MnCdS / crystalline silicon composite water photolysis photocathode, and preparation method and application thereof

Abstract

The application relates to a manganese-cadmium-sulfur / crystalline silicon composite water photolysis photocathode and a preparation method and application thereof. The method is as follows: manganese-cadmium-sulfur nanoparticles with a specific component ratio are synthesized through a hydrothermal method, then a drop-coating process is adopted, and drop-coating process parameters are controlled, so that a manganese-cadmium-sulfur / silicon heterojunction photocathode is successfully constructed on crystalline silicon with a pn junction structure and a surface pyramid light-trapping microstructure. The photocathode has excellent photocatalytic activity and water photolysis efficiency, and has good catalytic stability.

Description

Technical Field

[0001] This invention belongs to the field of nanocomposite materials and solar energy conversion technology, specifically relating to a manganese-cadmium-sulfur / crystalline silicon composite photocathode for water splitting, its preparation method, and its application. Background Technology

[0002] Photoelectrodes are key components in the photocatalytic water splitting process, enabling the production of clean and efficient hydrogen energy. Compared to powdered photocatalyst systems that must be suspended in an electrolyte solution, photocatalytic water splitting systems consisting of two separate photocathodes and photoanodes can directly separate the hydrogen generated from water splitting from other products (such as oxygen generated at the anode), facilitating hydrogen collection. Furthermore, the catalyst, fixed on a conductive substrate, does not need to be recovered from the reaction system, simplifying system operation and improving long-term stability. Semiconductor photoelectrode materials need to remain stable in the electrolyte solution for extended periods, possess a suitable band structure, and achieve high photoelectric conversion efficiency. Since most semiconductor materials are n-type semiconductors, most electrodes are photoanodes; photocathodes are difficult to fabricate using ordinary semiconductor materials.

[0003] Manganese cadmium sulfide (MnCdS) is a type of photocatalytic material developed based on cadmium sulfide (CdS). It exhibits superior photocatalytic performance compared to CdS, and its photocatalytic performance can be significantly improved by precisely optimizing the ratio of its components. Due to its suitable band structure, MnCdS is frequently used for photocatalytic water splitting to produce hydrogen. Existing technologies typically enhance the overall photocatalytic performance of MnCdS by constructing heterojunction structures with other semiconductor particles or films. For example, CN202510172564.1 discloses a manganese cadmium sulfide@manganese sulfide heterojunction composite photocatalytic material, which consists of MnCdS particles or films. 0.7 Cd 0.3 Composed of S and MnS, this heterojunction broadens the photoresponse range, significantly improves the transfer and separation efficiency of photogenerated electron-hole pairs, suppresses the recombination of photogenerated electron-hole pairs, and enhances the efficiency of photocatalytic uranium reduction. However, the photoelectric conversion efficiency of the nanopowder heterojunction material is low, the hydrogen gas generated by photocatalytic water splitting is difficult to collect, and the powder photocatalytic material is difficult to recycle.

[0004] One less-reported research direction in photoelectrodes is combining the advantages of solar silicon wafers, such as high visible light absorption and utilization rate and high photoelectric conversion efficiency, with semiconductor materials (e.g., MnCdS or CdS) to form composite electrodes. Specifically, in the preparation process, a CdS layer is typically prepared directly on the silicon wafer surface using chemical deposition. However, this method cannot achieve optimal photocatalytic performance by precisely controlling the Mn doping amount. For example, patent CN201710582109.4 discloses a silicon-based photocatalytic water splitting electrode comprising a p-type silicon substrate, a cadmium sulfide heterojunction layer, a titanium oxide protective layer, and a platinum cocatalyst. However, this method is unsuitable for effectively depositing MnCdS and cannot precisely control the specific Mn content in MnCdS.

[0005] Existing preparation methods focus on directly preparing CdS layers on silicon surfaces without further microstructure treatment via chemical deposition. This approach has significant limitations: First, it is difficult to achieve controllable and precise doping of the Mn element ratio during deposition, resulting in relatively low performance of this type of composite electrode; second, the film of this type of composite electrode is not dense and robust enough, leading to incomplete catalyst coverage and weak adhesion on the silicon surface, resulting in unstable electrode catalytic performance; finally, chemical deposition can only be performed on ordinary flat silicon wafers, making it impossible to construct composite electrode materials with specific silicon surface configurations, resulting in low photoelectric conversion efficiency.

[0006] The challenge lies in developing photoelectrode materials that significantly improve photoelectric conversion efficiency, facilitate the collection of hydrogen gas from water splitting, and allow for the easy recycling of photocatalytic materials. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide an improved method for preparing a manganese cadmium sulfur / crystalline silicon composite photocathode for water splitting, which addresses the shortcomings and deficiencies of the prior art. This method can prepare photocathode materials with significantly improved photoelectric conversion efficiency and water splitting efficiency. Furthermore, when this material is used for water splitting, hydrogen is easily collected and the photocatalytic material is easily recovered.

[0008] To solve the above technical problems, the present invention adopts the following technical solution: A method for preparing a manganese cadmium sulfur / crystalline silicon composite photocathode for photocatalytic water splitting, characterized in that the preparation method includes the following steps: dispersing MnCdS nanoparticles in a solvent to obtain a suspension; taking the suspension and dropping it onto a crystalline silicon wafer, and spin-coating the silicon wafer to spread the suspension; drying the spin-coated silicon wafer; repeating the spin-coating and drying process 1-2 times to obtain the manganese cadmium sulfur / crystalline silicon composite photocathode for photocatalytic water splitting; The molar ratio of Mn, Cd, and S in the MnCdS is 0.1-0.3:0.7-0.9:1; The silicon wafer has a pyramidal texture and a pn junction.

[0009] In some embodiments, the spin coating speed is 500-1500 rpm. For example, the speed can be 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, or 1500 rpm. Too low a speed will result in excessively thick MnCdS deposition on the silicon surface, disrupting the pyramid structure of the silicon surface. Too high a speed will result in uneven distribution of MnCdS on the silicon surface, with MnCdS accumulating at the bottom of the pyramid structure, preventing the formation of a continuous and uniform coating.

[0010] In some implementations, the spin coating time is 10-30 seconds per spin coating cycle. Examples of spin coating times are 10, 15, 20, 25, and 30 seconds. If the spin coating time is too short, the MnCdS deposits on the silicon surface will be too thick and uneven. If the spin coating time is too long, some MnCdS will be ejected, resulting in uneven distribution of MnCdS on the silicon surface.

[0011] In some embodiments, the solvent is selected from one or both of water and ethanol.

[0012] In some embodiments, the mass-volume concentration of the suspension is 0.1-3 g / L, and the amount of suspension used in each spin-coating is 50-100 μL. The mass-volume concentration of the suspension can be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, or 3.0 g / L. The amount of suspension used in each spin-coating can be, for example, 50, 60, 70, 80, 90, or 100 μL. It can be taken using a pipette or dropper. When the concentration of the suspension is too high, MnCdS accumulates too thickly and unevenly on the silicon surface; when the concentration of the suspension is too low, MnCdS will be unevenly distributed on the silicon surface, accumulating at the bottom of the pyramid structure on the silicon surface, making it impossible to form a continuous and uniform coating. When too much suspension is used in each spin coating, MnCdS accumulates too thickly and unevenly on the silicon surface; when too little suspension is used in each spin coating, MnCdS will be unevenly distributed on the silicon surface, accumulating at the bottom of the pyramid structure on the silicon surface, making it impossible to form a continuous and uniform coating.

[0013] In some embodiments, the silicon wafer has a size of 1-3cm × 1-3cm.

[0014] In some embodiments, the drying temperature is 40-60°C.

[0015] In some embodiments, the MnCdS is Mn 0.2Cd 0.8 S, Mn 0.1 Cd 0.9 S, Mn 0.3 Cd 0.7 S; preferred Mn 0.2 Cd 0.8 S. Mn 0.2 Cd 0.8 S can achieve optimal photoelectric conversion efficiency.

[0016] In some embodiments, the MnCdS nanoparticles have a particle size of 150-250 nm. Nanoparticles are more conducive to improving photocatalytic performance.

[0017] In some embodiments, the preparation method further includes a post-treatment step of annealing at 100-200°C for 0.5-2 hours after complete spin coating and drying. This annealing step can enhance the contact between MnCdS nanoparticles and between them and the silicon substrate, further making their bonding stronger.

[0018] Furthermore, the annealing step is carried out in an inert atmosphere or in air.

[0019] In some embodiments, the MnCdS nanoparticles are synthesized via a hydrothermal method.

[0020] In some embodiments, the hydrothermal method includes the following steps: dissolving a manganese source, a cadmium source, and a sulfur source in water to obtain a precursor solution; placing the precursor solution in a reaction vessel and carrying out a hydrothermal reaction under pressure and heating to obtain the MnCdS nanoparticles.

[0021] In some embodiments, the manganese source is selected from manganese sulfate or manganese acetate.

[0022] In some embodiments, the cadmium source is selected from cadmium chloride and cadmium acetate.

[0023] In some embodiments, the sulfur source is selected from thiourea or sodium thiosulfate.

[0024] In some embodiments, the molar ratio of manganese in the manganese source to cadmium in the cadmium source is 1-3:7-9.

[0025] In some embodiments, the reactor is a high-pressure reactor.

[0026] In some implementations, the hydrothermal reaction temperature is 160-200°C.

[0027] In some implementations, the hydrothermal reaction takes 4-8 hours.

[0028] In some implementations, after the hydrothermal reaction is completed, MnCdS nanoparticles are obtained by centrifugation, washing, and drying.

[0029] In some embodiments, the preparation method further includes the step of preparing the silicon wafer: etching the p-type single-crystal silicon wafer with an alkaline solution to form a micron-scale pyramid texture structure on its surface, and then forming an n+ emitter on the surface through a phosphorus diffusion process to form a pn junction.

[0030] The present invention also provides a manganese cadmium sulfur / crystalline silicon composite photocathode prepared by the aforementioned method for preparing a manganese cadmium sulfur / crystalline silicon composite photocathode for photocatalytic water splitting.

[0031] The present invention also provides the application of the aforementioned manganese cadmium sulfur / crystalline silicon composite photocathode for water splitting in the electrolysis of water to produce hydrogen.

[0032] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: Using the preparation method of the present invention, composite photocathode materials with significantly improved photocatalytic activity and photocatalytic water splitting efficiency can be obtained.

[0033] The photocathode material of this invention exhibits excellent photoelectrochemical performance: the optimal composite photoelectrode material performs well at a light source of 100 mW cm⁻¹. -2 Under a xenon lamp, in a 1 M HClO4 electrolyte solution, and with a bias voltage of -0.8 V (vs. NHE) (Ag / AgCl reference electrode), the photocurrent density reached -16.2 mA cm⁻¹. -2 It is a bare silicon electrode (-0.49 mA cm⁻¹). -2 33 times that of ), with an initial potential of -0.14V. NHE Positive shift to 0.19 V NHE .

[0034] The photocathode material of this invention exhibits high hydrogen production activity: at -0.6 V NHE Under constant potential, this electrode can achieve approximately 0.3 mmol cm⁻¹ -2 h -1 The stable hydrogen production rate.

[0035] The photocathode material of this invention exhibits excellent catalytic stability: after continuous operation in an acidic electrolyte for 60 hours, the photocurrent remains stable, and SEM analysis shows no significant change in electrode morphology, indicating that the MnCdS nanoparticle coating provides good protection. Attached Figure Description

[0036] Figure 1 Mn prepared in Example 1 0.2 Cd 0.8 TEM image of S powder.

[0037] Figure 2 Mn prepared in Example 1 0.2Cd 0.8 XRD pattern of S powder.

[0038] Figure 3 Si / Mn prepared in Example 1 0.2 Cd 0.8 Schematic diagram of the S-composite electrode.

[0039] Figure 4 Si / Mn prepared in Example 1 0.2 Cd 0.8 EDS composition analysis diagram of S composite electrode.

[0040] Figure 5 The Si / Mn ratio under different drop-coating times in the examples and comparative examples 0.2 Cd 0.8 SEM surface morphology of the S composite electrode; where a: 0 (silicon substrate); b, c: 1 (different sizes); d, e: 2 (different sizes); f, g: 3 (different sizes); h, i: 4 (different sizes).

[0041] Figure 6 The Si / Mn ratio under different drop-coating times in the examples and comparative examples 0.2 Cd 0.8 Photoelectrochemical performance of S-composite electrode (JV curve); where black represents 0 drop coatings (i.e., silicon substrate); red represents 1 drop coating; blue represents 2 drop coatings; green represents 3 drop coatings; and yellow represents 4 drop coatings.

[0042] Figure 7 The Si / Mn ratio under different drop-coating times in the examples and comparative examples 0.2 Cd 0.8 The diffuse reflectance spectrum of the S-composite electrode; where black represents 0 drop coatings (i.e., silicon substrate); red represents 1 drop coating; blue represents 2 drop coatings; green represents 3 drop coatings; and yellow represents 4 drop coatings.

[0043] Figure 8 The figure shows the stability test results of the photoelectrode in Example 1, with the inset showing the surface morphology of the photoelectrode after 60 hours of photo-water splitting reaction. Detailed Implementation

[0044] Existing technologies include the use of hydrothermally synthesized CdS or MnCdS nanoparticles to form heterojunction structures with other semiconductor materials, and the loading of CdS onto silicon substrates via chemical deposition for photocatalytic water splitting to produce hydrogen. However, the former involves nanoparticle heterojunction materials, which suffer from low photoelectric conversion efficiency, difficulty in collecting the hydrogen produced by photocatalytic water splitting, and difficulty in recovering the powdered photocatalytic material. The latter utilizes CdS with low photocatalytic activity; ordinary planar p-type silicon substrates lack more efficient pn junction structures and surface light-trapping structures, thus requiring improvement in photoelectric conversion efficiency; furthermore, the composition of CdS prepared by chemical deposition is difficult to precisely control, the proportion of doped other elements (such as Mn) is difficult to control, and the crystallinity is poor, all of which affect the overall photocatalytic water splitting performance of the CdS / silicon electrode.

[0045] Manganese cadmium sulfide (MnCdS) is a novel photocatalytic material formed by elemental doping and solid solution on cadmium sulfide (CdS). By controlling the ratio of manganese (Mn) to cadmium (Cd), its band structure can be precisely tuned, resulting in photocatalytic performance that is significantly superior to CdS in terms of photocatalytic activity, stability, and visible light response range. However, when using existing chemical deposition methods for CdS to deposit MnCdS, it is difficult to achieve controllable and precise doping of the Mn element ratio during the deposition process. Therefore, it is impossible to directly obtain a MnCdS solid solution layer with tunable composition and optimal photocatalytic performance. In the fabrication of silicon-based composite electrodes, although commonly used chemical deposition methods (such as chemical bath deposition) can directly generate CdS on the silicon surface, this method has poor precision in controlling the chemical composition of the deposited product and makes it difficult to accurately introduce and control the content of doping elements such as Mn. Therefore, it is not convenient to obtain specific components (such as Mn) with optimal photocatalytic activity. 0.2 Cd 0.8 S) Solid solution. In addition, existing chemical deposition methods can only deposit on ordinary flat silicon wafers and cannot form uniform, dense and firmly bonded CdS or MnCdS films on crystalline silicon surfaces with specific microstructures (such as better micron-scale pyramid light-trapping microstructures). This can easily lead to incomplete catalyst coverage and weak bonding on such silicon surfaces, affecting the catalytic performance and stability of photocathode materials.

[0046] This invention first synthesizes MnCdS nanoparticles via a hydrothermal method, and then innovatively loads them onto silicon wafers using a physical drop-coating method. The advantages of this approach are that it yields MnCdS nanoparticles with better crystallinity and more precise composition control. On the other hand, it selects crystalline silicon wafers with more precise pn junction structures and better surface light-trapping microstructures to replace ordinary planar silicon wafers that do not have pn junction structures and better surface light-trapping microstructures, thereby achieving higher photoelectric conversion efficiency.

[0047] This invention first prepares well-crystallized MnCdS with a specific component ratio (which has better photocatalytic activity) by hydrothermal method. Then, the MnCdS is drop-coated onto a crystalline silicon substrate with a pn junction structure and a pyramid light-trapping structure on the surface, which is more conducive to photocatalytic water splitting, through a specific drop-coating process, thereby forming the final composite crystalline silicon / MnCdS photoelectrode and achieving the optimal photocatalytic water splitting effect.

[0048] This invention employs a novel drop-coating process and, by controlling the drop-coating process parameters, can successfully prepare MnCdS nanoparticles with specific compositions on crystalline silicon with specific microstructures and pn junctions, thus obtaining a composite photocathode and significantly improving the photoelectric conversion efficiency of the photocathode material.

[0049] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples described.

[0050] Example 1 This embodiment provides a photocathode for water splitting, and its preparation method is as follows: (1) Fabrication of a silicon substrate with a pn junction and a surface pyramid light-trapping microstructure: The fabrication process begins with anisotropic etching of a planar p-type single-crystal silicon wafer using KOH solution to form a micro-pyramidal textured surface, aiming to enhance light-trapping capability and increase effective surface area. Subsequently, a pn junction is formed on the planar p-type single-crystal silicon substrate. The p-type single crystal is then n-type doped in an atmospheric pressure tube furnace using PCl3 vapor diffusion. After doping, the phosphorosilicon glass layer formed on the surface is completely removed by reactive ion etching. Then, an aluminum back electrode is deposited.

[0051] Specifically, a p-type single-crystal silicon wafer with a resistivity of 1-3 Ω·cm was etched in a 10% KOH solution at 80°C for 20 minutes to form a uniform pyramidal texture. Subsequently, phosphorus diffusion was performed in a tube furnace using a PCl3 source (900°C, 15 minutes) to form an n-type silicon wafer. + The silicon wafer was then subjected to a layer of phosphorosilicate glass (PSG) removed with HF acid. A 300 nm thick aluminum electrode was deposited on the back side of the silicon wafer via electron beam evaporation. The sample was then laser-cut into 1.5 × 1.5 cm sections. 2 The size. Before use, all silicon electrodes were ultrasonically cleaned for 15 minutes each in deionized water, acetone and ethanol, then rinsed with deaerated deionized water and finally dried in a nitrogen stream. (2) Hydrothermal preparation of Mn 0.2 Cd 0.8S powder: Weigh 0.147 g of manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O), 0.64 g of cadmium acetate dihydrate (Cd(CH3COO)2·2H2O), and 1.14 g of thiourea (CS(NH2)2), dissolve in 30 mL of deionized water, and stir for 30 minutes. Transfer the mixture to a 50 mL high-pressure reactor and react at 180 °C for 6 hours. After cooling, centrifuge and wash, and vacuum dry at 60 °C for 10 hours to obtain Mn. 0.2 Cd 0.8 S powder. (3) Take the above Mn 0.2 Cd 0.8 S powder was added to deionized water to prepare a suspension with a mass-volume concentration of 1.329 g / L. The suspension was ultrasonically dispersed for 30 minutes to obtain a well-dispersed suspension. (4) Take the silicon wafer prepared in step (1), use a pipette to draw 80 μL of the suspension in step (3), drop it onto the surface of the silicon wafer, and spin coat it at 1000 rpm for 20 seconds to make it spread evenly. The spin coater is a commonly used industrial spin coater. Then place it on a 60℃ hot plate to dry. (5) Repeat step (4) twice, and perform a total of 3 drop-coating-drying treatments to obtain a crude product.

[0052] (6) The crude product was annealed at 150°C for 1 hour in a nitrogen atmosphere to obtain a photocathode.

[0053] The Mn prepared in step (2) 0.2 Cd 0.8 The SEM and XRD images of the S powder are shown below. Figure 1-2 As shown, Mn with good crystallinity and uniform microstructure was obtained through step (2). 0.2 Cd 0.8 S particles. The Mn 0.2 Cd 0.8 The particle size of the S powder is approximately 150-250 nm. A schematic diagram of the final composite photocathode is shown below. Figure 3 As shown, its EDS component analysis diagram is as follows: Figure 4 As shown, the molar ratio of elements Mn, Cd, and S is 0.2:0.8:1, which confirms that the precise composition of MnCdS is Mn. 0.2 Cd 0.8 S.

[0054] The final SEM surface morphology image of the composite photocathode is shown below. Figure 5 As shown in f and 5g, where 5g is a magnified view of 5f, it can be seen that after spin coating, the Mn in the composite electrode... 0.2 Cd 0.8 S forms a uniform and good coating layer on the surface of the silicon substrate without affecting the pyramid structure of the silicon substrate itself.

[0055] The photocathode is based on a light source of 100 mW cm -2 Photocurrent performance was tested under a xenon lamp and a bias voltage of -0.8 V (vs. NHE) (Ag / AgCl reference electrode). Hydrogen production via water electrolysis was then performed on the aforementioned photocathode using the following method: Hydrogen production and oxygen evolution experiments were conducted in a closed quartz glass photoreactor. This reactor separated the photocathode and platinum counter electrode into different tubular chambers to prevent mixing of hydrogen generated by the photocathode with oxygen generated by the platinum counter electrode. Tests were performed in a solution containing 1 M HClO4 (analytical grade, Sinopharm Chemical Reagent Co., Ltd., pH ≈ 0) with a 100 mW cm⁻¹ light source. -2 Xenon lamp. To purge air from the reactor, argon gas was continuously bubbled into the system for 15 minutes before the experiment. During illumination, the circulating water system maintained the reaction temperature at 20°C to eliminate the thermal effect of the light. At regular intervals, 0.2 mL of gas was injected into a gas chromatograph equipped with a thermal conductivity detector (TCD) and a 5Å molecular sieve packed column (60 / 80 mesh) to monitor hydrogen production. Each data point was sampled three times. Argon was used as the carrier gas, and the pressure was maintained at 40 Psi. The gas chromatograph settings were: column oven 70°C, detector 130°C, injection valve 110°C. The results are shown in Table 1 below. The corresponding photoelectrochemical performance graph (JV curve) is shown below. Figure 6 The green line in the image shows the corresponding diffuse reflectance spectrum (test method: using an Agilent Cary 300 UV-Vis spectrophotometer, the light absorption performance of the sample in the 200-800 nm wavelength range was evaluated using UV-Vis DRS technology). Figure 7 As shown by the green line in the image. The stability of the electrode was tested (under the same conditions as the photocurrent test), and the results are as follows. Figure 8 As shown.

[0056] It is evident that this photocathode exhibits excellent photoelectric conversion efficiency, photo-water splitting efficiency, and excellent stability.

[0057] Example 2 Basically the same as Example 1, except that: Mn 0.2 Cd 0.8 S powder replaced with Mn 0.1 Cd 0.9S powder. Accordingly, step (2) is replaced by: weighing 0.0735 g of manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O), 0.72 g of cadmium acetate dihydrate (Cd(CH3COO)2·2H2O), and 1.14 g of thiourea (CS(NH2)2), dissolving them in 30 mL of deionized water, and stirring for 30 minutes. The mixture is then transferred to a 50 mL high-pressure reactor and reacted at 180 °C for 6 hours. After cooling, the mixture is centrifuged, washed, and vacuum dried at 60 °C for 10 hours to obtain Mn 0.1 Cd 0.9 S powder. Mn 0.1 Cd 0.9 The composition of the S powder was confirmed by EDS analysis.

[0058] The results for the corresponding photoelectrodes are shown in Table 1 below.

[0059] Example 3 Basically the same as Example 1, except that: Mn 0.2 Cd 0.8 S powder replaced with Mn 0.3 Cd 0.7 S powder. Accordingly, step (2) is replaced by: weighing 0.2205 g of manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O), 0.56 g of cadmium acetate dihydrate (Cd(CH3COO)2·2H2O), and 1.14 g of thiourea (CS(NH2)2), dissolving them in 30 mL of deionized water, and stirring for 30 minutes. The mixture is then transferred to a 50 mL high-pressure reactor and reacted at 180 °C for 6 hours. After cooling, the mixture is centrifuged, washed, and vacuum dried at 60 °C for 10 hours to obtain Mn 0.3 Cd 0.7 S powder. Mn 0.3 Cd 0.7 The composition of the S powder was confirmed by EDS analysis.

[0060] The results for the corresponding photoelectrodes are shown in Table 1 below.

[0061] As can be seen from the comparison of Examples 1-3, changing the molar ratio of Mn and Cd in MnCdS results in corresponding photoelectrodes exhibiting excellent photoelectric conversion efficiency and photocatalytic water splitting efficiency, as well as superior stability. Specifically, in Example 1, the Mn... 0.2 Cd 0.8 The photoelectrode corresponding to S exhibits the best performance. At this ratio, MnCdS demonstrates the best photoelectrocatalytic performance.

[0062] Example 4 (Secondary Drop Coating) The process is basically the same as in Example 1, except that in step (5), the drop-coating-drying process is repeated only once, meaning a total of two drop-coating-drying processes are performed. The results of the corresponding photoelectrodes are shown in Table 1 below. The SEM surface morphology images of the corresponding composite electrodes are shown below. Figure 5 As shown in d and 5e, Mn can be seen 0.2 Cd 0.8 The S nanoparticles cover the silicon substrate surface with slight imperfections. The corresponding photoelectrode performs well, but is slightly inferior to that of Example 1.

[0063] Example 5 The results are basically the same as in Example 1, except that the solvent of the suspension in step (3) is changed, and deionized water is replaced with ethanol. The results of the corresponding photoelectrodes are shown in Table 1 below.

[0064] Example 6 The results are basically the same as in Example 1, except that the mass-volume concentration of the suspension in step (3) is changed to 0.133 g / L. The results of the corresponding photoelectrodes are shown in Table 1 below.

[0065] Example 7 The process is basically the same as in Example 1, except that in step (4), 100 μL of the suspension from step (3) is taken each time.

[0066] Example 8 The process is basically the same as in Example 1, except that in step (4), the spin coating speed is changed to 500 rpm and the spin coating time is changed to 30 s each time.

[0067] Comparative Example 1 (Bare Silicon Wafer) The silicon substrate was prepared using the same steps as in Example 1, resulting in a crystalline silicon wafer with a pyramidal texture, a pn junction, and a back aluminum electrode. This sample was not subjected to any drop-coating process and was directly used as a photocathode for performance testing. The test results are shown in Table 1 below, revealing a very low photocurrent density, an extremely low hydrogen production rate, and poor catalytic stability.

[0068] Comparative Example 2 (single drop application) The process is basically the same as in Example 1, except that step (5) is omitted, i.e., only one drop-coating-drying process is performed. The test results are shown in Table 1 below. The corresponding SEM surface morphology images of the composite electrode are shown below. Figure 5 As shown in b and 5c, Mn can be seen 0.2 Cd 0.8 The S nanoparticles do not completely cover the silicon substrate surface.

[0069] Comparative Example 3 (Four applications) The process is basically the same as in Example 1, except that in step (5), the drop-coating-drying process is repeated three times, for a total of four drop-coating-drying processes. The results of the corresponding photoelectrodes are shown in Table 1 below. The SEM surface morphology of the corresponding composite electrodes is shown below. Figure 5 As shown in h, 5i, Mn can be seen 0.2 Cd 0.8S nanoparticles severely aggregate on the silicon wafer surface, even partially burying the pyramidal light-trapping microstructures on the silicon wafer surface, resulting in a significant reduction in the corresponding photoelectric properties.

[0070] The comparison shows that the performance of bare silicon wafers or photoelectrodes processed by a single drop-coating is poor because bare silicon wafers are not modified with Mn. 0.2 Cd 0.8 S nanoparticle catalysts, while a single drop-coating process only disrupts the hydrophobicity of the silicon substrate surface, slightly improving its photoelectric conversion performance, but Mn 0.2 Cd 0.8 The coverage of S nanoparticles was insufficient, while after the secondary drop-coating treatment, Mn 0.2 Cd 0.8 S nanoparticles largely cover the silicon substrate. A third drop-coating process can further compensate for the defects left by the second drop-coating, but after a fourth drop-coating, Mn... 0.2 Cd 0.8 The severe aggregation of S nanoparticles on the silicon wafer surface actually reduces the photoelectric conversion performance.

[0071] Comparative Example 4 (Planar P-type monocrystalline silicon wafer) The process is basically the same as in Example 1, except that step (1) is omitted, and a planar P-type single crystal silicon wafer without pn junction structure and surface pyramid light-trapping microstructure is directly used as the silicon wafer substrate. Steps (2)-(6) are the same as in Example 1.

[0072] The test results are shown in Table 1 below. Although Mn 0.2 Cd 0.8 S can also form a uniform and good coverage on the surface of planar P-type single crystal silicon, but its photoelectric conversion performance is significantly worse than that of Example 1.

[0073] Comparative Example 5 (Chemical Deposition) This comparative example provides a photocathode for water splitting, the preparation method of which is as follows: (1) Preparation of crystalline silicon substrate with pn junction and surface pyramid light-trapping microstructure: Same as in Example 1; (2) Preparation of chemical deposition solution: Weigh 0.338 g of manganese sulfate monohydrate (MnSO4·H2O), 1.668 g of cadmium sulfate trihydrate (CdSO4·3H2O), and 0.7612 g of thiourea (CS(NH2)2) and dissolve them in 100 mL of deionized water to obtain a chemical deposition solution with a molar ratio of Mn, Cd, and S of 0.2:0.8:1.

[0074] (3) After stirring and preheating the prepared chemical deposition solution in a water bath at 70-80℃ for 1-5 minutes, take the treated silicon wafer with the pn junction structure and surface pyramid light trapping microstructure, immerse it in the above chemical deposition solution, and perform chemical deposition for 5 minutes.

[0075] (4) Annealing at 150°C for 1 hour in a nitrogen atmosphere to obtain a photocathode.

[0076] The results are shown in Table 1 below. It is evident that the photocatalytic water splitting performance of the resulting photocathode material is significantly reduced when using the conventional chemical deposition method. This is because the Mn prepared via direct chemical deposition... 0.2 Cd 0.8 S cannot compare with Mn prepared by the hydrothermal method in terms of either crystallinity or morphological integrity. 0.2 Cd 0.8 Compared to S particles.

[0077] Comparative Example 6 The process is basically the same as in Example 1, except that step (5) is omitted, and the 80 μL in step (4) is replaced with 240 μL. That is, the total amount of suspension is the same, but only one spin coating is performed. The results are shown in Table 1 below. It can be seen that the performance of the photocathode is significantly reduced under this spin coating method because after the suspension is dropped, the Mn... 0.2 Cd 0.8 S nanoparticles are easy to precipitate. If too much suspension is added at once, most of the MCS particles will gather at the bottom of the pyramid structure on the crystalline silicon surface, and cannot form a uniform and continuous coverage.

[0078] Comparative Example 7 Basically the same as Example 1, except that: Mn 0.2 Cd 0.8 S powder replaced with Mn 0.4 Cd 0.6 S powder. Accordingly, step (2) is replaced by: hydrothermal preparation of Mn. 0.4 Cd 0.6 S powder: Weigh 0.294 g of manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O), 0.48 g of cadmium acetate dihydrate (Cd(CH3COO)2·2H2O), and 1.14 g of thiourea (CS(NH2)2), dissolve in 30 mL of deionized water, and stir for 30 minutes. Transfer the mixture to a 50 mL high-pressure reactor and react at 180 °C for 6 hours. After cooling, centrifuge and wash, and vacuum dry at 60 °C for 10 hours to obtain Mn. 0.4 Cd 0.6 S powder. The results are shown in Table 1 below. It can be seen that Mn 0.2 Cd 0.8The effect of S ratio is far better than other ratios.

[0079]

[0080] The theory in Table 1 refers to the fact that the Faraday efficiency of this sample has not been tested for a long time. Therefore, it is assumed that the Faraday efficiency is 100% to calculate the hydrogen production rate, which is the theoretical hydrogen production rate.

[0081] As shown in Table 1 above, the present invention achieves the successful growth of uniform and densely covered MnCdS nanoparticles on the surface of crystalline silicon with a specific microstructure by using a drop-coating process of a MnCdS nanoparticle suspension with a specific ratio on the surface of crystalline silicon with a pn junction structure and a pyramid light-trapping structure, and by controlling a specific number of drop-coating times (2-3 times). This results in a photoelectrode with excellent photoelectric conversion efficiency, photoelectric water splitting efficiency, and high catalytic stability.

[0082] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0083] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method for preparing a manganese-cadmium-sulfur / crystalline silicon composite photocathode for water splitting, characterized in that: The preparation method includes the following steps: dispersing MnCdS nanoparticles in a solvent to obtain a suspension; taking the suspension and dropping it onto a silicon wafer, then spin-coating the silicon wafer to spread the suspension; drying the spin-coated silicon wafer; repeating the spin-coating and drying process 1-2 times to obtain the manganese-cadmium-sulfur / crystalline silicon composite photocathode for photocatalytic water splitting. The molar ratio of Mn, Cd, and S in the MnCdS is 0.1-0.3:0.7-0.9:1; The silicon wafer has a pyramidal texture and a pn junction.

2. The method for preparing the manganese-cadmium-sulfur / crystalline silicon composite photocathode for water splitting according to claim 1, characterized in that: The spin coating speed is 500-1500 rpm; and / or, the spin coating time is 10-30 s for each spin coating.

3. The method for preparing the manganese-cadmium-sulfur / crystalline silicon composite photocathode for water splitting according to claim 1, characterized in that: The solvent is selected from one or both of water and ethanol; and / or the mass-volume concentration of the suspension is 0.1-3 g / L, and the suspension is 50-100 μL for each spin coating.

4. The method for preparing the manganese-cadmium-sulfur / crystalline silicon composite photocathode for water splitting according to claim 1, characterized in that: The silicon wafer has a size of 1-3cm × 1-3cm; and / or the drying temperature is 40-60℃.

5. The method for preparing the manganese-cadmium-sulfur / crystalline silicon composite photocathode for photocatalytic water splitting according to claim 1, characterized in that: The MnCdS is Mn 0.2 Cd 0.8 S, Mn 0.1 Cd 0.9 S, Mn 0.3 Cd 0.7 S; preferred Mn 0.2 Cd 0.8 S; and / or, the particle size of the MnCdS nanoparticles is 150-250 nm.

6. The method for preparing the manganese-cadmium-sulfur / crystalline silicon composite photocathode for photocatalytic water splitting according to claim 1, characterized in that: The preparation method further includes a post-treatment step of annealing at 100-200°C for 0.5-2 hours after complete spin coating and drying.

7. The method for preparing the manganese-cadmium-sulfur / crystalline silicon composite photocathode for photocatalytic water splitting according to claim 1, characterized in that: The MnCdS nanoparticles are synthesized by a hydrothermal method; preferably, the hydrothermal method includes the following steps: dissolving a manganese source, a cadmium source and a sulfur source in water to obtain a precursor solution; placing the precursor solution in a reaction vessel and carrying out a hydrothermal reaction under pressure and heating to obtain the MnCdS nanoparticles.

8. The method for preparing the manganese-cadmium-sulfur / crystalline silicon composite photocathode for photocatalytic water splitting according to claim 1, characterized in that: The preparation method further includes the step of preparing the silicon wafer: etching the p-type single-crystal silicon wafer with an alkaline solution to form a micron-level pyramid texture structure on its surface, and then forming an n+ emitter on the surface through a phosphorus diffusion process to form a pn junction.

9. The manganese cadmium sulfur / crystalline silicon composite photocathode for water splitting prepared by the method of any one of claims 1-8.

10. The application of the manganese-cadmium-sulfur / crystalline silicon composite photocathode for photocatalytic water splitting as described in claim 9 in the electrolytic water hydrogen production process.

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