CN109616670B - Morphology-controllable cobalt sulfide, preparation method thereof, cobalt sulfide/nitrogen-doped carbon nanotube catalyst and application thereof - Google Patents
Morphology-controllable cobalt sulfide, preparation method thereof, cobalt sulfide/nitrogen-doped carbon nanotube catalyst and application thereof Download PDFInfo
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Abstract
The invention provides a preparation method of cobalt sulfide, which comprises the steps of carrying out hydrothermal reaction on inorganic acid cobalt salt and cysteine in a solvent system; and then sequentially drying, grinding and calcining the product to obtain the cobalt sulfide. The invention can adjust the polarity and the carbon source concentration of the solvent system by changing the type and the dosage of the solvent in the solvent system, thereby achieving the purpose of controlling the micro-morphology of the cobalt sulfide, being capable of batch preparation and having good reproducibility. The cobalt sulfide provided by the invention has regular micro-morphology and takes on the micro-morphology of petal-shaped and spherical particles and the like. The invention adopts nitrogen-doped carbon nano tubes (N-CNT) as carriers, and the nitrogen-doped carbon nano tubes and cobalt sulfide with regular microcosmic appearance are compounded to obtain the cobalt sulfide/nitrogen-doped carbon nano tube catalyst.
Description
Technical Field
The invention belongs to the technical field of preparation of oxygen reduction catalytic materials, and particularly relates to morphology-controllable cobalt sulfide, a preparation method thereof, a cobalt sulfide/nitrogen-doped carbon nanotube catalyst and application thereof.
Background
The reaction speed of the air electrode of the metal-air battery and the fuel battery is very slow at normal temperature, and a catalyst is needed to catalyze the speed increase. The best catalyst at present is commercial JM 20% Pt/C, but platinum metal is rare and expensive, and is difficult to be commercially applied on a large scale. Therefore, the search for highly efficient non-platinum based catalysts has been a hot issue in this field.
Over the last decade, transition metal sulfides (e.g., manganese sulfide, cobalt sulfide, iron sulfide, etc.) have been developed for use as alternatives to Pt-based catalytic materials, especially cobalt sulfide. For example, the document "preparation and optimization of cobalt sulfide/carbon nanofiber membrane counter electrode, oceanic ocean, etc" describes a hydrothermal synthesis method of cobalt sulfide: 0.749g of CoCl is respectively weighed by an electronic balance2·6H2O and 0.473g CH3CSNH2(thioacetamide), pouring the thioacetamide into a reaction kettle, adding 63mI anhydrous ethanol into a reaction kettle with a 90mI polytetrafluoroethylene lining, treating the prepared solution with ultrasonic waves in an ultrasonic cleaner for 30min, after the solution is dissolved uniformly, putting the reaction kettle into an electric heating constant-temperature air blowing drying box, reacting for 24h at 160 ℃, repeatedly centrifuging the reacted solution for 3 times by using a centrifugal machine, drying the finally obtained gray black precipitate at 60 ℃ by using a vacuum drying box for l0h to obtain cobalt sulfide, loading cobalt sulfide (CoS) nanoparticles onto a nanofiber membrane, and carbonizing to obtain a cobalt sulfide/carbon nanofiber membrane (CoS/CNFs) counter electrode. However, the catalytic performance of the electrode obtained by the method is generally high, the use temperature is relatively high, and the performance requirement of replacing commercial JM 20% Pt/C is far from being met.
Researches find that the morphology of cobalt sulfide has certain influence on the catalytic performance of the composite catalyst formed by the cobalt sulfide, and the existing preparation method cannot control the morphology of the cobalt sulfide.
Disclosure of Invention
In view of this, the present invention aims to provide a morphology-controllable cobalt sulfide, a preparation method thereof, a cobalt sulfide/nitrogen-doped carbon nanotube catalyst, and applications thereof. The preparation method provided by the invention can control the appearance of the cobalt sulfide, and the oxygen reduction catalytic performance of the cobalt sulfide-based composite catalyst can be improved by using the cobalt sulfide prepared by the invention to prepare the composite catalyst.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a preparation method of morphology-controllable cobalt sulfide, which comprises the following steps:
(1) carrying out hydrothermal reaction on inorganic cobalt salt and cysteine in a solvent system to obtain a hydrothermal reaction product; the solvent system is an ethanol-diethyl ether mixed solvent, an ethanol-diethyl ether-water mixed solvent or an ethanol-diethyl ether-glycerol mixed solvent;
(2) sequentially drying, grinding and calcining the hydrothermal reaction product obtained in the step (1) to obtain cobalt sulfide; the calcination is carried out under nitrogen protection.
Preferably, the inorganic acid cobalt salt in the step (1) is cobalt chloride or cobalt nitrate; the molar ratio of the inorganic cobalt salt to the cysteine is 1:1.
Preferably, the temperature of the hydrothermal reaction in the step (1) is 130-150 ℃, and the time of the hydrothermal reaction is 20-28 h.
Preferably, the calcining temperature in the step (2) is 350-450 ℃, the heat preservation time is 1-3 h, and the heating rate of heating to the calcining temperature is 5 ℃/min.
The invention provides cobalt sulfide prepared by the preparation method in the scheme.
The invention provides a cobalt sulfide/nitrogen-doped carbon nanotube catalyst, which is obtained by mixing the cobalt sulfide and the nitrogen-doped carbon nanotube in the scheme; the mass ratio of the cobalt sulfide to the nitrogen-doped carbon nano tube is 1: 1.5-3.
Preferably, the preparation method of the nitrogen-doped carbon nanotube comprises the following steps: mixing carbon nano tubes, melamine and water to carry out hydrothermal reaction; drying, grinding, calcining and grinding the hydrothermal reaction product in sequence to obtain the nitrogen-doped carbon nanotube; the calcination is carried out under nitrogen protection.
Preferably, the temperature of the hydrothermal reaction is 110-130 ℃, and the time of the hydrothermal reaction is 20-28 h.
Preferably, the calcining temperature is 600-700 ℃, the heat preservation time is 1-3 h, and the heating rate of heating to the calcining temperature is 5 ℃/min.
The invention also provides application of the cobalt sulfide/nitrogen doped carbon nanotube catalyst in a metal-air battery and a fuel battery.
Has the advantages that: the invention provides a preparation method of morphology-controllable cobalt sulfide, which comprises the steps of carrying out hydrothermal reaction on inorganic cobalt salt and cysteine in a solvent system to obtain a hydrothermal reaction product; the solvent system is an ethanol-diethyl ether mixed solvent, an ethanol-diethyl ether-water mixed solvent or an ethanol-diethyl ether-glycerol mixed solvent; and drying, grinding and calcining the hydrothermal reaction product in sequence to obtain the cobalt sulfide. The preparation method of the cobalt sulfide provided by the invention can be used for batch preparation and has good reproducibility.
The invention controls the polarity and the carbon source concentration of the whole solvent system by changing the solvent system, thereby controlling the micro-morphology of the cobalt sulfide product, and the micro-morphology of the cobalt sulfide prepared by the invention comprises a petal-shaped morphology, a spherical particle morphology and a coexisting morphology of the petal-shaped morphology and the spherical particle morphology.
The invention provides a cobalt sulfide/nitrogen-doped carbon nanotube catalyst, which is obtained by mixing cobalt sulfide and nitrogen-doped carbon nanotubes; the mass ratio of the cobalt sulfide to the nitrogen-doped carbon nano tube is 1: 1.5-3. The invention can improve the oxygen reduction (ORR) catalytic performance of the composite catalyst by controlling the micro-morphology of the cobalt sulfide; the invention adopts nitrogen-doped carbon nano tube (N-CNT) as a carrier, and compounds cobalt sulfide for controlling the microscopic morphology to obtain the catalyst, wherein the nitrogen-doped carbon nano tube carrier has more oxygen reduction active sites than the common carbon nano tube.
The invention controls the micro-morphology of the cobalt sulfide and is assisted by the nitrogen-doped carbon nano tube with high oxygen reduction active sites, so that the obtained cobalt sulfide/nitrogen-doped carbon nano tube catalyst has greatly improved oxygen reduction catalytic performance compared with the cobalt sulfide material prepared by the traditional method.
The embodiment result shows that the cobalt sulfide/nitrogen doped carbon nanotube catalyst provided by the invention has regular micro-morphology and oxygen reduction catalytic performance close to that of commercial Pt/C, and can be applied to catalysis in fuel cells to accelerate the reaction speed of air electrodes.
Drawings
FIG. 1 is an SEM image of cobalt sulfide prepared in example 1 of the present invention;
FIG. 2 is an SEM image of cobalt sulfide prepared in example 3 of the present invention;
FIG. 3 is an SEM image of cobalt sulfide prepared in example 4 of the present invention;
FIG. 4 is a comparison graph of XRD diffraction peaks of cobalt sulfide prepared in examples 1-4 of the present invention, wherein the XRD diffraction patterns of cobalt sulfide adopted by cobalt sulfide/nitrogen-doped carbon nanotube catalysts with corresponding numbers AE-d, AEW-e, AEW-f, and PAE-g are shown from top to bottom;
FIG. 5 is a LSV graph of cobalt sulfide/nitrogen doped carbon nanotube catalysts of the present invention, numbered AE-d, AEW-e, AEW-f, and PAE-g;
FIG. 6 is a LSV graph of a cobalt sulfide/nitrogen doped carbon nanotube catalyst, numbered PAE-g, and a cobalt sulfide catalyst, numbered PAE-h, and a CNT, N-CNT, Pt/C catalyst, not doped with cobalt sulfide, numbered PAE-g, according to the present invention.
Detailed Description
The invention provides a preparation method of cobalt sulfide, which comprises the following steps:
(1) carrying out hydrothermal reaction on inorganic cobalt salt and cysteine in a solvent system to obtain a hydrothermal reaction product; the solvent system is an ethanol-diethyl ether mixed solvent, an ethanol-diethyl ether-water mixed solvent or an ethanol-diethyl ether-glycerol mixed solvent;
(2) sequentially drying, grinding and calcining the hydrothermal reaction product obtained in the step (1) to obtain cobalt sulfide; the calcination is carried out under nitrogen protection.
The invention carries out hydrothermal reaction on inorganic cobalt salt and cysteine in a solvent system to obtain a hydrothermal reaction product. In the present invention, the inorganic acid cobalt salt is preferably cobalt chloride or cobalt nitrate, more preferably cobalt chloride; the cysteine is a natural alpha-amino acid containing sulfur, and cobalt sulfide can be generated by performing hydrothermal reaction on inorganic cobalt salt and the cysteine. The cysteine is soluble in water, ethanol, acetic acid and ammonia water, is insoluble in diethyl ether and acetone, and the cobalt chloride is easily soluble in water and is also soluble in ethanol, ether and acetone. In the present invention, the solubility of the inorganic acid cobalt salt and cysteine in the solvent system, which is a mixed solvent of ethanol-ether, ethanol-ether-water or ethanol-ether-glycerol, is mainly considered. The invention has no special requirements on the sources of the inorganic acid cobalt salt, the cysteine and the solvent raw materials.
In the present invention, the molar ratio of the inorganic acid cobalt salt to cysteine is preferably 1:1.
According to the invention, the inorganic cobalt salt and the cysteine are preferably added into a solvent system, and the hydrothermal reaction is started after the uniform magnetic stirring. In the invention, the temperature of the hydrothermal reaction is preferably 130-150 ℃, more preferably 135-145 ℃, and most preferably 140 ℃, and the time of the hydrothermal reaction is preferably 20-28 h, more preferably 22-26 h, and most preferably 24 h. In the present invention, under the condition that the temperature and time parameters of the hydrothermal reaction are basically fixed, the micro-morphology of the generated cobalt sulfide is mainly related to the solvent system of the reaction; the invention can achieve the purpose of controlling the appearance of the cobalt sulfide by changing the mixing type and the proportion of the solvents (ethanol, ether, water and glycerol) in the solvent system.
In the invention, when the solvent system is an ethanol-diethyl ether mixed solvent, the volume ratio of ethanol to diethyl ether in the mixed solvent is preferably 1-2: 1, most preferably 1:1, and the obtained cobalt sulfide is in a micro-morphology mainly in a petal-shaped micro-morphology and occasionally shows spherical particles;
in the invention, when the solvent system is an ethanol-diethyl ether-water mixed solvent, the volume ratio of ethanol-diethyl ether-water in the mixed solvent is preferably 1-2: 1:1, and most preferably 1:1:1, and the obtained cobalt sulfide has a microscopic morphology mainly comprising spherical particles accompanied by a small amount of petal-shaped particles.
In the invention, when the solvent system is an ethanol-diethyl ether-glycerol mixed solvent, the volume ratio of ethanol-diethyl ether-glycerol in the mixed solvent is preferably 1-2: 1: 1-2, and most preferably 1:1:1, and the obtained cobalt sulfide has a spherical particle morphology in a microscopic morphology, and a petal-shaped morphology is basically not found.
In the solvent system, the main function of adding water is to adjust the polarity of the solvent system, and the main function of adding glycerol and changing the dosage of ethanol is to adjust the carbon source concentration of the solvent system, so that the aim of controlling the micro-morphology of the cobalt sulfide product is fulfilled.
After the hydrothermal reaction product is obtained, the hydrothermal reaction product is sequentially dried, ground and calcined to obtain the cobalt sulfide. After the hydrothermal reaction is finished, preferably, the hydrothermal reaction liquid is subjected to vacuum filtration, and then the obtained hydrothermal reaction product is subjected to drying treatment, wherein the vacuum filtration preferably adopts an organic filter membrane with the diameter of 0.1-0.2 mu m, and more preferably adopts an organic filter membrane with the diameter of 0.15 mu m.
In the present invention, the drying temperature is preferably 80 ℃, and the present invention preferably dries the hydrothermal reaction product to a constant weight; the invention preferably adopts an electric heating air blast drying oven for drying.
After the drying is finished, the dried hydrothermal reaction product is ground, and the grinding degree is not specially required, so that uniform fine powder can be obtained.
After the grinding is completed, the powder obtained by grinding is calcined, and the calcination is preferably carried out under the protection of nitrogen. In a specific embodiment of the invention, the ground powder is preferably transferred to a porcelain boat, which is wrapped with copper foil and bound with copper wire, and the boat is placed in a tube furnace and calcined under a continuous nitrogen atmosphere to obtain cobalt sulfide. In the invention, the calcination temperature is preferably 350-450 ℃, more preferably 400 ℃, the heat preservation time is preferably 1-3 h, more preferably 2h, and the heating rate of heating to the calcination temperature is preferably 5 ℃/min. And after the calcination is finished, naturally cooling to room temperature and taking out the product to obtain the cobalt sulfide.
The invention provides cobalt sulfide prepared by the preparation method in the scheme. The micro-morphology of the cobalt sulfide provided by the invention mainly comprises a petal-shaped micro-morphology, a spherical particle micro-morphology and a coexisting micro-morphology of the petal-shaped micro-morphology and the spherical particle micro-morphology; the invention can effectively control the microcosmic appearance of the cobalt sulfide by controlling the polarity of the solvent system and the concentration of the carbon source.
The invention provides a cobalt sulfide/nitrogen-doped carbon nanotube catalyst, which is obtained by mixing cobalt sulfide and nitrogen-doped carbon nanotubes prepared by the preparation method in the scheme; the mass ratio of the cobalt sulfide to the nitrogen-doped carbon nanotube is preferably 1: 1.5-3, and more preferably 1: 2.
In the present invention, the method for preparing the nitrogen-doped carbon nanotube preferably comprises the following steps: mixing carbon nano tubes, melamine and water to carry out hydrothermal reaction; drying, grinding, calcining and grinding the hydrothermal reaction product in sequence to obtain the nitrogen-doped carbon nanotube; the calcination is carried out under nitrogen protection.
The invention mixes the carbon nano tube, the melamine and the water to carry out hydrothermal reaction. Before hydrothermal reaction, the carbon nano tube and the melamine are preferably ultrasonically dispersed in water for 30 min. In the invention, the hydrothermal reaction temperature is preferably 110-130 ℃, more preferably 120 ℃, and the hydrothermal reaction time is preferably 20-28 h, more preferably 22-26 h, and most preferably 24 h. In the invention, the mass ratio of the carbon nanotubes to the melamine is preferably 1:6, and the mass ratio of the water to the carbon nanotubes is preferably 300-500: 1.
After obtaining the hydrothermal reaction product, the invention sequentially dries, grinds and calcines the hydrothermal reaction product to obtain the nitrogen-doped carbon nanotube. After the hydrothermal reaction is finished, preferably, the hydrothermal reaction liquid is subjected to vacuum filtration, and then the obtained hydrothermal reaction product is subjected to drying treatment, wherein the vacuum filtration preferably adopts an organic filter membrane with the diameter of 0.1-0.2 mu m, and more preferably adopts an organic filter membrane with the diameter of 0.15 mu m.
In the present invention, the drying temperature is preferably 80 ℃, and the present invention preferably dries the hydrothermal reaction product to a constant weight; the invention preferably adopts an electric heating air blast drying oven for drying.
After the drying is finished, the dried hydrothermal reaction product is ground, and the grinding degree is not specially required, so that uniform fine powder can be obtained.
After the grinding is completed, the powder obtained by grinding is calcined, and the calcination is preferably carried out under the protection of nitrogen. In one embodiment of the present invention, the ground powder is preferably transferred to a porcelain boat, the boat is wrapped with copper foil, the boat is bound with copper wire, and the boat is placed in a tube furnace and calcined in a continuous nitrogen atmosphere to obtain nitrogen-doped carbon nanotubes. In the invention, the calcination temperature is preferably 600-700 ℃, more preferably 650 ℃, the heat preservation time is preferably 1-3 h, more preferably 2h, and the heating rate of heating to the calcination temperature is preferably 5 ℃/min. And after the calcination is finished, naturally cooling to room temperature, and taking out the product to obtain the nitrogen-doped carbon nanotube.
After the nitrogen-doped carbon nano tube is obtained, the cobalt sulfide and the nitrogen-doped carbon nano tube in the scheme are mixed to prepare the cobalt sulfide/nitrogen-doped carbon nano tube catalyst. In the present invention, the mixing is preferably assisted by ultrasound, so that the cobalt sulfide is uniformly distributed in the nitrogen-doped carbon nanotube, and the frequency of the ultrasound is preferably 80 KHz.
The invention also provides the application of the cobalt sulfide/nitrogen doped carbon nanotube catalyst in the technical scheme in metal-air batteries and fuel batteries.
The application method of the cobalt sulfide/nitrogen doped carbon nanotube catalyst preferably comprises the following steps:
taking 6mg of the composite catalyst in a 5mL plastic sample tube with a cover, adding 950 mu L of absolute ethyl alcohol, and carrying out ultrasonic treatment for 20min to fully disperse the catalyst in the absolute ethyl alcohol to form uniform suspension. Then, 50. mu.L of Nafion (5 wt%) solution was added thereto, and ultrasonic dispersion was performed again for 20min to obtain a uniformly dispersed dark suspension.
The oxygen reduction catalytic performance of the composite catalyst was tested by using a CHI760E electrochemical station, a rotary electrode device and a five-port glass electrolytic cell. Wherein the reference electrode is a double-liquid connection Ag/AgCl electrode, the counter electrode is an ARCTR5 type platinum wire electrode, and the working electrode is a rotary glassy carbon disk electrode. For analytical comparison convenience, all potentials in the present invention were switched to Reversible Hydrogen Electrodes (RHE) depending on the actual electrolyte system.
The following will describe in detail a morphology-controllable cobalt sulfide, a preparation method thereof, a cobalt sulfide/nitrogen-doped carbon nanotube catalyst and applications thereof, with reference to the following examples, but they should not be construed as limiting the scope of the present invention.
Example 1
A preparation method of cobalt sulfide specifically comprises the following steps:
accurately weighing 12mmol of CoCl2Adding 12mmol of cysteine into a 150ml beaker, adding 72ml of ethanol-diethyl ether mixed solvent with the volume ratio of 1:1, uniformly stirring by magnetic force, transferring into a 100ml hydrothermal reaction kettle, placing in an electrothermal blowing dry box, heating to 140 ℃, and reacting for 24 hours at the temperature. Naturally cooling to room temperature, and performing vacuum filtration on the sand core filtering device by using a filter membrane with the diameter of 0.15 micron. The obtained residue was transferred to a beaker and dried in an electric hot blast drying oven at 80 ℃ to constant weight. The dried material was poured into an agate mortar and ground until a fine powder was obtained. Transferring the ground powder into porcelain boats, wrapping the porcelain boats by copper foil, and binding each porcelain boat by copper wires. Placing the porcelain boat in a tube furnace under a continuous N2Under the atmosphere, the temperature was raised to 400 ℃ at a rate of 5 ℃/min and maintained at this temperature for 2 h. And taking out the product after the temperature is reduced to the room temperature to obtain the cobalt sulfide.
Examples 2 to 4
More microcosmic cobalt sulfide is prepared in the embodiments 2-4 of the invention, the same preparation method as the embodiment 1 is adopted, and the only difference is that a solvent system is replaced, and the setting of the solvent system is shown in the table 1.
And (3) microscopic morphology verification: the microcosmic appearance of the cobalt sulfide prepared in the examples 1, 3 and 4 of the present invention was observed and analyzed by using a scanning electron microscope. Fig. 1 is an SEM image of cobalt sulfide prepared in example 1, fig. 2 is an SEM image of cobalt sulfide prepared in example 3, and fig. 3 is an SEM image of cobalt sulfide prepared in example 4 of the present invention; as can be observed from the drawings 1-3, the cobalt sulfide obtained in the embodiment 1 of the invention is mainly in a petal-shaped shape, and occasionally spherical particles are observed; the cobalt sulfide obtained in the embodiment 3 of the invention mainly takes spherical particles as main components and is accompanied with a small amount of petal-shaped particles; the cobalt sulfide obtained in the embodiment 4 of the invention has a spherical particle shape.
Example 5
The preparation method of the nitrogen-doped carbon nanotube specifically comprises the following steps:
0.2g of CNT and 1.2g of melamine were ultrasonically dispersed in 80ml of deionized water for 30min, and the resulting solution was then sealed into a 100ml stainless steel autoclave lined with Teflon and heated in an electric hot air drying oven at 120 ℃ for 24 h. Then cooling the mixture to room temperature, performing vacuum filtration on the mixture by using an organic filter membrane with the aperture of 0.15 mu m on a sand core filtering device, drying the obtained filter residue at 80 ℃ to remove water, and pouring the dried substance into an agate mortar for grinding until the dried substance is fine powder. The ground powder is put into porcelain boats, the porcelain boats are wrapped by copper foil, and then each porcelain boat is bound by copper wires. Placing the porcelain boat in a tube furnace under a continuous N2Raising the temperature to 650 ℃ at the speed of 5 ℃/min under the atmosphere, and preserving the temperature for 2 h. Cooling to room temperature, and grinding to obtain the nitrogen-doped carbon nano tube (N-CNT).
Example 6
Preparing a cobalt sulfide/nitrogen doped carbon nanotube catalyst: the cobalt sulfide prepared in the embodiments 1 to 4 of the present invention was mixed with the nitrogen-doped carbon nanotube prepared in the embodiment 5 by ultrasound to obtain a catalyst, the ultrasound frequency was 80KHz, and the obtained cobalt sulfide/nitrogen-doped carbon nanotube catalysts were numbered in order, and the specific numbering is shown in table 1.
TABLE 1 numbering of cobalt sulfide/N-doped carbon nanotube catalysts
As shown in table 1, in order to verify the respective functions of cobalt sulfide and nitrogen-doped carbon nanotubes in the catalyst, the present invention sets a group of examples without N-CNT as a control, specifically: the cobalt sulfide prepared in example 4 was directly used as a catalyst without adding N-CNT for performance testing, and was numbered PAE-h.
The following specific tests were performed on the various cobalt sulfide/nitrogen-doped carbon nanotube catalysts described in table 1 of the present invention:
XRD analysis: XRD analysis and comparison are respectively carried out on the cobalt sulfide prepared in the examples 1-4 in the table 1 of the invention, and the results are shown in the figure 4 of the invention, and in the figure 4, comparison graphs of XRD diffraction peaks of the cobalt sulfide adopted for preparing four cobalt sulfide/nitrogen-doped carbon nanotube catalysts with the serial numbers of AE-d, AEW-e, AEW-f and PAE-g are respectively shown from top to bottom.
As can be seen from fig. 4, strong diffraction peaks appear at positions such as 2 θ of 30.5 °, 35.6 °, 47.1 °, and 54.7 °, which substantially match the standard characteristic peak of CoS, and the peaks correspond to the standard well. This shows that in the present invention, by changing the components and the ratio of the solvent system, i.e. by changing the mixing ratio of ethanol, ether, water and glycerol, the microstructure of the cobalt sulfide product can be controlled, but the phase composition of the cobalt sulfide product is not affected.
And (3) electrochemical performance testing: obtaining LSV curves of various catalysts at a scanning speed of 10mV/s in a potential range of 0.2 to-1.0V (vs. Ag/AgCl);
the LSV Linear Sweep Voltammetry (Linear Sweep Voltammetry) determination method comprises the following steps:
a quantity of KOH was taken to make up a 0.1 molar aqueous solution (noted as 0.1M KOH). The 0.1m koh solution was charged to a five port glass electrolytic cell and high purity oxygen (99.999%) was continuously fed in for 30 minutes to achieve oxygen saturation. And (3) placing the reference electrode, the platinum wire counter electrode and the prepared working electrode containing the catalyst in an electrolytic cell to form a half cell of a three-electrode system. The test voltage range was set to 0.2 to-1.0V (vs. Ag/AgCl), and the scan rate was set to 10mV s-1The scanning direction was set to the negative direction, and the test was performed at a rotation speed of 1600 rpm. Oxygen must be continuously introduced into the electrolyte during the test to ensure that the electrolyte is saturated with oxygen.
FIG. 5 is an LSV curve of four cobalt sulfide/nitrogen doped carbon nanotube catalysts, numbered AE-d, AEW-e, AEW-f, and PAE-g; as can be seen from FIG. 5, the oxygen reduction performance of the four catalysts is relatively close, but the oxygen reduction catalytic performance of the cobalt sulfide/nitrogen doped carbon nanotube catalyst with the number of PAE-g is the best.
To further highlight the comparative effect, the LSV curves of PAE-g, PAE-h, Pt/C catalyst, CNT (cobalt sulfide free), N-CNT (cobalt sulfide free) were tested by the present invention and the results are shown in FIG. 6. FIG. 6 is a LSV graph of five catalysts, numbered PAE-g, PAE-h, Pt/C catalyst and CNT (cobalt sulfide free), N-CNT (cobalt sulfide free). As can be seen from FIG. 6 of the present invention, the oxygen reduction catalytic performance of the cobalt sulfide/nitrogen doped carbon nanotube catalyst with PAE-g of the present invention is better than that of CNT, N-CNT, PAE-h, and the limiting current density of PAE-g is much higher than that of commercial Pt/C.
In fig. 5 and 6 of the present invention, j represents current density, E represents voltage, V is voltage unit "volt", vs.
The present invention also provides specific data on the oxygen reduction performance of the various catalysts described above, as shown in table 2.
TABLE 2 oxygen reduction catalyst Performance data for various catalysts
In conclusion, under the condition that parameters of other preparation conditions are approximately fixed, the cobalt sulfide with different micro-morphologies can be prepared by changing the components and the proportion of the solvent system, namely changing the mixing type and the dosage proportion of ethanol, ether, water and glycerol; the cobalt sulfide prepared by using a solvent system of ethyl alcohol, diethyl ether and glycerol in a ratio of 2:1:1 has the most regular microscopic morphology, and the catalyst obtained by compounding the cobalt sulfide shows excellent electrochemical performance and can be used as a substitute material of Pt/C to be applied to a fuel cell to catalyze and accelerate the reaction speed of an air electrode.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A preparation method of morphology-controllable cobalt sulfide is characterized by comprising the following steps:
(1) carrying out hydrothermal reaction on inorganic cobalt salt and cysteine in a solvent system to obtain a hydrothermal reaction product; the solvent system is an ethanol-diethyl ether mixed solvent, an ethanol-diethyl ether-water mixed solvent or an ethanol-diethyl ether-glycerol mixed solvent;
(2) sequentially drying, grinding and calcining the hydrothermal reaction product obtained in the step (1) to obtain cobalt sulfide; the calcination is carried out under the protection of nitrogen;
the inorganic acid cobalt salt in the step (1) is cobalt chloride or cobalt nitrate; the molar ratio of the inorganic cobalt salt to the cysteine is 1:1.
2. the preparation method according to claim 1, wherein the temperature of the hydrothermal reaction in the step (1) is 130 to 150 ℃ and the time of the hydrothermal reaction is 20 to 28 hours.
3. The preparation method according to claim 1, wherein the calcination temperature in the step (2) is 350-450 ℃, the holding time is 1-3 h, and the heating rate for heating to the calcination temperature is 5 ℃/min.
4. The cobalt sulfide produced by the production method according to any one of claims 1 to 3.
5. A cobalt sulfide/nitrogen doped carbon nanotube catalyst, wherein the catalyst is obtained by mixing the cobalt sulfide and nitrogen doped carbon nanotube according to claim 4; the mass ratio of the cobalt sulfide to the nitrogen-doped carbon nanotube is 1:1.5 to 3;
the preparation method of the nitrogen-doped carbon nanotube comprises the following steps: mixing carbon nano tubes, melamine and water to carry out hydrothermal reaction; drying, grinding, calcining and grinding the hydrothermal reaction product in sequence to obtain the nitrogen-doped carbon nanotube; the calcination is carried out under nitrogen protection.
6. The cobalt sulfide/nitrogen doped carbon nanotube catalyst according to claim 5, wherein the hydrothermal reaction temperature is 110-130 ℃ and the hydrothermal reaction time is 20-28 h.
7. The cobalt sulfide/nitrogen doped carbon nanotube catalyst according to claim 5, wherein the calcination temperature is 600-700 ℃, the holding time is 1-3 h, and the heating rate of the heating to the calcination temperature is 5 ℃/min.
8. Use of the cobalt sulfide/nitrogen doped carbon nanotube catalyst of any one of claims 5 to 7 in metal-air batteries and fuel cells.
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