Multifunctional interlayer modified silicon-based nanowire photoelectric cathode and preparation method thereof

Abstract

The invention discloses a multifunctional interlayer modified silicon-based nanowire photoelectric cathode, which comprises a p-Si substrate layer, a nanowire morphology layer, a CdS layer and a MoS2 cocatalyst layer, the preparation method comprises the following steps: (1) cleaning the p-Si substrate, and blow-drying the p-Si substrate for later use; (2) depositing in a first deposition solution to prepare a p-Si substrate with silver particles adsorbed on the surface; (3) etching in an etching solution, and forming a nanowire structure on the p-Si substrate; (4) placing the nanowire structure in a second deposition solution for deposition, and forming a CdS layer on the nanowire structure; and (5) taking the p-Si substrate treated in the step (4) as a working electrode, and depositing in an electro-deposition solution to prepare the silicon-based nanowire photoelectric cathode. The CdS layer and the MoS2 co-catalyst layer in the photoelectric cathode reduce the lattice mismatch problem caused by direct loading of the CdS layer and the MoS2 co-catalyst layer, and meanwhile, the CdS layer and the MoS2 co-catalyst layer and the silicon substrate form a heterogeneous pn junction structure, and the photoelectrochemical performance is remarkably improved through a multi-layer synergistic effect.

Description

Technical Field

[0001] The invention relates to the field of photoelectrochemical technology, and in particular to a multifunctional intermediate layer modified silicon-based nanowire photocathode and a preparation method and application thereof. Background Art

[0002] Solar energy, as the cheapest, most environmentally friendly and most abundant natural energy on earth, has attracted widespread attention. There are many studies on directly using solar energy to generate electricity. Of course, another new energy source, hydrogen energy, has also received more and more attention, especially the combination of solar energy and the earth's abundant water resources. Electric energy is obtained through solar energy to drive the decomposition of water to obtain hydrogen energy. The whole process remains green and pollution-free, and the consumed solar energy and water resources can be regarded as unlimited resources and unlimited use. Therefore, hydrogen energy itself has many advantages: hydrogen energy is currently the most ideal and cleanest energy. Hydrogen and oxygen are obtained through photoelectrocatalytic decomposition of water. Hydrogen combustion consumes oxygen to obtain energy and water, and the obtained water can be used as the raw material for decomposition again. Moreover, the thermal efficiency of hydrogen is higher than that of fossil fuels, because the main product of hydrogen combustion is water, the combustion process is very clean, and there is little heat loss. In addition, it can be seen from its raw materials and products that the reserves of hydrogen energy are very rich. Most of the hydrogen on the earth is stored in the form of water, and solar energy can be regarded as unlimited energy. These advantages make the use of light energy to decompose water into hydrogen energy the most promising energy production model at present. Among them, photoelectrochemical technology can more effectively and stably use solar energy to decompose water to produce hydrogen and is considered to be one of the most promising energy production technologies.

[0003] In the field of photoelectrochemistry, the choice of substrate for photoelectrodes is very important. Silicon stands out among many materials due to its abundant earth reserves, mature industrial foundation, and suitable bandgap width. The narrow bandgap of silicon brings a wider range of light absorption efficiency, but its own surface's slow hydrogen evolution catalytic efficiency greatly limits the efficiency of photoelectric hydrogen production. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a multifunctional intermediate layer modified silicon-based nanowire photocathode and its application. The CdS layer deposited in the photocathode of the present invention can effectively combine the low-cost and high-efficiency silicon substrate and the MoS2 catalyst layer, reduce the lattice mismatch problem of the direct load of the two, and form a heterogeneous pn junction structure with the silicon substrate to effectively improve the separation and transfer of carriers, and accelerate the rate of hydrogen evolution catalytic reaction under the synergistic effect of the surface catalyst, significantly improving the photoelectrochemical performance; the nanowire structure greatly increases the surface area and hydrophilicity of the electrode reaction, while reducing the reflectivity of sunlight, and greatly improving the efficiency of water decomposition and hydrogen production per unit area.

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

[0006] The first object of the present invention is to provide a multifunctional intermediate layer modified silicon-based nanowire photocathode, comprising a p-Si substrate layer, a nanowire morphology layer, a CdS layer and a MoS2 catalyst promoter layer;

[0007] The line width of the nanowire morphology layer is 50-200 nm, and the line height is 3-4 μm.

[0008] In one embodiment of the present invention, the thickness of the CdS layer is 40-50 nm.

[0009] In one embodiment of the present invention, the thickness of the MoS2 promoter layer is 5 to 10 nm.

[0010] The CdS layer is located between the p-Si substrate and the MoS2 co-catalyst layer, and serves as a heterogeneous pn junction layer to provide a band bending layer to accelerate carrier separation and transfer, regulate the interface mismatch between the p-Si substrate and the MoS2 co-catalyst layer, and protect the p-Si substrate.

[0011] The second object of the present invention is to provide a method for preparing the above-mentioned silicon-based nanowire photocathode, the preparation method comprising the following steps:

[0012] (1) Clean the p-Si substrate and blow dry it for later use;

[0013] (2) depositing a p-Si substrate in a first deposition liquid to obtain a p-Si substrate with silver particles adsorbed on the surface;

[0014] (3) placing the p-Si substrate with silver particles adsorbed on the surface into an etching solution for etching to form a nanowire structure (p-Si NWS) on the p-Si substrate;

[0015] (4) placing the p-Si substrate on which the nanowire structure is formed into a second deposition solution for deposition to form a CdS layer (p-Si NWS / CdS) on the nanowire structure;

[0016] (5) The p-Si substrate treated in step (4) is used as a working electrode and deposited in an electroplating solution to obtain the silicon-based nanowire photocathode (p-Si NWS / CdS / MoS2).

[0017] In one embodiment of the present invention, in step (2), the first deposition liquid contains an aqueous solution of hydrofluoric acid and silver nitrate; the concentration of hydrofluoric acid in the first deposition liquid is 4.8 M, and the concentration of silver nitrate is 5 mM; the deposition process conditions are: immersing in the first deposition liquid for 2 minutes at room temperature.

[0018] In one embodiment of the present invention, in step (3),

[0019] The etching solution is an aqueous solution containing hydrofluoric acid and hydrogen peroxide; the concentration of hydrofluoric acid in the etching solution is 4.8M, and the concentration of hydrogen peroxide is 0.4M; the etching conditions are: immersing in the etching solution for 15 minutes at room temperature and away from light.

[0020] In one embodiment of the present invention, in step (4), the second deposition solution is an aqueous solution comprising cadmium sulfate, thiourea and ammonia water, wherein the concentration of cadmium sulfate is 2 mM, the concentration of thiourea is 80 mM, and the concentration of ammonia water is 1.8 M;

[0021] The deposition conditions were: hydrothermal at 70°C for 30 min.

[0022] In one embodiment of the present invention, in step (5), the electrodeposition solution is an aqueous solution of ammonium tetrathiomolybdate, and the concentration of ammonium tetrathiomolybdate is 2 mM.

[0023] In one embodiment of the present invention, in step (5), p-Si NWs / CdS is used as a working electrode, a platinum electrode is used as a counter electrode, and an Ag / AgCl electrode is used as a reference electrode; under a standard solar intensity, a bias voltage of -0.7V (vs.Ag / AgCl) is applied for deposition, and the deposited charge is controlled to be 50mC.

[0024] The third object of the present invention is to provide an application of the above-mentioned silicon-based nanowire photocathode for photoelectrocatalytic water decomposition to produce hydrogen.

[0025] The beneficial technical effects of the present invention are:

[0026] (1) The CdS layer deposited by the present invention can effectively combine the low-cost and high-efficiency silicon substrate and the MoS2 co-catalyst layer, reducing the lattice mismatch problem of the direct loading of the two. At the same time, the heterogeneous pn junction structure formed with the silicon substrate effectively improves the separation and transfer of carriers. The synergistic effect with the surface co-catalyst further accelerates the rate of hydrogen evolution catalytic reaction and significantly improves the photoelectrochemical performance. Therefore, the present invention provides a multifunctional photoelectrochemical device.

[0027] (2) The nanowire structure of the present invention greatly increases the surface area and hydrophilicity of the electrode reaction, while reducing the reflectivity of sunlight, greatly improving the efficiency of water decomposition and hydrogen production per unit area. In addition, the nanowire structure can effectively separate hydrogen bubbles on the surface of the photocathode, reducing the effect of bubble adsorption on the hydrogen evolution reaction.

[0028] (3) Through the photoelectrochemical test of the photocathode of the present invention, the photoelectric device provided by the present invention can reach 32mA / cm in a neutral solution. 2 The high photogenerated current density means that water can be efficiently decomposed to produce hydrogen in a safe and normal environment, and it is a photocathode device with application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the cross-sectional layer structure of p-Si NWS / CdS / MoS2 of the present invention;

[0030] Figure 2 This is a scanning electron microscope image of the cross section of the p-Si NWS obtained in Example 1;

[0031] Figure 3 This is a scanning electron microscope image of the cross section of p-Si NWS / CdS prepared in Example 1;

[0032] Figure 4 This is a cross-sectional SEM image of p-Si NWS / CdS / MoS2 obtained in Example 1;

[0033] Figure 5 The linear sweep voltammetry curves of the series of electrodes prepared in Example 1 and Comparative Example 1 are shown;

[0034] Figure 6 This is a comparison diagram of the linear sweep voltammetric curves of the p-Si NWS / MoS2 photocathode prepared in Comparative Example 1 and the p-Si NWS / CdS / MoS2 photocathode prepared in Example 1 after 1 hour of high-intensity work. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments. The present invention example adopts a step-by-step deposition method to wet chemically etch a nanowire structure on a p-Si substrate, then deposit a CdS layer on the p-Si NWs in a water bath, and finally photoelectrochemically deposit a MoS2 film on the p-Si NWs / CdS to prepare a composite structure photocathode (p-Si NWs / CdS / MoS2 composite electrode) for photoelectrochemical hydrogen production.

[0036] Example 1

[0037] A method for preparing a silicon-based nanowire photocathode comprises the following steps:

[0038] (1) Clean the p-Si substrate layer and blow dry it for later use;

[0039] (2) adding hydrofluoric acid and silver nitrate to pure water and stirring evenly to form a first deposition solution, wherein the concentration of hydrofluoric acid is 4.8 M and the concentration of silver nitrate is 5 mM, and immersing the prepared p-Si substrate in the first deposition solution for 2 min at room temperature to obtain a p-Si substrate with silver particles adsorbed;

[0040] (3) adding hydrofluoric acid and hydrogen peroxide into pure water and stirring to form an etching solution, wherein the concentration of hydrofluoric acid is 4.8 M and the concentration of hydrogen peroxide is 0.4 M, immersing the p-Si substrate adsorbed with silver particles in the etching solution for 15 minutes at room temperature and in the dark to obtain a p-Si NWs structure;

[0041] (4) Mixing cadmium sulfate, thiourea and ammonia water and adding them into pure water to form a second deposition solution, wherein the concentration of cadmium sulfate is 2 mM, the concentration of thiourea is 80 mM, and the concentration of ammonia water is 1.8 M, immersing p-Si NWs in the second deposition solution, and hydrothermal treatment at 70° C. for 30 min to form a CdS layer on the p-Si NWs structure, thereby obtaining p-Si NWS / CdS;

[0042] (5) Ammonium tetrathiomolybdate was added into pure water to form a photoelectrochemical deposition solution, wherein the concentration of ammonium tetrathiomolybdate was 2 mM. p-Si NWs / CdS was used as a working electrode, a platinum electrode was used as a counter electrode, and an Ag / AgCl electrode was used as a reference electrode. A MoS2 catalytic thin layer with a total of 50 mC was deposited on the basis of p-Si NWs / CdS by a photoelectrochemical deposition method to prepare a composite photocathode, which was named p-Si NWs / CdS / MoS2.

[0043] Comparative Example 1

[0044] A method for preparing a silicon-based nanowire photocathode comprises the following steps:

[0045] (1)-(3) are the same as in Example 1;

[0046] (4) Ammonium tetrathiomolybdate was added into pure water to form a photoelectrochemical deposition solution, wherein the concentration of ammonium tetrathiomolybdate was 2 mM. p-Si NWs was used as a working electrode, a platinum electrode was used as a counter electrode, and an Ag / AgCl electrode was used as a reference electrode. A MoS2 catalytic thin layer was deposited on the p-Si NWs by a photoelectrochemical deposition method. The deposited charge was controlled to be 50 mC, and a composite photocathode was prepared, which was named p-Si NWs / MoS2.

[0047] Test example:

[0048] (1) Cross-sectional electron microscopy scanning was performed on the p-Si NWs, p-Si NWs / CdS, and p-Si NWs / CdS / MoS2 composite structure electrodes in Example 1 of the present invention, respectively. Figure 2-4 shown.

[0049] Depend on Figure 2 It can be seen that the line width of the nanowire structure of p-Si NWs is between 50 and 200 nm, and the line length is between 3 and 4 μm; Figure 3It can be seen that a large amount of granular CdS is attached to the surface of p-Si NWs / Cd; Figure 4 It can be seen that the MoS2 of the p-Si NWs / Cd / MoS2 composite electrode is difficult to identify and the amount of attached MoS2 is very small.

[0050] (2) Linear sweep voltammetric curves were tested on p-Si, p-Si NWs, p-Si NWs / Cd / MoS2 in Example 1 of the present invention and p-SiNWs / MoS2 in Comparative Example 1. The series of results are shown in Figure 2. Figure 5 shown.

[0051] The turn-on voltage of the p-Si photocathode is -0.17V, and the photocurrent increases slowly with the voltage change. At a bias voltage of -0.6V, the photocurrent density is only 14mA / cm 2 The p-Si NWs photocathode exhibits better photoelectric performance, both in terms of photocurrent increase rate and photocurrent density under high bias. After the MoS2 film is deposited, the turn-on voltage of the composite electrode shifts to 0.3 V, and the photocurrent density reaches 22 mA / cm at -0.6 V. 2 This is mainly attributed to the good catalytic performance of MoS2 film, but the saturation rate and saturated photocurrent density of the photocathode are still insufficient. CdS is further deposited between p-Si NWs and the catalyst to obtain p-Si NWs / Cd / MoS2 photocathode. This photocathode shows the best performance in the series of photocathodes, and the photocurrent density is greatly improved. The photocurrent density at 0V reaches -14mA / cm 2 The saturation current density is comparable to that of pure silicon at -0.6V. At the same time, the rate of photocurrent density increase has increased significantly. At a bias voltage of -0.5V, the photocurrent density has reached a saturation value of -32mA / cm 2 .

[0052] The improvement in the performance of the composite electrode is mainly due to the carrier separation and transfer effect in the middle of CdS. The n-type CdS and p-type Si form a heterogeneous pn junction, which increases the curvature of the interface energy band and thus obtains a larger photogenerated voltage. The photogenerated carriers generated on the surface are quickly separated to reduce recombination, and electrons are transferred to the surface to participate in the reduction and hydrogen evolution reaction. At the same time, the interface defects of MoS2 directly loaded are reduced. Therefore, the presence of the multifunctional layer CdS gives the material better photoelectrochemical properties.

[0053] (3) Comparison of the linear sweep voltammetric curves of the p-Si NWS / MoS2 photocathode prepared in Comparative Example 1 and the p-Si NWS / CdS / MoS2 photocathode prepared in Example 2 after 1 h of high-intensity operation. Figure 6 shown.

[0054] Depend on Figure 6 It can be seen that after 1 hour of high-intensity work, the performance of the p-Si NWs / Cd / MoS2 photocathode remains relatively stable, especially the saturated photocurrent density remains unchanged, while the photocurrent density of the p-Si NWs / MoS2 photocathode without CdS layer deposition decreases significantly after 1 hour of high-intensity work. This result shows that the CdS multifunctional layer plays a protective role for the electrode.

[0055] In summary, the present invention introduces a multifunctional CdS intermediate layer between the silicon-based nanowire structure and the co-catalyst MoS2 for the first time, achieving an effective combination of photoelectrochemical energy conversion.

[0056] The present invention analyzes the linear sweep voltammetry curve and the 1h high-intensity working test results to find that the p-Si NWs / MoS2 photocathode designed in the present invention has good photoelectrochemical performance, which is mainly attributed to the excellent structure of the multifunctional n-type CdS and the excellent combination of the MoS2 co-catalyst.

[0057] The present invention has good stability in photoelectrochemical water decomposition to produce hydrogen and long-term high-intensity work, and a simple and low-cost preparation process, providing reliable theoretical experimental support for practical applications. Therefore, the present invention has good application prospects in the field of solar cells and new energy fields.

[0058] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A multifunctional intermediate layer modified silicon-based nanowire photocathode, characterized in that: It includes a p-Si substrate layer, a nanowire morphology layer, a CdS layer and a MoS2 catalyst promoter layer; The line width of the nanowire morphology layer is 50-200 nm, and the line height is 3-4 μm.

2. The silicon-based nanowire photocathode according to claim 1, characterized in that: The thickness of the CdS layer is 40 to 50 nm.

3. The silicon-based nanowire photocathode according to claim 1, characterized in that: The thickness of the MoS2 co-catalyst layer is 5 to 10 nm.

4. A method for preparing the silicon-based nanowire photocathode according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Clean the p-Si substrate and blow dry it for later use; (2) depositing a p-Si substrate in a first deposition liquid to obtain a p-Si substrate with silver particles adsorbed on the surface; (3) placing the p-Si substrate with silver particles adsorbed on the surface into an etching solution for etching to form a nanowire structure on the p-Si substrate; (4) placing the p-Si substrate formed with the nanowire structure into a second deposition liquid for deposition to form a CdS layer on the nanowire structure; (5) Using the p-Si substrate treated in step (4) as a working electrode, depositing it in an electroplating solution to obtain the silicon-based nanowire photocathode.

5. The preparation method according to claim 4, characterized in that: In step (2), the first deposition liquid contains an aqueous solution of hydrofluoric acid and silver nitrate; the concentration of hydrofluoric acid in the first deposition liquid is 4.8 M, and the concentration of silver nitrate is 5 mM; the deposition process conditions are: immersing in the first deposition liquid for 2 minutes at room temperature.

6. The preparation method according to claim 4, characterized in that: In step (3), the etching solution is an aqueous solution containing hydrofluoric acid and hydrogen peroxide; the concentration of hydrofluoric acid in the etching solution is 4.8M, and the concentration of hydrogen peroxide is 0.4M; the etching conditions are: immersing in the etching solution for 15 minutes at room temperature in the dark.

7. The preparation method according to claim 4, characterized in that: In step (4), the second deposition liquid is an aqueous solution comprising cadmium sulfate, thiourea and ammonia water, wherein the concentration of cadmium sulfate is 2 mM, the concentration of thiourea is 80 mM, and the concentration of ammonia water is 1.8 M; the deposition conditions are: hydrothermal at 70° C. for 30 min.

8. The preparation method according to claim 4, characterized in that: In step (5), the electrodeposition solution is an aqueous solution of ammonium tetrathiomolybdate, and the concentration of ammonium tetrathiomolybdate is 2 mM.

9. The preparation method according to claim 4, characterized in that: In step (5), p-Si NWs / CdS is used as a working electrode, a platinum electrode is used as a counter electrode, and an Ag / AgCl electrode is used as a reference electrode; under a standard solar intensity, a bias voltage of -07 V is applied for deposition, and the deposited charge is controlled to be 50 mC.

10. An application of the silicon-based nanowire photocathode according to claim 1, characterized in that: Used for photoelectrocatalytic water splitting to produce hydrogen.

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