CoNiOOH modified Sr doped BiVO4 photoelectrode and preparation method thereof

Abstract

The invention belongs to the field of photoelectrode material preparation, and particularly relates to a CoNiOOH modified Sr doped BiVO4 photoelectrode and a preparation method thereof. The photoelectrode comprises a conductive substrate; the Sr-doped BiVO4 layer is arranged on the conductive substrate; and the CoNiOOH layer is arranged on the Sr doped BiVO4 layer. The preparation method comprises the following steps: a) preparing the BiOI electrode on the conductive substrate through an electro-deposition method; b) applying a solution containing a strontium source and a vanadium source to the BiOI electrode, and performing heat treatment to form a Sr-doped BiVO4 photoelectrode; and c) immersing the Sr-doped BiVO4 photoelectrode into a solution containing a cobalt source and a nickel source, carrying out in-situ growth treatment so as to form a CoNiOOH layer on the surface of the Sr-doped BiVO4 photoelectrode, and finally obtaining the Sr: BiVO4 / CoNiOOH photoelectrode.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photoelectrode material preparation, and particularly relates to a CoNiOOH modified Sr-doped BiVO4 photoelectrode and a preparation method thereof. BACKGROUND

[0002] As an n-type semiconductor material, bismuth vanadate (BiVO4) has become one of the most potential photoanode materials in the field of photoelectrochemical (PEC) water splitting for hydrogen production due to its unique physical and chemical properties. The band gap of BiVO4 is about 2.4 eV, which can effectively absorb visible light with a wavelength of less than 520 nm, thereby efficiently utilizing the solar spectrum. The valence band top position is more positive than the water oxidation potential, meeting the thermodynamic requirements of water oxidation reaction. Compared with other narrow-bandgap semiconductors prone to photo-corrosion, BiVO4 exhibits good resistance to photo-corrosion in near-neutral electrolyte, and the constituent elements are abundant and low in cost. However, the actual photoelectrocatalytic efficiency of pure BiVO4 material is far lower than the theoretical expectation. Its performance is mainly restricted by two major intrinsic bottlenecks, which is the core problem that the current research field continues to focus on and strive to solve.

[0003] The first major drawback of BiVO4 is its poor photo-generated electron-hole separation efficiency. When BiVO4 is excited by light to generate electron-hole pairs, these carriers need to migrate to the semiconductor / conductive substrate interface (electrons) and the semiconductor / electrolyte interface (holes) to undergo water oxidation and reduction reactions. However, the electron mobility of BiVO4 is low, and the diffusion length of photo-generated carriers is short (about 100 nm), resulting in a high electron-hole recombination rate in the bulk phase.

[0004] The second major drawback of BiVO4 is the slow kinetics of its surface catalytic water oxidation reaction. Water oxidation is a complex four-electron transfer process involving multiple intermediate steps with a high activation energy barrier. The surface catalytic activity of BiVO4 itself is insufficient to effectively reduce this barrier. Therefore, even if the photo-generated holes successfully migrate to the electrode surface, they will accumulate in large quantities due to the slow interface reaction kinetics. This hole accumulation not only increases the probability of surface charge recombination, but also causes the initial potential of the photoanode to negatively shift insufficiently, requiring a higher bias to drive the water oxidation reaction, which reduces the conversion efficiency of solar energy to hydrogen energy.

[0005] To solve the above two bottlenecks, researchers and enterprises have developed various modification methods, mainly divided into bulk modification and surface modification.

[0006] Elemental doping is an effective means of controlling the electronic structure, carrier concentration, and conductivity of BiVO4 crystals by introducing heterovalent or homovalent metal / nonmetal ions. Currently, the most widely studied and mature method is n-type doping, which involves introducing high-valence metal cations (such as W ions) into the BiVO4 lattice. 6+ Mo 6+ (Replacing V in the BiVO4 lattice) 5+ This alternative doping can introduce additional free electrons into the system, increasing carrier concentration and conductivity, thereby promoting charge transport in the bulk phase. For example, in publications KR1020240085690A, CN120683548A, and CN109402656B, Mo doping is used. 6+ Improving photoelectrocatalytic efficiency. In contrast to n-type doping, p-type doping aims to generate holes or modulate the band structure, and is also considered a promising modification strategy. Theoretically, p-type doping can create a built-in electric field near the semiconductor / electrolyte interface, promoting the separation of photogenerated electron-hole pairs. However, current technologies mainly focus on mature n-type doping systems such as W and Mo.

[0007] Catalyst modification involves loading a highly catalytically active substance onto the surface of BiVO4 to accelerate the slow water oxidation reaction. The technical solution disclosed in CN119710803A provides a method for preparing a nickel-cobalt oxide modified molybdenum-doped bismuth vanadate composite photoanode and its application. This method obtains the Mo-BiVO4 photoanode through a combined electrodeposition and calcination method. A precursor solution containing bimetallic nickel and cobalt is then prepared using cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and boric acid. The Mo-BiVO4 photoanode is immersed in the precursor solution, and nickel-cobalt oxide (NiCoO4) is deposited onto the surface using photo-assisted electrodeposition. x The catalyst was grown on the surface of Mo-BiVO4 to obtain NiCoO4. x The best NiCoO4 composite photoanode was obtained by modifying the Mo-BiVO4 composite photoanode with a co-catalyst. x The photocurrent density of the Mo-BiVO4 composite photoanode modified with a co-catalyst is 5.2 times that of pure bismuth vanadate. However, the nickel-cobalt oxide (NiCoO4) in this technology... x Oxygen evolution reaction (OER) is a relatively broad concept in terms of composition and chemical state, and its activity and stability in the OER are relatively poor. Furthermore, the co-catalyst support employs a photo-assisted electrodeposition method, requiring precise control of illumination conditions, potential, and electrolyte formulation. This makes the process relatively complex, and its reproducibility and large-scale preparation difficult.

[0008] The application of BiVO4 photoelectrode is mainly restricted by its inherent low photoelectron-hole separation efficiency and slow surface water oxidation kinetics. The existing single modification method, whether element doping or cocatalyst modification, can improve the performance to some extent, but it is often difficult to optimally solve the above two problems at the same time. Therefore, it is urgent to propose a preparation method of CoNiOOH modified Sr doped BiVO4 photoelectrode to solve the problems in the prior art. SUMMARY

[0009] The application of BiVO4 photoelectrode in the prior art is mainly restricted by its inherent low photoelectron-hole separation efficiency and slow surface water oxidation kinetics. The existing single modification method, whether element doping or cocatalyst modification, can improve the performance to some extent, but it is often difficult to optimally solve the above two problems at the same time. Therefore, the present application provides a CoNiOOH modified Sr doped BiVO4 photoelectrode and a preparation method thereof, and the scheme of the present application is as follows: In one aspect, the present application provides a CoNiOOH modified Sr doped BiVO4 photoelectrode, characterized in that it comprises: a conductive substrate; a Sr doped BiVO4 layer disposed on the conductive substrate; and a CoNiOOH layer disposed on the Sr doped BiVO4 layer.

[0010] In another aspect, the present application provides a preparation method of a CoNiOOH modified Sr doped BiVO4 photoelectrode, characterized in that it comprises the following steps: a) preparing a BiOI electrode on a conductive substrate by an electrodeposition method; b) applying a solution containing a strontium source and a vanadium source to the BiOI electrode and performing heat treatment to form a Sr doped BiVO4 photoelectrode; c) immersing the Sr doped BiVO4 photoelectrode in a solution containing a cobalt source and a nickel source, performing in-situ growth treatment to form a CoNiOOH layer on the surface of the Sr doped BiVO4 photoelectrode, and finally washing with deionized water and anhydrous ethanol alternately and drying at room temperature to obtain a Sr:BiVO4 / CoNiOOH photoelectrode.

[0011] Preferably, in the step a), the precursor solution used for electrodeposition is prepared by first preparing a KI aqueous solution with a concentration of 0.4 mol / L and adjusting the pH of the KI aqueous solution to 1.7, then adding 0.04 mol / L Bi(NO3)3·5H2O into the KI aqueous solution, and finally adding a p-benzoquinone anhydrous ethanol solution with a concentration of 0.23 mol / L and stirring uniformly, wherein the molar ratio of KI, Bi(NO3)3·5H2O and p-benzoquinone is 0.4:0.04:0.09.

[0012] Preferably, the electrodeposition in the step a) is carried out in a three-electrode system, using FTO glass, Pt sheet and Ag / AgCl electrode as working electrode, counter electrode and reference electrode respectively, and the electrodeposition is carried out at a potential of -0.1 V vs. Ag / AgCl for 300 seconds.

[0013] Preferably, in the step b), the strontium source is strontium acetylacetonate, and the vanadium source is vanadyl acetylacetonate, both of which are dissolved in dimethyl sulfoxide.

[0014] Preferably, in the dimethyl sulfoxide solution containing 0.2 mol / L vanadyl acetylacetonate, strontium acetylacetonate is added, the concentration of the strontium acetylacetonate is 0.5 to 1.0 mmol / L, and the molar ratio of the vanadyl acetylacetonate to the strontium acetylacetonate is 400: (1-2).

[0015] Preferably, the heat treatment in the step b) comprises: heating to 450℃ at a heating rate of 2℃ / min, and calcining at 450℃ for 2 hours.

[0016] Preferably, after the heat treatment, the electrode is further soaked in a NaOH solution with a concentration of 1 mol / L for 15-30 min to remove excess V2O5.

[0017] Preferably, in the step c), the volume ratio of the cobalt source to the nickel source is 1:1; the cobalt source and the nickel source are CoCl2·6H2O and NiCl2·6H2O respectively, and the concentration ratio of the CoCl2·6H2O to the NiCl2·6H2O is (1-2):(1-2).

[0018] Preferably, in the step c), the Sr-doped BiVO4 photoelectrode is first immersed in a solution containing a cobalt source and a nickel source for 15 minutes, then the pH of the solution containing the cobalt source and the nickel source is adjusted to 11.0-11.5 by adding a NaOH solution with a concentration of 2 mol / L, and the electrode is further soaked at this pH for 1 hour.

[0019] The beneficial effects of the present application are as follows: The application improves the photoelectrochemical performance of the bismuth vanadate photoelectrode through the synergistic modification of strontium doping and cobalt-nickel oxyhydroxide cocatalyst.

[0020] Firstly, the Sr doping of the application effectively optimizes the energy band structure of BiVO4, and enhances its visible light response capability. The Sr doping makes the absorption edge of BiVO4 red-shift, and the band gap is reduced by 0.02 eV, which widens the absorption range of the material to the visible light band. This band control is derived from the Sr 2+ partially replacing Bi in the BiVO4 lattice 3+ , introducing positive charge compensation effect, reducing the oxygen vacancy concentration, thereby reducing the recombination center of photo-generated electron-hole pairs, and the design of narrowing the band gap width improves the light energy utilization rate, and provides more sufficient photo-generated carriers for subsequent surface reaction.

[0021] Secondly, the modification of CoNiOOH cocatalyst improves the separation and transfer efficiency of photo-generated charges. Electrochemical impedance spectroscopy shows that the arc radius of the Sr:BiVO4 / CoNiOOH composite photoelectrode is the smallest, indicating that the charge transfer resistance is reduced and the interface charge separation ability is enhanced. The photocurrent response test further confirms that the photocurrent density of pure BiVO4 is only 0.32 mA / cm 2 at 1.23 V vs. RHE, while the Sr-doped BiVO4 is improved to 1.50 mA / cm 2 , and the photocurrent density is further increased to 3.12 mA / cm 2 after loading CoNiOOH, which is 9.8 times that of pure BiVO4.

[0022] Thirdly, the water oxidation kinetics of the composite photoelectrode is optimized. Linear sweep voltammetry curves show that the Sr:BiVO4 / CoNiOOH photoelectrode exhibits higher photocurrent density in the whole test voltage range, and the initial potential is negatively shifted by 550 mV compared with BiVO4, indicating that the oxygen evolution reaction overpotential is reduced and the water oxidation reaction rate is accelerated.

[0023] Fourthly, the structural stability and uniformity of the elements of the material provide a basic guarantee for performance improvement. The scanning electron microscope image shows that the composite photoelectrode presents a porous structure stacked by nanoparticles, and CoNiOOH is uniformly covered on the electrode surface in the form of a thin film. The element mapping image confirms that the elements of Sr, Co, Ni and the like are uniformly distributed in BiVO4. This porous structure not only increases the specific surface area of the reaction, but also promotes the penetration of the electrolyte and the gas diffusion.

[0024] In summary, the application realizes the comprehensive improvement of the BiVO4 photoelectrode in light absorption, charge separation, reaction kinetics and stability through the synergistic effect of Sr-doped bulk modification and CoNiOOH surface modification, and provides a feasible scheme for the practical application of high-efficiency solar water splitting technology. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a scanning electron microscope image and an element mapping diagram of the Sr:BiVO4 / CoNiOOH photoelectrode; Figure 2 is an ultraviolet-visible diffuse reflectance spectrum diagram of the sample photoelectrode; Figure 3 is a band gap diagram calculated according to the ultraviolet-visible diffuse reflectance spectrum of the sample photoelectrode; Figure 4 is a linear sweep voltammetry curve diagram of the sample photoelectrode under simulated sunlight in a 0.5 M Na2SO4 electrolyte; Figure 5 is a photocurrent response diagram of the sample photoelectrode; Figure 6 is an electrochemical impedance spectrum diagram of the sample photoelectrode. DETAILED DESCRIPTION

[0026] To further illustrate the technical means and effects adopted by the application to achieve the predetermined invention purpose, the specific embodiments, structures, features and effects according to the application are described in detail as follows in combination with the drawings and preferred embodiments.

[0027] Example 1 The present embodiment provides a preparation method of a CoNiOOH modified Sr-doped BiVO4 photoelectrode, which is mainly realized through three steps. In the first step, a BiOI electrode is prepared on a conductive substrate by an electrodeposition method. In the second step, a solution containing a strontium source and a vanadium source is applied to the BiOI electrode, and heat treatment is performed to form a Sr-doped BiVO4 photoelectrode. In the third step, the Sr-doped BiVO4 photoelectrode is immersed in a solution containing a cobalt source and a nickel source, and in-situ growth treatment is performed to form a CoNiOOH layer on the surface of the Sr-doped BiVO4 photoelectrode. Finally, the Sr:BiVO4 / CoNiOOH composite photoelectrode is obtained by alternately washing with deionized water and anhydrous ethanol and drying at room temperature.

[0028] Specifically as follows: Step a): electrodeposition preparation of BiOI precursor film A potassium iodide solution was prepared by dissolving 0.4 mol / L KI in 50 mL of deionized water. The pH was adjusted to 1.7 with 65%–68% HNO3. Then, solid Bi(NO3)3·5H2O was added, maintaining a concentration of 0.04 mol / L. Next, 20 mL of anhydrous ethanol containing 0.23 mol / L p-benzoquinone was added, and the mixture was stirred until homogeneous to form the precursor solution. Electrodeposition was performed in a three-electrode system (FTO as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode) at room temperature with a potential of -0.1 V vs. Ag / AgCl for 300 seconds. After completion, the solution was rinsed with deionized water and dried.

[0029] Adjusting the pH to 1.7 can inhibit Bi. 3+ Hydrolysis and precipitation of ions ensure that they exist in solution as soluble complexes, thereby guaranteeing uniform film formation during electrodeposition; p-benzoquinone, acting as a reducing agent, is reduced to hydroquinone during electrodeposition, simultaneously promoting Bi... 3+ Partially reduced to metallic Bi, which then reacts with I in the solution. - and OH - The reaction generates BiOI with a porous nanosheet structure, which provides a high specific surface area and more active sites for subsequent conversion reactions.

[0030] Step b): Synthesis of Sr-doped BiVO4 photoelectrode Strontium acetylacetonate powder (with a concentration of 1.0 mmol / L) was added to a 0.2 mol / L vanadium acetylacetonate dimethyl sulfoxide solution. After stirring evenly, 200 μL of the mixed solution was dropped onto a BiOI electrode, dried at 65 °C, and then calcined at 450 °C for 2 hours at a heating rate of 2 °C / min. Finally, it was soaked in a 1 mol / L NaOH solution for 20 minutes to remove excess V2O5. After rinsing and drying, an Sr-doped BiVO4 electrode was obtained.

[0031] Sr 2+ Doping involves partially replacing Bi in the BiVO4 lattice. 3+ The introduction of a positive charge compensation effect reduces the oxygen vacancy concentration, thereby reducing the recombination centers of photogenerated electron-hole pairs. Simultaneously, it narrows the band gap of BiVO4, enhancing its absorption efficiency in the visible light region. Calcination at 450℃ causes BiOI to undergo a solid-state reaction with the vanadium / strontium precursor, transforming it into monoclinic BiVO4, and promoting the absorption of Sr... 2+ Successfully incorporated into the lattice; NaOH post-treatment can dissolve residual V2O5 impurities on the surface, preventing them from acting as charge recombination centers and reducing performance, while slight etching of the surface increases roughness and enhances light-harvesting capability.

[0032] Step c) Modification of CoNiOOH cocatalyst 10 mL of CoCl2-6H2O and NiCl2-6H2O solutions with different concentrations (10 mmol / L for CoCl2-6H2O and 10 mmol / L for NiCl2-6H2O) were mixed in proportion. The Sr-doped BiVO4 electrode was immersed in the solution for 15 minutes, then the pH was adjusted to 11.0 with a 2 mol / L NaOH solution, and the immersion was continued for 1 hour. Finally, the electrode was rinsed alternately with deionized water and anhydrous ethanol and dried.

[0033] The hydroxides of Co and Ni form a CoNiOOH cocatalyst under alkaline conditions, which has a nanosheet structure vertically anchored on the surface of BiVO4, providing active sites with high specific surface area, reducing the overpotential of the oxygen evolution reaction through synergistic effect, accelerating the transfer of holes from BiVO4 to the electrolyte, and thus improving the photoelectrochemical water oxidation efficiency. Adjusting the pH to 11.0 is crucial because this pH value ensures complete hydrolysis of Co and Ni ions to form CoNiOOH. Experiments show that the performance of the sample under this condition is optimal (the photoelectric performance of the sample at pH=11.0 is better than that at pH=8.0, 9.0, and 10.0), because the nanosheet morphology formed at pH=11.0 is more uniform, the interface contact is tighter, and the charge transfer resistance is reduced. Optimizing the Co / Ni ratio (e.g., 1:1) can adjust the electronic structure of CoNiOOH, making its Fermi level better match the energy band of BiVO4, forming an internal electric field at the interface, promoting the extraction and separation of photo-generated holes, and at the same time enhancing the long-term stability of the electrode. Pre-adsorption for 15 minutes and then reaction for 1 hour helps the uniform adsorption of precursor ions on the electrode surface, avoiding agglomeration caused by rapid precipitation.

[0034] In summary, this preparation method optimizes the bulk doping and surface modification of the electrode. Sr doping improves the bulk carrier transport capacity of BiVO4, while the CoNiOOH cocatalyst accelerates the surface reaction kinetics. The synergistic effect of the two improves the probability of photo-generated electron-hole separation and improves the water oxidation reaction kinetics, making the electrode have potential in solar water splitting applications.

[0035] Example 2 This example provides a method for preparing a CoNiOOH modified Sr-doped BiVO4 photoelectrode, as follows: A 0.4 mol / L KI solution was prepared by dissolving KI in 50 mL of deionized water, and then adjusting the pH to 1.7 with 65%-68% HNO3, and then adding Bi(NO3)3·5H2O solid to control the concentration of Bi(NO3)3·5H2O to be 0.04 mol / L, and then adding 20 mL of anhydrous ethanol with a concentration of 0.23 mol / L of p-benzoquinone, and stirring to form a precursor solution. In a three-electrode system (FTO as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode), a potential of -0.1 V vs. Ag / AgCl was applied at room temperature for 300 seconds, and after completion, the electrode was rinsed with deionized water and dried.

[0036] Step b): Synthesis of Sr-doped BiVO4 photoelectrode To a 0.2 mol / L vanadyl acetylacetonate dimethyl sulfoxide solution, Sr acetylacetonate powder was added (the concentration of Sr acetylacetonate was controlled to be 0.5 mmol / L), and after stirring, 200 μL of the mixed solution was drop-coated onto a BiOI electrode, which was then dried at 65°C and calcined at 450°C at a heating rate of 2°C / min for 2 hours, and finally immersed in a 1 mol / L NaOH solution for 20 minutes to remove excess V2O5, and then rinsed and dried to obtain a Sr-doped BiVO4 electrode.

[0037] Step c): Modification of CoNiOOH cocatalyst 10 mL of CoCl2·6H2O and NiCl2·6H2O solutions with different concentrations were mixed in a certain proportion (the concentration of CoCl2·6H2O was 5 mmol / L, and the concentration of NiCl2·6H2O was 10 mmol / L), and the Sr-doped BiVO4 electrode was immersed in the solution for 20 minutes, and then the pH was adjusted to 11.5 with a 2 mol / L NaOH solution, and the immersion was continued for 1 hour, and finally the electrode was rinsed with deionized water and anhydrous ethanol alternately and dried.

[0038] Example 3 The present example provides a method for preparing a CoNiOOH-modified Sr-doped BiVO4 photoelectrode, which is as follows: Step a): Electrodeposition preparation of BiOI precursor film A 0.4 mol / L KI solution was prepared by dissolving KI in 50 mL of deionized water, and then adjusting the pH to 1.7 with 65%-68% HNO3, and then adding Bi(NO3)3·5H2O solid to control the concentration of Bi(NO3)3·5H2O to be 0.04 mol / L, and then adding 20 mL of anhydrous ethanol with a concentration of 0.23 mol / L of p-benzoquinone, and stirring to form a precursor solution. In a three-electrode system (FTO as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode), a potential of -0.1 V vs. Ag / AgCl was applied at room temperature for 300 seconds, and after completion, the electrode was rinsed with deionized water and dried.

[0039] Step b): Synthesis of Sr-doped BiVO4 photoelectrode To a 0.2 mol / L vanadyl acetylacetonate dimethyl sulfoxide solution, Sr acetylacetonate powder was added (the concentration of Sr acetylacetonate was controlled to be 1.5 mmol / L), and after stirring, 200 μL of the mixed solution was drop-coated onto a BiOI electrode, which was then dried at 65°C and calcined at 450°C at a heating rate of 2°C / min for 2 hours, and finally immersed in a 1 mol / L NaOH solution for 20 minutes to remove excess V2O5, and then rinsed and dried to obtain a Sr-doped BiVO4 electrode.

[0040] Step c): Modification of CoNiOOH cocatalyst 10 mL of CoCl2·6H2O and NiCl2·6H2O solutions with different concentrations were mixed in a ratio (the concentration of CoCl2·6H2O was 10 mmol / L, and the concentration of NiCl2·6H2O was 10 mmol / L), and the Sr-doped BiVO4 electrode was immersed in the solution for 25 minutes, and then the pH was adjusted to 11.0 with a 2 mol / L NaOH solution, and the immersion was continued for 1 hour, and finally the electrode was rinsed with deionized water and anhydrous ethanol alternately and dried.

[0041] Example 4 The present example provides a method for preparing a CoNiOOH-modified Sr-doped BiVO4 photoelectrode, which is as follows: Step a): Electrodeposition preparation of BiOI precursor film A 0.4 mol / L KI solution was prepared by dissolving KI in 50 mL of deionized water, and then adjusting the pH to 1.7 with 65%-68% HNO3. Bi(NO3)3·5H2O was added to the solution to obtain a Bi(NO3)3·5H2O concentration of 0.04 mol / L. Then, 20 mL of anhydrous ethanol containing 0.23 mol / L p-benzoquinone was added to the solution to form a precursor solution. The precursor solution was then electrodeposited on an FTO substrate at room temperature for 300 s at a potential of -0.1 V vs. Ag / AgCl. After the electrodeposition, the FTO substrate was washed with deionized water and dried.

[0042] Step b): Synthesis of Sr-doped BiVO4 photoelectrode A 0.2 mol / L vanadyl acetylacetonate dimethyl sulfoxide solution was prepared. Sr(acetylacetonate)2 powder was added to the solution to obtain a Sr(acetylacetonate)2 concentration of 2.0 mmol / L. After stirring, 200 μL of the mixed solution was drop-coated onto a BiOI electrode. The coated electrode was dried at 65°C and then calcined at 450°C for 2 h at a temperature increase rate of 2°C / min. Finally, the electrode was immersed in a 1 mol / L NaOH solution for 20 min to remove excess V2O5. After washing and drying, a Sr-doped BiVO4 electrode was obtained.

[0043] Step c): Modification of CoNiOOH cocatalyst A 10 mL CoCl2·6H2O solution with a concentration of 10 mmol / L and a 10 mL NiCl2·6H2O solution with a concentration of 5 mmol / L were mixed in a certain ratio. The Sr-doped BiVO4 electrode was immersed in the mixed solution for 30 min, and then the pH of the solution was adjusted to 11.0 with a 2 mol / L NaOH solution. The electrode was further immersed in the solution for 1 h. Finally, the electrode was washed with deionized water and anhydrous ethanol alternately and dried.

[0044] Comparative Example 1 This comparative example provides a method for synthesizing a BiVO4 photoelectrode, Step a): Electrodeposition of BiOI precursor film A 0.4 mol / L KI solution was prepared by dissolving KI in 50 mL deionized water, and the pH was adjusted to 1.7 with 65%-68% HNO3. Then, 0.04 mol / L Bi(NO3)3·5H2O was added, followed by 20 mL of anhydrous ethanol containing 0.23 mol / L p-benzoquinone. The precursor solution was prepared by stirring. The electrodeposition was performed in a three-electrode system (FTO as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode) at room temperature by applying a potential of -0.1 V vs. Ag / AgCl for 300 s. After the electrodeposition, the electrode was rinsed with deionized water and dried.

[0045] Step b): Synthesis of the BiVO4 photoelectrode A 200 μL vanadyl acetylacetonate solution in dimethyl sulfoxide was dropped onto the BiOI electrode, which was dried at 65°C and calcined at 450°C at a heating rate of 2°C / min for 2 h. Finally, the electrode was immersed in a 1 mol / L NaOH solution for 20 min to remove excess V2O5. After rinsing and drying, the BiVO4 electrode was obtained.

[0046] Comparative Example 2 This comparative example provides a method for synthesizing a Sr-doped BiVO4 photoelectrode, Step a): Electrodeposition of the BiOI precursor film A 0.4 mol / L KI solution was prepared by dissolving KI in 50 mL deionized water, and the pH was adjusted to 1.7 with 65%-68% HNO3. Then, 0.04 mol / L Bi(NO3)3·5H2O was added, followed by 20 mL of anhydrous ethanol containing 0.23 mol / L p-benzoquinone. The precursor solution was prepared by stirring. The electrodeposition was performed in a three-electrode system (FTO as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode) at room temperature by applying a potential of -0.1 V vs. Ag / AgCl for 300 s. After the electrodeposition, the electrode was rinsed with deionized water and dried.

[0047] Step b): Synthesis of the Sr-doped BiVO4 photoelectrode

[0048] A 0.2 mol / L vanadyl acetylacetonate solution in dimethyl sulfoxide was prepared, and 0.5 mmol / L Sr(acetylacetonate)2 was added. After stirring, 200 μL of the mixed solution was dropped onto the BiOI electrode, which was dried at 65°C and calcined at 450°C at a heating rate of 2°C / min for 2 h. Finally, the electrode was immersed in a 1 mol / L NaOH solution for 20 min to remove excess V2O5. After rinsing and drying, the Sr-doped BiVO4 electrode was obtained.

[0049] Performance test Since Examples 1-4 are all within the scope of the present application, a photoelectrode material with excellent performance can be obtained, because when testing the performance, the CoNiOOH modified Sr doped BiVO4 photoelectrode prepared in Example 1, the BiVO4 photoelectrode prepared in Comparative Example 1, and the Sr doped BiVO4 photoelectrode prepared in Comparative Example 2 are selected, and the scanning electron microscope image, the ultraviolet-visible diffuse reflectance spectrum, the linear sweep voltammetry curve under simulated sunlight, the photocurrent response of the photoelectrode, and the electrochemical impedance spectrum of the photoelectrode are detected, respectively. The specific results are shown in the following tables. Figures 1-6 .

[0050] The detection instruments are as follows: The scanning electron microscope (SEM) uses the signals generated by the interaction of the sample and the electrons to obtain the surface information of the sample, and the Hitachi SU8600 type electron microscope is used for scanning and element mapping analysis.

[0051] The ultraviolet-visible spectrum analysis is determined by using a Shimadzu UV-3600 spectrophotometer, and the spectral scanning range is 200-800 nm, and the scanning speed is medium speed.

[0052] The photoelectrochemical performance test is carried out by using a CHI660E electrochemical workstation. In a typical three-electrode system, the working electrode is the prepared sample, the counter electrode is a Pt sheet, the reference electrode is an Ag / AgCl electrode, and the electrolyte is a 0.5 M Na2SO4 solution. A FX-300 xenon lamp and an AM 1.5G filter are used to simulate the sunlight source, and the light intensity is 100 mW / cm 2 . All PEC tests are irradiated from the back of the working electrode. The linear sweep voltammetry curve test is set at a scanning rate of 100 mV / s. The photocurrent response test is carried out at a constant bias of 1.23 V vs. RHE, and the light source switching period is set to 10 s. The electrochemical impedance spectrum is tested at the open circuit voltage, the perturbation amplitude is 0.01 V, and the frequency range is 1 Hz-1000 kHz.

[0053] Figure 1 The scanning electron microscope image and the element mapping image of the Sr:BiVO4 / CoNiOOH photoelectrode. From the scanning electron microscope image (a-b) of the Sr:BiVO4 / CoNiOOH photoelectrode, it can be seen that the Sr:BiVO4 / CoNiOOH photoelectrode presents a porous structure stacked by nanoparticles, and the deposited CoNiOOH is distributed in the form of a thin film on the surface of the Sr:BiVO4 electrode. From the element mapping image (c-h) of the Sr:BiVO4 / CoNiOOH photoelectrode, it can be seen that the elements Bi, V, O, Sr, Co and Ni are uniformly distributed in the BiOBr / BiVO4 / CoNiOOH photoelectrode, indicating that the Sr element is successfully doped into BiVO4. Figure 1 Figure 1 ​​

[0054] Figure 2 and Figure 3 are UV-Vis diffuse reflectance spectra of the sample photoelectrodes and calculated band gaps. The absorption edges of the Sr:BiVO4 and Sr:BiVO4 / CoNiOOH photoelectrodes are red-shifted compared to BiVO4, and Sr doping reduces the band gap of BiVO4 by 0.02 eV, enhancing the visible light absorption ability of BiVO4.

[0055] Figure 4 are linear sweep voltammetry curves of the sample photoelectrodes under simulated sunlight in 0.5 M Na2SO4 electrolyte. The photocurrent density of the Sr:BiVO4 / CoNiOOH photoelectrode is significantly higher than that of BiVO4, and the Sr:BiVO4 / CoNiOOH photoelectrode has a more negative onset potential, indicating that its photoelectrocatalytic water oxidation activity is superior to that of BiVO4.

[0056] Figure 5 are photocurrent responses of the sample photoelectrodes. At 1.23 V vs. RHE, the photocurrent density of BiVO4 is 0.32 mA / cm 2 , and Sr-doped BiVO4 has a higher current density (1.50 mA / cm 2 ). After loading the CoNiOOH cocatalyst, the photocurrent density of Sr:BiVO4 / CoNiOOH increases to 3.12 mA / cm 2 , which is 9.8 times that of BiVO4. This shows that Sr doping and CoNiOOH cocatalyst modification promote the separation and transfer of photo-generated carriers inside and on the surface of BiVO4.

[0057] Figure 6 are electrochemical impedance spectra of the sample photoelectrodes. The Sr:BiVO4 / CoNiOOH photoelectrode has the smallest arc radius, indicating that it has higher photo-generated charge separation and transfer ability.

[0058] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed as the above preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some minor changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present application. Any modification, change, equivalent change and modification of the above embodiments made in accordance with the technical essence of the present application, without departing from the technical solution content of the present application, are still within the scope of the technical solution of the present application.

Claims

1. A CoNiOOH modified Sr-doped BiVO4 photoelectrode, characterized in that, include: Conductive substrate; A Sr-doped BiVO4 layer is disposed on the conductive substrate; as well as A CoNiOOH layer is disposed on the Sr-doped BiVO4 layer.

2. A method for preparing the CoNiOOH-modified Sr-doped BiVO4 photoelectrode according to claim 1, characterized in that, Includes the following steps: a) Prepare BiOI electrodes on a conductive substrate by electrodeposition; b) A solution containing strontium and vanadium sources is applied to the BiOI electrode and subjected to heat treatment to form an Sr-doped BiVO4 photoelectrode. c) The Sr-doped BiVO4 photoelectrode is immersed in a solution containing a cobalt source and a nickel source for in-situ growth to form a CoNiOOH layer on the surface of the Sr-doped BiVO4 photoelectrode. Finally, it is rinsed alternately with deionized water and anhydrous ethanol and dried at room temperature to obtain the Sr:BiVO4 / CoNiOOH photoelectrode.

3. The method for preparing a CoNiOOH-modified Sr-doped BiVO4 photoelectrode according to claim 2, characterized in that, In step a), the precursor solution used for electrodeposition is prepared as follows: first, a 0.4 mol / L KI aqueous solution is prepared and the pH of the KI aqueous solution is adjusted to 1.7; then, 0.04 mol / L Bi(NO3)3∙5H2O is added to the KI aqueous solution; finally, an anhydrous ethanol solution of p-benzoquinone with a concentration of 0.23 mol / L is added and stirred evenly, wherein the molar ratio of KI, Bi(NO3)3∙5H2O and p-benzoquinone is controlled to be 0.4:0.04:0.

09.

4. The method for preparing a CoNiOOH modified Sr-doped BiVO4 photoelectrode according to claim 2, characterized in that, The electrodeposition in step a) is performed in a three-electrode system, using FTO glass, Pt sheet and Ag / AgCl electrode as working electrode, counter electrode and reference electrode respectively, and electrodeposition is performed for 300 seconds at a potential of -0.1 V vs. Ag / AgCl.

5. The method for preparing a CoNiOOH modified Sr-doped BiVO4 photoelectrode according to claim 2, characterized in that, In step b), the strontium source is strontium acetylacetonate, and the vanadium source is vanadium acetylacetonate, both of which are dissolved in dimethyl sulfoxide.

6. The method for preparing a CoNiOOH modified Sr-doped BiVO4 photoelectrode according to claim 5, characterized in that, Strontium acetylacetonate is added to a dimethyl sulfoxide solution containing 0.2 mol / L vanadium acetylacetonate, wherein the concentration of strontium acetylacetonate is 0.5 to 1.0 mmol / L, and the molar ratio of vanadium acetylacetonate to strontium acetylacetonate is 400:(1~2).

7. The method for preparing a CoNiOOH modified Sr-doped BiVO4 photoelectrode according to claim 2, characterized in that, The heat treatment in step b) includes: heating to 450°C at a heating rate of 2°C / min, and calcining at 450°C for 2 hours.

8. The method for preparing a CoNiOOH modified Sr-doped BiVO4 photoelectrode according to claim 7, characterized in that, After the heat treatment, the electrode is further immersed in a 1 mol / L NaOH solution for 15-30 min to remove excess V2O5.

9. The method for preparing a CoNiOOH modified Sr-doped BiVO4 photoelectrode according to claim 2, characterized in that, In step c), the volume ratio of the cobalt source to the nickel source is 1:1; the cobalt source and the nickel source are CoCl2·6H2O and NiCl2·6H2O, respectively, and the concentration ratio of CoCl2·6H2O to NiCl2·6H2O is (1~2):(1~2).

10. The method for preparing a CoNiOOH modified Sr-doped BiVO4 photoelectrode according to claim 2, characterized in that, In step c), the Sr-doped BiVO4 photoelectrode is first immersed in a solution containing cobalt and nickel sources for 15 minutes. Then, the pH of the solution containing cobalt and nickel sources is adjusted to 11.0-11.5 by adding a 2 mol / L NaOH solution, and the electrode is immersed in this pH for another hour.

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