CN112349918B - Method for preparing nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan and application thereof - Google Patents
Method for preparing nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan and application thereof Download PDFInfo
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Abstract
The invention relates to a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan and application thereof, belonging to the technical field of catalyst preparation. The invention prepares chitosan carbon powder by pyrolyzing chitosan; adding chitosan carbon powder into an ethanol solution containing polyalcohol and a dispersing agent, ultrasonically dispersing uniformly, adding a platinum precursor solution, carrying out a constant-temperature reduction reaction at 70-150 ℃ for 100-240min, washing the solid with deionized water at 70-80 ℃ until the washing liquid is neutral, drying, grinding and sieving to obtain the nitrogen-doped platinum-carbon catalyst. The highly dispersed PtNPs-loaded oxygen reduction cathode platinum-based catalyst with the average particle size of 3.5nm is prepared by controlling the pyrolysis temperature and time and the reduction reaction temperature and time, and has ultrahigh electrocatalytic stability and higher electrochemical activity.
Description
Technical Field
The invention relates to a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan and application thereof, belonging to the technical field of catalyst preparation.
Background
In the face of increasing energy consumption and the continuous decrease of other energy reserves, fuel cells are receiving attention due to their ultra-high energy conversion efficiency and environmental friendliness. However, the slow cathode kinetics and the high overpotential requirements severely limit their practical applications. Platinum-based materials are the most excellent ORR catalysts because of their effective promotion of the ORR reaction and the lower overpotential associated with the 4-electron reaction pathway. However, conventional Pt/C catalysts tend to increase activity at the expense of higher loading, where only a small fraction of the platinum atoms on the surface of each platinum nanoparticle participate in the reaction, resulting in lower platinum utilization and slow kinetics. Therefore, it is important to develop catalysts that reduce the required overpotential and platinum consumption and improve the cathode kinetic reaction performance.
Disclosure of Invention
The invention provides a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan, aiming at the problems of high cost, poor activity and stability and low dispersion degree of platinum nanoparticles (PtNPs) in the prior art and an application thereof 2 /g Pt The half-wave potential reaches 0.85V vsRHE )。
Heteroatom doping (N, P, B and the like) can improve the dispersity of platinum nanoparticles (PtNPs) and the activity and stability of the catalyst, the pyrolyzed chitosan carbon is used as a carbon source and a nitrogen source, more active sites can be introduced in a self-doping mode, the complicated synthesis process is avoided, and the pyrolyzed chitosan carbon contains amino groups and other nitrogen-containing groups and can anchor the PtNPs, so that the catalyst has excellent electrochemical performance and extremely high stability.
A method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute acid, adding a dispersing agent, and uniformly stirring to obtain chitosan gel;
(2) Drying the chitosan gel obtained in the step (1) in vacuum until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Heating the chitosan gel powder in the step (2) to 200-600 ℃ at a constant speed under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 60-180min, heating to 700-1000 ℃ at a constant speed, carrying out constant temperature treatment for 60-180 ℃, cooling to normal temperature along with a furnace, and grinding to obtain chitosan carbon powder; the organic dispersing agent can be removed by constant temperature treatment at 200-600 ℃, and a hole structure is formed at the same time; the chitosan gel powder can be carbonized by constant temperature treatment at 700-1000 ℃;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyalcohol and a dispersing agent, carrying out ultrasonic dispersion uniformly, adding a platinum precursor solution, carrying out constant-temperature reaction at 70-150 ℃ for 100-240min, washing the solid with deionized water at 70-80 ℃ until the washing liquid is neutral, drying, grinding and sieving to obtain the nitrogen-doped platinum-carbon catalyst.
The diluted acid in the step (1) is hydrochloric acid, sulfuric acid, acetic acid or nitric acid, and the pH value of the diluted acid is 2-5.
The solid-to-liquid ratio g: mL of the chitosan to the dilute acid in the step (1) is 1-50.
The dispersing agent in the step (1) and the step (1) is one or more of water glass, sodium hexametaphosphate, sodium lignosulfonate and polyoxyethylene polyoxypropylene ether block copolymer.
The mass ratio of the chitosan to the dispersant in the step (1) is 1.5-3.
The constant temperature rise rate in the step (3) is 2-15 ℃/min.
The mass ratio of the chitosan carbon powder to the dispersing agent in the step (4) is 1.1-5.
The polyhydric alcohol in the step (4) is one or more of ethylene glycol, polyethylene glycol, 1, 2-propylene glycol and glycerol, and the mass ratio of the chitosan carbon powder to the polyhydric alcohol is 1-10.
The platinum precursor in the step (4) is one or more of sodium chloroplatinate, potassium chloroplatinate and chloroplatinic acid, the concentration of the platinum precursor solution is 0.01-1mol/L, and the solid-to-liquid ratio g: mL of the chitosan carbon powder to the platinum precursor solution is 1.
The nitrogen-doped platinum-carbon catalyst is applied as an oxygen reduction cathode catalyst.
The invention has the beneficial effects that:
(1) According to the invention, chitosan is used as a carbon precursor as a carbon source and a nitrogen source, rich active sites are introduced in a self-doping manner, and a polyol is used as a reducing agent to load the high-dispersion platinum-based catalyst with the PtNPs particle size of 3.5nm on the premise of nitrogen doping, so that the high-dispersion platinum-based catalyst has the advantages of low reaction temperature and low platinum consumption;
(2) The electrochemical performance of common commercial platinum carbon can be achieved under the loading of 5wt% of Pt, and the platinum carbon has higher stability than the commercial platinum carbon;
(3) The method has the advantages of simple preparation process, wide carbon precursor source, low price and excellent environmental friendliness.
Drawings
FIG. 1 is a high resolution transmission electron micrograph (magnification 1000000) of a nitrogen-doped platinum-carbon catalyst of example 1;
FIG. 2 is a high resolution transmission electron micrograph (magnification 1000000) of nitrogen-doped platinum-carbon catalyst of example 2;
FIG. 3 is an XRD pattern of a nitrogen doped platinum carbon catalyst of example 1;
FIG. 4 shows the results of the electrochemical test and the photoelectron spectroscopy results of example 1: FIG. a is a comparison of cyclic voltammetry curves of CSC-Pt and JM 20wt% commercial platinum carbon, FIG. d is a comparison of linear sweep voltammetry curves of CSC-Pt and JM 20wt% commercial platinum carbon, FIGS. b and e are a comparison of accelerated aging tests of 10000 cycles CV sweeps of CSC-Pt and JM 20wt% commercial platinum carbon, and FIG. f is an XPS N1s fit plot of CSC-Pt, wherein P-N represents pyridine nitrogen, py-N represents pyrrole nitrogen, G-N represents graphite nitrogen, O-N represents oxidized nitrogen, and Pt-N represents platinum nitrogen; fig. c is a histogram of the calculated contents of each type of nitrogen in fig. 4 f.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but the scope of the present invention is not limited to the description.
Example 1: a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute acetic acid with the pH value of 2, adding a dispersing agent polyoxyethylene polyoxypropylene ether block copolymer, and uniformly stirring to obtain chitosan gel; wherein the solid-liquid ratio g: mL of the chitosan to the dilute acetic acid is 1;
(2) Placing the chitosan gel obtained in the step (1) at the temperature of 80 ℃ for vacuum drying until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Uniformly heating the chitosan gel powder in the step (2) to 350 ℃ at a speed of 5 ℃/min under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 120min, then uniformly heating to 900 ℃ for constant temperature treatment for 180 ℃, carrying out furnace cooling to normal temperature, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyalcohol (ethylene glycol) and a dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer), adding a platinum precursor solution (chloroplatinic acid solution) after uniform ultrasonic dispersion, reacting at constant temperature of 120 ℃ for 240min, washing the solid with deionized water at the temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding and sieving with a 800-mesh sieve to obtain the nitrogen-doped platinum-carbon catalyst; wherein the mass ratio of the chitosan carbon powder to the dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer) is 1;
the high-resolution transmission electron microscope image of the nitrogen-doped platinum-carbon catalyst of the embodiment is shown in fig. 1, and it can be known from fig. 1 that the average particle size of PtNPs is 3.5nm and the PtNPs are uniformly dispersed;
the XRD pattern of the nitrogen-doped platinum-carbon catalyst is shown in figure 3, and as can be seen from figure 3, the nitrogen-doped platinum-carbon catalyst only has a platinum simple substance phase and has no other impurity peaks;
the results of the contents of C, N and Pt elements in the nitrogen-doped platinum-carbon catalyst measured by ICP-OES and an element analyzer are shown in Table 1,
TABLE 1 partial element content in the catalyst
As can be seen from Table 1, the nitrogen content is up to 5.8%, and the platinum content is close to the target load;
the electrochemical test result of the nitrogen-doped platinum-carbon catalyst is shown in fig. 4, and as can be seen from the cyclic voltammetry curve and the linear sweep voltammetry curve, the oxygen reduction half-wave potential and the mass specific current of the catalyst are both greater than those of commercial JM 20wt% platinum-carbon, and after 10000 cycles of cyclic voltammetry sweep accelerated aging test, the catalyst shows a smaller half-wave potential drop than that of commercial platinum-carbon.
Example 2: a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute acetic acid with pH value of 5, adding sodium hexametaphosphate serving as a dispersing agent, and uniformly stirring to obtain chitosan gel; wherein the solid-liquid ratio g/mL of chitosan to dilute acetic acid is 1;
(2) Placing the chitosan gel obtained in the step (1) at the temperature of 80 ℃ for vacuum drying until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Uniformly heating the chitosan gel powder in the step (2) to 200 ℃ at a speed of 2 ℃/min under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 120min, then uniformly heating to 800 ℃ for carrying out constant temperature treatment for 180 ℃, cooling to normal temperature along with a furnace, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyalcohol (polyethylene glycol) and a dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer), uniformly dispersing by ultrasonic waves, adding a platinum precursor solution (chloroplatinic acid solution), reacting at the constant temperature of 80 ℃ for 180min, washing the solid by deionized water at the temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding, and sieving by a 800-mesh sieve to obtain a nitrogen-doped platinum carbon catalyst CSC-Pt; wherein the mass ratio of the chitosan carbon powder to the dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer) is 1;
the high-resolution transmission electron microscope image of the nitrogen-doped platinum-carbon catalyst of the embodiment is shown in fig. 2, and it can be seen from fig. 2 that the average particle size of PtNPs is 3.7nm, and the PtNPs are uniformly dispersed;
the XRD pattern of the nitrogen-doped platinum-carbon catalyst shows that the nitrogen-doped platinum-carbon catalyst only has a platinum simple substance phase and has no other impurity peaks;
the results of the contents of C, N and Pt elements in the nitrogen-doped platinum-carbon catalyst measured by ICP-OES and an element analyzer are shown in Table 2,
TABLE 2 partial element content in the catalyst
As can be seen from Table 2, the nitrogen content was as high as 5.7%, and the platinum content was close to the target loading;
the nitrogen-doped platinum-carbon catalyst is subjected to electrochemical test, the oxygen reduction half-wave potential and the mass specific current of the catalyst are respectively larger than commercial JM 20wt% platinum carbon from a cyclic voltammetry curve and a linear sweep voltammetry curve, and after 10000 cycles of cyclic voltammetry sweep accelerated aging test, the catalyst shows smaller half-wave potential drop than the commercial platinum carbon.
Example 3: a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute acetic acid with the pH value of 4, adding a dispersing agent polyoxyethylene polyoxypropylene ether segmented copolymer, and uniformly stirring to obtain chitosan gel; wherein the solid-liquid ratio g: mL of the chitosan to the dilute acetic acid is 1;
(2) Placing the chitosan gel obtained in the step (1) at the temperature of 90 ℃ for vacuum drying until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Uniformly heating the chitosan gel powder in the step (2) to 300 ℃ at a speed of 15 ℃/min under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 120min, then uniformly heating to 800 ℃ for 120 ℃ at constant temperature treatment, cooling to normal temperature along with a furnace, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyalcohol (1, 2-propylene glycol) and a dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer), adding a platinum precursor solution (potassium chloroplatinate solution) after uniform ultrasonic dispersion, reacting for 180min at a constant temperature of 150 ℃, washing the solid with deionized water at a temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding, and sieving with a 800-mesh sieve to obtain a nitrogen-doped platinum-carbon catalyst; wherein the mass ratio of the chitosan carbon powder to the dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer) is 1;
as can be seen from a high-resolution transmission electron micrograph of the nitrogen-doped platinum-carbon catalyst in the embodiment, the average particle size of PtNPs is 3.9nm, and the PtNPs are uniformly dispersed;
the XRD pattern of the nitrogen-doped platinum-carbon catalyst shows that the nitrogen-doped platinum-carbon catalyst only has a platinum simple substance phase and has no other impurity peaks; the results of the contents of C, N and Pt elements in the nitrogen-doped Pt-C catalyst measured by ICP-OES and an element analyzer are shown in Table 3,
TABLE 3 partial element content in catalyst
As can be seen from Table 3, the nitrogen content was as high as 5.1% and the platinum content was close to the target loading;
the nitrogen-doped platinum-carbon catalyst is subjected to electrochemical test, the oxygen reduction half-wave potential and the mass specific current of the catalyst are respectively larger than commercial JM 20wt% platinum carbon from a cyclic voltammetry curve and a linear sweep voltammetry curve, and after 10000 cycles of cyclic voltammetry sweep accelerated aging test, the catalyst shows smaller half-wave potential drop than the commercial platinum carbon.
Example 4: a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute acetic acid with the pH value of 2, adding a dispersing agent polyoxyethylene polyoxypropylene ether block copolymer, and uniformly stirring to obtain chitosan gel; wherein the solid-liquid ratio g: mL of the chitosan to the dilute acetic acid is 1;
(2) Placing the chitosan gel obtained in the step (1) at the temperature of 80 ℃ for vacuum drying until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Uniformly heating the chitosan gel powder in the step (2) to 400 ℃ at a speed of 5 ℃/min under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 120min, then uniformly heating to 900 ℃ for carrying out constant temperature treatment for 180 ℃, cooling to normal temperature along with a furnace, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyol (glycerol) and a dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer), uniformly dispersing by ultrasonic waves, adding a platinum precursor solution (chloroplatinic acid solution), reacting at a constant temperature of 150 ℃ for 180min, washing the solid by deionized water at a temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding and sieving to obtain the nitrogen-doped platinum-carbon catalyst; wherein the mass ratio of the chitosan carbon powder to the dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer) is 1;
as shown in a high-resolution transmission electron microscope picture of the nitrogen-doped platinum-carbon catalyst, the average particle size of PtNPs is 3.5nm, and the PtNPs are uniformly dispersed;
the XRD pattern of the nitrogen-doped platinum-carbon catalyst shows that the nitrogen-doped platinum-carbon catalyst only has a platinum simple substance phase and does not have other impurity peaks; the results of the contents of C, N and Pt elements in the nitrogen-doped Pt-C catalyst measured by ICP-OES and an element analyzer are shown in Table 4,
TABLE 4 partial element content in catalyst
As can be seen from Table 4, the nitrogen content was as high as 5.8%, and the platinum content was close to the target loading;
the nitrogen-doped platinum-carbon catalyst is subjected to electrochemical test, the oxygen reduction half-wave potential and the mass specific current of the catalyst are respectively larger than commercial JM 20wt% platinum carbon from a cyclic voltammetry curve and a linear sweep voltammetry curve, and after 10000 cycles of cyclic voltammetry sweep accelerated aging test, the catalyst shows smaller half-wave potential drop than the commercial platinum carbon.
Example 5: a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute acetic acid with the pH value of 3, adding sodium lignin sulfonate serving as a dispersing agent, and uniformly stirring to obtain chitosan gel; wherein the solid-liquid ratio g: mL of the chitosan to the dilute acetic acid is 1;
(2) Placing the chitosan gel obtained in the step (1) at the temperature of 80 ℃ for vacuum drying until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Uniformly heating the chitosan gel powder in the step (2) to 350 ℃ at a speed of 10 ℃/min under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 180min, then uniformly heating to 1000 ℃ for carrying out constant temperature treatment for 120 ℃, cooling to normal temperature along with a furnace, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyalcohol (ethylene glycol) and a dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer), uniformly dispersing by ultrasonic waves, adding a platinum precursor solution (potassium chloroplatinate solution), reacting at a constant temperature of 120 ℃ for 240min, washing the solid by deionized water at a temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding and sieving to obtain a nitrogen-doped platinum-carbon catalyst; wherein the mass ratio of the chitosan carbon powder to the dispersing agent (polyoxyethylene polyoxypropylene ether block copolymer) is 1;
as can be seen from a high-resolution transmission electron microscope picture of the nitrogen-doped platinum-carbon catalyst, the average particle size of PtNPs is 4.0nm, and the PtNPs are uniformly dispersed;
the XRD pattern of the nitrogen-doped platinum-carbon catalyst shows that the nitrogen-doped platinum-carbon catalyst only has a platinum simple substance phase and has no other impurity peaks; the results of the contents of C, N and Pt elements in the nitrogen-doped Pt-C catalyst measured by ICP-OES and an element analyzer are shown in Table 5,
TABLE 5 partial element content in catalyst
As can be seen from Table 5, the nitrogen content was as high as 5.0% and the platinum content was close to the target loading;
the nitrogen-doped platinum-carbon catalyst is subjected to electrochemical test, the oxygen reduction half-wave potential and the mass specific current of the catalyst are respectively larger than commercial JM 20wt% platinum carbon from a cyclic voltammetry curve and a linear sweep voltammetry curve, and after 10000 cycles of cyclic voltammetry sweep accelerated aging test, the catalyst shows smaller half-wave potential drop than the commercial platinum carbon.
Example 6: a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute hydrochloric acid with the pH value of 5, adding a dispersing agent polyoxyethylene polyoxypropylene ether segmented copolymer, and uniformly stirring to obtain chitosan gel; wherein the solid-liquid ratio g: mL of the chitosan to the dilute hydrochloric acid is 1;
(2) Placing the chitosan gel obtained in the step (1) at the temperature of 80 ℃ for vacuum drying until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Uniformly heating the chitosan gel powder in the step (2) to 200 ℃ at a speed of 2 ℃/min under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 120min, then uniformly heating to 800 ℃ for carrying out constant temperature treatment for 180 ℃, cooling to normal temperature along with a furnace, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyalcohol (ethylene glycol) and a dispersing agent (sodium lignosulfonate), adding a platinum precursor solution (potassium chloroplatinate solution) after ultrasonic dispersion is uniform, reacting for 180min at a constant temperature of 90 ℃, washing the solid with deionized water at a temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding and sieving to obtain a nitrogen-doped platinum-carbon catalyst; wherein the mass ratio of the chitosan carbon powder to the dispersing agent (sodium lignosulfonate) is 1;
as can be seen from a high-resolution transmission electron micrograph of the nitrogen-doped platinum-carbon catalyst in the embodiment, the average particle size of PtNPs is 3.4nm, and the PtNPs are uniformly dispersed;
the XRD pattern of the nitrogen-doped platinum-carbon catalyst shows that the nitrogen-doped platinum-carbon catalyst only has a platinum simple substance phase and does not have other impurity peaks; the results of the contents of C, N and Pt elements in the nitrogen-doped Pt-C catalyst measured by ICP-OES and an element analyzer are shown in Table 6,
TABLE 6 partial element content in catalyst
As can be seen from Table 6, the nitrogen content was as high as 5.3%, and the platinum content was close to the target loading;
the nitrogen-doped platinum-carbon catalyst is subjected to electrochemical test, the oxygen reduction half-wave potential and the mass specific current of the catalyst are respectively larger than commercial JM 20wt% platinum carbon from a cyclic voltammetry curve and a linear sweep voltammetry curve, and after 10000 cycles of cyclic voltammetry sweep accelerated aging test, the catalyst shows smaller half-wave potential drop than the commercial platinum carbon.
Example 7: a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute sulfuric acid with the pH value of 5, adding a dispersant polyoxyethylene polyoxypropylene ether block copolymer, and uniformly stirring to obtain chitosan gel; wherein the solid-liquid ratio g: mL of the chitosan to the dilute sulfuric acid is 1;
(2) Placing the chitosan gel obtained in the step (1) at the temperature of 80 ℃ for vacuum drying until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Uniformly heating the chitosan gel powder in the step (2) to 350 ℃ at a speed of 5 ℃/min under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 120min, then uniformly heating to 800 ℃ for 180 ℃, carrying out furnace cooling to normal temperature, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyalcohol (ethylene glycol) and a dispersing agent (sodium lignosulfonate), adding a platinum precursor solution (a potassium chloroplatinate solution) after uniform ultrasonic dispersion, reacting at the constant temperature of 140 ℃ for 180min, washing the solid with deionized water at the temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding, and sieving with a 800-mesh sieve to obtain the nitrogen-doped platinum-carbon catalyst; wherein the mass ratio of the chitosan carbon powder to the dispersing agent (sodium lignosulfonate) is 1;
as can be seen from a high-resolution transmission electron micrograph of the nitrogen-doped platinum-carbon catalyst in the embodiment, the average particle size of PtNPs is 3.9nm, and the PtNPs are uniformly dispersed;
the XRD pattern of the nitrogen-doped platinum-carbon catalyst shows that the nitrogen-doped platinum-carbon catalyst only has a platinum simple substance phase and has no other impurity peaks; the results of the contents of C, N and Pt elements in the nitrogen-doped Pt-C catalyst measured by ICP-OES and an element analyzer are shown in Table 7,
TABLE 7 partial element content in catalyst
As can be seen from Table 7, the nitrogen content was as high as 5.0%, and the platinum content was close to the target loading;
the nitrogen-doped platinum-carbon catalyst is subjected to electrochemical test, the oxygen reduction half-wave potential and the mass specific current of the catalyst are larger than those of commercial JM 20wt% from a cyclic voltammetry curve and a linear scanning voltammetry curve, and after 10000 cycles of cyclic voltammetry scanning accelerated aging test, the catalyst shows smaller half-wave potential drop than that of commercial platinum-carbon.
Example 8: a method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan comprises the following specific steps:
(1) Dissolving chitosan in dilute nitric acid with the pH value of 5, adding a dispersing agent polyoxyethylene polyoxypropylene ether block copolymer, and uniformly stirring to obtain chitosan gel; wherein the solid-liquid ratio g: mL of the chitosan to the dilute nitric acid is 1;
(2) Placing the chitosan gel obtained in the step (1) at the temperature of 80 ℃ for vacuum drying until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Uniformly heating the chitosan gel powder in the step (2) to 250 ℃ at a speed of 15 ℃/min under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 120min, then uniformly heating to 900 ℃ for constant temperature treatment for 180 ℃, carrying out furnace cooling to normal temperature, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing polyalcohol (ethylene glycol) and a dispersing agent (water glass), adding a platinum precursor solution (potassium chloroplatinate solution) after ultrasonic dispersion is uniform, reacting for 180min at a constant temperature of 130 ℃, washing the solid with deionized water at a temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding and sieving to obtain a nitrogen-doped platinum-carbon catalyst; wherein the mass ratio of the chitosan carbon powder to the dispersing agent (water glass) is 1;
as can be seen from a high-resolution transmission electron micrograph of the nitrogen-doped platinum-carbon catalyst in the embodiment, the average particle size of PtNPs is 3.5nm, and the PtNPs are uniformly dispersed;
the XRD pattern of the nitrogen-doped platinum-carbon catalyst shows that the nitrogen-doped platinum-carbon catalyst only has a platinum simple substance phase and does not have other impurity peaks; the results of the contents of C, N and Pt elements in the nitrogen-doped Pt-C catalyst measured by ICP-OES and an element analyzer are shown in Table 8,
TABLE 7 partial element content in catalyst
As can be seen from Table 8, the nitrogen content was as high as 5.6% and the platinum content was close to the target loading;
the nitrogen-doped platinum-carbon catalyst is subjected to electrochemical test, the oxygen reduction half-wave potential and the mass specific current of the catalyst are respectively larger than commercial JM 20wt% platinum carbon from a cyclic voltammetry curve and a linear sweep voltammetry curve, and after 10000 cycles of cyclic voltammetry sweep accelerated aging test, the catalyst shows smaller half-wave potential drop than the commercial platinum carbon.
While the present invention has been described in detail with reference to the specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
Claims (9)
1. A method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan is characterized by comprising the following specific steps:
(1) Dissolving chitosan in dilute acid, adding a dispersing agent, and uniformly stirring to obtain chitosan gel;
(2) Drying the chitosan gel obtained in the step (1) in vacuum until the chitosan gel is anhydrous, and grinding the chitosan gel into powder to obtain chitosan gel powder;
(3) Heating the chitosan gel powder in the step (2) to 200-600 ℃ at a constant speed under the protection of nitrogen atmosphere, carrying out constant temperature treatment for 60-180min, heating to 700-1000 ℃ at a constant speed, carrying out constant temperature treatment, cooling to normal temperature along with a furnace, and grinding to obtain chitosan carbon powder;
(4) Adding the chitosan carbon powder obtained in the step (3) into an ethanol solution containing a reducing agent and a dispersing agent, adding a platinum precursor solution after uniform ultrasonic dispersion, reacting at a constant temperature of 70-150 ℃ for 100-240min, washing the solid with deionized water at a temperature of 70-80 ℃ until the washing liquid is neutral, drying, grinding and sieving to obtain a nitrogen-doped platinum-carbon catalyst; wherein the reducing agent is polyhydric alcohol, the concentration of the platinum precursor solution is 0.01-1mol/L, and the solid-to-liquid ratio g: mL of the chitosan carbon powder to the platinum precursor solution is 1 to 2-30;
the dispersing agent in the step (1) and the dispersing agent in the step (4) are one or more of water glass, sodium hexametaphosphate, sodium lignosulfonate and polyoxyethylene polyoxypropylene ether block copolymer.
2. The method for preparing the nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan according to claim 1, wherein: the diluted acid in the step (1) is hydrochloric acid, sulfuric acid, acetic acid or nitric acid, and the pH value of the diluted acid is 2-5.
3. The method for preparing a nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan according to claim 1 or 2, wherein: the solid-to-liquid ratio g: mL of the chitosan to the dilute acid in the step (1) is 1 to 50-300.
4. The method for preparing the nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan according to claim 1, wherein: in the step (1), the mass ratio of the chitosan to the dispersant is 1.
5. The method for preparing the nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan according to claim 1, wherein: the constant temperature rise rate of the step (3) is 2-15 ℃/min.
6. The method for preparing the nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan according to claim 1, wherein: and (4) the mass ratio of the chitosan carbon powder to the dispersing agent is 1 to 0.1-5.
7. The method for preparing the nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan according to claim 1, wherein: and (3) the polyol in the step (4) is one or more of ethylene glycol, polyethylene glycol, 1, 2-propylene glycol and glycerol, and the mass ratio of the chitosan carbon powder to the polyol is 1 to 10 to 80.
8. The method for preparing the nitrogen-doped platinum-carbon catalyst by pyrolyzing chitosan according to claim 1, wherein: and (4) the platinum precursor is one or more of sodium chloroplatinate, potassium chloroplatinate and chloroplatinic acid.
9. Use of a nitrogen-doped platinum-carbon catalyst prepared by the method of claims 1 to 8 as an oxygen reduction cathode catalyst.
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