Fe-doped fluoride perovskite material, preparation method thereof and application thereof in photo-assisted electrocatalytic oxygen evolution or zinc-air battery

Abstract

The application belongs to the technical field of catalytic materials, and particularly relates to Fe-doped fluoride perovskite material, a preparation method thereof and application of the Fe-doped fluoride perovskite material in photo-assisted electrocatalytic oxygen evolution or zinc-air batteries. The Fe-doped KCoNiF3 realizes photo-electric dual enhancement of the fluoride perovskite, and further improves the photo-assisted electrocatalytic performance of the fluoride perovskite. In addition, the Fe-doped fluoride perovskite can also be used for overall water splitting under illumination and rechargeable zinc-air batteries to show its significant influence on the photo-assisted OER process. The Fe-doped photo-electric dual enhancement strategy proposed in the application is expected to widen the development path of the fluoride perovskite used for photo-assisted electrocatalytic OER, thereby promoting further research on the perovskite photo-assisted electrocatalysis.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, and specifically relates to Fe-doped fluoride perovskite materials, their preparation methods, and their applications in photo-assisted electrocatalytic oxygen evolution or zinc-air batteries. Background Technology

[0002] Electrocatalytic water splitting is an effective way to produce clean energy such as hydrogen and oxygen. However, due to its inherently slow kinetics, the oxygen evolution reaction (OER) in electrocatalytic water splitting requires a high overpotential, which increases energy consumption and limits its widespread application. Recently, photo-assisted electrocatalysis has been proven to be an effective way to improve the water splitting efficiency of OER catalysts. However, the catalyst (usually a semiconductor) needs to have a suitable band structure and good light absorption capacity to generate sufficient photogenerated holes to participate in improving the catalytic reaction efficiency. At the same time, the catalyst also needs to have good intrinsic electrocatalytic performance to further improve the utilization efficiency of photogenerated holes in the photo-assisted electrocatalytic OER process. Therefore, developing photo-assisted electrocatalytic OER catalysts with high light energy utilization and excellent electrocatalytic performance is a major challenge.

[0003] Perovskite-based catalysts (ABX3) have been widely used in photocatalysis and electrocatalysis due to their inherent 3D electron / ion diffusion channels, flexible composition, and tunable electronic structure. Fluoride perovskites (ABF3), as a branch of perovskites, possess abundant F- sites and 3D electron diffusion channels, and have been reported in OER catalysis in recent years. However, the large band gap of fluoride perovskites leads to poor electrical conductivity, which is the main reason limiting their application in photocatalysis and electrocatalysis. This inevitably affects the application of fluoride perovskites in photo-assisted electrocatalysis.

[0004] Due to the technical limitations of existing fluoride perovskites, a novel fluoride perovskite material is needed to address the issue of their large band gap affecting the catalytic performance of fluoride perovskite catalysts. Currently, there are no reports on improving the photo / electrocatalytic activity of fluoride perovskites through Fe doping, or on their application in photo-assisted electrocatalysis. Summary of the Invention

[0005] To address the aforementioned technical shortcomings, this invention provides Fe-doped fluoride perovskite materials, their preparation methods, and their applications in photo-assisted electrocatalytic oxygen evolution or zinc-air batteries. This invention shortens the band gap of KCoNiF3 by doping it with Fe, while simultaneously regulating the photo / electrochemical activity of the fluoride perovskite, achieving dual photo- and electrochemical enhancement of the fluoride perovskite. This, in turn, improves the photo-assisted electrocatalytic performance of the fluoride perovskite, making it an excellent photo-assisted oxygen evolution electrocatalyst. Furthermore, Fe-doped fluoride perovskite materials can also be used in the preparation of rechargeable zinc-air batteries.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] The preparation method of Fe-doped fluoride perovskite materials includes the following steps:

[0008] (1) Dissolve KF in deionized water and heat to boiling to obtain a KF solution;

[0009] (2) Mix cobalt salt, nickel salt and ferrous salt and grind them to obtain a metal source;

[0010] (3) The metal source from step (2) is added to the KF solution from step (1), and after heating, separation of precipitate, washing with water and vacuum drying, Fe-doped fluoride perovskite material is obtained.

[0011] Preferably, in step (2), the cobalt salt is selected from Co(OAc)2·4H2O; the nickel salt is selected from Ni(OAc)2·4H2O; the ferrous salt is selected from FeSO4·7H2O; and the molar ratio of cobalt salt, nickel salt, and ferrous salt is 0.35-0.45:0.35-0.45:0.1-0.3. In this invention, only the cobalt salt is selected from Co(OAc)2·4H2O and the nickel salt is selected from Ni(OAc)2·4H2O because OAc- is easily released in the form of CO2 during the preparation process, thereby reducing the influence of anions on Fe-doped fluoride perovskite materials.

[0012] Preferably, the particle size of the metal source after grinding in step (2) is 50-100 nm.

[0013] Preferably, the heating conditions in step (3) are: heating at boiling point for 8-15 minutes.

[0014] This invention also protects the Fe-doped fluoride perovskite material prepared by the above method, wherein the molecular formula of the Fe-doped fluoride perovskite material is KCoNiFe. x F3, where 0.1≤x≤0.3.

[0015] Preferably, x = 0.2, and the molecular formula of the Fe-doped fluoride perovskite material is KCoNiFe. 0.2 F3.

[0016] This invention also protects the application of Fe-doped fluoride perovskite materials in the preparation of catalysts for photo-assisted electrocatalytic water splitting anodic oxygen evolution reaction, wherein the Fe-doped fluoride perovskite materials can achieve dual photo-electric enhancement to induce photo-assisted electrocatalytic water splitting anodic oxygen evolution reaction.

[0017] This invention also protects the application of Fe-doped fluoride perovskite materials in the preparation of zinc-air batteries, wherein the zinc-air battery is assembled according to the following steps: using polished zinc foil as the anode, carbon fiber paper coated with Fe-doped fluoride perovskite material as the air cathode, and polyvinyl alcohol gel as the electrolyte, a solid zinc-air battery is assembled.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. Perovskites possess flexible and varied bandgap structures and excellent intrinsic electrocatalytic activity, making them potential materials for photo-assisted electrocatalytic oxygen evolution reaction (OER). Unfortunately, few researchers have integrated the photo / electrochemical properties of individual perovskite semiconductor catalysts for use in photo-assisted OER research. This application is the first to integrate the photoresponsive and electrocatalytic activities of fluoride perovskites through Fe doping, making it an excellent photo-assisted electrocatalyst belonging to the non-heterojunction class.

[0020] 2. This invention obtains a light-assisted OER electrocatalyst KCoNiFe with enhanced electrocatalytic activity by doping KCoNiF3 with Fe. 0.2 F3 hollow cube. Benefiting from Fe-doped photoelectric dual enhancement, fluoride perovskite at 193 mV @ 10 mA cm⁻¹ -2 The KCoNiFe catalyst exhibits excellent photo-assisted electrocatalytic OER performance, outperforming the standard noble metal catalyst RuO2 and ranking among the best reported perovskite-based catalysts. 0.2 The F3 also demonstrates excellent practical application value.

[0021] In constructing KCoNiFe 0.2 F3 is the anode, and Pt / C is the cathode (KCoNiFe). 0.2 When using a two-electrode cell for water splitting with F3||Pt / C, the current reaches 10 mA cm⁻¹ under illumination. -2 Only 1.52V is required. KCoNiFe 0.2 When used in zinc-air batteries, F3 has a high open-circuit voltage of 1.48V and excellent stability.

[0022] 3. The photo-assisted electrocatalytic OER mechanism of the Fe-doped fluoride perovskite material in this application is also reported for the first time, specifically: KCoNiFe 0.2The outstanding performance of the F3 hollow cube stems from the dual electro-optic enhancement induced by Fe doping. First, the synergistic effect of the B-site metal reduces the catalyst resistance, promoting electron transfer within the fluorine perovskite. Second, the Fe-doped fluoride perovskite exhibits a narrower band gap and enhanced light absorption, promoting carrier separation, exciting more oxidation holes, and accelerating the generation of M-OH / MOOH during surface reconstruction, thereby improving photo-assisted OER performance. This work not only advances the development of fluorine perovskites in the field of electrocatalysis but also provides a reference for the study of the photo-assisted electrocatalysis mechanism of fluorine perovskites, broadening the research horizons for the application of fluorine perovskites in OER catalysis. Attached Figure Description

[0023] Figure 1 In the example, (a) is KCoNiFe from Examples 1-3. x (a) Schematic diagrams of the crystal structures of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1; (b) KCoNiFe of Examples 1-3 x XRD patterns of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1;

[0024] Figure 2 KCoNiFe as described in Example 3 0.3 XRD pattern of F3;

[0025] Figure 3 In the example, (a) is KCoNiFe from Examples 1-3. x (a) TEM images of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1; (b) KCoNiFe of Example 2. 0.2 (c) EDS mapping diagrams of K, Co, Fe, Ni, and F elements in F3; (d) HRTEM image of KCoNiF3 nanoparticles in Comparative Example 1; (e) KCoNiFe 0.2 HRTEM image of F3 nanoparticles; insets in (c) and (d) are selected area electron diffraction patterns.

[0026] Figure 4 KCoNiFe from Examples 1-3 x ICP-MS plots of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1;

[0027] Figure 5 KCoNiFe from Examples 1-3 x XPS full spectra of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1;

[0028] Figure 6 KCoNiFe from Examples 1-3 x High-resolution XPS images of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 (Comparative Example 1); where (a) is Co 2p 3 / 2 (b) is Ni 2p 3 / 2 (c) is Fe 2p; (d) is KCoNiFe x The graph shows the variation of high-valence metal content in F3 with Fe doping amount; (e) represents K 2p; (f) represents F 1s.

[0029] Figure 7 KCoNiFe from Examples 1-3 x (a) DOS and PDOS plots of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1; (b) UV-vis DRS curve; (c) Tauc conversion plot of UV-Vis diffuse reflectance spectrum; (d) Mott-Schottky curve; (e) schematic diagram of band gap and band position;

[0030] Figure 8 KCoNiFe from Examples 1-3 x (a) PL spectrum of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1; (b) EIS curve; (c) transient photocurrent curve at a standard hydrogen electrode potential of 1.23 V;

[0031] Figure 9 KCoNiFe from Examples 1-3 x F3 (x = 0.1, 0.2, 0.3), KCoNiF3 and RuO of Comparative Example 1 before and after illumination: (a) LSV polarization curves; (b) corresponding Tafel curves; (c) η (@10 mA cm⁻¹) -2 (d) Comparison of Tafel slopes; EIS spectrum (inset shows the resistance change of the catalyst before and after illumination);

[0032] Figure 10 In the figures, (a)-(d) represent the KCoNiFe in Examples 1-3 under no light conditions. x F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1 were scanned at 0.9–0.95 V (vs. RHE) at rates of 20–120 mV s. -1 Cyclic volt-ampere curve at time )

[0033] Figure 11 In the figures, (a)-(d) represent KCoNiFe in Examples 1-3 under illumination. xF3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1 were scanned at 0.9–0.95 V (vs. RHE) at rates of 20–120 mV s. -1 Cyclic volt-ampere curve at time )

[0034] Figure 12 KCoNiFe from Examples 1-3 x The double-layer capacitance curves of F3 (x = 0.1, 0.2, 0.3) and KCoNiF3 of Comparative Example 1 at 0.9–0.95 V (vs. RHE) (inset shows C before and after illumination). dl (Value comparison chart);

[0035] Figure 13 KCoNiFe as in Example 2 0.2 F3 in its original state, after electrocatalysis, and after photo-assisted electrocatalysis: (a) HRTEM image; (b) XRD pattern; (c) Raman spectrum;

[0036] Figure 14 KCoNiFe as in Example 2 0.2 XPS high-resolution spectra of F3 in its original state, after electrocatalysis, and after photo-assisted electrocatalysis; where (a) is the Ni 2p 3 / 2 Co 2p 3 / 2 (a) Fe 2p and O 1s; (b) K 2p; (c) F 1s;

[0037] Figure 15 KCoNiFe for photo-assisted Example 2 0.2 F3 reconstruction process diagram;

[0038] Figure 16 KCoNiFe in Example 2 under different current densities 0.2 F3 potentiostatic curves during EC and P-EC processes;

[0039] Figure 17 In the middle, (a) is KCoNiFe 0.2 Schematic diagram of the overall water splitting device for F3||Pt-C; (b) and (c) are KCoNiFe respectively. 0.2 F3||Pt-C electrolyzer polarization curves and potential stabilization curves during EC and P-EC processes (Figure c, inset: KCoNiFe under illumination) 0.2 (d) is the potentiostatic curve of F3||Pt-C; (inset) is the apparatus for testing the Faraday efficiency of water splitting (details of gas generation by the OER electrode under both light and dark conditions); (e) is KCoNiFe 0.2F3||Pt / C H2 and O2 generation rates during EC and P-EC water splitting; (f) is KCoNiFe 0.2 F3||Pt / C OER and HER Faraday efficiency diagrams for EC and P-EC water splitting processes;

[0040] Figure 18 KCoNiFe 0.2 Open-circuit voltage diagram of F3||Pt / C zinc-air battery;

[0041] Figure 19 In the middle, (a) is composed of KCoNiFe 0.2 (a) Voltage and LED bulb powered by a zinc-air battery assembled with Pt / C; (b) Current density of 1.5 mA cm⁻¹ -2 The following is a diagram of a zinc-air battery charging test. Detailed Implementation

[0042] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0043] Example 1

[0044] The preparation method of Fe-doped fluoride perovskite materials includes the following steps:

[0045] (1) Mix 0.02 mol KF and 10 mL of deionized water and heat to boiling in an oil bath to obtain a KF solution;

[0046] (2) Grind a total of 0.02 mol of metal source in a mortar for 30 min to make the metal source evenly mixed;

[0047] The metal source consists of Co(OAc)2·4H2O, Ni(OAc)2·4H2O, and FeSO4·7H2O in a molar ratio of 0.45:0.45:0.1.

[0048] (3) The metal source from step (2) is added to a beaker containing boiling KF solution, heated continuously at 100°C for 15 min, then filtered under vacuum to separate the precipitate, washed with deionized water, and dried under vacuum at 40°C to obtain the final product, Fe-doped fluoride perovskite material, denoted as KCoNiFe. 0.1 F3 (abbreviated as KCNFe) 0.1 F3).

[0049] Example 2

[0050] The preparation method of Fe-doped fluoride perovskite materials includes the following steps:

[0051] (1) Mix 0.02 mol KF and 10 mL of deionized water and heat to boiling in an oil bath to obtain a KF solution;

[0052] (2) Grind a total of 0.02 mol of metal source in a mortar for 30 min to make the metal source evenly mixed;

[0053] The metal source consists of Co(OAc)2·4H2O, Ni(OAc)2·4H2O, and FeSO4·7H2O in a molar ratio of 0.4:0.4:0.2.

[0054] (3) The metal source from step (2) is added to a beaker containing boiling KF solution, heated continuously at 100°C for 15 min, then filtered under vacuum to separate the precipitate, washed with deionized water, and dried under vacuum at 40°C to obtain the final product, Fe-doped fluoride perovskite material, denoted as KCoNiFe. 0.2 F3 (abbreviated as KCNFe) 0.2 F3).

[0055] Example 3

[0056] The preparation method of Fe-doped fluoride perovskite materials includes the following steps:

[0057] (1) Mix 0.02 mol KF and 10 mL of deionized water and heat to boiling in an oil bath to obtain a KF solution;

[0058] (2) Grind a total of 0.02 mol of metal source in a mortar for 30 min to make the metal source evenly mixed;

[0059] The metal source consists of Co(OAc)2·4H2O, Ni(OAc)2·4H2O, and FeSO4·7H2O in a molar ratio of 0.35:0.35:0.3.

[0060] (3) The metal source from step (2) is added to a beaker containing boiling KF solution, heated continuously at 100°C for 15 min, then filtered under vacuum to separate the precipitate, washed with deionized water, and dried under vacuum at 40°C to obtain the final product, Fe-doped fluoride perovskite material, denoted as KCoNiFe. 0.3 F3 (abbreviated as KCNFe) 0.3 F3).

[0061] Comparative Example 1

[0062] The preparation method of fluoride perovskite materials includes the following steps:

[0063] (1) Mix 0.02 mol KF and 10 mL of deionized water and heat to boiling in an oil bath to obtain a KF solution;

[0064] (2) Grind a total of 0.02 mol of metal source in a mortar for 30 min to make the metal source evenly mixed;

[0065] The metal source consists of Co(OAc)2·4H2O and Ni(OAc)2·4H2O in a molar ratio of 1:1.

[0066] (3) Add the metal source from step (2) to a beaker containing boiling KF solution, heat continuously at 100°C for 15 min, filter under vacuum to separate the precipitate, wash with deionized water, and dry under vacuum at 40°C to obtain the final product, fluoride perovskite material, denoted as KCoNiF3 (abbreviated as KCNF3).

[0067] I. Testing Methods

[0068] (1) Photoelectrochemical performance testing:

[0069] 7 mg of catalyst sample was dispersed in 1 mL of LDM, and ultrasonicated to ensure uniform dispersion. Then, 50 μL of the dispersion was dropped onto carbon cloth and dried under infrared light to obtain the test electrode.

[0070] Photoelectrochemical tests were performed on a CHI660D electrochemical workstation equipped with a 300W Xe lamp, with the light intensity calibrated to 100mWcm². -2 A typical three-electrode testing system consists of a working electrode, namely a carbon cloth (0.5 × 0.5 cm). 2 The loading capacity is approximately 1.4 mg / cm³. -2 It consists of a reference electrode (saturated Ag / AgCl) and an auxiliary electrode (platinum wire). In 1.0 MkOH solution, at 2 mV / s... -1 The OER was tested using the linear sweep voltammetry (LSV) method at a given scan rate. The Tafel slope was derived from the Tafel formula (2.1), where b is the Tafel slope and j is the current density.

[0071] η = blogj + a2.1

[0072] All results were corrected using the following formula 2.2:

[0073] E RHE =E Ag / AgCl +0.059×pH+0.1982.2

[0074] Electrochemical impedance spectroscopy (EIS) was performed in 1.0 MkOH solution at a voltage of 1.46 V (vs. RHE) in the frequency range of 0.01 Hz to 100 kHz.

[0075] (2) Test of Faraday efficiency of water splitting

[0076] To determine the amounts of H2 and O2 produced during water splitting, an H-type photoelectrochemical electrolytic cell was connected to a self-made sealed device. The amounts of H2 and O2 produced were calculated by reading the volume of water in the corresponding glass tubes (total volume of 10 ml in each tube) using the water displacement method.

[0077] Faraday efficiency is tested using the following equation:

[0078]

[0079] Where m is the amount of H2 / O2 (mol), n is the number of electrons transferred, and F is the Faraday constant (96485 C mol). -1 Q is the total charge (C).

[0080] (3) Zinc-air battery assembly and testing

[0081] Polished zinc foil (2×1cm) 2 The anode is coated with a catalyst (loading 1.4 mg / cm³). -2 Carbon fiber paper (CFP, 2×1cm) 2 A solid-state zinc-air battery was assembled using an air cathode and polyvinyl alcohol (PVA) gel as the electrolyte. Constant current charge-discharge curves were recorded in a mixed solution of 6.0 M KOH and 0.2 M Zn(OAc)₂ using a LANDCT2001A multichannel battery testing system.

[0082] (4) DFT calculation

[0083] Density functional theory (DFT) calculations were performed using VASP. The projected augmented wave (PAW) method was employed to characterize the core-valence interaction. The plane wave energy cutoff was set to 450 eV. Calculations were performed using the generalized gradient approximation (GGA) and the Perdew-Burke-Ernzerhof (PBE) exchange-correlated functional. The first k-point sampling in the Berrian region utilized the Monhorst packet scheme, with an automatic grid determined by 18 times the reciprocal lattice vectors. The energy and force criteria for electron density convergence were set to 10. -5 eV and The electronic structure was calculated using the HSE06 mixed functional to obtain the correct bandgap.

[0084] II. Results and Discussion

[0085] A series of target products K(CoNi) were prepared using Fe-doped fluoride perovskite KCoNiF3. 1-x Fe x F3 (denoted as KCoNiFe) x F3x = 0, 0.1, 0.2, 0.3). Figure 1 a is a schematic diagram of the crystal structure of fluoride perovskite. The standard fluoride perovskite structure is based on the transition metal B. 2+ With F as the core, connected by corners - The resulting Pm-3m cubic structure was characterized by X-ray diffraction (XRD). Figure 1 b). The XRD patterns show that the diffraction peaks of the monometallic fluoride perovskite accurately correspond to those of the standard cubic fluoride perovskite (KCoF3: PDF#18-1006, KNiF3: PDF#21-1002). For the bimetallic fluoride perovskite KCoNiF3, its peak position lies between the corresponding diffraction peaks of the two monometallic phases, KCoF3 and KNiF3, indicating successful preparation of the bimetallic fluoride perovskite. Next, with Fe doping, KCoNiFe... x The main diffraction peak (110) of F3 shifts to a lower angle, as can be observed in the magnified XRD pattern on the right, indicating an increase in the lattice spacing of the perovskite caused by Fe doping. The lattice expansion also confirms the successful introduction of Ni-Co-Fe elements into the B-site atoms of ABF3 perovskite, rather than a simple mixture of three monolithic phases. Notably, when the Fe doping concentration is x = 0.3, the KCoNiFe... 0.3 A small number of impurity peaks appear near the (110) diffraction peak in F3, mainly due to partial segregation of FeF3 and K2FeF5 in fluoride perovskite. Figure 2 This is due to excessive Fe. 2+ Caused by oxidation under hydrothermal conditions.

[0086] Further investigation of KCoNiFe using transmission electron microscopy (TEM) x The structure of F3, shown in the figure, is KCoNiFe. x F3 exhibits a hollow cubic structure, and the hollow area of ​​Fe-doped fluoride perovskite further expands with increasing Fe doping concentration. This is caused by the Ostwald ripening phenomenon during crystal growth. During this process, the grains in the central region are smaller, and their surface energy is higher than that of the outer surface grains. Therefore, the smaller grains in the central region easily dissolve and redeposit on the outside, forming a hollow structure. The Ostwald ripening method solves the template removal problem in the traditional template method for manufacturing hollow structures, while also producing hollow structures with regular and small particle sizes. Fe 2+The doping enhances the instability of the intermediate particle structure, resulting in a more hollow structure than KCoNiF3. Figure 3 a). Energy-dispersive X-ray (EDX) element mapping ( Figure 3 b) Confirmed KCoNiFe 0.2 F3 exhibits a hollow structure and a uniform distribution of elements such as K, Co, Ni, Fe, and F. Inductively coupled plasma atomic emission spectrometry (ICP) analysis indicates that the Co:Ni:Fe ratio is approximately 2:2:1. Figure 4 High-resolution transmission electron microscopy (HRTEM) of perovskites before and after Fe doping revealed clear lattice fringes, with lattice spacings of [missing information]. and Corresponding to KCoNiF3 and KCoNiFe 0.2 F3's (110) plane ( Figure 3 c) and d), the corresponding electron diffraction patterns were also indexed as perovskite lattices. These results further confirm that Fe doping increases the lattice spacing.

[0087] XPS spectroscopy was used to study KCoNiFe x The chemical composition and electronic structure of F3, such as Figure 5 As shown. KCoNiFe can be detected in the full spectrum. x The target peaks of F3 are (K2p, F1s, Co2p, Ni2p). Due to the influence of the Ni / CoAuger peak, the Fe peak is not clearly detectable in the full spectrum, but it can be observed in a narrow spectrum. Compared to KCoNiF3, KCoNiFe... x The characteristic peaks of Ni2p and Co2p in F3 showed a slight chemical shift, which is due to the slight change in the chemical environment of the perovskite caused by the doping of some Fe elements in the system. This further indicates that Fe doping will cause changes in the chemical properties of fluoride perovskites.

[0088] XPS high-resolution spectroscopy was used to study KCoNiFe with different Fe doping levels. x The chemical states of the metallic elements in F3. In the XPS spectrum of Co2p, peaks at 782.1 eV and 783.1 eV correspond to KCoNiFe. x F-Co in F3 3+ and F-Co 2+ Bond, and it can also be observed that with Fe 2+ With increasing doping content, KCoNiFe x Co in F3 (x = 0.1, 0.2, 0.3) 3+ The content also increased ( Figure 6 a). For Ni 2p, 857.5 eV and 860.4 eV correspond to KCoNiFe xF-Ni in F3 2+ and F-Ni 3+ Ni 3+ The content showed the same trend as Co 2p, and also increased with Fe. 2+ Increased with increasing doping content ( Figure 6 (b) It has been reported that increasing the content of high-valence metals in fluoride perovskites can improve their electronic conductivity and induce more vacancy defects, which is beneficial to improving OER performance. For Fe 2p, the peaks at 712.1 eV and 714.6 eV are KCoNiFe, respectively. x F-Fe in F3 2+ and F-Fe 3+ contribute( Figure 6 c). Due to the strong electronegativity of F, Fe will also produce some high-valence Fe. 3+ However, when the Fe doping concentration reaches 0.3%, Fe... 3+ The content increased significantly, while Co 3+ and Ni 3+ The content of all decreased, which can be attributed to KCoNiFe 0.3 The perovskite crystal segregation in F3 is consistent with the XRD results mentioned above. Figure 6 Figure d shows the effect of Fe doping on the high-valence metal content in fluoride perovskites. It can be found that when the Fe doping content is 0.2%, it is beneficial to promote the formation of more abundant Ni inside the perovskite. 3+ and Co 3+ This also helps generate more F vacancies, promoting OER performance. (Regarding KCoNiFe) x Studies of K 2p and F1s in F3 show that K(2p and F1s) in fluoride perovskites change with the Fe doping content. Figure 6 e) and F( Figure 6 The chemical state of f) did not change significantly.

[0089] The effect of Fe doping on the bandgap structure of KCoNiF3 was analyzed using DFT calculations. The total density of states (DOS) and projected density of states (PDOS) show that... Figure 7 a) Through Fe doping, KCoNiFe x The valence band peak of F3 was significantly reduced, and the Fe 2p impurity energy level was introduced into the fluoride perovskite system, thereby greatly shortening the band gap of KCoNiF3. This indicates that Fe doping significantly improves the performance of KCoNiFe... x The semiconductor electronic structure of F3 was affected to some extent.

[0090] The effect of Fe doping on the light absorption capacity of KCoNiF3 perovskite was further evaluated using UV-vis DRS in the spectral range of 200–800 nm. Figure 7 As shown in b, Fe doping significantly increases the absorption range of fluoride perovskite in the visible light region. This is because the doping energy levels formed inside the semiconductor shorten the band gap of the fluoride perovskite. A narrower band gap and a wider light absorption range are beneficial for KCoNiFe... x F3 captures light energy and provides the energy basis for enhancing electrocatalytic efficiency through photogenerated electrons and holes. The band gap change of Fe-doped KCoNiF3 was calculated using the Kubelka-Munk equation, yielding the KCoNiFe... x The band gap values ​​of F3 (x = 0, 0.1, 0.2, 0.3) are 5.74, 3.43, 2.87, and 3.23 eV, respectively. Figure 7 c) KCoNiFe after Fe doping x The band gap of F3 is significantly reduced, which is consistent with the DFT calculation results. Among them, KCoNiFe 0.2 F3 has the smallest band gap, indicating that it generates more electrons and holes under illumination, resulting in higher photocatalytic efficiency. This provides a basis for using visible light to promote KCoNiFe... 0.2 The electrocatalytic performance of F3 provides the structural basis. To determine the KCoNiFe... x The semiconductor parameters of F3 were evaluated using Mott-Schottky analysis for KCoNiFe. x The semiconductor type of F3 was determined, and its flat-band potential was calculated. For example... Figure 7 As shown in d, KCoNiFe x The Mott-Schottky curves for F3 all have negative slopes, reflecting the KCoNiFe x The p-type semiconductor characteristics of F3. Furthermore, the KCoNiFe was calculated by deriving the intercept in the linear region. x Flat-band potential E of F3 (x = 0, 0.1, 0.2, 0.3) FB These are 1.21, 1.24, 1.35, and 1.25 V respectively (vs. RHE), where the flat-band potential is considered the Fermi level. The conduction band potential of a p-type semiconductor is more negative than the Fermi level, i.e., E VB =E FB +0.1. Then, according to formula E... g =E VB -E CB KCoNiFe was calculated x The conduction band and valence band positions of the F3 semiconductor. Calculated doping energy levels. Figure 7 As shown in e, KCoNiFe 0.2 F3 has the smallest band gap, and Figure 7The result for c is consistent.

[0091] Figure 8 a represents the steady-state photoluminescence (PL) spectra of the fluoride perovskite before and after Fe doping. It can be observed that the absorption peak of KCoNiF3 is significantly reduced after Fe doping, indicating that Fe doping can effectively suppress the recombination of photogenerated electrons and holes within the catalyst and promote carrier separation. To further understand charge transfer, the charge transfer behavior within the catalyst was studied using electrochemical impedance spectroscopy (EIS), and the results are as follows: Figure 8 As shown in b. The corresponding Nyquist diagram is simulated using an equivalent circuit diagram, where R s R represents the resistance of the electrolyte and the instrument. sc R represents the bulk transfer resistance of the catalyst. ct C represents the transfer impedance at the sample / electrolyte interface. sc and C ct The figures represent the chemical capacitance of the catalyst bulk and the catalyst / electrolyte interface, respectively. It can be seen that Fe doping can significantly reduce the Rc of KCoNiF3. ct ,KCoNiFe x R for F3 (x = 0, 0.1, 0.2, 0.3) ct The Ω values ​​are 65.75, 14.49, 3.61, and 5.46 Ω, respectively. Among them, KCoNiFe... 0.2 The smallest Rct of F3 indicates that KCoNiFe 0.2 F3 exhibits excellent charge transfer capabilities. Lower resistance and faster charge transfer not only positively impact the separation of photogenerated carriers in the catalyst but also enhance electron transfer, thus accelerating the OER reaction process in electrocatalysis. Therefore, KCoNiFe 0.2 F3 has a suitable band structure and optimal carrier separation capability, which is more conducive to improving electrocatalytic performance.

[0092] like Figure 8 As shown in c, the transient photocurrent curve (it) of the sample exhibits a stable photocurrent response, which is enhanced after Fe doping. Among them, KCoNiFe... 0.2 The transient photocurrent difference of F3 can reach 0.14 mA cm⁻¹ -2 It is KCoNiF3 (0.02mA cm) -2 The efficiency of photogenerated carrier separation was seven times that of the original photocatalyst, indicating a significant improvement in the efficiency of photogenerated carrier separation. Analysis of the experimental results regarding the changes in the optical properties of perovskite after Fe doping shows that the light absorption region of KCoNiF3 increased and the light absorption capacity was enhanced after Fe doping. Furthermore, Fe doping also improved the carrier separation efficiency of KCoNiF3, generating more electrons and holes under illumination, providing a foundation for further enhancement of photo-assisted electrocatalysis.

[0093] The OER performance of different catalysts was evaluated by testing their linear sweep voltammetry (LSV) curves. Figure 9 As shown in Figure a, the OER performance of KCoNiF3 is greatly improved after Fe doping. x The overpotentials of F3 (x = 0.1, 0.2, 0.3) are 248, 216, and 230 mV @ 10 mA cm⁻¹, respectively. -2 The values ​​are lower than those of the original KCoNiF3 (269 mV) and RuO2 (270 mV). Furthermore, under illumination conditions, KCoNiFe... x The OER performance of the F3 (x = 0, 0.1, 0.2, 0.3) catalysts was further improved, with overpotentials of 250, 218, 193, and 210 mV @ 10 mA cm⁻¹, respectively. -2 .

[0094] To further evaluate KCoNiFe x The reaction kinetics of F3 during the OER test were calculated to obtain the corresponding Tafel slope. For example... Figure 10 As shown in b, the reaction kinetics of KCoNiF3 are greatly improved after Fe doping, and the KCoNiFe... x The Tafel slopes of F3 (x = 0.1, 0.2, 0.3) are 75, 69, and 73 mV dec, respectively. -1 It is much smaller than the original KCoNiF3 sample (85 mVdec). -1 Furthermore, the kinetic properties of these perovskite catalysts are enhanced after photoirradiation.

[0095] By observing KCoNiFe x The electrochemical and photo-assisted electrochemical oxygen evolution performance of F3 can be used to draw conclusions, such as... Figure 9 As shown in c: Fe doping promotes the OER and photo-assisted OER performance of KCoNiF3, where KCoNiFe 0.2 F3 exhibits the best catalytic activity, with the greatest improvement observed after light irradiation. This is primarily due to the reduced band gap and significantly increased conductivity of the fluoride perovskite after Fe doping, which optimizes OER kinetics and increases the reaction rate. Simultaneously, the synergistic effect of the B-site metal alters the electronic structure and local environment of Co and Ni, promoting the exposure of more active sites and optimizing the binding energy of OER intermediates. However, excessively high Fe content leads to an increase in the low-activity FeF3 and K2FeF5 components within the catalyst, resulting in decreased catalyst activity. Therefore, KCoNiFe... 0.2 F3 exhibits the best catalytic and optical properties. KCoNiFe 0.2F3 can generate a large number of electrons and holes under light irradiation. These photogenerated charges accumulate on the catalyst surface and further activate metal sites, thus exhibiting the highest enhanced OER performance.

[0096] To understand the reaction kinetics of fluoride perovskites under light irradiation, electrochemical impedance spectroscopy (EIS) was used to study KCoNiFe. x F3's photo-induced charge transfer capability ( Figure 9 d), and further compared it with the resistance when there was no light. For example... Figure 9 As shown in illustration d, KCoNiFe 0.2 F3 generates a large number of electrons and holes under photoexcitation, leading to a sudden increase in the carrier concentration inside the catalyst, which greatly reduces the KCoNiFe 0.2 The F3's body resistance significantly improves OER performance.

[0097] By measuring the double-layer capacitance (C) of the catalyst dl The electrochemically active specific surface area (ECSA) of the catalyst was evaluated to verify the activated metal sites. Different scan rates (20-120 mV s⁻¹) were used. -1 The CV curve measured was used to calculate the darkness ( Figure 10 ) and light ( Figure 11 The double-layer capacitance under the given conditions was estimated by the slope of the linear relationship between the half-capacitance current density and the scan rate within the applied potential range. The results are as follows: Figure 12 As shown. Where KCoNiFe 0.2 F3's C dl The highest value was 6.32 mF cm. -2 After illumination, C dl The increase was also the highest (ΔC). dl =7.02mF cm -2 ), indicating KCoNiFe 0.2 F3 has more electrocatalytic active sites, and its performance improvement after light exposure is more significant.

[0098] To understand the reaction process, KCoNiFe was studied using in-situ HRTEM. 0.2 Morphology and phase evolution of F3 in electrocatalysis (EC) and photo-assisted electrocatalysis (P-EC) processes Figure 13 a) It was found that KCoNiFe was found after the OER test. 0.2 F3 exhibits minor lattice fracture and fragmentation, and some amorphous layers are formed. However, after illumination, the crystalline phase KCoNiFe... 0.2F3 further decreases, while the hydroxyl oxides of the amorphous phase increase accordingly. This is attributed to the surface reconstruction of the fluorinated perovskite, in which MF has a certain dissociation and transformation ability, which can transform the surface of the fluorinated perovskite into M-OH / MOOH (M = Ni, Co, Fe).

[0099] KCoNiFe 0.2 The photo-induced reconstruction of F3 can be verified by XRD and Raman spectroscopy. Figure 13 b is KCoNiFe 0.2 XRD patterns of F3 in its original state and after EC / P-EC. The figures show that during the OER process, KCoNiFe... 0.2 The diffraction peaks of F3 were preserved, and some characteristic peaks of hydroxides and hydroxyl oxides appeared, which became more obvious after illumination. In the Raman test ( Figure 13 c) A similar phenomenon also occurred. The Raman peak is at 473.4 cm. -1 and 530.9cm -1 Corresponding to the characteristic peaks of hydroxyl oxides, after illumination, due to the oxidation of photogenerated holes, KCoNiFe... 0.2 The greater transformation of F3 indicates that light irradiation promoted the surface reconstruction of fluorine-containing perovskites and the formation of mixed metal hydroxyl oxides.

[0100] The process of light-assisted OER was further investigated using high-resolution XPS, and the results are as follows: Figure 14 As shown. F1s ( Figure 14 a) and K 2p( Figure 14 The peaks of b) almost disappeared after the EC-OER process, while the peaks of Co 2p and Fe 2p ( Figure 14 The negative shift in binding energy (c) indicates that an evolution from MF to MO / OH on the perovskite surface occurred during the OER process. Specifically, after OER testing, Ni2p 3 / 2 Characteristic peaks of 855.7 eV and 857.4 eV appear in the orbital, corresponding to Ni in NiFeOOH, respectively. 3+ and Ni 2+ A similar trend was observed for Co, with peaks at 780.5 eV and 782.6 eV corresponding to Co-O bonds. Fe 2p 3 / 2 The characteristic peaks appearing at 709.6 eV and 712.2 eV are also related to the formation of NiFeOOH. After illumination, KCoNiFe... 0.2 F3 generates more high-valence metal ions through surface reconstruction, which is similar to KCoNiFe. 0.2 The large number of holes generated by F3 during the P-EC process is related to this. Meanwhile, the active hydroxyl oxides formed on the surface of fluoride perovskites are beneficial for improving KCoNiFe. 0.2OER activity of F3. In the O1s spectrum, in the pristine KCoNiFe... 0.2 In F3, only a characteristic peak of adsorbed O1s was found at 533.5 eV. After EC-OER, a characteristic peak of MO bond was found at 529.5 eV, and a characteristic peak of M-OH bond was shown at 531.3 eV, confirming the formation of MOOH. Furthermore, the increase in the peak value of M-OH bond after light irradiation indicates an increase in the content of high-valence metals in the hydroxide, leading to KCoNiFe... 0.2 The enhanced catalytic activity of F3 induces a configurational change in metal hydroxyl oxides. Comparing these data with electrochemical performance suggests that surface reconstruction of fluoride perovskites is a key step in achieving high OER activity.

[0101] KCoNiFe 0.2 The enhancement mechanism of F3 in the light-assisted OER process is as follows: Figure 15 As shown, Fe doping promotes the formation of high-valence Co and Ni, thereby generating more metal active sites, optimizing the binding energy of OER intermediates, and facilitating OER. Thanks to Fe doping, KCoNiFe... 0.2 F3 also has a wider light absorption range and a narrower band gap, which can promote KCoNiFe 0.2 F3 generates more holes under illumination, accelerating the formation of M-OH / MOOH during surface reconstruction, thereby enhancing the light-assisted OER performance of perovskite fluorides.

[0102] The stability of catalysts is fundamental to electrochemical applications. For example... Figure 16 As shown in figure a, the prepared KCoNiFe 0.2 The F3 exhibited excellent stability, maintaining good stability even after undergoing constant current testing at multiple current densities, and displaying ΔE = 50mV (@100mA cm⁻¹) under illumination. -2 Performance improvement Figure 16 b).

[0103] Subject to KCoNiFe 0.2 Inspired by the high activity and stability of F3 under light, KCoNiFe was assembled. 0.2 A photo-assisted electrolytic cell composed of F3||Pt / C is used for overall water decomposition. Figure 17 a). From Figure 17 The polarization curve of b shows that KCoNiFe 0.2 F3||Pt / C-based electrolytic cells only require 1.55V to achieve 10mA cm⁻¹ -2 The current density is reduced, and further decreases to 1.52V under illumination. Furthermore, KCoNiFe 0.2The F3||Pt / C-based electrolyzer also exhibited good water splitting stability. At 10 mA cm⁻¹ -2 It maintains good performance even after 20 hours of IT testing at a current density of [value missing], with a current loss of only 7%. Figure 17 c). Moreover, under illumination, the current density for water splitting can rapidly reach 20 mA cm⁻¹ in approximately 2000 s. -2 And maintain it for a relatively long time. In addition, transmission electron microscopy (TEM) Figure 17 (c-interpolation) shows that KCoNiFe 0.2 F3 maintained its hollow cubic shape after water splitting stability testing, indicating that fluoride perovskites have good structural stability.

[0104] KCoNiFe was collected and quantitatively analyzed using a self-made metering device based on the water displacement method. 0.2 O2 and H2 are generated on the F3 and Pt / C electrodes. This device can stably collect O2 and H2 under constant voltage. Calculations show that the volume ratio of O2 to H2 during electrolysis is close to the theoretical value of 1:2, indicating that KCoNiFe... 0.2 The water splitting Faraday efficiency of the F3∥Pt / C electrolysis unit is close to 100%. Figure 17 d). The amounts of O2 and H2 produced during EC and P-EC processes are as follows: Figure 17 As shown in e, the average oxygen production of EC and P-EC were 95.02 and 181.58 μmol / cm³, respectively. -2 h -1 The corresponding Faraday efficiencies were calculated based on the theoretical and actual yields of O2 and H2, such as... Figure 17 As shown in f, the calculated P-EC Faraday efficiency is higher than EC, indicating that illumination improves KCoNiFe 0.2 F3's charge utilization rate.

[0105] Additionally, KCoNiFe 0.2 A dual-electrode zinc-air cell module with F3||Pt / C as the anode can maintain an open-circuit voltage of 1.48V for over 10 hours, and this voltage can increase to 1.49V after illumination. Figure 18 Furthermore, two batteries connected in series can easily power a light-emitting diode (LED) bulb at 2.97V. Figure 19 a). Meanwhile, KCoNiFe 0.2 The F3 demonstrated stable performance in the cyclic charging test at 1.5mA cm -2 The voltage difference between charging and discharging is 0.93V. Figure 19(b) After 25 hours of cycling testing, there was almost no loss. Under LED illumination, the charge-discharge voltage difference could be reduced to 0.88V, and its stability could be maintained for nearly 4 hours, indicating that the fluorinated perovskite catalyst has excellent stability and applicability.

[0106] The above studies demonstrate that Fe doping simultaneously enhances the electrocatalytic activity and photoresponsiveness of the fluorine-containing perovskite KCoNiF3. In electrocatalysis, Fe doping, through the synergistic effect of B-site metals, modulates the electronic structure of KCoNiF3, promoting the formation of more high-valence metal ions within the perovskite and generating more active sites during OER catalysis. Furthermore, doping leads to a decrease in band gap and enhanced conductivity, thereby promoting electron transfer within the catalyst. Moreover, in terms of optical properties, the reduced band gap broadens the visible light absorption range, and Fe doping suppresses electron-hole recombination, increasing the carrier separation efficiency within the catalyst. Therefore, KCoNiFe… 0.2 F3 generates more holes under light, and these holes accumulate on the surface and react with OH groups. - The interaction promotes the transformation of fluoride perovskite, generating more high-valence metal hydroxides as highly active centers for the OER process. Therefore, KCoNiFe 0.2 F3 achieves highly efficient photo-assisted OER catalysis, providing a new strategy for further improving the electrocatalytic performance of fluorinated perovskites.

[0107] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing Fe-doped fluoride perovskite materials, characterized in that, Includes the following steps: (1) Dissolve KF in deionized water and heat to boiling to obtain a KF solution; (2) After mixing and grinding cobalt salt, nickel salt and ferrous salt, a metal source is obtained; (3) The metal source from step (2) is added to the KF solution from step (1), and after heating, separation of precipitate, washing with water and vacuum drying, Fe-doped fluoride perovskite material is obtained. In step (2), the cobalt salt is selected from Co(OAc)2·4H2O; the nickel salt is selected from Ni(OAc)2·4H2O; and the molar ratio of cobalt salt, nickel salt, and ferrous salt is 0.35-0.45:0.35-0.45:0.1-0.

3. The molecular formula of the Fe-doped fluoride perovskite material is KCoNiFe. x F3, where 0.1≤x≤0.

3.

2. The method for preparing Fe-doped fluoride perovskite material according to claim 1, characterized in that, Ferrous salts are selected from FeSO4·7H2O.

3. The method for preparing Fe-doped fluoride perovskite material according to claim 1, characterized in that, The particle size of the metal source after grinding in step (2) is 50-100 nm.

4. The method for preparing Fe-doped fluoride perovskite material according to claim 1, characterized in that, The heating conditions in step (3) are: heating at boiling point for 8-15 minutes.

5. An Fe-doped fluoride perovskite material prepared by the preparation method according to any one of claims 1-4, characterized in that, The molecular formula of the Fe-doped fluoride perovskite material is KCoNiFe. x F3, where 0.1≤x≤0.

3.

6. The Fe-doped fluoride perovskite material according to claim 5, characterized in that, Where x=0.2, the molecular formula of the Fe-doped fluoride perovskite material is KCoNiFe. 0.2 F3.

7. The application of the Fe-doped fluoride perovskite material according to claim 5 in the preparation of a catalyst for the photo-assisted electrocatalytic water splitting anodic oxygen evolution reaction, characterized in that, The Fe-doped fluoride perovskite material can achieve dual photo-electric enhancement to induce the photo-assisted electrocatalytic water splitting anodic oxygen evolution reaction.

8. The application of the Fe-doped fluoride perovskite material according to claim 7 in the preparation of a catalyst for the photo-assisted electrocatalytic water splitting anode oxygen evolution reaction, characterized in that, The test method for the photo-assisted electrocatalytic oxygen evolution performance of the catalyst is as follows: Fe-doped fluoride perovskite material was ultrasonically dispersed in N,N'-dimethylformamide, then drop-coated onto carbon cloth, and dried under infrared light to obtain the test electrode; A three-electrode system was formed by using a saturated Ag / AgCl electrode as the reference electrode, a platinum wire as the auxiliary electrode, and a test electrode as the working electrode. This system was connected to an electrochemical detection device, and a photo-assisted electrocatalytic water splitting anodic oxygen evolution reaction was carried out using KOH solution as the electrolyte.

9. The application of the Fe-doped fluoride perovskite material according to claim 5 in the preparation of zinc-air batteries, characterized in that, The zinc-air battery is assembled according to the following steps: using polished zinc foil as the anode, carbon fiber paper coated with Fe-doped fluoride perovskite material as the air cathode, and polyvinyl alcohol gel as the electrolyte, a solid zinc-air battery is assembled.

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