Tungsten-doped bismuth vanadate single crystal electrode and method for preparing the same

Abstract

This invention relates to the field of photoelectrochemistry and discloses a tungsten-doped bismuth vanadate single-crystal electrode and its preparation method. The single-crystal electrode comprises: an insulating support substrate; a conductive layer disposed on a designated area of ​​the insulating support substrate; and a tungsten-doped bismuth vanadate single-crystal layer bonded to the conductive layer. The surface roughness Sa of the tungsten-doped bismuth vanadate single-crystal layer is 0.5 nm to 5.0 nm, and the thickness is 0.2 mm to 1 mm. The periphery of the tungsten-doped bismuth vanadate single-crystal layer is encapsulated with an insulating and waterproof material, and the insulating and waterproof material covers the exposed area of ​​the conductive layer. This invention can improve the chemical stability and photo-water splitting capability of the single-crystal electrode.

Description

Technical Field

[0001] This invention relates to the field of photoelectrochemistry, and more particularly to a tungsten-doped bismuth vanadate single crystal electrode and its preparation method. Background Technology

[0002] With the increasing global energy demand and the growing severity of environmental problems, the development of clean and renewable solar energy conversion and storage technologies has become a research hotspot. Photoelectrochemical water splitting for hydrogen production can directly convert solar energy into chemical energy and store it in the form of hydrogen. Due to its clean products and high energy density, it is considered one of the effective ways to achieve energy structure transformation. In this system, the stability of the photoanode material and the photogenerated charge separation efficiency directly determine the long-term performance and energy conversion efficiency of the system.

[0003] Monoclinic bismuth vanadate (BiVO4) possesses a bandgap of approximately 2.4 eV, exhibits strong visible light absorption, and is inexpensive and environmentally friendly, making it a promising n-type photoanode material. However, existing BiVO4 photoanodes are mostly polycrystalline thin-film structures with numerous grain boundaries, pores, and defects. These defects not only act as carrier recombination centers, reducing photoelectric efficiency, but also easily undergo photocorrosion during long-term reactions, leading to structural collapse and performance degradation. In contrast, single-crystal BiVO4 offers advantages such as high crystal integrity, absence of grain boundaries, and low defect density, which can suppress photocorrosion at the material source and significantly improve stability. However, its practical application still faces key bottlenecks: firstly, achieving a robust, low-resistance, and long-term stable ohmic contact between the single crystal and the conductive substrate is difficult; secondly, its surface requires precise machining to meet the surface quality requirements of photoelectrochemical reactions.

[0004] In existing technologies, researchers have attempted to form ohmic contacts between liquid gallium-indium alloys and BiVO4 single crystals. However, this method suffers from problems such as uneven alloy spreading, limited contact area, and poor mechanical stability. Furthermore, encapsulation relies on epoxy resin, which has limitations such as long curing time, complex processes, and insufficient long-term electrolyte resistance. Another approach (CN202111032831.3) achieves alloying contact between indium gallium alloys and BiVO4 ceramics through annealing. However, the high-temperature process may affect the material structure, and the alloy is prone to seeping through residual pores, leading to electrode failure. Moreover, this method depends on the porous structure of the ceramic surface and is not applicable to single-crystal materials with dense surfaces.

[0005] Therefore, there is an urgent need to develop a new bismuth vanadate electrode to improve its photochemical stability and photo-water splitting capability. Summary of the Invention

[0006] To address the problem of poor stability in existing bismuth vanadate electrodes, this invention provides a tungsten-doped bismuth vanadate single-crystal electrode to improve its chemical stability and photocatalytic water splitting capability.

[0007] A tungsten-doped bismuth vanadate single crystal electrode, comprising:

[0008] Insulating support substrate;

[0009] A conductive layer disposed on the insulating support substrate in a designated area;

[0010] A tungsten-doped bismuth vanadate single crystal layer is bonded to the conductive layer; the surface roughness Sa of the tungsten-doped bismuth vanadate single crystal layer is 0.5 nm ~ 5.0 nm, and the thickness is 0.2 mm ~ 1 mm;

[0011] The periphery of the tungsten-doped bismuth vanadate single crystal layer is encapsulated with an insulating and waterproof material, and the insulating and waterproof material covers the exposed area of ​​the conductive layer.

[0012] Optionally, the tungsten-doped bismuth vanadate single crystal layer comprises tungsten-doped bismuth vanadate single crystal;

[0013] The tungsten doping concentration of the tungsten-doped bismuth vanadate single crystal is 0.1 at% to 0.5 at%;

[0014] The tungsten-doped bismuth vanadate single crystal was generated using the Czochralski method.

[0015] Optionally, the size range of the tungsten-doped bismuth vanadate single crystal includes 5.0 mm × 5.0 mm to 15.0 mm × 15.0 mm;

[0016] The crystal orientation of the tungsten-doped bismuth vanadate single crystal includes (110), (001), (100), (101) or (111).

[0017] Optionally, the conductive layer is provided with a flexible contact layer and an electrical contact area;

[0018] The thickness of the conductive layer is 10 μm to 50 μm.

[0019] Optionally, the flexible contact layer is a liquid gallium indium alloy; the electrical contact area is formed of silver paste.

[0020] Optionally, the insulating and waterproof material is a cured product of UV adhesive;

[0021] The insulating support substrate is glass.

[0022] A method for preparing any of the above-described tungsten-doped bismuth vanadate single crystal electrodes includes:

[0023] A liquid gallium-indium alloy is coated on a designated area of ​​a cleaned insulating support substrate to form a flexible contact layer; silver paste is applied to a local area of ​​the flexible contact layer, and an electrical contact area is formed after the silver paste cures; the flexible contact layer and the electrical contact area form a conductive layer.

[0024] The bottom surface of a tungsten-doped bismuth vanadate single crystal is attached to the conductive layer to form a tungsten-doped bismuth vanadate single crystal layer.

[0025] The tungsten-doped bismuth vanadate single crystal layer is encapsulated so that the periphery of the tungsten-doped bismuth vanadate single crystal layer and the exposed area of ​​the conductive layer are covered with insulating and waterproof material;

[0026] The encapsulated tungsten-doped bismuth vanadate single crystal layer is processed to form a working surface. By adjusting the surface roughness Sa and thickness to a preset range, the tungsten-doped bismuth vanadate single crystal electrode is prepared.

[0027] Optionally, the purification step of the insulating support substrate includes:

[0028] The insulating support substrate was ultrasonically cleaned sequentially with acetone, anhydrous ethanol and deionized water, with each cleaning session lasting 10 min to 20 min. Finally, it was dried to obtain a purified insulating support substrate.

[0029] The encapsulation of the tungsten-doped bismuth vanadate single crystal layer includes:

[0030] The periphery of the tungsten-doped bismuth vanadate single crystal layer and the exposed area of ​​the conductive layer are fully covered and sealed with UV adhesive for insulation. After UV curing, an integrated encapsulation structure is formed. The wavelength of the UV light is 365 nm and the curing time is 1 min to 5 min.

[0031] Optionally, the process of treating the working surface of the encapsulated tungsten-doped bismuth vanadate single crystal layer includes:

[0032] The working surface of the tungsten-doped bismuth vanadate single crystal layer is polished step by step using sandpaper with a grit of 800~5000 to make the thickness of the tungsten-doped bismuth vanadate single crystal layer 0.2mm~1mm.

[0033] The polished working surface is subjected to chemical mechanical polishing treatment to make the surface roughness Sa of the tungsten-doped bismuth vanadate single crystal layer 0.5 nm ~ 5.0 nm.

[0034] Optionally, the operating parameters of the chemical mechanical polishing treatment include:

[0035] Polishing slurry with a particle size of 0.02 μm to 0.10 μm was used at 400 g·cm⁻¹. -2 ~ 2000 g·cm -2 Polishing was performed under polishing pressure and at a turntable speed of 10 rpm to 50 rpm for 6 min to 180 min, while controlling the polishing slurry drop rate at 0.2 mL / min. -1 ~ 1.0 mL·min -1.

[0036] This invention uses high-quality BiV 1-X W X O4 single crystal, as the active material, inherently avoids defects such as grain boundaries and pores, significantly improving the intrinsic stability and corrosion resistance of the electrode. By setting a dedicated conductive layer and performing overall encapsulation, the electrode ensures low contact resistance, reliable interfacial bonding, and excellent electrolyte isolation during operation. Simultaneously, precise control of the roughness of the single crystal working surface effectively optimizes its surface states and reactivity. This invention improves the chemical stability and photocatalytic water-splitting capability of the single crystal electrode. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 BiV prepared in Example 1 of this invention 1-X W X A photograph of an O4 single crystal electrode;

[0039] Figure 2 The BiV prepared in Example 1 of this invention 1-X W X Atomic force microscopy (AFM) characterization of the surface of the O4 single crystal electrode;

[0040] Figure 3 BiV prepared in Example 2 of this invention 1-X W X AFM characterization of the O4 single crystal electrode surface;

[0041] Figure 4 The BiV prepared in Example 3 of this invention 1-X W X AFM characterization of the O4 single crystal electrode surface;

[0042] Figure 5 shows the BiV prepared in Example 1 of this invention. 1-X W X O4(001) single crystal electrode and BiV used for comparison 1-X W XA comparison of the chopper photocurrent density-time (Jt) curves of the O4 polycrystalline thin film electrode at 1.23 V vs. RHE, where Figure 5(a) shows the test results in 0.1 M NaPi electrolyte and Figure 5(b) shows the test results after adding 0.1 M Na2SO3 hole sacrificial agent;

[0043] Figure 6 The BiV prepared in Example 1 of this invention 1-X W X O4 (001) single crystal electrode (100 h) and BiV for comparison 1-X W X Long-term stability Jt test curve of O4 polycrystalline thin film electrode (4 h) at 1.23 V vs. RHE;

[0044] Figure 7 For long-term stability testing, BiV 1-X W X Comparison of X-ray diffraction (XRD) patterns and Raman spectra of O4 (001) single crystal electrode and BiV1-XWXO4 polycrystalline thin film electrode, wherein, Figure 7 a, Figure 7 c represents XRD comparison. Figure 7 b、 Figure 7 d represents the Raman spectrum comparison;

[0045] Figure 8 For long-term stability testing, BiV 1-X W X O4 (001) single crystal electrode and BiV 1-X W X Comparison of scanning electron microscopy (SEM) morphology of O4 polycrystalline thin film electrodes, among which Figure 8 a, Figure 8 b represents the morphology of the single-crystal electrode before and after testing. Figure 8 c. Figure 8 d represents the morphology of the polycrystalline thin film electrode before and after testing. Detailed Implementation

[0046] To make the technical problems solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0047] This embodiment provides a tungsten-doped bismuth vanadate single crystal electrode, comprising:

[0048] Insulating support substrate;

[0049] A conductive layer disposed on the insulating support substrate in a designated area;

[0050] A tungsten-doped bismuth vanadate single crystal layer is bonded to the conductive layer; the surface roughness Sa of the tungsten-doped bismuth vanadate single crystal layer is 0.5 nm ~ 5.0 nm, and the thickness is 0.2 mm ~ 1 mm;

[0051] The periphery of the tungsten-doped bismuth vanadate single crystal layer is encapsulated with an insulating and waterproof material, and the insulating and waterproof material covers the exposed area of ​​the conductive layer.

[0052] Understandably, this embodiment provides a high-performance tungsten-doped bismuth vanadate single-crystal electrode. Its core lies in achieving efficient and stable connection between the single-crystal active material and the external circuit through layered material and structural design, ensuring its long-term reliability in an electrochemical environment. From top to bottom, the electrode mainly comprises a tungsten-doped bismuth vanadate single-crystal layer, a conductive layer, and an insulating support substrate. Furthermore, insulating and waterproof materials are used to seal and protect the periphery of the tungsten-doped bismuth vanadate single-crystal layer and the conductive layer.

[0053] First, the insulating support substrate (such as optical glass) serves as the mechanical support basis for the entire electrode. Its core function is to provide rigid support while ensuring insulation from the test system, preventing current leakage from non-working surfaces, and ensuring that all electrical signals are transmitted only through the designed conductive path.

[0054] Secondly, the conductive layer located in a designated area of ​​the substrate is a critical interface layer. Typically, a room-temperature liquid gallium-indium alloy is used, its main function being to achieve a large-area, low-resistance, and adaptive ohmic contact with the upper single crystal layer. The liquid metal perfectly conforms to the microstructure of the single crystal substrate, greatly reducing contact resistance and alleviating thermal stress. To further stabilize the external leads, silver paste can be locally applied to this conductive layer and cured to form robust solid electrical contacts suitable for soldering or press-fitting.

[0055] Furthermore, the tungsten-doped bismuth vanadate single crystal layer bonded to the conductive layer is the functional core of the electrode. Its surface is treated to achieve a Sa roughness of 0.5 nm to 5.0 nm, which helps balance the specific surface area and the number of surface recombination centers. A thickness of 0.2 mm to 1 mm ensures sufficient light absorption and mechanical strength, while also guaranteeing the effective collection of photogenerated carriers. The excellent crystal quality of the single crystal itself, combined with the conductivity enhanced by W doping, endows it with highly efficient photoelectrochemical activity.

[0056] Finally, insulating and waterproof material is crucial for ensuring stable electrode operation. It is coated on all sidewalls (peripherals) of the monocrystalline layer and all exposed conductive layers except the working surface, forming a complete sealed enclosure. This encapsulation effectively isolates the electrolyte, preventing its penetration and subsequent corrosion of the conductive layer or internal short circuits, thus ensuring the electrode's performance stability and data reliability during long-term testing.

[0057] This embodiment uses high-quality BiV 1-X W X O4 single crystal, as an active material, inherently avoids defects such as grain boundaries and pores, significantly improving the intrinsic stability and corrosion resistance of the electrode. By setting a dedicated conductive layer and encapsulating it as a whole, it ensures that the electrode has low contact resistance, reliable interface bonding and excellent electrolyte isolation capability during operation. At the same time, the fine control of the roughness of the single crystal working surface effectively optimizes its surface state and reactivity.

[0058] Optionally, the tungsten-doped bismuth vanadate single crystal layer comprises tungsten-doped bismuth vanadate single crystal;

[0059] The tungsten doping concentration of the tungsten-doped bismuth vanadate single crystal is 0.1 at% to 0.5 at%;

[0060] The tungsten-doped bismuth vanadate single crystal was generated using the Czochralski method.

[0061] Understandably, the tungsten-doped bismuth vanadate single crystal layer is the core functional component of the electrode, its role being to effectively convert absorbed light energy into electrochemical energy (such as driving water splitting). The tungsten-doped bismuth vanadate single crystal layer comprises one or more tungsten-doped bismuth vanadate single crystals. These single crystals are grown using the Czochralski method to obtain single crystals with high crystallinity, large size, and few defects, which lays the foundation for their excellent intrinsic stability and charge transport capabilities. The tungsten doping concentration in the tungsten-doped bismuth vanadate single crystal is between 0.1 at% and 0.5 at%. Doping within this range significantly improves the material's electronic conductivity and optimizes carrier migration capabilities, while avoiding excessive doping that introduces unnecessary recombination centers or causes phase structure changes, thus achieving an optimal balance between photoelectrochemical performance and material stability.

[0062] Optionally, the size range of the tungsten-doped bismuth vanadate single crystal includes 5.0 mm × 5.0 mm to 15.0 mm × 15.0 mm;

[0063] The crystal orientation of the tungsten-doped bismuth vanadate single crystal includes (110), (001), (100), (101) or (111).

[0064] Understandably, the shape of tungsten-doped bismuth vanadate single crystals can be set according to actual needs, such as squares, rectangles, etc. In some examples, the size of tungsten-doped bismuth vanadate single crystals can be controlled within a square range of 5.0 mm × 5.0 mm to 15.0 mm × 15.0 mm. This size design aims to balance the practical needs of photoelectrochemical testing with process feasibility: it provides a sufficiently large working area to obtain a stable and significant photocurrent signal, while ensuring that the single crystal has good mechanical strength and maneuverability in subsequent bonding, encapsulation, and other processing stages, avoiding the disadvantages of being difficult to handle due to excessively small size or being fragile due to excessively large size.

[0065] The crystal orientation of tungsten-doped bismuth vanadate single crystals can be precisely controlled to specific crystal planes such as (110), (001), (100), (101), or (111) according to performance targets. This controllable orientation is the core element for achieving performance tunability. Different crystal planes have different surface atomic arrangements, electronic structures, and catalytic active sites. By selectively exposing highly active crystal planes (such as (010) or (110) planes) as working surfaces, their light absorption, carrier separation, and surface catalytic reaction kinetics can be optimized in a directional manner, thereby obtaining the best performance for specific applications (such as water-to-hydrogen production).

[0066] Optionally, the conductive layer is provided with a flexible contact layer and an electrical contact area;

[0067] The thickness of the conductive layer is 10 μm to 50 μm;

[0068] The flexible contact layer is a liquid gallium-indium alloy; the electrical contact area is formed by silver paste.

[0069] Understandably, the conductive layer includes a flexible contact layer and an electrical contact area. The flexible contact layer is made of room-temperature liquid gallium-indium alloy, and its core function is to act as an adaptive, flowable interface material that can perfectly conform to the microscopic unevenness that may exist on the bottom surface of the tungsten-doped bismuth vanadate single crystal, forming a low-resistance, large-area ohmic contact, thereby minimizing the interface contact resistance and alleviating thermal stress.

[0070] A localized area of ​​the liquid alloy layer is covered with an electrical contact area formed by the curing of silver paste. This provides a stable, solderable solid connection point for the external conductors, preventing connection instability or oxidation issues caused by direct contact between the conductors and the liquid metal, and ensuring efficient and reliable current conduction. The overall thickness of the conductive layer is controlled between 10 μm and 50 μm. This range ensures sufficient conductive cross-sectional area while avoiding material waste or increased encapsulation difficulty due to excessive thickness.

[0071] Optionally, the insulating and waterproof material is a cured product of UV adhesive;

[0072] The insulating support substrate is glass.

[0073] Understandably, UV adhesive is chosen as the insulating and waterproofing material, which rapidly cures into an encapsulation layer after being irradiated with ultraviolet light. Its core function is to achieve rapid and reliable sealing of all areas except the electrode working area (the upper surface of the single crystal). The cured product formed after UV adhesive curing can firmly adhere to the glass substrate, conductive layer, and single crystal sidewalls, effectively preventing electrolyte penetration and preventing internal short circuits and interface corrosion. Compared with traditional epoxy resin, UV adhesive encapsulation has a curing speed of seconds to minutes and the convenience of single-component operation, which greatly improves preparation efficiency and process consistency, and is conducive to large-scale preparation.

[0074] Glass, such as optical glass, can be used as the insulating support substrate. Glass primarily serves the following functions here: first, as a mechanically supporting substrate, providing rigid support for the entire electrode structure; second, as an insulating barrier, ensuring that current can only be transmitted through the designed conductive layer path, preventing lateral leakage. Furthermore, the high surface flatness of glass facilitates the uniform coating and formation of a high-quality conductive layer.

[0075] This embodiment also provides a method for preparing any of the above-described tungsten-doped bismuth vanadate single crystal electrodes, including:

[0076] A liquid gallium-indium alloy is coated on a designated area of ​​a cleaned insulating support substrate to form a flexible contact layer; silver paste is applied to a local area of ​​the flexible contact layer, and an electrical contact area is formed after the silver paste cures; the flexible contact layer and the electrical contact area form a conductive layer.

[0077] The bottom surface of a tungsten-doped bismuth vanadate single crystal is attached to the conductive layer to form a tungsten-doped bismuth vanadate single crystal layer.

[0078] The tungsten-doped bismuth vanadate single crystal layer is encapsulated so that the periphery of the tungsten-doped bismuth vanadate single crystal layer and the exposed area of ​​the conductive layer are covered with insulating and waterproof material;

[0079] The encapsulated tungsten-doped bismuth vanadate single crystal layer is processed to form a working surface. By adjusting the surface roughness Sa and thickness to a preset range, the tungsten-doped bismuth vanadate single crystal electrode is prepared.

[0080] Understandably, a layer of room-temperature liquid gallium-indium alloy is uniformly coated onto a designated area of ​​a cleaned insulating support substrate (such as optical glass) to form a flexible contact layer; subsequently, silver paste is applied to localized areas and cured. The liquid alloy layer serves to form a large-area, adaptive ohmic contact with the single-crystal substrate, while the cured silver paste area acts as a stable external electrical lead connection point. Together, they constitute a conductive layer with controllable thickness, providing an efficient and reliable charge dissipation channel for the single crystal.

[0081] Subsequently, the bottom surface of the pre-prepared tungsten-doped bismuth vanadate single crystal is precisely bonded to the aforementioned conductive layer. This step requires ensuring tight contact between the single crystal and the liquid alloy layer, free of air bubbles, to form a conductive bonding structure with extremely low interfacial resistance, thus constituting the core functional part of the electrode—the tungsten-doped bismuth vanadate single crystal layer.

[0082] After the single-crystal bonding is completed, the electrodes need to be insulated and waterproofed. Specific encapsulation materials (such as UV adhesive) are used to completely cover all sidewalls (peripherals) of the single-crystal layer and any uncovered exposed areas of the conductive layer. The purpose of this encapsulation layer is to provide absolutely reliable protection in the electrolyte environment, preventing electrolyte infiltration that could lead to internal short circuits or interface corrosion, and ensuring the long-term stability of the electrodes in photoelectrochemical testing.

[0083] Finally, the working surface of the encapsulated electrode undergoes fine finishing. Through processes such as mechanical grinding and chemical mechanical polishing, its surface roughness and overall thickness are precisely controlled to within preset ranges. This treatment aims to remove processing damage and reduce the density of surface recombination centers, thereby optimizing its photoelectrochemical activity. After this step, a high-performance tungsten-doped bismuth vanadate single-crystal electrode with surface condition and geometric dimensions meeting design requirements is finally obtained.

[0084] Optionally, the purification step of the insulating support substrate includes:

[0085] The insulating support substrate was ultrasonically cleaned sequentially with acetone, anhydrous ethanol and deionized water, with each cleaning session lasting 10 min to 20 min. Finally, it was dried to obtain a purified insulating support substrate.

[0086] The encapsulation of the tungsten-doped bismuth vanadate single crystal layer includes:

[0087] The periphery of the tungsten-doped bismuth vanadate single crystal layer and the exposed area of ​​the conductive layer are fully covered and sealed with UV adhesive for insulation. After UV curing, an integrated encapsulation structure is formed. The wavelength of the UV light is 365 nm and the curing time is 1 min to 5 min.

[0088] Understandably, cleaning the insulating support substrate is a critical pretreatment step to ensure the quality of subsequent interfaces. Specifically, the substrate needs to be ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water, with each solvent treatment lasting 10 to 20 minutes. This sequence aims to achieve deep cleaning by utilizing the polarity differences of the solvents: acetone effectively removes organic contaminants, anhydrous ethanol displaces moisture and further cleans, and deionized water is used for final rinsing to remove residual solvent and ions. After cleaning and drying, a clean, uncontaminated substrate is obtained, laying a crucial foundation for the uniform coating and firm adhesion of the subsequent conductive layer.

[0089] The encapsulation process aims to construct a reliable electrolyte barrier layer. Specifically, a UV adhesive is used to fully cover and seal all sidewalls (peripherals) of the tungsten-doped bismuth vanadate single crystal layer and any uncovered exposed areas of the conductive layer, ensuring a seamless seal. Subsequently, the UV adhesive is rapidly cured by irradiation with 365 nm ultraviolet light for 1 to 5 minutes. This photocuring process can be completed within minutes at room temperature, forming a dense, robust, and insulating integrated encapsulation structure. This structure effectively isolates the electrolyte, preventing its penetration and potential internal short circuits or interface corrosion, thereby ensuring the long-term operational stability of the electrode in photoelectrochemical testing.

[0090] Optionally, the process of treating the working surface of the encapsulated tungsten-doped bismuth vanadate single crystal layer includes:

[0091] The working surface of the tungsten-doped bismuth vanadate single crystal layer is polished step by step using sandpaper with a grit of 800~5000 to make the thickness of the tungsten-doped bismuth vanadate single crystal layer 0.2mm~1mm.

[0092] The polished working surface is subjected to chemical mechanical polishing (CMP) to achieve a surface roughness Sa of 0.5 nm to 5.0 nm for the tungsten-doped bismuth vanadate single crystal layer. The CMP parameters include:

[0093] Polishing slurry with a particle size of 0.02 μm to 0.10 μm was used at 400 g·cm⁻¹. -2 ~ 2000 g·cm -2 Polishing was performed under polishing pressure and at a turntable speed of 10 rpm to 50 rpm for 6 min to 180 min, while controlling the polishing slurry drop rate at 0.2 mL / min. -1 ~ 1.0 mL·min -1 .

[0094] Understandably, surface preparation is a crucial step in obtaining a high-quality functional surface. First, the surface of the encapsulated monocrystalline layer undergoes rough machining and thickness control through progressive mechanical polishing: using sandpaper ranging from 800 to 5000 grit for progressive polishing. The main purpose of this step is to precisely control the overall thickness of the monocrystalline layer to the target range of 0.2mm to 1mm and to remove any surface unevenness or residue that may be caused by encapsulation. Progressive polishing effectively avoids introducing excessively deep scratches and microcracks, laying a good foundation for subsequent fine polishing.

[0095] Subsequently, the polished working surface is subjected to chemical mechanical polishing to obtain a nanoscale smooth surface. Polishing is performed under specific process parameters: using a polishing slurry with a particle size of 0.02μm to 0.10μm, a polishing pressure of 400g·cm⁻² to 2000g·cm⁻², and a turntable speed of 10rpm to 50rpm, polishing is carried out continuously for 6min to 180min, and the drop rate of the polishing slurry is controlled at 0.2mL·min⁻¹ to 1.0mL·min⁻¹. This synergistic process, through the combined effect of chemical etching and mechanical grinding, can precisely control the surface roughness Sa to 0.5nm to 5.0nm, thereby effectively eliminating subsurface damage, reducing the density of surface recombination centers, and ultimately optimizing the photoelectrochemical performance of the electrode.

[0096] Example 1

[0097] 1. Substrate Pretreatment and Conductive Layer Preparation: An optical glass sheet with dimensions of 20 mm × 10 mm × 1 mm was selected as the insulating support substrate. It was sequentially ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 15 min to thoroughly remove surface oil, dust, and impurities. After drying, it was ready for use. A liquid gallium-indium alloy conductive layer with a thickness of approximately 20 μm was uniformly coated on the central area of ​​the clean optical glass sheet, ensuring a uniform and continuous coating without agglomeration or blank areas. Subsequently, silver paste was applied to a portion of the gallium-indium alloy conductive layer, and after drying at room temperature, it formed the electrical contact area for subsequent photoelectrochemical testing.

[0098] 2. Single crystal bonding: BiV1 crystals with (001) orientation, W doping concentration of 0.1 at%, and dimensions of 5.0 mm × 5.0 mm × 1.0 mm were selected. 1-X W X O4 single crystals are placed flat on the surface of the gallium-indium alloy conductive layer prepared in step 1, and then gently pressed and left to stand for 1 minute to ensure that the bottom surface of the single crystal is in close contact with the entire alloy layer, ensuring that there are no bubbles or gaps at the interface, thus forming a reliable and tight conductive bonding structure.

[0099] 3. UV adhesive encapsulation: UV adhesive that is resistant to acid and alkali electrolyte corrosion and photoelectric cycle aging is used to fully cover and seal the sides, bottom bonding gaps and non-photoelectric chemical reaction areas of the single crystal. The UV adhesive is rapidly cured by irradiation with a 365 nm wavelength UV lamp for 1 minute to form an integrated encapsulation structure, which effectively blocks electrolyte penetration and improves the overall mechanical bonding strength.

[0100] 4. Fine polishing: The single crystal functional working surface is finely polished step by step using 800-grit, 1200-grit, and 2000-grit sandpaper. The pressure and polishing speed are controlled throughout the process to avoid micro-cracks and internal stress damage to the single crystal. After polishing, the effective thickness of the single crystal is precisely controlled to 0.4 mm, and the thickness error is controlled within ±0.02 mm.

[0101] 5. Chemical mechanical polishing: Use a silica polishing slurry with a particle size of 0.06 μm, and set the polishing pressure to 800 g·cm⁻¹. -2 The polishing solution drop rate was set to 0.6 mL / min. -1 The turntable speed was set to 30 rpm and the polishing time was set to 60 min. After chemical mechanical polishing, the grinding scratches and surface mechanical stress damage were removed.

[0102] like Figure 1 As shown, Figure 1 BiV prepared in Example 1 1-X W X A photograph of the O4 single crystal electrode. (The image shows the BiV electrode prepared in Example 1.) 1-X W X The O4 single-crystal electrode was characterized by AFM (atomic force microscopy), and the results are as follows: Figure 2 As shown in Table 2, the crystal surface is flat, and the measured surface roughness Sa is 0.601 nm. This result indicates that a high-quality single-crystal functional surface was obtained through chemical mechanical polishing.

[0103] Example 2

[0104] The basic steps are the same as in Example 1, except that:

[0105] 1. The thickness of the liquid gallium indium alloy conductive thin film is 30 μm;

[0106] 2. BiV4 substrates with (110) orientation, W doping concentration of 0.2 at%, and dimensions of 10.0 mm × 10.0 mm × 1.0 mm were selected. 1-X W X O4 single crystal, its bottom surface is attached to the surface of gallium indium alloy coating, and it is gently pressed and left to stand for 2 minutes;

[0107] 3. Cure with ultraviolet light for 2 minutes;

[0108] 5. Use a silica polishing slurry with a particle size of 0.08 μm and set the polishing pressure to 600 g·cm⁻¹. -2 The polishing slurry drop rate was set to 0.8 mL / min. -1 The rotary table speed was set to 40 rpm, and the polishing time was set to 90 min. The AFM characterization results are as follows: Figure 3 As shown, the crystal surface is flat, and the surface roughness Sa is measured to be 1.290 nm. This result indicates that a high surface quality single-crystal functional surface was obtained through chemical mechanical polishing.

[0109] Example 3

[0110] The basic steps are the same as in Example 1, except that:

[0111] 1. The thickness of the liquid gallium indium alloy conductive thin film is 40 μm;

[0112] 2. BiV4 substrates with (100) orientation, W doping concentration of 0.3 at%, and dimensions of 15.0 mm × 15.0 mm × 1.0 mm were selected. 1-X W X O4 single crystal, its bottom surface is attached to the surface of gallium indium alloy coating, and it is gently pressed and left to stand for 3 minutes;

[0113] 3. Cure with ultraviolet light for 3 minutes;

[0114] 5. Use a silica polishing slurry with a particle size of 0.10 μm and set the polishing pressure to 400 g·cm. -2 The polishing slurry drip rate was set to 1.0 mL / min. -1 The rotary table speed was set to 50 rpm, and the polishing time was set to 120 min. The AFM characterization results are as follows: Figure 4 As shown, the crystal surface is flat, and the surface roughness Sa is measured to be 2.250 nm. This result indicates that a high surface quality single-crystal functional surface was obtained through chemical mechanical polishing.

[0115] Comparative Example 1

[0116] BiV synthesized on FTO conductive glass using an organometallic decomposition method 1-X W X The O44 polycrystalline thin-film electrode is used as a reference sample for comparison with the single-crystal electrode of the present invention.

[0117] Comparative Example 2

[0118] To verify the reliability of the ceramic electrode during long-term photoelectrochemical testing, BiV was prepared according to the alloying-encapsulation core process described in patent specification ZL202111032831.3. 1-X W X The specific steps for using the O4 ceramic electrode are as follows:

[0119] (1) Preparation of ceramic sheets: BiV was prepared by solid-state reaction method. 1-X W XO4 ceramic sheets were produced by ball milling Bi2O3, V2O5, and WO3 in a stoichiometric ratio, pressing the mixture into shape, and sintering at 750 °C for 10 h to obtain ceramic sheets with a diameter of 15 mm and a density of 97.6% of the theoretical density. The circular ceramic sheets were then cut into smaller ceramic pieces of 5.0 mm × 5.0 mm × 0.50 mm. Both sides of the ceramic pieces were then chemically and mechanically polished, and the paraffin wax on the ceramic surface was removed with xylene. Finally, the ceramic pieces were placed in a tube furnace and annealed at 500 °C for 2 h in air to remove residual organic carbon.

[0120] (2) Alloying treatment: After removing residual organic carbon from BiV 1-X W X O4 ceramic wafers are uniformly coated with an indium gallium alloy (In:Ga = 75.5:24.5, mass ratio) and annealed in a tube furnace at 550 °C for 10 min to achieve semiconductor-metal alloying.

[0121] (3) Wire fixing and encapsulation: Copper wires were fixed to the alloyed side using silver conductive adhesive and cured at room temperature for 30 min; then, the ceramic chip was embedded into a two-component epoxy resin encapsulation mold and cured at room temperature for 24 h to obtain BiV. 1-X W X O4 ceramic electrode.

[0122] Ceramic electrode permeation failure experiment

[0123] BiV prepared in Comparative Example 2 1-X W X O4 ceramic electrode, BiV prepared in Comparative Example 1 1-X W X O4 polycrystalline thin film electrode and BiV prepared in Example 1 1-X W X The O4 (001) single crystal electrode was simultaneously assembled in a three-electrode test system and subjected to long-term photoelectrochemical stability testing at a potential of 1.23 V vs. RHE (reversible hydrogen electrode potential).

[0124] Test results show that: BiV 1-X W X When the O4 ceramic electrode had been reacting for approximately 6 hours, a severe liquid metal infiltration failure occurred. Specifically, the indium gallium alloy gradually infiltrated along the residual pore network within the ceramic and covered the functional working surface of the ceramic photoanode. This resulted in an unexpected large-area conductivity on the photoanode surface, a sudden and abnormal increase in the photocurrent signal followed by rapid erratic behavior, and the electrode completely lost its photoelectrochemical activity, forcing the test to terminate. Disassembly revealed that the epoxy resin encapsulation layer had peeled off from the ceramic interface, and obvious traces of residual liquid metal were visible on the ceramic side and working surface.

[0125] This infiltration failure phenomenon indicates that the inherent residual porosity of the ceramic material provides indium gallium alloy with infiltration channels. During the high-temperature alloying process, the liquid metal that seeps into the pores gradually migrates to the electrode surface under prolonged electrolyte immersion and the influence of the electric field, ultimately leading to electrode failure. This problem was not fully exposed in the 10-hour stability test of patent ZL202111032831.3, but it may become a fatal defect in longer-term actual operation.

[0126] Given BiV 1-X W X The aforementioned permeation failure issue of the O4 ceramic electrode makes it unsuitable as a reliable reference for long-term stability comparison. Therefore, subsequent comparative tests of the photoelectrochemical performance and stability of the system only used BiV from Comparative Example 1. 1-X W X O4 polycrystalline thin film electrode and BiV of Example 1 1-X W X O4 (001) single crystal electrode is used.

[0127] Photoelectrochemical performance testing

[0128] The working electrodes were prepared using BiV prepared in Example 1. 1-X W X O4 (001) single crystal electrode and BiV prepared in Comparative Example 1 1-X W X The electrode used was an O4 polycrystalline thin-film electrode, with a platinum mesh electrode as the counter electrode and an Ag / AgCl electrode as the reference electrode. The electrolytic cell was a quartz electrolytic cell, and the electrolyte was a 0.1 M NaPi buffer solution (pH = 7). The light source was a 300 W xenon lamp equipped with an AM 1.5G filter, with a light power density of 100 mW·cm⁻¹. -2 .

[0129] Chopper Jt Test

[0130] The chopper photocurrent density-time curve was measured at 1.23 V vs. RHE potential, with a chopper period of 10 s (alternating between light and dark states), and a total test time of 300 s.

[0131] As shown in Figure 5(a), in 0.1 M NaPi electrolyte, BiV 1-X W X O4 (001) Single Crystal Electrode ( Figure 5a BiV 1- X W X The photocurrent density of O4 (represented as W-BiVO4, hereinafter the same) increased from 0.12 mA·cm⁻¹ during a 300 s test. -2 It decreased slightly to 0.11 mA·cm -2The attenuation is extremely small; while BiV 1-X W X The photocurrent density of the O4 polycrystalline thin-film electrode is 0.14 mA·cm⁻¹ -2 It decreased significantly to 0.08 mA·cm. -2 The attenuation is significant. In addition, at the moment the light is turned on, the photocurrent of the single crystal electrode rises rapidly and quickly reaches a steady state, while the photocurrent of the polycrystalline thin film electrode rises rapidly and then continues to decline, indicating that there are a large number of defects on the surface of the polycrystalline thin film, resulting in severe photogenerated carrier recombination.

[0132] To further verify the impact of surface defects on stability, 0.1 M Na₂SO₃ was added to the electrolyte as a hole sacrificial agent for a control test, and the results are shown in Figure 5(b). After adding the sacrificial agent, the photocurrent density of the polycrystalline thin-film electrode significantly increased to 0.51 mA·cm⁻¹. -2 Furthermore, the decay amplitude decreased significantly after 300 s testing (decaying to 0.40 mA·cm⁻²), confirming that surface defects in polycrystalline thin films are the key factor leading to photogenerated carrier recombination and decreased stability. In contrast, the performance change of single-crystal electrodes before and after adding sacrificial agents was smaller, indicating their low surface defect density and excellent intrinsic stability.

[0133] Long-term stability test

[0134] A long-term constant potential Jt test was performed at 1.23 V vs. RHE potential. During the test, a fan was used to cool the electrolytic cell to reduce the interference of temperature fluctuations caused by thermal radiation from the light source on the test results.

[0135] like Figure 6 As shown, BiV 1-X W X After 100 hours of continuous operation, the photocurrent density of the O4(001) single crystal electrode increased from the initial 0.13 mA·cm⁻¹. -2 It decreased only slightly to 0.12 mA·cm -2 It exhibits almost no degradation, demonstrating excellent long-term photoelectrochemical stability. BiV... 1-X W X The O4 polycrystalline thin-film electrode achieved a photocurrent density of 0.14 mA·cm² after only 4 hours of operation. -2 It rapidly decreased to 0.03 mA·cm. -2 Its stability is extremely poor.

[0136] Structure, morphology and composition characterization before and after stability testing

[0137] To explore the mechanism of the stability difference, the structure, morphology and surface chemical state of the electrodes before and after long-term testing were compared and characterized.

[0138] Figure 7 The results show a comparison between XRD and Raman spectroscopy. Figure 7 a, Figure 7 c represents XRD comparison. Figure 7 b、 Figure 7 d represents the Raman spectrum comparison. Before and after the test, BiV... 1-X W X O4 (001) single crystal electrode and BiV 1-X W X The phase composition of the O4 polycrystalline thin-film electrode remained unchanged, retaining the monoclinic phase, and no new impurity peaks appeared. However, the XRD and Raman peak intensities of the polycrystalline thin-film electrode after testing showed a significant decrease, indicating that its crystallinity degraded during the photoelectrochemical process; while the diffraction peak intensities of the single-crystal electrode remained almost unchanged, indicating that its crystal structure remained highly stable during 100 h of long-term operation.

[0139] Figure 8 The SEM morphology comparison is shown. BiV 1-X W X The surface of the O4 (001) single crystal electrode remained dense and smooth after 100 h of testing, with no obvious corrosion marks observed. Figure 8 a, Figure 8 b). In contrast, BiV 1-X W X After 4 hours of testing, the morphology of the O4 polycrystalline thin film electrode was severely damaged, with preferential corrosion and dissolution occurring at grain boundaries and on the surface, leading to structural collapse. Figure 8 c. Figure 8 d).

[0140] Tables 1 and 2 list the quantitative analysis results of EDS and XPS, respectively.

[0141] Table 1. EDS elemental analysis results of the electrode surface before and after long-term stability test

[0142]

[0143] Where at% represents the atomic percentage.

[0144] As can be seen from Table 1, for BiV 1-X W X The O4 (001) single-crystal sample showed only minor changes in the atomic percentages of Bi, V, and O on its surface and the Bi:V atomic ratio (from 0.970 to 0.984) after 100 hours of reaction, indicating that this single-crystal electrode possesses excellent structural and chemical stability. In contrast, BiV... 1-X W XAfter only 4 hours of reaction, the surface elemental composition of the O4 polycrystalline thin film sample changed significantly: the Bi content increased from 15.14 at% to 17.17 at%, the O content decreased from 66.80 at% to 64.56 at%, and the Bi:V atomic ratio increased significantly from 0.838 to 0.940. This indicates that the polycrystalline thin film electrode underwent significant surface reconstruction or element loss / enrichment in the early stage of the reaction, and its stability is far inferior to that of the (001) single crystal sample.

[0145] Table 2. XPS elemental analysis results of the electrode surface before and after long-term stability testing.

[0146]

[0147] As shown in Table 2, for the (001) single-crystal sample, after 100 hours of reaction, the atomic percentages of Bi, V, and O on its surface and the Bi:V atomic ratio (from a slight increase of 1.049 to 1.076) changed very little, indicating that the surface of this single-crystal electrode exhibits excellent chemical stability during long-term reactions. Conversely, for the polycrystalline thin-film sample, after only 4 hours of reaction, the surface Bi content increased significantly from 20.68 at% to 22.49 at%, while the V content decreased from 13.34 at% to 12.45 at%, resulting in a significant increase in the Bi:V atomic ratio from 1.550 to 1.806. This result indicates that significant elemental reconstruction occurred on the surface of the polycrystalline thin-film electrode in the early stages of the reaction, specifically involving the dissolution of V, and its surface chemical stability was significantly lower than that of the (001) single-crystal sample.

[0148] EDS and XPS results jointly confirmed that the elemental composition of the single-crystal electrode remained highly stable after long-term photoelectrochemical testing, while the polycrystalline thin-film electrode showed significant V loss and structural degradation.

[0149] Table 3 Comparison of photoelectrochemical performance, stability and process characteristics of different electrode structures

[0150]

[0151] Table 3 summarizes the comparison of key performance parameters between single-crystal electrodes and polycrystalline thin-film electrodes, and includes notes on the failure characteristics of the ceramic electrode in Comparative Example 2.

[0152] Based on the above functional tests, it can be seen that compared with polycrystalline thin film electrodes, the single crystal electrode of Example 1 significantly reduced the photocurrent attenuation rate from 78.6% (4 h) to 7.7% (100 h) by eliminating grain boundary defects, and improved the stability by more than 25 times; at the same time, it avoided the serious carrier recombination problem caused by a large number of defects on the surface of polycrystalline thin films.

[0153] Compared to ceramic electrodes, the single-crystal electrode of Example 1 completely avoids the inherent risk of liquid metal penetration failure in ceramic electrodes. Ceramic electrodes rely on residual pores to achieve alloying contact. During long-term operation, the indium gallium alloy penetrates along the pores to the working surface, leading to complete loss of electrode function (failure within 6 hours). In contrast, Example 1, through its interface design of "substrate pre-coated alloy + single-crystal bonding," fundamentally eliminates the penetration channel, achieving stable operation for over 100 hours. Furthermore, Example 1 eliminates the need for high-temperature annealing, reducing the encapsulation and curing time from over 24 hours to minutes, significantly lowering process energy consumption and operational complexity.

[0154] The same functional characterization tests as in Example 1 were performed on Examples 2 and 3, and the results showed similar patterns to those in Example 1, indicating that the single crystal electrodes prepared within this process parameter range all have excellent long-term photoelectrochemical stability.

[0155] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A tungsten-doped bismuth vanadate single crystal electrode, characterized in that, include: Insulating support substrate; A conductive layer disposed on the insulating support substrate in a designated area; A tungsten-doped bismuth vanadate single crystal layer is bonded to the conductive layer; the surface roughness Sa of the tungsten-doped bismuth vanadate single crystal layer is 0.5 nm ~ 5.0 nm, and the thickness is 0.2 mm ~ 1 mm; The periphery of the tungsten-doped bismuth vanadate single crystal layer is encapsulated with an insulating and waterproof material, and the insulating and waterproof material covers the exposed area of ​​the conductive layer.

2. The tungsten-doped bismuth vanadate single crystal electrode as described in claim 1, characterized in that, The tungsten-doped bismuth vanadate single crystal layer includes tungsten-doped bismuth vanadate single crystals; The tungsten doping concentration of the tungsten-doped bismuth vanadate single crystal is 0.1 at% to 0.5 at%; The tungsten-doped bismuth vanadate single crystal was generated using the Czochralski method.

3. The tungsten-doped bismuth vanadate single crystal electrode as described in claim 1, characterized in that, The size range of the tungsten-doped bismuth vanadate single crystals includes 5.0 mm × 5.0 mm ~ 15.0 mm × 15.0 mm; The crystal orientation of the tungsten-doped bismuth vanadate single crystal includes (110), (001), (100), (101) or (111).

4. The tungsten-doped bismuth vanadate single crystal electrode as described in claim 1, characterized in that, The conductive layer is provided with a flexible contact layer and an electrical contact area; The thickness of the conductive layer is 10 μm to 50 μm.

5. The tungsten-doped bismuth vanadate single crystal electrode as described in claim 4, characterized in that, The flexible contact layer is a liquid gallium-indium alloy; the electrical contact area is formed by silver paste.

6. The tungsten-doped bismuth vanadate single crystal electrode as described in claim 1, characterized in that, The insulating and waterproof material is a cured product of UV adhesive; The insulating support substrate is glass.

7. A method for preparing a tungsten-doped bismuth vanadate single crystal electrode as described in any one of claims 1 to 6, characterized in that, include: A liquid gallium-indium alloy is coated in a designated area on the surface of a purified insulating support substrate to form a flexible contact layer; A localized area of ​​the flexible contact layer is covered with silver paste, which, after curing, forms an electrical contact area; the flexible contact layer and the electrical contact area form a conductive layer. The bottom surface of a tungsten-doped bismuth vanadate single crystal is attached to the conductive layer to form a tungsten-doped bismuth vanadate single crystal layer. The tungsten-doped bismuth vanadate single crystal layer is encapsulated so that the periphery of the tungsten-doped bismuth vanadate single crystal layer and the exposed area of ​​the conductive layer are covered with insulating and waterproof material; The encapsulated tungsten-doped bismuth vanadate single crystal layer is processed to form a working surface. By adjusting the surface roughness Sa and thickness to a preset range, the tungsten-doped bismuth vanadate single crystal electrode is prepared.

8. The method for preparing a tungsten-doped bismuth vanadate single crystal electrode as described in claim 7, characterized in that, The purification steps for the insulating support substrate include: The insulating support substrate was ultrasonically cleaned sequentially with acetone, anhydrous ethanol and deionized water, with each cleaning session lasting 10 min to 20 min. Finally, it was dried to obtain a purified insulating support substrate. The encapsulation of the tungsten-doped bismuth vanadate single crystal layer includes: The periphery of the tungsten-doped bismuth vanadate single crystal layer and the exposed area of ​​the conductive layer are fully covered and sealed with UV adhesive for insulation. After UV curing, an integrated encapsulation structure is formed. The wavelength of the UV light is 365 nm and the curing time is 1 min to 5 min.

9. The method for preparing a tungsten-doped bismuth vanadate single crystal electrode as described in claim 7, characterized in that, The process of treating the working surface of the encapsulated tungsten-doped bismuth vanadate single crystal layer includes: The working surface of the tungsten-doped bismuth vanadate single crystal layer is polished step by step using sandpaper with a grit of 800~5000 to make the thickness of the tungsten-doped bismuth vanadate single crystal layer 0.2mm~1mm. The polished working surface is subjected to chemical mechanical polishing treatment to make the surface roughness Sa of the tungsten-doped bismuth vanadate single crystal layer 0.5 nm ~ 5.0 nm.

10. The method for preparing the tungsten-doped bismuth vanadate single crystal electrode as described in claim 9, characterized in that, The operating parameters for the chemical mechanical polishing treatment include: Polishing slurry with a particle size of 0.02 μm to 0.10 μm was used at 400 g·cm⁻¹. -2 ~ 2000 g·cm -2 Polishing was performed at a polishing pressure and a turntable speed of 10 rpm to 50 rpm for 6 min to 180 min, while controlling the polishing slurry droplet rate at 0.2 mL / min. -1 ~ 1.0 mL·min -1 .

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