Heterogeneous multiphase composite photoelectric material and preparation, application and analysis method thereof

Abstract

The invention relates to the technical field of photoelectrochemical cathode protection, in particular to a heterogeneous multi-phase composite photoelectric material (a heterogeneous multi-phase composite photoelectric material constructed based on TiO2 / alpha-Bi2O3 / t-BiVO4 / m-BiVO4), preparation of the heterogeneous multi-phase composite photoelectric material, application of the heterogeneous multi-phase composite photoelectric material in photoinduced cathode protection and a multi-metal photoelectric cathode protection response analysis method. Specifically, the mode of'electro-deposition precursor construction + thermochemical gradient conversion 'is adopted, and the alpha-Bi2O3, t-BiVO4 and m-BiVO4 multiphase gradient coexisting heterogeneous composite structure four-phase composite photoelectric material is constructed in situ on the same TiO2 nanosheet substrate. In a simulated natural marine environment, under the condition of simulating a 0.35 M Na2SO3 solution under sun illumination, the photoelectric cathode protection material has excellent photoelectric cathode protection characteristic on 316L SS. Due to the construction of the multiphase heterojunction energy band gradient and the negative shift of the common Fermi level, the heterogeneous multiphase heterostructure photoanode has more excellent photoelectric cathode protection performance. According to the invention, a good reference is provided for photoelectric cathode protection of metal with negative self-corrosion potential.

Description

Technical Field

[0001] This invention relates to the field of photoelectrochemical cathodic protection technology, and in particular to a heterogeneous multiphase composite photoelectric material (a heterogeneous multiphase composite photoelectric material based on TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4) and its preparation, application in photo-induced cathodic protection, and a method for analyzing the response of multimetal photoelectric cathodic protection. Background Technology

[0002] Photoelectrochemical cathodic protection (PCP) is a promising new technology for marine metal corrosion protection. This technology utilizes sunlight as an energy source, injecting photogenerated electrons into the coupled metal via a semiconductor photoanode to effectively inhibit its electrochemical corrosion behavior, representing a clean protection solution that "resists corrosion with light." Among numerous PCP candidate materials, TiO2 has been widely studied due to its good chemical stability, abundant raw materials, and environmental friendliness. In particular, structurally ordered TiO2 nanosheets, with their oriented crystal planes for preferred growth, can naturally form "surface junctions," which facilitate the directional migration and spatial separation of photogenerated electrons and holes at the nanoscale.

[0003] However, single-phase TiO2 is limited by its wide bandgap (~3.2 eV), resulting in weak light absorption in the visible light band and thus limiting its photocathode protection efficiency. Therefore, constructing multiphase heterojunction structures has become an effective strategy to improve the visible light response performance of TiO2-based photoanodes. In recent years, researchers have attempted to utilize polymorphic or multi-component heterostructures to enhance the separation and migration efficiency of photogenerated carriers. For example, three-phase composites: TiO2 three-phase junctions constructed from brookite, rutile, and anatase. [1] Two-phase junction: a combination of monoclinic phase and tetragonal phase BiVO4. [2] Or anatase-rutile TiO2 dual phase [3] and α- / γ-Bi2O3 structure [4] In other material systems, such as Yang et al. [5] Cu₂O / CuO bilayer photoanodes were constructed using electrodeposition and thermal oxidation methods; Jennifer et al. [6] A single-step chemical vapor deposition method was used to successfully achieve the coexistence of α-Fe2O3 / Fe3O4 phases by controlling the deposition time. Although the above-mentioned multiphase or two-phase structures improved the separation efficiency of photogenerated carriers to some extent, they still generally have the disadvantages of single heterostructure interface type, abrupt energy level transition, limited carrier migration paths, and prominent interface recombination. It is difficult to achieve both high electron output efficiency and long-term operational stability under visible light conditions.

[0004] In addition, Feng et al.[7] A TiO2 / MgTixOy multiphase heterojunction system was reported. Experiments showed that its electron mobility efficiency was superior to that of traditional two-phase junctions, further confirming that heterogeneous multiphase structures can significantly improve photoelectric performance. However, existing heterogeneous multiphase structures still generally have the following limitations: First, the construction mode of the multiphase interface lacks controllability, and the spatial distribution and interface position of different phases are difficult to adjust precisely. Second, the phases often exhibit a simple superposition relationship, lacking effective energy level gradient coordination. Third, related research focuses mainly on photocatalysis or photoelectrochemical water splitting, and there is still a lack of systematic material design schemes for key requirements in photocathode protection systems, such as "continuous electron injection stability, anti-polarization decay capability, and responsiveness to multi-metal structures". Based on these studies, if multiphase components such as α-Bi2O3, t-BiVO4, and m-BiVO4 can be introduced into the TiO2 host structure to construct a heterogeneous multiphase heterostructure with a stepwise transition characteristic of "wide bandgap – narrow bandgap – even narrower bandgap", it is expected to enhance the visible light absorption capacity, construct the gradient migration driving force of photogenerated carriers, and effectively suppress interfacial recombination. This structure has fundamental differences from traditional two-phase junction or simple multiphase superposition systems in terms of band continuity, electron migration directionality, and photocathode protection stability.

[0005] Furthermore, as a typical narrow bandgap semiconductor, BiVO4's electrical type and carrier transport behavior depend not only on its intrinsic band structure but also highly on the formation of point defects within the material. Studies have shown that Bi vacancies (V0) are easily formed in the BiVO4 crystal structure. Bi ) and oxygen vacancy (V O It has a significant regulatory effect on its n-type or p-type conductivity: oxygen vacancies, as donor defects, can introduce shallow energy levels and provide additional free electrons, making BiVO4 exhibit typical n-type semiconductor characteristics; while Bi vacancies, as acceptor defects, can introduce hole-type charge carriers, making BiVO4 locally exhibit p-type or weak p-type conductivity characteristics.

[0006] During the thermochemical transformation and vanadate reaction, metallic Bi undergoes oxidation and vanadate transformations sequentially. The local reaction environment (such as oxygen partial pressure, heating rate, and vanadium source supply concentration) inevitably induces the synergistic generation of Bi vacancies and oxygen vacancies, resulting in defect-regulated n / p mixed conductivity characteristics in the obtained t-BiVO4 and m-BiVO4. This defect-induced energy level modulation creates a built-in potential gradient between the conduction and valence bands of the multiphase BiVO4, which is beneficial for the spontaneous separation and directional migration of photogenerated electrons and holes at the multiphase interface.

[0007] Therefore, developing a heterogeneous nanocomposite photoanode material with TiO2 as the main system, combined with α-Bi2O3, t-BiVO4 and m-BiVO4 to construct a multiphase synergistic conductive channel, and exploring its application in photoelectric cathodic protection, is of great significance for improving the overall system performance and promoting the engineering application of PCP technology.

[0008] Meanwhile, while the widely studied photoanode materials have been proven to provide a certain degree of photocathode protection for metals such as 316L stainless steel and Q235 carbon steel, current research mainly focuses on the protective performance testing of single metals, lacking analysis of the response characteristics of multi-metal coupling systems.

[0009] Different metals possess distinct corrosion potentials, work functions, and Fermi levels, resulting in significant differences in band mismatch with photoanodes. This band mismatch affects the injection direction and efficiency of photogenerated electrons, thereby determining the effective potential, response speed, and stability of the protective effect. Therefore, evaluating only a single metal is insufficient to comprehensively guide the adaptive design of photoanode materials in multi-metal practical application environments.

[0010] Furthermore, factors such as the electronic structure state of the metal surface, charge transfer resistance, and the conduction band configuration and work function gradient of the photoanode all significantly influence interfacial electron migration behavior. The failure to systematically consider these synergistic parameters in existing testing and analysis systems severely restricts the optimization and targeted development of the broad-spectrum protective performance of photoanode materials.

[0011] Therefore, there is an urgent need to establish a set of methods for testing and analyzing the response mechanism of photoelectric cathodic protection in multi-metal systems.

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[0014] [3]X.Ruan,X.Cui,Y.Cui,X.Fan,Z.Li,T.Xie,K.Ba,G.Jia,H.Zhang,L.Zhang,W.Zhang,X.Zhao,J.Leng,S.Jin,D.J.Singh,W.Zheng,Favorable Energy Band Alignmentof TiO2Anatase / Rutile Heterophase Homojunctions Yields PhotocatalyticHydrogen Evolution with Quantum Efficiency Exceeding 45.6%,Advanced EnergyMaterials 12(2022)2200298.

[0015] [4]Y.Sun,W.Wang,L.Zhang,Z.Zhang,Design and controllable synthesis ofα- / γ-Bi2O3homojunction with synergetic effect on photocatalytic activity,Chemical Engineering Journal 211-212(2012)161-167.

[0016] [5]Y.Yang,D.Xu,Q.Wu,P.Diao,Cu2O / CuO Bilayered Composite as a High-Efficiency Photocathode for Photoelectrochemical Hydrogen Evolution Reaction,Scientific Reports 6(2016).

[0017] [6]J.Leduc,Y.Goenuellue,P.Ghamgosar,S.You,J.Mouzon,H.Choi,A.Vomiero,M.Grosch,S.Mathur,Electronically-Coupled Phase Boundaries inα-Fe2O3 / Fe3O4Nanocomposite Photoanodes for Enhanced Water Oxidation,ACS Applied NanoMaterials 2(2019)334-342.

[0018] [7]C.Feng,Z.Chen,J.Jing,M.Sun,G.Lu,J.Tian,J.Hou,A novel TiO2 nanotubearrays / MgTi x O y multiphase-heterojunction film with high efficiency for photoelectrochemical cathodic protection,Corrosion Science 166(2020)108441. Summary of the Invention

[0019] The purpose of this invention is to provide a heterogeneous multiphase composite optoelectronic material (a heterogeneous multiphase composite optoelectronic material based on TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4), its preparation, its application in photocathode protection, and a method for analyzing the response of multimetal photocathode protection.

[0020] To achieve the above objectives, the present invention adopts the following technical solution:

[0021] A method for preparing heterogeneous multiphase composite optoelectronic materials employs an "electrodeposition precursor construction + thermochemical gradient transformation" approach to in-situ construct a heterogeneous four-phase composite optoelectronic material (TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4, denoted as TiO2-BiVO4-T) on the same TiO2 nanosheet substrate, in which α-Bi2O3, t-BiVO4, and m-BiVO4 multiphase gradients coexist.

[0022] To elaborate further,

[0023] First, metallic Bi particles were deposited on the surface of TiO2 nanosheets by electrodeposition to form a TiO2 / Bi precursor structure.

[0024] Subsequently, by introducing a vanadium source and performing thermochemical treatment in an air atmosphere, the Bi particles undergo a gradient transformation from the inside to the outside, resulting in the formation of a multiphase composite structure on the same TiO2 nanosheet with a hierarchical distribution of α-Bi2O3, tetragonal BiVO4 (t-BiVO4), and monoclinic BiVO4 (m-BiVO4) along the normal direction.

[0025] Thus, a heterogeneous gradient multiphase composite optoelectronic material of TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4 is obtained, denoted as TiO2-BiVO4-T.

[0026] To go further,

[0027] (1) Construction of TiO2 / Bi precursor:

[0028] Using an FTO substrate with TiO2 nanosheets as the working electrode, and an Ag / AgCl electrode and a Pt electrode as the reference and counter electrodes, respectively, a Bi2O2-containing substrate was used. 3+ In an electrolyte solution, electrodeposition was performed at a potential of –0.6V (vs. Ag / AgCl) for 300-900s to deposit metallic Bi particles onto the surface of TiO2 nanosheets, thus obtaining the TiO2 / Bi precursor.

[0029] The Bi-containing electrolyte solution is prepared by dissolving Bi(NO3)3·5H2O in a mixed solution of ethylene glycol and deionized water in a volume ratio of 2:1 to form a homogeneous and transparent solution; wherein the final concentration of Bi(NO3)3·5H2O is preferably 5–10 mM, more preferably about 6–7 mM.

[0030] (2) Multiphase gradient in-situ transformation:

[0031] A DMSO solution containing vanadium acetylacetonate was introduced onto the surface of the TiO2 / Bi precursor and calcined in air at 450°C. Under the combined action of oxygen diffusion and vanadium source infiltration from the outside to the inside, the Bi particles underwent in-situ gradient oxidation and vanadication reactions along the normal direction, sequentially forming α-Bi2O3, t-BiVO4 and m-BiVO4 multiphase structures, thereby constructing a gradient-distributed heterogeneous multiphase composite structure on the same TiO2 nanosheet.

[0032] In this process, the deposition thickness and loading of Bi metal precursor on the TiO2 nanosheet surface are precisely controlled by adjusting the deposition time and the corresponding actual charge (Q) in step (1); and then, in the thermochemical oxidation and vanadium conversion process in step (2), the relative content ratio of the three phases α-Bi2O3, t-BiVO4 and m-BiVO4 and their spatial gradient distribution along the normal direction are regulated, thereby constructing a heterogeneous multiphase composite structure with multiphase gradient characteristics on the TiO2 nanosheet surface.

[0033] FTO of the TiO2 nanosheets

[0034] (1) Tetrabutyltitanium (C 16 H 36 O4Ti) was added to the mixed acid solution and stirred until homogeneous; wherein, tetrabutyltitanium (C 16 H 36 The volume ratio of O4Ti to the mixed acid solution is 1:(20-40).

[0035] (2) Add ammonium fluorotitanate ((NH4)2TiF6) to the above mixture as a crystal plane modifier and stir to mix well;

[0036] (3) Place the cleaned substrate with the conductive surface facing down in the reaction vessel, then add the mixture obtained in step (2), and seal it for hydrothermal reaction at 170-190℃ for 9-15 hours to obtain TiO2 nanosheet thin film material with a specific crystal surface exposure ratio on the substrate surface.

[0037] The mixed acid solution is a mixture of deionized water and concentrated hydrochloric acid in a volume ratio of 1:1; wherein the concentration of concentrated hydrochloric acid is 18%-19% (mass fraction);

[0038] The amount of ammonium fluorotitanate and tetrabutyl titanium added is based on the ratio of 1.0 g of ammonium fluorotitanate to 1.0 mL of tetrabutyl titanium, and the corresponding molar ratio is constant at approximately 1.83:1.

[0039] A method for preparing heterogeneous multiphase composite optoelectronic materials, wherein a gradient multiphase junction epitaxial structure is prepared by means of α-Bi2O3, tetragonal BiVO4 (t-BiVO4) and monoclinic BiVO4 (m-BiVO4) distributed sequentially from the inside to the outside along the normal direction on the TiO2(101) crystal plane of the matrix;

[0040] The structure consists of an α-Bi₂O₃ transition layer near the TiO₂ matrix, a t-BiVO₄ nanocrystalline layer in the middle, and an outer m-BiVO₄ rough epitaxial layer. The interfaces between the phases are continuously transitioned, resulting in a hierarchically graded multiphase composite morphology. This yields a heterogeneous multiphase composite optoelectronic material with a precise gradient loading of α-Bi₂O₃, t-BiVO₄, and m-BiVO₄ multiphase junctions on the TiO₂(101) crystal plane.

[0041] An application of the heterogeneous multiphase composite optoelectronic material, wherein the heterogeneous multiphase composite optoelectronic material is used as a semiconductor photoelectric conversion layer.

[0042] An application of the heterogeneous multiphase composite optoelectronic material, wherein the multiphase composite optoelectronic material is used as an anti-corrosion protective film to inhibit metal corrosion.

[0043] The heterogeneous multiphase composite optoelectronic material is used as a corrosion-resistant protective film to inhibit metal corrosion, and its protective effect on copper with a more negative self-corrosion potential is enhanced in sodium sulfite solution, a hole-removing agent.

[0044] A photoanode prepared from a TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4 composite material, wherein the electrode includes a photoelectric conversion layer and a conductive layer, wherein the heterogeneous multiphase composite photoelectric material serves as the semiconductor photoelectric conversion layer and FTO conductive glass serves as the conductive layer.

[0045] The heterogeneous multiphase composite optoelectronic material is used as a photocathode to inhibit metal corrosion and significantly improve the efficiency of photocathode protection in simulated marine environments.

[0046] An application of the electrode described above, wherein the composite photoanode is used as a photocathode for corrosion protection and anti-corrosion purposes to inhibit metal corrosion.

[0047] The TiO2-BiVO4-T composite photoelectric material prepared above for photoelectrochemical cathodic protection was fabricated as a photoanode, and its photoelectrochemical cathodic protection effect was tested. Specifically, the changes in photoinduced open-circuit potential and photogenerated current density were used to characterize the effect. These changes were measured by recording the changes in photogenerated current density and open-circuit potential over time under on / off lighting conditions. The specific measuring apparatus consisted of two reaction cells: a corrosion cell and a photoelectrochemical cell, as shown below. Figure 5 As shown in Figures a and 5b, the electrolyte in the photoelectrochemical cell was a 0.35M Na₂SO₃ solution, and the electrolyte in the corrosion cell was a 3.5% NaCl solution. The two cells were connected by a salt bridge. The photoanode was placed in the photoelectrochemical cell, and the 316L SS was placed in the corrosion cell. The light source used in this study was a 300-W xenon lamp (PLS-SXE300, Beijing Pofilai Lighting Co., Ltd., China). By adding an AM1.5 filter to the light source, simulated sunlight was obtained. The illumination intensity was 100mW / cm². 2 These tests were conducted under intermittent simulated sunlight. A quartz window, approximately 30 mm in diameter, is located at the center of the front of the photovoltaic cell, through which incident light illuminates the photoanode surface.

[0048] The basic principle of the heterogeneous multiphase composite optoelectronic material obtained in this invention:

[0049] This invention is based on a heterogeneous multiphase synergistic construction strategy. It constructs a TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4 composite photoanode by depositing metallic Bi particles on two-dimensional TiO2 nanosheets and further thermochemically transforming them into BiVO4. Due to spatial constraints, the Bi oxidation products undergo layered evolution along the TiO2 crystal plane from bottom to top, thereby constructing a heterogeneous multiphase structure on the TiO2 surface with a Bi-rich inner layer and a V-rich outer layer.

[0050] This four-phase system has a good conduction band matching relationship. Its band arrangement order is: TiO2>α-Bi2O3>t-BiVO4>m-BiVO4. The conduction band potential becomes negative step by step. Under light excitation, the photogenerated electrons generated in m-BiVO4 and t-BiVO4 migrate sequentially to TiO2 along the band gradient, forming a ladder-like directional electron migration channel, which significantly improves the carrier separation efficiency and suppresses bulk phase and interface recombination.

[0051] Furthermore, under illumination, photogenerated electrons accumulate in the conduction band of the n-type semiconductor TiO2-BiVO4 photoanode, causing its quasi-Fermi level (E0). F This significantly shifts the open-circuit potential (OCP) of the entire system, leading to a negative shift. Simultaneously, 0.35 mol·L⁻¹ N⁻¹ is used. a2SO3 As a hole trap, it further lowers the Fermi level, enhancing the ability of electrons to be injected into external metal electrodes (such as 316L stainless steel). Ultimately, after the TiO2-BiVO4 photoanode is coupled with 316L SS, photogenerated electrons can be effectively transferred to the stainless steel surface, thereby achieving a stable and efficient photoelectrochemical cathodic protection function.

[0052] A multi-metal photoelectric cathodic protection response analysis method is proposed, which constructs a coupling system between a heterostructure photoanode material and the metal component to be protected. By obtaining the response electrochemical parameters, the cathodic polarization amplitude and protection duration of each metal are determined. Furthermore, the band parameters of the photoanode and the metal are characterized by Mott-Schottky analysis to determine the response type of different metals and match the corresponding heterostructure photoanode material with the metal component to be protected.

[0053] The constructed coupled system was placed in a dual-cell electrochemical system and synchronously tested under simulated illumination (AM 1.5) conditions to obtain response electrochemical parameters, which were used to determine the cathodic polarization amplitude and protection duration of each metal. At the same time, a metal-semiconductor bandgap spectrum was established through Mott-Schottky analysis to analyze the energy difference driving conditions of photogenerated electron injection, and then to match the corresponding heterostructure photoanode material with the metal component to be protected.

[0054] The response electrochemical parameter is the photocurrent density (J / L).ph ), photoinduced open-circuit potential (OCP) change, mixed potential response (E) mix And the response hysteresis behavior during the illumination-off cycle;

[0055] The parameters for constructing the metal-semiconductor bandgap diagram are the conduction band bottom position (E) of the photoanode. CB The work function (Φm) of each metal surface was measured using a scanning Kelvin probe (SKP).

[0056] To elaborate further:

[0057] 1) Establish a multi-metal optoelectronic protection testing system

[0058] The heterogeneous photoanode material was coupled with metal components such as 316L stainless steel, pure copper, E40 marine steel, and Q235 carbon steel to form coupling systems. These systems were then placed in a dual-cell electrochemical system composed of 0.35 mol / L Na2SO3 and 3.5 wt.% NaCl to conduct synchronous tests under simulated illumination (AM 1.5) conditions.

[0059] 2) Obtain the response electrochemical parameters

[0060] Real-time recording of photocurrent density (J) of the coupled system ph ), photoinduced open-circuit potential (OCP) change, mixed potential response (E) mix The response hysteresis behavior during the illumination-off cycle is used to determine the cathodic polarization amplitude and protection duration of each metal.

[0061] 3) Characterizing the photoanode and metal band parameters

[0062] The conduction band bottom (E) of the photoanode was obtained using Mott-Schottky analysis. CB By combining scanning Kelvin probe (SKP) measurements of the work function (Φm) of each metal surface, a metal-semiconductor band structure comparison was established to analyze the energy difference driving conditions for photogenerated electron injection.

[0063] 4) Establish response mechanism and matching model

[0064] Based on experimental data and band parameters, a "photoanode-metal" energy level matching model was constructed to determine the response types of different metals (fully matched, partially injected, and mismatched) and identify the dominant factors affecting protection efficiency, including conduction band difference, charge migration resistance, and interface electrode dynamics.

[0065] Through the above steps, the constructed testing and analysis methods can effectively realize the visual identification and quantitative evaluation of the photocathode protection behavior of various metal materials, reveal the cooperative matching mechanism between the photoanode conduction band structure and the metal surface energy level, and provide important theoretical support and technical basis for the directional design of heterostructure photoanode materials, the optimization of multi-metal compatibility and the formulation of protection strategies.

[0066] The basic principle of the protection response analysis method of this invention:

[0067] This invention is based on the fundamental principle of photoelectrochemical cathodic protection (PECP). By constructing a TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4 composite photoanode with band gradient and multiphase synergistic effects, it achieves directional injection of photogenerated electrons into various metals, thereby achieving stable and efficient cathodic protection. Under sunlight irradiation, t-BiVO4 and m-BiVO4 in the photoanode first absorb visible light to generate electron-hole pairs. Driven by the band difference, some photogenerated electrons migrate along the path t-BiVO4→α-Bi2O3→TiO2, eventually accumulating at the bottom of the conduction band of TiO2 (approximately –0.83V vs Ag / AgCl). Because this conduction band position is significantly negative to the corrosion potential and Fermi level of most metals, photogenerated electrons can be thermodynamically and spontaneously injected into the metal electrode surface, inducing metal cathodic polarization and effectively inhibiting its corrosion reaction.

[0068] Different metals have different intrinsic corrosion potentials, electrode work functions, and interfacial electronic states. The degree of energy level matching between the metal and the photoanode directly affects the efficiency of photogenerated electron injection and the protective effect: when the metal has a high work function or a positive corrosion potential, the electron injection barrier of the photoanode is small, and the protective effect is significant (e.g., 316L SS, Cu); when the metal has a low work function or a negative corrosion potential, a higher conduction band potential difference is required to achieve electron migration (e.g., Q235 CS, E40); if the conduction band and the metal energy level cannot effectively overlap, an effective electron injection channel cannot be formed, and the protective effect is weak.

[0069] Furthermore, the band gradient in the anolyte multiphase structure not only facilitates the spatial separation of photogenerated electrons and holes but also suppresses bulk recombination, thereby increasing the migration distance and lifetime of photogenerated electrons. Holes can be rapidly dissipated by sacrificial agents in the electrolyte (such as SO32-), further enhancing the directionality and stability of electron flow towards the metal.

[0070] By analyzing the correlation between the photoelectric response behavior of different metals (such as OCP negative shift, i–t response, and delay effect) and the conduction band potential of the photoanode and the work function of the metal, this invention establishes a quantitative band matching model between metal and photoanode, realizing the theoretical prediction and experimental verification of the efficiency of multi-metal photocathode protection.

[0071] Advantages of this invention:

[0072] This invention is the first to achieve the preparation of a TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4 composite photoanode material with high efficiency in photoelectric conversion and cathodic protection through element enrichment / depletion regulation and multiphase synergistic construction mechanism. Furthermore, the invention provides a method for analyzing the multimetal photocathode protection response of the obtained heterogeneous multiphase composite photoelectric material, which has the following significant advantages:

[0073] 1. Construction of heterogeneous multiphase structures improves carrier separation efficiency:

[0074] By selectively loading α-Bi2O3, t-BiVO4 and m-BiVO4 onto the TiO2(101) crystal plane, a four-phase heterostructure with distinct spatial hierarchy was formed, and an internal conduction band gradient descending channel was successfully constructed. This promoted the directional transfer of photogenerated electrons and the rapid consumption of holes, effectively suppressed bulk recombination and interface loss, and thus significantly enhanced the photocurrent response and PEC performance.

[0075] 2. The photoanode exhibits strong negative shift capability of the quasi-Fermi level, resulting in stable photoelectric output:

[0076] Compared to traditional TiO2, TiO2-Bi2O3 or Bi x VO y The structure of the fabricated TiO2-BiVO4-T photoanode can significantly improve the photogenerated carrier density and output potential, exhibiting stronger quasi-Fermi level negative shift behavior, which is beneficial to enhancing the electron injection capability in the metal coupling system and providing more efficient cathodic protection for the metal.

[0077] 3. Excellent photoelectrochemical cathodic protection performance:

[0078] The typical sample TiO2-BiVO4-T-300 exhibited strong photoresponse characteristics to 316L stainless steel in 0.35M Na2SO3 solution, with a cathodic protection current density as high as 33 μA·cm. -2 The photopotential drop reached -0.54V (vs. Ag / AgCl), proving its excellent corrosion protection performance.

[0079] 4. The materials are green and environmentally friendly, and the preparation process is controllable.

[0080] All components used in this invention are non-toxic, environmentally friendly, and resource-rich oxide systems. Combined with solvothermal, electrodeposition, and thermal conversion methods, large-area, low-cost, and controllable preparation can be achieved, making it suitable for large-scale application and promotion.

[0081] 5. System evaluation and differentiation of the protection performance of multi-metal photocathodes:

[0082] This invention, by introducing conductor positioning, work function measurement, and response curve analysis, enables precise comparison of the response patterns of various metal materials such as stainless steel, carbon steel, and copper under the same photoanode system, filling the technical gap in the prior art where there is a lack of systematic analysis of the selective protection mechanism of multi-metal systems.

[0083] 6. Construct a multiphase heterogeneous photoanode with broad-spectrum protection capability:

[0084] The TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4 four-phase composite structure forms a stable band gradient and electron migration path, with a wide conduction band coverage (up to -0.83V), which can match the corrosion potential of a variety of metals, achieving broad-spectrum adaptability and high-efficiency protection.

[0085] 7. Provides quantifiable band matching models to facilitate material selection and design:

[0086] This invention establishes a quantitative matching relationship between the photoanode conduction band position, metal corrosion potential, and work function, and proposes a relationship based on "conduction band difference – OCP negative shift – J". ph The "output" is the core evaluation index system, providing a reliable basis for the subsequent targeted development of metal-specific protective materials.

[0087] 8. Providing new ideas for marine corrosion protection and PEC devices

[0088] By introducing the bandgap construction mechanism into the design of photoanode materials, this invention expands the functional boundaries of TiO2-type materials and provides new directions and key support for the engineering application of photoelectrochemical cathodic protection technology in marine engineering, shipping equipment and other fields. Attached Figure Description

[0089] Figure 1 This diagram illustrates the crystal plane orientation structure and bandgap matching of TiO2 nanosheets. The left figure shows the spatial arrangement of the {001} and {101} crystal planes in the TiO2 nanosheets and the electron (e) bandgap ratio. - The right figure shows the relative positions of the conduction band and valence band of the {001} and {101} crystal planes, forming a surface heterojunction to achieve directional carrier migration.

[0090] Figure 2This image shows structural models of different crystal planes of anatase TiO2. The left image shows the {101} crystal plane, which exposes active sites such as 2-coordinated oxygen (2c-O), 3-coordinated oxygen (3c-O), 5-coordinated titanium (5c-Ti), and 6-coordinated titanium (6c-Ti). The right image shows the {001} crystal plane, which mainly contains 2c-O and 5c-Ti structural units. The two crystal planes exhibit significant differences in structural stability and charge behavior.

[0091] Figure 3 Scanning electron microscope (SEM) images of TiO2 nanosheets provided in an embodiment of the present invention.

[0092] Figure 4 A flowchart illustrating the preparation process of optoelectronic materials provided in an embodiment of the present invention.

[0093] Figure 5 The TiO2-BiVO4-T-50(a), TiO2-BiVO4-T-300(b), TiO2-BiVO4-T-600(c), TiO2-BiVO4-T-900(d) provided in the embodiments of the present invention, and the TiO2-Bi2O3(e), Bi2O3(f) and Bi provided in the comparative examples are shown in the present invention. x VO y (g) SEM image.

[0094] Figure 6 XRD patterns of TiO2-BiVO4-T-50, TiO2-BiVO4-T-300, TiO2-BiVO4-T-600 and TiO2-BiVO4-T-900 provided in the embodiments of the present invention.

[0095] Figure 7 The intermediate process provided in the embodiments of the present invention uses TiO2-Bi, and the comparative examples use TiO2-Bi2O3, Bi2O3, and Bi. x VO y XRD patterns.

[0096] Figure 8 TEM, HRTEM images and mapping images of TiO2-BiVO4-T-300 provided in the embodiments of the present invention.

[0097] Figure 9 This is a schematic diagram of the connection of the photoelectrochemical cathodic protection and corrosion electrochemical testing device in an embodiment of the present invention. (a) Photogenerated current density (J) ph (a) Schematic diagram of the test setup connection; (b) Schematic diagram of the photoinduced open circuit potential (OCP) test setup connection; (c) Current density for corrosion of different metals (i corr ) and corrosion potential (E) corr(d) Schematic diagram of a three-electrode corrosion testing device for several photoelectrode models;

[0098] Figure 10 Transient photocurrent density (J) in coupling systems constructed with different metals and TiO2-BiVO4-T photoanodes ph ) Change curve.

[0099] Figure 11 Photoinduced mixing potential (OCP) response curves of coupling systems with different metals and TiO2-BiVO4-T photoanodes.

[0100] Figure 12 Long-term photogenerated current density (J) of different metals coupled with TiO2-BiVO4-T photoanode ph Response curve.

[0101] Figure 13 Long-term photoinduced mixing potential response curves of coupling systems of different metals with TiO2-BiVO4-T photoanodes.

[0102] Figure 14 Comparison of surface corrosion morphology of different metals under unprotected and photocathode protected conditions.

[0103] Figure 15 Linear polarization behavior of four metal electrodes (316L SS, Cu, E40, Q235 CS) in 3.5 wt% NaCl solution.

[0104] Figure 16 Tafel polarization curves of four metal electrodes (316L SS, Cu, E40, Q235 CS) in 3.5 wt% NaCl solution.

[0105] Figure 17 Cathodic polarization curves of four metal electrodes (316L SS, Cu, E40, Q235 CS) in 3.5 wt% NaCl solution.

[0106] Figure 18 Kelvin probe scanning potential (SKP) testing device.

[0107] Figure 19 Kelvin probe scanning potential (SKP) images of different metal surfaces. (a) 316L stainless steel; (b) pure copper; (c) E40 marine steel; (d) Q235 carbon steel.

[0108] Figure 20 Comparison of surface work functions of different metals.

[0109] Figure 21Electrochemical impedance spectroscopy (EIS) curves of impedance modulus (|Z|) versus frequency for four metal electrodes (316L SS, Cu, E40, and Q235 CS) in 3.5 wt% NaCl solution.

[0110] Figure 22 Electrochemical impedance spectroscopy (EIS) curves of phase angle versus frequency for four metal electrodes (316L SS, Cu, E40, and Q235 CS) in 3.5 wt% NaCl solution.

[0111] Figure 23 The present invention provides a three-electrode system in which TiO2, TiO2-Bi2O3, TiO2-BiVO4-T-300, Bi2O3 and Bi are present in a 0.1M Na2SO4 solution. x VO y The model Schottky curve of the photoanode, where b is Bi. x VO y Enlarged view of the M-S curve of the sample.

[0112] Figure 24 A schematic diagram showing the relationship between the band matching mechanism of four different metal-photoanodes (TiO2-BiVO4-T) and the photocathode protection efficiency.

[0113] Figure 25 The curves showing the change of current density over time in the coupling system of TiO2-BiVO4-T photoanode and 316L SS electrode prepared under intermittent on-off light conditions and different electrodeposition times are provided in the embodiments of the present invention.

[0114] Figure 26 The potential variation curves of the coupling system of TiO2-BiVO4-T photoanode and 316L SS electrode prepared under intermittent on-off light conditions and different electrodeposition times are shown in the embodiments of the present invention.

[0115] Figure 27 The present invention provides the following properties under intermittent on / off light conditions: TiO2, TiO2-Bi2O3, TiO2-BiVO4-T-300, Bi2O3, and Bi x VO y The coupling system of photoanode and 316L SS electrode, and the curve of current density changing with time.

[0116] Figure 28 The present invention provides the following properties under intermittent on / off light conditions: TiO2, TiO2-Bi2O3, TiO2-BiVO4-T-300, Bi2O3, and Bi x VO yThe potential change curve over time of the coupling system of photoanode and 316L SS electrode. Detailed Implementation

[0117] The present invention will be further described below with reference to the accompanying drawings and examples, but this description does not limit the invention in any way.

[0118] The material of this invention is obtained by in-situ electrodeposition of Bi metal particles on the surface of a two-dimensional substrate on which TiO2 nanosheets are grown, thereby obtaining a multiphase composite optoelectronic material; wherein, the two-dimensional substrate on which TiO2 nanosheets are grown is obtained by in-situ growth on the surface of an FTO conductive substrate by a solvothermal method.

[0119] There is an urgent need to establish a set of testing and mechanism analysis methods for photoelectric cathodic protection response in multi-metal systems.

[0120] This invention presents a multi-metal photocathode protection response analysis method based on heterostructure photoanodes. By constructing a photoanode system with a conduction band gradient structure and directional electron output capability, it enables a systematic evaluation and response mechanism analysis of the photocathode protection performance of various metal materials under simulated marine environments. It can systematically analyze the response mechanisms of different metals from aspects such as conduction band-Fermi level matching, current response laws, and interface polarization behavior, combining the band structure characteristics of heterostructure photoanodes. The construction of a metal-semiconductor band mapping model will provide crucial support for the directional design of photoanode materials, the synergistic protection of multi-metal structures, and the theoretical research on photocathode protection mechanisms.

[0121] Example 1: Preparation of TiO2 nanosheets with adjustable crystal plane exposure ratio

[0122] Mix 15 mL of concentrated hydrochloric acid (37%, Scharlau) with 15 mL of deionized water, stir well, and then add 1.00 mL of tetrabutyltitanium (C 16 H 36 After stirring for 5 minutes, 1.00 g of ammonium fluorotitanate ((NH4)2TiF6) was added to the system and stirring was continued for another 5 minutes. A 1 cm × 2 cm FTO conductive glass, pre-ultrasonicated with ethanol and deionized water for 30 minutes, was placed tilted downwards into a Teflon liner. The above reaction solution was slowly poured in to completely cover the substrate. The liner was sealed and placed in a high-pressure reactor, where it was reacted at 180°C for 12 hours. After the reaction, the mixture was cooled to room temperature, the FTO was removed, rinsed with deionized water, and dried at 60°C to obtain TiO2-1.00 (see [link to product description]). Figure 1-3 ).

[0123] Depend on Figure 1A schematic diagram of the crystal plane orientation structure and bandgap matching of TiO2 nanosheets. The left figure shows the spatial arrangement of the {001} and {101} crystal planes in the TiO2 nanosheets and the electron (e) bandgap. - ) and holes (h + The right figure shows the relative positions of the conduction band and valence band of the {001} and {101} crystal planes, forming a surface heterojunction to achieve directional carrier migration.

[0124] At the same time Figure 2 Models of different crystal planes of anatase TiO2. The left image shows the {101} crystal plane, whose surface exposes active sites such as 2-coordinated oxygen (2c-O), 3-coordinated oxygen (3c-O), 5-coordinated titanium (5c-Ti), and 6-coordinated titanium (6c-Ti); the right image shows the {001} crystal plane, which mainly contains 2c-O and 5c-Ti structural units. The two crystal planes show significant differences in structural stability and charge behavior.

[0125] like Figure 3 As shown, the prepared TiO2-1.0 nanosheets are uniformly grown on the surface of the FTO substrate, exhibiting a highly ordered two-dimensional nanosheet array structure (left figure). The low-magnification morphology reveals that a large number of nanosheets are stacked in a cross-stacking manner on the substrate surface, forming a three-dimensional open network structure, which is beneficial for electrolyte penetration and the transport of photogenerated carriers.

[0126] The magnified local morphology is shown in the right figure. It can be clearly observed that the individual TiO2 nanosheets exhibit a regular plate-like structure, with the sidewall crystal planes labeled as (001) high-energy crystal planes. The nanosheet thickness is approximately 560 nm, indicating that the sample successfully achieved stable exposure of the (001) crystal planes during growth. Simultaneously, the upper and lower basal planes of the nanosheets correspond to the more thermodynamically stable (101) crystal planes. Therefore, the TiO2-1.0 nanosheet sample simultaneously exposes both (001) and (101) typical crystal planes, forming a dual-crystal plane synergistic exposure structure with consistent single-crystal orientation. This single-crystal nanosheet structure with coexisting dual crystal planes provides an ideal structural basis for subsequent heterogeneous heterostructures.

[0127] Example 2

[0128] Preparation of TiO2-BiVO4-T multiphase composite optoelectronic materials for sustained photoelectrochemical cathodic protection (preparation process see...) Figure 4 ):

[0129] 1) Preparation of TiO2 / Bi thin films: Using FTO with tunable crystal plane exposure ratio obtained in the above examples as the working electrode, and Ag / AgCl and Pt electrodes as the reference and counter electrodes, respectively, 0.485 g Bi(NO3)3·5H2O was added to a mixed solution of 100 mL ethylene glycol and 50 mL water and stirred for 20 min to prepare the electrolyte solution. Electrodeposition was performed at E = -0.6 V (vs. Ag / AgCl) for 50, 300, 600, and 900 s. TiO2-Bi samples with different deposition times were obtained, washed with ethanol, and dried by air drying.

[0130] 3) Preparation of TiO2 / BiVO4 thin films: Bi metal particles were converted to BiVO4 via a thermochemical method. 200 μL of a 0.2 mol / L vanadium acetylacetonate dimethyl sulfoxide (DMSO) solution was dropped onto TiO2-Bi samples with different deposition times. After the samples were allowed to air dry, the films were heated in air at 450℃ for 2 h. The calcined samples were then placed in a 1 mol / L NaOH solution for 30 min, and gently stirred to remove residual V2O5. Finally, the samples were thoroughly washed with deionized water to obtain BiVO4 optoelectronic materials, and dried at 60℃ for 1 h to obtain heterogeneous multiphase composite optoelectronic materials (see [link to product description]). Figure 5 ad).

[0131] The TiO2-BiVO4 samples formed at the above different deposition times are denoted as TiO2-BiVO4-T-50, TiO2-BiVO4-T-300, TiO2-BiVO4-T-600 and TiO2-BiVO4-T-900, respectively.

[0132] Comparative Example

[0133] (1) Preparation of TiO2–Bi2O3 and Bi2O3 samples

[0134] Add 0.485 g Bi(NO3)3·5H2O to a mixed solution of 100 mL ethylene glycol and 50 mL deionized water, stir for 20 min, and prepare a solution containing Bi. 3 + electrolyte solution.

[0135] Using the TiO2 nanosheet / FTO substrate prepared in Example 1 as the first working electrode (WE-1), and clean FTO without TiO2 loading as the second working electrode (WE-2), Ag / AgCl was used as the reference electrode, and Pt as the counter electrode. Electrodeposition was performed under a constant potential E = –0.6V (vs. Ag / AgCl): 300 s for the TiO2 nanosheet / FTO substrate and 600 s for the bare FTO substrate, to obtain a visible Bi metal precursor layer. After electrodeposition, the samples were cleaned with ethanol and dried, then calcined at 450°C for 2 h in air to obtain TiO2–Bi2O3 samples (see [link to sample details]). Figure 5 e) and Bi2O3 / FTO (see e) Figure 5 f) Sample. This comparative example is used to characterize the photoelectric properties when only a single phase of Bi2O3 is introduced without the formation of BiVO4 and multiphase gradient structures.

[0136] (2)Bi x VO y Sample preparation

[0137] Based on the aforementioned Bi / FTO precursor sample, a Bi–V–O composite oxide film was prepared using a thermochemical conversion method. Specifically, 200 μL of a 0.2 mol / L vanadium acetylacetonate DMSO solution was dropped onto the surface of the Bi / FTO sample. After air drying, the sample was calcined at 450 °C for 2 h in air. The calcined sample was then gently stirred in a 1 mol / L NaOH solution for 30 min to remove residual V₂O₅, followed by thorough washing with deionized water and drying at 60 °C for 1 h to obtain Bi. x VO y / FTO sample (see) Figure 5 g). Among them, Bi x VO y This is a general term for Bi–V–O composite oxides, including coexistence systems of one or more phases such as Bi2O3, t-BiVO4, and m-BiVO4. This sample does not contain a TiO2 substrate and does not form a TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4 gradient multiphase structure. It is used to compare the photocathode protection behavior without a TiO2 substrate multiphase structure.

[0138] The composite optoelectronic materials prepared in the above embodiments and comparative examples are processed to obtain photoanodes. Specifically, the conductive surface of the long conductive edge of the FTO glass used to obtain the different composite optoelectronic materials is scraped out, and insulating adhesive is applied at the junction of the composite optoelectronic material and the conductive surface, so that the exposed test area is 10×10mm. 2 That is, to obtain TiO2-BiVO4-T (50, 300, 600 or 900) photoanodes and TiO2-Bi2O3, Bi2O3, Bi at different times.x VO y Photoanode.

[0139] To investigate the morphology, phase composition, and band structure of the TiO2-BiVO4-T series photoanodes, and to systematically compare their photocathode protection performance, scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Mott-Schottky (M-S), and scanning Kelvin probe (SKP) were used for systematic characterization.

[0140] 1. Microscopic morphology and particle distribution characteristics ( Figure 5 )

[0141] Figure 5 a–5d shows SEM top views of the TiO2-BiVO4-T photoanodes prepared at different electrodeposition times. With increasing Bi deposition time, the number of Bi particles loaded on the (101) crystal plane of the TiO2 nanosheets gradually increases, and their particle size also increases. This phenomenon may cause Bi particles to be difficult to completely oxidize to BiVO4 during subsequent thermal conversion, leading to an imbalance in the heterojunction composition.

[0142] contrast Figure 5 e and Figure 5 As can be seen from f, when Bi2O3 is deposited on TiO2 nanosheets (TiO2-Bi2O3), its particle size is smaller and its distribution is more uniform, which is conducive to the formation of a tightly bonded interface structure; while Bi2O3 is directly grown on FTO ( Figure 5 In case f), the particles are large and the gaps are large, which is not conducive to the transmission of photogenerated electrons. Figure 5 Bi shown by g x VO y The sample exhibits a uniform and dense nanoparticle structure, suggesting that its composite with the TiO2 substrate will facilitate the formation of a synergistic conductive network.

[0143] 2. Verification of crystal phase composition and heterostructure ( Figure 6 and 7 )

[0144] Figure 6 XRD patterns of TiO2-BiVO4 from T-50 to T-900 are shown. With the extension of Bi electrodeposition time, the characteristic peak of monoclinic BiVO4 (m-BiVO4, JCPDS No. 14-0688) continuously increases; when the deposition time reaches 600s, the characteristic peak of α-Bi2O3 (JCPDS No. 41-1449) begins to appear, indicating that there is partial retention of Bi2O3 phase due to insufficient oxidation in the Bi particle enrichment area, forming a multiphase structure of TiO2, α-Bi2O3, and m-BiVO4. Figure 7Further comparisons show TiO2-Bi2O3, Bi2O3, and Bi x VO y The high degree of matching between the materials and the standard spectrum verifies the accurate formation of the corresponding single-phase or two-phase system.

[0145] 3. HRTEM analysis and confirmation of the four-phase gradient structure ( Figure 8 )

[0146] To further investigate the actual distribution of the four phases and the crystal structure in the TiO2-BiVO4-T sample, high-resolution transmission electron microscopy (HRTEM) was used to analyze the TiO2-BiVO4-T-300 sample. Figure 8 c shows the (211) and (200) crystal planes of the tetragonal phase BiVO4(t-BiVO4), with lattice spacings of 0.280 nm and 0.249 nm, respectively, and an included angle of 32.1°. Figure 8 d simultaneously observed multiple crystal planes of TiO2 (112), Bi2O3 (012), m-BiVO4 (112) and t-BiVO4 (211), further confirming the coexistence of the four phases in the sample.

[0147] Analysis of SEM and mapping diagrams shows that the enrichment of Bi on the (101) crystal plane of TiO2 nanosheets makes it easier for the outer layer to react with vanadium source to generate m-BiVO4 and t-BiVO4, while the region near TiO2 is prone to Bi residue or partial conversion to Bi2O3, thus constructing a spatial gradient heterostructure of "inner layer Bi2O3 / middle layer t-BiVO4 / outer layer m-BiVO4".

[0148] Example 2

[0149] The materials obtained using the above embodiments were compared with four common marine-grade metallic materials as test subjects, specifically including:

[0150] 316L stainless steel (representing passive alloy steel), pure copper (representing high work function precious metal), E40 marine steel (typical high-strength structural steel), and Q235 carbon steel (representing active low-carbon steel) are described in Table 1.

[0151] Table 1

[0152]

[0153] As shown in Table 1, 316L stainless steel is rich in Cr (16.53%) and Ni (12.04%), which gives it excellent passivation properties; pure copper is a high-purity metal with a Cu content close to 100%; E40 and Q235 are mainly Fe, with small amounts of C, Mn, Si and other elements, which have weak self-passivation ability and are prone to corrosion.

[0154] All the above metal electrodes were cut to 10×10mm. 2 After polishing to 2000 grit, clean with anhydrous ethanol and dry for later use.

[0155] I. Experimental Apparatus and Testing Methods

[0156] The experiment used a self-assembled optocoupler testing system (such as...) Figure 9 As shown in the diagram, the system consists of two parts: a photoelectrochemical cell and a corrosion cell. These two cells are coupled via a membrane to achieve ion conduction, thus forming a complete circuit for photogenerated electron transport and metal cathode protection. The light source is AM 1.5G simulated sunlight (100 mW·cm⁻¹). -2 The light is generated by a 300W xenon lamp with a filter; all electrochemical tests were performed simultaneously using a Shanghai Chenhua CHI 660E electrochemical workstation.

[0157] The electrolyte settings were as follows: a 0.35M Na₂SO₃ aqueous solution was used in the photoelectrochemical cell, and a 3.5wt% NaCl aqueous solution was used in the corrosion cell. The photoanode material used was the TiO₂–BiVO₄–T–300 photoanode sample prepared in Example 1.

[0158] The main test parameters include: photocurrent density–time (i–t) response curve, photoinduced open circuit potential (OCP) response, and metal corrosion potential (E). corr ) and corrosion current density (i corr ) and the flat band potential of the photoanode material.

[0159] In the photoelectric coupling test, the protected metal electrode is placed in the corrosion cell on the left, and the photoanode is placed in the photoelectrochemical cell on the right. In the photoelectrochemical cell, the TiO2–BiVO4–T–300 photoanode serves as the working electrode (WE), and the Ag / AgCl electrode serves as the reference electrode (RE); the protected metal material is placed in the corrosion cell.

[0160] Under illumination, the photoinduced open-circuit potential (OCP) response of the coupled system was tested. Figure 9 a) and the response of photocurrent density–time (i–t) Figure 9 b) is used to characterize the generation, transport, and sustained output stability of photogenerated electrons in the photoanode-metal coupling system.

[0161] To quantitatively evaluate the corrosion behavior of different metals under photocathode protection conditions, an independent three-electrode corrosion testing system was used. Figure 9c). Using the metallic material prepared in Example 2 as the working electrode (WE), Ag / AgCl as the reference electrode (RE), and a platinum sheet as the counter electrode (CE), the electrolyte was a 3.5 wt% NaCl aqueous solution. The corresponding metal corrosion potential (Ecorr) and corrosion current density (icorr) were obtained by testing the linear polarization curve, Tafel polarization curve, cathodic polarization curve, and electrochemical impedance spectroscopy (EIS). These parameters were used to characterize the intrinsic corrosion characteristics of the metallic material under conditions of no light and no photocatheter coupling, and served as an important reference for evaluating the effectiveness of photocatheter protection.

[0162] also, Figure 9 (d) is a schematic diagram of the three-electrode device for testing the Mott-Schottky characteristics of the photoelectrode. The working electrode (WE) is a TiO2-BiVO4-T-300 photoanode and a photoelectrode prepared in the comparative example. The reference electrode (RE) is Ag / AgCl, the counter electrode is a platinum sheet, and the electrolyte is a 3.5wt% NaCl aqueous solution. By testing the change in interfacial capacitance of the photoelectrode under different bias voltages, the flat-band potential, semiconductor type, and carrier concentration of the photoelectrode material of the present invention are determined, thereby providing an electrochemical basis for the photogenerated carrier transport behavior and the photocathode protection mechanism.

[0163] II. Comparison of photoelectric response and protective behavior of different metals

[0164] use Figure 9 a and Figure 9 The photoelectric coupling test device shown in b, according to the "photoanode-metal electrode" coupling test mode, systematically compared the photoelectric response behavior and photocathode protection effect of four metals, 316L stainless steel (316L SS), copper (Cu), E40 steel and Q235 carbon steel (Q235CS), under TiO2–BiVO4–T photoanode coupling conditions.

[0165] Figure 10 The transient photocurrent density (i–t) response of four metal electrodes coupled with a TiO2-BiVO4-T photoanode is shown. The 316L SS-TiO2-BiVO4-T coupling system exhibits the highest photoresponse current (peak value approximately 820 μA / cm). 2 The excellent stability indicates superior interfacial electron transfer efficiency. Cu and E40 exhibit moderate responses, while the Q235 CS system shows the lowest response, indicating poor photogenerated electron injection capability.

[0166] Figure 11The changes in photoinduced open-circuit potential (OCP) of different metals are shown. Under illumination, TiO2-BiVO4-T can negatively shift the OCP of 316L SS and Cu to -0.54V and -0.47V, respectively, indicating its good cathodic protection capability. In contrast, although E40 and Q235 CS show some negative shift, their protection potential plateau is lower, indicating that their protective effect is limited by the intrinsic corrosion potential and the difference in interfacial band structure.

[0167] Figure 12 The i–t responses of four metal systems under 2000-second intermittent illumination are shown. Cu-TiO2-BiVO4-T exhibits the largest peak photocurrent in the initial stage (>0.25 mA / cm). 2 However, its stability is slightly inferior to 316L SS. 316L SS-TiO2-BiVO4-T, on the other hand, maintained good repeatability and stability in multiple cycles. E40 and Q235 CS had the weakest responses, indicating that their photocathode protection behavior is limited.

[0168] Figure 13 The changes in photoinduced mixing potential (OCP) of each coupled system are shown. The 316L SS system exhibits a significant negative displacement during each irradiation cycle and maintains a certain delay protection effect after the light is cut off. Cu shows a slightly lower value but a similar trend, while the potential changes of E40 and Q235 CS are smaller.

[0169] Figure 14 The surface morphology of various metals under different conditions was compared. Unprotected E40 and Q235 CS surfaces showed obvious corrosion products, while under TiO2-BiVO4-T photocathode protection, the corrosion area was significantly reduced, verifying the universality and effectiveness of the photocathode protection system on various metals.

[0170] III. Analysis of Metal Corrosion Characteristics and Cathodic Protection Window

[0171] use Figure 9 The three-electrode electrochemical testing apparatus shown in Figure c was used to test the intrinsic corrosion behavior and polarization characteristics of four metals—316L stainless steel (316L SS), copper (Cu), E40 steel, and Q235 carbon steel (Q235 CS)—in 3.5 wt% NaCl solution without photoanode coupling, in order to obtain their self-corrosion parameters and reasonable cathodic protection potential windows. In each test, the metal under test was used as the working electrode (WE), Ag / AgCl as the reference electrode (RE), and a platinum sheet as the counter electrode (CE).

[0172] Depend on Figure 15 and Figure 16The linear and Tafel polarization curves of four metals (316L SS, Cu, E40, and Q235 CS) in 3.5 wt% NaCl solution are shown in Table 2. The results are illustrated in Table 2. 316L SS exhibits the most positive self-corrosion potential (E...). corr = –0.113V) and the lowest corrosion current density (i corr =0.09μA / cm 2 This indicates that its passivation film is stable and has the strongest corrosion resistance. Cu's E corr For -0.192V, i corr Increased to 3.86 μA / cm 2 This reflects that the passivation film on its surface is more easily damaged by Cl-. The corrosion current densities of E40 and Q235CS are as high as 28.6 and 58.3 μA / cm, respectively. 2 This indicates that it is prone to severe corrosion in a seawater environment.

[0173] Table 2

[0174]

[0175] Figure 17 The cathodic polarization curves of four metals are shown. 316L SS exhibits a distinct current plateau in the range of -0.52 to -0.90 V, indicating that its cathodic process is limited by oxygen concentration polarization and may be accompanied by partial dissolution of the Cr2O3 passivation film. The hydrogen evolution initiation potentials of the different metals are, in descending order: Cu (-0.92 V), Q235 (-0.96 V), E40 (-0.98 V), and 316L (-1.0 V), suggesting that Cu and carbon steel-like metals begin hydrogen evolution at relatively positive potentials, making them prone to hydrogen embrittlement and protection failure risks.

[0176] Based on the combined standard electrode potentials (see Table 3) and polarization test results, the suitable cathodic protection potential range for 316L SS can be estimated to be -450 to -610 mV; for Cu it is -561 to -920 mV; and for carbon steel (Fe-dominated metal) it is -641 to -1000 mV.

[0177] Table 3

[0178]

[0179] It should be noted that the above protection window is a theoretical value. In actual marine applications, the effects of factors such as solution pH, dissolved oxygen, electrolyte concentration, and temperature must also be considered. Therefore, this window mainly serves as a parameter reference for the photoelectrochemical cathodic protection design of this invention.

[0180] IV. Metal Work Function and Fermi Level Analysis

[0181] use Figure 18The Kelvin probe test apparatus shown is used to test the surface potential of four metals—316L stainless steel (316L SS), copper (Cu), E40 steel, and Q235 carbon steel (Q235 CS)—under dark conditions, and the corresponding work function and Fermi level position are obtained from the test results. This is used to analyze the energy level matching relationship between different metals and photoanodes and the differences in the driving force for photogenerated electron injection.

[0182] Figure 19 and Figure 20 The table presents the statistical results of the surface potential (Kelvin probe method) and work function of the metal electrode. As the metal type changes from 316L SS to Q235 CS, the work function decreases sequentially (316L SS: 4.08 eV, Cu: 4.06 eV, E40: 3.86 eV, Q235 CS: 3.83 eV), indicating that its Fermi level (E... f (Gradually shifts to negative.) E f The more positive the value, the greater the energy level difference (ΔE = E) between the photoanode and the bottom of the conduction band. f –E CB The larger the value of E, the stronger the electron injection driving force, and the easier it is for the metal to obtain continuous photocathode protection. Conversely, E... f A negative shift will reduce ΔE, and may even lead to a mismatch between the conduction band and the metal level, hindering electron injection and significantly reducing the protection effect.

[0183] Tafel fitting results show that the exchange current density (i0) and corrosion current density (i) of different metals are related. corr This has a significant synergistic effect on photocathode protection behavior. Among them, i0 characterizes the intrinsic electron transfer kinetics activity at the metal interface, determining the upper limit of the rate at which the metal receives photogenerated electrons; while i corr It reflects the intrinsic corrosion intensity of a metal in a corrosive medium and represents its actual requirement for a protective electron flow.

[0184] As can be seen from the data in the table, the i0 of 316L SS is extremely low (0.10 μA·cm). -2 ), at the same time i corr It is also the lowest (0.04–0.09 μA·cm). -2 This indicates that its corrosion reaction rate is slow, its electron supply requirement is small, and its interface is easily polarized by a small number of photogenerated electrons, thus exhibiting the optimal and most stable photocathode protection response. Cu has a relatively large i0 (3.16–5.16 μA·cm). -2 The interface has high electron exchange activity, which is conducive to rapid electron injection, but its i corr Significantly higher than 316L (3.86–7.23 μA·cm). -2This indicates that although it can "receive electrons," the demand for electron supply increases simultaneously, leading to a decrease in the protective photoelectric potential, meaning that the cathode polarization of Cu by photogenerated electrons is lower than that of 316L. In contrast, E40 and Q235 CS, although possessing extremely high i corr (10–58 μA·cm) -2 The corrosion rate is fast, but its i0 is still within a limited range (≈25–40 μA·cm). -2 The interface electron transfer kinetics and corrosion consumption rate are severely mismatched, which can easily lead to a "supply and demand imbalance" in protection, resulting in unstable or even failed photocathode protection.

[0185] To further quantify the interfacial electron transport capabilities of different metals from an impedance perspective, this invention combines EIS electrochemical impedance spectroscopy (see...) Figure 21 and Figure 22 The interfacial charge transport characteristics of various metals in the uncoupled state with a photoanode were tested. The results show that the interfacial charge transfer resistance R of 316L SS is... ct Up to 64,857.5 Ω·cm 2 The corresponding equivalent exchange current density i0(EIS) is the smallest (0.396 μA·cm). -2 This indicates that the interface exhibits predominantly capacitive behavior with a low electron leakage rate, which is beneficial for the stable accumulation and sustained polarization of photogenerated electrons on the metal surface; Cu's R ct Reduced to 4,981.5 Ω·cm 2 The corresponding i0(EIS) is increased to 5.16 μA·cm. -2 This indicates a significant enhancement in the interfacial electron throughput, but simultaneously leads to faster cathode reaction consumption; while the Rct values ​​of E40 and Q235 CS are only 68.8 and 1,905.3 Ω·cm, respectively. 2 Its i0 (EIS) is as high as 373 and 13.5 μA·cm, respectively. -2 This indicates that electron leakage at the interface is extremely rapid, making it difficult to form a stable cathodic polarization state.

[0186] Combining Tafel–i0 / i_corr with EIS–R ct The cross-validation results of / i0(EIS) show that:

[0187] 1) 316L SS belongs to "low i0 + low i" corr +High R ct The ideal matching metal is best suited for achieving efficient and stable photocathode protection;

[0188] 2) Cu belongs to "high i0+ medium i" corr +Medium R ct"A fast-response metal, suitable for short-term, high-intensity protection;

[0189] 3) E40 and Q235 CS belong to the "high-i" category. corr +Low R ct The unbalanced metal system with "high i0 (EIS)" has a corrosion reaction rate that is much higher than the rate of photogenerated electrons that can be stably supplied, making it difficult to maintain photocathode protection in the long term.

[0190] V. Response Mechanism and Band Matching Modeling Analysis

[0191] Furthermore, utilizing Figure 9 (d) The Mott-Schottky (M-S) test setup shown in Figure d was used to perform band structure analysis on each photoanode sample. The results are as follows: Figure 23 As shown in (a–b).

[0192] like Figure 23 As shown in Figure a, the M-S curves of all samples exhibit a positive slope, indicating that they still mainly exhibit n-type semiconductor behavior. Among them, the TiO2–BiVO4–T sample shows the most negatively shifted flat-band potential, approximately -0.83V (vs. Ag / AgCl), which is significantly better than TiO2 (-0.39V), Bi2O3 (-0.40V), TiO2–Bi2O3 (-0.42V), and Bi x VO y (–0.80V) indicates that its conduction band position is more negative, and it has a stronger thermodynamic driving force for photogenerated electron output.

[0193] Figure 23 b is Bi x VO y The magnified M-S curve of the sample reveals a local slope that gradually decreases or even nearly reverses in different potential ranges, indicating the simultaneous presence of n-type and p-type electrical behaviors within the sample. This phenomenon is related to the Bi vacancies (V0.05) mentioned earlier. Bi ) Induced p-type characteristics, oxygen vacancies (V O The mechanism analysis of induced n-type properties in BiVO4 synergistically modulates the conductivity type is highly consistent, further confirming that in non-stoichiometric Bi... x VO y In multiphase BiVO4 structures, defect states can induce the formation of local n / p recombination features, thereby creating a built-in electric field at the phase interface.

[0194] The existence of this n / p composite electrical property means that the multiphase BiVO4 not only has the electron migration effect driven by the conduction band gradient, but also has the spatial separation effect of the p-n junction built-in potential on photogenerated carriers. This forms a complete experimental-theoretical closed loop with the previously proposed mechanism of "multiphase conduction band gradient + defect-controlled n / p junction synergistic promotion of electron directional migration".

[0195] Figure 24 The diagram illustrates the bandgap matching between the heterostructure photoanode and different metals. Within the heterostructure, photogenerated electrons are directionally transferred from BiVO4 → Bi2O3 → TiO2 through progressively positively shifting conduction band steps. TiO2 ultimately acts as an electron-rich layer, effectively injecting electrons into the metal.

[0196] Based on the work function of different metals and E corr Based on its location, the coupling behavior between it and the photoanode can be classified into three response types:

[0197] 1) Perfectly matched type: such as 316L SS and Cu, metal E f With a higher electron injection driving force than the photoanode CB, it exhibits a significant photoelectric protection response;

[0198] 2) Partially injected type: such as E40, E f Slightly higher but with a smaller ΔE, it provides some protection initially, but under prolonged irradiation, the corrosion potential shifts negatively, making it prone to losing electron injection drive.

[0199] 3) Mismatched type: such as Q235 CS, its E f Below the photoanode CB, there is a significant potential barrier, which hinders electron injection and limits the protective effect.

[0200] Further analysis revealed that the dominant factors influencing the differences in metal response included: conduction band difference ΔE. CB (Determines the driving force of electron migration); Interfacial charge migration resistance R ct (Reflecting the difficulty of photogenerated electrons flowing to the metal interface); exchange current density i0 (revealing the dynamic activity of electron injection at the interface). The cartoon diagram uses "electrons in a water tank" as a metaphor: electrons start from the photoanode, and the difficulty of receiving them varies among different metals. 316L is a shallow pool that is easy to inject, while Q235 is a deep pool that is difficult to inject, which intuitively reflects the relationship between the quality of band matching and protection capability.

[0201] In summary, based on multi-dimensional response data (OCP, J... ph (EIS, SKP, etc.) For the first time, a "conductor position – E" model was constructed. f The quantitative matching model of “difference-response category-protection efficiency” provides a theoretical basis and experimental support for the selective design and directional material development of photocathode protection in multi-metal systems.

[0202] reuse Figure 9 The photoelectric coupling testing devices shown in a and b are used to evaluate the photoelectric cathodic protection performance of the materials obtained above. Figure 25 –26). The results show that the TiO2-BiVO4-T-300 sample exhibits the best performance in 0.35M Na2SO3 electrolyte: the photogenerated current density reaches 33 μA·cm. -2 The maximum negative shift of the photoinduced mixing potential reached -0.542V (vs. Ag / AgCl). In contrast, although TiO2-BiVO4-T-50 and T-900 had higher currents in the initial stage, their overall protection effect was lower than that of T-300, which was limited by insufficient development of multiphase structure or bulk phase recombination caused by excessive enrichment of Bi2O3, respectively. Figure 27-28 The OCP response of TiO2-BiVO4-T-300 coupled with photoanodes such as TiO2, TiO2-Bi2O3, Bi2O3, and BixVOy in 316L SS was further compared. In 3.5 wt% NaCl, TiO2-BiVO4-T-300 shifted the 316L SSOCP from -0.16 V to -0.54 V, significantly exceeding that of other samples (such as Bi). x VO y (V is only -0.47V). At the same time, TiO2-BiVO4-T-300 can still maintain a certain cathodic protection effect after the light is turned off, showing obvious photoelectric delay protection capability.

[0203] Therefore, the TiO2-BiVO4-T-300 photoanode significantly optimizes interfacial electron separation and transport behavior by constructing a multilayer gradient heterostructure of α-Bi2O3, t-BiVO4, and m-BiVO4 on the (101) crystal surface of TiO2 nanosheets. The four-phase composite establishes a synergistic conduction band ladder and steric hindrance separation mechanism, significantly enhancing photoelectric conversion efficiency and photocathode protection capabilities. The heterogeneous multiphase composite strategy proposed in this invention provides a novel approach for the design of photoelectrochemical corrosion-resistant materials, exhibiting excellent tunability and broad application prospects in marine protection.

Claims

1. A method for preparing a heterogeneous multiphase composite optoelectronic material, characterized in that: A heterogeneous four-phase composite optoelectronic material (TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4, denoted as TiO2-BiVO4-T) with multiphase gradient coexistence of α-Bi2O3, t-BiVO4 and m-BiVO4 was constructed in situ on the same TiO2 nanosheet substrate using the method of "electrodeposition precursor construction + thermochemical gradient conversion".

2. The method for preparing heterogeneous multiphase composite optoelectronic materials according to claim 1, characterized in that: First, metallic Bi particles were deposited on the surface of TiO2 nanosheets by electrodeposition to form a TiO2 / Bi precursor structure. Subsequently, by introducing a vanadium source and performing thermochemical treatment in an air atmosphere, the Bi particles undergo a gradient transformation from the inside to the outside, resulting in the formation of a multiphase composite structure on the same TiO2 nanosheet with a hierarchical distribution of α-Bi2O3, tetragonal BiVO4 (t-BiVO4), and monoclinic BiVO4 (m-BiVO4) along the normal direction. Thus, a heterogeneous gradient multiphase composite optoelectronic material of TiO2 / α-Bi2O3 / t-BiVO4 / m-BiVO4 is obtained, denoted as TiO2-BiVO4-T.

3. The method for preparing heterogeneous multiphase composite optoelectronic materials according to claim 1, characterized in that: FTO of the TiO2 nanosheets (1) Tetrabutyltitanium (C 16 H 36 O4Ti) was added to the mixed acid solution and stirred until homogeneous; wherein, tetrabutyltitanium (C 16 H 36 The volume ratio of O4Ti to the mixed acid solution is 1:(20-40). (2) Add ammonium fluorotitanate ((NH4)2TiF6) to the above mixture as a crystal plane modifier and stir to mix well; (3) Place the cleaned substrate with the conductive surface facing down in the reaction vessel, then add the mixture obtained in step (2), and seal it for hydrothermal reaction at 170-190℃ for 9-15 hours to obtain TiO2 nanosheet thin film material with a specific crystal surface exposure ratio on the substrate surface.

4. The method for preparing heterogeneous multiphase composite optoelectronic materials according to claim 3, characterized in that: The mixed acid solution is a mixture of deionized water and concentrated hydrochloric acid in a volume ratio of 1:1; wherein the concentration of concentrated hydrochloric acid is 18%-19% (mass fraction); The amount of ammonium fluorotitanate and tetrabutyl titanium added is based on the ratio of 1.0 g of ammonium fluorotitanate to 1.0 mL of tetrabutyl titanium, and the corresponding molar ratio is constant at approximately 1.83:

1.

5. A heterogeneous multiphase composite optoelectronic material prepared by the method of claim 1, characterized in that: According to the method described in claim 1, a heterogeneous multiphase composite optoelectronic material is prepared by precisely gradient loading of α-Bi2O3, tetragonal BiVO4 (t-BiVO4) and monoclinic BiVO4 (m-BiVO4) multiphase junctions along the normal direction from the inside to the outside on the TiO2 (101) crystal plane. In this process, α-Bi2O3 is attached to the TiO2 surface in the form of dispersed nanoparticles or a dense transition layer, and t-BiVO4 and m-BiVO4 sequentially form a continuous coating layer and are distributed on the outside of the α-Bi2O3. The interfaces between the phases transition continuously, resulting in a multiphase rough composite morphology that exhibits a hierarchical gradient from the inside out.

6. An application of the heterogeneous multiphase composite optoelectronic material according to claim 1, characterized in that: Application of the heterogeneous multiphase composite optoelectronic material as a semiconductor optoelectronic conversion layer.

7. An application of the heterogeneous multiphase composite optoelectronic material according to claim 1, characterized in that: The application of the multiphase composite optoelectronic material as a corrosion-resistant protective film to inhibit metal corrosion.

8. A method for analyzing the response of multi-metal photocathode protection, characterized in that: A coupled system is constructed by combining heterostructured photoanode materials with the metal components to be protected. By obtaining the response electrochemical parameters, the cathodic polarization amplitude and protection duration of each metal are determined. Furthermore, the band parameters of the photoanode and the metal are characterized by Mott-Schottky analysis to determine the response type of different metals and to match the corresponding heterostructured photoanode materials with the metal components to be protected.

9. The method for analyzing the response of multi-metal photocathode protection is characterized by: The constructed coupled system was placed in a dual-cell electrochemical system and synchronously tested under simulated illumination (AM 1.5) conditions to obtain response electrochemical parameters, which were used to determine the cathodic polarization amplitude and protection duration of each metal. At the same time, a metal-semiconductor bandgap spectrum was established through Mott-Schottky analysis to analyze the energy difference driving conditions of photogenerated electron injection, and then to match the corresponding heterostructure photoanode material with the metal component to be protected.

10. The method for analyzing the response of multi-metal photocathode protection is characterized by: The response electrochemical parameter is the photocurrent density (J / L). ph ), photoinduced open-circuit potential (OCP) change, mixed potential response (E) mix And the response hysteresis behavior during the illumination-off cycle; The parameters for constructing the metal-semiconductor bandgap diagram are the conduction band bottom position (E) of the photoanode. CB The work function (Φm) of each metal surface was measured using a scanning Kelvin probe (SKP).

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