A boron and nitrogen doped carbon supported copper catalyst, its preparation method and use

Abstract

The application discloses a boron and nitrogen doped carbon loaded copper catalyst and a preparation method and application thereof. The catalyst is prepared by the following steps: treating carbon with excessive concentrated nitric acid, impregnating the treated carbon and copper nitrate at room temperature, grinding the obtained precursor and a nitrogen source and a boron source into powder at room temperature, and calcining the powder at a specific temperature and for a specific time. The catalyst can be applied to electrocatalytic reduction of carbon dioxide to oxygen-containing products. The catalyst mainly induces stronger metal-carbon support interaction by B and N co-doped carbon, improves the average valence state of copper to promote the CO-CO coupling route, effectively stabilizes oxygen-containing intermediates in the reaction process due to the relatively strong oxygen affinity of B, and inhibits the breaking of C-O bonds, so that high activity and high selectivity of ethanol are realized. The catalyst has excellent performance in the reduction of carbon dioxide to ethanol.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrocatalytic carbon dioxide reduction electrode, and particularly relates to a preparation method of carbon-loaded transition metal catalyst and application thereof in promoting the generation of oxygen-containing products. BACKGROUND

[0002] Reducing dependence on fossil fuels and reducing the concentration of CO2 in the atmosphere are global focus issues. To achieve this goal, various measures have been taken to promote CO2 storage and conversion, among which the use of electrocatalytic CO2 reduction (CO2RR) to prepare high-value chemicals (CH3OH, HCOOH, C2H4 and C2H5OH, etc.) is a new method for converting renewable electrical energy into chemical energy stored in fuels, which has attracted widespread attention. To promote the development of CO2RR technology, researchers have developed a series of metal and non-metal catalysts. Among the many metal catalysts, Cu has been widely concerned as the only metal catalyst that can produce C2H4, C2H5OH and CH3COOH and other C2+ products. However, so far, most Cu-based catalysts are more conducive to the production of C2H4 rather than liquid C2+ products. Although a small number of documents have reported that the Faraday efficiency (FE) of C2+ liquid products of oxide-derived Cu catalysts (OD-Cu) can reach 70% at an extremely low overpotential (>-0.3V vs. RHE), the current density is often less than 10mA / cm 2 (Zhou L, Lv R. Rational catalyst design and interface engineering for electrochemical CO2 reduction to high-valued alcohols [J]. Journal of Energy Chemistry, 2022, 70: 310-331). In order to meet the commercial viable current density (>100mA / cm 2)down, the corresponding FE tends to be lower than 40% (Gu J, Liu S, Ni W, et al. Modulating electric field distribution by alkali cations for CO2 electroreduction in strongly acidic medium [J]. Nature Catalysis, 2022, 5(4): 268-276). Combined with the literature analysis of the reasons for low activity and selectivity of C2H5OH, the main sources are as follows: first, HER competitive reaction; second, high coupling energy barrier of *CO-CO, leading to difficult coupling process; finally, in the actual reaction process, C2H4 and C2H5OH share the same reaction intermediate *OCCOH, while the breaking of C-O bond is easier in thermodynamics, leading to easier generation of C2H4 (Li M, Song N, Luo W, et al. Engineering surface oxophilicity of copper for electrochemical CO2 reduction to ethanol [J]. Advanced Science, 2023, 10(2): e2204579).

[0003] To improve the activity and selectivity of C2H5OH, researchers have proposed various strategies, such as catalysts with specific grain boundaries or crystal faces, bimetallic catalysts, molecular catalysts, metal oxide supported catalysts, etc. (Wang X, Wang Z, García de Arquer F P, et al. Efficient electrically powered CO2-to-ethanol via suppression of deoxygenation [J]. Nature Energy, 2020, 5(6): 478-486). For example: Tang et al. constructed Ag-modified Cu2O materials, by introducing CO-producing catalyst Ag to improve the coverage of *CO on the catalyst surface to promote the *CO-CO coupling process. The prepared CuAg catalyst has a C2H5OH FE of 21.0% at -0.71 V vs. RHE, and a partial current density of C2H5OH reaches 214.4 mA / cm 2, which is about 2 times of the catalyst without Ag modification (Tang H, Liu Y, Zhou Y, et al. Boosting the electroreduction of CO2 to ethanol via the synergistic effect of Cu-Ag bimetallic catalysts [J]. ACS Applied Energy Materials, 2022, 5(11): 14045-14052). Gao et al. designed a Cu-based electrocatalyst with abundant step sites, which selectively inhibited the generation of C2H4 by inhibiting the C-O bond rupture of *CH2CHO, thereby promoting the production of alcohol products. Using this catalyst, an alcohol FE of 40.5% and a partial current density of 56.3 mA / cm 2 (Gao H, Zhang G, Cheng D, et al. Steering electrochemical carbon dioxide reduction to alcohol production on Cu step sites [J]. Chinese Journal of Catalysis, 2023, 52: 187-195) were achieved. It can be found that although certain progress has been made in the corresponding research, in most of the research, the current density is still ≤100 mA / cm -2 , and the FE of C2H5OH is still lower than 60%. Therefore, it is still a challenge to develop a Cu-based catalyst that can simultaneously achieve high current density and high selectivity for the generation of C2H5OH. SUMMARY

[0004] The present application aims to solve the technical problem of low reaction activity and selectivity of Cu-based catalysts for the production of C2H5OH, and provides a boron and nitrogen doped carbon supported copper catalyst (Cu@BNC) and its preparation method and application. By means of impregnation and further calcination, B and N co-doped C (BNC) is used to induce stronger metal-carbon support interaction to improve the average valence state of Cu to promote the *CO-CO coupling pathway, and at the same time to improve the dispersion of Cu; secondly, the strong oxygen affinity of B is used to stabilize the oxygen-containing intermediates in the reaction process to inhibit the rupture of C-O bond, so that it exhibits excellent reaction activity and selectivity in the production of C2H5OH from CO2 reduction, and can be applied in the production of C2H5OH from CO2RR.

[0005] To solve the above technical problems, the present application is realized by the following technical solutions:

[0006] A boron and nitrogen doped carbon supported copper catalyst and a method for preparing the same, wherein Cu particles with a particle size of 10-70 nm, preferably 10-36 nm, are uniformly supported on the surface of the catalyst, and the catalyst is prepared according to the following steps:

[0007] Step 1: treating carbon powder with concentrated nitric acid to obtain carbon powder with a defective surface

[0008] In step 1, the carbon powder is ECP-600JD or Cabot VXC 72.

[0009] In step 1, the mass ratio of carbon powder to concentrated HNO3 solution is (0.5-1):100.

[0010] In step 1, the carbon powder is added to the concentrated HNO3 solution at a mass percentage of 65-68 wt%, and an ultrasonic dispersion is obtained; the suspension is refluxed in an oil bath at a temperature of 80-100°C for 3-10 hours; after it is cooled to room temperature of 20-25°C, the solid sample is separated to obtain carbon powder with a defective surface.

[0011] Step 2: uniformly dispersing the carbon powder obtained in step 1 in deionized water to obtain a carbon suspension, continuously dispersing under the condition, and adding copper nitrate solution dropwise; after the addition is completed, the dispersion is continuously carried out at room temperature of 20-25°C, and then the solid sample is collected; the amount of copper nitrate is 100-150% of the mass of the carbon powder.

[0012] In step 2, the dispersion is carried out by mechanical stirring or ultrasonic, such as stirring at a speed of 300-600 rpm, ultrasonic power of 500-1000 w, and time of 6-15 hours, preferably 10-12 hours.

[0013] In step 2, the dropwise addition speed is 0.1-0.5 ml per minute.

[0014] Step 3: calcining the solid sample obtained in step 2 or a mixture thereof, using the following scheme:

[0015] Scheme 1: heating the solid sample obtained in step 2 to 200-300°C at a heating rate of 5-10°C per minute from room temperature of 20-25°C under the protection of a reducing atmosphere, and calcining for 1-2 hours; after natural cooling to room temperature, it is ready.

[0016] Scheme 2: uniformly mixing the solid sample obtained in step 2 with at least one of a nitrogen source and a boron source to obtain a mixture of solid samples, heating to 800-900°C at a heating rate of 5-10°C per minute from room temperature of 20-25°C under the protection of an inert protective atmosphere, and calcining for 1-2 hours; after natural cooling to room temperature, it is ready.

[0017] In step 3, the nitrogen source is melamine or urea, and the boron source is boric acid; the mass ratio of the solid sample to the nitrogen source is (5-10), and the mass ratio of the solid sample to the boron source is (5:2)-(10:1), preferably (5:2)-(4:1).

[0018] In step 3, the inert protective atmosphere is nitrogen, helium or argon.

[0019] In step 3, the reducing atmosphere is hydrogen.

[0020] Application of the catalyst of the present application in the preparation of C2H5OH by CO2RR.

[0021] The catalyst of the present application is sprayed to a gas diffusion electrode (carbon paper) as a working electrode, a Hg / HgO electrode is a reference electrode, and an IrO2 electrode is a counter electrode, which are assembled into an electrochemical cell; CO2 is introduced, and an electrolyte is 1 mol / L of an aqueous KOH solution, and an electrocatalytic reaction is carried out by power supply.

[0022] Further, 0.5-1 mg of the catalyst of the present application is sprayed to each square centimeter of the gas diffusion electrode.

[0023] Compared with the prior art, the Cu@BNC catalyst of the present application obtains a catalyst in which Cu particles are in full contact with BNC, the introduction of the BNC carrier improves the dispersity of the Cu particles, and the Cu particles with a particle size of 10-40 nm are uniformly loaded on the BNC carrier. Meanwhile, the strong interaction between Cu and BNC improves the average valence state of Cu, promotes the CO-CO coupling route, and thus improves the CO2 reduction reaction activity and selectivity.

[0024] The preparation method of the Cu@BNC of the present application uses commonly used conductive carbon black (Cabot VXC 72 or Ketjen black) as a C source and copper nitrate as a copper source, and obtains a Cu@BNC catalyst through impregnation and further calcination. The raw materials required in the preparation process are simple, the preparation method is simple and easy to implement, batch preparation can be realized, and the method has certain industrialization prospects.

[0025] The Cu@BNC catalyst of the present application is used for CO2RR to prepare C2H5OH, the introduction of B and N co-doped C, which strengthens the electron transfer in the reaction process, at the same time, the strong interaction between Cu and BNC improves the average valence state of Cu, promotes the CO-CO coupling pathway; in addition, the introduction of B with strong oxygen affinity stabilizes the oxygen-containing intermediate in the reaction process and inhibits the breaking of C-O bond, so that the Cu@BNC catalyst shows good reaction activity and selectivity in the CO2RR to prepare C2H5OH. At-1.8V vs.RHE, the FE of C2H5OH reaches 68%, and the partial current density of C2H5OH reaches 179mA / cm 2 , which has superior performance in the CO2RR to prepare C2H5OH. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The Raman spectrum of C, BC, NC and BNC obtained in Examples 2, 4, 5 and 6.

[0027] Figure 2 The transmission electron microscope photo and particle size statistical diagram of Cu / C obtained in Example 7.

[0028] Figure 3 The XRD diffraction spectrum of Cu / C, Cu@BNC, Cu / BC and Cu@NC obtained in Examples 7, 12, 16 and 17.

[0029] Figure 4 The transmission electron microscope photo and particle size statistical diagram of Cu / C obtained in Example 10.

[0030] Figure 5 The transmission electron microscope photo and particle size statistical diagram of Cu@BNC obtained in Example 12.

[0031] Figure 6 The transmission electron microscope photo and particle size statistical diagram of Cu@BNC obtained in Example 15.

[0032] Figure 7 The transmission electron microscope photo and particle size statistical diagram of Cu / BC obtained in Example 16.

[0033] Figure 8 The transmission electron microscope photo and particle size statistical diagram of Cu@NC obtained in Example 17.

[0034] Figure 9 The CO2 reduction performance test diagram of C, BC, NC and BNC obtained in Examples 2, 4, 5 and 6 under the conditions of the examples.

[0035] Figure 10 The linear sweep voltammogram of Cu@BNC obtained in Examples 11-13 under the conditions of the examples.

[0036] Figure 11 The graph shows the CO2 reduction performance test results of Cu@BNC obtained in Examples 11-13 under the conditions of the examples.

[0037] Figure 12 The images show the electrochemical impedance spectroscopy and contact angle test results of Cu@BNC obtained in Examples 11-13.

[0038] Figure 13 Linear scan voltammetry plots of Cu / C, Cu@BNC, Cu / BC, and Cu@NC obtained in Examples 7, 12, 16, and 17 under the conditions of the examples.

[0039] Figure 14 The graphs show the CO2 reduction performance of Cu / C, Cu@BNC, Cu / BC, and Cu@NC obtained in Examples 7, 12, 16, and 17 under the conditions of the examples.

[0040] Figure 15 Auger plots of Cu for Cu / C, Cu@BNC, Cu / BC, and Cu@NC obtained in Examples 7, 12, 16, and 17.

[0041] Figure 16 The N1s plots are for Cu@BNC and Cu@NC obtained in Examples 12 and 17.

[0042] Figure 17 The images show in-situ infrared spectra of Cu / C, Cu@BNC, Cu / BC, and Cu@NC obtained in Examples 7, 12, 16, and 17. Detailed Implementation

[0043] The present invention will be further described in detail below through specific embodiments. These embodiments will enable those skilled in the art to have a more comprehensive understanding of the present invention, but will not limit the present invention in any way.

[0044] Preparation of Example 1—C

[0045] Accurately weigh 1 g of C (Ketjen Black) and disperse it in 200 mL of commercially available concentrated HNO3 solution (65-68 wt%), and sonicate for 1 h. Then, reflux in an oil bath at 80 °C for 3 h. After cooling to room temperature, collect the solid sample by centrifugation, wash with ultrapure water until the supernatant is neutral, and dry the resulting black solid sample at 60 °C to obtain C with a defect-rich surface.

[0046] Preparation of Example 2-C

[0047] Accurately weigh 1 g of C (Ketjen Black) into 100 mL of commercially available concentrated HNO3 solution (65-68 wt% mass percent) and sonicate for 1 h. Then, reflux in an oil bath at 100 °C for 9 h. After cooling to room temperature, centrifuge to collect the solid sample and wash with ultrapure water until the supernatant is neutral. Dry the resulting black solid sample at 60 °C to obtain C with surface rich in defects. Figure 1 The Raman spectrum of C obtained in Example 2 is shown in FIG. 1. As can be seen from FIG. 1, the ratio of the D band to the G band (I D :I G ) of C is 1.14.

[0048] Example 3 - Preparation of C

[0049] The difference from Example 2 is that Cabot VXC 72 is used instead of Ketjen Black (ECP-600JD).

[0050] Example 4 - Preparation of BC

[0051] Mix 0.1 g of C obtained in Example 2 with boric acid in a mass ratio of 4:1, then heat in a tube furnace excluding oxygen with inert protection atmosphere of N2 at 80 standard cubic centimeters per minute (seem) continuously, from room temperature 20-25 °C to 800 °C at a heating rate of 5 °C per minute and keep for 1 h to obtain the final BC. Figure 1 The Raman spectrum of BC obtained in Example 4 is shown in FIG. 2. As can be seen from FIG. 2, the ratio of the D band to the G band (I D :I G ) of C is 1.20.

[0052] Example 5 - Preparation of NC

[0053] Mix 0.1 g of C obtained in Example 2 with melamine in a mass ratio of 1:5, then heat in a tube furnace excluding oxygen with inert protection atmosphere of N2 at 80 standard cubic centimeters per minute (seem) continuously, from room temperature 20-25 °C to 800 °C at a heating rate of 5 °C per minute and keep for 1 h to obtain the final NC. Figure 1 The Raman spectrum of NC obtained in Example 5 is shown in FIG. 3. As can be seen from FIG. 3, the ratio of the D band to the G band (I D :I G ) of C is 1.25.

[0054] Example 6 - Preparation of BNC

[0055] The 0.1 g C obtained in Example 2 was mixed with melamine at a mass ratio of 1 :5, and then boric acid was added and mixed uniformly, wherein the mass ratio of C obtained in Example 2 to boric acid was 4:1. Then, the inert protective atmosphere was continuously provided at a rate of 80 standard cubic centimeters per minute (sccm) of N2 in an oxygen-excluded tube furnace, and the temperature was raised from room temperature 20-25 degrees Celsius to 800 degrees Celsius at a rate of 5 degrees Celsius per minute and maintained for 1 h, to obtain the final BNC. Figure 1 The Raman spectrum of the BNC prepared in Example 6 is shown in FIG. 6. As can be seen from FIG. 6, the I D :I G was 1.29.

[0056] Example 7 - Preparation of Cu / C

[0057] (1) 0.1 g of C obtained in Example 2 was added to 30 mL of deionized water, and ultrasonic treatment was performed for 1 h to obtain a C suspension. Then, 10 mL of an aqueous copper nitrate solution (15 mg / mL) was added dropwise to the C suspension under vigorous stirring (stirring speed: 300-600 revolutions per minute), and stirring was performed for 12 h, and then the product was collected by centrifugation and dried at 60 degrees Celsius.

[0058] (2) The obtained powder was placed in an oxygen-excluded tube furnace, a reducing atmosphere was maintained at a flow rate of 30 sccm of H2, and the temperature was raised from room temperature 20-25 degrees Celsius to 200 degrees Celsius at a rate of 10 degrees Celsius per minute and maintained for 1 h. After natural cooling to room temperature, Cu / C was obtained.

[0059] Figure 2 FIG. 7a is a transmission electron microscope (TEM) image of Cu / C prepared in Example 7, and FIG. 7b is a particle size distribution of Cu / C prepared in Example 7. As can be seen from FIG. 7a, Cu particles are uniformly loaded on the surface of C. As can be seen from FIG. 7b, the particle size distribution of Cu is 14-24 nm. Figure 3 FIG. 8 shows the XRD spectrum of Cu / C prepared in Example 7. As can be seen from FIG. 8, in addition to the diffraction peak of C at about 20° (2Theta), the remaining diffraction peaks are completely matched with the standard card of Cu (PDF #04-0836). This indicates that the obtained Cu has good crystallinity.

[0060] Example 8 - Preparation of Cu / C

[0061] The difference from Example 7 is that the C obtained in Example 1 is used instead of the C obtained in Example 2.

[0062] Example 9 - Preparation of Cu / C

[0063] The difference from Example 7 is that the concentration of the aqueous copper nitrate solution used is 10 mg / mL.

[0064] Example 10 - Preparation of Cu / C

[0065] The difference from Example 7 is that the carbon obtained in Example 2 is replaced by the carbon obtained in Example 3. Figure 4 Figure a is a transmission electron microscope image of Cu / C prepared in Example 10, from which it can be seen that Cu particles are uniformly loaded on the surface of C. Figure b is a particle size distribution of Cu / C prepared in Example 10, from which it can be seen that the particle size distribution of Cu is in the range of 20-70 nm.

[0066] Example 11 - Preparation of Cu@BNC

[0067] (1) 0.1 g of C obtained in Example 2 was added to 30 mL of deionized water and ultrasonically treated for 1 h to obtain a C suspension; then 10 mL of an aqueous copper nitrate solution (15 mg / mL) was added dropwise to the C suspension under vigorous stirring (stirring speed: 300-600 revolutions per minute), and stirring was continued for 12 h, after which the product was collected by centrifugation and dried at 60°C.

[0068] (2) The solid powder obtained in step (1) was mixed with melamine and boric acid, the mass ratio of the solid powder obtained in step (1) to melamine being 1:5, and the mass ratio of the solid powder obtained in step (1) to boric acid being 10:1, then a tube furnace was used to heat the mixture from room temperature (20-25°C) to 800°C at a temperature increase rate of 5°C per minute under an inert atmosphere provided by continuously supplying N2 at a rate of 50 standard cubic centimeters per minute (sccm) to exclude oxygen, and the temperature was maintained at 800°C for 1 h, after which the mixture was allowed to cool naturally to room temperature to obtain Cu@BNC.

[0069] Example 12 - Preparation of Cu@BNC

[0070] The difference from Example 11 is that in step (2), the solid powder is mixed with melamine at a mass ratio of 1:5 and with boric acid at a mass ratio of 4:1.

[0071] Figure 5 Figure a is a transmission electron microscope image of Cu@BNC prepared in Example 12, from which it can be seen that Cu particles are uniformly loaded on the surface of C; Figure b is a particle size distribution of Cu@BNC prepared in Example 12, from which it can be seen that the particle size distribution of Cu is in the range of 10-20 nm. Figure 3 Figure contains an XRD spectrum of Cu@BNC prepared in Example 12, from which it can be seen that in addition to the diffraction peak at about 20° (2Theta) which belongs to C, the remaining diffraction peaks are completely matched with the standard card of Cu (PDF #04-0836). This indicates that well-crystallized Cu is obtained.

[0072] Example 13 - Preparation of Cu@BNC

[0073] The difference from Example 11 is that in step (2), the solid powder is mixed with melamine at a mass ratio of 1:5 and with boric acid at a mass ratio of 5:2.

[0074] Example 14 - Preparation of Cu@BNC

[0075] The difference from Example 12 is that in step (2), urea is used instead of melamine and the mass ratio of the solid powder to urea is 1:10.

[0076] Example 15 - Preparation of Cu@BNC

[0077] The difference from Example 12 is that in step (3), the calcination temperature is 900°C and the time is 2h.

[0078] Figure 6 Figure 1 shows the TEM of Cu@BNC prepared in Example 15, from which it can be seen that the Cu particles are uniformly loaded on the surface of C. Figure 2 shows the particle size distribution of Cu@BNC prepared in Example 15, from which it can be seen that the particle size distribution of Cu is 14-24 nm.

[0079] Example 16 - Preparation of Cu / BC

[0080] The difference from Example 12 is that in step (2), no melamine is added.

[0081] Figure 7 Figure 1 shows the TEM of Cu@BNC prepared in Example 15, from which it can be seen that the Cu particles are uniformly loaded on the surface of C. Figure 2 shows the particle size distribution of Cu@BNC prepared in Example 15, from which it can be seen that the particle size distribution of Cu is 14-24 nm. Figure 3 Figure 1 shows the TEM of Cu@BNC prepared in Example 15, from which it can be seen that the Cu particles are uniformly loaded on the surface of C. Figure 2 shows the particle size distribution of Cu@BNC prepared in Example 15, from which it can be seen that the particle size distribution of Cu is 14-24 nm.

[0082] Example 17 - Preparation of Cu / NC

[0083] The difference from Example 12 is that in step (2), no boric acid is added.

[0084] Figure 8 Figure 1 shows the TEM of Cu@BNC prepared in Example 15, from which it can be seen that the Cu particles are uniformly loaded on the surface of C. Figure 2 shows the particle size distribution of Cu@BNC prepared in Example 15, from which it can be seen that the particle size distribution of Cu is 14-24 nm. Figure 3The XRD spectrum of Cu / BC prepared in Example 17 is shown in the figure, from which it can be seen that, in addition to the diffraction peak of C at about 20° (2Theta), the remaining diffraction peaks are completely matched with the standard card of Cu (PDF #04-0836). It is shown that the obtained Cu has good crystallinity.

[0085] Example 18

[0086] The catalysts prepared in Examples 1-17 were subjected to electrocatalytic CO2 reduction performance test.

[0087] The catalysts prepared in Examples 1-17 were sprayed onto carbon paper as working electrode (0.5-1 mg of catalyst was sprayed per square centimeter of electrode), Hg / HgO was reference electrode, and Ti mesh loaded with IrO2 was counter electrode, which were assembled into a flow electrochemical cell; CO2 was continuously introduced into the electrochemical cell, and the electrocatalytic CO2 reduction performance test and electrode stability test were carried out. The electrolyte was 1 mol / L aqueous KOH solution, and the working electrode area was 1 cm 2 . The gas phase products were detected by gas chromatography, and the liquid phase products were detected by liquid chromatography and nuclear magnetic resonance quantitative method.

[0088] The product distribution of 0.5 mg of catalyst prepared in Examples 1-3 at an applied potential of-1.8 V vs. RHE is shown in the following table.

[0089] CO FE (%) [ H2 FE (%) Example 1 1.9 98.1 Example 2 2.3 97.7 Example 3 1.8 98.2

[0090] The product distribution of 1 mg of catalyst prepared in Examples 2, 4, 5 and 6 at-0.8-2 V vs. RHE is shown in the following table. Figure 9 a is the CO2 reduction performance of C prepared in Example 2, and the experimental results show that the product of C catalyst is mainly H2, and a small amount of CO. b is the CO2 reduction performance of BC prepared in Example 4, and the experimental results show that the product of BC catalyst is mainly H2, and a small amount of CO and HCOOH. c is the CO2 reduction performance of NC prepared in Example 5, and the experimental results show that the product of NC catalyst is mainly H2 and CO. d is the CO2 reduction performance of BNC prepared in Example 6, and the experimental results show that the product of BNC catalyst is mainly H2, CO and HCOOH.

[0091] From the above results, it can be found that, compared with undoped C, the introduction of B induces the generation of more CO and HCOOH; the introduction of N element inhibits the generation of H2 and effectively promotes the generation of CO; on BNC, the generation of H2 is further inhibited, and the selectivity of carbon-containing products is further improved.

[0092] The FE of C2H5OH at -1.8 V vs. RHE for the 0.5 mg catalysts prepared in Examples 7-10 are shown in the following table.

[0093] [C2H5OH FE (%)] Example 7 22.9 Example 8 23.7 Example 9 23.1 Example 10 16.1

[0094] As can be seen from the above, compared with Example 7 and Example 9, the change of the amount of copper nitrate has basically no effect on the FE of C2H5OH within a given range. However, when Cabot VXC 72 is used instead of Ketjen black, it can be found that the FE of C2H5OH has a significant decrease, combined with Figure 4 It can be seen that the reason for the decrease in the FE of C2H5OH is mainly due to the significant increase in the particle size of Cu.

[0095] The reaction activity and product distribution of the 1 mg catalysts prepared in Examples 12, 14 and 15 at -1.8 V vs. RHE are shown in the following table. Figure 10 and 11

[0096] Figure 10 Linear sweep voltammetry (LSV) curves of Examples 11-13. In Figure 11 , a is the CO2reduction performance result of Cu@BNC prepared in Example 11, indicating that the FE of C2H5OH at -1.8 V vs. RHE is 52.4%; b is the CO2reduction performance result of Cu@BNC prepared in Example 12, indicating that the FE of C2H5OH at -1.8 V vs. RHE is 68.1%; c is the CO2reduction performance result of Cu@BNC prepared in Example 13, indicating that the FE of C2H5OH at -1.8 V vs. RHE is 28.4%.

[0097] It can be seen that with the increase of the amount of B element, the CO2RR activity shows a trend of first increasing and then decreasing, and the FE of C2H5OH also shows a similar trend. To analyze the reason for this phenomenon, on the one hand, a small amount of B doping can significantly reduce the electron transfer impedance, while too much B will adversely affect the electron conduction in the reaction process (as shown in a of Figure 12 On the other hand, excessive B doping will cause the hydrophobicity of the material surface to decrease significantly, and the decrease of hydrophobicity will cause the electrode surface to be covered by the aqueous solution, resulting in the accumulation of H intermediates on the catalyst surface during the reaction process, promoting the occurrence of HER side reactions (as shown in b of * Figure 12

[0098] The FE of C2H5OH at -1.8 V vs. RHE for the 1 mg catalysts prepared in Examples 12, 14 and 15 are shown in the following table. ​​​

[0099] [C2H5OH FE (%)] Example 12 68.0 Example 14 67.1 Example 15 60.7

[0100] In combination Figure 11 As can be seen from Table b and Table above, changing the loading of the catalyst and the type of nitrogen source has essentially no effect on the FE of C2H5OH. As can be seen from the table, as the calcination temperature is increased, the FE of C2H5OH is slightly reduced. The reaction activity and product distribution of 1 mg of catalyst prepared in Examples 7, 12, 16 and 17 at -0.8 to -2 V vs. RHE are shown in Table and Figure Figure 13 and Figure 14 .

[0101] Figure 13 LSV curves of Examples 7, 12, 16 and 17. Figure 14 Table a shows the CO2RR performance results of Cu / C prepared in Example 7, which indicates that the FE of C2H5OH is 23.7% at -1.8 V vs. RHE; Table b shows the CO2RR performance results of Cu@BNC prepared in Example 12, which indicates that the FE of C2H5OH is 68.0% at -1.8 V vs. RHE; Table c shows the CO2RR performance results of Cu / BC prepared in Example 16, which indicates that the FE of C2H5OH is 29.4% at -1.8 V vs. RHE; Table d shows the CO2RR performance results of Cu@NC prepared in Example 17, which indicates that the FE of C2H5OH is 34.0% at -1.8 V vs. RHE.

[0102] As can be seen from the LSV curves, the CO2RR activity of the catalysts obtained follows the order Cu@BNC > Cu@NC > Cu / BC > Cu / C. As can be seen from the product distribution, the CO2RR products of Cu / C are mainly gaseous products CO and C2H4 and liquid product C2H5OH (shown in Table a). With the introduction of B element, the FE of H2 is slightly reduced, the CO2RR product distribution is changed, the FE of CO and C2H4 is significantly reduced, and the liquid products HCOOH and C2H5OH are improved (shown in Table c). For Cu@NC, the doping of N element significantly inhibits the HER reaction, and the FE of the CO2RR product is significantly improved, but the product distribution is relatively uniform, and the FE of the single product is relatively low (shown in Table d). For Cu@BNC, the generation of H2 is further inhibited, and at the same time, the product distribution also changes very obviously: the generation of CO and C2H4 is significantly inhibited, and the FE of the products HCOOH and C2H5OH is significantly improved (shown in Table b). Figure 14 Figure 14 Figure 14 Figure 14 ​​​The results show that the introduction of B element is more conducive to the formation of liquid products HCOOH and C2H5OH. The results show that the introduction of N element can effectively inhibit the HER reaction, and the introduction of B element is more conducive to the formation of liquid products HCOOH and C2H5OH.

[0103] It can be seen from the Auger spectrum of Cu that with the introduction of B, N and B and N, the valence state of Cu gradually changes from Cu 0 to Cu + ( Figure 15 ). The reason for this phenomenon is mainly that the doping of B and N induces the metal carrier interaction, so that the charge at the interface site between Cu and the B and N doped C carrier is redistributed, thereby affecting the valence state of Cu. In addition, a higher proportion of Cu + means a stronger electronic metal-carrier interaction. Compared with single element doping, B and N co-doping obviously has a higher proportion of Cu + , that is, the order of the strength of the metal-carrier interaction of the four catalysts we prepared is Cu@BNC>Cu@NC>Cu / BC>Cu / C. It can be found that the CO2RR activity order is consistent with the strength of the metal-carrier interaction. In addition, it can be seen from the peak separation results of N1s that compared with pure N doping, the introduction of B induces the formation of more pyridine N species with stronger basicity Figure 16 ), which can effectively strengthen the adsorption of CO2. At the same time, as shown in Figure 17 , the in-situ infrared test diagram of examples 7, 12, 16 and 17, the peak at 2100 cm -1 is the C-O stretching vibration of *CO. The signal at 1650 cm -1 can be attributed to the δ(H-O-H) bending vibration in the interface H2O. In addition, on the surface of the catalyst obtained in example 12, the signal at 1610 cm -1A clear signal was also observed, which can be attributed to the intermediate OCCOH after CO-CO coupling. Compared with the catalysts obtained in examples 7, 16 and 17, CO can be observed in a wider voltage range on the catalyst obtained in example 12, indicating that the catalyst obtained in example 12 is more conducive to the stability of CO. According to the experimental and characterization results, the main reasons for promoting the generation of C2H5OH are as follows: first, in the catalyst obtained in example 12, there are more pyridine N species, which strengthens the adsorption of CO2, increases the local CO2 concentration, and is more conducive to subsequent conversion; on the other hand, the catalyst obtained in example 12 has a stronger metal-C support interaction, which induces the formation of more positive Cu species, which is conducive to the adsorption and stability of CO, and thus more conducive to the subsequent CO-CO coupling process. In addition, due to the relatively strong oxygenophilic property of B, it can effectively stabilize the oxygen-containing intermediates in the reaction process to inhibit the breakage of C-O bond, and individual more conducive to the generation of oxygen-containing products.

[0104] In summary, the boron and / or nitrogen doped carbon supported copper catalyst of the present application exhibits good activity and selectivity for electrocatalytic reduction of CO2 to C2H5OH. At -1.8V vs. RHE, the FE of C2H5OH reached 68%, and the partial current density of C2H5OH reached 179mA / cm 2 The results of in-situ ATR-SEIRAS and electrochemical experiments show that B and N co-doping induces a stronger metal-support interaction, increases the average valence of Cu, and promotes the CO-CO coupling pathway; the introduction of B induces the formation of more pyridine N species, enhances the adsorption of CO2, and enriches the local concentration of reactants; in addition, due to the relatively strong oxygenophilic property of B, it can effectively stabilize the oxygen-containing intermediates in the reaction process to inhibit the breakage of C-O bond, thereby realizing the high activity and high selectivity of the oxygen-containing product C2H5OH.

[0105] According to the process parameters according to the content of the present application, the preparation of the catalyst of the present application can be realized, which shows basically consistent performance with the present application. The above describes the present application by way of example, it should be explained that, without departing from the core of the present application, any simple modification, modification or other equivalent replacement which can not cost creative labor of those skilled in the art falls within the protection scope of the present application.

Claims

1. A boron and nitrogen doped carbon supported copper catalyst characterized in that, The Cu particles with a particle size of 10-70 nm are uniformly loaded on the surface of the catalyst, and are prepared according to the following steps: Step 1: carbon powder is treated with concentrated nitric acid to obtain carbon powder with defects on the surface, and the mass ratio of carbon powder to concentrated HNO3 solution is (0.5-1):100; Step 2: the carbon powder obtained in step 1 is uniformly dispersed in deionized water to obtain a carbon suspension, under continuous dispersion, a copper nitrate aqueous solution is added dropwise, after the dropwise addition is completed, sufficient dispersion is carried out at room temperature 20-25 degrees Celsius, and then the solid sample is collected; the amount of copper nitrate is 100-150% of the mass of the carbon powder; Step 3: the solid sample obtained in step 2 is calcined, and the following scheme is adopted: The solid sample obtained in step 2 is mixed with a nitrogen source and a boron source to obtain a mixture of solid samples, and is heated to 800-900 DEG C at a temperature increasing rate of 5-10 DEG C per minute from room temperature 20-25 DEG C under the protection of an inert protective atmosphere and is kept for 1-2 hours, and then is naturally cooled to room temperature; the nitrogen source is melamine or urea, and the boron source is boric acid; the mass ratio of the solid sample to the nitrogen source is 1:(5-10), and the mass ratio of the solid sample to the boron source is (5:2)-(10:1).

2. The boron and nitrogen doped carbon supported copper catalyst of claim 1, wherein, The particle size of the Cu particles is 10-36 nm.

3. The boron and nitrogen doped carbon supported copper catalyst of claim 1, wherein, In step 1, the carbon powder is Ketjen black or Cabot VXC 72; the carbon powder is added to the concentrated HNO3 solution with a mass percentage of 65-68 wt%, and an ultrasonic dispersion is obtained; the suspension is refluxed in an oil bath at a temperature of 80-100 DEG C for 3-10 hours; After it is cooled to room temperature 20-25 DEG C, the solid sample is separated to obtain carbon powder with defects on the surface.

4. The boron and nitrogen doped carbon supported copper catalyst of claim 1, wherein, In step 2, mechanical stirring or ultrasonic dispersion is used, and the time is 6-15 hours; the dropwise addition rate is 0.1-0.5 mL per minute.

5. The boron and nitrogen doped carbon supported copper catalyst of claim 4, wherein, In step 2, mechanical stirring or ultrasonic dispersion is used, and the stirring speed is 300-600 rpm, the ultrasonic power is 500-1000 w, and the time is 10-12 hours.

6. The boron and nitrogen doped carbon supported copper catalyst of claim 1, wherein, In step 3, the inert protective atmosphere is nitrogen, helium or argon; the reducing atmosphere is hydrogen; the mass ratio of the solid sample to the boron source is (5:2)-(4:1).

7. A process for the preparation of a boron and nitrogen doped carbon supported copper catalyst as claimed in claim 1, characterized in that, The Cu particles with a particle size of 10-70 nm are uniformly loaded on the surface of the catalyst, and are prepared according to the following steps: Step 1: carbon powder is treated with concentrated nitric acid to obtain carbon powder with defects on the surface, and the mass ratio of carbon powder to concentrated HNO3 solution is (0.5-1):100; Step 2: the carbon powder obtained in step 1 is uniformly dispersed in deionized water to obtain a carbon suspension, under continuous dispersion, a copper nitrate aqueous solution is added dropwise, after the dropwise addition is completed, sufficient dispersion is carried out at room temperature 20-25 degrees Celsius, and then the solid sample is collected; the amount of copper nitrate is 100-150% of the mass of the carbon powder; Step 3: the solid sample obtained in step 2 is calcined, and the following scheme is adopted: The solid sample obtained in step 2 is mixed with a nitrogen source and a boron source to obtain a mixture of solid samples, and then heated to 800-900°C at a temperature increasing rate of 5-10°C per minute from room temperature 20-25°C under the protection of inert atmosphere and kept for 1-2 hours, and then naturally cooled to room temperature; the nitrogen source is melamine or urea, and the boron source is boric acid; the mass ratio of the solid sample to the nitrogen source is 1:(5-10), and the mass ratio of the solid sample to the boron source is (5:2)-(10:1).

8. The method of claim 7, wherein the method further comprises the step of: In step 1, the carbon powder is Ketjen black or Cabot VXC 72; the carbon powder is added to a concentrated HNO3 solution with a mass percentage of 65-68wt%, and then ultrasonically dispersed to obtain a suspension; the suspension is refluxed in an oil bath at a temperature of 80-100°C for 3-10 hours; after being cooled to room temperature 20-25°C, the solid sample is separated to obtain the carbon powder with a surface containing defects; in step 2, the dispersion is carried out by mechanical stirring or ultrasonic, the time is 6-15 hours, and the dropping speed is 0.1-0.5ml per minute; in step 3, the inert atmosphere is nitrogen, helium or argon; the reducing atmosphere is hydrogen; the mass ratio of the solid sample to the boron source is (5:2)-(4:1).

9. The method of claim 8, wherein the method further comprises the step of: In step 2, the dispersion is carried out by mechanical stirring or ultrasonic, the stirring speed is 300-600rpm, the ultrasonic power is 500-1000w, and the time is 10-12 hours.

10. Use of the boron and nitrogen-doped carbon-supported copper catalyst according to any one of claims 1-6 in the preparation of C2H5OH by CO2RR.

11. Use according to claim 10, characterized in that, The boron and nitrogen-doped carbon-supported copper catalyst is sprayed onto a gas diffusion electrode as a working electrode, a Hg / HgO electrode is used as a reference electrode, and an IrO2 electrode is used as a counter electrode to assemble into an electrochemical cell; CO2 is introduced, and an aqueous solution of 1mol / L KOH is used as an electrolyte to perform an electrocatalytic reaction by applying electricity.

12. The use according to claim 10, characterized in that, 0.5-1 mg of the boron and nitrogen-doped carbon-supported copper catalyst is sprayed per square centimeter of the gas diffusion electrode.

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