Preparation method of high-performance photoelectrocatalytic silicon photoanode

Abstract

The application belongs to the technical field of photoelectrocatalytic water splitting, and particularly relates to a preparation method of a high-performance photoelectrocatalytic silicon photoanode. i The CuO intermediate layer film, the NiO film and the NiCoFe-B In the preparation process, by controlling the O2 gas flow rate in the reaction electron beam evaporation deposition system, the formation of the CuO phase in the intermediate layer film is controlled, the NiO / n-Si heterojunction photoanode interface is effectively regulated, the generation of a larger photoelectric voltage on the n-Si photoanode is promoted, and the photoelectrocatalytic water splitting performance of the n-Si photoanode is significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photoelectrocatalytic water splitting, and particularly relates to a preparation method of a high-performance photoelectrocatalytic silicon photoanode. BACKGROUND

[0002] Photoelectrocatalytic (PEC) water splitting technology is a method that can directly convert solar energy into hydrogen energy, and is one of the ideal ways for the global energy structure to transform to green, efficient and sustainable. PEC water splitting technology is usually composed of a cathode hydrogen evolution reaction (HER) and an anode oxygen evolution reaction (OER). The slow four-electron transfer process in OER causes more energy loss and is the main limiting factor of full water splitting reaction. Therefore, the research on the water oxidation reaction on the surface of the photoanode is the basis for the commercialization of PEC water splitting technology.

[0003] Monocrystalline silicon, as the mainstream semiconductor material on the market, is widely used in photovoltaic and microelectronic fields. Because of its abundant earth reserves, it can be produced on a large scale, has a high theoretical current density, and excellent carrier mobility and carrier diffusion length, and can be used as a model for the study of photoelectrode surface / interface in PEC water splitting to develop strategies. Because the band position of monocrystalline silicon is not conducive to water oxidation reaction, it has a low photovoltage and a high starting position. In order to obtain high PEC activity, a suitable interface layer is usually used to adjust the energy state of the buried interface. The interface layer can optimize the band edge (valence band top / conduction band bottom) position between the semiconductor and the protective layer / catalyst layer, promote the transfer of holes from the semiconductor to the surface active site, and thus effectively drive the OER process.

[0004] At present, the most advanced n-type silicon (n-Si) photoanode device usually uses NiO x , CoO x , SnO x and NiCoO x interface layer to improve its PEC activity. Lewis et al. pioneered the introduction of a CoO x intermediate layer into the interface of a NiO x / n-Si heterojunction photoanode, achieving a stable saturated photocurrent of up to 1700 hours, but the half-cell solar-to-hydrogen efficiency (HC-STH) of the device is only 2.2%. The most efficient silicon-based photoanode in the prior art is obtained by using SnO xThe middle layer achieved 4.1% of HC-SiTH, but the efficiency is still far below the minimum requirement of 10% commercial application. These pioneering research results highlight the importance of interface engineering to improve the efficiency of silicon-based photoanode. However, how to realize efficient PEC water oxidation on n-Si photoanode still needs to explore energy matching and chemically stable interface. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of high-performance photoelectrocatalytic silicon photoanode, which is aimed at the problems or deficiencies in the prior art. The CuO middle layer film is prepared by reactive electron beam evaporation method and introduced into the interface of NiO / n-Si heterojunction photoanode, so as to improve its performance.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of high-performance photoelectrocatalytic silicon photoanode, comprising the following steps:

[0008] Step 1, the n-Si wafer is sequentially cleaned with acetone and isopropyl alcohol by ultrasonic cleaning, and then dried by blowing;

[0009] Step 2, using Cu2O as Cu source, using reactive electron beam evaporation equipment to prepare a CuO middle layer on n-Si wafer;

[0010] Step 3, using NiO as Ni source, using electron beam evaporation equipment to deposit NiO film on the structure obtained in step 2;

[0011] Step 4, using TEM, XPS, UPS and other characterization methods to analyze the morphology, phase and energy band structure of the structure obtained in step 3, if the analysis result reaches the preset standard, then enter step 5;

[0012] Step 5, after etching the back surface of the sample obtained in step 3 using 5%-20% HF solution, rinsing with deionized water, coating indium-gallium (In-Ga) liquid alloy on the etched surface, and connecting the indium-gallium alloy on the back surface of the n-Si sample obtained in step 3 with the lead wire using silver paste, and then packaging it using epoxy resin;

[0013] Step 6, using three-electrode system to perform photo-assisted electrochemical deposition of NiCoFe-B i Oxygen evolution cocatalyst on the structure obtained in step 5, and then rinsing with deionized water;

[0014] Step 7, using three-electrode system to test and evaluate PEC water splitting of the structure obtained in step 6.

[0015] Furthermore, in step 2, using Cu2O as the Cu source, the conditions for preparing a CuO intermediate layer on an n-Si wafer using a reactive electron beam evaporation apparatus are as follows:

[0016] The equipment needs to be evacuated to a vacuum level of 5×10⁻⁶ before starting. -6 Torr;

[0017] During the preparation of the CuO intermediate layer, O2 was introduced into the deposition chamber at a gas flow rate of 0-17 sccm. The corresponding chamber vacuum degree for different gas flow rates was 2.0 × 10⁻⁶. -5 -2.1×10 -4 Torr is used to oxidize the evaporated Cu2O particles into CuO particles, which are then deposited on an n-Si wafer to prepare a CuO intermediate layer.

[0018] The deposition rate of the CuO thin film is Deposition thickness is

[0019] Furthermore, in step 3, NiO is used as the Ni source, and an electron beam evaporation apparatus is used to deposit a NiO thin film on the structure obtained in step 2, under the following conditions:

[0020] Without the introduction of O2 gas flow, the deposition rate is Deposition thickness is

[0021] Furthermore, in step 6, a three-electrode system is used to process the structure obtained in step 5 using NiCoFe-B. i Methods for photo-assisted electrochemical deposition of oxygen evolution co-catalysts include:

[0022] (1) Potassium borate with a pH of 10 was used as a buffer solution;

[0023] (2) Argon gas was introduced into the buffer solution and stirring was started. Then, 0.5 mM Co(NO3)2·6H2O, 2 mM NiSO4·6H2O and 0.8 mM FeSO4·7H2O were added to serve as ion sources.

[0024] (3) Simulate solar irradiation on the product obtained in (2), maintaining an irradiation intensity of 100 mW·cm⁻¹. -2 , at 10-50 μA·cm -2 A constant current density will be used to apply NiCoFe-B i The oxygen evolution co-catalyst is deposited onto the surface of the structure obtained in step 5.

[0025] Furthermore, the buffer solution is prepared by mixing H3BO3 and KOH at a concentration ratio of 1:0.6.

[0026] The application prepares CuO intermediate layer film, NiO film and NiCoFe-B film on the surface of n-Si photoanode by using a reactive electron beam evaporation deposition system, a common electron beam evaporation deposition system and a photo-assisted electrochemical deposition method in sequence i catalyst layer. In the preparation process, the formation of CuO phase in the intermediate layer film is controlled by controlling the O2 gas flow rate in the reactive electron beam evaporation deposition system, so as to effectively control the interface of the NiO / n-Si heterojunction photoanode, promote the generation of greater photovoltage on the n-Si photoanode, and further significantly improve the performance of the n-Si photoanode in the photoelectrocatalytic water splitting (see Figure 6 and Figure 7 ). BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a schematic diagram of the working principle of the reactive electron beam evaporation deposition system;

[0028] Figure 2 It is a cross-sectional view of the HR-TEM of the NiO / Cu x O / n-Si sample;

[0029] Figure 3 It is an element analysis of the EDS using TEM under the STEM mode of the NiO / Cu x O / n-Si sample; wherein a is a dark field STEM cross-sectional view, and b is an element analysis of the EDS using TEM under the STEM mode (including Si, Cu, Ni and O four elements);

[0030] Figure 4 It is an XPS phase characterization of the Cu x O film prepared by the reactive electron beam evaporation equipment with different O2 gas flow rates; wherein a is the Cu2O phase of the Cu x O film prepared by the reactive electron beam evaporation equipment with an O2 gas flow rate of 0 sccm, and b is the CuO phase of the Cu x O film prepared by the reactive electron beam evaporation equipment with an O2 gas flow rate of 17 sccm;

[0031] Figure 5 It is an UPS energy band structure characterization of the Cu x O film; wherein a is the UPS spectrum of the Cu2O film, and b is the UPS spectrum of the CuO film;

[0032] Figure 6 It is an energy band structure diagram of the n-Si photoanode; wherein a is the energy band diagram of the NiO / Cu2O / n-Si photoanode in the dark state, and b is the energy band diagram of the NiCoFe-B iFigure 1 is a band diagram of the / NiO / Cu2O / n-Si photoanode under light irradiation, Figure 2 is a band diagram of the / NiO / Cu2O / n-Si photoanode in the dark state, Figure 3 is a J-V curve of the / NiO / Cu2O / n-Si photoanode, Figure 4 is an HC-STH curve corresponding to the J-V curve in Figure 3, and Figure 5 is a statistical diagram of the highest HC-STH record of the silicon photoanode. i Figure 1 is a band diagram of the / NiO / Cu2O / n-Si photoanode under light irradiation, Figure 2 is a band diagram of the / NiO / Cu2O / n-Si photoanode in the dark state, Figure 3 is a J-V curve of the / NiO / Cu2O / n-Si photoanode, Figure 4 is an HC-STH curve corresponding to the J-V curve in Figure 3, and Figure 5 is a statistical diagram of the highest HC-STH record of the silicon photoanode.

[0033] Figure 7 Figure 1 is a band diagram of the / NiO / Cu2O / n-Si photoanode under light irradiation, Figure 2 is a band diagram of the / NiO / Cu2O / n-Si photoanode in the dark state, Figure 3 is a J-V curve of the / NiO / Cu2O / n-Si photoanode, Figure 4 is an HC-STH curve corresponding to the J-V curve in Figure 3, and Figure 5 is a statistical diagram of the highest HC-STH record of the silicon photoanode. i Figure 1 is a band diagram of the / NiO / Cu2O / n-Si photoanode under light irradiation, Figure 2 is a band diagram of the / NiO / Cu2O / n-Si photoanode in the dark state, Figure 3 is a J-V curve of the / NiO / Cu2O / n-Si photoanode, Figure 4 is an HC-STH curve corresponding to the J-V curve in Figure 3, and Figure 5 is a statistical diagram of the highest HC-STH record of the silicon photoanode. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings and examples.

[0035] Example 1

[0036] A method for preparing a high-performance photoelectrocatalytic silicon photoanode, comprising the following steps:

[0037] Step 1, ultrasonically clean the n-Si wafer with acetone and isopropyl alcohol for 10 minutes respectively, and then dry it with nitrogen.

[0038] Step 2, place Cu2O as a Cu source into a crucible slot of a reaction electron beam evaporation device, and place the n-Si wafer obtained in step 1 into a sample table of the electron beam evaporation device, and then perform vacuum pumping until the vacuum degree reaches 5x10 -6 Torr; introduce O2 into the deposition chamber at a gas flow rate of 17 sccm, and the vacuum degree under the working condition of the chamber is 2.1x10 -4 Torr. When the Cu source in the crucible is evaporated into the chamber, it will react with the introduced O2 to oxidize the Cu2O particles in the chamber into CuO particles, and deposit on the n-Si wafer to prepare a CuO intermediate layer (see Figure 1 ). A quartz crystal microbalance is used to detect the deposition rate and deposition thickness of the CuO film, the deposition rate of the CuO is the deposition thickness is

[0039] Step 3, then use the electron beam evaporation device to deposit a NiO film on the structure obtained in step 2 using NiO as a Ni source; this process does not require the introduction of O2 flow. A quartz crystal microbalance is used to detect the deposition rate and deposition thickness of the NiO film, the deposition rate is the deposition thickness is

[0040] Step 4, using characterization methods such as TEM, XPS, UPS, etc. to analyze the morphology, phase and band structure of the structure obtained in step 3, and the analysis is shown in Figures 2-6 , if the analysis result reaches the preset standard, step 5 is entered.

[0041] Step 5, after etching the back surface of the sample obtained in step 3 using a 10% HF solution, rinsing it with deionized water, coating an indium-gallium (In-Ga) liquid alloy on the etched surface, and connecting the indium-gallium alloy on the back surface of the n-Si sample obtained in step 3 with the wire using silver paste, and then packaging it using epoxy resin.

[0042] Step 6, using a three-electrode system to perform photo-assisted electrochemical deposition of NiCoFe-B i oxygen evolution co-catalyst on the structure obtained in step 5. The deposition process uses potassium borate with a pH value of 10 as a buffer solution, and the buffer solution in this embodiment is prepared by mixing H3BO3 and KOH at a concentration ratio of 1:0.6. Before deposition, high-purity argon gas is introduced into the buffer solution and stirring is started, and then 0.5mM of Co(NO3)2·6H2O, 2mM of NiSO4·6H2O and 0.8mM of FeSO4·7H2O are added as ion sources. Simulated sunlight is irradiated at an intensity of 100mW·cm -2 , and a constant current density of 30μA·cm -2 is used to deposit the NiCoFe-B i oxygen evolution co-catalyst on the surface of the n-Si photoanode. After deposition, the n-Si photoanode surface is thoroughly rinsed with deionized water.

[0043] Step 7, using a three-electrode system to perform PEC water splitting test and evaluation on the structure obtained in step 6.

[0044] Example 2

[0045] The same as Example 1, the difference from Example 1 is that the O2 gas flow rate introduced into the reaction electron beam evaporation device during deposition of the CuO thin film is set to 5sccm, and the PEC water splitting test is shown in Figure 7 .

[0046] Example 3:

[0047] The same as Example 1, the difference from Example 1 is that the O2 gas flow rate introduced into the reaction electron beam evaporation device during deposition of the CuO thin film is set to 0sccm, and the PEC water splitting test is shown in Figure 7 .

[0048] The product obtained in Example 1 is used as a sample to verify the technical effect:

[0049] Figure 2Cross-sectional image of HR-TEM for n-Si sample. From Figure 2 The layered structure of NiO / Cu x O / n-Si sample can be clearly observed, indicating the uniformity of the thin film prepared by the reactive e-beam evaporation equipment.

[0050] Figure 3 (a)- Figure 3 (b) Elemental analysis of n-Si sample using TEM analysis EDS in STEM mode, from Figure 3 (a)- Figure 3 (b) The layered elemental distribution of NiO / Cu x O / n-Si sample can be clearly observed, indicating the Cu x O interlayer was successfully inserted between the NiO thin film and n-Si wafer.

[0051] Figure 4 (a)- Figure 4 (b) XPS phase characterization of Cu x O thin films prepared by the reactive e-beam evaporation equipment with different O2 flow rates. From Figure 4 (a)- Figure 4 (b) it can be seen that with the increase of O2 flow rate in the reactive e-beam evaporation equipment, the prepared Cu x O thin film is transformed from Cu2O phase (0 sccm) to CuO phase (17 sccm).

[0052] Figure 5 (a)- Figure 5 (b) UPS band structure characterization of Cu x O thin films. From Figure 5 (a)- Figure 5 (b) it can be seen that the Fermi level of CuO thin film (17 sccm) is lower than that of Cu2O thin film (0 sccm).

[0053] Figure 6 (a)- Figure 6 (d) Band structure diagram of n-Si photoanode in dark state / illumination, from Figure 6 (a)- Figure 6 (d) it can be seen that the Fermi level difference between CuO semiconductor and n-Si semiconductor is greater than that between Cu2O semiconductor and n-Si semiconductor, which increases the potential barrier (Φ B ) of the band bending of n-Si semiconductor in dark state, and further increases the generation of higher photo-voltage (V ph ) of n-Si photoanode under illumination, and finally reduces the applied bias for water oxidation reaction.

[0054] Figure 7 (a)-Figure 7 (c) the performance of n-Si photoanode for PEC water splitting, from Figure 7 (a)- Figure 7 (c) it can be seen that the PEC performance of n-Si photoanode is significantly improved with the increase of O2 flow rate in the reaction electron beam evaporation equipment, and the prepared NiCoFe-B i The n-Si photoanode (17 sccm) obtained the current highest HC-STH value of 4.56%.

[0055] It can be understood that the present application is described by some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present application. In addition, under the guidance of the present application, modifications can be made to these features and embodiments to adapt to specific conditions and materials without departing from the spirit and scope of the present application. Therefore, the present application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application are within the scope of the present application.

Claims

1. A method for preparing high performance photoelectrocatalytic silicon photoanodes, characterized in that, The method comprises the following steps: Step 1, the n-Si wafer is sequentially cleaned by ultrasonic cleaning with acetone and isopropyl alcohol, and then is blown dry; Step 2, a CuO intermediate layer is prepared on the n-Si wafer by using Cu2O as a Cu source and using a reactive electron beam evaporation device; Step 3, NiO is used as a Ni source, and a NiO film is deposited on the structure obtained in step 2 by using an electron beam evaporation device; Step 4, the structure obtained in step 3 is analyzed in terms of morphology, phase and energy band structure by using TEM, XPS and UPS characterization methods, and if the analysis result reaches a preset standard, step 5 is entered; Step 5, the back surface of the sample obtained in step 3 is etched by using a 5%-20% HF solution, and after etching, the sample is cleaned by using deionized water, and an indium-gallium liquid alloy is coated on the etched surface to form an indium-gallium alloy layer, the indium-gallium alloy layer is connected to a lead wire by using silver paste, and then the structure is packaged by using epoxy resin; Step 6, the structure obtained in step 5 is subjected to photo-assisted electrochemical deposition of NiCoFe-B using a three-electrode system i The photo-assisted electrochemical deposition of oxygen evolution co-catalyst is completed, and then the structure is thoroughly rinsed with deionized water. Step 7, a three-electrode system is used to test and evaluate the PEC water splitting performance of the structure obtained in step 6.

2. The method according to claim 1, wherein the method is characterized by, In step 2, the Cu2O is used as a Cu source, and a CuO intermediate layer is prepared on the n-Si wafer by using a reactive electron beam evaporation device, and the conditions are as follows: The equipment needs to be vacuumed to 5x10 -6 Torr before starting. In the process of preparing CuO intermediate layer, O2 was introduced into the deposition chamber at a flow rate of 0-17 seem, and the chamber vacuum degree corresponding to different flow rates was: 2.0x10 -5 -2.1x10 -4 Torr, so that the evaporated Cu2O particles were oxidized into CuO particles and deposited on the n-Si wafer to prepare CuO intermediate layer; The deposition rate of the CuO film is 0.1-0.5 Å / s, and the deposition thickness is 3-20 Å.

3. The method according to claim 1, wherein the method is characterized by: In step 3, the NiO is used as a Ni source, and a NiO film is deposited on the structure obtained in step 2 by using an electron beam evaporation device, and the deposition rate is 1-3 Å / s, and the deposition thickness is 50-1000 Å.

4. The method for preparing a high-performance photocatalytic silicon photoanode according to claim 1, characterized in that, The step 6 uses a three-electrode system to perform NiCoFe-B i The method for photo-assisted electrochemical deposition of oxygen evolution co-catalyst includes: (1) Potassium borate with a pH value of 10 is used as a buffer solution; (2) argon is introduced into the buffer solution, and stirring is started, and then 0.5 mM of Co(NO3)2·6H2O, 2 mM of NiSO4·6H2O and 0.8 mM of FeSO4·7H2O are added as ion sources; (3) The product obtained in (2) is irradiated with a simulated sun, and the irradiation intensity is kept at 100 mW-cm -2 at a constant current density of 10-50 μA-cm -2 The oxygen evolution co-catalyst NiCoFe-B i is deposited onto the surface of the structure obtained in step 5.

5. The method according to claim 4, wherein the method is characterized by, The buffer solution is prepared by mixing H3BO3 and KOH at a concentration ratio of 1:0.6.

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