably 2 - 10 min; within the above conditions, an oxygen electrode with better tightness and smaller contact resistance is prepared. In the examples of the present invention, hot-pressing at 120 °C, 8 MPa for 2 min is used to exemplify the advantages of the present invention, but not limiting the scope of the present invention thereby.

[0050] The third aspect of the present invention provides an application of the oxygen electrode described in the present invention as a cathode in a flow battery. The oxygen electrode described in the present invention introduces an expandable integrated catalytic layer and has more excellent performance. When applied to a flow battery, it can significantly improve the discharge performance and cycle stability of the flow battery.

[0051] The fourth aspect of the present invention provides a zinc-air flow battery, which is characterized by including an anode, a cathode, a separator membrane separating the anode and the cathode, and an electrolyte; the cathode is the oxygen electrode described in the present invention. The zinc-air flow battery described in the present invention has the ability for higher power applications and has the characteristics of long-term stable use.

[0052] In the present invention, the types of the electrolyte have a relatively wide selection range, and conventional electrolytes in the art can be used in the present invention. For example, an aqueous solution with a potassium hydroxide concentration of 6 - 8 mol / L and a zinc oxide concentration of 0.4 - 0.6 mol / L is used.

[0053] According to a preferred embodiment of the present invention, the electrolyte further contains polyethylene glycol and / or tetrabutylammonium bromide. The average molecular weight of the polyethylene glycol is not less than 3000 g / mol. Preferably, the average molecular weight of the polyethylene glycol is 3500 - 5000 g / mol, and more preferably 4000 g / mol. Through research by the inventors, it is found that the polyethylene glycol and / or tetrabutylammonium bromide of the present invention, as additives, can improve the cycle life and voltage efficiency of the zinc-air flow battery.

[0054] According to a preferred embodiment of the present invention, in the electrolyte, the concentration of polyethylene glycol is 2.5×10 -6 -12.5×10 -6 mmol / L.

[0055] According to a preferred embodiment of the present invention, the concentration of tetrabutylammonium bromide is 1×10 -3 -35×10 -3 mmol / L; preferably 3×10 -3 -15×10 -3 mmol / L.

[0056] According to a preferred embodiment of the present invention, the electrolyte contains polyethylene glycol and tetrabutylammonium bromide. Using the polyethylene glycol and tetrabutylammonium bromide as additives can further improve the cycle life and voltage efficiency of the zinc-air flow battery.

[0057] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0058] In the following examples, in the Co3O4-Fe catalyst, the contents of Fe and Co are analyzed by an XPS analyzer (Thermo Scientific ESCALAB250Xi type XPS analyzer, USA).

[0059] In the following examples and comparative examples, the nickel foam is subjected to acid treatment and cleaning (removing the NiO layer and other impurities on the surface of the nickel foam) before use. Specifically:

[0060] The nickel foam is treated with 3 mol / L HCl for 30 min under an ultrasonic medium (ultrasonic frequency is 100 HZ), and is successively washed with acetone and distilled water to ensure surface cleanliness.

[0061] In the following examples, the gas diffusion layer is a commercial carbon paper (Freudenberg carbon paper, model H14CX653).

[0062] In the following examples, the electrolyte and its preparation are as follows:

[0063] Electrolyte 1

[0064] The concentration of potassium hydroxide is 7 mol / L, the concentration of zinc oxide is 0.5 mol / L, and the solvent is water.

[0065] Electrolyte 2

[0066] (1) Mix PEG-4000 (average molecular weight 4000 g / mol) and deionized water at 2.5×10 -6 mmol / L and sonicate for 10 min to obtain a mixed solution;

[0067] (2) Dissolve tetrabutylammonium bromide, potassium hydroxide, and zinc oxide in the mixed solution at 3.1×10 -3 mmol / L for tetrabutylammonium bromide, 7 mol / L for potassium hydroxide, and 0.5 mol / L for zinc oxide to obtain Electrolyte 2.

[0068] Electrolyte 3

[0069] (1) Mix PEG-4000 (average molecular weight 4000 g / mol) and deionized water at 2.5×10 -6 mmol / L and sonicate for 10 min to obtain a mixed solution;

[0070] (2) Dissolve potassium hydroxide and zinc oxide in the mixed solution at 7 mol / L for potassium hydroxide and 0.5 mol / L for zinc oxide to obtain Electrolyte 3.

[0071] Electrolyte 4

[0072] Dissolve tetrabutylammonium bromide, potassium hydroxide, and zinc oxide in the mixed solution at 3.1×10 -3 mmol / L for tetrabutylammonium bromide, 7 mol / L for potassium hydroxide, and 0.5 mol / L for zinc oxide to obtain Electrolyte 4.

[0073] In the following examples, the oxygen electrodes prepared in the examples were assembled into a zinc-air flow battery for testing, as follows:

[0074] Battery preparation: Use a small cell structure with a reaction area of 1*1 cm 2 for testing. The cathode uses the oxygen electrode prepared above, the anode uses a polished zinc sheet, the material of the middle flow channel is acrylic sheet, and the assembled battery uses a peristaltic pump to pump the electrolyte at 30 r min-1 Pump the rotational speed into the flow channel of the zinc-air battery.

[0075] Stability test of the cycle performance of the flow battery: The geometric area of the positive electrode exposed to air is 1 cm 2 , and charge for 10 minutes and discharge for 10 minutes at 10 mA cm -2 to test its cycle stability.

[0076] Charge-discharge performance test of the flow battery: After discharging, charge for 10 minutes, and use the Blue-Electric test equipment to test its charge-discharge performance.

[0077] Test method for the power density of the flow battery: Set the power program, and conduct the power density test with the current density ranging from 1 - 300 mA cm -2 . After the test is completed, observe the maximum power density according to the maximum value of the curve.

[0078] Example 1

[0079] (1) Dissolve 0.5 mmol of Fe(NO3)3, 5 mmol of Co(NO3)2·6H2O, 25 mmol of urea, and 10 mmol of NH4F in 50 mL of distilled water, and stir evenly to obtain a solution.

[0080] (2) Mix a 50 cm * 30 cm nickel foam with the solution obtained in step (1) in an autoclave, and heat at 120 °C for 12 hours for a solvothermal reaction; after the reaction is completed, take out the product in the reaction kettle and cool it naturally to room temperature.

[0081] (3) Wash the cooled product 3 times with deionized water, dry it in an oven at 50 °C for 10 hours to obtain nickel foam with purple powder loaded on its surface; place it in a muffle furnace and calcine it at 350 °C for 10 hours to obtain an integrated catalytic layer loaded with Co3O4-Fe material; the area of the integrated catalytic layer is 50 * 30 cm 2 , the thickness of the catalytic layer is 8 mm, and the loading amount of Co3O4-Fe active material on the layered nickel foam is 3.98 mg / cm 2 .

[0082] (4) Use commercial carbon paper as the gas diffusion layer and the integrated catalytic layer obtained in step (3) to hot-press for 2 minutes at 120 °C and 8 MPa pressure with a small hot press to obtain an oxygen electrode.

[0083] The SEM image of the Co3O4-Fe catalyst prepared in Example 1 is shown in Figure 1. Figure 1a It is the SEM image of the catalyst at a scale of 100 μm. Figure 1bIt is the SEM image of the catalyst at a scale of 1 μm. It can be observed that the metal particles on the surface of the Co3O4-Fe catalyst have successfully grown onto the nickel foam substrate, and the layered structure of the nickel foam substrate of the Co3O4-Fe catalyst can be clearly seen. Figure 2 It is the BET curve of the Co3O4-Fe catalyst. The specific surface area of the Co3O4-Fe catalyst is measured to be 16.98 m 2 g -1 , and the pore volume is 0.053 cm 3 g -1 . It is speculated that the Co3O4-Fe catalyst can have the characteristics of a high specific surface area and abundant catalytic active sites through its surface properties and structure.

[0084] The above characterization results show that the Co3O4-Fe catalyst grows in-situ on the nickel foam without a binder, thus enhancing the electrochemical performance; and the mesoporous structure of the Co3O4-Fe catalyst provides a large specific surface area and can shorten the mass diffusion distance, enhancing the structural stability and facilitating the improvement of the electrochemical performance.

[0085] Figure 3 It is the XPS spectrum of the Co3O4-Fe catalyst. In Co3O4-Fe, by element, the mass content of Fe is 33.9 wt%, and the mass content of Co is 36.08 wt%.

[0086] The oxygen electrode prepared in Example 1 is used to prepare a zinc-air flow battery according to the foregoing method, and the electrolyte is Electrolyte 1. Figure 4 It is the power density diagram of the zinc-air flow battery. The results show that the power density of the zinc-air flow battery is 80.4 mW / cm 2 , indicating that it has good power density. The stability test of the cycle performance of the flow battery is as shown in Figure 6 、 Figure 7 . It shows that the zinc-air flow battery prepared with the oxygen electrode prepared in Example 1 has a cycle life of up to 1000 cycles, a cycle stability of 95%, and an energy efficiency of up to 76.5% after 1000 cycles. Together, they verify that the flow battery has a good energy efficiency retention rate, indicating that the flow battery can also have high stability under alkaline electrolyte conditions.

[0087] Figure 5 It is the voltage ratio diagram of the oxygen electrodes prepared in Example 1 and Example 2 of the present invention applied to the zinc-air flow battery. It can be observed that as the number of battery cycles increases, the discharge voltage of the zinc-air flow battery becomes higher and the charge voltage becomes lower, that is, the performance of the battery becomes more excellent. And as the area of the integrated catalyst layer increases, the zinc-air flow battery prepared with the oxygen electrode has more excellent performance.

[0088] Example 2

[0089] (1) Dissolve 0.5 mmol of Fe(NO3)3, 5 mmol of Co(NO3)2·6H2O, 25 mmol of urea and 10 mmol of NH4F in 50 mL of distilled water, and stir evenly to obtain a solution.

[0090] (2) Mix a 5 cm * 2.5 cm nickel foam with the solution obtained in step (1) in an autoclave, and heat at 120 °C for 12 hours for a solvothermal reaction; after the reaction is completed, take out the product in the autoclave and cool it naturally to room temperature.

[0091] (3) Wash the cooled product 3 times with deionized water, dry it in an oven at 50 °C for 10 hours to obtain nickel foam with purple powder loaded on its surface; place it in a muffle furnace and calcine it at 350 °C for 10 hours to obtain an integrated catalytic layer loaded with Co3O4-Fe material; the area of the integrated catalytic layer is 5 * 2.5 cm 2 , the thickness of the catalytic layer is 8 mm, and the loading amount of Co3O4-Fe active material on the layered nickel foam is 2.98 mg / cm 2 .

[0092] (4) Use commercial carbon paper as the gas diffusion layer and the integrated catalytic layer obtained in step (3) to hot press for 2 min at 120 °C and 8 MPa pressure by a small hot press to obtain an oxygen electrode.

[0093] Prepare a zinc-air flow battery with the oxygen electrode prepared in Example 2 according to the aforementioned method, and the electrolyte is Electrolyte 1. The power density of the battery is 78 mW / cm 2 , after 1000 cycles, the capacity retention rate of the battery is 93.6%, and the energy efficiency is 75%.

[0094] Example 3

[0095] (1) Dissolve 0.5 mmol of Fe(NO3)3, 5 mmol of Co(NO3)2·6H2O, 25 mmol of urea and 10 mmol of NH4F in 50 mL of distilled water, and stir evenly to obtain a solution.

[0096] (2) Mix a 20 cm * 30 cm nickel foam with the solution obtained in step (1) in an autoclave, and heat at 110 °C for 10 hours for a solvothermal reaction; after the reaction is completed, take out the product in the autoclave and cool it naturally to room temperature.

[0097] (3) Wash the cooled product three times with deionized water, dry it in an oven at 50 °C for 10 hours to obtain nickel foam with purple powder loaded on its surface; place it in a muffle furnace and calcine it at 350 °C for 10 hours to obtain an integrated catalytic layer loaded with Co3O4-Fe material; the area of the integrated catalytic layer is 20*30 cm 2 , the thickness of the catalytic layer is 10 mm, and the loading amount of Co3O4-Fe active material on the layered nickel foam is 3.42 mg / cm 2 .

[0098] (4) Use commercial carbon paper as the gas diffusion layer and hot-press it with the integrated catalytic layer obtained in step (3) for 2 min at 120 °C and 8 MPa pressure using a small hot press to obtain an oxygen electrode.

[0099] Prepare a zinc-air flow battery with the oxygen electrode prepared in Example 3 according to the aforementioned method, and the electrolyte is Electrolyte 1. The power density of the battery is 79 mW / cm 2 , after 1000 cycles, the capacity retention rate of the battery is 93%, and the energy efficiency is 76%.

[0100] Example 4

[0101] (1) Dissolve 0.5 mmol of Fe2(SO4)3, 5 mmol of CoSO4, 25 mmol of urea, and 10 mmol of NH4F in 50 mL of distilled water, and stir evenly to obtain a solution.

[0102] (2) Mix 50 cm*30 cm of nickel foam with the solution obtained in step (1) in an autoclave, and heat it at 110 °C for 12 hours for a solvothermal reaction; after the reaction is completed, take out the product in the autoclave and cool it naturally to room temperature.

[0103] (3) Wash the cooled product three times with deionized water, dry it in an oven at 50 °C for 10 hours to obtain nickel foam with purple powder loaded on its surface; place it in a muffle furnace and calcine it at 350 °C for 10 hours to obtain an integrated catalytic layer loaded with Co3O4-Fe material; the area of the integrated catalytic layer is 50*30 cm 2 , the thickness of the catalytic layer is 9 mm, and the loading amount of Co3O4-Fe active material on the layered nickel foam is 3.65 mg / cm 2 .

[0104] (4) Use commercial carbon paper as the gas diffusion layer and hot-press it with the integrated catalytic layer obtained in step (3) for 2 min at 120 °C and 8 MPa pressure using a small hot press to obtain an oxygen electrode.

[0105] Prepare a zinc-air flow battery with the oxygen electrode prepared in Example 4 according to the foregoing method, and the electrolyte is Electrolyte 1. The power density of the battery is 79.3 mW / cm 2 . After 1000 cycles, the capacity retention rate of the battery is 94.7%, and the energy efficiency is 76%.

[0106] Example 5

[0107] (1) Dissolve 0.5 mmol of Fe(NO3)3, 5 mmol of Co(NO3)2·6H2O, 25 mmol of urea, and 10 mmol of NH4F in 50 mL of distilled water, and stir evenly to obtain a solution.

[0108] (2) Mix a 50 cm * 30 cm nickel foam with the solution obtained in step (1) in an autoclave, and carry out a solvothermal reaction by heating at 120 °C for 12 hours; after the reaction is completed, take out the product in the reaction kettle and cool it naturally to room temperature.

[0109] (3) Wash the cooled product 3 times with deionized water, dry it in an oven at 50 °C for 10 hours to obtain nickel foam with purple powder loaded on the surface; place it in a muffle furnace and calcine it at 350 °C for 10 hours to obtain an integrated catalytic layer loaded with Co3O4-Fe material; the area of the integrated catalytic layer is 50 * 30 cm 2 , the thickness of the catalytic layer is 8 mm, and the loading amount of Co3O4-Fe active material on the layered nickel foam is 3.98 mg / cm 2 .

[0110] (4) Use commercial carbon paper as the gas diffusion layer and the integrated catalytic layer obtained in step (3) to hot-press for 2 minutes at 120 °C and 8 MPa pressure with a small hot press to obtain an oxygen electrode.

[0111] Prepare a zinc-air flow battery with the oxygen electrode prepared in Example 5 according to the foregoing method, and the electrolyte is Electrolyte 2. The power density of the battery is 80.9 mW / cm 2 . After 1000 cycles, the capacity retention rate of the battery is 96.1%, and the energy efficiency is 81%.

[0112] Example 6

[0113] The implementation process is the same as that of Example 1, except that the electrolyte is Electrolyte 3; other conditions are the same as those of Example 1.

[0114] The power density of the battery is 80.5 mW / cm 2 . After 1000 cycles, the capacity retention rate of the battery is 95.3%, and the energy efficiency is 78.8%.

[0115] Example 7

[0116] The implementation process is the same as that of Example 1, except that the electrolyte is electrolyte 4; the other conditions are the same as those of Example 1.

[0117] The power density of the battery is 80.4mW / cm 2 After 1000 cycles, the battery capacity retention rate was 94.9% and the energy efficiency was 78.1%.

[0118] The results of Examples 5-7 show that the oxygen electrode prepared by the integrated catalytic layer of the present invention is applied to zinc-air flow batteries, especially when assembled into zinc-air flow batteries with an electrolyte containing polyethylene glycol and / or tetrabutylammonium bromide, which can have better discharge performance and cycle stability.

[0119] Comparative Example 1

[0120] (1) Dissolve 0.5 mmol Fe(NO3)3, 5 mmol Co(NO3)2·6H2O, 25 mmol urea and 10 mmol NH4F in 50 mL distilled water and stir to obtain a solution.

[0121] (2) The solution obtained in step (1) is mixed in an autoclave and heated at 120° C. for 12 hours to perform a solvent thermal reaction; after the reaction is completed, the product in the autoclave is taken out and naturally cooled to room temperature to prepare a granular Co3O4-Fe catalyst.

[0122] (3) The catalyst obtained in step (2), the binder (polytetrafluoroethylene), the conductive agent (metal nickel powder), and water were prepared into a slurry in a mass ratio of 1:0.1:0.2:0.5, coated on commercial carbon paper, dried, and rolled to a thickness of 8 mm to obtain a 50*30 cm 2 of oxygen electrode.

[0123] The oxygen electrode prepared in Comparative Example 1 was used to prepare a zinc-air flow battery according to the above method, and the electrolyte was electrolyte 1. The power density of the battery was 73 mW / cm 2 After 1,000 cycles, the battery's capacity retention rate was 89% and its energy efficiency was 61%.

[0124] Comparative Example 2

[0125] (1) Dissolve 0.5 mmol Fe(NO3)3, 5 mmol Co(NO3)2·6H2O, 25 mmol urea and 10 mmol NH4F in 50 mL distilled water and stir to obtain a solution.

[0126] (2) Mix the solution obtained in step (1) in an autoclave and carry out a solvothermal reaction by heating at 120 °C for 12 hours; after the reaction is completed, take out the product in the autoclave and naturally cool it to room temperature to prepare a granular Co3O4-Fe catalyst.

[0127] (3) Prepare a slurry from the catalyst obtained in step (2), a binder (polytetrafluoroethylene), a conductive agent (metal nickel powder), and water in a mass ratio of 1:0.1:0.2:0.5, coat it on a commercial carbon paper, dry it, and roll it to a thickness of 8 mm to obtain an oxygen electrode with an area of 5 * 2.5 cm 2 of the oxygen electrode.

[0128] Prepare a zinc-air flow battery with the oxygen electrode prepared in Comparative Example 2 according to the foregoing method, and the electrolyte is Electrolyte 1. The power density of the battery is 73 mW / cm 2 , after 1000 cycles, the capacity retention rate of the battery is 91.1%, and the energy efficiency is 66%.

[0129] The above results show that the present invention prepares an oxygen electrode with an integrated catalytic layer, which improves the performance of the oxygen electrode. The discharge performance and cycle stability of the flow battery prepared with this oxygen electrode are significantly improved; it is speculated that by enlarging the size of the integrated catalytic layer, it has a larger reaction area and more catalytic active sites, and thus the flow battery has the ability to be applied at a higher power and has the characteristics of long-term stable use.

[0130] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. An oxygen electrode, characterized in that The oxygen electrode comprises a gas diffusion layer and an integrated catalytic layer, wherein the integrated catalytic layer comprises a layered nickel foam and a Co3O4-Fe active material loaded on the layered nickel foam.

2. The oxygen electrode according to claim 1, wherein The area of ​​the integrated catalytic layer is not less than the area of ​​the gas diffusion layer; Preferably, the area of ​​the integrated catalytic layer is 10-1500 cm 2 ; Preferably, the thickness of the integrated catalytic layer is 7-10 mm.

3. The oxygen electrode according to claim 1 or 2, wherein In the integrated catalytic layer, the loading amount of Co3O4-Fe active material in the layered nickel foam is 3-10 mg / cm 2 .

4. The oxygen electrode according to any one of claims 1 to 3, wherein The preparation method of the integrated catalytic layer comprises: A solution containing an iron source, a cobalt source, ammonium fluoride and urea is mixed with the layered nickel foam, and subjected to a solvent thermal reaction, followed by washing, drying and roasting; In the solution containing iron source, cobalt source, ammonium fluoride and urea, the iron source is calculated as iron element, the cobalt source is calculated as cobalt element, the molar ratio of the cobalt source to the iron source is 1:0.1-1, the molar ratio of the cobalt source to ammonium fluoride is 1:1-2, and the molar ratio of the cobalt source to urea is 1:2-10.

5. The preparation method according to claim 4, wherein: In the solution containing an iron source, a cobalt source, ammonium fluoride and urea, the concentration of the cobalt element is 0.1-1 mol / L; Solvothermal conditions include: temperature of 100-120°C; and / or time of 10-15h; and / or Drying conditions include: temperature of 50-70°C; and / or time of 7-10h; and / or The calcination conditions include: a temperature of 300-400° C.; and / or a time of 7-10 h.

6. The preparation method according to claim 4 or 5, wherein: The area of ​​the layered nickel foam is 10-1500cm 2 ; and / or The iron source is selected from one or more soluble salts of iron, preferably one or more of ferric nitrate and ferric sulfate; and / or The cobalt source is selected from one or more soluble salts of cobalt, preferably one or more of cobalt nitrate and cobalt sulfate.

7. The method for preparing an oxygen electrode according to any one of claims 1 to 6, characterized in that: The method includes: The gas diffusion layer and the integrated catalyst layer are hot pressed to obtain an oxygen electrode; The integrated catalytic layer comprises a layered nickel foam and a Co3O4-Fe active material supported on the layered nickel foam; Preferably, the hot pressing conditions include: a temperature of 50-150° C.; and / or a pressure of 5-10 MPa; and / or a time of 2-10 min.

8. Use of the oxygen electrode according to any one of claims 1 to 6 as a cathode in a liquid flow battery.

9. A zinc-air flow battery, characterized in that: It includes an anode, a cathode, a separator separating the anode and the cathode, and an electrolyte; The cathode is the oxygen electrode according to any one of claims 1 to 6.

10. The zinc-air flow battery according to claim 9, wherein: The electrolyte includes water, zinc oxide and potassium hydroxide; Preferably, the electrolyte further contains polyethylene glycol and / or tetrabutylammonium bromide; The average molecular weight of the polyethylene glycol is not less than 3000 g / mol, preferably, the average molecular weight of the polyethylene glycol is 3500-5000 g / mol; In the electrolyte, the concentration of polyethylene glycol is 2.5×10 -6 -12.5×10 -6 mmol / L; The concentration of tetrabutylammonium bromide is 1×10 -3 -35×10 -3 mmol / L; Preferably, the electrolyte contains polyethylene glycol and tetrabutylammonium bromide.

Images