Nickel-iron hydroxide sheet array water oxidation electrocatalyst, and preparation method and application thereof

Abstract

The application discloses a kind of nickel-iron hydroxide sheet array water oxidation electrocatalyst and its preparation method and application, the method includes the following steps: sequentially ultrasonic cleaning and vacuum drying treatment to nickel-iron alloy foam, standby;One end of anode and cathode is placed in boric acid solution, the other end is connected on direct current power supply by wire, the nickel-iron alloy foam is placed in boric acid solution and contacts with the one end of the anode, the voltage of direct current power supply is set to 4V, the power-on time is 60-120s, nanosheet-shaped nickel-iron hydroxide material is generated on the surface of the nickel-iron alloy foam, and the nickel-iron hydroxide sheet array water oxidation electrocatalyst is prepared.The nanosheet-shaped nickel-iron hydroxide material is formed on the nickel-iron alloy foam by simple electrochemical corrosion method, the nanosheet-shaped nickel-iron hydroxide material is uniformly distributed on the electrode surface to form efficient three-dimensional structure anode NiFe-LDH-60-120, and nickel-iron is closely combined to form synergistic effect, which greatly improves the electrochemical performance of the material.

Description

Technical Field

[0001] This invention relates to the field of electrocatalyst technology, and in particular to a nickel-iron sheet array water oxidation electrocatalyst, its preparation method, and its application. Background Technology

[0002] Electrolysis of water is an effective method for producing hydrogen in modern clean energy. During electrolysis, the oxygen evolution reaction (OER), a key process at the anode, is considered a major obstacle to overall water splitting due to its large reaction kinetics as a four-electron transfer process. To address these issues, extensive research has been conducted to reduce the overpotential. Although noble metals ruthenium (RuO2) or iridium (IrO2) have been reported as the most active electrocatalysts in the OER, an overpotential of approximately 300 mV is still required to achieve 10 mA cm⁻¹. -2 The current density.

[0003] Furthermore, the high cost and low abundance of the constituent elements of noble metal catalysts limit their use. Transition metals such as nickel and iron are gradually attracting attention. Nickel-based porous foam materials are widely used due to the large specific surface area provided by the foam skeleton. However, numerous studies have shown that pure Ni oxides / hydroxides do not exhibit oxidation activity as electrocatalysts.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a nickel-iron sheet array water oxidation electrocatalyst, its preparation method and application, aiming to solve the problem of poor electrocatalytic performance of existing water oxidation electrocatalysts.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a nickel-iron hydroxide sheet array water oxidation electrocatalyst, comprising the following steps:

[0008] The foamed nickel-iron alloy was subjected to ultrasonic cleaning and vacuum drying in sequence, and then set aside for use.

[0009] One end of the anode and cathode is placed in a boric acid solution, and the other end is connected to a DC power supply through a wire. The foamed nickel-iron alloy is placed in the boric acid solution and in contact with one end of the anode. The voltage of the DC power supply is set to 4V and the energizing time is 60-120s. Nanosheet-like nickel-iron hydroxide material is generated on the surface of the foamed nickel-iron alloy, thus obtaining the nickel-iron hydroxide sheet array water oxidation electrocatalyst.

[0010] The method for preparing the nickel-iron hydroxide sheet array water oxidation electrocatalyst, wherein the energizing time is 90s.

[0011] A nickel-iron hydroxide sheet array water oxidation electrocatalyst, wherein the electrocatalyst is prepared by the method of the present invention.

[0012] An application of a nickel-iron hydroxide sheet array water oxidation electrocatalyst, wherein the nickel-iron hydroxide sheet array water oxidation electrocatalyst of the present invention is used for water electrolysis to produce hydrogen.

[0013] Beneficial Effects: This invention utilizes a simple electrochemical corrosion method to form nanosheet-like nickel-iron hydroxide material on foamed nickel-iron alloys. The nanosheet-like nickel-iron hydroxide material is uniformly distributed on the electrode surface to form a highly efficient three-dimensional anode, NiFe-LDH-60-120 (electrochemical corrosion time 60-120 s). Simultaneously, the tight bonding between nickel and iron creates a synergistic effect, significantly improving the material's electrochemical performance. Testing revealed that the NiFe-LDH-90 electrode (electrochemical corrosion time 90 s) requires only an overpotential of η = 174 mV to reach 10 mA cm⁻¹. -2 The catalytic current density is high, and the electrode exhibits a low Tafel slope (42 mVdec). -1 Furthermore, a two-electrode electrolytic cell at 1.95 V can produce 100 mAcm⁻¹. -2 It has a current density of 100% and a Faraday efficiency of 100%. Under two-electrode testing, it can run continuously for 20 hours without significant degradation. Attached Figure Description

[0014] Figure 1 This is a flowchart of a method for preparing a nickel-iron hydroxide sheet array water oxidation electrocatalyst according to the present invention.

[0015] Figure 2 This is a schematic diagram of the fabrication of a nickel-iron hydroxide sheet array water oxidation electrocatalyst.

[0016] Figure 3 In the image, a is the SEM image of NiFe foam, and bf are the NiFe-LDH SEM images at electro-corrosion times of 60s, 70s, 90s, 100s, and 120s, respectively.

[0017] Figure 4 In the image, a is the XRD pattern of NiFe-LDH-90 and the original foamed nickel-iron alloy foam, b is the SEM image of NiFe-LDH-90, cd is the HRTEM image of NiFe-LDH-90, and ef is the corresponding elemental mapping in the NiFe-LDH-90 nanosheets.

[0018] Figure 5In the image, a is the high-resolution XPS spectrum of Fe 2p in NiFe-LDH-60, b is the high-resolution XPS spectrum of Ni 2p in NiFe-LDH-60, c is the high-resolution XPS spectrum of Fe 2p in NiFe-LDH-90, and d is the high-resolution XPS spectrum of Ni 2p in NiFe-LDH-90.

[0019] Figure 6 In Figure 1, a is the LSV curve of NiFe foam and NiFe-LDH-90 electrode in 1.0m KOH, b is the corresponding Tafel plot, c is the corresponding impedance curve; d is the LSV curve of NiFe-LDH-90 electrode in 1.0m KOH without stirring.

[0020] Figure 7 In Figure a, LSV curves of OER of NiFe-LDH after different treatment times are shown; in Figure b, LSV curves of HER of NiFe-LDH after different treatment times are shown.

[0021] Figure 8 In the middle, a, c, e, and g are CV curves for NiFe-LDH-90, NiFe foam, NiFe-LDH-60, and NiFe-LDH-120 at different scan rates, respectively; b, d, f, and h are ECSA results for NiFe-LDH-90, NiFe foam, NiFe-LDH-60, and NiFe-LDH-120, respectively.

[0022] Figure 9 Figure a shows the results of ECSA NiFe-LDH-90 and foamed NiFe; Figure b shows the results of 10 mA cm⁻¹ in 1.0 m KOH. -2 Potential-time curves under a current density sustained for 10 h; c is the chronocurrent curve of NiFe-LDH-90 / NF || 1 * 1 cm -2 The Pt thin-plate electrode was subjected to a potential of 1.9 V (relative to RHE) for 10 h; d is a graph showing the relationship between the generation of H2 and O2 and the reaction time. Detailed Implementation

[0023] This invention provides a nickel-iron hydroxide sheet array water oxidation electrocatalyst, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] This invention provides a method for preparing a nickel-iron hydroxide sheet array water oxidation electrocatalyst, such as... Figure 1 As shown, it includes the following steps:

[0025] S10. After ultrasonic cleaning and vacuum drying of the foamed nickel-iron alloy, it is ready for use.

[0026] S20. Place one end of the anode and cathode in a boric acid solution, and connect the other end to a DC power supply through a wire. Place the foamed nickel-iron alloy in the boric acid solution and contact it with one end of the anode. Set the voltage of the DC power supply to 4V and the energizing time to 60-120s. Generate nanosheet-like nickel-iron hydroxide material on the surface of the foamed nickel-iron alloy to obtain the nickel-iron hydroxide sheet array water oxidation electrocatalyst.

[0027] Specifically, the study found that Fe 3+ Doped α-Ni(OH)₂ catalysts exhibit high activity in OER (Organic Etching Reduction). Adding Fe and Ni(OH)₂ to the NiOOH phase lattice can enhance the material's activity, producing NiOOH with OER activity. Before modifying active sites, a precursor morphology with a uniform shape and large specific surface area is typically required. However, existing modification processes are relatively complex, or methods such as hydrothermal etching or high-temperature calcination are used, which are complex and have low stability. Nickel-iron metals can form uniform, porous, lamellar morphologies under corrosion conditions. Furthermore, due to the varying corrosion rates and degrees during corrosion, the electro-etching morphology can be controlled by adjusting the corrosion conditions. Electrochemical acid etching is a promising method for preparing nanoarray structures, and the subsequently formed nickel hydroxyl oxide exposes numerous active sites, promoting gas escape, improving electron and charge transport, and enhancing water oxidation performance.

[0028] Based on this, the present invention forms nanosheet-like nickel-iron hydroxide materials on foamed nickel-iron alloys through a simple electrochemical corrosion method, such as... Figure 2 The nanosheet-like nickel-iron hydroxide material is uniformly distributed on the electrode surface to form a highly efficient three-dimensional anode, NiFe-LDH-60-120 (electrochemical corrosion time of 60-120 s). Simultaneously, the tight bonding between nickel and iron creates a synergistic effect, significantly improving the material's electrochemical performance. Testing revealed that the NiFe-LDH-90 electrode (electrochemical corrosion time of 90 s) requires only an overpotential of η = 174 mV to reach 10 mA cm⁻¹. -2 The catalytic current density is high, and the electrode exhibits a low Tafel slope (42 mVdec). -1 Furthermore, a two-electrode electrolytic cell can generate 100 mA cm⁻¹ at a voltage of 1.95 V. -2 It has a current density of 100% and a Faraday efficiency of 100%. Under two-electrode testing, it can run continuously for 20 hours without significant degradation.

[0029] In some embodiments, during the preparation of the nickel-iron sheet array water oxidation electrocatalyst, the preferred electro-corrosion energizing time is 90 s.

[0030] In some embodiments, a nickel-iron hydroxide sheet array water oxidation electrocatalyst is also provided, wherein it is prepared by the preparation method of the nickel-iron hydroxide sheet array water oxidation electrocatalyst of the present invention.

[0031] In some embodiments, an application of the nickel-iron hydroxide sheet array water oxidation electrocatalyst is also provided, wherein the nickel-iron hydroxide sheet array water oxidation electrocatalyst of the present invention is used for water electrolysis to produce hydrogen.

[0032] The present invention will be further explained and illustrated below through specific embodiments:

[0033] Example 1

[0034] Preparation of nickel-iron hydroxide sheet array water oxidation electrocatalyst:

[0035] Before the experiment, commercially available nickel-iron foam was pretreated, and a 2 x 1 cm area was prepared. 2 The foamed nickel-iron alloy was ultrasonically cleaned in ethanol and deionized water, and then vacuum dried for later use.

[0036] Preparation of nickel-iron bimetallic nanosheet array electrode: 2.0 g of boric acid was added to 60 mL of deionized water and stirred to dissolve on a magnetic stirrer. The nickel-iron foam was placed as the anode under DC voltage, and a carbon rod was used as the cathode. The etching was carried out at 4 V for 60 s, 70 s, 90 s, 110 s, and 120 s. The nickel-iron foam was then removed, rinsed with deionized water, and dried in a drying oven at 60 ℃ for 10 h for later use.

[0037] Characterization methods for nickel-iron hydroxide sheet array water oxidation electrocatalysts:

[0038] First, the microstructure and crystal structure of the samples were observed using FESEM and HRTEM. XRD analysis was then performed to determine the phase composition and crystal structure. Surface elements and their chemical valence states were investigated using XPS. ICP-OES was used to determine the molar amount of the final synthesized samples for samples with different molar ratios.

[0039] Electrochemical testing and product analysis of nickel-iron hydroxide sheet array water oxidation electrocatalyst:

[0040] In this embodiment, all electrochemical experiments were conducted at room temperature using 1.0 M KOH as the electrolyte. A conventional three-electrode system was used, with the prepared sample (NiFe-LDH, etc., 1.0 cm × 1.0 cm) as the working electrode, a platinum sheet (1.0 cm × 1.0 cm) as the counter electrode, and an Hg / HgO electrode (1.0 M KOH solution) as the reference electrode. All measurements were corrected for current impedance (iR). Cyclic voltammetry (CV) was performed at a scan rate of 5 mV s. -1 The potential range relative to the RHE was 1.1–1.7 V. Stability tests were performed at a constant potential (1.35 V vs. RHE) for 20 h. Electrochemical impedance spectroscopy measurements were conducted at an AC amplitude of 0.005 V within a frequency range of 0.01 Hz to 100 kHz at 1.35 V. Tests were performed at potential ranges from 0.91 V to 1.01 V relative to the RHE, with collection scan rates ranging from 2 to 10 mV s. -1 The rate interval is 2 mVs -1 The CV curves yielded the double-layer capacitor (C). dl ).

[0041] The volume of gas at the anode and cathode is collected and tested using the water displacement method. The Faraday efficiency can be calculated using the following formula: , where F is the Faraday constant (96,485 Cmol-1) and n is the number of electrons transferred.

[0042] Experimental results:

[0043] The morphology of the nickel-iron hydroxide sheet array water oxidation electrocatalyst sample prepared in Example 1 was controlled through experiments. The morphology of the bimetallic hydroxide nanoarrays grown at different time points was observed using SEM. Figure 3 As shown in the SEM image, the original NiFe foam was smooth before etching; after etching, NiFe-LDH, assembled from many nanosheets, interconnected and uniformly supported on the NiFe foam framework. Nanosheets ( Figure 3 The lateral dimensions of nanosheets (d) are less than 600 nm, and their thickness is less than 10 nm. This vertical array and ultrathin nanosheet structure exposes a large number of active sites and facilitates mass migration during electrochemical reactions. Furthermore, the well-developed porous microstructure and open spaces promote electrolyte mass transfer and the release of generated H2 and O2. Increasing the electrochemical corrosion time (60 s–90 s) leads to a transition in the morphology of the nanosheets from short to wide (e.g., ...). Figure 3 As shown in the image (ad), it becomes sharper. Conversely, if the time exceeds 90 s, severe aggregation of nanosheets occurs (as shown in the image). Figure 3 (As shown in ef), this may lead to a reduction in the surface area of ​​the active material.

[0044] like Figure 4 As shown in Figure a, the X-ray diffraction (XRD) pattern of the untreated NiFe foam electrode exhibits typical diffraction peaks at 2q = 43.604, 50.794, and 74.677, corresponding to Fe, respectively. 0.64 Ni 0.36 The (111), (2 0 0), and (2 20) crystal planes (PDF#47-1405). No new diffraction peaks appeared in the XRD pattern when NiFe-LDH was electrodeposited on a NiFe foam electrode. Figure 4 (As shown in a) This may be due to the small particle size and relatively low mass of NiFe-LDH, as well as the influence of the strong diffraction peaks of the NiFe foam substrate. Figure 4 The HRTEM image shown in the middle bd reveals a fringe spacing of 0.25 nm, which corresponds well to the (0 1 2) plane of NiFe LDH. To further investigate the microstructure, high-power scanning electron microscopy revealed the thickness of the sheet itself (approximately 10 nm). Incompletely formed crystal nuclei on the surface increase the surface roughness of the sheet, as shown in the scanning electron microscopy image (…). Figure 4 As shown in the test results (as shown in ef), the iron and nickel elements are evenly distributed.

[0045] To further investigate the impact of electrolithography on material structure, XPS spectroscopy was used to determine crystal characteristics and chemical valence states. Figure 5 As shown in Figures a and c, the number of Fe peaks decreases with increasing electro-erosion time. At 60 s, both ferrous and ferric iron exist simultaneously. As the electro-erosion time increases, the ferrous iron on the surface changes to ferric iron, indicating that with prolonged electro-erosion time, the elemental iron on the surface is completely oxidized. (Fe 2p) 1 / 2 and Fe 2p 3 / 2 The binding energies of NiFe-LDH-60 were 711.24 eV and 724.37 eV, respectively, with a spin-orbit spacing of approximately 13.13 eV. The Fe 2p region spin-orbit component clearly split into 13.1 eV, consistent with theoretical values. With increasing corrosion time, the spin-orbit spacing decreased to 12.75 eV, indicating that the valence of Fe became higher after electrochemical corrosion. Figure 5 Images b and d show the Ni 2p peaks at 855.22 eV and 873.07 eV, respectively. Typically, the Ni 2p peaks exhibit a distinctly split spin-orbit component (Δmetal = 17.3 eV), with the spin-orbit spacing changing from 17.85 eV to 17.74 eV with increasing etching time. The two prominent satellite peaks can be attributed to the Ni 2p component of Ni in NiFe-LDH-60. 1 / 2 and Ni 2p3 / 2 This indicates the existence of Ni 2 + and Ni 3 + Simultaneously, according to the XPS analysis above, NiFe-LDH was successfully grown on the surface of NiFe foam. The NiFe-LDH nanosheets have a large active surface area, high catalytic site activity, and a strongly coupled heterogeneous interface formed through synergistic and interfacial interactions, which is very beneficial for electrochemical reactions.

[0046] The electrocatalytic performance of the prepared NiFe-LDH-90 for the oxygen evolution reaction was evaluated under alkaline conditions. The electrocatalytic OER performance of NiFe-LDH was investigated in 1.0 M KOH using a standard three-electrode system. (e.g.) Figure 6 (As shown in the image) For comparison, the electrochemical performance of the original NiFe foam sample was also investigated. The OER activity of NiFe-LDH-90 was better than that of the precursor (50 mA cm⁻¹). -2 The overpotentials of 220 mV and 260 mV respectively indicate that the formed NiFe-LDH material has more active sites. Figure 6 Figure b shows the Tafel plot of the corresponding electrode. The Tafel plot of NiFe-LDH-90 is significantly lower than that of the precursor material (58 mVdec). -1 ), which is 46 mV dec -1 This indicates that electro-corrosion enhances OER kinetics. EIS curves show that the charge transfer resistance (Rct) of NiFe-LDH-90 is 2.33 Ω, lower than that of NiFe foam alloy (3.01 Ω), indicating that the kinetic response of NiFe-LDH-90 is faster (e.g., ...). Figure 6 (As shown in c). The overall water splitting performance was tested in a dual-electrolyte cell, with both the anode and cathode using NiFe-LDH-90 catalysts. A cell voltage of approximately 1.96 V was required to provide 100 mA cm⁻¹. -2 Water decomposition ( Figure 6 (as shown in d).

[0047] To investigate the influence of electrode composition, this embodiment tested the effect of NiFe-LDH treated for different times on the catalytic activity of OER (e.g., Figure 7 As shown in Figures ab), the performance comparison is related to the influence of the material's microstructure. It can be seen that with clearer and sharper nanosheet structures, the material exhibits better OER performance. As the nanosheets aggregate, the performance gradually declines. Furthermore, hydrogen evolution performance was tested, and it was found that the material properties remained almost unchanged before and after corrosion treatment.

[0048] To determine the source of the electrode's OER activity, this embodiment tested the electrochemical surface area (ECSA), which is proportional to the electrochemical double-layer capacitance (Cdl). Figure 8 As shown in Figures a-b, the Cdl of NiFe-LDH-90 is 2.0 mF cm⁻¹. -2 Slightly higher than NiFe foam (1.8 mF cm⁻¹) -2 ) and Cdl of other samples treated at different times (e.g. Figure 8 (as shown in ch), but the electrocatalytic activity is greatly improved, which indicates that the unit active site of this material has high electrochemical activity, and the OER activity comes from the NiFe-LDH generated by the electro-corrosion.

[0049] Figure 9 The results from the intermediate-ad assay show that NiFe-LDH-90 has a larger surface area to accommodate more active sites. Furthermore, the long-term stability of NiFe-LDH-90 for OER was investigated. The current density was 20 mA cm⁻¹. -2 Under normal circumstances, no significant decrease in anode current was observed within 10 hours of the OER test. Figure 9 (As shown in c). Furthermore, this embodiment also tested the electrode durability in a two-electrode co-electrolysis system (e.g., Figure 9 (As shown in d). It exhibits excellent stability in alkaline electrolytes, and the cell voltage remains almost constant during a co-electrolysis reaction lasting up to 20 hours. To accumulate potential products, long-term electrolysis was performed at a constant potential (1.41 V vs. RHE), and the gas was then calculated using the water displacement method. Quantitative analysis showed near-uniform Faraday efficiencies (~100%) for the anode and cathode products H2 and O2.

[0050] In summary, the NiFe-LDH-90 nanosheets on NiFe foam of this invention are prepared by an electrochemical etching method. The surface morphology of the catalyst is optimized by controlling the etching time. The nanosheet array helps to promote the mass transfer process, and it can provide 100 mA cm⁻¹ at 1.47 V. -2 The current density was [not specified]. NiFe-LDH-90 exhibited catalytic activity and excellent stability for OER in alkaline electrolytes, maintaining electrolysis for 20 h with almost no degradation. The Faradaic conversion efficiency of the cathode and anode was determined by the water displacement gas collection method, and the product conversion rates of both electrodes reached ~100%. This chapter explores a highly efficient non-noble metal nanocatalyst for electrochemical water oxidation by optimizing the chemical composition, material structure, and interfacial interactions of NiFe-LDH-90 nanosheets. It also verifies that the nickel-iron composite transition metal hydroxide catalyst has good electrochemical oxidation performance. In terms of hydrogen evolution at the cathode and oxygen evolution at the anode, this electrode material achieves a high Faradaic efficiency approaching 100%.

[0051] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a nickel-iron hydroxide sheet array electrocatalyst for water oxidation, characterized by, The method comprises the steps of: The foamed nickel-iron alloy is sequentially subjected to ultrasonic cleaning and vacuum drying treatment and is ready for use; One end of the anode and the cathode is placed in a boric acid solution, and the other end is connected to a direct current power supply through a wire. The foamed nickel-iron alloy is placed in the boric acid solution and is in contact with the one end of the anode. The voltage of the direct current power supply is set to 4 V, and the power-on time is 90 s. A nanosheet-shaped nickel-iron hydroxide material is generated on the surface of the foamed nickel-iron alloy, and the nickel-iron hydroxide sheet array water oxidation electrocatalyst is prepared.

2. A nickel-iron hydroxide sheet array water oxidation electrocatalyst characterized by, The nickel-iron hydroxide sheet array water oxidation electrocatalyst is prepared by the preparation method of claim 1.

3. Use of a nickel-iron hydroxide sheet array electrocatalyst for water oxidation, characterized in that, The nickel-iron hydroxide sheet array water oxidation electrocatalyst of claim 2 is used for electrolytic water to produce hydrogen.

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