Method for preparing high-performance electron transport self-supporting N-CuxO / CF photoelectric reduction CO2 catalyst

Abstract

The invention relates to a method for preparing a high-performance electron transport self-supporting N-CuxO / CF photoelectric reduction CO2 catalyst. According to the method, foamy copper (CF) serves as a self-supporting substrate, Cu (OH) 2 nanowires grow on the surface of the foamy copper (CF) through an impregnation method, then CuxO with a narrower band gap is obtained through roasting in air, and finally the CuxO and urea are roasted in the nitrogen atmosphere to obtain the nitrogen-doped CuxO self-supporting material. The obtained material is used as a catalyst for photoelectric reduction of CO2. The CO2 reduction efficiency is effectively improved, and the operation process is simplified.

Description

Technical Field

[0001] The present invention relates to a method for preparing a nitrogen-doped Cu x O / CF catalyst material with high efficient electron transport ability, belonging to the technical field of functional materials. Background Art

[0002] In recent years, the excessive consumption of fossil fuels has led to excessive CO2 emissions, triggering a very serious greenhouse effect. This has caused concerns about global warming in human society. Therefore, how to efficiently reduce CO2 has become a popular research direction at present. Among various methods for reducing CO2, photoelectrochemical reduction of CO2 (PEC) is considered an efficient method. The photoelectrocatalytic technology combines the advantages of photocatalysis and electrocatalysis, effectively solving the kinetic barriers and activity problems in the catalytic process.

[0003] CuO and Cu2O semiconductors have narrow bandgaps of 1.3 and 2.0 eV respectively, which enables them to effectively capture visible light energy. In addition, the sufficiently negative conduction band (CB) positions and the ability to effectively adsorb CO2 make these materials efficient photoactive catalysts for CO2 reduction. In recent years, copper-based catalysts have experienced rapid development, evolving from the initial pure copper oxides (CuO, Cu2O) to the current multi-component copper oxides and copper sulfides, as well as copper-based composite materials. However, copper-based catalysts also face common challenges, such as the low electron transfer efficiency of cathode materials. To solve these problems, various solutions have been proposed. Wang et al. (https: / / doi.org / 10.1016 / j.apcatb.2022.121616) obtained Cu2O by electrodeposition on conductive glass (FTO), dried it, calcined it at 500 °C to obtain CuO, and then calcined CuO at 400 °C for different times under a N2 gas flow using a urea treatment process to obtain CuNx / CuO catalysts. However, due to the relatively smooth surface of the conductive glass, this limits the adhesion ability of cuprous oxide, resulting in poor uniformity and compactness of the deposition layer, and there is no synergistic effect between the conductive substrate and the catalyst, and the interfacial charge transfer efficiency will also decrease. Therefore, it is of great significance to develop a catalyst that simultaneously has strong CO2 adsorption ability and high electron migration efficiency. Summary of the Invention

[0004] To make up for the above deficiencies, the present invention provides a method for preparing a nitrogen-doped Cu x O catalyst material. This method uses copper foam (CF) as a self-supporting substrate, grows Cu(OH)2 nanowires on its surface by the impregnation method, and then obtains Cu x O with a narrower bandgap by calcination in air, and finally obtains nitrogen-doped Cu xSelf-supporting material. The present invention effectively improves the CO2 reduction efficiency and simplifies the operation process.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing a high-performance electron-transporting self-supporting N-Cu x O / CF photocatalytic reduction of CO2 catalyst, the method comprising the following steps:

[0007] (1) Immerse the pretreated copper foam in a mixed solution of sodium hydroxide and ammonium persulfate for 20-40 min, take it out and wash it to obtain copper foam loaded with Cu(OH)2 / CF;

[0008] Among them, in the mixed solution, the concentration of sodium hydroxide is 1.8-2.2 M; the concentration of ammonium persulfate is 0.1-0.15 M; for every 2 cm 2 The required mixed solution for the size of copper foam is 10-20 mL;

[0009] The pretreatment is ultrasonic cleaning in dilute hydrochloric acid, ethanol and water in sequence.

[0010] (2) Place the copper foam loaded with Cu(OH)2 / CF in a muffle furnace and calcine it at 280-320 °C for 3-4 h in an air atmosphere to obtain a Cu x O / CF catalyst;

[0011] (3) Place the nitrogen source at the upper air inlet of the tubular furnace, place the Cu x O / CF in the middle of the tubular furnace, the distance between the nitrogen source and the Cu x O / CF is 4-5 cm, control the nitrogen gas flow rate, after aerating for 30-60 min, heat up to 300-500 °C at a heating rate of 3-5 °C / min and calcine for 2-3 h to finally obtain nitrogen-doped Cu x O / CF catalyst;

[0012] Among them; for every 2 cm 2 Cu x O / CF catalyst is placed with 0.005-0.03 g of nitrogen source; 1.5 < x < 2;

[0013] The nitrogen gas flow rate is 60-70 mL / min;

[0014] The nitrogen source is urea or melamine, preferably urea;

[0015] The application of the nitrogen-doped Cu x O / CF material as a catalyst for photocatalytic reduction of CO2.

[0016] Specifically, it includes the following steps. In an H-type reactor, using nitrogen-doped Cux O serves as the working electrode, the platinum electrode serves as the counter electrode, Ag / AgCl (saturated KCl) serves as the reference electrode, 0.1 - 0.2 M NaHCO3 serves as the electrolyte, and the light intensity is 100 - 120 mW / cm 2 Before the reaction, CO2 is introduced for half an hour to exhaust the air in the system. After sealing, reduction is carried out for 2 - 4 h under an external bias voltage of -1.3 to -1.5 V vs Ag / AgCl to obtain the reduction products CO and H2.

[0017] The essential features of the present invention are as follows:

[0018] The present invention uses Cu x O / CF as the precursor. Utilizing the reducing gas ammonia generated during the thermal decomposition of the nitrogen source, the ratio of Cu + / Cu° active sites is regulated through gradient reduction, increasing the oxygen vacancies of the catalyst. At the same time, it also promotes the formation of N - Cu bonds, reduces the resistance, and improves the electron migration efficiency, thereby improving the catalytic performance from two aspects;

[0019] Its mechanism is as follows: The innovation of the N - doped Cu x O / CF system is reflected in the combination of the interface collaborative design of the substrate - catalyst and the dynamic phase transition regulation technology: 1. A metal - semiconductor interface is formed between the copper substrate and the N - doped Cu x O material, and its Schottky barrier effectively promotes the separation of photo - generated electron - hole pairs; 2. The decomposition of urea or melamine will reduce Cu 2+ to Cu + through gradient reduction, and then reduce Cu + to Cu. By changing the calcination temperature of the nitrogen source, the ratio of Cu + / Cu° active sites, especially the proportion of the Cu2O(111) phase plane, is regulated to improve the activity of the catalyst. 3. The Cu2O(111) crystal plane naturally has a relatively high oxygen vacancy concentration, and these vacancies can serve as reaction active sites to promote nitrogen doping and subsequent catalytic reactions. This crystal plane is prone to form a hydroxyl (-OH) coverage layer during the reaction, inhibiting side reactions (such as H2 generation), enhancing selectivity, and moreover, appropriate nitrogen doping can adjust the electronic structure of Cu2O and stabilize the (111) crystal plane.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. Copper foam is not only the raw material of the catalyst, providing the required Cu, but also the conductive substrate of the photoelectric cathode. Growing the Cu x O catalyst directly on the copper foam enables the copper substrate and Cu xA metal-semiconductor interface is formed between the catalysts, and its Schottky barrier effectively promotes the separation of photo-generated electron-hole pairs, which not only avoids the use of binders but also can greatly improve the charge transfer efficiency between the catalyst and the substrate, thereby reducing the resistance of the reaction system.

[0022] 2. By utilizing the differences in the thermal decomposition products of nitrogen sources at different temperatures and the differences in product distributions at different heating rates, the degree of redox reaction on the catalyst surface is regulated, and the ratio of Cu + / Cu° active sites is regulated, effectively improving the oxygen vacancy concentration on the material surface, increasing it from 35.44% of Cu x O to 49.62%, and improving the selectivity for CO2.

[0023] 3. In the present invention, by controlling the amount of urea and the temperature, the degree of N doping on the material surface is regulated, greatly reducing the resistance of the catalyst, improving the electron transport efficiency and the utilization rate of light. The photocurrent increases from 0.35 mA·cm x of Cu -2 O to 1.05 mA·cm -2 .

[0024] 4. In the present invention, a higher oxygen vacancy concentration, more Cu2O(111) crystal planes and a suitable ratio of Cu + / Cu° active sites are effectively formed on the catalyst surface by chemical nitridation treatment. Using the prepared catalyst as a photocathode to directly reduce CO2, with an external bias of -1.5 V vs Ag / AgCl, an electrolyte of 0.1 M NaHCO3, a light intensity of 120 mW / cm 2 , reacting at room temperature for 3 h, the H2 production rate is 107.52 μmol·cm -2 ·h -1 , the CO production rate is 58.72 μmol·cm -2 ·h -1 , and the molar ratio of H2 to CO is 1.83. Compared with the Cu x O / CF catalyst, the CO production rate is increased by 257%, and the selectivity is also greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 are scanning electron microscope pictures of the samples obtained in Examples 1 and 2; among them, Figure 1 (a) is a picture of the Cu x O / CF sample, Figure 1 (b) is a picture of the N 0.01 -Cu x O / CF sample;

[0026] Figure 2 are the Cu obtained in Examples 1, 2, and 3x O / CF, N 0.01 -Cu x O / CF and N 0.01 -Cu x XRD image of the O(400℃) / CF sample;

[0027] Figure 3 is the N obtained in Example 2 0.01 -Cu x XPS image of the O / CF sample; among them, Figure 3 (a) is the O1s spectrum, Figure 3 (b) is the N1s spectrum;

[0028] Figure 4 is the Cu obtained in Examples 1 and 2 x O / CF, N 0.01 -Cu x Electrochemical impedance of the O / CF sample;

[0029] Figure 5 is the Cu obtained in Examples 1 and 2 x O / CF, N 0.01 -Cu x Photocurrent image of the O / CF sample. Detailed implementation mode

[0030] To further illustrate the present invention, the following examples are used for detailed description below. The experimental raw materials used in the following examples of the present invention are all general commercially available products. Among them, the copper foam was purchased from Suzhou Keshenghe Metal Materials, with a specification of 100*100*1.5mm and a pore density of 130ppi.

[0031] Example 1:

[0032] Cut the copper foam into pieces of 1*2*0.15 cm in size. First, ultrasonically clean it in 0.2 M dilute hydrochloric acid for 10 min, then ultrasonically clean it in absolute ethanol for 15 min, and finally ultrasonically clean it in deionized water for 10 min to remove surface oil and oxides. Prepare a mixed solution containing 20 mL of 2 M NaOH and 0.1 M ammonium persulfate. After stirring evenly, place two pieces of the cleaned copper foam flat in it. After standing for 20 min, wash it with deionized water and ethanol to obtain Cu(OH)2 / CF. After drying, raise the temperature to 300 °C at a heating rate of 5 °C / min in an air muffle furnace, and keep it warm for 3 h to obtain 2 pieces of Cu x O / CF.

[0033] It can be seen from Figure 1 (a) that some curved Cu x O nanowires have grown on the surface of the copper foam; it can be seen from XRD( Figure 2 ) that Cux The O contains monovalent and divalent copper, and it can be roughly concluded that the proportion of monovalent copper is higher, so 1.5 < x < 2 is obtained.

[0034] Example 2:

[0035] Place 1 piece of Cu x O / CF obtained in Example 1 in the middle of the tubular furnace, and place 10 mg of urea at the air inlet above Cu x O / CF (the urea is 4.5 cm away from the upper end of the copper foam), introduce nitrogen for 30 min (flow rate is 65 mL / min) to exhaust the air in the tubular furnace, heat it up to 450 °C at a heating rate of 4.5 °C / min, keep it warm for 2 h, take it out after cooling, and obtain nitrogen-doped Cu x O material, denoted as N 0.01 -Cu x O / CF.

[0036] From Figure 1 (b), it can be seen that the surface of the Cu x O nanowires is wrapped by an amorphous dense layer, which may be due to the formation of the Cu-N complex. From Figure 3 (b), it can be seen that N is successfully doped into the Cu x O material. From the attached Figure 4 It can be seen that after N doping, the resistance is greatly reduced, and the charge transfer ability of the catalyst is greatly enhanced. This is the main reason for the doubling of the photocurrent of N 0.01 -Cu x O / CF. The photocurrent increases from 0.35 mA·cm x of Cu -2 O to 1.05 mA·cm -2 (attached Figure 5 ). Through XRD (attached Figure 2 ), it can be seen that compared with Cu x O, the characteristic peak of monovalent copper of N 0.01 -Cu x O / CF is more obvious. This is because the reducing gas (such as NH3) generated during the thermal decomposition of urea undergoes a redox reaction with the surface of the metal oxide, which also leads to a higher oxygen vacancy concentration in N 0.01 -Cu x O / CF, increasing from 35.44% of Cu x O to 49.62% ( Figure 3 a).

[0037] Example 3:

[0038] Place the Cu x O / CF obtained in Example 1 in the middle of the tubular furnace, and place 10 mg of urea on the Cux At the air inlet above O / CF, maintain a spacing of 4.5 cm, introduce nitrogen for 30 min to exhaust the air in the tube furnace, keep the nitrogen flow rate at 65 mL / min, heat up to 400 °C at a heating rate of 4 °C / min, hold for 2 h, take out after cooling, and obtain nitrogen-doped Cu x O material, denoted as N 0.01 -Cu x O(400 °C) / CF.

[0039] It can be seen that by adjusting the calcination temperature, the intensity of the Cu2O(111) crystal plane of the material decreases significantly compared with Example 2. Figure 2

[0040] Example 4:

[0041] Place the Cu x O / CF obtained in Example 1 in the middle of the tube furnace, place 10 mg of melamine (MA) at the air inlet above Cu x O / CF, maintain a spacing of 4.5 cm, introduce nitrogen for 30 min to exhaust the air in the tube furnace, keep the nitrogen flow rate at 65 mL / min, heat up to 450 °C at a heating rate of 4.5 °C / min, hold for 2 h, take out after cooling, and obtain nitrogen-doped Cu x O material, denoted as N 0.01 -Cu x O / CF(MA).

[0042] Example 5 (application example):

[0043] In an H-type reactor, use the Cu x O / CF obtained in Example 1 as the working electrode, a platinum electrode as the counter electrode, Ag / AgCl (saturated KCl) as the reference electrode, 0.1 M NaHCO3 as the electrolyte, provide illumination with a 300 W xenon lamp (wavelength ≥ 320 nm), and the light intensity is 120 mW / cm 2 , before the reaction, introduce CO2 for half an hour to exhaust the air in the system, seal it, and reduce it for 3 h under an external bias voltage of -1.5 V vs Ag / AgCl. Extract the upper gas and analyze it in a gas chromatograph. The hydrogen production rate of the reduction product is 85.35 μmol·cm -2 ·h -1 , the CO production rate is 22.83 μmol·cm -2 ·h -1 , and the molar ratio of H2 to CO is 3.74.

[0044] Example 6:

[0045] Using the N 0.01 -Cu x obtained in Example 2The O / CF serves as the working electrode, the platinum electrode as the counter electrode, the Ag / AgCl (saturated KCl) as the reference electrode, 0.1 M NaHCO3 as the electrolyte, and illumination is provided by a 300 W xenon lamp (wavelength ≥ 320 nm) with a light intensity of 120 mW / cm 2 , before the reaction, CO2 is introduced for half an hour to exhaust the air in the system. After sealing, reduction is carried out for 3 h under an external bias voltage of -1.5 V vs Ag / AgCl. The yield of the reduction product H2 is 107.52 μmol·cm -2 ·h -1 , the yield of CO is 58.72 μmol·cm -2 ·h -1 , and the molar ratio of H2 to CO is 1.83.

[0046] It is necessary to note that the above embodiments are only some representative specific cases of the technology of the present invention, and are not limitations on the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0047] Matters not covered by the present invention are well-known technologies.

Claims

1. A method for preparing high-performance electron transport self-supporting N-Cu x The method of O / CF photoelectric reduction of CO2 catalyst is characterized by: The method comprises the following steps: (1) soaking the pretreated copper foam in a mixture of sodium hydroxide and ammonium persulfate for 20 to 40 minutes, taking it out and washing it to obtain a copper foam loaded with Cu(OH)2 / CF; Wherein, in the mixed solution, the concentration of sodium hydroxide is 1.8-2.2M; the concentration of ammonium persulfate is 0.1-0.15M; (2) The copper foam loaded with Cu(OH)2 / CF was placed in a muffle furnace and calcined at 280-320°C for 3-4 h in an air atmosphere to obtain Cu x O / CF; (3) Place the nitrogen source at the upwind side of the tube furnace. x O / CF is placed in the middle of the tube furnace, and the nitrogen source and Cu x The distance between O / CF is 4-5 cm, the nitrogen flow rate is controlled, and after ventilation for 30-60 min, the temperature is raised to 300-500 °C at a heating rate of 3-5 °C / min and calcined for 2-3 h to finally obtain nitrogen-doped Cu x O / CF catalyst; Among them; every 2cm 2 Cu x O / CF catalyst was placed with 0.005-0.03 g nitrogen source; The nitrogen source is urea or melamine.

2. Preparation of high performance electron transport self-supporting N-Cu as claimed in claim 1 x The method of O / CF photoelectric reduction of CO2 catalyst is characterized by: The pretreatment is ultrasonic cleaning in dilute hydrochloric acid, ethanol and water in sequence.

3. The preparation of high performance electron transport self-supporting N-Cu as claimed in claim 1 x The method of O / CF photoelectric reduction of CO2 catalyst is characterized by: The nitrogen flow rate is 60-70 mL / min.

4. The method for preparing a high performance electron transport self-supporting N-Cu x The method of O / CF photoelectric reduction of CO2 catalyst is characterized by: Every 2cm 2 The amount of mixed solution required for different sizes of foam copper is 10 to 20 mL.

5. Nitrogen-doped Cu prepared by the method of claim 1 x The application of O / CF materials is characterized by: Used as a catalyst for photoelectric reduction of CO2.

6. The use according to claim 5, characterized in that: The steps include: in an H-type reactor, Cu is doped with nitrogen x O is the working electrode, platinum electrode is the counter electrode, Ag / AgCl is the reference electrode, 0.1-0.2 M NaHCO3 is the electrolyte, and the light intensity is 100-120 mW / cm 2 Before the reaction, CO2 was introduced for half an hour to exhaust the air in the system. After being sealed, the system was reduced for 2 to 4 hours under an external bias voltage of -1.3 to -1.5 V vs Ag / AgCl to obtain the reduction products CO and H2.

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