CN113957478B - Sulfur and nitrogen co-doped graphene rich in edge defects, and preparation method and application thereof - Google Patents
Sulfur and nitrogen co-doped graphene rich in edge defects, and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses sulfur and nitrogen co-doped graphene rich in edge defects, and a preparation method and application thereof. The preparation method comprises the steps of uniformly mixing a precursor into a graphene suspension, and utilizing a rapid two-step synthesis method: the sulfur and nitrogen co-doped graphene with enriched edge defects can be prepared by hydrothermal and chemical vapor deposition, the inherent coordination structure of thiourea can be reserved in two-step synthesis, the edge defects are induced to be generated, and a large number of active sites are provided. The preparation method provided by the invention has the advantages of simple synthesis, high repeatability, mass preparation and cheap and easily obtained precursor.
Description
Technical Field
The invention belongs to the field of electrochemistry, and particularly relates to sulfur and nitrogen co-doped graphene rich in edge defects, and a preparation method and application thereof.
Background
Hydrogen peroxide (H) 2 O 2 ) Is an important chemical product and is widely applied in the fields of chemical industry, medicine, environmental protection and the like. At present, hydrogen peroxide is mainly prepared by an anthraquinone method with complex and high energy consumption, but an expensive palladium catalyst is needed, and a large amount of organic waste is generated. Thus, the formation of hydrogen peroxide (ORHP) by electrocatalytic oxygen reduction is a cost effective process that can be used to replace the traditional anthraquinone process. For ORHP, unlike conventional four electron transfer oxygen reduction (4 e-ORR) to water, H is directly produced by the two electron transfer pathway (2 e-ORR) 2 O 2 . Platinum, palladium and their alloys have high ORHP activity due to unique electronic structures. However, the cost for preparing the catalyst is too high to be practically applied on a large scale. Therefore, development of a catalyst material which is efficient, inexpensive, and can suppress 4e-ORR, for realizing green production of H 2 O 2 It is important.
Nonmetallic nanocarbon materials such as graphene, carbon black, carbon nanotubes, and the like have received a great deal of attention. Among them, graphene has a large specific surface area, and is a good catalyst carrier. But is directly used as a catalyst with poor intrinsic activity and slow dynamics. At present, transition metal or heteroatom is introduced into graphene for modification, so that the chemical stability and catalytic activity of the material can be enhanced. The active functional group is constructed by doping atoms in the framework of the regulating and controlling material to form a coordination structure, which is a main strategy for designing the catalyst at present.
Disclosure of Invention
The invention aims to provide sulfur and nitrogen co-doped graphene rich in edge defects, and a preparation method and application thereof, and thiourea (CH) 4 N 2 S) as precursor and sulfur source, ammonia (NH) 3 ) As a nitrogen source, the sulfur and nitrogen co-doped graphene (SNC) rich in edge defects is synthesized by a hydrothermal method and a Chemical Vapor Deposition (CVD), hetero atoms (N, S, O) can be covalently combined with carbon atoms in the graphene, pi orbits are excited to provide a large number of electrons, local electron transfer is accelerated, defect generation is induced, and more active sites are provided to improve the ORHP reaction kinetics. The co-doping of nitrogen and sulfur ensures the generation of externally introduced defects, and can regulate and control the coordination environment of active sites on an atomic scale to form active functional groups. The charge transfer around the functional group is accelerated by the high electronegativity nitrogen atom, the adsorption of the functional group to oxygen molecules can be enhanced by the oxygen homogroup sulfur atom, and the unique SNC coordinated by nitrogen, sulfur and carbon has high electrocatalytic activity to ORHP and generates H in continuous catalysis 2 O 2 Can maintain good selectivity and stability in the process.
The invention provides sulfur and nitrogen co-doped graphene rich in edge defects, which is prepared by adsorption and hydrothermal self-assembly of a thiourea precursor and graphene oxide, wherein the sulfur and nitrogen co-doped graphene is prepared by chemical vapor deposition, and the inherent coordination structure of thiourea can be chemically grafted on the edge of graphene by hydrothermal self-assembly and is reserved in CVD synthesis to induce the edge defects to generate and provide a large number of active sites. The S-C-N coordination group inherent to thiourea is connected to graphene through a chemical covalent bond, and finally an S-C-N-C active functional group is formed.
The preparation method of the sulfur and nitrogen co-doped graphene rich in edge defects comprises the following steps:
(1) Preparing graphene oxide, ultrasonically dispersing the graphene oxide in deionized water, and ultrasonically treating the deionized water by 8 to h to obtain a uniform suspension with the graphene oxide concentration of 2 mg/mL;
(2) Hydrothermal reaction: will CH 4 N 2 S is added into the graphene oxide suspension prepared in the step (1), stirred for 2 h, then placed in a hydrothermal kettle for heating reaction, the reaction temperature is 180-200 ℃, the reaction time is 12-24 hours, after the reaction is completed, the hydrothermal kettle is cooled, and a columnar product is taken out and placed in a freeze dryer for drying at least 24 h (-50 ℃ to 100 ℃), so as to obtain dried aerogel;
CH 4 N 2 the mass ratio of S in S to graphene oxide is 1-5:95-99;
(3) Chemical vapor deposition:
placing the aerogel prepared in the step (2) into the center of a tube furnace, setting the furnace temperature to be 800-900 ℃, and setting the gas flow to be Ar 100+/-5 sccm and NH 3 50+/-5 sccm, and the total air pressure is 2.8+/-0.1 Torr; and (3) performing chemical vapor deposition reaction for 0.5-2 hours in a tube furnace to obtain the sulfur and nitrogen co-doped graphene rich in edge defects.
Further, the sulfur atom loading in the thiourea in the step (2) accounts for 1.5% of the mass percentage of the graphene oxide.
Further, the reaction time of the chemical vapor deposition was 1 h, and the reaction temperature was 850 ℃.
The invention provides application of the sulfur and nitrogen co-doped graphene rich in edge defects as a catalyst for electrocatalytic ORHP, wherein the catalytic reaction is carried out on a rotary disc electric device, and the rotating speed is set at 1600 rpm; preparing electrode dispersion liquid by taking 2 mg catalyst, water, ethanol and Nafion (5 wt%) solution according to the volume ratio of 5:5:1, uniformly dripping the electrode dispersion liquid on 5 mu L of a ring disk electrode, wherein the loading capacity is 0.1 mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The catalytic process is carried out in a three-electrode system in which the electrolyte is 0.1M KOH and is fed under saturated oxygen conditionsAnd (3) row. The catalyst is capable of catalyzing O 2 Obtaining an electron-generating OOH intermediate and adsorbing the intermediate on an active site, and then obtaining an electron-generating hydrogen peroxide HO 2 ˉ。
The invention has the beneficial effects that:
(1) The preparation method provided by the invention has the advantages of simple synthesis, high repeatability, mass preparation and cheap and easily obtained precursor. And uniformly mixing the precursor into a graphene suspension, and preparing the sulfur and nitrogen co-doped graphene with enriched edge defects by using a rapid two-step synthesis method (hydrothermal and chemical vapor deposition).
(2) In the sulfur and nitrogen co-doped graphene prepared by the invention, CH 4 N 2 S can simultaneously provide high electronegativity nitrogen and sulfur atoms, can regulate and control the electronic structure on graphene, and generate a large number of in-plane edge defects, so that the intrinsic activity of the sulfur and nitrogen co-doped graphene is improved.
(4) In the sulfur and nitrogen co-doped graphene prepared by the invention, CH 4 N 2 S and NH 3 A source of dinitrogen is provided, forming carbon-nitrogen covalent bonds by hydrothermal and strengthening by high temperature nitridation during CVD.
(5) In the sulfur and nitrogen co-doped graphene prepared by the invention, CH 4 N 2 S-inherent coordination structure (S-C-N) can be reserved in the two-step synthesis process and is covalently connected in a graphene framework, so that S-C-N-C functional groups are further developed, the structural stability of sulfur and nitrogen co-doped graphene is improved, the rapid charge transfer is ensured, and H is further promoted 2 O 2 Is produced and stable.
(6) The sulfur and nitrogen co-doped graphene rich in edge defects, which is prepared by the method, has the advantages of ORHP performance, high activity, high selectivity, high current density, small Tafil slope, stable performance and the like.
Drawings
FIG. 1 is an XRD pattern of SNC@800 prepared in example 1 of the present invention;
FIG. 2 is a Raman spectrum of SNC@800 prepared in example 1 of the present invention;
FIG. 3 is a graph of performance of SNC@800 prepared in example 1 of the present invention as a catalyst in an electrocatalytic ORHP, wherein 3a is the polarization curve in 0.1M KOH electrolyte, 3b is the Tafil curve in 0.1M KOH electrolyte, and the scan rate is 5 mV/s;
FIG. 4 shows the SNC@800 prepared in example 1 of the present invention as H of the catalyst 2 O 2 A selectivity curve calculated from the disk current density and the ring current density of fig. 3 a;
FIG. 5 is an XRD pattern of SNC@850 prepared in example 2 of the present invention;
FIG. 6 is a Raman spectrum of SNC@850 prepared in example 2 of the present invention;
FIG. 7 is an SEM image of SNC@850 prepared in example 2 of the present invention;
FIGS. 8a and 8b are TEM images at low and high magnification of SNC@850 prepared in example 2 of the present invention, respectively;
FIG. 9 is an XPS chart of SNC@850 prepared in example 2 of the present invention, wherein the inset is the element content calculated by XPS;
FIGS. 10a, 10b and 10c are XANES (X-ray absorption near edge structure) spectra of C K-edge, N K-edge and S K-edge of SNC@850, respectively, and 10d is SNC@850 13 C ssNMR (solid state nuclear magnetic resonance);
FIGS. 11a and 11b are spherical aberration correcting transmission electron microscope (AC-TEM) pictures of SNC@850 prepared in example 2 of the present invention;
FIG. 12 is a graph of performance of SNC@850 prepared in example 2 of the present invention as a catalyst in an electrocatalytic ORHP, wherein 12a is a polarization curve in 0.1M KOH electrolyte and 12b is a Taphil plot in 0.1M KOH electrolyte, scanning rate is 5 mV/s;
FIG. 13 is a graph showing the reaction of SNC@850 prepared in example 2 of the present invention as H of the catalyst 2 O 2 A selectivity curve calculated from the disk current density and the ring current density of fig. 12 a;
FIG. 14 is an ORHP stability test curve for SNC@850 as a catalyst prepared in example 2 of the present invention;
FIG. 15 is an XRD pattern of SNC@900 prepared in example 3 of the present invention;
FIG. 16 is a Raman spectrum of SNC@900 prepared in example 3 of the present invention;
FIG. 17 is a graph of performance of SNC@900 prepared in example 3 of the present invention as a catalyst in an electrocatalytic ORHP, where 17a is the polarization curve in 0.1M KOH electrolyte and 17b is the Tafil curve in 0.1M KOH electrolyte, scan rate is 5 mV/s;
FIG. 18 is a graph showing the reaction of SNC@900 prepared in example 3 of the present invention as H of the catalyst 2 O 2 The selectivity curve was calculated from the disk current density and the ring current density of fig. 17 a.
Detailed Description
The present invention is further illustrated by, but not limited to, the following examples.
The graphene oxide in the following examples was prepared by Hummers improvement method, and the specific preparation process is as follows: at 0 o Under the ice water bath of C, 3.0 g graphite flake is dispersed in concentrated H with the volume ratio of 9:1 2 SO 4 /H 3 PO 4 To a mixture of (360:40 mL) was slowly added 18 g KMnO 4 Is continuously mechanically stirred to fully oxidize and slowly release heat, and then the water bath temperature is increased to 50 o C and hold 12 h. After the solution cooled to room temperature, it was poured into 400 mL pieces of ice prepared in advance, stirred until completely dissolved, and added slowly with H 2 O 2 (30%) until the solution appeared bright yellow. And then, repeatedly washing with a HCl solution with the mass concentration of 30%, deionized water and diethyl ether in sequence through centrifugal separation to obtain graphene oxide.
Example 1
(1) Preparing graphene oxide suspension: dispersing 0.15 g graphene oxide in 75 mL deionized water by ultrasonic treatment, and performing ultrasonic treatment on 8 h to obtain a uniform suspension with the graphene oxide concentration of 2 mg/mL;
(2) Hydrothermal reaction: CH with S accounting for 1.5 percent of the mass ratio of the graphene oxide 4 N 2 S is placed in the graphene oxide suspension prepared in the step (1), stirred and dispersed for 2 h, and then the reaction solution is placed in a hydrothermal kettle and heated to 180 DEG C o C, continuously reacting 12 to h, cooling the hydrothermal kettle after the reaction is finished, taking out the columnar product, and freeze-dryingDrying 30 h in a dryer to obtain a dried product;
(3) Chemical vapor deposition: the furnace temperature was set to 800 o C, the gas flow is Ar, 100 sccm and NH 3 50 sccm, total gas pressure of 2.85 Torr; and (3) placing the dried product prepared in the step (2) in the center of a tube furnace, performing chemical vapor deposition reaction 1 h in the tube furnace, rapidly removing a sample from the center of a hot zone of the tube furnace under the protection of continuous Ar flow, and cooling to room temperature to obtain the sulfur and nitrogen co-doped graphene SNC@800 rich in edge defects.
The application process comprises the following steps:
the sulfur and nitrogen co-doped graphene rich in edge defects prepared in the embodiment is used as a catalyst for electrocatalytic ORHP:
the ORHP performance of the sulfur and nitrogen co-doped graphene rich in edge defects, prepared by the invention, was tested on a Shanghai Chenhua electrochemical workstation (CHI 760E) U.S. Pine rotating disk electric device (RRDE, AFE6R 2) by using a three-electrode system. The sulfur, nitrogen co-doped graphene catalyst 2 mg rich in edge defects and 40 μl of 5 wt% nafion solution were dispersed in 400 μl of v/v 1:1 water/ethanol (containing 200 μl water and 200 μl ethanol), followed by water bath sonication until a uniform suspension was formed. Then 5. Mu.L of the catalyst suspension was loaded onto a rotating disk ring electrode (RRDE, AFE6R 2) with a disk area of 0.2376 cm 2 Platinum ring area 0.2356 cm 2 The electrode was dried 24 h at room temperature before measurement. The loading of the catalyst was 0.1 mg/cm 2 。
All catalytic processes were carried out in a three-electrode system in which the electrolyte was 0.1M KOH and under saturated oxygen. The catalyst is capable of catalyzing O 2 Obtaining an electron-generating OOH intermediate and adsorbing the intermediate on an active site, and then obtaining an electron-generating hydrogen peroxide HO 2 -a. At O 2 In a saturated 0.1M KOH electrolyte solution, a three-electrode system test OR is formed by using a platinum wire as a counter electrode, an Ag/AgCl (saturated potassium chloride) electrode as a reference electrode and RRDE coated with the prepared sulfur-nitrogen co-doped graphene catalyst rich in edge defects as a working electrodeHP performance. Pure nitrogen was bubbled for 30 minutes, air was removed, and a Linear Sweep Voltammetry (LSV) was performed at a sweep rate of 5 mV/s to collect background current for calculation of H 2 O 2 The yield was subtracted. Then bubbling pure oxygen for 30 minutes to remove dissolved oxygen, performing LSV test, setting the ring current collection voltage to 1.2V, setting the current collection voltage of stability test to 0.40V, setting the RRDE rotation speed to 1600 rpm, and changing all potentials to standard hydrogen electrode (RHE): e (RHE) =e (Ag/AgCl) +0.059×ph+ 0.1976.H 2 O 2 Yield = 200I R /I D N + I R Wherein I R For ring current density, I D Is the disk current density and N is the RRDE collection efficiency of 0.37.
The applications in the following examples were all carried out under the above-described process conditions.
The sulfur and nitrogen co-doped graphene SNC@800 rich in edge defects prepared by the embodiment can efficiently catalyze oxygen to generate hydrogen peroxide, and H of the hydrogen peroxide is generated under an electrochemical window of 0-0.6V 2 O 2 The selectivity reaches more than 80%, and the 2e-ORR performance is proved to be good.
As shown in fig. 1, the XRD spectrum of snc@800 has a strong diffraction of the graphite (002) crystal face, indicating a large crystal size on the c-axis. (100) The (004) and (110) crystal face exposure shows that the prepared graphene structure curls and can provide more ORHP active sites as a catalyst.
As shown in fig. 2, which is a raman spectrum of snc@800, the D peak representing the carbon atom defect is the strongest, indicating the enrichment of the prepared graphene defects. The appearance of the d+g peak indicates that the disorder of graphene is greater.
As shown in FIGS. 3a and 3b, SNC@800 as catalyst polarization curve in 0.1 KOH electrolyte and Tafel slope, respectively, wherein Tafel slope is 117 mA dec -1 The loop current density at a voltage of 0.1. 0.1V was 0.58 mA cm -2 The current density in the ring is 0.1 mA cm -2 The initial potential at this point was 0.77. 0.77V, demonstrating that the catalyst had some 2e-ORR performance.
As shown in FIG. 4, SNC@800 is used as a catalyst at H of 0 to 0.6V 2 O 2 Selectivity curveThe selectivity is kept above 80%, which indicates that the catalyst has good ORHP activity.
Example 2 preparation of edge defect-enriched Sulfur and Nitrogen co-doped graphene
(1) Preparing graphene oxide suspension: dispersing 0.15 g graphene oxide in 75 mL deionized water by ultrasonic treatment, and performing ultrasonic treatment on 8 h to obtain a uniform suspension with the graphene oxide concentration of 2 mg/mL;
(2) Hydrothermal reaction: CH with S accounting for 1.5 percent of the mass ratio of the graphene oxide 4 N 2 S is placed in the graphene oxide suspension prepared in the step (1), stirred and dispersed for 2 h, and then the reaction solution is placed in a hydrothermal kettle and heated to 180 DEG C o C, continuously reacting 12 to h, cooling the hydrothermal kettle after the reaction is finished, taking out the columnar product, and placing the columnar product in a freeze dryer for drying 30 to h to obtain a dried product;
(3) Chemical vapor deposition: the furnace temperature is set to 850 o C, the gas flow is Ar, 100 sccm and NH 3 50 sccm, total gas pressure of 2.85 Torr; and (3) placing the dried product obtained in the step (2) in the center of a tube furnace, performing chemical vapor deposition reaction 1 h in the tube furnace, rapidly removing a sample from the center of a hot zone of the tube furnace under the protection of continuous Ar flow, and cooling to room temperature to obtain the sulfur and nitrogen co-doped graphene SNC@850 rich in edge defects.
The doped graphene shows excellent catalytic activity and H in catalyzing ORHP 2 O 2 Yield, high ring current density and onset potential, H at electrochemical window of 0-0.6V 2 O 2 The selectivity reaches more than 90 percent, the highest selectivity reaches 99 percent, and the catalyst has good stability and circularity.
As shown in fig. 5, the XRD spectrum of snc@850 shows strong diffraction of the graphite (002) crystal face, indicating a large crystal size on the c-axis. (100) The (004) and (110) crystal face exposure shows that the prepared graphene structure curls and can provide more ORHP active sites as a catalyst.
As shown in FIG. 6, which is a Raman spectrum of SNC@850, the D peak representing the carbon atom defect is the strongest, indicating the enrichment of the prepared graphene defect. The appearance of the d+g peak indicates that the disorder of graphene is greater.
As shown in fig. 7, an SEM image of snc@850 shows that the prepared sulfur and nitrogen co-doped graphene has a loose dispersed layered structure.
As shown in fig. 8a and 8b, a TEM image of snc@850 is shown. 8a shows that the prepared sulfur and nitrogen co-doped graphene has a curled appearance and a layered structure, and has rich wrinkles and waves, and the appearance is favorable for the electrochemical reaction of the surface. Where 8b is a high resolution TEM image, snc@850 has a pronounced (002) graphite face stack around 0.30 nm, which is less than the typical graphene interlayer spacing (0.34 nm), indicating that thiourea as a precursor can induce the generation of a large number of defects, thus strengthening the interaction between the graphite faces.
As shown in fig. 9, the XPS full spectrum and calculated elemental content for snc@850 indicate that sulfur and nitrogen were successfully doped into graphene without the introduction of other transition metals and impurity elements.
As shown in fig. 10a, 10b and 10C, the C K-edge, N K-edge and S K-edge XANES spectra of snc@850, respectively, where 10a can be seen to have distinct pi (c=c) and sigma (C-C) signals, which are typical graphene characteristic peaks, with a weak bulge peak at 288 eV, which is intermediate to sp 2 Hybridization orbital sp 3 The interlayer state of the graphene in the hybrid orbit transition is caused by the introduction of covalent bonds such as C-N, C-S, C-O and the like in the doping of the hetero atoms. Fig. 10b reflects the presence of nitrogen in snc@850 as pyridine-nitrogen, pyrrole-nitrogen, graphite-nitrogen, respectively, and fig. 10c shows that sulfur in thiourea eventually remains on the graphene framework as thiophene-sulfur, as well as the sulfur oxide phase and sulfonic acid groups left over during graphene preparation due to oxidation with concentrated sulfuric acid. It can be seen from FIG. 10d that SNC@850 has a typical sp around 125 ppm 2 The NMR characteristic peaks of the hybridized carbon atoms, c=s and S-C-N groups at 128.6 ppm and 164.3 ppm, respectively, indicate that the coordination structure in thiourea is retained in the two-step synthesis and eventually forms S-C-N-C reactive functional groups.
As shown in fig. 11a and 11b, the images are AC-TEM images of snc@850, wherein 11a can clearly observe defects of six-membered rings, non-six-membered rings and in-plane holes of graphene, and in an enlarged view of 11b, the in-plane holes can be seen to be large enough to be regarded as edges, and the edges are distributed with defects of six-membered rings and non-six-membered rings of graphene, which indicates that sulfur and nitrogen co-doped graphene rich in edge defects is successfully prepared.
As shown in FIGS. 12a and 12b, SNC@850 as catalyst polarization curve in 0.1 KOH electrolyte and Tafel slope, respectively, where Tafel slope is 87 mA dec -1 The loop current density at a voltage of 0.1. 0.1V was 0.74 mA cm -2 The current density in the ring is 0.1 mA cm -2 The initial potential at this point was 0.81 and V, demonstrating excellent 2e-ORR performance of the catalyst.
As shown in FIG. 13, SNC@850 is used as a catalyst at 0 to 0.6. 0.6V H 2 O 2 The selectivity curve, selectivity remained above 90%, demonstrates that the catalyst has good ORHP activity.
As shown in FIG. 14, the SNC@850 is used as an ORHP stability test curve of the catalyst, and about 95% of H can be still maintained in the continuous polarization process exceeding 50000 and 50000 s 2 O 2 Selectivity, indicating that the catalyst has excellent cycle performance and stability.
Example 3 preparation of edge defect-enriched Sulfur and Nitrogen co-doped graphene
(1) Preparing graphene oxide suspension: dispersing 0.15 g graphene oxide in 75 mL deionized water by ultrasonic treatment, and performing ultrasonic treatment on 8 h to obtain a uniform suspension with the graphene oxide concentration of 2 mg/mL;
(2) Hydrothermal reaction: CH with S accounting for 1.5 percent of the mass ratio of the graphene oxide 4 N 2 S is placed in the graphene oxide suspension prepared in the step (1), stirred and dispersed for 2 h, and then the reaction solution is placed in a hydrothermal kettle and heated to 180 DEG C o C, continuously reacting 12 to h, cooling the hydrothermal kettle after the reaction is finished, taking out the columnar product, and placing the columnar product in a freeze dryer for drying 30 to h to obtain a dried product;
(3) Chemical vapor deposition: the furnace temperature is set to 900 o C, the gas flow is Ar, 100 sccm and NH 3 50 sccm, total gas pressure of 2.85 Torr; placing the dried product obtained in the step (2) into the center of a tube furnace, and placing the tube furnace in the tube furnaceAfter the chemical vapor deposition reaction 1 h, rapidly removing the sample from the center of the hot zone of the tube furnace under the continuous Ar flow protection, and cooling to room temperature to obtain the sulfur-nitrogen co-doped graphene SNC@900 rich in edge defects.
The doped graphene can efficiently catalyze oxygen to generate hydrogen peroxide, and H is shown in an electrochemical window of 0-0.6V 2 O 2 The selectivity reaches more than 80%, and the 2e-ORR performance is proved to be good.
As shown in fig. 15, the XRD spectrum of snc@900 shows strong diffraction of the graphite (002) crystal face, indicating a large crystal size on the c-axis. (100) The (004) and (110) crystal face exposure shows that the prepared graphene structure curls and can provide more ORHP active sites as a catalyst.
As shown in fig. 16, which is a raman spectrum of snc@900, the D peak representing the carbon atom defect was the strongest, indicating the enrichment of the prepared graphene defects. The appearance of the d+g peak indicates that the disorder of graphene is greater.
As shown in FIGS. 17a and 17b, SNC@900 as catalyst polarization curve in 0.1 KOH electrolyte and Tafel slope, respectively, wherein Tafel slope is 128 mA dec -1 The loop current density at a voltage of 0.1. 0.1V was 0.64 mA cm -2 The current density in the ring is 0.1 mA cm -2 The initial potential at this point was 0.75. 0.75V, demonstrating that the catalyst had some 2e-ORR performance.
As shown in FIG. 18, SNC@800 is used as a catalyst at H of 0 to 0.6V 2 O 2 The selectivity profile, selectivity remained at 80%, demonstrates that the catalyst had a certain ORHP activity.
Example 4 preparation of edge defect-enriched Sulfur and Nitrogen co-doped graphene
(1) Preparing graphene oxide suspension: dispersing 0.15 g graphene oxide in 75 mL deionized water by ultrasonic treatment, and performing ultrasonic treatment on 8 h to obtain a uniform suspension with the graphene oxide concentration of 2 mg/mL;
(2) Hydrothermal reaction: CH with S accounting for 1.5 percent of the mass ratio of the graphene oxide 4 N 2 S is placed in the graphene oxide suspension prepared in the step (1), stirred and dispersed for 2 h, and thenThe reaction solution is placed in a hydrothermal kettle and heated to 180 DEG C o C, continuously reacting 12 to h, cooling the hydrothermal kettle after the reaction is finished, taking out the columnar product, and placing the columnar product in a freeze dryer for drying 30 to h to obtain a dried product;
(3) Chemical vapor deposition: the furnace temperature is set to 850 o C, the gas flow is Ar, 100 sccm and NH 3 50 sccm, total gas pressure of 2.85 Torr; and (3) placing the dried product obtained in the step (2) in the center of a tube furnace, performing chemical vapor deposition reaction in the tube furnace for 0.5 h, rapidly removing a sample from the center of a hot zone of the tube furnace under the protection of continuous Ar flow, and cooling to room temperature to obtain the sulfur and nitrogen co-doped graphene SNC rich in edge defects.
Example 5 preparation of edge defect-enriched Sulfur and Nitrogen co-doped graphene
(1) Preparing graphene oxide suspension: dispersing 0.15 g graphene oxide in 75 mL deionized water by ultrasonic treatment, and performing ultrasonic treatment on 8 h to obtain a uniform suspension with the graphene oxide concentration of 2 mg/mL;
(2) Hydrothermal reaction: CH with S accounting for 1.5 percent of the mass ratio of the graphene oxide 4 N 2 S is placed in the graphene oxide suspension prepared in the step (1), stirred and dispersed for 2 h, and then the reaction solution is placed in a hydrothermal kettle and heated to 180 DEG C o C, continuously reacting 12 to h, cooling the hydrothermal kettle after the reaction is finished, taking out the columnar product, and placing the columnar product in a freeze dryer for drying 30 to h to obtain a dried product;
(3) Chemical vapor deposition: the furnace temperature is set to 850 o C, the gas flow is Ar, 100 sccm and NH 3 50 sccm, total gas pressure of 2.85 Torr; and (3) placing the dried product obtained in the step (2) in the center of a tube furnace, performing chemical vapor deposition reaction 2 h in the tube furnace, rapidly removing a sample from the center of a hot zone of the tube furnace under the protection of continuous Ar flow, and cooling to room temperature to obtain the sulfur and nitrogen co-doped graphene SNC rich in edge defects.
Claims (7)
1. A preparation method of sulfur and nitrogen co-doped graphene rich in edge defects is characterized by comprising the following steps of: the method is characterized in that thiourea is used as a precursor and a sulfur source, ammonia is used as a nitrogen source, thiourea and graphene oxide are adsorbed and subjected to hydrothermal self-assembly, sulfur and nitrogen co-doped graphene is prepared by adopting a hydrothermal method and chemical vapor deposition, the inherent coordination structure of the thiourea can be chemically grafted on the edge of the graphene through the hydrothermal self-assembly, edge defects are induced to be generated, and a large number of active sites are provided;
the preparation method of the sulfur and nitrogen co-doped graphene rich in edge defects comprises the following steps:
(1) Preparing graphene oxide, ultrasonically dispersing the graphene oxide in deionized water, and ultrasonically treating the deionized water by 8 to h to obtain a uniform suspension with the graphene oxide concentration of 2 mg/mL;
(2) Hydrothermal reaction:
thiourea CH 4 N 2 S is added into the graphene oxide suspension prepared in the step (1), stirred for 2 h, then placed in a hydrothermal kettle for heating reaction, the reaction temperature is 180-200 ℃ and the reaction time is 12-24 hours, after the reaction is completed, the hydrothermal kettle is cooled, and a columnar product is taken out and placed in a freeze dryer for drying at least 24 h, so that dried aerogel is obtained;
(3) Chemical vapor deposition:
placing the aerogel prepared in the step (2) into the center of a tube furnace, and setting the furnace temperature to be 800-900 DEG C o C, the gas flow is Ar, 100+/-5 sccm and NH 3 50+/-5 sccm, and the total air pressure is 2.8+/-0.1 Torr; and (3) carrying out a high-temperature heat treatment reaction for 0.5-2 hours to obtain the sulfur and nitrogen co-doped graphene rich in edge defects.
2. The method for preparing the sulfur-nitrogen co-doped graphene rich in edge defects according to claim 1, wherein the method comprises the following steps of: the sulfur atom loading in the thiourea in the step (2) accounts for 1.5% of the mass of the graphene oxide.
3. The method for preparing the sulfur-nitrogen co-doped graphene rich in edge defects according to claim 1, wherein the method comprises the following steps of: CH (CH) 4 N 2 The mass ratio of S in S to graphene oxide is 1-5:95-99.
4. The method for preparing the sulfur-nitrogen co-doped graphene rich in edge defects according to claim 1, wherein the method comprises the following steps of: the temperature of freeze drying is minus 100 ℃ to minus 50 ℃.
5. The method for preparing the sulfur-nitrogen co-doped graphene rich in edge defects according to claim 1, wherein the method comprises the following steps of: the reaction time for chemical vapor deposition in a tube furnace was 1 h and the reaction temperature was 850 ℃.
6. An application of the sulfur-nitrogen co-doped graphene rich in edge defects prepared by the preparation method of any one of claims 1-5 as a catalyst for electrocatalytic ORHP.
7. The use according to claim 6, characterized in that: the catalytic reaction is carried out on a rotary disc electric device, and the rotating speed is set at 1600 rpm; preparing an electrode dispersion by taking 2 mg catalyst, water, ethanol and 5 wt% Nafion solution according to the volume ratio of 5:5:1, uniformly dripping the electrode dispersion on 5 mu L of a ring plate electrode, wherein the loading capacity is 0.1 mg/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The catalytic process was carried out in a three-electrode system in which the electrolyte was 0.1M KOH and was carried out under saturated oxygen.
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