CN111933962B - N, S co-doped metal-free CNS oxygen reduction catalyst and preparation method thereof - Google Patents

N, S co-doped metal-free CNS oxygen reduction catalyst and preparation method thereof Download PDF

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CN111933962B
CN111933962B CN202010891644.XA CN202010891644A CN111933962B CN 111933962 B CN111933962 B CN 111933962B CN 202010891644 A CN202010891644 A CN 202010891644A CN 111933962 B CN111933962 B CN 111933962B
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CN111933962A (en
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李光兰
曹硕
徐晓存
路中发
王新
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Dalian University of Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/96—Carbon-based electrodes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M12/00—Hybrid cells; Manufacture thereof
    • H01M12/04—Hybrid cells; Manufacture thereof composed of a half-cell of the fuel-cell type and of a half-cell of the primary-cell type
    • H01M12/06—Hybrid cells; Manufacture thereof composed of a half-cell of the fuel-cell type and of a half-cell of the primary-cell type with one metallic and one gaseous electrode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M12/00—Hybrid cells; Manufacture thereof
    • H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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    • 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
    • Y02E60/10—Energy storage using batteries

Abstract

An N, S codoped metal-free CNS oxygen reduction catalyst and a preparation method thereof belong to the technical field of energy materials and electrochemistry. The invention takes glucose as a carbon source and g-C3N4As a nitrogen source and a soft template agent, polysulfide is used as a sulfur source, and the three-dimensional porous carbon material catalyst is synthesized by a hydrothermal-calcination two-step method. The obtained CNS catalyst is of a three-dimensional porous graphene structure, the surface of the CNS catalyst contains a large number of pore structures, and the initial potential of the ORR of the catalyst in alkaline electrolyte is 1.01V, the half-wave potential is 0.88V, and the catalyst has better catalytic performance than a commercial Pt/C catalyst. The invention has a large number of pore channels, can expose more active sites, is beneficial to transmitting ORR reaction substances and improving the ORR catalytic activity of the material; the selected reagent has low toxicity, wide raw material source, low cost, simple preparation process, no pollution, easy amplification production and large-scale application; can be used for fuel cells, metal-air batteries, and other acidic and alkaline primary and secondary batteries involving ORR.

Description

N, S co-doped metal-free CNS oxygen reduction catalyst and preparation method thereof
Technical Field
The invention belongs to the technical field of energy materials and electrochemistry, and relates to a catalyst for an oxygen reduction reaction of a fuel cell and a metal-air battery. In particular to a glucose-containing carbon source g-C3N4As an N source and polysulfide as a sulfur source, N, S codoped metal-free CNS oxygen reduction catalyst is synthesized by a hydrothermal-calcination two-step method, and a preparation method thereof.
Background
With the rapid development of society, the problems of energy crisis, environmental pollution and the like are increasingly aggravated. Therefore, a new energy source and a new transformation technology which are green and sustainable in development are urgently needed to be searched. Fuel cells and metal-air cells have the advantages of no pollution, high theoretical energy density, no noise and the like, and are the hot spots of current research. However, the development of fuel cells, metal-air cells, and the like, still faces a common challenge: the cathodic Oxygen Reduction Reaction (ORR) kinetics are slow. For this reason, researchers have conducted a great deal of work in catalyst development. The Pt/C catalyst is an ORR catalyst mainly applied at present, but has the problems of high cost, small precious metal Pt storage amount, poor catalyst stability and the like, and cannot be applied on a large scale. Therefore, the development of ORR catalysts with high catalytic activity, high stability and low cost is imminent.
Research shows that non-metal heteroatom doped carbon-based catalysts, such as N, S, P, B doped carbon-based catalysts, have excellent catalytic potential for ORR, and are considered to be the most promising ORR catalysts due to their low cost, high conductivity, excellent stability and methanol poisoning resistance. The reason why the ORR performance is improved by doping the heteroatom is mainly as follows: by doping these heteroatoms into the carbon layer, the sp of the carbon can be adjusted2The electronic structure changes the electron cloud density of the carbon, and simultaneously adjusts the hydrophilicity/hydrophobicity of the carbon, thereby being beneficial to the efficient reaction of ORR. For example, Jeon et al [ J.Power Sources 2015,275,73]Research shows that S/N precursors with different proportions can form different contents of thiophene sulfur and graphite nitrogen. The synergistic effect between sulfur and nitrogen atoms can jointly improve the ORR catalytic activity of the carbon material. Qiao et al [ angelw.chem.int.ed.2012, 51,11496]The research finds that the N and S double doping can change the spin and charge density of carbon atoms, thereby improving the catalytic activity of the carbon material. However, the preparation method of in-situ and efficient doping diatomic or polyatomic materials is still relatively limited, and new strategies need to be further developed. More importantly, the catalytic activity of the currently obtained non-metal heteroatom-doped carbon-based catalyst is still low, and the catalytic performance of the catalyst needs to be further improved. It is well known that the specific surface area of the catalyst plays an important role in the ORR catalytic activity. The catalyst with larger specific surface area has stronger mass transfer capability to reactants, intermediate products and the like related to ORR.However, most of the current methods of preparing high specific surface area catalysts employ a sacrificial hard template (silica, calcium carbonate, etc.). For example Li et al [ organic Chemistry communications.2020,114,107848 ]]By using SiO2As a template agent, and then a NaOH etching method is used for preparing the N, S double-doped hollow mesoporous carbon sphere (NS-HMCS) catalyst. These templates need to be etched by hydrofluoric acid or sodium hydroxide, which causes environmental pollution and complicated preparation process.
Based on the above analysis, the present invention proposes to utilize the graphite-like phase carbon nitride g-C3N4N, S co-doped metal-free CNS catalyst is synthesized by a hydrothermal-calcination two-step method by using a nitrogen source, polysulfide as a sulfur source and glucose as a carbon source. We propose that this preparation strategy is based primarily on the following considerations: g-C3N4The nitrogen content is very high, which is beneficial to doping a large amount of N elements efficiently; gas can be generated during high-temperature pyrolysis and is used as a pore-forming agent to increase the specific surface area of the carbon material; most importantly, hydrofluoric acid, sodium hydroxide and other substances can be avoided, the environment is protected, and the preparation process is simplified. Polysulfides can be doped in situ due to the unique chain-like structure and can promote more N atoms to be doped into the carbon layer during pyrolysis. Compared with the commercial Pt/C catalyst, the catalyst has higher catalytic activity and stability, simple preparation method, green and pollution-free property, can be produced in a large scale, and is expected to replace the Pt/C catalyst.
Disclosure of Invention
The invention provides an N, S codoped CNS metal-free ORR catalyst and a preparation method thereof. The invention takes glucose as a carbon source and g-C3N4As a nitrogen source and a soft template agent, polysulfide is used as a sulfur source, and the three-dimensional porous carbon material catalyst is synthesized by a hydrothermal-calcination two-step method. In the hydrothermal reaction, the glucose, sodium sulfide and sulfur powder can be in g-C3N4The polymer is formed on the surface, so that N, S in-situ co-doping can be realized in the pyrolysis process. The high-temperature calcination process can promote N, S, C atoms to be rearranged, and is beneficial to realizing in-situ and high-dispersion doping of N, S atoms in the graphite layer. The high-temperature calcination process can lead g-C3N4Decomposed gas can play a role in pore forming, the specific surface area of the catalyst is increased, more active sites are exposed, and the mass transfer of the ORR reactant is improved. The S-S bond breakage during the pyrolysis process of polysulfide is favorable for the doping of S atoms to form C-S-C and C-SOxthe-C structure, the C-S-C structure can change the spin density of adjacent carbon atoms, and the interaction between N and S promotes the progress of the ORR reaction.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a preparation method of N, S codoped metal-free oxygen reduction catalyst comprises the following steps:
1) n, S codoped metal-free CNS catalyst precursors were prepared.
G to C3N4Dissolving in solvent, adding carbon source, sodium sulfide and sulfur powder to obtain mixed solution A, wherein g-C3N4The mass concentration of (A) is 0.01-10 g mL-1(ii) a The mass concentration of the carbon source is 0.1-100 g mL-1The mass ratio of the sodium sulfide to the sulfur powder is 0.01-30: 0.01-30. Transferring the mixed solution A into a reaction container after stirring, reacting for 0.5-48 h at 120-180 ℃, and performing aftertreatment after the reaction is finished to obtain N, S codoped metal-free catalyst precursor (g-C)3N4/CS) material.
2) g-C obtained in step 1)3N4the/CS catalyst is placed in a tubular furnace, the temperature is raised from room temperature to the calcining temperature, high-temperature calcination is carried out, the high-temperature calcining temperature is 600-1200 ℃, and the calcining time is 0.1-48 hours, so that the CNS catalyst is obtained.
Further, the carbon source in the step 1) is one or more of glucose, melamine, dopamine, chitosan and other carbon precursors.
Further, the reaction vessel in the step 1) is an autoclave or a closed vessel.
Further, the post-treatment in step 1) includes, but is not limited to, cooling, filtering, drying, and the like, wherein the cooling may be one or more of natural cooling, rapid cooling, and the like, and the drying may be one or more of ordinary air oven drying, vacuum drying, and freeze drying.
Further, the high-temperature calcination atmosphere in step 2) may be one or more of air, inert gas (nitrogen, argon, etc.), ammonia gas, hydrogen gas, etc.
Further, the temperature rise rate in the step 2) is 1-20 ℃ min-1。
N, S codoped metal-free oxygen reduction catalyst, N, S codoped metal-free oxygen reduction catalyst is prepared by the preparation method. The obtained CNS catalyst is of a three-dimensional porous graphene structure, the surface of the catalyst contains a large number of pore structures, and the pore diameters are mainly distributed to be about 2.5nm and 13.1 nm. The initial potential of ORR of the catalyst in alkaline electrolyte is 1.01V, the half-wave potential is 0.88V, and the catalyst has better catalytic performance than that of a commercial Pt/C catalyst.
The invention has the beneficial effects that:
(1) n, S the co-doped metal-free CNS catalyst is a three-dimensional porous graphene-like structure and has a large number of pores, which can expose more active sites, facilitate the transmission of ORR reaction substances and accelerate the proceeding of ORR.
(2)g-C3N4A large number of pyridine nitrogen and graphite nitrogen configurations can be formed in the high-temperature pyrolysis process, and are active sites of ORR reaction, so that the ORR catalytic activity of the material is improved.
(3) In the pyrolysis process of polysulfide, the fracture of S-S bonds can better realize in-situ doping, and sulfur doping can fix more N atoms, thereby realizing high-content N doping. The pyrolysis process favors the formation of C-S-C and C-SOxthe-C structure and the C-S-C structure serve as ORR active sites to further promote the progress of ORR reaction.
(4) The synergy between nitrogen and sulfur may redistribute the carbon spin and charge density, effectively creating active sites.
(5) The ORR activity, stability and methanol resistance of the CNS catalyst are far higher than those of a commercial Pt/C catalyst under an alkaline condition, and the CNS catalyst is expected to replace the Pt/C catalyst to realize commercial application.
(6) The CNS catalyst has the advantages of low toxicity of selected reagents, wide raw material source, low cost, simple preparation process, greenness, no pollution, easy amplification production and contribution to large-scale application.
(7) The CNS catalyst of the invention can be used for acidic and alkaline primary and secondary batteries of fuel batteries, metal-air batteries and the like which relate to ORR.
Drawings
FIG. 1 shows the precursors g to C prepared in example 23N4SEM photograph of/CS; wherein a and b are g-C3N4SEM pictures of/CS at different magnifications.
Figure 2 is SEM and TEM photographs of the CNS catalyst prepared in example 2; wherein, a and b are SEM pictures of CNS with different magnifications; and c and d are TEM photographs of CNS with different magnifications.
Fig. 3 is an XRD pattern of example 2, comparative example 1 and comparative example 3.
FIG. 4 is a graph of the results of examples 1-3 in O2Saturated 0.1mol L-1ORR curve in KOH electrolyte, sweep rate: 10mVs-1And the rotating speed: 1600rpm, room temperature.
FIG. 5 shows the results of samples prepared in examples 2 and 7 in O2Saturated 0.1mol L-1ORR curve in KOH electrolyte, sweep rate: 10mVs-1And the rotating speed: 1600rpm, room temperature.
FIG. 6 shows the results of comparison between example 2 and comparative examples 1, 2 and 32Saturated 0.1mol L- 1ORR curve in KOH electrolyte, sweep rate: 10mVs-1And the rotating speed: 1600rpm, room temperature.
FIG. 7 shows the results of comparative example 2 and example 2 in O2Saturated 0.1mol L-1KOH electrolyte, O2Saturated 3mol L- 1CH3OH+0.1mol L-1Chronoamperometric curve in KOH electrolyte, potential: 0.57V (vs RHE), room temperature.
FIG. 8 shows the results of comparative example 2 and example 2 in O2Saturated 0.1mol L-1KOH electrolyte, O2Saturated 0.1mol L- 1Chronoamperometric curve in KOH electrolyte, potential: 057V (vs RHE), room temperature.
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: CN1S0.2-900-2(CN1S0.21 in-900-2 represents g-C in the starting material3N40.2 represents a mass ratio of the sulfur powder to the sodium sulfide of 0.2, 900 represents a calcination temperature of 900 ℃ and 2 represents a calcination time of 2 hours)
1gg-C3N4Added to 40mL of deionized water, and then 64mg of sulfur powder, 280mg of sodium sulfide and 200mg of glucose were added, and stirred for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4the/CS precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere, wherein the calcining temperature is 900 ℃, and the heating rate is 10 ℃/min. Finally obtain CN1S0.2-900-2 catalyst.
Example 2: CN2S0.2-900-2(CN2S0.22 in-900-2 denotes g-C in the starting Material3N40.2 represents a mass ratio of the sulfur powder to the sodium sulfide of 0.2, 900 represents a calcination temperature of 900 ℃ and 2 represents a calcination time of 2 hours)
2gg-C3N4Added to 40mL of deionized water, and then 64mg of sulfur powder, 280mg of sodium sulfide and 200mg of glucose were added, and stirred for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4Putting the/CS precursor into a tube furnaceIn N at2Calcining for 2h in the atmosphere, wherein the calcining temperature is 900 ℃, and the heating rate is 10 ℃/min. Finally obtain CN2S0.2-900-2 catalyst.
Example 3: CN3S0.2-900-2(CN3S0.23 in-900-2 represents g-C in the starting material3N40.2 represents a mass ratio of the sulfur powder to the sodium sulfide of 0.2, 900 represents a calcination temperature of 900 ℃ and 2 represents a calcination time of 2 hours)
3gg-C3N4Added to 40mL of deionized water, and then 64mg of sulfur powder, 280mg of sodium sulfide and 200mg of glucose were added, and stirred for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4the/CS precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere, wherein the calcining temperature is 900 ℃, and the heating rate is 10 ℃/min. Finally obtain CN3S0.2-900-2 catalyst.
Example 4: CN2S0.1-900-2(CN2S0.12 in-900-2 denotes g-C in the starting Material3N40.1 represents a mass ratio of the sulfur powder to the sodium sulfide of 0.1, 900 represents a calcination temperature of 900 ℃ and 2 represents a calcination time of 2 hours)
2gg-C3N4Added to 40mL of deionized water, and then 32mg of sulfur powder, 280mg of sodium sulfide and 200mg of glucose were added, and stirred for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4the/CS precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere at 900 deg.C, and heatingThe rate was 10 ℃/min. Finally obtain CN2S0.1-900-2 catalyst.
Example 5: CN2S0.2-600-2(CN2S0.2-600-2 denotes g-C in the starting material3N40.2 represents a mass ratio of the sulfur powder to the sodium sulfide of 0.2, 600 represents a calcination temperature of 600 ℃ and 2 represents a calcination time of 2 hours)
2gg-C3N4Added to 40mL of deionized water, and then 64mg of sulfur powder, 280mg of sodium sulfide and 200mg of glucose were added, and stirred for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4the/CS precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere, wherein the calcining temperature is 600 ℃, and the heating rate is 10 ℃/min. Finally obtain CN2S0.2-600-2 catalyst.
Example 6: CN2S0.2-1200-2(CN2S0.22 in-1200-2 represents g-C in the starting material3N40.2 represents a mass ratio of the sulfur powder to the sodium sulfide of 0.2, 1200 represents a calcination temperature of 1200 ℃ and 2 represents a calcination time of 2 hours)
2gg-C3N4Added to 40mL of deionized water, and then 64mg of sulfur powder, 280mg of sodium sulfide and 200mg of glucose were added, and stirred for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4the/CS precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere, wherein the calcining temperature is 1200 ℃, and the heating rate is 10 ℃/min. Finally obtain CN2S0.2-1200-2 of catalyst.
Example 7: CN2S0.2-800-2(CN2S0.22 in-800-2 represents g-C in the starting material3N40.2 represents a mass ratio of the sulfur powder to the sodium sulfide of 0.2, 800 means a calcination temperature of 800 ℃ and 2 means a calcination time of 2 hours)
2gg-C3N4Added to 40mL of deionized water, and then 64mg of sulfur powder, 280mg of sodium sulfide and 200mg of glucose were added, and stirred for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4the/CS precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere, wherein the calcining temperature is 800 ℃, and the heating rate is 10 ℃/min. Finally obtain CN2S0.2-800-2 catalyst.
Example 8: CN2S0.01-900-2(CN2S0.012 in-900-2 denotes g-C in the starting Material3N4The mass of (2) is 2g, 0.01 represents that the mass ratio of the sulfur powder to the sodium sulfide is 0.01, 900 represents that the calcination temperature is 900 ℃ and 2 represents that the calcination time is 2h)
2gg-C3N4Adding into 40mL deionized water, then adding 2.8mg of sulfur powder, 280mg of sodium sulfide and 200mg of glucose, and stirring for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4the/CS precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere, wherein the calcining temperature is 900 ℃, and the heating rate is 10 ℃/min. Finally obtain CN2S0.01-900-2 catalyst.
Examples9：CN2S30-900-2(CN2S0.012 in-900-2 denotes g-C in the starting Material3N4The mass of (2) represents that the mass ratio of the sulfur powder to the sodium sulfide is 30, 900 represents that the calcination temperature is 900 ℃ and 2 represents that the calcination time is 2 hours)
2gg-C3N4Added to 40mL of deionized water, and then 280mg of sulfur powder, 9.3mg of sodium sulfide and 200mg of glucose were added, and stirred for 30min to form a uniform mixed solution A. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/CS。
G to C3N4the/CS precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere, wherein the calcining temperature is 900 ℃, and the heating rate is 10 ℃/min. Finally obtain CN2S30-900-2 catalyst.
Comparative example 1: CN2-900-2(CN 22 in-900-2 denotes g-C in the starting Material3N4Has a mass of 2g, 900 denotes a calcination temperature of 900 ℃ and 2 denotes a calcination time of 2h)
2gg-C3N4Added to 40mL of deionized water, and then 200mg of glucose was added, and stirred for 30min to form a uniform mixed solution a. The mixed solution A is put into a high-pressure reaction kettle and reacts for 10 hours at 180 ℃. Then naturally cooling to room temperature. Filtering, washing, drying in an air oven for 10h at 80 deg.C, and grinding to obtain CNS catalyst precursor g-C3N4/C。
G to C3N4the/C precursor is placed in a tube furnace at N2Calcining for 2h in the atmosphere, wherein the calcining temperature is 900 ℃, and the heating rate is 10 ℃/min. Finally obtain CN2-900-2 catalyst.
Comparative example 2: commercial 20 wt.% Pt/C catalyst (JM 20% platinum carbon)).
Comparative example 3: self-made g-C3N4. (10g of melamine was calcined in air for 2h at 550 ℃ CTemperature rise rate 2.3 ℃/min.)
FIGS. 1a, b are examples precursors g-C, respectively3N4SEM pictures of/CS at scale 3um and 500 nm. g-C can be clearly seen in the diagrams of FIGS. 1a, bSEM3N4the/CS is a bulk stacked structure with fewer surface channels.
FIGS. 2a, b are SEM photographs at 5um and 500nm of the example precursor CNS, respectively; c. d are TEM photographs of the example precursor CNS at 100nm and 200nm, respectively. From FIG. 2a, bSEM pictures, it can be clearly seen that CNS is a sheet structure, the surface contains abundant three-dimensional pore channels, and the pore diameter is mainly concentrated at 2.5nm and 13.1 nm. As can be seen from the TEM images of fig. 2c and d, the catalyst is composed of a porous graphene structure.
Fig. 3 is an XRD pattern of example 2, comparative example 3 and comparative example 1. As can be seen from the figure, g-C3N4Characteristic peaks of XRD diffraction of (1) appear at 13.1 ° and 27.4 ° 2 θ, corresponding to the (100) and (002) crystal planes of the graphite structure. CN and CNs catalysts have broad characteristic diffraction peaks at 25.1 ° and 43.6 ° 2 θ, which can be assigned to the (002) and (100) crystal planes of graphene, indicating that CNs catalysts are an amorphous graphene structure.
FIG. 4 is a graph of the results of examples 1-3 in O2Saturated 0.1mol L-1ORR curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600rpm, room temperature. It can be seen from FIG. 4 that with g-C3N4The initial potential and half-wave potential of the solution are increased and then decreased when the input amount is increased, when g-C3N4The initial potential (1.01V) and the half-wave potential (0.88V) are maximized at a mass of 2 g.
FIG. 5 shows the results of samples prepared in examples 2 and 7 in O2Saturated 0.1mol L-1ORR curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600rpm, room temperature. As can be seen from FIG. 5, the calcination temperature is 900 ℃ when g-C3N4The initial potential (1.01V) and the half-wave potential (0.88V) are maximized at a mass of 2 g.
FIG. 6 shows the results of comparison of the sample prepared in example 2 with those of comparative example 1,Comparative examples 2 and 3 in O2Saturated 0.1mol L- 1ORR curve in KOH electrolyte, sweep rate: 10mV s-1And the rotating speed: 1600rpm, room temperature. It can be seen from fig. 6 that the half-wave potential and the onset potential of the CNS catalyst exceed those of the commercial Pt/C catalyst, respectively, when co-doped with nitrogen and sulfur, indicating that the interaction between nitrogen and sulfur can promote the ORR reaction.
FIG. 7 shows the results of comparative example 2 and example 2 in O2Saturated 0.1mol L-1KOH electrolyte, O2Saturated 3mol L- 1CH3OH+0.1mol L-1Timed current curve in KOH electrolyte, voltage: 0.57V (vs RHE), room temperature. It can be seen from fig. 7 that the current density of the Pt/C catalyst increases sharply when methanol is added at 500s, whereas the current density of the CNS catalyst decreases slightly and then remains unchanged, indicating that the CNS catalyst has excellent methanol resistance.
FIG. 8 shows the results of comparative example 2 and example 2 in O2Saturated 0.1mol L-1KOH electrolyte, O2Saturated 0.1mol L- 1Timed current curve in KOH electrolyte, voltage: 0.57V (vs RHE), room temperature. As can be seen from FIG. 8, the Pt/C catalyst decayed to 85% after 2400s, while the CNS catalyst only declined by 14% after 15000s, indicating that the stability of the CNS catalyst is better than that of the Pt/C catalyst.
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 (7)

1. A preparation method of N, S codoped metal-free CNS oxygen reduction catalyst is characterized by comprising the following steps:
1) n, S co-doped metal-free CNS catalyst precursor is prepared;
g to C3N4Dissolving in solvent, adding carbon source, sodium sulfide and sulfur powderObtaining a mixed solution A, wherein g-C3N4The mass concentration of (A) is 0.01-10 g mL-1(ii) a The mass concentration of the carbon source is 0.1-100 g mL-1The mass ratio of the sodium sulfide to the sulfur powder is 0.01-30: 0.01-30; transferring the mixed solution A into a reaction container after stirring, reacting for 0.5-48 h at 120-180 ℃, and performing aftertreatment after the reaction is finished to obtain N, S codoped metal-free catalyst precursor material g-C3N4/CS；
2) g-C obtained in step 1)3N4the/CS catalyst is placed in a tubular furnace, the temperature is raised from room temperature to the calcining temperature, high-temperature calcination is carried out, the high-temperature calcining temperature is 600-1200 ℃, and the calcining time is 0.1-48 hours, so that the CNS catalyst is obtained.
2. The method of claim 1, wherein the carbon source of step 1) is one or more of glucose, melamine, dopamine, and chitosan carbon precursor.
3. The method of claim 1, wherein the reaction vessel of step 1) is a closed vessel.
4. The method of claim 1, wherein the post-treatment of step 1) includes but is not limited to cooling, filtering, and drying, wherein the cooling is natural cooling or rapid cooling, and the drying is ordinary air oven drying, vacuum drying, or freeze drying.
5. The method of claim 1, wherein the high temperature calcination atmosphere in step 2) is one or more of air, inert gas, ammonia gas, and hydrogen gas.
6. An N, S copolymer as set forth in claim 1The preparation method of the doped metal-free CNS oxygen reduction catalyst is characterized in that the temperature rise rate in the step 2) is 1-20 ℃ min-1。
7. N, S codoped metal-free CNS oxygen reduction catalyst, wherein the N, S codoped metal-free CNS oxygen reduction catalyst is prepared by the preparation method of any one of claims 1 to 6; the obtained CNS catalyst is of a three-dimensional porous graphene-like structure, and the surface of the CNS catalyst contains a large number of pore structures.
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