Carbon nitride-graphene composite material and preparation method and application thereof
Technical Field
The invention belongs to the field of electrode materials, particularly relates to a carbon nitride-graphene composite material and a preparation method and application thereof, and particularly relates to a carbon nitride-graphene composite material with high specific capacity and a preparation method and application thereof.
Background
In order to deal with the increasingly serious environmental problems and reduce the environmental pollution caused by the traditional fossil energy, electrochemical energy storage has become an important requirement for the development of the world at present. The electrochemical energy source has the characteristics of being rich, clean, renewable and the like. In order to utilize this energy, it is imperative to create an electrochemical energy storage device that is durable, easy to maintain, and inexpensive. The super capacitor has a higher power capacity and a lower energy density than a conventional battery, and thus is widely used in portable electronic devices, power backup devices, and hybrid vehicles to provide starting power for a system. And the selection of the electrode material is the key for improving the performance of the super capacitor.
As a novel graphene-shaped two-dimensional material, the graphite-phase carbon nitride has the characteristics of high nitrogen content, good chemical and thermodynamic stability, unique electronic structure, environmental friendliness, simple synthesis process and the like, and becomes an ideal electrode material of the supercapacitor. However, carbon nitride prepared by direct thermal polymerization has small specific surface area and low conductivity, and is not suitable for electrochemical application under most conditions.
CN110828191B discloses a porous layered structure carbon nitride/graphene/nickel disulfide supercapacitor material and a preparation method thereof, and the invention is based on a porous layered structure g-C3N4Graphene and further with NiS2The pseudo-capacitive material is compounded to form a carbon nitride/graphene/nickel disulfide material with a heterostructure, and the electrode material has the characteristics of high specific capacity and good stability.
CN109003831B discloses a carbon nitride/graphene composite electrode material, which comprises, by weight, 0.1-1.0% of carbon nitride and 99.0-99.9% of graphene oxide, wherein the carbon nitride is used as a skeleton structure, and the graphene oxide is wrapped on the surface of the carbon nitride to form a core-shell structure. The composite material has good electrochemical performance and high Faraday capacitance, the Faraday capacitance is 221F/g at a scanning speed of 5mV/s, the stability of a battery and an electrode in short-distance charging and discharging is good, in an alternating current impedance test, the material reflects a small impedance value, the polarization of the material is small in the charging and discharging test, and compared with a complex treatment mode of the traditional composite material, the composite material is simple in composite mode, safe and reliable in production process, high in capacitance, simple in preparation, short in production period and capable of being popularized and applied in the market.
The graphite phase carbon nitride has the problems of small specific surface area and low conductivity when being used for preparing the electrode of the supercapacitor. Therefore, how to provide a supercapacitor electrode with high specific capacity becomes a problem to be solved urgently.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a carbon nitride-graphene composite material and a preparation method and application thereof, and particularly provides a carbon nitride-graphene composite material with high specific capacity and a preparation method and application thereof. The carbon nitride-graphene composite material provided by the invention has the advantages of high specific capacity, high surface reaction activity and strong electric conductivity.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a carbon nitride-graphene composite material, wherein the method for preparing the carbon nitride-graphene composite material comprises the following steps:
(1) mixing trithiocyanuric acid, thiourea and water, then drying to obtain blocks, crushing the blocks, heating and preserving heat to obtain sulfur-doped porous honeycomb carbon nitride;
(2) and (2) dispersing the sulfur-doped porous honeycomb-shaped carbon nitride obtained in the step (1) to obtain a carbon nitride solution, and mixing the carbon nitride solution with the graphene-HCl dispersion solution to obtain the carbon nitride-graphene composite material.
The preparation method comprises mixingThe poly thiocyanic acid and thiourea are baked to form a honeycomb structure, so that the specific surface area of the material is greatly improved, and the surface reaction activity of the carbon nitride-graphene composite material is increased; and the surface of the carbon nitride contains a large amount of residual-NH by sulfur doping2SH, N atoms and S atoms, which improve the wetting property of the electrolyte to the material, are beneficial to the full contact of the electrolyte and the carbon nitride-graphene composite material, and can increase the pseudo capacitance of the carbon nitride-graphene composite material through the Faraday reaction in the charge-discharge cycle process and improve the specific capacity of the carbon nitride-graphene composite material; meanwhile, the graphene and the carbon nitride are compounded, so that the electron transfer of the carbon nitride can be accelerated, and the conductivity of the carbon nitride-graphene composite material is effectively improved.
Preferably, the molar ratio of trithiocyanuric acid to thiourea in step (1) is 1:3.5 to 1: 4.5.
Preferably, the temperature of the baking in the step (1) is 58-62 ℃ and the time is 23-25 h.
Preferably, the temperature rise in step (1) is 590-610 ℃.
Preferably, the rate of temperature rise in step (1) is 4.5-5.5 ℃/min.
Preferably, the heat preservation time in the step (1) is 0.8-1.2 h.
Wherein, the molar ratio of the thiocyanic acid to the thiourea can be 1:3.5, 1:3.7, 1:3.9, 1:4, 1:4.1, 1:4.3 or 1:4.5, the baking temperature can be 58 ℃, 59 ℃, 60 ℃, 61 ℃ or 62 ℃, the time can be 23h, 23.5h, 24h, 24.5h or 25h, the heating rate can be 4.5 ℃/min, 4.6 ℃/min, 4.7 ℃/min, 4.8 ℃/min, 4.9 ℃/min, 5 ℃/min, 5.1 ℃/min, 5.2 ℃/min, 5.3 ℃/min, 5.4 ℃/min or 5.5 ℃/min, the heat preservation time can be 0.8h, 0.9h, 1.1h or more than 1.2h, the cited values can be but are not limited to, other values not listed in the above numerical ranges are equally applicable.
According to the preparation method, the prepared sulfur-doped porous honeycomb carbon nitride has a porous honeycomb structure through the processes of drying, heating and heat preservation and the control of the operating parameters of drying, heating and heat preservation, active groups such as-HS in trithiocyanuric acid and thiourea can be reserved, advanced decomposition of the active groups is avoided, and the specific capacity and the surface reaction activity of the carbon nitride-graphene composite material are higher.
Preferably, the concentration of the carbon nitride solution in the step (2) is 0.8-1.2 g/L.
Preferably, the volume ratio of the carbon nitride solution to the graphene-HCl dispersion is 1:0.8-1: 1.2.
Preferably, the graphene-HCl dispersion in the step (2) is prepared by a method comprising the following steps: and mixing the graphene solution with hydrochloric acid to obtain the graphene-HCl dispersion liquid.
Preferably, the concentration of the graphene solution is 4.5-5.5 g/L.
Preferably, the concentration of the hydrochloric acid is 0.8-1.2 mol/L.
Preferably, the volume ratio of the graphene solution to the hydrochloric acid is 1:4-1: 6.
Wherein the concentration of the carbon nitride solution may be 0.8g/L, 0.9g/L, 1g/L, 1.1g/L or 1.2g/L, the volume ratio of the carbon nitride solution to the graphene-HCl dispersion may be 1:0.8, 1:0.9, 1:1, 1:1.1 or 1:1.2, the concentration of the graphene solution may be 4.5g/L, 4.6g/L, 4.7g/L, 4.8g/L, 4.9g/L, 5g/L, 5.1g/L, 5.2g/L, 5.3g/L, 5.4g/L or 5.5g/L, the concentration of hydrochloric acid may be 0.8mol/L, 0.9mol/L, 1mol/L, 1.1mol/L or 1.2mol/L, the volume ratio of the graphene solution to hydrochloric acid may be 1:4, 1:6 or more, other values not listed in the above numerical ranges are equally applicable.
The specific parameters can complete the electrostatic assembly process of the graphene and the sulfur-doped porous honeycomb carbon nitride, and the graphene and the carbon nitride are compounded, so that the electron transfer of the carbon nitride is accelerated, and the conductivity of the carbon nitride-graphene composite material is effectively improved.
In a second aspect, the invention provides a carbon nitride-graphene composite material prepared by the preparation method of the carbon nitride-graphene composite material.
In a third aspect, the invention provides an application of the carbon nitride-graphene composite material in capacitor preparation.
In a fourth aspect, the present invention also provides a supercapacitor, the composition of which comprises an active material, a binder, a current collector and an electrolyte.
The active material includes the carbon nitride-graphene composite material as described above.
The carbon nitride-graphene composite material is adopted in the supercapacitor, so that the supercapacitor has good charge-discharge reversibility, can be normally used under a high current density (10A/g or above), and has good rate performance and cycling stability.
Preferably, the binder includes PVDF (polyvinylidene fluoride), the current collector includes aluminum foil, and the electrolyte includes NEt4BF4PC (tetraethylammonium boron tetrafluoride-propylene carbonate solution).
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention provides a carbon nitride-graphene composite material, wherein a honeycomb structure is formed by baking cyanuric acid and thiourea, so that the specific surface area of the material is greatly increased to 59.73m2The surface reactivity of the carbon nitride-graphene composite material is increased by more than/g; and the surface of the carbon nitride contains a large amount of residual-NH by sulfur doping2SH, N atoms and S atoms, which improve the wetting property of the electrolyte to the material, are beneficial to the full contact of the electrolyte and the carbon nitride-graphene composite material, and can increase the pseudocapacitance of the carbon nitride-graphene composite material through the Faraday reaction in the charge-discharge cycle process, improve the specific capacity of the carbon nitride-graphene composite material, and the specific capacitance of the material reaches above 194.84F/g when the current density is 1.0A/g; meanwhile, the graphene is compounded with the carbon nitride, so that the electron transfer of the carbon nitride can be accelerated, and the conductivity of the carbon nitride-graphene composite material is effectively improved;
(2) according to the invention, through specific drying, heating and heat preservation processes and control of drying, heating and heat preservation operation parameters, the prepared sulfur-doped porous honeycomb carbon nitride has a porous honeycomb structure, active groups such as-HS in trithiocyanuric acid and thiourea can be retained, advanced decomposition of the active groups is avoided, and the specific capacity and surface reaction activity of the carbon nitride-graphene composite material are higher; meanwhile, the graphene and the sulfur-doped porous honeycomb-shaped carbon nitride can be subjected to an electrostatic assembly process by adjusting specific parameters, and the graphene and the carbon nitride are compounded, so that the electron transfer of the carbon nitride is accelerated, and the conductivity of the carbon nitride-graphene composite material is effectively improved;
(3) the invention also provides a super capacitor, which has good charge-discharge reversibility, can be normally used under high current density, and has good rate performance and cycle stability, the specific capacitance of the capacitor reaches above 48.71F/g when the current density is 1.0A/g, the specific capacitance retention rate of the capacitor is above 74.86% when the current density is increased from 1A/g to 20A/g, after 2000 cycles, the specific capacitance retention rate of the capacitor is still higher than 98.5%, and the coulombic efficiency is higher than 99%.
Drawings
FIG. 1 is a scanning electron micrograph of sulfur-doped porous honeycomb carbon nitride in example 1;
fig. 2 is a scanning electron micrograph of the carbon nitride-graphene composite material in example 1;
FIG. 3 is an XRD spectrum of sulfur-doped porous honeycomb carbon nitride of example 1 versus bulk carbon nitride of comparative example 1;
fig. 4 is a graph of cyclic voltammetry tests of a supercapacitor made of the carbon nitride-graphene composite material provided in example 1;
fig. 5 is a graph showing the change of specific capacitance with current density of a supercapacitor made of the carbon nitride-graphene composite material provided in example 1;
fig. 6 is a graph of the cycle stability and coulombic efficiency test results of the supercapacitor made of the carbon nitride-graphene composite material provided in example 1.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a carbon nitride-graphene composite material, which is prepared by the following steps:
the method comprises the following steps: preparation of sulfur-doped porous honeycomb carbon nitride
1.77g of trithiocyanuric acid and 3.04g of thiourea are dispersed in 100mL of distilled water and mechanically stirred for 2h to form a hydrogel-like trithiocyanuric acid-thiourea supramolecular precursor. And (3) drying the cyanuric acid-thiourea supramolecular precursor in an oven at 60 ℃ for 24h until the cyanuric acid-thiourea supramolecular precursor becomes blocky. Grinding the massive trithiocyanuric acid-thiourea supermolecule precursor into powder, putting the powder into a crucible, putting the crucible into a muffle furnace, and keeping the temperature at 600 ℃ for 1h, wherein the heating rate is 5 ℃/min. After cooling, the sulfur-doped porous honeycomb carbon nitride is obtained, and the scanning electron micrograph thereof is shown in fig. 1. 0.1g of the sulfur-doped porous honeycomb carbon nitride is dispersed in 100mL of distilled water to prepare 1g/L of carbon nitride solution for standby.
Step two: preparation of carbon nitride-graphene composite material
Dispersing 0.05g of graphene in 10mL of distilled water to obtain 5g/L graphene aqueous solution, adding 20mL of graphene aqueous solution into 100mL of HCl with the concentration of 1mol/L, and stirring for 6h to obtain the graphene-HCl dispersion liquid. And adding 100mL of the carbon nitride aqueous solution into 100mL of graphene-HCl dispersion liquid, and stirring for 2h to obtain the carbon nitride-graphene composite material, wherein a scanning electron micrograph of the carbon nitride-graphene composite material is shown in FIG. 2.
Example 2
The embodiment provides a carbon nitride-graphene composite material, which is prepared by the following steps:
the method comprises the following steps: preparation of sulfur-doped porous honeycomb carbon nitride
1.77g of trithiocyanuric acid and 3.42g of thiourea are dispersed in 100mL of distilled water and mechanically stirred for 2h to form a hydrogel-like trithiocyanuric acid-thiourea supramolecular precursor. And (3) drying the cyanuric acid-thiourea supramolecular precursor in an oven at 62 ℃ for 23h until the cyanuric acid-thiourea supramolecular precursor becomes blocky. Grinding the massive trithiocyanuric acid-thiourea supermolecule precursor into powder, putting the powder into a crucible, putting the crucible into a muffle furnace, and keeping the temperature at 610 ℃ for 0.8h, wherein the heating rate is 5.5 ℃/min. And cooling to obtain the sulfur-doped porous honeycomb carbon nitride. 0.12g of the sulfur-doped porous honeycomb carbon nitride is dispersed in 100mL of distilled water to prepare 1.2g/L of carbon nitride aqueous solution for standby.
Step two: preparation of carbon nitride-graphene composite material
Dispersing 0.055g of graphene in 10mL of distilled water to obtain 5.5g/L graphene aqueous solution, adding 20mL of graphene aqueous solution into 120mL of HCl with the concentration of 1.2mol/L, and stirring for 6h to obtain the graphene-HCl dispersion liquid. And adding 100mL of the carbon nitride aqueous solution into 100mL of graphene-HCl dispersion liquid, and stirring for 2h to obtain the carbon nitride-graphene composite material.
Example 3
The embodiment provides a carbon nitride-graphene composite material, which is prepared by the following steps:
the method comprises the following steps: preparation of sulfur-doped porous honeycomb carbon nitride
1.77g of trithiocyanuric acid and 2.66g of thiourea are dispersed in 100mL of distilled water and mechanically stirred for 2h to form a hydrogel-like trithiocyanuric acid-thiourea supramolecular precursor. And (3) drying the cyanuric acid-thiourea supramolecular precursor in an oven at 58 ℃ for 25h until the cyanuric acid-thiourea supramolecular precursor becomes blocky. Grinding the massive trithiocyanuric acid-thiourea supermolecule precursor into powder, putting the powder into a crucible, putting the crucible into a muffle furnace, and preserving the heat for 1.2h at 590 ℃, wherein the heating rate is 4.5 ℃/min. And cooling to obtain the sulfur-doped porous honeycomb carbon nitride. 0.08g of the sulfur-doped porous honeycomb carbon nitride is dispersed in 100mL of distilled water to prepare 0.8g/L of carbon nitride solution for standby.
Step two: preparation of carbon nitride-graphene composite material
Dispersing 0.045g of graphene in 10mL of distilled water to obtain 4.5g/L graphene aqueous solution, adding 20mL of graphene aqueous solution into 80mL of HCl with the concentration of 0.8mol/L, and stirring for 6h to obtain the graphene-HCl dispersion liquid. And adding 100mL of the carbon nitride aqueous solution into 100mL of graphene-HCl dispersion liquid, and stirring for 2h to obtain the carbon nitride-graphene composite material.
And (3) performance testing:
the sulfur-doped porous honeycomb carbon nitride of example 1 was subjected to X-ray diffraction with ordinary bulk carbon nitride, and the XRD spectrum thereof is shown in fig. 3. Among them, it can be found that comparative example 1 is a diffraction peak of (002) crystal plane at 2 θ ═ 27.6 °, and the diffraction peak of (002) crystal plane of the sulfur-doped porous honeycomb carbon nitride in example 1 is shifted toward a small angle due to the doping of S atom, which proves the successful doping of S element in carbon nitride.
The carbon nitride-graphene composite materials provided in examples 1 to 3 were then tested for specific surface area, with the following results:
group of
|
Specific surface area (m)2/g)
|
Example 1
|
78.16
|
Example 2
|
66.15
|
Example 3
|
59.73 |
The data show that the carbon nitride-graphene composite material provided by the invention has a large specific surface area and improves the surface reactivity.
Then, the carbon nitride-graphene composite materials provided in examples 1 to 3 were used as active materials, respectively, toPVDF as adhesive, aluminum foil as collector, 1mol/L NEt4BF4And the-PC is electrolyte to assemble the symmetrical button type super capacitor.
The result of testing the cyclic voltammetry test curves (test instrument: Shanghai Chenghua CHI-660e electrochemical workstation) of the supercapacitor made of the carbon nitride-graphene composite material provided in example 1 at different scanning rates is shown in FIG. 4. From the figure, it can be seen that the CV curve of the carbon nitride-graphene supercapacitor presents a quasi-rectangular shape of symmetry, which indicates that the carbon nitride-graphene supercapacitor is mainly based on the electric double layer capacitance. The N element and the S element doped in the carbon nitride-graphene electrode material can react with the electrolyte to generate pseudo capacitance. When the scanning rate is increased to 100mV/s, the CV curve of the carbon nitride-graphene supercapacitor still keeps a better rectangular shape, which indicates that the carbon nitride/graphene supercapacitor has good charge-discharge reversibility. This indicates that the porous honeycomb structure is favorable for the transfer of electrolyte ions
Then, specific capacitance of the supercapacitors made of the carbon nitride-graphene composite materials provided in examples 1 to 3 was measured at a current density of 1.0A/g, and the specific capacitance of the carbon nitride-graphene composite materials was calculated, and the results were as follows:
group of
|
Capacitor specific capacitance (F/g)
|
Specific capacitance of material (F/g)
|
Example 1
|
53.99
|
215.95
|
Example 2
|
50.32
|
201.28
|
Example 3
|
48.71
|
194.84 |
The results show that the carbon nitride-graphene composite material provided by the invention has high specific capacitance.
The specific capacitance of the supercapacitor made of the carbon nitride-graphene composite material provided in example 1 was then tested as a function of current density, and the test results are shown in fig. 5.
From the figure, it can be found that the supercapacitor made of the carbon nitride-graphene composite material provided by the invention has good rate performance, and the specific capacitance gradually decreases with the increase of current density. When the current density is increased from 1A/g to 20A/g, the specific capacitance retention rate of the carbon nitride-graphene supercapacitor is 74.86%. This shows that the porous honeycomb structure can ensure the rapid diffusion of electrolyte ions on the surface of the electrode, and has good rate capability.
Then, the fixed current density is 5A/g, the cycle stability and the coulombic efficiency of the supercapacitor made of the carbon nitride-graphene composite material provided in example 1 are tested according to the change of the cycle number, the specific capacitance retention rate and the coulombic efficiency after 2000 cycles are calculated, and the test result is shown in fig. 6. The results show that the supercapacitor made of the carbon nitride-graphene composite material provided by the invention has excellent cycle stability, and after 2000 cycles, the specific capacitance retention rate of the carbon nitride-graphene supercapacitor is still higher than 98.5%. Calculated, the coulombic efficiency of the carbon nitride-graphene super capacitor is more than 99%. The stable porous cellular structure in the carbon nitride-graphene composite material provides a good channel for the diffusion of electrolyte ions, can realize the rapid transfer of electrons, does not collapse in the long-time charge-discharge cycle process, and obviously improves the cycle stability of the supercapacitor made of the carbon nitride-graphene composite material.
The applicant states that the carbon nitride-graphene composite material, the preparation method and the application thereof are illustrated by the above embodiments, but the invention is not limited to the above embodiments, that is, the invention is not limited to the above embodiments. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.