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

Abstract

The application prepares an NP co-doped graphite nanosheet electrocatalyst, and has the advantages of simple and efficient preparation method, easy operation, low cost and practical application significance. The application takes cheap graphite powder as raw material, takes melamine and sodium hypophosphite as nitrogen source and phosphorus source respectively, and prepares the NP co-doped graphite nanosheet in a tube furnace through a high-temperature gas phase method. The NP co-doped graphite nanosheet is activated by electrochemistry to generate adjacent quinone structures with basic OER activity and further oxidize P-containing functional groups to obtain more phosphoric acid functional groups with HER activity, and the NP co-doped graphite nanosheet exhibits excellent electrocatalytic performance. The overpotential of the basic OER is only 314 mV, and the overpotential of the acidic HER is only-69.4 mV.

Description

Technical Field

[0001] This invention relates to the field of electrocatalyst technology, and in particular to an NP co-doped graphite nanosheet electrocatalyst, its preparation method, and its application. Background Technology

[0002] Electrochemical water splitting mainly includes the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction at the anode. OER is also a crucial half-reaction in CO2 and N2 reduction, reversible fuel cells, and metal-air batteries, serving as a fundamental reaction in various electrochemical energy conversion and storage systems. Currently, the most efficient catalysts for HER and OER are Pt-based and Ru / Ir-based oxides, respectively; however, the scarcity and high cost of precious metal resources limit their application in the new energy field.

[0003] Carbon-based materials possess advantages such as abundant sources, low cost, light weight, high mechanical strength, excellent thermal and electrical conductivity, good chemical corrosion resistance, and environmental compatibility. Pure graphite-carbon materials, due to their... 2 The uniform electron distribution in conjugated carbon is not suitable for catalysis. Due to its tunable molecular structure, catalytically active sites can be introduced into the graphite carbon framework through heteroatom doping and co-doping, defect construction, and electrochemical oxidation. Electrochemical activation of heteroatom-doped graphite sheets or electrochemical oxidation of graphite sheets can yield graphite sheets containing ortho-quinone structures, thus significantly improving the performance of N, P single-doped electrocatalytic OER. However, single doping can only serve as a basic OER catalyst and cannot simultaneously function as a bifunctional electrocatalyst for both basic OER and acidic HER, or even a total water splitting catalyst. Summary of the Invention

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

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] This invention provides an electrocatalyst for alkaline electrocatalytic oxygen production and acidic electrocatalytic hydrogen production, wherein 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) The graphite powder was subjected to ultrasonic treatment with dilute hydrochloric acid, acetone, ethanol and deionized water in sequence, and then dried in a vacuum drying oven to obtain pretreated graphite powder.

[0009] (2) The pretreated graphite powder obtained in step (1) and melamine were placed in two different quartz boats and heated and calcined in a tube furnace to finally obtain N-doped graphite nanosheets.

[0010] (3) The N-doped graphite nanosheets obtained in step (2) and sodium hypophosphite were placed in two different quartz boats and calcined in a tube furnace to obtain NP co-doped graphite nanosheets.

[0011] Preferably, the pretreatment method for the graphite powder is as follows: 3.0g of graphite powder is ultrasonically treated with 40mL of dilute hydrochloric acid, acetone, ethanol and deionized water for 30 minutes in sequence, and then dried in a vacuum drying oven at 60℃ for 12 hours.

[0012] Preferably, the mass ratio of graphite powder to melamine during the N-doping process is 1:1, and the process is carried out under argon protection at 5°C·min. -1 The temperature was increased to 600℃ at a certain rate and held for 3 hours.

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

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

[0015] The present invention also provides the application 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] This invention prepares an NP-co-doped graphite nanosheet electrocatalyst. The preparation method is simple, efficient, easy to operate, and low in cost, making it practically applicable. Using inexpensive graphite powder as raw material, and melamine and sodium hypophosphite as nitrogen and phosphorus sources respectively, NP-co-doped graphite nanosheets are prepared in a tube furnace via a high-temperature gas-phase method. Electrochemical activation of the NP-co-doped graphite nanosheets generates ortho-quinone structures with basic OER activity, and further oxidation of P-containing functional groups yields more phosphate functional groups with HER activity, exhibiting excellent electrocatalytic performance. The overpotential for basic OER is only 314 mV, and the overpotential for acidic HER is only -69.4 mV. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

[0020] Figure 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);

[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 Scanning electron microscope (SEM) images of N-doped graphite nanosheets (N-GP), NP-co-doped graphite nanosheets (NP-GP), and NP-co-doped graphite nanosheets after stability testing;

[0023] Figure 5 The current-voltage cycling curves of the activated NP co-doped graphite nanosheets;

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

[0025] Figure 7 Current density-time curves of activated NP co-doped graphite nanosheets;

[0026] Figure 8 EIS Nyquist comparison of NP co-doped graphite nanosheets NP-GP, NP-GP-1, and NP-GP-2. Detailed Implementation

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

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0030] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

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

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

[0033] Example 1

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

[0035] 1.1 Add 3.0 g of graphite powder to 40 mL of dilute hydrochloric acid (4 mol·L⁻¹) sequentially. -1 Pretreated graphite powder (GP) was obtained by ultrasonic treatment with acetone, ethanol and deionized water for 30 minutes and then dried in a vacuum drying oven at 60°C for 12 hours.

[0036] 1.2 Graphite powder and melamine, in a 1:1 mass ratio, were placed separately in two different quartz boats and calcined using a tube furnace. The quartz boat containing melamine was placed on the upstream side of the tube furnace, and the quartz boat containing graphite was placed in the center of the tube furnace. The tube furnace was sealed and purged multiple times with argon gas to thoroughly remove air. Then, under an argon atmosphere, the furnace was calcined at 5°C / min. -1 The heating rate was increased to 600℃, and after holding at 600℃ for 3 hours, the temperature was naturally cooled to room temperature, finally obtaining N-doped graphite nanosheets (N-GP).

[0037] 1.3 N-doped graphite nanosheets and sodium hypophosphite (mass ratio 1:3) were placed in two separate quartz boats and calcined using a tube furnace. The quartz boat containing sodium hypophosphite was placed upstream of the tube furnace, and the quartz boat containing nitrogen-doped graphite powder was placed in the center of the furnace. The furnace was sealed and purged multiple times with argon gas to thoroughly remove air. Then, under an argon atmosphere, the furnace was calcined at 2 °C / min. -1 The heating rate was increased to 300℃, and after holding at 300℃ 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 preparation of NP co-doped graphite nanosheets, they were drop-coated onto carbon cloth as the working electrode. 1 M KOH was used as the electrolyte. Cyclic voltammetry 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 in Example 1, finally obtaining NP co-doped graphite nanosheet electrocatalyst (NP-GP-1).

[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 in Example 1, finally obtaining NP co-doped graphite nanosheet electrocatalyst (NP-GP-2).

[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 analyzed by XRD, infrared spectroscopy, XPS photoelectron spectroscopy and electron microscopy.

[0045] 2. Electrocatalytic performance test:

[0046] 2.1 Electrochemical Sample Preparation: The catalyst and acetylene black were thoroughly ground in a mortar at a 1:1 mass ratio until homogeneous. 20 mg of the ground solid mixture was weighed and dispersed in 1 ml of solution (750 μL distilled water, 230 μL anhydrous ethanol, and 20 μL perfluorinated resin solution). The mixture was ultrasonically treated at room temperature for 2 h to ensure uniform dispersion. The dispersed ink was then deposited onto conductive carbon fibers. Before deposition, the carbon fibers were ultrasonically cleaned with anhydrous ethanol and acetone, respectively. Next, concentrated nitric acid was used to react with the cleaned carbon fibers at 120 °C for 4 h. Finally, the carbon fibers were cleaned with a large amount of distilled water. After the conductive carbon fibers dried, the uniformly dispersed ink was drop-coated onto both sides of the carbon fibers (1 cm²). -2 The coating volume was 50 μL for each side. It was then dried using an infrared lamp.

[0047] 2.2 Electrochemical activation: Carbon cloth was used as the working electrode and 1M KOH was used as the electrolyte. Cyclic voltammetry was performed for 40 cycles in the Faraday range (1-2V vsRHE).

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

[0049] 2.4 LSV Curves: OER: Linear scan was measured in a three-electrode system (1M KOH electrolyte solution) at an initial potential of 0V, a final potential of 2V, and a scan rate of 0.005V / s. HER: Linear scan was measured in a three-electrode system (0.5M H2SO4 electrolyte solution) at an initial potential of 0.25V, a final potential of -0.75V, and a scan rate of 0.005V / s.

[0050] 2.5 Current Density-Time Test Curves: OER: Chronoamperometry at 314 mV under a three-electrode system (1 M KOH electrolyte solution). After 12 hours of testing, the curve shows no significant downward trend, indicating that the chronoamperometry curve of this electrode material exhibits no significant fluctuations and thus possesses strong electrochemical stability. HER: Chronoamperometry at -69.4 mV under a three-electrode system (0.5 M H₂SO₄ electrolyte solution).

[0051] 2.6 Electrochemical Impedance Testing: Under alkaline conditions, the voltage used for EIS testing was 1.583V vs RHE; under acidic conditions, the voltage used was -0.1V vs RHE. A constant potential mode was used, with an applied voltage of 5mV.

[0052] 3. Results Analysis:

[0053] 3.1 XRD patterns of pretreated graphite powder (GP), N-doped graphite nanosheets (N-GP), and NP-co-doped graphite nanosheets (NP-GP) are shown below. Figure 1 As shown in the figure, the curves of GP, N-GP, and NP-GP exhibit characteristic diffraction peaks at 2θ = 26.4°, 2θ = 42.19°, 2θ = 44.38°, and 2θ = 54.48°, respectively. These peaks correspond to the characteristic peaks in the graphite standard card (PDF#41-1487). From the graphite standard card, 2θ = 26.4°, 2θ = 42.19°, 2θ = 44.38°, and 2θ = 54.48° correspond to the (0 0 2), (1 0 0), (1 01), and (0 0 4) crystal planes, respectively. The peak positions are the same before and after doping and multiple calcinations, indicating that a good framework structure is still maintained, and the crystal phase is 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 below. Figure 2 As shown in the spectrum, GP shows no obvious infrared absorption peak. N-GP and NP-GP show a peak at 1540 cm⁻¹. -1 There is a small peak at 1200 cm⁻¹, which is the infrared absorption peak of pyridine nitrogen. -1 1450cm -1 The presence of extremely weak peaks at 1300 cm⁻¹ represents pyridine N oxide and pyrrole N oxide, confirming successful N atom doping. -1 and 1077cm -1 The presence of one infrared absorption peak each corresponds to P=O and (COP=O(OH)2), respectively, confirming the successful doping of P. After activation, NP-GP shows an absorption peak at 1115 cm⁻¹. -1 The peak at that location corresponds to PO. After activation, NP-GP peaks at 1620 cm⁻¹. -1 The carbonyl peak at 1653 cm⁻¹ -1 The o-benzoquinone peak at 730 cm⁻¹ -1 The presence of ortho-disubstituted benzene rings at this position further verifies 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 below. Figure 3 As shown in the figure, the P 2p spectra of NP-GP show that 134.5 eV, 133.8 eV, 132.7 eV, and 130 eV correspond to COP=O(OH)2, CP=O(OH)2 or C2-P=O(OH), C3-P=O, and C3-P, respectively. P atoms initially enter the graphite carbon framework in a reduced state, but since the reduced state of P is unstable, it is oxidized and hydrolyzed by O2 and moisture in the air, forming a series of oxygen-containing functional groups. During electrochemical activation, C3-P=O, CP=O(OH)2, or C2-P=O(OH) in NP-GP are further oxidized to COP=O(OH)2. Comparing the O1s spectrum of NP-GP with that of the activated NP-GP, the C-OH peak corresponding to 533.2 eV disappears after activation, and a COC peak corresponding to 535.3 eV and an ortho-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 testing are shown below. 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) After electrochemical stability test, the comparison between NP-GP and NP-GP shows that micropores appear on the surface of graphite nanosheets.

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

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

[0059] 3.7 Current density-time test curves of activated NP co-doped graphite nanosheets are shown in Figure 3.7. Figure 7 As shown in the figure, the electrode material was tested for 12 hours under acidic and alkaline conditions. The curves showed no obvious downward trend, and the chronocurrent curves of the electrode material did not fluctuate significantly, indicating that it has strong electrochemical stability.

[0060] 3.8 EIS Nyquist plots of NP-GP, NP-GP-1, and NP-GP-2 co-doped graphite nanosheets are shown below. Figure 8 As shown, under alkaline and acidic conditions, NP-GP has a small arc radius, the smallest impedance, and the highest charge transfer efficiency.

[0061] In summary, this invention prepares an NP-co-doped graphite nanosheet electrocatalyst. The preparation method is simple, efficient, low-cost, and easy to operate, making it practically applicable. Using inexpensive graphite powder as raw material, and melamine and sodium hypophosphite as nitrogen and phosphorus sources respectively, NP-co-doped graphite nanosheets were prepared in a tube furnace via a high-temperature gas-phase method. Electrochemical activation of the NP-co-doped graphite nanosheets generated o-quinone structures with basic OER activity, and further oxidation of P-containing functional groups yielded more phosphate functional groups with HER activity, exhibiting excellent electrocatalytic performance. The overpotential for basic OER was only 314 mV, and the overpotential for acidic HER was only -69.4 mV.

[0062] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An electrocatalyst for alkaline electrocatalytic oxygen evolution and acidic electrocatalytic hydrogen evolution, characterized by, The electrocatalyst is an NP co-doped graphite nanosheet electrocatalyst, a preparation method of the electrocatalyst, comprising the following steps: (1) The graphite powder is sequentially subjected to ultrasonic treatment with dilute hydrochloric acid, acetone, ethanol and deionized water, and dried in a vacuum drying box to obtain pretreated graphite powder; (2) The pretreated graphite powder obtained in step (1) and melamine are respectively placed in two different quartz boats, and heated and calcined in a tube furnace to obtain N-doped graphite nanosheets; (3) The N-doped graphite nanosheets obtained in step (2) and sodium hypophosphite are respectively placed in two different quartz boats, and heated and calcined in a tube furnace to obtain NP co-doped graphite nanosheets; (4) After electrochemical sample preparation, the NP co-doped graphite nanosheets are drop-coated on carbon cloth as a working electrode, 1M KOH is used as an electrolyte, and cyclic voltammetry test is performed in the Faraday interval for 40 cycles to obtain activated NP co-doped graphite nanosheets.

2. The method of claim 1, wherein the electrocatalyst is prepared by the steps of: comprising the following steps: (1) The graphite powder is pretreated: sequentially subjected to ultrasonic treatment with dilute hydrochloric acid, acetone, ethanol and deionized water, and dried in a vacuum drying box; (2) The pretreated graphite powder obtained in step (1) and melamine are respectively placed in two different quartz boats, and heated and calcined in a tube furnace to obtain N-doped graphite nanosheets; (3) The N-doped graphite nanosheets obtained in step (2) and sodium hypophosphite are respectively placed in two different quartz boats, and heated and calcined in a tube furnace to obtain NP co-doped graphite nanosheets; (4) After electrochemical sample preparation, the NP co-doped graphite nanosheets are drop-coated on carbon cloth as a working electrode, 1M KOH is used as an electrolyte, and cyclic voltammetry test is performed in the Faraday interval for 40 cycles to obtain activated NP co-doped graphite nanosheets.

3. The preparation method according to claim 2, characterized in that, The pretreatment method of the graphite powder is: 3.0g of graphite powder is sequentially subjected to ultrasonic treatment with 40mL of dilute hydrochloric acid, acetone, ethanol and deionized water for 30 minutes, and dried in a 60℃ vacuum drying box for 12 hours.

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

5. The preparation method according to claim 2, characterized in that, The mass ratio of the N-doped graphite nanosheet and sodium hypophosphite in the step (3) P-doping process is 1:3, and the temperature is raised to 300℃ at a rate of 2℃·min -1 under the protection of argon, and the temperature is kept for 3 hours.

6. The application of the electrocatalyst of claim 1 in alkaline electrocatalytic oxygen production and acidic electrocatalytic hydrogen production.

Images