Photoelectrochemical electrode and preparation method thereof, photoelectrochemical reaction device and preparation method of urea

Abstract

The present invention relates to a field of photoelectrochemical technology, and in particular to a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea. The photoelectrochemical electrode comprises a semiconductor light-absorbing substrate, an electron transport layer and a catalytic layer; the electron transport layer is located on the semiconductor light-absorbing substrate, and the catalytic layer is located on the electron transport layer; the material of the catalytic layer comprises a transition metal and nitrogen co-doped carbon composite material; the transition metal is selected from any two of iron, cobalt, manganese, nickel, copper and zinc. The photoelectrochemical electrode provided by the present invention can efficiently complete the photoelectrochemical reaction.

Description

Technical Field

[0001] The invention relates to the technical field of photoelectrochemical technology, and in particular to a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea. Background Art

[0002] Solar energy is a renewable energy source. Among the many renewable energy sources, solar energy has attracted much attention from researchers due to its abundant, clean and safe characteristics. Solar energy can be used in two ways: photothermal conversion and photoelectric conversion. With the decreasing fossil fuels, solar energy has become an important part of human energy and is constantly developing. Although the energy radiated by the sun to the earth's atmosphere is only 1 / 2.2 billion of its total radiation energy, it is as high as 173,000TW, which means that the energy radiated by the sun to the earth every second is equivalent to 5 million tons of coal, and the energy radiated to the earth every second is 1.465×10 14 Coke. The wind energy, water energy, ocean temperature difference energy, wave energy and biomass energy on the earth all come from the sun. Even the fossil fuels on the earth (such as coal, oil, natural gas, etc.) are fundamentally solar energy stored since ancient times, so the scope of solar energy in a broad sense is very large. However, due to the instantaneous and intermittent problems of solar energy and the existence of existing large-scale chemical fuel basic application facilities, simply using solar energy for power generation cannot meet the purpose of maximizing natural and social resources. Converting solar energy into chemical fuels that are easy to store, transport and use may be an effective supplementary route.

[0003] One of the limiting steps in utilizing solar energy is efficient photoelectrochemical electrodes, which affect the application scope and market prospects of solar energy resources. Summary of the invention

[0004] Based on this, the present invention provides a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea. The provided photoelectrochemical electrode can efficiently complete the photoelectrochemical reaction.

[0005] The first aspect of the present invention provides a photoelectrochemical electrode, and its technical solution is as follows:

[0006] A photoelectrochemical electrode comprises a semiconductor light-absorbing substrate, an electron transport layer and a catalytic layer;

[0007] The electron transport layer is located on the semiconductor light-absorbing substrate, and the catalytic layer is located on the electron transport layer;

[0008] The material of the catalytic layer includes a transition metal and nitrogen co-doped carbon composite material;

[0009] The transition metal is selected from any two of iron, cobalt, manganese, nickel, copper and zinc.

[0010] The second aspect of the present invention provides a method for preparing a photoelectrochemical electrode, and its technical solution is as follows:

[0011] A method for preparing a photoelectrochemical electrode comprises the following steps:

[0012] Providing a semiconductor light-absorbing substrate;

[0013] forming an electron transport layer on the semiconductor light-absorbing substrate by magnetron sputtering;

[0014] The slurry containing the transition metal and nitrogen co-doped carbon composite material is coated on the electron transport layer and dried to form the catalytic layer.

[0015] The third aspect of the present invention provides a photoelectrochemical reaction device, and its technical solution is as follows:

[0016] A photoelectrochemical reaction device comprises a working electrode compartment and a counter electrode compartment; the working electrode compartment and the counter electrode compartment are connected, and a proton conductive cation exchange membrane is provided between them for spacing;

[0017] The working electrode compartment is provided with a working electrode, a reference electrode, an air inlet and an air outlet, the working electrode is as described above, and the reaction gas entering from the air inlet can pass through the working electrode and be discharged from the air outlet;

[0018] The counter electrode compartment is provided with a counter electrode.

[0019] The fourth aspect of the present invention provides a method for preparing urea, and its technical scheme is as follows:

[0020] A method for preparing urea, using the above-mentioned photoelectrochemical reaction device, comprises the following steps:

[0021] Adding an electrolyte comprising nitrate ions to the working electrode compartment and the counter electrode compartment;

[0022] Introducing carbon dioxide from the air inlet;

[0023] The working electrode, the reference electrode and the counter electrode are electrically connected to the electrochemical workstation and the power is turned on;

[0024] · illuminating the working electrode;

[0025] On the surface of the working electrode, the carbon dioxide and the nitrate ions undergo a photoelectrocatalytic coupling reaction to prepare urea.

[0026] Compared with the traditional solution, the present invention has the following beneficial effects:

[0027] The photoelectrochemical electrode of the present invention comprises a semiconductor light-absorbing substrate, an electron transport layer located on the semiconductor light-absorbing substrate, and a catalyst layer located on the electron transport layer, wherein the semiconductor light-absorbing substrate can generate carriers (electrons and holes) under light illumination, and the electron transport material can block holes and transmit electrons to the catalyst layer, while playing a role in protecting the semiconductor light-absorbing substrate. The catalyst layer receives electrons, plays a role in adsorbing reactants, reducing the reaction energy barrier, and catalyzing the photoelectrochemical reaction. The photoelectrochemical electrode provided by the present invention can efficiently catalyze the photoelectrochemical reaction.

[0028] The photoelectrochemical electrode of the present invention can cause carbon dioxide and nitrate ions to undergo photoelectrocatalytic coupling reaction to prepare urea, and the urea yield can reach 10 mg·h -1 cm -2 ~200mg·h -1 cm -2 , the Faradaic efficiency can reach 10% to 60%, and the reaction can run stably for more than 300 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application and to more completely understand the present application and its beneficial effects, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0030] Figure 1 The schematic diagram of the process for preparing the photoelectrochemical electrode of Example 1;

[0031] Figure 2 is a morphology diagram of the photoelectrochemical electrode of Example 1;

[0032] Figure 3 is a schematic structural diagram of the photoelectrochemical reaction device of Example 1;

[0033] Figure 4 The figure is a comparison chart of the yield and Faraday efficiency of urea in Example 1, Example 2 and Example 3;

[0034] Figure 5 The figure is a comparison chart of the yield and Faraday efficiency of urea in Example 2 and Example 4;

[0035] Figure 6 The figure is a comparison chart of the urea yield and Faraday efficiency results of Example 2, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with specific embodiments. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0038] the term

[0039] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0040] In the present invention, the selection range involving "and / or", "or / and", and "and / or" includes any one of two or more related listed items, and also includes any and all combinations of related listed items, and the arbitrary and all combinations include any combination of two related listed items, any more related listed items, or all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that the technical solution undoubtedly includes technical solutions that are all connected by "logical and", and undoubtedly includes technical solutions that are all connected by "logical or". For example, "A and / or B" includes three parallel solutions of A, B and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, the technical solution that is all connected by "logical OR"), and also includes any and all combinations of A, B, C, and D, that is, the combination of any two or any three of A, B, C, and D, and also includes the combination of four of A, B, C, and D (that is, the technical solution that is all connected by "logical AND").

[0041] In the present invention, "plurality", "multiple", "multiple times", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0042] In the present invention, “preferred”, “better”, “more preferred” and “suitable” are only used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute limitations on the scope of protection of the present invention.

[0043] In the present invention, the terms “further”, “furthermore”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present invention.

[0044] In the present invention, "optionally", "optional" and "optional" refer to optional, that is, to any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0045] In the present invention, in the "first aspect", "second aspect", "third aspect", "fourth aspect", etc., the terms "first", "second", "third", "fourth", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0046] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0047] In the present invention, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0048] The temperature parameters in the present invention, if not specifically limited, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the precision range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0049] In the present invention, when it comes to percentage content, unless otherwise specified, for solid-liquid mixing and solid-solid mixing, it refers to mass percentage, and for liquid-liquid mixing, it refers to volume percentage.

[0050] In the present invention, when it comes to percentage concentration, unless otherwise specified, it refers to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of the component.

[0051] In the present invention, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage.

[0052] The present invention provides a photoelectrochemical electrode, which comprises a semiconductor light-absorbing substrate, an electron transport layer and a catalytic layer;

[0053] The electron transport layer is located on the semiconductor light-absorbing substrate, and the catalytic layer is located on the electron transport layer;

[0054] The material of the catalytic layer includes a transition metal and nitrogen co-doped carbon composite material;

[0055] The transition metal is selected from any two of iron, cobalt, manganese, nickel, copper and zinc.

[0056] The semiconductor light-absorbing substrate can generate carriers (electrons and holes) under light, and the electron transport material can block holes and transmit electrons to the catalyst layer, while protecting the semiconductor light-absorbing substrate. The catalyst layer receives electrons, adsorbs reactants, reduces the reaction energy barrier, and catalyzes the photoelectrochemical reaction. The photoelectrochemical electrode provided by the present invention can efficiently catalyze the photoelectrochemical reaction.

[0057] Optionally, the semiconductor light-absorbing substrate may be a p-type silicon substrate or an n+p-type silicon substrate, preferably an n+p-type silicon substrate, which is more conducive to absorbing photons and generating photocurrent.

[0058] Optionally, the semiconductor light-absorbing substrate has a porous structure. Preferably, the aperture of each pore is independently 20nm to 50nm, and the depth of each pore is independently 50nm to 200nm. The porous structure is conducive to zero-scattering full absorption of visible light and improves the saturation photocurrent of the photoelectrochemical electrode.

[0059] Optionally, the electron transport layer has a thickness of 5 nm to 10 nm.

[0060] Optionally, the electron transport layer is light-transmissive.

[0061] Optionally, the material of the electron transport layer is an amorphous structure.

[0062] Optionally, the energy band gap of the material of the electron transport layer is greater than 3.2 eV.

[0063] Optionally, the material of the electron transport layer is a metal oxide. Preferably, the metal oxide is selected from TiO2, ZrO2 or CrO2.

[0064] The electron transport layer has good optical properties, electrical properties and corrosion resistance, and provides good visible light transmittance and electron transport properties while maintaining a stable photoelectric reaction.

[0065] In a preferred embodiment, the transition metal elements are iron and nickel.

[0066] In a preferred embodiment, the transition metal elements are iron and copper.

[0067] Optionally, the loading of the catalytic layer is 10 μg cm -2 ~1000μg·cm -2 .

[0068] Optionally, the method for preparing the transition metal and nitrogen co-doped carbon composite material comprises the following steps:

[0069] In the presence of a catalyst, 2,6-diacetylpyridine and an amino-containing heterocyclic compound undergo a Schiff base condensation reaction to form an iminopyridine ligand polymer;

[0070] Mixing the iminopyridine ligand polymer and a transition metal salt to coordinate and form a polymer complexing metal ions;

[0071] The polymer complexed with metal ions is thermally cracked to prepare a transition metal and nitrogen co-doped carbon composite material.

[0072] Optionally, the catalyst is selected from one or more of formic acid, acetic acid and oxalic acid.

[0073] It is understood that the Schiff base condensation reaction is carried out under the protection of an inert gas.

[0074] Optionally, the reaction temperature of the Schiff base condensation reaction is 25° C. to 150° C., and the reaction time is 8 hours to 24 hours. It is understood that continuous stirring may be performed during the reaction.

[0075] Optionally, the transition metal salt is selected from any two of iron salts, cobalt salts, manganese salts, nickel salts, copper salts and zinc salts.

[0076] In a preferred embodiment, the transition metal salt is an iron salt or a nickel salt.

[0077] In a preferred embodiment, the transition metal salt is an iron salt or a copper salt.

[0078] Optionally, the iron salt is selected from one or more of ferric chloride, ferric nitrate, ferric acetate and ferric sulfate.

[0079] Optionally, the nickel salt is selected from one or more of nickel chloride, nickel nitrate, nickel acetate and nickel sulfate.

[0080] Optionally, the copper salt is selected from one or more of copper chloride, copper nitrate, copper acetate and copper sulfate.

[0081] Alternatively, the amino-containing heterocyclic compound may be 2,6-diaminopyridine.

[0082] It can be understood that before thermally cracking the polymer complexing metal ions, the step of drying the polymer complexing metal ions is also included.

[0083] It is understood that the thermal cracking is carried out under the protection of an inert gas.

[0084] Optionally, the thermal cracking treatment procedure includes maintaining a heating rate of 5°C / min to 10°C / min and heating to 650 to 1050°C for high temperature carbonization for 1 to 2 hours.

[0085] Optionally, after the thermal cracking is completed, it is naturally cooled to room temperature.

[0086] The black powder obtained by thermal cracking is dispersed in an acidic solution, heated to 80°C in an oil bath, magnetically stirred for 8-12 hours, filtered and washed with ethanol and deionized water for 5-10 times, and dried to obtain a transition metal and nitrogen co-doped carbon composite material.

[0087] A method for preparing a photoelectrochemical electrode comprises the following steps:

[0088] Providing a semiconductor light-absorbing substrate;

[0089] forming an electron transport layer on the semiconductor light-absorbing substrate by magnetron sputtering;

[0090] The slurry containing the transition metal and nitrogen co-doped carbon composite material is coated on the electron transport layer and dried to form the catalytic layer.

[0091] Optionally, before forming the electron transport layer, the method further includes performing a metal catalytic chemical etching treatment on the semiconductor light-absorbing substrate.

[0092] Further optionally, when the metal catalytic chemical etching treatment is performed, the etching solution includes piranha solution, aqueous solution of hydrofluoric acid, and hydrofluoric acid solution of silver nitrate. The component ratio and immersion time of the etching solution are controlled to obtain a semiconductor light-absorbing substrate with a porous structure.

[0093] Preferably, the component ratio and immersion time of the etching solution are controlled so that the diameter of each hole is independently 20 nm to 50 nm, and the depth of each hole is independently 50 nm to 200 nm.

[0094] Preferably, the semiconductor light-absorbing substrate is an n+p type silicon substrate, which can be obtained through channels on the market, or prepared by depositing n-type silicon on the surface of a p-type silicon substrate.

[0095] Optionally, the target material of the magnetron sputtering is a metal. Preferably, the metal is Ti, Zr or Cr.

[0096] Optionally, during the magnetron sputtering, the power of the radio frequency power applied to the target material is 40W to 300W.

[0097] Optionally, the distance between the magnetron sputtering target and the semiconductor light-absorbing substrate is 4 cm to 20 cm.

[0098] Optionally, the sputtering gas of the magnetron sputtering is a mixed gas of Ar and O2.

[0099] Optionally, the total pressure of the magnetron sputtering is 1.0Pa to 5.0Pa.

[0100] Optionally, the O2 partial pressure of the magnetron sputtering is 10-100%.

[0101] Optionally, the deposition time of the magnetron sputtering is 10 min to 100 min.

[0102] Optionally, the ambient temperature is within 50° C. when the magnetron sputtering deposition is completed.

[0103] It will be appreciated that magnetron sputtering can be performed at low temperatures.

[0104] Optionally, the method for preparing the slurry containing the transition metal and nitrogen co-doped carbon composite material comprises the following steps:

[0105] The transition metal and nitrogen co-doped carbon composite material is added to a mixed solution of isopropanol and perfluorosulfonic acid polymer and dispersed to prepare the slurry.

[0106] It is understood that the method of coating the slurry may be drip coating. By controlling the coating amount, the loading of the catalyst layer can be controlled. Preferably, the loading of the catalyst layer is 10 μg·cm -2 ~1000μg·cm -2 More preferably, the loading of the catalytic layer is 50 μg·cm -2 ~200 μg·cm -2 .

[0107] The photoelectrochemical electrode of the present invention can be used as a working electrode of a photoelectrochemical reaction device, and is suitable for various photoelectrochemical reactions, especially multi-electron and multi-step reactions with a hysteresis reaction rate.

[0108] A photoelectrochemical reaction device comprises a working electrode compartment and a counter electrode compartment; the working electrode compartment and the counter electrode compartment are connected, and a proton conductive cation exchange membrane is provided between them for spacing;

[0109] The working electrode compartment is provided with a working electrode, a reference electrode, an air inlet and an air outlet, the working electrode is as described above, and the reaction gas entering from the air inlet can pass through the working electrode and be discharged from the air outlet;

[0110] The counter electrode compartment is provided with a counter electrode.

[0111] Alternatively, the reference electrode may be a Ag / AgCl electrode.

[0112] Alternatively, the counter electrode may be a Pt mesh.

[0113] It can be understood that the air inlet is placed close to the working electrode to ensure that the reaction gas entering from the air inlet can easily reach the surface of the working electrode and be activated to react with the activated reactants in the electrolyte.

[0114] The photoelectrochemical reaction device of the present invention is suitable for various photoelectrochemical reactions, especially multi-electron and multi-step reactions with a hysteresis reaction rate.

[0115] In the past century, about 27% of the world's population has relied on nitrogen fertilizers for survival. Among them, urea has a high nitrogen content and is one of the most important nitrogen fertilizers. The development of the urea industry is of great significance to meet the growing needs of mankind. Nowadays, the industrial synthesis method of urea is mainly produced by reacting high-purity ammonia and carbon dioxide under high temperature (about 150-200°C) and high pressure (about 150-250 atmospheres). This process consumes a lot of energy. Moreover, the ammonia consumed for urea synthesis accounts for about 80% of the world's total ammonia production. The artificial synthesis of ammonia is mainly achieved under harsh conditions through the Haber process, which also requires a lot of energy to activate the inert nitrogen molecules, and hydrogen as one of the raw materials is mainly obtained from fossil fuels, which is accompanied by a large amount of greenhouse gas emissions, aggravating the global energy and environmental crisis.

[0116] Carbon dioxide, as a product of human activities, is a greenhouse gas that is harmful to the living environment. Measures need to be taken to fix and convert it for utilization. Carbon capture and storage (CCS) captures and stores gaseous carbon dioxide by combining carbon dioxide with materials to form a strong covalent bond (carbon-nitrogen bond). However, this measure has disadvantages such as high energy consumption, high cost, and the risk of leakage of captured carbon dioxide, which limits its further application. Therefore, it is very necessary to convert carbon dioxide into value-added chemicals through clean and renewable energy.

[0117] By using the above device, carbon dioxide and nitrate ions can undergo a photoelectrocatalytic coupling reaction to prepare urea.

[0118] A method for preparing urea, using the above-mentioned photoelectrochemical reaction device, comprises the following steps:

[0119] Adding an electrolyte comprising nitrate ions to the working electrode compartment and the counter electrode compartment;

[0120] Introducing carbon dioxide from the air inlet;

[0121] The working electrode, the reference electrode and the counter electrode are electrically connected to the electrochemical workstation and the power is turned on;

[0122] · illuminating the working electrode;

[0123] On the surface of the working electrode, the carbon dioxide and the nitrate ions undergo a photoelectrocatalytic coupling reaction to prepare urea.

[0124] It can be understood that, except for the step of preparing urea on the surface of the working electrode, there is no specific order in the other steps mentioned above.

[0125] Optionally, in the electrolyte, the concentration of nitrate ions is 10mM to 1000mM

[0126] Optionally, the electrolyte comprises nitrate and potassium bicarbonate. In a preferred embodiment, the concentration of potassium bicarbonate in the electrolyte is 1M.

[0127] Optionally, the nitrate is selected from one or more of KNO3, NaNO3, Pb(NO3)2, Ce(NO3)2 and Ca(NO3)2.

[0128] Optionally, the flow rate of the carbon dioxide is 2 sccm to 10 sccm.

[0129] Optionally, the illumination is provided by sunlight or monochromatic light. Further, the light source can be a simulated sunlight light source with sunlight intensity, or light with specific power and wavelength.

[0130] Optionally, the electrochemical workstation provides a voltage of 0.3 to -2.0 V (vs RHE) to the working electrode. The use of an external voltage can assist in enhancing the carrier separation and transfer of the photoelectrochemical electrode.

[0131] It can be understood that the above-mentioned photoelectric reaction can be carried out at room temperature and pressure without adding other chemical reagents, which is conducive to achieving green environmental protection. In addition, the instruments involved are relatively simple, easy to operate and use, and can be produced on a large scale.

[0132] The urea yield of the urea prepared by the above method can reach 10 mg·h -1 cm -2 ~200mg·h-1 cm -2 , the Faradaic efficiency can reach 10% to 60%, and the reaction can run stably for more than 300 hours.

[0133] The present invention combines carbon dioxide with nitrate reduction to form urea, adopts a method with simple operation and low cost, and rationally functionalizes the various layers of the photoelectric reaction electrode. Under the auxiliary effects of light and external voltage, at room temperature and pressure, a photoelectrochemical CN route is developed to achieve a CN coupling reaction and synthesize urea, which not only provides a feasible approach for green urea synthesis technology, but also expands the application scope and market prospects of solar energy resources.

[0134] The following is further described in conjunction with specific examples and comparative examples. The raw materials involved in the following specific examples, unless otherwise specified, can all be sourced from commercial sources. The instruments used, unless otherwise specified, can all be sourced from commercial sources. The processes involved, unless otherwise specified, are all routinely selected by those skilled in the art.

[0135] Example 1

[0136] This embodiment provides a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea, and the steps are as follows:

[0137] Step 1: See Figure 1 , Preparation of photoelectrochemical electrodes

[0138] 1) Take a p-type Si substrate and perform metal catalytic chemical etching to obtain a porous structure with a pore size of 20nm to 50nm and a pore depth of 50nm to 200nm, and deposit n-type Si on its surface to obtain an n+p-type porous Si substrate.

[0139] 2) By magnetron sputtering, an amorphous structured transparent TiO2 semiconductor film with a thickness of 8 nm is formed on the n+p type porous Si substrate of step 1) as an electron transport layer, wherein the target material is Ti, the sputtering gas is a mixed gas of Ar and O2, the total pressure is 3.0 Pa, the O2 partial pressure is 50%, the distance between the target material and the substrate is 10 cm, the deposition time is 80 min, the RF power applied to the target material is 150 W, and the chamber temperature is 40°C at the end of deposition.

[0140] 3) Under the protection of oxalic acid and inert gas, 2,6-diacetylpyridine and 2,6-diaminopyridine are subjected to Schiff base condensation reaction at a reaction temperature of 50°C and a reaction time of 15 hours to form an iminopyridine ligand polymer; the iminopyridine ligand polymer, ferric chloride and nickel chloride are mixed for coordination to form a polymer complexing metal ions; under the protection of inert gas, the polymer complexing metal ions is thermally cracked, and the thermal cracking program is set as follows: the heating rate is maintained at 8°C / min and the temperature is raised to 850°C for high-temperature carbonization for 1.5 hours, and the black powder obtained by thermal cracking is dispersed in a 0.5M H2SO4 solution, heated at 80°C in an oil bath, magnetically stirred for 10 hours, filtered and washed with ethanol and deionized water for 5-10 times, and dried to obtain a transition metal and nitrogen co-doped carbon composite material (NFDA).

[0141] 2 mg NFDA was dispersed in a mixed solution of 960 μL isopropanol and 40 μL nafion (perfluorosulfonic acid polymer, 5 wt%), and ultrasonically dispersed for 20 min to obtain a slurry containing transition metal and nitrogen co-doped carbon composite materials. Take the dispersed slurry and evenly drop it on the TiO2 semiconductor film in step 2). After natural drying, a loading of 50 μg cm -2 The catalytic layer was formed to obtain the photoelectrochemical electrode NFDA / TiO2 / Si.

[0142] The surface and cross-section of the obtained photoelectrochemical electrode were characterized by field emission scanning electron microscopy, e.g. Figure 2 As shown, from Figure 2 It was observed that the photoelectrochemical electrode consisted of a NFDA nanoparticle layer, a TiO2 layer and a Si substrate.

[0143] Step 2: See Figure 3 , assemble the photoelectrochemical reaction device

[0144] The electrochemical electrode of step 1 is used as the working electrode (cathode) 101, and Ag / AgCl is used as the reference electrode 102, which are placed in the working electrode compartment 10. The Pt mesh is used as the counter electrode 201 and is placed in the counter electrode compartment 20. The working electrode compartment 10 and the counter electrode compartment 20 are connected, and the working electrode compartment 10 and the counter electrode compartment 20 are separated by a proton conductive cation exchange membrane 30.

[0145] An air inlet 103 and an air outlet 104 are provided in the working electrode compartment, and the air inlet 103 is placed close to the working electrode 101 to ensure that the reaction gas entering from the air inlet 103 can pass through the working electrode 101 and be discharged from the air outlet 104, thereby completing the assembly of a photoelectrochemical device of a 2H-type reaction cell.

[0146] Step 3: Preparation of urea

[0147] Take the photoelectrochemical device of step 2, add electrolyte 40 to the working electrode compartment 10 and the counter electrode compartment 20, the electrolyte includes 1M KHCO3 and 50mM KNO3, and the rest is water. CO2 is introduced from the air inlet 103 at a flow rate of 5sccm, the working electrode 101, the reference electrode 102 and the counter electrode 201 are electrically connected to the electrochemical workstation 50, the power is turned on, and a light source with the intensity of 1 sun is used to illuminate the working electrode to drive CO2 and the NO3 - A photoelectrocatalytic coupling reaction is performed to prepare urea on the surface of the working electrode 101 .

[0148] The yield and Faraday efficiency of urea prepared in this example are recorded. Figure 4 As shown, it shows that CO2 and NO3 - The reductive coupling to form urea has a better urea yield (columns) and long-term stable operation (dots).

[0149] Example 2

[0150] This embodiment provides a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea. The main difference from Embodiment 1 is that the catalyst layer loading in Step 1 is different. Specifically, Step 1 is as follows:

[0151] 1) Same as Example 1.

[0152] 2) Same as Example 1.

[0153] 3) Under the protection of oxalic acid and inert gas, 2,6-diacetylpyridine and 2,6-diaminopyridine are subjected to Schiff base condensation reaction at a reaction temperature of 50°C and a reaction time of 15 hours to form an iminopyridine ligand polymer; the iminopyridine ligand polymer, ferric chloride and nickel chloride are mixed for coordination to form a polymer complexing metal ions; under the protection of inert gas, the polymer complexing metal ions is thermally cracked, and the thermal cracking program is set as follows: the heating rate is maintained at 8°C / min and the temperature is raised to 850°C for high-temperature carbonization for 1.5 hours, and the black powder obtained by thermal cracking is dispersed in a 0.5M H2SO4 solution, heated at 80°C in an oil bath, magnetically stirred for 10 hours, filtered and washed with ethanol and deionized water for 5-10 times, and dried to obtain a transition metal and nitrogen co-doped carbon composite material (NFDA).

[0154] 2 mg NFDA was dispersed in a mixed solution of 960 μL isopropanol and 40 μL nafion (perfluorosulfonic acid polymer, 5 wt%), and ultrasonically dispersed for 20 min to obtain a slurry containing transition metal and nitrogen co-doped carbon composite materials. Take the dispersed slurry and evenly drop it on the TiO2 semiconductor film in step 2). After natural drying, a loading of 100 μg cm-2 The catalytic layer is formed to obtain a photoelectrochemical electrode.

[0155] The yield and Faraday efficiency of urea prepared in this example are recorded. Figure 4 As shown, it shows that CO2 and NO3 - The reductive coupling to form urea has a better urea yield (columns) and long-term stable operation (dots).

[0156] Example 3

[0157] This embodiment provides a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea. The main difference from Embodiment 1 is that the catalyst layer loading in Step 1 is different. Specifically, Step 1 is as follows:

[0158] 1) Same as Example 1.

[0159] 2) Same as Example 1.

[0160] 3) Under the protection of oxalic acid and inert gas, 2,6-diacetylpyridine and 2,6-diaminopyridine are subjected to Schiff base condensation reaction at a reaction temperature of 50°C and a reaction time of 15 hours to form an iminopyridine ligand polymer; the iminopyridine ligand polymer, ferric chloride and nickel chloride are mixed for coordination to form a polymer complexing metal ions; under the protection of inert gas, the polymer complexing metal ions is thermally cracked, and the thermal cracking program is set as follows: the heating rate is maintained at 8°C / min and the temperature is raised to 850°C for high-temperature carbonization for 1.5 hours, and the black powder obtained by thermal cracking is dispersed in a 0.5M H2SO4 solution, heated at 80°C in an oil bath, magnetically stirred for 10 hours, filtered and washed with ethanol and deionized water for 5-10 times, and dried to obtain a transition metal and nitrogen co-doped carbon composite material (NFDA).

[0161] 2 mg NFDA was dispersed in a mixed solution of 960 μL isopropanol and 40 μL nafion (perfluorosulfonic acid polymer, 5 wt%), and ultrasonically dispersed for 20 min to obtain a slurry containing transition metal and nitrogen co-doped carbon composite materials. Take the dispersed slurry and evenly drop it on the TiO2 semiconductor film in step 2). After natural drying, a loading of 200 μg cm -2 The catalytic layer is formed to obtain a photoelectrochemical electrode.

[0162] The yield and Faraday efficiency of urea prepared in this example are recorded. Figure 4 As shown, it shows that CO2 and NO3 - The reductive coupling to form urea has a better urea yield (columns) and long-term stable operation (dots).

[0163] In Examples 1 to 3, the loading of NFDA catalyst layer in photoelectrochemical process was 50 μg cm -2 , 100 μg cm -2 and 200 μg cm -2 .from Figure 4 It can be seen that the loading of the NFDA catalytic layer is not positively correlated with the urea synthesis performance. When the loading of the NFDA catalytic layer is too much, it will affect the light absorption of the substrate and thus affect the urea synthesis performance.

[0164] Example 4

[0165] This embodiment provides a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea. The main difference from Embodiment 1 is that the catalyst layer material in Step 1 is different. Specifically, Step 1 is as follows:

[0166] 1) Same as Example 1.

[0167] 2) Same as Example 1.

[0168] 3) Under the protection of oxalic acid and inert gas, 2,6-diacetylpyridine and 2,6-diaminopyridine are subjected to Schiff base condensation reaction at a reaction temperature of 50°C and a reaction time of 15 hours to form an iminopyridine ligand polymer; the iminopyridine ligand polymer, ferric chloride and cupric chloride are mixed for coordination to form a polymer complexing metal ions; under the protection of inert gas, the polymer complexing metal ions is thermally cracked, and the thermal cracking program is set as follows: the heating rate is maintained at 8°C / min and the temperature is raised to 850°C for high-temperature carbonization for 1.5 hours, and the black powder obtained by thermal cracking is dispersed in a 0.5M H2SO4 solution, heated at 80°C in an oil bath, magnetically stirred for 10 hours, filtered and washed with ethanol and deionized water for 5-10 times, and dried to obtain a transition metal and nitrogen co-doped carbon composite material (CFDA).

[0169] 2 mg CFDA was dispersed in a mixed solution of 960 μL isopropanol and 40 μL nafion (perfluorosulfonic acid polymer, 5 wt%), and ultrasonically dispersed for 20 min to obtain a slurry containing transition metal and nitrogen co-doped carbon composite materials. Take the dispersed slurry and evenly drop it on the TiO2 semiconductor film in step 2). After natural drying, a loading of 100 μg cm -2 The catalytic layer was formed to obtain the photoelectrochemical electrode CFDA / TiO2 / Si.

[0170] The yield and Faraday efficiency of urea prepared in this example are recorded. Figure 5 As shown, the urea yield and Faradaic efficiency can reach 180 mg·h -1 cm -2The present embodiment also has a relatively good urea yield and long-term stable operation.

[0171] Comparative Example 1

[0172] This comparative example provides a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea, which is mainly different from Example 1 in that no electron transport layer is formed in step 1. The specific step 1 is as follows:

[0173] 1) Same as Example 1

[0174] 2) Under the protection of oxalic acid and inert gas, 2,6-diacetylpyridine and 2,6-diaminopyridine are subjected to Schiff base condensation reaction at a reaction temperature of 50°C and a reaction time of 15 hours to form an iminopyridine ligand polymer; the iminopyridine ligand polymer, ferric chloride and nickel chloride are mixed for coordination to form a polymer complexing metal ions; under the protection of inert gas, the polymer complexing metal ions is thermally cracked, and the thermal cracking program is set as follows: the heating rate is maintained at 8°C / min and the temperature is raised to 850°C for high-temperature carbonization for 1.5 hours, and the black powder obtained by thermal cracking is dispersed in a 0.5M H2SO4 solution, heated at 80°C in an oil bath, magnetically stirred for 10 hours, filtered and washed with ethanol and deionized water for 5-10 times, and dried to obtain a transition metal and nitrogen co-doped carbon composite material (NFDA).

[0175] 2 mg NFDA was dispersed in a mixed solution of 960 μL isopropanol and 40 μL nafion (perfluorosulfonic acid polymer, 5 wt%), and ultrasonically dispersed for 20 min to obtain a slurry containing transition metal and nitrogen co-doped carbon composite materials. Take the dispersed slurry and evenly drop it on the n+p type porous Si substrate in step 1). After natural drying, a loading of 100 μg cm -2 The catalytic layer is formed to obtain a photoelectrochemical electrode.

[0176] Record the yield and Faraday efficiency of urea prepared in this comparative example. The results are as follows: Figure 6 As shown, it can be seen that the lack of an electron transport layer will affect the synthesis efficiency of urea and the stability of the photoelectric reaction.

[0177] Comparative Example 2

[0178] This comparative example provides a photoelectrochemical electrode and a preparation method thereof, a photoelectrochemical reaction device and a preparation method of urea. The main difference from Example 1 is that in step 1, the electron transport layer is replaced by an Al2O3 film. The specific step 1 is as follows:

[0179] 2) By magnetron sputtering, an amorphous structured transparent Al2O3 semiconductor film with a thickness of 8 nm is formed on the n+p type porous Si substrate of step 1), wherein the target material is Al, the sputtering gas is a mixed gas of Ar and O2, the total pressure is 2 Pa, the O2 partial pressure is 600%, the distance between the target material and the substrate is 10 cm, the deposition time is 70 min, the RF power applied to the target material is 150 W, and the chamber temperature is 45°C at the end of deposition.

[0180] Record the yield and Faraday efficiency of urea prepared in this comparative example. The results are as follows: Figure 6 As shown, it can be seen that after the electron transport layer is replaced with Al2O3 film, although the Al2O3 film can protect the Si substrate, it cannot transport electrons, which will affect the synthesis efficiency of urea and the stability of the photoelectric reaction.

[0181] In summary, the photoelectrochemical electrode of the present invention can synthesize urea through photoelectrochemical reaction. The present invention develops a green urea synthesis channel with great potential, and realizes the conversion of solar energy into green chemical fertilizer at room temperature and pressure.

[0182] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0183] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A photoelectrochemical electrode, characterized in that It includes a semiconductor light-absorbing substrate, an electron transport layer and a catalytic layer; The electron transport layer is located on the semiconductor light-absorbing substrate, and the catalytic layer is located on the electron transport layer; The material of the catalytic layer includes a transition metal and nitrogen co-doped carbon composite material; The transition metal is selected from any two of iron, cobalt, manganese, nickel, copper and zinc; The preparation method of the transition metal and nitrogen co-doped carbon composite material comprises the following steps: In the presence of a catalyst, 2,6-diacetylpyridine and an amino-containing heterocyclic compound undergo a Schiff base condensation reaction to form an iminopyridine ligand polymer; Mixing the iminopyridine ligand polymer and a transition metal salt to coordinate and form a polymer complexing metal ions; The polymer complexed with metal ions is thermally cracked to prepare a transition metal and nitrogen co-doped carbon composite material.

2. The photoelectrochemical electrode according to claim 1, characterized in that The catalytic layer includes one or more of the following features: The transition metal elements are iron and nickel, or the transition metal elements are iron and copper; The loading of the catalytic layer is 10 μg cm -2 ~1000μg cm -2 .

3. The photoelectrochemical electrode according to any one of claims 1 to 2, characterized in that: The semiconductor light absorbing substrate comprises one or more of the following features: ·It is an n+p type silicon substrate; ·Porous structure.

4. The photoelectrochemical electrode according to any one of claims 1 to 2, characterized in that: The electron transport layer includes one or more of the following features: Thickness: 5nm~10nm; Light transmission; The material has an amorphous structure; The band gap of the material is greater than 3.2eV; ·The material is metal oxide.

5. A method for preparing a photoelectrochemical electrode according to any one of claims 1 to 4, characterized in that: The following steps are involved: Providing a semiconductor light-absorbing substrate; forming an electron transport layer on the semiconductor light-absorbing substrate by magnetron sputtering; The slurry containing the transition metal and nitrogen co-doped carbon composite material is coated on the electron transport layer and dried to form a catalytic layer.

6. The method for preparing a photoelectrochemical electrode according to claim 5, characterized in that: Include one or more of the following characteristics: Before forming the electron transport layer, the method further includes performing metal catalytic chemical etching on the semiconductor light-absorbing substrate; The method for preparing the slurry containing the transition metal and nitrogen co-doped carbon composite material comprises the following steps: adding the transition metal and nitrogen co-doped carbon composite material to a mixed solution of isopropanol and a perfluorosulfonic acid polymer, and dispersing the mixture to prepare the slurry.

7. The method for preparing a photoelectrochemical electrode according to any one of claims 5 to 6, characterized in that: The magnetron sputtering meets one or more of the following conditions: The target material is metal; The RF power applied to the target is 40W~300W; The distance between the target and the semiconductor light-absorbing substrate is 4 cm to 20 cm; The sputtering gas is a mixture of Ar and O2; Total pressure is 1.0Pa~5.0Pa; O2 partial pressure is 10~100%; ·Deposition time is 10min~100min; The ambient temperature is below 50°C at the end of deposition.

8. A photoelectrochemical reaction device, characterized in that: It comprises a working electrode compartment and a counter electrode compartment; the working electrode compartment and the counter electrode compartment are connected, and a proton conductive cation exchange membrane is provided between them for spacing; The working electrode compartment is provided with a working electrode, a reference electrode, an air inlet and an air outlet, the working electrode is as described in any one of claims 1 to 4, and the reaction gas entering from the air inlet can pass through the working electrode and be discharged from the air outlet; The counter electrode compartment is provided with a counter electrode.

9. A method for preparing urea, characterized in that: Using the photoelectrochemical reaction device according to claim 8 comprises the following steps: Adding an electrolyte comprising nitrate ions to the working electrode compartment and the counter electrode compartment; Introducing carbon dioxide from the air inlet; The working electrode, the reference electrode and the counter electrode are electrically connected to the electrochemical workstation and the power is turned on; · illuminating the working electrode; On the surface of the working electrode, the carbon dioxide and the nitrate ions undergo a photoelectrocatalytic coupling reaction to prepare urea.

10. The method for preparing urea according to claim 9, characterized in that: One or more of the following conditions are met: In the electrolyte, the concentration of nitrate ions is 10 mM to 1000 mM; The electrolyte comprises nitrate and potassium bicarbonate; The flow rate of the carbon dioxide is 2 sccm to 10 sccm; The illumination is provided by sunlight or monochromatic light; The electrochemical workstation provides -2.0V~0.3V to the working electrode vs Voltage of RHE.

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