A nitrogen-doped carbon-coated cobalt phosphide composite material, a preparation method and application thereof

Abstract

The application discloses a nitrogen-doped carbon-coated cobalt phosphide composite material and a preparation method and application thereof, and belongs to the technical field of aluminum-air battery cathode materials. The preparation method of the composite material comprises the following steps: ultrasonic dispersion of graphene oxide in water, then P123, cobalt acetate tetrahydrate, monocyane and diammonium hydrogen phosphate are added and stirred until the solution is clear; constant temperature stirring and evaporation of the clear solution to obtain a gelatinous precursor; calcination of the gelatinous precursor, and natural cooling to obtain the nitrogen-doped carbon-coated cobalt phosphide composite material. The application uses graphene oxide as a carbon source, P123 as a carbon source and nitrogen source fixing agent, and monocyane as a nitrogen source to prepare the composite material, cobalt phosphide nanoparticles are uniformly distributed on the nitrogen-doped carbon material to form a nitrogen-doped carbon material-coated cobalt phosphide nanoparticle composite material, the prepared composite material has a high specific surface area and excellent ORR and OER performances. In addition, the catalyst is loaded on carbon paper as a cathode of a self-assembled aluminum-air battery, and high power density and specific capacity are exhibited in the discharging process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum-air battery cathode materials, and particularly relates to a nitrogen-doped carbon-coated cobalt phosphide composite material and a preparation method and application thereof. BACKGROUND

[0002] The increasingly serious energy crisis and environmental pollution problems have become the focus of today's society. Therefore, people develop clean and sustainable green energy to replace the decreasing fossil fuels, and the demand for sustainable energy conversion and energy storage devices gradually increases. Among energy devices, metal-air batteries are considered to be extremely competitive energy conversion devices due to their small environmental pollution, high conversion rate, high energy density and other advantages. Metal-air batteries use air (oxygen) as the cathode active material and metal as the anode active material, including active metals such as lithium, sodium, potassium, iron, magnesium, zinc, and aluminum. Among them, aluminum-air batteries have the advantages of high energy density, zero emission, no pollution, low cost, and abundant storage, and are considered to be the most potential new generation of green energy conversion devices.

[0003] The air electrode (cathode) is an important part of the aluminum-air battery, which is composed of a conductive current collector, a waterproof and air-permeable layer, and a catalyst layer. The catalyst layer is the core part of the air electrode, and the performance of the catalyst will directly affect the performance of the aluminum-air battery. The oxygen reduction reaction (ORR) is an important reaction of the air battery, and its slow kinetics hinders the energy utilization rate and large-scale application of the aluminum-air battery. In order to improve the ORR reaction rate, high-activity catalysts are developed. Currently, platinum catalysts are considered to be effective catalysts for ORR, but their high cost and poor stability hinder their commercial application. Therefore, exploring and developing low-cost, high-activity, and high-stability catalysts to improve the performance of aluminum-air batteries has become a research hotspot. In view of the above-mentioned disadvantages of the current catalysts, there are mainly two solutions: the first is to develop low-platinum catalysts; the second is to develop non-noble metal or metal-free catalysts. From a long-term perspective, the second method is a more effective solution.

[0004] Transition metal phosphides are a kind of non-noble metal catalyst with great development potential, and their structures and compositions are diverse, and their conductivity is excellent, and they are currently widely used in water electrolysis catalysts. In the preparation of transition metal phosphides, the phosphorus source used is generally divided into organic phosphorus source and inorganic phosphorus source, the organic phosphorus source includes trioctylphosphine (TOP), triphenylphosphine (TPP) and the like, and such organic solvents will make the entire reaction system have corrosion at a certain reaction temperature; the inorganic phosphorus source includes sodium hypophosphite, red phosphorus and the like, which will decompose to generate PH3 or phosphorus vapor after heating to phosphorize the metal source into metal phosphide. The PH3 or white phosphorus gas generated in this phosphorization process is a toxic and harmful gas and needs to be harmlessly treated.

[0005] Patent application CN112331860A discloses that a melamine foam precursor containing cobalt, nitrogen, phosphorus and carbon is directly dried to obtain a carbon-coated cobalt phosphide nanoparticle, and then high-temperature annealing is performed to obtain the carbon-coated cobalt phosphide nanoparticle, so that the performance of the material in electrocatalytic ORR and OER is simultaneously improved. However, the preparation process of the carbon-coated cobalt phosphide nanoparticle material described in the patent application is complex, and the obtained product needs to be pickled, washed with water and washed with alcohol before drying, which makes the obtained product unstable, and the phosphorus source used in the patent application is an organic phosphorus source, which makes the entire reaction system corrosive at a certain reaction temperature, which has certain danger.

[0006] The present application simplifies the synthesis process of the cobalt phosphide composite material, and the obtained product is stable and non-toxic and harmless in the reaction process. SUMMARY

[0007] In view of the above-mentioned shortcomings of the prior art, the present application provides a nitrogen-doped carbon-coated cobalt phosphide composite material, a preparation method thereof and an application thereof.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] A preparation method of a nitrogen-doped carbon-coated cobalt phosphide composite material, comprising the following steps:

[0010] (1) ultrasonically disperse graphene oxide in water, and then add P123, cobalt acetate tetrahydrate, monocyamine and diammonium hydrogen phosphate and stir until the solution is clear, wherein P123 is used as a carbon source and a nitrogen source fixing agent, monocyanine is used as a nitrogen source, cobalt acetate tetrahydrate is used as a cobalt source, and diammonium hydrogen phosphate is used as a phosphorus source; graphene oxide is not only used as a carbon source, but also used as a structure control agent to form a nanorod structure of the composite material;

[0011] (2) constant-temperature stir the clear solution to obtain a gel-like precursor by evaporation;

[0012] (3) calcine the gel-like precursor, and obtain the nitrogen-doped carbon-coated cobalt phosphide composite material after natural cooling.

[0013] As a preferred embodiment of the present application, in the step (1), the mass ratio of graphene oxide, P123 and cobalt acetate tetrahydrate is (2.5-12.5):(1-3):1.

[0014] As a preferred embodiment of the present application, in the step (1), the mass ratio of cobalt acetate tetrahydrate, monocyanine and diammonium hydrogen phosphate is 2:4:0.25.

[0015] As a preferred embodiment of the present application, in the step (2), the temperature of the constant temperature is 60℃.

[0016] The application also claims the nitrogen-doped carbon-coated cobalt phosphide composite material prepared by the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material.

[0017] The application of the nitrogen-doped carbon-coated cobalt phosphide composite material in oxygen reduction and oxygen evolution reactions in an alkaline electrolyte.

[0018] The application of the nitrogen-doped carbon-coated cobalt phosphide composite material in an aluminum-air battery.

[0019] Compared with the prior art, the application has the beneficial effects that: the nanoscale cobalt phosphide nanoparticles prepared by using graphene oxide as a carbon source and a structure control agent, P123 as a carbon source, a nitrogen source fixing agent and a template agent, and monocyanoamine as a nitrogen source can be uniformly dispersed in the nitrogen-doped carbon material to form cobalt phosphide particles coated with nitrogen-doped carbon, thereby having excellent ORR and OER performance. In addition, the catalyst is loaded on carbon paper as a cathode of a self-assembled aluminum-air battery, and the battery has a high power density and specific capacity. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The XRD detection result graph of the Co2P@NC composite material obtained in examples 1 to 12 of the application.

[0021] Figure 2 The TEM graph of the Co2P@NC composite material obtained in example 1 of the application.

[0022] Figure 3 The ORR curve graph of the Co2P@NC composite material obtained in examples 1 to 4 of the application.

[0023] Figure 4 The OER curve graph of the Co2P@NC composite material obtained in examples 1 to 4 of the application.

[0024] Figure 5 The ORR curve graph of the Co2P@NC composite material obtained in examples 1, 5 to 8 of the application and the ORR curve graph of comparative examples 1 and 2.

[0025] Figure 6 The OER curve graph of the Co2P@NC composite material obtained in examples 1, 5 to 8 of the application and the OER curve graph of comparative examples 1 and 2.

[0026] Figure 7 The ORR curve graph of the Co2P@NC composite material obtained in examples 1, 9 to 12 of the application and the ORR curve graph of Co2P@NC-melamine obtained in comparative example 3.

[0027] Figure 8The OER curve of the Co2P@NC composite material obtained in Example 1, 9-12 of the present application and the Co2P@NC-melamine obtained in Comparative Example 3.

[0028] Figure 9 The discharge polarization curve and the corresponding power density curve of the Co2P@NC composite material obtained in Example 1-4 of the present application in an aluminum-air battery.

[0029] Figure 10 The discharge polarization curve and the corresponding power density curve of the Co2P@NC composite material obtained in Example 1, 5-8 of the present application and Comparative Examples 1, 2 in an aluminum-air battery.

[0030] Figure 11 The discharge polarization curve and the corresponding power density curve of the Co2P@NC composite material obtained in Example 1, 9-12 and Comparative Example 3 in an aluminum-air battery.

[0031] Figure 12 The rate performance of the Co2P@NC composite material obtained in Example 1-4 of the present application in an aluminum-air battery under different current densities.

[0032] Figure 13 The rate performance of the Co2P@NC composite material obtained in Example 1, 5-8 of the present application in an aluminum-air battery under different current densities.

[0033] Figure 14 The rate performance of the Co2P@NC composite material obtained in Example 1, 9-12 of the present application and the Co2P@NC-melamine obtained in Comparative Example 3 in an aluminum-air battery under different current densities.

[0034] Figure 15 The discharge curve of the Co2P@NC composite material obtained in Example 1, 9-12 of the present application when used as a cathode catalyst of an aluminum-air battery at 20 mA·cm -2 . DETAILED DESCRIPTION

[0035] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific examples.

[0036] Example 1

[0037] A preparation method of a nitrogen-doped carbon-coated cobalt phosphide composite material, comprising the following steps:

[0038] (1) 15 mg of graphene oxide was ultrasonically dispersed in deionized water, and then 4 g of P123, 2 g of cobalt acetate tetrahydrate, 4 g of monocyamide and 0.25 g of diammonium hydrogen phosphate were added and stirred until the solution was clear.

[0039] (2) The clear solution was placed in a constant temperature oil bath at 60°C and stirred until completely evaporated to obtain a gel precursor.

[0040] (3) The gel precursor was placed in a corundum crucible and placed in a tube furnace, and heated to 800°C under nitrogen protection for 1 h, and then naturally cooled to obtain a nitrogen-doped carbon-coated cobalt phosphide composite material, numbered Co2P@NC-800.

[0041] Example 2

[0042] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material described in this example and Example 1 is that in step (3), the temperature of the tube furnace is 700°C, which is denoted as Co2P@NC-700.

[0043] Example 3

[0044] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material described in this example and Example 1 is that in step (3), the temperature of the tube furnace is 900°C, which is denoted as Co2P@NC-900.

[0045] Example 4

[0046] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material described in this example and Example 1 is that in step (3), the temperature of the tube furnace is 1000°C, which is denoted as Co2P@NC-1000.

[0047] Example 5

[0048] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material described in this example and Example 1 is that in step (1), the amount of P123 added is 2 g, which is denoted as Co2P@NC-2.

[0049] Example 6

[0050] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material described in this example and Example 1 is that in step (1), the amount of P123 added is 3 g, which is denoted as Co2P@NC-3.

[0051] Example 7

[0052] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material described in this example and Example 1 is that in step (1), the amount of P123 added is 5 g, which is denoted as Co2P@NC-5.

[0053] Example 8

[0054] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material in this example and Example 1 is that in the step (1), the addition amount of P123 is 6 g, which is denoted as Co2P@NC-6.

[0055] Example 9

[0056] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material in this example and Example 1 is that in the step (1), the addition amount of graphene oxide is 5 mg, which is denoted as Co2P@NCNRs-5.

[0057] Example 10

[0058] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material in this example and Example 1 is that in the step (1), the addition amount of graphene oxide is 10 mg, which is denoted as Co2P@NCNRs-10.

[0059] Example 11

[0060] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material in this example and Example 1 is that in the step (1), the addition amount of graphene oxide is 20 mg, which is denoted as Co2P@NCNRs-20.

[0061] Example 12

[0062] The only difference between the preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material in this example and Example 1 is that in the step (1), the addition amount of graphene oxide is 25 mg, which is denoted as Co2P@NCNRs-25.

[0063] According to Figure 1 It can be seen that obvious diffraction peaks appear at 40.7°, 42.1°, 43.3°, 48.7°, 50.4° and 52.1°, and correspond to the (121), (220), (211), (031), (310) and (002) crystal faces of Co2P (PDF # 32-0306) respectively, proving that the nitrogen-doped carbon-coated cobalt phosphide nanoparticle composite material is successfully prepared.

[0064] Figure 2 The TEM image of the nitrogen-doped carbon-coated cobalt phosphide nanoparticle composite material prepared in Example 1 shows that the nanoparticles with a diameter of 30-50 nm are successfully coated in the carbon nanotubes, confirming the successful preparation of the nitrogen-doped carbon-coated cobalt phosphide nanoparticle material.

[0065] Comparative Example 1

[0066] The preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material in the present comparative example is only different from that in Example 1 in that: in the step (1), the addition amount of P123 is 0 g, which is denoted as Co2P@NC-0g.

[0067] Comparative Example 2

[0068] The preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material in the present comparative example is only different from that in Example 1 in that: in the step (1), P123 is replaced by F127 of the same mass, which is denoted as Co2P@NC-F127.

[0069] Comparative Example 3

[0070] A preparation method of a nitrogen-doped carbon-coated cobalt phosphide composite material, comprising the following steps:

[0071] (1) Ultrasonic dispersion of 15 mg of graphene oxide in deionized water, then add 2 g of P123, 2 g of cobalt acetate trihydrate, 4 g of melamine and 0.25 g of diammonium hydrogen phosphate, and stir until the solution is clear.

[0072] (2) Place the clear solution in a 60℃ constant temperature oil bath and stir until completely evaporated to obtain a gel-like precursor.

[0073] (3) Place the gel-like precursor in a corundum crucible and put it into a tube furnace, heat to 800℃ under nitrogen protection for 1h, and naturally cool to obtain a nitrogen-doped carbon-coated cobalt phosphide composite material, denoted as Co2P@NC-melamine.

[0074] Example 1

[0075] In order to accurately test the catalytic performance of the materials prepared in the examples and comparative examples, the LSV polarization curve was tested in an oxygen-saturated alkaline solution using a rotating disc electrode (RDE).

[0076] Figure 3 The ORR curve of Co2P@NC-700, Co2P@NC-800, Co2P@NC-900, Co2P@NC-1000; Figure 4 The OER curve of Co2P@NC-700, Co2P@NC-800, Co2P@NC-900, Co2P@NC-1000; from Figure 3 、 Figure 4 It can be observed that the catalytic activity of the Co2P@NC composite materials prepared by calcining the precursors at different temperatures is in the order of Co2P@NC-800 > Co2P@NC-900 > Co2P@NC-1000 > Co2P@NC-700, and it can be seen that the catalytic activity of Co2P@NC-800 is optimal.

[0077] Figure 5 、 Figure 6 LSV plots of Co2P@NC-2, Co2P@NC-3, Co2P@NC-800, Co2P@NC-5 and Co2P@NC-6, Co2P@NC-0, Co2P@NC-F127, from which it can be seen that the activity trend of Co2P@NC composite materials prepared by adding different amounts of P123 in the oxygen reduction reaction is: Co2P@NC-800 > Co2P@NC-3 > Co2P@NC-2 > Co2P@NC-5 > Co2P@NC-6 > Co2P@NC-F127 > Co2P@NC-0, Co2P@NC-800 has the most positive onset potential 0.9V vs RHE, half-wave potential 0.83V vs RHE and the largest limiting current density 5.2 mA·cm -2 -2. The overpotential at 10 mA·cm -2 -2. The overpotential at 10 mA·cm -2 -2. The overpotential at 10 mA·cm

[0078] Figure 7 、 Figure 8 LSV polarization curves of Co2P@NCNRs composite materials prepared by adding different amounts of graphene oxide and melamine as nitrogen source, which show that the Co2P@NC-800 catalyst exhibits the best ORR performance, with the most positive onset potential and the largest limiting current density and the lowest overpotential. And compared with Comparative Example 3 and when the amount of graphene is 0, the examples all exhibit better catalytic performance. First, the graphene oxide and cobalt phosphide particles form a coated relationship, and if no graphene oxide is added, it cannot form nitrogen-doped carbon-coated cobalt phosphide particles but forms a composite material in which cobalt phosphide particles are supported on nitrogen-doped carbon, which will cause its catalytic performance to decrease significantly. Second, monocyamine as a nitrogen source can promote the formation of nitrogen-doped carbon-coated cobalt phosphide particles, while melamine cannot achieve this effect in the system of the present application. And when the amount of graphene oxide added reaches 15 mg, its catalytic performance is optimal.

[0079] Example 2

[0080] The materials prepared in the examples and comparative examples were used for aluminum-air battery tests. For liquid aluminum-air battery tests, 99.9% pure aluminum sheets were used, and an electrolyte of 4M KOH aqueous solution was used. The composite material catalyst prepared in the examples and comparative examples was loaded on carbon paper, and the battery mold, aluminum sheet, separator, and dried catalyst-loaded carbon paper were sequentially assembled into an aluminum-air battery. Figures 9-15 are the discharge polarization curves and power density curves of Co2P@NC-700, Co2P@NC-800, Co2P@NC-900, Co2P@NC-1000, Co2P@NC-2, Co2P@NC-3, Co2P@NC-5, Co2P@NC-6, Co2P@NCNRs-5, Co2P@NCNRs-10, Co2P@NCNRs-20, Co2P@NCNRs-25, Co2P@NC-melamine, Co2P@NC-F127, Co2P@NC-0-based aluminum-air batteries, rate curves at different current densities, and specific capacity curves at 20 mA·cm -2 discharge curves.

[0081] from Figure 9 It can be seen that the peak power density of Co2P@NC-800 is 182.85 mW·cm -2 , and the current density at the peak power density is 334.16 mA·cm -2 . From Figures 9-11 it can be seen that when the sintering temperature is 800°C, the P123 addition amount is 4g, and the graphene oxide addition amount is 15mg, the catalyst prepared is applied to an aluminum-air battery, and the aluminum-air battery exhibits the highest peak power density. From Figure 12 it can be seen that when the discharge current density is 1 mA·cm -2 , 5 mA·cm -2 , 10 mA·cm -2 and 20 mA·cm -2 , a stable voltage platform appears. The voltage platform of the Co2P@NC-4-based aluminum-air battery is 1.41V, 1.38V, 1.35V, 1.32V and 1.41V, respectively. After high-current density discharge, when the current density returns to 1 mA·cm -2 , the voltage platform still appears at 1.4V, indicating that it has excellent high-rate discharge performance.

[0082] Figure 14 are the rate performance of Co2P@NCNRs-x and Co2P@NC-melamine used as cathode catalysts for aluminum-air batteries at different current densities, and Figure 11It can be seen that, compared with Comparative Example 3, the example shows better reversibility and high-rate discharge performance, and the catalyst without adding graphene oxide does not form nitrogen-doped carbon-coated cobalt phosphide particles but cobalt phosphide particles are supported on nitrogen-doped carbon, so the high-rate discharge performance is not ideal.

[0083] Figure 15 For Co2P@NC-x used as an air cathode catalyst for aluminum-air batteries, the voltage of the Co2P@NC-3 composite material only decreased by 0.07 V after discharging for six hours at a current density of 20 mA·cm -2 The voltage of the Co2P@NC-3 composite material only decreased by 0.07 V after discharging for six hours at a current density of 20 mA·cm

[0084] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing a nitrogen-doped carbon-coated cobalt phosphide composite material, characterized in that, The method comprises the following steps: (1) ultrasonic dispersion of graphene oxide in water, then adding P123, cobalt acetate tetrahydrate, monocyane and diammonium hydrogen phosphate, stirring until the solution is clear; the mass ratio of graphene oxide, P123 and cobalt acetate tetrahydrate is (2.5-12.5):(1-3):1; (2) constant temperature stirring of the clear solution to obtain a gelatinous precursor by evaporation; (3) calcination of the gelatinous precursor under nitrogen, and natural cooling to obtain a nitrogen-doped carbon coated cobalt phosphide composite material; the calcination temperature is 700-1000℃, and the holding time is 1h.

2. The preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material as described in claim 1, characterized in that, In the step (1), the mass ratio of cobalt acetate tetrahydrate, monocyane and diammonium hydrogen phosphate is 2:4:0.

25.

3. The preparation method of the nitrogen-doped carbon-coated cobalt phosphide composite material as described in claim 1, characterized in that, In the step (2), the constant temperature is 60℃.

4. The nitrogen-doped carbon coated cobalt phosphide composite material prepared by the method of any one of claims 1-3.

5. The application of the nitrogen-doped carbon coated cobalt phosphide composite material of claim 4 in oxygen reduction and oxygen evolution reactions in alkaline electrolyte.

6. The application of the nitrogen-doped carbon coated cobalt phosphide composite material of claim 4 in aluminum-air batteries.

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