A photoanode based on phosphonic acid chelation and photoelectrochemical activation and a preparation method thereof

Abstract

This invention relates to the field of photoelectrochemistry, and more particularly to a photoanode based on phosphonic acid chelation and photoelectrochemical activation, and its preparation method. The purpose of this invention is to provide a method for dynamic passivation of deep-level defects based on the synergistic activation of phosphonic acid chelation and photoelectrochemical activation. 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) molecules (ZISH) are introduced onto the surface of a zinc indium sulfide (ZIS) photoanode via a low-temperature water bath. Photoelectrochemical activation is then used to induce a chelation reaction between HEDP and Zn sites on the surface, forming a stable Zn–O–P coordination structure. Under photoelectric bias, this structure can reconstruct the Zn-S framework in situ, adjusting the coordination number of Zn and converting deep traps into shallow-level states (ZISA), thereby effectively suppressing interfacial recombination while maintaining a high hole injection rate.

Description

Technical Field

[0001] This invention relates to the field of photoelectrochemistry, and in particular to a photoanode based on phosphonic acid chelation and photoelectrochemical activation, and its preparation method. Background Technology

[0002] Photoelectrochemical water splitting can directly convert solar energy into green hydrogen energy, but the device efficiency has long been constrained by the slow oxygen evolution reaction (OER) kinetics and interfacial recombination problems on the photoanode side. The widespread deep-level defects within the devices themselves are a core obstacle to further improving their conversion efficiency. For example, the Fermi level pinning effect induces nonradiative recombination centers, thereby affecting the adsorption-desorption balance of key OER intermediates such as OH, O, and OOH. These deep-level defects are mostly introduced by structural imperfections such as vacancies, interstitial atoms, and grain boundaries, forming deep states within the band gap.

[0003] Generally, the electronic structure is adjusted and the density of trapped states is reduced by introducing heterogeneous elements (such as Ti, Zr, Ni, etc.) into the sulfide lattice. However, the doping process often requires high temperature or precise metrological control, and different dopants may introduce new defects or change the energy level structure, making it difficult to stably suppress deep traps. Another method is to passivate the photoanode surface by depositing oxides or dielectric layers (such as TiO2, Al2O3, ZnO, etc.) to block carrier recombination. This method is effective in the short term, but the passivation layer is prone to degradation under bias and illumination; in addition, the dense layer can hinder charge and proton transport, and even over-passivate active sites, leading to a decrease in reaction kinetics. Other techniques use external field-induced reconstruction or self-oxidative skin formation to generate an active shell to isolate defect regions. However, these methods have poor controllability and are prone to generating new deep defects during reconstruction. In addition, some schemes reduce the reaction barrier by constructing heterojunctions or supporting oxide co-catalysts (such as NiFeOOH, CoFe LDH, Co-Pi, etc.), but due to the chemical mismatch between oxides and sulfides, a sulfur-oxygen mixed layer will still be formed at the interface and induce new deep-level defects.

[0004] In existing technologies, when using doping or oxide coatings for defect passivation, the static passivation layer is prone to degradation under bias and illumination, failing to continuously suppress the regeneration of deep-level defects, resulting in insufficient photoanode stability and long-term efficiency. Secondly, when using oxide co-catalysts or interface reconstruction, the chemical mismatch between oxides and sulfide materials easily introduces new deep defects and generates strong interfacial recombination, hindering efficient transfer of photogenerated carriers. Thirdly, existing multi-step processes (such as ion exchange, reconstruction, and annealing) are cumbersome, have narrow process windows, and poor reproducibility, hindering large-scale preparation and widespread application.

[0005] To address the aforementioned issues, existing strategies encompass elemental doping, oxide capping layers (such as atomic layer deposition / spin-coating), epitaxial chemical reconstruction, self-oxidation layers, heterojunctions / gradient junctions, and various cocatalysts. While these methods can suppress or reduce overpotentials, they are generally performed in non-in-situ, non-operating conditions. Furthermore, dense capping layers may hinder charge transfer and over-passivate active sites; excessive reconstruction can easily generate new deep defect states, and these deep defects can regenerate under bias and illumination, making early passivation inherently insufficient. Therefore, a deep defect control approach compatible with sulfide systems and capable of in-situ adaptive modification is urgently needed. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a photoanode based on phosphonic acid chelation and photoelectrochemical activation, comprising the following steps:

[0007] S11: Prepare precursor solution and chelate precursor solution respectively; the precursor solution is obtained by mixing zinc salt, indium salt and thiourea in water, and the chelate precursor solution is obtained by adding zinc salt and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) to water and adjusting the pH to neutral.

[0008] S12: Fluorine-doped tin oxide (FTO) glass is added to the precursor solution, and after hydrothermal reaction, it is cooled to room temperature (20±5℃) to obtain ZIS photoanode;

[0009] S13: Add the ZIS photoanode to the chelation precursor solution and heat to carry out a coordination chelation reaction to obtain the ZISH photoanode;

[0010] S14: Under illumination, the ZISH photoanode is electrochemically activated to obtain the photoanode based on phosphonic acid chelation and photoelectrochemical activation.

[0011] Preferably, in the precursor solution, the concentration of zinc salt is 1-1.5 g / L, the concentration of indium salt is 4-4.5 g / L, and the concentration of thiourea is 3-3.5 g / L.

[0012] Preferably, the zinc salts are all zinc chloride and the indium salts are indium chloride.

[0013] Preferably, in step S11, the mixing method is magnetic stirring for 8-12 minutes.

[0014] Preferably, in the chelating precursor solution, the concentration of zinc salt is 0.02-0.12 mol / L, and the concentration of 1-hydroxyethylidene-1,1-diphosphonic acid is 200-400 mg / L.

[0015] Preferably, in step S12, the hydrothermal reaction temperature is 155-165℃ and the time is 5-7 h.

[0016] Preferably, in step S12, impurity removal is performed after cooling; the method for impurity removal is to wash with water and ethanol and then dry at 45-55℃ for 20-28 h.

[0017] Preferably, in step S13, the heating temperature is 50-80℃, and the coordination chelation reaction time is 10-30 min.

[0018] Preferably, in step S13, after the coordination chelation reaction, the mixture is washed with water and freeze-dried for 7-9 hours.

[0019] Preferably, in step S14, the electrochemical activation conditions are as follows: using a three-electrode system, electrochemical activation is performed for 15–40 s with an applied potential of -0.2 V to 0.6 V.

[0020] Furthermore, in the three-electrode system, the reference electrode is Ag / AgCl, the counter electrode is a platinum mesh, and the electrolyte is an aqueous solution containing sodium sulfate.

[0021] Furthermore, the concentration of the sodium sulfate is 0.4-0.6 mol / L.

[0022] Specifically, the method for preparing the photoanode based on phosphonic acid chelation and photoelectrochemical activation includes the following steps:

[0023] (1) Fluorine-doped tin oxide (FTO) conductive glass was selected as the substrate: using an ultrasonic cleaner, it was cleaned three times in sequence with acetone, ethanol and deionized water for 10 minutes each time to remove organic impurities and oil stains on the surface, and then air-dried for later use.

[0024] (2) Preparation of ZIS photoelectrode: Weigh 0.2-0.3 g zinc chloride (ZnCl2) and 0.8-0.9 g indium chloride tetrahydrate (InCl3·4H2O), add 0.6-0.7 g thiourea, dissolve in 200 mL ultrapure water, and stir magnetically for 10 min to obtain a transparent precursor solution. Place the cleaned FTO glass in a 25 mL polytetrafluoroethylene-lined stainless steel reactor with the conductive side facing down and attached to the wall. Add 10 mL of the above solution to each liner and seal. Perform hydrothermal reaction at 160℃ for 6 h. After the reaction is completed, allow it to cool naturally to room temperature, remove the sample, wash it successively with deionized water and anhydrous ethanol, and vacuum dry at 50℃ for 24 h to obtain ZnIn2S4 photoanode (denoted as ZIS).

[0025] (3) Preparation of ZISH intermediate: Add 40-80 mg of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) to a ZnCl2 solution (200 mL) in the range of 0.02-0.12 mol / L, stir well to form a chelation precursor solution, and adjust the pH to 7 with NaOH. Place the prepared ZIS photoanode vertically in a 20 mL glass bottle with the sample side facing down, add 10 mL of the chelation precursor solution, and react in a water bath at 50-80℃ for 10-30 min to induce coordination chelation between HEDP and Zn sites. Take out the sample, rinse with deionized water and freeze-dry for 8 h to obtain the intermediate ZISH sample.

[0026] (4) ZISA photoelectrochemical activation treatment: The obtained ZISA photoanode was placed in a three-electrode system, with Ag / AgCl as the reference electrode, a platinum mesh as the counter electrode, and 0.5 mol / L Na2SO4 solution as the electrolyte. An applied potential of -0.2 V to 0.6 V (relative to Ag / AgCl) was applied under illumination, and the activation time was controlled at 15–40 s. During this photoelectrochemical activation process, HEDP molecules and Zn sites further recombine to form a stable Zn-OP coordination structure, reconstructing the Zn-S local framework, achieving dynamic passivation of deep-level defects, and obtaining the final sample ZISA. Finally, the sample was washed with deionized water and stored in a vacuum drying oven.

[0027] The present invention also provides a photoanode based on phosphonic acid chelation and photoelectrochemical activation prepared by the above preparation method.

[0028] The present invention also provides the application of the above-mentioned photoanode based on phosphonic acid chelation and photoelectrochemical activation in photoelectrochemical water splitting for hydrogen production.

[0029] The purpose of this invention is to provide a dynamic passivation method for deep-level defects based on phosphonic acid chelation and photoelectrochemical synergistic activation. 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) molecules (ZISH) are introduced onto the surface of a zinc indium sulfide (ZIS) photoanode via a low-temperature water bath. Photoelectrochemical activation is then used to induce a chelation reaction between HEDP and Zn sites on the surface, forming a stable Zn-OP coordination structure. Under photoelectric bias, this structure can reconstruct the Zn–S framework in situ, adjusting the coordination number of Zn and converting deep traps into shallow-level states (ZISA), thereby effectively suppressing interfacial recombination while maintaining a high hole injection rate.

[0030] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0031] 1) This invention achieves dynamic adaptive passivation and precise bandgap control of defects under photoelectric operating conditions: This invention utilizes the in-situ chelation reaction between phosphonic acid molecules (HEDP) and Zn sites to form a stable Zn-OP coordination structure. Under photoelectric bias, the local coordination environment can be dynamically adjusted, effectively converting deep-level traps into shallow-level states and significantly reducing the formation of non-radiative recombination centers. Compared with traditional static coating or doping passivation methods, this invention achieves continuous adaptive passivation under operating conditions, significantly improving the structural stability and carrier separation efficiency of the photoanode.

[0032] 2) This invention constructs a defect-tolerant, highly active catalytic microenvironment, significantly improving photoelectric performance: Dynamic optimization of the surface coordination environment is achieved through short-range photoelectrochemical activation, promoting the transformation of deep traps to shallow energy levels, enhancing hole injection and surface reactivity, and reducing the OER overpotential. The resulting ZISA photoanode exhibits significantly enhanced photocurrent density and stability, with OER kinetics superior to traditional statically passivated photoanodes, demonstrating excellent catalytic performance and long-term structural stability.

[0033] 3) This invention possesses the combined advantages of simple process, low energy consumption, and high scalability: It employs a process combining a mild solution method with short-range photoelectrochemical activation, eliminating the need for high-temperature annealing or complex vacuum equipment. The process is simple, the conditions are mild, and it exhibits strong repeatability. The resulting ZnIn2S4 photoanode combines excellent photocurrent density, low onset potential, and long-term operational stability, demonstrating significant application potential in efficient and scalable photoelectrochemical hydrogen production systems. Attached Figure Description

[0034] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0035] Figure 1 These are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of Embodiment 1 of the present invention; wherein, a is a scanning electron microscope image of the ZIS photoanode, b is a scanning electron microscope image of the ZISA photoanode, c is a transmission electron microscope image of the ZIS photoanode, and d is a transmission electron microscope image of the ZISA photoanode.

[0036] Figure 2 These are the JV curves of the ZIS photoanode and ZISA photoanode of Embodiment 1 of the present invention; where the solid line represents the actual working state and the dashed line represents the dark current characteristic state.

[0037] Figure 3 These are the JV curves of the ZIS photoanode of Embodiment 1, the ZISH photoanode of Comparative Example 1, and the ZISA photoanode of Embodiment 1 of the present invention; wherein, the solid line represents the actual working state, and the dashed line represents the dark current characteristic state.

[0038] Figure 4 These are the JV curves of the ZISA photoelectrode with different photoelectric activation times in Embodiment 2 of the present invention; where the solid line represents the actual working state and the dashed line represents the dark current characteristic state. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0040] Example 1:

[0041] (1) Use an ultrasonic instrument to clean the conductive substrate fluorine-doped tin oxide conductive glass (FTO) three times with acetone, ethanol and deionized water, 15 minutes each time. After cleaning, dry it under nitrogen flow for later use.

[0042] (2) Weigh 0.2727 g zinc chloride (ZnCl2), 0.8795 g indium chloride tetrahydrate (InCl3·4H2O) and 0.6087 g thiourea, dissolve them in 200 mL deionized water, and stir for 10 min to form a transparent precursor solution. Place the cleaned FTO with the conductive side down into a 25 mL polytetrafluoroethylene-lined stainless steel reactor, add 10 mL of the precursor solution to each reactor, and perform a hydrothermal reaction at 160 °C for 6 h. After the reaction is completed, allow it to cool naturally to room temperature (25 °C), remove the sample and wash it successively with deionized water and anhydrous ethanol, and vacuum dry it at 50 °C for 24 h to obtain a uniformly grown ZnIn2S4 photoanode (ZIS photoanode).

[0043] (3) Dissolve 0.1 mol / L ZnCl2 in 200 mL of ultrapure water and add 45 mg of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). Stir until homogeneous to form a chelating solution. Place the obtained ZIS photoanode in a 20 mL glass bottle (conductive side down), add 10 mL of the above solution, and react in a 70 °C water bath for 20 min. After the reaction is complete, remove the sample, wash with deionized water, and freeze-dry for 8 h to obtain the HEDP-modified ZISH photoanode.

[0044] (4) The ZISH photoanode was used as the working electrode, Ag / AgCl as the reference electrode, a platinum sheet as the counter electrode, and 0.5 mol / L Na2SO4 solution as the electrolyte. Photoelectrochemical activation was performed for 30 s under AM (Air Mass) 1.5G illumination within a potential range of 0.2 V (vs Ag / AgCl). This process induced the formation of a Zn-OP bond structure (ZISA electrode) between HEDP and surface Zn sites, thereby reconstructing the Zn-S coordination environment, passivating deep-level defects, and enhancing interfacial charge transfer capability.

[0045] The morphology of the ZISA electrode is as follows Figure 1 As shown. From Figure 1 As can be seen, an amorphous structure exists on the surface of ZnIn2S4. A uniform amorphous chelate layer can be observed on the surface of the ZnIn2S4 nanosheets, which is a passivation structure rich in Zn-OP bonds. The formation of this structure effectively improves the interfacial charge transport rate and reduces interfacial recombination of photogenerated carriers.

[0046] The ZISA photoelectrode prepared above was used as the working electrode, forming a three-electrode system with a platinum mesh counter electrode and a saturated Ag / AgCl reference electrode, thus assembling a photoelectrochemical cell. A 0.5 mol / L Na₂SO₄ aqueous solution was injected into the cell as the electrolyte. Linear voltammetry was performed using an electrochemical workstation under AM 1.5G illumination, within a potential range of -0.2 VRHE (Reversible Hydrogen Electrode) to 1.3 VRHE, at a rate of 50 mV per second. Figure 2 As shown, at 1.23 VRHE, the photocurrent density of the ZISA photoelectrode can reach 5.38 mA / cm². 2 The onset potential (Von) is approximately -0.03VRHE, while that of the untreated ZIS electrode is only 0.60 mA / cm. 2 This demonstrates that the method described in this invention significantly improves the carrier separation efficiency of the photoanode and the surface OER kinetics.

[0047] Example 2:

[0048] ZISA photoelectrodes were prepared according to steps (1) to (4) of Example 1, except that in step (4), ZISA photoelectrodes with different activation levels were obtained by controlling the photoelectrochemical activation time (15-40 s).

[0049] The photoelectrodes prepared above were assembled into a photoelectrochemical cell, and then its photochemical water splitting under different voltages was tested, such as... Figure 4 As shown. At a voltage of 1.23 VRHE, the photoelectrode prepared by the method of this embodiment can achieve a photocurrent of 5.38 mA / cm². 2 The Von shifted negative to -0.03 VRHE; while the photocurrent of the ZnIn2S4 thin film (ZIS) was only 0.60 mA / cm. 2 .

[0050] Comparative Example 1:

[0051] The photoanode sample was prepared according to steps (1) to (3) of Example 1, except that step (4) photoelectrochemical activation was not performed. The resulting sample was named ZISH. Due to the lack of activation, a stable Zn-OP coordination structure was not formed at the interface, the surface coordination layer did not undergo in-situ reforming, and the deep-level defects were not effectively passivated.

[0052] The photoelectrodes prepared above were assembled into a photoelectrochemical cell, and then its photochemical water splitting under different voltages was tested, such as... Figure 3 As shown. At a voltage of 1.23 VRHE, the photoelectrode prepared by the method in this comparative example has a photocurrent of only 2.25 mA / cm². 2 Compared with the activated sample ZISA described in Example 1, the photocurrent density of the ZISH in this comparative example is significantly lower.

[0053] Effect evaluation:

[0054] This invention employs an in-situ chelation strategy activated by photoelectrochemical activation to achieve simultaneous deep and shallow energy level conversion and the construction of highly active Zn-OP sites, and has the following key technical points:

[0055] 1. Dynamic adaptive surface reconstruction: The in-situ chelation strategy activated by photoelectrochemical activation solves the long-standing scientific limitations of static passivation layer failure under working conditions, defect management and separation of active sites.

[0056] 2. Constructing a synergistic functional coordination microenvironment: By selectively inducing Zn-S lattice reconstruction through HEDP, a dual function of defect passivation and highly active OER catalysis is constructed on the material surface, realizing precise control of the lattice coordination environment of the photoanode host.

[0057] 3. Defect level reshaping mechanism: This coordination motif can transform the performance-limiting deep-level defect traps in the photoanode into shallow-level states, fundamentally suppressing nonradiative recombination and accelerating carrier separation.

[0058] 4. The Zn-OP group has the dual functions of defect passivation and high-activity OER, which significantly improves hole transfer efficiency and carrier separation efficiency.

[0059] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a photoanode based on phosphonic acid chelation and photoelectrochemical activation, characterized in that: Includes the following steps: S11: Prepare precursor solution and chelate precursor solution respectively; the precursor solution is obtained by mixing zinc salt, indium salt and thiourea in water, and the chelate precursor solution is obtained by adding zinc salt and 1-hydroxyethylidene-1,1-diphosphonic acid to water and adjusting the pH to neutral. S12: Fluorine-doped tin oxide glass is added to the precursor solution, and after hydrothermal reaction, it is cooled to room temperature to obtain ZIS photoanode; S13: Add the ZIS photoanode to the chelation precursor solution and heat to carry out a coordination chelation reaction to obtain the ZISH photoanode; S14: Under illumination, the ZISH photoanode is electrochemically activated to obtain the photoanode based on phosphonic acid chelation and photoelectrochemical activation; in step S14, the electrochemical activation conditions are a three-electrode system, with an applied constant potential of -0.2 V to 0.6 V for 15–40 s; in the three-electrode system, the reference electrode is Ag / AgCl, the counter electrode is a platinum mesh, and the electrolyte is an aqueous solution containing sodium sulfate.

2. The preparation method according to claim 1, characterized in that: In the precursor solution, the concentration of zinc salt is 1-1.5 g / L, the concentration of indium salt is 4-4.5 g / L, and the concentration of thiourea is 3-3.5 g / L.

3. The preparation method according to claim 1, characterized in that: In the chelating precursor solution, the concentration of zinc salt is 0.02-0.12 mol / L, and the concentration of 1-hydroxyethylidene-1,1-diphosphonic acid is 200-400 mg / L.

4. The preparation method according to claim 1, characterized in that: In step S12, the hydrothermal reaction temperature is 155-165℃ and the time is 5-7 h.

5. The preparation method according to claim 1, characterized in that: In step S12, after cooling, the product is washed with water and ethanol and dried at 45-55℃ for 20-28 hours.

6. The preparation method according to claim 1, characterized in that: In step S13, the heating temperature is 50-80℃, and the coordination chelation reaction time is 10-30 min.

7. A photoanode based on phosphonic acid chelation and photoelectrochemical activation prepared by the preparation method according to any one of claims 1-6.

8. The application of the photoanode based on phosphonic acid chelation and photoelectrochemical activation as described in claim 7 in photoelectrochemical water splitting for hydrogen production.

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