NP co-doped graphite nanosheet electrocatalyst as well as preparation method and application thereof

Abstract

The NP co-doped graphite nanosheet electrocatalyst is prepared, and the preparation method is simple, efficient, easy to operate and low in cost and has practical application significance. The NP co-doped graphite nanosheet is prepared in a tubular furnace by taking cheap graphite powder as a raw material and taking melamine and sodium hypophosphite as a nitrogen source and a phosphorus source respectively through a high-temperature gas phase method. An o-quinone structure with alkaline OER activity is generated through electrochemical activation of the NP co-doped graphite nanosheet, more phosphoric acid functional groups with HER activity are obtained through further oxidation of a P-containing functional group, and excellent electro-catalytic performance is shown. The overpotential of the alkaline OER is only 314 mV, and the overpotential of the acidic HER is only-69.4 mV.

Description

Technical Field

[0001] The invention relates to the technical field of electrocatalysts, and in particular to an NP co-doped graphite nanosheet electrocatalyst and a preparation method and application thereof. Background Art

[0002] Electrochemical water splitting mainly includes the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. 2 and N 2 Reduction is an important half-reaction in reversible fuel cells and metal-air batteries, and is the basic reaction for a variety of electrochemical energy conversion and storage systems. Currently, the most efficient catalysts for HER and OER are Pt-based and Ru / Ir-based oxides, respectively, but the scarcity of precious metal resources and high costs limit their application in the field of new energy.

[0003] Carbon-based materials have the advantages of abundant sources, low cost, light weight, high mechanical strength, excellent thermal conductivity and electrical conductivity, good chemical corrosion resistance and environmental compatibility. Pure graphite carbon materials are 2 -The uniform electron distribution in conjugated carbon is not suitable for catalysis. Due to its tunable molecular structure, catalytic active sites can be introduced into the graphite carbon skeleton by heteroatom doping and co-doping, defect structure, electrochemical oxidation, etc. Graphite sheets containing o-quinone structures can be obtained by electrochemical activation of heteroatom single-doped graphite sheets or electrochemical oxidation of graphite sheets, thereby greatly improving the N, P single-doped electrocatalytic OER performance. However, single doping can only be used as an alkaline OER catalyst, and cannot be used as a dual-functional electrocatalyst for alkaline OER and acidic HER or even a full water splitting catalyst at the same time. Summary of the invention

[0004] The purpose of the present invention is to provide a NP co-doped graphite nanosheet electrocatalyst and a preparation method and application thereof, so as to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The invention provides an electrocatalyst for alkaline electrocatalytic oxygen production and acidic electrocatalytic hydrogen production. The electrocatalyst is NP co-doped graphite nanosheets.

[0007] The present invention also provides a method for preparing the electrocatalyst, comprising the following steps:

[0008] (1) treating graphite powder with dilute hydrochloric acid, acetone, ethanol and deionized water in sequence by ultrasonic treatment, and drying in a vacuum drying oven to obtain pretreated graphite powder;

[0009] (2) placing the pretreated graphite powder obtained in step (1) and melamine in two different quartz boats, respectively, and heating and calcining them in a tube furnace to finally obtain N-doped graphite nanosheets;

[0010] (3) placing the N-doped graphite nanosheets obtained in step (2) and sodium hypophosphite in two different quartz boats, respectively, and heating and calcining them in a tube furnace to obtain NP co-doped graphite nanosheets.

[0011] Preferably, the graphite powder is pretreated by ultrasonically treating 3.0 g of graphite powder with 40 mL of dilute hydrochloric acid, acetone, ethanol and deionized water in sequence for 30 minutes, and drying in a vacuum drying oven at 60° C. for 12 hours.

[0012] Preferably, the mass ratio of graphite powder to melamine in the N-doping process is 1:1, and the temperature is kept at 5°C·min under argon protection. -1 The temperature was raised to 600°C at a heating rate and kept at this temperature for 3 hours.

[0013] Preferably, the mass ratio of graphite powder to sodium hypophosphite during the P doping process is 1:3, and the temperature is kept at 2°C·min under argon protection. -1 The temperature was raised to 300°C at a heating rate of 100°C and kept at this temperature for 3 hours.

[0014] Preferably, the concentration of the dilute hydrochloric acid is 4 mol·L -1 .

[0015] The present invention also provides the use of the electrocatalyst in alkaline electrocatalytic oxygen production and acidic electrocatalytic hydrogen production.

[0016] Based on the above technical solution, the present invention has the following technical effects:

[0017] The present invention prepares a NP co-doped graphite nanosheet electrocatalyst, and the preparation method is simple, efficient, easy to operate, low cost, and has practical application significance. The present invention uses cheap graphite powder as a raw material, melamine and sodium hypophosphite as a nitrogen source and a phosphorus source respectively, and prepares NP co-doped graphite nanosheets in a tubular furnace by a high-temperature gas phase method. The NP co-doped graphite nanosheets are electrochemically activated to produce an o-quinone structure with alkaline OER activity and further oxidize the P-containing functional groups to obtain more phosphate functional groups with HER activity, showing excellent electrocatalytic performance. The overpotential of alkaline OER is only 314mV, and the overpotential of acidic HER is only -69.4mV. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 XRD spectra of pretreated graphite powder (GP), N-doped graphite nanosheets (N-GP), and NP co-doped graphite nanosheets (NP-GP);

[0020] Figure 2 The infrared spectra of pretreated graphite powder (GP), N-doped graphite nanosheets (N-GP), NP co-doped graphite nanosheets (NP-GP), and activated NP co-doped graphite nanosheets (activated NP-GP);

[0021] Figure 3 XPS spectra of NP co-doped graphite nanosheets (NP-GP) and activated NP co-doped graphite nanosheets (activated NP-GP);

[0022] Figure 4 The scanning electron microscope images of N-doped graphite nanosheets (N-GP), NP co-doped graphite nanosheets (NP-GP), and NP co-doped graphite nanosheets after stability test;

[0023] Figure 5 is the voltammetric cycle curve of NP co-doped graphite nanosheets after activation;

[0024] Figure 6 Linear voltammetric scanning curves of NP co-doped graphene nanosheets NP-GP, NP-GP-1, and NP-GP-2;

[0025] Figure 7 Current density-time test curve of NP co-doped graphene nanosheets after activation;

[0026] Figure 8 EIS Enquist comparison diagram of NP co-doped graphene nanosheets NP-GP, NP-GP-1, and NP-GP-2. DETAILED DESCRIPTION

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0029] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0030] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0031] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0032] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or are publicly available.

[0033] Example 1

[0034] 1. Preparation of NP co-doped graphite nanosheet electrocatalysts

[0035] 1.1 3.0g of graphite powder was washed with 40mL of dilute hydrochloric acid (4mol·L -1 ), acetone, ethanol and deionized water were ultrasonically treated for 30 minutes and dried in a vacuum drying oven at 60°C for 12 hours to obtain pretreated graphite powder (GP).

[0036] 1.2 Place graphite powder and melamine in a mass ratio of 1:1 in two different quartz boats and heat and calcine them in a tube furnace. Place the quartz boat containing melamine on the upstream side of the tube furnace, and the quartz boat containing graphite in the center of the tube furnace. Seal the tube furnace, flush it with argon several times to completely remove the air, and then heat it at 5℃·min in an argon atmosphere.-1 The heating rate was increased to 600 °C, and after being kept at 600 °C for 3 hours, the temperature was naturally cooled to room temperature to finally obtain N-doped graphene nanosheets (N-GP).

[0037] 1.3 Place N-doped graphite nanosheets and sodium hypophosphite in a mass ratio of 1:3 in two different quartz boats and heat and calcine them in a tube furnace. Place the quartz boat containing sodium hypophosphite on the upstream side of the tube furnace, and place the quartz boat containing nitrogen-doped graphite powder at the center of the tube furnace. Seal the tube furnace, flush it with argon several times to completely remove the air, and then heat it at 2℃·min in an argon atmosphere. -1 The heating rate was increased to 300°C, and after being kept at 300°C for 3 hours, the temperature was naturally cooled to room temperature to obtain NP co-doped graphite nanosheets (NP-GP).

[0038] 1.4 After electrochemical sample preparation of NP co-doped graphite nanosheets, they were drop-coated on carbon cloth as working electrode, 1M KOH was used as electrolyte, and cyclic voltammetry test was performed in the Faraday range for 40 cycles to obtain activated NP co-doped graphite nanosheets.

[0039] Comparative Example 1

[0040] The difference from Example 1 is that in step 1.3, the mass ratio of N-doped graphite to sodium hypophosphite is 2:1, and the remaining steps are the same as Example 1, and finally NP co-doped graphite nanosheet electrocatalyst (NP-GP-1) is obtained.

[0041] Comparative Example 2

[0042] The difference from Example 1 is that in step 1.3, the mass ratio of N-doped graphite to sodium hypophosphite is 1:4, and the remaining steps are the same as Example 1, and finally NP co-doped graphite nanosheet electrocatalyst (NP-GP-2) is obtained.

[0043] Example 2

[0044] 1. The NP co-doped graphite nanosheet electrocatalysts NP-GP, NP-GP-1 and NP-GP-2 prepared in Example 1 and Comparative Examples 1-2 were subjected to XRD, infrared spectroscopy, XPS photoelectron spectroscopy and electron microscopy analysis.

[0045] 2. Electrocatalytic performance test:

[0046] 2.1 Electrochemical sample preparation: The catalyst and acetylene black are fully ground in a mortar according to a mass ratio of 1:1 to make them evenly mixed. Weigh 20 mg of the ground solid mixture and disperse it in 1 ml of solution (750 μL of distilled water, 230 μL of anhydrous ethanol, and 20 μL of perfluorinated resin solution). Ultrasonic treatment is performed at room temperature for 2 hours to make it evenly dispersed. The dispersed ink is then deposited on the conductive carbon fiber. Before deposition, the carbon fiber is first ultrasonically cleaned with anhydrous ethanol and acetone solvents, respectively. Next, concentrated nitric acid is used to react with the cleaned carbon fiber at 120°C for 4 hours. Finally, a large amount of distilled water is used to clean the carbon fiber. After the conductive carbon fiber is dried, the evenly dispersed ink is dropped on both sides of the carbon fiber (1 cm -2 ), the drop amount is 50μL on both sides. And use infrared lamp to dry.

[0047] 2.2 Electrochemical activation: Using carbon cloth as the working electrode and 1 M KOH as the electrolyte, a cyclic voltammetry test was performed in the Faraday range (1-2 V vs RHE) for 40 cycles.

[0048] 2.3 Cyclic voltammetry curves: Under the condition of three-electrode system (1 M KOH electrolyte solution) with voltage window in the non-Faraday range of 0.3-0.45 V, the cyclic voltammetry curves were calculated at 10, 20, 30, 40, 50 and 60 mV s -1 The cyclic voltammetry curves of the electrode materials were tested at a scan rate of .

[0049] 2.4LSV curve: OER: Under the conditions of three-electrode system (1M KOH electrolyte solution), the linear scan was measured at the starting potential of 0V, the final potential of 2V, and the scanning speed of 0.005V / s. HER: Under the conditions of three-electrode system (0.5M KOH electrolyte solution), the linear scan was measured at the starting potential of 0V, the final potential of 2V, and the scanning speed of 0.005V / s. 2 SO 4 Under the conditions of electrolyte solution), the linear scan was measured at a starting potential of 0.25 V, a final potential of -0.75 V, and a scan rate of 0.005 V / s.

[0050] 2.5 Current density-time test curve: OER: Chronoamperometry at 314 mV under three-electrode system (1 M KOH electrolyte solution). After 12 hours of testing, it can be seen from the figure that the curve has no obvious downward trend, and the chronoamperometry curve of the electrode material has no obvious fluctuation, indicating strong electrochemical stability. HER: Under three-electrode system (0.5 M H 2 SO 4 Electrolyte solution) under the condition of -69.4mV potential.

[0051] 2.6 Electrochemical impedance spectroscopy: The voltage used for the electrochemical impedance spectroscopy (EIS) under alkaline conditions was 1.583 V vs RHE, and the voltage used for the electrochemical impedance spectroscopy (EIS) under acidic conditions was -0.1 V vs RHE. The constant potential mode was used, and the applied voltage was 5 mV.

[0052] 3. Result analysis:

[0053] 3.1 XRD spectra of pretreated graphite powder (GP), N-doped graphite nanosheets (N-GP), and NP co-doped graphite nanosheets (NP-GP) are shown in Figure 3. Figure 1 As shown in the figure, the curves of GP, N-GP, and NP-GP have characteristic diffraction peaks at 2θ=26.4°, 2θ=42.19°, 2θ=44.38°, and 2θ=54.48°, which correspond to the characteristic peaks compared with the graphite standard card (PDF#41-1487). From the graphite standard card, it can be obtained that 2θ=26.4°, 2θ=42.19°, 2θ=44.38°, and 2θ=54.48° correspond to (0 0 2), (1 0 0), (1 0 1), and (0 0 4) crystal planes, respectively. The peak positions of the characteristic peaks are the same before and after doping and multiple calcinations, and it can still maintain a good skeleton structure, and the crystal phases are all hexagonal.

[0054] 3.2 Infrared spectra of pretreated graphite powder (GP), N-doped graphite nanosheets (N-GP), NP co-doped graphite nanosheets (NP-GP), and activated NP co-doped graphite nanosheets (activated NP-GP) are shown in Figure 3. Figure 2 As shown in the spectrum, GP has no obvious infrared absorption peak. N-GP and NP-GP have an absorption peak at 1540 cm -1 There is a small peak at 1200cm, which is the infrared absorption peak of pyridine nitrogen. -1 1450cm -1 The two extremely weak peaks are respectively oxidized pyridinic N and pyrrolic N, which proves the successful doping of N atoms. NP-GP is at 1300cm -1 and 1077cm -1 Each has an infrared absorption peak corresponding to P=O and (COP=O(OH) 2 ), proving the successful doping of P element. After activation, NP-GP has a peak at 1115 cm -1 The peak at 1620 cm -1 The carbonyl peak at 1653 cm -1 The o-benzoquinone peak at 730 cm -1 The benzene ring is disubstituted at the ortho position, which can further verify the existence of the ortho-quinone structure.

[0055] 3.3 XPS photoelectron spectra of NP co-doped graphite nanosheets (NP-GP) and activated NP co-doped graphite nanosheets (activated NP-GP) are shown in Figure 3 As shown in the figure, it can be seen that 134.5eV, 133.8eV, 132.7eV, and 130.eV in the P 2p spectrum of NP-GP correspond to COP=O(OH) 2 、CP=O(OH) 2 or C 2 -P=O(OH),C 3 -P=O、C 3 -P. The P atom initially enters the graphite carbon skeleton in a reduced state, but since the reduced P is not stable, it is replaced by O 2 and moisture oxidation and hydrolysis to form a series of oxygen-containing functional groups. 3 -P=O、CP=O(OH) 2 or C 2 -P=O(OH) is further oxidized to COP=O(OH) 2 Comparing the O1s spectrum of NP-GP with that of activated NP-GP, it can be seen that the C-OH peak corresponding to 533.2 eV disappears after activation, and the COC peak corresponding to 535.3 eV and the o-quinone peak corresponding to 530.7 eV appear.

[0056] 3.4 SEM images of N-doped graphite nanosheets (N-GP), NP co-doped graphite nanosheets (NP-GP), and NP co-doped graphite nanosheets after stability test Figure 4 As shown in the figure, it can be clearly seen from (a)-(b) that N-GP and NP-GP are nanosheet structures. (c) Comparison between NP-GP and NP-GP after electrochemical stability test shows that micropores appear on the surface of graphite nanosheets.

[0057] 3.5 The voltammetric cycling curves of NP co-doped graphene nanosheets after activation are shown in Figure 5 As shown, with the increase of scan rate, the shape of the cyclic voltammetry curve under alkaline and acidic conditions did not change, indicating that the compound has stable electrochemical performance.

[0058] The linear voltammetric scanning curves of 3.6NP co-doped graphene nanosheets NP-GP, NP-GP-1, and NP-GP-2 are shown in Figure 6 As shown, the rules of alkaline OER and acidic HER are consistent, and the catalytic performance of activated NP-GP is the best. That is, when the mass ratio of N-doped graphite powder to sodium hypophosphite is 1:3, the overpotential of alkaline OER is only 314 mV, and the overpotential of acidic HER is only -69.4 mV.

[0059] 3.7 The current density-time test curve of NP co-doped graphene nanosheets after activation is shown in Figure 7 As shown, the test was conducted under acidic and alkaline conditions for 12 hours respectively. From the figure, it can be seen that the curve has no obvious downward trend, and the chronoamperometric curve of the electrode material has no obvious fluctuation, indicating that it has strong electrochemical stability.

[0060] EIS Enerquist comparison of 3.8NP co-doped graphene nanosheets NP-GP, NP-GP-1, and NP-GP-2 is shown in the figure below. Figure 8 As shown, under alkaline and acidic conditions, the arc radius of NP-GP is small, the impedance of NP-GP is minimal, and the charge transfer efficiency is highest.

[0061] In summary, the present invention prepares a NP co-doped graphite nanosheet electrocatalyst, the preparation method is simple and efficient, the cost is low, it is easy to operate, and it has practical application significance. The present invention uses cheap graphite powder as a raw material, melamine and sodium hypophosphite as a nitrogen source and a phosphorus source, respectively, and prepares NP co-doped graphite nanosheets in a tubular furnace by a high-temperature gas phase method. The NP co-doped graphite nanosheets are electrochemically activated to produce an o-quinone structure with alkaline OER activity and further oxidize the P-containing functional groups to obtain more phosphate functional groups with HER activity, showing excellent electrocatalytic performance. The overpotential of alkaline OER is only 314mV, and the overpotential of acidic HER is only -69.4mV.

[0062] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. For ordinary technical users in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An electrocatalyst for alkaline electrocatalytic oxygen production and acidic electrocatalytic hydrogen production, characterized in that: The electrocatalyst is an NP co-doped graphite nanosheet electrocatalyst.

2. The method for preparing an electrocatalyst according to claim 1, characterized in that: The following steps are involved: (1) pre-treating graphite powder by ultrasonic treatment with dilute hydrochloric acid, acetone, ethanol and deionized water in sequence, and drying in a vacuum drying oven; (2) placing the pretreated graphite powder obtained in step (1) and melamine in two different quartz boats, respectively, and heating and calcining them in a tube furnace to finally obtain N-doped graphite nanosheets; (3) placing the N-doped graphite nanosheets obtained in step (2) and sodium hypophosphite in two different quartz boats, respectively, and heating and calcining them in a tube furnace to obtain NP co-doped graphite nanosheets.

3. The preparation method according to claim 2, characterized in that: The graphite powder pretreatment method is as follows: 3.0 g of graphite powder is subjected to ultrasonic treatment with 40 mL of dilute hydrochloric acid, acetone, ethanol and deionized water in sequence for 30 minutes, and then dried in a vacuum drying oven at 60° C. for 12 hours.

4. The preparation method according to claim 2, characterized in that: The mass ratio of graphite powder to melamine in the N-doping process was 1:1, and the temperature was kept at 5 °C·min under argon protection. -1 The temperature was raised to 600°C at a heating rate and kept at this temperature for 3 hours.

5. The preparation method according to claim 4, characterized in that: The mass ratio of graphite powder to sodium hypophosphite in the P doping process was 1:3, and the temperature was kept at 2 °C·min under argon protection. -1 The temperature was raised to 300°C at a heating rate of 100°C and kept at this temperature for 3 hours.

6. Use of the electrocatalyst as claimed in claim 1 in alkaline electrocatalytic oxygen production and acidic electrocatalytic hydrogen production.

Images