Tunable defect sub-nanometer gold supported nickel-iron composite photoanode catalyst, preparation method and application

Abstract

The application discloses a kind of adjustable defect sub-nanometer gold load nickel iron composite photoanode catalyst, preparation method and application, deionized water is introduced into nitrogen and is deoxidized, multi-walled carbon nanotube treated by strong acid is placed in deionized water after deoxidation, after ultrasonic dispersion is uniform, together with FeCl2, NiCl2, HMT and ammonium fluoride is added into reaction kettle, reaction is carried out at 120 DEG C for 6 hours, after cooling, it is taken out, using deionized water is filtered, washed after, HAuCl4 is quickly added, sealed and is stirred in dark room, after reaction is finished, it is filtered, washed, nitrogen is dried at room temperature and is preserved in oxygen-free atmosphere.The application is synthesized Au / NiFe (hydroxyl) oxide / CNT composite catalyst by in-situ oxidation technology one step.The method can be simultaneously controlled on the basis of heterojunction Defects, the synergistic effect of both makes the catalyst performance be further optimized.Synthesis method is simple and direct, and catalytic effect is obviously improved.

Description

Technical Field

[0001] This invention relates to a method for preparing a sub-nanometer gold-supported nickel-iron composite photoanode catalyst with tunable defect-enhanced photoelectrocatalytic water oxidation, belonging to the field of catalyst preparation technology. Background Technology

[0002] The main problems currently hindering the application of water electrolysis for hydrogen production are high energy consumption and high production costs. Water electrolysis involves hydrogen evolution and oxygen evolution reactions. The slow kinetics of the oxygen evolution reaction (OER), due to its complex four-electron process, severely limit the overall efficiency of the water electrolysis reaction. How to reduce the overpotential of OER through innovative catalyst structural design to increase the overall reaction rate of water splitting and thus improve the hydrogen yield remains a technological bottleneck in this field. Therefore, developing efficient, inexpensive, and stable advanced electrode materials to reduce electrolysis energy consumption is crucial.

[0003] Transition metal materials have been extensively studied due to their abundant raw materials and low cost. Among them, nickel-iron oxides, as excellent catalysts for the oxygen evolution reaction (OER), play a crucial role in improving the performance of water electrolysis. For example, NiFeOx, NiFe hydroxides, and hydroxyl oxides all exhibit good catalytic activity in the OER reaction of water electrolysis. To pursue high-performance OER catalysts, controlling the electronic structure of the material and the local chemical environment of the active sites is often an important catalyst design strategy. Currently, common methods for controlling the intrinsic catalytic activity of nickel-iron catalysts include: catalyst morphology control, composite substrates with high conductivity, and introducing defects. Zhang et al. loaded single-atom gold onto layered nickel-iron double hydroxides and significantly reduced the overpotential for oxygen evolution in water electrolysis (Zhang, J.; Liu, J.; Xi, L.; Yu, Y.; Chen, N.; Sun, S.; Wang, W.; Lange, KM; Zhang, B., Single-Atom Au / NiFe Layered Double Hydroxide Electrocatalyst: Probing the Origin of Activity for Oxygen Evolution Reaction. J Am Chem Soc 2018, 140 (11), 3876-3879.). Combined with calculations, they demonstrated that the iron active sites underwent charge rearrangement under the influence of surrounding atoms, thereby enhancing catalytic activity. Simultaneously, the introduction of high-valence metal ions and the interfacial interactions between nickel-iron hydroxides and hydroxyl oxides play crucial roles in regulating the local electronic structure of the active sites in the nickel-iron composite catalyst.

[0004] Furthermore, photoelectrocatalysis is an advanced technology ideally suited for utilizing solar energy to alleviate the energy crisis and solve environmental problems. It can convert low-density, discrete solar energy into high-density, easily stored hydrogen energy, further reducing energy loss. In photoelectrocatalysis, the rapid separation and migration of photogenerated carriers are fundamental conditions for achieving high catalytic efficiency. Strategies to increase the driving force are commonly used to promote charge separation, such as increasing the external electric field (photoelectrocatalysis) or constructing a built-in electric field (catalyst modification and structural optimization, heterojunction construction), to establish faster and more efficient charge migration pathways. Numerous studies have shown that loading electrocatalysts onto the surface of semiconductor photocatalysts can effectively increase charge concentration, improve the separation efficiency of photogenerated carriers, and overcome the slow water oxidation kinetics. Semiconductor / electrocatalyst coupling strategies play a crucial role in suppressing surface recombination, reducing the overpotential required for photoelectrocatalytic water splitting, and extending the lifespan of the photoelectrode. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a subnanometer gold-supported nickel-iron composite photoanode catalyst with tunable defects, its preparation method, and its application. Based on a semiconductor-electrocatalyst coupling strategy, this invention mildly prepares a subnanometer gold-supported nickel-iron oxide / hydroxyl oxide composite catalyst through a one-step redox method. By introducing a heterojunction, defects are further tunable, and the synergistic effect of the two components optimizes the catalyst performance, achieving highly efficient oxygen evolution through photo-assisted water electrolysis.

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

[0007] A method for preparing a nickel-iron composite photoanode catalyst with tunable defects is disclosed. This method involves an in-situ synthesis of a sub-nanometer gold-supported nickel-iron composite photoanode catalyst, specifically a sub-nanometer gold-supported NiFe(hydroxy) oxide / CNT composite photoanode catalyst, using a one-step redox method. The method includes the following steps: Nitrogen gas is passed through deionized water to remove oxygen. Multi-walled carbon nanotubes treated with strong acid are placed in the deionized water and ultrasonically dispersed. These nanotubes, along with FeCl2, NiCl2, HMT, and ammonium fluoride, are then added to a reaction vessel. The reaction is carried out at 120°C for 6 hours. After cooling, the reaction vessel is removed, filtered and washed with deionized water, and HAuCl4 is quickly added. The vessel is sealed and stirred in a dark room. After the reaction is complete, the vessel is filtered, washed, dried under nitrogen gas at room temperature, and stored in an oxygen-free environment.

[0008] Furthermore, the molar ratio of FeCl2, NiCl2, HMT, and ammonium fluoride is 1:1:13.3:4. Based on 0.15 mmol FeCl2, 10 mg of multi-walled carbon nanotubes treated with strong acid are required.

[0009] Furthermore, the addition of HAuCl4 makes the molar ratio of Fe ions to Au ions (3-36):1, specifically 3:1, 6:1, 12:1, 24:1, and 36:1.

[0010] Further, after adding HAuCl4, the container was sealed and stirred in a dark room for 24 hours.

[0011] A sub-nanometer gold-supported nickel-iron composite photoanode catalyst with tunable defects was prepared using the preparation method described in this invention.

[0012] The application of the sub-nanometer gold-supported nickel-iron composite photoanode catalyst with tunable defects described in this invention in the efficient oxygen evolution of light-assisted water electrolysis.

[0013] The technical principle of this invention is based on a one-step redox reaction, 3Fe²⁺ + Au³⁺ → 3Fe³⁺ + Au. By increasing the Fe:Au molar ratio, the loading of the noble metal Au is gradually reduced, allowing trace amounts of gold to be loaded onto the surface of a nickel-iron (hydroxyl) oxide composite catalyst. This avoids the need for strong reducing agents and complex conditions such as pH adjustment required when loading noble metals. To date, in nanoscale systems, catalyst design has shifted from bulk materials to ultrathin and ultrasmall nanomaterials to obtain more active sites. The key to this invention lies in reducing the size and number of nano-Au clusters and modifying the electronic structure of the catalyst by controlling defects in the material to enhance photoelectrocatalytic performance. The formation of sub-nanometer gold hinges on the rapid nucleation and slow growth of crystallites. By adding chloroauric acid (pH approximately 3) and controlling experimental conditions such as the Fe:Au ratio and mixing rate, a sub-nanometer gold cluster-supported catalyst was synthesized. Simultaneously, the formation of nickel-iron hydroxyl oxide plays a crucial supporting role in achieving efficient photoelectrocatalytic water splitting using a semiconductor / electrocatalyst coupling strategy. Details are as follows:

[0014] 1. A one-step redox method for mildly loading sub-nano gold.

[0015] The sub-nanometer-sized precious metal gold prepared by this invention utilizes the strong reducing property of ferrous ions in the catalyst. By adjusting the amount of chloroauric acid used, the content and particle size of the sub-nanometer-sized gold clusters can be directly controlled, avoiding the use of strong reducing agents and pH adjustments required when loading precious metals. By reducing the amount and size of the precious metal, the catalytic activity is significantly improved while reducing the consumption of raw materials.

[0016] 2. Photovoltaic-coordinated water splitting for efficient hydrogen production.

[0017] Simultaneously with the formation of sub-nanometer gold clusters, photoresponsive nickel-iron (hydroxy) oxides are generated, effectively utilizing light energy to assist in the electrolysis of water for oxygen evolution. The heterostructure of Au / NiFe (hydroxy) oxides / CNTs can effectively reduce the recombination of photogenerated electrons and holes, improve the utilization efficiency of charge carriers, and reduce energy consumption, which is a beneficial exploration for the development of green hydrogen energy.

[0018] 3. The introduction of defects effectively regulates the electronic structure of the composite catalyst, greatly improving the performance of photoelectrocatalytic water oxidation.

[0019] The catalyst structure of NiFe(hydroxy) oxide / CNT supported on sub-nanometer gold with different particle sizes was analyzed and the photoelectrochemical catalytic water splitting performance was studied. It was found that the introduction of defects can effectively regulate the local electronic structure of the catalyst and modulate its activity.

[0020] The beneficial effects of this invention are as follows: This invention synthesizes an Au / NiFe (hydroxy) oxide / CNT composite catalyst in one step via in-situ oxidation technology. This method guides charge migration through the construction of semiconductor heterojunctions and simultaneously introduces defects. While controlling the catalyst morphology and particle size, the defect regulation caused by in-situ oxidation has a direct and significant impact on the local electronic structure of the catalyst's reactive center. Compared to previous modification methods such as constructing photocatalyst heterojunctions or introducing defects into photoelectrocatalysts, this method can simultaneously regulate defects on the basis of heterojunctions, utilizing the synergistic effect of both to further optimize catalyst performance. The synthesis method is simple and direct, and the catalytic effect is significantly improved.

[0021] Expected economic benefits: This catalytic system can reduce catalyst costs by decreasing the loading of precious metals, and significantly reduce overpotential through photoelectric synergy, thereby reducing hydrogen production energy consumption and improving photoelectrocatalytic hydrogen production efficiency. It is expected that this catalytic system will further acquire more catalytically active units and higher catalytic efficiency, and can further save energy by utilizing surplus solar and electricity. Environmental benefits: It reduces the cost of green hydrogen production, develops clean and decarbonized water electrolysis hydrogen production technology, and achieves the recycling of renewable resources. Attached Figure Description

[0022] Figure 1 TEM image of Au / NiFe (hydroxy) oxide / CNT-12 prepared in Example 3;

[0023] Figure 2 From left to right: Au / NiFe (hydroxy) oxide / CNT-36, Au / NiFe (hydroxy) oxide / CNT-24, Au / NiFe (hydroxy) oxide / CNT-3;

[0024] Figure 3XRD patterns of NiFeOx / CNT and sub-nanometer Au / NiFe(hydroxy) oxide / CNT-n (n=3, 6, 12, 24, 36) are shown. The inset shows the calculated variation of gold cluster particle size with n.

[0025] Figure 4 Photoelectron spectra of NiFeOx / CNT and sub-nanometer Au / NiFe (hydroxy) oxide / CNT-n (n=3, 24);

[0026] Figure 5 (a) Absorption spectra, (b) PL spectra, and (c) valence band spectra of NiFeOx / CNT, FeOOH / NiFeOx / CNT, and Au / NiFe (hydroxy) oxide / CNT-n (n=3, 24) composite catalysts;

[0027] Figure 6 (a) is the LSV curve of water oxidation reaction of NiFeOx / CNT and sub-nanometer Au / NiFe(hydroxy) oxide / CNT-n (n=3, 24) under electrocatalytic (dark) and photoelectrocatalytic (light) conditions; (b) is a schematic diagram of photoelectrocatalytic water splitting of sub-nanometer Au / NiFe(hydroxy) oxide / CNT-n photoanode in a three-electrode system.

[0028] Figure 7 Comparison of oxygen evolution reaction overpotentials of NiFeOx / CNT, FeOOH / NiFeOx / CNT, and Au / NiFe (hydroxy) oxide / CNT-n in water electrolysis and photoelectrolysis reactions;

[0029] Figure 8 Electron paramagnetic resonance (EPR) spectra of NiFeOx / CNT, FeOOH / NiFeOx / CNT, and Au / NiFe (hydroxy) oxide / CNT-n at room temperature.

[0030] Figure 9 Stability test: XPS spectra of sub-nanometer Au / NiFe (hydroxy) oxide / CNT-n (n=3, 6, 12, 24, 36) composite catalysts after 1000 cyclic voltammetric scans. Detailed Implementation

[0031] The embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. It should be understood that the following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above description of the invention.

[0032] Example 1

[0033] The preparation method of the sub-nanometer Au / NiFe (hydroxy) oxide / CNT-n (n=3, 6, 12, 24, 36) photoanode catalyst in this embodiment is as follows:

[0034] 40 mL of deionized water was purged with nitrogen to remove oxygen. After half an hour, 10 mg of strong acid-treated multi-walled carbon nanotubes were added to the deionized water and sonicated for 40 minutes to disperse them evenly. Then, these nanotubes, along with 0.15 mmol FeCl2, 0.15 mmol NiCl2, 1.995 mol HMT, and 0.6 mmol NH4F, were added to a reactor (the molar ratio of FeCl2, NiCl2, HMT, and ammonium fluoride was 1:1:13.3:4). The reactor was reacted at 120 °C for 6 hours. After cooling, the reactor was removed, filtered and washed with deionized water, and then HAuCl4 was quickly added in the appropriate proportion to adjust the Fe:Au ratio to 3:1. The reactor was sealed and stirred in a dark room for 24 hours. After the reaction was complete, the reactor was filtered, dried under nitrogen at room temperature, and stored in an oxygen-free environment. This method was used to synthesize stable, dispersed trace amounts of sub-nanometer Au on the surface of a nickel-iron composite catalyst, and photoresponsive nickel-iron hydroxy oxides were precipitated, denoted as Au / NiFe(hydroxy)oxide / CNT-3.

[0035] Example 2

[0036] The preparation method of the nickel-iron composite photoanode catalyst with tunable defects in this embodiment is as follows:

[0037] In this embodiment, the Fe:Au ratio is adjusted to 6:1, and the remaining steps are the same as in Example 1. The resulting nickel-iron composite photoanode catalyst is denoted as Au / NiFe (hydroxy) oxide / CNT-6.

[0038] Example 3

[0039] The preparation method of the nickel-iron composite photoanode catalyst with tunable defects in this embodiment is as follows:

[0040] In this embodiment, the Fe:Au ratio is adjusted to 12:1, and the remaining steps are the same as in Example 1. The resulting nickel-iron composite photoanode catalyst is denoted as Au / NiFe (hydroxy) oxide / CNT-12.

[0041] Example 4

[0042] The preparation method of the nickel-iron composite photoanode catalyst with tunable defects in this embodiment is as follows:

[0043] In this embodiment, the Fe:Au ratio is adjusted to 24:1, and the remaining steps are the same as in Example 1. The resulting nickel-iron composite photoanode catalyst is denoted as Au / NiFe (hydroxy) oxide / CNT-24.

[0044] Example 5

[0045] The preparation method of the nickel-iron composite photoanode catalyst with tunable defects in this embodiment is as follows:

[0046] In this embodiment, the Fe:Au ratio was adjusted to 36:1, and the remaining steps were the same as in Example 1. The resulting nickel-iron composite photoanode catalyst was denoted as Au / NiFe (hydroxy) oxide / CNT-36.

[0047] Comparative Example 1

[0048] The preparation method of the NiFeOx / CNT photoanode catalyst in this comparative example is as follows:

[0049] Take 40 mL of deionized water and purge it with nitrogen to remove oxygen. After half an hour, add 10 mg of strong acid-treated multi-walled carbon nanotubes to the deionized water and sonicate for 40 minutes to disperse them evenly. Then, add them to the reaction vessel along with 0.15 mmol FeCl2, 0.15 mmol NiCl2, 1.995 mol HMT and 0.6 mmol NH4F (the molar ratio of FeCl2, NiCl2, HMT and ammonium fluoride is 1:1:13.3:4). React at 120 °C for 6 hours. After cooling, remove the catalyst, filter and wash it with deionized water, dry it at room temperature by purging with nitrogen and store it in the absence of oxygen. The resulting catalyst is denoted as NiFeOx / CNT.

[0050] Comparative Example 2

[0051] The preparation steps of this comparative catalyst are the same as those of comparative example 1. After the raw materials are added to the reactor, the reaction is carried out at 120 °C for 6 hours. After cooling, the catalyst is filtered and washed with deionized water, and stirred at room temperature for 24 hours using an air pump. The catalyst is then dried and stored at room temperature. The resulting catalyst is denoted as FeOOH / NiFeOx / CNT.

[0052] Photoanode construction method

[0053] 2.8 g of the prepared Au / NiFe(hydroxy)oxide / CNT-n (n=3, 6, 12, 24, 36) was weighed and dispersed in 1.6 mL of isopropanol aqueous solution (isopropanol to ultrapure water volume ratio 1:1). 14 L of Nafion was added, and the mixture was sonicated for 40 minutes to form a uniform dispersion. Before modifying the electrode, the bare L-type glassy carbon electrode (3 mm in diameter) was polished to a mirror finish using aluminum paste and then cleaned with ultrapure water and ethanol, respectively. Then, 9.6 L of the Au / NiFe(hydroxy)oxide / CNT-n (n=3, 6, 12, 24, 36) dispersion was drop-coated onto the surface of the L-type glassy carbon electrode (0.238 g cm⁻²) using a pipette. The coated electrode was then dried in an oven at 95 °C for 12 hours. For comparison, NiFeOx / CNT and FeOOH / NiFeOx / CNT photoelectrodes were prepared using the same method.

[0054] Construction of water electrolysis and photoelectric water splitting reactor

[0055] The electrolysis of water and the photoelectrolysis of water for oxygen evolution were carried out in a three-electrode system. The working electrodes were Au / NiFe (hydroxy) oxide / CNT-n photoanode, NiFeOx / CNT photoanode, and FeOOH / NiFeOx / CNT photoanode, respectively. The counter electrode was a platinum wire electrode (0.5 mm in diameter), and the reference electrode was an Ag / AgCl (3M KCl) electrode. The three electrodes were placed in transparent H-type quartz reaction cells. The electrolyte was 1.0 mol L⁻¹ KOH, and the electrochemical workstation was a Donghua DH7000.

[0056] I. Characterization of subnanometer Au / NiFe (hydroxy) oxide / CNT-n (n=3, 6, 12, 24, 36) photoanodes

[0057] The physicochemical properties of the composite photoelectrode were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Figure 1 This is a TEM image of Au / NiFe (hydroxy) oxide / CNT-12, by Figure 1 Sub-nanometer gold clusters are visible dispersed on the surface of the nickel-iron composite catalyst nanosheets. A lattice spacing of 0.23 nm corresponds to the (015) crystal plane of the layered nickel-iron hydroxyl oxide; a lattice spacing of 0.45 nm belongs to multi-walled carbon nanotubes; the in-situ oxidation reaction has a certain corrosive effect on the two-dimensional sheet-like NiFe (hydroxyl) oxide. Figure 2It can be seen that when the Fe:Au ratio is 36:1, the nickel-iron (hydroxy) oxide nanosheets are nearly transparent with a size of about 25 nm. The nanosheets have some defects on the surface that are thinned by corrosion, with a size of 2-4 nm. When the Fe:Au ratio is 24:1, the nickel-iron (hydroxy) oxide nanosheets are further corroded. When the Fe:Au ratio is 3:1, the size of the nickel-iron composite catalyst is 5-7 nm. Figure 3 The figures show the XRD diffraction patterns of NiFeOx and sub-nanometer Au / NiFe (hydroxy) oxides / CNT-n (n=3, 6, 12, 24, 36). As can be seen from the figures, in-situ oxidation resulted in the formation of FeOOH from some of the oxides, while HAuCl4 was reduced to sub-nanometer gold clusters. With increasing HAuCl4 content, the diffraction signal of gold increased. Calculations using the Scherrer equation showed that the grain size of the gold clusters varied with the Fe:Au ratio. The inset shows the calculated variation of the gold cluster grain size with n. However, considering that the Scherrer equation is applicable to a grain size range of 1-100 nm, the calculations indicate that the formed gold cluster grain size is at the sub-nanometer level.

[0058] based on Figure 4 XPS spectra of the catalysts NiFeOx / CNT, Au / NiFe(hydroxy)oxide / CNT-3, and Au / NiFe(hydroxy)oxide / CNT-24 were obtained, revealing the proportions of Ni3+ / Ni2+ and Fe3+ / Fe2+ in the respective catalysts, as shown in Table 1. When n=24, the catalyst exhibited the highest levels of Ni3+ and Fe3+, indicating that some nickel-iron oxides were oxidized to nickel-iron hydroxy oxides. These high-valence metal ions play a crucial role in enhancing the electrocatalytic activity of the catalysts. By comparing the FeOOH / NiFeOx / CNT catalyst of Comparative Example 2, air oxidation mainly promoted the formation of iron hydroxy oxides, which also indirectly proves the oxidation effect of the in-situ oxidation process on the metal elements in nickel-iron oxides. Compared with the Au 4f photoelectron spectrum of the NiFeOx / CNT catalyst of Comparative Example 1, Au / NiFe(hydroxy)oxide / CNT-24 showed peaks of elemental metals, proving the loading of sub-nanometer gold clusters. When n=3, excess chloroauric acid introduces some of the metal cation Au. + This process also inhibits the formation of high-valence nickel-iron metal ions. The in-situ oxidation process can also be demonstrated through Raman spectroscopy comparison, such as... Figure 4The shift from 680 cm⁻¹ to 658 cm⁻¹ indicates the formation of iron hydroxyl oxide from iron(III) oxide, and the merging and broadening of 467 cm⁻¹ and 560 cm⁻¹ indicates the formation of nickel hydroxyl oxide. Furthermore, analysis of the O1s photoelectron spectra of the catalysts revealed that, compared to the unoxidized NiFeOx / CNT (Comparative Example 1) catalyst, the partially oxidized Au / NiFe(hydroxy)oxide / CNT-24 catalyst and the air-oxidized FeOOH / NiFeOx / CNT catalyst (Comparative Example 2) introduced more oxygen vacancy (Ov) defects (see Table 2). Ov defects play a crucial regulatory role in enhancing the electrocatalytic and photocatalytic performance of the catalysts.

[0059] Table 1 Ni in the catalyst 3+ / Ni 2+ and Fe 3+ / Fe 2+ proportion

[0060]

[0061] Table 2. Ratios of MO / M-OH, Ov / M-OH, and H2O / M-OH in the catalyst.

[0062]

[0063] Figure 5 The optical properties of the catalyst were characterized, corresponding to a) light absorption capacity, b) recombination capacity of photogenerated electron-hole pairs, and c) comparison of photogenerated electron density in the valence band of the catalyst. As a photoanode material, the partially oxidized Au / NiFe (hydroxy) oxide / CNT-24 exhibits strong light absorption capacity and a low electron-hole recombination rate. However, the addition of excess chloroauric acid inhibited the catalyst's absorption of the light source. + The introduction of [a specific substance] may provide more recombination centers, thereby reducing the electron-hole pair separation efficiency and inhibiting the photoelectrocatalytic performance of the catalyst. Furthermore, the decrease in charge density in the low valence band region also demonstrates that electrons were transferred from nickel-iron oxide to hydroxyl oxide after partial oxidation.

[0064] II. Electrochemical and photoelectrocatalytic characterization of sub-nanometer Au / NiFe (hydroxy) oxide / CNT-n (n=3, 6, 12, 24, 36) photoanodes.

[0065] Before the oxygen evolution reaction (OER) experiment, the prepared Au / NiFe (hydroxy) oxide / CNT-n photoanode was placed in 1.0 mol L⁻¹ KOH and scanned for 10 cycles using cyclic voltammetry (potential range: -1.0 V to 1.0 V, scan rate: 0.01 V s⁻¹). After the scan stabilized, linear sweep voltammetry (LSV) was selected as the analytical method (potential range: 0.35 V to 0.55 V, scan rate: 0.005 V s⁻¹). A 300 W xenon lamp was used as the light source for the OER reaction, with a wavelength range of 200-800 nm. After obtaining the LSV curves for the OER reaction, the light source was immediately turned on to conduct the OER reaction, and the LSV curves were saved. The electrochemical active area was obtained by measuring and analyzing the cyclic voltammetry curves at different scan rates, ranging from 0.02 V s⁻¹ to 0.12 V s⁻¹. Electrochemical impedance spectroscopy was performed at a specific open-circuit voltage with an amplitude of 0.01V.

[0066] III. Construction of heterojunctions and the improvement of photoanode catalytic performance through defect modulation.

[0067] Figure 6 The LSV curves of water oxidation reactions of nickel-iron oxide and sub-nanometer Au / NiFe(hydroxy) oxide / CNT-n (n=3, 24) under electrocatalytic and photoelectrocatalytic conditions are shown. Comparison reveals that the overpotential for oxygen evolution reaction of the catalysts decreases under illumination, with the partially oxidized Au / NiFe(hydroxy) oxide / CNT-12 exhibiting the strongest photoelectrocatalytic performance. Based on this, a schematic diagram of the photoelectrocatalytic water splitting reaction in a three-electrode system using sub-nanometer Au / NiFe(hydroxy) oxide / CNT-n photoanodes is analyzed, as shown below. Figure 6 As shown in b, under illumination, the hydroxyl oxides formed by in-situ oxidation are excited to generate electrons and holes. Due to the strong electronegativity of gold, electrons are transferred to sub-nanometer gold and further migrate to the counter electrode under the action of an external voltage to participate in the hydrogen evolution reaction. Holes are effectively separated and aggregate on the surface of nickel-iron oxide to participate in the oxygen evolution reaction.

[0068] Figure 7The overpotentials of the oxygen evolution reaction (OER) were further compared between NiFeOx / CNT, FeOOH / NiFeOx / CNT, and Au / NiFe(hydroxy)oxide / CNT-n (n=3, 6, 12, 24, 36) composite catalysts under electrocatalytic (shallow) and photoelectrocatalytic (deep) conditions. Based on the semiconductor properties of iron oxides and hydroxy oxides, the electron-hole pairs generated by the conversion of light energy are effectively separated and further act on the oxygen evolution reaction, thereby further reducing the OER overpotential. In particular, the partially in-situ oxidized Au / NiFe(hydroxy)oxide / CNT-n catalyst, due to the establishment of the Au / NiFeOOH / NiFeOx heterostructure, reduces the recombination efficiency of electron-hole pairs, promotes charge separation and transfer, and enhances catalytic activity.

[0069] Figure 8 Electron paramagnetic resonance (EPR) spectra of the Au / NiFe(hydroxy)oxide / CNT-n catalyst system were compared. In the same heterostructure, in-situ oxidation effectively controls the introduction of defects, thereby further enhancing the oxygen evolution performance of the catalyst and reducing the overpotential. As shown in the figure, in-situ oxidation introduces Fe3+-related defects at g=2.10, and the Au / NiFe(hydroxy)oxide / CNT-24 obtained by partial oxidation exhibits the fewest defects; while the addition of a large amount of chloroauric acid introduces a large number of iron defects, which may act as new recombination centers, thus inhibiting the photoelectrocatalytic activity of the catalyst.

[0070] This invention constructs an Au / (Ni)FeOOH / NiFeOx heterostructure via in-situ oxidation of chloroauric acid, effectively enhancing light energy absorption and promoting the separation and migration of photogenerated electrons and holes. Simultaneously, this method can controllably prepare defect-tuned composite catalysts. Compared to unoxidized NiFeOx / CNT and air-oxidized FeOOH / NiFeOx / CNT catalysts, this composite catalyst significantly reduces the oxygen evolution reaction overpotential and enhances photoelectrocatalytic activity. The stability of this composite catalyst is also improved through… Figure 9 This has been further confirmed.

[0071] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a sub-nanometer gold-supported nickel-iron composite photoanode catalyst with tunable defects, characterized in that: The in-situ synthesis of sub-nanometer gold-supported nickel-iron composite photoanode catalysts using a one-step redox method includes the following steps: Nitrogen gas was passed through deionized water to remove oxygen. Multi-walled carbon nanotubes treated with strong acid were placed in the deionized water and ultrasonically dispersed. They were then added to the reactor along with FeCl2, NiCl2, HMT, and ammonium fluoride. The reactor was reacted at 120°C for 6 hours. After cooling, the reactor was removed, filtered and washed with deionized water, and HAuCl4 was quickly added. The reactor was sealed and stirred in a dark room. After the reaction was completed, the reactor was filtered, washed, dried under nitrogen gas at room temperature, and stored in an oxygen-free environment. The molar ratio of FeCl2, NiCl2, HMT and ammonium fluoride is 1:1:13.3:

4. Based on 0.15 mmol FeCl2, 10 mg of multi-walled carbon nanotubes treated with strong acid are required. The addition of HAuCl4 makes the molar ratio of Fe ions to Au ions (3-36):

1.

2. The method for preparing the sub-nanometer gold-supported nickel-iron composite photoanode catalyst with tunable defects according to claim 1, characterized in that: After adding HAuCl4, the container was sealed and stirred in a dark room for 24 hours.

3. A sub-nanometer gold-supported nickel-iron composite photoanode catalyst with tunable defects prepared by the preparation method according to claim 1 or 2.

4. The application of the sub-nanometer gold-supported nickel-iron composite photoanode catalyst with tunable defects as described in claim 3 in the efficient oxygen evolution of light-assisted water electrolysis.

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