Photocathode, photoanode and device for photoelectrochemical synthesis of ammonia

Abstract

The application relates to the technical field of photoelectrochemistry, in particular to a photoelectric cathode, a photoelectric anode and a device for photoelectrochemical synthesis of ammonia. The application solves the problems of extra energy consumption (such as an external bias) and low efficiency of photoelectrochemical reaction for ammonia production in the related art. The photoelectric cathode comprises a first light absorber, a protective layer and a cocatalyst layer which are sequentially arranged on the surface of the first light absorber; the protective layer is light-transmissive, and the material of the protective layer comprises one or more of graphene, graphite sheet and silicon oxide; and the material of the cocatalyst layer comprises one or more of transition metal materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoelectrochemical synthesis of ammonia, and particularly relates to a photoelectrode, a photoanode and a device for photoelectrochemical synthesis of ammonia. BACKGROUND

[0002] Ammonia (NH3) not only plays an important role in the agricultural, textile, plastic, pharmaceutical and other industries, but also is a high-efficiency hydrogen and energy storage medium due to its high energy density, convenient storage and transportation, for example, 1 liter of liquid ammonia is equivalent to 4.5 liters of hydrogen (35 MPa), and thus can be used as a carrier of the next generation of clean energy.

[0003] A traditional ammonia synthesis process mainly relies on the Haber process, which needs to reduce nitrogen into ammonia at high temperature and high pressure, and needs a large amount of coal and fossil energy, thereby causing a series of environmental problems and being not conducive to green and sustainable development. For example, China, as the world's largest ammonia production country, produces about 73 million tons of ammonia per year, accounting for about 34% of the world, and involves more than 240 enterprises. However, about 90% of the ammonia is synthesized by using coal as raw material, and about 84 million tons of standard coal are consumed per year, accounting for about 25% of the chemical energy consumption, and thus the ammonia synthesis industry urgently needs energy saving and emission reduction worldwide.

[0004] Photoelectrochemical synthesis of ammonia is a green and environmentally friendly ammonia production path driven by solar energy. Through the generation of electron-hole pairs under light, the electrons are transported to the surface of the electrode (such as a photoelectrode) and react with the electrolyte to generate ammonia in the presence of a catalyst, and the holes reach the anode through an external circuit to occur oxidation reaction. Compared with the traditional electrocatalysis in which the energy input is all electric energy, the photoelectrochemistry excited by solar energy is more energy-saving and environmentally friendly, and compared with the photocatalysis based on the particle suspension process, the photoelectrochemistry has higher yield and efficiency. At present, although great progress has been made in the field of photoelectrochemistry, there are still problems such as poor stability of the catalyst in the photoelectrochemical system, and the need to apply an additional bias (such as connecting the photoelectrode to an external power source) to improve the separation and mobility of the carriers during the photoelectrochemical reaction, which is not conducive to the efficient performance of the photoelectrochemical reaction. SUMMARY

[0005] Therefore, the present application provides a photoelectrode, a photoanode and a device for photoelectrochemical synthesis of ammonia, so as to solve the problems of additional energy consumption (such as an external bias) and low ammonia production efficiency in the photoelectrochemical reaction in the related art.

[0006] Principle of the application:

[0007] The semiconductor in the photoelectrode generates photo-generated electrons and photo-generated holes under the excitation of light. The electrons of the photo-cathode migrate to the surface of the electrode to participate in the reduction reaction, and the holes are transferred to the photo-anode through the external circuit to undergo oxidation reaction. The electron and hole pairs are prone to recombination, so an additional bias is generally applied to accelerate the migration of carriers. The additional bias requires a large amount of electrical energy. The application realizes the storage of photo-generated electrons in the local electron structure on the surface of the photo-cathode. The structure can also act as a Lewis acid site to promote the adsorption and activation of nitrate, which is beneficial to the efficient and selective synthesis of ammonia. The design and regulation of the micron-level photo-anode under high stress enhance the separation and transfer of carriers, which promotes the formation of a durable and efficient photo-electrochemical OER device for the reduction of nitrate to synthesize ammonia without external bias.

[0008] In a first aspect, the application provides a photo-cathode, comprising: a first light absorber, and a protective layer and a cocatalyst layer which are sequentially stacked on the surface of the first light absorber;

[0009] The protective layer is light-transmissive, and the material of the protective layer comprises one or more of graphene, graphite sheet and silicon oxide; the material of the cocatalyst layer comprises one or more of transition metal materials;

[0010] Optionally, the first light absorber is a p-type narrow-bandgap semiconductor material; optionally, the p-type narrow-bandgap semiconductor material comprises p-type silicon, heterojunction n + p-type silicon, cuprous oxide and indium phosphide;

[0011] Optionally, the graphene and / or graphite sheet are prepared by a hydrothermal high-temperature pyrolysis method, and the protective layer is prepared by applying a dispersion liquid of the graphene and / or graphite sheet on the surface of the first light absorber by at least one of spin coating, drop coating and spraying, and then annealing;

[0012] Optionally, the silicon oxide is prepared by magnetron sputtering;

[0013] Optionally, the thickness of the protective layer is 5-20 nm;

[0014] Optionally, the transition metal material comprises transition metal elements, and part of the transition metal elements exist in the form of metal cations and / or intermetallic compounds; optionally, the mass fraction of the metal cations and / or intermetallic compounds is 0-70%;

[0015] Optionally, the transition metal material comprises one or more of copper, nickel, iron, titanium and tungsten;

[0016] Optionally, the preparation method of the cocatalyst layer comprises:

[0017] The cocatalyst film was prepared by first magnetron sputtering;

[0018] To prepare the cocatalytic layer, a localized electronic structure was constructed on the cocatalyst film.

[0019] Optionally, the target material used in the first magnetron sputtering is selected from one or more transition metals; the power supply used in the first magnetron sputtering is a DC power supply or an AC power supply, and the power density of the first magnetron sputtering is 0.35~30W / cm³. 2 The working pressure is 0.5~4 Pa, the sputtering time is 0.5~360 min, and the temperature is 20~800 °C.

[0020] Thirdly, a photoanode is provided, comprising: a transparent substrate, and a second light absorber disposed on the transparent substrate, wherein the second light absorber is made of micron-sized titanium dioxide material; the compressive stress of the second light absorber is 10~100 MPa, and the ferromagnetism is 5~38 emu·cm. -3 .

[0021] Optionally, the micron-sized titanium dioxide material has columnar crystals, with each crystal oriented perpendicular to the transparent substrate and arranged in parallel with each other.

[0022] Optionally, the second light absorber is prepared by a second magnetron sputtering.

[0023] The second magnetron sputtering process uses either a DC or RF power supply, and its power density is 17–30 W / cm². 2 The deposition time is 1 to 6 hours; the working gas used in the second magnetron sputtering is argon, the reactant gas is oxygen, and the ratio of argon flow rate to oxygen flow rate is 5 to 0.5; the pressure in the cavity of the second absorber during deposition is 0.4 to 4 Pa.

[0024] Thirdly, a photoelectrochemical ammonia synthesis device is provided, comprising:

[0025] The photocathode as described in the first aspect and the photoanode as described in the second aspect;

[0026] The second light absorbers in the photocathode and photoanode are located on the same side of the transparent substrate contained in the photoanode, but in different regions.

[0027] Optionally, the area ratio of the second absorber included in the photocathode and the photoanode is 1:100 to 1:2, and the photocathode is located at the center of the transparent substrate, while the second absorber included in the photoanode is arranged around the photocathode to form a U-shaped structure.

[0028] Optionally, the transparent substrate and the photo-cathode are both square, and the side length of the square of the transparent substrate is greater than or equal to 50 cm, and the side length of the square of the photo-cathode is greater than or equal to 5 cm.

[0029] Optionally, the device further comprises an electrolyte, the electrolyte comprising a nitrogen source and an electrolyte, wherein the nitrogen source comprises one or more of nitrogen, nitrite and nitrate, and the electrolyte comprises one or more of potassium sulfate, potassium hydroxide and potassium bicarbonate.

[0030] Optionally, after the ammonia production is completed, the pH value of the electrolyte is 3-14, and / or the concentration of nitrogen atoms in the electrolyte is 0.02-0.3 mol / L.

[0031] The device can complete the following steps under light without other external voltage application:

[0032] The photo-cathode and the photo-anode simultaneously receive photons, form a built-in electric field based on the matching of the energy band structure, drive the photo-generated electrons and holes to the surface of the photo-cathode and the photo-anode respectively, and implement the reduction reaction of nitrate / nitrite to synthesize ammonia and the oxygen evolution reaction.

[0033] The device provided in the present application is simple and low in cost, and can enlarge the size of the reaction device (such as obtaining a photo-anode with an area of 50*50 cm 2 and a photo-cathode with an area of 5*5 cm 2 ), and is suitable for practical application.

[0034] Compared with the prior art, the present application has the following beneficial effects:

[0035] By arranging the protective layer and the assistant catalytic layer on the surface of the first light absorber, on the one hand, the protective layer can be used to load the assistant catalytic layer to realize the fixation and adsorption of the assistant catalytic layer, so as to improve the stability of the assistant catalytic layer. On the other hand, since the material of the protective layer has an electron transport function, the protective layer can also serve as an electron transport layer to improve the electron mobility when in use, so that the electrons are continuously transported to the surface of the protective layer, thereby improving the electron-hole separation efficiency and enabling the nitrogen source in the electrolyte to occur photoelectrochemical reaction to produce ammonia under the catalysis of the assistant catalytic layer. On the other hand, the protective layer can prevent the first light absorber from being corroded by directly contacting with the electrolyte, and can improve the overall stability of the photo-electrode.

[0036] Based on the above, when the photo-cathode is used in a photoelectrochemical reaction ammonia production device, the nitrate in the electrolyte can occur photoelectrochemical reaction to produce ammonia without applying a bias or with a small bias, thereby improving the ammonia production efficiency. The problems of requiring a bias in the related art photoelectrochemical reaction ammonia production and low photoelectrochemical reaction ammonia production efficiency are solved. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 A schematic structural diagram of a photoelectric cathode provided by an embodiment of the present application;

[0038] Figure 2 A schematic flow diagram of a preparation method of a photoelectric cathode provided by an embodiment of the present application;

[0039] Figure 3 A schematic structural diagram of a photoelectric device provided by an embodiment of the present application;

[0040] Figure 4 A test diagram of specific surface area of a photoelectric anode surface provided by an embodiment of the present application;

[0041] Figure 5 A test diagram of pore size distribution of a photoelectric anode surface provided by an embodiment of the present application;

[0042] Figure 6 A linear voltammetry characteristic curve diagram of a photoelectric anode provided by an embodiment of the present application under a three-electrode system (the saturation current density can reach 0.37 mA·cm -2 );

[0043] Figure 7 Linear voltammetry characteristic curve diagrams of a photoelectric cathode and a photoelectric anode in a photoelectric device of Example 1 provided by an embodiment of the present application under a single three-electrode system, respectively;

[0044] Figure 8 A curve diagram of current change with time of a photoelectric device of Example 1 provided by an embodiment of the present application under a constant voltage;

[0045] Figure 9 An ammonia production efficiency diagram of a photoelectric device of Example 1 provided by an embodiment of the present application under 0 V, 1 simulated sunlight (light power density is 100 mW / cm 2 , chopped light mode (dark-light-dark));

[0046] Figure 10 An ammonia production efficiency diagram of a photoelectric cathode of Examples 2-5 provided by an embodiment of the present application under a three-electrode system with a bias of-0.6 V vs. RHE under 1 simulated sunlight;

[0047] Figure 11 Linear voltammetry characteristic curve diagrams of a photoelectric cathode and a photoelectric anode in a photoelectric device of Example 6 provided by an embodiment of the present application under a single three-electrode system, respectively;

[0048] Figure 12A linear voltammetry curve of the photoanode of Example 7 provided by some embodiments of the present application under 1 simulated sunlight in a three-electrode system is shown in FIG. 7.

[0049] Figure 13 A plot of ammonia production efficiency of the photocathode of Example 8 provided by some embodiments of the present application under 1 simulated sunlight in a three-electrode system with a bias of -0.6 V vs. RHE is shown in FIG. 8. DETAILED DESCRIPTION

[0050] The present application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the application to those skilled in the art.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0052] Based on the above technical problems, some embodiments of the present application provide a photocathode 10, as shown in FIG. 1, which comprises a first light absorber 1, and a protective layer 2 and a cocatalyst layer 3 which are sequentially stacked on the surface of the first light absorber 1; wherein the protective layer 2 is light-transmissive, and the material of the protective layer 2 comprises one or more of graphene, graphite sheet and silicon oxide; and the material of the cocatalyst layer 3 comprises one or more of transition metal materials. Figure 1

[0053] The graphene and graphite sheet have excellent electrical conductivity, which is conducive to the transmission of electrons. By dispersing an appropriate amount of these carbon materials on the surface of the first light absorber 1, the porous structure of the carbon materials themselves can allow light to pass through, ensuring that the first light absorber 1 can receive sufficient light to generate a photoelectric effect. The silicon oxide is non-toxic, highly transparent and has strong stability, which ensures the light absorption of the first light absorber 1 and prevents the photo-etching of the semiconductor, thereby protecting the first light absorber 1. At the same time, the silicon oxide can be connected to the cocatalyst layer 3 through a chemical bond, thereby achieving the adsorption and fixation of the cocatalyst layer 3.

[0054] ​The protective layer 2 is light-transmissive and has an electron transport function. In this way, on the one hand, the electrons generated by the first light absorber 1 through the photovoltaic effect can be continuously transported to the surface of the cocatalyst layer 3, thereby facilitating the reduction reaction of the nitrogen source in the electrolyte on the surface of the cocatalyst layer 3 to produce ammonia. On the other hand, sunlight can pass through the protective layer 2 and be absorbed by the first light absorber 1, thereby not blocking the first light absorber 1. In addition, the protective layer 2 can prevent the electrolyte from contacting the first light absorber 1, thereby preventing the electrolyte from corroding the first light absorber 1 and facilitating the continuous and stable operation of the photoelectrode 10. In addition, the protective layer 2 can also load the cocatalyst layer 3, thereby facilitating the fixation and adsorption of the catalyst of the cocatalyst layer 3.

[0055] In the photoelectrode 10 provided in the embodiments of the present application, the protective layer 2 and the cocatalyst layer 3 are arranged on the surface of the first light absorber 1. On the one hand, the protective layer 2 can load the cocatalyst layer 3, thereby facilitating the fixation and adsorption of the cocatalyst layer 3 and improving the stability of the cocatalyst layer 3. On the other hand, since the material of the protective layer 2 has an electron transport function, the protective layer 2 can also serve as an electron transport layer to improve the electron mobility when in use, so that the electrons are continuously transported to the surface of the protective layer 2, thereby improving the electron-hole separation efficiency and facilitating the photoelectrochemical reaction of the nitrogen source in the electrolyte under the catalysis of the cocatalyst layer 3 to produce ammonia. In addition, the protective layer 2 can prevent the first light absorber 1 from being directly corroded by the electrolyte, thereby improving the overall stability of the photoelectrode.

[0056] Based on the above, when the photoelectrode is used in a photoelectrochemical ammonia production device, the nitrate in the electrolyte can be subjected to a photoelectrochemical reaction to produce ammonia without applying a bias or with a small bias, thereby improving the ammonia production efficiency. The problems of the related art, i.e., the need to apply a bias in the photoelectrochemical ammonia production and the low photoelectrochemical ammonia production efficiency, are solved.

[0057] In some embodiments, the first light absorber 1 is a p-type narrow-band-gap semiconductor material. Optionally, the p-type narrow-band-gap semiconductor material includes: a p-type silicon wafer, n + a p-type silicon wafer, cuprous oxide, and indium phosphide.

[0058] In these embodiments, the silicon semiconductor layer has a mature preparation process, low price, safety, and no toxicity, and has a relatively narrow energy band gap (about 1.1 eV) and a relatively wide solar spectrum absorption; cuprous oxide (Cu2O) has a rich earth reserve and is non-toxic, has a relatively narrow band gap (about 2.0 eV), a relatively high theoretical photocurrent density (14.7 mA·cm -2 ), and a relatively high light conversion efficiency (18%); and indium phosphide has a relatively high electron mobility and a relatively fast saturated carrier rate.

[0059] wherein, in the case that the first light absorber 1 is a p-type silicon wafer or an n + In the case that the first light absorber 1 is a p-type silicon wafer, the material of the protective layer 2 can further include silicon oxide. The silicon oxide is produced by oxidation in the process of preparing the protective layer 2. The silicon oxide itself is non-toxic, has high transparency and strong stability, and can ensure the light absorption of the semiconductor (such as the first light absorber 1) while preventing the photo-etching of the semiconductor.

[0060] In some embodiments, the thickness of the first light absorber 1 is 0.3-1.0 mm.

[0061] In these embodiments, by controlling the thickness of the first light absorber 1 within the above range, the problem that the electron-hole pair recombination is prone to occur due to the large transfer resistance caused by the excessively thick first light absorber 1, thereby adversely affecting the photoelectric conversion efficiency, can be prevented, and the problem of limited photoelectrons and holes caused by the excessively thin first light absorber 1 can also be prevented; in this way, the rapid separation of electrons and holes can be ensured to the greatest extent, and the photoelectric conversion efficiency can be improved.

[0062] In some embodiments, when the material of the protective layer 2 includes graphene and / or graphite sheet, the graphene and / or graphite sheet can be prepared by a hydrothermal high-temperature pyrolysis method, the protective layer 2 is prepared by at least one of spin coating, drop coating and spray coating to lay the dispersion liquid of the graphene and / or graphite sheet on the surface of the first light absorber 1, and annealing.

[0063] When the material of the protective layer 2 includes silicon oxide, the silicon oxide can be prepared by a magnetron sputtering method.

[0064] When the material of the protective layer 2 includes graphene and / or graphite sheet and silicon oxide, the protective layer 2 can be prepared by a combination of a solution method and a magnetron sputtering method. At this time, the protective layer 2 can be a laminated structure of carbon material (graphene and / or graphite sheet) and silicon oxide.

[0065] In some embodiments, when the protective layer with the above-mentioned material of silicon oxide is prepared, the power source used in the magnetron sputtering is an alternating current power source or a direct current power source, the power density of the magnetron sputtering is 0.35-30 W / cm 2 , the working pressure is 0.5-4 Pa, the sputtering time is 0.5-360 min, and the temperature is 20-800 °C.

[0066] In some embodiments, the thickness of the protective layer 2 is 5-20 nm. The light transmission, electron transmission and stable operation of the photoelectric cathode can be ensured at the same time.

[0067] In some embodiments, the transition metal material includes transition metal elements, and part of the transition metal elements in the transition metal material exist in the form of metal cations and / or intermetallic compounds; optionally, the mass ratio of the metal cations and / or intermetallic compounds in the transition metal material is 0-70%.

[0068] The transition metal material can be one or more of copper, nickel, iron, titanium and tungsten, and the metal cations can be one or more of copper ions, nickel ions, iron ions, titanium ions and tungsten ions. The metal cations can store photo-generated electrons and act as Lewis acid sites to facilitate the adsorption and activation of nitrogen sources in the electrolyte.

[0069] For example, the transition metal material can be copper, and the metal cations can be Cu + The metal cations Cu + The metal cations Cu + .

[0070] For example, the copper thin film can be locally doped with oxygen by magnetron sputtering, for example, by introducing an oxygen-containing gas during magnetron sputtering of the copper thin film to achieve local oxygen doping; or by high-temperature annealing, in which case local oxidation occurs in the copper thin film during high-temperature annealing, thereby achieving local oxygen doping.

[0071] The copper thin film can be alloyed by combining magnetron sputtering and annealing.

[0072] During the above-mentioned oxygen doping or alloying process, local electron exchange and transfer occur in the copper thin film, thereby achieving the construction of localized electronic structure.

[0073] In some optional embodiments, the mass ratio of the metal cations and / or intermetallic compounds in the transition metal material is 40%.

[0074] In these embodiments, the cocatalyst layer 3 can maximize the adsorption and activation of nitrogen sources and improve the catalytic effect.

[0075] In some embodiments, the transition metal material includes one or more of copper, nickel, iron, titanium and tungsten.

[0076] In these embodiments, these transition metal materials are safe, non-toxic, abundant, and possess good electrical and thermal conductivity. The d electrons of these transition metal elements participate in the formation of chemical bonds during chemical reactions, allowing them to exhibit various oxidation states. This is beneficial for adjusting the localized electronic structure in the co-catalyst layer, for example, enabling Cu... + The mass percentage in Cu thin films is adjustable within the range of 0%-70%.

[0077] In some embodiments, such as Figure 1 As shown, the surface of the first light absorber 1 facing the protective layer 2 has an anti-reflection structure 101.

[0078] In these embodiments, the anti-reflection structure 101 can enhance the absorption of light by the first light absorber 1, thereby increasing the photocurrent density.

[0079] In some embodiments, such as Figure 1 As shown, the photocathode 10 further includes a back electrode 4; the back electrode 4 is disposed on the surface of the first light absorber 1 away from the protective layer 2.

[0080] In these embodiments, by providing a back electrode 4, and if the back electrode 4 is made of a conductive metal, a low-resistance ohmic contact can be formed between the conductive metal and the first light absorber 1. This allows the photocathode 10 to be connected to an external circuit via the back electrode 4, further improving conductivity. By controlling the thickness of the back electrode within the aforementioned range, electron transport efficiency can be maximized while reducing costs.

[0081] In some embodiments, the material of the back electrode 4 includes one or more of Au, titanium, palladium, and silver.

[0082] Some embodiments of this application provide a method for preparing a photocathode, such as... Figure 2 As shown, the method includes:

[0083] S1) Provide a first light absorber 1, which can be p-Si;

[0084] S2) A protective layer 2 is formed on the first light absorber. The material of the protective layer 2 has the functions of light transmittance, electron transmission and protection of the first light absorber 1. For example, the material of the protective layer 2 includes carbon materials, such as graphene, graphite sheets, etc.

[0085] S3) The co-catalyst layer 3 is prepared on the surface of the protective layer 2 away from the first light absorber 1;

[0086] In some embodiments, the first light absorber 1 can be p-type silicon, cuprous oxide, or indium phosphide; alternatively, the p-type silicon can be pretreated chemically to obtain an antireflection structure, and a heterojunction can be constructed on the surface of the antireflection structure, such as... Figure 2As shown, phosphorus is doped on the p-type silicon, and a heterojunction n + p-type silicon, and the first light absorber 1 is a heterojunction n + p-type silicon.

[0087] In some embodiments, a protective layer 2 is formed on the first light absorber 1, mainly using organic solvent dispersion method and magnetron sputtering coating method, which includes:

[0088] Graphene and / or graphite sheets are prepared by hydrothermal pyrolysis, and then can be formed on the surface of the photoelectric cathode by spin coating, drop coating, spraying and the like, and finally the solvent is removed by annealing to obtain.

[0089] For example, an appropriate amount of 1-5 mg of graphene and graphite sheets are dispersed in 1 mL of isopropanol solution (containing 50 μL of nafion solution, and the nafion solution is a perfluorosulfonic acid type polymer solution, which is used to form a membrane electrode, and the nafion solution as a catalyst coating and carrier can greatly improve the utilization rate of the catalyst), to obtain a dispersion solution of graphene and graphite sheets.

[0090] In some embodiments, the loading amount of the dispersion solution on the first light absorber 1 is 50-200 μL / cm 2 .

[0091] In these embodiments, by controlling the concentration and loading amount of the dispersion solution within the above ranges respectively and the parameters of magnetron sputtering, it can be ensured that the finally formed protective layer has a suitable thickness, which does not affect the semiconductor light absorption while realizing the fixation of the cocatalyst and efficient electron transmission.

[0092] In some embodiments, the preparation method of the cocatalyst layer can include:

[0093] Preparation of a cocatalyst thin film by the first magnetron sputtering;

[0094] Construction of localized electronic structure on the cocatalyst thin film to prepare the cocatalyst layer.

[0095] In these embodiments, the deposition of the cocatalyst on the cocatalyst carrier by the first magnetron sputtering forms a cocatalyst thin film, and then the localized electronic structure can be constructed in the catalyst thin film by oxygen doping and / or alloying treatment, for example, by high-temperature annealing, the oxidation state can appear locally in the copper thin film, thereby realizing Cu + The mass ratio in the Cu thin film can be adjusted in the range of 1%-70%; and by depositing two or more metals and then annealing, the localized electronic structure can be constructed by the exchange of electrons between the metals in the alloy. The localized electronic structure can store photo-generated electrons, act as Lewis acid sites, and be beneficial to the adsorption and activation of nitrate / nitrite.

[0096] In some embodiments, the target material used in the first magnetron sputtering is selected from one or more of transition metals; the power source used in the first magnetron sputtering is a direct current power source or an alternating current power source, the power density of the first magnetron sputtering is 0.35-30 W / cm 2 , the working pressure is 0.5-4 Pa, the sputtering time is 0.5-360 min, and the temperature is 20-800 °C.

[0097] In these embodiments, by adjusting the target material type, deposition power source, deposition power, deposition time, deposition temperature and pressure to be within the above ranges, thin films of different compositions, structures and thicknesses can be obtained, thereby maximizing the catalytic effect of the co-catalyst.

[0098] In some embodiments, the deposition of the back electrode 4 on the back of the first light absorber 1 is performed by magnetron sputtering, and the sputtering deposition parameters are consistent with the co-catalyst layer sputtering deposition parameter range.

[0099] Some embodiments of the present application provide a photoanode 20, as shown in Figure 3 , comprising: a transparent substrate 201, and a second light absorber 202 disposed on the transparent substrate 201, the material of the second light absorber 202 being micron-sized titanium dioxide material; the compressive stress of the second light absorber 202 being 10-100 MPa, and the ferromagnetic property being 5-38 emu · cm -3 .

[0100] Wherein, the above transparent substrate 201 can be a quartz film substrate. In addition to the above transparent substrate 201 and the second light absorber 202, the photoanode 20 can also include a metal titanium conductive layer 203.

[0101] The photoanode 20 can be used for photoelectrochemical water splitting to produce oxygen.

[0102] The above second light absorber 202 and metal titanium conductive layer 203 can be prepared by second magnetron sputtering, such as by second magnetron sputtering deposition on the above transparent substrate 201. In this process, by controlling the compressive stress size (such as 10-100 MPa) of the material (such as the material of the second light absorber), the consistency of the high density and grain orientation of the prepared thin film is used to form a magnetic axis to enhance the directional movement of carriers, the prepared thin film has a ferromagnetic property (5-38 emu · cm -3 ), which drives the effective separation and transport of photo-generated carriers, and completes stable and efficient photoelectrochemical oxygen evolution reaction at very low voltage.

[0103] Specifically, the grains of the micron-sized titanium dioxide material are columnar crystals, the orientation of each grain is perpendicular to the transparent substrate, and the grains are arranged in parallel between the grains.

[0104] In some embodiments, the cavity is pre-evacuated to achieve a high vacuum state (e.g., a pressure of 5 × 10⁻⁶). -4 ~10 -5 The target and transparent substrate are cleaned under a specific argon atmosphere (10~100 sccm). After cleaning, a titanium conductive layer and a second absorber are deposited at a specific power. The power supply used for the second magnetron sputtering is either a DC power supply or an RF power supply, and the power density of the second magnetron sputtering is 17~30 W / cm². 2 The deposition time is 1 to 6 hours; the working gas used in the second magnetron sputtering is argon, and the reaction gas is oxygen. The ratio of the argon flow rate to the oxygen flow rate is 5 to 0.5, and the pressure inside the cavity of the second absorber during deposition is 0.4 to 4 Pa.

[0105] Some embodiments of this application provide a device 100 for photoelectrochemical ammonia synthesis, such as... Figure 3 As shown, it includes: a photocathode 10 as described above and a photoanode 20 prepared by the method described above; wherein, the second light absorber 202 in the photocathode 10 and the photoanode 20 is located on the same side of the transparent substrate 201 contained in the photoanode 20, but in different regions.

[0106] This device can be used for photoelectrochemical reactions to reduce ammonia production.

[0107] In use, the photocathode 10, photoanode 20, and electrolyte can be assembled into an electrolytic cell. Sunlight is then irradiated onto the side of the photocathode 10 facing the co-catalyst layer, causing the photocathode 10 to separate holes and electrons under illumination. This allows the nitrogen source in the electrolyte to continuously undergo a reduction reaction to produce ammonia under the catalysis of the co-catalyst.

[0108] In some embodiments, the photocathode 10 is located at the center of the transparent substrate 201, and the second light absorber 202 included in the photoanode 20 is arranged around the photocathode 10 to form a U-shaped structure.

[0109] In these embodiments, the photocathode 10 and photoanode 20 are located on the same plane. The photocathode 10 is located on the transparent substrate 201 and is in the center position, which facilitates the connection between the photoanode 20 and the photocathode 10 by preparing wires at the edge. The photocathode 10 and the photoanode 20 are illuminated by a light source set on the same side of the transparent substrate 201. The preparation method is simple and easy to implement, which can improve the utilization rate of the light source. Moreover, this type of structure is conducive to mass and charge transfer.

[0110] In some embodiments, the area ratio of the second absorber 202 included in the photocathode 10 and the photoanode 20 is 1:100 to 1:2.

[0111] In these embodiments, the cost of the photocathode 10 can be reduced to the greatest extent, and a high photocurrent density can be ensured.

[0112] In some embodiments, when being manufactured, the metal titanium conductive layer 203 and the second light absorber 202 contained in the photoanode 20 can be deposited on a partial region of the transparent substrate 201 in a manner of being shielded by silica gel, and then the photocathode 10 can be fixed on other regions of the transparent substrate 201 by epoxy, so that the photoanode 20 and the photocathode 10 are located on different regions of the transparent substrate 201.

[0113] As shown in Figure 4 and Figure 5 , the test case of the compactness of the second light absorber contained in the photoanode provided in the present application is shown. As shown in Figure 4 , the nitrogen is adsorbed throughout the adsorption process, and it can be known from Figure 4 that the adsorption and desorption process curves are basically coincided, which indicates that the specific surface area of the titanium oxide is very small, and the surface is basically a smooth plane, which indicates that the titanium oxide film is very compact, as shown in Figure 5 , the surface pore diameter of the titanium oxide is basically about 5 nm, which indicates that the surface pore diameter of the titanium oxide is very small, and the film is very compact.

[0114] In the present application, the ferromagnetism induced by the photoanode with high compressive stress accelerates the directional movement of the carriers, and improves the separation and injection efficiency of the carriers, as shown in Figure 6 , the photoanode exhibits a saturated current density of about 0.38 mA·cm -2 in 1 M KOH solution and under 1 sun illumination at 0.3 V vs. RHE.

[0115] It should be noted that the above-mentioned photocathode 10 and photoanode 20 can be connected to the external circuit through the back electrode. For example, the copper tape 300 can be pasted on the back electrode through the silver glue 200, and the photocathode 10 and the photoanode 20 are connected to the power supply through the copper tape 300, at this time, the bias voltage can be applied to the photocathode 10 by the power supply to realize the reduction of the nitrogen source to produce ammonia, or the photocathode 10 and the photoanode 20 are directly connected by the copper tape, at this time, only the photoelectric conversion can be used to realize the reduction of the nitrogen source to produce ammonia, and the bias voltage does not need to be applied to the photocathode 10.

[0116] In some embodiments, in order to suppress the dark current (current generated without light), the epoxy 400 can also be formed at the edge position of the transparent substrate 201, so that the silver glue 200 and the copper tape 300 can be sealed and wrapped, preventing the silver glue 200, the copper tape 300 and / or the back electrode from directly contacting the electrolyte, and at the same time, the photocathode 10 can be fixed on the transparent substrate 201.

[0117] In some embodiments, the device 100 can further comprise an electrolyte, the electrolyte comprising a nitrogen source and an electrolyte, wherein the nitrogen source comprises one or more of nitrogen, nitrite and nitrate, and the electrolyte comprises one or more of potassium sulfate, potassium hydroxide and potassium bicarbonate.

[0118] Optionally, after completing the ammonia production, the pH value of the electrolyte is 3-14, and / or the concentration of nitrogen atoms in the electrolyte is 0.02-0.3 mol / L. The nitrogen oxide resource utilization and recycling can be applied to industrial waste gas and automobile exhaust.

[0119] In summary, in the present application, due to the excellent light absorption and electron and hole separation and transfer efficiency of the photoelectrode 10, the significantly improved photovoltage and lower starting potential, the excellent nitrogen source reduction ammonia selectivity, the current matching (the current is the same at the same potential, such as Figure 7 In the present application, the current intersects at 0.1 V vs. RHE, which is 1 mA) of the titanium oxide photoanode, so that high-efficiency reduction ammonia can be realized without bias. Among them, Figure 7 In the above ammonia production process, the photoelectrode and the photoanode simultaneously receive photons, and based on the matching condition of the energy band structure, a built-in electric field is formed to drive the photo-generated electrons and holes to reach the surface of the photoelectrode and the photoanode, respectively, to implement the reduction reaction of the nitrogen source to synthesize ammonia and the oxygen evolution reaction.

[0120] Some embodiments of the present application provide an application of the device as described above in photoelectrochemical ammonia production.

[0121] By placing the photoelectric device in an electrolyte containing a nitrogen source, and irradiating the photoanode and the photoelectrode with simulated sunlight, the nitrogen source in the electrolyte can be electrolytically reduced to produce ammonia, and the ammonia production efficiency of the photoelectric device can be detected.

[0122] In order to objectively evaluate the technical effects of the embodiments of the present application, the following will be described in detail by way of example and comparative example.

[0123] In the following examples and comparative examples, all raw materials can be obtained by commercial form, and in order to maintain the reliability of the experiment, the raw materials used in the following examples and comparative examples all have the same physical and chemical parameters or are obtained by the same treatment.

[0124] Example 1

[0125] I. Preparation of photoelectrode:

[0126] (1) Preparation of semiconductor substrate layer:

[0127] A 0.5 mm thick boron-doped p-type silicon wafer was used as a substrate, ultrasonically cleaned with ethanol for 20 min, immersed in 2% KOH prepared in advance, heated in a water bath at 80 °C for 1 h, and taken out of the water surface every 5 min to eliminate the bubbles on the surface and then immersed again. Immediately after etching, the p-type silicon wafer was rinsed with ionized water, and a hair dryer was used to dry the p-type silicon wafer in one direction to obtain a conical surface roughened silicon wafer.

[0128] The surface roughened silicon wafer was immersed in a 1% mass fraction HF solution to remove the silicon oxide during the alkali etching process, and the immersion time was 3 min. After completion, it was taken out and rinsed with deionized water, and then dried with a hair dryer. 0.1419 g of phosphorus pentoxide (analytical purity of 99.995%) was dissolved in anhydrous ethanol, and 1 drop / cm 2 of the solution was dropped on the treated silicon wafer, which was immediately placed in a rapid vacuum annealing furnace at 800 °C for 8 min, and then taken out when the temperature dropped to about 100 °C. The silicon oxide produced during annealing was removed with a 1% mass fraction HF solution to obtain an n + p-type silicon wafer.

[0129] (2) Preparation of protective layer:

[0130] An appropriate amount of 5-amino uracil was placed in a tube furnace, and heated at 350 °C for 1 h under an argon atmosphere, then heated to 650 °C and kept at this temperature for 1 h, and finally heated to 900 °C for 1 h to obtain a graphite sheet. The entire process had a heating rate of 5 °C / min.

[0131] 2 mg of the graphite sheet was dispersed in 950 μL of isopropyl alcohol containing 50 μL of the film solution, and ultrasonically dispersed for 20 min. The solution was dropped on the treated n 2 p-type silicon wafer at a loading of 50 μL / cm + , and dried under an infrared lamp. Finally, an n + p-type silicon wafer with a protective layer on the surface was obtained, and the thickness of the protective layer was 6.67 nm.

[0132] (3) Preparation of catalyst promoter:

[0133] The above-prepared silicon wafer with a protective layer was fixed on a magnetron sputtering carrier plate, and copper deposition was performed using a direct current power source. The sputtering conditions were as follows: power density was 0.74 W / cm 2 , time was 7 min, chamber pressure was 1 Pa, gas was argon, and temperature was 50 °C.

[0134] After sputtering, the sample was placed in a rapid vacuum annealing furnace and annealed at 800 °C for 2 min to obtain a sample loaded with a catalyst promoter.

[0135] (4) Preparation of back electrode:

[0136] Gold was deposited on the back side of the annealed sample using magnetron sputtering physical deposition. A DC power supply was used for sputtering, and the sputtering power density was 0.49 W / cm². 2 The process took 5 minutes, the working atmosphere was argon with a flow rate of 39.7 sccm, and the chamber pressure was 1 Pa. Finally, a silicon-based photocathode with a protective layer supported by a nano-copper co-catalyst was prepared, with a thickness of 100 nm.

[0137] II. Fabrication of Optoelectronic Devices:

[0138] The optoelectronic device is assembled from the aforementioned photocathode and photoanode on quartz glass.

[0139] like Figure 3 The diagram shown is a schematic representation of the optoelectronic device. The specific fabrication method of this optoelectronic device is as follows:

[0140] (1) Substrate preparation:

[0141] The quartz glass was first ultrasonically cleaned in sodium hydroxide for 30 min, and then ultrasonically cleaned in analytical grade anhydrous ethanol for 30 min. It was then dried and set aside for later use.

[0142] (2) Preparation of photoanode:

[0143] A square area with a side length of 1.5 cm was left blank at the top of a quartz glass plate with a length of 4 cm and a width of 3 cm, and covered with silicone. A titanium layer was deposited on the remaining area as a hole transport layer. Two small areas of the titanium layer were covered with silicone. A titanium dioxide layer was deposited in the remaining area using magnetron sputtering as an anode absorber. After deposition, a copper strip was attached to the titanium layer covered with silicone using silver paste. After drying in the air overnight, the silver paste and the copper strip in the silver paste area were sealed with epoxy resin.

[0144] The above-mentioned titanium layer deposition was performed using a DC power supply, an argon inert atmosphere, a working pressure of 2 Pa, an argon flow rate of 39.7 sccm, and a sputtering power density of 21.22 W / cm². 2 The sputtering time was 5 min; when depositing titanium dioxide, only the gas introduced was changed to argon and oxygen, the flow rate of argon and oxygen was 20 sccm, the deposition time was 4 h, and the other conditions remained unchanged.

[0145] (3) Assemble optoelectronic devices:

[0146] The photoelectric cathode was assembled in a square area with a side length of 1.5 cm on the substrate on which the photoanode was prepared, and the steps mainly included: a copper strip was adhered to the back of the silicon substrate layer of the prepared square photoelectric cathode with a side length of 1 cm (i.e. the gold-plated surface) through silver glue, dried in a vacuum oven at 40 °C for 2 h, and then fixed on a quartz glass in a square area with a side length of 1.5 cm using epoxy resin glue, and the edges of the silicon substrate layer and the copper strip that might be immersed in the electrolyte containing 50 mM KNO3 and 1 M KOH were sealed with epoxy resin glue, thereby obtaining the photoelectric device.

[0147] Example 2

[0148] The preparation method of the photoelectric device in Example 2 was basically the same as that of the photoelectric device in Example 1, except that: the photoelectric cathode used p-type planar silicon as the light-absorbing substrate; the deposition promoter was Ni, the sputtering power was 30 W / cm 2 , the working pressure was 0.5 Pa, the sputtering time was 0.5 min, and the working temperature was 20 °C; the protective layer used graphene dispersed in isopropanol, and the dispersion solution was spin-coated onto the p-type planar silicon, and the thickness of the protective layer was 10 nm.

[0149] Example 3

[0150] The preparation method of the photoelectric device in Example 3 was basically the same as that of the photoelectric device in Example 1, except that: the photoelectric cathode used InP as the light absorber substrate; the deposition promoter was W, the sputtering power was 10 W / cm 2 , the working pressure was 2 Pa, the sputtering time was 3 min, and the working temperature was 50 °C; silicon oxide was deposited on the surface of the silicon substrate as a protective layer by a magnetron sputtering method, the working pressure was 2 Pa, the working atmosphere was oxygen / argon mixed gas (ratio 20 sccm / 20sccm), the deposition time was 5 min, and the thickness was 5 nm.

[0151] Example 4

[0152] The preparation method of the photoelectric device in Example 4 was basically the same as that of the photoelectric device in Example 1, except that: the photoelectric cathode used Cu2O as the light absorber substrate; the deposition promoter was Ti, the sputtering power was 0.35 W / cm 2 , the working pressure was 4 Pa, the sputtering time was 120 min, and the temperature was 400 °C.

[0153] Example 5

[0154] The preparation method of the photoelectric device in Example 5 is basically the same as that in Example 1, except that in the preparation of the co-catalyst of the photoelectric cathode, a thin film co-catalyst is deposited by a magnetron sputtering method, and no annealing treatment is performed.

[0155] Example 6

[0156] The preparation method of the photoelectric device in Example 6 is basically the same as that in Example 1, except that in the preparation of the photoelectric anode, the sputtering deposition time of the titanium dioxide photoelectric anode is 2 h, the sputtering power is 25 W / cm 2 , the flow ratio of oxygen to argon is 1.5, and the working pressure is 4 Pa.

[0157] Example 7

[0158] The preparation method of the photoelectric device in Example 7 is basically the same as that in Example 1, except that in the preparation of the photoelectric device, the area ratio of the photoelectric anode to the photoelectric cathode is 20.

[0159] Example 8

[0160] The preparation method of the photoelectric device in Example 8 is basically the same as that in Example 1, except that the electrolyte used is a 1 M potassium bicarbonate and 50 mM potassium nitrate aqueous solution.

[0161] Performance test:

[0162] 1. The photoelectric device prepared in Example 1 above was tested for linear voltammetry scan curve, and the specific test results are shown in Figure 7 .

[0163] The single three-electrode system refers to a system composed of the photoelectric cathode and the photoelectric anode prepared in Example 1 of the present application as the working electrode, Ag / AgCl as the reference electrode, and platinum sheet as the counter electrode. In this system, the electrolyte is a 50 mM potassium nitrate aqueous solution and a 1 M KOH aqueous solution, the light is 100 mW / cm 2 , the cathode and anode electrolyte are both 8 mL, and the test is completed in an H cell.

[0164] The scan speed is 0.02 V / s, the voltage range for the photoelectric cathode as the working electrode is from +0.6 to -0.6 V vs. RHE, and the voltage range for the photoelectric anode as the working electrode is -0.1 to +0.6 V vs. RHE. The photoelectric anode or the photoelectric cathode is irradiated with simulated sunlight, and the light power density of the simulated sunlight is 100 mW / cm 2, polytetrafluoroethylene H-cell. Both the photo-cathode and the photo-anode show very high onset potential, the onset potential of the photo-cathode is +0.083 V vs. RHE, and the onset potential of the photo-anode is +0.012 V vs. RHE. The onset potential of the photo-electric field is the potential corresponding to the current of 1 mA cm -2 -2 when the light is on, i.e. the onset potential of the photo-cathode is +0.083 V vs. RHE, and the onset potential of the photo-anode is +0.012 V vs. RHE. It can be seen from Figure 9 that the current intersects at 0.1 V vs. RHE, and the current density is 1 mA, which indicates that the photo-cathode and the photo-anode exist current matching, and reach the condition of theoretically forming a photoelectric device. The photo-cathode has good performance, which is reflected in that the saturation current density (i.e. the maximum current density) can reach 31.5 mA cm -2 -2, and the onset potential is low (+0.083 V vs. RHE).

[0165] 2. As shown in Figure 8 , it is a current-time curve diagram of the photoelectric device provided in Example 1 under the chopping mode (dark-light-dark) under constant voltage, and the generated photocurrent is basically stable. The chopping mode refers to: 3 seconds of light irradiation vertically irradiating the photo-electrode, and 3 seconds of darkness. Then the irradiation mode of the irradiation is repeated.

[0166] 3. As shown in Figure 9 , it is an ammonia production efficiency diagram of the photoelectric device provided in Example 1 under 0 V and 1 simulated sunlight (light power density is 100 mW / cm 2 ;

[0167] It can be seen from Figure 9 that Example 1 can efficiently reduce nitrate to produce ammonia, and under the condition of not applying any bias, has a yield of 13.1 μmol·cm -2 ·h -1 and a solar energy conversion efficiency of 1.55%, and a Faraday efficiency of 98.83%.

[0168] 4. As shown in Figure 10 , it is an ammonia production efficiency diagram of the photoelectric device provided in Examples 2-5 under 1 simulated sunlight in a three-electrode system with a bias of -0.6 V vs. RHE;

[0169] As shown in Figure 10 , efficient ammonia production can be achieved in Examples 2-5, especially when copper and Ti are used as co-catalysts, the ammonia production yield can reach 32 μmol·cm -2 ·h -1 and 18.24 μmol·cm -2 ·h -1, the faraday efficiencies are 67% and 75.21%, respectively.

[0170] 5. As shown in FIG. 5, the linear voltammetry curves of the photoelectrode and the photoanode in the photoelectric device of Example 6 are shown in a single three-electrode system, and the specific test method is the same as that of Example 1. Figure 11

[0171] As shown in FIG. 6, the current intersects at 0.1 V vs. RHE, and the current density is 1.77 mA, indicating that the photoelectrode and the photoanode exist current matching, and meet the theoretical conditions for forming a photoelectric device. Figure 11

[0172] 6. As shown in FIG. 7, the linear voltammetry curves of the photoanode of Example 7 in a three-electrode system under 1 simulated sunlight are shown, and the specific test method is the same as that of Example 1. Figure 12 As shown in FIG. 8, the photoanode shows a current density close to 0.1 mA·cm -2 at 0 V vs. RHE, indicating that it can match the current with the photoelectrode in Example 1, and under a certain area ratio of the photoelectrode and the anode, the two can form a photoelectric device for ammonia production by nitrate reduction without bias voltage.

[0173] Figure 12 7. As shown in FIG. 9, the ammonia production efficiency of the photoelectrode of Example 8 in a three-electrode system under 1 simulated sunlight with a bias voltage of -0.6 V vs. RHE is shown, wherein the concentration of different electrolytes is 1 mol / L.

[0174] As shown in FIG. 10, in Example 8, the composition of the electrolyte is changed (potassium sulfate, potassium bicarbonate, potassium hydroxide, etc.) while the nitrogen source remains the same (50 mM nitrate), and the photoelectrode in Example 8 shows a yield of 12.01 μmol·cm -2 ·h -1 , 17.8 μmol·cm -2 ·h -1 and 30.18 μmol·cm -2 ·h -1 , respectively, when the electrolyte is potassium bicarbonate (pH=3.5), potassium sulfate (pH=6.8), and potassium hydroxide (pH=14), respectively, and the faraday efficiencies are 54.43%, 55.34%, and 65%, respectively. This indicates that the photoelectrode can exhibit good nitrate reduction performance under different pH electrolyte conditions. Figure 13

[0175] Figure 13

[0176] ​​​​​​Any combination of the technical features in the above-described embodiments can be made, and for the sake of brevity, not all possible combinations are described, however, it is to be understood that the application embraces all such possible combinations.

[0177] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the application. It should be pointed out that for ordinary skilled persons in the art, some modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A device for photoelectrochemical synthesis of ammonia, characterized in that Comprise: a photo-cathode and a photo-anode; the photo-cathode comprises: a first light absorber, and a protective layer and a co-catalyst layer which are sequentially stacked on the surface of the first light absorber; wherein the protective layer is light-transmissive, and the material of the protective layer comprises one or more of graphene and graphite sheets; the material of the co-catalyst layer comprises one or more of transition metal materials; The photoelectric anode comprises a transparent substrate and a second light absorber arranged on the transparent substrate, the material of the second light absorber is micron-sized titanium dioxide material; the crystal grains of the micron-sized titanium dioxide material are columnar crystals, the orientation of each crystal grain is perpendicular to the transparent substrate, and the crystal grains and the crystal grains are arranged in parallel; the compressive stress of the second light absorber is 10-100 MPa, and the ferromagnetism is 5-38 emu cm -3 . wherein the second light absorber in the photo-cathode and the photo-anode is located on the same side of the transparent substrate contained in the photo-anode and in different regions; the area ratio of the second light absorbers contained in the photo-cathode and the photo-anode is 1:100~1:

2.

2. The device of claim 1, wherein, The first light absorber, the protective layer and the co-catalyst layer at least meet one of the following conditions: (1) the first light absorber is a p-type narrow-band-gap semiconductor material; (2) the graphene and / or graphite sheets are prepared by a hydrothermal high-temperature pyrolysis method, and the protective layer is prepared by at least one of spin coating, drop coating and spraying to apply a dispersion liquid of the graphene and / or graphite sheets on the surface of the first light absorber; (3) the thickness of the protective layer is 5~20 nm; (4) the transition metal material comprises transition metal elements, and part of the transition metal elements exist in the form of metal cations and / or intermetallic compounds in the transition metal material; (5) the transition metal material comprises one or more of copper, nickel, iron, titanium and tungsten.

3. The device of claim 2, wherein, The p-type narrow-bandgap semiconductor material comprises: p-type silicon, heterojunction n + p-type silicon, cuprous oxide, and indium phosphide.

4. The device of claim 2, wherein, The mass proportion of the metal cations and / or intermetallic compounds in the transition metal material is 0~70%.

5. The device of claim 1, wherein, The preparation method of the co-catalyst layer comprises: using a first magnetron sputtering to prepare a co-catalyst film; constructing a localized electronic structure on the co-catalyst film to prepare the co-catalyst layer.

6. The device of claim 5, wherein, The target material used in the first magnetron sputtering is selected from one or more of transition metals; the power source used in the first magnetron sputtering is a direct current power source or an alternating current power source, the power density of the first magnetron sputtering is 0.35-30 W / cm 2 , the working pressure is 0.5-4 Pa, the sputtering time is 0.5-360 min, and the temperature is 20-800 °C.

7. The device according to claim 1, wherein: the second light absorber is prepared by a second magnetron sputtering; The power supply for the second magnetron sputtering is a direct current power supply or a radio frequency power supply, and the power density of the second magnetron sputtering is 17-30 W / cm 2 The time is 1-6 h; the working gas for the second magnetron sputtering is argon, and the reaction gas is oxygen, and the ratio of the argon flow rate to the oxygen flow rate is 5-0.5; and the pressure in the cavity during deposition of the second light absorber is 0.4-4 Pa.

8. The device according to claim 1, wherein: the photo-cathode is located at the center of the transparent substrate, and the second light absorber contained in the photo-anode is arranged around the photo-cathode to form a U-shaped structure.

9. The device according to claim 1, wherein: the transparent substrate contained in the photo-anode and the photo-cathode are both square, and the side length of the square of the transparent substrate is greater than or equal to 50 cm, and the side length of the square of the photo-cathode is greater than or equal to 5 cm.

10. The device according to claim 1, wherein: the device further comprises an electrolyte, and the electrolyte comprises a nitrogen source and an electrolyte, wherein the nitrogen source comprises one or more of nitrogen, nitrite and nitrate, and the electrolyte comprises one or more of potassium sulfate, potassium hydroxide and potassium bicarbonate.

11. The device of claim 10, wherein, After completing the production of ammonia, the pH value of the electrolyte is 3~14, and / or the concentration of nitrogen atoms in the electrolyte is 0.001~2 mol / L.

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