A nitrogen-doped carbon-supported metal nickel-cobalt catalyst, a preparation method and application thereof

Abstract

The application discloses a nitrogen-doped carbon loaded metal nickel-cobalt catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: S1. nickel salt and cobalt salt are added into a carboxylic acid solution of chitosan, stirring until a sol state is obtained, and then drying to obtain a nitrogen-doped carbon loaded metal nickel-cobalt catalyst precursor; the ratio of the sum of the mass of the nickel salt and the cobalt salt to the mass of the chitosan is (1-1.5):1; the molar ratio of Ni in the nickel salt to Co in the cobalt salt is (3-7):(3-7); S2. the nitrogen-doped carbon loaded metal nickel-cobalt catalyst precursor is pyrolyzed under the condition of 400-600 DEG C for 2-5 hours to obtain a nitrogen-doped carbon loaded metal nickel-cobalt catalyst. The nitrogen-doped carbon loaded metal nickel-cobalt catalyst has high catalytic activity and stability when used for hydrogen production by alkaline electrolysis of water, and can be applied to the field of hydrogen production by alkaline electrolysis of water.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hydrogen production by water electrolysis, and more particularly, to a nitrogen-doped carbon-supported metal nickel-cobalt catalyst and a preparation method and application thereof. BACKGROUND

[0002] With the current situation of global fossil energy crisis and increasing greenhouse gas content, people urgently need to explore clean and sustainable energy resources to gradually reduce the use of fossil energy. Hydrogen has been considered as an ideal renewable energy carrier for a long time due to its high energy density (142 MJ kg -1 ), good utilization efficiency and ecological friendly properties, so realizing sustainable hydrogen production is one of the most attractive and competitive technologies. Hydrogen production by water electrolysis is one of the most promising ways because it has the advantages of zero carbon emission, high efficiency, energy storage, and can be combined with wind power, water conservancy and other renewable energy power generation to realize the recycling of energy. The cathode catalyst for hydrogen production by water electrolysis usually uses platinum-carbon catalyst, but the storage of platinum is low and the cost is high, which limits the large-scale industrial application of hydrogen production by water electrolysis.

[0003] To solve this problem, Chinese invention patent CN109499596A discloses a method for preparing a metal-nitrogen-phosphorus-doped porous carbon bifunctional electrocatalyst by carbonizing phosphatized chitosan and metal salt at 700-900℃. The catalyst has better performance than commercial Pt / C catalyst, but still has the problem of insufficient catalytic performance in alkaline medium (the overpotential is 240mV when the current density is 10mA·cm -2 ). SUMMARY

[0004] The primary object of the present application is to overcome the problem of insufficient catalytic performance of the existing water electrolysis hydrogen production catalyst in alkaline medium, and to provide a preparation method of a nitrogen-doped carbon-supported metal nickel-cobalt catalyst. The catalyst prepared by the method has an overpotential of less than 180mV when the current density is 10mA·cm -2 .

[0005] Another object of the present application is to provide a nitrogen-doped carbon-supported metal nickel-cobalt catalyst.

[0006] A further object of the present application is to provide the application of the nitrogen-doped carbon-supported metal nickel-cobalt catalyst in alkaline water electrolysis hydrogen production.

[0007] The above objects of the present application are achieved by the following technical solutions:

[0008] A preparation method of a nitrogen-doped carbon-supported metal nickel-cobalt catalyst, comprising the following steps:

[0009] S1. adding nickel salt and cobalt salt into a carboxylic acid solution of chitosan, drying after stirring to sol state to obtain a nitrogen-doped carbon supported metal nickel-cobalt catalyst precursor; the ratio of the sum of the mass of the nickel salt and the cobalt salt to the mass of the chitosan is (1-1.5):1; the molar ratio of Ni in the nickel salt to Co in the cobalt salt is (3-7):(3-7);

[0010] S2. pyrolyzing the nitrogen-doped carbon supported metal nickel-cobalt catalyst precursor at 400-600℃ for 2-5h to obtain a nitrogen-doped carbon supported metal nickel-cobalt catalyst.

[0011] The present application makes use of the chelation of the amino and hydroxyl groups contained in chitosan with cobalt and nickel ions, so that the material has a regular sheet-like morphology; at the same time, by controlling the pyrolysis temperature, the metal particles have a small particle size and good dispersity, and since cobalt and nickel have strong hydrogen adsorption capacity, the electronic structure is further optimized by constructing a nickel-cobalt alloy, so that it has more suitable water decomposition capacity and hydrogen adsorption free energy under alkaline conditions, thereby having higher catalytic activity and stability for alkaline electrolytic water hydrogen production.

[0012] The carboxylic acid in the present application is selected from one or both of acetic acid and formic acid.

[0013] The carboxylic acid solution of conventional concentration in the art can be used in the present application. Preferably, the concentration of the carboxylic acid solution is 1-3wt%. More preferably, it is 1.25wt%.

[0014] Preferably, in step S1, the nickel salt is selected from nickel nitrate, and the cobalt salt is selected from cobalt nitrate. Through repeated experiments, the inventors found that when the corresponding nitrate salt is selected for the cobalt salt and the nickel salt, the nitrogen dioxide produced during the pyrolysis process and the instantaneous strong pressure can pore the carbon.

[0015] Preferably, in step S1, the ratio of the sum of the mass of the nickel salt and the cobalt salt to the mass of the chitosan is (1.1-1.3):1. More preferably, it is 1.24:1.

[0016] Preferably, in step S1, the molar ratio of Ni in the nickel salt to Co in the cobalt salt is (5-7):(3-5).

[0017] More preferably, in step S1, the molar ratio of Ni in the nickel salt to Co in the cobalt salt is 7:3.

[0018] Preferably, in step S1, the stirring temperature is 50-100℃, and the stirring rate is 500-900rpm / min.

[0019] More preferably, in step S1, the stirring temperature is 80℃, and the stirring rate is 800rpm / min.

[0020] Preferably, in step S1, the drying temperature is 40-100 DEG C, and the time is 8-24h.

[0021] More preferably, in step S1, the drying temperature is 50 DEG C, and the drying time is 12h.

[0022] Preferably, in step S2, the pyrolysis treatment temperature is 450-550 DEG C, and the time is 2-3h.

[0023] More preferably, in step S2, the pyrolysis treatment temperature is 500 DEG C, and the time is 2h.

[0024] The pyrolysis treatment atmosphere according to the present application is a nitrogen atmosphere, and the nitrogen flow rate is 50-200ml / min.

[0025] The present application also provides a nitrogen-doped carbon supported metal nickel-cobalt catalyst prepared by the above method.

[0026] The nitrogen-doped carbon supported metal nickel-cobalt catalyst according to the present application has a sheet-like structure, a thickness of 15-20nm, and the metal is uniformly embedded in the carbon layer in the form of particles with a size of 5-10nm. Smaller metal particles and dispersion will provide more active sites for catalytic reactions.

[0027] The present application also provides the use of the nitrogen-doped carbon supported metal nickel-cobalt catalyst in the production of hydrogen by alkaline electrolysis of water.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] The present application provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst. The method utilizes the chelation of chitosan with nickel and cobalt salts to make the nitrogen-doped carbon supported metal nickel-cobalt catalyst have a regular sheet-like morphology. At the same time, by controlling the pyrolysis treatment temperature, the metal particles have a smaller particle size and good dispersion, and the nickel-cobalt alloy structure has an optimized electronic structure, which makes it have a more suitable water decomposition ability and hydrogen adsorption free energy, thereby having higher catalytic activity and stability in the production of hydrogen by alkaline electrolysis of water. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The XRD pattern of the nitrogen-doped carbon supported metal nickel-cobalt catalyst provided for Example 1 of the present application;

[0031] Figure 2 The scanning electron microscope pattern of the nitrogen-doped carbon supported metal nickel-cobalt catalyst provided for Example 1 of the present application;

[0032] Figure 3 The transmission electron microscope pattern of the nitrogen-doped carbon supported metal nickel-cobalt catalyst provided for Example 1 of the present application;

[0033] Figure 4 Linear sweep voltammetry curve of the nitrogen-doped carbon supported metal nickel-cobalt catalyst provided for the present embodiment 1-3 in 1M KOH solution.

[0034] Figure 5 Stability test curve of the nitrogen-doped carbon supported metal nickel-cobalt catalyst provided for the present embodiment 1. DETAILED DESCRIPTION

[0035] In order to more clearly, completely describe the technical solutions of the present application, the following will further illustrate the present application through specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. Various changes can be made within the scope of the present application.

[0036] Embodiment 1

[0037] The present embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, and the specific steps are as follows:

[0038] S1. 2g of chitosan was dissolved in an acetic acid solution with a concentration of 1.25wt%, and constant temperature stirring was carried out on a magnetic stirrer at a temperature of 80℃ and a stirring rate of 800rpm / min. After the chitosan was completely dissolved, nickel nitrate hexahydrate and cobalt nitrate hexahydrate were added, and constant temperature stirring was continued until a sol state was reached. Then, it was placed in a 50℃ drying oven for drying for 12h, and then taken out to obtain a nitrogen-doped carbon supported metal nickel-cobalt catalyst precursor. The ratio of the sum of the mass of the nickel nitrate hexahydrate and the cobalt nitrate hexahydrate to the mass of the chitosan was 1.24:1. The molar ratio of Ni in the nickel nitrate hexahydrate to Co in the cobalt nitrate hexahydrate was 7:3.

[0039] S2. The nitrogen-doped carbon supported metal nickel-cobalt catalyst precursor was ground and then loaded into a corundum crucible. Pyrolysis treatment was carried out in a tube furnace, 200ml / min of nitrogen was introduced, and the temperature was programmed to increase to 500℃ at a rate of 2℃ / min for 2h of pyrolysis. After the temperature was lowered to room temperature, a nitrogen-doped carbon supported metal nickel-cobalt catalyst was obtained.

[0040] Embodiment 2

[0041] The present embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from embodiment 1 in that the pyrolysis temperature in step S2 is 400℃.

[0042] Embodiment 3

[0043] The present embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from embodiment 1 in that the pyrolysis temperature in step S2 is 600℃.

[0044] Embodiment 4

[0045] The embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from the embodiment 1 in that in step S2, the pyrolysis temperature is 450 DEG C, and the pyrolysis time is 5h.

[0046] Embodiment 5

[0047] The embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from the embodiment 1 in that in step S2, the pyrolysis temperature is 550 DEG C, and the pyrolysis time is 2h.

[0048] Embodiment 6

[0049] The embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from the embodiment 1 in that in step S1, nickel nitrate and cobalt nitrate with a molar ratio of Ni:Co of 5:5 are added.

[0050] Embodiment 7

[0051] The embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from the embodiment 1 in that in step S1, nickel nitrate and cobalt nitrate with a molar ratio of Ni:Co of 3:7 are added.

[0052] Embodiment 8

[0053] The embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from the embodiment 1 in that in step S1, the ratio of the sum of the mass of the nickel nitrate hexahydrate and the mass of the cobalt nitrate hexahydrate to the mass of the chitosan is 1:1.

[0054] Embodiment 9

[0055] The embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from the embodiment 1 in that in step S1, the ratio of the sum of the mass of the nickel nitrate hexahydrate and the mass of the cobalt nitrate hexahydrate to the mass of the chitosan is 1.1:1.

[0056] Embodiment 10

[0057] The embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from the embodiment 1 in that in step S1, the ratio of the sum of the mass of the nickel nitrate hexahydrate and the mass of the cobalt nitrate hexahydrate to the mass of the chitosan is 1.3:1.

[0058] Embodiment 11

[0059] The embodiment provides a preparation method of a nitrogen-doped carbon supported metal nickel-cobalt catalyst, which is different from the embodiment 1 in that in step S1, the ratio of the sum of the mass of the nickel nitrate hexahydrate and the mass of the cobalt nitrate hexahydrate to the mass of the chitosan is 1.5:1.

[0060] Example 12

[0061] The present example provides a preparation method of a nitrogen-doped carbon supported metallic nickel-cobalt catalyst, which is different from example 1 in that in step S1, the stirring temperature is 50℃, the stirring rate is 900 rpm / min, the drying temperature is 100℃, and the drying time is 8h.

[0062] Example 13

[0063] The present example provides a preparation method of a nitrogen-doped carbon supported metallic nickel-cobalt catalyst, which is different from example 1 in that in step S1, the stirring temperature is 100℃, the stirring rate is 500 rpm / min, the drying temperature is 40℃, and the drying time is 24h.

[0064] Example 14

[0065] The present example provides a preparation method of a nitrogen-doped carbon supported metallic nickel-cobalt catalyst, which is different from example 1 in that formic acid is used instead of acetic acid.

[0066] Comparative Example 1

[0067] The present comparative example provides a preparation method of a metal-nitrogen-phosphorus doped porous carbon bifunctional electrocatalyst, and the specific preparation steps are as follows:

[0068] S1. 1.79g of chitosan was weighed with an electronic balance and added to a round-bottom flask containing 100mL of 1% (V / V) acetic acid solution, which was stirred uniformly with a magnetic stirrer; 20mmol of phosphoric acid was dissolved in 10mL of water, which was then added dropwise to the round-bottom flask containing the chitosan solution, and stirred uniformly; finally, 20mmol of formaldehyde solution was added, and placed in an 80℃ oil bath for overnight reaction. After the reaction, the flask was cooled to room temperature, and the solution in the flask was poured into a dialysis bag, dialyzed for two days, and freeze-dried, and the final solid was the phosphated chitosan;

[0069] S2. 0.1g of phosphated chitosan and 1mmol of cobalt nitrate were dissolved in 20mL of water, and stirred uniformly; then it was placed in an 80℃ oil bath for evaporation, and the obtained solid product was treated with carbonization at 900℃ for 2h in a tube furnace. The carbonized solid was dispersed in 1mmol / L hydrochloric acid solution, stirred for 3h, suction filtered, and dried to obtain a cobalt-nitrogen-phosphorus doped porous carbon bifunctional electrocatalyst.

[0070] Test characterization

[0071] Figure 1 The XRD pattern of the nitrogen-doped carbon supported metallic nickel-cobalt catalyst provided for example 1. From the XRD pattern, it can be seen that the catalyst has a face-centered cubic structure, and the diffraction peaks of the catalyst are consistent with the standard face-centered cubic structure of nickel-cobalt alloy. Figure 1As can be seen, Example 1 of this application successfully prepared a nitrogen-doped carbon-supported nickel-cobalt catalyst. The XRD patterns of the nitrogen-doped carbon-supported nickel-cobalt catalysts described in Examples 2-14 are basically consistent with those in Example 1.

[0072] Figure 2 Scanning electron microscope (SEM) image of the nitrogen-doped carbon-supported nickel-cobalt catalyst provided in Example 1. From Figure 2 It can be seen that the nitrogen-doped carbon-supported nickel-cobalt catalyst has a plate-like structure with a thickness of about 17 nm. The scanning electron microscope (SEM) images of the nitrogen-doped carbon-supported nickel-cobalt catalysts described in Examples 2-14 are similar to those in Example 1, with a plate-like structure thickness of 15-20 nm.

[0073] Figure 3 Transmission electron microscopy (TEM) image of the nitrogen-doped carbon-supported nickel-cobalt catalyst provided in Example 1. From... Figure 3 It can be seen that the metal is uniformly dispersed in the carbon layer, and the metal particles have a diameter of approximately 6.4 nm.

[0074] The nitrogen-doped carbon-supported nickel-cobalt catalysts described in Examples 1-3 of this application were subjected to alkaline HER performance tests, and the test results are as follows: Figure 4 As shown. From Figure 4 It can be seen that when the current density is 50 mA·cm -2 At that time, the nitrogen-doped carbon-supported nickel-cobalt catalysts described in Examples 1-3 exhibited hydrogen evolution overpotentials of 175 mV, 287 mV, and 256 mV, respectively, in 1 M KOH solution. The nitrogen-doped carbon-supported nickel-cobalt catalysts described in Examples 1-14 exhibited hydrogen evolution overpotentials of 175 mV, 287 mV, and 256 mV, respectively, at a current density of 10 mA·cm⁻¹. -2 and 50mA·cm -2 The overpotentials at that time are shown in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] As shown in Table 1 above, the nitrogen-doped carbon-supported nickel-cobalt catalysts described in Examples 1-14 of this invention all exhibit low overpotentials in alkaline media. In contrast, the electrocatalyst described in Comparative Example 1 exhibits low overpotentials at a current density of 10 mA·cm⁻¹. -2 At that time, the overpotential was 240 mV (CN109499596). Therefore, it can be seen that, compared with existing catalysts, the nitrogen-doped carbon-supported nickel-cobalt catalyst of this invention has higher catalytic activity.

[0079] The nitrogen-doped carbon-supported nickel-cobalt catalyst described in Example 1 of this application was subjected to stability testing. The test environment was 1M KOH electrolyte at room temperature, and the overpotential was 140mV. The test results are as follows. Figure 5As shown in Figure 6, the catalyst can be stably operated for more than 12 hours at a constant voltage of 140 mV overpotential, indicating that the nitrogen-doped carbon-supported metal nickel-cobalt catalyst described in Example 1 has excellent stability. Figure 5 As shown in Figure 6, the catalyst can be stably operated for more than 12 hours at a constant voltage of 140 mV overpotential, indicating that the nitrogen-doped carbon-supported metal nickel-cobalt catalyst described in Example 1 has excellent stability.

[0080] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and also impossible to exhaust all the implementation modes. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. Use of a nitrogen-doped carbon-supported metal nickel-cobalt catalyst in the production of hydrogen by alkaline electrolysis of water, characterized in that, The preparation method of the nitrogen-doped carbon-supported metal nickel-cobalt catalyst comprises the following steps: S1. Adding nickel salt and cobalt salt to a carboxylic acid solution of chitosan, stirring to a sol state, and drying to obtain a nitrogen-doped carbon-supported metal nickel-cobalt catalyst precursor; the ratio of the sum of the mass of the nickel salt and the cobalt salt to the mass of the chitosan is 1.24:1; the molar ratio of Ni in the nickel salt to Co in the cobalt salt is 7:3; S2. Pyrolysis treatment of the nitrogen-doped carbon-supported metal nickel-cobalt catalyst precursor at 500°C for 2h to obtain a nitrogen-doped carbon-supported metal nickel-cobalt catalyst; In step S1, the carboxylic acid is selected from one or both of acetic acid and formic acid; In step S1, the stirring temperature is 50-100°C, and the stirring rate is 500-900 rpm / min; In step S1, the drying temperature is 40-100°C, and the time is 8-24h.

2. The use according to claim 1, characterized in that, In step S1, the nickel salt is selected from nickel nitrate, and the cobalt salt is selected from cobalt nitrate.

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