CN111054423B - Nitrogen self-doped porous carbon catalyst and preparation method and application thereof - Google Patents
Nitrogen self-doped porous carbon catalyst and preparation method and application thereof Download PDFInfo
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Images
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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
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- B01J35/33—
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- B01J35/60—
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- B01J35/61—
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
The invention provides a nitrogen self-doped porous carbon catalyst and a preparation method and application thereof. The preparation method of the nitrogen self-doped porous carbon catalyst comprises the following steps: 1) mixing biomass aquatic algae with an activator solution to obtain a mixture A, and concentrating the mixture A to obtain a paste; 2) pyrolyzing the product obtained in the step 1) in an inert atmosphere; 3) and carrying out surface treatment on a solid product obtained by pyrolysis by using concentrated nitric acid or aqua regia to obtain the catalyst. The catalyst prepared by the preparation method contains carbon element, nitrogen element and transition metal element, wherein the transition metal comprises at least one of iron, magnesium and copper. The catalyst can be suitable for catalyzing cathode reduction reaction in a fuel cell, hydrogen evolution reaction in an electrolytic water cathode and oxygen evolution reaction in an electrolytic water anode. The catalyst has excellent HER, OER and ORR activity and stability.
Description
Technical Field
The invention belongs to the technical field of new energy nano materials, and particularly relates to a nitrogen self-doped porous carbon catalyst and a preparation method and application thereof.
Background
With the crisis of fossil fuels and the increasing problem of environmental pollution caused by over-dependence on traditional fossil fuels, scientists are forced to develop environment-friendly fuelsAnd renewable clean energy to replace fossil fuels. Wherein hydrogen (H)2) As a product of the cathodic reaction (HER) in water splitting, is a carrier that can be used as a clean energy source. Hydrogen energy is used as a green energy source with rich resources, high energy and no secondary pollution, and is considered as one of ideal energy sources for solving energy crisis and environmental crisis in the post-petroleum era. The water splitting anode reaction (OER), the oxygen produced can be applied to all aspects of life and production. While the Oxygen Reduction Reaction (ORR) is one of the most critical reactions in energy conversion systems, such as fuel cells, when combined with its reverse process (OER), it can be assembled into so-called rechargeable metal-air cells. The above three reactions play a crucial role in energy conversion and storage devices, however, the slow kinetics severely limit the energy conversion efficiency of these electrochemical devices. The catalyst is the key for improving the kinetics of the electrocatalytic reaction, and the high-efficiency electrocatalyst can effectively reduce the energy consumption required by the reaction process, so that the research on the high-efficiency electrocatalyst becomes the important factor for the sustainable energy technology exploration. But the material and preparation cost, electrochemical reaction activity and long-term effective stability of the current electrocatalyst are the biggest obstacles for realizing free conversion of low energy consumption. Taking the common noble metal catalysts such as Pt (science, 2011,334: 1256-. In recent years, non-noble metals and metal-free catalysts have become the focus and focus of research.
Carbon support materials have the advantages of good electrical conductivity, special pore structure, high specific surface area and the like, and are often used for supporting catalytic active components. However, the conventional carbon material is prepared from coal, petroleum or processed products thereof, etc. as main raw materials. But today the global energy, resource crisis and deterioration of the ecological environment present challenges to the further development of traditional carbon materials. Therefore, biomass carbon materials come into existence, such as forestry biomass, agricultural wastes, energy plants and the like, belong to renewable resources, and most biomass materials contain abundant carbon elements and become abundant raw materials for preparing various carbon materials. The biomass material is used as the raw material to prepare various carbon materials, so that the production cost of the carbon materials can be reduced, and the sustainable development of the carbon materials is realized. The biomass carbon material prepared by taking a natural high polymer material as a raw material has large specific surface area and developed gaps, and is favored in the aspects of energy, environment, medical materials, new functional materials and the like. Most of the biomass carbon materials reported at present are single-function catalysis, and the catalytic activity is not ideal when additional metal active sites are not doped (chem. Phys.,2016,18, 10392-. Therefore, the development of a biomass carbon-based material with three functions (HER, OER and ORR) as an electrocatalyst for energy conversion can effectively reduce the cost of the material and the pollution to the environment, and has important significance for the commercialization of fuel cells and electrolyzed water.
Disclosure of Invention
The present invention aims to provide a catalyst having three functions of HER, OER and ORR, that is, a catalyst which can be suitably used for catalyzing a cathode reduction reaction in a fuel cell, a hydrogen evolution reaction in an electrolytic water cathode, and an oxygen evolution reaction in an electrolytic water anode. The catalyst has excellent ORR activity and stability, and has excellent HER and OER activity.
In order to achieve the above object, the present invention provides a method for preparing a nitrogen self-doped porous carbon catalyst, comprising:
1) mixing biomass aquatic algae with an activator solution to obtain a mixture A, and concentrating the mixture A to obtain a paste;
2) pyrolyzing the product obtained in the step 1) in an inert atmosphere;
3) and carrying out surface treatment on the solid product obtained by pyrolysis by using concentrated nitric acid or aqua regia to obtain the nitrogen self-doped porous carbon catalyst.
In the above preparation method, the biomass aquatic algae is usually pulverized and then mixed with the activator solution; the concentration of the mixture A is usually carried out by removing part of water; the inert atmosphere refers to a protective atmosphere and not only to an inert gas.
In the above production method, preferably, the paste has a viscosity of 0.05 pas-3 pas.
In the above preparation method, preferably, the solid product obtained by pyrolysis is subjected to surface treatment with concentrated nitric acid to obtain the nitrogen self-doped porous carbon catalyst; more preferably, the concentrated nitric acid has a mass concentration of 65-72% (e.g., 69%). Concentrated nitric acid and aqua regia (analytically pure nitric acid volume: hydrochloric acid volume: 1:3) can achieve the same effect, but because aqua regia has volatility and can not effectively exert the effect for a long time, the aqua regia needs to be prepared for use at present, and the risk of the aqua regia is high, so the concentrated nitric acid is a relatively better choice. The concentrated nitric acid with the mass concentration of 65-72% has more proper reaction rate and can ensure safety because the mass concentration is too low, so that the reaction is slow, and the risk is increased because fuming nitric acid with the concentration higher than 85%. In a specific embodiment, the solid product obtained by pyrolysis is subjected to surface treatment by soaking in concentrated nitric acid with a mass concentration of 69% for 20-40 min.
In the above preparation method, preferably, the aquatic algae includes at least one of laver, kelp, water hyacinth, undaria pinnatifida, gulfweed, and the like, but is not limited thereto.
In the above preparation method, preferably, the active agent includes H3PO4At least one of an alkali metal salt, an alkaline earth metal salt, and a transition metal salt; more preferably, the active agent is H3PO4。
In the above production method, preferably, the concentration of the active agent in the active agent solution is 0.03mol/L to 50mol/L, more preferably 0.3mol/L to 50mol/L, and still more preferably 3mol/L to 30 mol/L.
In the above production method, the mass ratio of the biomass to the activator is preferably 0.1 to 50:1, more preferably 0.1 to 30:1, and further preferably 0.1 to 10: 1.
In the above preparation method, preferably, in the step 2), the temperature of the pyrolysis is 500-.
In the above preparation method, preferably, in the step 2), the pyrolysis time is 3 to 6 hours.
In the preparation method, the oxidation of the functional groups on the surface of the material is realized by using concentrated nitric acid or aqua regia for surface treatment, so that the wettability of the surface of the obtained material is adjusted, and the performance of the catalyst for catalyzing electrolyzed water is guaranteed.
In the above production method, preferably, the solid product obtained by pyrolysis is ground into a powder of 30 to 120 mesh and then subjected to surface treatment. More preferably, the solid product obtained by pyrolysis is ground into powder with the particle size of 120-550 microns and then subjected to surface treatment.
In the above production method, preferably, the solid product obtained by pyrolysis is washed before being subjected to surface treatment. In a specific embodiment, the solid product obtained by pyrolysis is washed at least 3 times by using deionized water, and subjected to suction filtration and then surface treatment. In another embodiment, the solid product obtained by pyrolysis is ground into a powder, washed and then subjected to surface treatment.
In the above preparation method, preferably, the solid product obtained by pyrolysis is further washed, dried, and ground after being subjected to surface treatment; wherein the grinding is grinding into powder with 50-150 meshes, and more preferably grinding into powder with particle size of 106-270 microns.
In the above preparation method, the biomass aquatic algae may be pulverized using a wall breaking machine. The process of mixing the crushed biomass aquatic algae and the activator solution can be realized by uniformly stirring at the rotation speed of 400-800rpm for 8-12 h. Dewatering concentration can be performed using an oven. Pyrolysis may be carried out in a tube furnace.
In one embodiment, the preparation method of the nitrogen self-doped porous carbon catalyst comprises the following steps:
(1) crushing biomass aquatic algae (preferably at least one of laver, kelp, water hyacinth, undaria pinnatifida and gulfweed) to obtain crushed aquatic algae, dissolving the crushed aquatic algae in an activator aqueous solution with the concentration of 0.03-50 mol/L (preferably 0.3-50 mol/L, more preferably 3-30 mol/L), and uniformly stirring (preferably stirring for 8-12h) at the rotation speed of 400-800rpm to obtain a mixture A; dewatering and concentrating the mixture A (the dewatering and concentrating are preferably carried out in an oven) to obtain a paste with the viscosity of 0.05 Pa.s-3 Pa.s; wherein the mass ratio of the biomass to the activating agent is 0.1-50: 1;
(2) pyrolyzing the paste obtained in the step 1) at the temperature of 500-900 ℃ in an inert atmosphere (the pyrolysis time is preferably 3-6h, and the pyrolysis is preferably carried out in a tubular furnace), and cooling to obtain a solid product B (the product B is usually expanded fluffy black blocky solid);
(3) and grinding the product B into powder, washing, then carrying out surface treatment by using a concentrated nitric acid solution with the mass concentration of 69% (preferably soaking for 20-40min), cleaning the product subjected to surface treatment to be neutral, drying, and grinding again to obtain the nitrogen self-doped porous carbon catalyst.
The invention also provides the nitrogen self-doped porous carbon catalyst prepared by the preparation method of the nitrogen self-doped porous carbon catalyst, which contains carbon element, nitrogen element and transition metal element, wherein the transition metal comprises at least one of iron, magnesium and copper.
In the nitrogen self-doping porous carbon catalyst, preferably, the mass of the nitrogen element accounts for 3-8% of the total mass of the catalyst, the mass of the carbon element accounts for 91-96% of the total mass of the catalyst, and the mass of the transition element accounts for 0.1-1% of the total mass of the catalyst.
The invention also provides application of the nitrogen self-doped porous carbon catalyst in water electrolysis reaction, and the nitrogen self-doped porous carbon catalyst is used for catalyzing at least one of cathode hydrogen evolution reaction and anode oxygen evolution reaction of water electrolysis.
The invention also provides application of the nitrogen self-doped porous carbon catalyst in a fuel cell, and the nitrogen self-doped porous carbon catalyst is used for catalyzing cathode reduction reaction in the fuel cell.
The invention provides a method for preparing a nitrogen self-doped biomass carbon-based catalyst with three functions (HER, OER and ORR) from simple raw materials, which firstly realizes the special pore-forming treatment by using aquatic algae as the raw materials and using an active agent, pyrolysis is carried out in an inert atmosphere, and the surface hydrophilicity of the material is improved by treating the pyrolysis product with concentrated nitric acid, so as to obtain a nitrogen self-doping porous carbon catalyst which takes a biomass carbon material as a substrate and self-doping nitrogen elements (mainly pyridine nitrogen and graphite nitrogen) as catalytic active sites (Energy environ. Sci.2012, 5, 7936-7942; Lai L, Potts J R, Zhan D, et al. Compared with the prior art, the invention has the following advantages:
(1) the nitrogen self-doped porous carbon catalyst provided by the invention is in a loose and porous sheet stack structure, has a large specific surface area, a multi-level pore structure (mostly existing in a mesoporous form) required in material transmission and good conductivity.
(2) The nitrogen self-doped porous carbon catalyst provided by the invention is applied to oxygen reduction reaction, and has high electrocatalytic activity and excellent stability, so that the catalyst can be successfully applied to cathode catalysis of a fuel cell; and the nitrogen self-doping porous carbon catalyst shows excellent hydrogen evolution activity and oxygen evolution activity when applied to the water electrolysis reaction. In other words, the nitrogen self-doped porous carbon catalyst provided by the invention is suitable for catalyzing the cathode reduction reaction in a fuel cell, the hydrogen evolution reaction in an electrolysis water cathode and the oxygen evolution reaction in an anode, has three functions of catalysis, and can effectively realize energy conversion with low consumption.
(3) The catalyst prepared by the preparation method of the nitrogen self-doped porous carbon catalyst provided by the invention contains a certain amount of nitrogen element besides a main element carbon element, and reserves a transition metal element contained in biomass.
(4) According to the preparation method of the nitrogen self-doping porous carbon catalyst, provided by the invention, the biomass carbon material is sequentially treated by using the chemical activating agent and the high-concentration pure nitric acid for the first time, so that the problem of surface wettability of the biomass carbon material after high-temperature carbonization is solved, the porous carbon material with high specific surface area is obtained, the contact property of the carbon material and water is improved, and the reaction of catalyzing and electrolyzing water is ensured.
(5) According to the preparation method of the nitrogen self-doping porous carbon catalyst, provided by the invention, the aquatic algae with moderate nitrogen element content is selected as the biomass material, so that the resistance value of the carbon carrier is essentially reduced, the transfer rate between electrons is improved, and a foundation is laid for the catalyst to have three functions (HER, OER and ORR).
In addition, the aquatic algae are rich in mineral elements (iron, magnesium, copper, etc.), which can act as active sites of the catalyst after carbonization to enhance the catalytic activity thereof.
(6) According to the preparation method of the nitrogen self-doped porous carbon catalyst, the nitrogen element introduced into the carbon material causes electron delocalization (defect) among carbon atoms, and the graphite nitrogen/pyridine nitrogen form is mainly used as an active site of the catalyst, so that the transfer rate of electrons among the carbon atoms is accelerated, the integral resistance value of the carbon material is reduced, the electrocatalytic catalytic performance is improved, and the prepared catalyst has relatively low voltage and overpotential in an electrolytic water reaction.
(7) According to the preparation method of the nitrogen self-doped porous carbon catalyst, the porous carbon catalyst with high specific surface area is obtained by using the active agent to realize pore forming of biomass aquatic algae, so that the mass transfer of the catalyst in an electrolyzed water reaction is accelerated.
(8) The preparation method of the nitrogen self-doped porous carbon catalyst provided by the invention does not need to introduce additional elements, realizes the preparation of the catalyst only by treating the elements of the aquatic algae, has the advantages of low cost, simple process, easy operation and environmental friendliness, and is beneficial to industrial popularization.
Drawings
Fig. 1 is a transmission microscope TEM image of a nitrogen self-doped porous carbon catalyst provided in example 1.
FIG. 2 is a graph of N for the nitrogen self-doped porous carbon catalyst N-PAC/800 provided in example 2 and the unperforated nitrogen-doped carbon catalyst N-C/800 provided in comparative example 12Adsorption and desorption curve chart.
FIG. 3 is a graph of ORR activity versus LSV for the nitrogen self-doped porous carbon catalyst N-PAC/900 provided in example 3, the nitrogen doped carbon catalyst N-C/900 provided in comparative example 2 that was not treated with nitric acid, and a commercial Pt/C catalyst; wherein the N-PAC/900 half-wave potential is 0.85V, the N-PC/900 half-wave potential is 0.73V, and the commercial 20% Pt/C catalyst half-wave potential is 0.81V.
FIG. 4 is a graph of stability side test i-t for nitrogen self-doped porous carbon catalyst provided in example 1.
FIG. 5 is a graph of HER activity versus LSV for nitrogen self-doped porous carbon catalyst N-PAC/800 provided in example 2, unperforated nitrogen-doped carbon catalyst N-C/800 provided in comparative example 1, and a commercial Pt/C catalyst; wherein the commercial 20% Pt/C catalyst has an initial potential of 32mV, an initial potential of 218mV for N-PAC/800, and an initial potential of 855mV for N-C/800.
FIG. 6 shows N-PAC/900 as a nitrogen self-doped porous carbon catalyst provided in example 3, N-C/900 as a nitrogen-doped carbon catalyst provided in comparative example 2 without nitric acid treatment, and IrO as a commercial catalyst2OER activity versus LSV profile for the catalyst; wherein IrO is commercially available2The initial potential of the catalyst was 1.42V, the initial potential of N-PAC/900 was 1.70V, and the initial potential of N-PC/900 was 1.82V.
FIG. 7 is an X-ray photoelectron spectroscopy XPS (for measuring elemental composition in catalyst materials) graph of nitrogen self-doped porous carbon catalysts N-PAC/700, N-PAC/800 and N-PAC/900 provided in examples 1-3 and nitrogen self-doped carbon catalysts N-C/800 and N-PC/900 provided in comparative examples 1-2.
Detailed Description
The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.
Example 1
This example provides a nitrogen self-doped porous activated carbon catalyst, wherein the catalyst is prepared by the following method:
(1) in beaker A, 5mL of 85% by mass H3PO4Dissolved in 50mL of deionized water to obtain H3PO4A solution; pulverizing thallus Porphyrae into powder with wall breaking machineWeighing 1.5g of the powder, and adding into the above H3PO4Beaker a of solution;
then, sealing and coating the beaker A with a film to ensure that the environment is sealed, placing the beaker A on a magnetic stirrer, and uniformly stirring the beaker A for 10 hours at the room temperature at the rotating speed of 400rpm to obtain a uniformly mixed mixture A (the mixture A is in a dark green colloid state);
then placing the beaker A in an oven in an open manner, standing at a constant temperature of 50 ℃ for 20h to remove most of water and realize dehydration and concentration to obtain a viscous purple black paste (the viscosity of the paste is 2.5 Pa.s);
(2) putting the paste obtained in the step (1) into a tubular furnace with a closed gas circuit, and heating for 3 hours at the constant temperature of 700 ℃ in an argon environment for pyrolysis;
(3) after the pyrolysis product is naturally cooled to room temperature, taking out the pyrolysis product from the tubular furnace (the taken out pyrolysis product is an expanded loose black blocky solid), then transferring the pyrolysis product into an agate mortar to grind the pyrolysis product into powder (the particle size of the powder obtained by grinding is within the range of 120-550 microns, and a 30-120-mesh sieve can be penetrated), and carrying out reduced pressure suction filtration and cleaning on the powder obtained by grinding for 3 times (1L of deionized water is used each time) by using deionized water to obtain black powder;
measuring 50mL of nitric acid solution with the mass concentration of 69% and placing the nitric acid solution into a 100mL beaker B, placing the black powder beaker into the beaker B containing the nitric acid solution, sealing the membrane of the beaker B, and placing the beaker B on a stirrer to stir at the rotating speed of 800rpm for 25 minutes for surface treatment;
and cleaning the solid product obtained after the surface treatment to be neutral by using deionized water, drying, and then grinding and refining again (the particle size of the powder obtained by grinding is within the range of 106-270 microns, and a sieve with 50-150 meshes can be penetrated) to obtain the nitrogen self-doped porous carbon catalyst.
Under a transmission electron microscope, the nitrogen self-doped porous carbon catalyst provided in this example is lamellar and loose and porous, and the pore diameter is about 25nm (as shown in fig. 1).
The XPS test results show that the mass of the nitrogen element accounts for 4.5 percent of the total mass of the catalyst, the mass of the carbon element accounts for 91.1 percent of the total mass of the catalyst, and the mass of the transition element accounts for 0.1 percent of the total mass of the catalyst (as shown in figure 7).
The nitrogen self-doped porous carbon catalyst provided in this example was subjected to stability testing:
(1) firstly, preparing a test mixed solution, putting 5mg of a catalyst, 400 mu L of deionized water, 80 mu L of ethanol and 20 mu L of ethanol into a 5mL test tube, and then carrying out ultrasonic treatment at 100 Hz for 20 minutes to obtain a mixed solution; dropping 5. mu.L of the mixture on a glassy carbon electrode (S ═ 0.071 cm)2And d ═ 3mm) to be naturally dried to obtain a first electrode.
(2) At room temperature, using a conventional three-electrode test, using an electrochemical analyzer (Shanghai Chenghua CHI760E) at 0.5M H2SO4Performing a chronoamperometry (i-t) test in the solution; the first electrode was used as the working electrode, the graphite rod as the counter electrode and the Ag/AgCl electrode (saturated KCl) as the reference electrode.
After the 30000-second continuous test, the current retention rate still remains above 80% (as shown in fig. 4), and it can be seen that the nitrogen self-doped porous carbon catalyst provided by the present embodiment has higher stability.
Example 2
This example provides a nitrogen self-doped porous activated carbon catalyst, N-PAC/800, wherein the catalyst was prepared by the following method:
(1) in beaker A, 1mL of 85% by mass H3PO4Dissolved in 20mL of deionized water to obtain H3PO4A solution; pulverizing Sargassum into powder with wall breaking machine, weighing 5g of Sargassum, and adding into the container H3PO4Beaker a of solution;
then, sealing and coating the beaker A with a film to ensure that the environment is sealed, placing the beaker A on a magnetic stirrer, and uniformly stirring the beaker A for 12 hours at the room temperature at the rotating speed of 600rpm to obtain a uniformly mixed mixture A (the mixture A is in a dark green colloid state);
then placing the beaker A in an oven in an open manner, standing at a constant temperature of 50 ℃ for 24h to remove most of water and realize dehydration and concentration to obtain a viscous purple black paste (the viscosity of the paste is 1.5 Pa.s);
(2) putting the paste obtained in the step (1) into a tubular furnace with a closed gas circuit, and heating at the constant temperature of 800 ℃ for 4 hours in an argon environment for pyrolysis;
(3) after the pyrolysis product is naturally cooled to room temperature, taking out the pyrolysis product from the tubular furnace (the taken out pyrolysis product is an expanded loose black blocky solid), then transferring the pyrolysis product into an agate mortar to grind the pyrolysis product into powder (the particle size of the powder obtained by grinding is within the range of 120-550 microns, and a 30-120-mesh sieve can be penetrated), and carrying out reduced pressure suction filtration and cleaning on the powder obtained by grinding for 3 times (1L of deionized water is used each time) by using deionized water to obtain black powder;
measuring 50mL of nitric acid solution with the mass concentration of 69% and placing the nitric acid solution into a 100mL beaker B, placing the black powder beaker into the beaker B containing the nitric acid solution, sealing the membrane of the beaker B, and placing the beaker B on a stirrer to stir for 30 minutes at the rotating speed of 600rpm for surface treatment;
and cleaning the solid product obtained after the surface treatment to be neutral by using deionized water, drying, and then grinding and refining again (the particle size of the powder obtained by grinding is within the range of 106-270 microns, and a 50-150-mesh sieve can be passed through) to obtain the nitrogen self-doped porous carbon catalyst N-PAC/800.
The nitrogen self-doping porous carbon catalyst provided by the embodiment carries out N2The results of the adsorption and desorption tests are shown in figure 2, and the nitrogen self-doped porous carbon catalyst has ultrahigh specific surface area which can reach 1300.66m2/g。
The XPS test results show that the mass of the nitrogen element accounts for 4.0 percent of the total mass of the catalyst, the mass of the carbon element accounts for 92.1 percent of the total mass of the catalyst, and the mass of the transition element accounts for 0.1 percent of the total mass of the catalyst (as shown in figure 7).
The nitrogen self-doped porous carbon catalyst provided by the embodiment has excellent HER performance, and the test process comprises the following steps:
(1) firstly, preparing a test mixed solution, putting 5mg of a catalyst, 400 mu L of deionized water, 80 mu L of ethanol and 20 mu L of Nafion into a 5mL test tube, and then carrying out ultrasonic treatment at 100 Hz for 20 minutes to obtain a mixed solution; dropping 5. mu.L of the mixture on a glassy carbon electrode (S ═ 0.071 cm)2And d ═ 3mm) to be naturally dried to obtain a first electrode.
(2) Then at room temperature, usingConventional three-electrode testing using an electrochemical analyzer (Shanghai Chenghua CHI760E) at 0.5M H2SO4Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) tests were performed in solution; the first electrode was used as the working electrode, the graphite rod as the counter electrode and the Ag/AgCl electrode (saturated KCl) as the reference electrode.
At 10mV/cm2The overpotential at the current density of (a) was 218mV, which is close to the performance of a commercial Pt/C catalyst (Maxin brand, 20% by mass Pt/C catalyst CAS number: 7440-06-4) (as shown in FIG. 5).
Example 3
This example provides a nitrogen self-doped porous activated carbon catalyst, N-PAC/900, wherein the catalyst was prepared by the following method:
(1) in beaker A, 2mL of 85% by mass H3PO4Dissolved in 100mL of deionized water to obtain H3PO4A solution; pulverizing Undaria Pinnatifida into powder with wall breaking machine, weighing 8g of the powder, and adding into the above container H3PO4Beaker a of solution;
then, sealing and coating the beaker A with a film to ensure that the environment is sealed, placing the beaker A on a magnetic stirrer, and uniformly stirring the beaker A for 12 hours at the room temperature at the rotating speed of 800rpm to obtain a uniformly mixed mixture A (the mixture A is in a dark green colloid state);
then placing the beaker A in an oven in an open manner, standing at a constant temperature of 45 ℃ for 24h to remove most of water and realize dehydration and concentration to obtain a viscous purple black paste (the viscosity of the paste is 0.152 Pa.s);
(2) putting the paste obtained in the step (1) into a tubular furnace with a closed gas circuit, and heating at the constant temperature of 900 ℃ for 5 hours in an argon environment for pyrolysis;
(3) after the pyrolysis product is naturally cooled to room temperature, taking out the pyrolysis product from the tubular furnace (the taken out pyrolysis product is an expanded loose black blocky solid), then transferring the pyrolysis product into an agate mortar to grind the pyrolysis product into powder (the particle size of the powder obtained by grinding is within the range of 120-550 microns, and a 30-120-mesh sieve can be penetrated), and carrying out reduced pressure suction filtration and cleaning on the powder obtained by grinding for 3 times (1L of deionized water is used each time) by using deionized water to obtain black powder;
measuring 50mL of nitric acid solution with the mass concentration of 69% and placing the nitric acid solution into a 100mL beaker B, placing the black powder beaker into the beaker B containing the nitric acid solution, sealing the membrane of the beaker B, and placing the beaker B on a stirrer to stir at the rotating speed of 700rpm for 40 minutes for surface treatment;
and cleaning the solid product obtained after the surface treatment to be neutral by using deionized water, drying, and then grinding and refining again (the particle size of the powder obtained by grinding is within the range of 106-270 microns, and a 50-150-mesh sieve can be passed through) to obtain the nitrogen self-doped porous carbon catalyst N-PAC/900.
The XPS test results show that the mass of the nitrogen element accounts for 5.9 percent of the total mass of the catalyst, the mass of the carbon element accounts for 93.5 percent of the total mass of the catalyst, and the mass of the transition element accounts for 0.4 percent of the total mass of the catalyst (as shown in figure 7).
The nitrogen self-doped porous carbon catalyst provided by the embodiment has excellent ORR performance, and the test process is as follows:
(1) firstly, preparing a test mixed solution, putting 5mg of a catalyst, 400 mu L of deionized water, 80 mu L of ethanol and 20 mu L of Nafion into a 5mL test tube, and then carrying out ultrasonic treatment at 100 Hz for 20 minutes to obtain a mixed solution; dropping 15 μ L of the mixture on a rotating disk electrode (American PINE brand RDE model, S ═ 0.196 cm)2And d ═ 5.0mm) of the surface, and naturally drying to obtain the first electrode.
(2) Then tested at room temperature using a conventional three-electrode test using an electrochemical analyzer (Shanghai Chenghua CHI760E) at O2Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) tests were performed in saturated 0.1M KOH solution; the first electrode was used as the working electrode, the graphite rod as the counter electrode and the Ag/AgCl electrode (saturated KCl) as the reference electrode.
The half-wave potential is 0.80V, and the limiting current is 5.56mA/cm2The performance was superior to that of a commercial Pt/C catalyst (Maxin brand, 20% by mass Pt/C catalyst CAS number 7440-06-4), and the results are shown in FIG. 3.
The nitrogen self-doped porous carbon catalyst provided by the embodiment has excellent OER performance, and the test process is as follows:
(1) configuration ofTesting the mixed solution, putting 5mg of catalyst, 400 mu L of deionized water, 80 mu L of ethanol and 20 mu L of Nafion into a 5mL test tube, and then carrying out ultrasonic treatment at 100 Hz for 20 minutes to obtain the mixed solution; dropping 5. mu.L of the mixture on a glassy carbon electrode (S ═ 0.071 cm)2And d ═ 3mm), and naturally drying to obtain the first electrode.
(2) Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) tests were performed in a 1M KOH solution at room temperature using an electrochemical analyzer (shanghai chenhua CHI760E) using conventional three electrodes; the first electrode was used as the working electrode, the graphite rod as the counter electrode, and the Hg/HgO electrode as the reference electrode.
At a current density of 10mV/cm2Lower overpotential of 1.70V, and commercial IrO2Catalyst (Maxin brand, IrO 20% by weight)2Catalyst, CAS No.: 12030-49-8) (1.42V) are close (as shown in fig. 6).
Comparative example 1
This comparative example provides a control experiment, nitrogen-doped carbon catalyst N-C/800 without pore formation, prepared by the following method:
(1) adding 100mL of deionized water into a beaker A, grinding gulfweed into powder by using a wall breaking machine, and then weighing 0.5g of gulfweed and adding the powder into the beaker A;
then, sealing and coating the beaker A with a film to ensure that the environment is sealed, placing the beaker A on a magnetic stirrer, and uniformly stirring the beaker A for 12 hours at the room temperature at the rotating speed of 600rpm to obtain a uniformly mixed mixture A (the mixture A is in a dark green colloid state);
then placing the beaker A in an oven in an open manner, standing at a constant temperature of 50 ℃ for 24h to remove most of water and realize dehydration and concentration to obtain a viscous purple black paste (the viscosity of the paste is 1.5 Pa.s);
(2) putting the paste obtained in the step (1) into a tubular furnace with a closed gas circuit, and heating at the constant temperature of 800 ℃ for 4 hours in an argon environment for pyrolysis;
(3) after the pyrolysis product is naturally cooled to room temperature, taking out the pyrolysis product from the tubular furnace (the taken out pyrolysis product is a black lamellar solid), then transferring the pyrolysis product into an agate mortar to grind the pyrolysis product into powder (the particle size of the powder obtained by grinding is within the range of 120-550 microns and can pass through a 30-120-mesh sieve), and performing reduced pressure suction filtration and cleaning on the powder obtained by grinding for 3 times (1L of deionized water is used each time) by using deionized water to obtain black powder;
measuring 50mL of nitric acid solution with the mass concentration of 69% and placing the nitric acid solution into a 100mL beaker B, placing the black powder beaker into the beaker B containing the nitric acid solution, sealing the membrane of the beaker B, and placing the beaker B on a stirrer to stir for 30 minutes at the rotating speed of 600rpm for surface treatment;
and cleaning the solid product obtained after the surface treatment to be neutral by using deionized water, drying, and then grinding and refining again to obtain the nitrogen-doped carbon catalyst N-C/800 without pore formation.
The N-C/800 specific surface area of the nitrogen-doped carbon catalyst without pore forming provided by the comparative example is very low and is 6.74m2The/g, pore canal is not developed, and the gyromagnetic curve without mesopores appears, which has a significant difference compared with the nitrogen-doped carbon catalyst N-PAC/800 provided in example 2 (as shown in FIG. 2). The specific surface area of the N-PAC/800 sample was much higher than that of the N-C/800 sample.
The XPS test results show that the mass of the nitrogen element accounts for 7.2 percent of the total mass of the catalyst, the mass of the carbon element accounts for 92.0 percent of the total mass of the catalyst, and the mass of the transition element accounts for 0.7 percent of the total mass of the catalyst (as shown in figure 7).
The comparative example provides a HER performance of N-C/800 according to the test procedure:
(1) firstly, preparing a test mixed solution, putting 5mg of a catalyst, 400 mu L of deionized water, 80 mu L of ethanol and 20 mu L of Nafion into a 5mL test tube, and then carrying out ultrasonic treatment at 100 Hz for 20 minutes to obtain a mixed solution; dropping 5. mu.L of the mixture onto a glassy carbon electrode (S ═ 0.071 cm)2And d ═ 3mm) of the surface, and naturally drying to obtain the first electrode.
(2) The cells were then tested at room temperature using a conventional three-electrode test using an electrochemical analyzer (Shanghai Chenghua CHI760E) at 0.5M H2SO4Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) tests were performed in solution; the first electrode was used as the working electrode, the graphite rod as the counter electrode and the Ag/AgCl electrode (saturated KCl) as the reference electrode.
Current density is in10mV/cm2The overpotential at this time was 855mV, which is a significant difference from the overpotential (218mV) obtained using N-PAC/800 as provided in example 2 (FIG. 5), and the unperforated sample was considered to be catalytically inactive.
Comparative example 2
This comparative example provides a control experiment nitrogen-doped carbon catalyst N-C/900 that was not treated with nitric acid, wherein the catalyst was prepared by the following method:
(1) in beaker A, 2mL of 85% by mass H3PO4Dissolved in 100mL of deionized water to obtain H3PO4A solution; pulverizing Undaria Pinnatifida into powder with wall breaking machine, weighing 8g of the powder, and adding into the above container H3PO4Beaker a of solution;
then, sealing and coating the beaker A with a film to ensure that the environment is sealed, placing the beaker A on a magnetic stirrer, and uniformly stirring the beaker A for 12 hours at the room temperature at the rotating speed of 800rpm to obtain a uniformly mixed mixture A (the mixture A is in a dark green colloid state);
then placing the beaker A in an oven in an open manner, standing at a constant temperature of 45 ℃ for 24h to remove most of water and realize dehydration and concentration to obtain a viscous purple black paste (the viscosity of the paste is 0.152 Pa.s);
(2) putting the paste obtained in the step (1) into a tubular furnace with a closed gas circuit, and heating at the constant temperature of 900 ℃ for 5 hours in an argon environment for pyrolysis;
(3) after the pyrolysis product is naturally cooled to room temperature, taking out the pyrolysis product from a tubular furnace (the taken out pyrolysis product is an expanded loose black massive solid), then transferring the pyrolysis product into an agate mortar to grind the pyrolysis product into powder, and performing reduced pressure suction filtration and cleaning on the powder obtained by grinding for 3 times (1L of deionized water is used each time) by using deionized water to obtain black powder, namely the nitrogen-doped carbon catalyst N-C/900 which is not treated by nitric acid;
the nitrogen-doped carbon catalyst N-C/900 which is not treated by nitric acid and is provided by the comparative example has certain ORR performance, and the test process is as follows:
(1) firstly preparing a test mixed solution, putting 5mg of catalyst, 400 mu L of deionized water, 80 mu L of ethanol and 20 mu L of Nafion into a 5mL test tube, and then carrying out ultrasonic treatment at 100 Hz for 20Obtaining mixed solution after minutes; dropping 15 μ L of the mixture on a rotating disk electrode (American PINE brand RDE model, S ═ 0.196 cm)2And d ═ 5.0mm) of the surface, and naturally drying to obtain the first electrode.
(2) The test was then carried out at room temperature using a conventional three-electrode test using an electrochemical analyzer (Shanghai Chenghua CHI760E) in O2Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) tests were performed in saturated 0.1M KOH solution; the first electrode was used as the working electrode, the graphite rod as the counter electrode and the Ag/AgCl electrode (saturated KCl) as the reference electrode.
The half-wave potential is 0.73V, and the limiting current is 4.86mA/cm2There is a difference from the case of using N-PAC/900 provided in example 3 (half-wave potential of 0.80V, limiting current of 5.56 mA/cm)2) (as shown in fig. 3).
The XPS test results show that the mass of the nitrogen element accounts for 3.4 percent of the total mass of the catalyst, the mass of the carbon element accounts for 95.6 percent of the total mass of the catalyst, and the mass of the transition element accounts for 0.6 percent of the total mass of the catalyst (as shown in figure 7).
The nitrogen-doped carbon catalyst N-C/900 which is not treated by nitric acid and is provided by the comparative example also has certain OER performance, and the test process is as follows:
(1) firstly, preparing a test mixed solution, putting 5mg of a catalyst, 400 mu L of deionized water, 80 mu L of ethanol and 20 mu L of Nafion into a 5mL test tube, and then carrying out ultrasonic treatment at 100 Hz for 20 minutes to obtain a mixed solution; dropping 5. mu.L of the mixture on a glassy carbon electrode (S ═ 0.071 cm)2And d ═ 3mm) of the surface, and naturally drying to obtain the first electrode.
(2) Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) tests were then performed in a 1M KOH solution at room temperature using an electrochemical analyzer (shanghai chenhua CHI760E) using conventional three electrodes; the first electrode was used as the working electrode, the graphite rod as the counter electrode, and the Hg/HgO electrode as the reference electrode.
The N-PC/900 sample provided by the comparative example was used at 10mV/cm2The overpotential at current density of (1.82V) is a certain difference from that of the N-PAC/900 sample (1.70V) provided by example 3 (as shown in FIG. 6).
Claims (14)
1. A method for preparing a nitrogen self-doped porous carbon catalyst, which comprises the following steps:
1) crushing biomass aquatic algae to obtain crushed aquatic algae, mixing the crushed aquatic algae with an activator solution with the concentration of 0.03-50 mol/L to obtain a mixture A, and concentrating the mixture A to obtain a paste with the viscosity of 0.05-3 Pa.s; wherein the mass ratio of the biomass to the activating agent is 0.1-50: 1; wherein the active agent is H3PO4；
2) Pyrolyzing the product obtained in the step 1) in an inert atmosphere;
3) grinding a solid product obtained by pyrolysis into powder of 30-120 meshes, and then carrying out surface treatment by using concentrated nitric acid or aqua regia to adjust the wettability of the surface of the powder to obtain the nitrogen self-doped porous carbon catalyst.
2. The production method according to claim 1, wherein the concentrated nitric acid has a mass concentration of 65 to 72%.
3. The preparation method of claim 1, wherein the aquatic algae includes at least one of laver, kelp, water hyacinth, undaria pinnatifida, and gulfweed.
4. The method of claim 1, wherein the concentration of the active agent in the active agent solution is 0.3mol/L to 50 mol/L.
5. The method of claim 4, wherein the concentration of the active agent is 3 to 30 mol/L.
6. The production method according to claim 1, wherein the mass ratio of the biomass to the activator is 0.1 to 30: 1.
7. The production method according to claim 6, wherein the mass ratio of the biomass to the activator is 0.1 to 10: 1.
8. The method as claimed in claim 1, wherein the pyrolysis temperature is 500-900 ℃; the pyrolysis time is 3-6 h.
9. The preparation method as claimed in claim 1, wherein the solid product obtained by pyrolysis is ground into powder with a particle size of 120-550 μm and then subjected to surface treatment, and the solid product obtained by pyrolysis is further subjected to washing, drying and grinding after being subjected to surface treatment.
10. The method of claim 1, wherein the grinding is milling to a powder of 50-150 mesh.
11. The production method according to any one of claims 1 to 10, wherein the production method of the nitrogen self-doped porous carbon catalyst comprises:
1) crushing biomass aquatic algae to obtain crushed aquatic algae, dissolving the crushed aquatic algae in an activating agent aqueous solution, and uniformly stirring at the rotation speed of 400-800rpm to obtain a mixture A; dewatering and concentrating the mixture A to obtain a paste with the viscosity of 0.05 Pa.s-3 Pa.s; wherein the aquatic algae comprises at least one of thallus Porphyrae, herba Zosterae Marinae, herba Eichhorniae, thallus laminariae, and Sargassum; wherein the active agent is H3PO4；
2) Pyrolyzing the paste obtained in the step 1) at the temperature of 500-900 ℃ in an inert atmosphere, and cooling to obtain a solid product B;
3) and grinding the product B into powder, washing, then carrying out surface treatment by using a concentrated nitric acid solution with the mass fraction of 65-72%, cleaning the product after the surface treatment to be neutral, drying, and grinding again to obtain the nitrogen self-doped porous carbon catalyst.
12. A nitrogen self-doped porous carbon catalyst prepared by the method for preparing a nitrogen self-doped porous carbon catalyst according to any one of claims 1 to 11, which contains carbon, nitrogen and a transition metal element, wherein the transition metal comprises at least one of iron, magnesium and copper; wherein, the mass of nitrogen element accounts for 4-8% of the total mass of the catalyst, the mass of carbon element accounts for 91-95% of the total mass of the catalyst, and the mass of transition element accounts for 0.1-1% of the total mass of the catalyst.
13. Use of the nitrogen self-doped porous carbon catalyst of claim 12 in an electrolyzed water reaction, wherein the nitrogen self-doped porous carbon catalyst is used to catalyze a cathodic hydrogen evolution reaction and an anodic oxygen evolution reaction of electrolyzed water.
14. Use of the nitrogen self-doped porous carbon catalyst of claim 13 in a fuel cell, wherein the nitrogen self-doped porous carbon catalyst is used to catalyze a cathode reduction reaction in a fuel cell.
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