CN114864967A - Preparation method of carbon-based single-atom catalyst - Google Patents
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Abstract
The invention belongs to the technical field of preparation of a single atom catalyst, and particularly relates to a preparation method of a carbon-based single atom catalyst. The method comprises the steps of mixing and pyrolyzing a sacrificial metal salt, a carbon carrier and a nitrogen-containing compound to synthesize a sacrificial metal-nitrogen co-doped carbon template, and then synthesizing a target metal-nitrogen co-doped carbon-based monatomic catalyst through ion exchange coordination of a target metal in a solution phase. The catalyst prepared by the invention can improve the problem of low load of the monatomic catalyst, and the metal load can reach 10.6 wt.%. The preparation method of the monatomic catalyst is convenient to operate, has universal applicability, is widely suitable for preparing most metal catalysts, and is applied to fuel cell catalysts.
Description
Technical Field
The invention belongs to the technical field of preparation of a single atom catalyst, and particularly relates to a preparation method of a carbon-based single atom catalyst.
Background
Since the 21 st century, energy problems become one of the most important factors restricting the development of human beings, and the search of new energy to replace the traditional non-renewable energy is an important way to solve the energy problems. Nowadays, high-efficiency clean electrochemical energy technologies such as fuel cells and metal-air batteries are becoming important directions for realizing sustainable development of human society. Among these techniques, electrocatalysts play an extremely important role, and the level of performance thereof directly affects the level of efficiency of the corresponding device. At present, the monatomic catalyst is widely applied to the electrocatalysis technology due to higher catalytic activity and selectivity, and has good research and application prospects.
Common methods for preparing monatomic catalysts include coprecipitation, stepwise reduction, impregnation, atomic layer deposition, etc., but these methods also have some disadvantages: (1) the single atom catalyst has low loading capacity; (2) the preparation process is complex; (3) the structure of the monatomic catalyst is not easy to regulate and control; (4) insufficient density of catalytic sites; (5) the range of synthetic metals has limitations. In view of this, it is necessary to develop a new and effective preparation method of the monatomic catalyst.
Disclosure of Invention
The invention provides a preparation method of a carbon-based single-atom catalyst, aiming at the problems of low single-atom catalyst loading capacity, complex preparation process and limitation of synthetic metal in the prior art.
In order to realize the purpose, the invention is realized by the following technical scheme:
a preparation method of a carbon-based single-atom catalyst comprises the steps of mixing and pyrolyzing a sacrificial metal salt, a carbon carrier and a nitrogen-containing compound to synthesize a sacrificial metal-nitrogen co-doped carbon template, and then synthesizing the target metal-nitrogen co-doped carbon-based single-atom catalyst through ion exchange coordination of target metal in a solution phase.
Preferably, the preparation method of the carbon-based single-atom catalyst specifically comprises the following steps:
step 1: adding concentrated nitric acid into a carbon carrier for oxidation treatment, then adding water and isopropanol into the carbon carrier for ultrasonic dispersion to obtain carbon carrier dispersion liquid with oxidized surface;
step 2: adding a sacrificial metal salt and a nitrogen-containing compound into an acid solution, mixing and stirring, and adding a carbon carrier dispersion liquid with oxidized surface into the acid solution to obtain precursor slurry;
and step 3: carrying out pyrolysis treatment on the precursor slurry, and washing and drying to obtain a sacrificial metal-nitrogen co-doped carbon template;
and 4, step 4: and mixing the sacrificial metal-nitrogen co-doped carbon template with a target metal salt solution, stirring, centrifugally washing and drying to obtain the target metal-nitrogen co-doped carbon-based single-atom catalyst.
Preferably, the carbon carrier in step 1 is one of carbon black, activated carbon, graphene and carbon nanotubes. This preference can increase catalyst dispersion and conductivity.
Preferably, the specific process of the oxidation treatment in step 1 is as follows: adding concentrated nitric acid into carbon carrier, stirring for 6-8h at 60-90 deg.C and 500-900rpm, washing, vacuum filtering, and vacuum drying at 40-80 deg.C. This preferred embodiment uses nitric acid to introduce an oxidizing group to the carbon support to increase the hydrophilicity of the catalyst.
Preferably, in the step 2, the sacrificial metal salt is one of chloride, acetate, nitrate and sulfate of sodium (Na), potassium (K), rubidium (Rb), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), aluminum (Al), cadmium (Cd), yttrium (Y), zirconium (Zr), tin (Sn) and cerium (Ce). The preferred embodiment selects non-noble metal atoms as sacrificial atoms to reduce the cost of catalyst preparation.
Preferably, in the step 2, the nitrogen-containing compound is one of aniline, phenylenediamine, phenanthroline and phthalocyanine. The preferred scheme selects nitrogen-containing compounds with soft and hard base group side chain modification.
Preferably, the molar ratio of the sacrificial metal salt to the nitrogen-containing compound in the step 2 is 5-10: 1. In the preferred embodiment, the mole number of the sacrificial metal salt is larger than that of the nitrogen-containing compound, so that the utilization rate of the nitrogen-containing site can be improved. The residual sacrificial metal with too high proportion is difficult to remove by subsequent acid washing, and the utilization rate of the nitrogen site with too low proportion is insufficient.
Preferably, the specific process of the pyrolysis treatment in the step 3 is as follows: under the atmosphere of nitrogen or argon, the room temperature is raised to 600-1200 ℃ at the heating rate of 5-30 ℃/min, and the temperature is kept for 0.5-3 h. This preferred approach employs heat treatment to improve the stability, conductivity, and structural integrity of the catalyst. Different heat treatment temperatures generate different coordination environments, and more conditions are created for subsequent ion exchange.
Preferably, the specific process of washing in step 3 is as follows: washing with 0.1-3mol/L hydrochloric acid solution for 12-48h, and then washing with deionized water.
Preferably, the solute of the target metal salt solution in step 4 is one of metal salts of vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), tungsten (W), iridium (Ir), platinum (Pt), chloride salt, acetate, nitrate, and sulfate. The preferable scheme selects metal with catalytic activity as target metal, and metal salt composed of target metal ion and non/weak coordination ion is subjected to ion exchange or vacancy point coordination in solvent environment.
Preferably, the solvent of the target metal salt solution in step 4 is methanol (MeOH), Acetonitrile (ACN), water (H) of the strong donor ligand with higher ligand field strength 2 O), Acetone (Acetone) and N, N-Dimethylformamide (DMF). The preferred embodiment employs a strong donor ligand of higher ligand field strength that promotes dissociation of the original coordination bonds at a higher rate, thereby destroying the structure prior to completion of metathesis with the incoming metal species.
Preferably, the concentration of the target metal salt solution in the step 4 is 0.1-0.5 mol/L. Higher concentrations may promote the exchange reaction, but too high a concentration may cause adsorption of the target metal on the catalyst surface, which is not conducive to subsequent washing.
Preferably, the amount ratio of the target metal salt to the sacrificial metal-nitrogen co-doped carbon template in the step 4 is 0.1 to 0.25 mol/g.
Preferably, the stirring temperature in the step 4 is 30-60 ℃, the stirring time is 1-4d, and the stirring speed is 500-800 rpm; the centrifugation speed is 8000-12000rpm, and the centrifugation time is 5-20 min. Increasing the reaction temperature and increasing the reaction time can increase the reaction rate kinetically, but too long a time can cause more side reactions.
Preferably, the method also comprises the step of carrying out heat treatment on the carbon-based single-atom catalyst, wherein the specific conditions of the heat treatment are as follows: the heat treatment atmosphere is one of nitrogen, argon, a hydrogen-nitrogen mixed gas and ammonia, the heat treatment temperature is 500-1000 ℃, and the heat treatment time is 1-3 h. This preferred embodiment stabilizes the carbon-based monatomic catalyst active sites by heat treatment.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention provides a carbon-based single-atom catalyst material, which is prepared by mixing non-noble metal salt serving as sacrificial metal salt with a carbon carrier and a nitrogen-containing compound, and pyrolyzing the mixture to synthesize a sacrificial metal-nitrogen co-doped carbon template; under the solution phase, a target metal with catalytic activity and a vacancy point generated by the induction of the sacrificial metal-nitrogen co-doped carbon template are coordinated, or the target metal with catalytic activity and the sacrificial metal are subjected to ion exchange to synthesize the target metal-nitrogen co-doped carbon-based single-atom catalyst. The catalyst can improve the problem of low load of a single-atom catalyst, and the metal load can reach 10.6 wt.%. Since the central metal atoms with different coordination structures exhibit different free energies in the elemental reactions, the reaction pathways can be controlled by the controlled synthesis of the specific coordination structure of the metal atom, thereby increasing the selectivity of the catalyst.
(2) The catalyst obtained by the invention is a single-atom catalyst, the particle size of the catalyst is reduced to an atomic scale, and no nano-particles exist under a high-resolution scanning transmission electron microscope. Atoms are exposed on the carrier as far as possible, so that each site is fully utilized, the utilization rate of the catalyst is obviously improved, and great help is provided for the mechanism research of the catalyst.
(3) According to the invention, the sacrificial metal catalyst templates with different carbonization degrees and different coordination environments can be obtained by changing the temperature of the high-temperature carbonization treatment of the sacrificial metal, and the influence of the pyrolysis temperature effect on the coordination capacity of the target metal is explored.
(4) The preparation method of the monatomic catalyst has the advantages of low cost of raw materials, convenient operation, high efficiency and universal applicability, and is widely applicable to preparation of most metal catalysts.
(5) The obtained target metal-nitrogen co-doped carbon-based single-atom catalyst is further subjected to heat treatment, so that the target metal is solidified on the catalyst template, and the single-atom catalyst has a stable chemical structure due to strong interaction between the metal and the carrier.
(6) The target metal-nitrogen co-doped carbon-based single-atom catalyst has excellent performance when applied to a fuel cell cathode catalyst.
Drawings
FIG. 1 is a schematic diagram of the synthesis of a sacrificial metal-nitrogen co-doped carbon template;
FIG. 2 is a schematic diagram of the synthesis of a target metal-nitrogen co-doped carbon-based monatomic catalyst;
FIG. 3 is SEM pictures of K-NC-800 and K (Co II) -NC-800 in example 3;
FIG. 4 is SEM pictures of K-NC-1000 and K (Co II) -NC-1000 in example 5;
FIG. 5 is a polarization diagram of a hydrogen-oxygen fuel cell assembled with K-NC-1000 and K (Co II) -NC-1000 as cathode catalysts in example 5;
FIG. 6 is SEM pictures of Mg-NC-1000 and Mg (MnIV) -NC-1000 in example 8;
FIG. 7 is a TEM image of Mg-NC-1000 and Mg (MnIV) -NC-1000 in example 8;
FIG. 8 is a STEM chart of Mg (Mn IV) -NC-1000 in example 8;
FIG. 9 is a TEM image of Ni-NC-1000 and Ni (FeII) -NC-1000 in example 26;
FIG. 10 is the EDS diagram for Ni (FeII) -NC-1000 in example 26;
FIG. 11 is a polarization diagram of a hydrogen-oxygen fuel cell assembled by using Ni (FeII) -NC-1000 and Ni (Pt IV) -NC-1000 as cathode catalysts in examples 26 and 39;
FIG. 12 is a graph showing the comparison of oxygen reduction polarization curves of Na-NC-1000, Na (Fe III) -NC-1000, and Na (Fe III) -NC-1000 + HT in example 43.
Detailed Description
In order that the invention may be more fully understood, reference will now be made to the following description. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
The invention provides a preparation method of a monatomic catalyst, and a schematic diagram of the monatomic catalyst is shown in figures 1-2. Inducing generation of a sacrificial metal-nitrogen co-doped carbon template with high site density as a site template (Ms-N) by introducing sacrificial metal atoms (Ms) x C); introducing target metal ions (M), ion-exchanging with sacrificial metal sites (Ms) in the site template, or coordinating with empty nitrogen sites induced by the catalyst template (Vacancy-N) x /C), thereby obtaining the target metal-nitrogen co-doped carbon-based single-atom catalyst.
Example 1
The embodiment provides a preparation method of a carbon-based single-atom catalyst with K as a sacrificial metal and Co as a target metal, which comprises the following steps:
step 1: adding 50mL of concentrated nitric acid with the mass concentration of 70% into 20g of carbon black, pretreating for 8h at 80 ℃ and 600rpm, washing by deionized water, carrying out suction filtration, and carrying out vacuum drying at 60 ℃ to obtain carbon black with oxidized surface; taking 0.2g of carbon black with oxidized surface, adding 100mL of deionized water and 10mL of isopropanol into the carbon black with oxidized surface, and carrying out ultrasonic treatment for 2h to obtain carbon black dispersion with oxidized surface;
step 2: dissolving 11mmol of aniline into 1 mol/L200 mL hydrochloric acid solution to form aniline solution; adding 55mmol of KNO 3 Dissolving the mixture into 1 mol/L200 mL hydrochloric acid solution; adding metal salt solution into aniline solution, stirring and polymerizing for 2h at 100rpm, adding the carbon black dispersion liquid with oxidized surface obtained in the step 1, and stirring at 600rpmStirring for 1d, heating to 60 ℃, and concentrating to obtain precursor slurry;
and step 3: loading the precursor slurry into an alumina combustion boat, heating to 600 ℃ at a heating rate of 10 ℃/min under the nitrogen atmosphere, and preserving heat for 30 min; then washing for 12h by using 1mol/L hydrochloric acid solution, then performing suction filtration and washing by using deionized water, and drying for 4h at 60 ℃ to obtain a sacrificial metal potassium-nitrogen co-doped carbon template, which is marked as K-NC-600;
and 4, step 4: 0.1g of K-NC-600 obtained in step 3 was taken and added to 0.2mol/L of 50mL of CoCl 2 Stirring the solution at room temperature for 2 d; and centrifuging the stirred solution at 10000rpm for 5min, centrifuging and washing the DMF solution for three times, and drying at 60 ℃ for 4h to obtain the target metal cobalt-nitrogen Co-doped carbon-based single-atom catalyst which is marked as K (Co II) -NC-600.
Examples 2 to 7
Examples 2 to 7 are modifications of example 1, respectively, and are only modified by: the heat treatment temperature of the precursor slurry in step 3 was changed from 600 ℃ to 700 ℃, 800 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, and is denoted as K-NC _ X (X = 700, 800, 900, 1000, 1100, 1200), and is detailed in table 1.
TABLE 1 Heat treatment temperature of precursor slurries of examples 1 to 7
FIG. 3 is a Scanning Electron Microscope (SEM) image of K-NC-800 and K (Co II) -NC-800, and FIG. 4 is a Scanning Electron Microscope (SEM) image of K-NC-1000 and K (Co II) -NC-1000. As can be seen from fig. 3 and 4, the morphology of the catalyst before and after coordination of the target metal Co has no significant difference, and the coordination retains the original morphology of the catalyst, which indicates that ion exchange in the solution phase has no influence on the original morphology of the catalyst.
Table 2 is the surface composition of the sacrificial metal-nitrogen co-doped carbon template K-NC _ X measured using EDS. As can be seen from Table 2, since K is difficult to coordinate with nitrogen sites, the content of K in the catalyst is low and the effect of temperature according to heat treatment is not so much affected. Table 3 shows the target metal-nitrogen co-doped carbon measured by EDSSurface composition of the radical monatomic catalyst K (Co II) -NC-X. As can be seen from Table 3, the proportion of Co increases gradually with the increase of the heat treatment temperature, and the proportion of Co decreases significantly when the heat treatment temperature is 1000 ℃ and the temperature is increased to 1000 ℃ or higher. In conclusion, the content of K in the sacrificial metal-nitrogen Co-doped carbon template is not high, but the target metal-nitrogen Co-doped carbon-based monatomic catalyst obtains high Co load, which is attributed to the fact that the catalyst template induces to generate higher empty nitrogen sites, Co 2+ Coordination is at the empty site.
Table 2 surface element composition (atomic percent, at.%) of sacrificial metal-nitrogen co-doped carbon template K-NC _ X in examples 1-7
Table 3 surface element composition (atomic percent, at.%) of target metal-nitrogen Co-doped carbon-based monatomic catalyst K (cii) -NC _ X in examples 1-7)
The K-NC-1000 and K (Co II) -NC-1000 catalysts from example 5 were subjected to hydrogen-oxygen fuel cell tests under the following conditions: 5cm 2 The fuel cell clamp has a cell temperature of 80 deg.C, an anode hydrogen flow rate of 500sccm, a cathode oxygen flow rate of 500sccm, a gas relative humidity of 100%, and an anode using a commercial platinum-carbon catalyst with a platinum loading of 0.1mg/cm 2 The cathode used K-NC-1000 or K (Co II) -NC-1000 catalyst, the perfluorosulfonic proton exchange membrane thickness was 12 microns. The range of the polarization curve test voltage is from open circuit voltage to 0.2V, the voltage step is 0.02V, and the voltage of each step is maintained for 1 min. Referring to FIG. 5, which shows polarization curves of hydrogen-oxygen fuel cells with K-NC-1000 and K (Co II) -NC-1000 as cathode catalysts, respectively, it can be seen from FIG. 5 that the hydrogen-oxygen fuel cell with the cathode catalyst of K (Co II) -NC-1000 has a higher open-circuit voltage and a higher current density at the same voltage than the hydrogen-oxygen fuel cell with the cathode catalyst of K-NC-1000 in the polarization curve test of hydrogen-oxygen fuel cells.
Example 8
This example provides a method for preparing a carbon-based single-atom catalyst with Mg as a sacrificial metal and Mn as a target metal, including the following steps:
step 1: adding 50mL of concentrated nitric acid with the mass concentration of 70% into 20g of activated carbon, pretreating for 7h at 60 ℃ and 500rpm, washing with deionized water, performing suction filtration, and performing vacuum drying at 80 ℃ to obtain activated carbon with oxidized surface; taking 0.2g of activated carbon with oxidized surface, adding 100mL of deionized water and 10mL of isopropanol into the activated carbon, and carrying out ultrasonic treatment for 2h to obtain activated carbon dispersion with oxidized surface;
step 2: dissolving 11mmol of o-phenylenediamine into 1mol/L of 200mL hydrochloric acid solution to form an o-phenylenediamine solution; adding 55mmol of MgCl 2 Dissolving the mixture into 1 mol/L200 mL hydrochloric acid solution; adding a metal salt solution into an o-phenylenediamine solution, stirring and polymerizing for 2h at 100rpm, adding the surface-oxidized activated carbon dispersion liquid obtained in the step (1), stirring for 1d at 600rpm, heating to 60 ℃, and concentrating to obtain precursor slurry;
and step 3: loading the precursor slurry into an alumina combustion boat, heating to 1000 ℃ at a heating rate of 5 ℃/min under the argon atmosphere, and preserving heat for 1 h; then washing for 48h by using 0.1mol/L hydrochloric acid solution, then performing suction filtration and washing by using deionized water, and drying for 4h at 60 ℃ to obtain a sacrificial metal magnesium-nitrogen co-doped carbon template, which is recorded as Mg-NC-1000;
and 4, step 4: 0.1g of Mg-NC-1000 obtained in step 3 was taken and added to 0.5mol/L of 50mL MnCl 4 Stirring the mixture at room temperature for 2 d; and centrifuging the stirred solution at 10000rpm for 5min, centrifuging and washing the acetonitrile solution for three times, and drying at 60 ℃ for 4h to obtain the target manganese-nitrogen co-doped carbon-based monatomic catalyst which is marked as Mg (Mn IV) -NC-1000.
FIG. 6 shows SEM images of Mg-NC-1000 and Mg (Mn IV) -NC-1000 under the same magnification, and it can be seen that the morphology of the catalyst is unchanged after coordination of the target metal Mn in the solution phase, the original morphology of the catalyst template is maintained, and the target metal Mn is coordinated with the active site on the template.
FIG. 7 is a Transmission Electron Microscope (TEM) image of Mg-NC-1000 and Mg (MnIV) -NC-1000 at the same magnification. As can be seen from the figure, no nano-particles exist before and after the exchange, the appearance is not obviously changed, the situation that no agglomeration occurs in the synthesis process is fully demonstrated, and the existence of the monoatomic group is proved.
Fig. 8 is a Scanning Transmission Electron Microscope (STEM) image of Mg (Mn iv) -NC — 1000, from which the target manganese-nitrogen co-doped carbon-based catalyst obtained without the presence of nanoparticles, metal Mn is uniformly distributed in the catalyst layer, no metal clusters are generated, and it is confirmed that the catalyst is a single atom.
Examples 9 to 25
Examples 9 to 25 are modifications of example 8, respectively, and are only modified by: MgCl sacrificial metal salt in step 2 2 Replacing with equimolar amount of NaCl, KCl, RbCl, SrCl 2 、CaCl 2 、BaCl 2 、CrCl 3 、FeCl 2 、CoCl 2 、NiCl 2 、CuCl 2 、ZnCl 2 、AlCl 3 、CdCl 2 、YCl 3 、SnCl 4 、CeCl 3 . The content (weight percent, wt.%) of sacrificial metal and target metal in the catalyst before and after ion exchange was measured using inductively coupled plasma atomic emission spectrometry (ICP-OES), and the results are detailed in table 4.
TABLE 4 sacrificial and target Metal contents in catalysts before and after ion exchange in examples 8-25
From the comparison of the metal contents of the catalysts before and after ion exchange shown in Table 4, it can be seen that the content of the sacrificial metal is decreasing, but the decrease amount is less than the increase amount of the target metal, which fully indicates that the coordination of the target metal is determined by two routes of ion exchange and coordination of vacancy points. The coordination amount of the target metal reaches 2-7 wt.%, high load of the single atom catalyst is realized, and the universality of the synthesis method of the single atom catalyst is proved.
Example 26
The embodiment provides a preparation method of a carbon-based single-atom catalyst with Ni as a sacrificial metal and Fe as a target metal, which comprises the following steps:
step 1: adding 50mL of concentrated nitric acid with the mass concentration of 70% into 20g of carbon black, pretreating for 6h at 90 ℃ and 900rpm, washing by deionized water, carrying out suction filtration, and carrying out vacuum drying at 40 ℃ to obtain carbon black with oxidized surface; taking 0.2g of carbon black with oxidized surface, adding 100mL of deionized water and 10mL of isopropanol into the carbon black with oxidized surface, and carrying out ultrasonic treatment for 2h to obtain carbon black dispersion with oxidized surface;
step 2: dissolving 11mmol of phthalocyanine into 1mol/L of 200mL hydrochloric acid solution to form a phthalocyanine solution; 77mmol of nickel acetate Ni (OAc) 2 Dissolving the mixture into 1 mol/L200 mL hydrochloric acid solution; adding a metal salt solution into a phthalocyanine solution, stirring and polymerizing for 2h at 100rpm, adding the carbon black dispersion liquid with the oxidized surface obtained in the step (1), stirring for 1d at 600rpm, heating to 60 ℃, and concentrating to obtain precursor slurry;
and step 3: putting the precursor slurry into an alumina combustion boat, heating to 1000 ℃ at a heating rate of 30 ℃/min under a nitrogen atmosphere, and preserving heat for 3 h; then washing for 12h by using 3mol/L hydrochloric acid solution, then performing suction filtration and washing by using deionized water, and drying for 4h at 60 ℃ to obtain a sacrificial metal nickel-nitrogen co-doped carbon template, which is recorded as Ni-NC-1000;
and 4, step 4: 0.1g of Ni-NC-1000 from step 3 was added to 0.3mol/L of 50mL FeCl 2 Stirring the aqueous solution of (1) at room temperature for 2 d; and centrifuging the stirred solution at 10000rpm for 5min, centrifuging and washing the aqueous solution for three times, and drying at 60 ℃ for 4h to obtain the target metal iron-nitrogen co-doped carbon-based monatomic catalyst which is recorded as Ni (FeII) -NC-1000.
FIG. 9 is a Transmission Electron Microscope (TEM) image of Ni-NC-1000 and Ni (FeII) -NC-1000 at the same magnification. It can be seen from the figure that no nanoparticles exist before and after the exchange, no metal clusters are generated, and the metal Fe exists in the form of single atoms.
FIG. 10 is EDS diagram of Ni (FeII) -NC-1000, from which the peak of Fe element of the target metal is clearly seen, demonstrating high loading of iron atom doping.
Examples 27 to 39
Examples 27 to 39 are modifications of example 26, which are only: FeCl which is the target metal salt in the step 4 2 Replacement with equimolar amounts of CrCl 3 、MnCl 4 、CoCl 2 、CuCl 2 、ZnCl 2 、MoCl 5 、RuCl 3 、RhCl 3 、PdCl 2 、AgCl、WCl 6 、IrCl 3 、PtCl 4 . The sacrificial and target metal contents (wt.%) in the catalyst before and after ion exchange were determined by EDS and the results are detailed in table 5.
TABLE 5 sacrificial and target Metal contents in catalysts before and after ion exchange in examples 26-39
From table 5, it can be seen that the target metal content obtained after coordination of different target metals is generally as high as 5wt.% or more, confirming the universality of the method for synthesizing high-load monatomic catalyst, and the coordination amount is different depending on the size and charge of the target metal ion and the sacrificial metal ion, the nature of the ligand, and the influence of the solvation shell layer.
The catalysts prepared in examples 26 and 39 were subjected to hydrogen-oxygen fuel cell tests under the following conditions: 5cm 2 The fuel cell clamp has a cell temperature of 80 deg.C, an anode hydrogen flow rate of 500sccm, a cathode oxygen flow rate of 500sccm, a gas relative humidity of 100%, a commercial platinum-carbon catalyst used as the anode, and a platinum loading of 0.1mg/cm 2 The cathode uses Ni (FeII) -NC-1000 catalyst or Ni (Pt IV) -NC-1000 catalyst, the thickness of the perfluorinated sulfonic proton exchange membrane is 12 microns. The range of the polarization curve test voltage is from open circuit voltage to 0.2V, the voltage step is 0.02V, and the voltage of each step is maintained for 1 min. As shown in FIG. 11, which is a polarization curve diagram of a hydrogen-oxygen fuel cell using Ni (FeII) -NC-1000 and Ni (Pt IV) -NC-1000 as cathode catalysts, respectively, it can be seen from FIG. 11 that the hydrogen-oxygen fuel cell using Ni (FeII) -NC-1000 or Ni (Pt IV) -NC-1000 as cathode catalysts shows excellent performance in the hydrogen-oxygen fuel cell polarization curve test.
Examples 40 to 42
Examples 40 to 42 are modifications of example 26, and the modifications are only: FeCl in the step 4 2 Is replaced by ferrous acetate (Fe (OAc) 2 ) Ferrous nitrate (Fe (NO) 3 ) 2 ) Or ferrous sulfate (FeSO) 4 ) The methanol solution of (1). The obtained target metal-nitrogen co-doped carbon-based single-atom catalyst is marked as Ni (M-L) x )-NC（M-L x Representing the target metal salt). The sacrificial and target metal contents (wt.%) of the catalyst before and after ion exchange were measured by XPS and are detailed in table 6.
TABLE 6 sacrificial and target Metal contents in catalysts before and after ion exchange in examples 26, 40-42
Similar results were obtained for the same target metal ion, different salt types, obtained from table 6, indicating that the coordination of the target metal ion on the sacrificial metal catalyst template is mainly dominant, the sites of coordination are similar, and the ligand has little effect on the metal loading of the catalyst.
Example 43
Step 1: adding 50mL of concentrated nitric acid with the mass concentration of 70% into 20g of graphene, pretreating at 80 ℃ and 600rpm for 8h, washing with deionized water, performing suction filtration, and performing vacuum drying at 80 ℃ to obtain graphene with an oxidized surface; adding 0.2g of graphene with oxidized surface into 100mL of deionized water and 10mL of isopropanol, and carrying out ultrasonic treatment for 2h to obtain graphene dispersion liquid with oxidized surface;
step 2: dissolving 11mmol of phenanthroline into 1mol/L of 200mL hydrochloric acid solution to form phenanthroline solution; adding 55mmol of Na 2 SO 4 Dissolving the mixture into 1 mol/L200 mL hydrochloric acid solution; mixing Na 2 SO 4 Adding a salt solution into the phenanthroline solution, stirring and polymerizing for 2h at 100rpm, adding the graphene dispersion liquid with the oxidized surface obtained in the step (1), stirring for 1d at 600rpm, heating to 60 ℃, and concentrating to obtain precursor slurry;
and step 3: putting the precursor slurry into an alumina combustion boat, heating to 1000 ℃ at a heating rate of 10 ℃/min under the nitrogen atmosphere, and preserving heat for 2 h; then washing the template for 24 hours by using 1mol/L hydrochloric acid solution, then performing suction filtration and washing by using deionized water, and drying the template for 4 hours at the temperature of 60 ℃ to obtain a sacrificial metal sodium-nitrogen co-doped carbon template, which is recorded as Na-NC-1000;
and 4, step 4: 0.1g of Na-NC-1000 obtained in step 3 was taken, and 0.4mol/L of 50mL of Fe (NO) 3 ) 3 Stirring the mixture at 50 ℃ for 1d in the acetone solution; centrifuging the stirred solution at 10000rpm for 5min, centrifuging and washing the aqueous solution for three times, and drying at 60 ℃ for 4h to obtain the target metal iron-nitrogen co-doped carbon-based monatomic catalyst which is marked as Na (Fe III) -NC-1000;
and 5: and (3) loading 50mg of the target metal iron-nitrogen co-doped carbon-based monatomic catalyst in the step (4) into an alumina combustion boat, heating to 600 ℃ at a heating rate of 10 ℃/min under the nitrogen atmosphere and the ambient pressure, and keeping the temperature for 1 h. The heat treated catalyst was ground well and the resulting catalyst was designated Na (Fe III) -NC-1000 + HT.
Table 7 shows the amounts (wt.%) of sacrificial metal and target metal for the Na-NC _1000, Na (Fe iii) -NC _1000+ HT catalysts determined using ICP-OES. It can be seen from table 7 that the loading of the target metal Fe does not change significantly after the optimization of the heat treatment.
TABLE 7 contents of sacrificial and target metals in Na-NC-1000, Na (Fe III) -NC-1000 + HT
The above-prepared Na-NC-1000, Na (Fe III) -NC-1000 and Na (Fe III) -NC-1000 + HT were subjected to electrochemical tests, respectively. Electrochemical tests were carried out at room temperature in the CHI 760E electrochemical station using a conventional three-electrode system. The specific test comprises the following steps: the Rotating Ring Disk Electrode (RRDE), the reversible hydrogen reference electrode (RHE) and the carbon rod electrode are respectively used as a working electrode, a reference electrode and a counter electrode. Under steady state conditions, using a 20mV potential step, will workThe electrode was swept from 1.0V to 0.2V at O 2 Saturated 0.5M H 2 SO 4 The ORR polarization curve was measured in the electrolyte and the results are shown in figure 12. FIG. 12 is a graph showing the comparison of oxygen reduction polarization curves of Na-NC-1000, Na (Fe III) -NC-1000, and Na (Fe III) -NC-1000 + HT. From FIG. 12, it can be seen that the target metal Fe 3+ The performance of the catalyst is not obviously increased after coordination in a solution phase, and the performance of the catalyst is effectively increased after heat treatment. We attribute the performance increase to the target metal Fe after heat treatment 3+ The coordination on the Na-NC-1000 template is more stable and is more tightly coordinated with nitrogen, so that the density of active sites is increased, and the activity of the catalyst is further optimized.
Example 44
This embodiment is a modification of embodiment 43, and is modified only in that: replacing the graphene in the step 1 with a carbon nano tube; 55mmol of Na in step 2 2 SO 4 Replaced by 110mmol of ZrSO 4 (ii) a In step 5, under the condition of hydrogen-nitrogen mixed gas (the volume content of hydrogen is 5%), the temperature is increased to 1000 ℃ at the temperature increasing rate of 10 ℃/min, and the temperature is kept for 3 h.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. The preparation method of the carbon-based single-atom catalyst is characterized in that a sacrificial metal-nitrogen co-doped carbon template is synthesized by mixing and pyrolyzing a sacrificial metal salt, a carbon carrier and a nitrogen-containing compound, and then a target metal-nitrogen co-doped carbon-based single-atom catalyst is synthesized by ion exchange coordination of a target metal in a solution phase.
2. The method of claim 1, comprising the steps of:
step 1: adding concentrated nitric acid into a carbon carrier for oxidation treatment, then adding water and isopropanol into the carbon carrier for ultrasonic dispersion to obtain carbon carrier dispersion liquid with oxidized surface;
and 2, step: adding a sacrificial metal salt and a nitrogen-containing compound into an acid solution, mixing and stirring, and adding a carbon carrier dispersion liquid with oxidized surface into the acid solution to obtain precursor slurry;
and step 3: carrying out pyrolysis treatment on the precursor slurry, washing and drying to obtain a sacrificial metal-nitrogen co-doped carbon template;
and 4, step 4: mixing the sacrificial metal-nitrogen co-doped carbon template with a target metal salt solution, stirring, centrifugally washing and drying to obtain the target metal-nitrogen co-doped carbon-based single-atom catalyst.
3. The method for preparing a carbon-based monatomic catalyst according to claim 2, wherein the carbon support in the step 1 is one of carbon black, activated carbon, graphene, and carbon nanotubes.
4. The method for preparing the carbon-based single-atom catalyst according to claim 2, wherein the oxidation treatment in the step 1 comprises the following specific steps: adding concentrated nitric acid into carbon carrier, stirring for 6-8h at 60-90 deg.C and 500-900rpm, washing, vacuum filtering, and vacuum drying at 40-80 deg.C.
5. The method for preparing the carbon-based single-atom catalyst according to claim 2, wherein the sacrificial metal salt in the step 2 is one of chloride, acetate, nitrate and sulfate of sodium, potassium, rubidium, magnesium, calcium, strontium, barium, chromium, manganese, iron, cobalt, nickel, copper, zinc, aluminum, cadmium, yttrium, zirconium, tin and cerium; the nitrogen-containing compound is one of aniline, phenylenediamine, phenanthroline and phthalocyanine.
6. The method for preparing a carbon-based monatomic catalyst according to claim 2, wherein the molar ratio of the sacrificial metal salt to the nitrogen-containing compound in the step 2 is 5 to 10: 1.
7. The preparation method of the carbon-based single-atom catalyst according to claim 2, wherein the pyrolysis treatment in the step 3 comprises the following specific steps: under the atmosphere of nitrogen or argon, the room temperature is raised to 600-1200 ℃ at the heating rate of 5-30 ℃/min, and the temperature is kept for 0.5-3 h; the specific washing process comprises the following steps: washing with 0.1-3mol/L hydrochloric acid solution for 12-48h, and then washing with deionized water.
8. The method for preparing a carbon-based monatomic catalyst according to claim 2, wherein the solute of the target metal salt solution in the step 4 is one of chloride salts, acetates, nitrates and sulfates of metals vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, molybdenum, ruthenium, rhodium, palladium, silver, tungsten, iridium, platinum; the solvent of the target metal salt solution is one of methanol, acetonitrile, water, acetone and N, N-dimethylformamide.
9. The method for preparing the carbon-based monatomic catalyst according to claim 2, wherein the concentration of the target metal salt solution in the step 4 is 0.1 to 0.5mol/L, and the ratio of the target metal salt to the sacrificial metal-nitrogen co-doped carbon template is 0.1 to 0.25 mol/g.
10. The preparation method of the carbon-based monatomic catalyst according to any one of claims 1 to 9, further comprising a heat treatment of the carbon-based monatomic catalyst, wherein the specific conditions of the heat treatment are as follows: the heat treatment atmosphere is one of nitrogen, argon, a hydrogen-nitrogen mixed gas and ammonia, the heat treatment temperature is 500-1000 ℃, and the heat treatment time is 1-3 h.
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