CN115180613A

CN115180613A - Boron-phosphorus co-doped carbon catalyst and preparation method and application thereof

Info

Publication number: CN115180613A
Application number: CN202211092226.XA
Authority: CN
Inventors: 宫宏宇; 丁孝涛; 于平; 刘志敏; 苏峰; 李杰先; 黄方
Original assignee: Shandong Green Hydrogen Energy Storage Technology Co ltd; SHANDONG SAIKESAISI HYDROGEN ENERGY CO Ltd
Current assignee: Shandong Green Hydrogen Energy Storage Technology Co ltd; SHANDONG SAIKESAISI HYDROGEN ENERGY CO Ltd
Priority date: 2022-09-08
Filing date: 2022-09-08
Publication date: 2022-10-14

Abstract

The invention belongs to the technical field of catalyst preparation, and discloses a boron-phosphorus co-doped carbon catalyst and a preparation method and application thereof.A sodium tetraphenylboron is uniformly dispersed in an ethanol solution, and a phosphorus source is added into the ethanol solution, wherein the phosphorus source is selected from phenyl phosphorus dichloride, diphenyl phosphorus chloride, methyl triphenyl phosphonium bromide and tetraphenyl phosphorus bromide; then stirring at 20-40 ℃ to ensure that the precursor reacts completely and is uniformly dispersed; and then carrying out hydrothermal reaction on the solution, drying the prepared product, and carrying out carbonization treatment to obtain the boron-phosphorus co-doped carbon nanosheet catalyst. With (C) ₆ H ₅ ) ₄ BNa is used as a boron source, phosphorus-containing precursors with different benzene ring numbers are used as phosphorus sources, and the doping amount of boron and phosphorus in the finally obtained material is changed. The doping amount of the hetero atoms and the number of benzene rings in the precursor are basically increased in a linear relationship. With the increase of the doping amount of the hetero atom, the oxygen reduction catalytic activity of the catalyst is also improvedThe improvement is obvious.

Description

Boron-phosphorus co-doped carbon catalyst and preparation method and application thereof

Technical Field

The invention belongs to the technical field of catalyst preparation, and particularly relates to a boron-phosphorus co-doped carbon catalyst and a preparation method and application thereof.

Background

The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.

The Oxygen Reduction Reaction (ORR) is an important process in fuel cells and metal air battery anodes, and Pt-based materials are representative catalysts for ORR, but the high cost limits its further large-scale application, so it is of great significance to develop low-cost ORR electrocatalysts.

Heteroatom-doped carbon-based materials are considered to be a potential alternative to platinum-based catalysts at present due to their low cost, abundant resources, and high stability in alkaline media.

The following two strategies are mainly adopted for the hetero atom doping. One is doping different kinds of hetero atoms such as boron (B), phosphorus (P), sulfur (S), nitrogen (N), and the like. Research shows that doping the carbon material with the hetero atoms can provide O ₂ Charged sites are adsorbed and ORR performance is facilitated by enhancing atomic charge density and/or spin electron density redistribution. And the doping amount of the hetero atoms is controlled, so that the number and intrinsic activity of defects can be regulated, and the morphology and structure of the material can be regulated. By properly increasing the doping amount of the hetero atoms, the ORR performance of the electrocatalyst is remarkably improved.

However, the carbon-based material doped with different atoms has the problem that the morphology of the carbon-based material and the doping amount of the different atoms are difficult to control, and the performance optimization is influenced.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a boron-phosphorus co-doped carbon catalyst and a preparation method and application thereof.

In order to realize the purpose, the invention is realized by the following technical scheme:

in a first aspect, the invention provides a preparation method of a boron-phosphorus co-doped carbon catalyst, which comprises the following steps:

uniformly dispersing sodium tetraphenylborate in an ethanol solution, and adding a phosphorus source selected from phenyl phosphorus dichloride, diphenyl phosphorus chloride, methyl triphenyl phosphonium bromide and tetraphenyl phosphorus bromide;

then stirring at 20-40 ℃ to ensure that the precursor reacts completely and is uniformly dispersed;

and then carrying out hydrothermal reaction on the solution, drying the prepared product, and carbonizing to prepare the boron-phosphorus co-doped carbon nanosheet catalyst.

In a second aspect, the invention provides a boron-phosphorus co-doped carbon catalyst prepared by the preparation method.

In a third aspect, the invention provides an application of the boron-phosphorus co-doped carbon catalyst in an oxygen reduction reaction.

The beneficial effects achieved by one or more of the embodiments of the invention described above are as follows:

used in the present invention (C) ₆ H ₅ ) ₄ BNa is used as a boron source, phosphorus-containing precursors with different benzene ring numbers are used as phosphorus sources, and the doping amount of boron and phosphorus in the finally obtained material is changed. Meanwhile, the doping amount of the hetero atoms and the number of benzene rings in the precursor are basically increased in a linear relationship. Furthermore, hetero atom doping has been shown to significantly affect ORR catalytic activity of carbon-based materials in a manner that regulates the amount of hetero atom doping.

Synthesis of boron and phosphorus double doped carbon nanoplates (BPC) were synthesized by a simple solvothermal method followed by a carbonization process. Different element doping materials with different benzene ring numbers are used as precursors of the experiment to regulate the doping amount of the hetero atoms, and finally the doping amount of the hetero atoms detected in the sample is basically in a linear relation with the number of the benzene rings in the precursors. Therefore, the different atom doping amount can be controlled by a simple method, and then the ORR electrocatalytic performance of the material can be optimized.

With the increase of the number of benzene rings in the precursor, the synthesized material tends to a stable and flat nanosheet structure, the electrochemical active area of the catalyst is promoted, and the ORR electrocatalytic activity of the catalyst is enhanced.

In the invention, BPC prepared by adopting the phosphorus source containing four benzene rings shows the best ORR electrocatalytic performance, which is caused by a smoother nano-sheet structure and more hetero-atom doping amount of a sample.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is an SEM image of each product prepared in an example of the present invention, wherein (a) is an SEM image of BPC-1; (b) SEM picture of BPC-2; (c) SEM picture of BPC-3; (d) SEM picture of BPC-4;

in FIG. 2, (a) a TEM image of BPC-1; (c) a TEM image of BPC-2; (e) a TEM image of BPC-3; (g) a TEM image of BPC-4;

(b) HRTEM image of BPC-1; (d) HRTEM image of BPC-2; (f) HRTEM image of BPC-3; (h) HRTEM image of BPC-4.

FIG. 3 is an element map image of each product prepared in an example of the present invention, wherein (a) the element map image of BPC-1; (b) an element mapping image of BPC-2; (c) an element map image of BPC-3; (d) an element map image of BPC-4;

FIG. 4 is a RAMAN map of BPC-1, BPC-2, BPC-3 and BPC-4 prepared in an example of the present invention.

In FIG. 5, (a) is BPC-1, BPC-2, BPC-3 and BPC-4 at N ₂ Cyclic voltammograms measured at a sweep rate of 50 mV/s in saturated (dashed line) and oxygen saturated (solid line) 0.1M KOH solution;

(b) ORR polarization curve in oxygen saturated 0.1M KOH electrolyte at 1600rpm sweep rate of 10 mV/s.

FIG. 6, (a) is the ring-disk current of ORR process of BPC-1, BPC-2, BPC-3 and BPC-4 prepared in the example of the present invention;

(b) According to the corresponding RRDE data, the electron transfer number (n) and the peroxide percentage (% HO) of the sample at different potentials are calculated ₂ ^- ）。

In FIG. 7, (a) RDE polarization curves of BPC-1 before (solid line) and after (dotted line) 25000 cycles of aging experiments scan at potentials in the range of 0.6 to 1.0V (relative to RHE) and at a scan rate of 100 mV/s;

(b) The RDE polarization curve of BPC-2 before (solid line) and after (dotted line) the 25000-turn aging experiment scan at a potential range of 0.6 to 1.0V (relative to RHE) and a scan rate of 100 mV/s.

In FIG. 8, (a) is the RDE polarization curve of BPC-3 before (solid line) and after (dotted line) 25000 aging test scans;

(b) RDE polarization curves before (solid line) and after (dotted line) for BPC-4 scan at 25000 cycles of aging experiments; the sweep potential ranged from 0.6 to 1.0V (relative to RHE) and the sweep rate was 100 mV/s.

In FIG. 9, (a) is a CV curve of BPC-1; (b) is the CV curve of BPC-2; (c) is the CV curve of BPC-3; (d) is the CV curve of BPC-4; CV curve in 0.1M KOH; scanning at scan rates of 5, 10, 25, 50 and 100 mV/s.

In FIG. 10, the current-scan velocity profiles obtained from the 0.91V (relative to RHE) scans of BPC-1, BPC-2, BPC-3 and BPC-4 in 0.1M KOH are at a potential of 0.91V.

In FIG. 11, XPS spectra of (a) C1s peaks of BPC-1, BPC-2, BPC-3 and BPC-4 and (b) hetero atom doping amounts obtained by analysis are plotted against the number of benzene rings in the precursor.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

then stirring at 20-40 ℃ to completely dissolve the phosphorus source precursor and uniformly disperse the phosphorus source precursor;

and then carrying out hydrothermal reaction on the solution, drying the prepared product, and carrying out carbonization treatment to obtain the boron-phosphorus co-doped carbon nanosheet catalyst. The tetraphenylboron compound contains four phenyl-substituted boron anions, is lipophilic, readily soluble in organic solvents, and soluble in ethanol.

In some embodiments, the phosphorus source is methyl triphenyl phosphonium bromide or tetraphenyl phosphonium bromide.

In some embodiments, the phosphorus source precursor is dissolved for a time period of 4 to 6 hours.

In some embodiments, the molar ratio of sodium tetraphenylborate to phosphorus source is 1.8 to 1.2.

In some embodiments, the temperature of the hydrothermal reaction is 160-200 ℃ and the time of the hydrothermal reaction is 4-6h. Preferably, the temperature of the hydrothermal reaction is 170-190 ℃, and the time of the hydrothermal reaction is 4-6h.

In some embodiments, the temperature of the carbonization is 750-850 ℃ and the carbonization time is 1.5-3h. Preferably, the carbonization is in N ₂ Is carried out in an atmosphere.

In a third aspect, the invention provides an application of the boron-phosphorus co-doped carbon catalyst in an electrocatalytic oxygen reduction reaction.

The present invention will be further described with reference to the following examples.

Table 1 experimental main chemicals for each example

TABLE 2 Main instruments and Equipment for the experiment of the examples

Example 1

Synthesis of boron-phosphorus co-doped carbon nanosheet sample 1 (BPC-1)

1.71 g sodium tetraphenylborate is ultrasonically dispersed in a centrifuge tube containing 5 mL ethanol to be a clear solution, then the solution is poured into 60 mL ethanol, 0.90 g phenylphosphorus dichloride is added dropwise, and magnetic stirring is carried out at room temperature for 5 hours, so that the precursor is completely reacted and uniformly dispersed in the solution. The solution was then transferred to a 100 mL hydrothermal reaction kettle and subjected to hydrothermal reaction at 180 ℃ for 5h. After the reaction, the solution was washed with ethanol by centrifugation, and then the sample was dried naturally for use.

Adding the dried material to N ₂ Raising the temperature to 800 ℃ at the temperature raising speed of 4.5 ℃/min in the atmosphere, and carbonizing for 2h in a tube furnace. Then the tube furnace is naturally cooled to the room temperature. The obtained black product was named boron-phosphorus co-doped carbon nanosheet sample 1 (BPC-1).

Example 2

Synthesis of boron-phosphorus co-doped carbon nanosheet sample 2 (BPC-2)

The precursor was changed to 1.71 g sodium tetraphenylborate as the boron source and 1.10 g diphenylphosphine chloride as the phosphorus source, relative to example 1. Other experimental conditions were consistent with BPC-1. The obtained sample is named as boron-phosphorus co-doped carbon nanosheet sample 2 (BPC-2).

Example 3

Synthesis of boron-phosphorus co-doped carbon nanosheet sample 3 (BPC-3)

1.71 g sodium tetraphenylborate and 1.79 g methyl triphenyl phosphonium bromide are respectively ultrasonically dispersed in a centrifuge tube containing 5 mL ethanol to be clear solution, then the solution is poured into 60 mL ethanol, and magnetic stirring is carried out for 5 hours at room temperature, so that the precursor is completely reacted and uniformly dispersed in the solution. The solution was then transferred to a 100 mL hydrothermal reaction kettle and subjected to hydrothermal reaction at 180 ℃ for 5h. After the reaction, the solution is centrifugally cleaned by ethanol, and then the sample is naturally dried for later use.

Adding the dried material to N ₂ The temperature is raised to 800 ℃ at the temperature raising speed of 4.5 ℃/min under the atmosphere, and carbonization is carried out in a tube furnace for 2h. Then the tube furnace is naturally cooled to the room temperature. The obtained black product was named boron-phosphorus co-doped carbon nanosheet sample 3 (BPC-3).

Example 4

Synthesis of boron-phosphorus co-doped carbon nanosheet sample 4 (BPC-4)

The precursor was changed to 1.71 g sodium tetraphenylborate as the boron source and 2.71 g tetraphenylphosphonium bromide as the phosphorus source. Other experimental conditions were consistent with BPC-3. The obtained sample is named as boron-phosphorus co-doped carbon nanosheet sample 4 (BPC-4).

Material characterization

Laser Raman spectroscopy

Raman spectroscopy (Raman spectroscopy) is an analysis method for analyzing a scattering spectrum having a frequency different from that of incident light based on a Raman scattering effect to obtain information on molecular vibration and rotation, and is applied to molecular structure research. The raman spectrometer used in the experiment was a product of Horiba Jobin Yvon of france, which is a LabRAM HR 800 laser confocal micro-raman spectrometer with a wavelength of 514 nm and a working power of 1 mW.

X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) is an X-ray photoelectron spectroscopy method in which a sample is irradiated with X-rays to excite electrons or valence electrons in the inner layer of atoms or molecules in the sample, the energy of the excited photoelectrons is measured, and a photoelectron energy spectrum is plotted with kinetic energy as abscissa and relative intensity as ordinate. And obtaining valence state information of the surface elements of the material by analyzing the spectrogram. An X-ray photoelectron spectrometer model ESCALAB 250Xi, manufactured by Thermo Fisher corporation, USA, was used, with monochromatic Al Ka (1486 eV) as the emission source.

Scanning electron microscope

Scanning Electron Microscopy (SEM) is mainly used to observe the surface morphology of a sample by imaging secondary electron signals. The instrument used was a Hitachi S-4700 scanning electron microscope, a product of Hitachi, japan, with an acceleration voltage of 10 kV.

Transmission electron microscope

Transmission Electron Microscope (TEM) projects an accelerated and focused electron beam onto a sample, and the electron collides with an atom in the sample to change its direction, thereby generating solid angle scattering. Since the magnitude of the scattering angle is related to the density and thickness of the sample, images with different brightness and darkness are formed. The instrument used was from FEI Inc., USA, model Tecnai G2F 20S-Twin, with a working voltage of 200 kV.

The preparation process of the sample comprises the following steps of dispersing a proper amount of the electrocatalyst sample into 1 mL ethanol, ultrasonically dispersing for 15 minutes, transferring a small amount of slurry by using a liquid transfer gun after uniform dispersion, dripping the slurry onto a copper net coated with a carbon support film, and drying under an infrared lamp. Energy spectrum analysis (EDS) and Selected Area Electron Diffraction (SAED) were done simultaneously on transmission electron microscopy.

Testing of Material Properties

Electrode system

All electrochemical tests in the experiment adopt a three-electrode system, and the three-electrode system consists of a working electrode, a reference electrode and a counter electrode. Wherein the working electrode is a glassy carbon electrode covered with a catalyst with the diameter of 5 mm, the reference electrode is an Ag/AgCl electrode (saturated KCl, tianjin Ida), and the counter electrode is a carbon rod.

The preparation process of the working electrode comprises the following steps:

(1) The electrode slurry is prepared by weighing 5 mg catalyst to be tested, grinding the catalyst in an agate mortar uniformly, transferring the powder into a 2 mL microcentrifuge tube, dispersing the powder in 350 mu L of ethanol, and dropwise adding 95 mu L of 0.2 wt% Nafion solution and ultrasonically dispersing for 0.5h until the slurry is uniform.

(2) Cleaning an electrode: the surface of the electrode head was wiped clean with an alcohol cotton ball.

(3) The preparation of the working electrode comprises the steps of sucking 3.5 mu L of electrode slurry by a pipette and dripping the electrode slurry on an electrode head with a clean surface to ensure that the catalyst material is uniformly attached to the surface of the electrode, and naturally drying the electrode for later use.

Cyclic voltammetry test (CV)

Cyclic voltammetry is a commonly used electrochemical test method, which is to control the electrode potential to scan repeatedly in a triangular wave pattern at a certain rate over time, in which the redox reaction alternately occurs on the working electrode during the scanning process, and record the current-potential curve by a computer. The method is mainly used for judging the microscopic reaction process on the surface of the electrode, judging the reversibility of the electrode reaction and the like. The test was performed using a potentiostat (Pine, usa) and CV was mainly used to provide information on the chemical composition of the catalyst surface.

The test method comprises the following steps: 30min N was passed through the electrolyte (0.1M KOH) before each test ₂ To remove dissolved oxygen from the electrolyte. At N ₂ Scanning in the saturated electrolyte at a sweep rate of 50 mV/s in the range of-0.9 to 0V relative to an Ag/AgCl reference electrode until the Cyclic Voltammetry (CV) curve stabilizes, obtaining N ₂ The CV curve of (2). Then, 0.5h O is introduced ₂ So that the electrolyte is in O ₂ Scanning under the same condition under saturated atmosphere to obtain O ₂ CV curve.

Linear scanning test technique (Linear sweep voltametry, LSV)

The linear scanning test technology is to control the electrode potential to carry out single scanning at a certain speed along with time, oxidation or reduction reaction occurs on the working electrode in the scanning process, and a current-potential curve is recorded by a computer. The LSV is mainly used for determining the overpotential of electrocatalytic oxidation or reduction, including the initial potential and the half-wave potential of oxygen reduction reaction.

Before Oxygen Reduction Reaction (ORR) testing, the electrolyte was saturated with oxygen by passing pure oxygen through the electrolyte for 30 min. The linear cyclic voltammograms were then tested at 400, 900, 1600 and 2500 rpm at a sweep rate of 10 mV/s in the potential range of-0.9 to 0V (relative to an Ag/AgCl reference electrode), respectively. In all rotating ring disk tests, the voltage of the ring electrode was constant at 1.5V, so thatEnsuring that the intermediate product produced on the disk electrode is fully oxidized during the reaction process. It is noted that in the data processing following this text, the electrode potentials were normalized, i.e. E in a 0.1M KOH solution _RHE = E _Ag/AgCl + E _{0 Ag/AgCl} + 0.059 pH。

The current density (J) is the saturated oxygen current value minus the saturated N ₂ The current value is divided by the area of the disk electrode or the ring electrode.

Percentage of intermediate produced during ORR (% HO) ₂ ^- ) And the number of transferred electrons (n) is calculated according to the following equations (1) and (2):

(1)

(2)

i in the formula _D A Faraday current that is a disk electrode; I.C. A _R A Faraday current that is a ring electrode; n =0.22, the capture efficiency of the ring electrode.

Accelerated aging test (Accelerated along test, ADT)

The accelerated aging test is a common method for testing the stability of the catalyst, and the basic principle of the accelerated aging test is to perform a multi-turn CV test on a catalyst material in a fixed potential window and observe the activity change condition of the catalyst in a long time. The test method comprises the following steps: CV scans were performed for 25000 cycles at potentials ranging from 0.6 to 1.0V (relative to RHE), after which the material was subjected to an ORR test and the stability of the catalyst was observed compared to the ORR curve before ADT. The experiment was tested using a potentiostat (Pine, usa).

Electrochemical active area test (ECSA)

The electrochemical active area of the catalyst is characterized and calculated by a CV method. When the catalyst is subjected to the CV test, the capacitance of the catalyst gradually increases with the increase of the sweep rate. The electric double layer capacitance of the catalyst is proportional to its corresponding electrochemically active area. In the experiment, under the potential of 0.91V relative to the Ag/AgCl reference electrode, line scanning is carried out at different scanning speeds to obtain a CV curve, and then the relation between the current and the scanning speed is obtained so as to evaluate the ESCA of the catalyst.

Structural characterization of materials

The microscopic morphology and structure of the samples were characterized using SEM and TEM. Through the two characterization methods, the synthesized material can be clearly determined to be of a nanosheet structure. From the SEM image (fig. 1) of the material, it can be clearly observed that as the number of benzene rings in the precursor increases, the area of the synthesized nanosheet increases, and the surface is also flat. The nanosheet structure of the material was further characterized by TEM, with the results shown in figure 2. From TEM images 2a, 2c, BPC-1 and BPC-2 are evident in the nanosheet structure as wrinkles and overlaps. HRTEM FIG. 2b, FIG. 2d show that the BPC-1 and BPC-2 materials are disordered structures. While in fig. 2e and 2g it is clearly observed that BPC-3 and BPC-4 are more flat in their nanosheet structure. HRTEM image 2f, FIG. 2h show that BPC-3 and BPC-4 materials are also disordered structures. As shown in the elemental maps of the four materials (fig. 3a, 3b, 3c, and 3 d), the boron, phosphorus, and carbon elements are uniformly distributed in the material, indicating that the boron and phosphorus elements are doped into the carbon nanoplatelets. Through the structural characterization of the material, the synthesized material tends to be a stable and flat nanosheet structure with the increase of the number of benzene rings in the precursor.

Further investigation of structural defects in the samples was performed using RAMAN, which is shown in figure 4: at 1340 cm ⁻¹ (D band) and 1599 cm ⁻¹ Two distinct signal peaks appear near the (G-band), respectively. Peak intensity ratio of D band and G band peaks (I) _D /I _G ) Generally used to describe the degree of defect in carbon materials. As shown in FIG. 4, I of BPC-1, BPC-2, BPC-3 and BPC-4 _D /I _G 1.13, 1.14, 1.15 and 1.17, respectively; this indicates that as the number of benzene rings in the precursor increases, more defects are generated in the carbon lattice, with BPC-4 being the most defective.

ORR electrocatalytic activity of materials

By ORR to boronAnd evaluating the electrocatalytic performance of the phosphorus co-doped carbon nanosheet. As shown in FIG. 5a, at N ₂ In saturated KOH solution, four materials did not have a reduction peak, whereas in oxygen saturated KOH solution, a significant oxygen reduction peak occurred. For further study and evaluation of the electrocatalytic performance of the four materials, they were subjected to a linear scan test in 0.1M KOH in an oxygen saturated atmosphere with a rotating ring disk electrode rotating at 1600rpm, a potential range of 0.06 to 0.96V (relative to RHE), and a sweep rate of 10 mV/s, and the test results are shown in fig. 5b, which clearly shows that the limiting current densities of the four materials increase with increasing number of benzene rings in the precursor, and that the limiting current density of BPC-4 is maximal, at 5.1mA/cm ² . The ORR onset potentials for BPC-1, BPC-2, BPC-3 and BPC-4 were 0.813,0.840,0.886 and 0.886V (relative to RHE), respectively; the half-wave potentials were 0.659, 0.671,0.675 and 0.675V (relative to RHE), respectively. Wherein BPC-4 exhibits better ORR catalytic activity. The potential range of 0.06 to 0.96 (relative to RHE) calculated from the ring plate current density of FIG. 6a gives the range of intermediates shown in FIG. 6b, with the ranges of BPC-1, BPC-2, BPC-3 and BPC-4 being 47.2-71.0%,48.2-60.9%,29.7-40.9% and 25.2-57.7%, respectively; the number of transferred electrons is 2.61-3.04,2.81-3.04,3.18-3.43 and 2.86-3.50 (FIG. 6 b), which can indicate that the ORR process of BPC-4 is quasi-four electron transfer process.

The stability of the BPC catalyst was next tested using an accelerated aging test. As shown in FIGS. 7 and 8, four materials were scanned at a scan rate of 100 mV/s over a potential range of 0.6-1.0V (relative to RHE). Wherein the half-wave potentials of BPC-3 and BPC-4 are attenuated by 14mV and 9mV, respectively, and the half-wave potentials of BPC-1 and BPC-2 are negatively shifted by 23 mV and 35 mV, respectively, which indicates that BPC-4 has the best ORR stability.

To further understand the number of active sites of the material, the electrochemically active surface area and the double layer capacitance of the material were tested. CV scans at different scan rates were therefore performed and the working electrode required to stabilize for 10 seconds before the next scan could be performed. The test results for the four materials are shown in FIG. 9 according to equation i _c =υC _DL The double electric layer capacitance of the material can be calculatedFurther according to the formula ECSA = C _DL /C _s Obtaining the electrochemically active area of the material, in 0.1M KOH solution, C _s =0.05mF/cm ² The calculation results are shown in fig. 10 and table 1. Wherein the electrochemical active area of BPC-4 is at most 135.4cm ² Thus, BPC-4 is believed to have the most active sites.

TABLE 1C of BPC-1, BPC-2, BPC-3 and BPC-4 _dl And ECSA

Through the analysis, the BPC-4 has the most flat structural morphology, which is beneficial to the contact of materials and substances and exposes the most active sites; and the maximum number of defects is beneficial to the catalyst to adsorb oxygen. Next, the amount of hetero atom doping in the catalyst was analyzed by XPS technique, and the relationship between the catalyst activity and the amount of hetero atom doping and the precursor was examined.

FIG. 11a shows the C1s peak for four materials, with two fitted peaks at 283.4 eV and 285.5 eV binding energies, representing B-C and P-C, respectively, indicating successful intercalation of boron and phosphorus heteroatoms into the carbon material.

TABLE 2 different atom doping levels in BPC-1, BPC-2, BPC-3 and BPC-4

Table 2 shows the contents of different four elements B, P, C and O obtained from the XPS spectrum results of the four samples, and fig. 11b shows the doping amount of hetero atoms in the carbon-based material and discusses the relationship between the number of benzene rings in the precursor and the doping amount of hetero atoms in the carbon-based material. The doping amounts of B and P in BPC can be regulated by using precursors with different numbers of benzene rings, the regulation ranges are 0.24-3.75% (B) and 0.26-1.42% (P), the doping amounts of B and P increase with the number of benzene rings in the precursors, and show a nearly linear growth trend, and the content of B and P is the highest in BPC-4 (3.75% and 1.42%, respectively). Meanwhile, the order of the doping amounts of B and P in the catalyst is consistent with the order of ORR activity. Therefore, the use of precursors with different numbers of benzene rings can easily control the doping amount of the hetero atoms in the carbon-based material, thereby affecting the ORR performance of the catalyst.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a boron-phosphorus co-doped carbon catalyst is characterized by comprising the following steps: the method comprises the following steps:

2. The method for preparing a boron-phosphorus co-doped carbon catalyst according to claim 1, characterized by comprising the following steps: the phosphorus source is methyl triphenyl phosphonium bromide or tetraphenyl phosphonium bromide.

3. The method for preparing a boron-phosphorus co-doped carbon catalyst according to claim 1, characterized by comprising the following steps: the dissolving time of the phosphorus source precursor is 4-6h.

4. The method for preparing a boron-phosphorus co-doped carbon catalyst according to claim 1, wherein: the molar ratio of the sodium tetraphenylborate to the phosphorus source is 1:0.8-1.2.

5. The method for preparing a boron-phosphorus co-doped carbon catalyst according to claim 1, characterized by comprising the following steps: the temperature of the hydrothermal reaction is 160-200 ℃, and the time of the hydrothermal reaction is 4-6h.

6. The method for preparing a boron-phosphorus co-doped carbon catalyst according to claim 5, wherein: the temperature of the hydrothermal reaction is 170-190 ℃, and the time of the hydrothermal reaction is 4-6h.

7. The method for preparing a boron-phosphorus co-doped carbon catalyst according to claim 1, wherein: the carbonization temperature is 750-850 ℃, and the carbonization time is 1.5-3h.

8. The method for preparing a boron-phosphorus co-doped carbon catalyst according to claim 1, wherein: the carbonization is carried out at N ₂ And (3) performing in an atmosphere.

9. A boron-phosphorus co-doped carbon catalyst is characterized in that: prepared by the preparation method of any one of claims 1 to 8.

10. The use of the boron phosphorus co-doped carbon catalyst of claim 9 in an electrocatalytic oxygen reduction reaction.