CN108906106B - FeNi/N-C high-dispersion core-shell structure catalyst and preparation method thereof - Google Patents
FeNi/N-C high-dispersion core-shell structure catalyst and preparation method thereof Download PDFInfo
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- CN108906106B CN108906106B CN201810723159.4A CN201810723159A CN108906106B CN 108906106 B CN108906106 B CN 108906106B CN 201810723159 A CN201810723159 A CN 201810723159A CN 108906106 B CN108906106 B CN 108906106B
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Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
-
- B01J35/398—
Abstract
A FeNi/N-C high-dispersion core-shell structure catalyst and a preparation method thereof are disclosed, wherein the FeNi/N-C high-dispersion core-shell structure catalyst is prepared by taking dicyanodiamine, glucose, ferric salt and nickel salt as precursors through a one-step high-temperature calcination method; the catalyst takes FeNi nano particles as a core and a nitrogen-doped carbon layer as a shell, and the obtained nano particles with the core-shell structure are uniformly dispersed on the surface of a graphene sheet layer with high conductivity. The invention has the beneficial effects that: the raw materials for preparing the catalyst are wide in source, low in cost, simple and controllable in preparation method, and easy to realize large-scale production; the catalyst has higher ORR/OER electrocatalytic activity, good methanol oxidation resistance and excellent stability, can be widely applied to various new energy conversion and storage devices such as fuel cells, electrolytic water, metal-air batteries and the like, and is expected to replace noble metal Pt-based, Ru-based and Ir-based catalysts to realize commercial application.
Description
Technical Field
The invention belongs to the technical field of energy materials and electrochemistry, relates to a bifunctional electrocatalyst applied to catalytic oxygen reduction reaction and oxygen precipitation reaction, and particularly relates to a FeNi/N-C high-dispersion core-shell structure catalyst and a preparation method thereof.
Background
With the rapid development of society, the use of fossil fuels is increasing, which leads to the continuous aggravation of problems such as energy exhaustion and environmental deterioration, and thus new energy storage and conversion devices such as metal-air batteries, fuel cells, electrolyzed water and the like, which have the advantages of high energy density, environmental protection and the like, become hot spots of global research and development. The Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) include fuel cell, electrolytic water, metal-key electrode reactions in various emerging energy conversion and storage devices, including air cells and the like. However, ORR/OER kinetics are slow and have high overpotentials, preventing their widespread use. To date, Pt-based materials are the most effective ORR electrocatalysts, but they are costly, have poor durability, and cannot be applied on a large scale. In addition, Pt has only moderate OER activity and is not suitable for use as an ORR/OER dual function electrocatalyst. RuO2And IrO2The catalyst is the catalyst with the most advanced performance for catalyzing OER, but the reserves of Ru and Ir are limited, the cost is high, and the catalyst does not have the catalytic activity on ORR like Pt. Therefore, it is of great practical significance to find a non-noble metal bifunctional oxygen electrode catalyst which is efficient and durable.
Transition metal (such as Fe, Co, Ni, Mn and the like) catalysts attract extensive attention of researchers due to the characteristics of low cost, good chemical stability, high catalytic efficiency, environmental friendliness, various active species and the like. Especially, the bimetallic catalyst and even the multi-metal catalyst can provide rich valence states, and have important research significance for improving the catalytic performance of ORR and OER. However, the transition metal catalyst tends to have poor conductivity and a low specific surface area, so that its catalytic activity is limited. Heteroatom (N, P, S, etc.) doped carbon materials (graphene, nanotubes, carbon black, etc.) are reported to have high specific surface area and high electrical conductivity, and therefore, combining a metal-based catalyst with a heteroatom doped carbon material will help to obtain a highly active catalytic material. Particularly, by reasonably designing the catalyst structure, such as a core-shell structure, a three-dimensional communicated porous structure, a three-dimensional ordered porous structure and the like, more excellent catalytic performance is probably obtained. In the catalyst structures, the core-shell structure active substance of the carbon-coated metal nanoparticles is dispersed on the surface of the heteroatom-doped graphene with a high specific area, so that the conductivity of the catalyst can be improved, the dispersion of the metal particles can be promoted, the agglomeration of the metal nanoparticles is prevented, the active sites of the catalyst are protected, and meanwhile, the metal particles and the heteroatom-doped carbon material can possibly generate a synergistic effect to further improve the ORR/OER catalytic performance of the catalyst.
How to controllably prepare the high-dispersion core-shell structure catalyst is a key point and a difficulty in current research and development. Li, etc. [ J.Ma ]ter.Chem.A.2018,6,3730–3737]Adopting CoFe double-layer hydroxide (CoFe-LDH) as a Co source and a Fe source, urea as a C source and P123 as a soft template, and adopting a one-step pyrolysis method to prepare carbon-coated Co3O4The doped Co/CoFe bifunctional catalyst has higher ORR and OER catalytic activity and stability under the alkaline condition, however, the catalyst firstly needs 48 hours to prepare CoFe-LDH, then carries out next pyrolysis, has long preparation process and complicated steps, and needs further improvement on experimental conditions. Wang et al [ Applied Surface science.2017,401, 89-99]Adopting electrostatic spinning technology to make polyvinylpyrrolidone and Ni (NO)3)2·6H2O and Fe (NO)3)2·6H2And preparing the mixed solution of O into nanofibers, and then performing high-temperature pyrolysis to obtain the nitrogen-doped carbon nanofiber coated FeNi nanoparticle catalyst which has excellent ORR and OER activities under an alkaline condition. However, the conditions of the process of preparing the catalyst by the electrostatic spinning technology are not easy to control, so that the prepared catalyst particles are not uniform in size, serious agglomeration phenomenon occurs, the full exposure of active sites is not facilitated, and the experimental method needs to be improved.
Aiming at the problems existing in the current research, the invention adopts low-cost glucose as a C source, dicyanodiamine as an N source and FeCl3·6H2O is a source of Fe, NiCl2·6H2O is used as an Ni source, the FeNi/N-C catalyst which is loaded on the graphene carbon layer with high specific surface area and is prepared by adopting a simple high-temperature calcination method through one step, wherein the core-shell structure of the nitrogen-doped carbon layer coated with the FeNi nano particles is prepared, the preparation raw materials of the catalyst are cheap and easy to obtain, the preparation process is simple, the ORR/OER electro-catalysis performance is excellent, and the catalyst is expected to replace Pt-based and Ir/Ru-based noble metal materials to realize large-scale commercial application.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a FeNi/N-C high-dispersion core-shell structure catalyst and a preparation method thereof. The catalyst takes FeNi nano particles with the diameter of about 11nm as a core, takes a nitrogen-doped carbon layer (N-C) with the thickness of about 2-5 nm as a shell, and the core-shell structure is uniformly distributed on the surface of a graphene carbon layer. The unique core-shell structure can prevent the catalytic reaction processThe growth and aggregation of medium metal particles avoid the direct contact between the electrolyte and FeNi nano particles, and the stability of the catalyst is improved; the existence of the N-C shell layer and the graphene sheet layer is beneficial to increasing the conductivity of the catalyst and improving the electron conduction performance of the catalyst; the specific surface area of the FeNi/N-C catalyst is 300-500 m2g-1The catalyst has a mesoporous structure with the pore diameter of 2-50nm, the larger specific surface area is beneficial to increasing the dispersion degree of active sites, fully exposing the active sites and increasing a reaction interface, and meanwhile, the mesoporous structure can provide a rapid transmission channel for reactants, intermediate products and improve the activity of the catalyst; the nitrogen atom content of the prepared catalyst reaches 8.13%, so that electron transfer can be effectively induced, the ORR potential energy is reduced, and the ORR catalytic reaction is promoted.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the catalyst takes glucose with low price as a C source, dicyandiamide as an C, N source and FeCl3·6H2O is a source of Fe, NiCl2·6H2O is a Ni source, is prepared by one step by adopting a high-temperature calcination method and has a mesoporous structure with the aperture of 2-50 nm; the catalyst takes FeNi nano particles as a core and a nitrogen-doped carbon layer as a shell, and the obtained nano particles with the core-shell structure are uniformly dispersed on the surface of a high-conductivity nitrogen-doped graphene sheet layer. Pyrolysis of dicyanodiamine to form flaky g-C3N4Insertion of carbon intermediates and metal species generated by pyrolysis of glucose into g-C3N4In the sheet form of (2), contribute to g-C3N4Graphene sheets are grown instead of carbon nanotubes. The FeNi nano particles coated by N-C in the catalyst are uniformly dispersed on the graphene carbon layer, the FeNi metal nano particles are uniform in size, the morphology growth of the catalyst can be controlled by regulating and controlling the calcination temperature and the molar charge ratio of the two metal precursors, and the catalyst with excellent ORR/OER performance is further optimized and screened. With conventional noble metal catalysts (Pt-based, RuO)2And IrO2) Compared with the prior art, the catalyst has the advantages of low cost and rich sources of raw materials, simple preparation process and contribution to large-scale production.
The preparation steps of the FeNi/N-C high-dispersion core-shell structure catalyst are as follows:
(1) respectively adding metal salt, glucose and dicyanodiamine into water, and stirring at the temperature of 50-100 ℃ for 0.1-48h to obtain a solution A; the metal salt comprises FeCl3·6H2O、NiCl2·6H2O, the molar ratio of dicyanodiamine to metal salt (iron and nickel) is 50-200: 1-10, the molar ratio of iron precursor: the molar ratio of the nickel precursor is 1-10: 1-10; the mass ratio of the glucose to the dicyanodiamine is 1-30: 1-30.
(2) Drying the solution A obtained in the step (1) to obtain a catalyst precursor;
(3) calcining the catalyst precursor obtained in the step (2) in an inert atmosphere at the calcining temperature of 500-1500 ℃ and the heating rate of 1-20 ℃ for min-1The calcination time is 0.5-48h, and the FeNi/N-C catalyst is obtained after cooling.
FeCl described in step (1)3·6H2O、NiCl2·6H2O can be replaced by one or more of Fe and Ni transition metal salts. Dicyanodiamine can be replaced by one or more of urea, melamine, thiourea, etc.
The drying method in the step (2) comprises vacuum drying, air atmosphere drying, inert atmosphere drying, freeze drying and the like, wherein the drying temperature is-40-200 ℃, and the drying time is 1-100 hours.
The inert gas used in the step (3) is one or more of nitrogen or argon, and the flow rate of the inert gas is 1-50 mL min-1。
The FeNi/N-C core-shell structure catalyst is used as an oxygen electrode (ORR/OER) electrocatalyst for metal-air batteries, fuel cells and water electrolysis.
Compared with the prior art, the FeNi/N-C high-dispersion core-shell structure catalyst and the preparation method have the following advantages:
1) the FeNi/N-C high-dispersion core-shell structure catalyst prepared by the method utilizes glucose as a C source, dicyanodiamine as an C, N source and FeCl3·6H2O、NiCl2·6H2Is a metal source and is prepared by a one-step pyrolysis method, and a catalyst is preparedThe raw materials are wide in source, low in cost, simple and controllable in preparation method, and easy to realize large-scale production;
2) according to the FeNi/N-C high-dispersion core-shell structure catalyst prepared by the method, the FeNi nano particles are coated in the N-doped carbon layer to form a core-shell structure, the particle size of the metal particles is close to that of the metal particles, and the metal particles are uniformly dispersed. The unique core-shell structure can avoid the FeNi nano particles from directly contacting with electrolyte, inhibit the growth and agglomeration of metal nano particles, and the FeNi nano particles are beneficial to graphitization of a carbon layer in the high-temperature calcination process, can improve the conductivity of the catalyst, and are beneficial to improving the electrochemical activity and stability of the catalyst;
3) the FeNi/N-C high-dispersion core-shell structure catalyst prepared by the method has a mesoporous structure with the aperture of 2-50nm, can provide a channel for the transfer and transportation of substances participating in the reaction in the ORR/OER process, and meets the mass transfer requirement of the reaction process;
4) according to the FeNi/N-C high-dispersion core-shell structure catalyst prepared by the method, N-C coated FeNi core-shell nanoparticles are uniformly dispersed on the surface of a graphene sheet layer, and the graphene sheet layer with high conductivity and high specific surface area is beneficial to exposing a large number of catalytic active sites and improving the ORR/OER activity of the material;
5) the FeNi/N-C high-dispersion core-shell structure catalyst prepared by the method can realize the controllable preparation of the catalyst by regulating and controlling preparation conditions, such as the molar charge ratio of dicyanodiamine and a metal source, calcination temperature, calcination time and the like;
6) according to the FeNi/N-C high-dispersion core-shell structure catalyst prepared by the method, the content of heteroatom nitrogen can reach 8.13% through X-ray photoelectron spectroscopy (XPS) test, rich pyridine type N and graphite type N active sites can be provided on the surface of the material, and the ORR/OER activity of the material can be improved;
7) the FeNi/N-C high-dispersion core-shell structure catalyst prepared by the method has the advantages that the ORR initial potential under the alkaline condition is close to that of a commercialized Pt/C catalyst, the half-wave potential is far greater than that of the commercialized Pt/C catalyst, the stability is good, and the methanol resistance is strong; and the OER under alkaline conditions has small over potential and shows excellent ORR/OER dual-functional catalytic activity. Can be used as oxygen electrode catalyst of metal-air battery, electrolytic water, fuel battery and other devices.
Drawings
FIG. 1 is an X-ray diffraction (XRD) pattern of a sample prepared according to example 1.
FIG. 2(a) is a Transmission Electron Microscope (TEM) photograph of a sample prepared according to example 1 under 500nm conditions.
FIG. 2(b) is a Transmission Electron Microscope (TEM) picture of a sample prepared according to example 1 under 100nm conditions.
FIG. 2(c) is a Transmission Electron Microscope (TEM) picture of a sample prepared according to example 1 under 20nm conditions.
FIG. 3(a) is a nitrogen adsorption and desorption curve of a sample prepared according to example 1.
FIG. 3(b) is a plot of the pore size distribution of a sample prepared according to example 1.
FIG. 4(a) is a total spectrum of X-ray photoelectron spectroscopy of a sample prepared according to example 1.
FIG. 4(b) is a high resolution Fe 2p X ray photoelectron spectrum of the sample prepared in example 1.
FIG. 4(c) is a high resolution Ni 2p X photoelectron spectroscopy spectrum of a sample prepared according to example 1.
FIG. 4(d) is a high resolution N1 s X ray photoelectron spectroscopy spectrum of a sample prepared according to example 1.
FIG. 5(a) is a graph of samples prepared according to examples 1-4 with a commercial Pt/C catalyst at room temperature with O2Saturated 0.1mol L-1Cyclic Voltammetry (CV) curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm.
FIG. 5(b) is a graph of samples prepared according to examples 1-4 and comparative example 1 at room temperature, O2Saturated 0.1mol L-1OER polarization curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm.
FIG. 6(a) is a graph of O at room temperature for samples prepared according to examples 1, 5-8 and comparative example 12Saturated 0.1mol L-1Cyclic Voltammetry (CV) curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm.
FIG. 6(b) is a graph of O at room temperature for samples prepared according to examples 1, 5-8 and comparative example 12Saturated 0.1mol L-1OER polarization curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm.
FIG. 7(a) is a graph of O at room temperature for samples prepared according to examples 1, 7, 8 and comparative example 12Saturated 0.1mol L-1Cyclic Voltammetry (CV) curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm.
FIG. 7(b) is a graph of O at room temperature for samples prepared according to examples 1, 7, 8 and comparative example 12Saturated 0.1mol L-1OER polarization curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm.
FIG. 8 is a sample prepared according to example 1 at room temperature, O2Saturated 0.1mol L-1Linear Sweep Voltammetry (LSV) curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 400rpm, 900rpm, 1600rpm, 2500 rpm.
FIG. 9 is a Koutecky-Levich (K-L) curve corresponding to the LSV curve of FIG. 8.
FIG. 10 is a graph of the samples prepared according to example 1 and comparative example 1 at room temperature, O2Saturated 0.1mol L-1Chronoamperometry in KOH electrolyte, sweep rate: 100mV s-1And the rotating speed: 400rpm, voltage was constant at-0.4V (vs. Ag/AgCl).
FIG. 11 shows the samples obtained in example 1 at room temperature and O2Saturated 0.1mol L-1KOH electrolyte, O2Saturated 3mol L-1CH3OH+0.1mol L-1CV curve in KOH electrolyte, sweep rate: 10mV s-1。
FIG. 12 shows comparative example 1 at room temperature and O2Saturated 0.1mol L-1KOH electrolyte, O2Saturated 3mol L- 1CH3OH+0.1mol L-1CV curve in KOH electrolyte, sweep rate: 10mV s-1. The reference electrodes used in the test of the invention are all KCl saturated Ag/AgCl electrodes. By V (vs. rhe) ═ V (vs. ag/AgCl) +0.059pH +0.26 cmThe formula performs potential conversion.
Detailed Description
The present invention will be described in detail with reference to specific examples, but the present invention is not limited to these specific examples.
Example 1: fe2Ni1/N-C-800(Fe2Ni1Refers to FeCl in the raw material3·6H2O and NiCl2·6H2The molar ratio of O to the total amount of metal was 2:1, N was dicyanodiamine, the molar ratio of N to the total amount of metal was about 150:1, C was glucose, the mass ratio of N to C was 15:1, 800 means a pyrolysis temperature of 800 ℃)
0.0216g of FeCl3·6H2O and 0.0095g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; drying the uniformly mixed solution in an air drying oven at the temperature of 80 ℃ for 12 hours to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1The temperature is programmed to 800 ℃ for calcining for 2h, and Fe is obtained after natural cooling2Ni1a/N-C-800 catalyst.
Example 2: Fe/N-C-800(Fe means FeCl in raw material)3·6H2O, N is dicyanodiamine, the molar ratio of N to metal Fe is about 150:1, C is glucose, the mass ratio of N to C is 15:1, 800 means the pyrolysis temperature is 800 ℃)
0.032g of FeCl3·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1And (3) heating to 800 ℃ by a program, calcining for 2h, and naturally cooling to obtain the Fe/N-C-800 catalyst.
Example 3: Ni/N-C-800(Ni means NiCl in raw material)2·6H2O, N is dicyanodiamine, the molar ratio of N to metal Ni is about 150:1, C is glucose, the mass ratio of N to C is 15:1, 800 means the pyrolysis temperature is 800 ℃)
0.028g of NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1And (3) heating to 800 ℃ by a program, calcining for 2h, and naturally cooling to obtain the Ni/N-C-800 catalyst.
Example 4: N-C-800(N means dicyanodiamine in the raw material, C is glucose, the mass ratio of N to C is 15:1, 800 means the pyrolysis temperature is 800℃)
Dissolving 1.5g of dicyanodiamine and 0.1g of glucose in 20mL of deionized water, and stirring for 3 hours at 80 ℃ in an oil bath to fully dissolve and mix uniformly; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1And (3) heating to 800 ℃ by a program, calcining for 2h, and naturally cooling to obtain the N-C-800 catalyst.
Example 5: fe1Ni1/N-C-800(Fe1Ni1Refers to FeCl in the raw material3·6H2O and NiCl2·6H2The molar ratio of O was 1:1, N was dicyanodiamine, the molar ratio of N to the total amount of metal was about 150:1, C was glucose, the mass ratio of N to C was 15:1, 800 means a pyrolysis temperature of 800 ℃)
0.016g FeCl3·6H2O and 0.014g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then 1.5g dicyanodiamine and 0.1g glucose are weighed and added respectively under the condition of magnetic stirring to obtain solution B, and stirred for 3 hours at 80 ℃ in oil bath for full useDissolving and mixing uniformly; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1The temperature is programmed to 800 ℃ for calcining for 2h, and Fe is obtained after natural cooling1Ni1a/N-C-800 catalyst.
Example 6: fe1Ni2/N-C-800(Fe1Ni2Refers to FeCl in the raw material3·6H2O and NiCl2·6H2The molar ratio of O was 1:2, N was dicyanodiamine, the molar ratio of N to the total amount of metal was about 150:1, C was glucose, the mass ratio of N to C was 15:1, 800 means a pyrolysis temperature of 800 ℃)
0.0108g FeCl3·6H2O and 0.0190g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1The temperature is programmed to 800 ℃ for calcining for 2h, and Fe is obtained after natural cooling1Ni2a/N-C-800 catalyst.
Example 7: fe1Ni4/N-C-800(Fe1Ni4Refers to FeCl in the raw material3·6H2O and NiCl2·6H2The molar ratio of O is 1:4, N is dicyanodiamine, the molar ratio of N to the total amount of metal is about 150:1, C is glucose, the mass ratio of N to C is 15:1, 800 means a pyrolysis temperature of 800 ℃)
0.0064g FeCl3·6H2O and 0.0225g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution to a reactorTransferring the solution to a culture dish, and drying the solution in an air drying oven at the temperature of 80 ℃ for 12 hours to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1The temperature is programmed to 800 ℃ for calcining for 2h, and Fe is obtained after natural cooling1Ni4a/N-C-800 catalyst.
Example 8: fe4Ni1/N-C-800(Fe4Ni1Refers to FeCl in the raw material3·6H2O and NiCl2·6H2O in a molar ratio of 4:1, N dicyanodiamine, N in a molar ratio to the total amount of metal of about 150:1, C in glucose, N in a mass ratio to C of 15:1, 800 indicating a pyrolysis temperature of 800 ℃)
0.0256g FeCl3·6H2O and 0.0056g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1The temperature is programmed to 800 ℃ for calcining for 2h, and Fe is obtained after natural cooling4Ni1a/N-C-800 catalyst.
Example 9: fe2Ni1/N-C-700(Fe2Ni1Refers to FeCl in the raw material3·6H2O and NiCl2·6H2The molar ratio of O to the total amount of metal was 2:1, N was dicyanodiamine, the molar ratio of N to the total amount of metal was about 150:1, C was glucose, the mass ratio of N to C was 15:1, 700 means a pyrolysis temperature of 700 ℃)
0.0216g of FeCl3·6H2O and 0.0095g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution to a culture dish, and drying in an air drying oven at 80 DEG C12h to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1Heating to 700 ℃ by program, calcining for 2h, and naturally cooling to obtain Fe2Ni1a/N-C-700 catalyst.
Example 10: fe2Ni1/N-C-900(Fe2Ni1Refers to FeCl in the raw material3·6H2O and NiCl2·6H2The molar ratio of O to the total amount of metal was 2:1, N was dicyanodiamine, the molar ratio of N to the total amount of metal was about 150:1, C was glucose, the mass ratio of N to C was 15:1, 900 means a pyrolysis temperature of 900 ℃)
0.0216g of FeCl3·6H2O and 0.0095g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1The temperature is programmed to 900 ℃ and calcined for 2h, and Fe is obtained after natural cooling2Ni1a/N-C-900 catalyst.
Example 11: fe2Ni1/N-C-1500(Fe2Ni refers to FeCl in raw material3·6H2O and NiCl2·6H2The molar ratio of O to the total amount of metal was 2:1, N was dicyanodiamine, the molar ratio of N to the total amount of metal was about 150:1, C was glucose, the mass ratio of N to C was 15:1, 1500 means the pyrolysis temperature was 1500 ℃)
0.0216g of FeCl3·6H2O and 0.0095g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor inGrinding in a mortar, placing in a quartz boat, and introducing under nitrogen protection at 3 deg.C for min-1Heating to 1500 ℃ by program, calcining for 2h, and naturally cooling to obtain Fe2Ni1a/N-C-1500 catalyst.
Example 12: fe2Ni1/N-C-500(Fe2Ni refers to FeCl in raw material3·6H2O and NiCl2·6H2O in a molar ratio of 2:1, N dicyanodiamine in a molar ratio of N to the total amount of metal of about 150:1, C glucose in a mass ratio of N to C of 15:1, 500 indicating a pyrolysis temperature of 500 ℃)
0.0216g of FeCl3·6H2O and 0.0095g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then weighing 1.5g of dicyanodiamine and 0.1g of glucose, respectively adding the dicyanodiamine and the glucose under the condition of magnetic stirring to obtain solution B, and stirring the solution B for 3 hours at the temperature of 80 ℃ in an oil bath to fully dissolve and uniformly mix the solution B; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1Heating to 500 deg.C by program, calcining for 2h, and naturally cooling to obtain Fe2Ni1a/N-C-500 catalyst.
Example 12: fe2Ni1/N-C-800(Fe2Ni refers to FeCl in raw material3·6H2O and NiCl2·6H2The molar ratio of O to the total amount of metal was 2:1, N was dicyanodiamine, the molar ratio of N to the total amount of metal was about 150:1, C was glucose, the mass ratio of N to C was 30:1, 800 means a pyrolysis temperature of 800 ℃)
0.0428g FeCl3·6H2O and 0.0188g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then 3g of dicyanodiamine and 0.1g of glucose are weighed and respectively added under the condition of magnetic stirring to obtain solution B, and the solution B is stirred for 3 hours at the temperature of 80 ℃ in an oil bath to be fully dissolved and uniformly mixed; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and heating at 3 deg.C under nitrogen protectionmin-1The temperature is programmed to 800 ℃ for calcining for 2h, and Fe is obtained after natural cooling2Ni1/N30-C1-800 catalyst.
Example 13: fe2Ni1/N-C-800(Fe2Ni refers to FeCl in raw material3·6H2O and NiCl2·6H2The molar ratio of O to the total amount of metal was 2:1, N was dicyanodiamine, the molar ratio of N to the total amount of metal was about 150:1, C was glucose, the mass ratio of N to C was 1:30, 800 means a pyrolysis temperature of 800 ℃)
0.00014g FeCl3·6H2O and 0.00006g NiCl2·6H2Dissolving O in 20mL of deionized water to obtain a solution A; then 0.1g of dicyanodiamine and 3g of glucose are weighed and respectively added under the condition of magnetic stirring to obtain solution B, and the solution B is stirred for 3 hours at the temperature of 80 ℃ in an oil bath to be fully dissolved and uniformly mixed; transferring the uniformly mixed solution into a culture dish, and drying for 12 hours in an air drying oven at the temperature of 80 ℃ to obtain a catalyst precursor; placing the dried precursor in a mortar, grinding uniformly, placing in a quartz boat, and keeping under nitrogen protection at 3 deg.C for min-1The temperature is programmed to 800 ℃ for calcining for 2h, and Fe is obtained after natural cooling2Ni1/N1-C30-800 catalyst.
Comparative example 1: a commercial 20 wt.% Pt/C catalyst (Alfa Aesar).
FIG. 1 is an X-ray diffraction (XRD) pattern of a sample prepared according to example 1. Analysis of the PCPDF card of the XRD spectrum shows that the metal species in the sample prepared in example 1 contains three crystal structures: cubic form [ Fe, C ] (JCPDS 23-0298), cubic form [ Ni, Fe ] (JCPDS 12-0736) and cubic form elemental Ni (JCPDS 01-1260), the corresponding peak positions are shown in the figure respectively. In addition, 2 θ ═ 26 ° or so is a characteristic diffraction peak of the (002) crystal plane of graphene, indicating that the sample obtained in example 1 contains highly graphitized carbon.
FIG. 2(a) is a Transmission Electron Microscope (TEM) photograph of a sample prepared according to example 1 under 500nm conditions. FIG. 2(b) is a Transmission Electron Microscope (TEM) picture of a sample prepared according to example 1 under 100nm conditions. FIG. 2(c) is a Transmission Electron Microscope (TEM) picture of a sample prepared according to example 1 under 20nm conditions. As shown in fig. 2(a, b, and c), the FeNi nanoparticles coated with the carbon layer are uniformly distributed on the surface of the graphitic carbon layer, the coated NANO carbon layer is about 2-5 nm, and the average diameter of the core calculated by the NANO calculation software is about 11nm for 100 particles at random, so that the coating structure can prevent the metal particles from directly contacting with the electrolyte solution, and improve the stability of the material.
FIG. 3(a) is a nitrogen desorption curve of the sample prepared in example 1, as can be seen from FIG. 3 (a): at a relative pressure P/P0At 0.6, a hysteresis loop (adsorption type IV) appeared, indicating that the catalyst is a mesoporous material with a specific surface area of 371.7m2g-1(ii) a FIG. 3(b) is a plot of the pore size distribution of the sample prepared in example 1, as can be seen in FIG. 3 (b): the pore diameter of the sample prepared in the example 1 is mainly distributed in the range of 2-50nm, which is beneficial to the transmission of substances participated in ORR/OER reaction and meets the mass transfer requirement of the reaction.
FIG. 4(a) is a total spectrum of X-ray photoelectron spectroscopy of a sample prepared according to example 1. From the test results, the content of nitrogen atoms of the prepared catalyst is as high as 8.13%, and the contents of metallic Fe and metallic Ni are respectively 0.78% and 0.56%, which indicates that the exposed metallic particles on the surface of the catalyst are few, and most of the metallic particles are wrapped by the graphite carbon layer, which is consistent with the TEM result. FIG. 4(b) is a high resolution Fe 2p X photoelectron spectrum of the sample prepared in example 1, in which Fe on the surface of the catalyst is mainly Fe 0 2p3/2，Fe 3+2p3/2，Fe 0 2p1/2，Fe 3+2p1/2Are present. FIG. 4(c) is a high resolution Ni 2p X photoelectron spectrum of the sample prepared in example 1, in which Ni is mainly Ni 0 2p3/2，Ni 0 2p1/2The different valence states can provide a 'donor-acceptor' chemical adsorption site, and can reversibly adsorb and desorb O2Therefore, the catalyst has excellent ORR/OER catalytic activity. FIG. 4(d) is a high resolution N1 s X ray photoelectron spectrum of a sample prepared according to example 1, which can be fitted to three types of nitrogen species: pyridine N, pyrrole N, graphite N, and pyridine N, graphite N content is higher, is favorable to catalyzing ORR.
FIG. 5(a) is a graph of samples prepared according to examples 1-4 and comparative example 1 at room temperature, O2Saturated 0.1mol L-1Cyclic Voltammetry (CV) curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm. FIG. 5(b) is a graph of samples prepared according to examples 1-4 and comparative example 1 at room temperature, O2Saturated 0.1mol L-1OER polarization curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm. As is clear from FIGS. 5(a) and 5(b), the catalyst (Fe) obtained in example 12Ni1/N-C-800) potential difference value
Has excellent ORR/OER double catalytic function.
FIG. 6(a) is a graph of O at room temperature for samples prepared according to examples 1, 5-8 and comparative example 12Saturated 0.1mol L-1Cyclic Voltammetry (CV) curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm. FIG. 6(b) is a graph of O at room temperature for samples prepared according to examples 1, 5-8 and comparative example 12Saturated 0.1mol L-1OER polarization curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm. As can be seen from FIGS. 6(a) and 6(b), FeCl3·6H2O and NiCl2·6H2The molar charge of O has a greater effect than the ORR/OER of the catalyst. When FeCl is added3·6H2O and NiCl2·6H2The molar charge ratio of O is 2:1, and the catalyst prepared in example 1 shows excellent ORR/OER catalytic activity.
FIG. 7(a) is a graph of O at room temperature for samples prepared according to examples 1, 9, 10 and comparative example 12Saturated 0.1mol L- 1Cyclic Voltammetry (CV) curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm. From FIG. 7(a), it can be seen that the ORR onset potential increases and then decreases as the calcination temperature increases from 700 ℃ to 900 ℃, which is probably caused by the increase in the graphitization degree of the carbon material and the increase in the crystallinity of the metal, and when the calcination temperature is increased to 90 DEGAt 0 ℃, catalytic activity decreases, probably due to the reduction of catalytic active sites at high temperatures. When the calcination temperature is 800 ℃, Fe3Ni1The ORR performance (half-wave potential reaches-0.832V, and the maximum limiting current density) of the/N-C catalyst is optimal; FIG. 7(b) is a graph of O at room temperature for samples prepared according to examples 1, 9, 10 and comparative example 12Saturated 0.1mol L-1OER polarization curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600 rpm. As can be seen from FIG. 7(b), the OER performance increase sequences of the samples prepared in examples 1, 9 and 10 are as follows: fe2Ni1/N-C-700<Fe2Ni1/N-C-900<Fe2Ni1/N-C-800，Fe2Ni1N-C-800 at jOER＝10mA cm-2The overpotential is the minimum, and the OER performance is the optimal. Indicating that the calcination temperature has a large effect on ORR and OER performance.
FIG. 8 is a sample prepared according to example 1 at room temperature, O2Saturated 0.1mol L-1Linear Sweep Voltammetry (LSV) curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 400rpm, 900rpm, 1600rpm, 2500 rpm. As can be seen from fig. 8, as the rotation speed increases, the ORR initial potential remains unchanged, and the limiting diffusion current density increases.
FIG. 9 is a Koutecky-Levich (K-L) curve obtained from the LSV curve (FIG. 8) of the sample prepared according to example 1. The electron transfer number of the surface-catalyzed ORR of example 1 was calculated to be about 4 according to the K-L equation, indicating that the catalyst prepared in example 1 catalyzes ORR in a 4 electron process.
FIG. 10 is a graph of the samples prepared according to example 1 and comparative example 1 at room temperature, O2Saturated 0.1mol L-1Timing current curve in KOH electrolyte, rotation speed: 400rpm, voltage was constant at-0.4V (vs. Ag/AgCl). By comparison, after the 1800s chronoamperometric stability test, the current density of the catalyst prepared in example 1 is reduced to 97.2 percent of the original current density, and is only attenuated by 2.8 percent; the reduction in current density of the catalyst of comparative example 1 to the initial 83% under the same conditions illustrates that the catalyst prepared in example 1 has better stability than the catalyst prepared in comparative example 1, which may be attributed to the highly dispersed core-shell structure effectively preventing metal nano-sized particlesShedding and agglomeration of particles during the catalytic process.
FIGS. 11 and 12 show the results of example 1 and comparative example 1 in O2Saturated 0.1mol L-1KOH electrolyte, O2Saturated 3mol L-1CH3OH+0.1mol L-1CV diagram in KOH electrolyte. As can be seen from fig. 11, the CV curves of the catalyst prepared in example 1 were not significantly changed in the presence or absence of methanol in the electrolyte solution, indicating that the catalyst prepared in example 1 was not affected by methanol fuel and could be used as a cathode catalyst for a methanol fuel cell. As can be seen from fig. 12, the catalyst of comparative example 1 has a significant methanol oxidation current (0.4-1.3V) in the electrolyte solution with methanol, and can catalyze methanol oxidation, which indicates that comparative example 1 has poor selectivity for fuel and is susceptible to methanol combustion.
The unique core-shell structure can avoid the FeNi nano particles from directly contacting with electrolyte, inhibit the growth and agglomeration of metal nano particles, and the FeNi nano particles are beneficial to graphitization of a carbon layer in the high-temperature calcination process, so that the conductivity of the catalyst is improved, and the electrochemical activity and stability of the catalyst are further improved; the different valences of the different metals may provide "donor-acceptor" chemisorption sites for reversible adsorption and desorption of O2The catalyst is provided with abundant ORR/OER catalytic active sites; the atomic percentage content of nitrogen is as high as 8.13%, and the contents of pyridine type N and graphite type N are high, so that the pyridine type N and graphite type N can be used as an active site to catalyze ORR. The catalyst has higher ORR/OER electrocatalytic activity, good methanol oxidation resistance and excellent stability, can be widely applied to various new energy conversion and storage devices such as fuel cells, electrolytic water, metal-air batteries and the like, and is expected to replace noble metal Pt-based, Ru-based and Ir-based catalysts to realize commercial application.
The above-mentioned embodiments only express the embodiments of the present invention, but not should be understood as the limitation of the scope of the invention patent, it should be noted that, for those skilled in the art, many variations and modifications can be made without departing from the concept of the present invention, and these all fall into the protection scope of the present invention.
Claims (3)
1. The FeNi/N-C high-dispersion core-shell structure catalyst is characterized in that glucose is used as a C source, dicyanodiamine is used as an C, N source, and FeCl is used as the catalyst3·6H2O is a source of Fe, NiCl2·6H2O is a Ni source, is prepared by one step by adopting a high-temperature calcination method and has a mesoporous structure with the aperture of 2-50 nm; FeNi nano particles coated by N-C in the catalyst are uniformly dispersed on the surface of a graphene carbon sheet layer, and the FeNi metal nano particles are uniform in size to form a core-shell structure catalyst taking the FeNi nano particles as a core and a nitrogen-doped carbon layer as a shell;
the preparation method of the FeNi/N-C high-dispersion core-shell structure catalyst comprises the following steps:
(1) respectively adding metal salt, glucose and dicyanodiamine into water, and stirring at the temperature of 50-100 ℃ for 0.1-48h to obtain a solution A; the metal salt comprises FeCl3·6H2O、NiCl2·6H2O, the molar ratio of dicyanodiamine to metal salt (iron and nickel) is 50-200: 1-10, the molar ratio of iron precursor: the molar ratio of the nickel precursor is 1-10: 1-10; the mass ratio of the glucose to the dicyanodiamine is 1-30: 1-30; the dicyanodiamine in the step (1) can be replaced by one or more of urea, melamine, thiourea and the like;
(2) drying the solution A obtained in the step (1) to obtain a catalyst precursor;
(3) calcining the catalyst precursor obtained in the step (2) in an inert atmosphere at the calcining temperature of 500-1500 ℃ and the heating rate of 1-20 ℃ for min-1The calcination time is 0.5-48h, and the FeNi/N-C catalyst is obtained after cooling.
2. The FeNi/N-C high-dispersion core-shell structure catalyst as claimed in claim 1, wherein the drying method in step (2) is vacuum drying, air atmosphere drying, inert atmosphere drying, freeze drying or the like, the drying temperature is-40 to 200 ℃, and the drying time is 1 to 100 hours.
3. The FeNi/N-C high-dispersion core-shell structure catalyst according to claim 1 or 2, wherein the inert gas in the step (3)The atmosphere is one or more of nitrogen or argon, and the flow rate of the inert atmosphere is 1-50 mL/min-1。
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