Carbon quantum dots modified nickel phosphorus cobalt nanosheet and preparation method and application thereof

Abstract

The application discloses carbon quantum dot modified nickel cobalt phosphide nanosheets and a preparation method and application thereof. The carbon quantum dot material with different diameters is synthesized by a solvent thermal method, the nickel cobalt precursor modified by the carbon quantum dot is prepared by a hydrothermal method, and finally the carbon quantum dot modified nickel cobalt phosphide nanosheet is prepared by a thermal phosphorization method. The carbon quantum dot modified nanosheet can effectively solve the problems of low electrocatalytic oxygen evolution activity and poor stability of the nickel cobalt phosphide. The carbon quantum dot modified nickel cobalt phosphide nanosheet prepared by the application has the overpotential of 240-350 mV when the current density is 10 mA / cm2 in the oxygen evolution reaction, and the catalytic current density can still maintain 75-93% of the initial current density after the oxygen evolution reaction for 100 hours under the condition.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of carbon quantum dots modified nickel phosphide cobalt nanosheet and its preparation method and application, belong to the design and development field of catalyst. BACKGROUND

[0002] In recent years, with the increasingly serious problems such as energy crisis and environmental pollution, the development of energy storage and conversion device is imperative. As an important half-reaction of metal-air battery and electrolytic water hydrogen production, the high energy barrier of oxygen evolution reaction affects the storage capacity of metal-air battery and the efficiency of electrolytic water hydrogen production. The development and use of high-efficiency catalyst can effectively reduce the energy barrier of oxygen evolution reaction. At present, in the field of oxygen evolution reaction, the commonly used catalyst is mainly based on noble metal catalyst. However, these noble metal-based catalysts are limited by the small natural reserves and poor stability. Therefore, designing economical and efficient non-noble metal-based catalyst is an effective way to promote the large-scale industrial application of metal-air battery and electrolytic water hydrogen production.

[0003] Nickel cobalt phosphide is considered as a potential material to replace noble metal-based catalyst due to its cost-effectiveness and simple preparation. However, in the oxygen evolution reaction, the oxidation modification and atomic overflow of nickel cobalt phosphide will cause the collapse of the surface structure, which will lead to the poor oxygen evolution activity and stability of nickel cobalt phosphide. The activity and stability of the catalyst are closely related to its surface interface structure, and the rational construction of the surface interface structure with specific properties will fundamentally improve the surface activity and structural stability of nickel cobalt phosphide nanosheet.

[0004] Therefore, it is of great significance to develop a nickel cobalt phosphide nanosheet with high surface activity and structural stability, which can essentially improve the electrocatalytic oxygen evolution performance of nickel cobalt phosphide nanosheet. SUMMARY

[0005] The first step of the present application is to provide a kind of carbon quantum dots modified nickel cobalt phosphide nanosheet, the second purpose of the present application is to provide a kind of preparation method of the carbon quantum dots modified nickel cobalt phosphide nanosheet, the third purpose of the present application is to provide the application of the carbon quantum dots modified nickel cobalt phosphide nanosheet in electrocatalytic oxygen evolution.

[0006] Technical scheme: the preparation method of a kind of carbon quantum dots modified nickel cobalt phosphide nanosheet of the present application, comprising the following steps:

[0007] (1) different diameter size carbon quantum dots materials are synthesized by solvothermal method;

[0008] (2) carbon quantum dots modified nickel cobalt precursor with different diameter size is prepared by hydrothermal method;

[0009] (3) preparing carbon quantum dots modified nickel cobalt phosphide nanosheets with different diameters by a thermal phosphating method.

[0010] Further, the average diameter of the carbon quantum dots material with different diameters is 1-10 nm; the average diameter of the carbon quantum dots modified nickel cobalt phosphide nanosheet is 5-30 nm, and the average thickness is 1-5 nm.

[0011] Further, step (1) comprises the following steps: preparing reaction solutions by using different amounts of citric acid, urea and N,N-dimethylformamide, respectively, carrying out solvothermal reactions, obtaining black-brown carbon quantum dot product solutions, adding the carbon quantum dot product solutions dropwise into a mixed solution of petroleum ether and ethyl acetate, centrifuging, washing, drying, uniformly dispersing in an ethanol solution, and obtaining carbon quantum dot ethanol solutions with different diameters.

[0012] Still further, the solid-liquid ratio of the citric acid, urea and N,N-dimethylformamide is 15-100: 30-65: 1 g / g / L.

[0013] Still further, the volume ratio of the carbon quantum dot product solution, petroleum ether and ethyl acetate is 1:3:1-5.

[0014] Still further, the relative content of the carbon quantum dots in the carbon quantum dot ethanol solution is 0.01-0.1 g / L.

[0015] Still further, the temperature of the solvothermal reaction is 120-200℃, and the time of the solvothermal reaction is 6-15 h.

[0016] Still further, the speed of the centrifugation is 6000-12000 rpm.

[0017] Further, step (2) comprises the following steps: dispersing nickel chloride, cobalt chloride and urotropin in deionized water with the carbon quantum dot ethanol solution with different diameters obtained in step (1), stirring until uniform dispersion, obtaining a mixed solution, adding a foamed nickel substrate to carry out a hydrothermal reaction, washing, drying, and obtaining a carbon quantum dot modified nickel cobalt precursor with different diameters.

[0018] Still further, the solid-liquid ratio of the nickel chloride, cobalt chloride, urotropin, carbon quantum dot ethanol solution: water is 1-20: 1-20: 5-30: 1-10: 1 g / g / g / L / L.

[0019] Still further, the thickness of the foamed nickel substrate is 0.5-3 mm.

[0020] Still further, the temperature of the hydrothermal reaction is 80-180℃, and the time of the hydrothermal reaction is 8-15 h.

[0021] Further, step (3) comprises the following steps: different diameter sizes of the nickel-cobalt precursor in step (2) are respectively phosphorized and calcined by a hot phosphorization method, so as to obtain carbon quantum dot modified nickel cobalt phosphide nanosheets with different diameter sizes.

[0022] Still further, the phosphorus source for the phosphorization and calcination is sodium hypophosphite, and the amount of the sodium hypophosphite is 5-20 times of the amount of the nickel-cobalt precursor.

[0023] Still further, the heating rate for the phosphorization and calcination is 2-5℃ / min, the temperature for the phosphorization and calcination is 200-400℃, and the time for the phosphorization and calcination is 1-5h.

[0024] The carbon quantum dot modified nickel cobalt phosphide nanosheet prepared by the preparation method is applied in electrocatalytic oxygen evolution.

[0025] Further, the application uses the carbon quantum dot modified nickel cobalt phosphide nanosheet as an anode oxygen evolution catalyst, a graphite rod as a counter electrode, a saturated calomel electrode as a reference electrode, and 1 mol / L of potassium hydroxide electrolyte to form a three-electrode system and perform an electrocatalytic oxygen evolution reaction.

[0026] The method uses foamed nickel as a substrate, is simple to operate, has mild conditions and low cost. The modification of carbon quantum dots not only provides more active sites for catalytic reactions, but also effectively protects the surface structure of nickel cobalt phosphide, enhancing the structural stability of the nickel cobalt phosphide nanosheet. Thus, high electrocatalytic oxygen evolution activity and stability are obtained. The carbon quantum dot modified nickel cobalt phosphide nanosheet prepared by the method has excellent electrocatalytic performance as an oxygen evolution catalyst.

[0027] Advantages: Compared with the prior art, the present application has the following significant advantages:

[0028] (1) The preparation method of the present application is simple to operate, controllable in conditions, safe in preparation process, does not require subsequent treatment, is friendly to the environment, and is suitable for large-scale promotion and production application.

[0029] (2) The present application uses foamed nickel as a self-supporting substrate, which is conducive to the transfer of electrons from the substrate to the catalyst surface to participate in the catalytic reaction, thereby promoting the progress of the oxygen evolution reaction; the strong combination is also conducive to reducing the loss of active substances, thereby improving the stability of the catalyst.

[0030] (3) The carbon quantum dot modified nickel cobalt phosphide nanosheet prepared by the present application has the advantages of unique morphology, stable structure, simple preparation, low cost, and excellent oxygen evolution catalytic performance.

[0031] (4) The carbon quantum dot modified nickel cobalt phosphide nanosheet prepared by the method has an overpotential of 240-350 mV when the current density is 10 mA / cm2 in an electrocatalytic oxygen evolution reaction test, and the catalytic current density remains 75-93% of the initial current density after 100 hours of oxygen evolution reaction under the condition. DETAILED DESCRIPTION

[0032] The technical solutions of the present application are further described below.

[0033] The preparation method of the carbon quantum dot modified nickel cobalt phosphide nanosheet comprises the following steps: first, controlling the conditions of the solvothermal reaction to accurately control the diameter of the carbon quantum dots; second, combining the carbon quantum dots and the nickel cobalt precursor by a hydrothermal method; and finally, preparing the carbon quantum dot modified nickel cobalt phosphide nanosheet by a phosphating calcination method.

[0034] The present application is realized by the following technical solutions, and the specific steps include:

[0035] (1) Synthesis of carbon quantum dots with different diameters: 50 mL of N,N-dimethylformamide solution, 15-100 g / L of citric acid, and 30-65 g / L of urea are prepared into a reaction solution, which is placed in a high-pressure reaction kettle and reacted at 120-200°C for 6-15 hours to obtain a black-brown carbon quantum dot solution with different diameters. The obtained carbon quantum dot solution is added dropwise into a mixed solution of petroleum ether and ethyl acetate at a volume ratio of 1:3:1-1:3:5. The carbon quantum dots are centrifuged at a speed of 6000-12000 rpm, and finally washed with deionized water and ethanol for 3-5 times, and then vacuum dried at 40-80°C for 8-24 hours. The carbon quantum dots are dispersed in an ethanol solution by ultrasonic dispersion. Thus, an ethanol dispersion of carbon quantum dots with different diameters is obtained, wherein the relative content of the carbon quantum dots is 0.01-0.1 g / L.

[0036] (2) Preparation of carbon quantum dot modified nickel cobalt precursor: under room temperature stirring conditions, 1-20 g / L of nickel chloride and cobalt chloride, 5-30 g / L of urotropine, and 1-10% of the carbon quantum dot ethanol dispersion solution are uniformly dispersed in 55 mL of deionized water to obtain a mixed solution. The 0.5-3 mm thick foam nickel substrate and the mixed solution are placed in a high-pressure reaction kettle and hydrothermally reacted at 80-180°C for 8-15 hours. Then, the substrate is washed with deionized water and ethanol for 3-5 times, and then vacuum dried at 40-80°C for 8-24 hours. Thus, a carbon quantum dot modified nickel cobalt precursor with different diameters is obtained.

[0037] (3) Preparation of carbon quantum dot modified nickel cobalt phosphide nanosheet: the carbon quantum dot modified nickel cobalt precursor prepared above is placed at the lower air inlet of the tube furnace, and sodium hypophosphite is placed at the upper air inlet. The amount of sodium hypophosphite is 5-20 times the amount of the precursor. The temperature rising rate of the tube furnace is set to 2-5 ℃ / min, the reaction temperature is 200-400 ℃, and the reaction time is 1-5 hours, so that carbon quantum dot modified nickel cobalt phosphide nanosheets of different diameters can be prepared.

[0038] (4) The material is applied to the oxygen evolution reaction, and the oxygen evolution performance is tested: the carbon quantum dot modified nickel cobalt phosphide nanosheet of different diameters prepared in step (3) is used as an anode oxygen evolution catalyst, a graphite rod and a saturated calomel electrode are used as a counter electrode and a reference electrode, and 1 mol / L potassium hydroxide is used as an electrolyte.

[0039] Example 1:

[0040] (1) Synthesis of carbon quantum dots: 50 mL of N,N-dimethylformamide solution, 90 g / L of citric acid, and 60 g / L of urea are prepared into a reaction solution, which is placed in a high-pressure reaction kettle and reacted at 120 ℃ for 8 hours to obtain a black-brown carbon quantum dot solution. The obtained carbon quantum dot solution is added dropwise into a mixed solution of petroleum ether and ethyl acetate at a volume ratio of 1:3:2. The carbon quantum dots are centrifuged at a speed of 10,000 rpm, and finally washed with deionized water and ethanol for 3 times respectively. After vacuum drying at 60 ℃ for 16 hours, carbon quantum dot solids are obtained, which are ultrasonically dispersed in an ethanol solution. The carbon quantum dot ethanol dispersion solution is obtained, wherein the relative content of carbon quantum dots is 0.02 g / L.

[0041] (2) Preparation of carbon quantum dot modified nickel cobalt precursor: under room temperature stirring conditions, 10 g / L of nickel chloride and cobalt chloride, 20 g / L of urotropine, and 5.62% of carbon quantum dot ethanol dispersion solution by volume of deionized water solution are uniformly dispersed in 55 mL of deionized water to obtain a mixed solution. A 1.5 mm thick nickel foam substrate and the above mixed solution are placed in a high-pressure reaction kettle and hydrothermally reacted at 140 ℃ for 8 hours. After being washed with deionized water and ethanol for 4 times respectively, the carbon quantum dot modified nickel cobalt precursor is obtained after vacuum drying at 80 ℃ for 24 hours.

[0042] (3) Preparation of carbon quantum dot modified nickel cobalt phosphide nanosheet: the carbon quantum dot modified nickel cobalt precursor prepared above is placed at the lower air inlet of the tube furnace, and sodium hypophosphite is placed at the upper air inlet. The amount of sodium hypophosphite is 10 times the amount of the precursor. The temperature rising rate of the tube furnace is set to 5 ℃ / min, the reaction temperature is 350 ℃, and the reaction time is 2 hours, so that carbon quantum dot modified nickel cobalt phosphide nanosheets can be prepared.

[0043] (4) The carbon quantum dots modified nickel cobalt phosphide nanosheet material obtained in step (3) is applied to an oxygen evolution reaction, and the oxygen evolution performance is tested: the carbon quantum dots modified nickel cobalt phosphide nanosheet prepared in step (3) is used as an anode oxygen evolution catalyst, a graphite rod and a saturated calomel electrode are used as a counter electrode and a reference electrode, and 1 mol / L potassium hydroxide is used as an electrolyte.

[0044] The carbon quantum dots solid and the carbon quantum dots modified nickel cobalt phosphide nanosheet synthesized in this example are analyzed by high-resolution transmission electron microscopy. The results show that the average size of the carbon quantum dots synthesized in this example is 4.09 nm, the average size of the carbon quantum dots modified nickel cobalt phosphide nanosheet is 10.51 nm, and the average thickness is 3.26 nm. The oxygen evolution performance test results show that when the current density is 10 mA / cm2, the overpotential is 240 mV, and after 100 hours of oxygen evolution reaction under this condition, the catalytic current density of the carbon quantum dots modified nickel cobalt phosphide nanosheet still maintains 93% of the initial current density.

[0045] Example 2:

[0046] (1) Synthesis of carbon quantum dots: 50 mL of N,N-dimethylformamide solution, 50 g / L of citric acid, and 46 g / L of urea are prepared into a reaction solution, which is placed in a high-pressure reaction kettle and reacted at 140°C for 13 hours to obtain a black-brown carbon quantum dots solution. The obtained carbon quantum dots solution is added dropwise into a mixed solution of petroleum ether and ethyl acetate at a volume ratio of 1:3:1. The carbon quantum dots are centrifuged at a speed of 8000 rpm, and finally washed with deionized water and ethanol for 3 times respectively, and then vacuum dried at 65°C for 14 hours to obtain carbon quantum dots solid, which is ultrasonically dispersed in an ethanol solution. Different diameter sizes of carbon quantum dots ethanol dispersion are obtained, and the relative content of carbon quantum dots is 0.04 g / L.

[0047] (2) Preparation of carbon quantum dots modified nickel cobalt precursor: under room temperature stirring conditions, 5 g / L of nickel chloride and cobalt chloride, 15 g / L of urotropine, and 9.11% of carbon quantum dots ethanol dispersion solution by volume of deionized water are uniformly dispersed in 55 mL of deionized water to obtain a mixed solution. A 1 mm thick nickel foam substrate and the above mixed solution are placed in a high-pressure reaction kettle and hydrothermally reacted at 100°C for 12 hours. After washing with deionized water and ethanol for 3 times respectively, vacuum drying is carried out at 60°C for 24 hours. The carbon quantum dots modified nickel cobalt precursor is obtained.

[0048] (3) Preparation of carbon quantum dot modified nickel cobalt phosphide nanosheet: the carbon quantum dot modified nickel cobalt precursor prepared above is placed at the lower air inlet of the tube furnace, and sodium hypophosphite is placed at the upper air inlet. The amount of sodium hypophosphite is 8 times the amount of the precursor. The temperature rising rate of the tube furnace is set to 3 ℃ / min, the reaction temperature is 300 ℃, and the reaction time is 1.5 hours. Thus, the carbon quantum dot modified nickel cobalt phosphide nanosheet is prepared.

[0049] (4) The carbon quantum dot modified nickel cobalt phosphide nanosheet material obtained in step (3) is applied to the oxygen evolution reaction, and the oxygen evolution performance is tested: the carbon quantum dot modified nickel cobalt phosphide nanosheet prepared in step (3) is used as an anode oxygen evolution catalyst, a graphite rod and a saturated calomel electrode are used as a counter electrode and a reference electrode, and 1 mol / L potassium hydroxide is used as an electrolyte.

[0050] The carbon quantum dot solid synthesized in this embodiment and the carbon quantum dot modified nickel cobalt phosphide nanosheet prepared are analyzed by high-resolution transmission electron microscopy. The results show that the average size of the carbon quantum dots synthesized in this embodiment is 4.59 nm; the average size of the carbon quantum dot modified nickel cobalt phosphide nanosheet is 8.33 nm, and the average thickness is 2.15 nm. The oxygen evolution performance test results show that when the current density is 10 mA / cm2, the overpotential is 256 mV. After 100 hours of oxygen evolution reaction under this condition, the catalytic current density of the carbon quantum dot modified nickel cobalt phosphide nanosheet remains 78% of the initial current density.

[0051] Example 3:

[0052] (1) Synthesis of carbon quantum dots: 50 mL of N,N-dimethylformamide solution, 95 g / L of citric acid, and 65 g / L of urea are prepared into a reaction solution, which is placed in a high-pressure reaction kettle and reacted at 200 ℃ for 15 hours to obtain a black-brown carbon quantum dot solution. The obtained carbon quantum dot solution is added dropwise into a mixed solution of petroleum ether and ethyl acetate at a volume ratio of 1:3:4. The carbon quantum dots are centrifuged at a speed of 9500 rpm, and finally washed with deionized water and ethanol for 3 times respectively. After vacuum drying at 75 ℃ for 22 hours, carbon quantum dot solid is obtained, which is ultrasonically dispersed in an ethanol solution. Thus, a carbon quantum dot ethanol dispersion liquid is obtained, in which the relative content of carbon quantum dots is 0.08 g / L.

[0053] (2) Preparation of carbon quantum dot modified nickel cobalt precursor: under room temperature stirring condition, 10 grams / liter of nickel chloride and cobalt chloride, 30 grams / liter of urotropine and 3.58% carbon quantum dot ethanol dispersion solution in deionized water were uniformly dispersed in 55 milliliters of deionized water to obtain a mixed solution. The 0.5 millimeter thick nickel foam substrate and the above mixed solution were placed in a high-pressure reaction kettle, and after hydrothermal reaction at 160°C for 8 hours, they were washed with deionized water and ethanol for 5 times respectively, and then vacuum dried at 75°C for 16 hours. The carbon quantum dot modified nickel cobalt precursor was obtained.

[0054] (3) Preparation of carbon quantum dot modified nickel cobalt phosphide nanosheet: the carbon quantum dot modified nickel cobalt precursor prepared above was placed at the lower wind port of the tube furnace, and sodium hypophosphite was placed at the upper wind port, and the amount of sodium hypophosphite was 15 times the amount of the precursor. The temperature rising rate of the tube furnace was set to 2°C / min, the reaction temperature was 400°C, and the reaction time was 3 hours, and the carbon quantum dot modified nickel cobalt phosphide nanosheet was prepared.

[0055] (4) The carbon quantum dot modified nickel cobalt phosphide nanosheet material obtained in step (3) was applied to the oxygen evolution reaction, and the oxygen evolution performance was tested: the carbon quantum dot modified nickel cobalt phosphide nanosheet prepared in step (3) was used as an anode oxygen evolution catalyst, a graphite rod and a saturated calomel electrode were used as a counter electrode and a reference electrode, and 1 mol / liter potassium hydroxide was used as an electrolyte.

[0056] The carbon quantum dot solid synthesized in this example and the carbon quantum dot modified nickel cobalt phosphide nanosheet prepared were analyzed by high-resolution transmission electron microscopy. The results show that the average size of the carbon quantum dots synthesized in this example is 5.18 nanometers; the average diameter of the carbon quantum dot modified nickel cobalt phosphide nanosheet is 12.23 nanometers, and the average thickness is 3.58 nanometers. The oxygen evolution performance test results show that when the current density is 10 milliamperes / square centimeter, the overpotential is 302 millivolts, and after 100 hours of oxygen evolution reaction under this condition, the catalytic current density of the carbon quantum dot modified nickel cobalt phosphide nanosheet still maintains 89% of the initial current density.

[0057] Example 4:

[0058] (1) Synthesis of carbon quantum dots: 50 mL of N, N-dimethylformamide solution, 70 g / L of citric acid and 55 g / L of urea were prepared into a reaction solution, which was placed in a high-pressure reaction kettle and reacted at 170°C for 10 hours to obtain a black-brown carbon quantum dot solution. The obtained carbon quantum dot solution was added dropwise into a mixed solution of petroleum ether and ethyl acetate at a volume ratio of 1:3:5. The carbon quantum dots were centrifuged at a speed of 8500 rpm, and finally washed with deionized water and ethanol for 4 times, respectively, and then vacuum dried at 50°C for 12 hours to obtain carbon quantum dot solids, which were ultrasonically dispersed in an ethanol solution. Thus, a carbon quantum dot ethanol dispersion was obtained, wherein the relative content of carbon quantum dots was 0.1 g / L.

[0059] (2) Preparation of carbon quantum dot modified nickel-cobalt precursor: under room temperature stirring conditions, 8 g / L of nickel chloride and cobalt chloride, 27 g / L of urotropine and 8.71% of carbon quantum dot ethanol dispersion by volume of deionized water solution were uniformly dispersed in 55 mL of deionized water to obtain a mixed solution. A 3 mm thick nickel foam substrate and the above mixed solution were placed in a high-pressure reaction kettle, and after hydrothermal reaction at 120°C for 10 hours, they were washed with deionized water and ethanol for 4 times, respectively, and then vacuum dried at 50°C for 20 hours. Thus, a carbon quantum dot modified nickel-cobalt precursor was obtained.

[0060] (3) Preparation of carbon quantum dot modified nickel cobalt phosphide nanosheet: the carbon quantum dot modified nickel cobalt precursor prepared above was placed at the lower wind port of a tube furnace, and sodium hypophosphite was placed at the upper wind port, and the amount of sodium hypophosphite was 20 times the amount of the precursor. The tube furnace was set to have a heating rate of 2°C / min, a reaction temperature of 280°C and a reaction time of 2.5 hours, and thus the carbon quantum dot modified nickel cobalt phosphide nanosheet was prepared.

[0061] (4) The carbon quantum dot modified nickel cobalt phosphide nanosheet material obtained in step (3) was applied to the oxygen evolution reaction, and the oxygen evolution performance was tested: the carbon quantum dot modified nickel cobalt phosphide nanosheet prepared in step (3) was used as an anode oxygen evolution catalyst, a graphite rod and a saturated calomel electrode were used as a counter electrode and a reference electrode, and 1 mol / L of potassium hydroxide was used as an electrolyte.

[0062] The carbon quantum dot solids synthesized in this embodiment and the carbon quantum dot modified nickel cobalt phosphide nanosheet prepared were analyzed by high-resolution transmission electron microscopy. The results showed that the average size of the carbon quantum dots synthesized in this embodiment was 5.18 nm; the average diameter of the carbon quantum dot modified nickel cobalt phosphide nanosheet was 12.23 nm, and the average thickness was 4.63 nm. The oxygen evolution performance test results showed that when the current density was 10 mA / cm2, the overpotential was 326 mV, and after 100 hours of oxygen evolution reaction under this condition, the catalytic current density of the carbon quantum dot modified nickel cobalt phosphide nanosheet still maintained 82% of the initial current density.

[0063] Comparative Example 1:

[0064] (1) Preparation of nickel-cobalt precursor: under stirring at room temperature, 10 g / L of nickel chloride and cobalt chloride and 20 g / L of urotropine were uniformly dispersed in 55 mL of deionized water to obtain a mixed solution. A 1.5 mm thick nickel foam substrate and the above mixed solution were placed in a high-pressure reaction kettle, and after hydrothermal reaction at 140°C for 8 hours, they were rinsed with deionized water and ethanol for 4 times respectively, and then vacuum dried at 40°C for 18 hours. Thus, the nickel-cobalt precursor was obtained.

[0065] (2) Preparation of nickel-cobalt phosphide nanosheet: the above prepared nickel-cobalt precursor was placed at the lower wind port of a tube furnace, and sodium hypophosphite was placed at the upper wind port, and the amount of sodium hypophosphite was 10 times the amount of the precursor. The tube furnace was set to have a heating rate of 3°C / min, a reaction temperature of 350°C, and a reaction time of 1.5 hours, and thus the nickel-cobalt phosphide nanosheet was prepared.

[0066] (3) The nickel-cobalt phosphide nanosheet material obtained in step (2) was applied to the oxygen evolution reaction, and the oxygen evolution performance was tested: the nickel-cobalt phosphide nanosheet prepared in step (2) was used as an anode oxygen evolution catalyst, a graphite rod and a saturated calomel electrode were used as a counter electrode and a reference electrode, and 1 mol / L of potassium hydroxide was used as an electrolyte.

[0067] The nickel-cobalt phosphide nanosheet was analyzed by high-resolution transmission electron microscopy. The results showed that the average size of the nanosheet was 3 nm, and the average thickness was 8 nm. The oxygen evolution performance test results showed that when the current density was 10 mA / cm2, the overpotential was 355 mV, and after 100 hours of oxygen evolution reaction under this condition, the catalytic current density of the unmodified carbon quantum dot nickel-cobalt phosphide nanosheet was only 65% of the initial current density.

Claims

1. Application of carbon quantum dots modified nickel phosphorus cobalt nanosheet in electrocatalytic oxygen evolution, characterized in that, The preparation method of the carbon quantum dot modified nickel cobalt phosphide nano comprises the following steps: (1) Synthesizing carbon quantum dot materials with different diameters by a solvothermal method: preparing a reaction solution by using different amounts of citric acid, urea and N, N-dimethylformamide, respectively performing solvothermal reaction to obtain a carbon quantum dot product solution, adding the carbon quantum dot product solution drop by drop into a mixed solution of petroleum ether and ethyl acetate, centrifuging, washing, drying, and uniformly dispersing in an ethanol solution to obtain a carbon quantum dot ethanol solution with different diameters; the solid-liquid ratio of the citric acid, urea and N, N-dimethylformamide is 15-100: 30-65: 1 g / g / L, the volume ratio of the carbon quantum dot product solution, petroleum ether and ethyl acetate is 1:3:1-5, the relative content of the carbon quantum dots in the carbon quantum dot ethanol solution is 0.01-0.1 g / L, the temperature of the solvothermal reaction is 120-200 DEG C, the time of the solvothermal reaction is 6-15 h, and the speed of the centrifugation is 6000-12000 r / min; (2) Preparing nickel cobalt precursors modified by carbon quantum dots with different diameters by a hydrothermal method: dispersing nickel chloride, cobalt chloride and urotropin in deionized water respectively and with the carbon quantum dot ethanol solution with different diameters obtained in step (1) to obtain a mixed solution, stirring until uniform dispersion, adding a foamed nickel substrate to perform hydrothermal reaction, washing and drying to obtain nickel cobalt precursors modified by carbon quantum dots with different diameters; the solid-liquid ratio of the nickel chloride, cobalt chloride, urotropin and carbon quantum dot ethanol solution to water is 1-20: 1-20: 5-30: 1-10: 1 g / g / g / L / L, the thickness of the foamed nickel substrate is 0.5-3 mm, the temperature of the hydrothermal reaction is 80-180 DEG C, and the time of the hydrothermal reaction is 8-15 h; (3) Preparing carbon quantum dot modified nickel cobalt phosphide nanosheets with different diameters by a thermal phosphating method: performing phosphating calcination on the nickel cobalt precursors with different diameters in step (2) by the thermal phosphating method to obtain carbon quantum dot modified nickel cobalt phosphide nanosheets with different diameters; the phosphorus source of the phosphating calcination is sodium hypophosphite, the amount of the sodium hypophosphite is 5-20 times of the amount of the nickel cobalt precursors, the heating rate of the phosphating calcination is 2-5 DEG C / min, the temperature of the phosphating calcination is 200-400 DEG C, and the time of the phosphating calcination is 1-5 h; the average diameter of the carbon quantum dot materials with different diameters is 1-10 nm, and the average diameter of the carbon quantum dot modified nickel cobalt phosphide nanosheets is 5-30 nm and the average thickness is 1-5 nm.