Nickel-doped chiral cobalt oxide catalyst, composite photo-anode, preparation method of composite photo-anode and photoelectrochemical water decomposition system

Abstract

The invention provides a nickel-doped chiral cobalt oxide catalyst, the chemical formula is L-Co (3-x) NixO4, and the preparation method comprises the following steps: mixing and stirring a reducing agent, L-cysteine, sodium citrate, cobalt chloride, nickel chloride and water, adding isopropanol, and standing to obtain the nickel-doped chiral cobalt oxide catalyst. The invention also provides a composite photo-anode for photoelectrochemical water decomposition, which comprises a BiVO4 photo-anode and a nickel-doped chiral cobalt oxide catalyst, the nickel-doped chiral cobalt oxide catalyst is loaded on the surface of the BiVO4 photo-anode, and the composite photo-anode is obtained by mixing the L-Co (3-x) NixO4 dispersion liquid and the BiVO4 photo-anode and carrying out heat treatment on the L-Co (3-x) NixO4 dispersion liquid and the BiVO4 photo-anode. The invention also provides a photoelectrochemical water decomposition device comprising the composite photo-anode. Spin selective charge transfer can be realized through a chiral induced spin selection effect, a reaction energy barrier is reduced, an OER path is optimized, the problems of high overpotential and low photocurrent density in the prior art are solved, H2O2 by-products can be inhibited, the stability is high, an external magnetic field is not needed, and a new thought is provided for photoelectrochemical water decomposition.

Description

Technical fields: This invention belongs to the field of photoelectrochemical water splitting technology, specifically relating to a nickel-doped chiral cobalt oxide catalyst and a composite photoanode supported on the nickel-doped chiral cobalt oxide catalyst, a preparation method thereof, and a photoelectrochemical water splitting system including the above-mentioned composite photoanode, for achieving water oxidation reaction efficiently and stably. Background technology: Photoelectrochemical (PEC) water splitting for hydrogen production is an important direction for clean energy conversion, but its core challenge lies in the bottleneck of four-electron transfer kinetics in the water oxidation reaction (OER) at the photoanode. In the traditional OER process, the continuous conversion of the intermediate (*OH→*O→*OOH) requires overcoming a high overpotential, which severely limits the solar-to-hydrogen (STH) conversion efficiency. This high overpotential stems from the spin sensitivity of the OER process, that is, the key intermediate (*O / *OOH) requires additional spin recombination energy to achieve reaction with triplet oxygen (*O / *OOH). 3 O2) has matching parallel spins. Intermediates with non-parallel spin alignment tend to form singlet oxygen molecules (O2). 1 O2 triggers a side reaction to generate hydrogen peroxide (H2O2), which not only increases the OER overpotential but also causes electrode passivation through reactive oxygen species, reducing stability. In existing technologies, ferromagnetic catalysts, while utilizing magnetic fields to modulate the spin arrangement of reaction intermediates and lower the spin-flip energy barrier, require external magnetic field energy input and are limited to specific 3d transition metals. While chiral organic molecules can achieve spin-selective electron transport through the CISS effect, they suffer from weak adhesion at the photoanode-organic coating interface and low polymer conductivity. Chiral inorganic materials (such as chiral ligand-induced CoO and MnO)... x and NiO x Although the CISS effect can be used to make the spin multiplicity of *OOH and 3 O2 is compatible, but its catalytic activity is limited by insufficient active site density.

[0001] Therefore, there is an urgent need to develop a novel photoelectrochemical water splitting system that can effectively control spin state recombination in the OER process through spin engineering strategies without relying on an external magnetic field, thereby reducing the reaction energy barrier and suppressing the generation of H2O2 byproducts, thus achieving efficient and stable hydrogen production through water splitting. Summary of the Invention: The purpose of this invention is to address the shortcomings of existing technologies by providing a nickel-doped chiral cobalt oxide catalyst, a composite photoanode, its preparation method, and a photoelectrochemical water splitting system.

[0002] The present invention adopts the following technical solution: (I) This invention provides a nickel-doped chiral cobalt oxide catalyst, synthesized via L-cysteine ​​induction, exhibiting strong chiral optical activity and high spin polarizability. The chemical formula of the nickel-doped chiral cobalt oxide catalyst is L-Co. (3-x) Ni x O4, x ranges from 0.1 to 0.6, and the nickel doping amount ranges from 3 to 20 mol.

[0003] Furthermore, nickel-doped chiral cobalt oxide catalysts L-Co (3-x) Ni x In O4, x=0.14, and the nickel doping amount is 5mol.

[0004] (ii) The present invention also provides a method for preparing the nickel-doped chiral cobalt oxide catalyst described above, comprising: mixing a reducing agent, L-cysteine, sodium citrate, cobalt chloride, nickel chloride and water, stirring; adding isopropanol and allowing it to stand, centrifuging and taking the solid to obtain the nickel-doped chiral cobalt oxide catalyst.

[0005] Furthermore, the ratio of the reducing agent, L-cysteine, sodium citrate, cobalt chloride, nickel chloride, isopropanol, and water is 0.008~0.012g: 0.04~0.08g: 0.01~0.04g: 0.02~0.06: 0.008~0.06g: 120~180ml: 10~40ml.

[0006] Furthermore, the ratio of the reducing agent, L-cysteine, sodium citrate, cobalt chloride, nickel chloride, isopropanol, and water is 0.0095 g: 0.059 g: 0.024 g: 0.048 g: 0.0095~0.038: 157.5 ml: 22.5 ml.

[0007] Furthermore, the ratio of the reducing agent, L-cysteine, sodium citrate, cobalt chloride, nickel chloride, isopropanol, and water is 0.0095 g: 0.059 g: 0.024 g: 0.048 g: 0.0095 g: 157.5 ml: 22.5 ml.

[0008] Furthermore, the reducing agent is sodium borohydride, and the standing time after adding isopropanol is 5-10 h, preferably 6 h.

[0009] (III) The present invention also provides a composite photoanode for photoelectrochemical water splitting, comprising a BiVO4 photoanode and the nickel-doped chiral cobalt oxide catalyst described in (I) of the present invention, wherein the nickel-doped chiral cobalt oxide catalyst is loaded on the surface of the BiVO4 photoanode to form a heterojunction.

[0010] Furthermore, the nickel-doped chiral cobalt oxide catalyst has a coverage of 60-90% on the surface of the BiVO4 photoanode and a thickness of 5-10 nm, and is uniformly distributed on the BiVO4 surface to form a tight interfacial contact.

[0011] (iv) The present invention also provides a method for preparing the composite photoanode for photoelectrochemical water splitting as described in (iii) of the invention, comprising: L-Co (3-x) Ni x O4 was dissolved in water to obtain a dispersion; a BiVO4 photoanode was placed in the dispersion and heat-treated to obtain L-Co. (3-x) Ni x O4 / BiVO4 heterostructure.

[0012] Furthermore, the heat treatment temperature is 50~80℃, preferably 60℃; the heat treatment time is 5~10 h, preferably 6 h.

[0013] (v) The present invention also provides a photoelectrochemical water splitting device, including a working electrode, a counter electrode, an alkaline electrolyte solution and a light irradiation system, wherein the working electrode is the composite photoanode for photoelectrochemical water splitting described in (iii) of the present invention.

[0014] Furthermore, the alkaline electrolyte solution is a potassium borate buffer solution with a concentration of 0.5 mol / L and a pH of 9.33.

[0015] The beneficial effects of this invention are: (1) The nickel-doped chiral cobalt oxide catalyst prepared in this invention has excellent spin polarization effect and can exhibit a spin polarization rate of 65%. It achieves spin-selective charge transport through chiral-induced spin selection effect and effectively suppresses interfacial charge recombination. (2) L-Co prepared in this invention (3-x) Ni x The O4 / BiVO4 composite photoanode, compared with the BiVO4 photoanode, can significantly improve the photocurrent density, solving the problem of slow water oxidation reaction kinetics in existing photoelectrochemical water splitting systems, which leads to high overpotential and low photocurrent density. (3) L-Co prepared in this invention (3-x) Ni x The O4 / BiVO4 composite photoanode regulates the spin-state recombination of key intermediates in water oxidation through chiral-induced spin selection effect, efficiently promoting the generation of triplet oxygen, while suppressing H2O2 byproducts. This overcomes the problem of excessive byproducts in existing technologies that reduce reaction efficiency and impair electrode stability. (4) L-Co prepared in this invention (3-x) Ni xThe O4 / BiVO4 composite photoanode exhibits strong stability and can operate continuously for 20 hours, reducing current decay. (5) This invention does not require an external magnetic field. It achieves spin control through the intrinsic chiral structure of the material, avoiding the dependence of traditional ferromagnetic catalysts on external magnetic fields. It overcomes the problem that traditional spin control relies on external magnetic fields or organic chiral materials and is difficult to achieve large-scale application, which is more conducive to practical application. Attached Figure Description

[0016] Figure 1 L-Co prepared in Example 1 (3-x) Ni x Micromorphological and structural characterization of O4 / BiVO4 composite photoanodes: (a) L-Co (3-x) Ni x SEM images of O4 / BiVO4; (b) L-Co (3-x) Ni x TEM images of O4 / BiVO4; Figure 2 L-Co prepared in Example 1 (3-x) Ni x XRD patterns of O4 / BiVO4 and BiVO4; Figure 3 L-Co prepared in Example 1 (3-x) Ni x Characterization of the chemical composition and spin polarization properties of the O4 / BiVO4 composite photoanode: (a) Co2p 3 / 2 XPS spectra of energy levels; (b) Ni2p 3 / 2 XPS spectra of energy levels; (c) L-Co (3-x) Ni x Circular dichroism spectra of O4 / BiVO4 and BiVO4; (d) L-Co (3-x) Ni x Spin polarization curves of O4 nanoparticles; Figure 4 L-Co prepared in Example 1 (3-x) Ni x Linear scan voltammetric curves of O4 / BiVO4 composite photoanode and BiVO4; Figure 5 L-Co prepared in Example 1 (3-x) Ni x The photocurrent density of O4 / BiVO4 composite photoanode and BiVO4 as a function of time; Figure 6 L-Co prepared in Example 1 (3-x) Ni xUV-Vis absorption spectra of O4 / BiVO4 composite photoanode and BiVO4 H2O2; Figure 7 L-Co prepared in Example 1 (3-x) Ni x Characterization of the Faraday efficiency of O4 / BiVO4 composite photoanode and BiVO4: (a) L-Co (3-x) Ni x (a) Bar chart of O2 and H2O2 Faraday efficiency of O4 / BiVO4 composite photoanode; (b) Bar chart of O2 and H2O2 Faraday efficiency of BiVO4 photoanode. Detailed implementation method: To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] Example 1 This embodiment provides a method for preparing a nickel-doped chiral cobalt oxide catalyst and a composite photoanode including a BiVO4 photoanode and the nickel-doped chiral cobalt oxide catalyst, as detailed below: Step 1: Nickel-doped chiral cobalt oxide catalyst L-Co (3-x) Ni x Preparation of O4 Take 22.5 ml of deionized water, and add 0.0095 g NaBH4, 0.059 g L-C3H7NO2S, 0.024 g sodium citrate, 0.048 g cobalt(II) hexahydrate, and 0.0095 g nickel(II) hexahydrate sequentially. Stir slowly for 4 h; add 157.5 mL of isopropanol and let stand for 6 h; centrifuge at 10000 rpm for 20 min each time, 5 times; filter and vacuum dry for 12 h to obtain L-Co. (3-x) Ni x O4 nanoparticle powder, x=0.14, with a nickel doping amount of 5mol.

[0018] Step 2: Preparation of BiVO4 photoanode 0.970 g of Bi(NO3)2·5H2O and 3.320 g of KI were weighed and dissolved in 50 ml of aqueous solution. The pH was adjusted to 1.7 using concentrated nitric acid, and this solution was designated as solution A. 0.497 g of p-benzoquinone was weighed and dissolved in 20 ml of anhydrous ethanol, and this solution was designated as solution B. Solution A and solution B were mixed and stirred uniformly for 10 min to obtain the precursor electrolyte. On a clean FTO glass surface, a BiOI film was electrodeposited using a three-electrode system with a voltage of -0.1 V vs Ag / AgCl and a deposition time of 200 s. A vanadium precursor solution (100 µL of 0.2 mol / L dimethyl sulfoxide solution of vanadium acetylacetonate) was added dropwise to the surface of the obtained BiOI film, and the film was calcined at 450 °C for 2 h to obtain a BiVO4 film. The calcined BiVO4 film was then immersed in a 1 M sodium hydroxide solution for 60 min to obtain a BiVO4 photoanode.

[0019] Step 3: L-Co composite photoanode for photoelectrochemical water splitting (3-x) Ni x Preparation of O4 / BiVO4 Take 10 mg L-Co (3-x) Ni x BiVO4 nanoparticle powder was dissolved in 10 ml of water to obtain a nanoparticle dispersion; the BiVO4 thin film electrode was placed horizontally in the dispersion and allowed to stand at 60 °C for 6 h.

[0020] Example 2 The preparation process in this embodiment is the same as that in Example 1, except that: In step one of this embodiment, the amounts of NaBH4, L-cysteine, sodium citrate, cobalt(II) hexahydrate, nickel(II) hexahydrate, isopropanol, and deionized water added are 0.0095 g, 0.059 g, 0.024 g, 0.048 g, 0.019 g, 157.5 ml, and 22.5 ml, respectively.

[0021] L-Co (3-x) Ni x O4 nanoparticle powder, x=0.3, with a nickel doping amount of 10 mol.

[0022] Example 3 The preparation process in this embodiment is the same as that in Example 1, except that: In step one of this embodiment, the amounts of NaBH4, L-cysteine, sodium citrate, cobalt(II) hexahydrate, nickel(II) hexahydrate, isopropanol, and deionized water added are 0.0095 g, 0.059 g, 0.024 g, 0.048 g, 0.038 g, 157.5 ml, and 22.5 ml, respectively.

[0023] L-Co (3-x) Ni x O4 nanoparticle powder, x=0.6, with a nickel doping amount of 20 mol.

[0024] Example 4 The preparation process in this embodiment is the same as that in Example 1, except that: In step three of this embodiment, after placing the BiVO4 thin film electrode in the dispersion, the heat treatment temperature is 50 ℃ and the heat treatment time is 5 h.

[0025] Example 5 The preparation process in this embodiment is the same as that in Example 1, except that: In step three of this embodiment, after placing the BiVO4 thin film electrode in the dispersion, the heat treatment temperature is 80 ℃ and the heat treatment time is 10 h.

[0026] Effect test: I. Composite Photoanode L-Co (3-x) Ni x Characterization of O4 / BiVO4: Figure 1 and Figure 2 L-Co prepared in Example 1 (3-x) Ni x Microstructure and structural characterization of O4 / BiVO4 composite photoanodes. Figure 1 As shown in (a) and (b), the worm-like BiVO4 surface after electrodeposition is uniformly loaded with L-Co atoms with a diameter of 5–10 nm. (3-x) Ni x O4 nanoparticles; composed of Figure 2 It can be seen that the BiVO4 electrode was successfully synthesized, while due to L-Co (3-x) Ni x O4 loading is low, L-Co (3-x) Ni x The XRD spectrum of O4 / BiVO4 remained unchanged.

[0027] Figure 3 L-Co prepared in Example 1 (3-x) Ni x Characterization of the chemical composition and spin polarization properties of the O4 / BiVO4 composite photoanode. Figure 3 From (a) and (b), we can see that L-Co (3-x) Ni x O4 has been successfully synthesized, from Figure 3 As shown in (c), the chirality of L-cysteine ​​successfully introduced L-Co. (3-x) Ni xO4 / BiVO4 composite photoanode; composed of Figure 3 From (d), we can see that L-Co (3-x) Ni x O4 can induce a spin polarization of up to 65%, enabling spin-selective charge transport through the CISS effect and effectively suppressing interfacial charge recombination.

[0028] II. Photoelectrochemical performance testing: L-Co prepared according to Examples 1-5 of the present invention (3-x) Ni x Using the O4 / BiVO4 composite photoanode as the test object and the BiVO4 photoanode prepared in step two of Example 1 as a comparative example, the photoelectrochemical performance of the composite photoanode was tested using a standard three-electrode system. The working electrode was the L-Co prepared in Examples 1-5 of this invention. (3-x) Ni x O4 / BiVO4 composite photoanode (effective illumination area 1 cm²) 2 The counter electrode is a platinum sheet; the reference electrode is Ag / AgCl (saturated KCl); the electrolyte is a 0.5 M potassium borate buffer solution (pH=9.33); the light source is simulated sunlight (AM 1.5G, 100mW cm⁻¹). -2 ).

[0029] Test results are available Figure 4 And Table 1. From Figure 4 As can be seen from Table 1, compared with the traditional BiVO4 photoanode, the L-Co provided in this embodiment of the invention... (3-x) Ni x The O4 / BiVO4 composite photoanode exhibits superior photoelectrochemical performance, with a photocurrent density reaching 5.41 mA / cm². -2 Compared to BiVO4 (1.28 mA / cm²), -2 The onset potential is increased by 4.2 times, and the starting potential is as low as 0.235 V vs. RHE.

[0030] III. Stability Testing: L-Co prepared according to Examples 1-5 of the present invention (3-x) Ni x The O4 / BiVO4 composite photoanode was used as the test object, and the BiVO4 photoanode prepared in step two of Example 1 was used as the comparative example for stability testing.

[0031] BiVO4 photoanode and L-Co (3-x) Ni x The O4 / BiVO4 composite photoanode was continuously operated for 20 h at a bias voltage of 1.23 V vs. RHE, and the change in photocurrent density over time was recorded. The test conditions were the same as those for the photoelectrochemical performance test.

[0032] Test results are available Figure 5 And Table 1. From Figure 5 It can be seen that the L-Co prepared in Example 1 (3-x) Ni x The O4 / BiVO4 composite photoanode maintained a current retention rate of 79.7% after 20 hours, showing only a 20.3% current decay, while the current of the BiVO4 photoanode decayed to almost zero in less than 6 hours. As shown in Table 1, the current retention rates of Examples 2-5 of this invention are also significantly higher than those of the BiVO4 photoanode. This result indicates that the chiral photoanode L-Co of this invention… (3-x) Ni x O4 / BiVO4 exhibits significantly enhanced long-term operational stability, which is attributed to the CISS effect-driven reaction pathway optimization, effectively suppressing the formation of H2O2 byproducts and the resulting electrode passivation.

[0033] IV. Reaction Mechanism Study: To elucidate the influence of the CISS effect on the OER mechanism, this invention quantitatively analyzed the effects of BiVO4 photoanode and L-Co using ultraviolet-visible absorption spectroscopy. (3-x) Ni x The amount of H2O2 generated during the OER process by the O4 / BiVO4 composite photoanode. The specific steps are as follows: 1) Place each photoanode in an electrochemical cell containing 0.1 M Na2SO4 (pH=6.55); 2) The reaction was carried out for 4 hours under a bias voltage of 2.05 V vs. RHE and an AM 1.5 G illumination. 3) Take the electrolyte after the reaction, acidify it, and then add o-tolidine to form a colored complex; 4) Measure the absorbance at 436 nm and calculate the H2O2 concentration based on the standard curve.

[0034] Test results are as follows Figure 6 , Figure 7 As shown in Table 1. From Figure 6 As can be seen from Table 1, the L-Co prepared in this invention... (3-x) Ni x The H2O2 generation in the O4 / BiVO4 composite photoanode system was significantly lower than that in the BiVO4 photoanode system. Figure 7 Faraday efficiency analyses of (a) and (b) confirm that chiral-induced spin polarization preferentially stabilizes parallel-spin *OH intermediates and promotes the generation of four-electron pathways by regulating the spin arrangement of intermediates. 3 O2, simultaneously suppresses the generation of two electron pathways. 1 H2O2.

[0035] Table 1 - Test Results

[0036] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A nickel-doped chiral cobalt oxide catalyst, characterized in that, The chemical formula of the nickel-doped chiral cobalt oxide catalyst is L-Co. (3-x) Ni x O4, x ranges from 0.1 to 0.6, and the nickel doping amount is 3 to 20 mol.

2. The method for preparing the nickel-doped chiral cobalt oxide catalyst according to claim 1, characterized in that, include: Mix the reducing agent, L-cysteine, sodium citrate, cobalt chloride, nickel chloride, and water, and stir. Isopropanol was added and allowed to stand. After centrifugation, the solid was collected to obtain a nickel-doped chiral cobalt oxide catalyst.

3. The method for preparing the nickel-doped chiral cobalt oxide catalyst according to claim 2, characterized in that, The ratio of the reducing agent, L-cysteine, sodium citrate, cobalt chloride, nickel chloride, isopropanol, and water is 0.008~0.012g: 0.04~0.08g: 0.01~0.04g: 0.02~0.06: 0.008~0.06g: 120~180ml: 10~40ml.

4. The method for preparing the nickel-doped chiral cobalt oxide catalyst according to claim 2, characterized in that, The reducing agent is sodium borohydride, and after adding isopropanol, the standing time is 5-10 h.

5. A composite photoanode for photoelectrochemical water splitting, characterized in that, It includes a BiVO4 photoanode and the nickel-doped chiral cobalt oxide catalyst of claim 1, wherein the nickel-doped chiral cobalt oxide catalyst is supported on the surface of the BiVO4 photoanode.

6. The composite photoanode for photoelectrochemical water splitting according to claim 5, characterized in that, The nickel-doped chiral cobalt oxide catalyst has a coverage of 60-90% on the surface of the BiVO4 photoanode and a thickness of 5-10 nm.

7. The method for preparing the composite photoanode for photoelectrochemical water splitting according to any one of claims 5 to 6, characterized in that, include: The L-Co as described in claim 1 (3-x) Ni x O4 is dissolved in water to obtain a dispersion; BiVO4 photoanode was placed in a dispersion and heat-treated to obtain L-Co. (3-x) Ni x O4 / BiVO4 heterostructure.

8. The method for preparing the composite photoanode for photoelectrochemical water splitting according to claim 7, characterized in that, The heat treatment temperature is 50~80℃, and the heat treatment time is 5~10 h.

9. A photoelectrochemical water splitting device, comprising a working electrode, a counter electrode, an alkaline electrolyte solution, and a light irradiation system; characterized in that, The working electrode is the composite photoanode for photoelectrochemical water splitting as described in claim 5.

10. The photoelectrochemical water splitting device according to claim 9, characterized in that, The alkaline electrolyte solution is a 0.5 mol / L potassium borate buffer solution with a pH of 9.33.

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